Polydopamine-based functional materials and their applications in energy, environmental, and catalytic fields: State-of-the-art review

Journal Pre-proofs Review Polydopamine-based functional materials and their applications in energy, environmental, and catalytic fields: State-of-the-art review Qiang Huang, Junyu Chen, Meiying Liu, Hongye Huang, Xiaoyong Zhang, Yen Wei PII: DOI: Reference:

S1385-8947(20)30010-3 https://doi.org/10.1016/j.cej.2020.124019 CEJ 124019

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Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

20 June 2019 31 October 2019 2 January 2020

Please cite this article as: Q. Huang, J. Chen, M. Liu, H. Huang, X. Zhang, Y. Wei, Polydopamine-based functional materials and their applications in energy, environmental, and catalytic fields: State-of-the-art review, Chemical Engineering Journal (2020), doi: https://doi.org/10.1016/j.cej.2020.124019

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Polydopamine-based functional materials and their applications in energy, environmental, and catalytic fields: State-of-the-art review Qiang Huanga, #, Junyu Chena, #, Meiying Liua, Hongye Huanga, Xiaoyong Zhanga, *, Yen Weib,c,* a Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China b Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084, P. R. China. c Department of Chemistry and Center for Nanotechnology, Chung-Yuan Christian University, Chung-Li 32023, Taiwan Yen WEI, Ph.D. Email: [email protected] Xiaoyong Zhang, Ph.D. Email: [email protected]

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Abstract Recently, polydopamine (PDA) has emerged as a popular material due to its striking properties. As a novel bio-inspired material, PDA can be easily formed in environmental conditions on virtually all kinds of inorganic and organic substrates. The abundant functional groups on PDA allow it to be a versatile platform for further loading of other components with desired functionalities. Along with its excellent performance in various fields, research interest and attention about PDA have significantly increased in recent years. Considering increasing interest and advances in energy, environmental, and catalytic fields, we present this mini-review regarding the latest development of PDA-based functional materials in these fields. The properties of PDA-based functional materials are briefly introduced at the beginning. Emphases are put on the latest applications in areas of batteries, supercapacitors, electrocatalysis, photo- and chemo-catalysis, removal of heavy metals and organic dyes, oil/water separation as well as seawater desalination. At the end of this mini-review, we give a straightforward summary and prospect about PDA-based functional materials in these applications. We hope this mini-review could provide some useful information to guide the future development of PDA-based functional materials.

Keywords: Polydopamine; functional materials; environment and energy applications, mussel-inspired chemistry 2

1 Introduction The properties of materials are determined by their structure and compositions while the applications are determined by their properties. In the last decade, a novel bio-inspired material, polydopamine (PDA), has aroused tremendous interest over energy, environmental, and catalytic fields because of its striking properties [1-4]. PDA is a dopamine (DA) derived synthetic eumelanin polymer, which contains catechol, imine, and amine functional groups [5]. On account of the similar molecular structure with tyrosine and L-3,4-dihydroxyphenylalanine in mussel adhesive proteins, PDA has properties similar to mussel which can strongly attach to diverse substrates with high binding strength, even on wet surfaces [6]. Based on this property, Tan et al [7] proposed that using PDA to modify polyaniline (PANI). Results showed that the surface modification greatly enhanced the dispersibility of PANI and adhesion force to the substrate. Besides, a wealth of functional groups on PDA coating provides additional active sites to bind with metal ions, organic molecules, functional polymers, etc. [8-10]. This allows it to be a multifunctional platform for secondary surface functionalization [11-14]. Chen et al [15] have reported a tight nanofiltration membrane with multi-charged nanofilms PA/PDA/PEI/PAA. The composite membrane was fabricated using PDA as the adhesive bio-glue layer. The positively charged PEI and negatively PAA were assembled to form dually charged nanofilm based on bio-glue PDA via Michael addition and/or Schiff-base reaction between amine in PEI and actives groups in PDA. The obtained composite membrane exhibited outstanding rejection performance to various diluted salts, heavy metal ions, and dyes by virtue of Donnan exclusion and steric hindrance [16]. In addition, the catechol and amine groups in PDA have strong chelation ability, which can be used to remove metal ions from water. Zhang et al [17] have fabricated a Fe3O4/PDA hybrid material and applied in environmental remediation. The resulting hybrid material exhibited surprising adsorption capacity for multiple pollutants. The maximum adsorption capacity for methylene blue, tartrazine, Cu2+, Ag+, and Hg2+ were as high as 204.1, 100.0, 112.9, 259.1, and 467.3 mg g−1, respectively. It is well known that DA is one of the most important neurotransmitters in central nervous system, which is crucial to physiological processes. The derived synthetic product from DA self-polymerization is anticipated to be equipped with excellent biocompatibility. The possible toxicity and carcinogenicity of PDA have also been investigated and have found no evidence of toxicity or carcinogenicity [18, 19]. More interestingly, the introduction of PDA can even promote cell adhesion and proliferation on substrates [20]. With these benefits, PDA has also attracted great research attention 3

in biomedical fields, including biosensing, bio-imaging, drug/gene delivery, tissue engineering, antibacterial, and theranostics [14, 21]. Moreover, PDA also exhibits a promising prospect in energy fields by utilizing as the carbon source because of its ease in preparation, controllable thickness, versatile adhesion properties and the possibility to achieve desired structures. Yang et al [22] have reported using PDA as carbonization reagent to fabricate MoO2-Mo2C-C (abbreviated as MMC) microspheres with high surface area and pretty conductivity. The obtained MMC hybrid product as anode materials for LIBs exhibited favorable reversible capacity of 1188 mAh g−1 after 250 cycles at the current density of 100 mAh g−1. Except for the excellent conductivity, PDA also shows extraordinary electrocatalytic activity after carbonization. Qu et al [23] have reported a graphene oxide–polydopamine (GD) based carbon nanosheets with adjustable thicknesses and uniform mesoporous structures without using any template. The optimized carbon nanosheet exhibited superior oxygen reduction reaction activity with an onset potential of -0.07 V and a kinetic current density of 13.7 mA cm−2 at −0.6 V. It was accepted that PDA provided nitrogen-doping on carbon matrix, which introduced defects and vacancies acting as new active sites of redox reactions. In addition to these properties as mentioned above, PDA has also demonstrated other potential functions, such as redox activities, photoprotective properties, and superparamagnetism, etc. [24-26]. These striking properties endow PDA with broad prospect in various areas. The reports about fabrication and broad applications of PDA-based functional materials have rapidly increased in recent years. Considering the increasing interest and advances in energy, environmental, and catalytic fields, we present this mini-review regarding the latest development of PDA-based functional materials in these fields. Emphases of this mini-review are put on the latest applications in the areas of batteries, supercapacitors, photo- and chemo catalysis, electrocatalysis, removal of heavy metals and organic dyes, oil/water separation as well as seawater desalination according to different physicochemical properties. We trust this review will attract attention of scientists from different disciplines and will promote the applications of PDA-based functional materials in energy, environmental and catalytical fields. 2 Applications of PDA-based functional materials 2.1 Energy field 2.1.1 Batteries As we all know that energy is the foundation of human activities. The development of technology 4

and sociality is inseparable from support of energy. However, fossil energy, as the major energy of global currently energy consumption, are limited and nonrenewable [27-29]. Besides, the wide applications of fossil energy play crucial roles in global weirding and environmental pollutions. In these cases, development of alternative, sustainable and clean energy technologies become an essential matter. The solar, wind and geothermal energies have been considered as a new generation of energy sources due to their non-pollution and renewability. Nevertheless, their intermittent and uncontrollable characteristics restrict their further applications. In view of the widespread applications of electronic and portable devices, such as mobile phones, laptops and so on, batteries are becoming major energy sources in modern society due to the rapid modification and improvement in these devices [30]. In the past decades, lithium-ion (Li-ion) batteries have been widely utilized in various devices due to its high energy density [31]. However, with ever-rising energy requirements for clean, safe and efficient high-density as well as high-capacity energy storage, significant improvements in their performance, such as energy density, cycle life, and safety reliability, are highly desirable [32, 33]. Separators are one of main components of batteries, which are designed to avoid direct contact of electrodes and sustains free transport of Li-ion batteries when absorbed liquid electrolyte [34]. The conventional PE and PP separators are usually suffering from shortcomings of weak thermal stability and poor wettability in liquid electrolytes [35-37]. While there are many substitute materials with good chemical stability, lightweight, high ionic conductivity, excellent wettability with electrolyte, such as polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride (PVDF), and polyacrylonitrile (PAN) nonwoven membranes, the limitations for Li-ion batteries still remain due to weak thermo-stability and mechanical strength of these nonwoven membranes [38-41]. Considering the excellent thermo-stability, versatile and wet-resistant adhesion ability of PDA, Shi et al reported a simple dip-coating method to modify PVDF-HFP separator with PDA for thermo-stability improvement [42]. Compared to traditional methods, this strategy is more simple and controllable, which can be adjusted by solution pH, DA concentrations, deposition time and atmosphere [43]. After PDA modification, the obtained PVDF-HFP composite membrane (denoted as PVDF-HFP-PDA) showed much higher thermal stability and enhanced mechanical strength and tensile strength than unmodified PVDF-HFP. The PVDF-HFP-PDA only suffered less than 15% of thermal shrinkage at 200 °C and without color change, while PP separator and PVDF-HFP nonwoven membrane showed obvious thermal shrinkage and color changes before 160 °C. After dropping liquid electrolyte, 5

PVDF-HFP nonwoven membrane formed a gel droplet, leading to distance reduction between PVDF-HFP nano-fibers caused by the gelation of the nonwoven membrane. By contrast, the PVDF-HFP-PDA did not suffer dimensional change after absorption of electrolyte. Moreover, tensile properties of PVDF-HFP-PDA composite membrane were significantly improved from 7.1 MPa to 11.2 MPa in dry state and 3.5 MPa to 7.1 MPa in wet state, respectively. The electrolyte uptake of PVDF-HFP-PDA was measured to be 254%, which is higher than unmodified PVDF-HFP-PDA membrane. More importantly, the lithium-ion batteries with PVDF-HFP-PDA composite membranes showed excellent cyclic stability and good rate performance.

Fig. 1. (a) Preparation of bifunctional electrode/binder material. Electrochemical performance for O-PDA-2 as SIBs anode: b) Rate performance. c) Long-term cycling profiles at a current density of 50 mA g-1. Electrochemical performance for O-PDA-2 as anode for LIBs: d) Comparison of rate performance of PDA samples in the absence and presence of binder. e) Long-term cycling profiles at a current density of 500 mA g-1. [Reproduced from Ref. [44]].

Aside from modification toward separators, PDA can also be directly used as electrode materials for batteries. It should be noted that improvement of battery performance is largely dependent on electrode 6

properties. The currently used anode materials are lithium transition metal oxides, including LiCoO2, LiFePO4, LiMn2O4, and LiNiO2, etc., which exhibit many disadvantages, including limited capacity upgrade space, large energy consumption, and the existence of security risks [45, 46]. Numerous efforts have been devoted to searching for alternative anode materials with better electrochemical performance for batteries. Inspired by physiological processes based on ion transport and energy conversion of functional biomolecules, Sun et al [44] proposed that PDA could be an ideal redox-active biomolecule-based electrode material for batteries (Fig. 1(a)). It is well known that the DA is one of the most important neurotransmitters in central nervous system, which play an essential role in the physiological processes. Under a mild condition, DA can be easily oxidized to o-benzoquinone by electron transfer and the resulting catechol/o-benzoquinone redox system [47, 48]. The role of oxygen atom in o-benzoquinone is similar to the lithium/sodium ions in batteries [49]. Moreover, the strong adhesive of PDA allows it to be excellent redox-active binder material. Compared to conventional fabrication methods of binder, PDA binder can be synthesized without hazardous reagents, complicated procedure, and requirement of specific equipment. On these bases, Sun and co-workers fabricated a biodegradable bifunctional electrode based on PDA [50]. Unexpectedly, the optimized PDA electrode exhibited superior electrochemical performance, including a high capacity (1818 mAh g-1 for LIBs and 500 mAh g-1 for SIBs) and a stable cyclability (93 % capacity retention after 580 cycles at a current density of 500 mAg-1 for LIBs; 100 % capacity retention after 1024 cycles at a current density of 50 mAg-1 for SIBs) (as shown in Fig. 1(c) and (e)). Fig. 1(d) showed the comparison of rate performance of PDA samples in the absence and presence of binder. The higher capacity than a binder-added battery with same current density revealed that existence of charge-transfer interactions in PDA would contribute movement of charge carriers through π-systems, resulting in improvement of the electrical conductivity of PDA. The capacity retention was 98%, 96%, 86%, 76%, 62%, and 47% at increased current density of 100, 200, 400, 800, 1600, and 3200 mA g-1, respectively. As current density dropped to 50 mA g-1, a reversible capacity can also be recovered even after 70 cycles. The outstanding rate performance was ascribed to fast redox kinetics of o-benzoquinone groups and charge transfer in PDA. Moreover, electrochemical performance of PDA is much better than most of state-of-the-art organic electrode materials, revealing great potential in practical applications. Moreover, porous carbon materials with structure of large surface area and high pore volume exhibit higher conductivity and abundant electrolyte channels, which has attracted attention from researcher 7

recent years. As an excellent surface functional material, DA can adhere to almost any material surfaces, giving a versatile platform for secondary coating, including organic and inorganic surfaces. Hence, DA can also be used as the carbon source for preparation of porous battery materials. Through investigation of recent literature, PDA has been served as porous carbon sources in batteries applications, e.g. fabrication of hierarchical porous carbon composite[51], carbon shell or hollow spheres[52, 53], carbon nano-boxes[54, 55]. Generally, electrode materials were immersed into the solution of DA (alkaline solution). After continuously stirring for several hours, PDA has been successfully modified onto the surface of electrode. Followed by calcining at high temperature for hours, porous carbon coating was obtained. Zhao et al[51] designed a Se/carbon hybrid (Se/HDHPC composite) cathode for both Li-Se and Na-Se batteries, where the hieratical porous carbon derived from self-polymerization of DA. After HDHPC was prepared by high-temperature decomposition of PDA at temperature of 600 ° C with heating rate of 3 ° C/min, Se50/HDHPC, Se60/HDHPC, and Se70/HDHPC composites were fabricated through a simple method of melt-diffusion. As expected, highly stable performance, high rate capability and high capacity retention of Se/HDHPC cathode were achieved. Fig. 1(c) represent the CV curves of Se50/HDHPC in Li-Se battery, perfect overlap of CV curves after the first cycle indicates the high stability of Se50/HDHPC composites. Besides, Fig. 1(d) also shows the highly stable electrochemical properties of Se50/HDHPC, the 613 mAh g-1 of irreversible capacity was ascribe to the formation of solid electrolyte interface (SEI) layer. Fig. 1(f) revealed only 0.0074% of capacity loss per cycle, indicating a reversibility electrochemical performance. The change in appearance of Se and Se50/HDHPC membranes after 1500 cycles can be seen in Fig. 1(e), compared with Se, there is no obvious change could be observed in the membrane of Se50/HDHPC, suggesting that Se has been confined in micropores of HDHPC successfully, this avoid the unexpected reaction between Se and carbonyl groups in carbonate based electrolyte.

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Fig. 1 (a) and (b) Schematic illustration of the synthesis process of Se/HDHPC composite. (c) CV curves of Se50/HDHPC at a scan rate of 0.1 mV s−1 in the cut off voltage range of 1.0–3.0 V. (d) Discharge-charge curves of Se 50 /HDHPC for different cycles at a current density of 0.5 C. (e) (b) Digital photos of the membranes from the Se and Se50/HDHPC cell after 1500 cycles. (f) Cycling performance of Se50/HDHPC at a current density of 0.5 C. [Reproduced from Ref. [51]]

2.1.2 Supercapacitors Supercapacitors, also known as electrochemical capacitors or ultracapacitors, are considered to be another widely explored energy storage device for ever-rising energy requirements [56]. Compared with batteries, advantages of supercapacitors are reflected in higher power density, ultra-fast charging and discharging rate, longer life stability as well as higher Coulombic efficiencies. Similar to batteries, electrode materials are also critical factors that influence performance of supercapacitors. The commonly used electrode materials for supercapacitors are conducting polymers, transition metal oxides and carbon materials with the characteristics of high specific surface area and easy accessibility. The utilization of these excellent materials as electrode endows supercapacitors with outstanding electrochemical performance. However, it can also bring some disadvantages to supercapacitors due to their intrinsic properties. For instance, graphene is one of the widely used electrode materials due to its large surface area (theoretical surface area of 2630 m2/g), superior conductivity (electrical conductivity up to 106 S/m) and abundant sandwich construction. But the intrinsic properties of graphene, including self-aggregation and re-stacking properties, lead to lower specific surface area (< 800 m2/g) and lower actual capacity (< 550 F/g) than theoretical values. Similar to graphene, MnO2 is also a promising electrode material because of its low cost, abundance, environmentally friendly and high theoretical specific capacitance. Due to the agglomeration of MnO2, it's surface area and electrical conductivity are 9

limited, leading to lower actual specific capacitance. For better performance, it is essential to modify these electrode materials to avoid these disadvantages. The facile and versatile surface modification technique based on strong adhesion of PDA has provided a new tool to address these problems. As a novel biomaterial, PDA possesses many striking properties in optics, electricity, and magnetic. More importantly, the presence of surface functional groups endows PDA with extraordinary surface activity and affinity, which lead PDA to be the best adhesive polymer. In view of these, Zheng et al [57] fabricated a novel three-dimensional composite electrode consisted of reduced graphene oxide (rGO), polydopamine (PDA) and nickel foam (rGO/PDA/NF). PDA was used to preferentially modify nickel foam surface to provide a platform for uniform GO coating. The rGO was obtained through annealing treatment. The resulted rGO/PDA/NF composite was used as electrode directly and showed excellent electrochemical performance. The specific capacitance of rGO/PDA/NF electrode was as high as 566.9 F/g at 1 A/g, and maximum energy density, as well as power density, was achieved at 172.7 W h/kg and 27.2 kW/kg in 1 mol/L Na2SO4 electrolyte, respectively. Apart from graphene oxide, transition metal nanoparticles with two-dimensional structure has also been involved in fabrication of high performance supercapacitors[58]. Recent years, MXenes as new favorite in the field of energy have attracted widely attention. Based on unique two-dimensional structure, it has been endowed high conductively, tunable surface groups, high mechanical strength and intercalation ability [59, 60]. Such properties render them potential candidates for electronic applications. For the first time, Wang et al[61] and co-workers report a high-performance Ti3C2Tx/PDA composite electrode for supercapacitors, the composite was designed by a one-step surface polymerization of DA on MXene nanosheets. The results show that Ti3C2Tx/PDA achieved a high areal capacitance of 715 mF/cm2 at a scan rate of 2 mV/s, while unmodified Ti3C2Tx was recorded only 506 mF/cm2 under identical conditions. Characterization analysis indicated that the improved electrochemical performance and stability mainly attributed to enlarged interlayer spacing and suppressing the restacking of Ti3C2Tx sheets by PDA modification. In addition, abundant hydroxyl and amino groups from PDA could form strong chelation interaction with Ti3C2Tx nanosheets, which helps stabilize Ti3C2Tx/PDA electrode.

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Fig. 2 (a) Schematic of the fabrication process of NHPCNs; (b) Galvanostatic charge/discharge curves at current densities ranged from 0.5 to 10 A g-1 of NHPCN-700; (c) The relationships between the specific capacitance and different current densities of NHPCNs and PDACS-700, (d) specific capacitance versus cycling number at 5 A g-1 of NHPCN-700 for 10000 cycles, and (e) Nyquist plots of as-prepared samples. [Reproduced from Ref. [62]].

Despite being used as adhesive layer, intercalation agent or interlayer spacer, PDA is primarily used as carbon source for enhancing conductivity of active materials [63, 64]. It is well known that PDA has characteristics of high carbon yield and high nitrogen content, which allow it to be a promising carbon precursor. Combined with advantages of PDA synthetic process involving simple operation, gentle experiment conditions, and controllable characteristic, PDA has long been applied for preparation of various carbon materials, such as carbon-based capsules, thin films, and nanotubes [65-67]. For instance, Xiong et al [62] reported a size-tunable nitrogen-doped hierarchical porous carbon nanosphere (NHPCN) with mesoscale and microscale pores. As shown in Fig. 2(a), NHPCN was prepared through carbonization of mesoporous PDA nanospheres, which were fabricated via polymerization of dopamine with F127 in alkaline aqueous solution. The assembled F127 micelles were adopted to introduce mesopores, while KOH activation brought about formation of micropores. This unique structure endows the material with several merits. One is that the mesopores can serve as channels for accelerating rapid transport of ions, while micropores can act as locations for charge accommodation [68, 69]. The other is that presence of heteroatoms can significantly affect electron donor characteristics of electrode materials. The lone electron pairs of nitrogen atoms can supply additional negative charges to carbon networks, and thereby markedly heighten electrochemical 11

performance of carbon materials [70]. Based on these advantages, when applied as supercapacitor electrodes materials, NHPCN exhibited excellent performances in capacitance retention and cycling stability. As illustrated in Fig. 2(b), the discharge curves at low current density exhibited lower rate of voltage drop from -0.4 V to -0.1 V. The specific capacitance of NHPCN-700 (carbonized at 700 °C) at a current density of 0.5 A/g was as high as 433 F/g (Fig. 2(c)). Fig. 2 (d) shows 95.7% capacitance of initial value was still maintained at a constant current density of 5 A/g for 10000 cycles, manifesting excellent cycling stability of NHPCN as supercapacitor electrodes materials. Moreover, NHPCN sample showed a shorter Warburg impedance region in comparison with PDACS-700 (porous carbon nanospheres without F127), implying lower impedance of ion transportation of NHPCN (Fig. 2(e)). On the basis of controllable characteristic of PDA, Cao et al and co-workers [71] have also fabricated a dispersible mesoporous nitrogen-doped hollow carbon nanoplates before the work from Xiong et al. The resulting hollow carbon nanoplates bear uniform hexagonal morphology with specific surface area of 460 m2/g, and accessible small mesopores (~3.8 nm), which also presented superior performance for both supercapacitor electrodes and binders’ materials. 2.2 Catalytic field 2.2.1 Chemo- and photocatalysis As noted above, the rapid development of technology is impossible without the utilization of large quantities of energy. In the past decades, non-renewable resources about coal, oil and natural gas, etc., were constantly consumed, environmental problem also became more and more serious. In order to solve the crisis of energy resource and environmental pollution, much attention has been focused on the development of clean renewable energy. Hydrogen is considered as ideal energy because of its high conversion efficiency, recyclability and nonpolluting nature. Hydrolysis of ammonia borane (AB) is current one of most widely accepted and well-studied technologies for hydrogen generation. In general, this method can give three moles hydrogen per mole of AB using a suitable catalyst at ambient temperature. The commonly used catalysts for hydrolysis of AB are zero-valent transition metal nanoparticles, including platinum [72], gold [73, 74], silver [75], palladium [76, 77], ruthenium [78] and rhodium [79] as well as nickel [80], etc. While catalytic effects are quite stunning, these nanoparticles are actually suffered from disadvantages of self-aggregation, leading to negative effect on long-term stability and catalytical activity. In addition, separation of these catalysts nanoparticles is another major problem. In this case, Joydev Manna and co-workers [81] proposed PDA coated 12

magnetic materials could be used as support materials for catalyst nanoparticles. It is well known that magnetic materials are promising supports in various fields as they can provide easy magnetic separation, which is also an ideal option for a catalyst to be used in practical application with excellent accessibility and reusability. PDA has long been considered and employed as an adhesive layer in various fields due to its robust and strong adhesion to virtually all types of surfaces. Moreover, the abundant functional groups, such as catechol, amine, imine groups, allow for facilitated metal binding, which provides a platform for the uniform loading of metal nanoparticles with the assistance of reductant [82, 83]. On the basis of these merits, palladium (0) nanoparticles supported on PDA coated cobalt ferrite (Pd0/PDA-CoFe2O4) composites were fabricated (Fig. 3(a)) and showed excellent performance in hydrolytic dehydrogenation of AB (Fig. 3(b-d)). It can be noticed that the Pd0/CoFe2O4 and Pd0/PDA–CoFe2O4 showed highly catalytic activity with turnover frequency (TOF) values of 290 and 175 min-1, respectively (Fig 3(b)). The magnetic separation avoided extra time consuming and significant loss of catalytic material during isolation process. While Pd0/CoFe2O4 has little higher catalytic activity than that of Pd0/PDA–CoFe2O4 catalyst, the initial catalytic activity of Pd0/CoFe2O4 catalyst was not preserved after reuse of catalyst in hydrolytic dehydrogenation of AB. The deactivation was ascribed to the slight agglomeration of palladium (0) nanoparticles. In contrast, the Pd0/PDA–CoFe2O4 catalyst preserved its initial catalytic activity in the subsequent run of hydrolysis of AB up to 10th run still providing 100% conversion in each run (Fig. 3(c-d)). The improvement in stability of Pd0/PDA–CoFe2O4 was attributed to the capacity of PDA to coordinate metal ions or atoms via N- and O- binding sites on the surface of polymer coating, which is crucial to prevent agglomeration of palladium (0) nanoparticles and to stabilize catalysts on the support. By means of similar protocol, Liu et al [84] and co-workers have also fabricated a magnetic Fe3O4–PDA hybrid hollow microsphere. PDA shell in this work provides a stable platform for uniform incorporation of Fe3O4 nanoparticles via coverage and isolation of PDA chain. The excellent stability endows magnetic Fe3O4 nanoparticles with better performance in quick oxidation catalytic process of typical substrates 3,3, 5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide.

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Fig. 3 (a) Synthesis of palladium(0) nanoparticles supported on polydopamine coated cobalt ferrite (Pd0/PDA–CoFe2O4); (b) Equivalent H2 versus time plot for hydrogen generation from the hydrolysis of AB (0.10 M) in presence of CoFe2O4, PDA–CoFe2O4, Pd0/CoFe2O4 (1.17 wt% Pd) and Pd0/PDA– CoFe2O4 (1.08 wt% Pd) at 25.0 ± 0.1 °C; (c) The percent initial catalytic activity and the percent conversion of AB for each run; (d) Plots of equivalent H2 per mole of AB versus time in successive runs of catalytic hydrolysis of AB (0.10 M) starting with 50 mg of Pd0/PDA–CoFe2O4 catalyst (1.08 wt% Pd) at 25.0 ± 0.1 °C. [Reproduced from Ref. [85]].

Besides the development of clean renewable energy, pollution cleanup is also an essential work for healthy ecological environment. Recently, photocatalytic oxidation technology has attracted considerable attention as a promising candidate for removal of hazardous organic contaminants from air or wastewater [82, 86, 87]. In the case of photocatalytic oxidation technology, a suitable catalyst is crucial to achieve high photocatalytic efficiency. The commonly used photocatalysts, such as TiO2 [88, 89], Cu2O [90], and ZnO [91], etc., are usually suffering from disadvantages of slow mass transport, easy to be eluted, and fast recombination of photo-generated electron-hole pairs, leading to low photocatalytic activity [91-93]. Given these problems, PDA provides a fairy generic solution to fabricate efficient photocatalysts with good activity, stability and recyclability. The strong adhesive ability of PDA has been known in various fields [94, 95]. More importantly, PDA possesses a 14

capability for light absorption under a broadband spectrum from UV to visible region [96, 97]. The catechol structure endows PDA with the ability to effectively transfer photo-induced electrons and protons, which is crucial for photocatalytic process [98]. On the basis of these merits, PDA decorated hybrid materials have been used for catalytic degradation of dyes or endocrine-disrupting chemical [99-101]. For example, Mao and co-workers [102] fabricated a TiO2@PDA nanocomposite with a core-shell structure and applied in degradation of Rhodamine B. PDA surface coating at around 1 nm in this work exhibited relatively high conversion efficiency of solar energy for photo-degradation of organic dyes compared with conventional photo-catalysts under visible light irradiation. Except higher catalytic activity, PDA is also crucial to achieve efficient use and recycle of photo-catalysts. For instance, Kim and co-workers [91] reported a novel PDA-assisted immobilization of hierarchical ZnO nanostructures on electrospun nanofibrous membrane and applied in degradation of methylene blue (MB). The as-synthesized composite membrane exhibited admirable photocatalytic performance using the low-intensity UV-LED device with good reusability, whereas unmodified membrane showed week photolytic activity in the degradation of MB. At the same period, Wang et al [92] also fabricated a PDA-coated PVDF membrane contained Au-TiO2 nanocomposites and used for tetracycline degradation under visible-light irradiation. The degradation ratio of composite membrane reached 92% within 120 min and remained about 90% after five cycle experiments. The high photocatalytic activity and excellent reusability reveal that PDA not only can be used as photosensitizer to improve the photocatalytic efficiency of catalysts, but also can be applied as a bio-adhesion interface to strengthen the bonding force between catalysts and membrane to increase the stability of catalysts. 2.2.2 Electrocatalysis With the appearance of worldwide-energy-crisis, development in clean and high-efficiency energy resources has been a hot issue for scientists [103, 104]. Except above mentioned Li-ion batteries and supercapacitors, regenerative fuel cells and rechargeable metal-air batteries are the other two currently advanced energy conversion and storage technologies [105, 106]. The high energy density, high power density and zero-pollution allow them to be promising technologies in the future broad applications [107-109]. The battery performance is mainly determined by electrocatalysts. The conventionally used materials for electrocatalytic reactions are noble metals like Pt [110], Ir [111], Pd [112] and Ru [113], etc., which are usually suffering from disadvantages of high cost, poor methanol resistance, and poor stability [114]. In this case, many researchers are engaged in research of novel alternative materials 15

with highly efficient catalytic performance. Recently, non-metallic heteroatom-doped carbon materials have been demonstrated to be promising alternative materials for electrocatalysts because of their competitive activity, low cost and significantly enhanced stability [115-118]. Yang and co-workers [119] have reported a novel N-doped graphene and an S-doped graphene prepared via thermal reaction between graphene oxide and guest gases (NH3 or H2S) on the basis of sandwich-like, ultrathin graphene oxide-porous silica sheets at high temperatures. The resulting N and S-doped graphene sheets exhibit good electrocatalytic activity, long durability, and high selectivity when they are employed as metal-free catalysts for oxygen reduction reactions (ORR). In theory, doped heteroatom within the carbon matrix can induce defects due to the difference of atomic radius, bond length and electronegativity, increasing the chemical reactivity for redox [120]. Different heteroatoms own different electronic structure and chemical properties, whether simultaneous doping two or more heteroatoms could further enhance the electrocatalytic performance of carbon matrix via synergetic effects. In 2015, Kim et al [120] reported about evaluation of ORR activity and electrochemical performance of single and multiple heteroatom-doped carbon in the application to an alkaline anion exchange membrane fuel cell (AAEMFC). The results demonstrated that multiple doping could induce additional active sites for ORR which further enhance ORR activity and stability. Hence, codoping two or more selected heteroatoms into designed sites of carbon matrix is becoming one of the major trends. Nevertheless, there is still a limitation arising from synthetic routes of multiple heteroatom-doped carbon, such as complex experimental conditions, low doping efficiency and toxic/ecologically unfriendly precursors [114, 121]. At the end of 2015, Qu et al [114] reported a novel, highly efficient and environmentally benign method for preparation of N, S-codoped mesoporous carbon nanosheets. As illustrated in Fig. 4(a), PDA was first coated on graphene oxide (GO), 2-mercaptoethanol was then reacted with PDA via Schiff base or Michael addition to produce sulfur modified GO-PDA (GDS). N, S-codoped mesoporous carbon nanosheets were obtained from pyrolysis of GDS hybrids. It is well known that PDA intrinsically contains carbon and nitrogen atoms, as well as its versatile adhesion and environmentally friendly properties, which is a promising N-containing precursor. The chemical reactivity of PDA with thiol-containing molecules further paves a wonderful path for N, S-codoping. The obtained N, S-codoped mesoporous carbon nanosheets (N, S-CN) exhibited a high S-doping efficiency (6.1%) with the assistance of PDA, which is higher than most previous reported methods. Generally, high doping efficiency means highly efficient catalytic 16

performance. The resulting N, S-CN displayed excellent ORR/OER bifunctional activity and durability as expected. It can be seen from Fig. 4(b) that N, S-CN showed a high ORR onset potential of −0.05 V vs. Ag/AgCl, which is much more positive than that of N-CN and RGO (−0.15 V and −0.16 V, respectively). The half-wave potential (E1/2) of N, S-CN was observed to be −0.20 V, and much closer to that of Pt/C (−0.15 V). The unique and wide current plateau from −0.3 to −0.8 V was observed on N, S-CN.

This

represented

a

diffusion-controlled

process

corresponding

to

efficient

four-electron-dominated ORR pathway, which revealed clearly best catalytic performance. Fig. 4(c) showed overall LSV curve of N, S-CN in the potential range of −0.8 to 0.8 V. The N, S-CN exhibited a ΔE of 0.88 V (Figure 4A), which is much lower than that of most non-metallic materials (e.g. N, P-carbon paper, ΔE = 0.96; N-graphene/CNT, ΔE = 1.00 V) and some highly active noble metal electrocatalysts (e.g. Pt/C, ΔE = 0.94 V; Ir/C, ΔE = 0.92 V) as well as transition-metals (e.g. CaMn4Ox, ΔE = 1.04 V; MnxOy/N-carbon, ΔE = 0.93 V). This result further demonstrated that superior catalytic activity of N, S-CN for both ORR and OER. Moreover, N, S-CN exhibited a high ORR stability with 92.5% retention under a constant cathodic voltage of −0.5 V with maintaining a very slow attenuation over 40 h. The CVs also demonstrated reliable cyclic stability of N, S-CN with almost no change during 1000 continuous potential cycles. By means of similar protocol, Zhao et al [121] also fabricated an N, S-codoped hierarchical porous carbon by utilizing CdS as the template without other N or S-contained molecules. The resulting N, S-codoped hierarchical porous carbon displayed hierarchically porous structures with high specific surface area, which are crucial to superior ORR performance. The optimal N, S-codoped hierarchical porous carbon exhibited highest ORR activity in terms of onset potential (0.95 V), half-wave potential (0.85 V), and limiting

current density (5.82 mA cm−2 ),

outperforming commercial Pt/C catalyst (0.945 V for onset potential, 0.85 V for half-wave potential, and 5.22 mA cm−2 for limiting current density). Apart from superior activity, the performance in methanol resistance and durability of N, S-codoped hierarchical porous carbon was found to be admirable with over 91% retention after 20,000s long-time measurement.

17

Fig. 4 (a) Fabrication of GDS derived carbon nanosheets (N, S-CNs), where R-SH refers to 2-mercaptoethanol; (b) ORR LSVs at a sweep rate of 5 mV s-1; (c) The overall LSV curve of N, S-CN in the potential range of −0.8 to 0.8 V, ΔE (Ej=10−E1/2) is a metric for bifunctional ORR and OER activity (Inset: the value of ΔE for various catalysts reported previously). [Reproduced from Ref. [114]].

2.3 Environmental field 2.3.1 Removal of heavy metals, organic dyes, and other toxic pollutants Recent rapid growth in economy has led to our quality of life become better and better, but subsequent environmental problems should not be ignored [122, 123]. Water pollution is one of the main environmental problems. Aquatic pollutants often contain insoluble oil, toxic heavy metals and organic dyes, as well as λ-cyhalothrin, etc., which have such characteristics as large pollution area, nonbiodegradable, highly toxic, and accumulation in organisms, etc. [124-128]. The existence of these pollutants in water is undoubtedly an enormous threat to the environment and human health. The development of effective technologies for the removal of these pollutants is urgent. Various methods that

are

being

used

to

remove

these

toxic

pollutants

include

chemical

precipitation,

oxidation-deoxidation, adsorption, ion-exchange, membrane filtration, coagulation, electrochemical treatment technologies, etc. [129-131]. Among these methods, membrane-based water purification 18

technologies attached great attention because of their low energy consumption, no phase change, easy integration and scale-up [132, 133]. As for membrane-based water purification method, one key to effective separation of pollutants is membrane itself. Over the years, polymer membranes, such as polyethylene (PE), polypropylene (PP), polyetherimide (PEI) and poly(vinylidene fluoride) (PVDF), are more widely used in water purification due to their flexibility, excellent film-forming ability, mechanical strength and chemical resistance as well as low cost [43, 134]. There are several drawbacks to these polymer membranes as well, though, as low hydrophilicity can lead to high trans-membrane pressure and fouling affinity [43, 135]. It was reported that the fouling by organic substances can eventually change membrane hydrodynamic permeability and properties [136, 137]. In addition, increasing wastewater complexity and more stringent emission standards require multifunctional membranes with high performance. Since the first report in 2007 by Lee et al [6], PDA has attached increasing attention for its striking properties. It is well known that PDA is DA derived synthetic eumelanin polymer, which contains abundant functional groups, such as catechol, amine, and imine groups [138]. These groups on PDA play an essential role in achieving strong adhesion towards substrate surface via surface affinity [139]. In addition, deposition of PDA coating is more simple and controllable than traditional methods and provides a new dimension for membrane surface modification [43]. For instance, Hebbar and co-workers fabricated a well-dispersed PDA functionalized halloysite nanotube polyetherimide mixed matrix membrane for heavy metal removal [140]. Results show that uniform distribution of additive into polyetherimide membrane truly enhanced its porosity, water uptake capacity, and hydrophilicity. The PWF of nanocomposite membrane exhibited lower membrane hydraulic resistance (0.88 Kpa/L m-2 h-1) compared to the pristine membrane (1.59 Kpa/L m-2 h-1). The modified membrane performed better than pristine membrane in anti-fouling with FRR of 74.5% and reversible fouling ratio of 60.7%. These results were attributed to hydrophilic groups from PDA coating and HNTs. Besides, modified membrane showed excellent resistance to microbial growth on the membrane surface. According to experiment and analysis, introduction of hydrophilic groups from PDA coating and HNTs changed the surface hydrophilicity of membrane, leading to weakening of interactions between foulants/microorganism and membrane surface. Moreover, polyetherimide membrane exhibited much higher rejection towards both Pb2+ and Cd2+ ions after modification with PDA functionalized halloysite nanotube, indicating positive contribution of PDA in removal of Pb2+ and Cd2+ ions. The reusability of prepared membranes for 19

heavy metal ion removal was found to be excellent. These positive contributions by PDA are also reflected in later reports [141-143].

Fig. 5. (a) Schematic illustration of the approach used for the preparation of the MPL assemblies; (b) Time profile of Cu(II), MO and CR removal by the MPL3 assembly at pH = 5.6 ± 0.1, I = 0.01 M NaNO3, CMO initial = CCR initial = 100.0 mg L-1, and m/V = 0.1 g L-1 ; (c) Recycling of the MPL3 assembly in the removal of Cu(II) from aqueous solutions, at pH = 5.6 ± 0.1, I = 0.01 M NaNO3, CCu(II) initial = 20.0 mg L-1, and m/V = 0.1 g L-1; Simultaneous removal of Cu(II) (d), MO (e, left) and CR (e, right) on the MPL3 assembly using binary solutions of the Cu(II)-dye. [Reproduced from Ref. [144]]. 20

Besides aforementioned membrane-based water purification technologies, adsorption is also considered as an efficient and widely used strategy for the removal of heavy metal ions and organic dyes [145, 146]. It is well known that adsorption ability is mainly governed by adsorption sites on adsorbents. For better performance, it is necessary and crucial to improving the properties of adsorbents, such as larger surface area, more active binding sites and/or improvement of utilization rates [147-149]. On the strength of abundant functional groups, including catechol, amine, and imine groups, PDA has been thought to be a promising alternative to adsorb toxic pollutants from wastewater [150-153]. But adsorption capacity of PDA adsorbent, on one level, is too low to meet practical demand. More importantly, different physicochemical properties of potentially toxic metals and dyes make treatment of co-contaminated wastewaters more challenging [154, 155]. Hence, effective and multifunctional adsorbents are highly desirable. Considering the strong adhesive and abundant functional groups of PDA, high removal capacity of layered materials for many pollutants, magnetic recovery capability of Fe3O4 particles, Li and co-workers [144] designed a novel kind of environmental friendly adsorbent consisting of Fe3O4, PDA and Mg-Al layered double hydroxides (denoted as MPL) via an easy and green approach (as shown in Fig. 5(a)). Three potentially toxic metals (i.e., Cu(II), Cd(II) and Pb(II)) and two typical anionic dyes (i.e., methyl orange (MO) and Congo red (CR)), were selected as model pollutants to investigate the adsorption performance of MPL. When in mono-component system, MPL showed great adsorption performances toward both toxic metals and anionic dyes pollutants with removal capacities of 67.7, 170.6 and 200.1 mg/g for Cu(II), methyl orange (MO) and Congo red (CR), respectively (Fig. 5(b)). As compared with MP and LDH, removal capacities of MPL were the highest, showing that MPL assemblies exerted synergetic effect from each building component [144]. The interesting studies are adsorption performance in binary solutions. As shown in Fig. 5(d), the removal of Cu(II) was slightly reduced by the existence of dyes at low initial Cu(II) concentrations (i.e., 5 and 10 mg/L), and was significantly enhanced by the existence of dyes at high Cu(II) concentrations (i.e., 15, 20 and 25 mg/L) in binary systems. Specifically, the removal capacity of Cu(II) at initial concentration of 20 mg/L in mono-component system (qe,[20,0]) was 67.7 mg/g, whereas 101.48 and 119.27 mg/g in Cu(II)-MO and Cu(II)-CR binary systems. (qe,[20,150], C[Cu(II)]initial = 20 mg/L and C[MO/CR]initial = 150 mg/L), respectively. The appearance of dyes on the surface of MPL3 assembly would offer additional nitrogen-containing groups which were taken as 21

adsorption sites for capturing Cu(II). These results showed great potential of MPL3 in practical Cu(II) removal. Interestingly, removal of Cu(II) was enhanced by the presence of dyes; but the adsorption amounts of dyes, including MO and CR (as shown in Fig. 5(e) ), in the presence of Cu(II) were approximately the same to/lower than those of dyes in mono-component system. These results were explained by saying that PDA-groups and LDH for metal binding can also play a role in anionic dye removal, leading to competition for available removal sites. More interestingly, Li and co-workers further investigated its application in practice using synthetic textile effluent. Thanks to the abundant functional groups of PDA and LDH, MPL3 assembly achieved a relatively high removal efficiency of Cu(II) (93.56%) and MO (90.79%). As for practical applications, the stability and reusability of adsorbent are crucial when it faces harsh environment. Experiment results showed that the regenerated adsorbent could be successfully reused for both mono-component pollutants and model textile effluent without a significant efficiency loss (Fig. 5(c)). Considering these excellent performances, MPL3 is hopeful and qualified for practical application in integrative and efficient treatment of coexistent toxic pollutants. Fabrication of PDA-modified nanomaterials usually suffers multiple synthesis and modification process, which makes the cost much higher for practical application, e.g. CS-PDA aerogels [156], PVDF@PDA@SiO2 membranes [157], TiO2@PDA composites [158], MnO2/PDA/PAN fibers [159], Fe3O4@PDA-Ag hollow microspheres [160]. Compared with PDA-modified nanomaterials, pure dopamine microspheres are easier to prepare and have more surface-active groups, the size of PDA microsphere was tunable ranging from tens to hundreds of nanometers, attracting extensive attention from researchers. In this regard, PDA microspheres have great potential in the field of environmental adsorption. Fu et al [161] synthesized PDA microspheres with uniform morphology and mean diameter of 590 nm, the preparation process was simply mixed dopamine hydrochloride ethanol solution with Tris buffer and stirred for three days. Adsorption towards MB shows that the removal capacity by PDA microspheres reached up to 90.7 mg/g at room temperature, which was much higher than that of ordinary adsorbents. Characterization revealed that the high performance mainly attributes to the existence of numerous negative charged phenolic groups and π-π stacking interaction between PDA and MB molecules. Compared with dye pollutants, PDA microspheres have a stronger chelation with heavy metal ions, which makes PDA microspheres more suitable for the adsorption of heavy metal ions. Most recently, heavy metal adsorption also has been reported by using PDA microspheres. For 22

example, Zhang et al [162] have also successfully prepared PDA microspheres with sizes at 520-570 nm via a facile self-polymerization process. Through a batch of adsorption experiments towards Cr(VI), result analysis shows that the maximum sorption capacity could reach up to 200.2 mg/g within 8 min. The experimental results showed that the capacity of PDA microspheres to treat Cr(VI) containing wastewater reached 42000 kg water/kg adsorbent. The Cr(VI) concentration of treated water could be reduced to below 50 ppm, which reached the drinking water standards recommended by WHO. Such excellent adsorption capacity was enough to demonstrate its potential application in water treatment. In addition, the preparation cost of adsorbents is very low, about 28,500 dollars per ton, which is equivalent to treating a ton of wastewater for only 0.16 dollars. Combined above, it is expected that the PDA microspheres could be more practical as an efficient adsorbent in environmental remediation. 2.3.2 Seawater desalination

23

Fig. 6 (a) Schematic diagram of fabrication and nanofiltration process of the prepared nanocomposite membrane; (b) Dynamic water contact angles and (c) ζ-potentials at different pH values of the substrate and the nanofiltration membrane surfaces. Concentration of GNPs for nanocomposite membrane fabrication is 0.05 mg/mL; (d) Antibacterial performance of the PAN substrates, PDA/PEI nanofiltration membrane and nanocomposite membrane against S. aureus and E. coli. Photograph of inhibition zone experiments of the PAN substrates, PDA/PEI nanofiltration membrane and nanocomposite membrane against (e) S. aureus and (f) E. coli. Concentration of GNPs for nanocomposite membrane fabrication is 0.4 mg/mL. [Reproduced from Ref. [163]].

As is well known, water is extremely critical not only to life demands but also to industrial 24

development [164]. In order to alleviate the water shortage situation, great efforts have been devoted to hunting for effective solutions [165, 166]. In addition to separation of heavy metal ions, organic dyes, and other pollutants from wastewater as mentioned above, the seawater desalination is also believed to provide an unlimited and steady supply of fresh water without impairing natural freshwater ecosystems [167]. The nanofiltration membrane is the key factor in nanofiltration technology. As mentioned above, polymeric membranes are the most widely used filtration membranes in membrane-based water purification applications because of their flexibility and low cost [168]. However, these membranes are usually suffering from the disadvantages of unsatisfying mechanical, structural, thermal and physicochemical stabilities, leading to limited application in seawater desalination [168, 169]. Nanocomposite membranes provide inspiration to combine the superiorities of inorganic nanomaterials and polymeric matrices for outstanding nanofiltration performance [170, 171]. Various inorganic nanomaterials, including silica nanoparticles [172, 173], titanium dioxide nanoparticles [174, 175] and silver nanoparticles [176], etc. [177], have been incorporated into the polymeric selective layers to enhance the membrane performance. Previous efforts were mainly engaged in modifying the inorganic fillers, developing organic nanoparticles and synthesizing molecule of frameworks containing organic ligands for the enhancement of interfacial compatibility [178, 179]. Nevertheless, the challenge for facile and environmentally friendly methods still remain. Inspired by the adhesive of mussel, Xu group [180] developed a highly efficient and environmentally friendly way to fabricate thin film nanocomposite (denoted as TFN) nanofiltration membrane. Typically, the polyacrylonitrile (PAN) ultrafiltration membrane was firstly decorated by PDA/PEI/SiO2 nanoparticles via co-deposition followed by crosslinking and PEI grafting. PDA/PEI co-deposited layer was designed as a dense and adhesive matrix due to the universal adhesive and film-forming ability of PDA, accompanied with the promoted homogeneity and uniform structure endowed by PEI. The interfacial compatibility of the inorganic nanomaterials and the polymer matrices were enhanced by the electrostatic interactions of silica nanoparticles with PEI and the adhesive characteristics of PDA, resulting in a defect-free selective layer and then good rejection for both bivalent cations and neutral solutes. On this basis, Xu groups further fabricated a novel positively charged nanocomposite membrane [163]. As shown in Fig. 6. (a), similar to the fabrication process of TFN nanofiltration membrane, the PAN ultrafiltration membrane was firstly modified by PDA/PEI with electropositive gold nanoparticles (GNPs) via co-deposition followed by crosslinking with glutaraldehyde (GA). The majorization for the method in 25

this work is the inorganic filler, the GNPs. The introduction of positively charged fillers not only avoided the aggregation caused by the electrostatic attraction between the negatively charged fillers (the silica nanoparticles) and the positively charged PEI molecules, but also strengthened the positive surface potentials of the prepared nanocomposite membrane. Besides, thanks to the promoted compatibility by the positively charged GNPs between PDA/PEI matrix and the inorganic fillers, the GNPs were uniform spread in PDA/PEI, which is beneficial for the enhancement of membrane performance. The structural stability of the nanocomposite membrane was improved effectively during long-term filtration. Of course, the obtained nanocomposite membrane also exhibited more stable nanofiltration performance compared to those without GNPs during a long-term filtration process. Fig. 6. (b) showed the ultrafiltration substrate exhibits the best wettability with a water contact angle (WCA) value decreasing to 0° in 20 s due to those abundant hydrophilic groups and the porous surface structures. The higher value than 70° for the prepared PDA/PEI nanofiltration membrane was ascribed to the reduced hydrophilic groups and the compacted surface structure. After the modification with GNPs, the WCA decreased to lower than 60°, indicating the enhanced wettability due to the inherent hydrophilicity of GNPs and the loosened surface structures. Fig. 6. (c) compared the surface ζ-potentials of the prepared nanofiltration membrane and substrates measured under different pH values. It can be noticed that the isoelectric point of nanocomposite membrane (pH 7.8) was higher than both of substrate (pH 4.0) and PDA/PEI nanofiltration membrane (pH 7.3), which was assigned to the adequate quaternary ammonium cations on GNPs. These endow the nanocomposite membrane with high retention ratio (> 90%) for bivalent cations, such as Mg2+, Ca2+, and various heavy metal ions. And the permeate flux of the nanocomposite membrane was observed to be doubles compared with those without GNPs. In addition, the quaternary amine moieties on GNPs and PDA endow the nanocomposite membrane with good antibacterial activity (Fig. 6. (d), (e) and (c)) [181-183], which is conducive for antimicrobial fouling and thus lifespan in the practical nanofiltration process. 2.3.3 Oil-water separation

26

Fig. 7. (a) Schematic illustration of the fabrication of PAN/HPEI/PDA electrospun nanofibrous membrane; (b) Permeation flux of PAN/HPEI/PDA, PAN/HPEI and PAN electrospun nanofibrous membranes for SDS-stabilized toluene-in-water emulsions; (c) Separation performance of PAN/HPEI/PDA electrospun nanofibrous membrane for SDS-stabilized toluene-in-water emulsions under 0.02 MPa; (d) Performance cycles of PAN/HPEI/PDA electrospun nanofibrous membrane when separating SDS-stabilized toluene. [Reproduced from Ref. [128]].

As we briefly mentioned above, the rapid development of technology brings the human with comfortable and convenient life as well as a series of severe environmental problems at the same time [184, 185]. A great deal of oily wastewater is produced from industrial discharge, household garbage, and frequent oil spill accidents [186, 187]. The effect toward ecology environment and threat toward human health are decidedly grim. The present work is to develop an efficient method to remove or separate the immiscible oil/water mixtures. Membrane separation processes, such as microfiltration (MF) and ultrafiltration (UF) processes have been regarded as promising methods in oil-water separation [43]. However, as we mentioned before, the traditional polymer-based filtration membranes are usually suffering from the disadvantage of quick fouling due to the oleophilic nature of C-H structures in polymer chains [188]. This fouling may cause obvious decline in permeation flux and separation efficiency. Numerous efforts, including functional membrane with superhydrophilic and underwater superoleophobic surfaces, have been developed to address the problem [126, 189-191]. Considering the abundant hydrophilic groups, PDA has been used as hydrophilic modifiers for 27

hydrophobic polymer membranes. For instance, Xiang and co-workers [192] prepared a PDA modified PVDF membrane and investigated the effect of immersed time toward the membrane performance. The hydrophilicity and superoleophobicity under seawater were achieved for M-P24 membrane which immersed in dopamine solution for 24 h. The modified membrane obtained stable superoleophobicity under seawater with an oil contact angle of 152 ± 0.3° and extremely low oil-adhesion. The permeability and selectivity of modified membrane were significantly higher than that of traditional filtration membranes. Moreover, the introduction of PDA coating endowed the membrane with good fouling resistance to proteins and quick flux recovery after membrane cleaning. For better separation performance, Cui et al[157] designed a SiO2 nanoparticles anchored PVDF@PDA membrane via simple hydrolysis and physical blending process. Underwater oil contact angels revealed that the superoleophobicity property of PVDF@PDA@SiO2 was obtained after nano-SiO2 modification, leading to a better performance in dichoroethane/water emulsion separation. Recently, Yin et al[193] also reported a SSM/PDA/GO mesh with multilevel structure through a series of dipping routes, the obtained mesh possessed high stability showed excellent separation efficiency (>99.95%) in oil/water mixture separation with flux up to ∼15000 L m−2 h−1 under an oil intrusion pressure (>3kPa), remarkable antifouling performance and recyclability also confirmed. Despite the enhanced antifouling properties and separation efficiency, the membrane separation processes were always operated under external pressure, which may accelerate the enrichment of organic pollutants and pore plugging by oil droplets, leading to the decline in permeation flux and separation efficiency. Based on this question, Wang and co-workers proposed that using electrospun nanofibrous membranes as candidates to treat oil/water emulsions [128]. The electrospun nanofibrous membranes have the characteristics of open-cell pores, high porosity and easily tunable structures, which endow the electrospun nanofibrous membranes with high permeabilities and higher fluxes [194, 195]. If combined with the hydrophilicity of PDA, the modified electrospun nanofibrous membrane can be an effective material for the separation

of

oil/water

emulsions.

polyacrylonitrile/hyperbranched

On

these

bases,

Wang

polyethyleneimine/polydopamine

et

al

[128]

(PAN/HPEI/PDA)

fabricated

a

electrospun

nanofibrous membrane constructed with nanoscale hierarchical surface structures (as shown in Fig. 7. (a)). The obtained PAN/HPEI/PDA electrospun nanofibrous membranes showed lower WCA and ultrafast water permeability than that of PAN electrospun nanofibrous membrane. Additionally, it was thought that surface hydrophilicity can be enhanced through creating nano- or micro- hierarchical 28

structure [196]. In this report, PDA nanoclusters were manufactured in larger sparse and smaller dense nanoparticles through controlling the self-polymerization time of DA. The subsequent experimental results showed the nanoscale hierarchical structures of electrospun nanofibrous membrane became more obvious with the increase of DA treatment time, the oil contact angle (OCA) increased from 139° to 163° and the affinity for oil droplets was greatly reduced as expected. The superhydrophilic and underwater superoleophobic properties of PAN/HPEI/PDA electrospun nanofibrous membranes endow their excellent anti-fouling property and oil/water separation capability. As seen from Fig. 7. (b), compared to PAN/HPEI and PAN electrospun nanofibrous membranes, the permeate flux of PAN/HPEI/PDA electrospun nanofibrous membrane decreased slowly, and flux remained at high level (~ 1200 L m-2 h-1) even when the permeate volume reached to 160 mL. The oil/water rejection of PAN/HPEI/PDA was slightly higher than that of PAN/HPEI and PAN membranes. And the membrane also exhibited high fluxes (>1600 L m-2 h-1) for SDS-stabilized oil-in-water emulsions, which were remarkably higher than that of commercial UF membranes (usually exhibit a flux of less than 300 L m-2 h-1 bar-1). Moreover, the PAN/HPEI/PDA electrospun nanofibrous membrane can also be applied under higher transmembrane pressure (0.02 MPa) and exhibited ultra-high permeate flux with stable oil rejection (Fig. 7. (c)). Meanwhile, the permeate flux decreased sharply in the initial stage, and then reached to a steady state. Fig. 7. (d) showed the performance cycles of PAN/HPEI/PDA electrospun nanofibrous membrane when separating SDS-stabilized toluene. After 10 cycles of separation, the membrane still maintained a stable performance for separating SDS-stabilized toluene. The flux remained at a high level (> 1500 L m-2 h-1) and the oil content of filtrate was still below 20 ppm. 3 Challenges and Opportunities In this review, we summarized the recent progress on PDA-based materials and their applications in energy, catalytic and environmental fields. Driven by the increasing demand for facile and efficient fabrication technology, mussel inspired chemistry has been developed and applied in various fields in the last decade. PDA is an emerged polymer that can be obtained from self-polymerization of DA under rather mild experimental conditions. Well-designed PDA-based materials were fabricated for different kinds of application requirements in recent years. The main context of this article is the second section, which can be divided into three subunits as following: 1) design and fabrication of PDA-based functional materials for energy applications such as batteries and supercapacitors, 2) preparation of PDA-based composites for chemical and electrochemical catalysis applications, 3) 29

utilization of PDA-based materials and PDA functionalized surface for environmental pollutants removal, seawater desalination and oil-water separation. The great research attention from PDA-based functional materials is majorly ascribed to facile preparation procedure and promising properties and applications of PDA-based functional materials. Although significant development has been achieved for fabrication of PDA-based functional materials for energy, environmental and catalytic applications, there are challenges and opportunities for practical applications of PDA-based functional materials in the above fields. First, the cost of DA is rather high for practical applications and the total amount of DA consumption for industrial application would be quite huge. Although these PDA-based functional materials can be facilely fabricated through self-polymerization of DA, DA needs to oxidize and polymerize on the surface of materials, while a large amount of DA will self-polymerize in solution, so the actual use efficiency of DA is very low, which would cause great waste in practical applications. Therefore, precise control of DA self-polymerize only on the surface of materials was urgent, developing new modification schemes to avoid waste is an important direction of future research on DA modification. Second, rational design principles for fabrication of PDA-based materials and optimum data for the above applications are still lacking. DA could be self-polymerized and coated on almost any solid surface and form PDA nano-film. Owing to the poor soluble property and limited by characterization method, its polymer structure and polymerization mechanism have not been fully understood[197]. Many mechanisms have been proposed, but some unexplained phenomena still exist, the mechanism of DA polymerization is still being explored. Third, PDA coated materials have great potential for practical applications, as discussed above. However, as a relatively expensive raw material, DA is difficult to store and easy to deteriorate for industrial manufacturing. As alternative, relatively cheap substitutes of ammonia and phenols, such as PEI and TA, are widely studied for surface modification. Searching for alternative molecules with similar properties of DA should be one of the future directions, the expand of more related materials in application of PDA derivatives should be prospected. Acknowledgments This research was supported by the National Natural Science Foundation of China (Nos. 21788102, 21865016, 21564006, 21561022, 21644014). References [1] Z. Li, J. Zhang, H.B. Wu, X.W. Lou, An improved Li–SeS2 battery with high energy density and long 30

cycle life, ADV ENERGY MATER 7 (2017) 1700281. [2] Y. Liu, K. Ai, L. Lu, Polydopamine and its derivative materials: synthesis and promising applications in energy, environmental, and biomedical fields, Chem Rev 114 (2014) 5057-5115. [3] J.H. Ryu, P.B. Messersmith, H. Lee, Polydopamine surface chemistry: a decade of discovery, ACS APPL MATER INTER 10 (2018) 7523-7540. [4] V. Ball, Polydopamine films and particles with catalytic activity, Catal Today 301 (2018) 196-203. [5] C.T. Chen, F.J. Martin-Martinez, G.S. Jung, M.J. Buehler, Polydopamine and eumelanin molecular structures investigated with ab initio calculations, Chem Sci 8 (2017) 1631-1641. [6] H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Mussel-inspired surface chemistry for multifunctional coatings, Science 318 (2007) 426-430. [7] J. Tan, Z. Xie, Z. Zhang, Y. Sun, W. Shi, D. Ge, Dopamine modified polyaniline with improved adhesion, dispersibility, and biocompatibility, J MATER SCI 53 (2018) 447-455. [8] G. Zeng, X. Liu, M. Liu, Q. Huang, D. Xu, Q. Wan, H. Huang, F. Deng, X. Zhang, Y. Wei, Facile preparation of carbon nanotubes based carboxymethyl chitosan nanocomposites through combination of mussel inspired chemistry and Michael addition reaction: Characterization and improved Cu2+ removal capability, J TAIWAN INST CHEM E 68 (2016) 446-454. [9] Q. Huang, M. Liu, J. Chen, K. Wang, D. Xu, F. Deng, H. Huang, X. Zhang, Y. Wei, Mussel inspired preparation of functional silica nanocomposites for environmental adsorption applications, Appl Surf Sci 387 (2016) 285-293. [10] S. Song, Y. Zhang, Construction of a 3D multiple network skeleton by the thiol-Michael addition click reaction to fabricate novel polymer/graphene aerogels with exceptional thermal conductivity and mechanical properties, J MATER CHEM A 5 (2017) 22352-22360. [11] E. Faure, C. Falentin-Daudré, C. Jérôme, J. Lyskawa, D. Fournier, P. Woisel, C. Detrembleur, Catechols as versatile platforms in polymer chemistry, Prog Polym Sci 38 (2013) 236-270. [12] M.E. Lynge, R. van der Westen, A. Postma, B. Städler, Polydopamine—a nature-inspired polymer coating for biomedical science, Nanoscale 3 (2011) 4916-4928. [13] X. Zhang, Q. Huang, F. Deng, H. Huang, Q. Wan, M. Liu, Y. Wei, Mussel-inspired fabrication of functional materials and their environmental applications: progress and prospects, APPL MATER TODAY 7 (2017) 222-238. [14] M. Liu, G. Zeng, K. Wang, Q. Wan, L. Tao, X. Zhang, Y. Wei, Recent developments in polydopamine: an emerging soft matter for surface modification and biomedical applications, Nanoscale 8 (2016) 16819-16840. [15] Y. Chen, F. Liu, Y. Wang, H. Lin, L. Han, A tight nanofiltration membrane with multi-charged nanofilms for high rejection to concentrated salts, J MEMBRANE SCI 537 (2017) 407-415. [16] Y.L. Chen, F. Liu, Y. Wang, H.B. Lin, L. Han, A tight nanofiltration membrane with multi-charged nanofilms for high rejection to concentrated salts, J MEMBRANE SCI 537 (2017) 407-415. [17] S. Zhang, Y. Zhang, G. Bi, J. Liu, Z. Wang, Q. Xu, H. Xu, X. Li, Mussel-inspired polydopamine biopolymer decorated with magnetic nanoparticles for multiple pollutants removal, J HAZARD MATER 270 (2014) 27-34. [18] S.H. Ku, J. Ryu, S.K. Hong, H. Lee, C.B. Park, General functionalization route for cell adhesion on non-wetting surfaces, Biomaterials 31 (2010) 2535-2541. [19] Y. Liu, K. Ai, J. Liu, M. Deng, Y. He, L. Lu, Dopamine‐melanin colloidal nanospheres: an efficient near ‐ infrared photothermal therapeutic agent for in vivo cancer therapy, ADV MATER 25 (2013) 1353-1359. 31

[20] R. Luo, L. Tang, S. Zhong, Z. Yang, J. Wang, Y. Weng, Q. Tu, C. Jiang, N. Huang, In vitro investigation of enhanced hemocompatibility and endothelial cell proliferation associated with quinone-rich polydopamine coating, ACS Appl Mater Interfaces 5 (2013) 1704-1714. [21] H. Zhang, T. Zhao, B. Newland, W. Liu, W. Wang, W. Wang, Catechol functionalized hyperbranched polymers as biomedical materials, PROG POLYM SCI (2017). [22] X. Yang, Q. Li, H. Wang, J. Feng, M. Zhang, R. Yuan, Y. Chai, In-situ carbonization for template-free synthesis of MoO2-Mo2C-C microspheres as high-performance lithium battery anode, CHEM ENG J 337 (2018) 74-81. [23] K. Qu, Y. Zheng, S. Dai, S.Z. Qiao, Polydopamine–graphene oxide derived mesoporous carbon nanosheets for enhanced oxygen reduction, Nanoscale 7 (2015) 12598-12605. [24] E. Pardieu, N.T. Chau, T. Dintzer, T. Romero, D. Favier, T. Roland, D. Edouard, L. Jierry, V. Ritleng, Polydopamine-coated open cell polyurethane foams as an inexpensive, flexible yet robust catalyst support: a proof of concept, Chem Commun (Camb) 52 (2016) 4691-4693. [25] M. Wu, D. Zhang, Y. Zeng, L. Wu, X. Liu, J. Liu, Nanocluster of superparamagnetic iron oxide nanoparticles coated with poly (dopamine) for magnetic field-targeting, highly sensitive MRI and photothermal cancer therapy, Nanotechnology 26 (2015) 115102. [26] R. Subair, B.P. Tripathi, P. Formanek, F. Simon, P. Uhlmann, M. Stamm, Polydopamine modified membranes with in situ synthesized gold nanoparticles for catalytic and environmental applications, CHEM ENG J 295 (2016) 358-369. [27] N.P. Deng, W.M. Kang, Y.B. Liu, J.G. Ju, D.Y. Wu, L. Li, B.S. Hassan, B.W. Cheng, A review on separators for lithium-sulfur battery: Progress and prospects, J POWER SOURCES 331 (2016) 132-155. [28] S. Abada, G. Marlair, A. Lecocq, M. Petit, V. Sauvant-Moynot, F. Huet, Safety focused modeling of lithium-ion batteries: A review, J POWER SOURCES 306 (2016) 178-192. [29] H. Long, D. Del Frari, A. Martin, J. Didierjean, V. Ball, M. Michel, H.I.E. Ahrach, Polydopamine as a promising candidate for the design of high performance and corrosion-tolerant polymer electrolyte fuel cell electrodes, J Power Sources 307 (2016) 569-577. [30] X.B. Cheng, R. Zhang, C.Z. Zhao, Q. Zhang, Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review, Chem Rev 117 (2017) 10403-10473. [31] D. Zheng, X. Zhang, J. Wang, D. Qu, X. Yang, D. Qu, Reduction mechanism of sulfur in lithium– sulfur battery: From elemental sulfur to polysulfide, J POWER SOURCES 301 (2016) 312-316. [32] G.Y. Wang, X.Y. Huang, P.K. Jiang, Bio-inspired polydopamine coating as a facile approach to constructing polymer nanocomposites for energy storage, J MATER CHEM C 5 (2017) 3112-3120. [33] Y. Deng, C. Fang, G. Chen, The developments of SnO 2/graphene nanocomposites as anode materials for high performance lithium ion batteries: A review, J POWER SOURCES 304 (2016) 81-101. [34] P. Arora, Z.J. Zhang, Battery separators, Chem Rev 104 (2004) 4419-4462. [35] H. Liao, H. Zhang, G. Qin, H. Hong, Z. Li, Y. Lin, L. Li, Novel Core-Shell PS-co-PBA@ SiO2 Nanoparticles Coated on PP Separator as “Thermal Shutdown Switch” for High Safety Lithium‐Ion Batteries, MACROMOL MATER ENG 302 (2017). [36] T. Knoche, R. Lund, O. Prymak, M. Epple, M. Ulbricht, Effect of annealing temperature on pore formation in preparation of advanced polyethylene battery separator membranes, MATER TODAY COMMUN 8 (2016) 23-30. [37] H.Y. Liao, H.Q. Hong, H.Y. Zhang, Z.H. Li, Preparation of hydrophilic polyethylene/methylcellulose blend microporous membranes for separator of lithium-ion batteries, J MEMBRANE SCI 498 (2016) 147-157. 32

[38] Y. Xia, X. Wang, X. Xia, R. Xu, S. Zhang, J. Wu, Y. Liang, C. Gu, J. Tu, A Newly Designed Composite Gel Polymer Electrolyte Based on Poly (Vinylidene Fluoride ‐Hexafluoropropylene)(PVDF ‐HFP) for Enhanced Solid‐State Lithium‐Sulfur Batteries, CHEM-EUR J 23 (2017) 15203-15209. [39] C. Zhu, T. Nagaishi, J. Shi, H. Lee, P.Y. Wong, J. Sui, K. Hyodo, I.S. Kim, Enhanced Wettability and Thermal Stability of a Novel Polyethylene Terephthalate-Based Poly(Vinylidene Fluoride) Nanofiber Hybrid Membrane for the Separator of Lithium-Ion Batteries, ACS Appl Mater Interfaces 9 (2017) 26400-26406. [40] J. Zhu, C. Chen, Y. Lu, J. Zang, M. Jiang, D. Kim, X. Zhang, Highly porous polyacrylonitrile/graphene oxide membrane separator exhibiting excellent anti-self-discharge feature for high-performance lithium–sulfur batteries, Carbon 101 (2016) 272-280. [41] Q.Y. Wu, H.Q. Liang, L. Gu, Y. Yu, Y.Q. Huang, Z.K. Xu, PVDF/PAN blend separators via thermally induced phase separation for lithium ion batteries, Polymer 107 (2016) 54-60. [42] C. Shi, J.H. Dai, S.H. Huang, C. Li, X. Shen, P. Zhang, D.Z. Wu, D.H. Sun, J.B. Zhao, A simple method to prepare a polydopamine modified core-shell structure composite separator for application in high-safety lithium ion batteries, J MEMBRANE SCI 518 (2016) 168-177. [43] H.C. Yang, J.Q. Luo, Y. Lv, P. Shen, Z.K. Xu, Surface engineering of polymer membranes via mussel-inspired chemistry, J MEMBRANE SCI 483 (2015) 42-59. [44] T. Sun, Z.J. Li, H.G. Wang, D. Bao, F.L. Meng, X.B. Zhang, A Biodegradable Polydopamine-Derived Electrode Material for High-Capacity and Long-Life Lithium-Ion and Sodium-Ion Batteries, Angew Chem Int Ed Engl 55 (2016) 10662-10666. [45] Z. Yang, J. Ren, Z. Zhang, X. Chen, G. Guan, L. Qiu, Y. Zhang, H. Peng, Recent advancement of nanostructured carbon for energy applications, Chem Rev 115 (2015) 5159-5223. [46] J.B. Goodenough, Y. Kim, Challenges for rechargeable Li batteries, CHEM MATER 22 (2009) 587-603. [47] N.F. Della Vecchia, R. Avolio, M. Alfè, M.E. Errico, A. Napolitano, M. d'Ischia, Building ‐ Block Diversity in Polydopamine Underpins a Multifunctional Eumelanin‐Type Platform Tunable Through a Quinone Control Point, ADV FUNCT MATER 23 (2013) 1331-1340. [48] F. Bernsmann, V. Ball, F. Addiego, A. Ponche, M. Michel, J.J.d.A. Gracio, V. Toniazzo, D. Ruch, Dopamine− melanin film deposition depends on the used oxidant and buffer solution, Langmuir 27 (2011) 2819-2825. [49] Y.J. Kim, W. Wu, S.E. Chun, J.F. Whitacre, C.J. Bettinger, Catechol‐Mediated Reversible Binding of Multivalent Cations in Eumelanin Half‐Cells, ADV MATER 26 (2014) 6572-6579. [50] T. Sun, Z.j. Li, H.g. Wang, D. Bao, F.l. Meng, X.b. Zhang, A Biodegradable Polydopamine‐Derived Electrode Material for High ‐ Capacity and Long ‐ Life Lithium ‐ Ion and Sodium ‐ Ion Batteries, ANGEW CHEM INT EDIT 128 (2016) 10820-10824. [51] X. Zhao, L. Yin, T. Zhang, M. Zhang, Z. Fang, C. Wang, Y. Wei, G. Chen, D. Zhang, Z. Sun, F. Li, Heteroatoms dual-doped hierarchical porous carbon-selenium composite for durable Li–Se and Na–Se batteries, Nano Energy 49 (2018) 137-146. [52] C.-H. Jung, J. Choi, W.-S. Kim, S.-H. Hong, A nanopore-embedded graphitic carbon shell on silicon anode for high performance lithium ion batteries, J MATER CHEM A 6 (2018) 8013-8020. [53] H. Wang, X. Jiang, Y. Chai, X. Yang, R. Yuan, Sandwich-like C@ SnO2/Sn/void@ C hollow spheres as improved anode materials for lithium ion batteries, J Power Sources 379 (2018) 191-196. [54] T. Chen, W. Kong, M. Fan, Z. Zhang, L. Wang, R. Chen, Y. Hu, J. Ma, Z. Jin, Chelation-Assisted Formation

of

Multi-Yolk-Shell

Co4N@

Carbon 33

Nanoboxes

for

Self-Discharge-Suppressed

High-Performance Li-SeS2 Batteries, J MATER CHEM A (2019). [55] C. Yue, Z. Liu, W.J. Chang, W.I. Park, T. Song, Hollow C nanobox: An efficient Ge anode supporting structure applied to high-performance Li ion batteries, Electrochim Acta 290 (2018) 236-243. [56] A. Borenstein, O. Hanna, R. Attias, S. Luski, T. Brousse, D. Aurbach, Carbon-based composite materials for supercapacitor electrodes: a review, J MATER CHEM A 5 (2017) 12653-12672. [57] Y. Zheng, S.X. Lu, W.G. Xu, G. He, Y.Y. Cheng, T.L. Yu, Y. Zhang, The fabrication of graphene/polydopamine/nickel foam composite material with excellent electrochemical performance as supercapacitor electrode, J SOLID STATE CHEM 258 (2018) 401-409. [58] X. Zhang, R. Zhang, C. Xiang, Y. Liu, Y. Zou, H. Chu, S. Qiu, F. Xu, L. Sun, Polydopamine-assisted formation of Co3O4-nanocube-anchored reduced graphene oxide composite for high-performance supercapacitors, Ceram Int 45 (2019) 13894-13902. [59] B. Anasori, M.R. Lukatskaya, Y. Gogotsi, 2D metal carbides and nitrides (MXenes) for energy storage,NAT REV MATER2 (2017) 16098. [60] W. Wu, D. Niu, J. Zhu, Y. Gao, D. Wei, C. Zhao, C. Wang, F. Wang, L. Wang, L. Yang, Hierarchical architecture of Ti3C2@PDA/NiCo2S4 composite electrode as high-performance supercapacitors, Ceram Int 45 (2019) 16261-16269. [61] H. Wang, L. Li, C. Zhu, S. Lin, J. Wen, Q. Jin, X. Zhang, In situ polymerized Ti3C2Tx/PDA electrode with superior areal capacitance for supercapacitors, J Alloys Compd 778 (2019) 858-865. [62] S.Q. Xiong, J.C. Fan, Y. Wang, J. Zhu, J.R. Yu, Z.M. Hu, A facile template approach to nitrogen-doped hierarchical porous carbon nanospheres from polydopamine for high-performance supercapacitors, J MATER CHEM A 5 (2017) 18242-18252. [63] Y. Zhou, H.J. Guo, Y. Yong, Z.X. Wang, X.H. Li, R. Zhou, Introducing reduced graphene oxide to improve the electrochemical performance of silicon-based materials encapsulated by carbonized polydopamine layer for lithium ion batteries, MATER LETT 195 (2017) 164-167. [64] X. Liu, T. Zhang, Y. Qu, G. Tian, H. Yue, D. Zhang, S. Feng, Carbonized polydopamine coated single-crystalline NiFe 2 O 4 nanooctahedrons with enhanced electrochemical performance as anode materials in a lithium ion battery, ELECTROCHIM ACTA 231 (2017) 27-35. [65] H. Jiang, T. Zhao, C. Li, J. Ma, Functional mesoporous carbon nanotubes and their integration in situ with metal nanocrystals for enhanced electrochemical performances, Chem Commun (Camb) 47 (2011) 8590-8592. [66] R. Liu, S.M. Mahurin, C. Li, R.R. Unocic, J.C. Idrobo, H. Gao, S.J. Pennycook, S. Dai, Dopamine as a Carbon Source: The Controlled Synthesis of Hollow Carbon Spheres and Yolk ‐ Structured Carbon Nanocomposites, ANGEW CHEM INT EDIT 50 (2011) 6799-6802. [67] Y.R. Liang, H. Liu, Z.H. Li, R.W. Fu, D.C. Wu, In situ polydopamine coating-directed synthesis of nitrogen-doped ordered nanoporous carbons with superior performance in supercapacitors, J MATER CHEM A 1 (2013) 15207-15211. [68] L. Miao, D.Z. Zhu, Y.H. Zhao, M.X. Liu, H. Duan, W. Xiong, Q.J. Zhu, L.C. Li, Y.K. Lv, L.H. Gan, Design of carbon materials with ultramicro-, supermicro- and mesopores using solvent- and self-template strategy for supercapacitors, MICROPOR MESOPOR MAT 253 (2017) 1-9. [69] W.-J. Lu, S.-Z. Huang, L. Miao, M.-X. Liu, D.-Z. Zhu, L.-C. Li, H. Duan, Z.-J. Xu, L.-H. Gan, Synthesis of MnO 2 /N-doped ultramicroporous carbon nanospheres for high-performance supercapacitor electrodes, CHINESE CHEM LETT 28 (2017) 1324-1329. [70] T.K. Zhao, J.K. Zhang, Z. Du, Y.H. Liu, G.L. Zhou, J.T. Wang, Dopamine-derived N-doped carbon decorated titanium carbide composite for enhanced supercapacitive performance, ELECTROCHIM 34

ACTA 254 (2017) 308-319. [71] J. Cao, C.J. Jafta, J. Gong, Q. Ran, X. Lin, R. Felix, R.G. Wilks, M. Bar, J. Yuan, M. Ballauff, Y. Lu, Synthesis of Dispersible Mesoporous Nitrogen-Doped Hollow Carbon Nanoplates with Uniform Hexagonal Morphologies for Supercapacitors, ACS Appl Mater Interfaces 8 (2016) 29628-29636. [72] M.A. Khalily, H. Eren, S. Akbayrak, H.H. Susapto, N. Biyikli, S. Özkar, M.O. Guler, Facile Synthesis of Three-Dimensional Pt-TiO2 Nano-networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia-Borane, ANGEW CHEM INT EDIT 128 (2016) 12445-12449. [73] S. Rej, C.F. Hsia, T.Y. Chen, F.C. Lin, J.S. Huang, M.H. Huang, Facet ‐ Dependent and Light ‐ Assisted Efficient Hydrogen Evolution from Ammonia Borane Using Gold–Palladium Core–Shell Nanocatalysts, ANGEW CHEM INT EDIT 55 (2016) 7222-7226. [74] Ş.U. Karabiberoğlu, Ç.C. Koçak, S. Koçak, Z. Dursun, Polymer Film Supported Bimetallic Au–Ag Catalysts for Electrocatalytic Oxidation of Ammonia Borane in Alkaline Media, NANO-MICRO LETT

8

(2016) 358-370. [75] M. Urushizaki, H. Kitazawa, S. Takano, R. Takahata, S. Yamazoe, T. Tsukuda, Synthesis and Catalytic Application of Ag44 Clusters Supported on Mesoporous Carbon, J PHYS CHEM C 119 (2015) 27483-27488. [76] Y. Tonbul, S. Akbayrak, S. Ozkar, Palladium(0) nanoparticles supported on ceria: Highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane, INT J HYDROGEN ENERG 41 (2016) 11154-11162. [77] W.D. Zhong, X.K. Tian, C. Yang, Z.X. Zhou, X.W. Liu, Y. Li, Active 3D Pd/graphene aerogel catalyst for hydrogen generation from the hydrolysis of ammonia-borane, INT J HYDROGEN ENERG 41 (2016) 15225-15235. [78] S. Akbayrak, Y. Tonbul, S. Ozkar, Ceria-supported ruthenium nanoparticles as highly active and long-lived catalysts in hydrogen generation from the hydrolysis of ammonia borane, Dalton Trans 45 (2016) 10969-10978. [79] S. Akbayrak, Y. Tonbul, S. Ozkar, Ceria supported rhodium nanoparticles: Superb catalytic activity in hydrogen generation from the hydrolysis of ammonia borane, APPL CATAL B-ENVIRON198 (2016) 162-170. [80] C. Wang, J. Tuninetti, Z. Wang, C. Zhang, R. Ciganda, L. Salmon, S. Moya, J. Ruiz, D. Astruc, Hydrolysis of Ammonia-Borane over Ni/ZIF-8 Nanocatalyst: High Efficiency, Mechanism, and Controlled Hydrogen Release, J Am Chem Soc 139 (2017) 11610-11615. [81] J. Manna, S. Akbayrak, S. Özkar, Palladium(0) nanoparticles supported on polydopamine coated CoFe 2 O 4 as highly active, magnetically isolable and reusable catalyst for hydrogen generation from the hydrolysis of ammonia borane, APPL CATAL B-ENVIRON208 (2017) 104-115. [82] C. Zhang, H.C. Yang, L.S. Wan, H.Q. Liang, H. Li, Z.K. Xu, Polydopamine-Coated Porous Substrates as a Platform for Mineralized beta-FeOOH Nanorods with Photocatalysis under Sunlight, ACS Appl Mater Interfaces 7 (2015) 11567-11574. [83] A.M. Xie, K. Zhang, F. Wu, N.N. Wang, Y. Wang, M.Y. Wang, Polydopamine nanofilms as visible light-harvesting interfaces for palladium nanocrystal catalyzed coupling reactions, CATAL SCI TECHNOL 6 (2016) 1764-1771. [84] S. Liu, J. Fu, M. Wang, Y. Yan, Q. Xin, L. Cai, Q. Xu, Magnetically separable and recyclable Fe 3 O 4– polydopamine hybrid hollow microsphere for highly efficient peroxidase mimetic catalysts, J COLLOID INTERF SCI 469 (2016) 69-77. 35

[85] J. Manna, S. Akbayrak, S. Özkar, Palladium(0) nanoparticles supported on polydopamine coated CoFe 2 O 4 as highly active, magnetically isolable and reusable catalyst for hydrogen generation from the hydrolysis of ammonia borane, APPL CATAL B-ENVIRON 208 (2017) 104-115. [86] W.N. Du, S.T. Chen, Photo- and chemocatalytic oxidation of dyes in water, J Environ Manage 206 (2018) 507-515. [87] W. Li, Z.Y. Ma, G.Q. Bai, J.M. Hu, X.H. Guo, B. Dai, X. Jia, Dopamine-assisted one-step fabrication of Ag@AgCl nanophotocatalyst with tunable morphology, composition and improved photocatalytic performance, APPL CATAL B-ENVIRON174 (2015) 43-48. [88] A.K. Sarkar, A. Saha, A. Tarafder, A.B. Panda, S. Pal, Efficient Removal of Toxic Dyes via Simultaneous Adsorption and Solar Light Driven Photodegradation Using Recyclable Functionalized Amylopectin–TiO2–Au Nanocomposite, ACS SUSTAIN CHEM ENG 4 (2016) 1679-1688. [89] Y.Z. Shi, D.Z. Yang, Y. Li, J. Qu, Z.Z. Yu, Fabrication of PAN@TiO2/Ag nanofibrous membrane with high visible light response and satisfactory recyclability for dye photocatalytic degradation, APPL SURF SCI 426 (2017) 622-629. [90] X.S. Zhou, B. Jin, J. Luo, X.X. Gu, S.Q. Zhang, Photoreduction preparation of Cu2O@polydopamine nanospheres with enhanced photocatalytic activity under visible light irradiation, J SOLID STATE CHEM 254 (2017) 55-61. [91] J.H. Kim, M.K. Joshi, J. Lee, C.H. Park, C.S. Kim, Polydopamine-assisted immobilization of hierarchical zinc oxide nanostructures on electrospun nanofibrous membrane for photocatalysis and antimicrobial activity, J Colloid Interface Sci 513 (2018) 566-574. [92] C. Wang, Y. Wu, J. Lu, J. Zhao, J. Cui, X. Wu, Y. Yan, P. Huo, Bioinspired Synthesis of Photocatalytic Nanocomposite Membranes Based on Synergy of Au-TiO2 and Polydopamine for Degradation of Tetracycline under Visible Light, ACS Appl Mater Interfaces 9 (2017) 23687-23697. [93] S.S. Yi, J.M. Yan, B.R. Wulan, S.J. Li, K.H. Liu, Q. Jiang, Noble-metal-free cobalt phosphide modified carbon nitride: An efficient photocatalyst for hydrogen generation, APPL CATAL B-ENVIRON200 (2017) 477-483. [94] Y.K. Jeong, S.H. Park, J.W. Choi, Mussel-Inspired Coating and Adhesion for Rechargeable Batteries: A Review, ACS Appl Mater Interfaces 10 (2018) 7562-7573. [95] K. Zhang, F. Zhang, Y. Song, J.B. Fan, S. Wang, Recent Progress of Mussel‐Inspired Underwater Adhesives, CHINESE J CHEM (2017). [96] C.T. Chen, C. Chuang, J. Cao, V. Ball, D. Ruch, M.J. Buehler, Excitonic effects from geometric order and disorder explain broadband optical absorption in eumelanin, Nat Commun 5 (2014) 3859. [97] M. d’Ischia, A. Napolitano, V. Ball, C.-T. Chen, M.J. Buehler, Polydopamine and eumelanin: from structure–property relationships to a unified tailoring strategy, ACCOUNTS CHEM RES 47 (2014) 3541-3550. [98] J.H. Kim, M. Lee, C.B. Park, Polydopamine as a biomimetic electron gate for artificial photosynthesis, Angew Chem Int Ed Engl 53 (2014) 6364-6368. [99] M. Wang, Z. Cui, M. Yang, L. Lin, X. Chen, M. Wang, J. Han, Core/shell structured CdS/polydopamine/TiO2 ternary hybrids as highly active visible-light photocatalysis, J Colloid Interface Sci 544 (2019) 1-7. [100] R. Qu, W. Zhang, N. Liu, Q. Zhang, Y. Liu, X. Li, Y. Wei, L. Feng, Antioil Ag3PO4 Nanoparticle/Polydopamine/Al2O3 Sandwich Structure for Complex Wastewater Treatment: Dynamic Catalysis under Natural Light, ACS SUSTAIN CHEM ENG 6 (2018) 8019-8028. [101] N. Li, G. Chen, J. Zhao, B. Yan, Z. Cheng, L. Meng, V. Chen, Self-cleaning PDA/ZIF-67@PP 36

membrane for dye wastewater remediation with peroxymonosulfate and visible light activation, J MEMBRANE SCI 591 (2019) 117341. [102] W.-X. Mao, X.-J. Lin, W. Zhang, Z.-X. Chi, R.-W. Lyu, A.-M. Cao, L.-J. Wan, Core–shell structured TiO2@ polydopamine for highly active visible-light photocatalysis, CHEM COMMUN 52 (2016) 7122-7125. [103] F.X. Ma, H.B. Wu, B.Y. Xia, C.Y. Xu, X.W.D. Lou, Hierarchical β‐Mo2C Nanotubes Organized by Ultrathin Nanosheets as a Highly Efficient Electrocatalyst for Hydrogen Production, ANGEW CHEM INT EDIT 54 (2015) 15395-15399. [104] J. Zhang, Z. Zhao, Z. Xia, L. Dai, A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions, Nat Nanotechnol 10 (2015) 444-452. [105] Y. Ji, J.L. Li, S.F.Y. Li, Synergistic effect of the bifunctional polydopamine–Mn 3 O 4 composite electrocatalyst for vanadium redox flow batteries, J MATER CHEM A 5 (2017) 15154-15166. [106] J. Xi, Y. Xia, Y. Xu, J. Xiao, S. Wang, (Fe, Co)@ nitrogen-doped graphitic carbon nanocubes derived from polydopamine-encapsulated metal–organic frameworks as a highly stable and selective non-precious oxygen reduction electrocatalyst, CHEM COMMUN 51 (2015) 10479-10482. [107] Y.F. Wang, D.Y.C. Leung, J. Xuan, H.Z. Wang, A review on unitized regenerative fuel cell technologies, part B: Unitized regenerative alkaline fuel cell, solid oxide fuel cell, and microfluidic fuel cell, RENEW SUST ENERG REV 75 (2017) 775-795. [108] C. Li, X. Han, F. Cheng, Y. Hu, C. Chen, J. Chen, Phase and composition controllable synthesis of cobalt manganese spinel nanoparticles towards efficient oxygen electrocatalysis, Nat Commun 6 (2015) 7345. [109] Y. Liu, F. Chen, W. Ye, M. Zeng, N. Han, F. Zhao, X. Wang, Y. Li, High ‐ Performance Oxygen Reduction Electrocatalyst Derived from Polydopamine and Cobalt Supported on Carbon Nanotubes for Metal–Air Batteries, ADV FUNCT MATER 27 (2017). [110] Y.J. Wang, N. Zhao, B. Fang, H. Li, X.T. Bi, H. Wang, Carbon-supported Pt-based alloy electrocatalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells: particle size, shape, and composition manipulation and their impact to activity, Chem Rev 115 (2015) 3433-3467. [111] E. Meku, C.Y. Du, Y.J. Wang, L. Du, Y.R. Sun, F.P. Kong, G.P. Yin, Concentration Gradient Pd-Ir-Ni/C Electrocatalyst with Enhanced Activity and Methanol Tolerance for Oxygen Reduction Reaction in Acidic Medium, ELECTROCHIM ACTA 192 (2016) 177-187. [112] R. Yue, H. Wang, D. Bin, J. Xu, Y. Du, W. Lu, J. Guo, Facile one-pot synthesis of Pd– PEDOT/graphene nanocomposites with hierarchical structure and high electrocatalytic performance for ethanol oxidation, J MATER CHEM A 3 (2015) 1077-1088. [113] Y. Sun, Y.-C. Hsieh, L.-C. Chang, P.-W. Wu, J.-F. Lee, Synthesis of Pd 9 Ru@ Pt nanoparticles for oxygen reduction reaction in acidic electrolytes, J POWER SOURCES 277 (2015) 116-123. [114] K.G. Qu, Y. Zheng, S. Dai, S.Z. Qiao, Graphene oxide-polydopamine derived N, S-codoped carbon nanosheets as superior bifunctional electrocatalysts for oxygen reduction and evolution, Nano Energy 19 (2016) 373-381. [115] S. Ratso, I. Kruusenberg, M. Kaarik, M. Kook, R. Saar, M. Pars, J. Leis, K. Tammeveski, Highly efficient nitrogen-doped carbide-derived carbon materials for oxygen reduction reaction in alkaline media, Carbon 113 (2017) 159-169. [116] X. Cui, Q. Yang, Y. Xiong, Z. Bao, H. Xing, S. Dai, Preparation of ordered N-doped mesoporous carbon materials via a polymer–ionic liquid assembly, CHEM COMMUN 53 (2017) 4915-4918. 37

[117] K. Qu, Y. Zheng, Y. Jiao, X. Zhang, S. Dai, S.-Z. Qiao, Polydopamine-Inspired, Dual Heteroatom-Doped Carbon Nanotubes for Highly Efficient Overall Water Splitting, ADV ENERGY MATER 7 (2017) 1602068. [118] K. Qu, Y. Zheng, X. Zhang, K. Davey, S. Dai, S.Z. Qiao, Promotion of Electrocatalytic Hydrogen Evolution Reaction on Nitrogen-Doped Carbon Nanosheets with Secondary Heteroatoms, ACS Nano 11 (2017) 7293-7300. [119] S. Yang, L. Zhi, K. Tang, X. Feng, J. Maier, K. Müllen, Efficient synthesis of heteroatom (N or S)‐ doped graphene based on ultrathin graphene oxide ‐ porous silica sheets for oxygen reduction reactions, ADV FUNCT MATER 22 (2012) 3634-3640. [120] D.W. Kim, O.L. Li, N. Saito, Enhancement of ORR catalytic activity by multiple heteroatom-doped carbon materials, Phys Chem Chem Phys 17 (2015) 407-413. [121] H. Zhao, C.C. Weng, Z.P. Hu, L. Ge, Z.Y. Yuan, CdS-Polydopamine-Derived N,S-Codoped Hierarchically Porous Carbons as Highly Active Electrocatalyst for Oxygen Reduction, ACS SUSTAIN CHEM ENG 5 (2017) 9914-9922. [122] M. Zubair, M. Daud, G. McKay, F. Shehzad, M.A. Al-Harthi, Recent progress in layered double hydroxides (LDH)-containing hybrids as adsorbents for water remediation, APPL CLAY SCI 143 (2017) 279-292. [123] Q. Huang, M. Liu, L. Mao, D. Xu, G. Zeng, H. Huang, R. Jiang, F. Deng, X. Zhang, Y. Wei, Surface functionalized SiO2 nanoparticles with cationic polymers via the combination of mussel inspired chemistry and surface initiated atom transfer radical polymerization: Characterization and enhanced removal of organic dye, J Colloid Interface Sci 499 (2017) 170-179. [124] G. Zhao, J. Li, X. Ren, C. Chen, X. Wang, Few-layered graphene oxide nanosheets as superior sorbents for heavy metal ion pollution management, Environ Sci Technol 45 (2011) 10454-10462. [125] S. Yu, X. Wang, W. Yao, J. Wang, Y. Ji, Y. Ai, A. Alsaedi, T. Hayat, X. Wang, Macroscopic, Spectroscopic, and Theoretical Investigation for the Interaction of Phenol and Naphthol on Reduced Graphene Oxide, Environ Sci Technol 51 (2017) 3278-3286. [126] H. Shi, Y. He, Y. Pan, H. Di, G. Zeng, L. Zhang, C. Zhang, A modified mussel-inspired method to fabricate TiO 2 decorated superhydrophilic PVDF membrane for oil/water separation, J MEMBRANE SCI 506 (2016) 60-70. [127] J. Zhao, Q. Huang, M. Liu, Y. Dai, J. Chen, H. Huang, Y. Wen, X. Zhu, X. Zhang, Y. Wei, Synthesis of functionalized MgAl-layered double hydroxides via modified mussel inspired chemistry and their application in organic dye adsorption, J Colloid Interface Sci 505 (2017) 168-177. [128] J. Wang, L.A. Hou, K.K. Yan, L. Zhang, Q.J. Yu, Polydopamine nanocluster decorated electrospun nanofibrous membrane for separation of oil/water emulsions, J MEMBRANE SCI 547 (2018) 156-162. [129] F. Fu, Q. Wang, Removal of heavy metal ions from wastewaters: a review, J Environ Manage 92 (2011) 407-418. [130] Y. Wang, Y. Zhang, C. Hou, M. Liu, Mussel-inspired synthesis of magnetic polydopamine– chitosan nanoparticles as biosorbent for dyes and metals removal, J TAIWAN INST CHEM E 61 (2016) 292-298. [131] B. Satilmis, P.M. Budd, Selective dye adsorption by chemically-modified and thermally-treated polymers of intrinsic microporosity, J Colloid Interface Sci 492 (2017) 81-91. [132] V.K. Thakur, S.I. Voicu, Recent advances in cellulose and chitosan based membranes for water purification: A concise review, Carbohydr Polym 146 (2016) 148-165. [133] M. Xie, H.K. Shon, S.R. Gray, M. Elimelech, Membrane-based processes for wastewater nutrient 38

recovery: Technology, challenges, and future direction, Water Res 89 (2016) 210-221. [134] P. Kanagaraj, A. Nagendran, D. Rana, T. Matsuura, S. Neelakandana, T. Karthikkumar, A. Muthumeenal, Influence of N-phthaloyl chitosan on poly (ether imide) ultrafiltration membranes and its application in biomolecules and toxic heavy metal ion separation and their antifouling properties, APPL SURF SCI 329 (2015) 165-173. [135] D. Li, Y.S. Yan, H.T. Wang, Recent advances in polymer and polymer composite membranes for reverse and forward osmosis processes, PROG POLYM SCI 61 (2016) 104-155. [136] F. Xiao, P. Xiao, W.J. Zhang, D.S. Wang, Identification of key factors affecting the organic fouling on low-pressure ultrafiltration membranes, J MEMBRANE SCI 447 (2013) 144-152. [137] P. Xiao, F. Xiao, D.S. Wang, T. Qin, S.P. He, Investigation of organic foulants behavior on hollow-fiber UF membranes in a drinking water treatment plant, SEP PURIF TECHNOL 95 (2012) 109-117. [138] X.Y. Zhang, Q. Huang, F.J. Deng, H.Y. Huang, Q. Wan, M.Y. Liu, Y. Wei, Mussel-inspired fabrication of functional materials and their environmental applications: Progress and prospects, APPL MATER TODAY 7 (2017) 222-238. [139] B.K. Ahn, Perspectives on Mussel-Inspired Wet Adhesion, J Am Chem Soc 139 (2017) 10166-10171. [140] R.S. Hebbar, A.M. Isloor, K. Ananda, A.F. Ismail, Fabrication of polydopamine functionalized halloysite nanotube/polyetherimide membranes for heavy metal removal, J MATER CHEM A 4 (2016) 764-774. [141] X.F. Fang, J.S. Li, X. Li, S.L. Pan, X. Zhang, X.Y. Sun, J.Y. Shen, W.Q. Han, L.J. Wang, Internal pore decoration with polydopamine nanoparticle on polymeric ultrafiltration membrane for enhanced heavy metal removal, CHEM ENG J 314 (2017) 38-49. [142] Z. Rao, K. Feng, B. Tang, P. Wu, Surface Decoration of Amino-Functionalized Metal-Organic Framework/Graphene Oxide Composite onto Polydopamine-Coated Membrane Substrate for Highly Efficient Heavy Metal Removal, ACS Appl Mater Interfaces 9 (2017) 2594-2605. [143] J. Wang, T. Huang, L. Zhang, Q.J. Yu, L. Hou, Dopamine crosslinked graphene oxide membrane for simultaneous removal of organic pollutants and trace heavy metals from aqueous solution, Environ Technol 39 (2018) 3055-3065. [144] J. Li, Q. Fan, Y. Wu, X. Wang, C. Chen, Z. Tang, X. Wang, Magnetic polydopamine decorated with Mg–Al LDH nanoflakes as a novel bio-based adsorbent for simultaneous removal of potentially toxic metals and anionic dyes, J MATER CHEM A 4 (2016) 1737-1746. [145] M.K. Uddin, A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade, CHEM ENG J 308 (2017) 438-462. [146] Q. Huang, M.Y. Liu, J.Y. Chen, K. Wang, D.Z. Xu, F.J. Deng, H.Y. Huang, X.Y. Zhang, Y. Wei, Mussel inspired preparation of functional silica nanocomposites for environmental adsorption applications, APPL SURF SCI 387 (2016) 285-293. [147] T.A. Saleh, A. Sari, M. Tuzen, Effective adsorption of antimony(III) from aqueous solutions by polyamide-graphene composite as a novel adsorbent, CHEM ENG J 307 (2017) 230-238. [148] Q.L. Fang, S.X. Duan, J.F. Zhang, J.X. Li, K.C.F. Leung, Dual shelled Fe3O4/polydopamine hollow microspheres as an effective Eu(III) adsorbent, J MATER CHEM A 5 (2017) 2947-2958. [149] Y.F. Pan, P.X. Cai, M. Farmahini-Farahani, Y.D. Li, X.B. Hou, H.N. Xiao, Amino-functionalized alkaline clay with cationic star-shaped polymer as adsorbents for removal of Cr(VI) in aqueous solution, APPL SURF SCI 385 (2016) 333-340. 39

[150] J.W. Fu, Z.H. Chen, M.H. Wang, S.J. Liu, J.H. Zhang, J.N. Zhang, R.P. Han, Q. Xu, Adsorption of methylene blue by a high-efficiency adsorbent (polydopamine microspheres): Kinetics, isotherm, thermodynamics and mechanism analysis, CHEM ENG J 259 (2015) 53-61. [151] Y. Yu, J.G. Shapter, R. Popelka-Filcoff, J.W. Bennett, A.V. Ellis, Copper removal using bio-inspired polydopamine coated natural zeolites, J Hazard Mater 273 (2014) 174-182. [152] N. Farnad, K. Farhadi, N.H. Voelcker, Polydopamine Nanoparticles as a New and Highly Selective Biosorbent for the Removal of Copper (II) Ions from Aqueous Solutions, WATER AIR SOIL POLL 223 (2012) 3535-3544. [153] Q. Zhang, Y. Li, Q. Yang, H. Chen, X. Chen, T. Jiao, Q. Peng, Distinguished Cr(VI) capture with rapid and superior capability using polydopamine microsphere: Behavior and mechanism, J Hazard Mater 342 (2018) 732-740. [154] D. Li, Q. Li, D. Mao, N. Bai, H. Dong, A versatile bio-based material for efficiently removing toxic dyes, heavy metal ions and emulsified oil droplets from water simultaneously, BIORESOURCE TECHNOL245 (2017) 649-655. [155] F. Zhao, E. Repo, D. Yin, Y. Meng, S. Jafari, M. Sillanpää, EDTA-cross-linked β-cyclodextrin: an environmentally friendly bifunctional adsorbent for simultaneous adsorption of metals and cationic dyes, ENVIRON SCI TECHNOL 49 (2015) 10570-10580. [156] D.-M. Guo, Q.-D. An, Z.-Y. Xiao, S.-R. Zhai, D.-J. Yang, Efficient removal of Pb(II), Cr(VI) and organic dyes by polydopamine modified chitosan aerogels, Carbohydr Polym 202 (2018) 306-314. [157] J. Cui, Z. Zhou, A. Xie, M. Meng, Y. Cui, S. Liu, J. Lu, S. Zhou, Y. Yan, H. Dong, Bio-inspired fabrication of superhydrophilic nanocomposite membrane based on surface modification of SiO2 anchored by polydopamine towards effective oil-water emulsions separation, Sep Purif Technol 209 (2019) 434-442. [158] X. Sun, L. Yan, R. Xu, M. Xu, Y. Zhu, Surface modification of TiO2 with polydopamine and its effect on photocatalytic degradation mechanism, CCOLLOID SURFACE A 570 (2019) 199-209. [159] Y. Li, R. Zhao, S. Chao, B. Sun, C. Wang, X. Li, Polydopamine coating assisted synthesis of MnO2 loaded inorganic/organic composite electrospun fiber adsorbent for efficient removal of Pb2+ from water, Chem Eng J 344 (2018) 277-289. [160] K. Cui, B. Yan, Y. Xie, H. Qian, X. Wang, Q. Huang, Y. He, S. Jin, H. Zeng, Regenerable urchin-like Fe3O4@PDA-Ag hollow microspheres as catalyst and adsorbent for enhanced removal of organic dyes, J Hazard Mater 350 (2018) 66-75. [161] J. Fu, Z. Chen, M. Wang, S. Liu, J. Zhang, J. Zhang, R. Han, Q. Xu, Adsorption of methylene blue by a high-efficiency adsorbent (polydopamine microspheres): Kinetics, isotherm, thermodynamics and mechanism analysis, Chem Eng J 259 (2015) 53-61. [162] Q. Zhang, Y. Li, Q. Yang, H. Chen, X. Chen, T. Jiao, Q. Peng, Distinguished Cr(VI) capture with rapid and superior capability using polydopamine microsphere: Behavior and mechanism, J Hazard Mater 342 (2018) 732-740. [163]

Y.

Lv,

Y.

Du,

Z.X.

Chen,

W.Z.

Qiu,

Z.K.

Xu,

Nanocomposite

membranes

of

polydopamine/electropositive nanoparticles/polyethyleneimine for nanofiltration, J MEMBRANE SCI 545 (2018) 99-106. [164] J. Yin, B.L. Deng, Polymer-matrix nanocomposite membranes for water treatment, J MEMBRANE SCI 479 (2015) 256-275. [165] R. Zhang, Y. Liu, M. He, Y. Su, X. Zhao, M. Elimelech, Z. Jiang, Antifouling membranes for sustainable water purification: strategies and mechanisms, Chem Soc Rev 45 (2016) 5888-5924. 40

[166] A. Politano, P. Argurio, G. Di Profio, V. Sanna, A. Cupolillo, S. Chakraborty, H.A. Arafat, E. Curcio, Photothermal Membrane Distillation for Seawater Desalination, Adv Mater 29 (2017). [167] K. Xu, B. Feng, C. Zhou, A.S. Huang, Synthesis of highly stable graphene oxide membranes on polydopamine functionalized supports for seawater desalination, CHEM ENG SCI 146 (2016) 159-165. [168] G. Amy, N. Ghaffour, Z.Y. Li, L. Francis, R.V. Linares, T. Missimer, S. Lattemann, Membrane-based seawater desalination: Present and future prospects, Desalination 401 (2017) 16-21. [169] Y.F. Li, G.W. He, S.F. Wang, S.N. Yu, F.S. Pan, H. Wu, Z.Y. Jiang, Recent advances in the fabrication of advanced composite membranes, J MATER CHEM A 1 (2013) 10058-10077. [170] V. Dalvi, Y.P. Tang, C. Staudt, T.S. Chung, Influential effects of nanoparticles, solvent and surfactant treatments on thin film nanocomposite (TFN) membranes for seawater desalination, Desalination 420 (2017) 216-225. [171] J. Yin, G.C. Zhu, B.L. Deng, Graphene oxide (GO) enhanced polyamide (PA) thin-film nanocomposite (TFN) membrane for water purification, Desalination 379 (2016) 93-101. [172] N. Niksefat, M. Jahanshahi, A. Rahimpour, The effect of SiO 2 nanoparticles on morphology and performance of thin film composite membranes for forward osmosis application, Desalination 343 (2014) 140-146. [173] Q. Li, Y.H. Wang, J. Song, Y.P. Guan, H. Yu, X.H. Pan, F.Y. Wu, M. Zhang, Influence of silica nanospheres on the separation performance of thin film composite poly(piperazine-amide) nanofiltration membranes, APPL SURF SCI 324 (2015) 757-764. [174] G.S. Lai, W.J. Lau, S.R. Gray, T. Matsuura, R.J. Gohari, M.N. Subramanian, S.O. Lai, C.S. Ong, A.F. Ismail, D. Emazadah, M. Ghanbari, A practical approach to synthesize polyamide thin film nanocomposite (TFN) membranes with improved separation properties for water/wastewater treatment, J MATER CHEM A 4 (2016) 4134-4144. [175] B. Rajaeian, A. Heitz, M.O. Tade, S.M. Liu, Improved separation and antifouling performance of PVA thin film nanocomposite membranes incorporated with carboxylated TiO2 nanoparticles, J MEMBRANE SCI 485 (2015) 48-59. [176] E.S. Kim, G. Hwang, M.G. El-Din, Y. Liu, Development of nanosilver and multi-walled carbon nanotubes thin-film nanocomposite membrane for enhanced water treatment, J MEMBRANE SCI 394 (2012) 37-48. [177] T.Y. Liu, H.G. Yuan, Q. Li, Y.H. Tang, Q. Zhang, W. Qian, B. Van der Bruggen, X. Wang, Ion-Responsive Channels of Zwitterion-Carbon Nanotube Membrane for Rapid Water Permeation and Ultrahigh Mono-/Multivalent Ion Selectivity, ACS Nano 9 (2015) 7488-7496. [178] S. Sorribas, P. Gorgojo, C. Tellez, J. Coronas, A.G. Livingston, High flux thin film nanocomposite membranes based on metal-organic frameworks for organic solvent nanofiltration, J Am Chem Soc 135 (2013) 15201-15208. [179] F.Y. Zhao, Y.L. Ji, X.D. Weng, Y.F. Mi, C.C. Ye, Q.F. An, C.J. Gao, High-Flux Positively Charged Nanocomposite Nanofiltration Membranes Filled with Poly(dopamine) Modified Multiwall Carbon Nanotubes, ACS Appl Mater Interfaces 8 (2016) 6693-6700. [180] Y. Lv, Y. Du, W.Z. Qiu, Z.K. Xu, Nanocomposite Membranes via the Co-deposition of Polydopamine/ Polyethyleneimine with Silica Nanoparticles for Enhanced Mechanical Strength and High Water Permeability, ACS APPL MATER INTER 9 (2017) 2966. [181] L. Su, Y. Yu, Y. Zhao, F. Liang, X. Zhang, Strong Antibacterial Polydopamine Coatings Prepared by a Shaking-assisted Method, Sci Rep 6 (2016) 24420. [182] H. Karkhanechi, R. Takagi, H. Matsuyama, Biofouling resistance of reverse osmosis membrane 41

modified with polydopamine, Desalination 336 (2014) 87-96. [183] Y. Jiao, L.N. Niu, S. Ma, J. Li, F.R. Tay, J.H. Chen, Quaternary ammonium-based biomedical materials: State-of-the-art, toxicological aspects and antimicrobial resistance, PROG POLYM SCI 71 (2017) 53-90. [184] Z. Wang, Y. Wang, G. Liu, Rapid and Efficient Separation of Oil from Oil‐in‐Water Emulsions Using a Janus Cotton Fabric, ANGEW CHEM INT EDIT 55 (2016) 1291-1294. [185] Y. Cao, N. Liu, W. Zhang, L. Feng, Y. Wei, One-Step Coating toward Multifunctional Applications: Oil/Water Mixtures and Emulsions Separation and Contaminants Adsorption, ACS Appl Mater Interfaces 8 (2016) 3333-3339. [186] Z.W. Yu, F.F. Yun, Z.Y. Gong, Q. Yao, S.X. Dou, K.S. Liu, L. Jiang, X.L. Wang, A novel reusable superhydrophilic NiO/Ni mesh produced by a facile fabrication method for superior oil/water separation, J MATER CHEM A 5 (2017) 10821-10826. [187] Z.L. Xu, K. Miyazaki, T. Hori, Fabrication of polydopamine-coated superhydrophobic fabrics for oil/water separation and self-cleaning, APPL SURF SCI 370 (2016) 243-251. [188] X. Yang, Y. He, G.Y. Zeng, X. Chen, H. Shi, D.Y. Qing, F. Li, Q. Chen, Bio-inspired method for preparation of multiwall carbon nanotubes decorated superhydrophilic poly(vinylidene fluoride) membrane for oil/water emulsion separation, CHEM ENG J 321 (2017) 245-256. [189] F. Zhang, S.J. Gao, Y.Z. Zhu, J. Jin, Alkaline-induced superhydrophilic/underwater superoleophobic polyacrylonitrile membranes with ultralow oil-adhesion for high-efficient oil/water separation, J MEMBRANE SCI 513 (2016) 67-73. [190] J.L. Ge, J.C. Zhang, F. Wang, Z.L. Li, J.Y. Yu, B. Ding, Superhydrophilic and underwater superoleophobic nanofibrous membrane with hierarchical structured skin for effective oil-in-water emulsion separation, J MATER CHEM A 5 (2017) 497-502. [191] R. Ou, J. Wei, L. Jiang, G.P. Simon, H. Wang, Robust Thermoresponsive Polymer Composite Membrane with Switchable Superhydrophilicity and Superhydrophobicity for Efficient Oil–Water Separation, ENVIRON SCI TECHNOL 50 (2016) 906-914. [192] Y.H. Xiang, F. Liu, L.X. Xue, Under seawater superoleophobic PVDF membrane inspired by polydopamine for efficient oil/seawater separation, J MEMBRANE SCI 476 (2015) 321-329. [193] Y. Yin, H. Li, L. Zhu, T. Guo, X. Li, W. Xing, Q. Xue, A durable mesh decorated with polydopamine/graphene oxide for highly efficient oil/water mixture separation, Appl Surf Sci 479 (2019) 351-359. [194] J.J. Li, L.T. Zhu, Z.H. Luo, Electrospun fibrous membrane with enhanced swithchable oil/water wettability for oily water separation, CHEM ENG J 287 (2016) 474-481. [195] M. Obaid, H.O. Mohamed, A.S. Yasin, M.A. Yassin, O.A. Fadali, H. Kim, N.A.M. Barakat, Under-oil superhydrophilic wetted PVDF electrospun modified membrane for continuous gravitational oil/water separation with outstanding flux, Water Res 123 (2017) 524-535. [196] J. Zhang, H. Liu, L. Jiang, Membrane ‐ Based Strategy for Efficient Ionic Liquids/Water Separation Assisted by Superwettability, ADV FUNCT MATER 27 (2017) 1606544. [197] J.H. Ryu, P.B. Messersmith, H. Lee, Polydopamine Surface Chemistry: A Decade of Discovery, ACS APPL MATER INTER 10 (2018) 7523-7540.

The authors declare that there is no confict of interest

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► Surface modification of materials through mussel-inspired chemistry ► The functional materials from mussel-inspired chemistry for environmental applications ► The utilization of materials from mussel-inspired chemistry for energy applications ► The utilization of materials from mussel-inspired chemistry for catalytical applications

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