Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 131–138
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Journal of Photochemistry and Photobiology A: Chemistry journal homepage: www.elsevier.com/locate/jphotochem
A biomimetic approach towards the synthesis of TiO2/carbon-clay as a highly recoverable photocatalyst Shu Huanga,1, Xi Lua,1, Zhenyu Lia , Harish Ravishankara , Jinfeng Wanga,b,* , Xungai Wanga,b a b
Deakin University, Institute for Frontier Materials, Geelong, Australia Wuhan Textile University, School of Textile Science and Engineering, Wuhan, China,
A R T I C L E I N F O
Article history: Received 8 June 2017 Received in revised form 20 September 2017 Accepted 9 October 2017 Available online 14 October 2017 Keywords: TiO2/carbon-clay Bio-mimetic Highly recoverable Strong adsorption capacity High photocatalytic activity
A B S T R A C T
Efficient use of sunlight for cleaning polluted water is a sustainable way of addressing the key environmental problems. Photocatalysts with high adsorption, good photocatalytic ability and highly recoverable performance are highly desirable to effective clean organic contaminates from water. In this study, a highly recoverable TiO2/carbon-clay photocatalyst was prepared by immobilizing TiO2 (commercial P25) on strong adsorbent (clay) via a bio-mimetic coating strategy and followed by a carbonization process. Superior separability of TiO2/carbon-clay was achieved by simple gravity sedimentation, in which most of TiO2/carbon-clay settled within 5 min and all the particles settled within 2 h. The obtained TiO2/carbon-clay composites possessed a maximum adsorption capacity (Qmax) of 95.4 mg/g and showed high photocatalytic activity, which removed 99% dye within 30 min under simulated sunlight irradiation. This TiO2/carbon-clay composites also exhibited excellent durability and no apparent reduction of dye removal efficiency was observed after 5 cycles reuse. © 2017 Published by Elsevier B.V.
1. Introduction With the rapid development of economy, vast of pollutants are discharged from industrial processes. The reckless discharge of untreated industrial wastewater into environment has caused seriously aqueous pollution [1,2]. Coloured compounds, comprising pigments or dyes, can colour the water and limit sunlight into the lower level, affecting the aquatic life [3]. Additionally, many of these compounds are toxic or even carcinogenic. Therefore, it is an urgent task to find an environmental friendly way to remove coloured compounds from environmental aqueous system. Among the diverse techniques for removing coloured compounds from water, physical adsorption is widely used because of its simplicity of operation [4]. Natural clay, as a typical physical adsorbent, has been widely used for its high adsorption capacity. It is reported that the adsorption property of clay could exceed that of activated carbon under the same conditions [5,6]. However, all the adsorbents suffered from the limitation of reuse owing to their non-destructive nature. The technology of physical adsorption produces large amounts of sludge that has to be further
* Corresponding author. E-mail address:
[email protected] (J. Wang). These authors contributed equally to this work.
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https://doi.org/10.1016/j.jphotochem.2017.10.017 1010-6030/© 2017 Published by Elsevier B.V.
regenerated or disposed of as a prescribed waste. Therefore, the regeneration of the used adsorbents is a critical step to achieve a cost-effective use of adsorbents for large-scale coloured compounds removal from environmental aqueous system [7]. One effective method to obtain reusable adsorbent is to functionalize the surface of adsorbent with photocatalysts. The existence of photocatalysts can degrade the adsorbed contaminates under irradiation and recover its adsorption capacity [8]. In general, the photocatalysts can convert inexhaustible solar energy into chemical energy to oxidize/reduce pollutants and bacteria in the environment [9–11]. Among all the semiconductors, TiO2 nanoparticles (NPs) gains special attention because of its intrinsic hydrophilicity, robust chemical stability, long durability, low cost, and high reactivity [12–19]. Dyestuffs, saccharides, and oils in wastewater could be mineralized to inorganic small molecules after photocatalytic reaction using TiO2 [9–11]. Many efforts have been devoted to obtain TiO2/clay composites. However the preparation is limited by sol-gel method [20]. Compared with commercialized TiO2, the synthesis of TiO2 NPs by sol-gel method is very sensitive to process conditions to keep the reproducibility of TiO2/clay composites for environmental remediation application [21]. Nature provides a wide range of materials with different functions, which serve as sources of bio inspiration for materials
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scientists. For example, dopamine (DOPA), a natural amino acid abundantly present in mussel adhesive proteins (MAP), has been found to be the key component responsible for the versatile adhesive capabilities of mussels. Lee, Messersmith, and others showed that catechol groups in DOPA or polydopamine (PDOPA) were capable of forming hydrogen bonds, metalligand complexes, and quinhydrone charge-transfer complexes with various surfaces [22]. Polydopamine has recently attracted considerable interest as a multifunctional thin film coating. More recently, theoretical calculations [23] and experiments [24] have proved there is strong interaction between TiO2 and dopamine (DOPA). In this study, for the first time, a simple biomimetic strategy for immobilizing commercial TiO2 (P25) on exfoliated clay nanosheets to construct P25/PDOPA/clay. By tuning the ratio of P25/clay, the density of P25 NPs on clay nanosheets can be well controlled. To prevent the decomposition of PDOPA, post-carbonization was used to convert the P25/PDOPA/clay to be P25/carbon-clay. The obtained P25/carbon-clay showed good dye removal efficiency, excellent durability and highly recoverable performance against removing dye Rhodamine B from water. 2. Experimental section 2.1. Materials Pristine clay (Na-montmorillonite: Na-MMT with the cationic exchange capacity of 145 mmol/100 g) was supplied by Nanocor Inc. TiO2 (P25, 20% rutile and 80% anatase), 3,4-dihydroxyphenethylamine hydrochloride (DOPA, 98%), tris(hydroxymethyl)-aminomethane (TRIS, 99%), and Rhodamine B were purchased from Sigma-Aldrich. All chemicals were used as received without further treatment. 2.2. Preparation of polydopamine modified clay solution In a typical experiment, 4 g of Na-MMT was dispersed in 2 L of deionized water and magnetically stirred for 48 h at a speed of 500 rpm, followed by vigorous stirring at 15 000 rpm for 1 h using a homogenizer. The suspension was centrifuged at 2000 rpm for 10 min to remove the un-exfoliated Na-MMT. The suspension was then collected for subsequent use. Dopamine-clay (D-clay) composites were then synthesized. In details, TRIS (2.4 g) and DOPA (3 g) were added into the exfoliated Na-MMT suspension, followed by stirring for 2 h in ambient atmosphere. The product was then centrifuged at 10 000 rpm for 10 min and subsequently washed with deionized water for 5 times. The as-prepared D-clay was re-dispersed into deionized water with a concentration of 18 mg/mL. 2.3. Preparation of P25 coated D-clay (P25/D-clay) and P25 coated carbon-clay (P25/C-clay) composites The procedure for P25/D-clay (4:1) synthesis is as follows: 20 mL of 0.5 mg/mL D-clay was sonicated for 30 min. Then 200 mL
of 0.2 mg/mL P25 water dispersion was slowly added into the above D-clay solution while stirring constantly at room temperature. After stirring for 12 h in dark, the final product was collected by centrifugation, washed 3 times with deionized water and followed by freeze dry. The obtained P25/D-clay powder was calcinated in a tube furnace at 600 C with a heating rate of 5 C/ min and kept for 2 h under N2 atmosphere. The obtained product was designated as P25/C-clay composites. 2.4. Dye degradation test under simulated sunlight irradiation The decomposition of the dye solution was carried out in a simulated sunlight irradiation instrument, Atlas Suntester XLS. The test method was described in our previous work [25]. The Atlas Suntester XLS instrument was equipped with a 150W xenon lamp and a filter (coated with quartz dish). Rhodamine B (RhB) was used as a probe molecule to evaluate the photocatalytic activity of P25/ C-clay in response to sunlight (UV and visible) irradiation. The characteristic absorption peak of RhB at 554 nm was chosen to monitor the photocatalytic degradation process. The absorption peaks corresponding to the dye RhB disappeared under simulated sunlight irradiation, indicating degradation of the dye [26,27]. The original concentration of RhB solution was 12 ppm. The details of photo-degradation process were described as follows: 1) the dried powder was dispersed in 20 mL of RhB aqueous solution (The amount of P25 was fixed for all experiments). 2) The suspension was kept stirring in the dark for 1 h to reach the adsorption and desorption equilibrium of RhB on the particle surface. 3) The suspension was kept stirring continuously and irradiated under simulated sunlight instrument with a flux of 300 wm2. 4) At a given time interval, 3 mL suspension was taken out, and centrifuged to remove the NPs from the mixture solution. 5) The supernatant was tested by the Cary 300 UV–vis spectrophotometer to measure the UV–vis absorbance spectra. All the results were based on the assumption that the concentration of catalysts and RhB did not change during the sampling process. 2.5. Characterizations TEM images were taken by a JEOL 2100 transmission electron microscope at 200 keV. WAXD tests were performed on a powder diffractometer (PANalytical/X’Pert Powder) using Cu Ka radiation. The exfoliated clay easily stacked and restores the layer by layer structure upon water evaporation. As a result, instead of drying exfoliated clay suspension, a gel-like clay sample centrifuged for 10 min from exfoliated clay suspension at a speed of 10 000 rpm was used for XRD study. Thermogravimetric analysis (TGA) was carried on TA-Q50 at a heating rate of 10 C/min in air atmosphere. Fourier transform infrared spectroscopy (FT-IR) was measured using a Burker Vertex 70 FT-IR spectrometer using ATR method. A Renishaw Raman system spectrometer (model 1000) was used to study the Raman spectra. The exciting source is a 514.5 nm radiation from 20 mW air-cooled argon ion laser. UV–vis
Scheme 1. Schematic description of preparation steps and structure of P25/C-clay.
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Fig. 1. (a) XRD patterns of pristine clay and colloidal clay aggregates in water obtained by mechanical shearing. (b) XRD of Pristine clay, P25, and P25/C-clay.
absorbance spectra were measured by a double beam Cary 300 UV–vis spectrophotometer (Agilent, Australia). 3. Results and discussions Scheme 1 shows the preparation steps of P25/C-clay. Na-MMT clay was exfoliated into nano-sheet with an average size of 430 nm. (Fig. S1) Then a natural “super glue”, polydopamine, was used to adhere P25 NPs onto the clay nano-sheet to get P25/D-clay. The obtained P25/D-clay was calcinated at 600 C to convert polydopamine into carbon. The conversion of dopamine to carbon layer could increase the stability of P25/C-clay composite during photodegradation process. This carbon layer could also assist the strong adsorption of dye molecule and promote the electron-hole separation for achieving improved photo-degradation property [28,29]. Pristine clay is usually in the form of crystal sheets with thickness of tens of nanometers, each sheet is composed of many individual silicate layers stacked together. To achieve large surface area, delamination of clay into single layers is necessary. Fig. 1(a) shows the XRD patterns of the pristine clay powder and the gel-like clay aggregate. For the pristine clay, the (001) basal plane of clay observed at 7.23 corresponds to an interlayer spacing of 1.22 nm (calculated from the Bragg equation) [30]. Besides, the pristine clay
shows a distinctive diffraction peak at 19.98 with d-spacing of 0.45 nm, corresponding to the reflection peak of (020). It is interesting to observe that the (001) basal plane disappears in the gel-like clay sample, indicating that the ordered stacking structure of clay has been destroyed by the shearing force. The pronounced halo in the range of 2u = 20 –30 can be ascribed to the scattering of liquid water. In addition, a very weak reflection at 2u = 19.8 is observed, which could be assigned to (020) plane for a twodimensional hexagonal unit cell. The XRD results prove that NaMMT clay was successfully exfoliated into nanosheets and the twodimensional structure of nanosheet is retained. Fig. 1(b) shows the X-ray diffraction pattern of the synthesized clay, P25 and P25/Cclay. P25/C-clay has very similar XRD pattern with pure P25 sample. Both anatase (101) and rutile (110) peaks are observed in the composites and there is no diffraction peaks from clay, which further proves clay remained as exfoliated nanosheets after the P25 loading and carbonization process. Fig. 2(a) shows the TEM image of polydopamine modified clay. The amount of P25 in the composite is a key parameter for high photocatalytic activity of the obtained composite. The P25 coating density is controlled by varying the feed ratio of P25 and clay. The initial mass ratios of the two components P25 NPs and clay nanosheets in this experiment were 1:1, 2:1 and 4:1, respectively. As shown in Fig. 2 (b, c, d), P25 NPs are successfully immobilized on
Fig. 2. TEM images of polydopamine modified clay (a), P25/C-clay composites with the two components P25 NPs and clay nano-sheets mass ratio of (b) 1:1, (c) 2:1, and (d) 4:1.
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Fig. 3. (a) FT-IR spectra of clay, P25, and P25/C-clay composites, (b) Raman spectra of P25/C-clay composites. (c) TGA cures of P25, Carbon-clay, and P25/C-clay composites.
the surface of clay nanosheets, and there are almost no free P25 NPs outside of the nanosheet. From the TEM images, the coating of P25 nanocrystals on clay sheets becomes denser as the P25/clay feed ratio is increased. At the ratio of 4:1, P25 NPs are fully coated on the surface of clay (Figs. 2 d and S2). The composite obtained at this ratio was chosen for further characterizations and application. In addition, P25 nanocrystals immobilized on clay nanosheets
appeared to exhibit strong interactions with the underlying clay nanosheets since sonication did not result in their dissociation. Fig. 3(a) displays the FT-IR spectra of clay, P25, and P25/C-clay. For the Na-MMT clay sample, the main peak at 988 cm1 is attributed to Si O in-plane stretching [31]. The broad bands at 3404 and 1634 cm1 are the stretching and bending vibrations for the hydroxyl groups of water molecules present in the clay. For
Fig. 4. (a) XPS survey spectra of P25/C-clay composites, high-resolution Ti 2p (b), O 1 s (c), and C 1 s (d) spectra.
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Fig. 5. PL spectra of P25/clay before and after carbonization in a 1 mmol/L solution of terephthalic acid under simulated sunlight irradiation after 30 min.
P25, the broad peak at 3352 cm1 is attributed to surface adsorbed water, and the peak at 1630 cm1 corresponds to the hydroxyl groups. The intensive band of P25 at around 716 cm1 is attributed to Ti O stretching and TiO Ti bridging stretching modes [32]. For the P25/C-clay composites, the peak at 1050 cm1 corresponds to the asymmetric vibration of the Si OSi of amorphous silica. Amorphous SiO2 may form when P25/D-clay powder was calcinated in a tube furnace at 600 C for 2 h. Comparing FT-IR spectra of the original clay, P25 and P25/C-clay, the characteristic peaks of both P25 and clay are found in the spectra of P25/C-clay, confirming the coexistence of P25 and clay in the obtained composite. After carbonization, a strong peak reduction is observed between 3300 and 3400 cm1. This is assigned to the OH groups present in clay greatly reduced after the carbonisation process. To further confirm the conversion of polydopamine into carbon after carbonization, Raman test was carried out. Fig. 3(b) shows the Raman spectra of P25/C-clay, in which the typical peaks located at 400, 514, and 640 cm1, corresponding the modes of anatase phase of TiO2 [33]. The peaks around 400 and 614 cm1 corresponds to the rutile phase of TiO2 [34]. Two dominating peaks are observed at 1331 and 1578 cm1, which correspond to D band and G band, respectively. The D band represents a disorder structure of the carbon and comes from the breathing mode of sp3 carbon, while the G-band comes from the stretching of C C bond in graphic carbon structure, and is due to the bond-stretching of C sp2 atoms. [35] This Raman spectrum of the P25/C-clay composite confirms that polydopamine has been converted into both amorphous carbon and graphitic carbon during the carbonization. The loading weight of P25 within the P25/C-clay was determined by thermogravimetric analysis (TGA) as shown in Fig. 3(c). TGA was conducted in air to remove the carbon layer. Weight loss before 120 C is attributed to water loss. P25, C-clay and P25/C-clay show weight loss of 1.81%, 3.27%, and 2.73%, respectively. Assume the loading weight of P25 in P25/C-clay is x: 0.0181x + 0.0327 (1 x) = 0.0273 Thus the loading weight of P25 within in P25/C-clay is calculated to be 36.94%.The XPS measurements were carried out to determine the chemical state of P25/C-clay composites (Fig. 4). As shown in Fig. 4(a), the full range surveys demonstrate that Ti, O and C elements co-exist in P25/C-clay composites. Fig. 4(b) demonstrates the Ti 2p high resolution spectra, in which the peak at 458.6 eV corresponds to Ti4+ 2p3/2 and the peak at 464.4 eV is assigned to Ti4+ 2p1/2 [36] . Fig. 4(c) shows the O 1 s spectra of P25/ C-clay composites. The binding energy at 530.6, 531.7, and 533 eV
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corresponds to Ti O, surface OH, and adsorbed H2O, respectively [37]. The C 1 s XPS spectra of P25/C-clay composites are shown in Fig. 4(d). The main C 1 s at 284.9 eV indicates that majority of the carbon layer is in the form of hydrocarbon. [38] Two peaks at 288 eV and 289 eV are assigned to oxygen bounded species C¼O and O C¼O, respectively [39]. No C 1 s peak at 281 eV (Ti C bond) was observed, strongly suggesting that C does not enter the TiO2 crystals during the calcination process [40]. It is worthy to note that, one C 1 s peak at 284.4 eV, which corresponds to the graphitic carbon, was observed in P25/C-clay composites [41]. The existence of graphite carbon is further supported by p–p* “shake-up” satellite at 290–291 eV, which is consistent with the Raman result [42]. We suggest that the formation of graphite-like carbon lies in the catalytic performances of P25 during the carbonization process [29]. This graphite-like carbon can promote the migration of photo-induced electrons at the graphite-like carbon/P25 interface, facilitating the electron/hole separation and improving the photocatalytic performances of P25 [29]. The generation of reactive OH was quantitatively analysed by the photoluminescence (PL) method with an aim of understanding the mechanism of the photo-induced charge carriers process and investigating the active species involved in the process. Fig. 5 shows the respective PL signals for P25/C-clay samples before and after the carbonized polydopamine formation. After carbonized polydopamine formation, the intensity of OH increased obviously, which indicates this carbon layer could inhibit the recombination of photo-induced charge carriers and prolong electron lifetime, resulting in an enhancement in their oxidation–reduction ability. This result is also consistent with the previous reported work, which was found that carbonized polydopamine was favourable for charge carrier separation and transfer in carbonized polydopamine-graphitic carbon nitride composites. [43] Compared with pure carbon nitride, the carbonized polydopamine-carbon nitride composites showed improved photocatalytic performance. Dye Rhodamine B (RhB) was used as a model molecule to evaluate the photocatalytic performance of the obtained P25/Cclay composite under simulated sunlight irradiation (Fig. 6b and d). For comparison, the photocatalytic performance of P25 was also carried out under the same conditions (Fig. 6a and c). As shown in Fig. 6(b), with the presence of P25/C-clay composite, the colour intensity reduced significantly after the adsorption in the dark, which indicates the good adsorption capacity of the C-clay component in the composite. The colour intensity reduced gradually under simulated sunlight irradiation and became colourless within 20 min (Fig. 6b and d). Compared with P25/Cclay composite, pure P25 showed a poor dye adsorption property in the dark (Fig. 6a). Under simulated sunlight irradiation, the degradation of RhB is completed within a longer time compared to P25/C-clay (Fig. 6a and c). Fig. 6(e) shows the relative change of the absorption peak intensity as a function of irradiation time. The Yaxis is reported as C/C0, where C0 and C is the initial and actual concentration of RhB at different reaction times, respectively. It can be clearly seen in Fig. 6(a–e) that under the identical test conditions, the decrease of RhB concentration was faster and more prominent with the presence of P25/C-clay than P25. One of the reasons is the difference in the adsorption capacity. As shown in Fig. 6(e), P25/C-clay shows much higher RhB adsorption capacity than P25. Therefore, RhB was adsorbed by P25/C-clay more than by P25 even before light-induced degradation, resulting in a drastic rapid decrease in the RhB concentration as shown in Fig. 6(e). The kinetic constant of P25 was found to be 0.15 min1. A comparable kinetic constant of 0.12 min1 was observed for P25/C-clay (Fig. S3). According to these results, the photocatalytic activity of P25 was only slightly affected by immobilization on clay nanosheets.
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Fig. 6. Photographs of the colour change in RhB solution containing P25 (a) and P25/C-clay (b), UV-spectra of RhB solution versus different times containing P25 (c) and P25/ C-clay (d), the photocatalytic performance of P25/C-clay and P25 against RhB (e), and Dye adsorption isotherms of RhB on P25/C-clay. C (P25/C-clay) = 4 mg/mL, C (RhB) initial = 4–450 ppm, T = 293 K (f).
The dye adsorption isotherm on P25/C-clay as a function of RhB concentration was shown in Fig. 6(f) and the maximum adsorption capacity (Qmax) of P25/C-clay was calculated to be 95.4 mg/g, which outperforms many other currently available adsorbents, demonstrating the potential of P25/C-clay as a superior adsorbent for practical applications in environmental pollutant removal. The photocatalytic activity of P25 has the advantage to degrade the adsorbed dye under simulated sunlight, and recover the adsorption property of P25/C-clay. Phenol was used as a model organic compound for non-dye pollutants for degradation. As shown in Fig. S4, Phenol was degraded under the same conditions. The result indicates that the high activity of P25/C-clay towards RhB degradation can be mainly attributed to photodegradation but not photosensitization process. The reusability of P25/C-clay against RhB removal was investigated by performing several adsorption and then degradation cycles. In each cycle, the dye RhB solution was stirred in the dark to reach its adsorption and desorption equilibrium before the photocatalytic test. Then the dye solution was subjected to simulated sunlight irradiation for 30 min. Catalyst were separated and used for next cycle without further treatment. As shown in Fig. 7, after the first cycle, 99.9% of RhB was degraded. After 5 cycles, the degradation ability of P25/C-clay still maintained at
99.9%, confirming the excellent reusability of the obtained P25/Cclay. It’s well known that easy recovery is important for photocatalyst usage in practice. Although ultra-fine catalyst powders with small particle can exhibit good activity for their large surface area, it has been a great challenges to recovering photocatalyst from aqueous systems after usage. The optical images of P25 and
Fig. 7. Reusability of P25/C-clay against adsorption and degradation of RhB for 5 cycles under simulated sunlight irradiation.
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Fig. 8. Photographs of the sedimentation of P25/C-clay (a), and P25 NPs (b) in deionized water with different settling times up to 4 days.
P25/C-clay suspensions in deionized water at pH 7.0 were taken at different sedimentation times as shown in Fig. 8. The concentrations of P25/C-clay and P25 were fixed at 1 mg/mL. P25 NPs dispersed well in water and settled very slowly. The supernatant was still turbid after 4 days of sedimentation and needed more than 1 week to become clear (Fig. 8a). This is compared with fast settling behaviour of P25/C-clay composite under the same conditions. Most of the P25/C-clay composites settled in 5 min, leaving a small fraction of P25/C-clay suspended in the supernatant. It became clear after 2 h of sedimentation (Fig. 8b). 4. Conclusion
[9] [10] [11] [12]
[13]
[14] [15]
In summary, an easily recycling photocatalyst was prepared by applying mussel-inspired coating strategy to immobilize P25 on the surface of clay nanosheets. Compared with P25, P25/C-clay showed superior separability from water by simple gravitational settling. P25/C-clay also showed high photocatalytic activity, robust reusability and excellent adsorptive ability (95.4 mg/g) against dye RhB. This work provides a simple, low-cost, scalable method for preparing P25-clay composite, which open the possibilities for applying P25 as an easy separation photocatalyst in real-world environmental remediation.
[16]
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Appendix A. Supplementary data
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Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.jphotochem.2017.10.017.
[21] [22] [23]
References [1] C.A. Martinez-Huitle, E. Brillas, Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods: a general review, Appl. Catal. B-Environ. 87 (3–4) (2009) 105–145. [2] F.L. Fu, Q. Wang, Removal of heavy metal ions from wastewaters: a review, J. Environ. Manage. 92 (3) (2011) 407–418. [3] C.I. Pearce, J.R. Lloyd, J.T. Guthrie, The removal of colour from textile wastewater using whole bacterial cells: a review, Dyes Pigm. 58 (3) (2003) 179–196. [4] G. Crini, Non-conventional low-cost adsorbents for dye removal: a review, Bioresour. Technol. 97 (9) (2006) 1061–1085. [5] A.S. Ozcan, B. Erdem, A. Ozcan, Adsorption of acid blue 193 from aqueous solutions onto Na-bentonite and DTMA-bentonite, J. Colloid Interface Sci. 280 (1) (2004) 44–54. [6] C.A.P. Almeida, N.A. Debacher, A.J. Downs, L. Cottet, C.A.D. Mello, Removal of methylene blue from colored effluents by adsorption on montmorillonite clay, J. Colloid Interface Sci. 332 (1) (2009) 46–53. [7] W. Zhang, L. Zou, L. Wang, Photocatalytic TiO2/adsorbent nanocomposites prepared via wet chemical impregnation for wastewater treatment: a review, Appl. Catal. A: Gen. 371 (1–2) (2009) 1–9. [8] Z.Y. Zhang, F. Xiao, Y.L. Guo, S. Wang, Y.Q. Liu, One-pot self-assembled threedimensional TiO2-graphene hydrogel with improved adsorption capacities
[24]
[25]
[26]
[27]
[28]
[29]
[30]
and photocatalytic and electrochemical activities, ACS Appl. Mater. Interfaces 5 (6) (2013) 2227–2233. A. Fujishima, X.T. Zhang, D.A. Tryk, TiO2 photocatalysis and related surface phenomena, Surf. Sci. Rep. 63 (12) (2008) 515–582. A. Kudo, Y. Miseki, Heterogeneous photocatalyst materials for water splitting, Chem. Soc. Rev. 38 (1) (2009) 253–278. A.L. Linsebigler, G.Q. Lu, J.T. Yates, Photocatalysis on TiO2 surfaces – principles, mechanisms, and selected results, Chem. Rev. 95 (3) (1995) 735–758. G. Liu, L.C. Yin, J.Q. Wang, P. Niu, C. Zhen, Y.P. Xie, H.M. Cheng, A red anatase TiO2 photocatalyst for solar energy conversion, Energy Environ. Sci. 5 (11) (2012) 9603–9610. T. Luttrell, S. Halpegamage, J.G. Tao, A. Kramer, E. Sutter, M. Batzill, Why is anatase a better photocatalyst than rutile? – Model studies on epitaxial TiO2 films, Sci. Rep. (2014) 4. K. Nakata, A. Fujishima, TiO2 photocatalysis: design and applications, J. Photochem. Photobiol. C-Photochem. Rev. 13 (3) (2012) 169–189. T. Ochiai, A. Fujishima, Photoelectrochemical properties of TiO2 photocatalyst and its applications for environmental purification, J. Photochem. Photobiol. CPhotochem. Rev. 13 (4) (2012) 247–262. I. Paramasivam, H. Jha, N. Liu, P. Schmuki, A review of photocatalysis using selforganized TiO2 nanotubes and other ordered oxide nanostructures, Small 8 (20) (2012) 3073–3103. B.C. Qiu, M.Y. Xing, J.L. Zhang, Mesoporous TiO2 nanocrystals grown in situ on graphene aerogels for high photocatalysis and lithium-ion batteries, J. Am. Chem. Soc. 136 (16) (2014) 5852–5855. J. Schneider, M. Matsuoka, M. Takeuchi, J.L. Zhang, Y. Horiuchi, M. Anpo, D.W. Bahnemann, Understanding TiO2 photocatalysis: mechanisms and materials, Chem. Rev. 114 (19) (2014) 9919–9986. W. Zhou, W. Li, J.Q. Wang, Y. Qu, Y. Yang, Y. Xie, K.F. Zhang, L. Wang, H.G. Fu, D.Y. Zhao, Ordered mesoporous black TiO2 as highly efficient hydrogen evolution photocatalyst, J. Am. Chem. Soc. 136 (26) (2014) 9280–9283. D. Kibanova, J. Cervini-Silva, H. Destaillats, Efficiency of clay- TiO2 nanocomposites on the photocatalytic elimination of a model hydrophobic air pollutant, Environ. Sci. Technol. 43 (5) (2009) 1500–1506. H. Zhang, X. Lv, Y. Li, Y. Wang, J. Li, P25-graphene composite as a high performance photocatalyst, ACS Nano 4 (1) (2010) 380–386. H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Mussel-inspired surface chemistry for multifunctional coatings, Science 318 (5849) (2007) 426–430. I. Urdaneta, A. Keller, O. Atabek, J.L. Palma, D. Finkelstein-Shapiro, P. Tarakeshwar, V. Mujica, M. Calatayud, Dopamine adsorption on TiO2 anatase surfaces, J. Phys. Chem. C 118 (35) (2014) 20688–20693. W.-X. Mao, X.-J. Lin, W. Zhang, Z.-X. Chi, R.-W. Lyu, A.-M. Cao, L.-J. Wan, Coreshell structured TiO2@polydopamine for highly active visible-light photocatalysis, Chem. Commun. 52 (44) (2016) 7122–7125. J.F. Wang, T. Tsuzuki, B. Tang, X.L. Hou, L. Sun, X.G. Wang, Reduced graphene Oxide/ZnO composite: reusable adsorbent for pollutant management, ACS Appl. Mater. Interfaces 4 (6) (2012) 3084–3090. A.K. Verma, R.R. Dash, P. Bhunia, A review on chemical coagulation/ flocculation technologies for removal of colour from textile wastewaters, J. Environ. Manage. 93 (1) (2012) 154–168. G. Liu, J. Zhao, Photocatalytic degradation of dye sulforhodamine B: a comparative study of photocatalysis with photosensitization, New J. Chem. 24 (6) (2000) 411–417. W.J. Ren, Z.H. Ai, F.L. Jia, L.Z. Zhang, X.X. Fan, Z.G. Zou, Low temperature preparation and visible light photocatalytic activity of mesoporous carbondoped crystalline TiO2, Appl. Catal. B-Environ. 69 (3–4) (2007) 138–144. L.W. Zhang, H.B. Fu, Y.F. Zhu, Efficient TiO2 photocatalysts from surface hybridization of TiO2 particles with graphite-like carbon, Adv. Funct. Mater. 18 (15) (2008) 2180–2189. B. Tarablsi, C. Delaite, J. Brendle, C. Croutxe-Barghorn, Maghemite intercalated montmorillonite as new nanofillers for photopolymers, Nanomaterials 2 (4) (2012) 413–427.
138
S. Huang et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 131–138
[31] B. Tyagi, C.D. Chudasama, R.V. Jasra, Determination of structural modification in acid activated montmorillonite clay by FT-IR spectroscopy, Spectrochim. Acta Part A 64 (2) (2006) 273–278. [32] M. Vasei, P. Das, H. Cherfouth, B. Marsan, J.P. Claverie, TiO2@C core-shell nanoparticles formed by polymeric nano-encapsulation, Front. Chem. 2 (47) (2014). [33] X. Chen, Y.B. Lou, A.C.S. Samia, C. Burda, J.L. Gole, Formation of oxynitride as the photocatalytic enhancing site in nitrogen-doped titania nanocatalysts: comparison to a commercial nanopowder, Adv. Funct. Mater. 15 (1) (2005) 41– 49. [34] H. Wang, Y. Wu, B.-Q. Xu, Preparation and characterization of nanosized anatase TiO2 cuboids for photocatalysis, Appl. Catal. B: Environ. 59 (3–4) (2005) 139–146. [35] F. Cesano, D. Scarano, S. Bertarione, F. Bonino, A. Damin, S. Bordiga, C. Prestipino, C. Lamberti, A. Zecchina, Synthesis of ZnO–carbon composites and imprinted carbon by the pyrolysis of ZnCl2-catalyzed furfuryl alcohol polymers, J. Photochem. Photobiol. A: Chem. 196 (2-3) (2008) 143–153. [36] C.-C. Chen, Y.-P. Fu, S.-H. Hu, Characterizations of TiO2/SiO2/Ni–Cu–Zn ferrite composite for magnetic photocatalysts, J. Am. Ceram. Soc. 98 (9) (2015) 2803– 2811.
[37] F. Dong, S. Guo, H. Wang, X. Li, Z. Wu, Enhancement of the visible light photocatalytic activity of C-doped TiO2 nanomaterials prepared by a green synthetic approach, J. Phys. Chem. C 115 (27) (2011) 13285–13292. [38] P. Zhang, C. Shao, Z. Zhang, M. Zhang, J. Mu, Z. Guo, Y. Liu, TiO2@carbon core/ shell nanofibers: controllable preparation and enhanced visible photocatalytic properties, Nanoscale 3 (7) (2011) 2943–2949. [39] N. Dwivedi, R.J. Yeo, N. Satyanarayana, S. Kundu, S. Tripathy, C.S. Bhatia, Understanding the role of nitrogen in plasma-assisted surface modification of magnetic recording media with and without ultrathin carbon overcoats, Sci. Rep. 5 (2015) 7772. [40] H. Irie, Y. Watanabe, K. Hashimoto, Carbon-doped anatase TiO2 powders as a visible-light sensitive photocatalyst, Chem. Lett. 32 (8) (2003) 772–773. [41] F.T. Johra, J.-W. Lee, W.-G. Jung, Facile and safe graphene preparation on solution based platform, J. Ind. Eng. Chem. 20 (5) (2014) 2883–2887. [42] Z.R. Ismagilov, A.E. Shalagina, O.Y. Podyacheva, A.V. Ischenko, L.S. Kibis, A.I. Boronin, Y.A. Chesalov, D.I. Kochubey, A.I. Romanenko, O.B. Anikeeva, T.I. Buryakov, E.N. Tkachev, Structure and electrical conductivity of nitrogendoped carbon nanofibers, Carbon 47 (8) (2009) 1922–1929. [43] F. He, G. Chen, Y. Yu, Y. Zhou, Y. Zheng, S. Hao, The synthesis of condensed CPDA–gC 3 N 4 composites with superior photocatalytic performance, Chem. Commun. 51 (31) (2015) 6824–6827.