- Email: [email protected]
Preparation of ionic liquids functionalized nanodiamonds-based composites through the Michael addition reaction for efficient removal of environmental pollutants
Journal of Molecular Liquids 296 (2019) 111874
Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Preparation of ionic liquids functionalized nanodiamonds-based composites through the Michael addition reaction for efficient removal of environmental pollutants Guang Yang a, Hongye Huang a, Junyu Chen a, Defu Gan a, Fengjie Deng a, Qiang Huang a, Yuanqing Wen a, Meiying Liu a, ***, Xiaoyong Zhang a, *, Yen Wei b, c, ** a
Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang, 330031, China Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084, China c Department of Chemistry and Center for Nanotechnology and Institute of Biomedical Technology, Chung-Yuan Christian University, Chung-Li, 32023, Taiwan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 September 2019 Received in revised form 29 September 2019 Accepted 2 October 2019 Available online 3 October 2019
Nanodiamonds (ND) is a novel type of carbon nanomaterials with small size, large specific surface areas, low cost and some other physicochemical properties. However, the environmental applications of ND are still rarely reported because of its low adsorption performance. In this work, we reported for the first time for the surface modification of ND with ionic liquids through a facile and effective Michael addition reaction. To synthesis of the ternary ND@IL composites, ND was first linked with APTES by a silanization reaction and then [C16VImþ] [Br] was conjugated on the surface of amino groups functionalized ND via the Michael addition reaction. The ND@IL composites were applied as adsorbents for removal of Congo red (CR) from aqueous solution and displayed high removal efficiency (92.78%) at room temperature and neutral solution. Under certain adsorption conditions, the adsorption capacities of pristine ND and ND@IL towards CR is 61.1 and 226.4 mg g1, respectively. The pseudo-second-order model fitting the adsorption kinetic data is superior to pseudo-first-order model and Freundlich isotherm model describes the experimental data well. Further experiments showed that the removal process was pH dependence, exothermic and spontaneous. More importantly, ND@IL composites could be regenerated via adjustment of pH values and still maintain high adsorption capacity after five regeneration cycles. All of the above results demonstrated that these ionic liquids modified ND are promising adsorbents for highly efficient and quick removal of environmental pollutants from aqueous effluents. © 2019 Elsevier B.V. All rights reserved.
Keywords: Nanodiamond-based composite Ionic liquid Environmental adsorption Michael addition reaction
1. Introduction Nowadays, dyes play a decisive role in textile, paper and leather manufacturing industries, producing about 1.6 million tons of dyes every year [1,2]. Dyes are usually classified on the basis of their functional groups or colors and by the nature of ionic charge dissolved in the aqueous solution. In the process of using dyes, a significant portion of dyes will be lost as wastes, causing main sources
* Corresponding author. ** Corresponding author. Department of Chemistry and Center for Nanotechnology and Institute of Biomedical Technology, Chung-Yuan Christian University, Chung-Li, 32023, Taiwan. *** Corresponding author. E-mail addresses: [email protected] (M. Liu), [email protected] (X. Zhang), [email protected] (Y. Wei). https://doi.org/10.1016/j.molliq.2019.111874 0167-7322/© 2019 Elsevier B.V. All rights reserved.
of water pollution [3]. Some of them are highly toxic, posing a serious threat to human health. Even trace of dyes existed in water can result in high chemical oxidation demand and cause peculiar smell to aquatic systems [4]. Therefore, developing efficient technologies for dye removal from effluent of manufacturing industries become more and more significance. To date, a series of approaches have been developed to treat dyes in sewage including physical, chemical, and biological decoloration scientific methods [5e9]. However, these dyes are difficult to remove since they are recalcitrant organic molecules and are stable to oxidizing agents. Commonly used techniques are flocculation [10], photo-catalysis [11], electrochemical [12], ion exchange [13], and microbial degradation [14]strategies, but few of them has been proved to be effective in actual wastewater treatment. In addition to these technologies, the adsorption technology is the most promising and effective technique due to its simple operation, low cost and good
2
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
designability. Selection of an appropriate adsorbent is the key to the effectiveness of adsorption technology. Up to now, various conventional decoloration adsorbents, including carbon-based materials [15e20], clay materials [21,22] and biosorbents [23e28], and many other composite adsorbents[29e34] have been widely reported previously. Nanodiamonds (ND) is one of the most synthetic materials on the market, with size range of 5e10 nm particles being produced via detonation [35]. ND has shown extensive applications in various applications such as energy storage [36], gene therapy [37], biological imaging [38e44] and drug-delivery carriers [45e50] due to its distinctive morphology, electronic and thermal properties. Moreover, ND has some specific properties such as mesopores, large specific surface area, and oxygen functional groups. These features make ND to be easily modified with different agents and providing enough active sites for the adsorption process. Therefore, ND and its composites have been regarded as one of the promising adsorbents in environmental treatment. For example, Zhao et al. [51] reported that the adsorption capacities of ND/amide thiourea composites for metal ions uranium were enhanced after the coordination with single-armed ligand and double -armed ligand, with the maximum values were calculated about 200 mg g1, and the selectivity is as high as 82% and 72%, respectively. Wang et al. [52] reported that the adsorption of azo dye acid orange 7 onto ND surface, which confirming the adsorption behavior and the mechanism by comparing with another azo compound adsorption into ND as control groups, and pointing out that the affinity between ND and acid orange is obviously higher than the other azo compounds through electrostatic interaction. In general, the study of the removal of dyes from sewage through ND-based composites is a relative new field. Recently, the monomers of ionic liquids have been widely used to adsorb dyes by combining with nanomaterials to form novel adsorbents [53e55]. For example, Xing et al. [53] successfully obtained a zeolite/ionic liquid composite material and used it as an adsorbent to remove anionic dyes. The removal rate of methyl orange was fast, following a pseudo-second-order kinetics with a maximum adsorption capacity of 116 mmol kg1. However, to the best of authors knowledge, the surface modification of ND with ionic liquids and the adsorption behavior of ND-based ionic liquids has not been reported thus far. Herein, the main task is to investigate the adsorption behavior and mechanism for removal of azo dye by ND@IL composites. To this end, Congo red (CR) was chosen as the textile dye (an anion azo dye, the chemical structure of CR was listed in Fig. S1), 3-n-Hexadecyl-1-vinylimidazolium Bromide [C16VImþ] [Br] as modifying monomer. The ionic liquid functionalized ND composites were prepared via the Michael addition reaction for the first time. The composites were used as adsorbents to remove CR from stock solution. To be specific, ND was modified with APTES by silanization reaction. Then, ND@IL composites with a charged imidazole ring were obtained via the Michael addition reaction between ethenyl and amino groups on the surface of ND-NH2 (Scheme 1). The samples of synthesized ND, ND-NH2 and ND@IL composites were characterized by a series of characterization methods in details. Studies on adsorption properties of materials were also performed under different conditions, with emphasis on the factors affecting the contact time, dye concentration, initial pH and temperature affect for the adsorption capacity. Furthermore, kinetic models, isotherm models, thermodynamic calculations and regeneration experiments were used to evaluate the adsorption process onto ND@IL composites.
2. Experimental sections 2.1. Materials and characterization Nanodiamond (average diameter of 10 nm, Beijing Grish Hitech Co. Ltd., China), 1-bromohexadecane, 1-vinylimidazole, triethylamine (TEA), (3-aminopropyl) triethoxysilane (APTES) and bismuth trifluoromethane sulfonate were purchased from Aladdin Chemical reagents Co, Ltd. (Shanghai, China). Methanol, diethyl ether, ethanol, HCl and NaOH were of analytical grade and used as received (from Damao Chemical Industrial Company, Tianjin) without further purification. The samples were characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), thermo-gravimetric analysis (TGA), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The detailed information was provided in ESI. 2.2. Preparation of 3-n-Hexadecyl-1-vinylimidazolium bromide 3-n-Hexadecyl-1-vinylimidazolium bromide ([C16VImþ] [Br]) was synthesized according to previous reference[56]. Simply, a mixture of 0.15 mol 1-bromohexadecane, 0.1 mol 1-vinylimidazole and 30 mL methanol was placed in a 50 mL flask at 80 C for 24 h, and the reaction system was purged with N2 for 30 min to remove O2. When the reaction was completed, the orange viscous liquid was washed through diethyl ether and the final product was stored at low temperature. (1H NMR spectrum in Fig. S2A. DMSO, d, ppm. 9.40 (1H, -N-CH]Nþ-), 8.21 (1H, -N-CH]CHeNþ ¼ ), 7.84 (1H, -NCH]CHeNþ ¼ ), 7.41 (2H, CH2]CH-), 7.34 (1H, CH2¼CH-), 5.26 (2H, eNþ-CH2-CH2-), 4.18 (2H, eNþ-CH2-CH2-)1.21 (26H, -CH2CH2-), 0.83 (3H, eCH2-CH3).) 2.3. Synthesis of adsorbents The modified ND (ND-NH2) nanoparticles were prepared via APTES hydrolysis as followed procedure: 500 mg ND was added to a reaction bottle containing 30 mL of ethanol, and the particles were uniformly dispersed by sonication. Then, 3 mL triethylamine was added slowly and the mixture was stirred at 40 C for 3 h. Subsequently, a mixture of 2 mL APTES and 10 mL distilled water was quickly added into the suspension solution and stirred for 12 h. The obtained ND-NH2 particles were washed many times with distilled water and dried in freeze dryer. The functionalized ND particles with charged imidazole ring (ND@IL) were prepared based on the following procedure. 400 mg ND-NH2, 400 mg [C16VImþ] [Br] and 50 mg bismuth trifluoromethane sulfonate were added into 30 mL dried ethanol, and the system was washed with nitrogen and sonicated for 10 min to form a homogeneous suspension. The reaction system was vigorously stirred at 60 C for 8 h. When the reaction was completed, the crude product was washed with ethanol and distilled water, and further dried in a vacuum oven. 2.4. Adsorption studies The whole batch adsorption study of the ND before and after being modified was performed at 50 mL centrifuge tube containing 10 mg samples and a certain concentration of CR. The residual CR concentration was calculated according to the absorbance of the solution after adsorption, and was used UVeVisible spectrophotometer (TU-1810, Beijing) as detector. 3. Results and discussion 3.1. Characterization of materials The 1H NMR scan spectra was used to determine the chemical
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
3
Scheme 1. Schematic illustration of the functionalization of ND combined with silanization reaction and Michael addition reaction.
structure information of ND@IL composites (Fig. S2B). Peaks at 7.83, 7.16 and 6.64 ppm were attributed to protons of eC]N and eC]Cof the imidazole ring. The signals at 5.31 and 0.83 ppm can be assigned to the chemical shift of the methylene group on alkane chain linked to N and of methyl group of the alkane chain, respectively. The strongest peak at 3.31 and 2.51 ppm was belonged to protons of solvent (d6-DMSO). The chemical shifts of the remaining methylene groups at different sites were distributed at 1e2 ppm. These results indicated that APTES and [C16VImþ] [Br] were grafted to surface of ND successfully via two steps reaction. In addition, the FT-IR spectra of ND, ND-NH2 and ND@IL were shown in Fig. 1A. The broad peak at 3411 cm1 was the Oxygen hydrogen bond and bound water in the pristine material. Obviously, the adsorption peaks at 3460, 2926, 1220, and 1028 cm1 were ascribed to the characteristic peaks of NeH, CeH, CeSi and CeOeSi stretching vibrations in the sample of ND-NH2, respectively. Demonstrated that some of the CeOeSi and eNH2 were formed on the ND surface. The new broad band of 1625 cm1 was mainly assigned to the C]N stretching vibration of imidazole ring in the spectrum of ND@IL. Moreover, the absorbance band near 1150 cm1 became stronger was related to CeN stretching
vibration. In brief, the bonds of OeH, NeH, CeH, CeSi, CeOeSi and C]N were changed before and after modification, which was attributed to the introduction of [C16VImþ] [Br]. These changes illustrated that ND was successfully modified by the Michael addition reaction. The TGA was performed to get more evidence for the surface functionalization with ionic liquid of ND. Thus, the content of surface-modified molecule was further evaluated based on the weight loss ratio by TGA measurement. As shown in Fig. 1B, the mass loss of ND, ND-NH2 and ND@IL were 10.1%, 4.7%, and 3.9%, respectively, at below 373 K, which was considered as free water content in all samples. For the pristine ND, the weight loss in the temperature range from 373 to 1000 K was 12.2%, which ascribed to the decomposition of the surface eOH. The total mass loss was 18.2% for the sample of ND-NH2 at 1000 K, and the content of decomposed APTES could be calculated to be as 1.3%. In a similar way, the weight percentage of IL conjugated on the surface of NDNH2 to be as 11.4% in the curve of ND@IL. These results suggested that APTES and IL were facilely grafted to ND surfaces by silanization reaction and Michael addition reaction, respectively. Fig. 2(A-C) shows the TEM image of the samples. The TEM image of the pristine ND particles displays randomly stacked
Fig. 1. FT-IR spectrum of ND, ND-NH2 and ND@IL (A); TGA curves of samples (B).
4
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
Fig. 2. TEM images of particles (AeC); X-ray energy dispersive spectroscopy (EDS) of ND@IL (D).
characteristics. The size of individual nanoparticles about 10 nm. After successfully grafting APTES onto its surface, the small particles in TEM become blurred and the contour of the particles becomes less obvious. Surprisingly, we can clearly observe the thick polymer layer covering the surface of ND from Fig. 2C. In addition, the X-ray energy dispersive spectrum of ND@IL was described in Fig. 2D. The related elements such as C, O, Si, Br were found in the spectrum. The emergence of Si and Br elements further proves that the composite has been successfully modified with APTES and IL. XPS was carried out as an technique to obtain the surface chemical information of ND samples before and after
functionalization of APTES and organic molecules. The XPS wide survey spectrum range from 0 to 1200 eV is shown in Fig. 3A, that illustrated the different elements exist in the ND-based samples. We can clearly see these elements, including the C, O, N, Si and Br (Fig. 3A). In addition, narrow survey spectra were fitted to the elements of C, O, N, Si and Br in different samples. As shown in Fig. 3BeF. The major elements C 1s, N 1s and O 1s showed obvious signal peaks in the three samples, respectively (Fig. 3BeD). For the element Si 2p (Fig. 3E), there is no characteristic signal peak in the spectrum of original ND. However, there are obvious silicon signal peaks in the narrow scan spectra of ND-NH2 and ND@IL samples at
Fig. 3. XPS overview spectra of ND, ND-NH2 and ND@IL particles (A); high-resolution XPS spectra of C 1s (B), O 1s (C), N 1s (D) Si 2p (E) and Br 3d (F) of ND, ND-NH2 and ND@IL.
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
101.3 and 101.1 eV, respectively. As we can see from the Br 3d narrow scan spectra, no significant peak strength was observed in the curves of original ND and ND-NH2 samples. In the sample of ND@IL, a stronger signal peak appeared at 66.9 eV of the Br 3d spectrum. This result strongly proves that the organic molecules APTES and IL were successfully grafted onto the surface of ND. On the other hand, the contents of C, O, N, Si and Br in all samples were calculated on the basis of XPS scan spectra. Detailed values were listed in Table 1. For the samples of ND-NH2, the percentages of C, O, N, Si and Br were 78.23%, 16.97%, 2.76%, 2.03% and 0%, respectively. Before modification with APTES, the contents of C, O, N, Si and Br in ND were changed to 85.57%, 12.62%, 1.81%, 0% and 0%, respectively. The Si content changed sharply to 0 because of the lack of Si in the original ND. Moreover, increasing of N content in the sample of ND-NH2 also clearly evidences the introduction of APTES on the surface of ND. After modification with [C16VImþ] [Br], the contents of C, O, N, Si and Br in ND@IL changed to 80.97, 14.26, 3.23, 1.16 and 0.38%, respectively. Because the element Br only existed in IL, it is clear that there is obvious increase of Br contents in the sample of ND@IL. Moreover, we could also find that the contents of C and N were boosted from 78.23% to 2.76%e80.97% and 3.23%, respectively. Based on the change of N contents in NDNH2 and ND@IL, we could calculate that the weight percentage of IL on ND@IL should be about 9.13%. This result is close to the calculated result of TGA. Therefore, we could also confirm that the surface functionalization of ND with APTES and [C16VImþ] [Br]. It is well known that the Michael addition reaction is a useful tool for surface conjugation between the amino groups and ene bonds. The Michael addition reaction could be occurred under mild conditions such as low temperature, organic solvents and aqueous solution without gas protection and with simple operation procedure. In this work, we demonstrated that the ionic molecule could be facilely introduced on the surface of ND@NH2. Therefore, the ionic molecules could be acted as the active adsorption sites to improve the adsorption efficiency towards ionic environmental pollutants. On the other hand, the hydrophobic environmental pollutants could also be adsorbed by the ionic liquids modified ND@IL owing to the existence of hydrophobic alkyl chains. 3.2. Removal of CR In actual dye pollution control and treatment, the adsorption equilibrium time is a key factor to predict the feasibility and efficiency of an adsorbent. Fig. 4A indicates the impact of time on the CR adsorption onto the pristine ND and ND@IL. It is clear that the amount of CR adsorbed by ND@IL composites increases rapidly in the first 5 min. After that, the Q of ND@IL composites was enhanced slowly until the adsorption capacity was 226.4 mg g1 at 39 min and remained almost alike. The increased Q may be the reason for the large number of vacant surface adsorption active sites in the initial stage. After the active sites are occupied by lots of CR molecules, the remaining active sites are reduced. So, there are fewer dye molecules diffusing to the surface of ND@IL, and the adsorption capacity grows slowly until the equilibrium is reached. The adsorption capacity of the original material only reached 61.1 mg g1 at 49 min due to few adsorption sites on its surface.
Table 1 Atom percentage of ND, ND-NH2 and ND@IL. sample
Atom percentage (%) C
O
N
Si
Br
ND ND-NH2 ND@IL
85.57 78.23 80.97
12.62 16.97 14.26
1.81 2.76 3.23
0.00 2.03 1.16
0.00 0.00 0.38
5
Thus, the ND@IL composites functionalized with IL have better adsorption properties than original ND particles. To gain deep understanding for the behavior of adsorption process, the adsorption kinetics were studied by three models to fit the experimental adsorption data. The fitted curves and parameters of models are shown in Fig. 4B and listed in Table 2, respectively. From Table 2, the R2 value of pseudo-second-order model (0.9281) is closer to 1 than other model. On the other hand, the value of Qe (cal) (mg g1) from pseudo-second-order model (231 mg g1) is closer to the actual adsorption capacity. These results suggested that the adsorption of dye onto the surface of ND@IL at room temperature, is better described by pseudo-second-order. Further calculation indicated that the rate-control step is the chemical adsorption mechanism. For intraparticle diffusion model, the correlation coefficients R2 and constant C are 0.9634 and 35.55, respectively. These value results show that the physical adsorption is also one of the control steps. The amount of CR per unit volume of solution plays a vital role. Fig. 5A shows the effect of initial CR concentration on the adsorption capacity of ND@IL from 50 mL CR at 298 K and pH ¼ 7, for the initial CR concentration was 50e250 mg L1 and contact time of 39 min, the adsorption capacities of the ND@IL composites were 219.7 mg g1 and 395.1 mg g1, respectively. On the whole, with the increase of C0, the adsorption capacity of adsorbents also gradually increases and tends to moderate growth. Since the number of active sites is fixed, increasing the initial concentration of CR over a wide range cannot effectively promote the linear growth of the Q of the material. Therefore, the growth of adsorption capacity of the nanomaterials has become moderate. In order to study the relationship between C0 and Qe, the isotherm models were applied to fitting experimental data of the adsorption. The correlation coefficient (R2) and constant calculated from the Langmuir and Freundlich isotherm models are listed in Table 3 and the curves of sorption isotherms are described in Fig. 5A. From the data of Table 3, it could be obviously observed that the value of R2 of Freundlich (0.9905) was greater than that of Langmuir isotherm model (0.9637). The results indicate that the adsorption of CR onto ND@IL composites conforms to the heterogeneity sorption. On the other hand, the Freundlich model constant n1 was 0.3649, which reflected that the ND@IL composites is effective. Although the adsorption process of this experiment could not be well described by the Langmuir isotherm model, the Langmuir model has a large adsorption capacity, indicating that the composites could be used as effective adsorbents to remove dyes from contaminated water. Moreover, the value of separation factor RL (0.2139-0.5764) was less 0.6, further indicating that the adsorption is favorable. The pH is another crucial factor affecting the adsorption efficiency. To further research the adsorption mechanism of CR on the surface of materials, the effect of different pH (pH ¼ 6e11) values CR on the adsorption capacity of ND@IL was studied at room temperature. According to the data, the curves of Q of composites and the removal efficiency of CR with the change of pH values of solution are fitted in Fig. 5B. The removal efficiency of CR quickly decreased from 92.78% (231.94 mg g1) to 71.67% (179.17 mg g1) (Fig. 5B). This phenomenon can be explained: When the pH is less than 7, the ND@IL composites was positively charged and interacted with the negatively charged CR molecule via electrostatic attraction. When the solution pH is above 7, the quaternary ammonium deionization was very strong, and the ND@IL surface positively charged active sites gradually decrease with the increasing pH, which is unfavorable CR adsorption onto the surface of composites. Meanwhile, the hydrophobic interaction between the alkyl chains and the CR was also an important mechanism of adsorption. So the optimum pH for removing CR by using IL functionalized ND as adsorbent was 6.
6
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
Fig. 4. The effect of contact time on adsorption of CR (50 mg L1) by ND and ND@IL (m ¼ 10 mg, 298 K) (A); kinetic curves for adsorption of CR on ND@IL (B).
Table 2 Adsorption kinetics data for CR adsorption on ND@IL nanocomposites. Models
Parameters
Initial concentration (mg L1)
Pseudo-first-order equation
Qe (cal) (mg g1) k1 (min1) R2 Qe (cal) (mg g1) k2 (g mg1 min1) R2 kp (mg g1 min0.5) C R2
198.5 0.04873 0.8914 231 0.0002538 0.9281 16.47 35.55 0.9634
50
Pseudo-second-order equation
Intraparticle diffusion
Fig. 5. Adsorption isotherms of CR on ND@IL (A), effect of pH values on the ND@IL to remove CR (B).
Table 3 Isotherms data of models for CR adsorption on ND@IL. Isotherms
Parameters
Langmuir
Qm (mg g1) KL (L mg1) RL R2 KF [(mg g1)(L mg1)1/n] n1 R2
Temperatures (K) 298
Freundlich
491.9 0.0147 0.2139e0.5764 0.9637 52.94 0.3649 0.9905
The effects of temperatures on the adsorption capacity of ND@IL composites in 50 mL CR solution were investigated. By changing, the thermodynamic parameters DG0, DH0 and DS0 can provide some meaningful information, which can reveal the feasibility, spontaneous and endothermic or exothermic nature of the
adsorption process. The influence curve of temperature on adsorption capacity and the thermodynamic parameters are fitted in Fig. 6A and listed in Table 4, respectively. Although the DG0 increases gradually, it is always negative value in the temperature range of 298e348 K, that indicated that the CR onto ND@IL composites was highly spontaneous and thermodynamically favorable. The negative value of DH0 (17.65 kJ mol1) reflects the exothermic nature of adsorption. The value of DS0 (0.02794 kJ mol1 K1) was also negative, indicated that the decrease the randomness of the solid/solution interface. All the thermodynamic parameters also implied that the adsorption of CR on the composites is hindered as the temperature gradually increases. The above results clearly suggested that the ND@IL are favorable for removal of CR at room temperature. The regeneration ability of the adsorbent is a significant factor in estimating the commercial feasibility. For the desorption studies, the CR-adsorbed ND@IL was dispersed in a solution of hot ethanol containing 50 mg NaOH to removal CR molecular and then washed
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
7
Fig. 6. The effect of temperature on adsorption of CR by ND@IL (A); Van't Hoff plot for the adsorption of CR by ND@IL (B).
Table 4 Data of the thermodynamic parameters for the adsorption of CR onto ND@IL. Isotherms
Parameters
Temperatures (K) 298
Langmuir
Freundlich
Qm (mg g1) KL (L mg1) RL R2 KF [(mg g1)(L mg1)1/n] n1 R2
491.9 0.0147 0.2139e0.5764 0.9637 52.94 0.3649 0.9905
Fig. 7. Recyclability of ND@IL for the CR adsorption (V ¼ 50 mL, C0 ¼ 50 mg L1, m ¼ 10 mg).
with distilled water until the solution was no red color was observed and it's neutral. The adsorptiondesorption experiments were repeated for five consecutive cycles, the adsorption capacity and CR removal efficiency of the materials (before and after desorption) were depicted in Fig. 7. From Fig. 7, it is worth to noting that ND@IL composites maintain a high adsorption capacity and removal efficiency. Although the removal rate was reduced by 11.67% after five consecutive adsorption-desorption cycles. The decrease of adsorption capacities after reusability may possibly ascribed to the hydrophobic interaction between adsorbent and organic dye, which will not be influenced by the change of pH. Therefore, ND@IL could be used in multiple cycles with sufficient chemical stability during the adsorption process. Taking together, the adsorption experimental results demonstrated that the surface modification of ND with IL could effectively improve the adsorption capacity of ND. The modified ND (ND@IL) could display high adsorption performance at room temperature and acidic/neutral
Table 5 Compare with the maximum adsorption capacities (Qmax) of various composite for dyes. Composite
Dye
Qmax
Refs
Nanodiamond Thermally oxidized nanodiamond Diamond@graphite Nanodiamond@ionic liquid
Acid orange 7
1288 mmol kg1
[57]
Methylene blue Methylene blue Congo red
47.62 mg g1 23.3 mg g1 226.4 mg g1
[58] [59] This work
solution. More importantly, the adsorbent could be regenerated and still keep high adsorption capacity after five cycles. These features make ND@IL promising for removal of ionic organic dyes and other ionic environmental pollutants. Table 5 lists the maximum adsorption properties of different nano-diamond-based composites on various dyes, which has been reported in the literature. The adsorption of environmental pollutants by ND and related composites are mainly relied on their particle size, specific surface areas and the surface functional groups. In this work, the maximum adsorption of ND@IL composites is as high as 226.4 mg g1, which is obviously larger than the ND materials and composites with other treatment methods. The surface modification of IL on the surface of ND could not only improve the dispersibility of ND composites in aqueous solution and kept their high surface areas and small size, but also could introduce a larger number of functional groups. These functional groups with ionic components could also interact with the ionic organic dyes through the hydrophobic interaction and electrostatic interaction. Moreover, based on the above role, we could expect that the ND@IL composites could also be utilized for adsorptive removal other environmental pollutants through the similar interactions with desirable adsorption capacity. More importantly, this method is simple, effective and universal. It could therefore be a useful surface modification method with great potential for fabrication of functionalized adsorbents with promising applications in environmental fields.
4. Conclusions In summary, we reported a simple and effective method for preparation of IL modified ND via the Michael addition reaction. Owing to the introduction of IL with hydrophobic alkyl chains and ionic segment, the ND@IL could be acted as promising adsorbents for removal of anionic CR from colored solution. Compared with pristine ND, ND@IL composites display obvious enhancement of adsorption capacity towards CR. After equilibrium, the adsorption capacity of ND@IL composites reaches 226.4 mg g1 (pH ¼ 7 at room temperature). This value is obvious greater than that of
8
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
unmodified ND (61.1 mg g1) at identical adsorption conditions. The pseudo-second-order model and Freundlich model can well describe the data of CR adsorption process. The mechanism of CR adsorption involves not only electrostatic interaction, but also the hydrophobic interaction between alkyl chains and aromatic rings of CR. Besides, ND@IL composites can be regenerated by washing with alkaline solution, and still keep high adsorption capacity after regeneration. All the above results show that ND@IL composites are promising adsorbents that can efficiently remove CR from contaminated aqueous media. Moreover, we believe that this work will provide a new avenue for the environmental adsorption applications of ND-based composites. Declaration of competing interest The authors declare that there have no conflict of interest. Acknowledgments This research was supported by the National Natural Science Foundation of China (Nos. 21865012, 21788102, 21564006, 21561022, 21644014). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molliq.2019.111874. References [1] V. Gupta, J. Environ. manage. 90 (2009) 2313. [2] K. Hunger, Industrial Dyes: Chemistry, Properties, Applications, John Wiley & Sons, 2007. [3] N. Sharma, D. Tiwari, S. Singh, Int. J. Sci. Eng. Res. 3 (2012) 1. [4] M.S. Field, R.G. Wilhelm, J.F. Quinlan, T.J. Aley, Environ. Monit. Assess. 38 (1995) 75. [5] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Bioresour. Technol. 77 (2001) 247. [6] P. Nigam, G. Armour, I. Banat, D. Singh, R. Marchant, Bioresour. Technol. 72 (2000) 219. € z, S. Atalay, J. Forss, U. Welander, Separ. Purif. Technol. 79 [7] O. Türgay, G. Erso (2011) 26. [8] N.P. Tantak, S. Chaudhari, J. Hazard Mater. 136 (2006) 698. [9] V. Katheresan, J. Kansedo, S.Y. Lau, J. Environ. Chem. Eng. 6 (2018) 4676. [10] C.-Z. Liang, S.-P. Sun, F.-Y. Li, Y.-K. Ong, T.-S. Chung, J. Membr. Sci. 469 (2014) 306. [11] M. Rauf, S.S. Ashraf, Chem. Eng. J. 151 (2009) 10. [12] E. Brillas, C.A. Martínez-Huitle, Appl. Catal. B Environ. 166 (2015) 603. [13] M.M. Hassan, C.M. Carr, Chemosphere 209 (2018) 201. [14] M. Chengalroyen, E. Dabbs, World J. Microbiol. Biotechnol. 29 (2013) 389. [15] J. Abdi, M. Vossoughi, N.M. Mahmoodi, I. Alemzadeh, Chem. Eng. J. 326 (2017) 1145. mez, S. Allen, G. Walker, Chem. Eng. J. 219 (2013) [16] J. Gal an, A. Rodríguez, J. Go 62. [17] J. Xie, Z. Ming, H. Li, H. Yang, B. Yu, R. Wu, X. Liu, Y. Bai, S.-T. Yang, Chemosphere 151 (2016) 324. [18] H. Yang, X. Wu, Q. Ma, A. Yilihamu, S. Yang, Q. Zhang, S. Feng, S.-T. Yang, Chemosphere 216 (2019) 9. [19] L. Chen, C. Wang, S. Yang, X. Guan, Q. Zhang, M. Shi, S.-T. Yang, C. Chen, X.L. Chang, Environ. Sci. Nano 6 (2019) 1077. [20] L. Chen, C. Wang, H. Li, X. Qu, S.-T. Yang, X.-L. Chang, Environ. Sci. Technol. 51 (2017) 10146.
[21] V. Vimonses, S. Lei, B. Jin, C.W. Chow, C. Saint, Chem. Eng. J. 148 (2009) 354. [22] M. Sabzi, N. Shafagh, M. Mohammadi, J. Appl. Polym. Sci. (2019) 48266. [23] F. Silva, L. Nascimento, M. Brito, K. da Silva, W. Paschoal, R. Fujiyama, Materials 12 (2019) 2486. [24] Z. Zhang, S. Xia, X. Wang, A. Yang, B. Xu, L. Chen, Z. Zhu, J. Zhao, N. JaffrezicRenault, D. Leonard, J. Hazard Mater. 163 (2009) 279. [25] L. Bai, X. Jiang, Z. Sun, Z. Pei, A. Ma, W. Wang, H. Chen, H. Yang, L. Yang, D. Wei, Cellulose 26 (2019) 5305. [26] G. Wang, M. Xi, L. Bai, Y. Liang, L. Yang, W. Wang, H. Chen, H. Yang, Cellulose 26 (2019) 5947. [27] S. Liu, Z. Rao, R. Wu, Z. Sun, Z. Yuan, L. Bai, W. Wang, H. Yang, H. Chen, J. Agric. Food Chem. 67 (2019) 1061. [28] M. Chen, D. Fan, S. Liu, Z. Rao, Y. Dong, W. Wang, H. Chen, L. Bai, Z. Cheng, Polym. Chem. 10 (2019) 503. [29] Q. Huang, J. Zhao, M. Liu, J. Chen, X. Zhu, T. Wu, J. Tian, Y. Wen, X. Zhang, Y. Wei, J. Taiwan Inst. Chem. E. 82 (2018) 92. [30] Q. Huang, J. Zhao, M. Liu, Y. Li, J. Ruan, Q. Li, J. Tian, X. Zhu, X. Zhang, Y. Wei, J. Taiwan Inst. Chem. E. 86 (2018) 174. [31] Q. Huang, M. Liu, L. Mao, D. Xu, G. Zeng, H. Huang, R. Jiang, F. Deng, X. Zhang, Y. Wei, J. Colloid Interface Sci. 499 (2017) 170. [32] X. Zhang, Q. Huang, F. Deng, H. Huang, Q. Wan, M. Liu, Y. Wei, Appl. Mater. Today 7 (2017) 222. [33] Q. Huang, M. Liu, J. Chen, Q. Wan, J. Tian, L. Huang, R. Jiang, Y. Wen, X. Zhang, Y. Wei, Appl. Surf. Sci. 419 (2017) 35. [34] G. Zeng, T. Chen, L. Huang, M. Liu, R. Jiang, Q. Wan, Y. Dai, Y. Wen, X. Zhang, Y. Wei, J. Taiwan Inst. Chem. E. 82 (2018) 205. [35] A. Krueger, Adv. Mater. 20 (2008) 2445. [36] W. Gu, N. Peters, G. Yushin, Carbon 53 (2013) 292. [37] H. Kim, H.B. Man, B. Saha, A.M. Kopacz, O.-S. Lee, G.C. Schatz, D. Ho, W.K. Liu, J. Phys. Chem. Lett. 3 (2012) 3791. [38] Q.-y. Cao, R. Jiang, M. Liu, Q. Wan, D. Xu, J. Tian, H. Huang, Y. Wen, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 80 (2017) 578. [39] Q.-y. Cao, R. Jiang, M. Liu, Q. Wan, D. Xu, J. Tian, H. Huang, Y. Wen, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 80 (2017) 411. [40] L. Huang, S. Yang, J. Chen, J. Tian, Q. Huang, H. Huang, Y. Wen, F. Deng, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 94 (2019) 270. [41] R. Jiang, H. Liu, M. Liu, J. Tian, Q. Huang, H. Huang, Y. Wen, Q.-y. Cao, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 81 (2017) 416. [42] R. Jiang, M. Liu, C. Li, Q. Huang, H. Huang, Q. Wan, Y. Wen, Q.-y. Cao, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 80 (2017) 708. [43] Y. Shi, R. Jiang, M. Liu, L. Fu, G. Zeng, Q. Wan, L. Mao, F. Deng, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 77 (2017) 972. [44] J. Tian, R. Jiang, P. Gao, D. Xu, L. Mao, G. Zeng, M. Liu, F. Deng, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 79 (2017) 563. [45] K. Zhang, Q. Zhao, S. Qin, Y. Fu, R. Liu, J. Zhi, C. Shan, J. Colloid Interface Sci. 537 (2019) 316. [46] H. Ouyang, M. Zhou, Y. Guo, M. He, H. Huang, X. Ye, Y. Feng, X. Zhou, S. Yang, Fitoterapia 96 (2014) 152. [47] X. Zhang, J. Li, B. Xie, B. Wu, S. Lei, Y. Yao, M. He, H. Ouyang, Y. Feng, W. Xu, S. Yang, Front. Pharmacol. 9 (2018). [48] X. Zhang, M. He, S. Lei, B. Wu, T. Tan, H. Ouyang, W. Xu, Y. Feng, J. Pharmaceut. Biomed. 156 (2018) 221. [49] H. Huang, M. Liu, R. Jiang, J. Chen, L. Mao, Y. Wen, J. Tian, N. Zhou, X. Zhang, Y. Wei, J. Colloid Interface Sci. 513 (2018) 198. [50] J. Chen, M. Liu, Q. Huang, L. Huang, H. Huang, F. Deng, Y. Wen, J. Tian, X. Zhang, Y. Wei, Chem. Eng. J. 337 (2018) 82. [51] X. Zhao, S. Zhang, C. Bai, B. Li, Y. Li, L. Wang, R. Wen, M. Zhang, L. Ma, S. Li, J. Colloid Interface Sci. 469 (2016) 109. [52] H.-D. Wang, Q. Yang, C.H. Niu, I. Badea, Diam. Relat. Mater. 26 (2012) 1. [53] X. Xing, P.-H. Chang, G. Lv, W.-T. Jiang, J.-S. Jean, L. Liao, Z. Li, J. Taiwan Inst. Chem. E. 59 (2016) 237. [54] F. Shojaeipoor, D. Elhamifar, B. Masoumi, D. Elhamifar, B. Barazesh, Arab. J. Chem. (2016). [55] M.K. Purkait, A. Maiti, S. Dasgupta, S. De, J. Hazard Mater. 145 (2007) 287. [56] C. Fang, L. Kong, Q. Ge, W. Zhang, X. Zhou, L. Zhang, X. Wang, Polym. Chem. 10 (2019) 209. [57] H.-D. Wang, Q. Yang, C. Hui Niu, I. Badea, Diam. Relat. Mater. 26 (2012) 1. [58] H. Molavi, A. Pourghaderi, A. Shojaei, J. Chem. Eng. Data 64 (2019) 1508. [59] X. Zhao, K. Ma, T. Jiao, R. Xing, X. Ma, J. Hu, H. Huang, L. Zhang, X. Yan, Sci. Rep. 7 (2017) 44076.
Contents lists available at ScienceDirect
Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Preparation of ionic liquids functionalized nanodiamonds-based composites through the Michael addition reaction for efficient removal of environmental pollutants Guang Yang a, Hongye Huang a, Junyu Chen a, Defu Gan a, Fengjie Deng a, Qiang Huang a, Yuanqing Wen a, Meiying Liu a, ***, Xiaoyong Zhang a, *, Yen Wei b, c, ** a
Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang, 330031, China Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084, China c Department of Chemistry and Center for Nanotechnology and Institute of Biomedical Technology, Chung-Yuan Christian University, Chung-Li, 32023, Taiwan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 September 2019 Received in revised form 29 September 2019 Accepted 2 October 2019 Available online 3 October 2019
Nanodiamonds (ND) is a novel type of carbon nanomaterials with small size, large specific surface areas, low cost and some other physicochemical properties. However, the environmental applications of ND are still rarely reported because of its low adsorption performance. In this work, we reported for the first time for the surface modification of ND with ionic liquids through a facile and effective Michael addition reaction. To synthesis of the ternary ND@IL composites, ND was first linked with APTES by a silanization reaction and then [C16VImþ] [Br] was conjugated on the surface of amino groups functionalized ND via the Michael addition reaction. The ND@IL composites were applied as adsorbents for removal of Congo red (CR) from aqueous solution and displayed high removal efficiency (92.78%) at room temperature and neutral solution. Under certain adsorption conditions, the adsorption capacities of pristine ND and ND@IL towards CR is 61.1 and 226.4 mg g1, respectively. The pseudo-second-order model fitting the adsorption kinetic data is superior to pseudo-first-order model and Freundlich isotherm model describes the experimental data well. Further experiments showed that the removal process was pH dependence, exothermic and spontaneous. More importantly, ND@IL composites could be regenerated via adjustment of pH values and still maintain high adsorption capacity after five regeneration cycles. All of the above results demonstrated that these ionic liquids modified ND are promising adsorbents for highly efficient and quick removal of environmental pollutants from aqueous effluents. © 2019 Elsevier B.V. All rights reserved.
Keywords: Nanodiamond-based composite Ionic liquid Environmental adsorption Michael addition reaction
1. Introduction Nowadays, dyes play a decisive role in textile, paper and leather manufacturing industries, producing about 1.6 million tons of dyes every year [1,2]. Dyes are usually classified on the basis of their functional groups or colors and by the nature of ionic charge dissolved in the aqueous solution. In the process of using dyes, a significant portion of dyes will be lost as wastes, causing main sources
* Corresponding author. ** Corresponding author. Department of Chemistry and Center for Nanotechnology and Institute of Biomedical Technology, Chung-Yuan Christian University, Chung-Li, 32023, Taiwan. *** Corresponding author. E-mail addresses: [email protected] (M. Liu), [email protected] (X. Zhang), [email protected] (Y. Wei). https://doi.org/10.1016/j.molliq.2019.111874 0167-7322/© 2019 Elsevier B.V. All rights reserved.
of water pollution [3]. Some of them are highly toxic, posing a serious threat to human health. Even trace of dyes existed in water can result in high chemical oxidation demand and cause peculiar smell to aquatic systems [4]. Therefore, developing efficient technologies for dye removal from effluent of manufacturing industries become more and more significance. To date, a series of approaches have been developed to treat dyes in sewage including physical, chemical, and biological decoloration scientific methods [5e9]. However, these dyes are difficult to remove since they are recalcitrant organic molecules and are stable to oxidizing agents. Commonly used techniques are flocculation [10], photo-catalysis [11], electrochemical [12], ion exchange [13], and microbial degradation [14]strategies, but few of them has been proved to be effective in actual wastewater treatment. In addition to these technologies, the adsorption technology is the most promising and effective technique due to its simple operation, low cost and good
2
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
designability. Selection of an appropriate adsorbent is the key to the effectiveness of adsorption technology. Up to now, various conventional decoloration adsorbents, including carbon-based materials [15e20], clay materials [21,22] and biosorbents [23e28], and many other composite adsorbents[29e34] have been widely reported previously. Nanodiamonds (ND) is one of the most synthetic materials on the market, with size range of 5e10 nm particles being produced via detonation [35]. ND has shown extensive applications in various applications such as energy storage [36], gene therapy [37], biological imaging [38e44] and drug-delivery carriers [45e50] due to its distinctive morphology, electronic and thermal properties. Moreover, ND has some specific properties such as mesopores, large specific surface area, and oxygen functional groups. These features make ND to be easily modified with different agents and providing enough active sites for the adsorption process. Therefore, ND and its composites have been regarded as one of the promising adsorbents in environmental treatment. For example, Zhao et al. [51] reported that the adsorption capacities of ND/amide thiourea composites for metal ions uranium were enhanced after the coordination with single-armed ligand and double -armed ligand, with the maximum values were calculated about 200 mg g1, and the selectivity is as high as 82% and 72%, respectively. Wang et al. [52] reported that the adsorption of azo dye acid orange 7 onto ND surface, which confirming the adsorption behavior and the mechanism by comparing with another azo compound adsorption into ND as control groups, and pointing out that the affinity between ND and acid orange is obviously higher than the other azo compounds through electrostatic interaction. In general, the study of the removal of dyes from sewage through ND-based composites is a relative new field. Recently, the monomers of ionic liquids have been widely used to adsorb dyes by combining with nanomaterials to form novel adsorbents [53e55]. For example, Xing et al. [53] successfully obtained a zeolite/ionic liquid composite material and used it as an adsorbent to remove anionic dyes. The removal rate of methyl orange was fast, following a pseudo-second-order kinetics with a maximum adsorption capacity of 116 mmol kg1. However, to the best of authors knowledge, the surface modification of ND with ionic liquids and the adsorption behavior of ND-based ionic liquids has not been reported thus far. Herein, the main task is to investigate the adsorption behavior and mechanism for removal of azo dye by ND@IL composites. To this end, Congo red (CR) was chosen as the textile dye (an anion azo dye, the chemical structure of CR was listed in Fig. S1), 3-n-Hexadecyl-1-vinylimidazolium Bromide [C16VImþ] [Br] as modifying monomer. The ionic liquid functionalized ND composites were prepared via the Michael addition reaction for the first time. The composites were used as adsorbents to remove CR from stock solution. To be specific, ND was modified with APTES by silanization reaction. Then, ND@IL composites with a charged imidazole ring were obtained via the Michael addition reaction between ethenyl and amino groups on the surface of ND-NH2 (Scheme 1). The samples of synthesized ND, ND-NH2 and ND@IL composites were characterized by a series of characterization methods in details. Studies on adsorption properties of materials were also performed under different conditions, with emphasis on the factors affecting the contact time, dye concentration, initial pH and temperature affect for the adsorption capacity. Furthermore, kinetic models, isotherm models, thermodynamic calculations and regeneration experiments were used to evaluate the adsorption process onto ND@IL composites.
2. Experimental sections 2.1. Materials and characterization Nanodiamond (average diameter of 10 nm, Beijing Grish Hitech Co. Ltd., China), 1-bromohexadecane, 1-vinylimidazole, triethylamine (TEA), (3-aminopropyl) triethoxysilane (APTES) and bismuth trifluoromethane sulfonate were purchased from Aladdin Chemical reagents Co, Ltd. (Shanghai, China). Methanol, diethyl ether, ethanol, HCl and NaOH were of analytical grade and used as received (from Damao Chemical Industrial Company, Tianjin) without further purification. The samples were characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), thermo-gravimetric analysis (TGA), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The detailed information was provided in ESI. 2.2. Preparation of 3-n-Hexadecyl-1-vinylimidazolium bromide 3-n-Hexadecyl-1-vinylimidazolium bromide ([C16VImþ] [Br]) was synthesized according to previous reference[56]. Simply, a mixture of 0.15 mol 1-bromohexadecane, 0.1 mol 1-vinylimidazole and 30 mL methanol was placed in a 50 mL flask at 80 C for 24 h, and the reaction system was purged with N2 for 30 min to remove O2. When the reaction was completed, the orange viscous liquid was washed through diethyl ether and the final product was stored at low temperature. (1H NMR spectrum in Fig. S2A. DMSO, d, ppm. 9.40 (1H, -N-CH]Nþ-), 8.21 (1H, -N-CH]CHeNþ ¼ ), 7.84 (1H, -NCH]CHeNþ ¼ ), 7.41 (2H, CH2]CH-), 7.34 (1H, CH2¼CH-), 5.26 (2H, eNþ-CH2-CH2-), 4.18 (2H, eNþ-CH2-CH2-)1.21 (26H, -CH2CH2-), 0.83 (3H, eCH2-CH3).) 2.3. Synthesis of adsorbents The modified ND (ND-NH2) nanoparticles were prepared via APTES hydrolysis as followed procedure: 500 mg ND was added to a reaction bottle containing 30 mL of ethanol, and the particles were uniformly dispersed by sonication. Then, 3 mL triethylamine was added slowly and the mixture was stirred at 40 C for 3 h. Subsequently, a mixture of 2 mL APTES and 10 mL distilled water was quickly added into the suspension solution and stirred for 12 h. The obtained ND-NH2 particles were washed many times with distilled water and dried in freeze dryer. The functionalized ND particles with charged imidazole ring (ND@IL) were prepared based on the following procedure. 400 mg ND-NH2, 400 mg [C16VImþ] [Br] and 50 mg bismuth trifluoromethane sulfonate were added into 30 mL dried ethanol, and the system was washed with nitrogen and sonicated for 10 min to form a homogeneous suspension. The reaction system was vigorously stirred at 60 C for 8 h. When the reaction was completed, the crude product was washed with ethanol and distilled water, and further dried in a vacuum oven. 2.4. Adsorption studies The whole batch adsorption study of the ND before and after being modified was performed at 50 mL centrifuge tube containing 10 mg samples and a certain concentration of CR. The residual CR concentration was calculated according to the absorbance of the solution after adsorption, and was used UVeVisible spectrophotometer (TU-1810, Beijing) as detector. 3. Results and discussion 3.1. Characterization of materials The 1H NMR scan spectra was used to determine the chemical
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
3
Scheme 1. Schematic illustration of the functionalization of ND combined with silanization reaction and Michael addition reaction.
structure information of ND@IL composites (Fig. S2B). Peaks at 7.83, 7.16 and 6.64 ppm were attributed to protons of eC]N and eC]Cof the imidazole ring. The signals at 5.31 and 0.83 ppm can be assigned to the chemical shift of the methylene group on alkane chain linked to N and of methyl group of the alkane chain, respectively. The strongest peak at 3.31 and 2.51 ppm was belonged to protons of solvent (d6-DMSO). The chemical shifts of the remaining methylene groups at different sites were distributed at 1e2 ppm. These results indicated that APTES and [C16VImþ] [Br] were grafted to surface of ND successfully via two steps reaction. In addition, the FT-IR spectra of ND, ND-NH2 and ND@IL were shown in Fig. 1A. The broad peak at 3411 cm1 was the Oxygen hydrogen bond and bound water in the pristine material. Obviously, the adsorption peaks at 3460, 2926, 1220, and 1028 cm1 were ascribed to the characteristic peaks of NeH, CeH, CeSi and CeOeSi stretching vibrations in the sample of ND-NH2, respectively. Demonstrated that some of the CeOeSi and eNH2 were formed on the ND surface. The new broad band of 1625 cm1 was mainly assigned to the C]N stretching vibration of imidazole ring in the spectrum of ND@IL. Moreover, the absorbance band near 1150 cm1 became stronger was related to CeN stretching
vibration. In brief, the bonds of OeH, NeH, CeH, CeSi, CeOeSi and C]N were changed before and after modification, which was attributed to the introduction of [C16VImþ] [Br]. These changes illustrated that ND was successfully modified by the Michael addition reaction. The TGA was performed to get more evidence for the surface functionalization with ionic liquid of ND. Thus, the content of surface-modified molecule was further evaluated based on the weight loss ratio by TGA measurement. As shown in Fig. 1B, the mass loss of ND, ND-NH2 and ND@IL were 10.1%, 4.7%, and 3.9%, respectively, at below 373 K, which was considered as free water content in all samples. For the pristine ND, the weight loss in the temperature range from 373 to 1000 K was 12.2%, which ascribed to the decomposition of the surface eOH. The total mass loss was 18.2% for the sample of ND-NH2 at 1000 K, and the content of decomposed APTES could be calculated to be as 1.3%. In a similar way, the weight percentage of IL conjugated on the surface of NDNH2 to be as 11.4% in the curve of ND@IL. These results suggested that APTES and IL were facilely grafted to ND surfaces by silanization reaction and Michael addition reaction, respectively. Fig. 2(A-C) shows the TEM image of the samples. The TEM image of the pristine ND particles displays randomly stacked
Fig. 1. FT-IR spectrum of ND, ND-NH2 and ND@IL (A); TGA curves of samples (B).
4
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
Fig. 2. TEM images of particles (AeC); X-ray energy dispersive spectroscopy (EDS) of ND@IL (D).
characteristics. The size of individual nanoparticles about 10 nm. After successfully grafting APTES onto its surface, the small particles in TEM become blurred and the contour of the particles becomes less obvious. Surprisingly, we can clearly observe the thick polymer layer covering the surface of ND from Fig. 2C. In addition, the X-ray energy dispersive spectrum of ND@IL was described in Fig. 2D. The related elements such as C, O, Si, Br were found in the spectrum. The emergence of Si and Br elements further proves that the composite has been successfully modified with APTES and IL. XPS was carried out as an technique to obtain the surface chemical information of ND samples before and after
functionalization of APTES and organic molecules. The XPS wide survey spectrum range from 0 to 1200 eV is shown in Fig. 3A, that illustrated the different elements exist in the ND-based samples. We can clearly see these elements, including the C, O, N, Si and Br (Fig. 3A). In addition, narrow survey spectra were fitted to the elements of C, O, N, Si and Br in different samples. As shown in Fig. 3BeF. The major elements C 1s, N 1s and O 1s showed obvious signal peaks in the three samples, respectively (Fig. 3BeD). For the element Si 2p (Fig. 3E), there is no characteristic signal peak in the spectrum of original ND. However, there are obvious silicon signal peaks in the narrow scan spectra of ND-NH2 and ND@IL samples at
Fig. 3. XPS overview spectra of ND, ND-NH2 and ND@IL particles (A); high-resolution XPS spectra of C 1s (B), O 1s (C), N 1s (D) Si 2p (E) and Br 3d (F) of ND, ND-NH2 and ND@IL.
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
101.3 and 101.1 eV, respectively. As we can see from the Br 3d narrow scan spectra, no significant peak strength was observed in the curves of original ND and ND-NH2 samples. In the sample of ND@IL, a stronger signal peak appeared at 66.9 eV of the Br 3d spectrum. This result strongly proves that the organic molecules APTES and IL were successfully grafted onto the surface of ND. On the other hand, the contents of C, O, N, Si and Br in all samples were calculated on the basis of XPS scan spectra. Detailed values were listed in Table 1. For the samples of ND-NH2, the percentages of C, O, N, Si and Br were 78.23%, 16.97%, 2.76%, 2.03% and 0%, respectively. Before modification with APTES, the contents of C, O, N, Si and Br in ND were changed to 85.57%, 12.62%, 1.81%, 0% and 0%, respectively. The Si content changed sharply to 0 because of the lack of Si in the original ND. Moreover, increasing of N content in the sample of ND-NH2 also clearly evidences the introduction of APTES on the surface of ND. After modification with [C16VImþ] [Br], the contents of C, O, N, Si and Br in ND@IL changed to 80.97, 14.26, 3.23, 1.16 and 0.38%, respectively. Because the element Br only existed in IL, it is clear that there is obvious increase of Br contents in the sample of ND@IL. Moreover, we could also find that the contents of C and N were boosted from 78.23% to 2.76%e80.97% and 3.23%, respectively. Based on the change of N contents in NDNH2 and ND@IL, we could calculate that the weight percentage of IL on ND@IL should be about 9.13%. This result is close to the calculated result of TGA. Therefore, we could also confirm that the surface functionalization of ND with APTES and [C16VImþ] [Br]. It is well known that the Michael addition reaction is a useful tool for surface conjugation between the amino groups and ene bonds. The Michael addition reaction could be occurred under mild conditions such as low temperature, organic solvents and aqueous solution without gas protection and with simple operation procedure. In this work, we demonstrated that the ionic molecule could be facilely introduced on the surface of ND@NH2. Therefore, the ionic molecules could be acted as the active adsorption sites to improve the adsorption efficiency towards ionic environmental pollutants. On the other hand, the hydrophobic environmental pollutants could also be adsorbed by the ionic liquids modified ND@IL owing to the existence of hydrophobic alkyl chains. 3.2. Removal of CR In actual dye pollution control and treatment, the adsorption equilibrium time is a key factor to predict the feasibility and efficiency of an adsorbent. Fig. 4A indicates the impact of time on the CR adsorption onto the pristine ND and ND@IL. It is clear that the amount of CR adsorbed by ND@IL composites increases rapidly in the first 5 min. After that, the Q of ND@IL composites was enhanced slowly until the adsorption capacity was 226.4 mg g1 at 39 min and remained almost alike. The increased Q may be the reason for the large number of vacant surface adsorption active sites in the initial stage. After the active sites are occupied by lots of CR molecules, the remaining active sites are reduced. So, there are fewer dye molecules diffusing to the surface of ND@IL, and the adsorption capacity grows slowly until the equilibrium is reached. The adsorption capacity of the original material only reached 61.1 mg g1 at 49 min due to few adsorption sites on its surface.
Table 1 Atom percentage of ND, ND-NH2 and ND@IL. sample
Atom percentage (%) C
O
N
Si
Br
ND ND-NH2 ND@IL
85.57 78.23 80.97
12.62 16.97 14.26
1.81 2.76 3.23
0.00 2.03 1.16
0.00 0.00 0.38
5
Thus, the ND@IL composites functionalized with IL have better adsorption properties than original ND particles. To gain deep understanding for the behavior of adsorption process, the adsorption kinetics were studied by three models to fit the experimental adsorption data. The fitted curves and parameters of models are shown in Fig. 4B and listed in Table 2, respectively. From Table 2, the R2 value of pseudo-second-order model (0.9281) is closer to 1 than other model. On the other hand, the value of Qe (cal) (mg g1) from pseudo-second-order model (231 mg g1) is closer to the actual adsorption capacity. These results suggested that the adsorption of dye onto the surface of ND@IL at room temperature, is better described by pseudo-second-order. Further calculation indicated that the rate-control step is the chemical adsorption mechanism. For intraparticle diffusion model, the correlation coefficients R2 and constant C are 0.9634 and 35.55, respectively. These value results show that the physical adsorption is also one of the control steps. The amount of CR per unit volume of solution plays a vital role. Fig. 5A shows the effect of initial CR concentration on the adsorption capacity of ND@IL from 50 mL CR at 298 K and pH ¼ 7, for the initial CR concentration was 50e250 mg L1 and contact time of 39 min, the adsorption capacities of the ND@IL composites were 219.7 mg g1 and 395.1 mg g1, respectively. On the whole, with the increase of C0, the adsorption capacity of adsorbents also gradually increases and tends to moderate growth. Since the number of active sites is fixed, increasing the initial concentration of CR over a wide range cannot effectively promote the linear growth of the Q of the material. Therefore, the growth of adsorption capacity of the nanomaterials has become moderate. In order to study the relationship between C0 and Qe, the isotherm models were applied to fitting experimental data of the adsorption. The correlation coefficient (R2) and constant calculated from the Langmuir and Freundlich isotherm models are listed in Table 3 and the curves of sorption isotherms are described in Fig. 5A. From the data of Table 3, it could be obviously observed that the value of R2 of Freundlich (0.9905) was greater than that of Langmuir isotherm model (0.9637). The results indicate that the adsorption of CR onto ND@IL composites conforms to the heterogeneity sorption. On the other hand, the Freundlich model constant n1 was 0.3649, which reflected that the ND@IL composites is effective. Although the adsorption process of this experiment could not be well described by the Langmuir isotherm model, the Langmuir model has a large adsorption capacity, indicating that the composites could be used as effective adsorbents to remove dyes from contaminated water. Moreover, the value of separation factor RL (0.2139-0.5764) was less 0.6, further indicating that the adsorption is favorable. The pH is another crucial factor affecting the adsorption efficiency. To further research the adsorption mechanism of CR on the surface of materials, the effect of different pH (pH ¼ 6e11) values CR on the adsorption capacity of ND@IL was studied at room temperature. According to the data, the curves of Q of composites and the removal efficiency of CR with the change of pH values of solution are fitted in Fig. 5B. The removal efficiency of CR quickly decreased from 92.78% (231.94 mg g1) to 71.67% (179.17 mg g1) (Fig. 5B). This phenomenon can be explained: When the pH is less than 7, the ND@IL composites was positively charged and interacted with the negatively charged CR molecule via electrostatic attraction. When the solution pH is above 7, the quaternary ammonium deionization was very strong, and the ND@IL surface positively charged active sites gradually decrease with the increasing pH, which is unfavorable CR adsorption onto the surface of composites. Meanwhile, the hydrophobic interaction between the alkyl chains and the CR was also an important mechanism of adsorption. So the optimum pH for removing CR by using IL functionalized ND as adsorbent was 6.
6
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
Fig. 4. The effect of contact time on adsorption of CR (50 mg L1) by ND and ND@IL (m ¼ 10 mg, 298 K) (A); kinetic curves for adsorption of CR on ND@IL (B).
Table 2 Adsorption kinetics data for CR adsorption on ND@IL nanocomposites. Models
Parameters
Initial concentration (mg L1)
Pseudo-first-order equation
Qe (cal) (mg g1) k1 (min1) R2 Qe (cal) (mg g1) k2 (g mg1 min1) R2 kp (mg g1 min0.5) C R2
198.5 0.04873 0.8914 231 0.0002538 0.9281 16.47 35.55 0.9634
50
Pseudo-second-order equation
Intraparticle diffusion
Fig. 5. Adsorption isotherms of CR on ND@IL (A), effect of pH values on the ND@IL to remove CR (B).
Table 3 Isotherms data of models for CR adsorption on ND@IL. Isotherms
Parameters
Langmuir
Qm (mg g1) KL (L mg1) RL R2 KF [(mg g1)(L mg1)1/n] n1 R2
Temperatures (K) 298
Freundlich
491.9 0.0147 0.2139e0.5764 0.9637 52.94 0.3649 0.9905
The effects of temperatures on the adsorption capacity of ND@IL composites in 50 mL CR solution were investigated. By changing, the thermodynamic parameters DG0, DH0 and DS0 can provide some meaningful information, which can reveal the feasibility, spontaneous and endothermic or exothermic nature of the
adsorption process. The influence curve of temperature on adsorption capacity and the thermodynamic parameters are fitted in Fig. 6A and listed in Table 4, respectively. Although the DG0 increases gradually, it is always negative value in the temperature range of 298e348 K, that indicated that the CR onto ND@IL composites was highly spontaneous and thermodynamically favorable. The negative value of DH0 (17.65 kJ mol1) reflects the exothermic nature of adsorption. The value of DS0 (0.02794 kJ mol1 K1) was also negative, indicated that the decrease the randomness of the solid/solution interface. All the thermodynamic parameters also implied that the adsorption of CR on the composites is hindered as the temperature gradually increases. The above results clearly suggested that the ND@IL are favorable for removal of CR at room temperature. The regeneration ability of the adsorbent is a significant factor in estimating the commercial feasibility. For the desorption studies, the CR-adsorbed ND@IL was dispersed in a solution of hot ethanol containing 50 mg NaOH to removal CR molecular and then washed
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
7
Fig. 6. The effect of temperature on adsorption of CR by ND@IL (A); Van't Hoff plot for the adsorption of CR by ND@IL (B).
Table 4 Data of the thermodynamic parameters for the adsorption of CR onto ND@IL. Isotherms
Parameters
Temperatures (K) 298
Langmuir
Freundlich
Qm (mg g1) KL (L mg1) RL R2 KF [(mg g1)(L mg1)1/n] n1 R2
491.9 0.0147 0.2139e0.5764 0.9637 52.94 0.3649 0.9905
Fig. 7. Recyclability of ND@IL for the CR adsorption (V ¼ 50 mL, C0 ¼ 50 mg L1, m ¼ 10 mg).
with distilled water until the solution was no red color was observed and it's neutral. The adsorptiondesorption experiments were repeated for five consecutive cycles, the adsorption capacity and CR removal efficiency of the materials (before and after desorption) were depicted in Fig. 7. From Fig. 7, it is worth to noting that ND@IL composites maintain a high adsorption capacity and removal efficiency. Although the removal rate was reduced by 11.67% after five consecutive adsorption-desorption cycles. The decrease of adsorption capacities after reusability may possibly ascribed to the hydrophobic interaction between adsorbent and organic dye, which will not be influenced by the change of pH. Therefore, ND@IL could be used in multiple cycles with sufficient chemical stability during the adsorption process. Taking together, the adsorption experimental results demonstrated that the surface modification of ND with IL could effectively improve the adsorption capacity of ND. The modified ND (ND@IL) could display high adsorption performance at room temperature and acidic/neutral
Table 5 Compare with the maximum adsorption capacities (Qmax) of various composite for dyes. Composite
Dye
Qmax
Refs
Nanodiamond Thermally oxidized nanodiamond Diamond@graphite Nanodiamond@ionic liquid
Acid orange 7
1288 mmol kg1
[57]
Methylene blue Methylene blue Congo red
47.62 mg g1 23.3 mg g1 226.4 mg g1
[58] [59] This work
solution. More importantly, the adsorbent could be regenerated and still keep high adsorption capacity after five cycles. These features make ND@IL promising for removal of ionic organic dyes and other ionic environmental pollutants. Table 5 lists the maximum adsorption properties of different nano-diamond-based composites on various dyes, which has been reported in the literature. The adsorption of environmental pollutants by ND and related composites are mainly relied on their particle size, specific surface areas and the surface functional groups. In this work, the maximum adsorption of ND@IL composites is as high as 226.4 mg g1, which is obviously larger than the ND materials and composites with other treatment methods. The surface modification of IL on the surface of ND could not only improve the dispersibility of ND composites in aqueous solution and kept their high surface areas and small size, but also could introduce a larger number of functional groups. These functional groups with ionic components could also interact with the ionic organic dyes through the hydrophobic interaction and electrostatic interaction. Moreover, based on the above role, we could expect that the ND@IL composites could also be utilized for adsorptive removal other environmental pollutants through the similar interactions with desirable adsorption capacity. More importantly, this method is simple, effective and universal. It could therefore be a useful surface modification method with great potential for fabrication of functionalized adsorbents with promising applications in environmental fields.
4. Conclusions In summary, we reported a simple and effective method for preparation of IL modified ND via the Michael addition reaction. Owing to the introduction of IL with hydrophobic alkyl chains and ionic segment, the ND@IL could be acted as promising adsorbents for removal of anionic CR from colored solution. Compared with pristine ND, ND@IL composites display obvious enhancement of adsorption capacity towards CR. After equilibrium, the adsorption capacity of ND@IL composites reaches 226.4 mg g1 (pH ¼ 7 at room temperature). This value is obvious greater than that of
8
G. Yang et al. / Journal of Molecular Liquids 296 (2019) 111874
unmodified ND (61.1 mg g1) at identical adsorption conditions. The pseudo-second-order model and Freundlich model can well describe the data of CR adsorption process. The mechanism of CR adsorption involves not only electrostatic interaction, but also the hydrophobic interaction between alkyl chains and aromatic rings of CR. Besides, ND@IL composites can be regenerated by washing with alkaline solution, and still keep high adsorption capacity after regeneration. All the above results show that ND@IL composites are promising adsorbents that can efficiently remove CR from contaminated aqueous media. Moreover, we believe that this work will provide a new avenue for the environmental adsorption applications of ND-based composites. Declaration of competing interest The authors declare that there have no conflict of interest. Acknowledgments This research was supported by the National Natural Science Foundation of China (Nos. 21865012, 21788102, 21564006, 21561022, 21644014). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molliq.2019.111874. References [1] V. Gupta, J. Environ. manage. 90 (2009) 2313. [2] K. Hunger, Industrial Dyes: Chemistry, Properties, Applications, John Wiley & Sons, 2007. [3] N. Sharma, D. Tiwari, S. Singh, Int. J. Sci. Eng. Res. 3 (2012) 1. [4] M.S. Field, R.G. Wilhelm, J.F. Quinlan, T.J. Aley, Environ. Monit. Assess. 38 (1995) 75. [5] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Bioresour. Technol. 77 (2001) 247. [6] P. Nigam, G. Armour, I. Banat, D. Singh, R. Marchant, Bioresour. Technol. 72 (2000) 219. € z, S. Atalay, J. Forss, U. Welander, Separ. Purif. Technol. 79 [7] O. Türgay, G. Erso (2011) 26. [8] N.P. Tantak, S. Chaudhari, J. Hazard Mater. 136 (2006) 698. [9] V. Katheresan, J. Kansedo, S.Y. Lau, J. Environ. Chem. Eng. 6 (2018) 4676. [10] C.-Z. Liang, S.-P. Sun, F.-Y. Li, Y.-K. Ong, T.-S. Chung, J. Membr. Sci. 469 (2014) 306. [11] M. Rauf, S.S. Ashraf, Chem. Eng. J. 151 (2009) 10. [12] E. Brillas, C.A. Martínez-Huitle, Appl. Catal. B Environ. 166 (2015) 603. [13] M.M. Hassan, C.M. Carr, Chemosphere 209 (2018) 201. [14] M. Chengalroyen, E. Dabbs, World J. Microbiol. Biotechnol. 29 (2013) 389. [15] J. Abdi, M. Vossoughi, N.M. Mahmoodi, I. Alemzadeh, Chem. Eng. J. 326 (2017) 1145. mez, S. Allen, G. Walker, Chem. Eng. J. 219 (2013) [16] J. Gal an, A. Rodríguez, J. Go 62. [17] J. Xie, Z. Ming, H. Li, H. Yang, B. Yu, R. Wu, X. Liu, Y. Bai, S.-T. Yang, Chemosphere 151 (2016) 324. [18] H. Yang, X. Wu, Q. Ma, A. Yilihamu, S. Yang, Q. Zhang, S. Feng, S.-T. Yang, Chemosphere 216 (2019) 9. [19] L. Chen, C. Wang, S. Yang, X. Guan, Q. Zhang, M. Shi, S.-T. Yang, C. Chen, X.L. Chang, Environ. Sci. Nano 6 (2019) 1077. [20] L. Chen, C. Wang, H. Li, X. Qu, S.-T. Yang, X.-L. Chang, Environ. Sci. Technol. 51 (2017) 10146.
[21] V. Vimonses, S. Lei, B. Jin, C.W. Chow, C. Saint, Chem. Eng. J. 148 (2009) 354. [22] M. Sabzi, N. Shafagh, M. Mohammadi, J. Appl. Polym. Sci. (2019) 48266. [23] F. Silva, L. Nascimento, M. Brito, K. da Silva, W. Paschoal, R. Fujiyama, Materials 12 (2019) 2486. [24] Z. Zhang, S. Xia, X. Wang, A. Yang, B. Xu, L. Chen, Z. Zhu, J. Zhao, N. JaffrezicRenault, D. Leonard, J. Hazard Mater. 163 (2009) 279. [25] L. Bai, X. Jiang, Z. Sun, Z. Pei, A. Ma, W. Wang, H. Chen, H. Yang, L. Yang, D. Wei, Cellulose 26 (2019) 5305. [26] G. Wang, M. Xi, L. Bai, Y. Liang, L. Yang, W. Wang, H. Chen, H. Yang, Cellulose 26 (2019) 5947. [27] S. Liu, Z. Rao, R. Wu, Z. Sun, Z. Yuan, L. Bai, W. Wang, H. Yang, H. Chen, J. Agric. Food Chem. 67 (2019) 1061. [28] M. Chen, D. Fan, S. Liu, Z. Rao, Y. Dong, W. Wang, H. Chen, L. Bai, Z. Cheng, Polym. Chem. 10 (2019) 503. [29] Q. Huang, J. Zhao, M. Liu, J. Chen, X. Zhu, T. Wu, J. Tian, Y. Wen, X. Zhang, Y. Wei, J. Taiwan Inst. Chem. E. 82 (2018) 92. [30] Q. Huang, J. Zhao, M. Liu, Y. Li, J. Ruan, Q. Li, J. Tian, X. Zhu, X. Zhang, Y. Wei, J. Taiwan Inst. Chem. E. 86 (2018) 174. [31] Q. Huang, M. Liu, L. Mao, D. Xu, G. Zeng, H. Huang, R. Jiang, F. Deng, X. Zhang, Y. Wei, J. Colloid Interface Sci. 499 (2017) 170. [32] X. Zhang, Q. Huang, F. Deng, H. Huang, Q. Wan, M. Liu, Y. Wei, Appl. Mater. Today 7 (2017) 222. [33] Q. Huang, M. Liu, J. Chen, Q. Wan, J. Tian, L. Huang, R. Jiang, Y. Wen, X. Zhang, Y. Wei, Appl. Surf. Sci. 419 (2017) 35. [34] G. Zeng, T. Chen, L. Huang, M. Liu, R. Jiang, Q. Wan, Y. Dai, Y. Wen, X. Zhang, Y. Wei, J. Taiwan Inst. Chem. E. 82 (2018) 205. [35] A. Krueger, Adv. Mater. 20 (2008) 2445. [36] W. Gu, N. Peters, G. Yushin, Carbon 53 (2013) 292. [37] H. Kim, H.B. Man, B. Saha, A.M. Kopacz, O.-S. Lee, G.C. Schatz, D. Ho, W.K. Liu, J. Phys. Chem. Lett. 3 (2012) 3791. [38] Q.-y. Cao, R. Jiang, M. Liu, Q. Wan, D. Xu, J. Tian, H. Huang, Y. Wen, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 80 (2017) 578. [39] Q.-y. Cao, R. Jiang, M. Liu, Q. Wan, D. Xu, J. Tian, H. Huang, Y. Wen, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 80 (2017) 411. [40] L. Huang, S. Yang, J. Chen, J. Tian, Q. Huang, H. Huang, Y. Wen, F. Deng, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 94 (2019) 270. [41] R. Jiang, H. Liu, M. Liu, J. Tian, Q. Huang, H. Huang, Y. Wen, Q.-y. Cao, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 81 (2017) 416. [42] R. Jiang, M. Liu, C. Li, Q. Huang, H. Huang, Q. Wan, Y. Wen, Q.-y. Cao, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 80 (2017) 708. [43] Y. Shi, R. Jiang, M. Liu, L. Fu, G. Zeng, Q. Wan, L. Mao, F. Deng, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 77 (2017) 972. [44] J. Tian, R. Jiang, P. Gao, D. Xu, L. Mao, G. Zeng, M. Liu, F. Deng, X. Zhang, Y. Wei, Mater. Sci. Eng. Mater. 79 (2017) 563. [45] K. Zhang, Q. Zhao, S. Qin, Y. Fu, R. Liu, J. Zhi, C. Shan, J. Colloid Interface Sci. 537 (2019) 316. [46] H. Ouyang, M. Zhou, Y. Guo, M. He, H. Huang, X. Ye, Y. Feng, X. Zhou, S. Yang, Fitoterapia 96 (2014) 152. [47] X. Zhang, J. Li, B. Xie, B. Wu, S. Lei, Y. Yao, M. He, H. Ouyang, Y. Feng, W. Xu, S. Yang, Front. Pharmacol. 9 (2018). [48] X. Zhang, M. He, S. Lei, B. Wu, T. Tan, H. Ouyang, W. Xu, Y. Feng, J. Pharmaceut. Biomed. 156 (2018) 221. [49] H. Huang, M. Liu, R. Jiang, J. Chen, L. Mao, Y. Wen, J. Tian, N. Zhou, X. Zhang, Y. Wei, J. Colloid Interface Sci. 513 (2018) 198. [50] J. Chen, M. Liu, Q. Huang, L. Huang, H. Huang, F. Deng, Y. Wen, J. Tian, X. Zhang, Y. Wei, Chem. Eng. J. 337 (2018) 82. [51] X. Zhao, S. Zhang, C. Bai, B. Li, Y. Li, L. Wang, R. Wen, M. Zhang, L. Ma, S. Li, J. Colloid Interface Sci. 469 (2016) 109. [52] H.-D. Wang, Q. Yang, C.H. Niu, I. Badea, Diam. Relat. Mater. 26 (2012) 1. [53] X. Xing, P.-H. Chang, G. Lv, W.-T. Jiang, J.-S. Jean, L. Liao, Z. Li, J. Taiwan Inst. Chem. E. 59 (2016) 237. [54] F. Shojaeipoor, D. Elhamifar, B. Masoumi, D. Elhamifar, B. Barazesh, Arab. J. Chem. (2016). [55] M.K. Purkait, A. Maiti, S. Dasgupta, S. De, J. Hazard Mater. 145 (2007) 287. [56] C. Fang, L. Kong, Q. Ge, W. Zhang, X. Zhou, L. Zhang, X. Wang, Polym. Chem. 10 (2019) 209. [57] H.-D. Wang, Q. Yang, C. Hui Niu, I. Badea, Diam. Relat. Mater. 26 (2012) 1. [58] H. Molavi, A. Pourghaderi, A. Shojaei, J. Chem. Eng. Data 64 (2019) 1508. [59] X. Zhao, K. Ma, T. Jiao, R. Xing, X. Ma, J. Hu, H. Huang, L. Zhang, X. Yan, Sci. Rep. 7 (2017) 44076.