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montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline
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Facile synthesis of g-C3 N4 /montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline Chunquan Li, Zhiming Sun∗, Weixin Huang, Shuilin Zheng School of Chemical and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083, PR China
a r t i c l e
i n f o
Article history: Received 27 January 2016 Revised 1 June 2016 Accepted 16 June 2016 Available online xxx Keywords: Montmorillonite g-C3 N4 Visible-light Rhodamine B Tetracycline
a b s t r a c t A novel g-C3 N4 /montmorillonite (CN/M) composite with enhanced visible light photocatalytic activity was synthesized via a facile two-step process including wet-chemical and calcination method. The microstructure, interfacial and optical properties of the obtained CN/M composites were characterized by scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), surface area measurement (BET) and UV-visible diffused reflectance spectroscopy (UV-vis DRS). It is indicated that a tight interfacial combination between g-C3 N4 nanosheets and montmorillonite layers was formed in the composite photocatalysts. Compared with the other reference samples, the as-received CN/M composites possess significantly enhanced photocatalytic activity towards rhodamine B and tetracycline. The optimal mass ratio of g-C3 N4 with respect to montmorillonite is determined to be 31.86 wt% and the corresponding reaction constant rate is almost 3.0 times that of the pure g-C3 N4 under visible light. The enhanced photocatalytic activity of the g-C3 N4 /montmorillonite composite could be attributed not only to its relatively higher surface area and enhanced light-adsorption ability under visible light but also the synergistic effect arising from the tight combination between g-C3 N4 and montmorillonite due to the electrostatic interaction, which leads to efficient separation of the photo-generated charge carriers. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction In recent decades, with the rapid development of human beings’ industry and civilization, environmental problems have become globalized in terms of their existence and impacts. Both dyes and antibiotics are gradually becoming the most concerning issues due to their great threat to human health and the suspected resistant bacterial strains even at low concentrations [1]. Various methods have been adopted so far for the removal of dyes and antibiotics from aqueous solution including adsorption [2], membrane filtration [3], electrochemical technique [4] and photocatalysis [5]. However, most of antibiotics in wastewater such as tetracycline (TC) are not biodegraded in traditional water treatment processes, and can even hinder the removal of other organic pollutants. Among these techniques, photocatalysis seems to be one of the most promising techniques for mineralization of organic pollutants in the future because of its high efficiency, low cost and environmental friendly. During the past decades, various photocatalysts have been introduced since TiO2 was firstly used in generating H2 [6], such as ZnO [7], CdS [8], WO3 [9], BiOBr [10] and g-C3 N4 [11]. In recent ∗
Corresponding author. Tel.: +86 10 62330972; fax: +86 10 62330972. E-mail address: [email protected], [email protected] (Z. Sun).
years, considerable attention has been focused on the environmental applications of g-C3 N4 photocatalyst because of its visible-light responding band gap (2.70 eV), high thermal and chemical stability, and simple preparation. Polymeric g-C3 N4 photocatalyst with two-dimensional lamellar structure possesses high thermal and chemical stability due to its extended π -conjugated frameworks connected by the sp2 hybridization of carbon and nitrogen [12]. Nevertheless, similar to the other semiconductors, g-C3 N4 photocatalyst suffers high recombination rate of photo-generated electrons and holes as well. Hence, numerous strategies have been carried out to enhance the quantum efficiency of g-C3 N4 , such as metal and nonmetal ions doping [13,14], porous templating fabrication [15], heterojunction construction [16,17], and noble metals deposition [18]. Although the photocatalytic activity of g-C3 N4 can be enhanced by modification, some drawbacks of single g-C3 N4 significantly limit its practical applications, such as easy agglomeration and weak adsorption ability. It has been reported that these above-mentioned practical application problems of pure photocatalysts can be solved via using natural minerals as catalyst carriers [19–21]. Among these catalyst carriers, layered montmorillonite seems to be one of the most promising candidates for layered g-C3 N4 [22]. Montmorillonite, composed of two tetrahedrally coordinated sheets of silicon and one octahedrally coordinated sheet of aluminum ions has been extensively applied in various fields
http://dx.doi.org/10.1016/j.jtice.2016.06.014 1876-1070/© 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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because of its low cost, abundant, non-toxic and environmental friendly. To the best of our knowledge, there are few reports about the synthesis of g-C3 N4 /montmorillonite composite. In our present study, we synthesize a novel kind of gC3 N4 /montmorillonite composite with strong interfacial interaction through a facile two-step process. The physicochemical properties of as received composites were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), N2 adsorption/ desorption instrument, UV-visible diffused reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and electron spin resonance (ESR). Additionally, the photocatalytic performance of g-C3 N4 /montmorillonite composites was evaluated by the photodegradation of rhodamine B and tetracycline in water under visible light. The effects of montmorillonite in composites on the visible-light-driven photocatalytic efficiency were investigated. Moreover, the possible enhancement mechanism of g-C3 N4 /montmorillonite composite was also proposed based on the obtained experimental results. It is anticipated that this novel g-C3 N4 /montmorillonite composite with strong interfacial contact and enhanced photocatalytic activity is a potential photocatalytic material for dyes and antibiotics wastewater treatment. 2. Experimental 2.1. Materials The purified montmorillonite (M) is obtained from Jiayi Mineral Corporation, Liaoning Province. Cetyltrimethylammonium bromide was purchased from Tianjin Jinke Fine Chemical Research Institute. The melamine was achieved from Tianjin Guangfu Fine Chemical Research Institute. Tetracycline hydrochloride (C22 H24 N2 O8 .HCl, USP Grade) was obtained from Amresco Biosciences. Dimethyl sulfoxide (DMSO) was achieved from Xilong Chemical Co. (Guangdong, China). Ethanol, rhodamine B (C28 H31 Cl N2 O3 , RhB), edetate disodium (EDTA-2Na), benzoquinone (BQ), t-butyl alcohol (t-BuOH) and the other chemicals used in the experiments were purchased from Beijing Reagent Co. (Beijing, China). All chemicals were analytical reagent grade and used without any further purification. The deionized water was used throughout this study. 2.2. Preparation of g-C3 N4 /montmorillonite composites The preparation of g-C3 N4 (denoted as CN) powders followed a modified reported procedure [23]. Typically, 15 g of melamine was put into an alumina crucible with a cover and heated to 550 °C for 4 h with a heating rate of 2.3 °C min−1 . Then the sample was further heated at 500 °C for 2 h in the open air to obtain a better performance. After being cooled down to room temperature, the final resulting yellow product was collected, and then ground into powder for further use. The g-C3 N4 /montmorillonite (CN/M) composites were synthesized by following a facile two-step process including wet-chemical and calcination method. First, organic montmorillonite (OM) was prepared followed a reported route [24]. Then, the prepared OM was used as raw material to fabricate the CN/M composite as follows. Typically, various amounts of melamine were added to 100 mL ethanol, and then sonicated for 30 min. In the following step, 2 g of OM powder was dispersed in the above container with a uniform stirring under 60 °C for 12 h. Afterwards, the mixture solution was transferred to a rotary evaporation apparatus to generate homogeneous CN/M precursor. Finally, after simple grinding, the product was calcined followed by the synthesis parameters of the pure CN. The CN/M photocatalytic composites with different mass ratios of CN with respect to M were synthesized and labeled as CN/M-1, CN/M-2, CN/M-3 and CN/M-4, respectively. According
to the thermogravimetric analysis (TG) results, the content of gC3 N4 in the composites can be calculated as 10.29%, 22.08%, 31.86%, and 38.76%, respectively. For comparison, the CN/M physical mixture (CN+M) was also prepared. The physical mixture sample was prepared as follows: 2 g of OM powder (after experiencing calcination exactly as pure CN) and 0.935 g of pure CN were added to 100 mL ethanol, and then mixed for 12 h through a magnetic stirring process. The final product was dried in an oven for 12 h at 60 °C. 2.3. Characterizations The thermogravimetric analysis (TG) were carried out on a METTLER SF/1382 thermal analyzer at a heating rate of 10 °C min−1 under a O2 atmosphere from room temperature to 10 0 0 °C. An S-4800 scanning electron microscopy (Hitachi, Japan) was applied to investigate the surface morphology of samples. High-resolution transmission electron microscope (HRTEM) of samples was performed on a Tecnai G2 F20 FE-TEM operating at 200 kV. X-ray diffraction (XRD) were performed on a D8 advance X-ray diffractometer (Bruker, Germany) equipped with Cu-Kα radiation (λ = 0.154056 nm). The as-received samples were scanned in the range of 2θ from 3 ° to 70 ° with a 0.02 ° step at a scanning speed of 4 °/min. The surface areas of samples were measured by N2 adsorption at 77 K on a constant volume adsorption apparatus (JW-BK, JWGB Sci. & Tech., China) and calculated by the Brunaer-Emmett-Teller (BET) method. The optical properties of the as-received samples were studied by UV-vis diffuse reflectance spectroscopy (DRS) using a UV-vis spectrophotometer (U-3010, Hitachi), where BaSO4 was used as the reference. PL spectra of the catalysts were measured on the F-70 0 0 spectrometer (Hitachi, Japan) with an excitation wavelength of 370 nm. The electron spin resonance (ESR) signals of radical spin-trapped by spin-trap reagent DMPO (Sigma Chemical Co.) in water or DMSO were examined on a JEOL FA-200 spectrometer. 2.4. Photoactivity measurements The photocatalytic activities of as-prepared photocatalysts were conducted under a 500 W Xenon lamp (BL-GHX-V, Shanghai Bilang plant, China) with a 420 nm cut-off filter. Rhodamine B (RhB) and tetracycline (TC) were applied to evaluate the photocatalytic activities of the samples. In a typical experiment, 0.2 g of the as-prepared catalysts was suspended in 100 mL of standard RhB (30 ppm) or TC (100 ppm) aqueous solution. Prior to illumination, the suspension was magnetically stirred in the dark for 1 h to achieve the adsorption-desorption equilibrium. At a given time interval, 2 mL of suspension was sampled and separated through centrifugation at 80 0 0 rpm for 5 min. Photodegradation effect was determined by measuring the absorbance of the solution at 554 nm (RhB) or 359 nm (TC) on a UV-vis spectrophotometer. Comparative experiments were carried out under the same conditions using pure CN, M, CN+M as references. All the removal data of batch experiments were obtained in parallel. 3. Results and discussion 3.1. Morphological analysis As illustrated in Fig. 1, the morphology and structures of montmorillonite, g-C3 N4 and CN/M-3 composite are presented. From Fig. 1(a), the pure montmorillonite has a lamellar structure with relatively smooth surface, and different sizes of flakes are aggregating together. The layered structure of natural montmorillonite might provide large surface area for adsorbing pollutants. From
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 1. FESEM images of (a) montmorillonite, (b) g-C3 N4 , (c and d) CN/M-3.
Fig. 2. HRTEM of (a) montmorillonite, (b and c) g-C3 N4 , (d) CN/M-3.
Fig. 1(b), the single g-C3 N4 displays sheet structures agglomerating with each other, which account for its poor adsorption ability [25]. Compared with pure montmorillonite, it is obvious that the surface of the as prepared CN/M composite becomes rougher as illustrated in Fig. 1 (c and d), and the g-C3 N4 sheets are densely and evenly decorated on the surface of montmorillonite layers.
HRTEM images of montmorillonite, g-C3 N4 and CN/M-3 composite are displayed in Fig. 2. As shown in Fig. 2(a), layered structure of montmorillonite was presented clearly. From Fig. 2(b and c), the g-C3 N4 with distinct sheet structure and clear fringe was observed. As for the CN/M composite, layered montmorillonite was closely integrated with the g-C3 N4 layers as illustrated in
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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more g-C3 N4 precursor molecules into the interlayer of montmorillonite [30]. 3.3. BET analysis
Fig. 3. XRD patterns of montmorillonite, organic montmorillonite, g-C3 N4 and the as-prepared CN/M composites. Table 1 The d (001) data of montmorillonite, organic montmorillonite and CN/M composites. Sample
M
OM
CN/M-1
CN/M-2
CN/M-3
CN/M-4
d (001)/A˚
12.58
17.87
10.08
11.09
11.53
12.16
Fig. 2(d). The close combination between montmorillonite and gC3 N4 would facilitate the improvement of the electron transfer velocity and quantum efficiency [26]. 3.2. XRD analysis XRD patterns of montmorillonite, g-C3 N4 , organic montmorillonite, and CN/M composites are displayed in Fig. 3. As for pure g-C3 N4 , the characteristic diffraction peaks at 12.8 ° and 27.8 ° can be indexed as (100) and (002) diffraction planes [11]. The former peak can be attributed to the inter-layer structural packing arrangement and the latter peak is due to the long-range interplanar stacking of the conjugated aromatic system [27]. From the XRD pattern of montmorillonite, it is clear that montmorillonite exhibits five peaks at 7.02 °, 19.74 °, 28.53 °, 34.84 ° and 61.94 °, which correspond to the (0 01), (10 0), (0 04), (110) and (30 0) planes of montmorillonite respectively (JCPDS No.43-0688). After organic modification, the intensity of the d (001) peak of obtained organic ˚ The augmentamontmorillonite increased from 12.58 A˚ to 17.87 A. tion of basal spacing is assigned to quaternary ammonium cations substituted for inorganic cations through ion exchange [28]. As for CN/M composites, the characteristic peak of g-C3 N4 at 12.8 ° could not be observed in CN/M composites due to its low intensity. However, the peak intensity of CN/M at 27.8 ° enhanced with increasing the amount of g-C3 N4 . It is obvious that the intensity of the d (001) peak decreased after calcination, which could be attributed to that the conformation of the surfactant in organoclays would change from solid-like all trans to liquid-like gauche and completely removed when the temperature over 400 °C [29]. The (001) lattice planes of montmorillonite, organic montmorillonite and CN/M composites were calculated according to the full width half maximum (FWHM) of pattern peaks and Debye– Scherrer equation, which were listed in Table 1. It is indicated that the (001) lattice plane distance of CN/M composites is gradually amplified with increasing the amount of melamine. The hydrophobic effect of organic modifier is in favor of the intercalation of
N2 adsorption-desorption isotherms and BJH pore size distributions of g-C3 N4 , montmorillonite and CN/M-3 composite are shown in Fig. 4. The specific surface area (SBET ), pore volume (VP ), as well as the average adsorption and desorption pore size of g-C3 N4 , montmorillonite and the as-prepared CN/M-3 composite are displayed in Table 2. From Fig. 4 (a), it is observed that montmorillonite and CN/M-3 show a type IV adsorption isotherm with a H2 hysteresis loop in the range (P/P0 ) of 0.45–0.9 according to the International Union of Pure and Applied Chemistry (IUPAC), which indicates the presence of mesoporous (2∼50 nm) [31]. Compared with the hysteresis loop of montmorillonite, it seems that the as-prepared CN/M composite possesses a greater hysteresis loop, which might be due to its relatively larger surface area. As for g-C3 N4 , no such hysteresis loop appeared in virtue of its bulk property. The pore size of the as-received CN/M composite is 1∼10 nm, which could contribute to the adsorption of contaminant molecules in water. According to Table 2, it is investigated that CN/M-3 had the largest BET surface area, pore volume and the minimum pore size. With increasing the g-C3 N4 content, some adsorption sites of montmorillonite might be covered by g-C3 N4 . It is concluded that the introduction of montmorillonite is beneficial for the formation of high specific surface area composites, which would enhance the adsorption ability and provide more active sites in the process of pollutant degradation [22]. 3.4. Optical properties To investigate the optical absorption properties of montmorillonite, g-C3 N4 and the as-prepared CN/M composites, the UV–Vis diffuse reflection spectrum (DRS) were collected as shown in Fig. 5. It is indicated that all the samples show good absorption from UV light to visible light. As illustrated in Fig. 5, pure g-C3 N4 absorbs the light from the UV to the visible region starting from 480 nm, while montmorillonite exhibits more evenly light-adsorption ability within the scope of full spectrum. It is worth noting that the as-received CN/M composites present stronger absorption intensity in the range of both visible light and UV light in comparison with that of pure g-C3 N4 or montmorillonite, which is ascribed to intimate interfacial contact between g-C3 N4 and montmorillonite. Considering the strong light-adsorption ability of CN/M composites, more electron-hole pairs could be generated under illumination, which might play a key role in the process of oxidation and reduction. As for the CN/M composites, the optical absorption intensity of the as-received composites is greatly enhanced, which might be due to the defects or vibration produced by interfacial combination between g-C3 N4 and montmorillonite. Among these as received CN/M composites with different g-C3 N4 ratios, the CN/M-3 exhibits the strongest adsorption and the adsorption edge extended to the visible light region, which would be beneficial for photocatalysts to absorb a larger range of wavelengths of photons during the photoreaction process. 3.5. Adsorption and photocatalytic performance The adsorption and photocatalytic activities of CN/M composites were mainly evaluated by photocatalytic degradation of RhB and TC aqueous solution under visible light irradiation (λ>420 nm). As illustrated in Fig. 6, the RhB and TC degradation curves of the as prepared photocatalysts and linear transform Ln(C0 /C) of the kinetic curves under visible light are presented. For comparison, the removal effects of montmorillonite, g-C3 N4
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 4. (a) N2 adsorption and desorption isotherms measured at 77 K; (b) BJH pore size distribution plots.
Table 2 Surface and structural characterizations of CN/M composites. Sample
SBET (m2 /g)
Pore volume (cm3 /g)
Average pore radius(nm)
M CN/M-1 CN/M-2 CN/M-3 CN/M-4 CN
54.075 52.230 51.115 60.089 54.832 21.464
0.081 0.093 0.091 0.103 0.096 0.050
5.983 7.134 7.116 6.833 7.008 9.290
Fig. 5. UV–Vis DRS of montmorillonite, g-C3 N4 and as-prepared CN/M composites.
and CN+M physical mixture were also determined under the same conditions. As demonstrated, all the samples experienced 1 h in dark to reach the equilibrium of adsorption and desorption prior to illumination. As shown in Fig. 6 (a) and (b), it is indicated that the as-obtained CN/M composites possess larger adsorption ability for both RhB and TC in comparison with pure g-C3 N4 . As for RhB, the negatively charged montmorillonite would adsorb positively charged RhB molecules via electric attraction [32]. On the other hand, as for TC, the cation exchange property of montmorillonite might play a more important role in the adsorption process [33]. The improvement of the adsorption ability for both RhB and TC would be in favor of higher photocatalytic performance. In addition, the CN/M composites showed higher degradation
activity than the CN+M mixture. Hence, the higher degradation activity of the CN/M composites is not mainly ascribed to the adsorption capability alone. The enhanced photocatalytic activity should also be attributed to the significant differences in the interface of the CN+M mixture and composites. Compared with the physical mixture, the as-received composites showed a much stronger combination between g-C3 N4 and montmorillonite. Among these CN/M composites with different g-C3 N4 dosages, when the theoretical content of g-C3 N4 was up to 31.86%, the CN/M composite displayed the optimal photocatalytic activity. With increasing the g-C3 N4 dosage, it could be observed that the removal rate would exhibit a slight decrease, which might be due to the agglomeration effect of g-C3 N4 under high dosages. The final removal rates of RhB and TC for the CN/M-3 composite were up to 87% and 76%, respectively, which are almost two times those of pure g-C3 N4 . As for the final degraded products of RhB and TC, many previous reports have mentioned it, which is beneficial for acquiring more intermediate products information about the photodegradation process in this study [34,35]. To further quantitatively evaluate the photocatalytic abilities of the various CN/M composites, the photodegradation kinetics of RhB and TC over CN/M composites under visible light are plotted and displayed in Fig. 6 (c) and (d). The as-prepared photocatalysts fit well with the pseudo-first order model. The apparent rate constants of RhB and TC under visible light are compared and listed in Fig. 7. It is indicated that the reaction constant rate of CN/M-3 is higher than that of the other photocatalysts towards both RhB and TC. The degradation rates of CN/M-3 are around 3 times as much as that of the pure g-C3 N4 under visible light. According to the previous microstructure analysis, the dispersity of g-C3 N4 layers would be significantly improved after interfacial combination compared with that of the pure g-C3 N4 , which would provide more reactive sites for pollutants degradation. In conclusion, the improved adsorption capacity as well as the strong combination structural feature and synergetic effect between g-C3 N4 and montmorillonite should be the key factors for the enhancement of the photocatalytic activity. 3.6. Possible mechanism The photocatalytic activity of a photocatalyst has relationship with its microstructure, such as crystal plane, BET specific surface area, crystallinity degree and surface properties. Compared with the pure g-C3 N4 , the light-adsorption ability of CN/M composites is higher, which indicates the CN/M composites could be
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 6. Photocatalytic degradation of RhB (a) and TC (b) as well as the linear transform Ln(C0 /C) of the kinetic curves of RhB (c) and TC (d) under visible light.
Fig. 8. PL spectra of pure g-C3 N4 and CN/M composite. Fig. 7. The reaction constant rate for RhB and TC degradation under visible light over various catalysts.
excited by more visible light photons. Besides, the large surface area of the CN/M composites makes it possible to offer more surface active sites for adsorption and photocatalytic reactions, which is crucial for the process of photodegradation [5,36,37]. Furthermore, because of the electrostatic interaction, the strong interfacial
combination between montmorillonite and g-C3 N4 was formed which would be beneficial for the immigration of carriers and suppressing the charge recombination. To further confirm the effect of montmorillonite towards the immigration of carriers, photoluminescence (PL) spectra were performed to reveal the charge recombination processes of the pure g-C3 N4 and CN/M composite (Fig. 8). For pure g-C3 N4 , a strong
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 9. The effects of different scavengers on the degradation of (a) RhB and (b) TC in the presence of CN/M-3 composite.
Fig. 10. DMPO spin-trapping ESR spetra for blank (a) in aqueous dispersion for DMPO-•OH (b) in DMSO dispersion for DMPO-•O2 − and CN/M-3 (c) in aqueous dispersion for DMPO-•OH (d) in DMSO dispersion for DMPO-•O2.
emission peak appears at around 465 nm, while the CN/M composite presents PL emission peak with a much lower intensity, implying that the improved interfacial charge transfer between montmorillonite and g-C3 N4 in the composites was achieved.
It is generally known that the photogenerated holes, •OH radical and •O2 − are three main active species in the photocatalytic process [38]. To elucidate the mechanism of the CN/M-3 composite, three scavengers were used to explore the reactive species in photocatalytic degradation. As shown in Fig. 9, t-BuOH, EDTA-2Na
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 11. Schematic illustration of the charge separation and photocatalytic mechanism of CN/M composites under visible light irradiation.
and BQ were used as the radical scavengers for •OH radical, hole (h+ ) and superoxide anion radical (•O2 − ), respectively. There was just a slight decrease in the presence of t-BuOH no matter towards RhB or TC, which indicates that •OH has minor effect on the degradation of RhB or TC. However, with the addition of EDTA-2Na and BQ, the photocatalytic degradation rate of RhB or TC was significantly depressed, suggesting that both h+ and •O2 − play a primary role for RhB or TC degradation over CN/M-3 composite. To further verify the radical generation in the photocatalytic system under visible light irradiation, the ESR spin-trap with DMPO technique was carried out to detect the existence of •OH and •O2 − radicals. As displayed in Fig. 10, ESR spectra of blank and CN/M-3 under dark and visible light at room temperature in air were presented. It can be observed that there is no ESR signal for blank under both dark and visible light conditions. For the CN/M composite, there is no ESR signal under the dark as well. However, when the light is on, the characteristic signals of the DMPO-•O2 − could be observed, confirming the formation of •O2 − during the photocatalytic process. On the other hand, the characteristic peaks of DMPO-•OH was very weak. In conclusion, the •O2 − radical plays an important role while few •OH radicals were involved in the photocatalytic system, which is consistent with the previous scavenger result [39,40]. On the basis of the above experimental results, a synergistic mechanism for degradation of RhB and TC over the CN/M composites was proposed as illustrated in Fig. 11. Under visible light illumination, the valence band (VB) electrons (e− ) of g-C3 N4 in the composite can be easily excited to the conduction band (CB) by photons, resulting in the formation of holes (h+ ) in the VB of gC3 N4 . The holes (h+ ) have the ability to directly oxidize the target pollutants. As for •O2 − and •OH, •O2 − was generated by the dissolved O2 in the solution which was able to react with photoexcited electrons, while the •OH radicals were induced through the reaction of •O2 − with H+ or H2 O. The introduction of montmorillonite resulted in the well distribution of the g-C3 N4 species and the formation of a well interfacial combination between gC3 N4 nanosheets and montmorillonite layers via the electrostatic interaction. Hence, the excited electron-hole pairs of g-C3 N4 would be driven to migrate efficiently because of electrostatic repulsion between the negatively charged electrons and the negatively charged montmorillonite layers as displayed in Fig. 11. Compared
with pure g-C3 N4 , the probability of electron-hole recombination in CN/M photocatalysts could be significantly decreased and then more electrons can react with adsorbed O2 to produce enough •O2 − , leading to the enhanced photocatalytic activity. 4. Conclusions In summary, a novel kind of visible-light responding gC3 N4 /montmorillonite composite was successfully synthesized by a facile two-step reaction. The SEM, HRTEM and XRD analysis results reveal that the g-C3 N4 nanosheets are well immobilized on the surface of montmorillonite. The tight combination between g-C3 N4 nanosheets and montmorillonite layers results in an enhanced photocatalytic activity due to the strong electrostatic interaction effect. The as-synthesized CN/M-3 sample exhibits the optimal photocatalytic activity in photodegradation of RhB and TC under visible light, the reaction constant rate of which is almost 3 times that of pure g-C3 N4 . The enhancement in the photocatalytic performance of the composites could mainly be attributed to not only its relatively higher BET specific surface area and optical absorption but also the synergistic effect arising from the strong combination between g-C3 N4 nanosheets and montmorillonite layers, which can effectively reduce the recombination probability of photogenerated electron-hole pairs. This work may provide a new approach to develop more highly efficient visible-light- driven photocatalysts for wastewater treatment. Acknowledgments The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (Grant no. 51504263) and the Fundamental Research Funds for the Central Universities (2015QH01). References [1] Patil M, Shrivastava V. Photocatalytic degradation of carcinogenic methylene blue by using polyaniline-nickel ferrite Nano-composite. Pelagia Res Libr 2014;5:8–17. [2] Tian G, Wang W, Kang Y, Wang A. Palygorskite in sodium sulphide solution via hydrothermal process for enhanced methylene blue adsorption. J Taiwan Inst Chem Eng 2016;58:417–23.
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C. Li et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–9 [3] Urase T, Kagawa C, Kikuta T. Factors affecting removal of pharmaceutical substances and estrogens in membrane separation bioreactors. Desalination 2005;178:107–13. [4] Özcan A, Oturan MA, Oturan N, S¸ ahin Y. Removal of Acid Orange 7 from water by electrochemically generated Fenton’s reagent. J Hazard Mater 2009;163:1213–20. [5] Sun Z, Bai C, Zheng S, Yang X, Frost RL. A comparative study of different porous amorphous silica minerals supported TiO2 catalysts. Appl Catal, A 2013;458:103–10. [6] Fujishima A, Honda K. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972;238:37–8. [7] Yang JL, An SJ, Park WI, Yi GC, Choi W. Photocatalysis using ZnO thin films and nanoneedles grown by metal-organic chemical vapor deposition. Adv Mater 2004;16:1661–4. [8] Reutergådh LB, Iangphasuk M. Photocatalytic decolonization of reactive azo dye: a comparison between TiO2 and CdS photocatalysis. Chemosphere 1997;35:585–96. [9] Xiang Q, Meng GF, Zhao HB, Zhang Y, Li H, Ma WJ, et al. Au nanoparticle modified WO3 nanorods with their enhanced properties for photocatalysis and gas sensing. J Phys Chem C 2010;114:2049–55. [10] Xu J, Li L, Guo C, Zhang Y, Wang S. Removal of benzotriazole from solution by BiOBr photocatalysis under simulated solar irradiation. Chem Eng J 2013;221:230–7. [11] Wang X, Maeda K, Thomas A, Takanabe K, Xin G, Carlsson JM, et al. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat Mater 2009;8:76–80. [12] Wang Y, Wang X, Antonietti M. Polymeric graphitic carbon nitride as a heterogeneous organocatalyst: from photochemistry to multipurpose catalysis to sustainable chemistry. Angew Chem Int Ed 2012;51:68–89. [13] Yan SC, Li ZS, Zou ZG. Photodegradation of Rhodamine B and Methyl Orange over Boron-Doped g-C3 N4 under Visible Light Irradiation. Langmuir 2010;26:3894–901. [14] Xiufang C, Jinshui Z, Xianzhi F, Markus A, Xinchen W. Fe-g-C3N4-catalyzed oxidation of benzene to phenol using hydrogen peroxide and visible light. J Am Chem Soc 2009;131:11658. [15] Zhang J, Guo F, Wang X. An optimized and general synthetic strategy for fabrication of polymeric carbon nitride nanoarchitectures. Adv Funct Mater 2013;23:3008–14. [16] Sridharan K, Jang E, Park TJ. Novel visible light active graphitic C3 N4 -TiO2 composite photocatalyst: Synergistic synthesis, growth and photocatalytic treatment of hazardous pollutants. Appl Catal B Environ 2013;142-143:718–28. [17] Sun JX, Yuan YP, Qiu LG, Jiang X, Xie AJ, Shen YH, et al. Fabrication of composite photocatalyst g-C3 N4 -ZnO and enhancement of photocatalytic activity under visible light. Dalton Trans 2012;41:6756–63. [18] Fan Y, Li X, He X, Zeng C, Fan G, Liu Q, et al. Effective hydrolysis of ammonia borane catalyzed by ruthenium nanoparticles immobilized on graphic carbon nitride. Int J Hydrogen Energy 2014;39:19982–9. [19] An T, Chen J, Li G, Ding X, Sheng G, Fu J, et al. Characterization and the photocatalytic activity of TiO2 immobilized hydrophobic montmorillonite photocatalysts: Degradation of decabromodiphenyl ether (BDE 209). Catal Today 2008;139:69–76. [20] Chong MN, Tneu ZY, Poh PE, Jin B, Aryal R. Synthesis, characterisation and application of TiO2 -zeolite nanocomposites for the advanced treatment of industrial dye wastewater. J Taiwan Inst Chem Eng 2015;50:288–96. [21] Peng K, Fu L, Ouyang J, Yang H. Emerging parallel dual 2D composites: natural clay mineral hybridizing MoS2 and interfacial structure. Adv Funct Mater 2016;26:2666–75.
9
[22] Li Y, Zhan J, Huang L, Xu H, Li H, Zhang R, et al. Synthesis and photocatalytic activity of a bentonite/g-C3 N4 composite. RSC Adv 2014;4:11831–9. [23] Yan SC, Li ZS, Zou ZG. Photodegradation performance of g-C3 N4 fabricated by directly heating melamine. Langmuir ACS J Surf Coll 2009;25:10397–401. [24] Zheng S, Sun Z, Park Y, Ayoko GA, Frost RL. Removal of bisphenol A from wastewater by Ca-montmorillonite modified with selected surfactants. Chem Eng J 2013;234:416–22. [25] Dong G, Zhang L. Porous structure dependent photoreactivity of graphitic carbon nitride under visible light. J Mater Chem 2012;22:1160–6. [26] Li J, Liu E, Ma Y, Hu X, Wan J, Sun L, et al. Synthesis of MoS2 /g-C3 N4 nanosheets as 2D heterojunction photocatalysts with enhanced visible light activity. Appl Surf Sci 2016;364:694–702. [27] Xu H, Yan J, Xu Y, Song Y, Li H, Xia J, et al. Novel visible-light-driven AgX/graphite-like C3 N4 (X = Br, I) hybrid materials with synergistic photocatalytic activity. Appl Catal, B 2013;129:182–93. [28] Park Y, Ayoko GA, Frost RL. Characterisation of organoclays and adsorption of p-nitrophenol: environmental application. J Coll Interf Sci 2011;360:440–56. [29] Sun Z, Park Y, Zheng S, Ayoko GA, Frost RL. XRD, TEM, and thermal analysis of Arizona Ca-montmorillonites modified with didodecyldimethylammonium bromide. J Coll Interf Sci 2013;408:75–81. [30] Sándi Á, Nagy M, Szepesy L. Characterization of reversed-phase columns using the linear free energy relationship. III. Effect of the organic modifier and the mobile phase composition. J Chromatogr A. 20 0 0;893:215–34. [31] Sridharan K, Jang E, Park TJ. Novel visible light active graphitic C3 N4 -TiO2 composite photocatalyst: Synergistic synthesis, growth and photocatalytic treatment of hazardous pollutants. Appl Catal, B 2013;142-143:718–28. [32] Al-Ghouti MA, Khraisheh MAM, Ahmad MNM, Allen S. Adsorption behaviour of methylene blue onto Jordanian diatomite: a kinetic study. J Hazard Mater 2009;165:589–98. [33] Parolo ME, Savini MC, Vallés JM, Baschini MT, Avena MJ. Tetracycline adsorption on montmorillonite: pH and ionic strength effects. Appl Clay Sci 2008;40:179–86. [34] Maroga Mboula V, Hequet V, Gru Y, Colin R, Andres Y. Assessment of the efficiency of photocatalysis on tetracycline biodegradation. J Hazard Mater 2012;209-210:355–64. [35] Shalom M, Inal S, Neher D, Antonietti M. SiO2 /carbon nitride composite materials: the role of surfaces for enhanced photocatalysis. Catal Today 2014;225:185–90. [36] Kibanova D, Sleiman M, Cervini-Silva J, Destaillats H. Adsorption and photocatalytic oxidation of formaldehyde on a clay-TiO2 composite. J Hazard Mater 2012;211-212:233–9. [37] Wang B, Zhang G, Sun Z, Zheng S. Synthesis of natural porous minerals supported TiO2 nanoparticles and their photocatalytic performance towards Rhodamine B degradation. Powder Technol 2014;262:1–8. [38] Khodja AA, Sehili T, Pilichowski J-F, Boule P. Photocatalytic degradation of 2-phenylphenol on TiO2 and ZnO in aqueous suspensions. J Photochem Photobiol, A 2001;141:231–9. [39] Zhang Z, Jiang D, Li D, He M, Chen M. Construction of SnNb2 O6 nanosheet/g-C3 N4 nanosheet two-dimensional heterostructures with improved photocatalytic activity: Synergistic effect and mechanism insight. Appl Catal, B 2016;183:113–23. [40] Li FT, Zhao Y, Wang Q, Wang XJ, Hao YJ, Liu RH, et al. Enhanced visible-light photocatalytic activity of active Al2 O3 /g-C3 N4 heterojunctions synthesized via surface hydroxyl modification. J Hazard Mater 2014;283:371–81.
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Facile synthesis of g-C3 N4 /montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline Chunquan Li, Zhiming Sun∗, Weixin Huang, Shuilin Zheng School of Chemical and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083, PR China
a r t i c l e
i n f o
Article history: Received 27 January 2016 Revised 1 June 2016 Accepted 16 June 2016 Available online xxx Keywords: Montmorillonite g-C3 N4 Visible-light Rhodamine B Tetracycline
a b s t r a c t A novel g-C3 N4 /montmorillonite (CN/M) composite with enhanced visible light photocatalytic activity was synthesized via a facile two-step process including wet-chemical and calcination method. The microstructure, interfacial and optical properties of the obtained CN/M composites were characterized by scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), surface area measurement (BET) and UV-visible diffused reflectance spectroscopy (UV-vis DRS). It is indicated that a tight interfacial combination between g-C3 N4 nanosheets and montmorillonite layers was formed in the composite photocatalysts. Compared with the other reference samples, the as-received CN/M composites possess significantly enhanced photocatalytic activity towards rhodamine B and tetracycline. The optimal mass ratio of g-C3 N4 with respect to montmorillonite is determined to be 31.86 wt% and the corresponding reaction constant rate is almost 3.0 times that of the pure g-C3 N4 under visible light. The enhanced photocatalytic activity of the g-C3 N4 /montmorillonite composite could be attributed not only to its relatively higher surface area and enhanced light-adsorption ability under visible light but also the synergistic effect arising from the tight combination between g-C3 N4 and montmorillonite due to the electrostatic interaction, which leads to efficient separation of the photo-generated charge carriers. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction In recent decades, with the rapid development of human beings’ industry and civilization, environmental problems have become globalized in terms of their existence and impacts. Both dyes and antibiotics are gradually becoming the most concerning issues due to their great threat to human health and the suspected resistant bacterial strains even at low concentrations [1]. Various methods have been adopted so far for the removal of dyes and antibiotics from aqueous solution including adsorption [2], membrane filtration [3], electrochemical technique [4] and photocatalysis [5]. However, most of antibiotics in wastewater such as tetracycline (TC) are not biodegraded in traditional water treatment processes, and can even hinder the removal of other organic pollutants. Among these techniques, photocatalysis seems to be one of the most promising techniques for mineralization of organic pollutants in the future because of its high efficiency, low cost and environmental friendly. During the past decades, various photocatalysts have been introduced since TiO2 was firstly used in generating H2 [6], such as ZnO [7], CdS [8], WO3 [9], BiOBr [10] and g-C3 N4 [11]. In recent ∗
Corresponding author. Tel.: +86 10 62330972; fax: +86 10 62330972. E-mail address: [email protected], [email protected] (Z. Sun).
years, considerable attention has been focused on the environmental applications of g-C3 N4 photocatalyst because of its visible-light responding band gap (2.70 eV), high thermal and chemical stability, and simple preparation. Polymeric g-C3 N4 photocatalyst with two-dimensional lamellar structure possesses high thermal and chemical stability due to its extended π -conjugated frameworks connected by the sp2 hybridization of carbon and nitrogen [12]. Nevertheless, similar to the other semiconductors, g-C3 N4 photocatalyst suffers high recombination rate of photo-generated electrons and holes as well. Hence, numerous strategies have been carried out to enhance the quantum efficiency of g-C3 N4 , such as metal and nonmetal ions doping [13,14], porous templating fabrication [15], heterojunction construction [16,17], and noble metals deposition [18]. Although the photocatalytic activity of g-C3 N4 can be enhanced by modification, some drawbacks of single g-C3 N4 significantly limit its practical applications, such as easy agglomeration and weak adsorption ability. It has been reported that these above-mentioned practical application problems of pure photocatalysts can be solved via using natural minerals as catalyst carriers [19–21]. Among these catalyst carriers, layered montmorillonite seems to be one of the most promising candidates for layered g-C3 N4 [22]. Montmorillonite, composed of two tetrahedrally coordinated sheets of silicon and one octahedrally coordinated sheet of aluminum ions has been extensively applied in various fields
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Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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because of its low cost, abundant, non-toxic and environmental friendly. To the best of our knowledge, there are few reports about the synthesis of g-C3 N4 /montmorillonite composite. In our present study, we synthesize a novel kind of gC3 N4 /montmorillonite composite with strong interfacial interaction through a facile two-step process. The physicochemical properties of as received composites were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), N2 adsorption/ desorption instrument, UV-visible diffused reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and electron spin resonance (ESR). Additionally, the photocatalytic performance of g-C3 N4 /montmorillonite composites was evaluated by the photodegradation of rhodamine B and tetracycline in water under visible light. The effects of montmorillonite in composites on the visible-light-driven photocatalytic efficiency were investigated. Moreover, the possible enhancement mechanism of g-C3 N4 /montmorillonite composite was also proposed based on the obtained experimental results. It is anticipated that this novel g-C3 N4 /montmorillonite composite with strong interfacial contact and enhanced photocatalytic activity is a potential photocatalytic material for dyes and antibiotics wastewater treatment. 2. Experimental 2.1. Materials The purified montmorillonite (M) is obtained from Jiayi Mineral Corporation, Liaoning Province. Cetyltrimethylammonium bromide was purchased from Tianjin Jinke Fine Chemical Research Institute. The melamine was achieved from Tianjin Guangfu Fine Chemical Research Institute. Tetracycline hydrochloride (C22 H24 N2 O8 .HCl, USP Grade) was obtained from Amresco Biosciences. Dimethyl sulfoxide (DMSO) was achieved from Xilong Chemical Co. (Guangdong, China). Ethanol, rhodamine B (C28 H31 Cl N2 O3 , RhB), edetate disodium (EDTA-2Na), benzoquinone (BQ), t-butyl alcohol (t-BuOH) and the other chemicals used in the experiments were purchased from Beijing Reagent Co. (Beijing, China). All chemicals were analytical reagent grade and used without any further purification. The deionized water was used throughout this study. 2.2. Preparation of g-C3 N4 /montmorillonite composites The preparation of g-C3 N4 (denoted as CN) powders followed a modified reported procedure [23]. Typically, 15 g of melamine was put into an alumina crucible with a cover and heated to 550 °C for 4 h with a heating rate of 2.3 °C min−1 . Then the sample was further heated at 500 °C for 2 h in the open air to obtain a better performance. After being cooled down to room temperature, the final resulting yellow product was collected, and then ground into powder for further use. The g-C3 N4 /montmorillonite (CN/M) composites were synthesized by following a facile two-step process including wet-chemical and calcination method. First, organic montmorillonite (OM) was prepared followed a reported route [24]. Then, the prepared OM was used as raw material to fabricate the CN/M composite as follows. Typically, various amounts of melamine were added to 100 mL ethanol, and then sonicated for 30 min. In the following step, 2 g of OM powder was dispersed in the above container with a uniform stirring under 60 °C for 12 h. Afterwards, the mixture solution was transferred to a rotary evaporation apparatus to generate homogeneous CN/M precursor. Finally, after simple grinding, the product was calcined followed by the synthesis parameters of the pure CN. The CN/M photocatalytic composites with different mass ratios of CN with respect to M were synthesized and labeled as CN/M-1, CN/M-2, CN/M-3 and CN/M-4, respectively. According
to the thermogravimetric analysis (TG) results, the content of gC3 N4 in the composites can be calculated as 10.29%, 22.08%, 31.86%, and 38.76%, respectively. For comparison, the CN/M physical mixture (CN+M) was also prepared. The physical mixture sample was prepared as follows: 2 g of OM powder (after experiencing calcination exactly as pure CN) and 0.935 g of pure CN were added to 100 mL ethanol, and then mixed for 12 h through a magnetic stirring process. The final product was dried in an oven for 12 h at 60 °C. 2.3. Characterizations The thermogravimetric analysis (TG) were carried out on a METTLER SF/1382 thermal analyzer at a heating rate of 10 °C min−1 under a O2 atmosphere from room temperature to 10 0 0 °C. An S-4800 scanning electron microscopy (Hitachi, Japan) was applied to investigate the surface morphology of samples. High-resolution transmission electron microscope (HRTEM) of samples was performed on a Tecnai G2 F20 FE-TEM operating at 200 kV. X-ray diffraction (XRD) were performed on a D8 advance X-ray diffractometer (Bruker, Germany) equipped with Cu-Kα radiation (λ = 0.154056 nm). The as-received samples were scanned in the range of 2θ from 3 ° to 70 ° with a 0.02 ° step at a scanning speed of 4 °/min. The surface areas of samples were measured by N2 adsorption at 77 K on a constant volume adsorption apparatus (JW-BK, JWGB Sci. & Tech., China) and calculated by the Brunaer-Emmett-Teller (BET) method. The optical properties of the as-received samples were studied by UV-vis diffuse reflectance spectroscopy (DRS) using a UV-vis spectrophotometer (U-3010, Hitachi), where BaSO4 was used as the reference. PL spectra of the catalysts were measured on the F-70 0 0 spectrometer (Hitachi, Japan) with an excitation wavelength of 370 nm. The electron spin resonance (ESR) signals of radical spin-trapped by spin-trap reagent DMPO (Sigma Chemical Co.) in water or DMSO were examined on a JEOL FA-200 spectrometer. 2.4. Photoactivity measurements The photocatalytic activities of as-prepared photocatalysts were conducted under a 500 W Xenon lamp (BL-GHX-V, Shanghai Bilang plant, China) with a 420 nm cut-off filter. Rhodamine B (RhB) and tetracycline (TC) were applied to evaluate the photocatalytic activities of the samples. In a typical experiment, 0.2 g of the as-prepared catalysts was suspended in 100 mL of standard RhB (30 ppm) or TC (100 ppm) aqueous solution. Prior to illumination, the suspension was magnetically stirred in the dark for 1 h to achieve the adsorption-desorption equilibrium. At a given time interval, 2 mL of suspension was sampled and separated through centrifugation at 80 0 0 rpm for 5 min. Photodegradation effect was determined by measuring the absorbance of the solution at 554 nm (RhB) or 359 nm (TC) on a UV-vis spectrophotometer. Comparative experiments were carried out under the same conditions using pure CN, M, CN+M as references. All the removal data of batch experiments were obtained in parallel. 3. Results and discussion 3.1. Morphological analysis As illustrated in Fig. 1, the morphology and structures of montmorillonite, g-C3 N4 and CN/M-3 composite are presented. From Fig. 1(a), the pure montmorillonite has a lamellar structure with relatively smooth surface, and different sizes of flakes are aggregating together. The layered structure of natural montmorillonite might provide large surface area for adsorbing pollutants. From
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 1. FESEM images of (a) montmorillonite, (b) g-C3 N4 , (c and d) CN/M-3.
Fig. 2. HRTEM of (a) montmorillonite, (b and c) g-C3 N4 , (d) CN/M-3.
Fig. 1(b), the single g-C3 N4 displays sheet structures agglomerating with each other, which account for its poor adsorption ability [25]. Compared with pure montmorillonite, it is obvious that the surface of the as prepared CN/M composite becomes rougher as illustrated in Fig. 1 (c and d), and the g-C3 N4 sheets are densely and evenly decorated on the surface of montmorillonite layers.
HRTEM images of montmorillonite, g-C3 N4 and CN/M-3 composite are displayed in Fig. 2. As shown in Fig. 2(a), layered structure of montmorillonite was presented clearly. From Fig. 2(b and c), the g-C3 N4 with distinct sheet structure and clear fringe was observed. As for the CN/M composite, layered montmorillonite was closely integrated with the g-C3 N4 layers as illustrated in
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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more g-C3 N4 precursor molecules into the interlayer of montmorillonite [30]. 3.3. BET analysis
Fig. 3. XRD patterns of montmorillonite, organic montmorillonite, g-C3 N4 and the as-prepared CN/M composites. Table 1 The d (001) data of montmorillonite, organic montmorillonite and CN/M composites. Sample
M
OM
CN/M-1
CN/M-2
CN/M-3
CN/M-4
d (001)/A˚
12.58
17.87
10.08
11.09
11.53
12.16
Fig. 2(d). The close combination between montmorillonite and gC3 N4 would facilitate the improvement of the electron transfer velocity and quantum efficiency [26]. 3.2. XRD analysis XRD patterns of montmorillonite, g-C3 N4 , organic montmorillonite, and CN/M composites are displayed in Fig. 3. As for pure g-C3 N4 , the characteristic diffraction peaks at 12.8 ° and 27.8 ° can be indexed as (100) and (002) diffraction planes [11]. The former peak can be attributed to the inter-layer structural packing arrangement and the latter peak is due to the long-range interplanar stacking of the conjugated aromatic system [27]. From the XRD pattern of montmorillonite, it is clear that montmorillonite exhibits five peaks at 7.02 °, 19.74 °, 28.53 °, 34.84 ° and 61.94 °, which correspond to the (0 01), (10 0), (0 04), (110) and (30 0) planes of montmorillonite respectively (JCPDS No.43-0688). After organic modification, the intensity of the d (001) peak of obtained organic ˚ The augmentamontmorillonite increased from 12.58 A˚ to 17.87 A. tion of basal spacing is assigned to quaternary ammonium cations substituted for inorganic cations through ion exchange [28]. As for CN/M composites, the characteristic peak of g-C3 N4 at 12.8 ° could not be observed in CN/M composites due to its low intensity. However, the peak intensity of CN/M at 27.8 ° enhanced with increasing the amount of g-C3 N4 . It is obvious that the intensity of the d (001) peak decreased after calcination, which could be attributed to that the conformation of the surfactant in organoclays would change from solid-like all trans to liquid-like gauche and completely removed when the temperature over 400 °C [29]. The (001) lattice planes of montmorillonite, organic montmorillonite and CN/M composites were calculated according to the full width half maximum (FWHM) of pattern peaks and Debye– Scherrer equation, which were listed in Table 1. It is indicated that the (001) lattice plane distance of CN/M composites is gradually amplified with increasing the amount of melamine. The hydrophobic effect of organic modifier is in favor of the intercalation of
N2 adsorption-desorption isotherms and BJH pore size distributions of g-C3 N4 , montmorillonite and CN/M-3 composite are shown in Fig. 4. The specific surface area (SBET ), pore volume (VP ), as well as the average adsorption and desorption pore size of g-C3 N4 , montmorillonite and the as-prepared CN/M-3 composite are displayed in Table 2. From Fig. 4 (a), it is observed that montmorillonite and CN/M-3 show a type IV adsorption isotherm with a H2 hysteresis loop in the range (P/P0 ) of 0.45–0.9 according to the International Union of Pure and Applied Chemistry (IUPAC), which indicates the presence of mesoporous (2∼50 nm) [31]. Compared with the hysteresis loop of montmorillonite, it seems that the as-prepared CN/M composite possesses a greater hysteresis loop, which might be due to its relatively larger surface area. As for g-C3 N4 , no such hysteresis loop appeared in virtue of its bulk property. The pore size of the as-received CN/M composite is 1∼10 nm, which could contribute to the adsorption of contaminant molecules in water. According to Table 2, it is investigated that CN/M-3 had the largest BET surface area, pore volume and the minimum pore size. With increasing the g-C3 N4 content, some adsorption sites of montmorillonite might be covered by g-C3 N4 . It is concluded that the introduction of montmorillonite is beneficial for the formation of high specific surface area composites, which would enhance the adsorption ability and provide more active sites in the process of pollutant degradation [22]. 3.4. Optical properties To investigate the optical absorption properties of montmorillonite, g-C3 N4 and the as-prepared CN/M composites, the UV–Vis diffuse reflection spectrum (DRS) were collected as shown in Fig. 5. It is indicated that all the samples show good absorption from UV light to visible light. As illustrated in Fig. 5, pure g-C3 N4 absorbs the light from the UV to the visible region starting from 480 nm, while montmorillonite exhibits more evenly light-adsorption ability within the scope of full spectrum. It is worth noting that the as-received CN/M composites present stronger absorption intensity in the range of both visible light and UV light in comparison with that of pure g-C3 N4 or montmorillonite, which is ascribed to intimate interfacial contact between g-C3 N4 and montmorillonite. Considering the strong light-adsorption ability of CN/M composites, more electron-hole pairs could be generated under illumination, which might play a key role in the process of oxidation and reduction. As for the CN/M composites, the optical absorption intensity of the as-received composites is greatly enhanced, which might be due to the defects or vibration produced by interfacial combination between g-C3 N4 and montmorillonite. Among these as received CN/M composites with different g-C3 N4 ratios, the CN/M-3 exhibits the strongest adsorption and the adsorption edge extended to the visible light region, which would be beneficial for photocatalysts to absorb a larger range of wavelengths of photons during the photoreaction process. 3.5. Adsorption and photocatalytic performance The adsorption and photocatalytic activities of CN/M composites were mainly evaluated by photocatalytic degradation of RhB and TC aqueous solution under visible light irradiation (λ>420 nm). As illustrated in Fig. 6, the RhB and TC degradation curves of the as prepared photocatalysts and linear transform Ln(C0 /C) of the kinetic curves under visible light are presented. For comparison, the removal effects of montmorillonite, g-C3 N4
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 4. (a) N2 adsorption and desorption isotherms measured at 77 K; (b) BJH pore size distribution plots.
Table 2 Surface and structural characterizations of CN/M composites. Sample
SBET (m2 /g)
Pore volume (cm3 /g)
Average pore radius(nm)
M CN/M-1 CN/M-2 CN/M-3 CN/M-4 CN
54.075 52.230 51.115 60.089 54.832 21.464
0.081 0.093 0.091 0.103 0.096 0.050
5.983 7.134 7.116 6.833 7.008 9.290
Fig. 5. UV–Vis DRS of montmorillonite, g-C3 N4 and as-prepared CN/M composites.
and CN+M physical mixture were also determined under the same conditions. As demonstrated, all the samples experienced 1 h in dark to reach the equilibrium of adsorption and desorption prior to illumination. As shown in Fig. 6 (a) and (b), it is indicated that the as-obtained CN/M composites possess larger adsorption ability for both RhB and TC in comparison with pure g-C3 N4 . As for RhB, the negatively charged montmorillonite would adsorb positively charged RhB molecules via electric attraction [32]. On the other hand, as for TC, the cation exchange property of montmorillonite might play a more important role in the adsorption process [33]. The improvement of the adsorption ability for both RhB and TC would be in favor of higher photocatalytic performance. In addition, the CN/M composites showed higher degradation
activity than the CN+M mixture. Hence, the higher degradation activity of the CN/M composites is not mainly ascribed to the adsorption capability alone. The enhanced photocatalytic activity should also be attributed to the significant differences in the interface of the CN+M mixture and composites. Compared with the physical mixture, the as-received composites showed a much stronger combination between g-C3 N4 and montmorillonite. Among these CN/M composites with different g-C3 N4 dosages, when the theoretical content of g-C3 N4 was up to 31.86%, the CN/M composite displayed the optimal photocatalytic activity. With increasing the g-C3 N4 dosage, it could be observed that the removal rate would exhibit a slight decrease, which might be due to the agglomeration effect of g-C3 N4 under high dosages. The final removal rates of RhB and TC for the CN/M-3 composite were up to 87% and 76%, respectively, which are almost two times those of pure g-C3 N4 . As for the final degraded products of RhB and TC, many previous reports have mentioned it, which is beneficial for acquiring more intermediate products information about the photodegradation process in this study [34,35]. To further quantitatively evaluate the photocatalytic abilities of the various CN/M composites, the photodegradation kinetics of RhB and TC over CN/M composites under visible light are plotted and displayed in Fig. 6 (c) and (d). The as-prepared photocatalysts fit well with the pseudo-first order model. The apparent rate constants of RhB and TC under visible light are compared and listed in Fig. 7. It is indicated that the reaction constant rate of CN/M-3 is higher than that of the other photocatalysts towards both RhB and TC. The degradation rates of CN/M-3 are around 3 times as much as that of the pure g-C3 N4 under visible light. According to the previous microstructure analysis, the dispersity of g-C3 N4 layers would be significantly improved after interfacial combination compared with that of the pure g-C3 N4 , which would provide more reactive sites for pollutants degradation. In conclusion, the improved adsorption capacity as well as the strong combination structural feature and synergetic effect between g-C3 N4 and montmorillonite should be the key factors for the enhancement of the photocatalytic activity. 3.6. Possible mechanism The photocatalytic activity of a photocatalyst has relationship with its microstructure, such as crystal plane, BET specific surface area, crystallinity degree and surface properties. Compared with the pure g-C3 N4 , the light-adsorption ability of CN/M composites is higher, which indicates the CN/M composites could be
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 6. Photocatalytic degradation of RhB (a) and TC (b) as well as the linear transform Ln(C0 /C) of the kinetic curves of RhB (c) and TC (d) under visible light.
Fig. 8. PL spectra of pure g-C3 N4 and CN/M composite. Fig. 7. The reaction constant rate for RhB and TC degradation under visible light over various catalysts.
excited by more visible light photons. Besides, the large surface area of the CN/M composites makes it possible to offer more surface active sites for adsorption and photocatalytic reactions, which is crucial for the process of photodegradation [5,36,37]. Furthermore, because of the electrostatic interaction, the strong interfacial
combination between montmorillonite and g-C3 N4 was formed which would be beneficial for the immigration of carriers and suppressing the charge recombination. To further confirm the effect of montmorillonite towards the immigration of carriers, photoluminescence (PL) spectra were performed to reveal the charge recombination processes of the pure g-C3 N4 and CN/M composite (Fig. 8). For pure g-C3 N4 , a strong
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 9. The effects of different scavengers on the degradation of (a) RhB and (b) TC in the presence of CN/M-3 composite.
Fig. 10. DMPO spin-trapping ESR spetra for blank (a) in aqueous dispersion for DMPO-•OH (b) in DMSO dispersion for DMPO-•O2 − and CN/M-3 (c) in aqueous dispersion for DMPO-•OH (d) in DMSO dispersion for DMPO-•O2.
emission peak appears at around 465 nm, while the CN/M composite presents PL emission peak with a much lower intensity, implying that the improved interfacial charge transfer between montmorillonite and g-C3 N4 in the composites was achieved.
It is generally known that the photogenerated holes, •OH radical and •O2 − are three main active species in the photocatalytic process [38]. To elucidate the mechanism of the CN/M-3 composite, three scavengers were used to explore the reactive species in photocatalytic degradation. As shown in Fig. 9, t-BuOH, EDTA-2Na
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014
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Fig. 11. Schematic illustration of the charge separation and photocatalytic mechanism of CN/M composites under visible light irradiation.
and BQ were used as the radical scavengers for •OH radical, hole (h+ ) and superoxide anion radical (•O2 − ), respectively. There was just a slight decrease in the presence of t-BuOH no matter towards RhB or TC, which indicates that •OH has minor effect on the degradation of RhB or TC. However, with the addition of EDTA-2Na and BQ, the photocatalytic degradation rate of RhB or TC was significantly depressed, suggesting that both h+ and •O2 − play a primary role for RhB or TC degradation over CN/M-3 composite. To further verify the radical generation in the photocatalytic system under visible light irradiation, the ESR spin-trap with DMPO technique was carried out to detect the existence of •OH and •O2 − radicals. As displayed in Fig. 10, ESR spectra of blank and CN/M-3 under dark and visible light at room temperature in air were presented. It can be observed that there is no ESR signal for blank under both dark and visible light conditions. For the CN/M composite, there is no ESR signal under the dark as well. However, when the light is on, the characteristic signals of the DMPO-•O2 − could be observed, confirming the formation of •O2 − during the photocatalytic process. On the other hand, the characteristic peaks of DMPO-•OH was very weak. In conclusion, the •O2 − radical plays an important role while few •OH radicals were involved in the photocatalytic system, which is consistent with the previous scavenger result [39,40]. On the basis of the above experimental results, a synergistic mechanism for degradation of RhB and TC over the CN/M composites was proposed as illustrated in Fig. 11. Under visible light illumination, the valence band (VB) electrons (e− ) of g-C3 N4 in the composite can be easily excited to the conduction band (CB) by photons, resulting in the formation of holes (h+ ) in the VB of gC3 N4 . The holes (h+ ) have the ability to directly oxidize the target pollutants. As for •O2 − and •OH, •O2 − was generated by the dissolved O2 in the solution which was able to react with photoexcited electrons, while the •OH radicals were induced through the reaction of •O2 − with H+ or H2 O. The introduction of montmorillonite resulted in the well distribution of the g-C3 N4 species and the formation of a well interfacial combination between gC3 N4 nanosheets and montmorillonite layers via the electrostatic interaction. Hence, the excited electron-hole pairs of g-C3 N4 would be driven to migrate efficiently because of electrostatic repulsion between the negatively charged electrons and the negatively charged montmorillonite layers as displayed in Fig. 11. Compared
with pure g-C3 N4 , the probability of electron-hole recombination in CN/M photocatalysts could be significantly decreased and then more electrons can react with adsorbed O2 to produce enough •O2 − , leading to the enhanced photocatalytic activity. 4. Conclusions In summary, a novel kind of visible-light responding gC3 N4 /montmorillonite composite was successfully synthesized by a facile two-step reaction. The SEM, HRTEM and XRD analysis results reveal that the g-C3 N4 nanosheets are well immobilized on the surface of montmorillonite. The tight combination between g-C3 N4 nanosheets and montmorillonite layers results in an enhanced photocatalytic activity due to the strong electrostatic interaction effect. The as-synthesized CN/M-3 sample exhibits the optimal photocatalytic activity in photodegradation of RhB and TC under visible light, the reaction constant rate of which is almost 3 times that of pure g-C3 N4 . The enhancement in the photocatalytic performance of the composites could mainly be attributed to not only its relatively higher BET specific surface area and optical absorption but also the synergistic effect arising from the strong combination between g-C3 N4 nanosheets and montmorillonite layers, which can effectively reduce the recombination probability of photogenerated electron-hole pairs. This work may provide a new approach to develop more highly efficient visible-light- driven photocatalysts for wastewater treatment. Acknowledgments The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (Grant no. 51504263) and the Fundamental Research Funds for the Central Universities (2015QH01). References [1] Patil M, Shrivastava V. Photocatalytic degradation of carcinogenic methylene blue by using polyaniline-nickel ferrite Nano-composite. Pelagia Res Libr 2014;5:8–17. [2] Tian G, Wang W, Kang Y, Wang A. Palygorskite in sodium sulphide solution via hydrothermal process for enhanced methylene blue adsorption. J Taiwan Inst Chem Eng 2016;58:417–23.
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C. Li et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–9 [3] Urase T, Kagawa C, Kikuta T. Factors affecting removal of pharmaceutical substances and estrogens in membrane separation bioreactors. Desalination 2005;178:107–13. [4] Özcan A, Oturan MA, Oturan N, S¸ ahin Y. Removal of Acid Orange 7 from water by electrochemically generated Fenton’s reagent. J Hazard Mater 2009;163:1213–20. [5] Sun Z, Bai C, Zheng S, Yang X, Frost RL. A comparative study of different porous amorphous silica minerals supported TiO2 catalysts. Appl Catal, A 2013;458:103–10. [6] Fujishima A, Honda K. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972;238:37–8. [7] Yang JL, An SJ, Park WI, Yi GC, Choi W. Photocatalysis using ZnO thin films and nanoneedles grown by metal-organic chemical vapor deposition. Adv Mater 2004;16:1661–4. [8] Reutergådh LB, Iangphasuk M. Photocatalytic decolonization of reactive azo dye: a comparison between TiO2 and CdS photocatalysis. Chemosphere 1997;35:585–96. [9] Xiang Q, Meng GF, Zhao HB, Zhang Y, Li H, Ma WJ, et al. Au nanoparticle modified WO3 nanorods with their enhanced properties for photocatalysis and gas sensing. J Phys Chem C 2010;114:2049–55. [10] Xu J, Li L, Guo C, Zhang Y, Wang S. Removal of benzotriazole from solution by BiOBr photocatalysis under simulated solar irradiation. Chem Eng J 2013;221:230–7. [11] Wang X, Maeda K, Thomas A, Takanabe K, Xin G, Carlsson JM, et al. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat Mater 2009;8:76–80. [12] Wang Y, Wang X, Antonietti M. Polymeric graphitic carbon nitride as a heterogeneous organocatalyst: from photochemistry to multipurpose catalysis to sustainable chemistry. Angew Chem Int Ed 2012;51:68–89. [13] Yan SC, Li ZS, Zou ZG. Photodegradation of Rhodamine B and Methyl Orange over Boron-Doped g-C3 N4 under Visible Light Irradiation. Langmuir 2010;26:3894–901. [14] Xiufang C, Jinshui Z, Xianzhi F, Markus A, Xinchen W. Fe-g-C3N4-catalyzed oxidation of benzene to phenol using hydrogen peroxide and visible light. J Am Chem Soc 2009;131:11658. [15] Zhang J, Guo F, Wang X. An optimized and general synthetic strategy for fabrication of polymeric carbon nitride nanoarchitectures. Adv Funct Mater 2013;23:3008–14. [16] Sridharan K, Jang E, Park TJ. Novel visible light active graphitic C3 N4 -TiO2 composite photocatalyst: Synergistic synthesis, growth and photocatalytic treatment of hazardous pollutants. Appl Catal B Environ 2013;142-143:718–28. [17] Sun JX, Yuan YP, Qiu LG, Jiang X, Xie AJ, Shen YH, et al. Fabrication of composite photocatalyst g-C3 N4 -ZnO and enhancement of photocatalytic activity under visible light. Dalton Trans 2012;41:6756–63. [18] Fan Y, Li X, He X, Zeng C, Fan G, Liu Q, et al. Effective hydrolysis of ammonia borane catalyzed by ruthenium nanoparticles immobilized on graphic carbon nitride. Int J Hydrogen Energy 2014;39:19982–9. [19] An T, Chen J, Li G, Ding X, Sheng G, Fu J, et al. Characterization and the photocatalytic activity of TiO2 immobilized hydrophobic montmorillonite photocatalysts: Degradation of decabromodiphenyl ether (BDE 209). Catal Today 2008;139:69–76. [20] Chong MN, Tneu ZY, Poh PE, Jin B, Aryal R. Synthesis, characterisation and application of TiO2 -zeolite nanocomposites for the advanced treatment of industrial dye wastewater. J Taiwan Inst Chem Eng 2015;50:288–96. [21] Peng K, Fu L, Ouyang J, Yang H. Emerging parallel dual 2D composites: natural clay mineral hybridizing MoS2 and interfacial structure. Adv Funct Mater 2016;26:2666–75.
9
[22] Li Y, Zhan J, Huang L, Xu H, Li H, Zhang R, et al. Synthesis and photocatalytic activity of a bentonite/g-C3 N4 composite. RSC Adv 2014;4:11831–9. [23] Yan SC, Li ZS, Zou ZG. Photodegradation performance of g-C3 N4 fabricated by directly heating melamine. Langmuir ACS J Surf Coll 2009;25:10397–401. [24] Zheng S, Sun Z, Park Y, Ayoko GA, Frost RL. Removal of bisphenol A from wastewater by Ca-montmorillonite modified with selected surfactants. Chem Eng J 2013;234:416–22. [25] Dong G, Zhang L. Porous structure dependent photoreactivity of graphitic carbon nitride under visible light. J Mater Chem 2012;22:1160–6. [26] Li J, Liu E, Ma Y, Hu X, Wan J, Sun L, et al. Synthesis of MoS2 /g-C3 N4 nanosheets as 2D heterojunction photocatalysts with enhanced visible light activity. Appl Surf Sci 2016;364:694–702. [27] Xu H, Yan J, Xu Y, Song Y, Li H, Xia J, et al. Novel visible-light-driven AgX/graphite-like C3 N4 (X = Br, I) hybrid materials with synergistic photocatalytic activity. Appl Catal, B 2013;129:182–93. [28] Park Y, Ayoko GA, Frost RL. Characterisation of organoclays and adsorption of p-nitrophenol: environmental application. J Coll Interf Sci 2011;360:440–56. [29] Sun Z, Park Y, Zheng S, Ayoko GA, Frost RL. XRD, TEM, and thermal analysis of Arizona Ca-montmorillonites modified with didodecyldimethylammonium bromide. J Coll Interf Sci 2013;408:75–81. [30] Sándi Á, Nagy M, Szepesy L. Characterization of reversed-phase columns using the linear free energy relationship. III. Effect of the organic modifier and the mobile phase composition. J Chromatogr A. 20 0 0;893:215–34. [31] Sridharan K, Jang E, Park TJ. Novel visible light active graphitic C3 N4 -TiO2 composite photocatalyst: Synergistic synthesis, growth and photocatalytic treatment of hazardous pollutants. Appl Catal, B 2013;142-143:718–28. [32] Al-Ghouti MA, Khraisheh MAM, Ahmad MNM, Allen S. Adsorption behaviour of methylene blue onto Jordanian diatomite: a kinetic study. J Hazard Mater 2009;165:589–98. [33] Parolo ME, Savini MC, Vallés JM, Baschini MT, Avena MJ. Tetracycline adsorption on montmorillonite: pH and ionic strength effects. Appl Clay Sci 2008;40:179–86. [34] Maroga Mboula V, Hequet V, Gru Y, Colin R, Andres Y. Assessment of the efficiency of photocatalysis on tetracycline biodegradation. J Hazard Mater 2012;209-210:355–64. [35] Shalom M, Inal S, Neher D, Antonietti M. SiO2 /carbon nitride composite materials: the role of surfaces for enhanced photocatalysis. Catal Today 2014;225:185–90. [36] Kibanova D, Sleiman M, Cervini-Silva J, Destaillats H. Adsorption and photocatalytic oxidation of formaldehyde on a clay-TiO2 composite. J Hazard Mater 2012;211-212:233–9. [37] Wang B, Zhang G, Sun Z, Zheng S. Synthesis of natural porous minerals supported TiO2 nanoparticles and their photocatalytic performance towards Rhodamine B degradation. Powder Technol 2014;262:1–8. [38] Khodja AA, Sehili T, Pilichowski J-F, Boule P. Photocatalytic degradation of 2-phenylphenol on TiO2 and ZnO in aqueous suspensions. J Photochem Photobiol, A 2001;141:231–9. [39] Zhang Z, Jiang D, Li D, He M, Chen M. Construction of SnNb2 O6 nanosheet/g-C3 N4 nanosheet two-dimensional heterostructures with improved photocatalytic activity: Synergistic effect and mechanism insight. Appl Catal, B 2016;183:113–23. [40] Li FT, Zhao Y, Wang Q, Wang XJ, Hao YJ, Liu RH, et al. Enhanced visible-light photocatalytic activity of active Al2 O3 /g-C3 N4 heterojunctions synthesized via surface hydroxyl modification. J Hazard Mater 2014;283:371–81.
Please cite this article as: C. Li et al., Facile synthesis of g-C3N4/montmorillonite composite with enhanced visible light photodegradation of rhodamine B and tetracycline, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.06.014