Chinese Journal of Catalysis 39 (2018) 495 501 催化学报 2018 年第 39 卷第 3 期 www.cjcatal.org available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/chnjc Article (Special Issue of Photocatalysis for Solar Fuels) Biomolecule assisted, cost effective synthesis of a Zn0.9Cd0.1S solid solution for efficient photocatalytic hydrogen production under visible light Hongmei Zhao, Yunfei He, Meiying Liu *, Ran Wang, Yunhe Li, Wansheng You # School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, Liaoning, China A R T I C L E I N F O A B S T R A C T Article history: Received 22 October 2017 Accepted 19 November 2017 Published 5 March 2018 Keywords: Zn0.9Cd0.1S L cystine Green synthesis Photocatalytic hydrogen production A series of alloyed Zn Cd S solid solutions with a cubic zinc blende structure were fabricated hydrothermally with the assistance of L cystine under mild conditions. The products were characterized by XRD, TEM, HRTEM, XPS, UV vis, and BET techniques, and the photocatalytic performance for the reduction of water to H2 on the solid solutions was evaluated in the presence of S 2 /SO3 2 as hole scavengers under visible light illumination. Among all the samples, the highest photocatalytic activity was achieved over Zn0.9Cd0.1S with a rate of 4.4 mmol h 1 g 1, even without a co catalyst, which far exceeded that of CdS. Moreover, Zn0.9Cd0.1S displayed excellent anti photocorrosion properties during the photoreduction of water into H2. The enhancement in the photocatalytic performance was mainly attributed to the efficient charge transfer in the Zn0.9Cd0.1 alloyed structure and the high surface area. This work provides a simple, cost effective and green technique, which can be generalized as a rational preparation route for the large scale fabrication of metal sulfide photocatalysts. 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved. 1. Introduction The development of visible light responsive photocatalysts to realize water splitting is a challenging research topic but essential because of the potential to generate clean hydrogen fuel from renewable energy resources [1]. So far, a variety of nanomaterials, such as sulfides, nitrides, carbides, and silicides, have been developed as potential candidates for visible light driven photocatalysts [2 5]. Among photocatalyst candidates, CdS has been a focus of great interest owing to its suitable band gap (Eg = 2.4 ev) for visible light absorption and a more negative conduction band level ( 0.9 ev vs. NHE) than the reduction potential of H + /H2 [6]. However, short lived charge carriers, photocorrosion under visible light, environmental risk of toxic cadmium as well as the requirement for noble metals as co catalysts prohibits the wide application of CdS [6 10]. The alloying of semiconductors of different band gap potentials with CdS to construct solid solution photocatalysts with tunable electronic structure, such as Cd1 xznxs, Cd1 xmnxs, and Cd1 xnixs, is considered a feasible strategy to address these problems [11 13]. Among them, the ternary Zn Cd S alloy system has gained significant interest owing to the easy formation of uniform solid solutions, composition tunable optoelectronic properties as well as the various potential applications, especially in photocatalysis [14 23]. To date, several techniques have been reported for the growth of ZnxCd1 xs solid solutions with various sizes and morphologies to achieve superior photocatalytic performance. Unfortunately, these conventional * Corresponding author. Tel: +86 411 82159256; E mail: myliu312@yahoo.com # Corresponding author. Tel: +86 411 82159378; E mail: wsyou@lnnu.edu.cn This work was supported by the National Natural Science Foundation of China (21573100, 21573099) and the Open Project of State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences (N 14 04). DOI: 10.1016/S1872 2067(17)62946 2 http://www.sciencedirect.com/science/journal/18722067 Chin. J. Catal., Vol. 39, No. 3, March 2018
496 Hongmei Zhao et al. / Chinese Journal of Catalysis 39 (2018) 495 501 approaches usually involve the use of high temperatures above 160 C and the presence of toxic chemicals including organic solvents, surfactants, and reducing agent to control the activity of the ions [14 17]. In particular, the use of expensive and highly poisonous sulfur agents including Na2S, thioactamide, thiourea, and dimethyl sulfoxide leads to the liberation of a large amount of environmentally toxic H2S, and thus, is not suitable for large scale production [18 23]. Keeping the above points in mind, our aim was to develop a facile, green, template free hydrothermal route under mild conditions for the synthesis of ZnxCd1 xs solid solutions by employing the nontoxic biomolecule L cystine as the sulfur source. As known, L cystine contains several functional groups, such as SH, NH2 and COOH, which exhibit a strong affinity towards metal cations to form a metal ligand complex [24 27]. The complex would release S 2 by thermal decomposition in a sustained manner at a relatively slow rate, which is beneficial for the nucleation and growth of well dispersed ZnxCd1 xs nanoparticles. Hence, in this case, L cystine acts as both a sulfur source and the coordinating agent. Unlike the aforementioned methods, no additional templates, highly toxic sulfur precursors, and poisonous organic solvents are involved in this process. More interestingly, the as obtained Zn0.9Cd0.1S with less cadmium exhibits an efficient and stable activity towards H2 production under visible light irradiation without a co catalyst, with a rate of 4.4 mmol h 1 g 1, which far exceeds that of CdS. The origin of such a super high photocatalytic performance of Zn0.9Cd0.1S under visible light was studied by BET specific surface area measurements, the transient photocurrent (TPC) responses, and electrochemical impedance spectroscopy (EIS) techniques. 2. Experimental 2.1. Materials Zinc acetate dihydrate (Zn(CH3COO)2 2H2O), L cystine (C6H12N2O4S2), cadmium acetate dihydrate (Cd(CH3COO)2 2H2O), and NaOH were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). All chemicals used in the experiments were of analytical grade. 2.2. Synthesis of ZnxCd1 xs In a typical synthesis, 1.5 mmol of L cystine was dissolved in 16 ml of deionized water. The ph of the solution was adjusted to 10 11 by the addition of an aqueous NaOH solution. Meanwhile, different molar ratios of Zn(OAc)2 2H2O and Cd(OAc)2 2H2O with a total sum of 6 mmol were dissolved in another 16 ml of deionized water. Then, the above two solutions were mixed together with vigorous stirring to form a milky suspension. Finally, the mixed slurry was transferred into a 45 ml stainless steel autoclave, which was heated to 140 C and maintained at this temperature for 10 h. After they were cooled naturally to room temperature, the samples were collected, alternately rinsed with deionized water and ethanol, and then dried at 60 C prior to use. 2.3. Characterization The structure and phase of the products were identified by X ray diffraction (XRD) analysis on a Bruker D8 Advance diffractometer with Cu Kα irradiation operating at 40 kv and 40 ma. UV visible spectra were recorded on a Perkin Elmer Lambda 3 spectrophotometer by adopting BaSO4 as a 100% reference standard and were converted from reflectance to absorbance by the Kubelka Munk function. The morphologies and particle sizes of the samples were revealed by transmission electron microscopy (TEM, FEI Tecnai Spirit) and high resolution transmission electron microscopy (HRTEM, FEI Tecnai F30). The samples were grounded, ultrasonically dispersed in ethanol, and then stuck to a Cu grid. The surface electronic state was analyzed with an ESCALAB250 X ray photoelectron spectroscopy (XPS) with Al Kα (1486.6 ev) radiation under ultrahigh vacuum (< 2 10 9 Torr). All the binding energies were calibrated to the C 1s peak at 284.6 ev. The Brunauer Emmett Teller (BET) specific surface areas were evaluated by N2 adsorption desorption isotherms at 196 C (Beckman Coulter SA3100) after the samples were outgassed at 100 C for 2 h under vacuum. 2.4. Photocatalytic hydrogen production Photocatalytic H2 production experiments were conducted in a closed gas circulation using a 300 W Xe lamp with a cut off filter (λ 420 nm). 50 mg of the ZnxCd1 xs powder was dispersed into 200 ml of an aqueous solution of 0.43 mol L 1 Na2S 0.5 mol L 1 Na2SO3. Prior to the reaction, the system was thoroughly evacuated and then filled with approximately 30 Torr of Ar gas. A shutter window filled with water was positioned between the lamp and the reaction pool to eliminate infrared irradiation. The temperature of the working solution was maintained at about 10 C by circulating water. The evolved H2 was analyzed online by gas chromatography (TCD, molecular sieve 5 Å column, and Ar carrier). 2.5. Photoelectrochemical measurements The TPC and EIS analysis were measured in a standard three electrode quartz cell with a CHI604B electrochemical workstation (Shanghai Chenhua Instrument Corp., China). A Pt foil and a saturated calomel electrode (SCE) were used as the counter and reference electrodes, and the as obtained samples coated on F doped SnO2 (FTO) conductive glass was employed as the working electrode. The working electrode was fabricated using the screen printing technique described in previous work [28]. All electrodes had a similar thickness (10 11 µm). A 0.43 mol L 1 Na2S 0.5 mol L 1 Na2SO3 aqueous solution was used as the electrolyte and a 300 W Xe lamp (λ 420 nm) was used as the visible light source. 3. Results and discussion Powder XRD was conducted to analyze the crystalline phase and purity of the products. The XRD patterns of the ZnxCd1 xs (x
Hongmei Zhao et al. / Chinese Journal of Catalysis 39 (2018) 495 501 497 111 220 JCPDS Cubic ZnS 311 5.9 5.8 (3) (2) (1) 111 220 311 JCPDS Cubic CdS 20 25 30 35 40 45 50 55 60 65 70 2 ( ) (7) (6) (5) (4) a axis length (Å) 5.7 5.6 5.5 5.4 5.3 0.0 0.2 0.4 0.6 0.8 1.0 Fig. 1. XRD patterns of ZnxCd1 xs solid solutions with various x values: (1) 0; (2) 0.1; (3) 0.3; (4) 0.5; (5) 0.7; (6) 0.9; (7) 1. Dependence of lattice constants on the Zn content (x) of ZnxCd1 xs solid solutions. Value of x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) solid solutions as well as the standard diffraction peaks of CdS and ZnS reported by the JCPDS are shown in Fig. 1. All the samples exhibited similar diffraction characteristics that could be assigned to a zinc blende type structure. The absence of any other phases or impurities indicated the high purity of the as obtained products. With an increasing amount of Zn 2+ content, the diffraction peaks systematically shifted to the higher angle sides from CdS (JCPDS 65 2887) to ZnS (JCPDS 80 0020), indicating the formation of homogeneous cubic ZnxCd1 xs solid solutions instead of merely a physical mixture of CdS and ZnS. The calculated lattice constants for the ZnxCd1 xs solid solutions obtained by fitting the XRD patterns according to the MDI Jade5.0 software are listed in Table 1. Fig. 1 displays the dependence of the lattice parameters (1) on the Zn 2+ content x. The lattice constant decreased almost linearly as the Zn 2+ content increased. This phenomenon obeyed the well known Vegard s law [29,30], which rules out the separate nucleation of CdS or ZnS nanocrystals. The subsequent fringe lattice constriction was attributed to the larger ionic radius of Cd 2+ (0.97 Å) relative to that of Zn 2+ (0.74 Å) [31]. Additionally, the relatively small discrepancy in the electronegativity between Cd (1.69) and Zn (1.65) was favorable for the formation of Zn Cd S solid solutions [32]. Meanwhile, the structural similarity between ZnS and CdS confirmed by XRD data also facilitated the formation of a Zn Cd S alloyed structure [32]. Fig. 2 displays the UV vis diffuse reflectance absorption spectra of ZnxCd1 xs, CdS, and ZnS. All the ZnxCd1 xs samples showed an intense absorption band with a steep edge, which Table 1 Samples and their physicochemical properties and H2 evolution rates. Sample Lattice constant (Å) ABET (m 2 g 1 ) Eg (ev) H2 evolution rate ( mol h 1 m 2 ) CdS 5.8327 81.7 2.11 2.93 Zn0.1Cd0.9S 5.7974 101.2 2.29 7.56 Zn0.3Cd0.7S 5.7148 105.7 2.34 18.37 Zn0.5Cd0.5S 5.6225 118.4 2.40 19.34 Zn0.7Cd0.3S 5.5196 129.7 2.45 35.64 Zn0.9Cd0.1S 5.4161 154.9 2.51 89.81 ZnS 5.3478 178.6 3.19 0 indicated that the absorption was caused by an intrinsic band gap transition from the valence band to the conduction band rather than the transition from impurity levels [33]. The absorption edges of the ZnxCd1 xs solid solutions shifted monotonically to longer wavelengths with increasing Cd 2+ /Zn 2+ molar ratio, which was consistent with the shift of the XRD peaks to higher angles (Fig. 1), further confirming the formation of ZnxCd1 xs solid solutions. The band gaps of the solid solutions were estimated to be 2.11 3.19 ev (x = 0 1) from the plots of ( h ) 2 versus h (in which and h are the absorption coefficient and the incident photon energy, respectively) by linearly extrapolating to zero across the x axis (a straight line to the x axis). The TEM and HRTEM images of the Zn0.9Cd0.1S sample with the maximum H2 generation rate are displayed in Fig. 3. Clearly, the sample was composed of nanoparticles with a size range from 30 to 100 nm. Further observation indicated that each nanoparticle was composed of smaller primary nanocrystals with a size of 3 8 nm. The well defined lattice fringes of the Zn0.9Cd0.1S nanocrystal demonstrate its highly crystalline nature. The spacing of the lattice fringes was approximately 0.326 nm, corresponding to the interplanar distance of the (111) plane of Zn0.9Cd0.1S with a cubic zinc blende phase [34]. The Absorption (a.u.) (6) (7) (1) (2) 2 3 4 hn (ev) 200 300 400 500 600 700 800 Wavelength (nm) Fig. 2. UV Vis absorption spectra and the plots of ( h ) 2 versus h (inset) of ZnxCd1 xs solid solutions with various x value: (1) 0; (2) 0.1; (3) 0.3; (4) 0.5; (5) 0.7; (6) 0.9; (7) 1. (3) (4) (5) (ahn) 2 (ev) 2 a g
498 Hongmei Zhao et al. / Chinese Journal of Catalysis 39 (2018) 495 501 Fig. 3. TEM and HRTEM (inset) images of the Zn0.9Cd0.1S solid solution. surface compositions and electronic structures of the Zn0.9Cd0.1S sample were further analyzed by XPS, as presented in Fig. 4. The spectrum of the survey scan clearly demonstrated the existence of Zn, Cd, and S as well as C and O. The appearance of very small amounts of C and O signals resulted from the carbon tape and the adsorbed oxygen, respectively. The doublet peaks for Zn 2p (1021.7 and 1044.5 ev), Cd 3d (411.5 and 404.7 ev), and S 2p (161.3 and 162. 1 ev) were assigned to the spin orbit split components of the Cd 2+, Zn 2+, and S 2 ions. The binding energies were in good agreement with the data reported in the literature [35,36]. The photocatalytic performance of the ZnxCd1 xs solid solutions for the decomposition of water to H2 under visible light irradiation (λ > 420 nm) was evaluated using S 2 /SO3 2 as hole scavengers, as presented in Fig. 5. The H2 production rate was monitored during 3 h of continuous illumination. No H2 was detected over ZnS because ZnS (3.21 ev) is only active under UV light [37]. Only a trace amount of hydrogen was produced over naked CdS (0.03 mmol h 1 g 1 ), owing to the rapid recombination of the photogenerated e h + pairs [6]. In contrast, the ZnxCd1 xs solid solutions exhibited much superior performance for photocatalytic water reduction compared to CdS. A gradual improvement in the H2 evolution activity was observed with the increase of the Zn 2+ content. The highest activity was achieved over the Zn0.9Cd0.1S catalyst, with a H2 evolution rate of 4.4 mmol h 1 g 1 even without the addition of a cocatalyst, which far exceeded that of CdS. A further increase of the Zn 2+ content led to a deterioration of the photocatalytic performance. In previous reports, the optimum activity was generally realized in a solid solution with a higher Cd/Zn molar ratio in the hexagonal wurtzite structure [14,38]. However, in this work, the optimum composition consisted of a very low Cd 2+ content in the cubic blende structure. The difference in the optimum composition is considered to originate from the difference in the crystalline structure, resulting in different charge transfer paths [34,39,40]. The stability of the Zn0.9Cd0.1S catalyst was investigated by performing consecutive recycle experiments under identical reaction conditions, as demonstrated in Fig. 5. There was a slight decrease in activity in the second run owing to the consumption of the sacrificial reagents survey Cd 3d 5/2 Cd 3d Cd 3d1/2 Cd 3d3/2 S 2s S 2p Zn 3p Cd 4d Zn 2p1/2 Zn 2p3/2 Cd 3d 3/2 1200 1000 800 600 400 200 0 420 415 410 405 400 (c) Zn 2p 3/2 Zn 2p (d) S 2p3/2 S 2p S 2p1/2 Zn 2p 1/2 1050 1045 1040 1035 1030 1025 1020 1015 166 164 162 160 158 Fig. 4. XPS spectra of the Zn0.9Cd0.1S solid solution. Survey spectrum; Zn 2p; (c) Cd 3d; (d) S 2p.
Hongmei Zhao et al. / Chinese Journal of Catalysis 39 (2018) 495 501 499 200 1600 1st run evca 2nd run evca 3rd run fresh solution Rate of H 2 evolution (mmol h -1 ) 150 100 50 Amount of H 2 evolution (mmol) 1200 800 400 0 CdS Zn 0.1 Cd 0.9 S Zn 0.3 Cd 0.7 S Zn 0.5 Cd 0.5 S Zn 0.7 Cd 0.3 S Zn 0.9 Cd 0.1 SZn 0.92 Cd 0.08 S Samples 0 0 6 12 18 Reaction time (h) Fig. 5. Comparison of the photocatalytic activity of the ZnxCd1 xs solid solutions for H2 evolution under visible light irradiation. Reaction conditions: 50 mg catalyst, 100 ml aqueous solution containing 0.43 mol L 1 Na2S and 0.5 mol L 1 Na2SO3, 300 W Xe lamp (λ > 420 nm). Recyclability test by monitoring the time courses of H2 evolution over the Zn0.9Cd0.1S solid solution under visible light irradiation. with prolonged reaction time. The activity was recovered in the third cycle by adopting a fresh aqueous solution of S 2 /SO3 2, indicating that the photocatalyst was essentially stable during the photocatalytic water reduction to H2 under visible light illumination. Generally, photocatalysts with higher specific surface areas are favorable for the improvement of the H2 production activity owing to the increase in the surface to volume ratio [41]. The BET surface areas of the as synthesized samples were investigated by nitrogen adsorption desorption measurement and are listed in Table 1. The high BET surface area of Zn0.9Cd0.1S is self explanatory to validate higher activity. In addition, the charge separation and transfer efficiency of photoinduced e h + pairs was also considered to significantly influence the photocatalytic activity [42 44]. Thus, the surface and bulk charge transfer behavior was examined by the TPC response and EIS by constructing a three electrode system. A comparison of the photocurrent time (I t) curves for the as fabricated CdS, Zn0.9Cd0.1S, and ZnS electrodes with five on off cycles of intermittent visible light illumination is shown in Fig. 6. All electrodes showed an instant and reproducible photocurrent response upon irradiation. Further observations showed that the photocurrent of the Zn0.5Cd0.5S electrode was significantly enhanced as compared to those of the ZnS and CdS electrodes, indicating the improvement of the charge transfer and the suppression of the charge recombination by constructing an alloyed Zn0.9Cd0.1S solid solution [45,46]. The electron transfer behavior occurring in the Zn0.9Cd0.1S electrode was further corroborated by the EIS Nyquist plot (Fig. 6). Generally, the semicircle in the Niquist plot reflects a lower charge transfer resistance [47,48]. The alloyed Zn0.9Cd0.1S electrode exhibited the smallest arc radius, which implied more efficient interfacial charge carrier separation and transfer. Based on the TPC and EIS analysis, the separation and transport of photoinduced electron hole pairs was facilitated owing to the formation of alloyed Zn1 xcdxs solid solutions, which, in turn, significantly boosted the photocatalytic performance for water reduction to hydrogen under visible light. 4. Conclusions A series of efficient visible light responsive Zn1 xcdxs solid solutions with a cubic zinc blende structure were successfully synthesized through a low temperature L cystine assisted hydrothermal approach. The whole process was facile, cost effective, and ecofriendly, which is very promising for large scale applications. The optimum activity was achieved over the Zn0.9Cd0.1S catalyst, which had a H2 generation rate of 4.4 mmol h 1 g 1 even without the loading of a noble metal co catalyst. In addition, this photocatalyst contained a lower 0.12 0.10 CdS Zn 0.9 Cd 0.1 S ZnS 10000 Current density (ma cm -2 ) 0.08 0.06 0.04 0.02 -Z'' (ohm) 5000 CdS Zn 0.9Cd 0.1S ZnS 0.00 260 280 300 320 340 Time (s) 0 0 1000 2000 3000 4000 Z' (ohm) Fig. 6. TPC responses and EIS Nyquist plots of CdS, Zn0.9Cd0.1S, and ZnS electrodes in 0.43 mol L 1 Na2S 0.5 mol L 1 Na2SO3 aqueous solution under visible light irradiation.
500 Hongmei Zhao et al. / Chinese Journal of Catalysis 39 (2018) 495 501 Graphical Abstract Chin. J. Catal., 2018, 39: 495 501 doi: 10.1016/S1872 2067(17)62946 2 Biomolecule assisted, cost effective synthesis of a Zn0.9Cd0.1S solid solution for efficient photocatalytic hydrogen production under visible light Hongmei Zhao, Yunfei He, Meiying Liu *, Ran Wang, Yunhe Li, Wansheng You * Liaoning Normal University Zn0.9Cd0.1S with a cubic zinc blende structure was synthesized by a mild L cystine assisted hydrothermal strategy and exhibited excellent and stable performance for photocatalytic H2 evolution under visible light irradiation. amount of toxic Cd, which is significantly important from an environmental point of view. Acknowledgments We sincerely thank Dr. Jingying Shi of State Key Laboratory of Catalysis, National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, for the helpful suggestions and discussions. References [1] A. Fujishima, Honda, Nature, 1972, 238, 37 38. [2] T. Hisatomi, J. Kubota, K. Domen, Chem. Soc. Rev., 2014, 43, 7520 7535. [3] S. U. M. Khan, M. Alshahry, W. B. Ingler, Science, 2002, 297, 2243 2245. [4] P. Ritterskamp, A. Kuklya, M. A. Wüstkamp, K. Kerpen, C. Weidenthaler, M. Demuth, Angew. Chem. Int. Ed., 2007, 46, 7770 7774. [5] T. Ohmori, H. Mametsuka, E. Suzuki, Int. J. Hydrogen Energy, 2000, 25, 953 955. [6] J. R. Ran, G. P. Gao, F. T. Li, T. Y. Ma, A. J. Du, S. Z. Qiao, Nat. Commun., 2017, 8, 13907 13917. [7] H. J. Yan, J. H. Yang, G. J. Ma, G. P. Wu, X. Zong, Z. B. Lei, J. Y. Shi, C. Li, J. Catal., 2009, 266, 165 168. [8] M. Y. Liu, W. S. You, Z. B. Lei, G. H. Zhou, J. J.Yang, G. P. Wu, G. J. Ma, G. Y. Luan, T. Takata, M. Hara, K. Domen, C. Li, Chem. Commun., 2004, 2192 2193. [9] H. Du, Y. N. Liu, C. C. Shen, A. W. Xu, Chin. J. Catal., 2017, 38, 1295 1306. [10] D. C. Jiang, Z. J. Sun, H. X. Jia, D. P. Lu, P. W. Du, J. Mater. Chem. A, 2016, 4, 675 683. [11] K. Manjodh, C. M. Nagaraja, ACS Sustainable Chem. Eng., 2017, 5, 4293 4303. [12] K. IKeua, S. Shiiba, M. Machida, Chem. Mater., 2010, 22, 743 745. [13] W. Chen, G. R. Duan, T. Y. Liu, Z. M. Jia, X. H. Liu, S. M. Chen, X. J. Yang, J. Mater. Sci., 2015, 50, 3920 3928. [14] L. H. Zhu, Y. Wang, D. Z. Zhang, C. Li, D. M. Sun, S. P. Wen, Y. Chen, S. P. Ruan, ACS Appl. Mater. Interfaces, 2015, 7, 20793 20800. [15] Y. F. Chai, G. F. Huang, L. L. Wang, W. Q. Huang, J. Zhou, Mater. Lett., 2015, 142, 133 136. [16] Z. W. Mei, B. K. Zhang, J. X. Zheng, S. Yuan, Z. Q. Zhuo, X. G. Meng, Z. H. Chen, K. Amine, W. L. Yang, L. W. Wang, W. Wang, S. F. Wang, Q. H. Gong, J. Li, F. S. Liu, F. Pan, Nano Energy, 2016, 26, 405 416. [17] Y. Y. Hsu, N. T. Suen, C. C. Chang, S. F. Hung, C. L. Chen, T. S. Chan, C. L. Dong, C. C. Chan, S. Y. Chen, H. M. Chen, ACS Appl. Mater Interfaces, 2015, 7, 22558 22569. [18] I. Levchuk, C. Würth, F. Krause, A. Osvet, M. Batentschuk, U. Resch Genger, C. Kolbeck, H. P. Steinrueck, W. H. Peukert, C. J. Brabec, Energy Environ. Sci., 2016, 9, 1083 1094. [19] M. C. Liu, D. W. Jing, Z. H. Zhou, L. J. Guo, Nat. Commun., 2013, 4, 2278 2285. [20] S. N. Garaje, S. K. Apte, S. D. Naik, J. D. Ambekar, R. S. Sonawane, M. V. Kulkarni, A. Vinu, B. B. Kale, Environ. Sci. Technol., 2013, 47, 6664 6672. [21] A. P. Ma, Z. H. Tang, S. L. Shen, L. J. Zhi, J. H. Yang, RSC Adv., 2015, 5, 27829 27836. [22] Z. H. Han, G. Chen, C. M. Li, Y. G. Yu, Y. S. Zhou, J. Mater. Chem. A, 2015, 3, 1696 1702. [23] J. U. Kim, Y. K. Kim, H. Yang, J. Colloid Interf. Sci., 2010, 341, 59 63. [24] A. K. Nayak, S. Lee, Y. Sohnb, D. Pradhan, CrystEngComm, 2014, 16, 8064 8072. [25] E. Furia, G. Sindona, J. Chem. Eng. Data, 2010, 55, 2985 2989. [26] M. D. Đurović, Ž. D. Bugarčić, F. W. Heinemann, R. Van. Eldik, Dal
Hongmei Zhao et al. / Chinese Journal of Catalysis 39 (2018) 495 501 501 ton Trans., 2014, 43, 3911 3921. [27] A. Frank, A. S. Wochnik, T. Bein, C. Scheu, RSC Adv., 2017, 7, 20219 20230. [28] M. Y. Liu, H. Chen, H. M. Zhao, Y. F. He, Y. H. Li, R. Wang, L. C. Zhang, W. S. You, Dalton Trans., 2017, 46, 9407 9414. [29] L. Vegard, H. Schjelderup, Phys. Z., 1917, 18, 93 96. [30] H. S. Zhou, H. Sasahara, I. Honma, H. Komiyama, J. W. Haus, Chem. Mater., 1994, 6, 1534 1541. [31] J. S. Steckel, J. P. Zimmer, S. CoeSullivan, N. E. Stott, V. Bulovi, M. G. Bawendi, Angew. Chem. Int. Ed., 2004, 43, 2154 2158. [32] D. H. Wang, L. Wang, A. W. Xu, Nanoscale, 2012, 4, 2046 2053. [33] I. Tsuji, H. Kato, H. Kobayashi, A. Kudo, J. Phys. Chem. B, 2005, 109, 7323 7329. [34] W. Lu, W. Z. Wang, M. Shang, W. Z. Yin, S. M. Sun, L. Zhang, Int. J. Hydrogen Energy, 2010, 35, 19 25. [35] M. Marychurch, G. C. Morris, Surf. Sci., 1985, 154, 251 254. [36] H. Du, K. Liang, C. Z. Yuan, H. L. Guo, X. Zhou, Y. F. Jiang, A. W. Xu, ACS Appl. Mater. Interfaces, 2017, 4, 24550 24558. [37] J. F. Reber, K. Meier, J. Phys. Chem., 1984, 88, 5903 5913. [38] M. Y. Liu, Y. F. He, H. Chen, H. M. Zhao, W. S. You, J. Y. Shi, L. C. Zhang, J. S. Li, Int. J. Hydrogen Energy, 2017, 42, 20970 20978. [39] L. W. Yin, Y. Bando, J. H. Zhan, M. S. Li, D. Golberg, Adv Mater., 2005, 17, 1972 1977. [40] Y. C. Zhu, Y. Bando, D. F Xue, D. Golberg. J. Am. Chem. Soc., 2003, 125, 16196 16177. [41] Q. Li, H. Meng, P. Zhou, Y. Q. Zheng, J. Wang, J. G. Yu, J. R. Gong, ACS Catal., 2013, 3, 882 889 [42] X. Zong, H. J. Yan, G. P. Wu, G. J. Ma, F. Y. Wen, L. Wang, C. Li, J. Am. Chem. Soc., 2008, 130, 7176 7177. [43] J. Bisquert, A. Zaban, M. Greenshtein, I. Mora Sero, J. Am. Chem. Soc., 2004, 126, 13550 13559. [44] Z. H. Han, G. Chen, C. M. Li, Y. G. Yu, Y. S. Zhou, J. Mater. Chem. A, 2015, 3, 1696 1702. [45] S. Chakrabarty, K. Chakraborty, A. Laha, T. Pal, S. Ghosh, J. Phys. Chem. C, 2014, 118, 28283 28290. [46] A. Hagfeldt, H. Lindstrçm, S. Sçdergren, S. E. Lindquist, J. Electroanal. Chem., 1995, 381, 39 46. [47] A. Jana, C. Bhattacharya, J. Datta, Electrochim. Acta, 2010, 55, 6553 6562. [48] J. Zhang, J. G. Yu, M. Jaroniec, J. R. Gong, Nano Lett., 2012, 12, 4584 4589. 生物分子辅助低成本制备 Zn 0.9 Cd 0.1 S 固溶体及其高效可见光光催化制氢 赵红梅, 何云飞, 刘美英 * #, 王冉, 李云贺, 由万胜辽宁师范大学化学化工学院, 辽宁大连 116029 摘要 : 如何提高光催化制氢量子产率是太阳能分解水制氢研究的重点和焦点. Zn-Cd-S 固溶体因具有窄的带隙宽度及合适 的导带和价带位置而显示了广阔的应用前景. 然而, 两方面的问题限制了其规模化应用 : (1) 往往需负载 Pt, Pd, Ru 和 Rh 等 贵金属助催化剂才能获得可观的光催化性能 ; (2) 传统合成技术通常采用硫代乙酰胺 硫脲及硫化钠等昂贵且有毒的化学 试剂作硫源. 与上述硫源相比, 生物小分子 L- 胱氨酸分子中含有 COOH NH 2 及 SH 基团, 这些基团易于与金属阳离子配 位, 因此能够有效调控硫源释放 S 2 的速度, 硫化物的形貌 尺寸以及取向能够灵活地得到调控. 另外, 在强碱或强酸性介质 中, L- 胱氨酸具有良好的水溶性, 因此材料的合成可选择在水介质中, 这对光催化过程是非常关键的, 有利于改善材料在光 催化反应过程中的稳定性. 基于此, 本文以经济环保的生物小分子作硫源, 制备了高效 稳定且有可见光响应的纳米硫化 物光催化体系, 旨在发展环境友好 条件温和 成本低廉 操作简单和易于工业化生产的绿色制备技术,. 以 L- 胱氨酸为硫源和结构导向剂, 采用水热合成技术在温和条件下制备了立方相结构的 Zn-Cd-S 固溶体光催化剂, 采 用 XRD, TEM, HRTEM, XPS, UV-vis 及 N 2 吸附等手段表征了其结构和形貌. 结果表明, 随 Zn 含量增加, 其带隙在 2.11 3.19 ev 间连续可调. 在可见光 (λ > 420 nm) 照射 无助催化剂和 Na 2 S/Na 2 SO 3 水溶液为牺牲剂的条件下研究了其光催化制氢的性 能. 其中 Zn 0.9 Cd 0.1 S 具有最佳的光催化活性, 其产氢速率约为 4.4 mmol h 1 g 1 ( 无助催化剂, 远高于 CdS), 且显示优良的稳定 性及抗光腐蚀能力. 通过经验公式计算得出了其能带结构示意图, 结果表明, Zn x Cd 1-x S 固溶体的导带和价带的位置随着 Zn 含量的增加而向更负的导带和更正的价带移动. 固溶体导带电位更负促进更有效的氢产生, 电位价带更正导致电荷更容 易发生转移. Zn 0.9 Cd 0.1 S 高的光催化活性可能归因于中等的导带边缘和最合适的带隙. 最后利用光电流及交流阻抗阐明了 其光生电子 - 空穴对的分离及迁移机理. 与 CdS 相比, Zn-Cd-S 固溶体的形成促进了光生载流子在界面间的传输, 抑制了其 快速复合, 从而大幅度改善了光催化活性及稳定性. 该硫化物纳米晶的绿色制备技术期望可推广到其它硫化物可见光光 催化体系. 关键词 : Zn 0.9 Cd 0.1 S; 胱氨酸 ; 绿色合成 ; 光催化制氢 收稿日期 : 2017-10-22. 接受日期 : 2017-11-19. 出版日期 : 2018-03-05. * 通讯联系人. 电话 : (0411)82159256; 电子信箱 : myliu312@yahoo.com # 通讯联系人. 电话 : (0411)82159378; 电子信箱 : wsyou@lnnu.edu.cn 基金来源 : 国家自然科学基金 (21573100, 21573099); 中国科学院大连化学物理研究所催化基础国家重点实验室开放基金 (N-14-04). 本文的英文电子版由 Elsevier 出版社在 ScienceDirect 上出版 (http://www.sciencedirect.com/science/journal/18722067).