Simultaneous Realization of Enhanced Photoactivity and Promoted

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Simultaneous realization of enhanced photoactivity and promoted photostability by mutilayered-MoS2-coating on CdS nanowire structure via compactly coating methodology Yu Yang, Yan Zhang, Zhibin Fang, Lulu Zhang, Zuyang Zheng, Zhenfeng Wang, Wenhui Feng, Sunxian Weng, Shiying Zhang, and Ping Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b09873 • Publication Date (Web): 01 Feb 2017 Downloaded from http://pubs.acs.org on February 2, 2017

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ACS Applied Materials & Interfaces

Simultaneous Realization of Enhanced Photoactivity and Promoted Photostability by Mutilayered-MoS2Coating on CdS Nanowire Structure via Compactly Coating Methodology Yu Yanga, Yan Zhanga, Zhibin Fanga, Lulu Zhanga, Zuyang Zhenga, Zhenfeng Wanga, Wenhui Fenga, Sunxian Wengc，Shiying Zhangb and Ping Liu*a a

State Key Laboratory Breeding Base of Photocatalysis, Research Institute of Photocatalysis,

Fuzhou University, Fuzhou350002,P.R.China. b

Hunan Key Laboratory of Applied Environmental Photocatalysis, Changsha University,

Changsha 410022,P.R.China. c.

State grid Fujian electric power research institute, Fuzhou350002, P.R.China.

ACS Paragon Plus Environment

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ABSTRACT

CdS has been regarded as a promising photocatalytic water splitting visible-light photocatalyst while low catalytic activities and photocorrosion seriously limited its practical application. Here, inspired by core-shell principle, we try to fabricate CdS@MoS2 core-shell structure by utilizing unstable CdS nanowires as core and multilayered MoS2 as shell. Multilayered MoS2 not only serves as protective shell to preserve CdS, but also provides abundant reactive sites and form type-I junction, giving rise to a remarkable hydrogen production activities. The optimum hydrogen production rate bases on CdS@MoS2 core-shell composite reaches 26.14 mmol h-1g-1, which is about 54 times greater than pure CdS and about twice of CdS nanowires with 1% Pt. Impressively, the presentation of MoS2 nanosheets can effectively avoid the photocorrosion which resulting in 12 hours stable hydrogen production.

Keywords: photocatalyst; photocorrosion; Multilayered MoS2; CdS nanowires; core-shell structure.


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1．．Introduction Photocatalytic water-splitting represents one of the most promising solutions to converting solar energy to hydrogen for addressing both environmental problems and energy crisis.1-4 Major challenge of this technique to achieve practical application is development of efficient and stable photocatalysts.5-7 In the recent decades, a series of superior visible-light catalysts have been discovered, such as CdS8-9, g-C3N410-11, BiVO412-13, AgX (X=Br,I)14-15, Ag3PO416-17 etc. Cadmium sulfide (CdS) is one of the most popular visible-light photocatalysts for hydrogen production for its wide-range light absorption, efficient photoexciton generation and appropriate photoredox potentials.18-19 Unfortunately, there are mainly two inferior issues that restrict nanoscale CdS photocatalyst to be extensively utilized. On one hand, pristine CdS usually exhibits low photocatalytic activities of hydrogen production due to the ultrafast photoexciton recombination and the lack of reactive sites.20 Thus the addition of noble metal co-catalysts such as Pt was widely conducted to improve the charge separation by electron trap as well as to decrease the overpotential by providing active sites21, while noble metal brings about the expense of high cost. On the other hand, CdS photocatalyst has been suffering from the instability caused by the well-known photocorrison.22 Although a great many research efforts have been made with positive progress, there is still a long way to go to promote the photostability of CdS. In order to lower the high cost that caused by introduced precious metal on CdS, numerous effort has been guided to the development of non-noble-metal co-catalysts. In substantial investigations, a lot of attention begins to be paid to the molybdenum sulphide (MoS2), which is composed of earth-abundant elements, for its desirable hydrogen


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evolution reactivity and low cost. Consequently, MoS2 has become one of the most promising materials to replace noble metal.23-25 Generally, the photocorrosion of CdS, where surface sulphions are oxidized to sulphurs via holes, leads to the loss of sulphide ions. Therefore, it is crucial to stabilize surface sulphions and to transfer holes for the photo-corrosion problem. Actually, rational structure designs are desperately needed.

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Inspired by the core-shell principle, we try to build protective shell on unstable CdS for protective shell can passivate the surface trap states of CdS core and core-shell structure can provide perfectly intimate interfacial contact which is beneficial to the migration of photo-induced charges. In fact, there have been some related researches so far that would serve as good examples of coating strategies to protect unstable photocatalysts, such as ZnO nanospheres coated with reduced graphene oxide30, PANI@CdS core-shell nanospheres,31 Carbon-Coated CdS petalous nanostructures32 etc. Based on these studies, with the purpose of realizing the shell protection, some requirements should be followed: firstly, the shell favours a soft two-dimension structure with large surface area to totally cover the core materials, facilitating the coating process. Secondly, the stability of the shell material should be relatively better. On account of above analyses, two-dimension MoS2 is considered to be the applicable shell material. Up to now, CdS and MoS2 composites have been reported in numerous researches. However, most of them tend to the MoS2 nanosheets sporadic load on CdS.22-23, 33-34 Studies about the MoS2 coating CdS core-shell structure to simultaneous realization of enhanced photoactivity and promoted photostability are still rare. Meanwhile, those reports of MoS2/CdS composites mainly focus on few-layer or single-layer MoS2 nanosheets approaching metallic properties, while multilayered MoS2


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nanosheets with semiconductor nature are rarely considered.33,35-40 Normally, the multilayered MoS2 is an indirect band-gap n-type semiconductor (0.23~1.40ev),

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which can composited with CdS (direct-band-gap, -0.52~1.88ev) to form a type-I junction.35, 43 Due to the unique structure of type-I junction, photogenerated charges of CdS could be directly migrated to MoS2, which possesses inferior recombination rate of photo-generated holes and electrons, resulting in extended lifetimes of charges. Hence, the photocorrosion of CdS could be suspended because of missing holes and photocatalytic water splitting rate could be increasing because active sites of MoS2 would receive more electrons to react with hydrogen ions. Thus, adopting multilayered MoS2 as protective shell coating CdS is a promising approach to improve photocatalytic activity and photostability at the same time. Actually, investigations of MoS2/CdS composites prefer to CdS nanoparticles or nanospheres which are easy to aggregate.23, 34, 44-46 Compared with CdS nanoparticles, one-dimensional (1D) structural materials can provide a larger aspect-ratio47, higher electron mobility48 and larger specific surface area.49 To the best of our knowledge, constructing core-shell structure by utilizing 1D CdS nanowires (NWs) and multilayered MoS2 nanosheets (NSs) has not been reported before. Therefore, developing a new methodology to realize this promising structure is still a big challenge. Herein, we try to fabricate compactly-coated CdS@MoS2 core-shell composites via a two-step method. Firstly, surface characteristics of CdS were adjusted through a protonation process, which strengthened relationship between MoO42- and CdS. Secondly, after a hydrothermal process, CdS@MoS2 core-shell was successfully built and MoS2 NSs were grown directly on CdS NWs surface with close interfacial contact. Due to the unique core-shell structure and large amount of active sites provided by multilayered


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MoS2, the hydrogen production rate of CdS@MoS2 is up to 26.14 mmol h-1 g-1 under visible-light, which is about 54 times greater than pure CdS and about twice of CdS NWs with 1% Pt co-catalyst. Impressively, the presentation of MoS2 NSs can effectively avoid the photocorrosion which resulting in 12 hours stable hydrogen production.

2. Experimental Section 2.1. Preparation. All CdS nanowires are prepared via a literature method.50 The CdS NWs are suspended in hydrochloric acid solution (0.1 mol/L) for 18 hours. Then the CdS NWs are washed with deionized water and absolute ethanol to get protonated CdS NWs. The formation process of CdS NWs and multilayered MoS2 NSs composites (50 wt% of MoS2) is depicted as below. 50 mg protonated CdS NWs are dispersed in 40 mL deionized water, then 25 mg sodium molybdate (Na2MoO4 2H2O) and 50 mg thioacetamide (C2H5NS) are added into the above mixture. The mixture is migrated to the Tefion-lined stainless steel autoclave and heated at 200 °C for 24 hours. An olivine product, CdS NWs and multilayered MoS2 NSs composites is harvested after centrifugation and named as CdS@MoS2. The CdS@MoS2 with different weight ratios (30 wt% and 70 wt%) of the MoS2 to CdS are synthesized via similar way except for the amount of S and Mo resource. Pure MoS2 NSs are prepared under the identical conditions without the presence of the protonated CdS NWs. For comparison, Pt loaded CdS is obtained through photoreduction method and the products is defined as CdS-Pt. 2.2. Characterization. The crystallographic structures of all samples were identified via Xray diffractometer (XRD, Bruker D8 Advance) with Cu Kα radiation (λ = 0.15418 nm) which handled at 40000 V and 0.04 A. The scan rate was 0.05°2θ s-1. Zeta potential (ࣈ) of all products were investigated on a Zetasizer Nano 2S at a normal temperature. Transmission electron microscopy (TEM) images and scanning electron microscopy (SEM) images were determined by


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a TecnaiG2F20 S-TWIN with a field emission gun at 200000 V and an FEI Nova NanoSEM 230 field-emission scanning electron microscope, respectively. X-ray photoelectron spectroscopy (XPS) studies were performed on a Thermo Scientific ESCA Lab 250 system, with monochromatic Al Ka as the X-ray source. UV-vis diffuse reflectance spectroscopy (UV-vis DRS) investigation was carried out on a UV-vis spectrophotometer (Cary-5000, Agilent), in which BaSO4 was used as the background. Photoluminescence (PL) emission spectrogram of the products were detected by a Cary Eclipse spectrophotometer. The excitation wavelength is 450 nm. Electrochemical analysis was measured by a ZENNIUM electrochemical system equipped with a common three electrodes system. The counter electrode is Pt plate and the reference electrode is Ag/AgCl. The electrolyte is 0.2 mol/L Na2SO4 solution (pH = 6.8). 5 mg CdS@MoS2 composite was added in 0.5 milligrams of N,N-dimethyl formamide. The slurry was spread on ITO glass substrate that served as the working electrode. The visible-light source is a 300 W xenon lamp with a 410 nm filter. The photocatalytic activity of the products was done by photocatalytic H2 evolution with a top irradiation reaction vessel connected to a closed gas circulation system. 20 mg sample was bathed in 100 milligrams of 10 mL lactic acid solution under magnetic stirring. The system was degassed for 1 h before irradiation and the reaction was carried out by a 300 W Xe lamp with a 410 nm cutoﬀ ﬁlter. The hydrogen was detected by a TECHCOMP GC7900 gas chromatograph with a thermal conductivity detector.

3. Result and discussion CdS@MoS2 composites were prepared through two step methods. The primary mechanism of this process is explored and displayed in Scheme 1. The CdS NWs were


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synthesized through a hydrothermal process. After through a protonation process, the surface characteristics of CdS were adjusted in order to strengthen the inter-attraction between MoO42- and CdS. After the protonation process, MoO42- was introduced to coat the as-prepared CdS NWs by a surface adsorption process, which can be proved to be an electrostatic interaction via the zeta potential (ࣈ) (See Figure S1). Clearly, the zeta potential values of CdS and the protonated CdS NWs dispersed in water are +10.66 mV and +63.34 mV, respectively, indicating the protonation process probably change the surface electronic properties, which make it more easily to absorb the negative MnO42via the electrostatic interaction. After negatively charged MnO42- was introduced, protonated CdS NWs show a zeta potential value of -11.71mV while CdS NWs remain nearly the same (+11.09 mV). The apparent variation of zeta potential is probably caused by the introduction of the negatively ions on the positive CdS NWs. Because of above interaction, MnO42- was closely attached to the surface of CdS NWs, which make sure that after the second hydrothermal process, MoS2 NSs were grown directly on CdS NWs surface to construct compactly-coated core-shell composites with close interfacial contact. The aforementioned synthesis mechanism can be certified by SEM and TEM. The pure CdS NWs are 30-80 nm in diameter (see Figure 1a). No obvious difference can be observed on this two images suggesting the morphology of the CdS@MoS2 composites did not change a lot before and after MoS2 is loaded (See Figure 1a and 1b). The reason of no MoS2 observed is that MoS2 NSs were compactly-coated on CdS NWs surface. The TEM and HRTEM can further identified the conclusion. It can be seem from the inset in Figure 1c that CdS NWs was compactly-coated by the multilayered MoS2, forming core-shell structure. Obvious borderlines between separated units of multilayered MoS2 and CdS were observed (See Figure 1c),


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indicating that CdS was successfully integrated with multilayered MoS2 with intimate interfacial contract. The 0.6 nm lattice spacing is consistent with the (002) plane of multilayered MoS2. Due to the close contact, interfacial charge transfer should be significantly increase, which would greatly affect the activity of CdS@MoS2. As displayed Figure 1d (the selected area electron diffraction image), the diffraction spots referred to (110) and (102) planes of CdS were observed, indicating that CdS NWs show single crystal characteristic. Clearly diffraction ring is corresponding to the (002) plane of multilayered MoS2 NSs were observed, revealing MoS2 NSs show certain degree of crystal characteristic which is constant with the analysis of HRTEM. The rings in the centre of selected area electron diffraction image may derived from the stacking of MoS2 NSs with different crystallographic orientations. The existence of the Mo, S and Cd elements was also certified by energy dispersive X-ray spectrometry (EDS) (See Figure S4). XRD analysis was conducted to characterize the crystal structure and phase purity of the products. For pure MoS2 sample (Figure S5), the diffraction peaks can be attributed to (110), (100), and (002) planes in the MoS2 which are well-matched with JPCDS card no. 37-1492, represents the hexagonal phase MoS2 with lattice constants of c=1.230 nm and a=b=0.316 nm. None of detected peaks of impurities was observed. As illustrated in Figure 2, for pristine CdS and CdS@MoS2, the diffraction peaks are well-matched with JCPDS no.41-1049 (a=b=0.414 nm and c=0.671nm). CdS maintains the essential crystal structure after the hydrothermal process. However, none of diffraction peaks belong to MoS2 crystal was detected in the XRD of the CdS@MoS2 composites. The absence of the diffraction peaks of MoS2 NSs is probably because compared to that of CdS NWs, the diffraction intensity of MoS2 is too weak to be detected. XPS analysis was measured to further confirm the existence of MoS2 in CdS@MoS2 composites and research their surface chemical states. Figure 3a shows the XPS spectrum of Cd


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3d, which can be assigned to Cd 3d5/2 and Cd 3d3/2 of Cd2+ in CdS appeared at 404.68 and 411.40 eV, respectively.51 Two peaks at 162.47 and 161.12 eV were detected which can be fitted into S 2p1/2 and S 2p3/2 of S2-, respectively (see Figure 3b).52 Figure 3c displayed the XPS spectrum of Mo 3d, three peaks at 231.12, 227.77 and 225.47 eV are attributed to Mo 3d3/2, Mo 3d5/2 and S 2s, respectively, demonstrating existence of Mo4+ in the composites. To be noticed, the binding energy of Mo 3d5/2 and Mo 3d3/2 shifted about 0.7eV to the lower energy direction and the same phenomenon also observed on those of S 2s, S 2p1/2 and S 2p3/2, 53,54 which could be result from the interactive effect between the multilayered MoS2 NSs and CdS NWs. Hence, the multilayered MoS2 NSs and 1D CdS NWs were successfully combined to form core-shell structure. The multilayered MoS2 NSs with indirect band gap in the composites not merely offer more active sites but also served as a sink for photoexcited electrons and holes which may greatly enhance the photocatalytic performance and stability. Special core-shell structure is conducive to improve the optical performances. DRS was conducted to investigate the optical performances of the samples. Pure CdS shows a remarkable absorption at wavelengths shorter than 520 nm (see Figure 3d), which can be attributed to its essential band-gap absorption. The absorption edge for CdS@MoS2 is about 530 nm and obvious enhancement of absorption in the visible-light area was detected. The red-shift is probably caused by narrow band gap of MoS2 NSs.55 The remarkable impact on optical property of CdS@MoS2 samples also agrees well with the colour change sequence from yellow to yellow green. The optimized optical property may greatly affect the photocatalytic performance. The photocatalytic H2 evolution was measured to evaluate the photocatalytic activity of the aforementioned products and the result is illustrated in Figure 4a. The pure CdS NWs present a very low hydrogen production rate, which could be assigned to the quick recombination of


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photoexcited electrons and holes. After introducing the multilayered MoS2 on CdS, hydrogen production rate increases significantly. There is an optimal loading amount of MoS2 in terms of photocatalytic performance. The supreme photocatalytic H2 evolution rate of CdS@MoS2 composites is observed 26.14 mmol h-1 g-1 when loading quality of MoS2 to 50%, which is about 54 times of the pristine CdS NWs. Probably reasons for that are as below: low loading of MoS2 (30 wt%) result in an decrease of density of active sites for the H2 production evolution, while a further increasement in the introducing quality of MoS2 to 70% resulted in the shading effect of MoS2, which impedes the visible-light absorption of CdS in the composites. Similar phenomenon has been founded in some former researches in which the MoS2 NSs were used as a cocatalyst.52,

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Additionally, the photocatalytic activity of CdS@MoS2 (50 wt% of MoS2)

composite is higher than that of pure MoS2. The unique core-shell structure, which can provide intimate interfacial contact, is probably responsible for promoting the separation and transfer of the photoinduced charge carriers to enhance the photocatalytic performance. It is well-known that noble metal e.g. Au, Pt, Rh, Ru and Pd acts as a promising H2 evolution promoters for many photocatalysts.58-60 Hence, for comparison, CdS-Pt was obtained through photoreduction method and performed H2 evolution test under visible-light. As shown in Figure 4b, the hydrogen-generating efficiency of CdS@MoS2 (50 wt%) is almost two times as high as that of CdS-Pt. Moreover, the introducing of protective shell MoS2 could significantly improve the stability of CdS. As displayed in the Figure 4c, the H2 production rate of both CdS-Pt and CdS@MoS2 decreases with cycle going on. After three cycles (12 hours), the rate of H2 evolution on CdS-Pt and CdS@MoS2 decreased by 30.8% and 19.8% (Figure 4d), respectively, indicating that MoS2 shell plays a significant role in improving stability during the reaction. On one hand, the photoinduced holes of CdS could be migrate to multilayered MoS2 NSs, blocking


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the oxidation approach of surface sulphide ions. On the other hand, the compactly-coated MoS2 shell can effectively protect CdS from losing sulphide ions. To determine the damage caused by photocorrosion, XRD pattern of CdS@MoS2 composites before and after four cycles of photocatalytic hydrogen production was recorded and the result is shown in Figure S9a. It can be apparent found that crystal structure is remain intact, suggesting that multilayered MoS2 shell could availably slow down the photocorrosion of CdS NWs and efficiently protect CdS. Generally, CdS is prone to photocorrosion due to oxidation of surface sulphions to sulphurs by photoexcited holes. Therefore, to further study the stability of CdS@MoS2 composites, XPS analysis was conducted to examine the composites after reaction. As displayed in Figure S9b, XPS peaks at 411.64 and 404.9 eV are ascribed to Cd 3d3/2 and Cd 3d5/2 of Cd2+ in CdS, respectively. Three peaks at 231.83, 227.78 and 225.55 eV were detected in the Mo 3d spectrum (See Figure S9c), which are attributed to Mo 3d3/2, Mo 3d5/2 and S 2s,, respectively, exhibiting existence of Mo4+. As for the XPS spectrum of the S 2p region (see Figure S9d), two peaks at 162.42 and 161.21 eV are assigned to S 2p1/2 and S 2p3/2 of S2-, respectively. However, no apparent peak at 163.7 eV, which is unequivocally attributed to elemental sulphur,61-62 meaning surface sulphide ions of CdS scarely were oxidized to sulphurs by photogenerated holes. Meanwhile, the CdS@MoS2 composites after reaction were studied by SEM (see Figure S10) to research the impact of photocorrosion on morphology. The main structure of CdS@MoS2 composites after reaction did not significant change. Consequently, MoS2 shell can effective protect CdS NWs from photocorrsion and the composites have relatively high stability. Based on aforementioned experimental results, tentative mechanism why CdS@MoS2 composites show such a superior activity and stability was concluded and displayed in Figure 5.


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It is reported that valance band (VB) of CdS is lower than that of MoS2, while conduction band (CB) of CdS is higher than that of MoS2.35, 63 Therefore, A type-I junction is formed between CdS and MoS2. Photoexcited holes and electrons from exited CdS would be transferred to the VB and CB of multilayered MoS2 respectively. Meanwhile, the core-shell structure can provide close contact between MoS2 and CdS, which can make sure the fast migration of electrons and holes from CdS to MoS2. Photogenerated electrons and holes are harder to recombination in indirect band gap of multilayered MoS2 NSs relative to direct band gap of CdS NWs. Thus, lives of photogenerated electrons and holes are prolonged which result in enhanced H2 evolution activity. Moreover, the selected transfer of holes from CdS to MoS2, which would remarkably weaken the photocorrosion. As a famous substitute for noble metal, multilayered MoS2 not only act as the protective shell for CdS NWs core by preventing the loss of sulphur but also can construct type-I junction with direct band gap CdS and provide large amount of hydrogen generation sites, which would significantly enhance the photocatalytic activity and stability. Consequently, the compactly-coated CdS@MoS2 core-shell composites show enhanced photocatalytic activity and stability for photocatalytic hydrogen production. Based on experimental results and mechanism analysis, we believe that the increased photocatalytic performance of CdS@MoS2 composites is accredited to valid separation and transmission of photoexcited electron-hole pairs. This hypothesis can be confirmed by photoelectrochemical tests. As displayed in Figure 6a, the clearly photocurrent response is detected for two samples under visible-light irradiation. It is worth noting that pristine CdS NWs show a quite low photocurrent density, while the transient photocurrent response is increased by about 35 times after compactly-coated with multilayered MoS2 shell. The photocurrent is primary decided by efficient separation of photoexcited holes and electrons within the photo-electrode.64 Hence,


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the improved photocurrent means that more effective charge separation and transmission were realized after forming the core-shell composites, which induced a prominent increment of photocatalytic performance in photocatalytic hydrogen process. Electrochemical impedance spectroscopy (EIS) was also performed to further prove above results. As shown in Figure 6b, the impedance radius of CdS@MoS2 is smaller than CdS, which suggests a smaller charge migration resistance across the interface between CdS and multilayered MoS2. Therefore, a remarkable increment of photocatalytic performance in photocatalytic hydrogen production can be predicted from the notable enhanced life-time and more effective separation of the photoinduced charge carriers. The above results of electronicchemistry indicate that the improved photocatalytic activity could be assigned to the decreasing recombination rate of photoinduced carriers, which could be also investigated by Photoluminescence (PL) measurement. As mirror in Figure 7, the PL emission spectra shows that pure CdS has strong PL and the wavelength of PL maximum for CdS is at 750 nm. Usually, two emissions of CdS were detected from trapped luminescence and semiconductor nanoparticles-excitonic.65-66 The PL peak at around 517 nm has an essential character while the peak at 750 nm is ascribed to surface states or trap.67-68 The peak at 750 nm detected from the prepared CdS is trap emission, which primarily because of the overmuch of interface sulfur.68 The nanowires should have more surface flaws for the high ratios (length/diameter). It is therefore rational to convince that the emission from the CdS NWs in our paper can be assigned to the above-mentioned surface states. In comparison, the emission intensity of pure CdS NWs is more intense than that of CdS@MoS2 composites under the uniform excitation power, which reveals that the high-efficiency migration of photogenerated holes and electrons between the CdS and MoS2. The results are corresponding to the exhibition


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of transient photocurrent responses and EIS measurements and the CdS@MoS2 composites exhibit a higher photo-performance.

4. Conclusions In summary, the CdS NWs @ multilayered MoS2 NSs core-shell composites was successfully prepared via the hydrothermal process. The CdS@MoS2 composites displayed an outstanding photocatalytic performance. The highest H2 production rate is 26.14 mmol h-1 g-1 when the loading amount of MoS2 was 50 wt%, which is about 2 times of CdS-Pt composites. By contrast to Pt load CdS, the stability of CdS@MoS2 is also improved. The compactly-coated core-shell structure and unique properties of multilayered MoS2 NSs are responsible for the improvement. Actually, the core-shell structure could provide the intimate contact interfaces which are beneficial to the high-efficiency migration and separation of the photoexcited electron/hole pairs. Simultaneous, mutilayered MoS2 not only can act as protective shell, but also could accept the photogenerated holes of CdS. It is believer that the progress of newfangled photo-catalyst with compactly-coated composites and the extensive light absorption, formed by composition of 2D and 1D nano-structures, is hopeful to the high-efficiency photocatalysis applications.

ASSOCIATED CONTENT Supporting Information. Additional experimental details and results. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author


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* E-mail: [email protected]. Tel: 0591-83779239.

ACKNOWLEDGMENT The work is supported by National Natural Science Foundation of China (21473031 and 21203026) and National Key Technologies R & D Program of China (2014BAC13B03).

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Evaporation

and

Their


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Figure Caption Figure 1 SEM image of (a) CdS NWs; (b)CdS@MoS2 composites; (c) HR-TEM image of CdS@MoS2 composites; (d) the corresponding SEAD pattern. Figure 2 Typical XRD patterns of bare CdS NWs; CdS@MoS2 composites. Figure 3 XPS spectra of CdS@MoS2 composites (a) Cd 3d; (b) S 2p; (c) Mo 3d; (d) DRS spectrogram of CdS@MoS2 composites and pristine CdS. Figure 4 Rate of H2 evolution on the (a) pristine CdS NWs, CdS@MoS2 (30 wt%), CdS@MoS2 (50 wt%), CdS@MoS2 (70 wt%) and pure MoS2; (b) CdS-Pt and CdS@MoS2 composites.; (c) Time-circle photocatalytic H2 evolution rate on CdS@MoS2 composites and the CdS-Pt; (d) Time-circle H2 evolution kinetics traces on the CdS-Pt and CdS@MoS2 composites. Reaction conditions: 0.02g photocatalysts; 100 ml solution containing 10 ml lactic acid; A 300W Xe Lamp with a 410 nm


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filter was used as the visible-light source. In the cycle measurement, the sacrificial reagents were no longer added. Figure 5 Schematic graph of the photoinduced holes and electrons migration in the CdS@MoS2 composites and photocatalytic hydrogen process under visible-light (λ＞410 nm). Figure 6 Photoelectrochemical properties of pristine CdS NWs and CdS@MoS2 composites. (a) Transient photocurrent responses in10 ml lactic acid + 10 ml H2O solution at 0.5 V vs. Ag/AgCl under visible-light (λ＞410 nm). (b) EIS Nyquist plots of the samples. Figure 7 Comparsion of the PL spectrogram for the pristine CdS and CdS@MoS2 composites. Scheme Scheme 1 Mechanism for the construction of CdS@MoS2 composites.


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Figure 1

Figure 2


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Figure 3

Figure 4


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Figure 5

Figure 6


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Figure 7

Scheme 1


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Contents graphic


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Simultaneous Realization of Enhanced Photoactivity and Promoted

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