Electronic Supplementary Material (ESI) for Energy & Environmental Science. This journal is The Royal Society of Chemistry 2014 Supporting Information CdS/mesoporous ZnS core/shell particles for efficient and stable photocatalytic hydrogen evolution under visible light Ying Peng Xie, Zong Bao Yu, Gang Liu,* Xiu Liang Ma and Hui-Ming Cheng* Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua RD, Shenyang 110016, China E-mail: gangliu@imr.ac.cn; cheng@imr.ac.cn Sample preparation procedure. Preparation of CdS/ZnS core/shell particles by a hydrothermal process. The CdS/ZnS core/shell particles were synthesized by a one-pot hydrothermal process. Different amounts (250 mg, 500 mg, 1000 mg and 2000 mg) of zinc oxide (ZnO) suspension (50 wt% in water, ZnO with a size of 50-100 nm, Aldrich), 460 mg of cadmium acetate dihydrate (Cd(CH 3 CO 2 ) 2 2H 2 O), and 660 mg of thiourea (CH 4 N 2 S) were added in 20 ml of deionized water under stirring to form a suspension. The suspension was then transferred to a Teflon-lined autoclave with a volume of 80 ml, and treated at 180 o C for 2 h. After the reaction, a yellow CdS/ZnS product was collected by centrifugation and washed with deionized water several times to remove dissolvable ionic impurities. The sample was then dried at 80 o C in air. Heating the obtained CdS/ZnS core/shell particles at 500 o C in an argon atmosphere led to the collapse of mesoporous structure of the shell. In control experiments, CdS and ZnS were prepared by the same procedure but without the addition of ZnO or Cd(CH 3 CO 2 ) 2 2H 2 O, and Zn x Cd 1-x S (x = 0.27) solid solution was synthesized by the same procedure but with the replacement of ZnO with Zn(CH 3 CO 2 ) 2 2H 2 O. Co-catalyst Pt or PdS loading on the CdS/ZnS core/shell structure. Pt loading was conducted by an impregnation method in an aqueous solution of H 2 PtCl 6 6H 2 O. 300 mg of the CdS/ZnS powder was added to 20 ml of an aqueous solution containing the desired amount of H 2 PtCl 6 6H 2 O (1 wt% Pt vs. CdS/ZnS) in an evaporating dish at 80 o C. The suspension was evaporated under stirring, and the resultant powder was collected and heated at 180 o C for 2 h. PdS loading was conducted by chemical deposition as follows. 300 mg of the CdS/ZnS powder was suspended in 20 ml of an aqueous solution containing the desired amount of PdCl 2 (1 wt% PdS vs. CdS/ZnS). The suspension was stirred for 0.5 h and then 1 ml 0.02 M Na 2 S aqueous solution was added to the suspension. After the chemical deposition, the product was collected by centrifugation and washed with deionized water several times to remove dissolvable ionic impurities. The sample was dried at 80 o C in air. Photodeposition of Pt or PbO 2 on ZnS, CdS and the CdS/ZnS core/shell structure. 200 mg of ZnS, CdS or the obtained CdS/ZnS powder was suspended in 20 ml water/methanol solution (1/1 in volume) S1
containing H 2 PtCl 6 6H 2 O (1 wt% Pt vs. ZnS, CdS or CdS/ZnS). The suspension was stirred for 0.5 h and then exposed to visible light ( > 400 nm) for 1 h. 200 mg of ZnS, CdS or the CdS/ZnS powder was suspended in 20 ml water containing Pb(NO 3 ) 2 (1 wt% PbO 2 vs. ZnS, CdS or CdS/ZnS). The suspension was stirred for 0.5 h and then exposed to visible light ( > 400 nm) for 1 h. After photodeposition, the products were collected by centrifugation and washed with deionized water several times to remove dissolvable ionic impurities. The sample was dried at 80 o C in air. Characterization. X-ray diffraction patterns of the samples were recorded on a Rigaku diffractometer using Cu irradiation (λ = 1.54056 Å). The sample morphology was determined by scanning and transmission electron microscopy performed on Nova NanoSEM 430 and Tecnai F20 electron microscopes, respectively. The Tecnai F20, equipped with high-angle-angular-dark-field detector and energy X-ray dispersive spectroscopy systems, was also used for Z-contrast imaging and composition mapping analysis. The Brunauer-Emmett-Teller surface area was determined by nitrogen adsorptiondesorption isotherm measurements at 77 K (ASAP 2020). The optical absorbance spectra of the samples were recorded in a UV-visible spectrophotometer (JASCO-550). Chemical composition and chemical state of the samples were analyzed using X-ray photoelectron spectroscopy (Thermo Escalab 250, a monochromatic Al Kα X-ray source). All binding energies were referenced to the C 1s peak (284.6 ev) arising from adventitious carbon. Photoluminescence emission and photoluminescence decay spectra were recorded at room temperature with a fluorescence spectrophotometer (Edinburgh Instruments, FLSP-920). Hydrogen evolution measurements. Photocatalytic water splitting reactions were carried out in a topirradiation vessel connected to a glass enclosed gas circulation system. 100 mg of the photocatalyst powder was dispersed in 270 ml aqueous solution of 0.1 M Na 2 SO 3 and 0.1 M Na 2 S as the sacrificial reagents. The light source was a 300 W Xe lamp (Beijing Trusttech Co. Ltd, PLS-SXE-300UV). A cutoff filter of 400 nm was used for the visible light irradiation. The reaction temperature was maintained around 20 C. The amount of H 2 evolved was determined using a Shimadzu gas chromatography system (GC-2014). S2
: ZnO : CdS : ZnS 2.0 h 1.5 h 1.0 h 0.5 h b 0.5 h 20 30 40 50 60 70 2-Theta / degree 1.0 h 1.5 h Fig. S1 XRD patterns and SEM images of the intermediate solid products during the hydrothermal synthesis of CdS/ZnS core/shell structure at 180 o C for 0.5 h, 1.0 h, 1.5 h (and 2.0 h). S3
(a) 20 30 40 50 60 2-Theta / degree (b) (c) 10 μm 2 μm Fig. S2 (a) XRD pattern, and (b), (c) SEM images of the Zn x Cd 1-x S solid solution (x = 0.27). The XRD pattern of Zn 0.73 Cd 0.27 S synthesized in our case is similar to that of Zn 0.8 Cd 0.2 S in the literature (Nonferrous Met. Soc. China, 2011, 21, 1767) S4
a b 1 μm e 1 μm 20 nm d 1 μm g f 200 nm i c 1 μm h 200 nm g k l 50 nm. 50 nm 50 nm Fig. S3 (a)-(d) SEM and (e)-(h) TEM images of the CdS/ZnS core/shell particles synthesized by using different amounts (250 mg, 500 mg, 1000 mg and 2000 mg) of ZnO dispersion in the reaction system. The corresponding TEM images of single CdS/ZnS core/shell particle of each sample are shown in (i)-(l). With increasing the amount of ZnO precursor in the reaction system from 250 mg to 500 mg, 1000 mg and 2000 mg, the thickness of ZnS shell increases from ~20 nm to ~50 nm, ~90 nm and ~100 nm. On the contrary, the diameter of CdS core gradually decreases from ~150 nm to 60 nm. S5
a (100) (101) (002) (200) (103) (004) (201) (112) (202) (203) (210) (211) (114) (105) (110) (102) 20 30 40 50 60 70 80 b 2-Theta / degree 400 nm Fig. S4 (a) XRD pattern and (b) SEM image of the synthesized hexagonal CdS. S6
a (111) (100) (002) (200) (101) (220) (102) (311) (110) (400) ZnS ZnO (103) (200) (112) (201) (004) (331) (202) 20 30 40 50 60 70 80 2-Theta / degree b ZnO c ZnS Fig. S5 (a) XRD patterns and (b, c) SEM images of the ZnO precursor and synthesized cubic ZnS. H 2 evolution / mol g -1 8000 6000 4000 2000 0 250 mg 500 mg 1000 mg 2000 mg 0 2 4 6 8 10 Time / h Fig. S6 Hydrogen evolution as a function of time from an aqueous solution containing Na 2 S and Na 2 SO 3 by CdS/ZnS core/shell particles synthesized with different amounts (250 mg, 500 mg, 1000 mg and 2000 mg) of ZnO suspension in the reaction system. The average hydrogen evoluton rate of each sample is 259, 513, 792 and 633 µmol h -1 g-1. S7
a b After H 2 evolution reaction Before H 2 evolution reaction 20 30 40 50 60 70 80 2-Theta / degree Fig. S7 (a) SEM image of the CdS/ZnS heterostructure after 60-hour photocatalytic H 2 evolution; (b) XRD patterns of the CdS/ZnS heterostructure before and after the 60-hour photocatalytic H 2 evolution. S8
a Volume adsorbed / cm 3 g -1 60 50 40 30 20 10 0 Adsorption of CdS-ZnS Desorption of CdS-ZnS Adsorption of CdS-ZnS-500 Desorption of CdS-ZnS-500 0.0 0.2 0.4 0.6 0.8 1.0-1 Relative pressure / pp 0 b 0.010 Pore volume / cm 3 g -1 nm -1 0.008 0.006 0.004 0.002 0.000 CdS-ZnS CdS-ZnS-500 0 10 20 30 40 50 Pore diameter / nm c d 1 μm 200 nm Fig. S8 (a) Nitrogen adsorption-desorption isotherms and (b) pore size distribution curves of CdS/ZnS particles before/after heating at 500 o C in argon atmosphere; (c) SEM and (d) TEM images of the heated CdS/ZnS particles. 3000 H 2 evolution / mol g -1 2000 1000 0 0 2 4 6 8 10 Time / h Fig. S9 Hydrogen evolution as a function of irradiation time from an aqueous solution containing Na 2 S/Na 2 SO 3 agents by the heated CdS/ZnS core/shell particles at 500 o C in argon. S9
H 2 evolution / mol g -1 20000 15000 10000 5000 0 CdS/ZnS CdS/ZnS after loading Pt CdS/ZnS after loading PbS 0 1 2 3 4 5 6 7 Irradiation time / h Fig. S10 Hydrogen evolution as a function of time from an aqueous solution containing Na 2 S and Na 2 SO 3 by CdS/ZnS, CdS/ZnS with Pt loading and CdS/ZnS with PbS loading where Pt and PdS co-catalysts were loaded by the thermal-deposition and chemical-deposition, respectively. Ex: 470 nm 500 550 600 650 700 750 800 Wavelength / nm Fig. S11 Fluorescence emission spectrum of ZnS recorded at room temperature. The wavelength of the excitation light is 470 nm. S10
Absorbance / a.u. ZnS CdS/ZnS CdS 200 300 400 500 600 700 800 900 Wavelength / nm Fig. S12 UV-visible absorption spectra of ZnS, CdS and ZnS/CdS particles. Table S1 Summary of the photoluminescence decay time (τ) and their relative amplitude (f) in CdS, CdS/ZnS, PdS (1 wt%)-cds/zns and Pt (1 wt%)-cds/zns derived from the time-resolved photoluminescence spectroscopy (Fig. 8) by triexponential decays. Sample Decay time (ns) Relative amplitude (%) Average χ 2 τ 1 τ 2 τ 3 f 1 f 2 f 3 lifetime (<τ>, ns) a CdS 21.12 164.78 1141.18 9.55 28.28 62.17 1078.18 1.093 CdS/ZnS 11.62 100.92 825.36 14.61 32.85 52.54 771.15 1.172 PdS (1 wt%)- CdS/ZnS 8.36 74.58 712.91 19.17 35.69 45.14 661.14 1.115 Pt (1 wt%)- CdS/ZnS 9.02 103.26 1025.89 7.35 23.81 68.84 993.96 1.143 a The average lifetime was calculated using equation: <τ> = (f 1 τ 1 2 + f 2 τ 2 2 + f 3 τ 32 )/ (f 1 τ 1 + f 2 τ 2 + f 3 τ 3 ) χ 2 : the goodness of fit parameter. S11