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ZnO-dotted porous ZnS cluster microspheres for high efficient, Pt-free photocatalytic hydrogen evolution.

Wu A, Jing L, Wang J, Qu Y, Xie Y, Jiang B, Tian C, Fu H - Sci Rep (2015)

Bottom Line: Importantly, a series of the experiments and theoretical calculation demonstrate that the dotting of ZnO not only makes the photo-generated electrons/hole separate efficiently, but also results in the formation of the active catalytic sites for PHE.As a result, the PCMS-1 shows the promising activity up to 367 μmol h(-1) under Pt-free condition.The easy synthesis process, low preparation cost of the PCMS makes their large potential for Pt-free PHE.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of the People's Republic of China, Heilongjiang University, Harbin 150080 (P. R. China).

ABSTRACT
The Pt-free photocatalytic hydrogen evolution (PHE) has been the focus in the photocatalysis field. Here, the ZnO-dotted porous ZnS cluster microsphere (PCMS) is designed for high efficient, Pt-free PHE. The PCMS is designed through an easy "controlling competitive reaction" strategy by selecting the thiourea as S(2-) source and Zn(Ac)₂·2H₂O as Zn source in ethylene glycol medium. Under suitable conditions, one of the PCMS, named PCMS-1, with high SBET specific area of 194 m(2)g(-1), microsphere size of 100 nm and grain size of 3 nm can be obtained. The formation of PCMS is verified by TEM, XAES, XPS, Raman and IR methods. Importantly, a series of the experiments and theoretical calculation demonstrate that the dotting of ZnO not only makes the photo-generated electrons/hole separate efficiently, but also results in the formation of the active catalytic sites for PHE. As a result, the PCMS-1 shows the promising activity up to 367 μmol h(-1) under Pt-free condition. The PHE activity has no obvious change after addition 1 wt.% Pt, implying the presence of active catalytic sites for hydrogen evolution in the PCMS-1. The easy synthesis process, low preparation cost of the PCMS makes their large potential for Pt-free PHE.

No MeSH data available.


(a) XRD pattern, (b–e) TEM and HRTEM of PCMS-1; the f-i are TEM and HRTEM images of PCMS-2.5.
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f2: (a) XRD pattern, (b–e) TEM and HRTEM of PCMS-1; the f-i are TEM and HRTEM images of PCMS-2.5.

Mentions: The PCMS were prepared through an easy one-pot “controlling competitive reaction” strategy in EG. A typical sample, PCMS-1, was prepared at 180°C for 12 h with MR 1:1 of thiourea and Zn(Ac)2. The XRD pattern of PCMS-1 can be indexed to the hexagonal zinc sulfide (No. 80-0007), and no other phase is found (Figure 2a). The size of the sphere is about 100 nm with good uniform both in the size and morphology (Figure 2b). The images in Figure 2c, d confirm that the spheres are composed of the small clusters of 3 nm. The small grain is favorable for the transfer of e− from the interior to surface of catalysts, thus enhancing the PHE activity29. The high-resolution TEM image (Figure 2d) shows the lattice fringe of 0.31 nm that is an inter-planar distance of the (002) plane of hexagonal ZnS. In addition, the pores from the accumulation of the small particle can be observed. The porous structure and small size of particles implies the high surface area of the PCMS-1. Indeed, the N2 adsorption-desorption test indicates a high BET surface area (SBET) of 194 m2/g of the sample (Figure S1 and Table S1). The porous structure with high SBET can provide the highly accessible interface for efficient injection of photo-generated e−, and allow light-scattering inside the pore, thus enhance the activity of materials3031. In present system, the presence of ZnO is quite possible because of the formation of ZnO and ZnS is competive reaction. However, no evidence for the formation of the ZnO is observed both in XRD and TEM tests. This should be due to the very small size and/or amount of ZnO components that are difficult to be detected by TEM and XRD test. Therefore, the X-ray energy dispersive spectrometry (EDS) element mapping is done to analyze the element composition of the PCMS-1. The EDS mapping indicates the homogeneous distribution of Zn, S and O elements throughout the sphere, implying the presence of ZnO in the PCMS-1 homogeneously (Figure S2). By changing the MR value, we can also obtain the PCMS with similar microstructure and crystalline orientation. Typically, the porous microspheres with sphere size of 70 nm and grain size of 5 nm can be obviously seen in PCMS-2.5 sample (Figure 2f to i).


ZnO-dotted porous ZnS cluster microspheres for high efficient, Pt-free photocatalytic hydrogen evolution.

Wu A, Jing L, Wang J, Qu Y, Xie Y, Jiang B, Tian C, Fu H - Sci Rep (2015)

(a) XRD pattern, (b–e) TEM and HRTEM of PCMS-1; the f-i are TEM and HRTEM images of PCMS-2.5.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4352920&req=5

f2: (a) XRD pattern, (b–e) TEM and HRTEM of PCMS-1; the f-i are TEM and HRTEM images of PCMS-2.5.
Mentions: The PCMS were prepared through an easy one-pot “controlling competitive reaction” strategy in EG. A typical sample, PCMS-1, was prepared at 180°C for 12 h with MR 1:1 of thiourea and Zn(Ac)2. The XRD pattern of PCMS-1 can be indexed to the hexagonal zinc sulfide (No. 80-0007), and no other phase is found (Figure 2a). The size of the sphere is about 100 nm with good uniform both in the size and morphology (Figure 2b). The images in Figure 2c, d confirm that the spheres are composed of the small clusters of 3 nm. The small grain is favorable for the transfer of e− from the interior to surface of catalysts, thus enhancing the PHE activity29. The high-resolution TEM image (Figure 2d) shows the lattice fringe of 0.31 nm that is an inter-planar distance of the (002) plane of hexagonal ZnS. In addition, the pores from the accumulation of the small particle can be observed. The porous structure and small size of particles implies the high surface area of the PCMS-1. Indeed, the N2 adsorption-desorption test indicates a high BET surface area (SBET) of 194 m2/g of the sample (Figure S1 and Table S1). The porous structure with high SBET can provide the highly accessible interface for efficient injection of photo-generated e−, and allow light-scattering inside the pore, thus enhance the activity of materials3031. In present system, the presence of ZnO is quite possible because of the formation of ZnO and ZnS is competive reaction. However, no evidence for the formation of the ZnO is observed both in XRD and TEM tests. This should be due to the very small size and/or amount of ZnO components that are difficult to be detected by TEM and XRD test. Therefore, the X-ray energy dispersive spectrometry (EDS) element mapping is done to analyze the element composition of the PCMS-1. The EDS mapping indicates the homogeneous distribution of Zn, S and O elements throughout the sphere, implying the presence of ZnO in the PCMS-1 homogeneously (Figure S2). By changing the MR value, we can also obtain the PCMS with similar microstructure and crystalline orientation. Typically, the porous microspheres with sphere size of 70 nm and grain size of 5 nm can be obviously seen in PCMS-2.5 sample (Figure 2f to i).

Bottom Line: Importantly, a series of the experiments and theoretical calculation demonstrate that the dotting of ZnO not only makes the photo-generated electrons/hole separate efficiently, but also results in the formation of the active catalytic sites for PHE.As a result, the PCMS-1 shows the promising activity up to 367 μmol h(-1) under Pt-free condition.The easy synthesis process, low preparation cost of the PCMS makes their large potential for Pt-free PHE.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of the People's Republic of China, Heilongjiang University, Harbin 150080 (P. R. China).

ABSTRACT
The Pt-free photocatalytic hydrogen evolution (PHE) has been the focus in the photocatalysis field. Here, the ZnO-dotted porous ZnS cluster microsphere (PCMS) is designed for high efficient, Pt-free PHE. The PCMS is designed through an easy "controlling competitive reaction" strategy by selecting the thiourea as S(2-) source and Zn(Ac)₂·2H₂O as Zn source in ethylene glycol medium. Under suitable conditions, one of the PCMS, named PCMS-1, with high SBET specific area of 194 m(2)g(-1), microsphere size of 100 nm and grain size of 3 nm can be obtained. The formation of PCMS is verified by TEM, XAES, XPS, Raman and IR methods. Importantly, a series of the experiments and theoretical calculation demonstrate that the dotting of ZnO not only makes the photo-generated electrons/hole separate efficiently, but also results in the formation of the active catalytic sites for PHE. As a result, the PCMS-1 shows the promising activity up to 367 μmol h(-1) under Pt-free condition. The PHE activity has no obvious change after addition 1 wt.% Pt, implying the presence of active catalytic sites for hydrogen evolution in the PCMS-1. The easy synthesis process, low preparation cost of the PCMS makes their large potential for Pt-free PHE.

No MeSH data available.