Study On Co?dmgH?₂PyCl As Noble-metal-free Co-catalyst For ZnIn₂S₄ Photocatalytic Water Splitting System

Hydrogen is known as a clean and efficient energy,which is considered as a promising alternative to fossil fuels.Semiconductor-based Photocatalysis is one of the most ideal technologies in production of hydrogen.ZnIn2S4 has attracted much attention in photocatalytic hydrogen production due to its suitable band gap.Usually noble metal nanoparticles like Pt should be deposited in ZnIn2S4 as a co-catalyst for efficient hydrogen production.In order to reduce the cost of semiconductor photocatalytic hydrogen production,the development of some new,inexpensive and efficient co-catalyst is necessary.In this paper,we choose the ternary chalcogenide ZnIn2S4 as research object.According to the structure characteristic of ZnIn2S4,we modified the study object that introduced non-noble-metal as co-catalyst loaded on the surface of ZnIn2S4.The composition and structures,photoresponse,and band structures of the photocatalysts are characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),UV-Vis diffuse reflectance spectroscopy(UV-Vis DRS)and Fourier-transform infrared spectroscopy(FT-IR)techniques.The main contents obtained from the present research are as follows:(1)Co(dmgH)2pyCl/ZnIn2S4 composites(dmgH = dimethylglyoxime and py = pyridine)with different amount of Co(dmgH)2pyCl loaded were prepared from hexagonal ZnIn2S4 and Co(dmgH)2pyCl via an impregnation method.The photocatalytic activity for hydrogen evolution over the as-prepared Co(dmgH)2pyCl/ZnIn2S4 composites under visible light irradiations was investigated.It was found that the hydrogen evolution over hexagonal ZnIn2S4 can be significantly increased by loading Co(dmgH)2pyCl as a co-catalyst.An optimum activity was achieved over 3.0 wt%-Co(dmgH)2pyCl/ZnIn2S4 composite,with 1438.5 ?mol hydrogen generated and a turnover number of 387(based on Co(dmgH)2pyCl)reached in 8 h visible light irradiations.This value is much higher than that obtained over Pt loaded ZnIn2S4 under similar conditions,indicating that Co(dmgH)2pyCl can be a highly efficient noble-metal-free co-catalyst for photocatalytic hydrogen evolution over hexagonal ZnIn2S4.This work pave a way to the development of highly efficient noble-metal-free photocatalytic systems for hydrogen evolution.(2)Co/CQDs/ZnIn2S4 composite was prepared by a facile microwave hydrothermal method,in which method carbon quantum dots(CQDs)with strong electron transport ability was successfully coupled with Co(dmgH)2pyCl/ZnIn2S4 composites.The photocatalytic activity for hydrogen evolution over the as-prepared Co/CQDs/ZnIn2S4 composites under visible light irradiations was investigated.An optimum activity was achieved over Co/CQDs/ZnIn2S4 composites loaded with 1.0 wt%of Co(dmgH)2PyCl and 5.0 wt%of CQDs.It was found that the Co/CQDs/ZnIn2S4 composite exhibited much higher visible-light photocatalytic H2 production activity than CQDs/ZnIn2S4 composites and Co(dmgH)2pyCl/ZnIn2S4 samples,and which is about 21 times of that over pure ZnIn2S4 under otherwise similar condition.This indicates that CQDs can significantly promote the photocatalytic hydrogen evolution over Co(dmgH)2pyCl/ZnIn2S4 composite.This is mainly attributed to the good electrical conductivity of CQDs and the presence of CQDs also resulted in the enhancement of light absorption intensity of Co(dmgH)2pyCl/ZnIn2S4 composites.