Study On The Preparation And Performance Enhancement Mechanism Of Z-scheme Typed Zns-based Photocatalytic Material

As a typical semiconductor with a wide band gap,ZnS has been widely investigated in the fields of photocatalysts because of its high potential,simple preparation and lower price.However,it is limited by the inherently direct band gap resulting in the low production of photogenerated carriers,poor charge carrier mobility,and rapid charge recombination.At present,heterojunction engineering is considered to be a valid method to improve the efficiency of photocarrier separation.In view of it,we propose to construct Z-scheme typed ZnS-based photocatalytic materials to improve the separation efficiency of photogenerated carriers.Herein,sea-urchin-like ZnS/SnO2 and ZnS/GaOOH rods were successfully constructed.The results showed that Z-scheme heterostructure can lead to high oxidation and reduction potentials for ZnS-based photocatalytic materials and improve the separation efficiency of photogenerated carriers,thus the photocatalytic hydrogen production and photocatalytic degradation of organic pollutant were enhanced effectively.The main research results are summaried as follows:(1)Z-scheme typed ZnS/SnO2 photocatalyst was in-situ prepared by hydrothermal decomposition of ZnSn(OH)6 precursor in ZnCl2/Na2SnO3/CH4N2S/H2O system.The morphology and component of the product could be regulated effectively by controlling the hydrothermal time at 200℃.ZnS/SnO2 heterostructures with sea urchin shapes(The products were named as ZnS/SnO2-t,in which t was the hydrothermal time,and the unit is hour).The photocatalytic results of water splitting showed that the hydrogen production rate of ZnS/SnO2-4 sample was 2170 μmol-h-1·g-1,which was 15 times of pure ZnS.The superior photocatalytic activity of ZnS/SnO2-4 can be attributed to the matchable and stable interface between ZnS and SnO2 in ZnS/SnO2 heterostructure that by in situ synthesis.Besides,the Z-scheme formed in ZnS/SnO2 heterostructure,which not only led high oxidation reduction ability,but also improved the separation efficiency of photogenerated carriers,thus the photoreactivity was enhanced effectively.Furthermore,the effects of the acid radical ions in metal zinc salts on the microstructure and water splitting performance of the products were preliminarily explored.It was found that the ZnS/SnO2 heterostructure prepared by zinc acetate system had worse performance of water splitting than that prepared by zinc chloride system.The reason can be speculated that exposed crystal faces were different in SnO2.(2)Z-scheme typed ZnS/GaOOH photocatalysts were successfully prepared by hydrothermal method in ZnCl2/Ga(NO3)3/CH4N2S/H2O system.The morphology and component of the product can be regulated by controlling the hydrothermal time at 200℃.The heterojunctions were formed by ZnS spheres attaching on GaOOH rods gradually with hydrothermal time increasing(The products were named as ZnS/GaOOH-t,in which t was the hydrothermal time,and the unit is hour).The photocatalytic results of water splitting showed that the hydrogen production rate of ZnS/GaOOH-3 sample was higher than pure ZnS and GaOOH because of the high reduction potential in Z-scheme heterostructures.Moreover,the photocatalytic degradation of rhodamine B and tetracycline results showed that the degradation rates over ZnS/GaOOH-3 sample were 0.4594 min-1 and 0.0123 min-1,respectively,which were higher than pure ZnS and GaOOH.Moreover,the ZnS/GaOOH heterostructure exhibited an excellent stability of photocatalytic degradation.The photocatalytic degradation activity and stability of ZnS/GaOOH-3 can be attributed to the matchable and stable interface between ZnS and GaOOH in ZnS/GaOOH heterostructure.Besides,the Z-scheme formed in ZnS/GaOOH heterostructure,which not only led high oxidation ability,but also improved the separation efficiency of photogenerated carriers,thus the photoreactivity in degradation was enhanced effectively.