Preparation,characterization And Properties Of Ag₃PO₄-based Semiconductor Composite Photocatalytic Materials

As a kind of "green" technology,semiconductor photocatalysts have great potential in environmental purification and energy conversion.Although the traditional photocatalysts,such as TiO2,have good photocatalytic activity and stability,they can not be widely used due to their wide band gap.In recent years,silver-based photocatalysts,such as AgX,Ag₂ O,Ag₂CO3 and Ag₃PO₄,have been developed and applied in photocatalytic degradation of organic and oxygen evolution.Ag₃PO₄ has been envisioned as one of the most promising photocatalysts for purifying environment and cleaning energy production due to its excellent photocatalytic ability for water splitting and degrading organic contaminants.However,Ag₃PO₄ is slightly soluble in water,and it is prone to photo-corrosion under visble light,so it is rarely used in practical areas.The efficient solar energy utilization,encanced oxidation ability and improved photo-stability of single semiconductor materials could be achieved in Z-scheme system,in which progress the generated-hole from the photo-reduction catalyst and the electron from the photo-oxidation catalyst could recombine at the electron transport medium,remaining more positive oxidation potential and negative reduction potential.In this paper,from the perspective of energy band structure and Z-scheme principle,a novel Z-scheme system for the photocatalytic water splitting reaction over Ag₂MoO₄/Ag₃PO₄,GO/Ag₂MoO₄/Ag₃PO₄ and g-C₃N₄/Ag₂MoO₄/Ag₃PO₄ composites were constructed for the first time.The aim is to improve the photocatalytic stability and photoactivity of Ag₃PO₄ through the combination with other semiconductor materials.The structure,morphology,optical absorption capacity and the separation efficiency of photogenerated carriers of the composites were also explored.The main research contents are as follows:?1?On the base of semiconductor coupling technology,the high-efficiency visible-light-driven Z type Ag₂MoO₄/Ag₃PO₄ semiconductor photocatalysts were prepared by a facile solution reaction method by regulating the molar ratio of MoO3 and AgNO3.The morphology and structure were studied by SEM,TEM,XRD,FTIR and BET,the photocatalytic efficiency of degradation for organic pollutants and oxygen evolution from water splitting.The photocurrent and EIS experiments were carried out to analyze the separation and transmission efficiency of photogenerated carriers.Research shows that Ag nanoparticles formed on the surface of Ag₃PO₄/Ag₂MoO₄ in the early stage of the photocatalytic reaction act as a Z-scheme charge transmission bridge,improving the separation efficiency of photogenerated carriers,thus greatly improving the photocatalytic activity and photostability.?2?On the basis of energy band matching principle,a series of Z-scheme g-C₃N₄/Ag₂MoO₄/Ag₃PO₄ composites were prepared by solid state and precipitation method using g-C₃N₄ as precursor.The morphology,microstructure and valency were analyzed by comprehensivly using various test methods and the effects of different g-C₃N₄ addition on oxygen evolution efficiency of water splitting under visible light were discussed.The photocatalytic mechanism of the composites was revealed through photocurrent,EIS,PL and ESR.It was found that the synergistic effect of Z type g-C₃N₄/Ag/Ag₃PO₄ and Z type Ag₂MoO₄/Ag/Ag₃PO₄ in the double Z-scheme configuration can effectively prevent the recombination of photogenerated electrons and holes and improve the separation efficiency of electrons and holes.?3?The GO/Ag₂MoO₄/Ag₃PO₄ photocatalysts were prepared by simple precipitation method using GO as precursor.The morphology,structure and optical absorption of the composites were analyzed by SEM,TEM,XRD,XPS and DRS,and the effects of GO addition on oxygen evolutions from photocatalytic water splitting were discussed.The separation and transport efficiency of electron-hole pair of GO/Ag₂MoO₄/Ag₃PO₄ were analyzed by photocurrent,EIS and PL.Electron spin resonance?ESR?spectroscopy was used to analyze the formation of active groups in the photocatalytic process.Due to the special electronic structure of graphene,photogenerated electron in the GO/Ag₂MoO₄/Ag₃PO₄ photocatalyst can easily transfer in photocatalytic process,so that the photogenerated electrons and holes can be separated effectively,so the quantum efficiency of photocatalysts can be further improved.