Design,synthesis And Photocatalytic Properties Study Of Bi₂WO₆-based Composite

The global energy structure continues to evolve,and the energy intensity demand brings serious environmental problems,especially the organic wastewater is biodegradable.Traditional treatment pathways,such as precipitation separation and adsorption separation,cannot be effectively eliminated.Modern technology is based on the heterogeneous photocatalytic reaction process of semiconductors and the activation of the catalyst directly under sunlight to drive the oxidation-reduction reaction.It is an ideal environmental pollution control by using a heterogeneous photocatalytic reaction system to convert resource-rich light energy into chemical energy to achieve 100%mineralized toxic organic waste liquid or organic waste gas without causing secondary environmental pollution technology.A photocatalyst represented by TiO₂ has a narrow range corresponding to light,at the same time,it is limited to the ultraviolet light region and low quantum efficiency.At present,many studies have focused on the synthesis of photocatalysts with good absorbance,high quantum efficiency,high stability,large specific surface area,and easy recovery,which have high photocatalytic efficiency.Among many catalytic materials,bismuth-based composite materials,especially bismuth tungstate-based modified materials,are formed by the cross-stacking of perovskite type（WO₆）^2-layer and[Bi₂O₂]²⁺.The valence band is composed of hybrid structure of Bi 6s orbital and O 2p orbital,the valence band is composed of W 5d orbital to make unique structure and excellent visible light catalytic performance.The modification synthesis and properties of bismuth tungstate nanomaterials have also become one of the hotspots of photocatalytic materials research.In this paper,g-C₃N₄/PPy/Bi₂WO₆ ternary flower-like composite material and Bi₂WO₆/TiO₂ binary nano-belt composite material were successfully prepared by solvothermal method.The structural growth mechanism and photocatalytic properties of the two composites were systematically studied.The master’s research work mainly includes the following two parts:（1）The bismuth nitrate and sodium tungstate were used as the source of bismuth and tungsten respectively.The g-C₃N₄/PPy/Bi₂WO₆ composite with flower-like structure was successfully prepared by hydrothermal method using PPy,g-C₃N₄ and Bi₂WO₆ material.Among them,melamine（C₃H₆N₆）was used as raw material to prepare graphite phase carbon nitride（g-C₃N₄）nanosheets by heat-shrink polymerization;polypyrrole（PPy）was prepared by chemical oxidation method using pyrrole as monomer.The morphology,structure and absorbance of g-C₃N₄/PPy/Bi₂WO₆ were studied by XRD,SEM,TEM,BET,FT-IR,XPS and DRS.The flower-like g-C₃N₄/PPy/Bi₂WO₆ was modified on the nanosheet of 3D Bi₂WO₆ flower sphere by g-C₃N₄ nanoparticles with diameter of 25 nm and PPy particles with diameter of 100-200 nm,and the flower sphere size was about 3-5μm.We explored its growth principle and found that Ostwald ripening is the key to the formation of flower-like structures.Finally,the efficiency of degradation of rhodamine B under visible light was evaluated and compared with g-C₃N₄,Bi₂WO₆,PPy/Bi₂WO₆,PPy/g-C₃N₄,g-C₃N₄/Bi₂WO₆ samples to explore the influence of polymer materials on the photocatalytic properties of composites.The experimental results show that PPy acts as a charge transport bridge between g-C₃N₄ and Bi₂WO₆ in multi-component composites.Z system retains electrons with high reducing ability and Bi₂WO₆ valence band in g-C₃N₄ conduction band（CB）.Among the holes with high oxidizing power,the photocatalytic effect of Z system g-C₃N₄/PPy/Bi₂WO₆ under visible light is better than that of g-C₃N₄,Bi₂WO₆,PPy/Bi₂WO₆,PPy/g-C₃N₄,g-C₃N₄/Bi₂WO₆ samples.（2）TiO₂ nanobelts were prepared by self-assembly using P25 nanoparticles in three steps:alkaline hydrothermal method,acid treatment and thermal annealing.The Bi₂WO₆/TiO₂nanobelts were prepared by solvothermal method and Bi³⁺successfully supported on the surface of TiO₂ by solvothermal method.The effect of different Bi₂WO₆ molar content on Bi₂WO₆/TiO₂heterojunction was investigated by evaluating the degradation efficiency of Rhodamine B（RhB）under ultraviolet light and visible light.When Bi₂WO₆ and TiO₂ are at the optimal molar ratio,the heterojunction effect optimizes the photocatalytic performance.Under visible light irradiation,when the molar ratio of Bi₂WO₆:TiO₂ is 0.3:1,50 mg of Bi₂WO₆/TiO₂ catalyst degraded 60%of RhB（25 mg/L）in 150 min.