Preparation And Photocatalytic Properties Of 3D-g-C₃N₄-based Composite Photocatalysts

With the development of industrialization,water pollution is becoming more and more serious.In many water pollution control studies,photocatalytic technology has become one of the most effective methods to solve water pollution due to its characteristics of high efficiency,green,safety and sustainability.g-C₃N₄has been widely studied in energy and environment because of its unique electronic band structure,easy preparation and stable physicochemical properties.However,the disadvantages of low effective surface area and high recombination rate of photogenerated carriers,in addition,the material sheet-like easy stacking makes g-C₃N₄photocatalytic efficiency low,which hinders its practical application.How to improve the visible light photocatalytic activity of g-C₃N₄has become a hot topic in this field.The porous three-dimensional g-C₃N₄（3D-C₃N₄）was obtained by controlling the gas production during the preparation of the materials.Then,two heterojunction composites were obtained by coupling Bi₂WO₆and Ui O-66-NH₂with three-dimensional g-C₃N₄,respectively,thus increasing the specific surface area of the g-C₃N₄,simultaneously reducing its electron-hole recombination rate and improving its visible light utilization efficiency.The main elements are as follows:（1）Composite photocatalyst of 3D-C₃N₄/Bi₂WO₆:A porous three-dimensional g-C₃N₄（3D-C₃N₄）was prepared by simple hydrothermal and calcination using dinitrogen source as precursor,and then 3D-C₃N₄/Bi₂WO₆composite visible photocatalyst was prepared by in situ assembly.The structure,composition and properties of 3D-C₃N₄/Bi₂WO₆composites were characterized in detail.The visible-light photocatalytic degradation performance of tetracycline（TC）was studied.It was found that the degradation rate of 20%3D-C₃N₄/Bi₂WO₆composites was as high as 98%under 120 min of light,which was 2.2 times that of pure 3D-C₃N₄.This article further investigated the photocatalytic degradation performance of the catalyst to the actual wastewater.Within 12 h,the removal rate of COD in the actual wastewater reached 70%.The catalytic degradation mechanism of the materials was studied,it was found that the three-dimensional structure reduced the stacking of the lamellae,and the larger surface area was beneficial to the adsorption of pollutant molecules and provided more reactive sites.The close contact interface of the other two materials could improve the charge transfer rate,thus improving the electron-hole separation efficiency.（2）Composite photocatalyst of 3D-C₃N₄/Ui O-66-NH₂:The aminoated Zr metal MOFs material（Ui O-66-NH₂）was coupled with 3D-C₃N₄by in situ assembly to obtain 3D-C₃N₄/Ui O-66-NH₂composite photocatalysts.The structure,composition and photophysical properties of the materials were characterized by XRD、FT-IR、TEM、SEM、XPS、PL spectroscopy.The visible-light photocatalytic properties of p-nitrophenol（4-NP）and tetracycline（TC）were evaluated as model compounds.The degradation rates of p-nitrophenol（4-NP）and tetracycline（TC）were found to be 2.3and 2.5 times higher than 3D-C₃N₄in 180 min,respectively.And then,the COD removal of pharmaceutical and domestic wastewater was studied.After 12 h,the removal rate was about 73%and 66%,respectively;after 480 min,the mineralization rate of 60%3D-C₃N₄/Ui O-66-NH₂composites to pharmaceutical wastewater reached46%.The enhancement mechanism of its photocatalytic performance was studied,and it was found that the high surface area of the composite improved the adsorption of pollutants by the material.At the same time,the heterojunction interface made the electron hole separated effectively and made it have high photocatalytic performance.