Preparation And Characterization Of Novel Heterojunction Composite Photocatalysts And Its Photocatalytic Degradation Of Organic Pollutants In Industrial Wastewater

In recent years,with rapid industrialization and population explosion,global environmental pollution has become increasingly serious.Photocatalytic technology is easy to operate,green and environmentally friendly.It can directly use the energy of sunlight to completely mineralize organic pollutants in toxic industrial wastewater without secondary pollution.It is an ideal choice to solve environmental problems.According to the electronic structure and unique light absorption properties of heterojunction catalytic materials,it is an important research direction in the field of photocatalysis to make full use of rare earth resources in China and prepare visible light responsive heterojunction catalysts with high catalytic activity.In this paper,according to the characteristics of heterojunction photocatalyst,three heterojunction composite visible light catalysts were constructed by constructing Z-type heterojunction to solve the above problems.This paper explores the controllable preparation and performance characterization of photocatalyst,explores the catalytic performance of the composite photocatalyst heterojunction,the relationship between microscopic structure and photocatalytic activity,in-depth analysis of the heterojunction structure,morphology,optical light was born in the process of catalytic reaction carrier in the interface and the efficiency of the composite influence mechanism.The specific research contents and results are as follows:（1）a novel Gd₂Bi Ta O₇nano-catalyst was synthesized by high temperature solid-phase method,and the heterostructure photocatalyst composed of Gd₂Bi Ta O₇ and silver phosphate was prepared by simple in situ precipitation method for the first time.The photocatalytic properties of Gd₂Bi Ta O₇ and Ag₃PO₄/Gd₂Bi Ta O₇ heterojunction photocatalysts were studied.Gd₂Bi Ta O₇ and Ag₃PO₄/Gd₂Bi Ta O₇ heterojunction photocatalysts were investigated by X-ray diffrotometer,Scanning electron microscope-X-ray energy dispersive spectroscopy,X-ray photoelectron spectroscopy,synchrotron ultraviolet photoelectron spectroscopy,Fourier transform infrared spectrometer,UV-visible diffuse reflectance spectrometer and electron paramagnetic resonance spectrometer.The structural properties were characterized.The results show that Gd₂Bi Ta O₇ crystallizes well and has stable cubic crystal system and space group Fd3m.The lattice parameters and bandgap energies of Gd₂Bi Ta O₇ are a=10.740051?and 2.35 e V,respectively.After30 minutes of visible light irradiation,the removal rate of BISphenol A was 99.52%with Ag₃PO₄/Gd₂Bi Ta O₇ heterojunction photocatalyst,95.53%with Ag₃PO₄ and potassium persulfate（AP-PS）as photocatalyst.The removal rate of Bisphenol A using N-doped Ti O₂ as photocatalyst was 37.00%.According to the experimental data,it could be found that the removal rate of Bisphenol A by Ag₃PO₄/Gd₂Bi Ta O₇heterogeneous photocatalyst was 2.69 times that of N-Ti O₂ photocatalyst.Compared with Gd₂Bi Ta O₇,AP-Ps and N-Ti O₂,Ag₃PO₄/Gd₂Bi Ta O₇ heterojunction showed higher photocatalytic activity for the photocatalytic degradation of BPA under visible light irradiation.After 30 minutes of visible light irradiation,the removal rate of total organic carbon was 96.21%with Ag₃PO₄/Gd₂Bi Ta O₇ heterocatalysts,88.10%with AP-PS and30.55%with N-Ti O₂ photocatalysts.The results show that the Ag₃PO₄/Gd₂Bi Ta O₇heterojunction has the highest mineralization rate during the degradation of Bisphenol A.During the degradation of BPA,the main oxidizing free radical was-OH.The photocatalytic degradation of Bisphenol A with Ag₃PO₄/Gd₂Bi Ta O₇ heterojunction as photocatalyst conforms to the first-order kinetics.（2）The novel A₂B₂O₇ compounds Ga₂Yb Sb O₇ and Yb₂Bi Sb O₇ nanocatalysts were synthesized by high temperature solid-state method for the first time.Ga₂Yb Sb O₇/Fe₂Bi Ta O₇ heterojunction photocatalyst was synthesized by hydrothermal method,and Yb₂Bi Sb O₇/Cd Bi YO₄ heterojunction photocatalyst was synthesized by in-situ precipitation method.The structural characteristics of Ga₂Yb Sb O₇ and Yb₂Bi Sb O₇ catalysts were characterized.The results show that the two A₂B₂O₇compounds have good crystallization,pyroclase structure,stable cubic crystal system and space group Fd3m.Moreover,the lattice parameter of Yb₂Bi Sb O₇ was a=10.492749?,and the band gap energy of Yb₂Bi Sb O₇ was 2.377 e V.The lattice parameters and bandgap energies of Ga₂Yb Sb O₇ was a=10.457113?or 2.772 e V,respectively.After 140 minutes of visible light irradiation,the removal rate of methyl orange（MO）reached 98.90%with Yb₂Bi Sb O₇/Cd Bi YO₄ heterojunction and 99.66%with methylene blue（MB）with Ga₂Yb Sb O₇/Fe₂Bi Ta O₇ heterojunction as photocatalyst.The total organic carbon（TOC）removal rate of Yb₂Bi Sb O₇/Cd Bi YO₄ heterogeneous photocatalyst was 94.12%,and that of Ga₂Yb Sb O₇/Fe₂Bi Ta O₇ heterogeneous photocatalyst was 93.61%.In addition,with Yb₂Bi Sb O₇/Cd Bi YO₄ heterojunction as photocatalyst,the kinetic constant K obtained from the dynamic curves of MO concentration and visible light irradiation time reaches 0.02433 min^-1.When Ga₂Yb Sb O₇/Fe₂Bi Ta O₇ heterojunction was used as photocatalyst,the kinetic constant K for MB degradation was 0.02748 min^-1.The photocatalytic degradation of MO in dye wastewater was carried out by using Yb₂Bi Sb O₇/Cd Bi YO₄ heterogeneous photocatalyst under visible light irradiation,in accordance with the first-order reaction kinetics.The experimental results show that Yb₂Bi Sb O₇/Cd Bi YO₄ heterojunction photocatalysts and Ga₂Yb Sb O₇/Fe₂Bi Ta O₇ heterojunction photocatalysts had high stability.The experimental results showed that the removal ability of MO from dye wastewater by superoxide anion was greater than that of hole and hydroxyl radical,and hydroxyl radical has the largest removal ability in the removal process of MB.Finally,the possible degradation pathways and mechanisms of MO and MB were revealed in detail.The results showed that the toxic pollutants in pharmaceutical wastewater could be effectively removed by visible light irradiation through thin film electroplating research of heterojunction catalyst and construction of complete photoluminescence thin film catalytic reaction system.At the same time,visible light heterojunction photocatalyst and photocatalytic reaction system with high catalytic activity could effectively remove organic pollutants in dye wastewater.This work provided a new scientific idea for improving the performance of single catalyst and a new method for removing organic pollutants that were difficult to biodegrade in industrial wastewater.