Study On Design And Photocatalytic Properties Of Composite Materials Based On Bi4_Ti₃O₁₂

Nowadays,with the continuous development of human beings,there are also two extremely serious challenges,which are energy shortage and environmental pollution.How to solve these problems is a grim test for the sustainable development of human society.The antibiotic wastewater and heavy metal wastewater produced in human production and life are characterized by complex composition,high concentration of organic pollutants,high toxicity and difficulty in biodegradation.If they are not treated direct discharge,they will pose a great threat to the water environment and biology.As a new green environmental protection technology with high photocatalytic activity and fine stability,photocatalysis technology is widely regarded as one of the effective solutions to solve the environmental problems of water pollution,and it has a wide application prospect because of its high efficiency,low cost,no pollution and other characteristics.Besides,Photocatalytic technology can convert solar energy into chemical energy.Perovskite bismuth titanate(Bi₄Ti₃O₁₂)is a kind of wide band gap semiconductor.Because of its unique layered crystal structure and good ferroelectric and photoelectric properties,it has been one of the hot spots in the field of photocatalysis.However,due to the wide band gap and the high recombination rate of electron-hole pair,the photocatalysis efficiency of using pure Bi₄Ti₃O₁₂ as photocatalyst is poor.In this dissertation,Bi₄Ti₃O₁₂ photocatalyst was prepared by molten salt method,and then it was compounded with silver-based material to get heterojunction composite.Its photocatalytic performance was studied in visible light.The main contents of this dissertation are as follows:?1?Ag₃PO₄/Bi₄Ti₃O₁₂ heterojunction composites were prepared by the synthesis of bismuth titanate and silver phosphate.The photocatalytic activity and stability of the samples were studied by using the antibiotic sulfamethoxazole?SMX?.The results showed that with the increase of Ag₃PO₄ content in the composite,the photocatalytic activity also increased.When the ratio reached 20%,the photocatalytic activity showed the best performance.The kinetic rate constant of the composite was 124 times and 1.3 times higher than that of the pure Bi₄Ti₃O₁₂ and Ag₃PO₄,respectively.XPS results show that the binding energy of the composite is shifted,which can be attributed to the interaction between Bi₄Ti₃O₁₂ and Ag₃PO₄,which indicates that the heterojunction between the two components has been successfully formed.PC and EIS tests show that the composite sample has better efficiency of electron hole separation and transfer,which improves the photocatalytic activity of the composite sample.In addition,through the experiments of free radical trapping,it can be seen that in the process of photocatalytic degradation of SMX,hole?h⁺?plays an important role.?2?Ag₂CO₃/Bi₄Ti₃O₁₂ heterojunction composite was prepared by in-situ growth method.When the composite ratio of Ag₂CO₃ and Bi₄Ti₃O₁₂ is 20%,it shows the highest photocatalytic performance of reducing hexavalent chromium Cr?VI?in potassium dichromate?PD?solution.The kinetic rate constants of the best samples are 4.9 and 35.6times of those of pure Bi₄Ti₃O₁₂ and Ag₂CO₃.The results of cycling experiments show that the best sample has good stability and recoverability.Through various characterization and experimental results,it can be seen that the combination of them forms a direct Z-scheme photocatalytic system,which promotes the separation of carriers and improves the reduction performance of the composite sample for hexavalent chromium.