Study On The Modification Of Bismuth-Based Catalysts And The Performance Of Thermal Catalytic Degradation Of Phenolic Wastewater

Phenolic pollution can result in serious health risks to humans,animals and plants,which is one of the harsher environmental problems facing human society today.Traditional advanced oxidation technology in wastewater treatment mostly uses chemical oxidation method,which suffers from defects such as high energy consumption and harsh conditions.Low temperature thermal catalysis technology can use industrial activities and natural waste heat,and has good environmental benefits.Therefore,in this study,in order to solve the problem of phenol pollution and improve the defects of traditional advanced oxidation,a modified bismuth-based catalyst was used to design an experimental system for low-temperature thermal catalytic degradation of phenolic wastewater.The details are as follows.（1）In this study,Bi₂₅FeO₄₀/Bi₂O₂CO₃ composite catalyst with thermal catalytic properties was prepared using bismuth ferrite(Bi₂₅FeO₄₀)as the precursor material and irradiated by a high pressure mercury lamp.Under the heating environment,the composite catalyst showed good degradation effect on 4-chlorophenol（4-CP）,the degradation rate of4-CP was about 100%and the TOC removal rate was 84.87%within 70 min.In addition,the low temperature thermal catalytic treatment of phenol,Bisphenol A（BPA）and2,4-Dichlorophenoxyacetic acid（2,4-D）with Bi₂₅FeO₄₀/Bi₂O₂CO₃showed good results.In addition,reuse experiments demonstrated the good stability of the Bi₂₅FeO₄₀/Bi₂O₂CO₃catalyst,with the degradation of 4-CP still up to 90%at the fifth reaction.The effects of temperature,anions,impurities and H₂O₂addition on the thermocatalytic reaction were further investigated.The results showed that the optimum reaction temperature was around65℃,the influence of humic acid and sulphate ions was greater and the optimum addition of H₂O₂was between 1.0-1.2 m L.The results of radical trapping experiments and ESR tests showed that superoxide radicals（·O₂^-）and hydroxyl radicals（·OH）were the main active species in the catalytic reaction.（2）In the previous part,the low temperature thermocatalytic reaction required the use of H₂O₂,which limited the practical application of the technology.Therefore,in the second part of this paper an efficient low-temperature thermocatalyst was developed to achieve the treatment of phenolic pollutants without H₂O₂.Oxygen vacancy-rich BiO_2-xwas synthesised by a one-step hydrothermal method and investigated for the low-temperature thermocatalytic treatment of phenolic pollutants.The SEM results showed that BiO_2-xformed nanosheet cluster morphology and the particle size was significantly smaller thanα-Bi₂O₃.The catalytic oxidation of 4-CP at 65℃resulted in nearly 100%degradation and the TOC was removed by 76.5%within 40 min using BiO_2-xas catalyst.In addition,BPA,phenol and2,4-Dichlorophenol（2,4-DCP）all showed relatively good catalytic degradation under the same conditions.The cycling experiments as well as the XRD and FT-IR test results of the reacted materials proved its good stability,and the ICP results showed no bismuth ion leaching phenomenon.This study also investigated the effect of various factors in the experiment,temperature,p H,catalyst addition,pollutant concentration and anions in solution on the reaction.The mechanism of low temperature thermocatalytic 4-CP degradation was investigated by means of radical capture experiments,ESR,i-t curves and XPS.It was found that the pollutant reacted with Bi-O,which resulted in the release of lattice oxygen and caused the conversion of Bi⁵⁺to Bi³⁺and the released lattice oxygen to reactive oxygen species（ROS）.In addition,molecular oxygen contained a small amount of reactive oxygen species,which formed electron transfer reactions in oxygen vacancies to generate ROS for the attack of 4-CP,which eventually degraded to CO₂and H₂O.