Preparation Of Bi₄O₇-based Composite Catalyst And Its Photocatalytic Degradation Performance Of Phenol

The rapid development of global industry has caused serious environmental problems,such as water pollution.Phenol is one of the most toxic organic compounds and persists in the environment.Phenol can directly affect the health of ecosystems and pose a threat to humans by contaminating drinking water.In addition,the oxidation and disinfection processes routinely used to remove phenol produce potentially carcinogenic compounds.Therefore,the removal of phenol in an environmentally friendly way is the main content of current research.Photocatalytic technology is an advanced oxidation technology for efficient and green removal of pollutants.As an emerging Bi-based oxide,Bi₄O₇ has attracted extensive attention because of its simultaneous presence of Bi³⁺and Bi⁵⁺valences and high mineralization rate to pollutants.However,how to quickly and efficiently prepare Bi₄O₇ and avoid the deactivation of Bi₄O₇during the photocatalytic reaction are the main problems to be solved at this stage.In the research of this paper,Bi₄O₇ catalyst was prepared by one-step hydrothermal method,CeO₂was introduced into the preparation process to prepare CeO₂/Bi₄O₇ heterojunction catalyst,and Bi OI/Bi/Bi₄O₇ heterojunction catalyst was prepared by introducing Bi OI and Bi.The two composite catalysts improved the activity and stability of Bi₄O₇ degradation of phenol to a certain extent,especially the latter,greatly improved the stability of Bi₄O₇ catalyst.The specific work is as follows:1.Bi₄O₇ and CeO₂/Bi₄O₇ heterojunction catalysts were prepared by a simple one-step hydrothermal method,and the preparation of the heterojunction catalysts was proved by XRD,FT-IR,Raman,SEM,TEM,XPS and other characterizations.The performance of the catalyst was evaluated by degrading phenol under simulated sunlight.The results showed that the degradation activity of the CeO₂/Bi₄O₇ heterojunction catalyst was higher than that of the single Bi₄O₇（40%phenol was degraded in 120 min）,and the 10%CeO₂/Bi₄O₇ heterojunction catalyst showed the best degradation activity（92%phenol was degraded in 120 min,TOC removal rate of 53%）,DRS results show that the introduction of CeO₂ increased the CeO₂/Bi₄O₇heterojunction catalyst in the light absorption capacity of the ultraviolet region.The results of cycling experiments show that the catalyst is almost completely deactivated after three cycles of Bi₄O₇,which is because Bi⁵⁺is reduced to Bi³⁺and reacts with CO₂ to generate Bi₂O₂CO₃impurities during the reaction.After three cycles of 10%CeO₂/Bi₄O₇,the phenol activity decreased by 41.6%.Compared with Bi₄O₇,the photocatalytic stability of 10%CeO₂/Bi₄O₇heterojunction has been improved to a certain extent,which is due to the type II heterojunction.The construction of,accelerates the separation speed of electron holes;the conversion between Ce³⁺/Ce⁴⁺in CeO₂ can generate more·O₂^-active species.But unfortunately,the CeO₂/Bi₄O₇heterojunction catalyst still has Bi₂O₂CO₃ impurity generated,which leads to serious deactivation.Finally,the degradation mechanism of phenol was deduced by trapping agent experiments,ESR and DFT calculations.2.On the basis of the first part of the work,in order to further improve the activity and stability of Bi₄O₇-based catalysts,Bi OI and Bi were introduced to prepare Bi OI/Bi/Bi₄O₇heterojunction catalysts.XRD,FT-IR,SEM,TEM,The successful preparation of the heterojunction catalyst was demonstrated by XPS and other characterizations,and the activity and stability of the catalyst were investigated by photocatalytic degradation of phenol.The results show that the photodegradation activity of Bi OI/Bi/Bi₄O₇ heterojunction catalyst is higher than that of Bi OI and Bi₄O₇ alone,and the degradation rate of phenol by 30%Bi OI/Bi/Bi₄O₇ heterojunction catalyst under simulated sunlight for 120 min is 91%.,TOC removal rate was 62%.The cycle test results show that the stability of the Bi OI/Bi/Bi₄O₇heterojunction catalyst is greatly improved,and the activity only decreases by 13%after three cycle experiments.The XRD analysis of the Bi OI/Bi/Bi₄O₇ heterojunction catalyst after the reaction does not observe the Bi₂O₂CO₃ impurity peak.Finally,the degradation mechanism of phenol was deduced through trapping agent experiment,ESR and DFT calculation.The improvement of stability was attributed to the construction of Z-scheme heterojunction and the acceleration of electron hole separation efficiency by using Bi as electron transport medium.