Preparation Of Defect-improved Cerium/Cobalt Based Catalysts And Catalytic Decomposition Of VOCs

As the acceleration of industrialization and economic growth,the annual emission of VOCs has increased dramatically,which poses an immediate threat to human health,while forming secondary environmental pollution such as photochemical smog and organic aerosols.In recent years,photocatalytic oxidation technology has been considered an efficient method for removing VOCs for its easy popularization and application,simpler reaction conditions,low cost,and complete decomposition.However,the role of active species,surface defects,and charge separation mechanisms on the photocatalytic degradation of VOCs reaction is complex and uncertain.Hence,this thesis investigates the degradation behavior and reaction mechanism of photocatalytic oxidation of VOCs with well-stocked cerium-based/cobalt-based semiconductor materials,explores the corresponding optimization measures to improve the catalyst stability and catalytic activity,and provides technical support for the design and preparation of high-efficiency catalysts for the purification of environmental pollution.The main research contents are as follows:（1）A Z-type heterojunction Ag/Ag₃PO₄/Ce O_2-xcomposites with in situ grown Ag~0were successfully prepared by a simple precipitation method and applied for photocatalytic oxidation of gaseous benzene and formaldehyde.Ag~0used as the electron relay platform between Ag₃PO₄and Ce O_2-xcomponents to effectively promote the separation and transport of photogenerated electron-hole pairs,and the SPR effect to further enhance the response of the catalyst to the solar light.The composite catalyst showed the best catalytic activity for gaseous benzene at 15 wt.%mass fraction of Ag₃PO₄,with a degradation rate of 90.18%,corresponding CO₂yield of 46.72%,and TOC removal efficiency of 74.17%within 3 hours solar light irradiation at an initial 600 ppm benzene concentration.The defect engineering introduced in the Ce O_2-xsubstrate material helps to enhance the pre-sorption of VOCs,while the defect trap can enhance the separation of photogenerated electrons and holes,and produces more reactive oxygen species to the oxidation reaction of VOCs.The photoelectrochemical and EPR tests confirmed that the heterojunction structure promoted the photogenerated electron transfer and the separation properties,while the generation of O₂^·-and·OH radicals enabled the catalyst to be versatile and to have good oxidative removal ability for gaseous formaldehyde as well.（2）A Cu O/CQDs/Ce O_2-xmultiphase catalytic system mediated by carbon quantum dots（CQDs）was successfully prepared by a simple hydrothermal method.The morphology and defect modulation of the Ce O_2-xsubstrate material has enabled more adsorption sites and active sites to accelerate the catalytic reaction.With the target pollutant toluene at an initial concentration of 1200 ppm,the gaseous toluene was completely decomposed after 3 hours of simulated solar irradiation,while the CO₂yield was 83.41%,and only a slight decrease in activity was observed after seven consecutive cycles.The CQDs with excellent photoconversion and electron transfer capabilities were used as a relay platform to composite with the full-spectrum responsive and narrow bandgap Cu O materials,and the indirect Z-type heterojunction structure was established within the Cu O/CQDs/Ce O_2-xmultiphase catalyst to achieve efficient photogenerated charge separation in space,enabling the composite catalyst to exhibit strong oxidation activity for rapid and complete decomposition of VOCs.The strong electrical interactions at the Ce-Cu interface connected by the oxygen bridge enhanced the charge transport of Cu O/CQDs/Ce O_2-xcomposite and improved the catalytic activity and stability of the catalyst.（3）The Cu Bi₂O₄-Ce O_2-xcomposite catalysts were successfully prepared by a simple hydrothermal method,and photocatalytic oxidative removal of gaseous toluene and formaldehyde under simulated solar light irradiation was realized.The composite material showed the best catalytic activity at a mass fraction of 20 wt.%of Cu Bi₂O₄material,completely degrading a high concentration of gaseous toluene at1800 ppm within two hours,with a corresponding CO₂yield of 87.05%and TOC removal efficiency of 89.33%.The presence of interfacial interactions enhanced the stability of the catalyst,which remained active in 32 cycles of testing as a highly efficient and stable catalyst.The defect engineering improved by alkali etching produces more lattice defects on the Ce O_2-xsubstrate material with more active sites,enhancing the pre-sorption ability of VOCs and the rapid oxidation reaction.The spinel Cu Bi₂O₄material with excellent photoelectrochemistry and stability forms a Z-type heterojunction structure with Ce O_2-xsubstrate material,which enables high-efficiency electrons separation in space under the interfacial interaction.（4）The oxygen-deficient Co₃O₄and La Mn O₃materials were prepared by defect engineering,and the composite showed excellent photocatalytic activity for gaseous toluene at high concentration of 2800 ppm under simulated solar light irradiation.The La Mn O₃/Co₃O₄composites completely decomposed gaseous toluene after 2 hours of light irradiation,while the CO₂yield was 94.33%and the TOC removal efficiency was 94.76%,with excellent stability in 57 consecutive cycles of the reaction without any activity reduction.In-depth study of the excellent activity of La Mn O₃/Co₃O₄revealed that Co O,a mixed-phase component in the Co₃O₄material,was the active central of the oxidation reaction,while superoxide radicals were identified as the key active species for the generation of CO₂products.As a result,a double Z-type heterojunction structure is formed between the La Mn O₃/Co₃O₄materials,and the strong electronic interactions at the La Mn O₃/Co₃O₄interface,the Co₃O₄material continuously acquires electrons from the interface,ensuring the long-term stable existence of the Co O component in the Co²⁺valence state,thus enabling La Mn O₃/Co₃O₄to exhibit excellent catalytic activity and stability.（5）The La Co O₃with Co O mixed-phase coexistence photocatalyst was successfully prepared in situ by a modified sol-gel method,and a direct Z-type heterojunction structure with efficient charge separation was formed between the Co O material and La Co O₃.By using GQDs with full spectral response and strong electrical conductivity as a relay platform for electron separation and transfer,compounding with ultrathin nanosheet Co Bi₂O₄materials,an indirect Z-type heterojunction structure is formed in La Co O₃/GQDs/Co Bi₂O₄nanocomposites,and La Co O₃-Co O/GQDs/Co Bi₂O₄nanocomposites with double Z-type heterojunction structure are prepared to achieve complete spatial separation of photogenerated carriers.The best catalytically active LGC25 composite completely decomposed gaseous toluene at an initial concentration of 3400 ppm and converted to 94.37%CO₂yield within 2 hours,and it exhibited stable catalytic activity in continuous cycling tests.The introduction of defect engineering also resulted in the La Co O₃and Co Bi₂O₄samples with oxygen-rich vacancies,while the advantage of nanostructure prompted the rapid oxidation reaction.Thus,the solution of defect introduction and establishment of double Z-type heterojunction structure can provide a new idea for the degradation of high concentration VOCs.