Construction Of S-Scheme BiVO₄-Based Composite Photocatalytic Functional Materials And Research On Environmental Purification

In recent years,environmental pollution has seriously affected the life and survival of human beings and natural plants and animals,and has become an urgent problem to be solved at this stage.Photocatalytic oxidation technology,as a novel green method to reduce the environmental crisis,is widely favored.Suitable semiconductor materials are selected to generate a variety of active species under the excitation of sunlight,so as to completely mineralize the pollutant molecules into water and carbon dioxide.Based on many advantages of photocatalytic technology,this paper designed and synthesized a variety of excellent S-scheme composite functional materials based on BiVO₄ semiconductor for the purpose of efficiently removing environmental pollutants,and combined with a variety of catalytic technologies applied to the degradation of volatile organic pollutants(VOCs)and tetracycline antibiotics.The research contents are as follows:(1)The Bi-modified S-scheme BiVO₄/g-C₃N₄ composite photocatalytic material was successfully constructed by in-situ reduction method,which was used to coordinately and efficiently oxidize formaldehyde gas into CO₂ and H₂O under simulate full-spectrum sunlight.The BiVO₄/Bi/g-C₃N₄ three-phase catalyst exhibits excellent photocatalytic formaldehyde oxidation activity and carbon dioxide selectivity.After 6 hours,the degradation rate of BiVO₄/Bi/g-C₃N₄ to 800 ppm formaldehyde reached 96.39%,the carbon dioxide selectivity was 98.41%,and the reaction rate was 4.16 ppm^-1·h^-1.Besides,the decomposition efficiency of formaldehyde in the visible light and near-infrared regions reached 49.35%and32.23%,respectively.Through photoelectrochemical performance testing and DFT calculations,the photocatalytic mechanism was further in-depth explored,that the photogenerated electrons transfer between BiVO₄ and g-C₃N₄ in an S-scheme path,which not only facilitates the effective separation of photogenerated carriers,but also maintains the original high redox ability of the material,thereby helping to improve the photocatalytic reaction activity.At the same time,Bi nanoparticles not only broaden the photoresponse range,making the photocatalyst have a broader application prospect in the near-infrared field;and its SPR electrons help to improve the catalytic activity of the material.This work provides new ideas for the collaborative construction of high-activity photocatalytic materials,and BiVO₄/Bi/g-C₃N₄ is expected to be further developed and applied in the field of environmental purification due to its excellent photocatalytic activity.(2)The double S-scheme BiVO₄/g-C₃N₄/Bi₂O₃ photocatalytic functional material,was designed and synthesized to oxidize and decompose formaldehyde into CO₂ and H₂O under simulated full-spectrum sunlight.BiVO₄/g-C₃N₄/Bi₂O₃-80%has excellent photocatalytic activity for the oxidation of formaldehyde and high carbon dioxide selectivity.After 3 hours,the HCHO degradation rate reached 97.72%,the reaction rate constant was 23.75×10^-3 min^-1,and the CO₂ selectivity reached 99.56%.The photocatalytic mechanism was proposed through the photoelectrochemical performance test and DFT calculation,that the photogenerated electrons between BiVO₄ and g-C₃N₄ and Bi₂O₃ and g-C₃N₄ are transferred in a similar S-scheme path under the built-in electric field effect.This not only improves the separation and transfer efficiency of the photogenerated carriers,but also effectively inhibits its recombination;and a large number of photogenerated electrons gather on the CB of g-C₃N₄,and the holes remain in the VBs of BiVO₄ and Bi₂O₃,respectively;and maintain the original strong redox ability of each phase catalyst;thereby helping to improve the photocatalytic formaldehyde degradation activity.This work provides a new double S-scheme catalytic material design idea for improving the activity of photocatalytic materials and BiVO₄/g-C₃N₄/Bi₂O₃ is expected to be popularized and applied in the field of environmental purification in the future.(3)The S-scheme heterojunction composite catalyst Cu Bi₂O₄/BiVO₄ was successfully constructed by a simple hydrothermal method and low-temperature calcination method to degrade antibiotics under visible light.Compared with the pristine BiVO₄ and Cu Bi₂O₄,the photocatalytic activity of the composite catalyst Cu Bi₂O₄/BiVO₄ is significantly improved.The degradation rate of TC and OTC(20ppm)reached 79.66%and 81.11%,respectively,within 60 min,and the apparent rate constant is 21.58×10^-3 min^-1 and 21.08×10^-3 min^-1,and after four cycles test,the catalyst has excellent stability.Based on a series of characterization tests,the photocatalytic mechanism was clarified.(4)The S-scheme BiVO₄/Fe₂O₃ composite catalyst was successfully prepared by the sol-gel method and low-temperature calcination method,which was used to degrade TC under the synergistic conditions of visible light and PMS.The BiVO₄/Fe₂O₃/PMS/Light system has excellent TC degradation activity.It almost completely decomposes TC(20 ppm)in 30 minutes;the degradation rate of TC reaches 98.36%,and it has good stability.Based on the analysis results of photoelectric properties,EPR test and active species capture experiment,combined with DFT calculations,the reaction mechanism of BiVO₄/Fe₂O₃/PMS/Light system is proposed,that is,the S-scheme heterojunction effectively improves the separation and transfer of photogenerated charges,and retains the strong redox ability,and the synergistic effect of the cyclic conversion of transition metal ions Bi³⁺/Bi⁰ and Fe³⁺/Fe²⁺can better activate PMS to generate more active species·SO₄^-and ¹O₂,thereby improving the reaction system catalytic activity.Therefore,the BiVO₄/Fe₂O₃synergistic visible light and PMS system is expected to be applied in the treatment of water pollutants.(5)The S-scheme BiVO₄/Cu₂O composite catalyst was successfully prepared by the low-temperature oil bath solvothermal method,which was used to degrade TC under the synergistic conditions of photoelectricity and PMS.Comparing with the PC,EC and PEC,BiVO₄/Cu₂O/PEC/PMS showed excellent TC degradation ability.The construction of S-scheme heterojunction,the conversion of transition metal ions Cu⁺(?)Cu²⁺and a certain external electric field can effectively promote the effective separation and transfer of photo-generated charges,improve the solar energy conversion rate and promote the activation of PMS,thereby generating more activity species,such as·O₂^-,·SO₄^-,and·OH,thereby promoting the degradation of antibiotic organic pollutants.Through a series of characterization tests,the optical,electrical,and physicochemical properties were studied,and free radical trapping experiments and electron spin resonance were used to explore the catalyst mechanism.Therefore,this work provides a feasible scheme to effectively improve the carrier separation efficiency,which is expected to be applied in the green antibiotic degradation.