Construction Of Biomass Carbon Based Photocatalysts For Charge Separation Enhancement And Study Of Enhanced Photocatalytic Performance

Biomass is abundant,cheap and easy to obtain,and is a green energy source to replace non-renewable fuels,which has received a lot of attention in recent years.Biomass carbon materials prepared from biomass have the advantages of pore structure,adjustable specific surface area,rich functional groups and excellent electrical conductivity,which have great potential for application in the field of photocatalysis.The use of waste biomass as raw material to construct biomass carbon based photocatalysts for pollutant treatment and clean energy production can not only transform various wastes to reduce the pressure on the surrounding environment,but also alleviate the problem of energy shortage in China.The photocatalytic process is mainly divided into three steps,（1）photoexcitation of semiconductor to generate electron-hole pairs,（2）spatial separation of photogenerated electron-hole pairs,and（3）redox reaction of electron-hole pairs.Among them,the separation and transport of photogenerated electron-hole pairs are the most critical steps in the photocatalytic process.The low separation efficiency of photogenerated electron-hole pairs in biomass carbon based materials severely limits its photocatalytic efficiency and practical applications.To address the above problems,this thesis constructs biomass char-based composite photocatalysts with high photogenerated charge separation efficiency through heterostructure construction,elemental doping,and co-catalyst modification,and explores the potential applications of composite photocatalysts in the fields of photocatalytic degradation of pollutants and photocatalytic CO₂ reduction.The mechanism of charge separation enhancement of biomass charcoal-based catalysts is analyzed,which provides an experimental basis and theoretical foundation for the synthesis and regulation of nature-based biomaterials and practical applications.The specific research of this thesis is as follows:1.A photocatalyst of cuprous oxide composite biomass carbon（Cu₂O/BC）was prepared by low-temperature sintering and in situ reduction using rape pollen as raw material and used for photocatalytic degradation of tetracycline（TC）under visible light irradiation.Under visible light irradiation,Cu₂O/BC exhibited excellent photocatalytic activity for the degradation of tetracycline,with degradation rates approximately 6.0 and 3.2 times higher than those of biomass carbon（BC）monomer and Cu₂O monomer,respectively.The enhanced performance was attributed to the construction of heterojunction,which promoted the effective separation of photogenerated charges.In addition,the Cu₂O/BC composite photocatalyst still exerted better degradation in a wide temperature and p H range and in the presence of various inorganic ions and organic matter（humic acid）,which verified its application potential.Meanwhile,the Cu₂O/BC composite photocatalyst shows great potential in practical wastewater treatment.This work provides new ideas and insights for the synthesis of high-performance photocatalysts from biomass materials combined with semiconductors.2.A composite photocatalyst（NHC/CNM）consisting of honeycomb carbon flakes and carbon nitride mixture was prepared by chemical activation and nitrogen doping method using seaweed as raw material and used for photocatalytic reduction of CO₂ under solar irradiation.The NHC/CNM catalyst exhibited enhanced performance for CO₂ reduction and better stability compared to biomass carbon monolithic catalyst.The improved photocatalytic performance was attributed to the enhanced CO₂ adsorption capacity and enhanced photogenerated carrier separation efficiency,as demonstrated by low-temperature CO₂ adsorption and photoelectrochemical characterization experiments,respectively.The in situ FTIR spectra showed that*COOH is a key intermediate in the CO₂ reduction reaction and follows the reaction route of CO₂→*COOH→CO.This study not only illustrates a facile method to synthesize non-metallic biomass carbon composite photocatalysts,but also reveals the important role of the synergistic effect of CO₂ adsorption and charge separation on CO₂ photoconversion.3.A composite photocatalyst of cobalt oxide loaded biomass carbon（Co O-SBC）was prepared by chemical activation and one-step sintering method using seaweed as raw material and used for photocatalytic reduction of CO₂ under solar irradiation.1%Co O-SBC photocatalyst showed relatively strong performance for the reduction of CO₂ and had good cycling stability.The results showed that the introduction of Co O co-catalyst formed Co-O-C bonds with the biomass carbon catalyst,constructed electron transfer channels,shortened the electron transfer distance,and greatly enhanced the separation efficiency of photogenerated charges of the catalyst.The photocurrent response,electrochemical impedance spectroscopy and fluorescence spectroscopy also successfully demonstrated the high efficiency of photogenerated charge separation and low electron transfer resistance of 1%Co O-SBC composite photocatalyst.This study provides a simple strategy and research idea for the synthesis of efficient biomass carbon composite semiconductor photocatalysts.