The Preparation And Photocatalytic Properties Of Bismuth Subcarbonate Based Nanomaterials

In recent years,the photocatalysis has attracted more and more attention duo to its broad application in dealing with the energy crisis and environmental pollution,which is of great importance and application prospect.As a promising photocatalyst,bismuth subcarbonate?Bi₂O₂CO₃?consists of Bi₂O₂²⁺layers and CO₃^2-layers,which is beneficial for the separation and transfer of photogenerated electron and hole.However,Bi₂O₂CO₃is a wide band gap semiconductor which possesses low utilization rate of light energy and high recombination of electron and hole,thus hindering its photocatalytic activity.In this thesis,Bi₂O₂CO₃is selected as research object,the energy band structure,light response range and electron transfer process of Bi₂O₂CO₃are mediated through bromine doping,carbon quantum loading and construction of ternary composite materials,which could improve the ability of molecular oxygen activation,expand the light absorption range and enhance the ability of reactive oxygen species generation.Moreover,the mechanism of improved photocatalytic efficiency of Bi₂O₂CO₃was also discussed,which lay a foundation for further explore high-efficient photocatalysts.The main research works are summarized as follows:1.Bismuth subcarbonate with different bromine doping amount were synthesized via a hydrothermal method in alkaline solution.Power X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?results illustrated that the doped bromine atoms enter the lattice of bismuth carbonate by replacing the oxygen atoms in bismuth oxygen layer.The photodegradation efficiency of ciprofloxacin?CIP?over Br-doped Bi₂O₂CO₃was determined under UV-Vis light irradiation.It is found that bromine doping could promote the photodegradation of ciprofloxacin.In order to understand the mechanism of photocatalytic activity improvement via bromine doping,the energy band structure and photoelectrical properties of the materials were characterized by model schottky spectra,X-ray photoelectron spectroscopy?XPS?,current density spectra and fluorescence spectra?PL?.The theoretical calculation further confirmed the up shift of energy band structure of bismuth carbonate via bromine doping.Electron spin resonance?ESR?and trapping experiment indicated that the reactive species generation ability of bismuth subcarbonate could be improved via bromine doping.The conversion of superoxide radical to hydroxyl radical was also detected.Through the analysis of the generation of reactive species,the structure of ciprofloxacin degradation products and bacteriostatic test,it was found that pyrrolidone ring was the main bacteriostatic group of ciprofloxacin and the destroy of pyrrolidone ring was closely related to the generation of superoxide radical.2.Bismuth subcarbonate with different N-doped carbon quantum dots loading amounts were synthesized via a hydrothermal method.N-doped carbon quantum dots had been successfully loaded on the surface of bismuth carbonate,which was confirmed by high resolution transmission electron microscopy?HRTEM?and X-ray photoelectron spectroscopy?XPS?.Compared with pure bismuth carbonate,N-doped carbon quantum dots modified bismuth carbonate showed higher photocatalytic activity under UV-vis,visible and near-infrared light irradiation.N-doped carbon quantum dots modified bismuth subcarbonate showed visible light and near-infrared light response due to N-doped carbon quantum dots.According to the electron spin resonance?ESR?and trapping experiment,superoxide radicals?·O₂^-?,hydroxyl radicals?·OH?and holes?h⁺?are the main reactive species for the ciprofloxacin degradation under UV-visible light irradiation.And holes are the main reactive species for the ciprofloxacin degradation under visible and near-infrared light.According to the generation of different reactive species under different light,the Z-scheme electron transfer pathway under UV light and Type II electron transfer pathway under visible and NIR light between N-doped carbon quantum dots and Bi₂O₂CO₃were proposed.3.BiOBr/Bi₂O₂CO₃ heterojunction composites were synthesized via a solvothermal method in the ethylene glycol and ethanol mixed solution.Further enhance the reaction temperature,metallic bismuth was generated and BiOBr/Bi/Bi₂O₂CO₃heterojunction composite was produced.The CIP photodegradation efficiency over the two heterojunction was measured under UV-Vis light irradiation.The results indiated that the ternary composite materials could degrade 90.5%of ciprofloxacin within 60 min,displayed 2.41 times degradation rate higher than that of BiOBr/Bi₂O₂CO₃heterojunction.Bi played as carrier intermediary in this ternary composite system which could accelerate the process of Z-scheme electrons transfer.According to electron spin resonance?ESR?result,BiOBr/Bi/Bi₂O₂CO₃processed stronger ability of oxidation and reduction compared with BiOBr/Bi₂O₂CO₃.The main reactive species of ciprofloxacin degradation are superoxide radicals,hydroxyl radicals and holes according to the trapping experiments.