Preparation Of Long Afterglow Light Emitting Z-Scheme Photocatalyst And Investigation On Degradation Of Organic Pollutants With Simultaneous Hydrogen Production Under No-Light Irradiation

Nowadays,with the rapid development of modern society,environmental deterioration and energy crisis have become two important problems for human society.Semiconductor photocatalytic technology can degrade organic pollutants and produce hydrogen under sunlight irradiation,which is considered to be an ideal approach to solve the above problems in the future.However,the amount of time that any country on Earth can receive sunlight each day is limited.If the photocatalytic reactions are only carried out under sunlight irradiation,it means that the organic pollutants degradation and hydrogen production would be unable to be proceeded for more than half a day.Therefore,it is necessary to develop a new photocatalytic system,which can still maintain high photocatalytic performance under no external light irradiation.The long afterglow material is a kind of photo-luminescent material with relatively high luminescence intensity,which can be used as an auxiliary light source for photocatalytic reaction under no external light irradiation.In addition,some of the long afterglow materials also possess the photocatalytic activities,which can be used as photocatalysts.However,the photo-generated carriers in the monomer photocatalyst are easy to recombine and the sunlight utilization of the monomer photocatalyst is low.Therefore,in this study,Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺long afterglow material with photocatalytic activity is selected to combine with the traditional photocatalysts to construct novel Z-scheme photocatalytic systems,in which the recombination of the photo-generated carriers in the monomer photocatalyst can be effectively inhibited,the light response range can be broadened and the more positive valence band and the more negative conduction band can be retained simultaneously.The hole on the valence band possesses good oxidation ability and can degrade organic pollutants.The electron on the conduction band can combine with H⁺to produce hydrogen.The introduction of long afterglow material leads to the fact that the photocatalytic system can still be excited and maintain the photocatalytic activity under no external light irradiation.Besides,after the introduction of Ag metal nanoparticles,the separation efficiency of photo-generated carriers improves,the amounts of the reactive sites increase and the luminescence property of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺long afterglow material enhance.Moreover,after the construction of the dual Z-scheme photocatalytic system,more photo-generated carriers transfer paths can be provided and the utilization of long afterglow light can be enhanced.The results show that the improved Z-scheme photocatalytic systems possess superior photocatalytic property.The photocatalytic organic pollutants degradation with simultaneous hydrogen production can be carried out both under sunlight and no external light irradiation.The main research contents are as follows.In the second chapter,Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag₃PO₄photocatalysts were prepared by using ethanol as the reaction solvent.The crystal structures,morphologies,optical properties and elemental compositions of the prepared samples were characterized by a variety of characterization methods.In addition,levofloxacin（LEV）was selected as the target pollutant.The photocatalytic activities of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag₃PO₄photocatalysts on photocatalytic LEV degradation with simultaneous hydrogen production were studied under sunlight and no external light irradiation.The results show that when the mass ratio of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺and Ag₃PO₄is 15:1,the Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag₃PO₄photocatalyst possesses the most outstanding photocatalytic activity and good stability on photocatalytic LEV degradation and hydrogen production.Finally,according to the results of experiments and characterization tests,the possible mechanism of the round-the-clock photocatalytic organic pollutant degradation with simultaneous hydrogen production caused by the Z-scheme Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag₃PO₄photocatalyst is proposed.Based on the relevant research results of the second chapter,in the third chapter,Ag nanoparticles were introduced by the photo-reduction method and the Z-scheme BiFeO₃/Ag/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag photocatalyst was prepared.The photocatalytic activity and stability of the Z-scheme BiFeO₃/Ag/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag photocatalyst were evaluated by the photocatalytic metronidazole（MNZ）degradation with simultaneous hydrogen production under simulated sunlight irradiation and no external light irradiation.The results show that the Z-scheme BiFeO₃/Ag/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag photocatalyst possesses high photocatalytic activity under both sunlight and no external light irradiation.As the conductive channel,Ag nanoparticles can improve the separation efficiency of photo-generated carriers.Meanwhile,Ag nanoparticles loaded on the surface of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺long afterglow material can be used as the co-catalyst,increasing the amount of active sites on the surface of the photocatalyst and enhancing the photocatalytic activity of the photocatalyst.In addition,the surface plasma resonance（SPR）effect generated by Ag nanoparticles is beneficial for the improvement of the luminescence intensity of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺long afterglow material,which enables the Z-scheme photocatalyst still possess good photocatalytic activity under no external light irradiation.Finally,the possible mechanism of the round-the-clock photocatalytic organic pollutant degradation with simultaneous hydrogen production caused by the Z-scheme BiFeO₃/Ag/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/Ag photocatalyst is proposed.To enhance the photocatalytic performance of the photocatalyst,in the fourth chapter,a dual Z-scheme BiVO₄/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/BiFeO₃photocatalyst was prepared.The construction of the dual Z-scheme photocatalytic system can increase the utilization of long afterglow light as much as possible so that the photocatalyst can still maintain an outstanding photocatalytic activity under no external light irradiation.In addition,in the dual Z-scheme photocatalyst,the separation efficiency of the photo-generated electrons and holes can be improved,which means that more photo-generated carriers can be transferred to the surface of the photocatalyst to participate in the photocatalytic reaction.The photocatalytic activity of the dual BiVO₄/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/BiFeO₃photocatalyst was evaluated by photocatalytic ceftriaxone（CFX）degradation with simultaneous hydrogen production under simulated sunlight and no external light irradiation.The results show that the photocatalytic activity of the dual Z-scheme photocatalytic system is high under both sunlight and no external light irradiation.Moreover,the possible mechanism of the round-the-clock photocatalytic degradation of the organic pollutant with simultaneous hydrogen production caused by the dual Z-scheme BiVO₄/Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺/BiFeO₃photocatalyst is proposed.