| Because of its unique electronic structure,bismuth-based semiconductors are a class of visible light catalytic materials with good application prospects.As a new member of the bismuth family,n-type Bi2O4has a narrow band gap??2.0 e V?and mixed valence states of Bi3+and Bi5+,showing good visible light catalytic activity.However,single-component Bi2O4photocatalysts have the disadvantage that photo-generated carriers are easily recombined.In addition,the submicrorod-like structure leads to a small specific surface area and a low surface active concentration,which seriously affects the photocatalytic efficiency of Bi2O4.In theory,any p-type semiconductor and any n-type semiconductor can be recombined to form a p-n heterojunction.Therefore,a variety of p-type semiconductors can be combined with n-type Bi2O4to construct Bi2O4-based p-n heterojunctions.The built-in electric field of the p-n junction can promote the directional migration of photo-generated electrons and holes at the heterostructure interface,thereby separating the photo-generated electron-hole pairs in space and improving the efficiency of photo-generated carrier separation.Therefore,this paper takes Bi2O4as the research object,and aims to construct p-n heterojunctions and regulate the morphology of Bi2O4.The following research work has been carried out:First,using Na Bi O3·2H2O as the bismuth source and hydrothermal and dilute HCl acid etching methods to prepare submicrorod-shaped Bi2O4and oxygen-deficient Bi OCl-OVs;Then,using Bi2O4and Bi OCl-OVs as raw materials to disperse through the liquid phase.The Bi OCl-OVs/Bi2O4p-n heterojunction was prepared by stirring.Spatial separation of visible light-excited carriers in Bi2O4by the built-in electric field of the p-n junction,and capture of photogenerated electrons by the oxygen vacancies of Bi OCl-OVs promote the separation of photogenerated electron-hole pairs and reduce the probability of photogenerated carrier recombination;In addition,oxygen defects cause Bi OCl-OVs to absorb a part of visible light,generate carriers,and increase the carrier concentration,thereby improving the visible light catalytic activity of the Bi OCl-OVs/Bi2O4p-n junction.The photocatalytic activity results show that when the molar ratio of Bi OCl-OVs to Bi2O4is 2:5,the Bi OCl-OVs/Bi2O4p-n heterojunction has the best visible light catalytic performance and the degradation performance is 1.66 and 2.71 times compared with that of Bi2O4,respectively.The active species capture results show that holes?h+?and superoxide radicals?·O2-?are the main active species in the photocatalytic degradation reaction process.Second,using Bi?NO3?3·5H2O,KCl and Na Bi O3·2H2O as raw materials,a one-pot hydrothermal method was used to in-situ prepare the Bi2O4/Bi2O3-O p-n heterojunction.Scanning and transmission electron microscopy results show that Bi2O4in Bi2O4/Bi2O3-O has both rod-like and granular structures,and is in close contact with Bi2O3sheet-like structures to form heterojunctions.The results of photocatalytic experiments showed that the optimal performance of the Bi2O4/Bi2O3-O-3 sample was 2.4 times that of Bi2O4for methyl orange and 1.49times that of Bi2O4for phenol.The in-situ synthesis of p-n heterojunction is simple and the interface charge interaction is stronger.In addition,since Bi2O3is a narrow band gap semiconductor,the light utilization efficiency of the heterojunction can be further improved.Thirdly,nano-Bi2O4/Bi2O3-AH p-n heterojunction was synthesized by the dilute hydrochloric acid etching and following hydrothermal method,using Na Bi O3·2H2O as the only bismuth precursor.Through changing the amount of dilute hydrochloric acid,the content of Bi2O3in the heterojunction can be controlled.The results of photocatalytic experiments showed that the degradation performance of Bi2O4/Bi2O3-AH-5 samples under visible light on methyl orange and phenol was5.06 times and 2.16 times that of pure Bi2O4samples,respectively.Scanning and transmission electron microscopy results show that Bi2O4in Bi2O4/Bi2O3-AH is of nanoparticle structure,which can effectively shorten the distance of photo-generated carrier migration and extend the carrier life.Therefore,this method realizes nano-scale Bi2O4and constructs nano-scale Bi2O4/Bi2O3-AH p-n junction,which further improves the carrier separation efficiency and photocatalytic activity.Active species capture experiments and electron paramagnetic resonance?ESR?spectroscopy results show that during photocatalytic degradation,holes?h+?and superoxide radicals?·O2-?are the first and second active species,respectively. |
PDF Full Text Request