Interfacial Charge Transfer And Photocatalytic Properties Of Bismuth-Based Heterojunction Composites

Photocatalysis is widely used in the fields of organic pollutant degradation and hydrocarbon fuel preparation.Therefore,it is considered as an emerging technology to solve the problems of environmental pollution and energy shortage.Since the proportion of visible light in the solar spectrum is much higher than ultraviolet light,researchers have been devoting themselves to developing semiconductor photocatalytic materials with visible light response.The special outer electron structure of the bismuth element leads to the generally narrow forbidden bandwidth of its compounds,so most of them have good visible light absorption ability.However,the photocatalytic activity of single bismuth-based photocatalysts is limited by the problem of low carrier separation efficiency.Construction of heterojunctions with other semiconductors is one of the most effective strategies to improve their photocatalytic activity,because charge transfer between interfaces can effectively suppress photogenerated carrier complexation.Although a large number of bismuth-based heterojunction composites have been developed,the interfacial resistance leads to a low efficiency of charge transfer between semiconductors.To address these problems,this paper promotes interfacial charge transfer by optimizing the interfacial structure of bismuth-based heterojunction composites to enhance photocatalytic performance.The mechanism of interfacial charge transfer and photocatalytic performance enhancement is investigated in depth through experiments and theoretical calculations as follows:（1）Bi OCl/Bi₃Nb O₇heterojunction composite photocatalysts with high interfacial matching were prepared by in situ chemical reaction.Based on the fact that Bi₃Nb O₇can react with HCl to form Bi OCl,the in situ chemical transformation from Bi₃Nb O₇to Bi OCl can be achieved at room temperature.This strategy allows the formation of a shared atomic-level heterojunction interface between two semiconductors.Therefore,the Bi OCl/Bi₃Nb O₇ heterostructure exhibits excellent photocatalytic performance in photodegradation experiments of canonical antibiotics and dyes.The optimized sample B/BN-160 almost completely degraded 10 mg/L of CIP in 120 min,and the Rh B solution at high concentration（50 mg/L）could be completely degraded in 40 min.The obtained photocatalysts were characterized by various characterization techniques.The results show that the tightly connected interfaces in Bi OCl/Bi₃Nb O₇ heterojunctions constructed by in situ chemical transformation can effectively promote charge transfer between the interfaces.（2）In this work,Bi₄Nb O₈Cl-OV/Ag Fe O₂ heterojunction photocatalysts were designed and synthesized by a defect induction strategy.Ag Fe O₂ was generated in situ in the surface defect region of Bi₄Nb O₈Cl,and the Ag Fe O₂ with narrow band gap generation extended the light absorption range of the heterojunction photocatalysts.The Bi₄Nb O₈Cl-OV/Ag Fe O₂ heterojunction photocatalysts constructed by oxygen defect induction showed higher photocatalytic activity in the broad spectral range from the visible to near-infrared region.The optimized samples exhibited first-order degradation kinetic constants of up to 8.89×10^-2 min^-1 and 3.08×10^-2 min^-1 for the photodegradation of rhodamine B and ciprofloxacin under visible light,which were 2.7 and 1.4 times higher than those of the samples without oxygen vacancies,respectively.The experimental results and theoretical calculations show that the defective region on the surface of Bi₄Nb O₈Cl has a high degree of coordination unsaturation and a large number of dangling bonds,so the defective region can be used as an anchor point for Ag Fe O₂ to form a tighter heterojunction interface by forming new chemical bonds with Ag Fe O₂,which provides a fast channel for the transfer of photogenerated charges.This work provides a feasible strategy for the defect-induced construction of high-quality heterojunction interfaces for interfacial charge transfer.（3）In this work,Zn In₂S₄/Bi₄Nb O₈Cl heterojunction photocatalysts containing sulfur vacancies were designed and synthesized using defect engineering and interface engineering.The photocatalytic hydrogen evolution experiments showed that the formation of heterojunctions and the introduction of sulfur vacancies could significantly enhance the photocatalytic hydrogen evolution performance of Zn In₂S₄/Bi₄Nb O₈Cl,and the S_V-Zn In₂S₄/Bi₄Nb O₈Cl composite sample exhibited a hydrogen precipitation rate of1084.9μmol·g^-1h^-1,which was about 2.2 and 19.8 times higher than Zn In₂S₄and Bi₄Nb O₈Cl 19.8 times.The experimental results show that the formation of heterojunctions and the introduction of sulfur vacancies can significantly enhance the photocatalytic hydrogen precipitation performance of Zn In₂S₄.Experimental and theoretical analyses show that the presence of sulfur vacancies leads to strong interactions between Zn In₂S₄ and Bi₄Nb O₈Cl,which induce strong coupling between the atomic layers of Zn In₂S₄ and Bi₄Nb O₈Cl and promote interfacial charge transfer.This work provides a feasible strategy for defect engineering to enhance interfacial interactions to promote the directional and efficient transport of carriers.