Design Of N-type Bi-based Oxide/p-type Cual₂O₄ Heterojunction Nanofibers And Its Photocatalytic Activity

The development of science and technology have accelerated the consumption of material resources,providing great convenience to human society,also causing increasingly serious energy and environmental problems at the same time.The development of photocatalysis based on semiconductor materials can convert solar energy into chemical energy,providing an effective means to solve these problems.Photocatalysts represented by Bi-based oxide semiconductor materials have become widely studied as a series of visible-light-driven materials due to their wide light response range and good physicochemical stability.In particular,Bi-based oxide nanomaterials can provide more active sites and exhibit desirable photocatalytic performance due to their large specific surface area.However,there are still some vital problems in these semiconductors:First,the photogenerated electron-hole pairs will easily recombine within the semiconductor,causing much lower quantum efficiency.Second,it is easy to agglomerate and inactivate during the reaction because of the small size of nanomaterials.Third,they will suspend in the solution after the reaction,which is difficult to separate.Therefore,it is important to find Bi-based photocatalytic nanomaterials which have good photocatalytic activity and separable properties.Based on above consideration,in this paper,a series of p-n heterojunction nanofibers from binary to ternary were prepared by electrospinning,heat treatment and solvothermal methods.The heterostructures can be used to promote the charge separation,and then improving the photocatalytic performance.The ultra-long 1D structures can be used to solve the problems of agglomeration during reactions and the difficulties in separation after the reactions.The specific researches are list as follows:（1）CuAl₂O₄ hollow nanofibers were prepared by electrospinning technique.Results show that as-prepared CuAl₂O₄ hollow nanofibers exhibit good visible light photocatalytic performance for photodegradation of organic pollutants（RhB,MO）,and good stability against acid/alkali（pH=3¹1）,enabling its practical applications under harsh conditions.In addition,the CuAl₂O₄ hollow nanofibers can be easily separated by natural sedimentation due to its ultra-long 1D nanostructures.Thus,the p-CuAl₂O₄ hollow nanofibers can be used as substrate and loaded n-type semiconductors to build a series of p-n heterosturctures with enhanced photocatalytic activity and separable properties.（2）Using CuAl₂O₄ hollow nanofibers as template,CuAl₂O₄/Bi₂MoO₆,CuAl₂O₄/Bi₂WO₆,CuAl₂O₄/BiVO₄ heterosturctures were built via solvothermal methods.Result show that as a traditional type II heterojunction,CuAl₂O₄/Bi₂MoO₆ will facilitate photogenerated charge separation and the photocatalytic activities for degradation of RhB,MO,Cr（VI）and 4-NP are increased by an order of magnitude compared to single-component CuAl₂O₄ and Bi₂MoO₆.While as a Z-scheme heterojunction,CuAl₂O₄/Bi₂WO₆ and CuAl₂O₄/BiVO₄ can also facilitate photogenerated charge separation and trigger overall water splitting reactions under visible light irradiation because of their stronger redox power.Moreover,he heterojunctions can be easily separated by natural sedmentation due to its ultra-long 1D nanostructures.（3）CuAl2O4 hollow nanofibers were coated by carbon layer via hydrothermal reaction,and then CuAl₂O₄@C/Bi₂MoO₆ and CuAl₂O₄@C/Bi₂WO₆ ternary heterojunction system were constructed by secondary hydrothermal reactions.Results show that in CuAl2O4@C/Bi2MoO6,the carbon layer can be used as a bridge for charge transfer in a Z-scheme manner at the interfaces of the heterojunction,achieving the transformation from traditional type II heterojunction to the Z-scheme heterojunction and then trigger overall water splitting reactions.While in CuAl2O4@C/Bi2WO6,the carbon layer as a high-speed channels,will further facilitate spatial separation of charge carriers,and then enhance the photocatalytic activity of photodegradation and overall water splitting.Moreover,the ternary heterojunctions can be easily separated by natural sedmentation due to its ultra-long 1D nanostructures.