Preparation And Properties Of BiVO₄/g-C₃N₄ Nano-heterojunction Photocatalystic Materials

Nowadays,there remains to be a great challenge to governance environment,alleviate energy crisis effectively for realizing sustainable development.Photocatalytic materials and technologies can take advantage of the inexhaustible solar energy in nature to perform photocatalytic degradation and energy conversion under mild conditions,providing a new way to solve energy problems.However,the development of traditional UV-responsive photocatalytic materials typified by TiO₂ is limited by low utilization of sunlight energy?<5%?.Therefore,many efforts have been devoted to excavating a new type of photocatalysts that are capable of harnessing the visible light energy.In this paper,a typical visible light responsive semiconductor such as bismuth vanadate?BiVO₄?was studied.Aiming at the poor mobility and easy recombination of photo-generated carriers in BiVO₄,g-C₃N₄ nanoparticles were applied to modify the BiVO₄ by constructing a BiVO₄/g-C₃N₄ Z-type nano-heterojunction.Using low-dimensional materials and their combination on the nanometer scale resulted in high-efficient migration and separation of photo-generated carriers,as well as stronger redox capacity,thereby improving the photocatalytic degradation performance of the composite materials.The main research contents and conclusions are as follows:?1?The g-C₃N₄/BiVO₄ composite photocatalytic material was prepared by in-situ generation method.During the preparation of this composite material,BiVO₄ grew around the g-C₃N₄ nanoparticles,and the bonding between the two phases was further enhanced by calcination.The results show that the composite photocatalytic material is composed of BiVO₄ nanoparticles loaded by smaller g-C₃N₄ nanoparticles.These nanoparticles of different sizes form a nano-scale Z-type heterogeneous junction.Such structure promotes the separation efficiency of photo-generated carriers.The reaction active groups of this composite material are·OH and h⁺.This composite material exhibits good visible-light photocatalytic degradation performance.Its first-order reaction rate constant k for degradation of rhodamine B?20mg/L aqueous solution?can reach 0.242h^-1,which is 2.2 times higher than that of pure BiVO₄ nano particles(0.109h^-1).?2?The influences of preparation conditions on the structure and properties of BiVO₄ were studied in this paper,including the amount of CTAB,the amount of H₂O and the hydrothermal reaction conditions.The results show that CTAB is the key to form BiVO₄ nanosheets,which can refine the size of BiVO₄ nanosheets.The addition of H₂O can promote the peeling of bulk BiVO₄,and through the synergy with CTAB,small and uniform BiVO₄ nanosheets can be obtained.Hydrothermal reaction conditions affect the crystal phase of BiVO₄ nanoplatelets,and a lower hydrothermal temperature is beneficial to obtain BiVO₄ with a single monoclinic phase.Under optimized preparation conditions,the prepared BiVO₄ nanosheets have small size and good uniformity,and their first-order reaction rate constant k for the degradation of rhodamine B?10mg/L aqueous solution?can reach 0.545h^-1,which is 4.3 times higher than that of bulk BiVO₄.?3?The composite photocatalytic material with g-C₃N₄ nanoparticles loaded on the surface of BiVO₄ nanosheets was prepared by using the electrostatic self-assembly method.The structure-property relationship of composite materials was investigated.The results show that g-C₃N₄ nanoparticles are uniformly loaded on the surface of BiVO₄ nanosheets by forming surface-dispersed heterojunction.Free radical capture experiments show that the main active groups in the photocatalytic reaction of the composite are·OH and O^2-.Combined with semiconductor redox potential activity analysis,it can be seen that the formed heterojunction is a Z-type heterojunction.On the one hand,the surface-dispersed composite structure increases the area of heterojunction formed by g-C₃N₄ and BiVO₄,which promotes the migration and separation efficiency of photo-generated carriers;on the other hand,the Z-type heterojunction improves the redox potential and thus enhances the photocatalytic redox ability.With the loading of g-C₃N₄ nanoparticles,the photocatalytic activity of BVS/CNN shows a trend of first increase and then decrease.The maximum first-order reaction rate constant k for the degradation of rhodamine B?20mg/L aqueous solution?is 2.326 h^-1,which is 16.38 and 12.44 times higher than that of pure g-C₃N₄ nanoparticle and pure BiVO₄ nanosheet,respectively.