Preparation And Visible-light Photocatalytic Performance Of Novel Carbon Nitride Based Composite Photocatalysts

Breaking through the serious challenge environment brings is the inevitable requirement to realize the continuous development of humans.Photocatalytic technology was born through using sunlight to degrade pollutes efficiently.The synthesis of high performance and high stability photocatalysts is the primary question we need to solve.Traditional photocatalysts,take TiO₂ for an example,can only absorb ultraviolet light,resulting in a poor utilization in practical application.Therefore,the development of visible-light response photocatalysts with high efficiency and low cost has become the hot spot.In this article,2D g-C₃N₄ was used as a basic material to develop bismuth hybrid photocatalysts.Different analysis measures were taken to explore the changes of morphology,structure and performance after the introducing of 2D g-C₃N₄.The possible mechanisms of photocatalytic processes were studied at the same time.The research is stated in detail as follows:（1）Bi₂WO₆ with sphere-like hierarchical structure was synthesized through a hydrothermal process.After that,different scales of 2D g-C₃N₄/Bi₂WO₆ were assembled successfully using a high temperature hydrothermal method.Considering the characterization results of such as XRD,SEM,TEM,BET,it can be proved that the introducing of 2D g-C₃N₄ improved the specific surface area of Bi₂WO₆ greatly.Besides,a big thin film layer was deposited on the surface of Bi₂WO₆.The optical and electrical test demonstrated that the recombination of electrons and holes got suppressed when composited with 2D g-C₃N₄.When the amount of 2D g-C₃N₄increased to 30%,it showed the best photocatalytic activity in degrading RhB.ESR and free radicals trapping experiments were performed and the results implied the enhanced photocatalytic performance followed by a Z-Scheme mechanism,through which·O₂^-,·OH and h⁺work together in degrading the pollutes.（2）Bi（NO₃）₃·5H₂O and Na₂WO₄·2H₂O were used to prepare Bi₂MoO₆ with a hollow spherical morphology.2D g-C₃N₄ was then introduced to synthesize 2D g-C₃N₄/Bi₂MoO₆ composites through an in-situ method.In order to investigate the structure,morphology and photocatalytic performance,the as-prepared samples were characterized by XRD,FT-IR,XPS,SEM,TEM,DRS,PL,BET,EIS and so on.The results showed that the crystal structure of Bi₂MoO₆ got unchanged after introducing2D g-C₃N₄ while only enlarged the specific surface area and accelerated the separation of charge carriers.From the degradation of RhB,it can be known that when the mass fraction of 2D g-C₃N₄ reach to 30%,the composite showed the best photocatalytic activity and the rate content was 14 times than pure Bi₂MoO₆.During the degradation,the electrons on the CB of 2D g-C₃N₄ combined with O₂ to produce·O₂^-and part of holes on the VB of Bi₂MoO₆ took part in oxiding H₂O/OH^-to produce·OH or degrading directly.It has proved that the build of Z-Scheme is the key to improve of photocatalytic performance of Bi₂MoO₆.（3）Oil bath was used to fabricate monoclinic BiVO₄ and 2D g-C₃N₄/BiVO₄composites.The characteristic results such as XRD,XPS,SEM and BET found that introducing a certain amount of 2D g-C₃N₄ can increase the surface areas of BiVO₄vastly,while keeping the structure unchanged.In addition,2D g-C₃N₄/BiVO₄ had a higher separation efficiency of charge carriers than pure BiVO₄ tested by optical and electrical measures.When the amount of 2D g-C₃N₄ reached to 30%,the degradation efficiency of RhB under visible light was 62%,which is 12 times than BiVO₄.It can be found from the mechanism that the electron on the CB of BiVO₄ recombined with the holes on the VB of 2D g-C₃N₄ quickly.The holes left on the VB of BiVO₄ can produce·OH and electrons left on the CB of 2D g-C₃N₄ reacted with oxygen to produce·O₂^-.As a result,·OH,·O₂^-and holes worked together to degrade pollutes.