Study On Photocatalytic Degradation Of Environmental Pollutant Rh B By Mo-based Cocatalysts/g-C₃N₄ Composite Materials

Along with the rapid development of industrial civilization and the continuous improvement of people's living standards,environmental pollution and energy crisis problems have become increasingly serious.Semiconductor photocatalysis technology is an effective method to solve these crisis problems.The development of high-efficiency and stable semiconductor photocatalysts to utilize solar energy to produce clean energy and to control environmental pollution,such as photocatalytic hydrogen evolution,photocatalytic CO₂ reduction and photocatalytic environmental pollutants degradation,has excellent application prospects.Polymer semiconductor graphitic carbon nitride?g-C₃N₄?has the advantages of non-toxicity,visible light response,high stability and low cost,and is regarded as a star material in the field of photocatalysis.However,bulk g-C₃N₄ always exhibits poor photocatalytic performance due to its small specific surface area and low photogenerated carrier separation rate,which greatly restricts its practical application.In this paper,two-dimensional g-C₃N₄?2D g-C₃N₄?was selected as the supporting photocatalyst and improve its photocatalytic performance by loading different noble-metal-free co-catalysts.The visible-light catalytic performance of the prepared photocatalysts were tested by degradation of Rhodamine B?Rh B?,and the relationship between material structure and properties was researched and revealed.The main research contents and conclusions of this paper are as follows:?1?MoO₂-C was prepared by high temperature reduction under inert atmosphere,and 2D g-C₃N₄ was prepared by two-step method?thermal polymerization and thermal exfoliation?.Finally,MoO₂-C/2D g-C₃N₄ composite photocatalyst was prepared by self-assembly method successfully.The performance of MoO₂-C/2D g-C₃N₄ composite photocatalyst was tested by using Rh B solution?10 mg/L?as model pollutant and the optimal loading amount of MoO₂-C was explored.The 15%MoO₂-C/2D g-C₃N₄ composite photocatalyst showed the highest photocatalytic performance,and the degradation rate of Rh B was 95%within 60 min under visible light irradiation,which was much higher than bulk 2D g-C₃N₄.The photocurrent test showed that the photocurrent intensity of the MoO₂-C/2D g-C₃N₄ composite was significantly higher than that of the bulk 2D g-C₃N₄,indicating that the separation rate of photogenerated carriers can be improved by introducing MoO₂-C.MoO₂-C has many advantages such as cheap and high carrier mobility,which are beneficial for its commercial application.?2?MoN was prepared by high temperature reduction of MoO₃ precursor under NH₃ atmosphere,and MoN/2D g-C₃N₄ composite photocatalysts with different MoN loading amount were prepared by self-assembly method.The 10%MoN/2D g-C₃N₄composite showed the best photocatalytic activity,95.5%of Rh B can be degraded within 60 min of visible light irradiation.The results show that the photogenerated electrons of 2D g-C₃N₄ can be trapped and exported by MoN effectively.The PL lifetime of the 10%MoN/2D g-C₃N₄?1.36 ns?was decreased significantly than that of2D g-C₃N₄?6.93 ns?,indicating that more photogenerated electrons can participate in the photocatalytic reaction.In addition,the ESR test results confirmed that the introduction of MoN can enrich the concentration of photogenerated electrons,and then generated·OH radicals after a series of reactions,finally improving the ability of composite to generate highly reactive free radicals.This work can also provide new ideas for finding newly noble-metal-free materials as photocatalytic co-catalysts.?3?Mo₂C@C was synthesized by a temperature programmed method in reduction atmosphere?5%H₂/Ar?and combined with 2D g-C₃N₄.Mo₂C@C has a large work function and its electronic structure is similar to platinum?Pt?,which means it may exhibit similar co-catalytic behavior with noble metal.The experiment results show that the introduction of Mo₂C@C can effectively improve the photocatalytic performance of 2D g-C₃N₄.15%Mo₂C@C is the optimum loading amount,and the degradation rate of Rh B reached 97.5%within 60 min of visible light irradiation.Photoelectrochemical test results show that the photocurrent response of Mo₂C@C is almost negligible,meaning that it mainly plays the role of photogenerated carriers transporter in the composite photocatalytic system.The PL intensity of the composie is much lower than that of the 2D g-C₃N₄,indicating that the recombination of photogenerated electron-hole pairs can be inhibited effectively by Mo₂C@C.The composite photocatalyst showed good performance in photocatalytic test,especially in the photocatalytic hydrogen production,its co-catalytic performance was better that of Au,which has certain reference significance for the design and preparation of photocatalytic materials according to theoretical guidance.