Preparation Of Transition Metal Composites And Photo/electrocatalytic Performance Study

The problem of indoor environmental pollution and the energy crisis caused by the depletion of traditional fossil energy sources are of increasing concern.In the environmental field,formaldehyde,as the main pollutant of indoor air,will seriously endanger human health with long-term exposure and content exceeding national standards.Photocatalytic technology has the advantages of simple preparation process,low price and cost,non-polluting process and complete and efficient mineralization,which makes it an effective way to deal with environmental pollution problems,and it can completely catalyze the oxidation of formaldehyde to water and carbon dioxide.The key issues limiting the application of photocatalysis are:weak visible light response of photocatalysts,low separation of photogenerated carriers and low redox of photogenerated carriers.A number of approaches have been used to improve the activity and stability of photocatalysts,but all these approaches have certain drawbacks.Therefore,the development of advanced photocatalysts remains a great challenge.In the field of clean energy development,hydrogen energy has attracted much attention due to the advantages of abundant surface resources and easy transportation,and hydrogen energy is also considered to be the most promising new energy source to replace non-renewable energy sources such as coal and oil.Hydrogen produced by hydroelectric reaction is of high purity;the raw material is water,which can come from natural rivers and streams;and no other pollutants are produced during the whole reaction process except oxygen,which is a way of hydrogen production in line with the concept of green chemistry.The electrolytic hydrogen production reaction under alkaline conditions has been limited by the slow reaction kinetics,so it is imperative to explore the development of efficient electrocatalysts.Based on the above problems,Bi/g-C₃N₄ and K-C₃N₄/Ag/Ag₃PMo₁₂O₄₀ transition metal composite photocatalysts and Mo Ni₄/Mo O_2.5-NF transition metal self-supporting composite electrocatalysts were prepared in this paper;the microscopic appearance,crystal structure,elemental composition,specific surface area and other physicochemical properties of the catalysts were characterized and analyzed by various techniques.The catalytic performance was systematically studied and the corresponding catalytic mechanism was proposed.Graphite phase g-C₃N₄ nanosheets were prepared by thermal condensation method with melamine as precursor.A series of Bi/g-C₃N₄ heterojunction photocatalysts were prepared by introducing metallic Bi through a simple solvothermal reaction.Experiments show that the degradation effect of Bi/g-C₃N₄ composites on formaldehyde gas is better than that of pure g-C₃N₄ under visible light irradiation.Among them,when the Bi content is 20%,the degradation rate of Bi/g-C₃N₄heterojunction to formaldehyde gas can reach 53.6%,which is 1.54 times that of g-C₃N₄.The results of cycling experiments show that the prepared photocatalyst has good cycling stability,and the photocatalytic mechanism of the heterojunction is also proposed.Ag/Ag₃PMo₁₂O₄₀（APM）heterogeneous nanoparticles obtained by photoreduction were uniformly loaded on K-C₃N₄ nanosheets,and the ternary heterojunction photocatalyst K-C₃N₄/Ag/Ag₃PMo₁₂O₄₀（abbreviated as K-C₃N₄/Ag/APM）was successfully synthesized.K-C₃N₄/Ag/APM was characterized and explored,and the degradation efficiency of K-C₃N₄/Ag/APM on HCHO under visible light irradiation was used as the evaluation criterion for photocatalytic activity.The results show that the K-C₃N₄/Ag/APM heterojunction can degrade 60%of gaseous HCHO(0.16 mg L^-1)（λ>400 nm）within 60 min.The best experimental parameters are temperature 20℃,relative humidity 70%,catalyst dosage 20mg,initial HCHO concentration 0.16mg L^-1.The Z-scheme charge transfer mechanism was confirmed by radical trapping experiments and electron spin resonance（ESR）experiments,and it was proved that·O₂^-and h⁺were the main active species in the oxidation reaction of HCHO.The intermediate species during the photocatalytic degradation of HCHO were tested by the in situ DRIFTS technique.A novel two-dimensional nanosheet self-supported composite electrocatalyst Mo Ni₄/Mo O_2.5-NF derived from Ni Mo O₄ nanosheets was prepared by a simple hydrothermal reaction and hydrogen reduction using nickel foam（NF）as a substrate.The prepared catalyst showed high electrocatalytic HER activity in 1 M KOH solution,and Mo Ni₄/Mo O_2.5-NF required an overpotential of 49 m V to reach 10 m A cm^-2,and the HER activity of Mo Ni₄/Mo O_2.5-NF can be further enhanced by an electrochemical cycle activation（CV）process.After 10 cycles,the overpotential of the catalyst to reach 10 m A cm^-2 decreased from 49 m V to 27 m V,even more than 20%Pt/C（32 m V）...