Study On The Performance Of GC₃N₄ With Transition Metal As Auxiliary Agent In Photocatalytic Decomposition Of Water To Produce Hydrogen

The global energy crisis and environmental problems are a serious threat to the sustainable development of human society.Since the photocatalytic decomposition of water to hydrogen on TiO₂ electrodes has been discovered,the technology of photocatalytic decomposition of water has been considered as the most promising method for solving energy and environmental problems.Moreover,TiO₂ has also become a semiconductor catalyst widely studied.However,due to the wide band gap of TiO₂,the utilization of light is low,which limits its practical application.Therefore,the development of a highly efficient,non-toxic,visible light-responsive and stable photocatalyst is a major challenge for photocatalytic decomposition of water.In the past few decades,in order to make greater use of visible light in the solar spectrum.Researchers have made great strides in developing new types of photocatalysts with visible light response.In recent years,the polymer n-type semiconductor photocatalytic material based on graphite phase carbon nitride?g-C₃N₄?has been deeply studied,which shows good visible light absorption properties and stable performance of photocatalytic splitting of water to produce hydrogen.Compared with most traditional semiconductor photocatalytic materials,g-C₃N₄ has a unique electronic band structure?E_g=2.7eV?,simple preparation method,rich precursor source,good chemical stability and non-toxicity.These excellent properties make g-C₃N₄ a good photocatalytic material.However,g-C₃N₄ alone as a photocatalyst,due to the rapid recombination of photogenerated electron-hole pairs,the photocatalytic efficiency is low,which greatly limits its practical application.In this paper,g-C₃N₄ was used as a research object to inhibit the rapid recombination of photogenerated carriers by supporting a cocatalyst on the surface to promote photogenerated electron transfer.The photocatalytic performance of the g-C₃N₄ material was improved by optimizing experimental conditions and preparation methods.The main research contents are as follows:The first part:Melamine is used as the precursor of g-C₃N₄,and cobalt acetate tetrahydrate is used as the cobalt source.First,sodium carbonate is used as a precipitant in a glycol solvent to obtain the mixture of cobalt precipitate and melamine.Then,the resulting mixture is subjected to a simple calcination method to obtain the CoO/g-C₃N₄?denoted by CoO/CN?material in the argon atmosphere.Finally,the CoO/g-C₃N₄material is reduced in the Ar-H₂ mixed gas to obtain the Co/g-C₃N_4-x?denoted by Co-/CN?composite photocatalyst.In this process,nitrogen-deficient graphitic carbon nitride(denoted by g-C₃N_4-x)was successfully prepared due to the catalytic hydrogenation of metal Co.The size of the metal Co particles can be adjusted by changing the reduction temperature and the amount of cobalt acetate tetrahydrate.The results show that under visible light??>420 nm?,Co/CN exhibits excellent photocatalytic decomposition of water to produce hydrogen compared with pure CN and CoO/CN.When the reduction temperature is 400°C,the mass of cobalt acetate tetrahydrate is 0.1 g,and the activity of the Co/CN catalyst having a metal Co particle size of?3.6±2.2?nm is optimal.On the one hand,the doping of the metal Co into the CN lattice and the N-defect generation reduce the band gap of the catalyst.On the other hand,smaller metal Co nanoparticles are highly dispersed on the surface of g-C₃N_4-x,which more efficiently transfers photogenerated electrons,inhibits photo-generated carrier recombination,and enhances photocatalytic activity.The second part:We use urea as the precursor and obtain g-C₃N₄ nanosheets by secondary baking.Then,the mixture of nickel acetate and g-C₃N₄ is obtained by conventional impregnation.And the mixture was calcined to obtain the NiO/g-C₃N₄material.The ratio of Ni to g-C₃N₄ was adjusted by changing the mass fraction of nickel acetate in g-C₃N₄.As a result,it is confirmed that the activity is the best when the content of Ni added is 0.7625%in g-C₃N₄.The surface-loaded cocatalyst on g-C₃N₄facilitates efficient separation of photogenerated electron-hole pairs.