Conceive For Doping Modification Of G-C₃N₄ Or Its Hybrids And Their Photocatalytic Water Splitting Performance

In the current energy structure of the world,fossil fuels still dominate.However,the resulting energy shortage and environmental pollution problems are becoming more and more serious.Therefore,it is particularly important to seek a cleaner,more efficient and renewable new energy source.Semiconductor photocatalytic water splitting to produce hydrogen technology is known as the most promising and most effective way to solve the energy shortage problem.Graphite phase carbon nitride?g-C₃N₄?is favored by the majority of photocatalysis researchers because of its non-toxicity,suitable band gap and excellent stability.However,the monomer g-C₃N₄ has the disadvantages of small specific surface area and easy recombination of photogenerated carriers,which leads to its low performance of photocatalytic decomposition of water to produce hydrogen and low utilization rate of visible light,thus limiting its industrial application.To this end,this article takes g-C₃N₄ as the research object,through element doping and morphology control to modify it,and then improve the performance of photocatalytic decomposition of water to produce hydrogen.The research focused on the riveting of transition metal elements to improve the adsorption of hydrogen on the surface of g-C₃N₄ nanosheets,the co-doping of nonmetallic elements with g-C₃N₄ nanosheets,and the control of g-C₃N₄ nanotubes loaded with Au and CoO nanoparticles to construct three-phase composite photocatalyst.The preparation method can be controlled,through the evaluation of the photocatalytic decomposition of water to produce hydrogen,the visible light catalytic performance of the photocatalyst is studied,and the mechanism of action is revealed.The specific research content and conclusions are as follows:?1?The introduction of transition metal atoms?Fe,Co,Ni?can obtain Fe/g-C₃N₄,Co/g-C₃N₄,Ni/g-C₃N₄ nanosheets thinner than the monomer g-C₃N₄.Urea is used as a precursor,and transition metal nitrate is used as a source of transition metal ions.Mix the water phase uniformly,then remove the water.After sufficient grinding,heat-condensation at 550?to obtain transition metal element doped Fe/g-C₃N₄,Co/g-C₃N₄,Ni/g-C₃N₄ photocatalyst.The effect of metal content on its photocatalytic performance is discussed.The results show that the introduction of transition metal elements enhances the absorption of visible light by photocatalytic materials,especially after Co doping,the catalyst has additional absorption at 500-600 nm.And the catalyst doped with transition metal ions has a great influence on the absorption and desorption of hydrogen,which is conducive to the enhancement of photocatalytic activity.Among the Co/g-C₃N₄ series samples,the best Co content?0.03 g?has the best photocatalytic performance.Its photocatalytic hydrogen release rate can reach 12400?mol g^-1 h^-1,and it has good stability.?2?The soluble P source and S source are evenly mixed with melamine in water,and the white powder obtained by evaporating the water.Three-element co-doped g-C₃N₄ nanosheet photocatalyst was obtained by thermal polycondensation at 550?with O₂ in air as the O source.The effects of single-element doping and dual-element doping on their structural morphology and photocatalytic performance were investigated respectively.Combining the results and analysis of AFM,TEM,and BET,it can be seen that the photocatalyst obtained by the three-element co-doping has a thinner nanometer size and a larger specific surface area.From the theoretical calculation results,it can be seen that the three-element co-doping provides a relatively special electron transmission path.This provides more active sites and lower photogenerated carrier recombination rate for the photocatalytic decomposition of water to produce hydrogen.The hydrogen release rate of g-C₃N₄ with single element,single element doping,double element doping and three element doping is 467.3?mol g^-1 h^-1,586?mol g^-1 h^-1?CNP?,1158?mol g^-1 h^-1?CNS?,1487.7?mol g^-1 h^-1?CNPS?,2479?mol g^-1 h^-1?CNPSO?.Obviously,the three-element co-doped g-C₃N₄ nanosheets have better photocatalytic activity for hydrogen production by water splitting than the monomer and single?dual?element co-doped g-C₃N₄.?3?By controlling the mass ratio of melamine to urea,one-dimensional porous g-C₃N₄ nanotubes can be obtained by one-step calcination.CoO nanoparticles were grown on porous g-C₃N₄ nanotubes by in-situ growth method.Then,Au nanoparticles were deposited on the CoO/g-C₃N₄ nanotubes by the light reduction method to obtain a three-phase composite photocatalyst CoO/g-C₃N₄/Au.The experimental results show that the three-phase composite photocatalysis has an efficient photocatalytic activity for the decomposition of water to produce hydrogen.The optimal CoO/g-C₃N₄/Au(1492?mol g^-1 h^-1)releases hydrogen at a rate of about 5.7 times g-C₃N₄ nanotubes.Due to the presence of the heterostructure,the charge transfer rate at the interface is significantly accelerated,thereby enhancing the photocatalytic hydrogen production activity.The photoelectric performance test results show that the electron transmission rate of the composite material is faster,and the recombination rate of photogenerated carriers is lower,thereby better improving the photocatalytic performance.