The Preparation Of The G-C₃N₄ Composites And Their Photocatalytic Performance For Water Splitting

With the acceleration of the industrialization process,energy problems become more prominent.Photocatalytic water splitting via the solar offers a new way for realizing the new energy.The process of photocatalytic splitting is that the solar energy is absorbed by the photocatalyst,resuting in electrons and holes,which induces the redox of water and then produces the hydrogen and oxygen.Undoubtedly,the key of this process is the photocatalytic materials.At present,the photocatalytic materials that can reach the prospective efficiency of the overall water spliting is mainly focused in the precious metal catalytic materials.Obviously,the precious metals do not have an advantage cost.Recent studies have shown that the g-C3N4,as a lower cost and visible region responsed catalyst,is a promising photocatalytic material for water spliting.However,the electron-hole recombination often occurs on the unmodified g-C3N4,which usually exhibts poor performance.Therefore,the main work of this study is that the preparation of the g-C3N4 composites and studing their photocatalytic performance for water splitting based on the g-C3N4 material.The effects of the linked way between C and g-C3N4 on their microstructure and catalytic performance was stuied.Three kinds of preparation way were explored to consturct the C/g-C3N4 via impregnation,hydrothermal impregnation and doping methods,respectively.The effects of the linked way on the surface graphite carbon/hybrid carbon(Cg/Cs),combined nitrogen/hybrid nitrogen(Nt/Ns)and band structure were investigated in detail.The results reveal that the introduction of C can effectively improve the visible light absorption of g-C3N4.Compared with the hydrothermal impregnation and doping method,the conventional impregnation is benefit to obtianing the higher proportion of Cg/Cs and Nt/Ns,and the lower conduction band energy(-0.69 eV).The photocatalytic performance of water spliting shows that a high proportion of Cg/Cs and Nt/Ns and low conduction band is helpful to improving the hydrogen evolution rate of photolytic water.the C/g-C3N4 preapered by the conventional impregnation shows the highest efficiency with the hydrogen production rate about 10.7 ?mol·h-1.The effects of the reduction way on the microstructures of Pt/g-C3N4 and their catalytic performance were stuied.To study the effects of the reduction rate on the structure of Pt nanoparticles and the bonding situation between the Pt nanoparticles and the g-C3N4,the effects of alcohol(methanol,ethanol,ethylene glycol)reduction,hydrazine hydrate reduction and photoreduction on the microstructure and the catalytic properties of Pt/g-C3N4 were investigated.The results show that the relative bigger Pt particles(5.0 nm)can be obtained by reduction of ethylene glycol than that by ethanol and methanol.About 7.0 nm Pt particles can be obtained by the reduction of hydrazine hydrate.The sizes of the Pt nanocrystals obtained by the photoreduction are about 2.0 nm.The introduction of Pt promoted the response of g-C3N4 in the visible light absorption region.The band gaps of these composites can be varied from 2.60 to 2.95 eV.The results show that the catalyst prepared by the ethylene glycol presented the highest hydrogen production rate up to 136.5 ?mol·h-1 among the three alcohol.The hydrogen production rate of the Pt/g-C3N4 reduced by the hydrazine hydrate can reach 62.9 ?mol·h-1,while the catalyst prepared by the light reduction can achieve 19.7 ?mol·h-1.The effects of the reduction way on the microstructures of Au/g-C3N4 and their catalytic performance were stuied.To study the effects of the reduction rate on the structure of Au nanoparticles and the bonding situation between the Au nanoparticles and the g-C3N4,the effects of three alcohol reduction and hydrazine hydrate reduction on the microstructure and the catalytic properties of Au/g-C3N4 were investigated.The results show that the sizes of the Au particles are about 6.2-7.5 nm prepared by the alcohol reduction,while the sizes about 9.7-13.9 nm constructed by the hydrazine hydrate reduction.The introduction of Au also promoted the response of g-C3N4 in the visible light absorption region.The band gaps of these composites can be varied from 2.14 to 2.88 eV.The results show that the Au/g-C3N4 prepared by the ethylene glycol presented the highest hydrogen production rate wiht 136.5 tmol.h-1 among the three alcohol,while the hydrogen production rate of the Au/g-C3N4 reduced by the hydrazine hydrate can reach 22.3 ?mol·h-1.