Structural Control And Photocatalytic Activity Graphite-Carbonnitride Prepared By Molten Salt Method

With the development of society and demand for industrialization,the consumption of fossil fuel is gradually increased,resulting in the reduction of fossil fuel.Therewith,the biggest problem for human being will be the shortage of resources in the future.Hence,much attention should be paid to finding clean energy.Recently,photocatalysis using solar energy had attracted extensive attention on account of clean,high efficiency and non-extra pollution merits.Graphite-phase carbon nitride as a metal-free semiconductor has aroused the interest of researchers because of its excellent response in the visible region,stable chemical properties,low synthesis cost,and rich natural elements.However,the photocatalytic activity of conventional bulk carbon nitride is unsatisfactory,attributing to its relatively narrow visible light response region and high recombination efficiency of photogenerated carriers.The molten method was applied to synthesize the photocatalysts in this work.Meanwhile,oxygen and nitrogen defects were introduced into the samples,which were contributed to enhance the light absorption capacity and separation efficiency of photo-generated charges,aiming to promote the photocatalytic activity.The main contents are as follows:(1)The triazine-based carbon nitride PTI was synthesized by molten salt method,which exhibited a higher benzyl alcohol conversion efficiency and selectivity toward benzaldehyde compared with the conversional bulk carbon nitride.The optimal conversion efficiency(59%)was nearly twice times than that of bulk carbon nitride.Meanwhile,aerobic oxidation of a series of aromatic implied an unprecedented application of PTI.XPS and EPR analyses proved that the more oxygen vacancies content was existed in the obtained samples in comparison of conversional carbon nitride,which was beneficial to accelerating the separation efficiency of photoinduced electron-hole pairs,leading to a higher photocatalytic oxidation performance.(2)A series of 46 DP samples with a triazine structure was prepared by using melamine and 4,6-diaminopyrimidine as precursor and copolymer,respectively.Meanwhile,the proportion of molten salt was consisted with the last chapter.Photocatalytic experimental results demonstrated that the high selectivity toward benzaldehyde was still retained.The high selectivity toward benzaldehyde was remained in this section,indicating that the proper ratio of molten salt has a critical effect on the selectivity.Meanwhile,the optimal conversion efficiency of benzyl alcohol was 85%,which was higher than that of previous chapter(59.3%).XRD,IR and XPS analyses demonstrated that the structure of catalyst was modulated by copolymer doped into PTI and nitrogen defects were successfully induced into the obtained samples.Additionally,light response in visible light region was improved in a degree,contributing to the photocatalytic performance of photocatalysts.(3)2,4-diamino-6-hydroxypyrimidine has a similar structure with melamine,which was selected as the copolymer to synthesize heptazine/triazine structural carbon nitride(6HPT)using thermal polycondensation-melting salt method.Hydrogen evolution under visible light irradiation was selected as a model reaction to investigate the photocatalytic activity of 6HPT samples.And the optimal hydrogen production was 4707 ?mol/g in 6 hours for 6HPT-10% catalyst with a highest apparent quantum yield of 14.75% at 435 nm,which was higher than that of prepared by thermal polycondensation or melting salt method.