| Imines and their derivatives are an important class of textile chemicals that can be used as fluorescent pigments and dyes for synthetic fibers such as nylon,vinylon.Traditional methods for imine synthesis involve highly active reactants and environmentally unfriendly catalysts,which lead to high environmental pollution in the reaction process,complex of the products composition,difficult separation and purification.On the other hand,polyester fiber has become one of the most widely used and seriously discarded textile materials.At present,most waste polyester textiles are treated through landfill or incineration,which causes serious waste of resources and environmental pollution.Therefore,it is urgent to improve the extent of resource utilization.The application and development of various new materials and technologies in the fields of solving environmental pollution,energy shortages and green synthesis of chemicals has become an important scientific issue.In this thesis,g-C3N4-based composite catalysts were prepared through multiple methods using graphitic carbon nitride(g-C3N4)modified with different morphologies or functional groups as the structural unit.The visible light-driven activity of g-C3N4-based composite for high-selectivity green synthesis of imine,the dual function of green synthesis of imine synergistic hydrogen production and reforming polyester fiber to produce hydrogen were studied.The relevant disciplines were summarized by exploring the influences of the chemical composition and microstructure of the catalyst on the photocatalytic performance.Combined with nuclear magnetic resonance spectroscopy,high-resolution mass spectrometry and active species capture experiments,the plausible photocatalytic reaction mechanism was proposed.Our work demonstrates the potential applications of g-C3N4/MOF photocatalysts in the green synthesis of textile chemicals and the reuse of waste textiles.The thesis contains the following four aspects:1.Non-precious metal Ni-loaded g-C3N4 hollow spheres were prepared by calcination and subsequent photoreduction using melamine and cyanuric acid as raw materials.The effects of Ni content on the catalytic performance of visible-light catalytic oxidation of amines to imines and reforming polyester fiber for hydrogen production were investigated.The results demonstrate that Ni contributes to the separation of electron-hole pairs and the rapid transfer of charge carriers,thereby improving the photocatalytic activity of g-C3N4 hollow spheres.The optimal hydrogen production rate is 15.0?mol?g-1?h-1.The optimal conversion rate of benzylamine after five hours'illumination is 61.3%with>99%of selectivity,which is 2.4 times that of pure g-C3N4 hollow spheres.By investigating the conversion rate and selectivity of benzylamine with different substituents,the universality and high selectivity of the photocatalytic oxidation of amines to imines over Ni-loaded g-C3N4 hollow sphere were verified.Dyeing polyester fabrics with(E)-anthracen-10-yl-N-(anthracene-10-ylmethylene)methanamine dye exhibited good dye uptake and color fastness,indicating that it has the potential to be utilized as disperse dyes.Combining active species capture experiments with nuclear magnetic resonance and high-resolution mass spectrometry,the reaction mechanism of Ni-supported g-C3N4 hollow spheres for photocatalytic oxidation of amines to imines and reforming polyester fiber for hydrogen production was proposed.2.As a typical MOF semiconductor,Uio-66-NH2 has the characteristics of large specific surface area,high porosity,and visible light response,as well as good thermal stability.In this chapter,the g-C3N4/Uio-66-NH2 heterojunction was prepared by the annealing method.The influence of weight ratio of g-C3N4/Uio-66-NH2 on catalytic performance of oxidation of amines to imines and reforming polyester fiber for hydrogen production was studied,and the results indicated that the tight interface between g-C3N4 and Uio-66-NH2 at high temperature played a key role for enhancing the photocatalytic activity.Under visible light irradiation,the optimal hydrogen production rate of the heterojunction is 23.3?mol?g-1?h-1,which is 1.7 times that of g-C3N4.After 5 hours of visible light irradiation,the optimal benzylamine conversion is51.5%,which is 3.2 and 9.2 times that of g-C3N4 and Uio-66-NH2,respectively.Based on electrochemical impedance spectroscopy,transient photocurrent response,fluorescence spectroscopy,and active species capture experiments,the photocatalytic reaction mechanism for the selective oxidation of amines to imines was proposed.3.g-C3N4/Uio-66-NH2 nanotubes composites were prepared by an in-situ deposition method through loading Uio-66-NH2 on g-C3N4 nanotubes.The combination of g-C3N4and Uio-66-NH2 is beneficial to the separation of photogenerated electron-hole pairs and the enhancement of visible light absorption.The optimal hydrogen production rate of the composite photocatalyst is 41.9?mol·g-1·h-1,which is 1.3 times that of g-C3N4.The best conversion of benzylamine is 58.9%with selectivity>99%after 5 hours of reaction,which is 3.4 and 10.5 times that of g-C3N4 and Uio-66-NH2,respectively.Paramagnetic resonance spectrum and active species capture experiments show that·O2-is the main active species in the oxidation process of benzylamine.Combined with the high-resolution mass spectrometry of the intermediate product in the oxidation process of benzylamine,a photocatalytic reaction mechanism for selective oxidation of amines to imines is proposed.The results show the potential application of g-C3N4/MOF photocatalyst in the field of green synthesis of textile chemicals and hydrogen production from reforming polyester fibers.4.g-C3N4/Uio-66-NH2 composite was prepared via convent bond-connecting after the g-C3N4 nanotube was grafted with benzoic acid by diazotization reaction.The obtained g-C3N4/Uio-66-NH2 composite was employed as photocatalyst for synergetic hydrogen production and selective oxidation of benzylamine,reforming polyester fiber to produce hydrogen under visible light irradiation.Under the optimized conditon,the conversion rate of benzylamine is 707?mol?g-1?h-1,which is about 3.9 and 18.1 times that of g-C3N4 and Uio-66-NH2,respectively.The rate of synergistic hydrogen production is 575?mol?g-1?h-1,which is about 3.5 and 18.5 times that of g-C3N4 and Uio-66-NH2,respectively.After investigating the effect of different substituents of benzylamine on the photocatalytic activity,the universality and high selectivity of the photocatalytic synergistic reaction were verified.Using polyester fibers dispersed in an alkaline solution as a substrate,the optimal hydrogen production rate of the composite catalyst is 58.6?mol?g-1?h-1.The result suggests that the covalent bonding structure makes?electrons easier to delocalize between g-C3N4 and Uio-66-NH2,and therefore improving the separation efficiency of electron-hole pairs.Combining active species capture experiments with nuclear magnetic resonance and high-resolution mass spectrometry,we proposed a possible reaction mechanism of g-C3N4/Uio-66-NH2 for synergetic photocatalytic hydrogen production and benzylamine oxidation.This is currently one of the few examples of g-C3N4/MOF as a dual-functional catalyst for photocatalytic hydrogen production coupled with organic synthesis,which shows that a suitable photocatalyst can fully convert light energy into chemical energy.In the future,it is expected to produce clean energy while green synthesizing textile chemicals.The research results also show that photocatalytic technology can convert rich sources of waste textiles into hydrogen energy and small molecule organic chemicals under mild conditions,which has potential application prospects. |
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