Photocatalytic Selective Oxidation Of 5-hydroxymethylfurfural To 2,5-diformylfuran Over G-C₃N₄-based Catalyst

Diminishing fossil reserves and degradation of the environment are two severe problems of nowadays society.Currently,the conversion of renewable biomass resources into chemicals and fuels has received a growing interest,as it can substitute fossil resources to improve the sustainability of the chemical industry.5-hydroxymethylfurfural(5-HMF)is one of the most promising platform chemicals in the biorefinery area.5-HMF can be further transformed into diverse high-quality fuels and high-value chemicals such as 2,5-diformylfuran(DFF).Previous studies were reported on the oxidation of 5-HMF to DFF in the presence of stoichiometric oxidants,however the processes require amount of stoichiometric oxidant and generate a large amount of hazardous waste,which is undesirable environmentally and economically.Therefor,in recent years,conversion of 5-HMF to DFF with molecular oxygen as the oxidant by heterogeneous or homogeneous catalysis has drawn increasing attention.Although a relatively high yield,can be obtained by this way,this kind of catalysts has high price and is difficult to be removed in the product separation process.Hence it is necessary to develop novel low price catalysts and reacting under mild condition via an environmental-benign technique.Photocatalytic technology has been applied in various fields because of its green,light stability,low cost advantages.For environmental and economic reasons,the ideal system for selective oxidation of 5-HMF to DFF is using molecular oxygen as oxide and reactunder visible light.In this paper with cheap g-C3N4-based photocatalysts selective oxidation of 5-HMF to DFF activity were investigated the following work.1.g-C3N4 photocatalyst was prepared using a simple calcination method The optical properties and structure of samples were investigated by the of TEM,FT-IR,XRD,XPS,BET,PL,and UV-vis characterization.The effects of incident light wavelength,catalyst loading amount,reaction time and reaction solvent on the catalytic oxidation 5-HMF to DFF were also studied.The results suggest that under visible-light(>400nm)irradiation,the highest DFF yield of 26.7%is achieved with the selectivity of 85.6%in the presence of O2 after 6 h reaction.There is no significant decrease in photocatalytic rate after five consecutive cycles,implying that the obtained g-C3N4 photocatalyst has high stability.In addition,we also discussed the possible mechanism of the reaction.2.VO@g-C3N4 composite photocatalyst was prepared using a facile method and the structure and optical properties of samples were investigated in detail.The results of FT-IR and XPS show that loading of VO did not change the structure of g-C3N4.The result of UV-vis reveals that the absorption wavelength of VO@g-C3N4 has an obvious red shifted.PL spectra indicate that the recombination of the photogenerated carrier is distinctly decreased in the VO@g-C3N4 composite photocatalyst.The experimental results shows that VO@g-C3N4(10%V)composite exhibited excellent performance on the catalytic oxidation 5-HMF to DFF.Under visible-light(>400nm)irradiation,5-HMF conversion of 35.7%and selectivity of 86.0%can be achieved in the presence of O2 after 4 h reaction.