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

Biomass resources are potential substitutes for chemical production because of its advantages of cheapness,abundance and fast regeneration.5-Hydroxymethylfurfural(HMF)is one of the most potential compounds among a large number of biomass platform compounds and can be used as an intermediate in the conversion of various industrial value added products such as 2,5-diformylfuran(DFF).In the earlier study,DFF was mainly prepared from HMF by traditional stoichiometric oxidants,but this method has the disadvantages of low atomic utilization,high cost and toxic and hazardous substances.The molecular oxygen as an oxidant has the advantages of green,clean and cheap,so get more and more attention.With the maturing of photocatalytic technology,its advantages of non-pollution,environmental friendliness and low cost have been applied in various cutting-edge research fields.Therefore,it is an ideal reaction process to use photocatalytic method selective oxidation of HMF to DFF from using molecular oxygen as oxidant,which is of practical significance to solve the current energy shortage and environmental pollution problems.In this paper,two kinds of g-C3N4-based composite photocatalysts were prepared,and their properties of selectively photocatalytic oxidation of HMF to DFF under visible light were investigated.1.WO3/g-C3N4 composite photocatalyst was prepared by a simple calcination method.The catalysts were characterized by XRD,FT-IR,XPS,TEM,UV-vis DRS,PL and PC methods.The structure,morphology and optical properties of the catalysts were studied.In the reaction system of photocatalytic selective oxidation of HMF to DFF,the effects of different W contents of WO3/g-C3N4 composite photocatalyst,incident light wavelength,reaction time and reaction solvent on the reaction performance were investigated.The results showed that WO3(10.5%)/g-C3N4 composite photocatalyst showed the best catalytic activity in 6 h of visible light irradiation in a mixed solvent of 3 mL of acetonitrile and 2 mL of trifluorotoluene.The conversion of HMF was 27.4%and the selectivity of DFF was 87.2%.Moreover,the catalyst has a high stability.In addition,we further explored the mechanism of the reaction by capturing the active species.2.Nb2O5/g-C3N4 composite photocatalyst was prepared by the same method,and a series of characterizations of the structure,morphology and optical properties of each sample were carried out.The results show that that loading of Nb2O5 did not change the structure of g-C3N4,and Nb2O5/g-C3N4 composite photocatalyst effectively inhibits the recombination of photogenerated carriers,so that the photocatalytic performance is significantly improved.In this reaction system,Nb2O5(13.9%)/g-C3N4 composite photocatalyst showed the best catalytic activity under the optimal reaction conditions.The conversion of HMF was 25.1%and the selectivity of DFF was 91.2%.