Selective Oxidation of Biomass over Modified Carbon Nitride Photocatalysts

Using carbon nitride photocatalysts to catalyze the selective conversion of biomass platform molecules could not only expand the application fields of non-metallic catalysts but also alleviate the dependence on fossil energy in chemical manufacturing.2,5-diformylfuran is an indispensable intermediate for the production of value-added chemicals.In this study,pyromellitic dianhydride and melem were used as the precursors.The pyromellitic dianhydride monomer was incorporated into the carbon nitride skeleton by high-temperature heat-treatment,and the catalysts were further treated with H2O2.Finally non-metallic carbon nitride photocatalysts containing nitrogen hydroxyl groups were prepared.Moreover,its performance in the selective oxidation of 5-hydroxymethylfurfural into2,5-diformylfuran under visible light excitation was investigated.The results showed that H2O2-treated samples could generate nitroxide radicals under light irradiation,resulting in the selective oxidation of hydroxyl groups on the side chains of 5-hydroxymethylfurfural molecules into aldehyde groups,avoiding undesired side-reactions （ring-opening,mineralization reactions,etc.） caused by various reactive oxygen species that may be generated in aqueous solutions.In particular,under the excitation of an LED light source with a specific wavelength （400 nm）,when the ratio of melem to PMDA precursor was 1:2,the selectivity of 2,5-diformylfuran over the photocatalyst could reach 96.2%.