Aqueous Photocatalytic Oxidation of Biomass-Derived 5-Hydroxymethylfurfural for Customizable Product Synthesis

The utilization of biomass to produce fuels and chemicals is pivotal in addressing the energy crisis and mitigating environmental pollution. Biomass-derived 5-hydroxymethylfurfural (HMF) can be oxidized into high-value products such as 2,5-furandicarboxylic acid (FDCA), 2,5-diformylfuran (DFF), 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), and 5-formyl-2-furancarboxylic acid (FFCA). These products have extensive applications in bioplastics, pharmaceuticals, fragrances, and fuel additives. Photocatalysis has emerged as a promising approach for the oxidation of biomass-derived HMF due to its green and environmentally friendly nature, making the development of efficient photocatalytic systems for HMF oxidation highly significant.

Despite advances, current photocatalytic systems face several limitations: (i) The need for organic solvents to achieve high conversion/selectivity, with aqueous systems often yielding low product yields (<30%) due to solvent effects and radical-induced HMF degradation. (ii) The instability and photodegradation of commonly used metal sulfide catalysts, limiting their application. (iii) Most catalysis systems produce DFF only, with few systems capable of generating FDCA or valuable intermediates like FFCA, hindering the regulation and on-demand production of desired products. (iv) The unclear reaction mechanisms of aqueous-phase photocatalytic oxidation of HMF, which hampers the effective control over product types.

This project aims to establish a sustainable photocatalytic system using alkali and carbon co-doped g-C3N4 catalysts for the switchable and selective synthesis of DFF, FFCA, and FDCA in aqueous solution. Carbon doping enhances the oxidative capability of g-C3N4's holes and retards HMF mineralization, while generating numerous active amino/amine defect sites to facilitate the production of DFF. Alkali doping provides a mildly alkaline environment, facilitating the conversion of aldehyde groups to carboxyl groups for the selective production of FFCA and FDCA. These modifications promote the activation of the hydroxymethyl and aldehyde groups of HMF, enabling selective product formation. Our research plan includes: (i) Synthesizing and characterizing alkali metal and carbon co-doped g-C3N4 catalysts to understand their structural properties. (ii)
Investigating the performance and mechanisms of selective HMF oxidation using these catalysts, optimizing reaction parameters, and elucidating microscopic reaction processes. (iii) Expanding the application of these catalysts to the selective oxidation of other alcohols and aldehydes.

The significance of this project lies in its potential to improve the efficiency and selectivity of aqueous-phase HMF oxidation, providing crucial insights for the design and development of efficient photocatalysts. This research will advance the utilization of biomass resources and contribute to achieving the goal of "carbon neutrality."