Heterogeneous photocatalysis for biomass valorization to organic acids

Biomass is the most abundant and renewable carbon resource with great potential to replace traditional fossil fuels in the production of high-value organic acids, which can be applied in pharmaceuticals, food additives, and preservatives. Under relatively mild conditions, the photocatalytic oxidation of raw biomass and its derivatives has been developed as a more attractive technical approach for producing organic acids, due to the high reactivity of the active species produced by photoexcitation. Here, this review highlights recent important contributions to the photocatalytic conversion of biomass into organic acids, with an emphasis on the mechanisms involved and pathways toward specific products, mainly those including the direct oxidation of oxygen-containing functional groups of biomass with in situ generated active species, or active species inducing biomass to further form free radical intermediates that can promote the oxidative cleavage of C-C/C-O bonds. Strategies for tailored photocatalyst construction to enhance biomass upgrading processes with improved selectivity toward organic acids are elaborated. Finally, the challenges and perspectives for the efficient photocatalytic production of organic acids from biomass are presented. This review outlines recent progress in the photocatalytic conversion of biomass into organic acids with an emphasis on the mechanisms involved and strategies for the rational design/regulation of photocatalytic systems to enhance performance.