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Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O 2 − during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (∼56 μmol g−1 h−1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition. [Display omitted] • Bifunctional CN with K, S co-doping is synthesized via a facile calcination process. • Acidic cellobiose photoreforming to simultaneously obtain gluconic acid and syngas. • Cellobiose conversion (>80%) and gluconic acid selectivity (>70%) can be achieved. • Favorable generation of •O 2 − proved by DFT is essential for gluconic acid production. [ABSTRACT FROM AUTHOR]

Biomass photorefining is a promising approach for sustainable clean energy and high-value chemical production. However, selectively converting glucose into glucaric acid, the most valuable derivative, still poses a significant challenge due to the difficulty in transforming the terminal hydroxyl group into a carboxy group. Here, we demonstrate that highly selective glucose photorefining into glucaric acid can be achieved by synergistically coupling alkalizing modification of polymeric carbon nitride (CN) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) mediation, which promotes the oxidation of the primary alcohol group attached to the C6 site of gluconic acid. Density functional theory (DFT) calculations affirm the enhanced performance of modified CN in glucaric acid production. When medicated with TEMPO, the optimized photocatalysis achieves ∼ 100 % glucose conversion and > 30 % glucaric acid yield, setting a record for photocatalytic glucaric acid production. This work showcases the significance of combining photocatalyst modification and redox mediation for inspiring high-efficiency photocatalysis systems for biomass photorefining. [Display omitted] • Alkalized CN with potassium doping synthesized through simple calcination. • Constructed synergistic system of photocatalyst and organocatalyst. • Achieved highest reported glucaric acid yield (> 30 %) via photocatalysis. • Proven superior performance of modified CN for glucaric acid production by DFT. [ABSTRACT FROM AUTHOR]