Enhanced nitrogen vacancy density induced by sulfur doping on carbon nitride facilitates selective lactic acid production

Abstract

The integration of biorefining and photocatalysis represents a highly promising approach for enabling the green and efficient synthesis of high-value chemicals derived from biomass. Herein, we successfully synthesized a metal-free carbon nitride photocatalyst doped with sulfur (S), which induced the formation of nitrogen vacancies (N_V). The optimized catalyst (S₂₀–CN–N_V) exhibits outstanding photocatalytic activity, achieving 95.5 % of glucose conversion and 95.1 % of lactic acid (LA) selectivity within 60 min under visible-light irradiation. Remarkably, the LA yield remains impressively high at the initial 97.5 % even after 6 cycles. Experimental studies and characterizations reveal that S doping significantly increased the concentration of N_V, and the synergistic effect of N_V and S doping enhanced the visible-light absorption and facilitated the separation of photogenerated carriers as well as the activation of oxygen, thereby promoting the generation of superoxide radicals. Density functional theory simulations further reveal that S₂₀–CN–N_V exhibits exceptional glucose adsorption capacity and requires low activation energy in the rate-limiting step. Consequently, S doping induced the formation of N_V thus boosted the photocatalytic oxidation process of glucose into LA. This study provides valuable insights for guiding the design of photocatalyst through nonmetal-doping and defect engineering strategies, facilitating the efficient valorization of biomass-derived platform chemicals.