Minireview: Selective production of hydrogen peroxide as a clean oxidant over structurally tailored carbon nitride photocatalysts

Hydrogen peroxide (H₂O₂) is a clean oxidant, and its demand has continuously risen in various industries for pulp/paper bleaching, chemical synthesis, wastewater treatment, etc. H₂O₂ is commercially produced by the anthraquinone method, which has some drawbacks, including (i) toxic solvent, (ii) explosive hydrogen gas as a precursor, and (iii) a high energy input; therefore, a new technology based on cost-effective and green processes is required. Photocatalytic production of H₂O₂ can be considered the most environmentally benign and economically feasible process because it requires only dissolved oxygen, water, and sunlight. Among various photocatalysts, polymeric carbon nitride (C₃N₄) is a promising candidate for H₂O₂ production by virtue of its (i) simple synthesis by a thermal polymerization, (ii) structure consisting of earth-abundant carbon and nitrogen, (iii) effective bandgap size for visible light absorption, and (iv) suitable position of conduction band for reduction of oxygen dissolved in water. In this minireview, the mechanism of H₂O₂ formation over C₃N₄ has been discussed, and the strategies to optimize the photocatalytic activity have been summarized regarding structural and surface modification techniques. This overview of diverse methodologies to selectively control electron transfer to dissolved oxygen should be in demand not only for developing new-generation C₃N₄-based materials, but also for commercialization of solar-light-driven photocatalytic H₂O₂ production system.