Selective Toluene Oxidation Using Sulfur-Doped Polymeric Carbon Nitride Photocatalysts

Selective traditional oxidation of toluene to high-value products like benzyl alcohol, benzaldehyde, and benzoic acid faces significant challenges due to high dissociation energy requirements, harsh reaction conditions, and complex product distributions. While photocatalysis using O₂ as an oxidant offers a green alternative, developing efficient and durable photocatalysts for selective oxidation in both batch and flow systems remains challenging. Here, sulfur-doped polymeric carbon nitride (S-CN) is demonstrated as a versatile photocatalyst for selective toluene oxidation, applicable in both powder form and as binder-free panels across various reactor configurations and solvents. Tuning S monomer content within supramolecular assemblies that serve as S-CN precursors, allows enhanced light absorption, optimized band positions, high specific surface area, and tailored structural properties of the ensuing catalysts. The optimized photocatalyst achieves high product selectivity, yielding ∼72% benzaldehyde and ∼26% benzoic acid after 24 h. Mechanistic studies confirm the concurrent oxidation and reduction reactions occurring and the roles of O₂ ^{· -} and ¹O₂. Extended reaction time (48 h) enables selective benzoic acid production (73.4%) with minimal benzaldehyde formation (<1%), demonstrating excellent product control.