Biomimetic donor-acceptor motifs in carbon nitrides: Enhancing red-light photocatalytic selective oxidation by rational surface engineering

Abstract

Oxidation, especially selective oxidation by a heterogeneous catalyst with molecular oxygen, is a core technology for the conversion of petrochemical feedstock to commodity chemicals and pharmaceuticals. Existing catalytic approaches for efficient aerobic oxidation normally rely on the engagement of organometallic centers or transition-metal nanoparticles. In light of the necessity to develop sustainable production methodologies, multiple approaches for the metal-free polymeric carbon nitride (PCN) photocatalytic selective oxidation have been evaluated. However, the insufficient visible light optical absorption, poor charge-carriers separation and the weak driving force towards oxidation reaction impart a serious restriction on the efficiency and selectivity of the organic photosynthesis, especially under extended wavelength solar light irradiation. Here, we report a surface engineering photochemical modification method to fabricate a donor-acceptor (D-A) functional carbon nitride photocatalyst (ECN) under ambient conditions. The well-developed d-A structure, preserved high crystallinity and enlarged π-conjugation framework of the hybrid semiconductor-molecule ECN samples favor the improvement of the optical absorption, as well as the enhanced separation and migration of the photo-generated charge carriers. As a result, the obtained ECN photocatalysts exhibited remarkable enhancement in the photocatalytic aerobic oxidation of alcohols, even under an extended light wavelength of 620 nm red-light irradiation. The photocatalytic aerobic sulfides and sp3 C–H oxidation reactions were also considerably accelerated over ECN and may serve as a direct approach for the construction of value-added sulfoxide and ketone products.