Textural and electronic structure engineering of carbon nitride via doping with π-deficient aromatic pyridine ring for improving photocatalytic activity

Abstract

Molecular doping of conjugated carbon nitride (CN) with π-deficient pyridine ring was applied for the modification of CN photocatalysts. According to the density functional theory (DFT) calculations, the incorporation of π-deficient pyridine ring entities in the conjugated CN matrix can effectively modulate the intrinsic electronic and band structure of CN by relocating its π-electrons. And then, a series of pyridine-doped CN photocatalysts were synthesized via thermal copolymerizing dicyandiamide (DCDA) with 2, 6-diaminopyridine (DPY). Integrating π-deficient pyridine ring into the CN network by modification with DPY does not alter the crystal structures or the core chemical skeleton of CN. A significant alteration in the texture and morphology was also observed for the modified CN samples. Moreover, integrating π-deficient pyridine ring into the conjugated CN network can actually engineer the electronic structure with tunable band-gap and promotes the migration and separation of photo-generating electron–hole pairs, which are in well agreement with the theoretical calculation results. The combined benefits of the molecular doping in terms of electronic, optical, surface and texture properties lead to a significant improvement in the photocatalytic activity for methyl orange (MO) degradation under visible light irradiation. The O2−/OOH radical is the major oxidation species in the photocatalytic oxidation process. The modulated CN incorporating π-deficient aromatic systems possess a higher reduction potential because the extension of optical absorption of CN mostly results from the up-shift of HOMO, which is favorable for the photocatalytic degradation of organic pollutant.