Highly Efficient Photo-Reduction of p-Nitrophenol by Protonated Graphitic Carbon Nitride Nanosheets

Photocatalytic reduction of p-nitrophenol to p-aminophenol is important because of the high toxicity of p-nitrophenol and the wide application of p-aminophenol. Graphitic carbon nitride (g-CN) is an excellent photocatalyst for various photo-reduction reactions, but inefficient for photo-reduction of p-nitrophenol due to the electrostatic exclusion. In this work, we control the morphology and surface property of g-CN and achieve significantly enhanced activity. The obtained protonated g-CN nanosheet (pg-CNNS) material has positively charged surface that can adsorb p-nitrophenolate anions, therefore facilitating the transfer of photo-generated electrons from catalyst to p-nitrophenol. Its reaction rate is 1626 times higher than that of the pristine g-CN. Besides the surface charge, the morphology of photocatalyst also has important effect on activity, which is demonstrated by the relatively low activity of protonated g-CN in comparison to pg-CNNS. The pg-CNNS photocatalyst has an excellent stability and superior catalytic universality for photo-reduction of various nitroaromatic compounds. This work does not only expand the application of a well-known material, but also highlights the importance of understanding photocatalytic mechanism for designing photocatalyst.