Catalytic hydrogenation of p-nitrophenol using a metal-free catalyst of porous crimped graphitic carbon nitride

Currently, most catalysts for hydrogenation of p-nitrophenol employ the size- and shape-controlled noble metal (Au, Ag, Pd and Pt, etc.) nanomaterials or which supported on appropriate supports. Nevertheless, their high prices and low reserves severely limit the industrial application. Here we report a metal-free catalyst of porous crimped graphitic carbon nitride, which is prepared by calcining dicyandiamidine (a new precursor). This catalyst possesses abundant amino groups on the terminal edges of in-planar tri-s-triazine ring and large specific surface area, thus exhibits extremely high catalytic activity for catalytic hydrogenation of p-nitrophenol in the presence of NaBH4, which can be equivalent to (or even higher than) those of the previously reported noble metal-based catalysts. Interestingly, the kinetics analysis of hydrogenation of p-nitrophenol to p-aminophenol shows that the reaction follows the zero-order kinetics, different from the pseudo-first-order kinetics for the hydrogenation over the noble metal-based catalysts. In fact during reaction process, the catalytic oxidation of BH4- and the generation of hydride ion (H-) occur on the catalyst surface, while the hydrogenation process of p-nitrophenol proceeds in the bulk solution. This work establishes a new understanding of the hydrogenation process of p-nitrophenol using the metal-free catalyst based on graphitic carbon nitride.