Metal-Nanoparticles-Loaded Ultrathin g-C₃N₄ Nanosheets at Liquid-Liquid Interfaces for Enhanced Biphasic Catalysis

Exploiting new interface-active solid catalysts is crucial to construct efficient Pickering emulsion systems for biphasic catalysis. In this work, ultrathin g-C₃N₄ nanosheets (g-C₃N₄-NSs) were developed as a new solid emulsifier to directly position catalytic sites at oil-water interfaces for improving the reaction efficiency of a biphasic reaction. Exemplified by a metal-involved biphasic reaction of nitroarenes reduction, the developed Pd/g-C₃N₄-NSs catalyst with Pd nanoparticles loaded on the surface of g-C₃N₄-NSs exhibited excellent activity with a catalytic efficiency of 1220 h^-1. Such activity was 4.2 and 17.9 times higher than those of Pd/g-C₃N₄-bulk and the ordinary Pd/C₈-SiO₂ catalyst, respectively. Also, in the biphasic oxidation reaction of alcohols, Pd/g-C₃N₄-NSs achieved a 2.3-fold activity enhancement. It was found by analyzing the solidified emulsion droplets that the Pd/g-C₃N₄-NSs catalyst was parallelly assembled at the oil-water interfaces. Because of the ultrathin thickness of g-C₃N₄-NSs, such a unique interfacial assembly behavior allowed precise positioning of Pd nanoparticles at the oil-water interfaces. As a result, the oil-soluble reactant could directly react with the water-soluble reactant at the oil-water interface hosting the Pd nanoparticles. Our elaborately designed reaction interface was believed to substantially avoid the diffusion barrier between oil-soluble and water-soluble reactants and then to significantly enhance the reactivity of biphasic reactions. This work highlights the importance of the interfacial location of catalytic sites in biphasic catalysis.