Copper Sulfide Nanosheets for Photocatalytic Oxidation of Benzyl Alcohols and Hydroxylation of Arylboronic Acids

Two classes of semiconductor copper sulfide (CS) nanostructures with a sheet-like architecture were designed via a hydrothermal route merely by varying the sulfur source concentration. The newly developed CS nanoparticles showed a breakthrough in catalytic performances and served as a very efficient, versatile, and recyclable multifunctional catalyst. The hexagonal plate-shaped pure covellite (CuS) phase of CS nanoparticles synthesized for this purpose showed excellent results, enabling complete removal of water pollutants [MB degradation and Cr­(VI) reduction] under visible light irradiation within a few seconds of time. Contrarily, under ambient conditions, the mixed phase (covellite–digenite, CuS–Cu1.8S) with a broken nanosheet morphology was found to be a highly effective heterogeneous photocatalyst for the quantitative conversion of many aromatic and aliphatic alcohols to their respective aldehydes selectively. The direct band gaps of 2.06 and 1.90 eV calculated from UV–visible absorption spectroscopy data for CuS and CuS–Cu1.8S, respectively, suggested the semiconducting ability of the as-synthesized nanoparticles, which mainly assisted effortless visible light photocatalytic activity. Additionally, one more interesting development was achieved in this work: using CuS nanoparticles as a room-temperature catalyst for the oxidative hydroxylation of an array of arylboronic acid to prepare quantitative yields of corresponding phenols in a short period of time. Our designed catalyst outperforms most of the recently reported catalysts in terms of product yield and reaction time under mild reaction conditions in the synthesis of aromatic aldehydes and phenols. All the catalytic reactions were carried out at room temperature in this present work without using any expensive noble metals and harsh oxidizing agents. The enhacned catalytic performance of CS nanoparticles compared to that of other catalysts can be attributed to the size and specific composition and thereby the surface charge and exposed high energy facets of the nanoparticles due to the presence of sodium dodecyl sulfate as a surfactant in the synthetic procedure.