A comparative study of medium-entropy oxide and metal oxide nanoparticles on graphene oxide for benzyl alcohol oxidation under solvent-free conditions

Abstract

A series of monometallic catalysts, such as Fe₃O₄, CoO, NiO, and CuO, along with their entropy-stabilized nanoparticles [(Fe,Co,Ni,Cu)₃O₄ medium-entropy oxide (MEO)], were synthesized and subsequently utilized for the solvent-free and selective aerobic oxidation of benzyl alcohol when supported on graphene oxide (GO). The resulting nanocomposites underwent characterization through various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis, thermogravimetric analysis (TGA), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), which collectively confirmed the successful formation of monometallic and spinel (Fe,Co,Ni,Cu)₃O₄ MEO nanoparticles integrated into GO. Among the utilized catalysts, the (Fe,Co,Ni,Cu)₃O₄ MEO–GO nanoparticles exhibit remarkable catalytic efficiency. A conversion rate of up to 17.2% and 28.8%, along with selectivity rates of 71.4% and 65.7% for benzaldehyde, can be attained in just 5 h at air pressures of 1 and 10 atm, respectively. A comprehensive analytical investigation indicates that the remarkable performance of (Fe,Co,Ni,Cu)₃O₄ MEO–GO nanocomposites can be ascribed to the synergistic interaction between the active sites of GO and the plentiful oxygen vacancies present in the (Fe,Co,Ni,Cu)₃O₄ MEO nanoparticles. The exceptional catalytic behavior of (Fe,Co,Ni,Cu)₃O₄ MEO–GO nanocomposites is attributed, according to detailed analyses, to the synergy between GO active sites and the numerous oxygen vacancies within the MEO nanoparticles. In summary, the extensive experimental findings indicate the promising use of (Fe,Co,Ni,Cu)₃O₄ MEO–GO nanocomposites within the chemical sector for the targeted oxidation of alcohols into high-value products.