Thermal catalysis vs. photocatalysis: A case study with FeVO4/g-C3N4 nanocomposites for the efficient activation of aromatic and benzylic C H bonds to oxygenated products

Abstract

Three semiconductor metal vanadates FeVO4, BiVO4, and LaVO4 were synthesized. To improve the thermal catalytic and photocatalytic activity of highly efficient metal vanadate FeVO4, nanocomposites of FeVO4 and graphitic C3N4 were prepared. Nanocomposites were prepared via thermal annealing method by varying the composition of FeVO4 and g-C3N4. Catalysts were characterized by a series of complementary combination of powder X-ray diffraction, thermogravimetric analysis, N2 adsorption-desorption, scanning/transmission electron microscopy, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, photoluminescence, and photoelectrochemical techniques. Catalysts were investigated in the liquid phase oxidation of benzene, phenol, hydroquinone, naphthalene, anthracene, toluene, ethyl benzene, di-phenyl methane, and p-xylene under conventional thermal condition and visible light irradiation condition. Kinetic and thermodynamic parameters (such as k, Ea, H, G, and S) were calculated for the benzene hydroxylation by varying the reaction parameters under thermal catalytic condition. In order to confirm the active species responsible for the thermal catalytic and photocatalytic processes, UV–vis, fluorescence, cyclic voltammetry, and radical scavenging experiments were carried out with the help of suitable probe molecules. Based on the results obtained, reaction mechanism was proposed, and the structure-activity relationship was established. The catalyst was magnetically separated and recycled with negligible loss in the activity which is important for the sustainable heterogeneous catalysis. The developed catalytic process has the potential for the sustainable synthesis of a wide range of industrially important fine chemicals. Such a unique and detailed investigation of comparative study between thermal catalysis and photocatalysis using FeVO4/g-C3N4 nanocomposite will be highly useful to design optimum catalyst for an appointed catalytic reaction.