Combustion-assisted synthesis of molybdenum trioxide (α-MoO3) and their photocatalytic activity

This study focuses on the preparation of orthorhombic α-MoO 3 microplate using peroxide-assisted thermal decomposition method for photodegradation application. The structural and surface characterization were done using X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) that confirms the formation of pure orthorhombic MoO 3 crystal structure predominated with Mo +6 and a minor fraction of Mo +5 oxidation state, indicative of oxygen vacancies. The Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) reveals the plate-like morphology composed of Mo and O as the only predominant elements. The crystalline orthorhombic α-MoO 3 exhibit 8.54 m 2 /g specific surface area with mesoporous characteristics and optical band gap of 2.73 eV as evident by BET analysis and UV-Visible spectra. The photocatalytic activity was assessed by examining the photodegradation of methylene blue (MB). Studies were carried out to examine the impact of the catalyst dose, dye concentration, and pH. The results showed that the MB organic dye in the aqueous solution could be broken down by the strong photocatalytic activity of the generated orthorhombic α-MoO 3 . The higher the catalyst dosage, the faster MB is removed with α-MoO 3 . Additionally, a decrease in MB removal is observed as the dye concentration rises. The optimal conditions for MB degradation using MoO 3 photocatalysts was 96.70% at 40 mg of catalyst dose, 96.52% at 5 ppm dye concentration and 90.24% at pH 10 (using 30 mg catalyst) after 1140 min of UV irradiation. The improved photocatalytic efficiency was consistent with reduced charge-carrier recombination due to oxygen vacancy, suitable band gap and improved adsorption kinetics. The kinetic study follows Langmuir-Hinshelwood model obeying first-order reaction kinetics. Further, the recyclability test confirms the retention of 84.5% photodegradation efficiency after four consecutive catalytic cycles.