Visible light-assisted photocatalytic degradation kinetics of methylene blue (MB) dye by β-MoO3 nanoplates and α-MoO3 nanorods

In this study, α-MoO 3 and β-MoO 3 photocatalysts were synthesized using an ultrasonic-assisted hydrothermal method and annealed in air at 450 °C and 650 °C. The physicochemical properties of the catalysts were investigated using X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), field emission-scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), surface area analysis (BET), photoluminescence (PL), and ultraviolet-visible DRS spectroscopy. The photocatalytic performance of the photocatalyst in the degradation of methylene blue (MB) dye in an aqueous solution under visible light illumination was evaluated under different conditions such as photocatalytic dose, irradiation time, initial pH, and MB concentration. The progress of the degradation was monitored using a UV-visible spectrophotometer and COD analyser. Although both catalysts showed good photocatalytic degradation of MB after 150 min of irradiation time, α-MoO 3 nanorods exhibited better degradation efficiency and a higher rate constant (97% and 0.211 min⁻¹) than β-MoO 3 nanoplates (90% and 0.1511 min⁻¹), which could be attributed to their smaller size, better adsorption capacity, and lower PL intensity, which leads to a lower recombination rate of photogenerated electrons and holes. Through the action of scavengers such as EDTA, BQ, and tBuOH, the dominant reactive species responsible for the degradation of MB were the hole (h + ) and hydroxyl radicals (.OH) under visible light irradiation. The α-MoO 3 can be reused up to five times without any chemical treatment and without losing its stability or effectiveness.