In situ real-time assessment of wavelength dependent degradation of methyl orange on rGO-TiO2 photocatalyst

Titanium dioxide (TiO₂) has been extensively incorporated with reduced graphene oxide (rGO) to synthesize visible light (Vis) active photocatalysts. Here, we synthesized such rGO-TiO₂ nanocomposite with 10% rGO by mass. The photocatalytic activity of rGO-TiO₂ was quantitatively evaluated using quartz crystal microbalance (QCM). The <i>in situ</i> real-time QCM data resulted in different photocatalytic degradation percentages of methyl orange (MO) at the solid-air interface under ultraviolet (UV) and Vis irradiations. Conventional UV-Vis studies at the solid-liquid interface revealed that a unique hypsochromic effect occurs selectively under Vis irradiation. Radical scavenger studies confirmed that photogenerated holes are the primary active species contributing to this wavelength dependence. The degradation mechanisms under both irradiations are proposed based on the co-catalyzing and photosensitizing dual nature of rGO. The results of this study enhance the empirical knowledge of modified TiO₂ photocatalysts while signifying the impact of irradiation wavelength on the extent and mechanism of photocatalytic degradation.