Anomalistic Wavelength Dependence of the Photocatalytic Behavior of rGO-TiO₂ Nanocomposite Against Methyl Orange

Methyl orange (MO) is an industry-based water pollutant that can be effectively removed with the aid of photocatalysts. In order to completely utilize the solar spectrum, visible light active photocatalysts are widely engineered by employing nano titanium dioxide (TiO₂) and reduced graphene oxide (rGO). In the current study, a nanocomposite of rGO-TiO₂ was synthesized and its potential for photocatalytic degradation of MO was studied in the aqueous medium. Interestingly, under visible light irradiation, a remarkable continuous blue shift of the maximum absorption wavelength of MO was observed for the first time. However, under UV irradiation, the absorption signature of MO disappeared rapidly as reported in previous literature. The underlying mechanism for the observed phenomenon was thoroughly investigated through radical scavenging assessments. It was found to be resulting from rGO, which acts as a photosensitizer only under visible light irradiation. The results of this study widen the empirical understanding of hidden mechanistic pathways of degrading MO using photocatalysis.