Riboflavin-Immobilized CeO2–RGO Nanohybrid as a Potential Photoredox Catalyst for Enhanced Removal of Organic Pollutants under Visible Light

We report a facile immobilization of riboflavin (RF) over in situ synthesized CeO2–reduced graphene oxide (RGO) nanohybrid surface synthesized through a simple wet-chemical approach for photocatalytic degradation of organic pollutants under visible light (λ ≥ 420 nm). The hybrid containing 3% w/w RGO shows an excellent photocatalytic activity under visible light. The UV–visible diffuse reflectance spectra, photoluminescence (PL) analysis, and transient photocurrent measurements corroborate that the hybrid RF@CeO2–RGO significantly absorbs visible light and exhibits lower recombination of charge carriers in comparison to RF@CeO2. The catalyst, RF@CeO2–RGO, offers enhancement in photocatalytic rate, i.e., 2.8-fold increase for methyl orange (MO) and 3.5-fold for p-nitrotoluene (PNT) in comparison to RF@CeO2 under visible light (2 h). This enhancement could be attributed to the synergistic effect among CeO2, RF (broadens visible light absorption region), and RGO (an electron-shuttling agent), which lead to an efficient separation of charge carriers. Consequently, the hybrid photocatalyst shows higher rate constant values, 2.31 × 10–2 and 2.00 × 10–2 min–1 for PNT and MO dye, respectively. The catalytic studies were monitored using UV–vis spectroscopy, high-performance liquid chromatography–photodiode array (HPLC–PDA), and gas chromatography–mass spectrometry (GC–MS) techniques. From the radical trapping experiments, the involvement of both superoxide and hydroxyl radicals was inferred. The present study provides more insights into the photochemical activity of metal-free sensitizer, RF, on metal oxide/hybrids (CeO2 and CeO2–RGO hybrids) and its viability for the remediation of water pollutants.