Highly efficient solar photocatalytic degradation of a textile dye by TiO₂/graphene quantum dots nanocomposite

Herein, two sunlight responsive photocatalysts including TiO₂ nanoparticles (NPs) and TiO₂/graphene quantum dots (GQDs) nanocomposite for degrading a textile dye, Reactive Black 5 (RB5), were prepared. The results showed that 100% of 50 ppm RB5 could be degraded by TiO₂ NPs and TiO₂/GQDs within 60 and 30 min sunlight irradiation, respectively. Hence, much better photocatalytic activity in degradation of RB5 was achieved by TiO₂/GQDs under sunlight irradiation compared with pure TiO₂ NPs due to its lower band gap (2.13 eV) and electron/hole recombination rate. The photocatalytic degradation mechanism of RB5 by TiO₂ NPs was elucidated by adding some scavengers to the solution. The main reactive species contributing to RB5 degradation were surface hydroxyl radicals. The first-order solar degradation rate constant of RB5 for TiO₂/GQDs is greater than that of TiO₂ NPs under sunlight illumination.