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 con-tributing 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.

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