Graphene oxide/ZnO nanocomposites applied in photocatalysis of dyes: Tailoring aqueous stability of quantum dots

Abstract

Nanocomposites between ZnO Quantum Dots (QDs) and Graphene Oxide (GO) were synthesized by sol-gel method in isopropanol. The proportion of GO aqueous dispersion was evaluated and ZnO QDs were also prepared with addition of water, for comparison. Indeed, the GO or water addition had a huge impact in the ZnO QDs size and photoluminescence, once the greater the GO/water addition, the greater the ZnO QDs size (from 4.5 ± 0.1–23.8 ± 0.4 nm) and the 50 µL of GO (or water) added to the synthesis led to a higher intensity emission. The photocatalytic activity of the ZnO-based materials was evaluated for methylene blue (MB) and astrazon blue (AB) degradation in isopropanol and water using two different sources of light irradiation (fluorescence and Hg vapor lamps). Once again, the GO/water addition affected their photocatalytic behavior and stability in aqueous medium. The ZnO QDs/GO had an impressive photocatalytic performance in both sources of light irradiation in isopropanol and aqueous medium (99% and 93% of degradation after 30 min of irradiation with Hg vapor lamp, respectively). In addition, the photocatalytic activity of this nanocomposite was stable when submitted up to 5 photodegradation cycles and to higher MB concentrations, besides being successfully reused in aqueous medium.