Shape controllers enhance the efficiency of graphene–TiO2 hybrids in pollutant abatement

Abstract

The addition of graphene nanoplatelets (GNP) to TiO₂ nanoparticles (NPs) has been recently considered as a method to improve the photocatalytic efficiency of TiO₂ by favoring charge carrier separation. Here, we show that it is possible to improve the efficiency of GNP–TiO₂ composites by controlling the shape, stability, and facets of TiO₂ NPs grown on GNP functionalized with either COOH or NH₂ groups, while adding ethylendiamine (EDA) and oleic acid (OA) during a hydrothermal synthesis. We studied the photocatalytic activity of all synthesized materials under UV-A light using phenol as a target molecule. GNP–TiO₂ composites synthesized on COOH-functionalized GNP, exposing {101} facets, were more efficient at abating phenol than those synthesized on NH₂-functionalized GNP, exposing {101} and {100} facets. However, neither of these composites was stable under irradiation. The addition of both OA and EDA stabilized the materials under irradiation; however, only the composite prepared on COOH-functionalized GNP in the presence of EDA showed a significant increase in phenol degradation rate, leading to results that were better than those obtained with TiO₂ alone. This result can be attributed to Ti–OH complexation by EDA, which protects GNP from oxidation. The orientation of the most reducing {101} facets toward GNP and the most oxidizing {100} facets toward the solution induces faster phenol degradation owing to a better separation of the charge carriers.