Graphene quantum dots enhanced photocatalytic activity of zinc porphyrin toward the degradation of methylene blue under visible-light irradiation

A novel nanocomposite of zinc porphyrin functionalized graphene quantum dots (GQDs/ZnPor) was prepared and used as a photocatalyst for the degradation of an organic pollutant under visible-light irradiation. In order to synthesise the nanocomposites, large graphene sheets were first cleaved into small pieces of graphene oxide by a mixture of concentrated H2SO4 and HNO3. Then, the GQDs/ZnPor was synthesized by a simple hydrothermal route with ZnPor and the as-synthesized graphene oxide as precursors. The resultant GQDs/ZnPor nanocomposites were characterized by transmission electron microscopy (TEM) and optical measurements. The photocatalytic activity of GQDs/ZnPor was evaluated by the degradation of methylene blue (MB) under visible-light irradiation. Enhancement of the photocatalytic activity of GQDs/ZnPor compared with pure zinc porphyrin was achieved. The photocatalytic degradation mechanism of GQDs/ZnPor was also illustrated by photoluminescence measurements and free radical and hole scavenging experiments. The proposed GQDs/ZnPor has potential application for decomposing organic pollutants in water.