Laser assisted photocatalytic reduction of metal ions by graphene oxide

Abstract

This work provides a new approach for the solution processable synthesis of metal–graphene oxide nanocomposites in aqueous solutions at ambient conditions. Using 532 nm laser or tungsten lamp irradiation of a mixture of graphene oxide (GO) and metal ions derived from HAuCl₄ or AgNO₃ we report the photocatalytic reduction of the metal ions simultaneously with partial reduction of GO, and the synthesis of metal–graphene nanocomposites. The gold and silver ions are reduced following the laser or the tungsten lamp irradiation of GO for a few minutes in water–ethanol, water–polyethylene glycol (PEG) or pure water solvents. The reduction of GO in the presence of ethanol or PEG is much faster than in pure water under identical experimental conditions. This is attributed to the role of ethanol or PEG in scavenging the holes generated by the irradiation of GO thus leaving the photogenerated electrons to reduce GO. In pure water in the presence of gold ions, partial reduction of GO occurs due to the efficient capturing of the photogenerated electrons in GO by the gold ions and the strong absorption of the 532 nm photons by the newly formed Au nanoparticles. Strong photothermal effects are observed leading to a significant increase in the temperature of the solution and suggesting that metal–graphene nanocomposites could be promising materials for the efficient conversion of solar energy into usable heat for a variety of thermal, thermochemical and thermomechanical applications.