Influence of light wavelength on the photoactivity, physicochemical transformation, and fate of graphene oxide in aqueous media

The rapidly increasing production and application of graphene oxide (GO) calls for much-needed attention to aspects related to the environmental implications of this unique nanomaterial. To date, very little is known about the transformation of GO when exposed to electromagnetic radiation at different wavelengths, which can occur in natural water systems. This study explored the changes in the physicochemical properties of GO when exposed to the UV and visible wavelength ranges of simulated solar light. Irradiation, especially under UV light, led to remarkable changes in the surface oxygen (O)-functionalities of GO, and cleavage of GO's graphitic bond. The carbon/oxygen (C/O) ratio of GO increased by 41% and 31% after irradiation with simulated solar light and UV irradiation, respectively. Visible light also changed the morphology of GO, but the C/O ratio only increased by 5.5%. The formation of hydroxyl radicals (OH), superoxide (O-2(-)) and singlet oxygen (O-1(2)) by GO was observed during irradiation with both UV and visible lights, but the proportions were different. O-1(2) was primarily formed during visible light irradiation, while O-2(-) and OH were mostly formed under UV light. OH hydroxylated GO, which mainly resulted in the decomposition of GO. The changes in O-containing functional groups on GO by irradiation influenced the colloidal stability of GO in aqueous media, but the physical wrinkle on GO surface may strongly affect its interactions with other organic materials.