Microplasma-assisted synthesis of TiO2–Au hybrid nanoparticles and their photocatalytic mechanism for degradation of methylene blue dye under ultraviolet and visible light irradiation

Plasmonic photocatalysts consisting of TiO2 and Au nanoparticles (NPs) have recently been intensively studied to overcome the limited photocatalytic activity of pristine TiO2 NPs. Here, we synthesized TiO2–Au hybrid NPs using atmospheric microplasma–liquid interaction and demonstrated their enhanced photocatalytic activity, under both ultraviolet (UV) and visible light irradiation, for the degradation of the organic dyes methylene blue (MB) in water. Through mechanism studies using a hole scavenger and external source of hydroxyl radicals, it was also revealed that the contribution of hole oxidation and electron reduction pathways for degradation of MB via hydroxyl radicals by the TiO2–Au hybrid NPs differed depending on the wavelength of irradiating light. This is because the MB dye is likely remotely oxidized under UV irradiation, but not under visible light. This systematic study on the role of hole and electron pathways for photocatalytic dye degradation by TiO2–Au hybrid NPs at different light and pH conditions is helpful for understanding and developing plasmonic photocatalysts.