Visible-light photocatalytic oxidation of CO over plasmonic Au/TiO2: Unusual features of oxygen plasma activation

To seek an efficient activation of plasmonic Au/TiO2 photocatalysts, atmospheric-pressure cold plasmas of oxygen (OP) and argon (ArP) were employed to activate the Au/TiO2 coating samples on glass substrate and compared with the conventionally calcination. The activated samples were evaluated in a continuous flow photocatalytic oxidation (PCO) reactor under visible light (lambda > 420 nm) for CO removal from synthetic air and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, CO chemisorption and electron paramagnetic resonance (EPR). Although Au nanoparticles (NPs) of the three activation samples averaged at around 4 nm by TEM, the OP and ArP samples exhibited the highest and lowest PCO activity, respectively. An unusual feature of oxygen plasma activation is high content of surface oxygen, which favors superoxide (O-2(-)) formation by accepting hot electron generated from absorption of visible light through local surface plasmon resonance (LSPR) of Au NPs. The OP sample has the lowest metallic Au content but its cationic Au can be rapidly reduced to form numerous low-coordinated metallic Au around the interface between Au NPs and TiO2 support in the induction period, which is another unusual feature of oxygen plasma activation. (C) 2016 Elsevier B.V. All rights reserved.