Synergy of Adsorption and Plasmonic Photocatalysis in the Au-CeO 2 Nanosystem: Experimental Validation and Plasmonic Modeling.

Adsorption-mediated water treatment leaves adsorbents as secondary pollutants in the environment. However, photocatalysis aids in decomposing the contaminant into its nontoxic forms. In this context, we demonstrate an adsorption-photocatalysis pairing in Au-CeO 2 nanocomposites for a total methylene blue (MB) removal from water. We synthesized Au-CeO 2 through the citrate ( cit ) reduction method at different Au loading and studied its adsorption capacity with kinetics and thermodynamic models. We observe that the high adsorption capacity of Au-CeO 2 is primarily because of the presence of Ce 3+ states in CeO 2 and citrate ligands on Au NPs. The Ce 3+ states interact and transfer their electrons to supported Au NPs, rendering a negative charge over Au. The negatively charged Au surface and the carboxyl (-COO - ) group of citrate ligands mediate an electrostatic interaction/adsorption of cationic MB. The total removal of MB is expedited under white light and lasers. A control experiment with Au NPs shows less adsorption-photocatalysis. The size of Au NPs and Au-CeO 2 interfacial interaction is responsible for the surface plasmon resonance spectral position at 550-600 nm. Linear sweep voltammetry (LSV) and plasmonic field simulation show surface plasmon-driven photocatalysis in Au-CeO 2 . LSV shows a 3-fold higher photocurrent density in Au-CeO 2 than colloidal Au NPs under white light. The simulated electric field intensity in Au-CeO 2 is maximum at SPR excitation and the closest interfacial separation ( d = 0 nm). The plasmon-driven photocatalysis in colloidal Au NPs is mainly due to the interaction of hot electrons with the adsorbed MB molecule. Notably, near-field light concentration, hot electrons, and interfacial charge separation are responsible for excellent MB removal in the Au-CeO 2 nanosystem. The total MB removal through adsorption-photocatalysis pairing is 99.3% (Au-CeO 2 ), 30.7% (Au NPs), and 13% (CeO 2 ).