Fabrication of Periodically Ordered MnO₂ Arrays Decorated with Au Nanoparticles for Interference Enhanced SPR-Mediated Visible-Light Responsive Photocatalysis

Periodically ordered δ-MnO₂ arrays were fabricated by polystyrene (PS) nanosphere lithography combined with following hydrothermal synthesis. The periodicity of δ-MnO₂ arrays was varied by choosing PS nanospheres of different diameters. Then Au nanoparticles (NPs) were deposited on the δ-MnO₂ units to form Au-MnO₂ arrays samples. The PATP-to-DMAB model reaction was applied to detect the influence of MnO₂ units periodicity on surface plasmon resonance (SPR)-mediated photocatalytic performance of Au-MnO₂ arrays samples under 633 nm irradiation. The photocatalytic performance on the Au-MnO₂ array sample of 500 nm period presented ~ 16% superior photocatalytic activities relative to that of Au-MnO₂ array sample of 800 nm period. The surface plasmon polaritons (SPP) of plasmonic NPs can change the propagation path of incident light to vertical direction after scattering on them. The Au-MnO₂ array sample of 500 nm period possessed the distance between neighbor MnO₂ units smaller than the wavelength of irradiation light, and thus the scattered light interfered with each other after the incident light was scattered by the Au NPs on the neighbor MnO₂ units. Then the electric field (E-field) intensities near Au NPs were elevated due to the interference effect. Since the SPR-mediated photocatalytic activity is proportional to the square value of local E-field intensity (E²), thus the photocatalytic activities on Au NPs were enhanced. Therefore, our finding may provide a novel avenue to design SPR-enhanced photocatalysts by the deposition of plasmonic metals on periodically ordered arrays.