Investigating the effect of MnO2 band gap in hybrid MnO2–Au materials over the SPR-mediated activities under visible light

Abstract

In this paper, K-doped δ-MnO₂ nanoflowers decorated with Au nanoparticles (MnO₂–Au) were synthesized by a hydrothermal method. To probe the effect of the band gaps in the MnO₂ support over the surface plasmon resonance (SPR)-mediated catalytic conversions on Au nanoparticles (NPs), the oxidation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) was used as a model reaction. We found that the PATP conversion was significantly higher for the MnO₂–Au hybrid compared with its individual Au NPs under excitation at 633 nm. Furthermore, the activities of the MnO₂–Au materials increased as the MnO₂ support displayed higher K-doped levels, which led to narrower band gaps. These results could be explained based on the transfer of photogenerated electrons from MnO₂ to Au, increasing the electron density in Au NPs and thus contributing to improved SPR-mediated activity. In this case, our observations show that tuning the band gaps can have a significant impact on SPR-mediated conversions, in which narrower band gaps should facilitate the charge transfer of SPR-excited charge carriers and thus lead to better performances. Our findings presented may provide important insights into the role of the support materials in plasmonic catalysis, indicating that, in addition to the control over several physical and chemical parameters (such as shape, surface area, defects, among others), the proper tuning of the band gap can serve as an effective strategy for the optimization of activities.