Enhanced Catalysis of Plasmonic Silver Nanoparticles by a Combination of Macro-/Mesoporous Nanostructured Silica Support
Yukari Yamazaki, Yasutaka Kuwahara, Kohsuke Mori, Takashi Kamegawa, Hiromi Yamashita
Abstract
Porous silica with a unique nanostructure and interesting properties has a versatile range of applications. Hierarchically ordered macroporous silica (MacroS) can trap incident light inside the pores through a multiple scattering process, which is attractive for light harvesting. Mesoporous silica (MesoS) with a high specific surface area has been widely employed as a support material. Macro-/mesoporous silica (MMS) that combines both characteristics can provide multi-functionality, such as light scattering properties, high surface area, and efficient mass transfer. In this study, MMS, MacroS, MesoS, and bulk silica without pores were utilized as supports for plasmonic Ag catalysts, and the structural effect of silica supports on plasmonic Ag catalysis was investigated. Macropores with a diameter of ca. 300 nm and mesopores with diameters of ca. 2–3 nm were fabricated by a template method with a hybrid of polymethylmethacrylate colloidal crystals and octadecyltrimethylammonium chloride. Under dark conditions, Ag/MMS exhibited the highest activity for 4-nitrophenol reduction due to effective mass transfer through the mesopores that connected neighboring macropores, which provided accessibility of the reactants to the Ag nanoparticles (NPs). Ag/MMS exhibited the largest enhancement of activity under visible light irradiation not only because of its effective mass transfer and multiple scattering process but also because of the formation of moderate-sized plasmonic Ag NPs.