Preparation and catalytic performance of macro-mesoporous Ag/PDA/MMS composite

A millimeter-sized macro-mesoporous SiO2 (MMS) was prepared by a dual-templating method, using an epoxy resin macroporous polymer with 3D skeleton structure as the macroscopic shape and macropore structure directing agent and PEG 2000 as the mesopore porogen and the PDA-modified MMS (PDA/MMS, PDA=polydopamine) was obtained via the oxidative self-polymerization of dopamine (DA) on the pore wall of MMS, then the in situ reduction of Ag+ by the PDA on the surface of PDA/MMS formed the macro-mesoporous Ag/ PDA/MMS composite. The as-prepared materials were characterized by scanning electron microscope, transmission electron microscope, N-2 adsorption-desorption, X-ray photoelectron spectroscopy, X-ray diffraction, UV-Vis, FT-IR, and thermogravimetry techniques. The results show that MMS has the advantages of both nano-mesoporous materials and macro-sized macroporous materials, and possesses large specific surface area and pore volume, and high mechanical strength. Ag/PDA/MMS exhibited high catalytic activity in the reduction of p-nitrophenol (4-NP), and the turnover frequency (TOF) reached 2.97 min(-1), which is attributed to its unique structure: the interconnected macropores greatly reduce mass transfer resistance, the short mesopore channels significantly increase the accessibility of active sites and effectively confine the size of silver nanoparticles, and the large specific surface area provides a large number of active sites for reactants. Moreover, the millimeter-sized Ag/PDA/MMS could be easily separated from the reaction system, and it could still convert 4-NP to p-aminophenol (4-AP) completely after five cycles. In addition, Ag/PDA/MMS also showed a good catalytic effect in the reduction of methylene blue (MB).