A Magnetic Plasmonic Catalyst Based on Monodisperse-Porous Silica Microspheres for Rapid Reduction of 4-Nitrophenol

In this work, the degradation of 4-nitrophenol (4-NP) was investigated by using plasmonic gold nanoparticles decorated magnetic-porous silica microspheres (AuNP@Mag–SiO2) as catalyst in the presence of excess sodium borohydride (NaBH4) in batch fashion. Magnetic silica microspheres (Mag–SiO2), 6.20 µm in size synthesized with high surface area and good magnetic properties were functionalized with amine groups. Using these particles as support, immobilization of gold nanoparticles (AuNP) was performed. The morphological, chemical and magnetic properties of the catalyst were analyzed by Scanning electron microscopy (SEM), Surface area and pore size analyzer, X-ray diffraction spectroscopy (XRD), Vibrating sample magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS). The plasmonic catalytic activities of AuNP@Mag–SiO2 microparticles were investigated by the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) monitored by UV–Vis spectroscopy by changing the reaction parameters such as amount of catalyst, Au loading, initial 4-NP concentration, and reaction temperature. Reaction times ranging between 5 and 30 min were obtained in the quantitative reduction of 4-NP using gold nanoparticles decorated magnetic silica (AuNP@Mag–SiO2) microspheres. The plasmonic catalyst was recovered efficiently by magnetic separation and highly stable without exhibiting no significant activity decrease with the repeated use.