Clara Pereira - Gold-supported magnetically recyclable nanocatalysts: a sustainable solution for the reduction of 4-nitrophenol in water

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      Gold-supported   magnetically recyclable nanocatalysts: a sustainable solution for   the reduction of 4-nitrophenol in   water”,   Mariana Rocha, Carlos Fernandes, Clara Pereira,* Susana L. H.   Rebelo,* Manuel F. R. Pereira, Cristina Freire,* RSC Advances  2015, 5, 5131–5141. DOI:    10.1039/C4RA15865B

        *corresponding authors


      In this work mesoporous silica-coated   manganese(II) ferrite   (MnFe2O4)   magnetic nanoparticles functionalized with amine and thiol groups   were prepared and used as supports for the in situ  immobilization of gold nanoparticles (Au NPs). The resulting   Au-supported magnetic nanocatalysts, denoted as   Mn@SiO2_NH2@Au   and Mn@SiO2_SH@Au, were tested in the   reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), at   room temperature in water, in the presence of   NaBH4 reducing agent. This organic   compound is typically used in the production of pesticides and   dyes and commonly found in the resulting wastewaters. The   chemical, morphological, textural and magnetic properties of the   nanosupports and resulting Au-supported nanocatalysts were   characterized by X-ray photoelectron spectroscopy, Fourier   transform infrared spectroscopy, transmission electron   microscopy, X-ray diffraction, N2  adsorption–desorption isotherms at −196 °C and SQUID   magnetometry. The influence of the type of organosilane linker   between the magnetic nanosupport and the Au NPs on the in   situ immobilization of the Au NPs was evaluated:   Mn@SiO2_NH2@Au   presented lower Au loading than   Mn@SiO2_SH@Au, but the anchored Au NPs   showed a higher degree of crystallinity. The magnetic   Au-supported nanocatalysts led to almost 100% reduction of 4-NP   to 4-AP, monitored by UV-vis spectroscopy, with the reaction time   depending on the type of nanocatalyst/linker: 12 and 17 min, for   the amine- and thiol-based nanocatalysts respectively, what   corresponded to pseudo first-order rate constants normalized for   Au loading of K = 6117 mmol−1  min−1 and 827   mmol−1 min−1,   respectively. Both catalysts could be efficiently recovered by   magnetic separation and were highly stable upon reuse in four   further cycles, preserving their catalytic performance with   negligible Au leaching.

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