Mariana Rocha

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

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.

A new, efficient and recyclable [Ce(L-Pro)]2(Oxa) heterogeneous catalyst used in the Kabachnik–Fields reaction

Herein we introduce a new catalyst for the Kabachnik–Fields reaction, [Ce(L-Pro)]2(Oxa), using a very accessible, simple and efficient methodology for α-aminophosphonate synthesis using an aromatic aldehyde, an aromatic amine and diphenyl phosphite. This procedure was developed using a low catalyst loading of cerium(III) prolinate and it has allowed for the recycling of the catalyst.

Highly Active Ruthenium Supported on Magnetically-Recyclable Chitosan-Based Nanocatalyst for Nitroarenes Reduction

A Ru supported on a magnetically separable chitosan‐based nanomaterial (Mn@CS@Ru) was prepared by wet impregnation based on ionic gelation using sodium tripolyphosphate as a cross‐linking agent. The ionic gelation of chitosan leads to a supporting matrix to promote the embedding of manganese(II) ferrite and Ru nanoparticles (NPs) by electrostatic interactions. The effects of the formulation and method parameters on the fabrication process were investigated, and the resulting as‐prepared Mn@CS@Ru nanocatalyst was characterized. The catalytic activity of the Mn@CS@Ru nanomaterial was evaluated in the reduction of 4‐nitrophenol (4‐NP) and 4‐nitroaniline (4‐NA) in the presence of sodium borohydride as a reducing agent at room temperature. The turnover frequency values in the reduction of 4‐NP and 4‐NA were 273.9 and 336.5 min−1, respectively, which were attributed to the very small size of the hybrid nanomaterial (32.0±2.8 nm with 3.9±0.1 nm Ru NPs) that provided a large surface‐area‐to‐volume ratio for the chemical reaction. Furthermore, the hybrid nanocatalyst was recovered easily by magnetic separation after the catalytic reaction and could be reused in at least 10 cycles without a loss of catalytic activity, which confirms its high stability. The present route is a new approach to synthesize highly active magnetic heterogeneous catalysts for the reduction of nitroarenes based on metallic NPs with easy accessibility, excellent activity, and convenient recovery.

Lipase catalyzed 1,2-addition of thiols to imines under mild conditions

This is the first report of enzymes used as biocatalysts for a 1,2-sulfur addition. In this study, we describe the synthesis of N,S-acetals using an environmentally friendly process with low catalyst loading and in short reaction times using porcine pancreatic lipase, chymosin, and bovine serum albumin (BSA). The hydrogen bond between the enzyme and the N-Boc imine is a key factor in this reaction.