Gold-decorated polymeric monoliths: In-situ vs ex-situ immobilization strategies and flow through catalytic applications towards nitrophenols reduction

- Monolithic micro-reactors with surface immobilized gold nanoparticles for flow through catalytic processes.
- Porous polymer with protonated amino surface groups as supports for gold nanoparticles.
- Surface adsorption of gold nanoparticles through in-situ and ex-situ strategies.

Monolithic polymers with micrometer-sized channel-like pores and primary amine as chelating surface functionality were prepared via a two-step synthetic route. UV-induced free radical polymerization of N-acryloxysuccinimide (NAS) and ethylene dimethacrylate (EDMA) yielded to nucleophilic sensitive monolith. Subsequent surface grafting of ethylene diamine through displacement of the N-hydroxysuccinimide (NHS) leaving groups provided pores with dual hydrophilic and chelating surface properties. Amino-containing monolith was used as versatile platform for supporting gold nanoparticles (GNPs) through complexation of either preformed Au0 nanoparticles or Au3+ precursor salt followed by in situ reduction. All synthesis and surface functionalization steps were performed within micro-columns and were confirmed to occur to a large extent using a combination of experimental methods such as in-situ micro-Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and pressure permeability tests providing information on morphology, porosity, flow-through properties and surface distribution of gold nanoparticles. Continuous flow catalytic activity of the nanostructured monolithic columns towards hydride-mediated reduction of nitrophenol isomers, namely 2-nitrophenol, 3-nitrophenol and 4-nitrophenol, and 4-nitroaniline was postulated on the basis of UV-vis spectroscopy characterization suggesting presence of the corresponding amino-derivatives. This study conclusively shows that the in-situ strategy for the surface immobilization of gold nanoparticles enables high reaction yield while maintaining unaffected the monolithic column permeability.

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