Comparison of bacterial cells and amine-functionalized abiotic surfaces as support for Pd nanoparticle synthesis

An increasing demand for catalytic Pd nanoparticles has motivated the search for sustainable production methods. An innovative approach uses bacterial cells as support material for synthesizing Pd nanoparticles by reduction of Pd(II) with e.g. hydrogen or formate. Nevertheless, drawbacks of microbially supported Pd catalysts are the low catalytic activity compared to conventional Pd nanocatalysts and the possible poisoning of the catalyst surface by sulfur originating from bacterial proteins. A recent study showed that amine groups were a key component in surface-supported synthesis of Pd nanoparticles, and that abiotic surfaces could support the Pd particle synthesis as efficiently as bacteria. In this study, we explore the possibility of replacing bacteria with amine-functionalized materials, and we compare different functionalization strategies. Pd nanoparticles formed on the support materials were visualized by transmission electron microscopy, and their activity was evaluated by catalysis of p-nitrophenol reduction. Surfaces functionalized with 3-aminopropyltriethoxysilane and chitosan were interesting alternatives to bacterial cells, as the catalytic activity of Pd particles formed on these surfaces was higher than for Pd particles formed on Shewanella oneidensis cells. Smaller Pd nanoparticles generally have better catalytic properties, and previous studies have shown that the particle size can be lowered by increasing the amount of support material used during Pd particle formation. However, increasing the concentration of S. oneidensis cells beyond a certain threshold lead to deactivation of the Pd catalyst. This was not observed for the sulfur-free support materials, implying that such amine-rich materials can provide an excellent support for environmentally friendly synthesis of surface-immobilized Pd nanoparticles.