Biogenic Synthesis of Pd-Based Nanoparticles with Enhanced Catalytic Activity

Searching efficient sustainable approaches for the metal nanoparticles (NPs) synthesis has become a research focus. Bioreduction with metal-reducing bacterium at ambient temperature provides a green route for metal NPs synthesis, especially for precious metals. In this work, activated Pd NPs were synthesized by contacting Pd²⁺ solution with an efficient metal-reducing Shewanella oneidensis bacterium, in which the bacterium acted as reducing, capping, and stabilizing agents, and the shape and composition of the Pd NPs could be tuned with the activation of KOH at elevated temperatures. The as-activated Pd NPs showed a favorable performance toward catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), with a remarkable apparent kinetic constant of 5.0 × 10^–3 s^–1, which was 12 times greater than that of the raw biogenic Pd NPs, even comparable to that of the commercial 5.0 wt % Pd/C. Changes of the Pd NPs aggregates, ratio of Pd to S, and surface area of the support at different temperatures and with different activation reactants were tested to explore the improvement associated with the KOH activation at elevated temperatures. Such an activation approach was also successfully applied for improving the catalytic activity of biogenic Au NPs. This work may offer a sustainable, cost-effective, and efficient approach to prepare biogenic metal nanomaterials for catalytic organic reaction or polutants removal.