Direct and Quinone-Mediated Palladium Reduction by Geobacter sulfurreducens: Mechanisms and Modeling

摘要

Palladium(Ⅱ) reduction to Pd(0) nanoparticles by Geobacter sulfurreducens was explored under conditions of neutral pH, 30 ℃ and concentrations of 25, 50, and 100 mg of Pd(Ⅱ)/L aiming to investigate the effect of solid species of palladium on their microbial reduction. The influence of anthraquinone-2,6- disulfonate was reported to enhance the palladium reaction rate in an average of 1.7-fold and its addition is determining to achieve the reduction of solid species of palladium. Based on the obtained results two mechanisms are proposed: (1) direct, which is fully described considering interactions of amide, sulfur, and phosphoryl groups associated to proteins from bacteria on palladium reduction reaction, and (2) quinone-mediated, which implies multiheme c-type cytochromes participation. Speciation analysis and kinetic results were considered and integrated into a model to fit the experimental data that explain both mechanisms. This work provides elements for a better understanding of direct and quinone-mediated palladium reduction by G. sulfurreducens, which could facilitate metal recovery with concomitant formation of valuable palladium nanoparticles in industrial processes.