Abstract
Although chemical and physical synthetic routes to noble metal nanoparticles have been extensively developed, another possibility is biological synthesis by reduction of noble metal ions using microorganism. We focused on the Fe(III)-reducing bacteria Shewanella algae and Shewanella oneidensis as a candidate microbe for rapid reductive deposition of noble metal at room temperature, because the reduction potential of Fe(III) ions is almost equal to that of noble metal ions. Intracellular synthesis of noble metal (Au, Pd, Pt) nanoparticles was achieved at room temperature using resting cells of the Fe(III)-reducing bacteria, when either formate or lactate was provided as the electron donor. The bioreductive deposition of noble metal was a fast process: 1-10 mol/m3 aqueous Pd(II) ions were completely reduced to crystalline Pd(0) nanoparticles within 60 min. Biogenic metal nanoparticles 5-10 nm in size were located in the periplasmic space of bacterial cells. The dried biomass-supported palladium was applicable to a heterogeneous catalyst in a chemical reaction and an anode catalyst in a fuel cell for power production. Our methodology for the room-temperature synthesis of noble metal nanoparticles using the Fe(III)-reducing bacteria is an attractive green process that is cost-effective and environmentally benign.
