Production of highly catalytic, archaeal Pd(0) bionanoparticles using Sulfolobus tokodaii.

The thermo-acidophilic archaeon, Sulfolobus tokodaii, was utilized for the production of Pd(0) bionanoparticles from acidic Pd(II) solution. Use of active cells was essential to form well-dispersed Pd(0) nanoparticles located on the cell surface. The particle size could be manipulated by modifying the concentration of formate (as electron donor; e-donor) and by addition of enzymatic inhibitor (Cu) in the range of 14-63 nm mean size. Since robust Pd(II) reduction progressed in pre-grown S. tokodaii cells even in the presence of up to 500 mM Cl, it was possible to conversely utilize the effect of Cl to produce even finer and denser particles in the range of 8.7-15 nm mean size. This effect likely resulted from the increasing stability of anionic Pd(II)-chloride complex at elevated Cl concentrations, eventually allowing involvement of greater number of initial Pd(0) crystal nucleation sites (enzymatic sites). The catalytic activity [evaluated based on Cr(VI) reduction reaction] of Pd(0) bionanoparticles of varying particle size formed under different conditions were compared. The finest Pd(0) bionanoparticles obtained at 50 mM Cl (mean 8.7 nm; median 5.6 nm) exhibited the greatest specific Cr(VI) reduction rate, with four times higher catalytic activity compared to commercial Pd/C. The potential applicability of S. tokodaii cells in the recovery of highly catalytic Pd(0) nanoparticles from actual acidic chloride leachate was, thus, suggested.