Sustainable production methods for catalytic palladium (Pd) nanoparticles are currently being investigated due to their increasing use, limited availability and price volatility. The bio-palladium (bio-Pd) method uses bacteria as a producer and carrier of Pd nanoparticles. In this method, Pd leaching results in economical loss and environmental risk. In this study we therefore investigate the influence of different parameters on the leaching process: temperature (4-21°C), medium (H2O or mineral medium), pH (1–12), atmosphere (air, O2, N2, H2) and bacterial carrier. We show leaching is an important phenomenon for biosupported Pd: 20% of the Pd was released at 21°C in water after 100 days. Minimal leaching occurred at lower temperatures, low pH and in an isotonic medium. Up to 5 times more leaching was observed under anaerobic conditions (H2 or N2 atmosphere) than under aerobic conditions (O2 or air atmosphere). The producer/carrier Cupriavidus metallidurans leached up to 5% zerovalent Pd compared with 20% in Shewanella oneidensis. No loss of catalytic activity due to leaching was observed when the leachate remained in the reaction medium. This paper shows for the first time that release of Pd nanoparticles from the bacterial carrier of bio-Pd can be significant particularly under anaerobic conditions, at high temperature or high pH.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.