Ultrafine, air-stable elemental copper (Cu) nanoparticles (NPs) were synthesized in aqueous solution by a microbial process using anaerobic, metal-reducing Thermoanaerobacter sp. X513 bacteria. Surfactants were used to biotically produce size-controllable Cu NPs with the results compared to abiotic crystals (without bacteria). Abiotic Cu crystals were formed during a 2-day incubations via chemical reduction by glucose, but the crystals exhibited a micron size with bimodal distribution with diameters of 1.54�0.34 �m (n=18) and 0.56�0.17�m (n=21). The biotic Cu crystals also were micron size (1.75�0.46 �m (n=20)) after 3-day incubations, but they were more air-stable and uniform than abiotic crystals. In situ  addition of nitrilotriacetic acid as a metal chelating agent facilitated the growth of Cu NPs within 2 days and limited bimodal distribution to 70.1 �21.3 nm (n=147) for large NPs and 2.7�0.8 nm (n=420) for small NPs, but the harvested Cu NPs were composed of Cu and Cu2O mixture. Addition of capping agents including oleic acid, oleylamine, ascorbic acid, and L-cysteine resulted in well suspended colloidal Cu NPs in aqueous solution and effectively quadrupled their stability in air up to 6 hrs. The effectiveness of capping agents for suspending NPs and resistance to oxidation were quantitatively evaluated by UV-vis absorption measurements tracking the Cu localized surface plasmon resonance and time-dependent XPS studies of Cu NPs films. FTIR spectroscopy suggests that these chelating and capping agents were effectively chemisorbed on the NP surface and provided oxidation resistance in aqueous and dry condition. Finally, this process was found to be highly reproducible and scale-up conditions were evaluated in the range of 10�1,000 mL growth medium.

Air-stable elemental copper nanoparticle synthesis by anaerobic bacteria controls size and enables scalability in aqueous solutions

248th National Meeting (2014)

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