Biosynthesis of Metallic Nanoparticles and Their Applications - Intracellular Delivery: Fundamentals and Applications - page 383

used to biologically treat contaminated wastewaters by reduction of Cr(VI) - known
as carcinogen and mutagen - to Cr(III) - relatively non-toxic and non-carcinogenic
form. Nevertheless, some studies showed that “bio-Pd(0)” is more efficient at Cr(VI)
reduction than live cells of D. desulfuricans or chemically reduced Pd(II), using
hydrogen as the electron donor (Mabbett and Macaskie 2002 ). Pd(0) mediates
hemolytic bond cleavage of H 2 , with the production of radical H * , which can then
donate its electron to Cr(VI). Continuous-flow studies using D. vulgaris Bio-Pd(0)
with agar as the immobilization matrix were also investigated (Humphries et al.
2006 ), showing the effect of Bio-Pd(0) loading, inlet Cr(VI) concentration, and flow
rate on the efficiency of Cr(VI) reduction. Mabbett et al. ( 2005 ) presents possibility
of mixed-metal-bioPd(O) catalysts employing D. desulfuricans , Pd(II) and Pt(IV) or
industrial waste leachates (contains e.g. Rh, Cu, Fe, Al, Pt). Two flow-through reac-
tor systems were also compared by aforementioned work. Similar experiments were
performed by Beauregard et al. ( 2010 ) using Serratia sp. and formate as the electron
donor. Remarkably, Cr species concentrations within the reactor were controlled by
spatial mapping using magnetic resonance imaging technique (Cr(VI) (aq) is non-
paramagnetic while Cr(III) (aq) is paramagnetic).
Moreover, Chidambaram et al. ( 2010 ) published experiments where the electron
donor is substituted by fermentation process (fermentatively produce hydrogen in
presence of glucose) in bacteria Clostridium pasteurianum , which also serves for
reduction Pd(II) ions to form PdNPs “bio-Pd(0)” that primarily precipitated on the
cell wall and in the cytoplasm. Finally, the most scientifically explored organism in
the world, Escherichia coli (or its mutants), contribute to the “bioPd(0)” catalyst
knowledge. Experiments with three types of hydrogenases encoded by bacterial
DNA were performed by Deplanche et al. ( 2010 ), based on optimal catalytic activity
in Cr(VI)/Cr(III) system.

3.2.2 “BioPd(0)” and “BioPt(0)” as a Fuel Cells Electro-Catalysts

Similar approach to utilization of microorganisms with ability to enzymatically
reduce and absorb palladium, platinum and other precious metals was also used for
manufacturing of a bio-fuel cell for power production. Since fuel cells have been
identified as a future technology to power motor vehicles, generators and portable
electronic device, authors recommend overall review papers (Andújar and Segura
2009 ; Winter and Brodd 2005 ) for more information and historical context in fuel
cells topic.
In work by Yong et al. ( 2007 ) Pt(0) and Pd(0) bio-accumulated by D. desulfuri-
cans was applied onto carbon paper and tested as anodes in a polymer electrolyte
membrane (PEM) fuel cell for power production and compared to commercial fuel
cell grade Pt catalyst. A similar strategy is also suggested using yeast-based bio-
mass, immobilized in polyvinyl alcohol cryogels, for the manufacture of fuel cell
Pt(0). This is then used to generate electrical energy from renewable sources such as
glucose and ethanol (Dimitriadis et al. 2007 ). Finally, the dried biomass-supported
palladium ( Shewanella oneidensis ) was tested as an anode catalyst in a PEM fuel