Abstract
BackgroundPlatinum nanomaterial is one of the significant noble metal catalysts, and the interaction of platinum with microbe is one of the key factors in influencing the size and the distribution of the platinum nanoparticles on the microbial biomass. Some properties of Pt(IV) adsorption and reduction by resting cells of Bacillus megatherium D01 biomass have once been investigated, still the mechanism active in the platinum biosorption remains to be seen and requires further elucidating.ResultA further insight into the biosorption mechanism of Pt(IV) onto resting cells of Bacillus megatherium D02 biomass on a molecular level has been obtained. The image of scanning electron microscopy (SEM) of the D02 biomass challenged with Pt(IV) displayed a clear distribution of bioreduced platinum particles with sizes of nanometer scale on the biomass. The state of Pt(IV) bioreduced to elemental Pt(0) examined via X-ray photoelectron spectroscopy (XPS) suggested that the biomass reduces the Pt(IV) to Pt(II) followed by a slower reduction to Pt(0). The analysis of glucose content in the hydrolysates of D02 biomass for different time intervals using ultraviolet-visible (UV-vis) spectrophotometry indicated that certain reducing sugars occur in the hydrolyzed biomass and that the hydrolysis of polysaccharides of the biomass is a rapid process. The infrared (IR) spectrometry on D02 biomass and that challenged with Pt(IV), and on glucose and that reacted with Pt(IV) demonstrated that the interaction of the biomass with Pt(IV) seems to be through oxygenous or nitrogenous chemical functional groups on the cell wall biopolymers; that the potential binding sites for Pt species include hydroxyl of saccharides, carboxylate anion and carboxyl of amino acid residues, peptide bond, etc.; and that the free monosaccharic group bearing hemiacetalic hydroxyl from the hydrolyzed biomass behaving as an electron donor, in situ reduces the Pt(IV) to Pt(0). And moreover, the binding of the Pt(IV) to the oxygen of the carbonyl group of peptide bond caused a change in the secondary structure of proteins; i.e. a transformation, in polypeptide chains, of β-folded to α-helical form; it might be expected to be more advantageous than β-folded form to the platinum nanoparticles under shelter from gathering although the both special conformations of proteins could be much probably responsible for the stabilization of the particles.ConclusionThat knowledge could serve as a guide in the researches for improving the preparation of highly dispersive supported platinum catalyst and for fabricating new advanced platinum nanostructured devices by biotechnological methods.
Highlights
Platinum nanomaterial is one of the significant noble metal catalysts, and the interaction of platinum with microbe is one of the key factors in influencing the size and the distribution of the platinum nanoparticles on the microbial biomass
scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) examinations SEM examination: Two samples of (I) blank D02 biomass powder and (II) that challenged with Pt(IV) at pH 3.5 and 37°C for 48 h followed by drying under vacuum at 80°C and by grinding were sprayed with gold prior to examination
The reductive ratio of Pt(II) is 57.8%, Pt(0) 15.1% for 12 h and Pt(II) 61.2%, Pt(0) 22.8% for 24 h; indicating that the biosorption of the Pt(IV) by the biomass involves the reduction of Pt(IV) to Pt(II) followed by a slower reduction to Pt(0). The both examinations reflected that the bioreduction of Pt(IV) to elemental Pt(0) at near normal temperature was catalyzed by D02 biomass and that certain enzymes originating from the biomass could be much responsible for this catalysis
Summary
Platinum nanomaterial is one of the significant noble metal catalysts, and the interaction of platinum with microbe is one of the key factors in influencing the size and the distribution of the platinum nanoparticles on the microbial biomass. Some properties of Pt(IV) adsorption and reduction by resting cells of Bacillus megatherium D01 biomass have once been investigated, still the mechanism active in the platinum biosorption remains to be seen and requires further elucidating. Some properties of the interaction of Pt(IV) with resting cells of Bacillus megatherium D01 biomass were described previously [8], and yet the biosorption mechanism involved is still disputable and requires further expounding. The aim of our current research is based on our previous studies to make a further investigation into the mechanism responsible for the platinum biosorption by resting cells of Bacillus megatherium D02 biomass using IR and other spectroscopic techniques. The strain is Gram-positive and identified as Bacillus megatherium D02 and easy to obtain and culture. It was cultured in an aqueous solution containing beef gels, peptone, salt, etc. The adsorptive capacity of the resting cells of the strain for Pt(IV) attained 76.6 mg/g when the biomass suspension (pH 3.5, 1 mg/ml) mixed with a 0.5 mM chloroplatinic acid (H2PtCl6·6H2O) aqueous solution at pH 3.5 and 37°C for 2 hours (h)
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