Microbial Nano-palladium Synthesis And Electrocatalytic Activity Analysis

Biological systems, especially using microorganisms, have the potential tooffer cheap, scalable and highly tunable green synthetic routes for the production ofthe latest generation of nanomaertials. Recently, researchers have proposedelectrode, as a promising configuration for the gentle delivery of a hydrogen donorfor impoving microbial nano-palladium (MN-Pd) catalytic reduciton capacity.However, Due to the bacterial matrix which is electrically less conductive, coatingthe electrode with MN-Pd might negatively affect electron transfer. Carbonnanotube can promote electron transfer from electrode to MN-Pd, therefore, increasebio-Pd catalytic activity dramatically for contaminants treatment.Based on the capability of MN-Pd synthesis by Shewanella oneidensis MR-1using formate as electron donor, considering that microbial nano-palladium couldget electrons from electrode to produce nascent hydrogen and catalyze the reductivedegradation of recalcitrant contaminants, this dissertation studied the effets of theratio of cell dry weight to palladium (CDW: Pd) on MN-Pd synthesis and elucidatedthe mechanism of electrocatalytic activity of nitrobenzene reduction by amination ofmulti-walled carbon nanotubes.Both the reduction rate of Pd2+and the yield of MN-Pd were increased withthat ratio with1:1,5:1,9:1. Moreover, after15minutes, above70%of the Pd2+werereduced to Pd(0) in all of three ratios. The maximum reduction amount was achievedto92.26%under the reaction condition of CDW: Pd=9:1. This disseration analyzedthe effect of CDW:Pd on the morphology and particle size distribution of MN-Pd.Results showed that Pd(0) particle size decreased at in increasing CDW: Pd ratios.Pd nanoparticles were wrapped around by A-MWCNT, which successfully chargedby electrode as superior electron transfer properties of A-MWCNT.CV results showed that catalytic current of hydrogen evolution increased withthe increasing content of Pd(0). The onset potential of hydrogen evolution andcatalytic current increased to0.3V and0.14mA, respectively, for electrode modifiedwith composite nanomaterials. Such catalytic current was3times larger than thatonly modified with A-MWCNT and5times larger than that only modified withMN-Pd. Carbon nanotube can promote electron transfer from electrode to MN-Pd,therefore, increase MN-Pd catalytic activity dramatically for contaminants treatment.However, the content of A-MWCNT should be better less than0.2387mg/cm2.