Study Of The Reduction Of Pd(0)NPs By Pseudomonas Putida Mediating Microorganism Electron Transfer And Phenol Biodegradation

Zero valent palladium nanoparticles?Pd?0?NPs?have been widely studied for their good selectivity and large catalytic area.There are various methods to synthesize Pd?0?NPs,in which the microbiological in situ reduction method has attracted much attention due to its economic,easy manipulation and mild reaction conditions.In this study,Pseudomonas putida?P.putida?was used as mediators to synthesize Pd?0?NPs.The effects of Pd?0?NPs on the microbiological electron transfer and microbial activity of P.putida were analyzed.The microbial-Pd?0?system was applied to the biodegradation of phenol.Under the anaerobic condition,Pd?0?NPs was biosynthesized by P.putida.The results showed that P.putida had impact on adsorption and reduction of Pd?II?.SEM-EDS,TEM,XRD and XPS proved that Pd?0?NPs were successfully in situ bio-synthesized by P.putida and the particles?¹0 nm?were distributed evenly in cell surface and the extracellular space.The effects of the presence of Pd?0?NPs in the intracellular presence of P.putida on the electron transport properties of cell were measured by electrochemical methods.CV results showed that P.putida with Pd?0?NPs had a higher redox current compared to pure P.putida.As the initial concentration of Pd?II?increased to 0.07 mM and 0.1 mM,the oxidation current of lactate in the potentiostatic experiment increased to 10.6±5.2 nA and 22.5±9.7 nA respectively,which were 1.85 and 3.95 times respectively compared to pure P.putida?5.7±2.8nA?.The electron transfer rates,TTC-ETS and INT-ETS,were increased to 89.02 and 209.09g/?mg h?,respectively,which ware 1.64 and 1.34 times to P.putida,respectively.Pd?0?NPs had positive effects on the extracellular electron transfer process of P.putida.The effects of 0.07 mM,0.1 mM and 0.5 mM Pd?II?on P.putida were analyzed by growth curve and inhibition zone circle,which indicated that P.putida could tolerate 0.5 mM Pd?II?.CSLM images showed that low amount of Pd?0?NPs had great biocompatibility.The experimental Pd?II?concentration had small impact on the activity of P.putida,and it was beneficial to the subsequent phenol biodegradation.When the reaction concentration of Pd?II?was increased to 5 mM,Pd?II?and Pd?0?NPs both had negative impact on P.putida,which means too much Pd?II?and Pd?0?NPs still have certain toxicity on P.putida.After the biosynthesis of Pd?0?NPs,this microbial-Pd?0?system was applied to the biodegradation of phenol.Compared to P.putida,the first-order rate constant of phenol utilization was increased and the biggest value could reach 0.2992 h^-1.The Haldane model was used to fit the microorganism growth.The best results were get when the initial Pd?II?concentration was 0.1 mM:?_m=0.035 h^-1,K_s=76.39 mg L^-1,K_i=714.29 mg L^-1,which was better than P.putida without Pd?0?NPs.Under this situation,the toxic inhibition was the weakest and the affinity of P.putida to phenol was the best.The presence of Pd?0?NPs in the extracellular and periplasmic of cell could promote the electron transfer process,which was benefit to the use of electrons after entering the cells and thus enhanced the properties of phenol biodegradation by P.putida.Pd?0?NPs had high reaction activity in the process of phenol biodegradation.