Bio-recovery Of Secondary Platinum Resources And Application Of Its Products As Oxygen Reduction Catalysts

Precious metal platinum is widely used in industrial catalysts,electronic products,sensors,biopharmaceuticals,jewelry and other fields due to its unique physical,chemical and catalytic properties.After years of exploitation,most of the platinum-containing source has been transferred from the ground to the ground,and in the form of waste around the people.Recovering precious metals from the waste has become a research hotspot in recent years.The microbial recovery method can achieve the harmless and waste disposal of waste in the field of recycling concern.In this study,the method of recovering platinum nanoparticles by Enterococcus faecalis was established.The main steps of the recovery process and the possible material basis of the recovery process were discussed.On this basis,the recovery products-the platinum nanoparticles,and the microbial cell were prepared for oxygen reduction catalysts.Moreover,the molecule model of the catalyst was established and the density functional theory(DFT)was used to explain the oxygen reduction process may exist during the oxygen reduction reaction(ORR).The main results are as follows:(1)Controlled variable method was used to studied the effect of recovery conditions on the recovery of platinum nanoparticles from Enterococcus faecalis Z5.The results showed that Enterococcus faecalis Z5 could recover platinum nanoparticles.The initial concentration of platinum was 286.46 mg · L-1,the biomass was 3.2 g · L-1,the temperature was 50 ? and the pH value was 6.X-ray diffraction analysis and transmission electron microscopy(TEM)show that the recovered product is a platinum nanoparticle with a diameter of about 5 nm,which is mainly distributed in the cell periplasm.Through the monitoring of the concentration of platinum in the recovery system and the characterization of the physical and chemical properties of the product,Main Process and Recovery Mechanism of Recombinant Platinum Nanoparticles in Enterococcus.The results show that the recovery process mainly includes biosorption and bioreduction.By X-ray spectroscopy(XPS)analysis,Pt(+4)is first reduced to Pt(+2)and then reduced to Pt(0)Pt(+2)is reduced to Pt(0)as a limiting step,and Fourier transform infrared(FTIR)analysis shows that the hydroxyl and amide functional groups on the cell surface may play a role in the recovery process.(2)Preparation of ORR catalyst by the platinum nanoparticles and microbial cells.The heteratom-doped graphene platinum-based catalyst(HDG-Pt@C)shows good catalytic activity.The HDG-Pt@C have a significant reduction peak at-0.182 V and-0.22V(vs Ag/AgCl),and the limiting current density is 3.5 mA / cm2 and 2.4 mA/cm2.This study provide a new approach for the synthesis of high efficiency electrocatalysts,and also provide a new idea for the high value of bio-recovered platinum products.Moreover,a molecular model of HDG-Pt@C is constructed.The oxygen reduction mechanism of the target catalyst was analyzed by functional theory.The interaction between Pt4 and N,O-doped substrates was found by density functional theory.In addition,the catalyst was analyzed by molecular model active sites for oxygen molecules adsorption process,derived catalytic oxygen reduction reaction may exist in the reaction equation.This provides a new theoretical basis for the design of catalysts for the preparation of bio-recovered precious metal nanoparticles.