Research On Biorecovery Of Second Noble Metals And Their Performance On Degradation And Transform For Environmental Pollutants

Precious metals have many excellent properties and play an important role in modern industry,and are hailed as"the vitamins of modern industrial life."Demand for precious metals continues to increase.However,nearly half a century of mining has turned the limited amount of palladium mineral resources from underground to ground,and exists in the waste,so the recovery of precious metals from secondary resources has become an increasing concern.problem.Because of its advantages of abundant resources,cheap,easily available,resulting pollution,microorganisms are attempted to recover precious metals from ionic state to elemental state through bio-adsorption and reduction,thereby realizing the recovery of precious metals.The noble metal nanomaterial possesses unique physical and chemical properties of precious metals and special properties of nanomaterials,and has broad application prospects in the fields of biomedicine,optics,electromagnetism,catalysis and so on.Synchronously achieving the efficient recovery of precious metals and the preparation of precious metal nanomaterials is an important challenge.Based on the above issues,this study proposed the use of the fungus Pycnoporus sanguineus and bacteria Enterococcus faecalis for recovery of precious metal gold and palladium to obtain gold nanoparticles?AuNPs?,palladium nanoparticles?PdNPs?,and AuNPs and PdNPs for catalytic applications of research ideas.firstly,confirming P.sanguineus and E.faecalis to recover AuNPs and PdNPs is explored,respectively.Secondly,microbial cells containing AuNPs and PdNPs are treated to be doped with zero-valent iron?nZVI?or iron oxides.Finally,the above compounds are investigated for degradation or transform tetrabromobisphenol A.Removal effects and mechanisms of?TBBPA?,Cr?VI?,diclofenac sodium?DS?and methylene blue.The main results obtained are as follows:?1?The AuNPs were synthesized by using P.sanguineus,and the obtained bio-AuNPs were calcined for obtaining Au@biocarbon,which was co-precipitated with nZVI for obtaining Au/Fe@biocarbon.TEM,XPS,XRD and BET analysis showed that Au/Fe@biocarbon has a porous structure with a specific surface area of about 71.62 m²/g.Au and nZVI are uniformly distributed on the surface of it.The application of Au/Fe@biocarbon in debromination of TBBPA showed that the debromination effect of Au/Fe@biocarbon on TBBPA was significantly stronger than that of Fe@biocarbon and pure nZVI.Meanwhile,1g/L Au/Fe@biocarbon with the 2%molar ratio of Au-Fe can completely remove 10 mg/L TBBPA within 20 min at pH 3,and the debromination rate is close to 100%.The debromination of TBBPA by Au/Fe@biocarbon is due to the formation of a primary cell between Au and iron,which accelerates the process of nZVI to reduce TBBPA.?2?In the simulation of the waste circuit board waste liquid,E.faecalis was added to synthesize PdNPs under the condition of Fe²⁺as electron donors,and then Fe²⁺and Fe³⁺in waste liquid were reduced to nZVI in situ to precipitate on the surface of PdNPs-containing cells for obtaining Pd/Fe@biomass.TEM,XRD,SEM and XPS analysis showed that the prepared Pd/Fe@biomass,Pd was distributed in the periplasm and cytoplasm,and nZVI was spherically distributed on the cell surface.When Pd/Fe@biomass was used in the Cr?VI?reduction to Cr?III?process,it was found that the addition of PdNPs could significantly increase the Cr?VI?reduction derived by nZVI,The Cr?VI?removal of 0.5 mM can be completely removed within 5 min by 1 g/L Pd/Fe@biomass with Pd-Fe molar ratio of 1:100at pH 3.The main reaction mechanism is that Pd and Fe form galvanic cells to accelerate the reduction of Cr?VI?by nZVI.At the same time,PdNPs can catalyze the oxidation of H₂produced by iron into H*with stronger reduction activity.?3?The PdNPs were reduced by the use of E.faecalis in the presence of sodium formate as an electron donor,and the obtained bio-Pd was subjected to cell disruption and centrifugation for obtaining PdNPs.TEM,XPS,and XRD analysis showed that the released PdNPs were uniform in size,ranging from 10 to 20 nm in size.The obtained PdNPs were doped with Fe₃O₄ for Fenton reaction and degraded with methylene blue.The catalytic effect of Fe₃O₄ doped with PdNPs on methylene blue is much better than that of single Fe₃O₄.The removal rate of methylene blue in Pd@Fe₃O₄ is within 80 min in the Fenton reaction.?4?The PdNPs released from E.faecalis were used to be doped with Fe@Fe₃O₄.SEM,XPS,XRD,and other characterization results showed that the Pd and Fe elements were uniformly distributed on the material.The average particle size of nZVI was 31 nm.The prepared Pd/Fe@Fe₃O₄ was used to catalyze the degradation of DS.The results show that the composite of iron and iron oxides doped with PdNPs has a significant effect on the catalytic degradation of 1 g/L Pd/Fe@biomass.Under the condition of pH 3,10 mg/L of DS can be completely removed by 1 g/L of Pd/Fe@Fe₃O₄ within 20 min.TOC results show that the mineralization and dechlorination rate of DS derived by Pd/Fe@Fe₃O₄ can be achieved 68.92%and 85.16%,respectively.The main reaction mechanism is that PdNPs can catalyze the H₂O₂produced more.