Biofabrication Of Novel Electrode Materials For Lithium-ion Batteries And Complete Biodegradation Of Chlorpyrifos Through Bacteial Biooxidation Approaches

Manganese?Mn?oxides are highly reactive minerals formed via Mn²⁺oxidation.Mn oxides are widely distributed in various soil and aqueous sediments with spherical,cloddy or irregularly shaped aggregates and associate with the content,morphology,migration,and transformation processes of many heavy metals,radioactive and trace elements through their strong adsorption capacities,thereby playing a crucial role in the biogeochemical cycle of these elements.Numerous previous investigations have confirmed that various microorganisms,particularly a variety of bacterial and fungi with Mn²⁺-oxidizing activity,are the primary driving forces in the biological formation of Mn oxides.In this dissertation,based on the distinctive characteristics of forming the Mn oxide aggregates of a Mn²⁺-oxidizing Pseudomonas sp.T34 and an engineered Pseudomonas putida MB285 surface-displaying bacterial multicopper oxidase upon Mn²⁺induction,several nanoscale-microscale Mn oxide aggregates doped with heterologous Co²⁺ and Ni²⁺ were initially prepared,and were subjected to multiple characterizations in terms of morphology and fundamental capacities.These aggregates were subsequently fabricated to be MnO-based hollow and porous electrochemical materials with high electric potential through biological template technology,and were further used as electrodes for lithium-ion batteries for detection of their electrochemical capacities.Moreover,the ability of the engineered P.putida MB285 to biodegrade chlorpyrifos was investigated.The results of compositional analyses of the degraded products demonstrate that MB285 was capable of completely eliminating chlorpyrifos via direct biodegradation.The main studies and results can be summarized as following.1.The ability of Pseudomonas sp.T34 and engineered P.putida MB285 cells to form Mn oxide aggregates upon continuous Mn²⁺ induction in laboratory trials were verified.The effects of Co²⁺or Ni²⁺on Mn oxidation activity during biominealization processes were analyzed.The interaction of metal ions with Mn oxide was also confirmed in the experiments.The surface morphologies and major phases of the aggregates formed by wild-type Pseudomonas sp.T34 and engineered MB285 were subsequently characterized.The aggregates of the strain T34 were found to be multiply layered,whereas those formed by MB285 were microspheres.Both aggregates were mesoporous materials with high specific surface area,and the main components were mainly organic matter.Structurally,these aggregates were microscale or nanoscale structures with high-valent Mn oxides dispersed in biomasses that were constituted of bacterial cell bodies and extracellular polysaccharides.Bycomparing the structural properties of the two mineralized aggregates,the structure and properties of the composite materials obtained from this biomineralization are more clearly understood.The factors influencing Mn-oxidizing activity,particularly Mn oxidases,were analyzed,and the optimum reaction conditions of Mn mineralization were also investigated.2.The combination of biotemplate and bioconversion strategies,which is used to fabricate the novel materials with a unique morphology and a complicated structure,represents a sustainable and an environmentally friendly approach to material manufacturing.In the current study,biogenic Mn oxide aggregates of Mn?II?-oxidizing bacterium Pseudomonas sp.T34 and the engineered P.putida MB285 cells with surface-immobilized multicopper oxidase were used for the first time as a precursor to synthesize a biocomposite that was doped with Co?CMC-Co?and Ni?CMC-Ni?under mild shake-flask conditions,based on the biomineralization process of biogenic Mn oxides and the characteristics of metal ion subsiders.X-ray photoelectron spectroscopy,phase composition and fine structure analyses demonstrated that hollow porous carbonaceous MnO-based cation-doped multiphasic composites were fabricated after high temperature annealing of these biocomposites.The degree of composite graphitization was enhanced gradually with increase in carbonation temperature.A hollow or porous structure could be obtained at a suitable carbonation temperature.The cycling and rate performance of anode materials for lithium-ion batteries,prepared under various conditions,were compared using different electrochemical analyses.Because of the unique hollow porous structure and multiphasic doping state,The composite materials CMC-Co and CMC-Ni obtained from the wild strain T34 showed good cycle stability and reversible specific capacity,the reversible discharge capacities of CMC-Co and CMC-Ni were 650 m Ah g^-1 and 547.2 m Ah g^-1(0.1 Ag^-1,50 cycles),while the materials from the engineering strain MB285 were 361.44 and 379.29 m Ah g^-1(0.1 Ag^-1,50 cycles),respectively.The cycling stability of the nickel-doped oxide material obtained from both strains has been significantly improved,with near-zero capacity loss?200 cycles?in the cycle performance test,and the polarization phenomenon completely disappeared,which also shows the effectiveness of the doping element modificationThe hollow porous structure provided a large reaction area between active materials and electrolyte and shortened the diffusion distance of the lithium ions.A suitable carbonization temperature improved the material conductive property.The mutual doping of several oxides restricted the aggregation and dissimilation phenomenon of materials in electrochemical lithiation and deintercalation cycles.Therefore,the stability and capacity in cycle process were improved further.It is also worth noting that the easy and cost-effective preparation ofthese materials indicates their potential use in the bioenergy field.3.The long-term abuse use of chlorpyrifos-like pesticides in agriculture and horticulture has resulted in significant soil or water contamination and a worldwide ecosystem threat.P.putida MB285 has been previously characterized as a solvent-tolerant bacterium that was capable of degrading different recalcitrant organic compounds,such as synthetic dyes,endocrine-disrupting chemicals,among others.In this study,the ability of MB285 cells to biodegrade chlorpyrifos was investigated.The results of compositional analyses of the degraded products demonstrate that the engineered MB285 was capable of completely eliminating chlorpyrifos via direct biodegradation whereas the free laccase only transform chlorpyrifos to 3,5,6-trichloro-2-pyridinol,as determined by high-performance liquid chromatography and gas chromatography-mass spectrometry assays.Two intermediate metabolites,namely 3,5,6-trichloro-2-pyridinol and diethyl phosphate,were temporarily detectable,verifying the joint and stepwise degradation of chlorpyrifos by surface laccases and certain cellular enzymes.The degradation reaction can be conducted over a wide range of p H values?2-7?and temperatures?5-55 °C?without the need for Cu2+.Bioassays using Caenorhabditis elegans as an indicator organism demonstrated that the medium was completely detoxified of chlorpyrifos by degradation.Moreover,the engineered cells exhibited a high capacity of repeated degradation and good performance in continuous degradation cycles,as well as a high capacity to degrade real effluents containing chlorpyrifos.Therefore,the developed system exhibited a high degradation capacity and performance and constitutes an improved approach to address chlorpyrifos contamination in chlorpyrifos-remediation practice.