Formation Of Nanomaterials Mediated By Shewanella Putrefaciens And Catalytic Properties Towards Nitrobenzene

As a kind of dissimilatory metal-reducing bacteria,Shewanella can produce electrons by metabolizing various organic compounds and transfer electrons to extracellular soluble or insoluble electron acceptors via their own special electron transfer pathways.Therefore,the genus has attracted wide attention in recent years in the field of nanomaterials biosynthesis.Biosynthesis of nanomaterials is environmentally friendly,and the formed nanomaterials have great application prospects in the environmental field.In order to reach their full potential,it is necessary to further investigate the structure-effect relationship between the structure of biosynthesized nanomaterials and the degradation of pollutants.This paper summarizes the species of Shewanella and their extracellular electron transfer pathways,and reviews the synthesized nanomaterials by Shewanella and their applications.On this basis,we took advantage of the extracellular electron transfer capability of Shewanella putrefaciens(CN)to reduce graphene oxide(GO)and palladium ion(Pd(?))respectively,and synthesized Shewanella@graphene core-shell material(CN@rGO)and palladized cells loaded with palladium nanoparticles(PdO)under different conditions.The structure characteristics were characterized by Fourier Transform Infrared Spectroscopy(FTIR),Raman Spectroscopy(Raman),Thermogravimetry(TG-DTG),Electron Microscopy(SEM,TEM)and X-ray Diffractometry(XRD);Nitrobenzene(NB)was used as a model pollutant and the reduction properties of the nanomaterials synthesized under different conditions were discussed;Finally,we explored the structure-effect relationship between the structure of synthesized nanomaterials and the reduction efficiency of NB,which provided a theoretical basis for further application of the biosynthesized nanomaterials.The main innovations and research results of this paper are as follows:(1)CN@rGO was formed by one-step self-assembly during the process of bioreduction of GO by CN,which enhances the contact between CN and rGO,shortens the electron transfer distance from CN to NB and finally improves the reduction efficiency of NB.The study found that although GO has a toxic effect on CN,the synthesized CN@rGO promotes the reduction of NB by enhancing the direct contact between CN and rGO and the adsorption capacity to NB;The effect of different proportions of CN@rGO on the reduction of NB was different.The reduction efficiency of NB increased first and then decreased with the concentration of added GO.The optimal ratio was GO=10 mg/L:OD600=0.6,at this ratio,the reduction efficiency of NB can be increased by 30%compared with the control group;In addition,CN@rGO has a better cycle stability than the control and can be recycled at least 5 times.(2)Pd(?)was reduced by CN,and palladium cells loaded with Pd0 were successfully synthesized,besides,the influence of different factors(the ratio of CN to palladium and pH)on the process of Pd0 synthesis,the structural characteristics and microstructures of Pd0 and their catalytic reduction property were investigated.The study found that the formed Pd0 were mainly distributed in the outer cell membrane and periplasm,and the size is smaller than the Pd0 synthesized by other bacteria,it is maintained in the range of 1.5-3.5 nm.The size of Pd0 synthesized by CN is not obviously affected by the ratio of CN to palladium,within a certain range,the higher the ratio,the less extracellular aggregated Pd0 and the higher the reduction efficiency of NB,but when the concentration of CN is too high,the sulfur-containing functional group will have a toxic effect on Pdu and the reduction efficiency of NB is lowered;CN can synthesize Pd0 in the range of pH 3-9,but pH affects the kinetics of the reaction and the shape and position of Pd0 formed,when the pH is in the range of 5-9,the synthesized Pd0 are distributed in the outer membrane and periplasm,and the higher the pH,the slower the synthesis of Pd0,the more irregular the shape of the synthesized Pd0 and the better the catalytic reduction effect of NB;But when the pH is 3,the cell integrity of CN is destroyed,and some large-sized Pd0 are synthesized in the cytoplasm,so the catalytic reduction rate of NB is low,besides,the synthesis of Pd0 is the slowest at this pH because the activity of some biomacromolecules decreased under strong acidic conditions.