Interaction Of Silver Nanoparticles With Liposome Or Humic Acid And Their In-situ Synthesis And Photocatalytic Applications

Silver nanoparticles(AgNPs)are widely used on account of their broad spectrum in antimicrobial activities,thus the problem of ecological security caused by their emission to the environment has attracted people's attention.For the biological toxicity of AgNPs,many detailed studies have been studied in the aspect of protein and organism.However,attachment to the cell membrane is a critical initial process of its toxicity to cells,and the analysis of this process can thus to help fully understand the toxic mechanism of AgNPs.Natural organic matter(NOM)is widely distributed in surface water,which can change final fates and environmental toxicity of AgNPs by affecting the morphology,property,transformation and migration of AgNPs.Moreover,the amino groups in NOM have the ability to reduce silver ions(Ag+),so it can capture and immobilize free Ag+which released by the dissolution of AgNPs,and further mitigate the toxicity of AgNPs.Based on the above analysis,the intraction of AgNPs with cell membrane and the influence of main functional groups of humic acid(HA),an important component of NOM,on stability of AgNPs are investigated by theoretical calculation and spectral analysis.Besides,the possible pathway of formation of AgNPs in natural water and its photocatalytic performance are explored in this dissertation.The main research contents and results in this dissertation are listed below:1.Interaction mechanism of AgNPs and the cell membrane model.AgNPs attached to cell membrane can cause an increase in membrane permeability and expose the cell to a high concentration of Ag+,which will result in disturbance of cell respiration and further cell death.Due to the complexity of cell structures,interaction between AgNPs and cell membranes is still unclear.Using liposome composed of lipid bilayer as cell membrane model,the binding process and mechanism of AgNPs and liposomes were investigated by two-dimensional(2D)correlation spectroscopy(COS).The results show that AgNPs were bound to ester C=O,-PO2--and N+-CH3 groups in liposomes,and the sequential order of these bands in bonding affinities with AgNPs was N+-CH3>ester C=O>-PO2--.The binding mechanism changed in the presence of electrolytes(i.e.,NaCl and CaCl2),leading to the enhancement of attachment of AgNPs to liposomes,especially CaCl2.In addition,soft protein coronas surrounding on the nanoparticles could also improve the interaction between AgNPs with liposomes.As supplements of biological toxic effects,the results are helpful to understand toxic mechanisms of AgNPs at a membrane level and further promote research on the toxic regulation of AgNPs.2.Interaction mechanism of main functional groups of HA for stabilizing AgNPs.To analyze intraction mechanism of HA for stablizing AgNPs in depth,HA was classified into benzoquinone(BQ),phenol(PhOH),catechol(CT)and glucose(Glc)based on the various functional groups.Through density functional theory(DFT)calculations and molecular dynamics(MD)simulations,the bonding affinities between AgNPs and the four partitions followed the sequence order BQ>PhOH>CT>Glc.The bonding affinities of main functional groups of HA with AgNPs were further confirmed by spectroscopic analysis including excitation-emission matrix(EEM)and two-dimensional(2D)infrared(IR)correlation spectroscopy(COS)These results show that AgNPs mostly interact with HA molecules by bonding with quinonyl groups,leading to substantially mitigated migration and dissolution of AgNPs.The theoretical calculation method along with spectroscopic analysis highlights the critical role of quinonyl groups of HA in the transformation and migration of AgNPs in the aquatic environment.In addition,this method could also be employed to investigate other complicated interaction processes in the engineering and natural environments.3.Synthesis of AgNPs via photo-assisted reduction and its photocatalytic performance.Besides its effect on stability of AgNPs,HA also has ability to in situ reduce silver ions(Ag+)in the formation of AgNPs,which can realize capture and immobilization of free Ag+ in water.Meanwhile,AgNPs of this new form showed excellent activity on degradation of tetrabromobisphenol A(TBBPA),a typical organic halogenated pollutant in water.With AgNPs generated in the mixture of 1 mg/L HA and 2 mM/L Ag+,74.9%TBBPA was degraded in 1 h.This degradation efficiency is much better than that of commercial AgNPs.Through controlling the reaction conditions,neutral pH was found to be beneficial for the degradation of TBBPA,which would lower the requirements of equipments and reaction conditions in practical applications.By the inhabitation test of active species,singlet oxygen(1O2),hydroxyl radical(·OH)and superoxide anion(O2·-)generated via the surface plasmon resonance(SPR)effect of the in situ formed AgNPs under illumination,were simultaneously identified to be the active species in the degradation of TBBPA.Therefore,the AgNPs with high photocatalytic activity are in situ synthesized by using cheap HA under mild conditions,exhibiting potential applications in photocatalytic degradation of organic pollutants in wastwater.