The Characteristic Of Nanoparticle-biocorona And Effects On Adsorption Of Heavy Metals

A large number of biological macromolecules in the water environment,such as natural organic matter,carbohydrates,protein and surfactant,etc.,easily interact with metal oxide nanoparticles（NPs）discharged into the water body,forming a nano-level organic coating on their surface,that is,"biocorona".The biocorona would change the surface characteristics and stability of NPs,and affect the adsorption of heavy metal ions by NPs,thereby changing the migration and transformation of NPs in water environment.In order to study the characteristics of the biocorona and their effect on the adsorption of heavy metals by NPs,the activated sludge proteins,natural organic matter（NOM）and extracellular polymeric substance（EPS）were selected as research objects.The characteristics of these biocoronas on NPs were explored,their effects on the aggregation and sedimentation of NPs were studied,and the roles of biocorona on heavy metals adsorption and biotoxicity were discussed.The main research contents and results are as follows:In this work,the protein coronas structure formed on the surface of Ti O₂nanoparticles（TNPs）and Zn O nanoparticles（ZNPs）by activated sludge proteins were characterized by TEM.The results of shotgun proteomics showed that thirty and nine proteins with high affinities to TNPs and ZNPs,respectively,and their effects on the distribution of TNPs and ZNPs in activated sludge were concluded.In addition,the effects of protein coronas on the aggregations of TNPs and ZNPs were evaluated.The aggregation and sedimentation percentages of ZNPs at 35,53,and 106 mg/L of proteins were 13%,14%,and 18%,respectively,whereas those of TNPs were 21%,30%,41%,respectively.The proteins contributed to ZNPs aggregation by dissolved Zn ion-bridging,whereas the increasing protein concentrations enhanced the TNPs aggregation through macromolecule bridging flocculation.It was investigated that the effects of protein（bovine serum albumin,BSA）,carbohydrate（sodium alginate,Na Alg）,and humic acid（HA）on the aggregation and sedimentation of TNPs and Ce O₂NPs（CNPs）,and on the adsorption of Cd²⁺and Pb²⁺by TNPs and CNPs.In the range of 20-120 mg/L of Pb²⁺and Cd²⁺,BSA had little effect on the adsorption,whereas HA and Na Alg significantly accelerated these metals adsorption by TNPs and CNPs（p<0.05）.In the presence of HA and Na Alg,the adsorption by TNPs increased 14%-41%and 16%-57%for Pb²⁺,and 12%-112%and 22%-143%for Cd²⁺,respectively.Compared with CNPs alone,HA and Na Alg increased 21%-71%and 23%-65%for Pb²⁺,and 26%-45%and 45%-91%for Cd²⁺,respectively.The adsorption of Pb²⁺and Cd²⁺by NPs and NPs-NOM was well fitted by Freundlich model.The increase in ionic strength（0-100 m M NaCl）reduced the adsorption of Pb²⁺and Cd²⁺by NPs and NPs-HA/Na Alg.The effects of EPS corona on the adsorption of heavy metals by NPs and the biotoxicity were studied.Proteomics identification showed that there were 42 and 13proteins in the EPS corona of TNPs and CNPs,respectively,and three proteins were common among the top 10 proteins.The EPS corona promoted the adsorption of heavy metals by NPs（p<0.05）.The adsorption capacity of TNPs-EPS to Cd²⁺,Cu²⁺,Ni²⁺,Pb²⁺and Ag⁺was about 4.4,4.2,3.9,6.7 and 8.8 times than that of TNPs to five metal ions,respectively,while the adsorption capacity of CNPs-EPS to Cd²⁺,Cu²⁺,Ni²⁺,Pb²⁺and Ag⁺was about 5.0,5.4,7.0,7.6 and 8.5 times that of CNPs to five metal ions,respectively.Both NPs and heavy metals were toxic to E.coli,and in addition to NPs-Cd/Ag with heavy metal concentration of 50 mg/L,the inhibition of combination of them on the growth of E.coli was significantly enhanced（p<0.05）.NPs-EPS corona enhanced the inhibition of E.coli by enhancing NPs carrying heavy metals,showing greater biological toxicity.