Purified Separation, Concentration And Preservation Of Polydispersion Gold Nanoparticles

The physical and chemical properties of nanoparticles (NPs) are highlydependent on particle size and shape, therefore, controlling their size and shape isvery important. Although some sorts of monodisperse NPs can be directly synthesized,for many other sorts of NPs, their large-scale synthesis with controlled size and shapeis still a huge challenge. As the synthesized NPs are usually polydispersed, it isinterest to obtain monodisperse NPs from the usuall polydispersed NPs by simplesize-and shape-selective separation. Among many separaton strategies, salt-inducedprecipitation, which relies on finely tuning interparticle interactions, is relativelystraightforward and low-cost for high-throughout separation of NPs. However, thedifference in critical coagulation concentrations (CCC) of different sized NPs is low,size-and shape-selective separation of the polydispersed NPs is still a great chanllege.Therefore, the research interest of this thesis is focusing on polydispersed gold NPs,and aiming at finding out effective strategy for size-selective separation ofpolydispersed NPs. The main research contents and results are outlined as follows:Firstly, a zwitterion disulfide ligand was synthesized for the modification ofdifferent sized gold NPs.Secondly, the stability of the zwitterion ligand-modified gold NPs in saltsolutions was studied. The experimental results reveal that the zwitterionligand-modified gold NPs show distinct size-dependent CCC and reversibleaggregation properties.Thirdly, salt-induced strategy for size-selective separation and concentration ofAu NPs was developed, on the basis of the size-dependent CCC and reversibleaggregation properties of the zwitterion ligand-modified gold NPs. The experimentalresults reveal that the concentrated gold NPs can be long-term preserved, and onceneeded, can be recovered into well-dispersed dilute dispersions without losing theproperties of single, isolated particles. Therefore, the results of this study will havesignificance in large-scale fractionation, storage, and transport of NPs for commercialapplications.Fourthly, in order to avoid ligand synthesis and reduce separation cost, weaccording to the structural features of the zwitterionic ligand, directly use the1:1mole ratio mixtures of commerce-available positively charged and negatively charged thiol ligands to modify gold NPs. The two ligand-modified small sized gold NPs showremarkable stability in the complex environment and pH-dependent reversibleaggregation property. On the basis of the pH-dependent reversible aggregationproperty, we further develop a pH-induced strategy for the concentration of smallsized gold NPs.