Tuning The Formation Processes Of Nanoparticles In A Plasma Electrochemical System

If gas discharge plasma is used to substitute one of the two solid electrodes in a traditional electrochemical system,one obtains a plasma electrochemical system,and then the traditional electrochemistry changes to the plasma electrochemistry.In the plasma electrochemical system,the reactive species produced in the gaseous plasma and at the plasma-liquid interface via the plasma-liquid interactions can enter the liquid,inducing the bulk liquid change by secondary processes.By taking advantage of these plasma-induced liquid chemistry,the plasma electrochemical system can be used for a great number of applications such as nanomaterial synthesis,wastewater treatment,and plasma medicine.In the case of discharge plasma generated above a liquid system,the generated species usually include both reducing and oxidizing reactants,such as hydrated electron(eaq),atomic hydrogen(H),hydroxyl(OH)radical,ozone(O3),and hydrogen peroxide(H2O2).Thus,two types of reactions might co-exist in the liquid:reduction and oxidization.It is possible to tune the liquid reactions by adjusting the liquid chemical processes from which the nanomaterial synthesis by the plasma electrochemical process might take benefit.In this thesis,we demonstrate the possibility of tuning the formation process of silver nanoparticles(AgNPs)in the plasma electrochemical system by controlling the liquid chemistry with additives.For the AgNPs synthesis,Ag+ ions(aqueous solution of AgNO3)might be simultaneously involved in a forward(reduction)as well as a backward reaction(oxidation).,Reduction/Oxidation Ag+ Reduction/Oxidation Ag+(?)AgFor the AgNPs formation,a surfactant,polyvinyl pyrrolidone(PVP),is added into the aqueous solution of AgNO3 to prevent the forming NPs from aggregation.Electron scavenger,5-Bromouracil(5-BrU),is added into the solution to investigate the effect of eaq on the AgNPs formation.OH radical scavengers,ethanol and dimethyl sulfoxide(DMSO),are used to study the effect of oxidizing species on the AgNPs formation.To probe the formation process of nanoparticles,we consider the well-known localized surface plasmon resonance(LSPR)property of the metal NPs.The results indicate that there exists Ag+ reduction and Ag oxidation simultaneously during the AgNPs formation,and the hydrated electrons formed by the dissolution of plasma electrons are the main reducing agents for the Ag+ reduction,while the hydrogen peroxide produced by the plasma-liquid interactions plays a role in etching the formed AgNPs to Ag+.For the Gold nanoparticles(AuNPs)formation,we adjusted the plasma electrochemical system current.The results indicate that AuNPs synthetic rate decreased with decreasing current and AuNPs with other shapes appeared at low current.