Aggregated Mechanism And Ion Adsorption Of MgO Nanoparticle:A Molecular Dynamics Study

Nanometer materials have been widely used in many filed,include medical,semiconductors,catalysis,micro components,and so on,due to their unique physical and chemical properties.Thus,researchers show much interest for them.Nanoparticles trend to aggregate with each other during the preparation and application,whichwill lead to the increase of the production particle size.Hence,it is necessary to study the aggregation mechanism.Because,the purification standard of nanomaterial were very strict,in medcial and semiconductors field.They must be purificated by washing process.During which,inorganic salt ions will adsorb on particle surface.Whether this phenomenon could be ignore should be study,detailedly.MgO was chosen as the model particle,based on the two questions.A advanced suspension model with complete solvent environment was built.The aggregation and ion adsorption of nanoparticles was studied by molecular dynamics(MD)method.The affection of surface charge on aggregation was investigated by comparing the polar MgO and the nonpolar(carbon,silicon)systems.Direct at the behavior analyzing of nanoparticles,a series of analyzing methods were developed,based nearest particle distance(DNPD),nearest particle distance distribution function(NPDDF)and aggregation lifetime(?AL).And the advantages of NPDDF were verified by comparing with classical radial distribution function(RDF),in terms of distinguishing aggregation and dispersion.The investigating of nanoparticle distribution in pure aqueous environment shows that the spontaneous aggregation was found in all three types of suspensions,and the aggregation and the dispersion were concomitant,simultaneously.The proportion of aggregated nanoparticles was increased with the increasing of its concentration(mass fraction).The polar MgO nanoparticles show stronger aggregated trend and irreversibility.However,its aggregation balance distance was 3.1 ? which was larger than 2.5 ? of nonpolar nanoparticle.This phenomenon was attributed to the adsorbed water layer between aggregated MgO particles,hindering the further close of them.The investigating of the ion adsorption on MgO nanoparticles shows that double electric layer was found on its surface.The thickness of it was about 10?,and the positive ions were adsorbed,preferentially.The ion adsorption will become the control factor of the desalt effect,when the ion number and the particle number were at the same order of magnitudes.For instance,the apparent concentration of Na+ was only 0.54 times of the actual concentration,in the aqueous based nanosuspension environment with 4 nm particles.when the specific value between ion number and particle number was 3.In this condition,decreasing the ion adsorption will became the key factor of the development of desalting process.In a word,the microscopic behaviors of nanoparticles and ions were simulated and clearly described;the affection of particle surface polarity on aggregation was investigated and the question of that whether the ion adsorption can be ignored was answered,in this study.The research conclusion was instructive for the development of high-efficiency desalting process.