Aggregation Kinetics Of Nanoparticles During Environmental Transport

Nanoparticles(NPs)are ubiquitous in aquatic environment,soil,and sediment.These NPs inevitably enter the environment or contact with the skin and undergo complex environmental behaviors,which may cause aggregation and sedimentation,thus affecting their fate and transformation.Their environmental transport are largely controlled by aggregation behaviors.Soot nanoparticles(SNPs)and titanium dioxide nanoparticles(Ti O₂ NPs)are selected as the research objects to further understand the aggregation behaviors of these NPs during environmental transport.In this study,dynamic light scattering(DLS)was used to measure the dynamic change of particle size,and study aggregation kinetics of NPs in four artificial sweat solutions(AATCC p H 4.3?ISO p H 5.5?EN p H 6.5?ISO p H 8.0).The effects of NPs and sweat concentrations,sweat components(organic components including L-histidine,lactic acid,and urea,and inorganic components including Na Cl,Na₂HPO₄,and Na H₂PO₄)on these NPs aggregation and differences were also studied.In addition,through the determination of zeta potentials of NPs and calculation of critical coagulation concentrations(CCC),the aggregation mechanism was explained and aggregation model was constructed following the Derjaguin-Landau-Verwey-Overbeek(DLVO)theory.The aim was to explore the stability of two kinds of NPs in sweat and to provide theoretical basis for better predicting the migration and destination of NPs in contact with skin.The main results are as follows:(1)The influence of the four artificial sweat solutions on the stability of the two NPs was clarified.The aggregation rate of 10 mg/L SNPs in the four artificial sweat followed the order of AATCC p H 4.3>EN p H 6.5>ISO p H 5.5>ISO p H 8.0,which was related to the different components contained in the sweat.While the aggregation rates of 10 mg/L three different Ti O₂ NPs were all different.(2)The aggregation behaviors and mechanisms of NPs in the presence of sweat and a single component of sweat were investigated.10 mg/L NPs aggregated in the four artificial sweat,except for SNP in ISO p H 8.0.The aggregation of these two NPs was promoted with the increase of the concentration of each component,except urea.(3)The destabilization effect of organic components of sweat including L-histidine and lactic acid on the aggregation behavior of NPs and the stabilization effect of urea on the aggregation behavior of NPs were ascertained.FTIR and XPS were used to characterize the binding mechanism of NPs in the presence of organic components of sweat.(4)The aggregation behaviors of these NPs in human sweat were studied.These NPs in contact with sweat will aggregate leading to particle size increase,which could not yet penetrate the healthy dermis.However,these NPs may remain stable in some sweat solutions that could pose risks of skin penetration.In summary,the aggregation behaviors of SNPs and Ti O₂ NPs were affected by different sweat solutions,concentrations,and components of sweat and were also related to their particle size and material morphology.Adsorption and other processes can change the strength of electrostatic repulsion between NPs,thus affecting their colloidal stability.