| Diesel soot carbon nanoparticles(SNPs)are produced by incomplete combustion of fuel.They are one of the main components of smog and an important carbon sink in nature,which are very harmful to the environment and human health.SNPs entered into the water through rainfall or direct discharge.Their transport process and final fate depend largely on the colloidal stability of the nanoparticles.In this paper,the time-resolved dynamic light scattering method was used to study the aggregation kinetics of SNPs in aquatic environments.By measuring the attachment efficiency and zeta potential of SNPs,the key environmental factors such as solution chemistry,environmental macromolecules and solar aging were quantified.This study revealed the mechanism of aggregation and stabilization of SNPs in aqueous solutions,and clarified the interaction between carbon nanoparticles in the aquatic environment and its influencing factors.The main conclusions were as follows:(1)The surface of fresh and UV-aged SNPs particles were negatively charged,and the particle size of individual particles was 40-50 nm.They all followed the classic Derja-guin-Landau-Verwey-Overbeek(DLVO)theory with the aggregation behavior exhibiting reaction-limited and diffusion-limited regimes.The electrolyte accelerated their aggregation through charge screening,and the effect of the divalent electrolyte was stronger.The stability of fresh and UV-aged SNPs was greatly reduced under acidic conditions.(2)The presence of environmental macromolecules such as humic acid(HA),fulvic acid(FA),sodium alginate(ALG),and bovine serum albumin(BSA)will inhibit the aggregation of SNPs due to the steric repulsive caused by adsorption,with the degree of influence following BSA>HA>ALG>FA.However,in the aqueous solution of high concentration ALG and high concentration Ca Cl2,the formation of gel promoted the aggregation of SNPs.Whether being destabilized or stabilized,aged SNPs were more susceptible to macromolecules than fresh SNPs.(3)After UV irradiation,the surface of SNPs was decarboxylated and the benzene ring was cracked into chain hydrocarbons.The change in the structure of SNPs increased the Hamaker constant and the van der Waals attraction ofaged SNPs,and decreased the electrical repulsion,causing the aggregation of aging SNPs 3-4 times faster than those of fresh SNPs.(4)After Xenon lamp irradiation,there was no significant change on aggregation of SNPs,which suggested that the UV light of sunlight played an important role in the stability of SNPs.After UV irradiation,SNPs were more likely to aggregate and settle in the aquatic system,indicating that it may be an important part of the carbon sink in the bottom sediment of the river bed,which can be largely removed by appropriate means.This study proved that the solution chemical conditions and photochemical aging in the water environment played an important role in the transport and fate of SNPs in natural aquatic systems,which provided new ideas for solving the adverse effects of smog on water and human bodies. |
