The Stability Of Natural Soil Nanoparticles:Effect Of PH And Dissolved Organic Matter

Natural nanoparticles (NNPs) have been in the environment with the evolution of organisms and showed very good compatibility with the environment compared to manufactured nanoparticles, so their environmental risk has been lessened. This paper mainly concerns on the stability of NNPs. We hope what we have done could be useful to following studies on NNPs.Ultrasonic extraction technology, a purely physical means, was used to extract NNPs from soil samples. We have continually optimized the extraction conditions, and good NNPs were successfully extracted from four soils respectively collected from Jilin, Liaoning, Jiangxi and Hainan. The average diameters of this four NNPs were all about90nm. Although they had something different in zeta potential, pH, content of organic matter and so on, four NNPs all possessed good stability and then-size enlarged only a few nanometers after a few months.Changes of the stability of NNPs were studied with the pH of the NNPs suspension varying between3and11. Saltations of the stability of NNPs were observed at a pH point between4and5. Saltation points of three NNPs were about4, and saltation point of the other NNPs was about5. If the pH of the NNPs suspension was below this pH point, the stability of NNPs would fell sharply and aggregation between particles would be very fierce. On the contrary, if the pH of the NNPs suspension was higher than this pH point, the NNPs system would show good stability.The dissolved natural organic matter (NOM) extracted, respectively, from a black soil, a wormcast and a Chinese milk vetch was added to NNPs suspension in order to figure out the effect of NOM on the stability of SNPs. We found that coating of NOM could enhance the stability of NNPs. However, the enhanced effect by the same amount of NOM would be weaker and weaker as the concentration of NOM used for coating being higher and higher. To different NNPs, the stability changes caused by the presence of NOM were different. The stability of less stable NNPs was changed by the presence of NOM more obviously. Meanwhile, the properties of NOM, such as aromatic degree, made big differences in the effect on the stability of NNPs. In general, the stability changes of NNPs caused by the presence of NOM were bigger as the aromatic degrees of NOM were higher.