Study On Titanium Dioxide Nanoparticles Characteristics In The Aquatic Environment And Interaction With Humic Acids

TiO₂ nanoparticles is one of the most widely used nanomaterials, with the production and use of a large number of TiO₂ nanoparticles, it escapes into the environment and induce potential threat to human health. Through the characterization on TiO₂ nanoparticles in the aqueous environment, the issue has research on the particle size distribution, aggregation, morphology and surface charge properties of TiO₂ nanoparticles. This article reviews the effects of different factors on the stability of TiO₂ nanoparticles, and also use the ultrafiltration technology to separate humic acids into four fractions (<1K, 1K 10K, 10K 100K,> 100K). By studying interactions between the TiO₂ nanoparticles with different ultrafiltration fractions of humic acids , we acquire the morphological characteristics of TiO₂ nanoparticles in the aqueous environment, the changes after the interaction and study of TiO₂ nanoparticles concentration, concentration of humic acid and pH value, ionic strength of the aqueous environment and interaction between the two effects by Ca²⁺, forming reserves technology against the removal to TiO₂ nanoparticles in the aqueous environment.This paper, firstly characterize the TiO₂ nanoparticles, we certify get the homogeneous distribution of TiO₂ nanoparticles in aqueous solution, its dispersion is good, and effective diameter is 198.3nm, the zero potential is 6.5. The stability studies on TiO₂ nanoparticles in the aqueous environment have shown that particle size of nano- TiO₂ aggregates varied little by the pH changes, and has negative relationship to its absolute value, the more charge TiO₂ nanoparticles has, the smaller their aggregate size becomes, the more stable. Adding the humic acids, the negative charge of TiO₂ nanoparticles is greatly reduced, due to interaction between electrostatic repulsion and ligand exchange, TiO₂ nanoparticle size becomes small under the influence of humic acid. With the existence of Ca²⁺ , size increased significantly after the reaction between nano TiO₂ nanoparticle size and humic acids, because Ca²⁺ counteract the negative electrical properties of TiO₂ nanoparticles , the aggregate size increases and the stability decreased.Humic acids is divided into four fractions by molecular weight using ultrafiltration technology.Humic acids particle size increased with increasing levels of molecular weight.Based on the infrared spectra of humic acids, low molecular weight contains more carboxyl, phenolic and other oxygen-containing functional groups, while high molecular weight of humic acid polymer contains more fat carbon chain structure. With the increase of the humic acid molecular weight, the E4/E6 ratios of humic fractions decreased, indicating that there are more chromogenic functional groups in low molecular weights humic acids, such as carbonyl, carboxyl, aromatic conjugated double bonds. The fluorescence intensity of low molecular weight is stronger than high molecular weight, mainly because the low molecular weight has more oxygen e-group.The main mechanism of humic acids and TiO₂ nanoparticles is ligand exchange and electrostatic interaction, the surface hydroxyl of TiO₂ nanoparticles and carboxyl and phenolic hydroxyl of humic acid exchange. At the same time, there is electrostatic attraction between the two and then adsorption occurs. The smaller molecular weight of humic acids is, the more oxygen groups such as carboxyl and phenolic hydroxyl it contains, the more reaction between the low molecular weight and humic acid, the greater absorption of humic acid. At the course of interaction between TiO₂ nanoparticles and humic acids, the lower pH value is, the more active sites on the surface of TiO₂ nanoparticles, the more groups as a resulting from the exchange reaction of humic acids. It is also more conducive of both ligand exchange, while the enhancement of electrostatic interaction between humic acids and TiO₂ nanoparticles, promoting the adsorption reaction, and thus resulting a large quantity of humic acids adsorption. The ionic strength increases and plays the role of compressing double layer, and can reduce the solubility of humic acids, and promote adsorption between humic acids and TiO₂ nanoparticles.Adsorption capacity to humic acids increases. Ca²⁺ plays a bridging role between the TiO₂ nanoparticles and humic acids, it increases the electrostatic interaction between nano TiO₂ nanoparticles humic acids, promoting the adsorption, as a result, humic acids adsorption increased.