Effect of Dissolved Organic Matter on Titanium Dioxide Nanoparticles in Aquatic Environment: Molecular Weight Fractions

At present, a growing number of consumer products contain engineered nanoparticle TiO2 (nano-TiO2), which has resulted in the consequences of nano-TiO2 entering the aquatic environment directly or indirectly at some stage. The fate of nano-TiO2 in the aquatic environment has become the key factor which affects its safety application and nanoecotoxicology. This paper aims to investigate how the dissolved organic matters (DOM), especially the molecular weight fractions in the aquatic environment, affect the aggregation, stability, and fate of nano-TiO2, and the interaction mechanism of DOM and nano-TiO2. Results of dynamic light scattering (DLS) showed that the molecular weight of DOM molecules caused different aggregation rates of nano-TiO2 in aqueous solution. Fourier Transform infrared spectroscopy (FTIR) results indicated the molecular structure is characteristics of DOM fractions and the mechanisms of bonds formation between DOM and nano-TiO2. Results of three-dimensional excitation-emission matrices (3D-EEM) confirmed the FTIR results and implied the increase of the stability of the π-π conjugated system in the presence of DOM. In addition, low molecular weight of DOM fractions appeared to show more affinity with nano-TiO2 than high molecular weight fractions.