Heteroaggregation of CeO2 and TiO2 engineered nanoparticles in the aqueous phase: Application of turbiscan stability index and fluorescence excitation-emission matrix (EEM) spectra

CeO2 and TiO2 engineered nanoparticles (ENPs) are being increasingly used in many applications. Due to their properties, heteroaggregation between these two types of ENPs is very likely, which can determine their fate and transport. However, the heteroaggregation behavior of CeO2 and TiO2 ENPs is still not clear, partly due to the lack of appropriate tools. In this study, we investigated the application of Turbiscan Stability Index (TSI) for the measurements of CeO2/TiO2 ENP heteroaggregation. TSI was found to be effective to investigate the heteroaggregation and stability of the CeO2-TiO2 ENPs system. Increasing CeO2/TiO2 ENPs ratio reduces the TSI values, indicating higher stability. Fluorescence excitation-emission matrix (EEM) spectra were used to study the interface interaction between humic acid (HA) and CeO2/TiO2 ENPs. The TSI value of ENPs were rising with the increasing of CeO2/TiO2 ENPs ratios in the H River or Q Reservoir water. In addition, their variation trends were similar to those in well-controlled synthetic water. Proposed interaction mechanisms include surface charge attraction and competitive adsorption.