Aggregation of Fe₂O₃ nanoparticle in the presence of organophosphate esters (OPEs)

Aggregation is a key process for determining the environmental behavior and impact of a nanoparticle (NP). Since organophosphate esters (OPEs), which are recognized as emerging contaminants, are distributed widely in the natural aquatic environment, they may contribute to interacting with NPs and ultimately influence their transport and fate. Here, we investigated two typical organophosphate esters OPEs on aggregation the Fe₂O₃ NP in aquatic environments. The results showed that both tri-ethylhexyl phosphate (TEHP) and tris (chloroisopropyl) phosphate (TCPP) improved the colloidal stability of Fe₂O₃ NP in artificial water and environmental matrices. TEHP exhibited an obvious effect than TCPP on the Zeta potential and aggregation rates of Fe₂O₃ NP in artificial water. In the presence of electrolyte, 10 mg/L TCPP and TEHP increased the critical coagulation concentration (CCC) by 3.6 times and 17.4 times, respectively. Compared with pore-water, the aggregation rates of Fe₂O₃ NP in river water were slightly higher than those in pore-water, which can be attributed to the higher DOC in pore-water. We suggested that the high hydrophobicity and molecular weight of OPEs were considered important factors against the aggregation of Fe₂O₃ NP in water. Greater surface charge and steric hindrance originating from TCPP and TEHP dominated the colloidal stability of Fe₂O₃ NP.