Properties of different natural organic matter influence the adsorption and aggregation behavior of TiO2 nanoparticles

Abstract Natural organic matter (NOM) has considerable influence on the aggregation and stability of titanium dioxide nanoparticles (TiO 2 NPs). However, the effect of chemical properties of NOM on the interface interaction and the aggregation process is still not clear. In this study, we investigated the effects of two typical types of NOM (fulvic acid (FA) and humic acid (HA)) on its adsorption onto TiO 2 nanoparticles and their aggregation behavior in aqueous phase. Nuclear Magnetic Resonance (NMR) was used to study their functional groups, indicating that HA has a stronger hydrophobicity than FA. The presence of HA or FA lowered the critical coagulation concentration (CCC) of TiO 2 NPs, while FA showed a more significant effect. HA promotes the aggregation of TiO 2 NPs when ionic strength (IS) > CCC, which was likely due to the bridging effect. Contact angle measurements indicate that HA has higher hydrophobic properties than FA, and it is easier to transfer from water to the surface of TiO 2 NPs. Transmission Electron Microscopy (TEM) was applied to investigate the aggregate formation and colloid interface morphology of NOM-coated-TiO 2 NPs and NOM entanglement. Different structures of HA and FA result in various behavior and their interface interaction mechanisms including IS-induced entanglement and NOM/IS bridging.