Interactions between zinc oxide nanoparticles and hexabromocyclododecane in simulated waters

Abstract

The zinc oxide nanoparticles (ZnO-NPs) have been increasingly applied in industries and consumer products, causing release of these nanoparticles in environments. The behaviour of ZnO-NPs in the water systems is complicated due to the presence of different cations, anions, organic substances (e.g. humic acid HA) and other organic pollutants (e.g. commonly used brominated flame retardant, BFR). In particular, the aggregation and alteration of these nanoparticles can be influenced by co-existence contaminants. In this study, the interactions between hexabromocyclododecane (HBCD) and ZnO-NPs were investigated for the physicochemical properties and colloidal stability changes in various simulated waters. This is significant to understand the fate and behaviour of ZnO-NPs at environmental relevant conditions. The surface chemistry and particle size distribution (PSD) of ZnO-NPs with and without the existence of HBCD, HA and electrolytes (NaCl, CaCl 2 and MgCl 2 ) after different periods (1 and 3 weeks) were investigated at pH 7.00 ± 0.02. The size of the ZnO-NPs increased from nanometres to micrometres with the addition of numerous concentrations of HBCD, HA, and cations and their mixtures. The zeta potential of ZnO-NPs increased upon addition of HBCD, HA and electrolytes indicating a more stable agglomeration form while less agglomeration was observed in the ZnO-NPs and HA suspension after 3 weeks. Hydrophobic and electrostatic interactions, van der Waals forces, including hydrogen bonding and cation bridging could be potential interactive driving forces. The results indicated agglomeration of ZnO-NPs in the existence of organic substances, salts and contaminants, thus sedimentation and precipitation are promising under salty surface water/sea water. • Enhanced aggregation of ZnO-NPs after interactions with HBCD, HA and electrolytes. • Alterations in the surface charge of ZnO-NPs after the interactions. • Ageing influences the changes in size, shape and zeta potential of ZnO-NPs.