Stability and characterization of mixture of three particle system containing ZnO-CuO nanoparticles and clay.

The aim of this study was to understand heteroaggregation of mixture of ZnO and CuO nanoparticles (NPs) with clay, for the first time as per the authors' knowledge. Aggregation studies of mixture of ZnO and CuO nanoparticles with clay was done (ionic strength =5 mM; pH 7; nanoparticles concentration = 0.1 mg/L, 1 mg/L, 10 mg/L; Clay concentration = 1, 10, and 100 mg/L and HA concentration = 0.1,1, and 10 mg/L as total organic carbon). Critical coagulation concentration (CCC) and attachment efficiency values of suspensions with ZnO: CuO ratio = 0.1, 1, 10 were also determined. Aggregation and liquid portions of mixture suspension at equal mass ratio were characterized for size, zeta potential (ZP), metal and ion contents, pH and conductivity. Results indicated that CCC was found to be 120.7 mM for ZnO: CuO ratio 10 and 1144 mM for ZnO: CuO ratio 1. Values of attachment efficiency were obtained to be 0.9 and 0.8 for these two ZnO:CuO ratio. At natural water ionic strength (IS) condition, aggregate rate constant of mixture of particles ranged from 0.281 to 8.63 nm/min for 10 mg/L NP concentration. Aggregation in suspension containing mixture of particles was found to be affected by NP concentration, clay concentration, and humic acid (p < 0.05). During a 1-h aggregation study, 2.67 mg Cu metal/g aggregate and 0.38 mg Zn/g aggregate were found in aggregates of 5 mM suspension. Overall, this study provided information on aggregation characterization of mixture of metal oxide nanoparticles (ZnO and CuO) in HA and clay presence, which is useful in understanding aggregation formation and in characterizing exposure dose for environmental risk assessment. More detailed information on a three -particle system with natural colloids is required for predicting their fate in aquatic system and defining risk.