Instability of β-phase silver iodide nanoparticles in an aqueous medium by ozone

Artificial ice nucleation in cloud seeding could produce restricted sources of drinking water to be contaminated by silver iodide nanoparticles (AgI NPs). The toxicity of NPs depends on their aggregation in aqueous media which is affected by the treatment method. In this study, the effect of ozone on the stability of beta-phase AgI NPs was investigated with respect to z-average, zeta potential, polydispersity index (PdI), and colloidal turbidity. A quadratic model based on response surface methodology was presented to correlate the impact of temperature (10-40 degrees C), initial pH of colloid (4-10), ozonation time (15-45 min) and NPs concentration (50-150 mg/L) on NPs aggregation. The results showed that temperature and pH had the most significant effect on the colloidal stability, with an average contribution of 37.9% and 24.4%, respectively, considering all responses. Under the optimum level of investigated variables, z-average, zeta potential, PdI and turbidity varied from 25.5 to 1320 nm, -45.8 to -4.1 mV, 0.125 to 1 and 41.2 to 1.5 NTU, respectively. The dissolved ozone affected instantly the negative electric charge, iodide ions, created by the partial dissociation of surface groups, while its reaction with silver ions was much slower. Further oxidation of Ag+ led to the formation of Ag-0 and AgO/Ag2O, which increased the attractive force and aggregation of NPs. Inclusion an ozonation stage in water treatment facilities in arid countries with water scarcity would effectively reduce the disadvantage of cloud seeding using AgI.