Fate of Nano Zinc Oxide in the Aquatic Environment
Date Issued
2009
Date
2009
Author(s)
Chen, Li-Hua
Abstract
This study was mainly focused on the behavior of aqueous nano-zinc-oxide under different pH, concentration of cations and humic acid. The amount of the stably dispersed nano-zinc-oxide was determined by measuring the total particle concentration in the supernatant (detected by atomic absorption spectrometry) and zeta potential of the particle surface.The results showed that the nano-zinc-oxide existed mainly in dissolved form, at lower pH(<8),and the amount of zinc particles in the supernatant could not be determined. On the contrary, under higher pH the nano-zinc-oxide particles formed aggregated easily when the pH of the solution equaled approximately to 8, the isoelectric point (IEP).The effects of the concentration of cations on nano-zinc-oxide aggregation and dispersion were investigated by adding 0.1mM KCl or CaCl2 to the nano-zinc-oxide suspensions. The variations of the energy barrier between supernatant nano-zinc-oxide particles were calculated by using Derjaguin Landau Verwey Overbeek (DLVO) theory. The results revealed that the energy barrier between particles in the presence of K+ was higher than that of Ca2+, and the efficiency of nano-zinc-oxide dispersion by adding K+ was higher than that with Ca2+ by 20%. Besides, the nano-zinc-oxide dispersion was also affected by the presence of humic acid ( a naturally occuringe organic matter in the aquatic environment). Under lower humic acid concentrations(0.5 to 50 mg/L), due to that the zeta potential of the nano-zinc-oxide decreased from 30.7 ± 1.13 mV from without humic acid to -3.93 ± 3.32 mV and the static-electric repulsion between particles diminished, there were dramatic particle collision and sedimentation. The stably dispersed nano-zinc-oxide in the supernatant was only 20%. However, with higher humic acid concentration(2.0 to 50 mg/L), the concentration of the stably dispersed nano-zinc-oxide was higher than that with lower humic aicd concentration by 60% due to that the surface of nano-zinc-oxide particles were thoroughly covered with negatively charged humic acid, and the static-electric repulsion increased significantly.eywords: nano zinc oxidep; humic acid; DLVO theory; Van der Waalsorces
Subjects
nano zinc oxide
humic acid
DLVO theory
Van der Waals
Type
thesis
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