Durable Nanocellulose-Stabilized Emulsions of Dithizone/Chloroform in Water for Hg²⁺ Detection: A Novel Approach for a Classical Problem

Abstract

The use of dithizone (DTZ) for colorimetric heavymetal detection is approximately one century old. However, its pending stability issues and the need for simple indicators justify further research. Using cellulose nanofibers, we attained DTZcontaining emulsions with high stability. These emulsions had water (at least 95 wt %) and acetic acid (1−8 mL/L) conforming the continuous phase, while dispersed droplets of diameter <1 μm contained chloroform-solvated DTZ (3 wt %). The solvation cluster was computed by molecular dynamics simulations, suggesting that chloroform slightly reduces the dihedral angle between the two sides of the thiocarbazone chain. Nanocellulose concentrations over 0.2 wt % sufficed to obtain macroscopically homogeneous mixtures with no phase separation. Furthermore, the rate of degradation of DTZ in the nanocellulose-stabilized emulsion did not differ significantly from a DTZ/chloroform solution, outperforming DTZ/toluene and DTZ/acetonitrile. Not only is the emulsion readily and immediately responsive to mercury(II), but it also decreases interferences from other ions and from natural samples. Unexpectedly, neither lead(II) nor cadmium(II) triggered a visual response at trace concentrations. The limit of detection of these emulsions is 15 μM or 3 mg/L, exceeding WHO limits for mercury(II) in drinking water, but they could be effective at raising alarms.

Stabilization of Beeswax-In-Water Dispersions Using Anionic Cellulose Nanofibers and Their Application in Paper Coating

“…This partial trapping of water, along with a high aspect ratio, is translated into a higher viscosity and yield stress [ 2 , 3 ]. On the other hand, according to the DLVO theory, the electrostatic repulsion between the nanofibers that are adsorbed to the dispersed phase of an oil-in-water emulsion provides a potential energy barrier that prevents coalescence of oil droplets [ 4 , 5 ].…”