Ion transfer at polarised liquid-liquid interfaces modified with adsorbed silica nanoparticles

Magnetic particles (Fe3O4) magnify ion transfer processes at the electrified liquid-liquid interface. Case study: Levamisole detection

This article describes the effect of non-stabilized magnetic particles Fe3O4 (nanoparticles aggregates) addition to the aqueous phase of the polarized liquid-liquid interface (LLI) on the interfacial ion transfer processes. LLI was formed between 1,2-dichloroethane and water solutions (1,2 DCE)|water. The synthesis of Fe3O4 magnetic particles (MPs) was achieved by the co-precipitation method, after which their appearance, size of aggregates, and zeta potential were assessed. All electrochemical measurements reported in this study were performed using cyclic voltammetry (CV). We evaluated the effect of pH and the presence of different concentrations of magnetic Fe3O4 nanoparticles aggregates always initially added to the aqueous phase on tetramethylammonium cation (TMA+), and 4-octylbenzenesulfonic acid (OBS-) ion transfer. We have found that the addition of Fe3O4 MPs followed by their precipitation and LLI interface modification leads to pH dependent magnification of the recorded ionic currents attributed to the cation and anion transfer from the aqueous to the organic phase and vice versa. As such, we have plotted the calibration curves of TMA+ and OBS- in the concentration range of (10-200 μM) revealing that Fe3O4 MPs have a significant effect on detection sensitivity, which is dependent on the interaction between Fe3O4 MPs and the analyte being studied. Finally, we assessed the electrochemical behavior of levamisole at the 1,2-dichloroethane|water interface in the presence and absence of Fe3O4 MPs.

Adsorption of Hydrophilic Silica Nanoparticles at Oil-Water Interfaces with Reversible Emulsion Stabilization by Ion Partitioning

Adsorption of particles at oil-water interfaces is the basis of Pickering emulsions, which are common in nature and industry. For hydrophilic anionic particles, electrostatic repulsion and the absence of wetting inhibit spontaneous adsorption and limit the scope of materials that can be used in emulsion-based applications. Here, we explore how adding ions that selectively partition in the two fluid phases changes the interfacial electric potential and drives particle adsorption. We add oil-soluble tetrabutyl ammonium perchlorate (TBAP) to the nonpolar phase and Ludox silica nanoparticles or silica microparticles to the aqueous phase. We find a well-defined threshold TBAP concentration, above which emulsions are stable for months. This threshold increases with the particle concentration and with the oil's dielectric constant. Adding NaClO₄ salt to water increases the threshold and causes spontaneous particle desorption and droplet coalescence even without agitation. The results are explained by a model based on the Poisson-Boltzmann theory, which predicts that the perchlorate anions (ClO₄^-) migrate into the water phase and leave behind a net positive charge in the oil. Our results show how a large class of inorganic hydrophilic, anionic nanoparticles can be used to stabilize emulsions in a reversible and stimulus-responsive way, without surface modifications.

Electrochemical investigation of adsorption of graphene oxide at an interface between two immiscible electrolyte solutions

Graphene oxide (GO) has been recognized as an amphiphilic molecule or a soft colloidal particle with the ability to adsorb and assemble at the liquid/liquid (L/L) interface. However, most extant works concerning the adsorption behaviors of GO at the L/L interface have been limited to the non-polarized L/L interface. Here, we studied what would happen if GO nanosheets met with a polarizable L/L interface, namely an interface between two immiscible electrolyte solutions (ITIES). On one hand, the adsorption behavior of GO nanosheets at the L/L interface was electrochemically investigated firstly by using cyclic voltammetry (CV) and alternating current voltammetry (ACV). On the other hand, the influence of the adsorbed GO layers at the L/L interface on the ion transfer reactions was studied by employing ion-transfer voltammetry of TEA⁺ and ClO₄⁻ selected as probe ions. Capacitance measurements show that the interfacial capacitance increases greatly in the presence of GO nanosheets inside the aqueous phase, which can be attributed to the increases of interfacial corrugation and charge density induced by the parallel adsorption and assembly of GO at the L/L interface. In addition, it is found that the application of an interfacial potential difference by external polarization can promote the adsorption of GO at the L/L interface. Moreover, the ion-transfer voltammetric results further demonstrate that the GO layers formed at the interface can suppress the ion transfer reactions due to interfacial blocking and charge screening, as well as the hindrance effect induced by the GO layers. All the results with insights into the interfacial behavior of GO under polarization with an external electric field enable understanding the adsorption behavior of GO at the L/L interface more comprehensively.

The adsorption behavior of graphene oxide (GO) nanosheets at an interface between two immiscible electrolyte solutions (ITIES) was electrochemically investigated firstly by using cyclic voltammetry (CV) and alternating current voltammetry (ACV).