engleski

Determination of electroneutrality point temperature dependence for various materials in an aqueous electrolyte solution.

Electrical interfacial layer forms upon the contact of aqueous electrolyte solution with a surface of solid colloid or nanoparticles. Inside the electrical interfacial layer, apart from the accumulation of the electrolyte ions, potential determining ions OH– and H+ accumulate as well. There are several different models that describe process of accumulation of ions on interfaces [1- 2]. For an inert surfaces accumulation of potential determining ions is achieved through distribution between the bulk of the solution and interfacial layer, while for metal oxides it is achieved by a process of protonation and deprotonation of the charged surface group. The electrical interfacial layer is characterized by electroneutrality point. At the electroneutrality point (pHeln) all electrical properties at the surface diminish. The values of surface potentials and the net surface charge density equal zero. In the case of negligible or symmetric counter ion association electroneutrality point has the same values as the isoelectric point and point of zero charge (pHeln = pHiep = pHpzp). Determining temperature dependence of electroneutrality point (isoelectric point or point of zero charge) enables the evaluation of the difference in standard distribution enthalpy of H+ and OH- on inert surface. This data enables us to better understand the behavior of the electrical interfacial layer and creation of the suitable mathematical and physical models. To achieve a better understanding, experimental results obtained for different inert as well as non-inert materials, i.e. metal oxides, were compared. For this purpose, two inert (Teflon and diamond) and one metal oxide (TiO2) surfaces were studied. Colloid particles in general have very different physical properties, so one method for evaluation of thermodynamic parameters of interfacial processes cannot be applied for all material. In this respect, we have chosen three distinct methods: potentiometric mass titration, streaming potential measurements and calorimetry. Potentiometric mass titration is a standard method for determining point of zero charge. Streaming potential measurement is a reliable method to determine electrokinetic potential. Lastly, calorimetry is a standard method for observing changes in enthalpy of the system during chemical reactions or physical processes. Differences in standard distribution enthalpy of H+ and OH ions on the diamond, Teflon and TiO2 surfaces were calculated and compared.

Teflon, diamond, TiO2, inert surfaces, electroneutrality point, temperature dependency, Streaming potential, Potentiometric mass titration

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