High Temperature Microelectrophoresis Studies of the Rutile/Aqueous Solution Interface

Abstract

A recently developed high temperature microelectrophoresis cell was employed for ζ-potential measurements at the rutile/aqueous solution interface over a wide range of pH at temperatures of 25, 120, and 200 °C. Water, 0.001 mol kg -1 NaCl(aq), and 0.01 mol kg -1 NaCl(aq) solutions were tested at these temperatures. The desired pH values were attained by adding either HCl(aq) or NaOH(aq). The obtained experimental data allowed us to estimate isoelectric point pH values (pHiep) of 5.26 ((0.45) at 25 °C, 5.13 ((0.37) at 120 °C, and 4.50 ((0.55) at 200 °C. This decrease in pHiep values with increasing temperature agrees with the decease in point of zero net proton charge (pHznpc) pH values (as determined by potentiometric titration) observed for similar rutile powders in our previous studies. ζ-potential data were combined with the proton charge results and rationalized using a surface complexation modeling approach. Modeling results indicate that ζ-potentials are expressed at a distance that is generally equal to (within error) the so-called diffuse double layer thickness (κ -1 ).

Adsorption of l-aspartate to rutile (α-TiO2): Experimental and theoretical surface complexation studies

“…For this particular rutile sample, a pH PPZC around pH 5.4 is well established in the literature (Machesky et al, 1998;Ridley et al, 2002;Fedkin et al, 2003) and was also confirmed during our previous potentiometric titration study (Jonsson et al, 2009). In the latter study, we established the point of zero salt effect (pH PZSE ) of rutile in NaCl solutions as 5.37 (±0.1), which was used to estimate the pristine point of zero charge, pH PPZC = 5.4 (±0.1) with the relation…”

“…In a parallel study, we will be reporting ATR-FTIR spectroscopic measurements of both aspartate and glutamate on rutile together with theoretical molecular calculations on these systems. We focused on rutile in the present study because it is a model colloidal substance: identically prepared rutile samples have been the subject of numerous intensive studies of proton and cation adsorption (Machesky et al, 1998;Ridley et al, 1999Ridley et al, , 2004Ridley et al, , 2005Fedkin et al, 2003;Zhang et al, 2004). Rutile was also probably present on the prebiotic Earth , which makes it relevant to origin of life studies.…”

Estimation of zeta potentials of titania nanoparticles by molecular simulation

“…4). These results are in the range of experimental measurements at titania-water interfaces [46]. In particular, recent experimental measurements of zeta potentials of (non-spherical) titania nanoparticles with characteristic diameters of 30-40 nm in ultra-pure water at room temperature were 34 mV in magnitude [47], and the current estimated values are also in that range.…”

Surface complexation of organic arsenic on nanocrystalline titanium oxide

“…This simplified approach fails to describe the TiO 2 ζ values obtained in this study although the trend of the ionic strength effect could be predicted. The second way to calculate the ζ potential is based on the empirical distance between the slip ζ plane and the head end of the diffuse layer by the following equation [43]:…”