Pristine point of zero charge (p.p.z.c.) and zeta potentials of boehmite’s nanolayer and nanofiber surfaces

The pristine point of zero charge(p.p.z.c)and zeta potential as a function of pH of boehmite oxide/hydroxide(α-Al_(2)O_(3)·H_(2)O)have been determined for three filter media.The active component in the first two filter media is boehmite nanofibers,only 2 nm in diameter and about 300 nm long.Boehmite nanofibers create high zeta potential(ζtrue≥46 mV)in aqueous solutions in the pH range of 3–8.The p.p.z.c.values were determined to be 11.60±0.15 for nanofibers grafted onto microglass fibers and 11.40±0.15 for agglomerated nanofibers.In the third filter media,a boehmite nanolayer in the form of monocrystalline oxide/hydroxide with a thickness of approximately 1.2 nm is electroadhesively deposited onto siliceous support material with large surface area of about 50 m^(2)/g,therefore forming a highly electropositive composite of boehmite nanolayer on the second highly electronegative solid.Boehmite’s oxide-hydroxide nanolayer surface creates high zeta potential(ζtrue≥50 mV)in aqueous solutions in the pH range of 3–8.The p.p.z.c.value was determined to be 11.38±0.15.The reported values are within accuracy,but they are much higher than the values reported in the literature.X-ray powder diffraction data were supplemented by microscopy,infrared spectroscopy in order to characterize fully synthetic boehmite surfaces.

The Isoelectric Point and the Points of Zero Charge of Fe-Al-Mg Hydrotalcite-like Compounds

The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc, which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations.

Reflections on the Mechanism of Calcium Phosphate Nucleation on Titanium in Simulated Body Fluids

The results and main findings of studies reported in the literature in relation to the deposition of calcium phosphate on Ti in simulated body fluids are summarized. The effects of the surface hydroxyl groups and the sign of surface charge on the nucleation of calcium phosphate are reviewed. One major controversy among the conclusions of different studies is the order of adsorption of the calcium ions and the phosphate ions in the initial stage of immersion. A simple model based on the amphoteric nature of the hydroxyl groups on Ti is proposed in an attempt to delineate the nucleation process for calcium phosphate on Ti in simulated body fluids. HPO4^2- ions interact with the hydroxyl groups via ion exchange and/or electrostatic attraction, and Ca^2＋ ions, via electrostatic attraction only. There is no preferential order of adsorption. Seemingly inconsistent results in different studies possibly arise from different prior treatments of the samples, which affect the adsorption properties.

Intrinsic Surface Reaction Constant in 1-pK Model of Mg-Fe Hydrotalcite-like Compounds

The relationship among intrinsic surface reaction constant (K) in 1-pK model, point of zero net charge (PZNC) and structural charge density (st) for amphoteric solid with structural charges was established in order to investigate the effect of st on pK. The theoretical analysis based on 1-pK model indicates that the independent PZNC of electrolyte concentration (c) exists for amphoteric solid with structural charges. A common intersection point (CIP) should appear on the acid-base titration curves at different c, and the pH at the CIP is pHPZNC. The pK can be expressed as pK=-pHPZNC+log[(1+2aPZNC)/(1-2aPZNC)], where aPZNC≡st/eNANs, in which e is the elementary charge, NA the Avogadro抯 constant and Ns the total density of surface sites. For solids without structural charges, pK=-pHPZNC. The pK values of hydrotalcite-like compounds (HTlc) with general formula of [Mg1-xFex(OH)2](Cl, OH)x were evaluated. With increasing x, the pK increases, which can be explained based on the affinity of metal cations for H+ or OH- and the electrostatic interaction between charging surface and H+ or OH-.