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Protonation and charging of nanosized gibbsite (alpha-Al(OH)(3)) particles in aqueous suspension

Rosenqvist, J.; Persson, Per LU and Sjoberg, S. (2002) In Langmuir 18. p.4598-4604
Abstract
Synthetic gibbsite was prepared and thoroughly characterized using X-ray diffraction, high-resolution transmission electron microscopy, atomic force microscopy, and Fourier transform infrared techniques. The protonation and charging of the particle surface(s) in 20 and 100 mM (Na)Cl ionic media were investigated using potentiometric titrations and zeta potential measurements. These measurements indicated a pH(pznpe) = 9.0 +/- 0.2 and pH(IEP) = 10.0 +/- 0.1. Furthermore, it was concluded that the concentration of singly coordinated sites (equivalent toAlOH) located at the edges of the particles is too low (less than 7% of the total number of crystallographic sites) to explain the proton uptake. Therefore, the doubly coordinated sites... (More)
Synthetic gibbsite was prepared and thoroughly characterized using X-ray diffraction, high-resolution transmission electron microscopy, atomic force microscopy, and Fourier transform infrared techniques. The protonation and charging of the particle surface(s) in 20 and 100 mM (Na)Cl ionic media were investigated using potentiometric titrations and zeta potential measurements. These measurements indicated a pH(pznpe) = 9.0 +/- 0.2 and pH(IEP) = 10.0 +/- 0.1. Furthermore, it was concluded that the concentration of singly coordinated sites (equivalent toAlOH) located at the edges of the particles is too low (less than 7% of the total number of crystallographic sites) to explain the proton uptake. Therefore, the doubly coordinated sites (equivalent toAl(2)OH) on the basal planes must be proton reactive. Both proton data and zeta potentials could be described using a three-plane model where adsorbed Na+ at the basal planes was placed in the I-plane and all other adsorbed medium ions were placed in the 2-plane. The following results were obtained: Basal planes equivalent toAl(2)OH + H+ + Cl- reversible arrowequivalent toAl(2)OH(2) Cl-+(-) Igk = 8.49 +/- 0.01 (1) equivalent toAl(2)OH + Na+ reversible arrowequivalent toAl(2)O(-)Na(+) + H+ IgK = -9.62 +/- 0.01 (2) Edges: equivalent toAIOH(0.5-) + H+ reversible arrowequivalent to AlOH20.5+ IgK = 10.0 (3) equivalent toAlOH(0.5-) + Na+ reversible arrowequivalent to -AlOH0.5-Na+ IgK = 0.1 (4) equivalent toAlOH(2)(0.5+) + Cl- reversible arrowequivalent to AlOH20.5+Cl- Igk = 0.1 (5) The protonation constant for the singly coordinated sites (reaction 3) was set equal to pH(IEP). The values of reactions 4 and 5 were taken from the literature. The effect of different reaction times on proton uptake and zeta potential is highlighted. It is clear that increased "equilibrium times" will result in an increased proton uptake, whereas the zeta potential remains constant. This is also reflected in the divergent models presented in the literature with respect to the protonation and charging properties of gibbsite particles. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
18
pages
4598 - 4604
publisher
The American Chemical Society
external identifiers
  • scopus:0037062803
ISSN
0743-7463
DOI
10.1021/la015753t
language
English
LU publication?
no
id
eef769a1-071c-43cc-aa11-61b32b871f37 (old id 4332566)
date added to LUP
2014-03-04 09:41:36
date last changed
2017-11-19 03:25:18
@article{eef769a1-071c-43cc-aa11-61b32b871f37,
  abstract     = {Synthetic gibbsite was prepared and thoroughly characterized using X-ray diffraction, high-resolution transmission electron microscopy, atomic force microscopy, and Fourier transform infrared techniques. The protonation and charging of the particle surface(s) in 20 and 100 mM (Na)Cl ionic media were investigated using potentiometric titrations and zeta potential measurements. These measurements indicated a pH(pznpe) = 9.0 +/- 0.2 and pH(IEP) = 10.0 +/- 0.1. Furthermore, it was concluded that the concentration of singly coordinated sites (equivalent toAlOH) located at the edges of the particles is too low (less than 7% of the total number of crystallographic sites) to explain the proton uptake. Therefore, the doubly coordinated sites (equivalent toAl(2)OH) on the basal planes must be proton reactive. Both proton data and zeta potentials could be described using a three-plane model where adsorbed Na+ at the basal planes was placed in the I-plane and all other adsorbed medium ions were placed in the 2-plane. The following results were obtained: Basal planes equivalent toAl(2)OH + H+ + Cl- reversible arrowequivalent toAl(2)OH(2) Cl-+(-) Igk = 8.49 +/- 0.01 (1) equivalent toAl(2)OH + Na+ reversible arrowequivalent toAl(2)O(-)Na(+) + H+ IgK = -9.62 +/- 0.01 (2) Edges: equivalent toAIOH(0.5-) + H+ reversible arrowequivalent to AlOH20.5+ IgK = 10.0 (3) equivalent toAlOH(0.5-) + Na+ reversible arrowequivalent to -AlOH0.5-Na+ IgK = 0.1 (4) equivalent toAlOH(2)(0.5+) + Cl- reversible arrowequivalent to AlOH20.5+Cl- Igk = 0.1 (5) The protonation constant for the singly coordinated sites (reaction 3) was set equal to pH(IEP). The values of reactions 4 and 5 were taken from the literature. The effect of different reaction times on proton uptake and zeta potential is highlighted. It is clear that increased "equilibrium times" will result in an increased proton uptake, whereas the zeta potential remains constant. This is also reflected in the divergent models presented in the literature with respect to the protonation and charging properties of gibbsite particles.},
  author       = {Rosenqvist, J. and Persson, Per and Sjoberg, S.},
  issn         = {0743-7463},
  language     = {eng},
  pages        = {4598--4604},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Protonation and charging of nanosized gibbsite (alpha-Al(OH)(3)) particles in aqueous suspension},
  url          = {http://dx.doi.org/10.1021/la015753t},
  volume       = {18},
  year         = {2002},
}