ROTATING-DISC ELECTRODE VOLTAMMETRY AS A PROBE OF ADSORPTION RATES ONSOLID PARTICLES IN LIQUIDS - APPLICATION TO ZN-II ADSORPTION AT THE HYDROXYAPATITE AQUEOUS INTERFACE
Rd. Martin et al., ROTATING-DISC ELECTRODE VOLTAMMETRY AS A PROBE OF ADSORPTION RATES ONSOLID PARTICLES IN LIQUIDS - APPLICATION TO ZN-II ADSORPTION AT THE HYDROXYAPATITE AQUEOUS INTERFACE, Journal of the Chemical Society. Faraday transactions, 90(20), 1994, pp. 3109-3115
Citations number
56
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
A simple new approach for the measurement of the extent and kinetics o
f adsorption at the interface between a solid particle and a liquid is
proposed. The technique employs a rotating-disc electrode to suspend
the particles fully in the liquid under study, while the temporal depe
ndence of the transport-limited current for the electrolysis of the so
lution component of the adsorbate serves as a concentration probe. The
technique is used to study Zn-II adsorption on hydroxyapatite (HAP) f
rom aqueous solution (containing 0.1 mol dm(-3) KCl as a supporting el
ectrolyte). In the absence of dissolved Ca2+, adsorption is effectivel
y irreversible with Zn-II adsorbed on HAP at a coverage of 7.5 x 10(-1
0) mol cm(-2). Adsorption appears to involve at least two rate process
es: ca. 70% of adsorption sites (fraction theta(1)) are filled in an i
nitial rapid process which is complete on the timescale (ca. 5 s) of m
ixing the adsorbate solution with the suspension of hydroxyapatite par
ticles. The remaining sites (fraction theta(2)) are filled in an irrev
ersible, surface-controlled process governed by the following kinetic
rate law: d theta(2)/dt = {k'[Zn2+(aq)](1 - theta(1) - theta(2))}/N, w
here N is the surface density of (total) adsorption sites (7.5 x 10(-1
0) mol cm(-2)), [Zn2+(aq)] is the bulk solution concentration, t is ti
me and the adsorption rate constant, k', has a value of 2.6 (+0.6, -0.
3) x 10(-5) cm s(-1).