BORAH , J M and DAS , M R and MAHIUDDIN , S
(2007)
Influence of anions on the adsorption kinetics of salicylate onto alpha aluminium in aqueous medium.
J Colloid Interface Science, 316 (2).
pp. 260-267.
Abstract
Kinetics of adsorption of p-hydroxy benzoate and phthalate on hematite–electrolyte interface were investigated at a constant ionic strength,
I
=5×10−4 moldm−3,pH5andatthreedifferenttemperatures.Thestateofequilibriumfortheadsorptionofp-hydroxybenzoateontohematite
surfaces was attained at 70 h, whereas it was 30 h for phthalate–hematite system. None of the three kinetics models (Bajpai, pseudo first order
and pseudo second order) is applicable in the entire experimental time period; however, the pseudo second order kinetics model is considered
to be better than the pseudo first order kinetics model in estimating the equilibrium concentration both the p-hydroxy benzoate–hematite and
phthalate–hematite systems. The variation of adsorption density of p-hydroxy benzoate and phthalate onto hematite surfaces as a function of
concentration of adsorbate was studied over pH range 5–9 at a constant ionic strength, I
= 5×10−4 moldm−3 and at constant temperature.
The adsorption isotherms for both the systems were Langmuir in nature and the maximum adsorption density (Γmax)ofp-hydroxy benzoate is
∼1.5timesmorethanthatofphthalateonhematiteatpH5and30◦Cinspiteofanadditionalcarboxylicgroupatorthopositioninphthalate.This
is due to the more surface area coverage by phthalate than that ofp-hydroxy benzoate on hematite surface. The activation energy was calculated
using Arrhenius equation and the activation energy for adsorption of p-hydroxy benzoate at hematite–electrolyte interface is∼1.8 times more
than that of phthalate–hematite system. The negative Gibbs free energy indicates that the adsorption of p-hydroxy benzoate and phthalate on
hematite surfaces is favourable. The FTIR spectra of p-hydroxy benzoate and phthalate after adsorption on hematite surfaces were recorded for
obtaining the bonding properties of adsorbates. The phenolic νC–O appears at∼1271 cm−1 after adsorption of p-hydroxy benzoate on hematite
surfaces, which shifted by 10 cm−1 to higher frequency region. The phenolic group is not deprotonated and is not participating in the surface
complexation. The shifting of theνas(–COO−)andνs(–COO−) bands and non-dissolution of hematite suggest that thep-hydroxy benzoate and
phthalate form outer-sphere surface complexwith hematite surfaces in the pH range of 5–7.
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