Popis: |
Adsorption kinetics and isotherms and the surface complexation of 3,4-dihydroxybenzoic acid (3,4-DHBA) and catechol at the α-alumina/electrolyte interface were investigated. The state of equilibrium for adsorption of 3,4-DHBA onto α-alumina surface at pH 5 was attained at 120 min, whereas it was 90 min for catechol, but at pH 10 the state of equilibrium for the both the systems was same (∼60 min). The pseudo-second-order kinetic equation of nonlinear form (Eq. (3) ) fits the experimental kinetic data significantly better than the linear form (Eq. (2) ) in the entire time duration. The adsorption density of 3,4-DHBA onto the α-alumina surfaces at pH 10 and at similar experimental conditions is equivalent to catechol. DRIFT spectra indicate that 3,4-DHBA forms both outer- and inner-sphere complexes and catechol forms bidentate mononuclear complex with the α-alumina surface. |