RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Studies of the adsorption and desorption of H⁺ ions and the adsorption of Cu²⁺ ions on TiO₂ (anatase) were made by alkalimetric titration in 0.1 M (K)NO₃ solutions at 298.2 K using ion-selective electrodes and atomic absorption spectrometry. The adsorption is explained in terms of surface-complex formation. The active surface groups were defined as multifunctional sites consisting of bridged and terminal hydroxyl groups. With help of the computer program "GRFIT," a model for the sorption behavior was designed. The surface potentials were accounted for by the constant capacity approximation. The experimental results are explained by the general equilibria

>S + pH⁺ + qCu²⁺ = >SH_pCu_q^(p+2q)+;
β_p,q,(int)^S = ([>SH_pCu_q^(p+2q)+]/([>S][H⁺]^p[Cu²⁺]^q))e^(p+2q)Fψ/RT,

where >S denotes the neutral surface sites, and the stability constants

logβ_1,0,(int)^S = 5.40,   logβ_1,0,(int)^S = −7.75,
logβ_−2,0,(int)^S = −17.21,   logβ_0,1,(int)^S = 4.76,
logβ_−1,1,(int)^S = −1.13,   logβ_−2,1,(int)^S = −6.74.