RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

The simultaneous adsorption of Cu²⁺ and organic ligands L (L: 2,2′-bipyridyl (BIPY), 8-aminoquinoline (AQ), and o -phenylenediamine (OPDA)) in 0.1 M (K)NO₃ or 0.1 M (Na)ClO₄ solutions at TiO₂ was investigated at 298.2 K. The experiments were performed by alkalimetric titrations. The experimental results for TiO₂ are explained by assuming the formation of ternary surface complexes according to the general equation >SH₂ + pH⁺ + qCu²⁺ + rL = >SH_2+pCu_qL_r^(p+2q)+, where >SH₂ denotes an uncharged surface site. The stability of these complexes as defined by the stability constants β_p,q,(int)^S = ([>SH_2+pCu_qL_r^(p+2q)+]/ ([>SH₂][H⁺]^p[Cu²⁺]^q[L]^r))e^(p+2q)Fψ/RT was found to be:
(a) for L = BIPY,
log β_0,1,1,(int)^S = 11.37,   log β_{−1,1,1,(int)}^S = 6.00,   log β_{−2,1,1,(int)}^S = −1.57,
(b) for L = AQ,
log β_0,1,1,(int)^S = 9.80,   log β_{−1,1,1,(int)}^S = 4.11,   log β_{−2,1,1,(int)}^S = −2.78,
and (c) for L = OPDA,
log β_0,1,1,(int)^S = 8.52,   log β_{−1,1,1,(int)}^S = 1.86,   log β_{−2,1,1,(int)}^S = −4.75.
The possible structures of the postulated complexes are discussed.