Surface Complexation on TiO 2: II. Ternary Surface Complexes: Coadsorption of Cu(II) and Organic Ligands (2,2′-Bipyridyl, 8-Aminoquinoline, and o-Phenylenediamine) onto TiO 2 (Anatase)

Abstract

The simultaneous adsorption of Cu 2+ and organic ligands L ( L: 2,2′-bipyridyl (BIPY), 8-aminoquinoline (AQ), and o -phenylenediamine (OPDA)) in 0.1 M (K)NO 3 or 0.1 M (Na)ClO 4 solutions at TiO 2 was investigated at 298.2 K. The experiments were performed by alkalimetric titrations. The experimental results for TiO 2 are explained by assuming the formation of ternary surface complexes according to the general equation 〉SH 2 + pH + + q Cu 2+ + rL = 〉SH 2+pCu qL (p+2q)+ r , where 〉 SH 2 denotes an uncharged surface site. The stability of these complexes as defined by the stability constants β S p,q,r(int) = [〉SH 2+pCu qL (p+2q)+ r] [〉SH 2][H +] p[Cu 2+] q[L] r e (p+2q)F↓/RT was found to be: (a) for L = BIPY, log β S 0,1,1,(int) = 11.37, log βS -1,1,1,(int) = 6.00, log β S -2,1,1,(int) = -1.57, (b) for L = AQ, log β S 0,1,1,(int) = 9.80, log β S -1,1,1,(int) = 4.11, log β S -2,1,1,(int) = -2.78, and (c) for L = OPDA, log β S 0,1,1,(int) = 8.52, log β S -1,1,1,(int) = 1.86, log β S -2,1,1,(int) = -4.75. The possible structures of the postulated complexes are discussed.