An experimental study of the stability of TiO2 particles in organic-water mixtures

The stability of TiO2 (Anatase) particles in various organic-water mixtures is examined experimentally. The results obtained reveal that the addition of AlCl3 to a methanol-water dispersion leads to charge reversal on particl e surface. If the concentration of methanol is high, CaCl2 also leads to ch arge reversal, but NaCl does not have this effect. This implies that if the concentration of methanol is low, the coagulation between TiO2 particles i s due to double-layer compression for Na (+) and Ca2 +, and due to charge a dsorption and neutralization for Al3 +. A methanol dispersion is unstable w ithout the addition of electrolyte, and the addition of both CaCl2 and AlCl 3 has the effect of stabilizing the dispersion; the addition of NaCl does n ot have this effect. The qualitative behaviors of an acetone-water dispersi on are similar to those of a methanol-water dispersion. It is interesting t o observe, however, that the absolute mobility of a pure acetone dispersion has a maximum as the concentrations of both CaCl2 and AlCl3 vary, but char ge reversal does not occur. Among the dispersions without the addition of e lectrolyte, a 50% organic-water mixture is most stable. Also, a methanol-wa ter dispersion is more stable than an acetone-water dispersion, which can b e explained based on the degree of dissociation of an electrolyte. (C) 2000 Elsevier Science B.V. All rights reserved.