An experimental study of the stability of TiO 2 particles in organic–water mixtures

Abstract

The stability of TiO 2 (Anatase) particles in various organic-water mixtures is examined experimentally. The results obtained reveal that the addition of AlCl 3 to a methanol–water dispersion leads to charge reversal on particle surface. If the concentration of methanol is high, CaCl 2 also leads to charge reversal, but NaCl does not have this effect. This implies that if the concentration of methanol is low, the coagulation between TiO 2 particles is due to double-layer compression for Na + and Ca 2+, and due to charge adsorption and neutralization for Al 3+. A methanol dispersion is unstable without the addition of electrolyte, and the addition of both CaCl 2 and AlCl 3 has the effect of stabilizing the dispersion; the addition of NaCl does not have this effect. The qualitative behaviors of an acetone–water dispersion are similar to those of a methanol–water dispersion. It is interesting to observe, however, that the absolute mobility of a pure acetone dispersion has a maximum as the concentrations of both CaCl 2 and AlCl 3 vary, but charge reversal does not occur. Among the dispersions without the addition of electrolyte, a 50% organic–water mixture is most stable. Also, a methanol–water dispersion is more stable than an acetone–water dispersion, which can be explained based on the degree of dissociation of an electrolyte.