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 particle surface. If the concentration of methanol is high, CaCl2 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 TiO2 particles is due to double-layer compression for Na+ and Ca2+, and due to charge adsorption and neutralization for Al3+. A methanol dispersion is unstable without the addition of electrolyte, and the addition of both CaCl2 and AlCl3 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 CaCl2 and AlCl3 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.