TiO2 nanoparticles have been widely explored as photocatalysts in the degradation of organic matters present in water. However, spontaneous agglomeration of TiO2 nanoparticles in a suspension is a crucial issue that must be addressed before the photocatalyst can be used for water treatment. In the present work, the nature of the agglomeration of TiO2 nanoparticles in aqueous suspension was investigated. Two approaches to minimize the agglomeration of colloidal TiO2 particles were investigated. A careful control over the pH of the system was found to be an effective method for stabilizing colloidal TiO2 particles and to significantly enhance the adsorption of orange II. As a result, the overall photocatalytic degradation rate was greatly accelerated. In addition to pH control, modification of TiO2 particles using polyelectrolyte poly allylamine hydrochloride (PAH) was observed to be an effective approach for preventing colloidal TiO2 particles from agglomeration. (C) 2010 Elsevier Inc. All rights reserved.