A systematic analysis of the main parameters affecting the characteristics of titania sols for photocatalytic applications prepared from the hydrolysis of titanium i-propoxide (TIP) is presented. Stable monomodal sols were obtained at peptization temperatures between 50 degrees C and 70 degrees C, for water/alkoxide molar ratios ranging from 250 to 1000 and acid/alkoxide molar ratios ranging from 0.4 to 0.7. Unstable sols with bimodal distributions were obtained at higher peptization temperatures. The peptization temperature was the parameter with the greatest influence, followed by acid concentration, whereas the water/alkoxide ratio showed little influence. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to verify the primary particle size as measured by photon correlation spectroscopy (PCS). The observations are explained using the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory on suspension stability. (c) 2005 Springer Science + Business Media, Inc.