Nowadays, it is a great challenge to synthesize crystalline TiO2 nanostructures using low-temperature methods without annealing stage. Such an approach allows to perform functional and structural modification in the formed crystalline phase by thermally unstable compounds, such as biomaterials, MOFs, dye sets in situ, which was previously considered impossible. In this work, we have developed and analyzed the effect of acidic peptization on formation of highly photoactive titania crystallites in an aqueous solution using titanium tetraisopropylate as a precursor. Acids with different dissociation degrees in water were used as peptizing mediators to determine the effect of protonation on sol formation. The dip-coating films were obtained with consequent drying of the sols via evaporation of the solvent. The as-prepared catalysts were characterized by X-ray diffraction, AFM microscopy, UV–V is spectroscopy, Brunauer–Emmett–Teller surface area. The aggregate size of TiO2 in the colloidal suspension solution was measured by dynamic light scattering. Photocatalytic activity of films was studied by decomposition of Rhodamine B dye. It is found that the size of colloids in an aqueous solution is proportional to the protonation degree of the surface of particles and does not depend on the [Ti4+]/[H+] ratio, and peptization under weakly acidic conditions leads to anisotropic rod-like nanoparticles. The highest photocatalytic activity was exhibited by the TiO2–HCl-based coatings, ~3.5 times higher than that of the Acet.-prepared sample.