Stable TiO2 dispersions for nanocoating preparation

In this research the preparation and characterization of titanium (TiO2) coated self-cleaning cellulose materials starting from TiO2 P25 powder (Degussa. Germany) was studied. The aim of the research was to decrease high aggregation of TiO2 P25 nanoparticles, using surfactant species as dispersant and/or stabilisers (considering the balance between repulsive and attractive forces), in view of the fact that TiO2 nanoparticles, when optimally separated into smaller particle populations, present the best properties in the system they are used in (coatings). For this purpose cationic alkanediyl-alpha,omega-bis-N-dodecyl-N, N'-dimethyl-ammonium bromide (Gemini) and anionic sodium dodecyl sulphate (SDS) surfactants were applied, with concentrations under their CMSs. Size and zeta-potential (zeta-potential) characterization of stable colloidal dispersions were performed. For stable 0.5, 2.5 and 5.0 mg/mL TiO2 dispersions in the presence of 250 x 10(-6) mol/L Gemini surfactant (zeta-potential similar to 40 mV) only two scattering populations were determined, at 78-95 nm and at similar to 280 nm. As a proof of stabilized TiO2 P25-surfactant colloidal dispersions uniform coatings were obtained, generated at the fibre surfaces, which were analyzed by scanning electron microscopy (SEM). With the usage of proper amounts of surfactants, homogeneous thin TiO2 coatings were formed. Superior dense coatings on the fibre surfaces were formed after treatment in 5.0 mg/mL aqueous TiO2 P25 dispersions, in the presence of 250 x 10(-6) mol/L Gemini surfactant in 5.0 x 10(-3) Mol/LKBr at 25 degrees C. In addition to that, self-cleaning test was performed. Higher photocatalytic activity was determined for samples with denser coatings. Fibres with thin coatings had a lack of photocatalytic activity. (C) 2009 Elsevier B.V. All rights reserved.