Use of Gemini surfactants to stabilize TiO2 P25 colloidal dispersions

Photocatalytically active TiO2 P25 nanoparticles, widely used for practical applications, were investigated. The nominal size of TiO2 P25 nanoparticles is 21 nm, but they easily agglomerate in aqueous media, depending on pH and ionic strength. TiO2 P25 aqueous dispersions were stabilized by alkanediyl-alpha,omega-bis-N-dodecyl-N, N'-dimethyl-ammonium bromide, cationic Gemini surfactant. The optimal conditions required to obtain stable dispersions, without formation of large agglomerates, were experienced. The stabilization of TiO2 P25 nanoparticles by cationic Gemini surfactant was investigated in some details. Different amounts of Gemini surfactant were used, at concentrations between 1.0 and 250 x 10(-6) mol L-1, well below the critical micelle concentration. Dynamic light scattering and zeta potential analyses estimated the particle size and the dispersions stability. When the proper amount of Gemini surfactant was used, the resulting nanoparticles were still poly-disperse, but large agglomerates disappeared and were remarkably redispersible.