Effects of solution pH and UV irradiation on the streaming potential of the titanium dioxide membranes

This study focused on the effect of electrolyte solution pH, fluid pressure and UV irradiation on the tangential streaming potential (TSP) and filtration streaming potential (FSP) of Degussa P-25 titanium dioxide membrane. Both TSP and FSP measuring systems for TiO2 membrane were developed. Experimental results depicted TSP and FSP measurements were sensitive to solution pH, temperature, fluid pressure and UV irradiation. Zeta potentials of TiO2 membranes calculated with TSP data were different from those of TiO2 suspensions measured by electrophoretic light-scattering technique, but the isoelectric point (pHiep) was measured to be almost the same value of 6.8. The pH drifts (difference of initial and final pH) were observed during the TSP measurements of TiO2 membranes. A modified model was developed to calculate the change in Fermi energy of the electrolyte/TiO2 membranes system presented at different solution pH levels. A hysteresis phenomenon was found that two zeta potentials were observed at the same pH through different pH adjustment paths. Slight decreases of TSP (<15 mV) were observed in acidic solutions under UV irradiation; however, more considerable decreases of FSP (20–60 mV) were examined in both acidic and alkaline solutions. The FSP increased with increasing filtration pressures and exhibited an exponential decay with increasing light intensity.