Effects of TiO2 nanostructure and operating parameters on optimized water disinfection processes: A comparative study

• Hierarchical porous structure of 3DD-TiO2 did greatly improve photocatalytic activity.
• Without and with UV illumination, the removal efficiency of E. coli by 3DD-TiO2 are 8.7% and 33.9%.
• Optimum 3DD-TiO2 concentration is around 100 mg/L.
• Humic acid and anions (SO42−) exhibit an inhibitory effect on water disinfection process.
• Cations (Ca2+) enhance the disinfection rate.

This paper reports the performance of bacterial disinfection using 3D dendritic titanium dioxide with nanoribbon structures (3DD-TiO2), which is newly developed by the researchers. Characterization of 3DD-TiO2 using SEM and TEM shows that the diameter of nanoribbons is nearly 18 nm only, resulting in an aspect ratio of more than 50. The hierarchical porous structure of the 3DD-TiO2 would greatly favor the improvement of photocatalytic activity via enlarging the specific surface area. In comparison with the same-sized microspheres and commercial Degussa P25, which are both spherically structured, 3DD-TiO2 displays a consistently better performance under the tested environment. Without UV illumination, the removal efficiency of Escherichia coli by 3DD-TiO2 is 6.4% and 8.7% higher than that of microspheres and P25, respectively. Under UV radiation, the disinfection kinetic constant k of the disinfection reaction using 3DD-TiO2 is 23.2% and 33.9% higher than that of using microspheres and P25, respectively. A series of optimization studies have been carried out to identify the optimum operating parameters of a photocatalytic process using 3DD-TiO2. The results tend to suggest: (a) optimum catalyst concentration is around 100 mg/L; (b) the optimum temperature for bacteria inactivation ranges between 10 °C and 20 °C; (c) presence of humic acid and anions (SO42−) exhibits an inhibitory effect on water disinfection process; and (d) cations (Ca2+) enhance the disinfection rate. These optimum operating parameters could be directly referenced for full-scale applications in future.