Effect of washing pH on the properties of titanate nanotubes and its activity for photocatalytic oxidation of NO and NO2

This study reports for the first time on the role of contaminant sodium to neutralize the acidic reaction products during the NOx photocatalytic reaction and prevent surface deactivation of TNTs (titanate nanotubes and their derived materials). TNTs were synthesized by the hydrothermal method and washed under different pH values. The materials were then characterized by SEM, TEM, BET, ICP, TPD, and XRD analyses. The photocatalytic oxidations of NO and NO2 were tested under the ambient condition to evaluate the activity of the materials. The results showed that the value of washing pH was an effective control factor for achieving TNTs with desired microstructure and physical-chemical properties. In the photocatalytic removals of NO and NO2, it revealed that both of the Na content and the structure of TNTs materials play important roles on the NOx removal pathway, initial efficiency and decay rate. The highest efficiencies were achieved by TNTs washed at pH 3-5 (T-3-5), which may be due to their high amount of crystalline anatase for photocatalytic reaction and high sodium content for neutralization of acidic products. The mechanism based on the neutralization of the HNO3 resultant from the NOx photo-oxidation was also proposed. (C) 2015 Elsevier B.V. All rights reserved.