“…For TiO 2 -NF-H, however, its BET surface area is approximately identical to those of P25, TiO 2 -NF and TiO 2 -NF-400, suggesting that other structural factors of TiO 2 -NF-H account for the enhanced photocatalytic activity for phenol degradation. It is noteworthy that surface hydroxyl groups of TiO 2 are believed to be favorable for the generation of the highly active hydroxyl radical beneficial for oxidative degradation of organic compounds [38,39]. In contrast to other TiO 2 nanoparticles obtained using thermal post-treatment, TiO 2 nanoparticle prepared by the hydrothermal route is generally abundant in surface hydroxyl groups [20,40], which facilitates the generation of hydroxyl radical upon UV irradiation and eventually enhances phenol degradation.…”