Synergistic oxygen vacancy and surface hydroxyl engineering on TiO ₂ hollow microspheres for boosted photocatalytic ozonation performance

The practical implementation of photocatalytic ozonation technology faces challenges due to inefficient charge carrier separation and suboptimal ozonolysis efficiency. Herein, TiO2 hollow microspheres (C-TiO2) were conducted via a sol-gel method combined with hydrothermal synthesis with cetyltrimethylammonium bromide (CTAB) employed as a surface agent. Following a series of physical phase characterizations, the C-TiO2 surface was identified to be abundant in oxygen vacancies and surface hydroxyl groups (-OH). The oxygen vacancies promote the separation of electron-hole pairs in the photocatalytic process; the surface hydroxyl groups (-OH) act as the active center of the ozone catalytic process, which is conducive to the adsorption and decomposition of ozone to produce more ·OH. Additionally, we found that oxygen vacancies have a promotional effect on the formation of surface hydroxyl groups. Oxygen vacancies enriched surface hydroxyl groups and promoted the adsorption of O3, which in turn acted as electron traps to capture photogenerated electrons and inhibited electron-hole pair complexation, and the two synergistically enhanced the photocatalytic ozone oxidation performance. The sample of 0.25 C-TiO2 with the optimal molar ratio was used for the degradation of phenol by photocatalytic ozone oxidation, and the degradation of 20 mg/L phenol by 0.25 C-TiO2 for 60 min of the reaction was 93.1%, which was increased by 28.2% and 36.3% compared with photocatalytic oxidation and ozone-catalytic oxidation alone, respectively. By calculating the synergy factor (1.6), it indicates that the coupling of photocatalytic oxidation and ozone-catalytic oxidation has a synergistic effect. This work provides a reference value for designing catalysts for photocatalytic ozone oxidation.