Oxygen vacancies and Lewis sites activating O3/H2O2 at wide pH range via surface electron transfer over CeOx@SiO2 for nitrobenzene mineralization

Abstract

The low efficiency of peroxone (O3/H2O2) at acidic and neutral pH restrained its application in water purification. To overcome this shortcoming, CeOX@SiO2 with large surface area, abundant surface oxygen vacancies (Vo), Lewis sites (L sites) and high Ce(III)/Ce(IV) ratio were synthesized to change the traditional electron transfer pathway between O3 and H2O2. Vo was facile in absorbing H2O2 to form Vo-H2O2 and L sites were capable of absorbing O3 to form L-O3. The electron at Vo could be donated to Vo-H2O2 and generate Vo-HO2−, which then effectively triggered the decomposition of L-O3 at CeOX@SiO2’s interface and O3 in bulk solution. The electron transfer at the solid-liquid interface with the help of Ce3+/Ce4+ redox cycle and Vo was pH independent and different from the traditional electron transfer of peroxone reaction. Nitrobenzene (NB) mineralization was promoted to 92.5% in CeOX@SiO2-peroxone, but only 63.8% TOC was removed in tradition peroxone process. Moreover, CeOX@SiO2-peroxone had a wide pH application range. NB’s degradation in CeOX@SiO2-peroxone process followed the co-oxidation mechanism of superoxide free (•O2−) and hydroxyl radical (•OH). The finding of this study could broaden the popularization of peroxone in water treatment and provided a strategy for catalyst design.