Synthesis of CeOx@SiO2 with tandem effect of mass transfer and activation for enhancing sulfanilamide degradation with ozone

Abstract

In this work, a hollow mesoporous CeOx@SiO2 was synthesized and used to promote sulfanilamide (SA) mineralization in ozonation. SA mineralization was promoted to 68.2% by O3/CeOx@SiO2 in 120 min, but only 30.0% in O3 process. O3/CeOx@SiO2 behaved the better at acidic and alkaline condition than that at neutral condition. CeOx@SiO2 had the great ability in enhancing O3 utility rate. Silanol (SiOH) in pore channel of SiO2 shell was non-reactive with O3 but could provide transmission way for O3 to reach the inner CeOx core. Lewis sites, oxygen vacancies and surface hydroxyl groups induced by CeOx favored for the activation of O3. The excess electron at oxygen vacancies would be transferred to the absorbed O3 molecular, which then generated reactive oxygen species (ROS) to mineralize SA. Hydroxyl radicals (OH) and superoxide radicals (O2−) were the main ROS, which were recorded by EPR. The interfacial electron transfer process was revealed by LSV and ESI characterizations. SA degradation intermediates were also identified by HPLC-MS and IC, a possible degradation pathway was proposed. Moreover, CeOx@SiO2 showed a good reusability, no obvious decline of TOC removal was found in four times’ uses. Water matrix would complete ROS with SA, which inhibited the SA removal of both O3 and O3/CeOx@SiO2 processes, but the better TOC removal efficiency was still obtained by O3/CeOx@SiO2 in actual water.