Jinxin Xie,Xukai Li,Weirui Chen,Xianglin Sun,Kexin Chen,Yiming Tang,Laisheng Li
The mesoporous core-shell CeO x @SiO 2 was synthesized and characterized by XRD, pyridine-FTIR, BET, SEM, TEM and XPS. CeO x @SiO 2 was the hollow nanosphere with high surface area of 1291.4 m 2 g −1 , which benefited for mass transfer of reactants. CeO x @SiO 2 exhibited the excellent catalytic activity for oxidizing oxalic acid (OA) in O 3 /H 2 O 2 /CeO x @SiO 2 . The greatest OA mineralization (91.2%) was achieved at pH = 3.2 in O 3 /H 2 O 2 /CeO x @SiO 2 , which was 5.5 times higher than that in peroxone (O 3 /H 2 O 2 , 15.9%). Influence of pH, HSO 3 − , PO 4 3− and detection of ozone and H 2 O 2 concentration were conducted to explore the mechanism. The interface reaction played vital role for OA removal in O 3 /H 2 O 2 /CeO x @SiO 2 process. Protonated surface hydroxyl groups (Ce-OH 2 + ) was the active sites, where OA, O 3 and H 2 O 2 were chemi-absorbed. The peroxide-like species (≡(Ce(IV)-O 2 H 2 )) formed by the complex of H 2 O 2 with active sites were the important intermediates, which initiated ozone decomposition into hydroxyl radical (·OH) and led to the high OA mineralization. Moreover, Lewis acid sites and electron transfer effect of Ce(III)/Ce(IV) also accounted for the high catalytic activity of CeO x @SiO 2 . In addition, CeO x @SiO 2 maintained stable structure and catalytic activity in three cycles.
Jinxin Xie,Weirui Chen,Yanfeng Lv,Haoyao Chen,Xukai Li,Laisheng Li
In this work, a hollow mesoporous CeO x @SiO 2 was synthesized and used to promote sulfanilamide (SA) mineralization in ozonation . SA mineralization was promoted to 68.2% by O 3 /CeO x @SiO 2 in 120 min, but only 30.0% in O 3 process. O 3 /CeO x @SiO 2 behaved the better at acidic and alkaline condition than that at neutral condition. CeO x @SiO 2 had the great ability in enhancing O 3 utility rate. Silanol (Si OH) in pore channel of SiO 2 shell was non-reactive with O 3 but could provide transmission way for O 3 to reach the inner CeO x core. Lewis sites, oxygen vacancies and surface hydroxyl groups induced by CeO x favored for the activation of O 3 . The excess electron at oxygen vacancies would be transferred to the absorbed O 3 molecular, which then generated reactive oxygen species (ROS) to mineralize SA. Hydroxyl radicals ( OH) and superoxide radicals ( O 2 − ) 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, CeO x @SiO 2 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 O 3 and O 3 /CeO x @SiO 2 processes, but the better TOC removal efficiency was still obtained by O 3 /CeO x @SiO 2 in actual water.
The low efficiency of peroxone (O 3 /H 2 O 2 ) at acidic and neutral pH restrained its application in water purification . To overcome this shortcoming, CeO X @SiO 2 with large surface area, abundant surface oxygen vacancies (V o ), Lewis sites (L sites) and high Ce(III)/Ce(IV) ratio were synthesized to change the traditional electron transfer pathway between O 3 and H 2 O 2 . V o was facile in absorbing H 2 O 2 to form V o -H 2 O 2 and L sites were capable of absorbing O 3 to form L-O 3 . The electron at V o could be donated to V o -H 2 O 2 and generate V o -HO 2 − , which then effectively triggered the decomposition of L-O 3 at CeO X @SiO 2 ’s interface and O 3 in bulk solution. The electron transfer at the solid-liquid interface with the help of Ce 3+ /Ce 4+ redox cycle and V o was pH independent and different from the traditional electron transfer of peroxone reaction. Nitrobenzene (NB) mineralization was promoted to 92.5% in CeO X @SiO 2 -peroxone, but only 63.8% TOC was removed in tradition peroxone process. Moreover, CeO X @SiO 2 -peroxone had a wide pH application range. NB’s degradation in CeO X @SiO 2 -peroxone process followed the co-oxidation mechanism of superoxide free (•O 2 − ) 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.
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