TiO2/C coated Co3O4 nanocages for peroxymonosulfate activation towards efficient degradation of organic pollutants.

Developing new catalysts for efficient degradation of micropollutants in water is of significant importance in advanced oxidation processes (AOPs). Herein, TiO2/C coated Co3O4 nanocages (Co3O4@TiO2/C) were synthesized and their performance on micropollutants degradation was evaluated. Specifically, cobalt-based Zeolitic imidazolate framework (ZIF-67) coated by a thin layer of titanium species and polydopamine (PDA) was used as a precursor for the preparation of Co3O4@TiO2/C by two-step calcination. The catalytic performance of peroxymonosulfate (PMS) activation towards the degradation of organic pollutants was investigated by using atrazine (ATZ) and Bisphenol A (BPA) as typical micropollutants. The efficiency and the effect of TiO2/C shell on the as-synthesized catalyst were analyzed by comparing Co3O4 derived from ZIF-67 and Co3O4/C derived from ZIF-67/PDA. ATZ degradation results showed that the Co3O4@TiO2/C catalyst was the most efficient for catalytic oxidation when 99.5% of ATZ was removed within 4 min, which is 57.5% and 74.6% faster than that of Co3O4@C and Co3O4, respectively. The enhanced performance of Co3O4@TiO2/C is attributed to their unique nanocages structure and improved specific surface area. The catalysis mechanisms and ATZ degradation pathways were presented based on the results of electron paramagnetic resonance (EPR), XPS, and LC-MS analysis. Our results might have added to the design of heterogeneous catalysts of large surface area for efficient PMS activation in AOPs.

Mechanism of peroxymonosulfate activation and the utilization efficiency using hollow (Co, Mn)3O4 nanoreactor as an efficient catalyst for degradation of organic pollutants.

Development of efficient catalysts for peroxymonosulfate (PMS) activation and further understanding its mechanism on organic pollutants degradation is of significant importance for advanced oxidation processes (AOPs). Herein, hollow (Co, Mn)3O4 catalysts were synthesized by calcination of Co, Mn containing metal-organic frameworks (MOFs) and further used to evaluate the effectiveness of organic pollutants (Bisphenol A (BPA), atrazine (ATZ), and diethyl phthalate (DEP)) degradation by PMS activation. The PMS utilization efficiency in (Co, Mn)3O4/PMS system (36.4%) was estimated to be 28.0% and 43.8% higher than that of Co3O4/PMS and Mn5O8/PMS system, respectively. Notably, the metal leaching in (Co, Mn)3O4/PMS system was significantly suppressed. The utilization efficiency also reveals an inverse proportionality relationship with BPA mineralization but decreases with increasing initial pH value. A synergy between oxides of Co and Mn was perceived to enhance PMS utilization efficiency and BPA degradation. The results indicate enhanced catalytic performance with (Co, Mn)3O4 compared to Co3O4 derived from Co-MOF and other reported catalysts, with 99% of BPA degradation within 4 min. The oxidation mechanism was then proposed based on the electron paramagnetic resonance (EPR) and XPS results. Our findings might have contributed to designing heterogeneous catalysts for efficient PMS utilization in AOPs.

Singlet oxygen-dominated non-radical oxidation process for efficient degradation of bisphenol A under high salinity condition.

The degradation of organic contaminants under high salinity condition is still a challenge for environmental remediation due to the inhibiting effect resulted from the side reactions between radicals and anions. Here, we demonstrate the non-radical oxidation process via peroxymonosulfate (PMS) activation by metal-free carbon catalyst for efficiently decomposing bisphenol A (BPA) in saline water. The nitrogen-doped graphitic carbon (NGC700) exhibits excellent catalytic activity for depredating BPA at acid and neutral pH. Based on the scavenger experiments and electron paramagnetic resonance (EPR) analyses, the mechanism of catalytic oxidation was elucidated as the non-radical pathway, and singlet oxygen was identified as the primary reactive species. Experiments on the influence of anions (5-500 mM) further show that the inhibiting effect was overcame due to the non-radical process. Interestingly, Cl- markedly facilitated the catalytic performance by generating HOCl in the catalytic process. The results highlight leveraging the non-radical pathway dominated by singlet oxygen to conquer the inhibitory effect of anions in NGC700/PMS system, which represents a crucial step towards environmental remediation under high salinity condition.