Catalytic Performance of Layered Double Hydroxides Co-Mn-Al for Ozonation of Organic Pollutants in Water

Dispersed cobalt embedded nitrogen-rich carbon framework activates peroxymonosulfate for carbamazepine degradation: cobalt leaching restriction and mechanism investigation

Metal leaching is a key issue in cobalt-based catalysts/PMS systems, which results in the decline of catalytic ability and serious secondary pollution. Hence, a nitrogen-rich carbon framework with cobalt node (Co-NC-920) with low cobalt leaching was synthesized based on zeolite imidazole framework (ZIF) and g-C₃N₄ to activate peroxymonosulfate (PMS) for the degradation of carbamazepine (CBZ). With the restriction of nitrogen-rich carbon framework, cobalt can disperse better and form stable cobalt-nitrogen bonds, thus only 0.09 mg/L cobalt ions were leached in the solution. More than 99.9% of CBZ can be removed within 30 min of PMS addition. Further investigation revealed that ¹O₂, SO₄^•- and high-valent cobalt species were primarily responsible for CBZ degradation in the Co-NC-920/PMS system and different reactive oxygen species (ROS) were distinguished and quantified, finding ¹O₂ was predominant. The degradation process was realized by the coexistence of free radicals and non-free radicals. Moreover, CBZ degradation capacity of the catalyst was evaluated under the influence of common anions and in actual waterbody. Finally, the possible degradation pathways of CBZ were proposed and the toxicity of the intermediates was analyzed. This work provides a new approach for the synthesis of cobalt-based nitrogen-rich carbon catalysts with low leaching and high efficient.

High performance ozone decomposition over MnAl-based mixed oxide catalysts derived from layered double hydroxides

Mesoporous and dispersed MnAl-based mixed metal oxide catalysts (Mn_xAlO) were fabricated via the calcination of layered double hydroxide (LDH) precursors prepared by the coprecipitation method. Their physiochemical properties were characterized and their catalytic activities for ozone decomposition were evaluated. The results indicate that the prepared Mn_xAlO catalysts have excellent catalytic activity owing to their large specific surface area, abundant surface oxygen vacancies and lower average Mn oxidation states. The Mn/Al atomic ratio and calcination temperature are found to significantly affect the textural properties and catalytic activity for ozone decomposition. The Mn₂AlO-400 catalyst (Mn/Al = 2, calcined at 400 °C) exhibited 84.8% ozone conversion after 8 h reaction under an initial ozone concentration of 45 ± 2 ppm, 30 ± 1 °C, a relative humidity of 50% ± 3%, and a space velocity of 550 000 h⁻¹. The results also show that the catalytic activity of Mn₂AlO-400, which was deactivated owing to the accumulation of oxygen-related intermediates, was recovered by calcination at 400 °C under a N₂ atmosphere for 1 h. A possible reason for catalyst deactivation and regeneration is proposed. This work provides a facile method for fabricating Mn_xAlO catalysts with excellent characteristics to achieve better catalytic activity, which are promising candidates for practical ozone decomposition.

Mesoporous and highly dispersed MnAl-based mixed metal oxide catalysts (Mn_xAlO) were fabricated via the calcination of layered double hydroxides (LDHs), which presented excellent catalytic activity for ozone decomposition.

Surface acidity and basicity of Mg/Al hydrotalcite for 2, 4-dichlorophenoxyacetic acid degradation with ozone: Mineralization, mechanism, and implications to practical water treatment

The Mg/Al hydrotalcite (Mg/Al HT) was firstly used as a heterogeneous ozonation catalyst and 2,4-dichlorophenoxyacetic acid (2,4-D) was efficiently degraded by Mg₃/Al HT with a COD removal of 68 %. It was higher than that of α-FeOOH with a COD removal of 50 %. The effects of Mg/Al atomic ratio, phosphate and pyrrole on the ozonation performance of Mg/Al HTs were also investigated. The X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption experiment and temperature programmed desorption of adsorbed CO₂ or NH₃ were used to characterize the surface properties of Mg/Al HT. The surface acidity and basity was proven to be responsible to the excellent ozonation activity of Mg/Al HT. The results of electron spin resonance (ESR) analysis and probe experiments confirmed that OH, O₂^- and ¹O₂ were involved in the 2,4-D degradation process and their contributions are as followed: OH > O₂- > ¹O₂. The synergistic effect of surface acid (ozone adsorption center) and base sites (catalytic center) determines Mg/Al HT in the enhanced catalytic ozone decomposition into reactive species. More important, the transition metal free based Mg/Al HTs is steady, non-toxic, naturally abundant and environment friendly, which provided a promising alternative in practical water treatment by catalytic ozonation.