Herein, we reported postsynthetic incorporation of generally believed catalytically inert Al 3+ ion into the lattice of commercial Co 3 O 4 to form a series of Al doped Co 3 O 4 (ACO) catalysts, and demonstrated that the Al incorporation with suitable concentration could induce a surprising boost in activation of peroxymonosulfate (PMS). Unlike conventional direct synthesis that might lead to the formation of bimetallic spinel oxides in an uncontrollable manner, the presented method could produce ACO catalysts with almost unchanged particle size and morphology, which was beneficial for a reliable assess on the composition-dependent catalytic performance to avoid possible misjudgment caused by other factors. More importantly, the Al incorporation could not only promote the adsorption affinity and electron transfer ability of Co to PMS but also facilitate the O O bond cleavage of the adsorbed PMS, thereby leading to an enhanced catalytic ability. As a result, the optimal ACO (Co 2.98 Al 0.02 O 4 ) exhibited a high degradation efficiency with a rate constant (0.127 min −1 ) 2.6-folds that of pure Co 3 O 4 (0.049 min −1 ) in PMS activation for degradation of metronidazole (MNZ). Besides, Co 2.98 Al 0.02 O 4 manifested low cobalt leaching (≤79 μg L –1 ). Both degradation pathway and catalytic mechanism were proposed comprehensively, and the superb reusability of Co 2.98 Al 0.02 O 4 was also confirmed. This study enriches the current synthesis methodology for bimetallic spinel oxides and provides new insights into inert metal-promoted heterogeneous cobalt-based catalysis for robust advanced oxidation processes.
Cobalt–aluminum oxide clusters-embedded γ-Al 2 O 3 nanosheets (CAO@AO) were facilely fabricated and developed for peroxymonosulfate (PMS) activation. Interestingly, the Al–OH-rich amphiphilic surface of CAO@AO endowed the catalyst with unique interfacial pH-buffering property, which stabilized the reaction media at nearly neural level and thus prevented the cobalt sites from leaching. Moreover, the presence of Al–OH groups around the Co−Al oxide clusters facilitated the activation of PMS and the redox cycle of Co 2+ /Co 3+ , which resulted in a boosted catalytic activity. Consequently, the CAO@AO exhibited zero leaching of cobalt and high efficacy for PMS activation, enabling complete and ultrafast removal of metronidazole with a significantly higher turnover frequency (TOF, 1.83 min −1 ) than that of Co 3 O 4 (0.004 min −1 ). It was also demonstrated that introducing suitable foreign metal into CAO@AO could further enhance the catalytic activity (e.g., TOF of Mn(40%)-CAO@AO: 5.80 min −1 ). Furthermore, Mn(40%)-CAO@AO-decorated granular support was synthesized that dominated a continuous-flow degradation in column reaction system.
In this study, three Co/N-C catalysts were prepared by pyrolysis of bimetallic zeolitic imidazole frameworks with different Co/Zn ratio, and the critical active Co species in peroxymonosulfate (PMS) activation was investigated. The three catalysts had distinct cobalt species but similar N configuration and graphitization degree. The Co species were distributed as single atoms (Co SAs) at a Co/Zn molar ratio of 1:8, while Co nanoclusters (Co NCs) and Co nanoparticles (NPs) would be formed with further increase in Co content. The degradation efficiency of BPA did not show correlation with the increasing of Co content in catalyst. Based on the catalytic performance comparison and reactive species detection, Co SAs was identified as active sites, which could interact with PMS to generate 1 O 2 via path of PMS→HOO*→O*→ 1 O 2 . However, the role of NCs and NPs in directly activating PMS was negligible. In addition, the increase of Co content in Co/N-C catalyst would result in mass cobalt leaching, which enhanced the BPA degradation via homogeneous catalytic reactions with Co IV as reactive species. It is an effective way to design the Co/N-C catalyst with high catalytic activity and stability via regulating the formation of Co SAs.
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