Electron cycling mechanism in Fe/Mn DSAzyme accelerates BPA degradation and nanoenzyme regeneration.

Peroxidase-like (POD-like) as a kind of new Fenton-like catalyst can effectively activate H2O2 to degrade organic pollutants in water, but improving the catalytic activity and stability of POD-like remains a challenging task. Here, we synthesized a novel dual single-atom nanoenzyme (DSAzyme) FeMn/N-CNTs with Fe-N4 and Mn-N4 bimetallic single-atom active centers by mimicking the active centers of natural enzymes and taking advantage of the synergistic effect between the dual metals. FeMn/N-CNTs DSAzyme showed significantly enhanced POD-like activity compared to monometallic-loaded Fe/N-CNTs and Mn/N-CNTs. Within the FeMn/N-CNTs/H2O2 system, bisphenol A (BPA) could be removed 100 % within 20 min. DFT calculations show that Mn-N4 in FeMn/N-CNTs can readily adsorb negatively charged BPA molecules and capture electrons. Meanwhile, Fe-N4 sites can easily adsorb H2O2 molecules, leading to their activation and splitting into strongly oxidizing hydroxyl radicals (·OH). Throughout this process, electrons are continuously recycled in BPA → Mn-N4 → Fe-N4 → H2O2, effectively promoting the regeneration of Fe2+. Practical studies on wastewater and cycling experiments have demonstrated the great potential of this method for remediating water environments.

Critical role of zero-valent iron in the efficient activation of H2O2 for 4-CP degradation by bimetallic peroxidase-like.

Peroxidase-like based on double transition metals have higher catalytic activity and are considered to have great potential for application in the field of pollutant degradation. First, in this paper, a novel Fe0-doped three-dimensional porous Fe0@FeMn-NC-like peroxidase was synthesized by a simple one-step thermal reduction method. The doping of manganese was able to reduce part of the iron in Fe-Mn binary oxides to Fe0 at high temperatures. In addition, Fe0@FeMn-NC has excellent peroxidase-like mimetic activity, and thus, it was used for the rapid degradation of p-chlorophenol (4-CP). During the degradation process, Fe0 was able to rapidly replenish the constantly depleted Fe2+ in the reaction system and brought in a large number of additional electrons. The ineffective decomposition of H2O2 due to the use of H2O2 as an electron donor in the reduction reactions from Fe3+ to Fe2+ and from Mn3+ to Mn2+ was avoided. Finally, based on the experimental results of LC-MS and combined with theoretical calculations, the degradation process of 4-CP was rationally analyzed, in which the intermediates were mainly p-chloro-catechol, p-chloro resorcinol, and p-benzoquinone. Fe0@FeMn-NC nano-enzymes have excellent catalytic activity as well as structural stability and perform well in the treatment of simulated wastewater containing a variety of phenolic pollutants as well as real chemical wastewater. It provides some insights and methods for the application of peroxidase-like enzymes in the degradation of organic pollutants.

Efficient Degradation of Sulfamethoxazole by Diatomite-Supported Hydroxyl-Modified UIO-66 Photocatalyst after Calcination.

Sulfamethoxazole (SMX) is a widely used antibiotic to treat bacterial infections prevalent among humans and animals. SMX undergoes several transformation pathways in living organisms and external environments. Therefore, the development of efficient remediation methods for treating SMX and its metabolites is needed. We fabricated a photo-Fenton catalyst using an UIO-66 (Zr) metal-organic framework (MOF) dispersed in diatomite by a single-step solvothermal method for hydroxylation (HO-UIO-66). The HO-UIO-66-0/DE-assisted Fenton-like process degraded SMX with 94.7% efficiency; however, HO-UIO-66 (Zr) is not stable. We improved the stability of the catalyst by introducing a calcination step. The calcination temperature is critical to improving the catalytic efficiency of the composite (for example, designated as HO-UIO-66/DE-300 to denote hydroxylated UIO-66 dispersed in diatomite calcined at 300 °C). The degradation of SMX by HO-UIO-66/DE-300 was 93.8% in 120 min with 4 mmol/L H2O2 at pH 3 under visible light radiation. The O1s XPS signatures signify the stability of the catalyst after repeated use for SMX degradation. The electron spin resonance spectral data suggest the role of h+, •OH, •O2-, and 1O2 in SMX degradation routes. The HO-UIO-66/DE-300-assisted Fenton-like process shows potential in degrading pharmaceutical products present in water and wastewater.

Synthesis of Fused or Spiro Polyheterocyclic Compounds via the Dehydrogenative Annulation Reactions of 2-Arylindazoles with Maleimides.

A dehydrogenative annulation of 2-arylindazoles with maleimides for the switchable synthesis of indazolo[2,3-a]pyrrolo[3,4-c]quinolinones or spiroindolo[1,2-b]indazole-11,3'-pyrrolidinones is presented. Mechanistically, the formation of the title compounds involves a Rh(III)-catalyzed C-H metalation of 2-arylindazole, followed by maleimide insertion and intramolecular cyclization. Interestingly, the selectivity to form the fused or spiro compounds could be switched by resorting to different additives. The notable features of this protocol include simple substrates and excellent atom economy and regioselectivity.