Ethylene cross-bridged tetraazamacrocycles are known to produce kinetically stable transition metal complexes that can act as robust oxidation catalysts under harsh aqueous conditions. We have synthesized ligand analogs with single acetate pendant arms that act as pentadentate ligands to Mn, Fe, Co, Ni, Cu, and Zn. These complexes have been synthesized and characterized, including the structural characterization of four Co and Cu complexes. Cyclic voltammetry demonstrates that multiple oxidation states are stabilized by these rigid, bicyclic ligands. Yet, redox potentials of the metal complexes are modified compared to the “parent” ligands due to the pendant acetate arm. Similarly, gains in kinetic stability under harsh acidic conditions, compared to parent complexes without the pendant acetate arm, were demonstrated by a half-life seven times longer for the cyclam copper complex. Due to the reversible, high oxidation states available for the Mn and Fe complexes, the Mn and Fe complexes were examined as catalysts for the bleaching of three commonly used pollutant model dyes (methylene blue, methyl orange, and Rhodamine B) in water with hydrogen peroxide as oxidant. The efficient bleaching of these dyes was observed.
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Earth Abundant Oxidation Catalysts for Removal of Contaminants of Emerging Concern from Wastewater: Homogeneous Catalytic Screening of Monomeric Complexes
Twenty novel Mn, Fe, and Cu complexes of ethylene cross-bridged tetraazamacrocycles with potentially copolymerizable allyl and benzyl pendant arms were synthesized and characterized. Multiple X-ray crystal structures demonstrate the cis-folded pseudo-octahedral geometry forced by the rigidifying ethylene cross-bridge and show that two cis coordination cites are available for interaction with substrate and oxidant. The Cu complexes were used to determine kinetic stability under harsh acidic and high-temperature conditions, which revealed that the cyclam-based ligands provide superior stabilization with half-lives of many minutes or even hours in 5 M HCl at 50–90 °C. Cyclic voltammetry studies of the Fe and Mn complexes reveal reversible redox processes indicating stabilization of Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+ oxidation states, indicating the likelihood of catalytic oxidation for these complexes. Finally, dye-bleaching experiments with methylene blue, methyl orange, and rhodamine B demonstrate efficient catalytic decolorization and allow selection of the most successful monomeric catalysts for copolymerization to produce future heterogeneous water purification materials.
more » « less- Award ID(s):
- 1946093
- NSF-PAR ID:
- 10494276
- Editor(s):
- Pellegrini, M; Saccani, C; Guzzini, A
- Publisher / Repository:
- Molecules 2023
- Date Published:
- Journal Name:
- Earth Abundant Oxidation Catalysts for Removal of Contaminants of Emerging Concern from Wastewater: Homogeneous Catalytic Screening of Monomeric Complexes
- Volume:
- 28
- Issue:
- 18
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 6466
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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