Cobalt(II) Dioxygen Carriers Based on Simple Diamino Ligands: Kinetic and ab Initio Studies

Performance of Several Cobalt-Amine Denitration Solutions and Their Catalytic Regeneration by Graphene

Little attention has been focused on the use of cobalt(II)-amine chelates for the absorption of nitric oxide (NO) in flue gas, and research on the regeneration of cobalt denitration solutions is relatively rare. To supplement this research gap, several promising ethylenediamine derivatives were screened out. They are N-(2-hydroxyethyl)ethylenediamine, 1,2-propanediamine, and 1,2-cyclohexanediamine. These cobalt(II)-amine solutions are effective for denitration and have not been reported yet. However, they are also easily oxidized to the corresponding cobalt(III) species. In the presence of a nanocarbon material, cobalt(III) components are reduced to cobalt(II) components and release oxygen by reacting with acids. The effects of solution pH, temperature, and graphene dosage on the regeneration process were investigated. A proper addition of graphene as a catalyst contributes to the progress of regeneration. Catalytic mechanisms and regeneration performance have been discussed as much as possible. These mechanisms are related to the oxidation reactions and oxygenated species of cobalt complexes. The carbon material here acts as a catalyst for adsorbing cobalt chelates and accelerating charge transfer in the oxygen evolution reaction.

Reversible Oxygenation of α-Amino Acid-Cobalt(II) Complexes

We systematically investigated the reversibility, time lapse, and oxygenation-deoxygenation properties of 15 natural α-amino acid-Co(II) complexes through UV-vis spectrophotometer, polarographic oxygen electrode, and DFT calculations, respectively, to explore the relationship between the coordinating structure and reversible oxygenation of α-amino acid-Co(II) complexes. Results revealed that the α-amino acid structure plays a key role in the reversible oxygenation properties of these complexes. The specific configuration of the α-amino acid group affects the eg (1) electron of Co(II) transfer to the π (⁎) orbit of O2; this phenomenon also favors the reversible formation and dissociation of Co-O2 bond when O2 coordinates with Co(II) complexes. Therefore, the co-coordination of amino and carboxyl groups is a determinant of Co complexes to absorb O2 reversibly. The group adjacent to the α-amino acid unit evidently influences the dioxygen affinity and antioxidation ability of the complexes. The presence of amino (or imino) and hydroxy groups adjacent to the α-amino acid group increases the oxygenation-deoxygenation rate and the number of reversible cycles. Our findings demonstrate a new mechanism to develop reversible oxygenation complexes and to reveal the oxygenation of oxygen carriers.

Ethylenediamine-modified oriented MCM-41 at the electrode surface, cobalt adsorption ability and electrochemical performance

Mesoporous silica thin films (MCM-41) functionalized with ethylenediamine groups were electrochemically fabricated on electrode surfaces. These ligand functionalized film were a promising matrix for the immobilization of cobalt ions and preparation of cobalt complexes covalently bound to the MCM-41 support. The constructed MCM-41 were characterized by TEM, EDS and TGA analysis. This method yields uniform thin films with hexagonal mesochannels aligned and accessible to electrode surface. Well-defined electrode responses were, therefore, observed for the anchored complexes which made the electrochemical analysis of the structure possible as well. Voltammetric studies revealed the reactivity of the covalently bound complexes differed significantly from the dissolved ones. The anchored complexes preferred to be in their oxidized form which inhibits formation of oxygen adducts. The covalently bound complexes had relatively good leaching stability with good catalytic performance towards hydrogen peroxide reduction.