Construction of Pyrazine-Appended 1D and 3D Cobalt(II) Succinate Coordination Polymers: Influence of Solvent on Architectures and Applications in Gas Adsorption and NAC Detection

An underexplored reaction of pyrazine (rigid and linear) and succinic acid (flexible) with Co(NO₃)₂·6H₂O afforded four new coordination polymers (CPs): [Co(H₂O)(pyz)(suc)] (1), [Co(H₂O)₂(pyz)(suc)] (2), [Co(H₂O)₄(pyz)](suc) (3) and [Co₂(H₂O)₂(pyz)(suc)₂] (4), as well as [Co(HCO₂)₂(pyz)] (5) being lately reported along with well-known 6 and 7. The CPs were obtained as stable crystalline materials and characterized by conventional solid-state techniques, including X-ray crystallography. Hydrothermally produced compounds 1 and 2 were both 3D CPs. While 3 and 4 obtained under ambient/solvothermal conditions in DMSO generated 1D and 3D structures, 5 isolated from DMF under solvothermal conditions had a 3D structure. The topologies of the coordination polymers 1-7 were described by underlying nets 3D 5-c fet, 3D 4-c cds, 1D 2-c 2C1, 3D 5-c bnn, 3D 6-c rob, 1D 2-c 2C1, and 3D 6-c pcu, respectively. The plot of χ_M ^-1 versus T was essentially linear in the entire temperature range following the Curie-Weiss law with a Curie constant (C) of 2.525 and a negative Weiss constant (ϕ) of -46.24 K, suggesting weak antiferromagnetic (AF) exchange interactions. CO₂ and N₂ adsorption studies of 1-5 featured type III isotherms. 1 was found to show remarkably higher quenching efficiencies for nitrophenols (η = 98% for o-NP) over other NACs. The Stern-Volmer plot exhibited deviation in linearity with K _sv values about 200 times greater than that for the simplest nitroaromatic compound (NB), signifying its exclusive quenching ability toward 1. The LOD for p-NP addition to 1 was found to be 0.995 ppm.

CoO x nanoparticle anchored on sulfonated-graphite as efficient water oxidation catalyst

Ultrasmall CoO_x nanoparticles on sulfonated graphite exhibit highly efficient water oxidation activity and can be used for electrochemical and solar water oxidation.

Development of efficient, robust and earth-abundant water oxidation catalysts (WOCs) is extremely desirable for water splitting by electrolysis or photocatalysis. Herein, we report cobalt oxide nanoparticles anchored on the surface of sulfonated graphite (denoted as “CoO_x@G-Ph-SN”) to exhibit unexpectedly efficient water oxidation activity with a turnover frequency (TOF) of 1.2 s^–1; two or three orders of magnitude higher than most cobalt-based oxide WOCs reported so far. The CoO_x@G-Ph-SN nanocomposite can be easily prepared by a soft hydrothermal route to have an average CoO_x size below 2 nm. Additionally, the loading of CoO_x@G-Ph-SN catalyst on the surface of a BiVO₄ or Fe₂O₃ photoanode can boost remarkably the photoanode currents for robust photocatalytic water oxidation under visible light irradiation. Its excellent activity and photochemical stability for water oxidation suggest that this ultrasmall cobalt-based composite is a promising candidate for solar fuel production.