Hybrid Coordination Networks for Removal of Pollutants from Wastewater.

The adsorption properties of two coordination polymers, resulting from the reaction of divalent metal (Ca2+ or Co2+) salts with (2-carboxyethyl)(phenyl)phosphinic acid, are presented in this paper. The structural and textural characterization before and after adsorption experiments is presented. The adsorbent materials were prepared using the hydrothermal procedure. The compound Ca[O2P(CH2CH2COOH)(C6H5)]2 (CaCEPPA) has a layered topology, with the phenyl groups oriented into the interlayer space and crystallizes in the monoclinic system. Compound Co2[(O2P(CH2CH2COO)(C6H5)(H2O)]2·2H2O (CoCEPPA) has a 1D structure composed of zig-zag chains. The adsorption performances of CaCEPPA and CoCEPPA materials were tested in the removal of cadmium and lead from aqueous solutions. The optimum pH of ions adsorption was found to be five for both adsorbent materials. Pseudo-first and second-order kinetic models were used for fitting kinetic experimental data, and Langmuir and Freundlich isotherms were used for modeling the equilibrium experimental data. The pseudo-second-order kinetic model and Langmuir isotherm best described the adsorption of Cd and Pb ions onto the studied materials, judging from the results of the error function (correlation coefficient, sum of square error, chi-square test, and average relative error) analysis. The studied materials present a higher affinity for Cd ions compared with the adsorption capacity developed for the removal of Pb ions from aqueous solutions. CoCEPPA showed the highest adsorption performance in the removal process of metal ions from aqueous solutions compared with CaCEPPA (qm = 54.9 mg Cd2+/g of CoCEPPA, qm = 36.5 mg Cd2+/g of CaCEPPA).

Synthesis and electrochemical properties of metal(ii)-carboxyethylphenylphosphinates.

We report herein the synthesis, structural characterization and electrocatalytic properties of three new coordination polymers, resulting from the combination of divalent metal (Ca2+, Cd2+ or Co2+) salts with (2-carboxyethyl)(phenyl)phosphinic acid. In addition to the usual hydrothermal procedure, the Co2+ derivative could also be prepared by microwave-assisted synthesis, in much shorter times. The crystal structures were solved by ab initio calculations, from powder diffraction data. Compounds MII[O2P(CH2CH2COOH)(C6H5)]2 {M = Cd (1) or Ca (2)} crystallize in the monoclinic system and display a layered topology, with the phenyl groups pointing toward the interlayer space in a interdigitated fashion. Compound Co2[(O2P(CH2CH2COO)(C6H5)(H2O)]2·2H2O (3) presents a 1D structure composed of zig-zag chains, formed by edge-sharing cobalt octahedra, with the phenyl groups pointing outside. Packing of these chains is favored by hydrogen bond interactions via lattice water molecules. In addition, H-bonds along the chains are established with the participation of the water molecules and the hydrophilic groups from the ligand. However, the solid exhibits a low proton conductivity, attributed to the isolation of the hydrophilic regions caused by the arrangement of hydrophobic phenyl groups. Preliminary studies on the electrocatalytic performance for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have been conducted for compound 3 and its pyrolytic derivatives, which were previously thoroughly characterized. By comparison, another Co2+ phosphinate, 4, obtained by microwave-assisted synthesis, but with distinct stoichiometry and a known structure was also tested. For the OER, the best performance was achieved with a derivative of 3, prepared by heating this compound in N2 at 200 °C. This derivative showed overpotential (339 mV, at a current density of 10 mA cm-2) and Tafel slope (51.7 mV dec-1) values comparable to those of other Co2+ related materials.