Co(II) ethylene glycol carboxylates for Co3O4 nanoparticle and nanocomposite formation

Abstract

Ethylene glycol-functionalized Co(II) carboxylates [Co(CO2CH2(OC2H4) n OMe)2] (2a, n = 1; 2b, n = 2), [Co(CO2CHPh(OC2H4)2OMe)2] (2c) and [Co(CO2CMe2(O–C2H4)2OMe)2] (2d) have been synthesized by the reaction of [Co(OAc)2·4H2O] with the corresponding acids MeO(C2H4O) n CRR′CO2H (n = 1, 2; R=H, R′=Me; R=H, R′=Ph). Based on the IR spectroscopic studies, the binding motif of the carboxylato ligands to cobalt is discussed. Thermogravimetry and mass spectrometry studies were carried out in order to investigate the thermal decomposition mechanism of 2a–2d in the solid state. Based on the result obtained, complex 2b was chosen as single-source precursor for the generation and stabilization of Co3O4 nanoparticles (NPs) by solid-state thermal decomposition in air. Depending on the decomposition time, NPs with different chemical composition (consisting of Co3O4, CoO and Co) and with crystallite sizes ranging from 9 to 18 nm were obtained. Furthermore, the preparation of cobalt oxide-based nanocomposites by twin polymerization of 2,2′-spirobi[4H-1,3,2-benzodioxasiline] (3) in the presence of 2b is reported. After treatment of the as-prepared hybrid material by either oxidation or etching, the respective mesoporous carbon/silica (IUPAC type IV isotherms) matrices were obtained. Quenched solid and nonlinear density functional theory calculations gave a surface area of 1040 cm2 g−1 for the respective carbon and 336 cm2 g−1 for the appropriate silica material. Powder X-ray diffraction measurements confirm the formation of Co3O4 NPs in both components. High-angle annular dark field scanning transmission electron microscopy revealed well-distributed particles within the silica matrix, whereas no particles were found in the carbon material. The electrochemical properties of the composite materials have been investigated by cyclic voltammetry. The respective silica material shows five reduction events (Co3O4 to CoO, CoO to Co), while no redox potentials occurred for the Co3O4 NPs embedded in the carbon matrix.