Synthesis and characterization of magnesium-aluminum layered double hydroxides containing (tetrasulfonated porphyrin)cobalt

摘要

We report the synthesis and characterization of a magnesium-aluminum layered double hydroxide (LDH) containing [ 5,10,15,2 0-tetrakis (4-sulfonatophenyl) porphyrinato]cobalt (it) (CoTPhsP) by two routes: (i) CoTPhsP intercalation by structure reconstruction of the calcined pristine LDH [Mg2.8Al(CoTPhsP)(int)] and (ii) adsorption of the CoTPhsP on the external surfaces of the noncalcined pristine LDH [Mg3.0Al(CoTPhsP)(ads)]. The intercalation and adsorption of CoTPhsP in the LDHs were evaluated using different techniques, such as X-ray diffraction, thermogravimetry, scanning electronic microscopy, and surface area and porosity analysis. Further characterization by electron spin resonance and UV/Vis spectroscopy showed that the CoTPhsP molecules adsorbed and intercalated in the LDHs are present as two predominant species: the complex formed with molecular oxygen (CoTPhsP-O-2) and the corresponding deoxy monomeric species (CoTPhsP). The stability and reactivity of the CoTPhsP immobilized in the LDHs were evaluated in the presence of hydrogen peroxide solution. CoTPhsP in homogeneous conditions is deactivated by molecular aggregation and/or oxidative self-destruction in the presence of H2O2, On the other hand, CoTPhsP stability and reactivity were improved when adsorbed and intercalated in the LDHs. Mg3.0Al(CoTPhsP)(ads) is more active than Mg2.8Al(CoTPhsP)(int) in the decomposition of hydrogen peroxide to H2O and O-2. A porosity analysis carried out by N-2 adsorption-desorption experiments for the intercalated material exhibited a type-IV isotherm characteristic of nonmicroporous materials. Hence, the CoTPhsP molecules located in the LDH galleries are not acessible to the H2O2, while the metal centers in the Mg3.0Al(CoTPhSP)(ads) sample are more available, which may explain the enhanced reactivity. (c) Wiley-VCH Verlag GmbH & Co. KGaA.