Carlos M. Granadeiro

An efficient oxidative desulfurization process using terbium-polyoxometalate@MIL-101(Cr)

An efficient and recyclable oxidative desulfurization process (ODS) to remove the most refractory sulfur-compounds (dibenzothiophene, 1-benzothiophene and 4,6-dimethyldibenzothiophene) from fuel is reported. The ODS process was catalyzed by terbium-polyoxometalate [Tb(PW11O39)2]11− (Tb(PW11)2) and its composite Tb(PW11)2@MIL-101. The tetrabutylammonium (TBA) salt of Tb(PW11)2 was prepared and further incorporated in the porous metal–organic framework MIL-101(Cr). The TBA compound and its composite were characterized by various techniques (powder X-ray diffraction, FT-IR, FT-Raman, SEM and elemental analysis), and their electrochemical behavior was investigated, indicating that the structure of the polyoxometalate anion must be retained after immobilization. The studied ODS process was based on a biphasic system formed by a model oil with various refractor sulfur-compounds and an extracting solvent using H2O2 as the oxidant. Two main steps in the process were carefully investigated: the initial extraction and the oxidative catalytic stage. The optimization of the ODS process was performed by the analysis of the most suitable extracting solvent and also comparing the desulfurization performance of the homogeneous Tb(PW11)2 and the heterogeneous Tb(PW11)2@MIL-101 catalysts. Acetonitrile was selected as the best solvent because it allowed the highest desulfurization rate, conciliating good initial extraction and high catalytic performance. The presence of the porous catalyst Tb(PW11)2@MIL-101 seemed not to influence the initial extraction step; however, with this porous hybrid catalyst were obtained higher desulfurization rates during the catalytic stage. Remarkably, using Tb(PW11)2@MIL-101 and the oil–acetonitrile system complete desulfurization of oil was achieved only after 5 h. The recyclability of the solid catalyst was investigated for three consecutive ODS cycles and its stability was confirmed by several techniques.

FT-IR, FT-Raman, SERS and computational study of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole.

FT-IR, FT-Raman and surface-enhanced Raman scattering spectra of 5-ethylsulphonyl-2-(o-chlorobenzyl)benzoxazole were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian09 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution calculations. The presence of CH(2), SO(2) and CH(3) modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface which affects the orientation and metal molecule interaction. The synthesis, NMR spectra and antibacterial properties are reported. The title compound shows more inhibitory effect against Pseudomonas aeruginosa than ampicillin and found to be more potent against Klebsiella pneumoniae and drug-resistant Bacillus subtilis than the other microorganisms. A computation of the first hyperpolarizability indicates that the compound may be a good candidate as a NLO material. The RMS errors of the observed Raman and IR bands are found to be 30.93, 29.77 for HF and 9.57, 6.75 for DFT methods, respectively.

Lanthanopolyoxotungstates in silica nanoparticles: multi-wavelength photoluminescent core/shell materials

Photoluminescent lanthanopolyoxotungstate core/shell nanoparticles are prepared by the encapsulation of lanthanide-containing polyoxometalates (POMs) with amorphous silica shells. The preparation of morphological well-defined core/shell nanoparticles is achieved by the hydrolysis of tetraethoxysilane in the presence of POMs using a reverse microemulsion method. The POMs used are decatungstolanthanoates of [Ln(W5O18)2]9− type (Ln(III) = Eu, Gd and Tb). Photoluminescence studies show that there is efficient emission from the POM located inside the SiO2 shells, through excitation paths that involve O → Eu/Tb and O → W ligand-to-metal charge transfer. It is also shown that the excitation of the POM containing europium(III) may be tuned towards longer wavelengths via an antenna effect, by coordination of an organic ligand such as 3-hydroxypicolinate. The POM/SiO2 nanoparticles form stable suspensions in aqueous solution having the advantage of POM stabilization inside the core and the possibility of further surface grafting of chemical moieties via well known derivatization procedures for silica surfaces. These features together with the possibility of tuning the excitation wavelength by modifying the coordination sphere in the lanthanopolyoxometalate, make this strategy promising to develop a new class of optical bio-tags composed of silica nanobeads with multi-wavelength photoluminescent lanthanopolyoxometalate cores.

IR, Raman and SERS Spectra of 2-(Methoxycarbonylmethylsulfanyl)-3,5-dinitrobenzene Carboxylic Acid

O acido carboxilico 2-(metoxicarbonilmetilsulfanil)-3,5-dinitrobenzeno foi preparado por substituicao nucleofilica. Seus espectros de infravermelho e Raman com transformada de Fourier foram obtidos e analisados. O espalhamento Raman intensificado pela superficie (SERS) foi obtido sobre prata coloidal. Os numeros de onda vibracionais foram computados pela teoria do funcional de densidade (DFT) com a base hibrida B3LYP/6-31G* e foram comparados com valores experimentais com boa concordância. Interacoes metal-molecula significativas foram substanciadas por um sinal Ag-O intenso nos espectros SERS, indicando a proximidade dos grupos nitro e carbonila a superficie de prata. Estudos SERS sugerem uma orientacao inclinada da molecula sobre a superficie metalica. 2-(Methoxycarbonylmethylsulfanyl)-3,5-dinitrobenzenecarboxylic acid was prepared by nucleophilic substitution. FT-IR and FT-Raman spectra of 2-(methoxycarbonylmethylsulfanyl)-3,5dinitrobenzenecarboxylic acid were recorded and analyzed. Surface enhanced Raman scattering (SERS) spectrum was recorded on a silver colloid. The vibrational wavenumbers were computed by density functional theoretical (DFT) computations at the B3LYP/6-31G* level and they were found to be in good agreement with the experimental values. Significant metal-molecule interaction has been substantiated by the appearance of intense Ag-O mode in the SERS spectrum and this is indicative of the nearness of nitro and carbonyl group to the silver surface. SERS studies suggest a tilted orientation of the molecule at the metal surface.

Oxidative catalytic versatility of a trivacant polyoxotungstate incorporated into MIL-101(Cr)

The first immobilization of the trivacant Keggin-type polyoxometalate ([A-PW9O34]9−, PW9) to prepare a novel heterogeneous oxidative catalyst is here reported. PW9 was incorporated into the cavities of the chromium terephthalate metal–organic framework MIL-101(Cr). Characterization of the composite PW9@MIL-101 by powder X-ray diffraction, SEM-EDX, FT-IR, FT-Raman spectroscopy, N2 adsorption–desorption isotherms and 31P solid-state NMR confirmed that the structures of MIL-101 and the polyoxometalate anion were retained after immobilization. The composite PW9@MIL-101 revealed versatility as a heterogeneous catalyst to oxidize efficiently monoterpenes as well as to reach a complete desulfurization of a model oil containing the most refractory sulfur compounds in fuel, using in both systems acetonitrile as the solvent and H2O2 as the oxidant. Complete conversion of geraniol to 2,3-epoxygeraniol was achieved after the first 30 min at room temperature, while the total desulfurization of the model oil containing 1707 ppm of sulfur was attained after 2 h. In both systems the catalyst was recyclable for various cycles without a significant loss of activity. The stability and heterogeneity of the catalyst were confirmed by several techniques and by leaching tests.

Influence of a porous MOF support on the catalytic performance of Eu-polyoxometalate based materials: desulfurization of a model diesel

An aluminum 2-aminoterephthalate based metal–organic framework (MOF) material was applied for the first time to prepare highly efficient heterogeneous catalysts in desulfurization processes. Sandwich-type [Eu(PW11O39)2]11− polyoxometalate (POM) was supported on Al(III) and Cr(III) MIL-type MOFs, NH2-MIL-53(Al) and MIL-101(Cr), and extensive characterization confirmed the incorporation of the POM on the two supports. The catalytic performance of the two composite materials, POM/MIL(Al) and POM/MIL(Cr), was evaluated in the oxidative desulfurization (ODS) of a model fuel containing some of the most common refractory sulfur compounds in diesel. Both composite materials have shown to be active and robust heterogeneous catalysts for the efficient removal of the sulfur-containing compounds from the model diesel, and the influence of the solid support on the catalytic performance of the active species was further assessed. The POM/MIL(Al) revealed notable catalytic performance, since complete desulfurization was obtained after 2 h of reaction. Furthermore, this remarkable heterogeneous catalyst revealed to be stable and recyclable for various catalytic cycles.

IR, Raman and SERS spectra of 2-phenoxymethylbenzothiazole

The FT-IR and FT-Raman spectra of 2-phenoxymethylbenzothiazole were recorded and analyzed. The surface enhanced Raman scattering (SERS) spectrum was recorded in a silver colloid. The vibrational wavenumbers of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values. The appearance of the Ag-O stretching mode at 237cm(-1) in the SERS spectrum along with theoretically calculated atomic charge density, leads us to suggest that the molecule is adsorbed through the oxygen atom with the molecular plane tilted on the colloidal silver surface. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory.

Dinuclear Lanthanide(III) Complexes by Metal-Ion-Assisted Hydration of Di-2-pyridyl Ketone Azine

The initial employment of di-2-pyridyl ketone azine in 4f metal chemistry has led to a unique ligand transformation; the resulting anionic ligand is able to bridge two Ln(III) ions, affording neutral and cationic dinuclear complexes with interesting properties.

Photoluminescent bimetallic-3-hydroxypicolinate/graphene oxide nanocomposite

A new photoluminescent bimetallic-3-hydroxypicolinate/graphene oxide composite was prepared by incorporation of the complex Na5[EuW2O6(picOH)8] (1; HpicOH being 3-hydroxypicolinic acid) on graphene oxide (GO). Photoluminescence studies (emission and excitation spectra and 5D0 emission decay curves) were performed on 1 and the composite 1/GO suggesting an effective interaction between the picOH− ligands and the graphene oxide.

Cobalt aluminate nanoparticles supported on MIL-101 structure: catalytic performance investigation

The first catalytic active composites based on CoAl2O4 nanoparticles with different size (5.5 and 2.5 nm) were successfully prepared using a simple methodology of incorporation into MIL-101(Cr) framework, CoAl-x@MIL(Cr). Characterization of CoAl-x@MIL(Cr) composites by elemental analysis, vibrational spectroscopy (FT-IR and FT-Raman), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) confirmed the successful preparation and stability of the support structure after nanoparticle immobilization. A remarkable catalytic performance was found for thioanisole oxidation under sustainable conditions (95% of conversion after 30 min of reaction) and the catalytic application of the most active composite was extended to styrene oxidation. Higher catalytic performance was achieved for the composite prepared with larger CoAl2O4 nanoparticles. The recyclability and the stability of composites after catalytic use were investigated. For the CoAl-x@MIL(Cr) catalytic systems, the loading parameter instead of the nanoparticle size seemed to have a pronounced influence in the heterogeneous catalytic performance. The confinement effect promoted by MIL-101(Cr) cavities associated to the higher number of catalytic active centers (CoAl2O4) is clearly more important than the size of the catalytic nanoparticles used.