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Orthorhombic niobium pentoxide (T-Nb2O5) possesses an intercalation pseudocapacitive behavior, which is a promising candidate of high-rate anodes for Li-ion capacitors. However, its low electric conductivity hinders the realization of this property. In our study, niobium oxides/carbon composites were prepared by calcinating a niobium peroxo-PAA complex (NbPAA) precursor to improve the electric conductivity. It has been found that the calcination temperature played an important role on the chemical compositions of obtained composites. A reduction phenomenon of niobium oxides by carbon was observed at high temperatures. At the medium temperature of 900 °C, the sample was composed of T-Nb2O5, monoclinic Nb2O5 (M-Nb2O5), amorphous carbon and niobium dioxide (NbO2). Due to the high conductivity of carbon, semi-conductivity of NbO2, and high specific capacity of M-Nb2O5, this sample exhibits a good specific capacity of 142 mAh g−1 (0.25 C) and a high-rate capability (capacity retention of 33.1%, 0.25 C to 25 C). It could be used as one of high-rate anodes for Li-ion capacitors. [ABSTRACT FROM AUTHOR]

In this work, the microwave-assisted synthesis of manganese metal–organic framework (MOF) material is presented. Synthesis procedure is based on a microwave-assisted solvothermal reaction of manganese(III) acetylacetonate with biphenyl-4,4′-dicarboxylic acid (Bpdc) in N,N′-dimethylformamide at the temperature of 160 °C. The obtained Mn-based metal–organic framework, labeled as Mn-Bpdc, was used as a precursor for the preparation of a porous MnO/carbon nanocomposite, which was obtained via thermal transformation in a nitrogen atmosphere at 700 °C. It was found that this approach provides an effective and simple preparation pathway for porous carbon decorated with homogeneously embedded manganese(II) oxide nanoparticles. Both Mn-Bpdc and MnO/C nanocomposite materials were characterized by a variety of physicochemical methods. The prepared MnO/C nanocomposite material was deposited on a cathode surface of lithium-sulfur batteries and utilized as a shuttle suppressing layer. This electrode structure immobilizes polysulfides inside the cathode and improves the stability during cycling. The electrode with MnO/C nanocomposite shuttle suppressing layer maintains high stability during cycling in comparison with a standard electrode. The electrode with MnO/C composite layer exhibits 84.8% capacity retention after 50 cycles at different C-rates compared to 76.2% obtained for the standard electrode. [ABSTRACT FROM AUTHOR]

A one-step microwave-assisted polyol method was used to fabricate FexZn1−xO (x = 0.01, 0.05, 0.10) nanoparticles. Zinc acetate dihydrate, iron (III) acetylacetonate, oleic acid and diethylene glycol were placed in a Teflon-lined reaction vessel. The reaction mixture was heated up to 250 °C for 15 min in a microwave reactor. The surface modification with oleic acid prevented agglomeration of the nanoparticles. The X-ray diffraction analysis revealed characteristics wurtzite hexagonal structure of ZnO and successful incorporation of the Fe dopant into the host crystal lattice. Doping of ZnO by Fe led to bandgap modification as estimated by Tauc plot. The as-prepared nanopowders were dispersed in toluene and mixed with a poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer to make stable homogenous dispersions. Then, the FexZn1−xO/MEH-PPV nanocomposite thin films were prepared by spin coating and used as thin active layers in polymer light-emitting diodes. The thickness of deposited FexZn1−xO/MEH-PPV film was ca. 30 nm and that of reference neat MEH-PPV film was ca. 25 nm. The electroluminescent spectroscopy study showed that direct blending of MEH-PPV with Fe-doped ZnO nanoparticles is a simple and effective approach to significantly increase the luminance intensity of the diode in comparison to the diode fabricated by neat MEH-PPV. [ABSTRACT FROM AUTHOR]

The gadolinium (Gd3+) substituted zinc ferrite nanoparticles (ZnFe2−xGdxO4) for Gd3+ (x = 0.00, 0.05, 0.10, 0.20) have been synthesized by honey mediated sol-gel auto-combustion method. The X-ray diffraction study revealed the formation of spinel ferrite crystal structure. The Raman spectroscopy and Fourier transform infrared spectroscopy study well support the XRD results analysis. The field emission scanning electron microscopy micrograph revealed spherical morphology and grain size around 10-30 nm for ZnFe2−xGdxO4 (x = 0.10) nanoparticles. The presence of Zn2+ and Fe3+ oxidation state in synthesized nanoparticles was confirmed by X-ray photoelectron spectroscopy. Magnetic properties of the Gd3+ substituted zinc ferrite nanoparticles were investigated by vibrating sample magnetometer at room temperature. The conversion of magnetic hysteresis curves from ferromagnetic to a paramagnetic with the substitution of Gd3+ in zinc ferrite nanoparticles was observed. Frequency dependent dielectric constant and ac conductivity measurements revealed that Gd3+ substitution improved the value of dielectric constant and ac conductivity of the Gd3+ substituted zinc ferrite nanoparticles. Further, the existence of two semicircles in Cole-Cole plot demonstrated the role of both grains and grain boundaries to conduction process in synthesized Gd3+ ion substituted zinc ferrite nanoparticles. Furthermore, the grain relaxation time (τg), grain boundary relaxation time (τgb), grain resistance (Rg), grain capacitance (Cg), grain boundary resistance (Rgb) and grain boundary capacitance (Cgb) for synthesized ZnFe2−xGdxO4 (x = 0.00, 0.05, 0.10, 0.20) nanoparticles have been calculated using modulus spectroscopy analysis. [ABSTRACT FROM AUTHOR]

A novel templated non-hydrolytic sol-gel synthesis of titanosilicate xerogels is reported. Acetamide elimination from silicon acetate and titanium diethylamide allows obtaining titanosilicates with a high content of Si-O-Ti bonds but low surface areas. These xerogels lose porosity on calcination. However, with addition of Pluronic P123 as a structure-directing agent, we synthesized mesoporous titanosilicate materials with large surface areas (up to 615 m g) and well dispersed tetrahedral Ti that are stable at temperatures up to 500 °C. These potential catalysts were characterized by variety of physico-chemical methods (IR, GC-MS, XRD, Si and C CPMAS NMR, DRUV-Vis, and N porosimetry) and tested in cyclohexene epoxidation with cumyl hydroperoxide in toluene. They display catalytic activity with the 100 % selectivity to cyclohexene oxide and high catalytic yields up to 96 % which is comparable to previously reported titanosilicate catalysts. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel non-hydrolytic sol-gel (NHSG) synthesis of mesoporous zirconium silicate xerogels is presented. The condensation between silicon acetate, Si(OAc), and Zr(NEt) resulting in acetamide elimination leads to homogeneous zirconium silicate xerogels containing Si-O-Zr linkages. The addition of Pluronic P123 template provides stiff gels that are after template removal by calcination at 500 °C in air converted to stable mesoporous xerogels with wormhole-type pores, high surface area over 500 m g, and tetrahedrally coordinated Zr atoms in the framework. The composition and morphology of the xerogels, volatile reaction byproducts, and thermal transformations were followed by elemental analysis, IR spectroscopy, thermal analysis TG-DSC, nitrogen adsorption, C and Si solid-state NMR spectroscopy, DRUV-Vis spectroscopy, SAXS, and HT powder XRD. These potential catalysts were tested for the Meerwein-Ponndorf-Verley reduction of 4- tert-butylcyclohexanone and for aminolysis of styrene oxide with aniline. Resulting reaction systems display good activity and selectivity. [ABSTRACT FROM AUTHOR]

Novel non-hydrolytic syntheses of titanosilicate xerogels by polycondensation of silicon acetate, Si(OAc), with titanium (IV) dimethylamide or diethylamide, Ti(NR) (R = Me, Et), are presented. The reactions are based on acetamide elimination and yield gels with a high content of Si-O−Ti bonds in comparison with the ester elimination route. Although a ligand exchange was observed, it was interestingly not followed by homo-condensation and during the synthesis the phase separation to SiO and TiO was avoided. The degree of condensation reached up to 68 %. The xerogels prepared for a comparison by ester elimination from Si(OAc) and titanium (IV) isopropoxide featured a significantly lower content of the Si-O-Ti bonds. The initial tests in the epoxidation of cyclohexene by cumyl hydroperoxide (CHP) indicated a high selectivity and moderate activity of the xerogels. The catalytic properties were significantly improved by combining non-hydrolytic and hydrolytic methods yielding mesoporous and homogeneous Si/Ti mixed oxides. The catalysts prepared by these methods provided a complete epoxidation of cyclohexene in 2 h at 65 °C. [ABSTRACT FROM AUTHOR]