16 research outputs found
Ionic LiquidâAssisted Microwave Synthesis of Solid Solutions of Perovskite Sr1âxBaxSnO3 for Photocatalytic Applications
Nanocrystalline Sr1âxBaxSnO3 (x=0, 0.2, 0.4, 0.8, 1) perovskite photocatalysts were prepared by microwave synthesis in an ionic liquid (IL) and subsequent heat-treatment. The influence of the Sr/Ba substitution on the structure, crystallization, morphology, and photocatalytic efficiency was investigated and the samples were fully characterized. On the basis of X-ray diffraction results, as the Ba content in the SrSnO3 lattice increases, a symmetry increase was observed from the orthorhombic perovskite structure for SrSnO3 to the cubic BaSnO3 structure. The analysis of the sample morphology by SEM reveals that the Sr1âxBaxSnO3 samples favor the formation of nanorods (500â
nmâ5â
ÎŒm in diameter and several micrometers long). The photophysical properties were examined by UV/Vis diffuse reflectance spectroscopy. The band gap decreases from 3.85 to 3.19â
eV with increasing Ba2+ content. Furthermore, the photocatalytic properties were evaluated for the hydroxylation of terephthalic acid (TA). The order of the activities for TA hydroxylation was Sr0.8Ba0.2SnO3\u3eSrSnO3\u3eBaSnO3\u3eSr0.6Ba0.4SnO3\u3eSr0.2Ba0.8SnO3. The highest photocatalytic activity was observed for Sr0.8Ba0.2SnO3, and this can be attributed to the synergistic impacts of the modification of the crystal structure and morphology, the relatively large surface area associated with the small crystallite size, and the suitable band gap and band-edge position
Luminescence properties of mechanochemically synthesized lanthanide containing MIL-78 MOFs
Three metalâorganic framework (MOF) compounds, Ln0.5Gd0.5{C6H3(COO)3}; Ln = Eu, Tb, and Dy with a MIL-78 structure, have been synthesized by a solvent-free mechanochemical method from stoichiometric mixtures of benzene 1,3,5-tricarboxylic acid, C6H3(COOH)3, also known as trimesic acid, and the respective lanthanide carbonates, Ln2(CO3)3·xH2O, Ln = Eu, Gd, Tb and Dy. MIL-78 (Ln0.5Gd0.5) shows the characteristic red, green, and yellow luminescence of Eu3+, Tb3+, and Dy3+, respectively. Efficient intramolecular energy transfer from the ligand triplet state to the excited states of Ln3+ ions can be observed. The lifetimes and quantum yields of these compounds are studied and discussed in detail. Among the three compounds, the Tb3+ containing compound shows the longest lifetime and highest quantum yield due to a smaller contribution from non-radiative decay pathways and better matching of the lowest triplet energy level of the benzenetricarboxylate ligand and the resonance level of Tb3+
Rationally designed rare earth separation by selective oxalate solubilization
A simple, environmentally benign, and efficient chemical separation of rare earth oxalates (CSEREOX) within two rare earth element (REE) subgroups has been developed. The protocol allows for selective solubilization of water-insoluble oxalates of rare earth elements, and results in efficient REE extraction even at low initial concentrations (\u3c5%) from processed magnet wastes
Synthesis and exploration of Barium Stannate-Zirconate BaSn1-xZrxO3 (0 †X †1) solid solutions as photocatalysts
Employing ionic liquid-assisted microwave synthesis and moderate heat treatment allows for the preparation of otherwise difficult-to-obtain perovskite-type BaSn1-xZrxO3 solid solutions (0 †x †1). The impact of substituting Sn for the crystal structure, crystallinity, morphology, and photocatalytic performance was investigated. The obtained materials are characterized by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and Raman and IR spectroscopy. SEM images show that the morphology of the samples varies from rods for x = 0, 0.2 to spherical for x = 0.5, 0.8, 1. Upon Zr for Sn substitution, the band gap changes from 3.1 to 5.0 eV as the valence and conduction bands move to lower and higher energies. The photocatalytic activities of the BaSn1-xZrxO3 samples in the hydroxylation of terephthalic acid (TA) follow the order BaSn0.5Zr0.5O3> BaSn0.8Zr0.2O3> BaSnO3> BaSn0.2Zr0.8O3> BaZrO3. The superior photocatalytic activity of BaSn0.5Zr0.5O3 can be attributed to the synergistically favorable combination of a suitable band structure, band gap size, and increased surface area-to-volume ratio, resulting in a diminished crystalline particle size unattainable from samples prepared via traditional synthetic routes or without ionic liquid
Mild yet phase-selective preparation of nanoparticles from ionic liquids â a critical study
The phase selective synthesis of nanocrystalline TiO2, titania, in ionic liquids (ILs) is explored. The influence not only of the IL but also of the Ti-precursor, pH, and temperature is investigated. Sonochemical synthesis, microwave synthesis and conventional heating are compared. In the case of Ti(OiPr)4 (OiPr = isopropyl) as the Ti-source the ILs [C4mim][Tf2N] (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide), [C3mimOH][Tf2N] (1-(3-hydroxypropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amide), [C4Py][Tf2N] (butylpyridinium bis(trifluoromethanesulfonyl)amide), [N1888][Tf2N] (methyltrioctylammonium bis(trifluoromethanesulfonyl)amide), and [P66614][Tf2N] (tetradecyltrihexyl phosphonium bis(trifluoromethanesulfonyl)amide) led at ambient temperature to TiO2 in the form of anatase. The morphology of nano-anatase is controlled by the IL cation. Anatase nanospheres with a crystal size below 10 nm are obtained in [C3mimOH][Tf2N], [P66614][Tf2N] and [C4Py][Tf2N], whilst nanorods with a length and diameter of [similar]10 to 20 and 5 nm are formed in [N1888][Tf2N] and spindle-shaped particles with an average length of 10â25 nm are formed in [C4mim][Tf2N]. Calcination at temperatures above 730 °C leads to rutile. When using TiCl4 as the Ti-precursor an anataseârutile mixture forms under ambient conditions. Pure rutile can be obtained under ambient conditions in the presence of an appropriate volume of aqueous HCl. At moderate to high pH values pure anatase can be obtained even from TiCl4. The photocatalytic activity of the obtained TiO2 materials has been assessed by the photodegradation of an aqueous methyl orange solution under UV light. The results indicate that the photocatalytic activity of anataseâbrookite mixtures obtained in [C4mim][Tf2N], [N1888][Tf2N] and [P66614][Tf2N] is higher than that of pure anatase which is formed in [C3mimOH][Tf2N] and [C4Py][Tf2N] and competitive with commercially available catalysts
Ionic LiquidâAssisted Microwave Synthesis of Solid Solutions of Perovskite Sr1âxBaxSnO3 for Photocatalytic Applications
Nanocrystalline Sr1âxBaxSnO3 (x=0, 0.2, 0.4, 0.8, 1) perovskite photocatalysts were prepared by microwave synthesis in an ionic liquid (IL) and subsequent heat-treatment. The influence of the Sr/Ba substitution on the structure, crystallization, morphology, and photocatalytic efficiency was investigated and the samples were fully characterized. On the basis of X-ray diffraction results, as the Ba content in the SrSnO3 lattice increases, a symmetry increase was observed from the orthorhombic perovskite structure for SrSnO3 to the cubic BaSnO3 structure. The analysis of the sample morphology by SEM reveals that the Sr1âxBaxSnO3 samples favor the formation of nanorods (500â
nmâ5â
ÎŒm in diameter and several micrometers long). The photophysical properties were examined by UV/Vis diffuse reflectance spectroscopy. The band gap decreases from 3.85 to 3.19â
eV with increasing Ba2+ content. Furthermore, the photocatalytic properties were evaluated for the hydroxylation of terephthalic acid (TA). The order of the activities for TA hydroxylation was Sr0.8Ba0.2SnO3>SrSnO3>BaSnO3>Sr0.6Ba0.4SnO3>Sr0.2Ba0.8SnO3. The highest photocatalytic activity was observed for Sr0.8Ba0.2SnO3, and this can be attributed to the synergistic impacts of the modification of the crystal structure and morphology, the relatively large surface area associated with the small crystallite size, and the suitable band gap and band-edge position.This article is published as Mudring, Anja Verena, Tarek Alammar, Igor Slowing, and Jim Anderegg. "Ionic LiquidâAssisted Microwave Synthesis of Solid Solutions of Perovskite Sr1âxBaxSnO3 for Photocatalytic Applications." ChemSusChem (2017). doi: 10.1002/cssc.201700615. Posted with permission.</p
Ionic Liquid-Assisted Sonochemical Preparation of CeO2 Nanoparticles for CO Oxidation
CeO2 nanoparticles were synthesized via a one-step ultrasound synthesis in different kinds of ionic liquids based on bis(trifluoromethanesulfonylamide, [Tf2N]â, in combination with various cations including 1-butyl-3-methylimidazolium ([C4mim]+), 1-ethyl-2,3-dimethylimidazolium ([Edimim]+), butyl-pyridinium([Py4]+), 1-butyl-1-methyl-pyrrolidinium ([Pyrr14]+), and 2-hydroxyethyl-trimethylammonium ([N1112OH]+). Depending on synthetic parameters, such as ionic liquid, Ce(IV) precursor, heating method, and precipitator, formed ceria exhibits different morphologies, varying from nanospheres, nanorods, nanoribbons, and nanoflowers. The morphology, crystallinity, and chemical composition of the obtained materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and N2 adsorption. The structural and electronic properties of the as-prepared CeO2 samples were probed by CO adsorption using IR spectroscopy under ultrahigh vacuum conditions. The catalytic activities of CeO2 nanoparticles were investigated in the oxidation of CO. CeO2 nanospheres obtained sonochemically in [C4mim][Tf2N] exhibit the best performance for low-temperature CO oxidation. The superior catalytic performance of this material can be related to its mesoporous structure, small particle size, large surface area, and high number of surface oxygen vacancy sites.Reprinted with permission from ACS Sustainable Chem. Eng., 2015, 3 (1), pp 42â54. Copyright 2015 American Chemical Society.</p
Luminescence properties of mechanochemically synthesized lanthanide containing MIL-78 MOFs
Three metalâorganic framework (MOF) compounds, Ln0.5Gd0.5{C6H3(COO)3}; Ln = Eu, Tb, and Dy with a MIL-78 structure, have been synthesized by a solvent-free mechanochemical method from stoichiometric mixtures of benzene 1,3,5-tricarboxylic acid, C6H3(COOH)3, also known as trimesic acid, and the respective lanthanide carbonates, Ln2(CO3)3·xH2O, Ln = Eu, Gd, Tb and Dy. MIL-78 (Ln0.5Gd0.5) shows the characteristic red, green, and yellow luminescence of Eu3+, Tb3+, and Dy3+, respectively. Efficient intramolecular energy transfer from the ligand triplet state to the excited states of Ln3+ ions can be observed. The lifetimes and quantum yields of these compounds are studied and discussed in detail. Among the three compounds, the Tb3+ containing compound shows the longest lifetime and highest quantum yield due to a smaller contribution from non-radiative decay pathways and better matching of the lowest triplet energy level of the benzenetricarboxylate ligand and the resonance level of Tb3+.</p
Ionic Liquid-Assisted Sonochemical Preparation of CeO<sub>2</sub> Nanoparticles for CO Oxidation
CeO<sub>2</sub> nanoparticles were synthesized via a one-step ultrasound
synthesis in different kinds of ionic liquids based on bisÂ(trifluoromethanesulfonylamide,
[Tf<sub>2</sub>N]<sup>â</sup>, in combination with various
cations including 1-butyl-3-methylimidazolium ([C<sub>4</sub>mim]<sup>+</sup>), 1-ethyl-2,3-dimethylimidazolium ([Edimim]<sup>+</sup>),
butyl-pyridiniumÂ([Py<sub>4</sub>]<sup>+</sup>), 1-butyl-1-methyl-pyrrolidinium
([Pyrr<sub>14</sub>]<sup>+</sup>), and 2-hydroxyethyl-trimethylammonium
([N<sub>1112</sub>OH]<sup>+</sup>). Depending on synthetic parameters,
such as ionic liquid, CeÂ(IV) precursor, heating method, and precipitator,
formed ceria exhibits different morphologies, varying from nanospheres,
nanorods, nanoribbons, and nanoflowers. The morphology, crystallinity,
and chemical composition of the obtained materials were characterized
by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray
photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy
(EDX), Raman spectroscopy, and N<sub>2</sub> adsorption. The structural
and electronic properties of the as-prepared CeO<sub>2</sub> samples
were probed by CO adsorption using IR spectroscopy under ultrahigh
vacuum conditions. The catalytic activities of CeO<sub>2</sub> nanoparticles
were investigated in the oxidation of CO. CeO<sub>2</sub> nanospheres
obtained sonochemically in [C<sub>4</sub>mim]Â[Tf<sub>2</sub>N] exhibit
the best performance for low-temperature CO oxidation. The superior
catalytic performance of this material can be related to its mesoporous
structure, small particle size, large surface area, and high number
of surface oxygen vacancy sites
Microwave-Assisted Synthesis of Perovskite SrSnO<sub>3</sub> Nanocrystals in Ionic Liquids for Photocatalytic Applications
Nanosized SrSnO<sub>3</sub> photocatalysts
have been successfully synthesized by microwave synthesis in various
ionic liquids (ILs) followed by a heat treatment process to optimize
the materialsâ crystallinity. The influence of the ILs with
various cations such as 1-butyl-3-methylimidazolium ([C<sub>4</sub>mim]<sup>+</sup>), 6-bisÂ(3-methylimidazolium-1-yl)Âhexane ([C<sub>6</sub>(mim)<sub>2</sub>]<sup>2+</sup>), butylpyridinium ([C<sub>4</sub>Py]<sup>+</sup>), and tetradecyltrihexylphosphonium ([P<sub>66614</sub>]<sup>+</sup>) and bisÂ(trifluoromethanesulfonyl)Âamide
([Tf<sub>2</sub>N]<sup>â</sup>) as the anion on the structure,
crystallization, and morphology of the products was investigated.
The samples were characterized by X-ray diffraction (XRD), thermogravimetry
(TG), scanning electron microscopy (SEM), surface area analysis by
gas adsorption, X-ray photoelectron spectroscopy (XPS), diffuse reflectance
UVâvis spectroscopy, and Raman and IR spectroscopy. According
to structure characterization by XRD and Raman spectroscopy all samples
crystallized phase-pure in the orthorhombic GdFeO<sub>3</sub> perovskite
structure type. SEM reveals that, on the basis of the IL, the obtained
SrSnO<sub>3</sub> nanoparticles exhibit different morphologies and
sizes. Rod-shaped particles are formed in [C<sub>4</sub>mim]Â[Tf<sub>2</sub>N], [C<sub>6</sub>(mim)<sub>2</sub>]Â[Tf<sub>2</sub>N]<sub>2</sub>, and [P<sub>66614</sub>]Â[Tf<sub>2</sub>N]. However, the particle
dimensions and size distribution vary depending on the IL and range
from quite thin and long needlelike particles with a narrow size distribution
obtained in [P<sub>66614</sub>]Â[Tf<sub>2</sub>N] to relatively larger
particles with a broader size distribution obtained in [C<sub>6</sub>(mim)<sub>2</sub>]Â[Tf<sub>2</sub>N]<sub>2</sub>. In contrast, in
[C<sub>4</sub>Py]Â[Tf<sub>2</sub>N] nanospheres with a diameter of
about 50 nm form. For these particles the highest photocatalytic activity
was observed. Our investigations indicate that the improved photocatalytic
activity of this material results from the synergistic effect of the
relatively large surface area associated with nanosize and an appropriate
energy band structure