| 1. |
- Bajnoczi, Eva G., et al.
(author)
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The influence of the local structure of Fe(III) on the photocatalytic activity of doped TiO2 photocatalysts-An EXAFS, XPS and Mossbauer spectroscopic study
- 2011
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 103:1-2, s. 232-239
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Journal article (peer-reviewed)abstract
- Fe(III)-doped TiO2 based heterogeneous photocatalysts were prepared by the sol-gel technique (S samples) or flame hydrolysis (F samples). In photocatalytic phenol decomposition, the undoped F-sample performed much better, than the undoped S one. However, for the S samples, photocatalytic activity first increased with the increasing Fe(III) concentration, and then passed through a maximum, while Fe(III)-doping in F samples significantly decreased it, even at the smallest dopant level. Since the same dopant caused opposite photocatalytic effects in the two series, their structure was systematically compared to identify the underlying chemical and/or physical reasons. The photocatalysts were first characterized by AAS, DRS, XRD and TEM methods and it has been shown that the differences in the photocatalytic activity cannot be explained by the minor variations in the bulk structural properties of TiO2. Mossbauer and XP spectroscopic measurements performed on representative samples qualitatively proved that the local structure of Fe(III) is different in the two series. To quantify these effects, Fe-K edge X-ray absorption measurements were performed. From the pre-edge and XANES region it was learnt that Fe(III) was present in a distorted octahedral environment in both series, however, the extent of distortion is much more significant within the S than within the F one. Information obtained from the EXAFS region indicated that the structure of Fe2O3 was much more ordered in the F-series then in the S one and vacancies were more abundant in the S than in the F series. Moreover, the geometry around Fe(III) systematically varied within the S-series, which could explain, why photocatalytic activity passed through a maximum with the increasing Fe(III) concentration in these samples. (C) 2011 Elsevier B.V. All rights reserved.
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| 2. |
- Csendes, Zita, et al.
(author)
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Superoxide dismutase inspired immobilised Ni(II)-protected amino acid catalysts Synthesis, characterisation, and catalytic activity
- 2014
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In: Journal of Molecular Catalysis A: Chemical. - : Elsevier BV. - 1381-1169. ; 395, s. 93-99
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Journal article (peer-reviewed)abstract
- Covalently anchored Ni(II)-C-protected amino acid (L-histidine, L-cysteine, and L-cystine) complexes inspired by the active site of the Ni-superoxide dismutase enzyme were synthesised using chloropropylated silica gel as support. The structural features of the surface complexes were studied by the Kjeldahl method and ICP-MS, mid/far IR, UV-vis diffuse reflectance, and X-ray absorption spectroscopies. The enzyme-like activities of the materials were determined in a biochemical test reaction. Covalent grafting and building the complex onto the surface of the support were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Ni(II)-complexes displayed enzyme-like activity. They also were active in the liquid-phase oxidation of cyclohexene, providing the epoxide with high selectivity. (C) 2014 Elsevier B.V. All rights reserved.
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| 3. |
- Pallagi, Attila, et al.
(author)
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Multinuclear Complex Formation between Ca(II) and Gluconate Ions in Hyperalkaline Solutions
- 2014
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In: Environmental Science & Technology. - : American Chemical Society (ACS). - 1520-5851 .- 0013-936X. ; 48:12, s. 6604-6611
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Journal article (peer-reviewed)abstract
- Alkaline solutions containing polyhydroxy carboxylates and Ca(II) are typical in cementitious radioactive waste repositories. Gluconate (Gluc(-)) is a structural and functional representative of these sugar carboxylates. In the current study, the structure and equilibria of complexes forming in such strongly alkaline solutions containing Ca2+ and gluconate have been studied. It was found that Gluc(-) significantly increases the solubility of portlandite (Ca(OH)(2)(s)) under these conditions and Ca2+ complexes of unexpectedly high stability are formed. The mononuclear (CaGluc(+) and [CaGlucOH](0)) complexes were found to be minor species, and predominant multinuclear complexes were identified. The formation of the neutral [Ca(2)Gluc(OH)(3)](0) (log beta(213) = 8.03) and [Ca(3)Gluc(2)(OH)(4)](0) (log beta(324) = 12.39) has been proven via H-2/Pt-electrode potentiometric measurements and was confirmed via XAS, H-1 NMR, ESI-MS, conductometry, and freezing-point depression experiments. The binding sites of Gluc- were identified from multinuclear NMR measurements. Besides the carboxylate group, the O atoms on the second and third carbon atoms were proved to be the most probable sites for Ca2+ binding. The suggested structure of the trinuclear complex was deduced from ab initio calculations. These observations are of relevance in the thermodynamic modeling of radioactive waste repositories, where the predominance of the binuclear Ca2+ complex, which is a precursor of various high-stability ternary complexes with actinides, is demonstrated.
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| 4. |
- Sranko, David, et al.
(author)
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Synthesis and properties of novel Ba(II)Fe(III) layered double hydroxides
- 2010
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In: Applied Clay Science. - : Elsevier BV. - 1872-9053 .- 0169-1317. ; 48:1-2, s. 214-217
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Journal article (peer-reviewed)abstract
- Double hydroxides of Ba(II) and Fe(III) were prepared by the co-precipitation method. Co-precipitation was facilitated by applying highly alkaline, carbonate free NaOH solutions with varying base concentrations (2-20 M). The substances, thus obtained, were characterised by thermal methods. XRD spectra of samples treated at various temperatures, Mossbauer and X-ray absorption spectroscopies. It was found that in extremely concentrated base solutions (>= 10 M) layered double hydroxides, most probably with intercalated OH ions, were formed, indeed, while at low base concentration the Fe(III) ions were precipitated as various oxyhydroxides and the Ba(II) ions remained dissolved. (C) 2009 Elsevier B.V. All rights reserved.
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| 5. |
- Szabados, Márton, et al.
(author)
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Effects of ultrasonic irradiation on the synthesis, crystallization, thermal and dissolution behaviour of chloride-intercalated, co-precipitated CaFe-layered double hydroxide
- 2019
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In: Ultrasonics Sonochemistry. - : Elsevier BV. - 1350-4177. ; 55, s. 165-173
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Journal article (peer-reviewed)abstract
- The output power (30–150 W) and the periodicity (20–100%) of ultrasound emission were varied in a wide range to regulate and improve the crystallization process in the commonly used co-precipitation technique of chloride-intercalated CaFe-layered double hydroxides. The influence of ultrasound irradiation on the as-prepared materials was studied by X-ray diffractometry, dynamic light scattering, UV–Vis–NIR diffuse reflectance spectroscopy, specific surface area measurement, pore size analysis, ion-selective electrode potentiometric investigations and thermogravimetry. Additionally, structural alterations due to heat treatment at various temperatures were followed in detail by Fourier-transform infrared and X-ray absorption spectroscopies as well as scanning electron microscopy. The ultrasonic treatment was capable of controlling the sizes of primarily formed (from 19 nm to 30 nm) as well as the aggregated (secondary) particles (between 450 nm and 700 nm), and thus modifying their textural parameters and enhancing the incorporation of chloride anions into the interlamellar space. For the first time, the optical energy gap of CaFe-LDH was reported here depending on the nature of applied stirring (4.18–4.34 eV). The heat-treatment investigations revealed that the layered structure was stabile until 200 °C, even at the atomic level.
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| 6. |
- Szabados, Márton, et al.
(author)
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Synthesis of high-quality, well-characterized CaAlFe-layered triple hydroxide with the combination of dry-milling and ultrasonic irradiation in aqueous solution at elevated temperature
- 2016
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In: Ultrasonics Sonochemistry. - : Elsevier BV. - 1350-4177. ; 32, s. 173-180
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Journal article (peer-reviewed)abstract
- The combination of mechanochemical and ultrasonic treatment was applied to synthesize CaAlFe-layered triple hydroxides with carbonate or chloride anions in the interlamellar space. The optimal parameters of the preparation were explored by altering the initial ratio of the metal ions and the temperature of ultrasonic irradiation. The resulting triple hydroxides were characterized by X-ray diffractometry, infrared and X-ray absorption spectroscopies, thermogravimetric analysis and scanning electron microscopy. The products were close-to-phase-pure CaAlFe-layered triple hydroxides. Elevation of the temperature transformed the CaAlFe-Cl--layered triple hydroxide to rare oxyhalides (Ca2FeO3Cl and Ca12Al14O32Cl2).
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| 7. |
- Szabados, Márton, et al.
(author)
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Ultrasonically-enhanced preparation, characterization of CaFe-layered double hydroxides with various interlayer halide, azide and oxo anions (CO3 2−, NO3 −, ClO4 −)
- 2018
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In: Ultrasonics Sonochemistry. - : Elsevier BV. - 1350-4177. ; 40, s. 853-860
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Journal article (peer-reviewed)abstract
- An ultrasonically-enhanced mechanochemical method was developed to synthesize CaFe-layered double hydroxides (LDHs) with various interlayer anions (CO3 2−, NO3 −, ClO4 −, N3 −, F−, Cl−, Br− and I−). The duration of pre-milling and ultrasonic irradiation and the variation of synthesis temperature in the wet chemical step were investigated to obtain the optimal parameters of preparation. The main method to characterize the products was X-ray diffractometry, but infrared and synchrotron-based X-ray absorption spectroscopies as well as thermogravimetric measurements were also used to learn about fine structural details. The synthesis method afforded successful intercalation of the anions, among others the azide anion, a rarely used counter ion providing a system, which enables safe handling the otherwise highly reactive anion. The X-ray absorption spectroscopic measurements revealed that the quality of the interlayered anions could modulate the spatial arrangement of the calcium ions around the iron(III) ions, but only in the second coordination sphere.
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| 8. |
- Varga, Gabor, et al.
(author)
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Bioinspired covalently grafted Cu(II)-C protected amino acid complexes: selective catalysts in the epoxidation of cyclohexene
- 2015
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In: Reaction Kinetics, Mechanisms and Catalysis. - : Springer Science and Business Media LLC. - 1878-5204 .- 1878-5190. ; 115:1, s. 33-43
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Journal article (peer-reviewed)abstract
- In this work, the syntheses of covalently grafted C-protected Cu(II)-amino acid (methylesters of l-histidine and l-cystine) uniform and mixed ligand complexes with two different amino acid esters are described using chloropropylated silica gel as the support. The conditions of the syntheses were systematically altered. The structural features of the substances obtained were studied by the Kjeldahl method, ICP-MS, X-ray absorption and mid/far infrared spectroscopies. The superoxide dismutase-like activities of the materials were determined in a biochemical test reaction and these substances were also tested as catalysts in the oxidation of cyclohexene. It was possible to prepare metal ion-amino acid complexes grafted with covalent bonds onto the supports. All the covalently anchored materials displayed superoxide dismutase-like activity and most of them were active in the oxidation of cyclohexene, providing the epoxide with high selectivity.
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| 9. |
- Varga, Gábor, et al.
(author)
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Cu(II)-amino acid–CaAl-layered double hydroxide complexes, recyclable, efficient catalysts in various oxidative transformations
- 2016
-
In: Journal of Molecular Catalysis A: Chemical. - : Elsevier BV. - 1381-1169. ; 423, s. 49-60
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Journal article (peer-reviewed)abstract
- Intercalated composite materials were prepared with CaAl-layered double hydroxide as host and Cu(II)-amino acid (L-cysteine, L-histidine and L-tyrosine) complex anions as guests. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the synthesis conditions were performed to obtain composites having the complex exclusively among the layers. The composite materials were structurally characterized by powder X-ray diffractometry, mid infrared (IR) spectroscopy with ATR (attenuated total reflectance) or photoacoustic detections, transmission and scanning electron microscopies and X-ray photoelectron spectroscopy. Structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR (electron paramagnetic spectroscopy), X-ray absorption and far IR spectroscopies. Structural models based on these methods are also given. Catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants in the liquid phase. The catalysts were active in the Ullmann coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities.
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| 10. |
- Varga, Gabor, et al.
(author)
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Fe-amino acid complexes immobilized on silica gel as active and highly selective catalysts in cyclohexene epoxidation
- 2015
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In: Research on Chemical Intermediates. - : Springer Science and Business Media LLC. - 0922-6168 .- 1568-5675. ; 41:12, s. 9155-9169
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Journal article (peer-reviewed)abstract
- In this work, the syntheses, structure, superoxide dismutase (SOD) activity, and the catalytic use in the oxidative transformations of cyclohexene of covalently grafted Fe(III)-complexes formed with various or various combinations of C-protected amino acid (l-histidine, l-tyrosine, l-cysteine and l-cystine) ligands are presented. The structural features of the surface complexes were studied by XANES/EXAFS and mid/far-IR spectroscopies. The compositions of the complexes were determined by ICP-MS and the Kjeldahl method. The SOD activities of the materials were evaluated in a biochemical test reaction. The obtained materials were used as catalysts for the oxidation of cyclohexene with peracetic acid in acetone. Both covalent grafting and building the complex onto the surface of the chloropropylated silica gel were successful in most cases. In many instances, the obtained structures and the coordinating groups were found to substantially vary upon changing the conditions of the syntheses. All the covalently immobilized Fe(III)-complexes displayed SOD activities, and most of them were found to be capable of catalyzing the oxidation of cyclohexene with appreciably high activities and outstanding epoxide selectivities.
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| 11. |
- Varga, Gábor, et al.
(author)
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Mn(II)-amino acid complexes intercalated in CaAl-layered double hydroxide - Well-characterized, highly efficient, recyclable oxidation catalysts
- 2016
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In: Journal of Catalysis. - : Elsevier BV. - 0021-9517. ; 335, s. 125-134
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Journal article (peer-reviewed)abstract
- Intercalated composite materials were prepared with CaAl-layered double hydroxide as the host and Mn(II)-amino acid (l-cysteine, l-histidine and l-tyrosine) complex anions as the guest. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the auxiliary conditions were performed to arrive at composites having the complex exclusively among the layers. The obtained substances were structurally characterized by powder X-ray diffractometry, mid IR spectroscopy in diffuse reflectance mode and with ATR or photoacoustic detections, and scanning electron microscopy. The structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR, X-ray absorption and far IR spectroscopies. Structural models are also given. The catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants and allylic alcohol with peracetic acid, in the liquid phase. The intercalated substances proved to be efficient and highly selective (with peracetic acid: outstanding epoxide, with iodosylbenzene superior diol selectivities) catalysts with very good recycling abilities.
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| 12. |
- Varga, Gábor, et al.
(author)
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Ni-Amino Acid–CaAl-Layered Double Hydroxide Composites : Construction, Characterization and Catalytic Properties in Oxidative Transformations
- 2017
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In: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 60:17-18, s. 1429-1438
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Journal article (peer-reviewed)abstract
- Host–guest composite materials were prepared applying the anionic forms of Ni(II)-amino acid (l-histidine, l-cysteine, and l-tyrosine) as the guests and CaAl-layered double hydroxide (CaAl-LDH) as the host. The syntheses were performed either by introducing the amino acid anions first and then constructing the metal ion–amino acid complexes or intercalating the pre-prepared complexes in anionic forms. The pristine as well as the composite LDH samples were structurally characterized by X-ray diffractometry, mid IR spectroscopy and scanning electron microscopy. The structural features of the interlayer complexes were studied by UV–Vis, inductively coupled plasma optical emission, mid and far IR and X-ray absorption spectroscopies as well as energy-dispersed X-ray analysis. On the basis of the acquired data, structural models were constructed. The composites were applied as catalysts in the liquid-phase oxidation of cyclohexene applying peracetic acid and the in situ formed iodosyl benzene as oxidants. Using peracetic acid afforded epoxide, while applying iodosyl benzene provided cis diol as the major or exclusive oxidation product. The catalysts displayed good recycling properties.
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| 13. |
- Varga, Gábor, et al.
(author)
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Syntheses, characterization and catalytic activities of CaAl-layered double hydroxide intercalated Fe(III)-amino acid complexes
- 2018
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In: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 306, s. 42-50
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Journal article (peer-reviewed)abstract
- Synthesis of intercalated composites were carried out using CaAl-LDH (layered double hydroxide) as host and the anionic form of Fe(III)-amino acid complexes as guest materials. Intercalation was attempted with two methods either introducing the preformed complexes or constructing the complex among the layers of the LDH. After optimization of the synthesis parameters, structural characterization was performed by X-ray diffractometry, scanning electron microscopy as well as mid and far infrared spectroscopies. Quantitative data about the intercalated complexes were collected by chemical analysis and X-ray absorption spectroscopy investigating the near edge region as well as the extended fine structure. Structural models based on characterization measurements are also given. Catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and . in situ formed iodosylbenzene as oxidants in the liquid phase. The catalysts were active in the Ullmann-type etherification coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities.
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