| 1. |
- Adnan, Mohammed Mostafa, et al.
(författare)
-
The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO2
- 2021
-
Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 13:9
-
Tidskriftsartikel (refereegranskat)abstract
- Epoxy nanocomposites have demonstrated promising properties for high-voltage insulation applications. An in situ approach to the synthesis of epoxy-SiO2 nanocomposites was employed, where surface-functionalized SiO2 (up to 5 wt.%) is synthesized directly in the epoxy. The dispersion of SiO2 was found to be affected by both the pH and the coupling agent used in the synthesis. Hierarchical clusters of SiO2 (10–60 nm) formed with free-space lengths of 53–105 nm (increasing with pH or SiO2 content), exhibiting both mass and surface-fractal structures. Reducing the amount of coupling agent resulted in an increase in the cluster size (~110 nm) and the free-space length (205 nm). At room temperature, nanocomposites prepared at pH 7 exhibited up to a 4% increase in the real relative permittivity with increasing SiO2 content, whereas those prepared at pH 11 showed up to a 5% decrease with increasing SiO2 content. Above the glass transition, all the materials exhibited low-frequency dispersion effect resulting in electrode polarization, which was amplified in the nanocomposites. Improvements in the dielectric properties were found to be not only dependent on the state of dispersion, but also the structure and morphology of the inorganic nanoparticles.
|
|
| 2. |
- Aleksis, Rihards, et al.
(författare)
-
Artefact-free broadband 2D NMR for separation of quadrupolar and paramagnetic shift interactions
- 2019
-
Ingår i: Solid State Nuclear Magnetic Resonance. - : Elsevier BV. - 0926-2040 .- 1527-3326. ; 101, s. 51-62
-
Tidskriftsartikel (refereegranskat)abstract
- Two new two-dimensional, broadband, solid-state NMR experiments for separating and correlating the quadrupolar and shift interactions of spin I = 1 nuclei in paramagnetic systems are proposed. The new pulse sequences incorporate the short, high-power adiabatic pulses (SHAPs) into the shifting d-echo experiment of Walder et al. [J. Chem. Phys., 142, 014201 (2015)], in two different ways, giving double and quadruple adiabatic shifting d-echo sequences. These new experiments have the advantage over previous methods of both suppressing spectral artefacts due to pulse imperfections, and exhibiting a broader excitation bandwidth. Both experiments are analysed with theoretical calculations and simulations, and are applied experimentally to the H-2 NMR of deuterated CuCl2 center dot 2H(2)O, and two deuterated samples of the ion conductor oxyhydride BaTiO3-xHy prepared using two different methods. For the CuCl2 center dot 2H(2)O sample, both new methods obtain very high-quality spectra from which the parameters describing the shift and quadrupolar interaction tensors, and their relative orientation, were extracted. The two BaTiO3-xHy samples exhibited different local hydride environments with different tensor parameters. The H-2 spectra of these oxyhydrides exhibit inhomogeneous broadening of the H-2 shifts, and so whilst the quadrupolar interaction parameters were easily extracted, the measurement of the shift parameters was more complex. However, effective shift parameters were extracted, which combine the effects of both the paramagnetic shift tensor and the inhomogeneous broadening.
|
|
| 3. |
- Aleksis, Rihards, et al.
(författare)
-
Probing the electronic structure and hydride occupancy in barium titanium oxyhydride through DFT-assisted solid-state NMR
- 2022
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 24:46, s. 28164-28173
-
Tidskriftsartikel (refereegranskat)abstract
- Perovskite-type oxhydrides such as BaTiO3−xHy exhibit mixed hydride ion and electron conduction and are an attractive class of materials for developing energy storage devices. However, the underlying mechanism of electric conductivity and its relation to the composition of the material remains unclear. Here we report detailed insights into the hydride local environment, the electronic structure and hydride conduction dynamics of barium titanium oxyhydride. We demonstrate that DFT-assisted solid-state NMR is an excellent tool for differentiating between the different feasible electronic structures in these solids. Our results indicate that upon reduction of BaTiO3 the introduced electrons are delocalized among all Ti atoms forming a bandstate. Furthermore, each vacated anion site is reoccupied by at most a single hydride, or else remains vacant. This single occupied bandstate structure persists at different hydrogen concentrations (y = 0.13–0.31) and a wide range of temperatures (∼100–300 K).
|
|
| 4. |
- Berniak, Tomasz, et al.
(författare)
-
Covalent bonding of N-hydroxyphthalimide on mesoporous silica for catalytic aerobic oxidation of p-xylene at atmospheric pressure
- 2024
-
Ingår i: ChemPlusChem. - 2192-6506.
-
Tidskriftsartikel (refereegranskat)abstract
- The surface of SBA-15 mesoporous silica was modified by N-hydroxyphthalimide (NHPI) moieties acting as immobilized active species for aerobic oxidation of alkylaromatic hydrocarbons. The incorporation was carried out by four original approaches: the grafting-from and grafting-onto techniques, using the presence of surface silanols enabling the formation of particularly stable O-Si-C bonds between the silica support and the organic modifier. The strategies involving the Heck coupling led to the formation of NHPI groups separated from the SiO2 surface by a vinyl linker, while one of the developed modification paths based on the grafting of an appropriate organosilane coupling agent resulted in the active phase devoid of this structural element. The successful course of the synthesis was verified by FTIR and H-1 NMR measurements. Furthermore, the formed materials were examined in terms of their chemical composition (elemental analysis, thermal analysis), structure of surface groups (C-13 NMR, XPS), porosity (low-temperature N-2 adsorption), and tested as catalysts in the aerobic oxidation of p-xylene at atmospheric pressure. The highest conversion and selectivity to p-toluic acid were achieved using the catalyst with enhanced availability of non-hydrolyzed NHPI groups in the pore system. The catalytic stability of the material was additionally confirmed in several subsequent reaction cycles.
|
|
| 5. |
- Brant, William, et al.
(författare)
-
Selective Control of Composition in Prussian White for Enhanced Material Properties
- 2019
-
Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 31:18, s. 7203-7211
-
Tidskriftsartikel (refereegranskat)abstract
- Sodium-ion batteries based on Prussian blue analogues (PBAs) are ideal for large-scale energy storage applications due to the ability to meet the huge volumes and low costs required. For Na2-xFe[Fe(CN)(6)](1-y)center dot zH(2)O, realizing its commercial potential means fine control of the concentration of sodium, Fe(CN)(6) vacancies, and water content. To date, there is a huge variation in the literature of composition leading to variable electrochemical performance. In this work, we break down the synthesis of PBAs into three steps for controlling the sodium, vacancy, and water content via an inexpensive, scalable synthesis method. We produce rhombohedral Prussian white Na1.88(5)Fe[Fe-(CN)(6)]center dot 0.18(9)H2O with an initial capacity of 158 mAh/g retaining 90% capacity after 50 cycles. Subsequent characterization revealed that the increased polarization on the 3 V plateau is coincident with a phase transition and reduced utilization of the high-spin Fe(III)/Fe(II) redox couple. This reveals a clear target for subsequent improvements of the material to boost long-term cycling stability. These results will be of great interest for the myriad of applications of PBAs, such as catalysis, magnetism, electrochromics, and gas sorption.
|
|
| 6. |
- Budnyak, Tetyana, et al.
(författare)
-
LignoPhot : Conversion of hydrolysis lignin into the photoactive hybrid lignin/Bi4O5Br2/BiOBr composite for simultaneous dyes oxidation and Co2+ and Ni2+ recycling
- 2021
-
Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 279
-
Tidskriftsartikel (refereegranskat)abstract
- Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We demonstrate the synthesis of photoactive lignin/Bi4O5Br2/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by semiconducting nanosheets. The XPS analysis reveals that growing these nanosheets on lignin instead on cellulose prevents the formation of Bi5+ ions at the surface region, yielding thus a modified hetero-junction Bi4O5Br2/BiOBr. The material contains 18.9% of Bi4O5Br2/BiOBr and is effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under light irradiation. Lignin/Bi4O5Br2/BiOBr decreases the dye concentration from 80 mg L-1 to 12.3 mg L-1 for RhB (85%) and from 80 mg L-1 to 4.4 mg L-1 for MB (95%). Complementary to the dye degradation, the lignin as a main component of the composite, was found to be efficient and rapid biosorbent for nickel, lead, and cobalt ions. The low cost, stability and ability to simultaneously photo-oxidize organic dyes and adsorb metal ions, make the photoactive lignin/Bi4O5Br2/BiOBr composite a prospective material for textile wastewaters remediation and metal ions recycling.
|
|
| 7. |
- Budnyak, Tetyana M., et al.
(författare)
-
Chitosan Deposited onto Fumed Silica Surface as Sustainable Hybrid Biosorbent for Acid Orange 8 Dye Capture : Effect of Temperature in Adsorption Equilibrium and Kinetics
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:28, s. 15312-15323
-
Tidskriftsartikel (refereegranskat)abstract
- Chitosan was deposited on fumed silica without the addition of cross-linkers or activating agents. The chitosan surface layer has a high affinity toward organic molecules, e.g., Acid Orange 8 (AO8) dye, robust to a broad range of simulated conditions (variance with respect to temperature, time, and concentration of solute). Experimental equilibrium data were analyzed by the generalized Langmuir equation taking into consideration the energetic heterogeneity of the adsorption system. The effect of temperature on dye uptake and adsorption rate was studied. According to the calculated thermodynamic functions Delta G degrees, Delta H degrees, and Delta S degrees from the equilibrium data at different temperatures, the adsorption of AO8 onto chitosan-fumed silica composite is exothermic and spontaneous. The studies of temperature effect on adsorption equilibrium show that the maximum adsorption capacity (determined from the Langmuir-Freundlich equation) of synthesized composite toward AO8 is about one-third higher in the case of an isotherm measured at 5 degrees C than this value obtained for the isotherm measured at 45 degrees C. The quantitative binding of dye molecules to chitosan coating on the surface of silica was proved by H-1 MAS NMR. The deep kinetics study through the application of various theoretical models-the first-order equation, pseudo-first-order equation, second-order equation, pseudo-second-order equation, mixed first, second-order equation, and multiexponential equation-was applied for getting inside the mechanism of AO8 binding to the chitosan coating. Structural characteristics of chitosan-coated silica were obtained from the low-temperature adsorption/desorption isotherms of nitrogen and imaging by scanning electron microscopy. The effects of a synthetic route for polymer coating on thermal stability and the ability to degrade were studied by differential scanning calorimetry.
|
|
| 8. |
- Budnyak, Tetyana M., et al.
(författare)
-
Tailored Hydrophobic/Hydrophilic Lignin Coatings on Mesoporous Silica for Sustainable Cobalt(II) Recycling
- 2020
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 8:43, s. 16262-16273
-
Tidskriftsartikel (refereegranskat)abstract
- Lignin is a renewable biopolymer, and its chemical functionalization renders it a prospective material for a plethora of applications. Within this respect, we present a method for lignin immobilization on the surface of mesoporous silica. Two types of lignins were used to prove the feasibility of the fabrication of either hydrophilic or hydrophobic biocoatings on silica. The procedure permits to immobilize 17 mg of lignosulfonate (LS) or 37 mg of kraft lignin (KL) per gram of silica. The bioinorganic composites display a synergistic effect in the adsorption of cobalt(II) ions from aqueous solutions because the adsorption efficiency outperforms the individual constituents. These results demonstrate that thin lignin overlayers, exhibiting polymer concentrations of 0.07 mg.m(-2) for LS-SiO2, and 0.14 mg.m(-2) for KL-SiO2, provide new functionality in comparison to bulk lignin and metal oxides. According to the Langmuir isotherm model, the adsorption capacity toward aqua complexes of Co(II) was found to be 75 and 59 mg.g(-1) for the LS- or KL-coated silica, respectively. The kinetic study revealed that lignin-SiO2 composites gained the features of inorganic sorbents because 1-1.5 h was sufficient for effective cobalt extraction. The adsorption on the bioinorganic composites proceeds with the pseudo-second-order kinetics model. The adsorption of Co(II) ions was confirmed by means of solid-state H-1 magic-angle spinning (MAS) NMR spectroscopy. The simplicity of the synthesis, low-cost and abundancy of substrates, high capacity, and fast kinetics make such lignin-coated silica a promising material for cobalt recovery.
|
|
| 9. |
- Carretero Cerdan, Alba, et al.
(författare)
-
One-step microwave-assisted synthesis of amino-functionalized chromium(III) terephthalate MIL-101-NH2
- 2023
-
Ingår i: Materials Today Chemistry. - 2468-5194. ; 31
-
Tidskriftsartikel (refereegranskat)abstract
- A single-step microwave (MW)-assisted protocol for the synthesis of MIL-101(Cr) and of MIL-101(Cr)-NH2 is described herein, based on the addition of NaF as the modulator instead of hydrofluoric acid to obtain the corresponding polymers in only 1 h with high crystallinity and yields (>70%, 0.5 g). Compared to classic solvothermal protocols (12-72 h, <30%), MW-assisted synthesis allowed shorter reaction time and improved yields, replacing N,N-dimethylformamide by water. Physicochemical properties of MIL-101(Cr)-NH2 and MIL-101(Cr) obtained through this MW-assisted procedure are more homogenous than those observed for the corresponding solvothermal counterparts, and interestingly, enhanced higher control over nanometric particle size (80-130 vs 400-1000 nm), lower polydispersity, and higher Brunauer-Emett-Teller surface area (2000-2700 vs 1800-2300 m2/g) were observed because of the better accessibility and diffusion of gases throughout the internal pores.& COPY; 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
|
|
| 10. |
- Carvalho, José P., et al.
(författare)
-
Separation of quadrupolar and paramagnetic shift interactions with TOP-STMAS/MQMAS in solid-state lighting phosphors
- 2020
-
Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 58:11, s. 1055-1070
-
Tidskriftsartikel (refereegranskat)abstract
- A new approach for processing satellite-transition magic-angle spinning(STMAS) and multiple-quantum magic-angle spinning (MQMAS) data, basedon the two-dimensional one-pulse (TOP) method, which separates thesecond-rank quadrupolar anisotropy and paramagnetic shift interactions viaa double shearing transformation, is described. This method is particularlyrelevant in paramagnetic systems, where substantial inhomogeneous broadeningmay broaden the lineshapes. Furthermore, it possesses an advantage overthe conventional processing of MQMAS and STMAS spectra because it overcomesthe limitation on the spectral width in the indirect dimension imposedby rotor synchronization of the sampling interval. This method was appliedexperimentally to the 27Al solid-state nuclear magnetic resonance of a seriesof yttrium aluminum garnets (YAGs) doped with different lanthanide ions,from which the quadrupolar parameters of paramagnetically shifted and bulkunshifted sites were extracted. These parameters were then compared withdensity functional theory calculations, which permitted a better understandingof the local structure of Ln substituent ions in the YAG lattice.
|
|
