| 1. |
- Abebe, Mihret, et al.
(författare)
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Spherical and Porous Particles of Calcium Carbonate Synthesized with Food Friendly Polymer Additives
- 2015
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 15:8, s. 3609-3616
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Tidskriftsartikel (refereegranskat)abstract
- Porous calcium carbonate particles were synthesized by adding solutions of Ca2+ to solutions of CO32- containing polymeric additives. Under optimized conditions well-defined aggregates of the anhydrous polymorph vaterite formed. A typical sample of these micrometer-sized aggregates had: a pore volume of 0.1 cm(3)/g, a pore width of similar to 10 nm, and a specific surface area of similar to 25-30 m(2)/ g. Only one mixing Order (calcium to carbonate) allowed the formation of vaterite, which was ascribed to the buffering capacity and relatively high pH of the CO32- solution. Rapid addition of the calcium chloride solution and rapid stirring promoted the formation of vaterite, due to the high supersaturation levels achieved. With xanthan gum, porous and micrometer-sized vaterite aggregates could be synthesized over a wide range of synthetic conditions. For the Other food grade polymers, hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and sodium carboxyl methylcellulose, several intensive and extensive synthetic parameters had to be optimized to obtain pure vaterite and porous aggregates. HPMC and MC allowed well-defined spherical micrometer-sited particles to form. We expect that these spherical and porous particles of vaterite could be relevant to model studies as well as a controlled delivery of particularly large molecules.
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| 2. |
- Asfaw, Habtom D., et al.
(författare)
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Boosting the thermal stability of emulsion–templated polymers via sulfonation : an efficient synthetic route to hierarchically porous carbon foams
- 2016
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Ingår i: ChemistrySelect. - : Wiley. - 2365-6549. ; 1:4, s. 784-792
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchically porous carbon foams with specific surface areas exceeding 600 m2 g−1 can be derived from polystyrene foams that are synthesized via water-in-oil emulsion templating. However, most styrene-based polymers lack strong crosslinks and are degraded to volatile products when heated above 400 oC. A common strategy employed to avert depolymerization is to introduce potential crosslinking sites such as sulfonic acids by sulfonating the polymers. This article unravels the thermal and chemical processes leading up to the conversion of sulfonated high internal phase emulsion polystyrenes (polyHIPEs) to sulfur containing carbon foams. During pyrolysis, the sulfonic acid groups (-SO3H) are transformed to sulfone (-C-SO2-C-) and then to thioether (-C−S-C-) crosslinks. These chemical transformations have been monitored using spectroscopic techniques: in situ IR, Raman, X-ray photoelectron and X-ray absorption near edge structure spectroscopy. Based on thermal analyses, the formation of thioether links is associated with increased thermal stability and thus a substantial decrease in volatilization of the polymers.
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| 3. |
- Atluri, Rambabu, et al.
(författare)
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Self-Assembly Mechanism of Folate-Templated Mesoporous Silica
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:38, s. 12003-12012
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Tidskriftsartikel (refereegranskat)abstract
- A method to form ordered mesoporous silica based on the use of folate supramolecular templates has been developed. Evidence based on in situ small-angle X-ray scattering (SAXS), electron microscopy, infrared spectroscopy, and in situ conductivity measurements are used to investigate the organic inorganic interactions and synthesis mechanism. The behavior of folate molecules in solution differs distinctively from that of surfactants commonly used for the preparation of ordered mesoporous silica phases, notably with the absence of a critical micellar concentration. In situ SAXS studies reveal fluctuations in X-ray scattering intensities consistent with the condensation of the silica precursor surrounding the folate template and the growth of the silica mesostructure in the initial stages. High-angle X-ray diffraction shows that the folate template is well-ordered within the pores even after a few minutes of synthesis. Direct structural data for the self-assembly of folates into chiral tetramers within the pores of mesoporous silica provide evidence for the in register stacking of folate tetramers, resulting in a chiral surface of rotated tetramers, with a rotation angle of 30 degrees. Additionally, the self-assembled folates within pores were capable of adsorbing a considerable amount of CO2 gas through the cavity space of the tetramers. The study demonstrates the validity of using a naturally occurring template to produce relevant and functional mesoporous materials.
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| 4. |
- Atluri, Rambabu, et al.
(författare)
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Structural variations in mesoporous materials with cubic Pm(3)over-barn symmetry
- 2010
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 133:1-3, s. 27-35
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Tidskriftsartikel (refereegranskat)abstract
- The fine structural details of mesoporous materials possessing Pmn symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity–windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity–windows. Results support that whilst attainment of Pmn cubic packing is due to the overall surfactant geometry, the formation of cavity–windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall. The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.
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| 5. |
- Atluri, Rambabu, 1981-, et al.
(författare)
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Structural variations in mesoporous materials with cubic Pm3n symmetry
- 2010
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 133:1-3, s. 27-35
-
Tidskriftsartikel (refereegranskat)abstract
- The fine structural details of mesoporous materials possessing Pm3n symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity-windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity-windows. Results support that whilst attainment of Pm3n cubic packing is due to the overall surfactant geometry, the formation of cavity-windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall. The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.
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| 6. |
- Aziz, Baroz, 1980-, et al.
(författare)
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Quantification of chemisorption and physisorption of carbon dioxide on porous silica modified by propylamines : Effect of amine density
- 2012
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 159, s. 42-49
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Tidskriftsartikel (refereegranskat)abstract
- Detailed molecular aspects of carbon dioxide sorption on porous silica with different amounts of tethered and cross-linked n-propylamine groups were investigated. Infrared spectroscopy was applied to directly quantify physisorbed and chemisorbed CO2 on the amine modified silicas. The fractions of physisorbed CO2 and various chemisorbed species were determined as functions of CO2 pressure and the amine density on the modified silica. Physisorbed CO2 was a minor portion of the total CO2 uptake at low pressures, but it’s contribution increased to ∼35% at 1 bar of CO2 when the propylamine surface density was low or medium (0.87-1.67 NH2/nm2). Chemisorption of CO2 dominated when the propylamine content was high (2.74 NH2/nm2). The quantities of propylammonium propylcarbamate ion pairs increased with increasing propylamine content. At low or medium amine surface densities (0.87-1.67 NH2/nm2) this increase was approximately proportional to the amine density, but the quantity of ion pairs increased very significantly when the propylamine content was high (2.74 NH2/nm2). This dependency on amine density is consistent with the idea that a sufficiently close proximity of propylamine groups allows a formation of ion pairs. The relative fractions of carbamic acid and silylpropylcarbamate were significant for materials on which ion pairs could not form. Furthermore, the quantities of carbamic acid increased with increasing amine densities suggesting that the ion pairs have a role to stabilize the labile carbamic acid through hydrogen bonds.
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| 7. |
- Bacsik, Zoltán, et al.
(författare)
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Adsorption of Carbonyl Sulfide on Propylamine Tethered to Porous Silica
- 2018
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 34:26, s. 7708-7713
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Tidskriftsartikel (refereegranskat)abstract
- Carbonyl sulfide (COS) reacts slowly with amines in the aqueous solutions used to absorb CO2 from natural gas and flue gas and can also deactivate certain aqueous amines. The effects of COS on amines tethered to porous silica, however, have not been investigated before. Hence, the adsorption of COS on aminopropyl groups tethered to porous silica was studied using in situ IR spectroscopy. COS chemisorbed mainly and reversibly as propylammonium propylthiocarbamate ion pairs [R-NH(C= O)S- +H3N-R] under dry conditions. In addition, a small amount of another chemisorbed species formed slowly and irreversibly. Nevertheless, the CO2 capacities of the adsorbents were fully retained after COS was desorbed.
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| 8. |
- Bacsik, Zoltan, et al.
(författare)
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Ammonium-Carbamate-Rich Organogels for the Preparation of Amorphous Calcium Carbonates
- 2017
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Ingår i: Minerals. - : MDPI AG. - 2075-163X. ; 7:7
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Tidskriftsartikel (refereegranskat)abstract
- Amine-CO2 chemistry is important for a range of different chemical processes, including carbon dioxide capture. Here, we studied how aspects of this chemistry could be used to prepare calcium carbonates. Chemically crosslinked organogels were first prepared by reacting hyperbranched polyethylene imine (PEI) dissolved in DMSO with carbon dioxide. The crosslinks of the organogel consisted of ammonium-carbamate ion pairs as was shown by IR spectroscopy. These carbamate-rich organogels were subsequently subjected to aqueous solutions of calcium acetate, and amorphous calcium carbonate (ACC) precipitated. The ACC did not crystalize during the mixing for up to 20 h, as was shown by a combination of IR spectroscopy, X-ray diffraction, scanning electron microscopy, and thermal analysis. Some PEI had been included or adsorbed on the ACC particles. Traces of calcite were observed in one sample that had been subjected to water in a work-up procedure.
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| 9. |
- Bacsik, Zoltan, et al.
(författare)
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Effects of carbon dioxide captured from ambient air on the infrared spectra of supported amines
- 2016
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Ingår i: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031 .- 1873-3697. ; 87, s. 215-221
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Tidskriftsartikel (refereegranskat)abstract
- Amino groups in highly dense coatings of amines on solid supports react with CO2 of ambient air and form ammonium-carbamate ion pairs. These ion pairs change the properties of the amine-modified supports. In numerous studies, the corresponding infrared (IR) spectra have been misinterpreted. The presumption has been that such ion pairs would not form in ambient air, and therefore IR bands have been assigned to moieties of the support and the amines. Here, we discuss common misunderstandings of the IR spectra of amine-modified supports and highlight that proper sample handling is necessary before employing different characterization techniques. We exemplify by performing an IR spectroscopic study of a propylamine-modified porous silica. Such amine-modified supports are relevant to applications in gas separation, catalysis, controlled drug delivery and adsorption of pollutants from water.
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| 10. |
- Bacsik, Zoltan, et al.
(författare)
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Mechanisms and Kinetics for Sorption of CO(2) on Bicontinuous Mesoporous Silica Modified with n-Propylamine
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:17, s. 11118-11128
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Tidskriftsartikel (refereegranskat)abstract
- We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.
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| 11. |
- Bacsik, Zoltan, et al.
(författare)
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Selective separation of CO2 and CH4 for biogas upgrading on zeolite NaKA and SAPO-56
- 2016
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 162, s. 613-621
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Tidskriftsartikel (refereegranskat)abstract
- Several commercial and potential adsorbents were investigated for the separation of CO2 from CH4, which is relevant for the upgrading of raw biogas. The main focus of the paper was on the working capacities and selectivities of the adsorbents for a generic vacuum swing adsorption (VSA) process. Zeolites 4A and 13X had good estimated CO2-over-CH4 selectivities and reasonably high working capacities for the removal of CO2. A variant of zeolite A - vertical bar Na12-Kx vertical bar-LTA (with 1.8 <= x <= 3.2), had at least the same working capacity as zeolite 4A but with a significantly improved selectivity. Hence, the environmentally important CH4 slip can be minimized with this vertical bar Na12-Kx vertical bar-LTA sorbent. If a high working capacity for CO2 removal is the most important characteristic for a VSA process, then silicoaluminum phosphate, specifically SAPO-56, appeared to be the best candidate among the studied sorbents. In addition, SAPO-56 had a substantially high estimated CO2-over-CH4 selectivity with a value between similar to 20 and 30.
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| 12. |
- Bacsik, Zoltan, et al.
(författare)
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Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:12, s. 10013-10024
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption-mediated CO2 separation can reduce the costs of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO2 sorption and high CO2-over-N2 selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO2 adsorption in such materials, we studied mesocaged (cubic, Pm3n symmetry) silica adsorbents with tethered propylamines using Fourier transform infrared (FTIR) spectroscopy and volumetric uptake experiments. The degree of heterogeneity in these coatings was varied by either co-synthesizing or post-synthetically introducing the propylamine modification. In situ FTIR spectroscopy revealed the presence of both physisorbed and chemisorbed CO2 in the materials. We present the first direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO2-over-N2 selectivity in amine-rich sorbents. Samples with homogenous coatings showed typical CO2 adsorption trends and large quantities of IR-observable physisorbed CO2. The uptake of CO2 in mesocaged materials with heterogeneous propylamine coatings was higher at high temperatures than at low temperatures. At higher temperatures and low pressures, the post-synthetically modified materials adsorbed more CO2 than did the extracted ones, even though the surface area after modification was clearly reduced and the coverage of primary amine groups was lower. The principal mode of CO2 uptake in post-synthetically modified mesoporous silica was chemisorption. The chemisorbed moieties were present mainly as carbamate–ammonium ion pairs, resulting from the quantitative transformation of primary amine groups during CO2 adsorption as established by NIR spectroscopy. The heterogeneity in the coatings promoted the formation of these ion pairs. The average propylamine–propylamine distance must be small to allow the formation of carbamate–propylammonium ion pairs.
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| 13. |
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| 14. |
- Bae, Juna, et al.
(författare)
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Phase Transformation Behavior of a Two-Dimensional Zeolite
- 2019
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 58:30, s. 10230-10235
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the molecular-level mechanisms of phase transformation in solids is of fundamental interest for functional materials such as zeolites. Two-dimensional (2D) zeolites, when used as shape-selective catalysts, can offer improved access to the catalytically active sites and a shortened diffusion length in comparison with their 3D analogues. However, few materials are known to maintain both their intralayer microporosity and structure during calcination for organic structure-directing agent (SDA) removal. Herein we report that PST-9, a new 2D zeolite which has been synthesized via the multiple inorganic cation approach and fulfills the requirements for true layered zeolites, can be transformed into the small-pore zeolite EU-12 under its crystallization conditions through the single-layer folding process, but not through the traditional dissolution/recrystallization route. We also show that zeolite crystal growth pathway can differ according to the type of organic SDAs employed.
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| 15. |
- Blaschek, Leonard, et al.
(författare)
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Determining the Genetic Regulation and Coordination of Lignification in Stem Tissues of Arabidopsis Using Semiquantitative Raman Microspectroscopy
- 2020
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 8:12, s. 4900-4909
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Tidskriftsartikel (refereegranskat)abstract
- Lignin is a phenolic polymer accumulatig in the cell walls of specific plant cell types to confer unique properties such as hydrophobicity, mechanical strengthening, and resistance to degradation. Different cell types accumulate lignin with specific concentration and composition to support their specific roles in the different plant tissues. Yet the genetic mechanisms controlling lignin quantity and composition differently between the different lignified cell types and tissues still remain poorly understood. To investigate this tissue-specific genetic regulation, we validated both the target molecular structures as well as the linear semi-quantitative capacity of Raman microspectroscopy to characterize the total lignin amount, S/G ratio, and coniferyl alcohol content in situ directly in plant biopsies. Using the optimized method on stems of multiple lignin biosynthesis loss-of-function mutants revealed that the genetic regulation of lignin is tissue specific, with distinct genes establishing nonredundant check-points to trigger specific compensatory adjustments affecting either lignin composition and/or cell wall polymer concentrations.
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| 16. |
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| 17. |
- Bogár, Krisztián, et al.
(författare)
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Heterogenized Wilkinson's Catalyst for Transfer Hydrogenation of Carbonyl Compounds
- 2011
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Ingår i: European Journal of Organic Chemistry. - : Wiley-VCH Verlag GmbH 3690 & Co. KGaA, Weinheim. - 1434-193X .- 1099-0690. ; :23, s. 4409-4414
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Tidskriftsartikel (refereegranskat)abstract
- Wilkinson’s catalyst [RhCl(PPh3)3] was heterogenized on common silica by the use of a grafting/anchoring technique. The immobilized catalyst showed high activity and selectivity in transfer hydrogenation reactions of a range of carbonyl compounds in 2-propanol. Reactions carried out in 2-propanol at reflux afforded the corresponding alcohols in high yields in short reaction times. The heterogeneous feature ofthe catalyst allows for easy recovery and efficient reuse in the same reaction up to 5 times without any detectible loss of catalytic activity.
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| 18. |
- Cavalcante, Larissa Lopes, et al.
(författare)
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Analysis of fossil plant cuticles using vibrational spectroscopy: A new preparation protocol
- 2023
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Ingår i: Review of Palaeobotany and Palynology. - : Elsevier. - 0034-6667 .- 1879-0615. ; 316
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Tidskriftsartikel (refereegranskat)abstract
- Analyses for organic “fingerprints” on fossilized plant cuticles and pollen hold valuable chemotaxonomic and palaeoclimatic information, and are thus becoming more utilized by palaeobotanists. Plant cuticle and pollen composition are generally analyzed after standard treatments with several chemical reagents for mineral and mesophyll removal. However, the potential alterations on the fossil composition caused by the different cleaning reagents used are still poorly understood. We tested the effects of commonly used palaeobotanical processing methods on the spectra of fossilized cuticles from successions of Late Triassic to Early Jurassic age, including the gymnosperms Lepidopteris, Ginkgoites, Podozamites, Ptilozamites and Pterophyllum astartense. Our study shows that standard chemical processing caused chemical alterations that might lead to erroneous interpretation of the infrared (IR) spectra. The difference in pH caused by HCl induces changes in the proportion between the two bands at ~1720 and 1600 cm 1 (carboxylate and C-C stretch of aromatic compounds) indicating that the band at ~1610 cm 1 at least partially corresponds to carboxylate instead of C-C stretch of aromatic compounds. Interestingly, despite being used in high concentration, HF did not cause changes in the chemical composition of the cuticles. The most alarming changes were caused by the use of Schulze ’s solution, which resulted in the addition of both NO2 and (O)NO2 compounds in the cuticle. Consequently, a new protocol using H2CO3, HF, and H2O2 for preparing fossil plant cuticles aimed for chemical analyses is proposed, which provides an effective substitute to the conventional methods. In particular, a less aggressive and more sustainable alternative to Schulze’s solution is shown to be hydrogen peroxide, which causes only minor alteration of the fossil cuticle ’s chemical composition. Future work should carefully follow protocols, having in mind the impacts of different solutions used to treat leaves and other palaeobotanical material such as palynomorphs with aims to enable the direct comparison of spectra obtained in different studies.
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| 19. |
- Chang, Ribooga, et al.
(författare)
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Achieving Molecular Sieving of CO2 from CH4 by Controlled Dynamical Movement and Host–Guest Interactions in Ultramicroporous VOFFIVE-1-Ni by Pillar Substitution
- 2024
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Ingår i: Nano Letters. - 1530-6984 .- 1530-6992. ; 24:25, s. 7616-
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Tidskriftsartikel (refereegranskat)abstract
- Engineering the building blocks in metal–organic materials is an effective strategy for tuning their dynamical properties and can affect their response to external guest molecules. Tailoring the interaction and diffusion of molecules into these structures is highly important, particularly for applications related to gas separation. Herein, we report a vanadium-based hybrid ultramicroporous material, VOFFIVE-1-Ni, with temperature-dependent dynamical properties and a strong affinity to effectively capture and separate carbon dioxide (CO2) from methane (CH4). VOFFIVE-1-Ni exhibits a CO2 uptake of 12.08 wt% (2.75 mmol g–1), a negligible CH4 uptake at 293 K (0.5 bar), and an excellent CO2-over-CH4 uptake ratio of 2280, far exceeding that of similar materials. The material also exhibits a favorable CO2 enthalpy of adsorption below −50 kJ mol–1, as well as fast CO2 adsorption rates (90% uptake reached within 20 s) that render the hydrolytically stable VOFFIVE-1-Ni a promising sorbent for applications such as biogas upgrading.
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| 20. |
- Chen, Hong, et al.
(författare)
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Construction of Mesoporous Frameworks with Vanadoborate Clusters
- 2014
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 53:14, s. 3608-3611
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Tidskriftsartikel (refereegranskat)abstract
- A new porous vanadoborate was synthesized by employing the scale chemistry theory with the vanadoborate cluster V10B28. The twofold interpenetrated lvt network was assembled with zinc-containing elliptical vanadoborate clusters and Zn polyhedra. The single lvt framework contains a three-dimensional 38x38x20 ring channel system with the pore size (24.7x12.7 angstrom) reaching the mesoscale, thus indicating the possibility of constructing 3D ordered mesopores with vanadoborate clusters. The porosity of the SUT-7 structure was confirmed by CO2 adsorption of the as-synthesized materials.
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| 21. |
- Cheung, Ocean, et al.
(författare)
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Adsorption kinetics for CO2 on highly selective zeolites NaKA and nano-NaKA
- 2013
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 112, s. 1326-1336
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide removal from flue gas via swing adsorption processes requires adsorbents with a high CO2 selectivity and capacity. These properties are particularly valuable to reduce the cost of carbon capture and storage (CCS). Zeolite NaKA was studied for its ability to selectively adsorb CO2 from flue gas, as we previously observed that zeolite NaKA, with a K+/(K+ + Na+) ratio of 17 atomic%, was highly selective towards CO2 over N-2 adsorption by tuning the size of the pore window apertures [1]. The reduced pore apertures may, however, retard the adsorption rate of CO2. Here, we studied the kinetics of CO2 adsorption on regularly sized zeolite NaKA and on nano-sized zeolite NaKA. We used in situ infrared (IR) spectroscopy and observed that CO2 physisorbed relatively rapidly. Density functional theory (DFT) was used for quantum chemical calculations, and the results indicated that CO2 molecules bridged across two or three Na+ ions in the samples with no or very small amount of K. When more K+ ions are present the CO2 molecules no longer bridged across multiple metal ions and adopted an end-on configuration. The calculation showed a shift in the stretching vibration frequency of physisorbed CO2 as observed by IR spectroscopy. Nano-sized zeolite NaKA were synthesised and studied to improve the rate of CO2 adsorption, as the diffusion rate typically increases quadratically with decreasing particle size. Still, the CO2 adsorption rate on nano-sized zeolites NaA and NaKA did not increase significantly. For nano-sized zeolite NaA, we speculate that the absence of such an increased rate is an effect from a skin layer that had formed on the nano-sized zeolite NaA, a layer that was possibly related to intergrowths with extremely small crystals on the surface. The apparently slow adsorption kinetics of CO2 on nano-sized zeolite NaKA was more difficult to explain because it could relate to imperfections within the small crystals, remaining water, or other effects. Overall, the CO2 adsorption rates on zeolite NaKA crystals of different sizes were fast and relevant for the time scales required for adsorption based CCS processes, such as vacuum and temperature swing adsorption (VSA/TSA).
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| 22. |
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| 23. |
- Cheung, Ocean, et al.
(författare)
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CO2 selective NaMg-CTS-1 and its structural formation from the titanium silicate based molecule sieve NaMg-ETS-4 upon dehydration
- 2014
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 198, s. 63-73
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A range of titanium silicates (ETS-4 and CTS-1) with interesting gas separation properties were studied as CO2 adsorbents. Some of these adsorbents, in particular NaMg-CTS-1, showed the ability to selectively adsorb CO2-over-N2. Partially exchanged NaM-ETS-4 (M = Mg, Ca, Sr and Ba) were synthesised in the Na+ form and ion exchanged with group 2 cations. All but NaBa-ETS-4 transformed into their CTS-1 counterparts, when these partially exchanged Na-ETS-4 were dehydrated. The transformation from ETS-4 to CTS-1 was monitored and studied extensively using diffraction and spectroscopic techniques. Powder X-ray diffraction allowed us to follow the changes of the unit cell parameters occurred at different temperatures. We combined high energy X-ray total scattering (analysed by pair distribution functions – PDF analysis), electron diffraction, infrared, Raman and Nuclear Magnetic Resonance (NMR) spectroscopy to study the transformation of ETS-4 to CTS-1. We understood that under dehydration steps, there was significant disruption to the Ti–O–Ti chain along the b-axis, which occurred concurrently with the distortion of the double 3-rings alongside of these chains. These changes were partly responsible for the contraction of the ETS-4 framework (and successive transformation to CTS-1). The new information allowed us to understand the interesting structures and sorption properties of these adsorbents
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| 24. |
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| 25. |
- Cheung, Ocean, et al.
(författare)
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Highly selective uptake of carbon dioxide on the zeolite vertical bar Na10.2KCs0.8 -LTA - a possible sorbent for biogas upgrading
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:24, s. 16080-16083
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Tidskriftsartikel (refereegranskat)abstract
- The vertical bar Na10.2KCs0.8(8)[Al12Si12O48](8)(Fm3c)-LTA zeolite adsorbs CO2-over-CH4 with a high selectivity (over 1500). The uptake of carbon dioxide is also high (3.31 mmol g(-1), 293 K, 101 kPa). This form of zeolite A is a very promising adsorbent for applications such as biogas upgrading, where keeping the adsorption of methane to a minimum is crucial.
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| 26. |
- Cheung, Ocean, et al.
(författare)
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K+ Exchanged Zeolite ZK-4 as a Highly Selective Sorbent for CO2
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:32, s. 9682-9690
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorbents with high capacity and selectivity for adsorption of CO2 are currently being investigated for applications in adsorption-driven separation of CO2 from flue gas. An adsorbent with a particularly high CO2-over-N-2 selectivity and high capacity was tested here. Zeolite ZK-4 (Si:Al similar to 1.3:1), which had the same structure as zeolite A (LTA), showed a high CO2 capacity of 4.85 mmol/g (273 K, 101 kPa) in its Na+ form. When approximately 26 at % of the extraframework cations were exchanged for K+ (NaK-ZK-4), the material still adsorbed a large amount of CO2 (4.35 mmol/g, 273 K, 101 kPa), but the N-2 uptake became negligible (<0.03 mmol/g, 273 K, 101 kPa). The majority of the CO2 was physisorbed on zeolite ZK-4 as quantified by consecutive volumetric adsorption measurements. The rate of physisorption of CO2 was fast, even for the highly selective sample. The molecular details of the sorption of CO2 were revealed as well. Computer modeling (Monte Carlo, molecular dynamics simulations, and quantum chemical calculations) allowed us to partly predict the behavior of fully K+ exchanged zeolite K-ZK-4 upon adsorption of CO2 and N-2 for Si:Al ratios up to 4:1. Zeolite K-ZK-4 with Si:Al ratios below 23:1 restricted the diffusion of CO2 and N-2 across the cages. These simulations could not probe the delicate details of the molecular sieving of CO2 over N-2. Still, this study indicates that zeolites NaK-ZK-4 and K-ZK-4 could be appealing adsorbents with high CO2 uptake (similar to 4 mmol/g, 101 kPa, 273 K) and a kinetically enhanced CO2-over-N-2 selectivity.
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| 27. |
- Cheung, Ocean, et al.
(författare)
-
Selective Adsorption of CO2 on Zeolites NaK-ZK‑4 with Si/Al of 1.8−2.8
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:39, s. 25371-25380
-
Tidskriftsartikel (refereegranskat)abstract
- Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO2 over N2. Here, we showed that the exchangeable cations (e.g., Na+ or K+) on zeolite ZK-4 play an important role in the CO2 selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8–2.8 had very high CO2 selectivity when an intermediate number of the exchangeable cations were K+ (the rest being Na+). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO2 uptake capacity and very high CO2-over-N2 selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO2 selectivity with an intermediate number of K+ cations. The high CO2 selectivity was related to the K+ cation in the 8-rings of the α-cage, together with Na+ cations in the 6-ring, obstructing the diffusion of N2 throughout the zeolite. The positions of the K+ cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO2, as revealed by in situ X-ray diffraction. The CO2-over-N2 selectivity was somewhat reduced when the number of K+ cations approached 100%. This was possibly due to the shift in the K+ cation positions in the 8-ring when the number of Na+ was going toward 0%, allowing N2 diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO2 was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO2 could be relevant for applications in carbon capture and bio- and natural gas upgrading.
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| 28. |
- Cheung, Ocean, et al.
(författare)
-
Selective Adsorption of CO2on Zeolites NaK-ZK-4 with Si/Al of 1.8-2.8
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:39, s. 25371-25380
-
Tidskriftsartikel (refereegranskat)abstract
- Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO2 over N2. Here, we showed that the exchangeable cations (e.g., Na+ or K+) on zeolite ZK-4 play an important role in the CO2 selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8-2.8 had very high CO2 selectivity when an intermediate number of the exchangeable cations were K+ (the rest being Na+). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO2 uptake capacity and very high CO2-over-N2 selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO2 selectivity with an intermediate number of K+ cations. The high CO2 selectivity was related to the K+ cation in the 8-rings of the α-cage, together with Na+ cations in the 6-ring, obstructing the diffusion of N2 throughout the zeolite. The positions of the K+ cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO2, as revealed by in situ X-ray diffraction. The CO2-over-N2 selectivity was somewhat reduced when the number of K+ cations approached 100%. This was possibly due to the shift in the K+ cation positions in the 8-ring when the number of Na+ was going toward 0%, allowing N2 diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO2 was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO2 could be relevant for applications in carbon capture and bio- and natural gas upgrading.
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| 29. |
- Cheung, Ocean, et al.
(författare)
-
Silicoaluminophosphates as CO2 sorbents
- 2012
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 156, s. 90-96
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Tidskriftsartikel (refereegranskat)abstract
- Silicoaluminophosphates (SAPO-17, SAPO-35, SAPO-56 and SAPO-RHO) synthesised via hydrothermal means are tested for their abilities to adsorb carbon dioxide. These 8-ring microporous phosphates show high capacities to adsorb CO2. SAPO-RHO has a high uptake of CO2 and a very low uptake of N-2 due to its narrow pore window aperture at 273 K. Its significant uptake of N-2 at 77 K is rationalised by a temperature induced shrinkage effect. SAPO-56 has a slightly higher CO2 capacity (5.42 mmol/g, 273 K, 101 kPa) and is less water sensitive than zeolite 13X. Cyclic adsorption and in situ infrared spectroscopy (IR) reveal that SAPOs retain 95% of their original CO2 capacity after six cycles and that adsorption occurs via physisorption. The calculated heat of adsorption for CO2 (at 0.2-0.7 mmol/g loading) on SAPO-56 and SAPO-RHO lies in the physisorption range (similar to 35 kJ/mol). SAPOs, in particular SAPO-56 and SAPO-RHO, possess many desirable properties and are potentially good adsorbents for CO2 capture in swing adsorption processes.
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| 30. |
- Debatin, Franziska, et al.
(författare)
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An Isoreticular Family of Microporous Metal-Organic Frameworks Based on Zinc and 2-Substituted Imidazolate-4-amide-5-imidate : Syntheses, Structures and Properties
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:37, s. 11630-11640
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a new series of isoreticular frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate (IFP-14, IFP=imidazolate framework Potsdam) that form one-dimensional, microporous hexagonal channels. Varying R in the 2-substitued linker (R=Me (IFP-1), Cl (IFP-2), Br (IFP-3), Et (IFP-4)) allowed the channel diameter (4.01.7 angstrom), the polarisability and functionality of the channel walls to be tuned. Frameworks IFP-2, IFP-3 and IFP-4 are isostructural to previously reported IFP-1. The structures of IFP-2 and IFP-3 were solved by X-ray crystallographic analyses. The structure of IFP-4 was determined by a combination of PXRD and structure modelling and was confirmed by IR spectroscopy and 1H MAS and 13C CP-MAS NMR spectroscopy. All IFPs showed high thermal stability (345400?degrees C); IFP-1 and IFP-4 were stable in boiling water for 7 d. A detailed porosity analysis was performed on the basis of adsorption measurements by using various gases. The potential of the materials to undergo specific interactions with CO2 was investigated by measuring the isosteric heats of adsorption. The capacity to adsorb CH4 (at 298 K), CO2 (at 298 K) and H2 (at 77 K) at high pressure were also investigated. In situ IR spectroscopy showed that CO2 is physisorbed on IFP-14 under dry conditions and that both CO2 and H2O are physisorbed on IFP-1 under moist conditions.
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| 31. |
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| 32. |
- Deiana, Luca, 1982-, et al.
(författare)
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Enantioselective Heterogeneous Synergistic Catalysis for Asymmetric Cascade Transformations
- 2014
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Ingår i: Advanced Synthesis and Catalysis. - : Wiley. - 1615-4150 .- 1615-4169. ; 356:11-12, s. 2485-2492
-
Tidskriftsartikel (refereegranskat)abstract
- A modular design for a novel heterogeneous synergistic catalytic system, which simultaneously activates the electrophile and nucleophile by the combined activation modes of a separate metal and non-metal catalyst, for asymmetric cascade transformations on a solid surface is disclosed. This modular catalysis strategy generates carbocycles (up to 97.5: 2.5 er) as well as spirocyclic oxindoles (97.5: 2.5 to > 99: 0.5 er), containing all-carbon quaternary centers, in a highly enantioselective fashion via a one-pot dynamic relay process.
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| 33. |
- Farzaneh, Amirfarrokh, et al.
(författare)
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Adsorption of Butanol and Water Vapors in Silicalite‑1 Films with a Low Defect Density
- 2016
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32, s. 11789-11798
-
Tidskriftsartikel (refereegranskat)abstract
- Pure silica zeolites are potentially hydrophobic and have therefore been considered to be interesting candidates for separating alcohols, e.g., 1-butanol, from water. Zeolites are traditionally synthesized at high pH, leading to the formation of intracrystalline defects in the form of silanol defects in the framework. These silanol groups introduce polar adsorption sites into the framework, potentially reducing the adsorption selectivity toward alcohols in alcohol/water mixtures. In contrast, zeolites prepared at neutral pH using the fluoride route contain significantly fewer defects. Such crystals should show a much higher butanol/water selectivity than crystals prepared in traditional hydroxide (OH−) media. Moreover, silanol groups are present at the external surface of the zeolite crystals; therefore, minimizing the external surface of the studied adsorbent is important. In this work, we determine adsorption isotherms of 1-butanol and water in silicalite-1 films prepared in a fluoride (F−) medium using in situ attenuated total reflectance−Fourier transform infrared (ATR−FTIR) spectroscopy. This film was composed of well intergrown, plate-shaped b-oriented crystals, resulting in a low external area. Single-component adsorption isotherms of 1-butanol and water were determined in the temperature range of 35− 80 °C. The 1-butanol isotherms were typical for an adsorbate showing a high affinity for a microporous material and a large increase in the amount adsorbed at low partial pressures of 1-butanol. The Langmuir−Freundlich model was successfully fitted to the 1-butanol isotherms, and the heat of adsorption was determined. Water showed a very low affinity for the adsorbent, and the amounts adsorbed were very similar to previous reports for large silicalite-1 crystals prepared in a fluoride medium. The sample also adsorbed much less water than did a reference silicalite-1(OH−) film containing a high density of internal defects.The results show that silicalite-1 films prepared in a F− medium with a low density of defects and external area are very promising for the selective recovery of 1-butanol from aqueous solutions.
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| 34. |
- Farzaneh, Amirfarrokh, et al.
(författare)
-
Adsorption of Water and Butanol in Silicalite-1 Film Studied with in-situ ATR-FTIR Spectroscopy
- 2015
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 31:17, s. 4887-4894
-
Tidskriftsartikel (refereegranskat)abstract
- Biobutanol produced by, e.g., acetone–butanol–ethanol (ABE) fermentation is a promising alternative to petroleum-based chemicals as, e.g., solvent and fuel. Recovery of butanol from dilute fermentation broths by hydrophobic membranes and adsorbents has been identified as a promising route. In this work, the adsorption of water and butanol vapor in a silicalite-1 film was studied using in situ attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy to better understand the adsorption properties of silicalite-1 membranes and adsorbents. Single-component adsorption isotherms were determined in the temperature range of 35–120 °C, and the Langmuir model was successfully fitted to the experimental data. The adsorption of butanol is very favorable compared to that of water. When the silicalite-1 film was exposed to a butanol/water vapor mixture with 15 mol % butanol (which is the vapor composition of an aqueous solution containing 2 wt % butanol, a typical concentration in an ABE fermentation broth, i.e., the composition of the gas obtained from gas stripping of an ABE broth) at 35 °C, the adsorption selectivity toward butanol was as high as 107. These results confirm that silicalite-1 quite selectively adsorbs hydrocarbons from vapor mixtures. To the best of our knowledge, this is the first comprehensive study on the adsorption of water and butanol in silicalite-1 from vapor phase.
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| 35. |
- Farzaneh, Amirfarrokh, et al.
(författare)
-
Adsorption of Water and Butanol in Silicalite-1 Film Studied with in Situ Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy
- 2015
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 31:17, s. 4887-4894
-
Tidskriftsartikel (refereegranskat)abstract
- Biobutanol produced by, e.g., acetone-butanol-ethanol (ABE) fermentation is a promising alternative to petroleum-based chemicals as, e.g., solvent and fuel. Recovery of butanol from dilute fermentation broths by hydrophobic membranes and adsorbents has been identified as a promising route. In this work, the adsorption of water and butanol vapor in a silicalite-1 film was studied using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy to better understand the adsorption properties of silicalite-1 membranes and adsorbents. Single-component adsorption isotherms were determined in the temperature range of 35-120 degrees C, and the Langmuir model was successfully fitted to the experimental data. The adsorption of butanol is very favorable compared to that of water. When the silicalite-1 film was exposed to a butanol/water vapor mixture with 15 mol % butanol (which is the vapor composition of an aqueous solution containing 2 wt % butanol, a typical concentration in an ABE fermentation broth, i.e., the composition of the gas obtained from gas stripping of an ABE broth) at 35 degrees C, the adsorption selectivity toward butanol was as high as 107. These results confirm that silicalite-1 quite selectively adsorbs hydrocarbons from vapor mixtures. To the best of our knowledge, this is the first comprehensive study on the adsorption of water and butanol in silicalite-1 from vapor phase.
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| 36. |
- Fijoł, Natalia, 1994-, et al.
(författare)
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MOF@Cell : 3D printed biobased filters anchored with a green metal–organic framework for effluent treatment
- 2023
-
Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 11:23, s. 12384-12394
-
Tidskriftsartikel (refereegranskat)abstract
- Multifunctional, biobased materials processed by means of additive manufacturing technology can behighly applicable within the water treatment industry. This work summarizes a scalable and sustainablemethod of anchoring a green metal–organic framework (MOF) SU-101 onto the surface of 3D printed,biobased matrices built of polylactic acid (PLA)-based composites reinforced with TEMPO-oxidizedcellulose nanofibers (TCNFs). The two tested anchoring methods were hydrolysis via either concentratedhydrochloric acid treatment or via a photooxidation reaction using UV–ozone treatment. Stabledeposition of SU-101 distributed homogenously over the filter surface was achieved and confirmed byFT-IR, XPS and SEM measurements. The obtained 3D printed and functionalized MOF@PLA andMOF@TCNF/PLA (aka MOF@Cell) filters exhibit high efficiency in removing heavy metal ions from mineeffluent and methylene blue from contaminated water, as demonstrated through batch adsorptionexperiments. In addition to their potential for removal of contaminants from water, the MOF@Cell filtersalso exhibit excellent mechanical properties with a Young's modulus value of about 1200 MPa,demonstrating their potential for use in practical water treatment applications. The MOF@Cell filterswere able to maintain their structural integrity and filtration performance even after multiple cycles ofuse and regeneration. This study highlights the potential of multifunctional, biobased materials processedby additive manufacturing technology as a cost-effective alternative to traditional water treatmentmethods. The MOF@Cell filters presented in this study demonstrate high efficiency, durability, andreusability, making them promising candidates for practical applications in the modern water treatmentindustry.
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| 37. |
- Fischer, Christian E., et al.
(författare)
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Vibrational spectroscopic study of SiO2-based nanotubes
- 2013
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Ingår i: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031 .- 1873-3697. ; 66, s. 104-118
-
Tidskriftsartikel (refereegranskat)abstract
- Novel organic-inorganic hybrid nanotubes containing silica and ethane (EtSNT), ethylene (ESNT) and acetylene (ASNT) units, as well as brominated ESNT (Br-ESNT) and glycine-modified Br-ESNT (Gly-ESNT) have been studied by IR and Raman spectroscopy. The results are compared with the spectral features for conventional silica nanotubes (SNT) and amorphous silica. Bands peculiar to organic moieties have been detected and assigned. Assignment of the silicate backbone vibrations was based on the results of normal coordinate calculations. Furthermore, characteristic silicate, so-called 'nanotube' vibrations have been identified and their band positions have been summarized to serve as a future reference for such compounds. SiOSi antisymmetric stretchings were observed in the range 1000-1110 cm(-1), while the symmetric stretchings appeared between 760 and 960 cm(-1) for EtSNT, ESNT and Br-ESNT. Force constants have been refined for models of the repeating structure units: O3SiOSi(OSi)(3) for SNT and SiCHnCHnSi(OSi)(3) for organosilica nanotubes (n = 2, EtSNT: n = 1, ESNT and n = 0, ASNT). The calculated SiO stretching force constants were increased from 4.79 to 4.88 and 5.11 N cm(-1) for EtSNT, ESNT and ASNT, respectively. The force constants have been compared with those for several silicates and SiO bond length are predicted and discussed.
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| 38. |
- Gebauer, Denis, et al.
(författare)
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Proto-Calcite and Proto-Vaterite in Amorphous Calcium Carbonates
- 2010
-
Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 49:47, s. 8889-8891
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous order: Amorphous calcium carbonates (ACC) have an intrinsic structure relating to the crystalline polymorphs of calcite and vaterite. The proto-crystalline structures of calcite and vaterite (pc-ACC and pv-ACC) are analyzed by NMR (see picture), IR, and EXAFS spectroscopy, which shows that the structuring of ACC relates to the underlying pH-dependent equilibria.
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| 39. |
- Guo, Hua, et al.
(författare)
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Trapping of different stages of BaTiO3 reduction with LiH
- 2020
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 10:58, s. 35356-35365
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the hydride reduction of tetragonal BaTiO3 using LiH. The reactions employed molar H : BaTiO3 ratios of 1.2, 3, and 10 and variable temperatures up to 700 °C. The air-stable reduced products were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy, thermogravimetric analysis (TGA), X-ray fluorescence (XRF), and 1H magic-angle spinning (MAS) NMR spectroscopy. Effective reduction, as indicated by the formation of dark blue to black colored, cubic-phased, products was observed at temperatures as low as 300 °C. The product obtained at 300 °C corresponded to oxyhydride BaTiO∼2.9H∼0.1, whereas reduction at higher temperatures resulted in simultaneous O defect formation, BaTiO2.9−xH0.1□x, and eventually – at temperatures above 450 °C – to samples void of hydridic H. Concomitantly, the particles of samples reduced at high temperatures (500–600 °C) display substantial surface alteration, which is interpreted as the formation of a TiOx(OH)y shell, and sintering. Diffuse reflectance UV-VIS spectroscopy shows broad absorption in the VIS-NIR region, which is indicative of the presence of n-type free charge carriers. The size of the intrinsic band gap (∼3.2 eV) appears only slightly altered. Mott–Schottky measurements confirm the n-type conductivity and reveal shifts of the conduction band edge in the LiH reduced samples. Thus LiH appears as a versatile reagent to produce various distinct forms of reduced BaTiO3 with tailored electronic properties.
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| 40. |
- Hao, Wenming, et al.
(författare)
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Core-Shell and Hollow Particles of Carbon and SiC Prepared from Hydrochar
- 2019
-
Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 12:11
-
Tidskriftsartikel (refereegranskat)abstract
- The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (-SiC) but also significant amounts of the 2H or the 6H polytypes (-SiC) in the SiC.
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| 41. |
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| 42. |
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| 43. |
- Hedin, Niklas, et al.
(författare)
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Perspectives on the adsorption of CO2 on amine-modified silica studied by infrared spectroscopy
- 2019
-
Ingår i: Current Opinion in Green and Sustainable Chemistry. - : Elsevier BV. - 2452-2236. ; 16, s. 13-19
-
Tidskriftsartikel (refereegranskat)abstract
- Amine-modified adsorbents are being researched for their potential to capture CO2 from various gas mixtures, and we review how IR spectroscopy has been used to study the associated CO2-amine chemistry. It has been used to reveal that CO2 chemisorbs as ammonium-carbamate ion pairs especially when the amine density is high. Carbamic acid and related other moieties tend to form in parallel to the ion pairs when the amine density is low. The amines have been shown to degrade on cyclic heat treatment. To further study the formation of bicarbonates on reactive adsorption of CO2 and H2O, degradation of the organics, and the use of other supports than silica are suggested.
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| 44. |
- Jasso-Salcedo, Alma Berenice, et al.
(författare)
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Synthesis of SAPO-56 using N,N,N',N'-tetramethyl-1,6-hexanediamine and co-templates based on primary, secondary, and tertiary amines
- 2021
-
Ingår i: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693 .- 1873-3255. ; 525
-
Tidskriftsartikel (refereegranskat)abstract
- Biomethane is a renewable fuel with a small environmental footprint. In its production, the removal of CO2 from the fermentation gas is critical. Pressure and vacuum swing adsorption (PSA and VSA) processes have certain advantages over other processes for the removal. Silicoaluminophosphate-56 (SAPO-56) has promising properties as an adsorbent for PSA- or VSA-based upgrading of raw biogas. It is typically synthesized by using N,N,N', N'-tetramethyl-1,6-hexanediamine (TMHD) as a structure directing agent (SDA). In this study, TMHD was partly replaced with three different low-cost templates: isopropylamine (IPA), dibutylamine, and tripropylamine. SAPO-56 was co-crystallized with mixtures of templating amines with up to a ratio of 30%:70% of TMHD:IPA. With using TMHD and IPA, small and defined crystals of SAPO-56 plus SAPO-47 formed instead of the large aggregates of SAPO-56 that formed when only TMHD was used. Solid-state 13C NMR spectroscopy was used to show that the IPA and TMHD had not been decomposed and that both molecules were included within the assynthesized crystals of SAPO-56. Synthetic composition diagrams were drawn with respect to the P2O5, SiO2, and Al2O3 compositions of the reaction mixtures and the formed crystalline SAPOs. In relation to these diagrams, the domains for stability of SAPO-56 were contrasted with those of SAPO-11, -17, -20, and -47. In particular, it was observed that SAPO-47 co-crystallized with SAPO-56 when a very large fraction of IPA was used under otherwise optimized conditions. As consistent with other studies, the SAPO-56 synthesized with dual SDAs had a very high uptake of CO2 at conditions relevant for PSA- or VSA-driven upgrading of raw biogas into methane.
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| 45. |
- Kausar, Hira, et al.
(författare)
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Ultramicroporous polyureas synthesized with amines and 1,1′-Carbonyldiimidazole and their CO2 adsorption
- 2023
-
Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 296
-
Tidskriftsartikel (refereegranskat)abstract
- Microporous polyureas can be highly stable, but isocyanates or phosgene are normally used for the synthesis. Here, it was postulated and demonstrated that 1,1′-carbonyl diimidazole (CDI) could be used for the synthesis. By reacting tetrakis(4-aminophenyl)methane with CDI, a series of new polyureas with ultramicropores (pores <0.7 nm) were synthesized. To tailor thermal properties and porosity, the ratio of tetraamine-to-CDI and the reaction temperature were varied. The CO2 adsorption capacities (with values up to 0.74 mmol/g at 0.15 bar/273 K and 1.91 mmol/g at 1 bar/273 K) were ascribed to the ultramicroporosity. The CO2-based Dubinin-Radushkevich surface areas reached 395 m2/g (at 273 K), while the N2-based BET surface areas (at 77 K) were small. The apparent CO2-over-N2 selectivity was also high for the polymers at 273 K with estimated values of 31–92 for 15/85 v/v mixtures of CO2 and N2. This high selectivity was ascribed to the kinetic hindrance of N2 diffusion. It was noted that one of the polymers changed color irreversibly upon heating. In conclusion, it was shown that CDI and amines could be used to synthesize ultramicroporous polyureas, and that these polymers can exhibit irreversible thermochromism. This thermal effect was attributed to the electron-rich urea moieties, aromatic units, and conjugation.
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| 46. |
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| 47. |
- Limaye, Mukta, V, et al.
(författare)
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Functionalization and patterning of nanocellulose films by surface-bound nanoparticles of hydrolyzable tannins and multivalent metal ions
- 2019
-
Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 11:41, s. 19278-19284
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Tidskriftsartikel (refereegranskat)abstract
- Inspired by the Bogolanfini dyeing technique, we report how flexible nanofibrillated cellulose (CNF) films can be functionalized and patterned by surface-bound nanoparticles of hydrolyzable tannins and multivalent metal ions with tunable colors. Molecular dynamics simulations show that gallic acid (GA) and ellagic acid (EA) rapidly adsorb and assemble on the CNF surface, and atomic force microscopy confirms that nanosized GA assemblies cover the surface of the CNF. CNF films were patterned with tannin-metal ion nanoparticles by an in-fibre reaction between the pre-impregnated tannin and the metal ions in the printing ink. Spectroscopic studies show that the Fe-III/II ions interact with GA and form surface-bound, stable GA-Fe-III/II nanoparticles. The functionalization and patterning of CNF films with metal ion-hydrolyzable tannin nanoparticles is a versatile route to functionalize films based on renewable materials and of interest for biomedical and environmental applications.
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| 48. |
- Limaye, Mukta V., et al.
(författare)
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On the role of tannins and iron in the Bogolan or mud cloth dyeing process
- 2012
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Ingår i: Textile research journal. - : SAGE Publications. - 0040-5175 .- 1746-7748. ; 82:18, s. 1888-1896
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the chemistry of the Bogolan or mud cloth dyeing process, a traditional technique of coloring cotton cloths deeply rooted in Mali. Textiles produced by the traditional Bogolan process, using tannin-rich plant extract and iron-rich clay-based mud, were compared using infrared (IR) spectroscopy, scanning electron microscopy (SEM) and X-ray absorption near-edge spectroscopy (XANES) with cotton fibers that were impregnated with tannin and iron salt solutions. IR spectroscopy in both reflective mode on the cloth and cotton and in transmission mode on single fibers, together with SEM, showed that gallic and tannic acid adsorb and precipitate onto the cotton fiber surface. IR spectroscopy and comparison with tannin and iron solution-impregnated cotton showed that the black color of the traditional Bogolan cloth is dominated by the formation of iron-tannin complexes. The presence of iron in the Bogolan cloth was confirmed using XANES data, supporting the notion that iron has been transferred from the iron-rich clay-based mud to the cloth. The chemistry of Bogolan cloth is not only historically and culturally significant and of importance in textile conservation, but may also inspire future research on sustainable dyeing and processing techniques based on natural products.
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| 49. |
- Liu, Qingling, et al.
(författare)
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NaKA sorbents with high CO2-over-N2 selectivity and high capacity to adsorb CO2
- 2010
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 46, s. 4502-4504
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Tidskriftsartikel (refereegranskat)abstract
- The uptake of carbon dioxide and nitrogen gas by zeolite NaKA was studied. A very high ideal CO2-over-N2 selectivity and a high CO2 capacity were observed at an optimal K+ content of 17 at.%. NaKA is a very promising adsorbent for CO2 separation from water-free flue gases.
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| 50. |
- Ménard, Delphine, et al.
(författare)
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Dynamic incorporation of specific lignin residues controls the biomechanics of the plant vasculature and its resilience to environmental changes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The accumulation of the cell wall polymer lignin in vascular cells enables long-distance water conduction and structural support in plants. Independently of the plant species, each different vascular cell type accumulates specific lignin amount and composition affecting both aromatic and aliphatic substitutions of its residues. However, the biological role of this conserved and specific lignin chemistry for each cell type remains unclear. Herein, we performed single cell analyses on plant vascular cell morphotypes to investigate the role of specific lignin composition for cellular function. We showed that distinct amounts and compositions of lignin accumulated in the different morphotypes of the sap conducting vascular cells. We discovered that lignin accumulates dynamically, increasing in quantity and changing composition, to fine-tune the cell wall mechanical properties of each conducting cell morphotype. Modification this lignin specificity impaired specifically the cell wall mechanical properties of each morphotype and consequently their capacity to optimally conduct water in normal but also to recover from drought conditions. Altogether, our findings provide the biological role of specific lignin chemistry in sap conducting cells, to dynamically adjust the hydraulic properties of each conducting cell during developmental and environmental constraints.
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