| 1. |
- Hedenstedt, Kristoffer, 1979, et al.
(författare)
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Study of Hypochlorite Reduction Related to the Sodium Chlorate Process
- 2016
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Ingår i: Electrocatalysis. - : Springer Science and Business Media LLC. - 1868-2529 .- 1868-5994. ; 7:4, s. 326-335
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Tidskriftsartikel (refereegranskat)abstract
- Reduction of hypochlorite is the most important side reaction in the sodium chlorate reactor leading to high energy losses. Today chromate is added to the reactor solution to minimize the hypochlorite reduction but a replacement is necessary due to health and environmental risks with chromate. In order to understand the effect of different substrates on the hypochlorite reduction, α-FeOOH, γ-FeOOH, Cr2O3 and CrOH3 were electrodeposited on titanium and subjected to electrochemical investigations. These substances are commonly found on cathodes in the chlorate process and can serve as model substances for the experimental investigation. The mechanism of hypochlorite reduction was also studied using DFT calculations in which the reaction at Fe(III) and Cr(III) surface sites were considered in order to single out the electrocatalytic properties. The experimental results clearly demonstrated that the chromium films completely block the reduction of hypochlorite, while for the iron oxyhydroxides the process can readily occur. Since the electrocatalytic properties per se were shown by the DFT calculations to be very similar for Fe(III) and Cr(III) sites in the oxide matrix, other explanations for the blocking ability of chromium films are addressed and discussed in the context of surface charging, reduction of anions and conduction in the deposited films. The main conclusion is that the combined effect of electronic properties and reduction of negatively charged ions can explain the reduction kinetics of hypochlorite and the effect of chromate in the chlorate process.
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| 2. |
- Busch, Michael, 1983, et al.
(författare)
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Adsorption of NO on Fe3O4(111)
- 2018
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 693, s. 84-87
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of NO on Fe 3 O 4 (111) is studied by density functional theory (DFT) calculations. NO is preferably adsorbed atop the octahedral site which has a clearly higher adsorption energy than the tetrahedral site. The difference in adsorption energy correlates with differences in adsorption geometries and N–O stretch vibrations. The results are in good agreement with temperature programmed desorption (TPD) and reflection-adsorption IR spectroscopy (RAIRS) measurements and provide an explanation of the observation of only one vibrational mode despite two distinct TPD features.
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| 3. |
- Busch, Michael, 1983
(författare)
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Water oxidation: From mechanisms to limitations
- 2018
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Ingår i: Current Opinion in Electrochemistry. - : Elsevier BV. - 2451-9111 .- 2451-9103. ; 9, s. 278-284
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Forskningsöversikt (refereegranskat)abstract
- Water oxidation is a central reaction for energy conversion and storage. On the basis of the detailed analysis of different reaction mechanisms the limitations associated with the O2evolution reaction is analysed. We find that overpotentials lower than the 0.4 eV, which have been observed for a mono-nuclear mechanism, are possible if the problematic *-OOH intermediate is avoided. This is the case for the bi-nuclear and bi-functional reaction paths. 3-dimensional volcano plots are constructed and used to explore the performance of these reaction mechanisms. Our results suggest, that in contrast to previous analysis of the mono-nuclear mechanism, the true top of the water oxidation volcano is placed at slightly lower *=O binding energies of only 2.46 eV if combined with a suitable co-catalyst. On the basis of this new analysis, design criteria for improved catalysts are developed.
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| 4. |
- Patra, Anuttam, et al.
(författare)
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Selective flotation of calcium minerals using double-headed collectors
- 2019
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Ingår i: Journal of Dispersion Science and Technology. - : Taylor & Francis. - 0193-2691 .- 1532-2351. ; 40:8, s. 1205-1216
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Tidskriftsartikel (refereegranskat)abstract
- A study was performed involving a series of double-headed carboxylate collectors with varying distance between the head groups (one, two or three carbon atoms). A collector with the same alkyl chain length but with only one carboxylate group was also included. All these were amino-acid based amphiphiles and the polar head group was connected to the hydrophobic tail via an amide linkage. Selective flotation recovery of different calcium minerals using these collectors was investigated. The double-headed collector with one carbon atom between the carboxylate groups was an apatite and fluorite specific reagent while the monocarboxylate surfactant showed high specificity for calcite. The flotation behavior of a simple conventional collector of the same alkyl chain length, a fatty acid salt, was also determined under identical flotation conditions in order to understand the effect of the amide group. Complementary experiments (ζ potential measurements, adsorption isotherm determinations) were also performed for these reagents. In order to shed light on the selectivity obtained with the dicarboxylate surfactants, the distances between the head groups were calculated and compared with the distances between neighboring calcium atoms on the surface of the minerals. It was found that the high degree of selectivity could be rationalized by perfect matching of these distances. To the best of our knowledge this is the first study where flotation selectivity in complex calcium mineral systems has been explained in terms of molecular recognition governing the interaction between the collector and the mineral surface.
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| 5. |
- Prajapati, Preeti, et al.
(författare)
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Molecular Structural, Hydrogen Bonding Interactions, and Chemical Reactivity Studies of Ezetimibe-L-Proline Cocrystal Using Spectroscopic and Quantum Chemical Approach
- 2022
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Ingår i: Frontiers in Chemistry. - : Frontiers Media S.A.. - 2296-2646. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Ezetimibe (EZT) being an anticholesterol drug is frequently used for the reduction of elevated blood cholesterol levels. With the purpose of improving the physicochemical properties of EZT, in the present study, cocrystals of ezetimibe with L-proline have been studied. Theoretical geometry optimization of EZT-L-proline cocrystal, energies, and structure–activity relationship was carried out at the DFT level of theory using B3LYP functional complemented by 6-311++G(d,p) basis set. To better understand the role of hydrogen bonding, two different models (EZT + L-proline and EZT + 2L-proline) of EZT-L-proline cocrystal were studied. Spectral techniques (FTIR and FT-Raman) combined with quantum chemical methodologies were successfully implemented for the detailed vibrational assignment of fundamental modes. It is a zwitterionic cocrystal hydrogen bonded with the OH group of EZT and the COO− group of L-proline. The existence and strength of hydrogen bonds were examined by a natural bond orbital analysis (NBO) supported by the quantum theory of atoms in molecule (QTAIM). Chemical reactivity was reflected by the HOMO–LUMO analysis. A smaller energy gap in the cocrystal in comparison to API shows that a cocrystal is softer and chemically more reactive. MEPS and Fukui functions revealed the reactive sites of cocrystals. The calculated binding energy of the cocrystal from counterpoise method was −11.44 kcal/mol (EZT + L-proline) and −26.19 kcal/mol (EZT + 2L-proline). The comparative study between EZT-L-proline and EZT suggest that cocrystals can be better used as an alternative to comprehend the effect of hydrogen bonding in biomolecules and enhance the pharmacological properties of active pharmaceutical ingredients (APIs).
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| 6. |
- Verma, Priya, et al.
(författare)
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Experimental and Quantum Chemical Studies of Nicotinamide-Oxalic Acid Salt: Hydrogen Bonding, AIM and NBO Analysis
- 2022
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Ingår i: Frontiers in Chemistry. - : Frontiers Media S.A.. - 2296-2646. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- The computational modeling supported with experimental results can explain the overall structural packing by predicting the hydrogen bond interactions present in any cocrystals (active pharmaceutical ingredients + coformer) as well as salts. In this context, the hydrogen bonding synthons, physiochemical properties (chemical reactivity and stability), and drug-likeliness behavior of proposed nicotinamide–oxalic acid (NIC–OXA) salt have been reported by using vibrational spectroscopic signatures (IR and Raman spectra) and quantum chemical calculations. The NIC–OXA salt was prepared by reactive crystallization method. X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) techniques were used for the characterization and validation of NIC–OXA salt. The spectroscopic signatures revealed that (N7–H8)/(N23–H24) of the pyridine ring of NIC, (C═O), and (C–O) groups of OXA were forming the intermolecular hydrogen bonding (N–H⋯O–C), (C–H⋯O═C), and (N–H⋯O═C), respectively, in NIC–OXA salt. Additionally, the quantum theory of atoms in molecules (QTAIM) showed that (C10–H22⋯O1) and (C26–H38⋯O4) are two unconventional hydrogen bonds present in NIC–OXA salt. Also, the natural bond orbital analysis was performed to find the charge transfer interactions and revealed the strongest hydrogen bonds (N7–H8⋯O5)/(N23–H24⋯O2) in NIC–OXA salt. The frontier molecular orbital (FMO) analysis suggested more reactivity and less stability of NIC–OXA salt in comparison to NIC–CA cocrystal and NIC. The global and local reactivity descriptors calculated and predicted that NIC–OXA salt is softer than NIC–CA cocrystal and NIC. From MESP of NIC–OXA salt, it is clear that electrophilic (N7–H8)/(N23–H24), (C6═O4)/(C3═O1) and nucleophilic (C10–H22)/(C26–H38), (C6–O5)/(C3–O2) reactive groups in NIC and OXA, respectively, neutralize after the formation of NIC–OXA salt, confirming the presence of hydrogen bonding interactions (N7–H8⋯O5–C6) and (N23–H24⋯O2–C3). Lipinski’s rule was applied to check the activeness of salt as an orally active form. The results shed light on several features of NIC–OXA salt that can further lead to the improvement in the physicochemical properties of NIC.
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| 7. |
- Khasevani, Sepideh Gholizadeh, et al.
(författare)
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Empowering Adsorption and Photocatalytic Degradation of Ciprofloxacin on BiOI Composites: A Material-by-Design Investigation
- 2023
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 8:46, s. 44044-44056
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Tidskriftsartikel (refereegranskat)abstract
- Binary and ternary composites of BiOI with NH2-MIL-101(Fe) and a functionalized biochar were synthesized through an in situ approach, aimed at spurring the activity of the semiconductor as a photocatalyst for the removal of ciprofloxacin (CIP) from water. Experimental outcomes showed a drastic enhancement of the adsorption and the equilibrium (which increased from 39.31 mg g–1 of bare BiOI to 76.39 mg g–1 of the best ternary composite in 2 h time), while the kinetics of the process was not significantly changed. The photocatalytic performance was also significantly enhanced, and the complete removal of 10 ppm of CIP in 3 h reaction time was recorded under simulated solar light irradiation for the best catalyst of the investigated batch. Catalytic reactions supported by different materials obeyed different reaction orders, indicating the existence of different mechanisms. The use of scavengers for superoxide anion radicals, holes, and hydroxyl radicals showed that although all these species are involved in CIP photodegradation, the latter play the most crucial role, as also confirmed by carrying out the reaction at increasing pH conditions. A clear correlation between the reduction of BiOI crystallite sizes in the composites, as compared to the bare material, and the material performance as both adsorbers and photocatalyst was identified.
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| 8. |
- Purnomo, Victor, 1992, et al.
(författare)
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New approach for particle size and shape analysis of iron-based oxygen carriers at different oxidation degrees
- 2024
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Ingår i: Particuology. - : Elsevier. - 2210-4291 .- 1674-2001. ; 90, s. 493-503
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Tidskriftsartikel (refereegranskat)abstract
- One of the crucial issues in the chemical looping technology lies in its bed material: the oxygen carrier. Particle size analysis of an oxygen carrier is important since in a fluidized bed the material can only work well within a specific size range. While the favorable size ranges for oxygen carrier materials have already been reported, none of the published studies has analyzed the particle size and shape of oxygen carriers in detail. Furthermore, the effect of oxygen carriers’ oxidation degree on such properties has not been considered either. This study aimed to report the particle size and shape analysis of five iron-based oxygen carriers, one natural ore, one synthetic material, and three residue products, at different oxidation degrees using dynamic image analysis (DIA). The oxygen carriers were prepared at different mass conversion degrees in a fluidized bed batch reactor. The size distribution, sphericity, and aspect ratio of the oxygen carrier particles were examined experimentally using a Camsizer instrument. Our results show that the DIA method was successfully able to analyze the particle size and shape of our oxygen carriers with satisfying accuracy for comparison. The oxidation state of the investigated materials seems to only affect the particle size and shape of oxygen carriers to a minor extent. However, exposures to redox cycles in a fluidized bed reactor may alter the particle size and shape of most oxygen carriers.
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| 9. |
- Shah, Faiz Ullah, 1981-, et al.
(författare)
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Comparing the thermal and electrochemical stabilities of two structurally similar ionic liquids
- 2020
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Ingår i: Molecules. - : MDPI AG. - 1420-3049 .- 1420-3049 .- 1431-5157. ; 25:10
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Tidskriftsartikel (refereegranskat)abstract
- Here we focus on the thermal and variable temperature electrochemical stabilities of two ionic liquids (ILs) having a common tributyloctyl phosphonium cation [P4,4,4,8]+ and two different orthoborate anions: bis(mandelato)borate [BMB]− and bis(salicylato)borate [BScB]−. The thermogravimetric analysis data suggest that [P4,4,4,8][BScB] is thermally more stable than [P4,4,4,8][BMB] in both nitrogen atmosphere and air, while the impedance spectroscopy reveals that [P4,4,4,8][BScB] has higher ionic conductivity than [P4,4,4,8][BMB] over the whole studied temperature range. In contrast, the electrochemical studies confirm that [P4,4,4,8][BMB] is more stable and exhibits a wider electrochemical stability window (ESW) on a glassy carbon electrode surface as compared to [P4,4,4,8][BScB]. A continuous decrease in the ESWs of both ILs is observed as a function of operation temperature.
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| 10. |
- Shah, Faiz Ullah, 1981-, et al.
(författare)
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Structural and Ion Dynamics in Fluorine-Free Oligoether Carboxylate Ionic Liquid-Based Electrolytes
- 2020
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 124:43, s. 9690-9700
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Tidskriftsartikel (refereegranskat)abstract
- Here, we investigate the physicochemical and electrochemical properties of fluorine-free ionic liquid (IL)-based electrolytes with two different cations, tetrabutylphosphonium, (P-4,4,4,(4))(+), and tetrabutylammonium, (N-4,N-4,N-4,N-4)(+), coupled to a new anion, 2-[2-(2-methoxyethoxy)ethoxylacetate anion (MEEA), for both neat and (P-4,P-4,P-4,P-4) (MEEA)(-), also doped with 10-40 mol % of Li(MEEA). We find relatively weaker cation-anion interactions in (P-4,P-4,P-4,P-4)(MEEA) than in (N-4,N-4,N-4,N-4)(MEEA), and for both ILs, the structural flexibility of the oligoether functionality in the anion results in low glass transition temperatures, also for the electrolytes made. The pulsed field gradient nuclear magnetic resonance (PFG NMR) data suggest faster diffusion of the (MEEA)(-) anion than (P-4,P-4,P-4,P-4)(+) cation in the neat IL, but the addition of a Li salt results in slightly lower mobility of the former than the latter and lower ionic conductivity. This agrees with the combined Li-7 NMR and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy data, which unambiguously reveal preferential interactions between the lithium cations and the carboxylate groups of the IL anions, which also increased as a function of the lithium salt concentration. In total, these systems provide a stepping stone for further design of fluorine-free and low glass transition temperature IL-based electrolytes and also stress how crucial it is to control the strength of ion-ion interactions.
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