| 1. |
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| 2. |
- Barišić, Antun, et al.
(författare)
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Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media
- 2021
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Ingår i: Colloids and interfaces. - : MDPI. - 2504-5377. ; 5:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrations showed that these surfaces acquired less charge from proton-related reactions than oxide minerals. The data from batch-type titrations for PTFE powder did not show an effect of ionic strength, which was also in contrast with results for classical colloids. In agreement with classical colloids, the electrokinetic results for inert surfaces showed the typical salt level dependence. In some cases, the point of zero net proton charge as determined from mass and tentatively from acid–base titration differed from isoelectric points, which has also been previously observed, for example by Chibowski and co-workers for ice electrolyte interfaces. Finally, we found no evidence for surface contaminations of our PTFE particles before and after immersion in aqueous solutions. Only in the presence of NaCl-containing solutions did cryo-XPS detect oxygen from water. We believe that our low isoelectric points for PTFE were not due to impurities. Moreover, the measured buffering at pH 3 could not be explained by sub-micromolar concentrations of contaminants. The most comprehensive explanation for the various sets of data is that hydroxide ion accumulation occurred at the interfaces between inert surfaces and aqueous solutions.
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| 3. |
- Khokarale, Santosh G., et al.
(författare)
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One-Pot, Metal-Free Synthesis of Dimethyl Carbonate from CO2 at Room Temperature
- 2020
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Ingår i: Sustainable Chemistry. - : MDPI. - 2673-4079. ; 1:3, s. 298-314
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report on the metal-free, one-pot synthesis of industrially important dimethyl carbonate (DMC) from molecular CO2 under ambient conditions. In this process, initially the CO2 was chemisorbed through the formation of a switchable ionic liquid (SIL), [DBUH] [CH3CO3], by the interaction of CO2 with an equivalent mixture of organic superbase 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) and methanol. The obtained SIL further reacted with methyl iodide (CH3I) to form DMC. The synthesis was carried out in both dimethyl sulfoxide (DMSO) and methanol. Methanol is preferred, as it not only served as a reagent and solvent in CO2 capture and DMC synthesis, but it also assisted in controlling the side reactions between chemical species such as CH3I and [DBUH]+ cation and increased the yield of DMC. Hence, the use of methanol avoided the loss of captured CO2 and favored the formation of DMC with high selectivity. Under the applied reaction conditions, 89% of the captured CO2 was converted to DMC. DBU was obtained, achieving 86% recovery of its salts formed during the synthesis. Most importantly, in this report we describe a simple and renewable solvent-based process for a metal-free approach to DMC synthesis under industrially feasible reaction conditions.
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| 4. |
- Vucetic, Nemanja, et al.
(författare)
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Tuned Bis-Layered Supported Ionic Liquid Catalyst (SILCA) for Competitive Activity in the Heck Reaction of Iodobenzene and Butyl Acrylate
- 2020
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Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 10:9
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Tidskriftsartikel (refereegranskat)abstract
- A thorough experimental optimization of supported ionic liquid catalyst (SILCA) was performed in order to obtain a stable and efficient catalyst for the Heck reaction. Out of fifteen proposed structures, propyl imidazolium bromide-tetramethylguanidinium pentanoate modified SiO2 loaded with PdCl2 appeared to be the most stable and to have a good activity in the reaction between butylacrylate and iodobezene, resulting in a complete conversion in 40 min at 100 °C, in four consecutive experiments. This study elucidated on the stability of the catalytic system with an ionic liquid layer during the catalyst synthesis but also under reaction conditions. In the bis-layered catalyst, the imidazolium moiety as a part of internal layer, brought rigidity to the structure, while in external layer pentanoic acid gave sufficiently acidic carboxylic group capable to coordinate 1,1,3,3-tetramethylguanidine (TMG) and thus, allow good dispersion of Pd nanoparticles. The catalyst was characterized by means of XPS, FT-IR, TEM, ICP-OES, ζ-potential, EDX, TGA, and 13C NMR. The release and catch mechanism was observed, whereas Pd re-deposition can be hindered by catalyst poisoning and eventual loss of palladium.
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| 5. |
- Armanious, Antonius, 1981, et al.
(författare)
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Determination of Nanosized Adsorbate Mass in Solution Using Mechanical Resonators: Elimination of the So Far Inseparable Liquid Contribution
- 2021
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:41, s. 22733-22746
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Tidskriftsartikel (refereegranskat)abstract
- Assumption-free mass quantification of nanofilms, nanoparticles, and (supra)molecular adsorbates in a liquid environment remains a key challenge in many branches of science. Mechanical resonators can uniquely determine the mass of essentially any adsorbate; yet, when operating in a liquid environment, the liquid dynamically coupled to the adsorbate contributes significantly to the measured response, which complicates data interpretation and impairs quantitative adsorbate mass determination. Employing the Navier-Stokes equation for liquid velocity in contact with an oscillating surface, we show that the liquid contribution for rigid systems can be eliminated by measuring the response in solutions with identical kinematic viscosity but different densities. Guided by this insight, we used the quartz crystal microbalance (QCM), one of the most widely employed mechanical resonators, to experimentally demonstrate that the kinematic-viscosity matching can be utilized to quantify the dry mass of rigid and in many cases also nonrigid adsorbate systems, including, e.g., rigid nanoparticles, tethered biological nanoparticles (lipid vesicles), as well as highly hydrated polymeric films. For all the adsorbates, the dry mass determined using the kinematic-viscosity matching was within the uncertainty limits of the corresponding mass determined using complementary methods, i.e., QCM in air, scanning electron microscopy, surface plasmon resonance, and theoretical estimations. The same approach applied to the simultaneously measured energy dissipation made it possible to quantify the mechanical properties of the adsorbate and its attachment to the surface, as demonstrated by, for example, probing the hydrodynamic stabilization induced by nanoparticle crowding. In addition to a unique means to quantify the liquid contribution to the measured response of mechanical resonators, we also envision that the kinematic-viscosity-matching approach will open up applications beyond mass determination, including a new means to investigate orientation, spatial distribution, and binding strength of adsorbates without the need for complementary techniques.
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| 6. |
- Barker, David, 1993, et al.
(författare)
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Filter function of graphene oxide: Trapping perfluorinated molecules
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 152:2
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Tidskriftsartikel (refereegranskat)abstract
- We need clean drinking water, but current water purification methods are not always sufficient. This study examines the binding and binding mechanisms when graphene oxide is used as a filter material for removing perfluorinated substances and trihalomethanes. We use density functional theory calculations to examine the binding of the harmful molecules on graphene oxide. Our results indicate that the binding energies between graphene oxide and the investigated molecules are in the range of 370-1450 meV per molecule, similar to the binding energies obtained in other studies, where adsorption of similar size molecules onto graphene oxide has been investigated. This indicates that graphene oxide has the potential to separate the molecules of interest from the water. Significant contribution to the binding energies comes from the van der Waals (dispersion) interaction between the molecule and graphene oxide, while the hydrogen bonding between the functional groups of graphene oxide and the hydrogen atoms in functional groups on the molecules also plays a role in the binding.
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| 7. |
- Brownwood, B., et al.
(författare)
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Gas-Particle Partitioning and SOA Yields of Organonitrate Products from NO3-Initiated Oxidation of Isoprene under Varied Chemical Regimes
- 2021
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Ingår i: Acs Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 5:4, s. 785-800
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl nitrate (AN) and secondary organic aerosol (SOA) from the reaction of nitrate radicals (NO3) with isoprene were observed in the Simulation of Atmospheric PHotochemistry In a large Reaction (SAPHIR) chamber during the NO(3)Isop campaign in August 2018. Based on 15 day-long experiments under various reaction conditions, we conclude that the reaction has a nominally unity molar AN yield (observed range 90 +/- 40%) and an SOA mass yield of OA + organic nitrate aerosol of 13-15% (with similar to 50 mu g m(-3) inorganic seed aerosol and 2-5 mu g m-3 total organic aerosol). Isoprene (5-25 ppb) and oxidant (typically similar to 100 ppb O-3 and 5-25 ppb NO2) concentrations and aerosol composition (inorganic and organic coating) were varied while remaining close to ambient conditions, producing similar AN and SOA yields under all regimes. We observe the formation of dinitrates upon oxidation of the second double bond only once the isoprene precursor is fully consumed. We determine the bulk partitioning coefficient for ANs (K-p similar to 10(-3) m(3) mu g(-1)), indicating an average volatility corresponding to a C-5 hydroxy hydroperoxy nitrate.
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| 8. |
- Damas, Giane Benvinda, et al.
(författare)
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Carbon dioxide reduction mechanism on Ru-based electrocatalysts [Ru(bpy)(2)(CO)(2)](2+) : insights from first-principles theory
- 2021
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry. - 2398-4902. ; 5:23, s. 6066-6076
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Tidskriftsartikel (refereegranskat)abstract
- Solar fuel production through the so-called artificial photosynthesis has attracted a great deal of attention to the development of a new world energy matrix that is renewable and environmentally friendly. This process is characterized by light absorption with enough photon energy to generate conduction electrons, which drive the carbon dioxide reduction to produce organic fuels. It is also common to couple Ru-complex electrocatalysts to form a more efficient and selective hybrid system for this application. In this work, we have undertaken a thorough investigation of the redox reaction mechanism of Ru-based electrocatalysts by means of density functional theory (DFT) methods under the experimental conditions that have been previously reported. More specifically, we have studied the electrochemistry and catalytic activity of the [Ru(bpy)(2)(CO)(2)](2+) coordination complex. Our theoretical assessment supports the following catalytic cycle: (i) [Ru(bpy)(2)(CO)(2)](2+) is transformed into [Ru(bpy)(2)(CO)](0) upon two-electron reduction and CO release; (ii) [Ru(bpy)(2)(CO)](0) is protonated to form the [Ru(bpy)(2)(CO)H](+) hydride complex; (iii) CO2 is activated by the hydride complex through an electrophilic addition to form the [Ru(bpy)(2)(CO)(OCHO)](+) intermediate; (iv) the resulting formic acid ligand is released in solution; and, finally, (v) the CO ligand is reattached to the complex to recover the initial [Ru(bpy)(2)(CO)(2)](2+) catalyst.
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| 9. |
- Wu, R. R., et al.
(författare)
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Molecular composition and volatility of multi-generation products formed from isoprene oxidation by nitrate radical
- 2021
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 21:13, s. 10799-10824
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Tidskriftsartikel (refereegranskat)abstract
- Isoprene oxidation by nitrate radical (NO3) is a potentially important source of secondary organic aerosol (SOA). It is suggested that the second or later-generation products are the more substantial contributors to SOA. However, there are few studies investigating the multi-generation chemistry of isoprene-NO3 reaction, and information about the volatility of different isoprene nitrates, which is essential to evaluate their potential to form SOA and determine their atmospheric fate, is rare. In this work, we studied the reaction between isoprene and NO3 in the SAPHIR chamber (Julich) under near-atmospheric conditions. Various oxidation products were measured by a high-resolution time-offlight chemical ionization mass spectrometer using Br as the reagent ion. Most of the products detected are organic nitrates, and they are grouped into monomers (C-4 and C-5 products) and dimers (C-10 products) with 1-3 nitrate groups according to their chemical composition. Most of the observed products match expected termination products observed in previous studies, but some compounds such as monomers and dimers with three nitrogen atoms were rarely reported in the literature as gas-phase products from isoprene oxidation by NO3. Possible formation mechanisms for these compounds are proposed. The multi-generation chemistry of isoprene and NO3 is characterized by taking advantage of the time behavior of different products. In addition, the vapor pressures of diverse isoprene nitrates are calculated by different parametrization methods. An estimation of the vapor pressure is also derived from their condensation behavior. According to our results, isoprene monomers belong to intermediate-volatility or semi-volatile organic compounds and thus have little effect on SOA formation. In contrast, the dimers are expected to have low or extremely low volatility, indicating that they are potentially substantial contributors to SOA. However, the monomers constitute 80% of the total explained signals on average, while the dimers contribute less than 2 %, suggesting that the contribution of isoprene NO3 oxidation to SOA by condensation should be low under atmospheric conditions. We expect a SOA mass yield of about 5% from the wall-loss- and dilution-corrected mass concentrations, assuming that all of the isoprene dimers in the low- or extremely low-volatility organic compound (LVOC or ELVOC) range will condense completely.
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| 10. |
- Ye, Chen, et al.
(författare)
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Optimizing photon upconversion by decoupling excimer formation and triplet triplet annihilation
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:3, s. 1715-1720
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Tidskriftsartikel (refereegranskat)abstract
- Perylene is a promising annihilator candidate for triplet-triplet annihilation photon upconversion, which has been successfully used in solar cells and in photocatalysis. Perylene can, however, form excimers, reducing the energy conversion efficiency and hindering further development of TTA-UC systems. Alkyl substitution of perylene can suppress excimer formation, but decelerate triplet energy transfer and triplet-triplet annihilation at the same time. Our results show that mono-substitution with small alkyl groups selectively blocks excimer formation without severly compromising the TTA-UC efficiency. The experimental results are complemented by DFT calculations, which demonstrate that excimer formation is suppressed by steric repulsion. The results demonstrate how the chemical structure can be modified to block unwanted intermolecular excited state relaxation pathways with minimal effect on the preferred ones.
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