| 1. |
- Oberg, K., et al.
(author)
-
Comparison of monolayer films of stearic acid and methyl stearate on an Al2O3 surface
- 2001
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In: Thin Solid Films. - : Elsevier. - 0040-6090. ; 397:1-2, s. 102-8
-
Journal article (peer-reviewed)abstract
- Both stearic acid and methyl stearate chemisorbs onto an oxide surface of aluminum with an asymmetric coordination of the carboxylate group as concluded from infrared (IR) spectroscopy data. Similarities in the IR spectra of the films from the two compounds suggest that the ester is bonded in the same way as the acid, and that the ester therefore undergoes hydrolysis during the surface reaction. X-Ray photoelectron spectroscopy (XPS) and IR data are interpreted in terms of self-assembled monolayer formation and a more dense film from the carboxylic acid in comparison with that from the ester. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 2. |
- Ajaikumar, Samikannu, et al.
(author)
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Oxidation of α-pinene over gold containing bimetallic nanoparticles supported on reducible TiO2 by DPU method
- 2011
-
In: Applied Catalysis A. - Amsterdam : Elsevier. - 0926-860X .- 1873-3875. ; 392:1-2, s. 11-18
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Journal article (peer-reviewed)abstract
- A series of bimetallic catalysts Au–M (where M = Cu, Co and Ru) were supported on a reducible TiO2 oxide via deposition-precipitation (DP) method with a slow decomposition of urea as the precipitating agent. The characteristic structural features of the prepared materials were characterized by various physico-chemical techniques such as X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). XPS results indicated the formation of alloyed bimetallic particles on the TiO2 support. TEM results confirmed the fine dispersion of metal nanoparticles on the support with an average particle size in the range of 3–5 nm. An industrially important process, oxy-functionalization of α-pinene was carried out over the prepared bimetallic heterogeneous catalysts under liquid phase conditions. Reaction parameters such as the reaction time, temperature, and the effect of solvent were studied for optimal conversion of α-pinene into verbenone. The major products obtained were verbenone, verbenol, α-pinene oxide and alkyl-pinene peroxide. The activity of the catalysts followed the order; AuCu/TiO2 > AuCo/TiO2 > Cu/TiO2 > Au/TiO2 > AuRu/TiO2. Upon comparison of the various catalysts, AuCu/TiO2 was found to be an active and selective catalyst towards the formation of verbenone. The temperature, nature of the catalysts and the choice of solvents greatly influenced the reaction rate.
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| 3. |
- Annamalai, Alagappan, et al.
(author)
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Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation
- 2018
-
In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:19, s. 16467-16473
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Journal article (peer-reviewed)abstract
- To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm–3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.
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| 4. |
- Artemenko, A., et al.
(author)
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Reference XPS spectra of amino acids
- 2021
-
Conference paper (peer-reviewed)abstract
- In this report we present XPS data for five amino acids (AAs) (tryptophan, methionine, glutamine, glutamic acid, and arginine) with different side chain groups measured in solid state (powder form). The theoretically and experimentally obtained chemical structure of AAs are compared. Here, we analyse and discuss C 1 s, N 1 s, O 1s and S 2p core level binding energies, FWHMs, atomic concentrations of the functional groups in AAs. The experimentally obtained and theoretically calculated ratio of atomic concentrations are compared. The zwitterionic nature of methionine and glutamine in solid state was determined from protonated amino groups in N 1s peak and deprotonated carboxylic groups in the C 1s spectrum. The obtained XPS results for AAs well correspond with previously reported data.
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| 5. |
- Asres, Georgies Alene, et al.
(author)
-
Ultrasensitive H2S gas sensors based on p-type WS2 hybrid materials
- 2018
-
In: Nano Reseach. - : Springer. - 1998-0124 .- 1998-0000. ; 11:8, s. 4215-4224
-
Journal article (peer-reviewed)abstract
- Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm-1) as well as high selectivity towards H2S relative to CO, NH3, H2, and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm-1, respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS2 alone are not sufficient to explain the observed high sensitivity towards H2S. A major role in this behavior is also played by O doping in the S sites of the WS2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.
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| 6. |
- Aulin, Christian, 1980-, et al.
(author)
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Wetting kinetics of oil mixtures on fluorinated model cellulose surfaces
- 2008
-
In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 317:2, s. 556-567
-
Journal article (peer-reviewed)abstract
- The wetting of two different model cellulose surfaces has been studied; a regenerated cellulose (RG) surface prepared by spin-coating, and a novel multilayer film of poly(ethyleneimine) and a carboxymethylated microfibrillated cellulose (MFC). The cellulose films were characterized in detail using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM indicates smooth and continuous films on a nanometer scale and the RMS roughness of the RG cellulose and MFC surfaces was determined to be 3 and 6 nm, respectively. The cellulose films were modified by coating with various amounts of an anionic fluorosurfactant, perfluorooctadecanoic acid, or covalently modified with pentadecafluorooctanyl chloride. The fluorinated cellulose films were used to follow the spreading mechanisms of three different oil mixtures. The viscosity and surface tension of the oils were found to be essential parameters governing the spreading kinetics on these surfaces. XPS and dispersive surface energy measurements were made on the cellulose films coated with perfluorooctadecanoic acid. A strong correlation was found between the surface concentration of fluorine, the dispersive surface energy and the contact angle of castor oil on the surface. A dispersive surface energy less than 18 mN/m was required in order for the cellulose surface to be non-wetting (Ξe > 90 °) by castor oil.
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| 7. |
- Barišić, Antun, et al.
(author)
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Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media
- 2021
-
In: Colloids and interfaces. - : MDPI. - 2504-5377. ; 5:1
-
Journal article (other academic/artistic)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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| 8. |
- Behravesh, Erfan, et al.
(author)
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Synthesis and characterization of Au nano particles supported catalysts for partial oxidation of ethanol : Influence of solution pH, Au nanoparticle size, support structure and acidity
- 2017
-
In: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 353, s. 223-238
-
Journal article (peer-reviewed)abstract
- Partial oxidation of ethanol to acetaldehyde was carried out over gold catalysts supported on various oxides and zeolites by deposition precipitation. The special focus of this work was on the influence of H-Y zeolite surface charge on Au cluster size and loading linking it to activity and selectivity in ethanol oxidation and comparing with other studied catalysts. The catalysts were characterized by nitrogen physisorption, transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. pH of the solution governed the Au NPs size within the range of 5.8–13.2 nm with less negatively charged surfaces leading to formation of smaller clusters. Au loading on H-Y zeolite with silica to alumina ratio of 80 was increased by raising the pH. In fact, H-Y-12 and H-Beta-25 were selective towards diethyl ether while acetaldehyde was the prevalent product on less acidic H-Y-80. The results demonstrated strong dependency of the catalytic activity on the Au cluster size. Namely turn over frequency (TOF) decreased with an increase in metal size from 6.3 to 9.3 nm on H-Y-80. Selectivity towards acetaldehyde and ethyl acetate did not change significantly on H-Y-80 within 6.3–9.3 nm Au particle size range. On Al2O3 support, however, selectivity towards acetaldehyde increased considerably upon diminishing Au average particle size from 3.7 to 2.1 nm.
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| 9. |
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| 10. |
- Bengtsson, Åsa, et al.
(author)
-
A solubility and surface complexation study of a non-stoichiometric hydroxyapatite
- 2009
-
In: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 73:2, s. 257-267
-
Journal article (peer-reviewed)abstract
- The dissolution and surface complexation of a non-stoichiometric hydroxyapatite (Ca8.4(HPO4)1.6(PO4)4.4(OH)0.4), (HAP) was studied in the pH range 3.5 – 10.5, at 25 ºC in 0.1 M Na(Cl). The results from well-equilibrated batch experiments, potentiometric titrations, and zeta-potential measurements were combined with information provided by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The information from the analyses was used to design an equilibration model that takes in to account dissolution, surface potential, solution and surface complexation, as well as possible phase transformations. The results from the XPS measurements clearly show that the surface of the mineral has a different composition than the bulk and that the Ca/P ratio of the surface layer is 1.4 ± 0.1. This ratio was also found in solution in the batches equilibrated at low pH where the dominating reaction is dissolution. In the batches equilibrated at near neutral pH values, however, the Ca/P ratio in solution attains values as high as 25, which is due to re-adsorption of phosphate ions to the HAP surface. The total concentration of protons as well as the total concentration of dissolved calcium and phosphate in solution were used to calculate a model for the dissolution and surface complexation of HAP. The constant capacitance model was applied in designing the following surface complexation model.
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| 11. |
- Bengtsson, Åsa, et al.
(author)
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Phase Transformations, Ion-Exchange, Adsorption, and Dissolution Processes in Aquatic Fluorapatite Systems
- 2009
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:4, s. 2355-2362
-
Journal article (peer-reviewed)abstract
- A synthetic fluorapatite was prepared that undergoes a phase transformation generated during a dialysis step. A surface layer with the composition Ca9(HPO4)2(PO4)4F2 is formed, which is suggested to form as one calcium atom is replaced by two protons. A surface complexation model, based upon XPS measurements, potentiometric titration data, batch experiments, and zeta-potential measurements was presented. The CaOH and OPO3H2 sites were assumed to have similar protolytic properties as in a corresponding nonstoichiometric HAP (Ca8.4(HPO4)1.6(PO4)4.4(OH)0.4) system. Besides a determination of the solubility product of Ca9(HPO4)2(PO4)4F2, two additional surface complexation reactions were introduced; one that accounts for a F/OH ion exchange reaction, resulting in the release of quite high fluoride concentrations (∼1 mM) that turned out to be dependent on the surface area of the particles. Furthermore, to explain the lowering of pHiep from around 8 in nonstoichiometric HAP suspensions to about 5.7 in FAP suspensions, a reaction that lowers the surface charge due to the readsorption of fluoride ions to the positively charged Ca sites was introduced: ≡CaOH2+ + F− ⇋ ≡CaF + H2O. The resulting model also agrees with predictions based upon XPS and ATR-FTIR observations claiming the formation of CaF2(s) in the most acidic pH range.
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| 12. |
- Biasi, P., et al.
(author)
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Revealing the role of bromide in the H2O2 direct synthesis with the catalyst wet pretreatment method (CWPM)
- 2017
-
In: AIChE Journal. - : American Institute of Chemical Engineers. - 0001-1541 .- 1547-5905. ; 63:1, s. 32-42
-
Journal article (peer-reviewed)abstract
- A tailor-made Pd0/K2621 catalyst was subjected to post synthesis modification via a wet treatment procedure. The aimwas the understanding of the role of promoters and how—if any—improvements could be qualitatively related to the cat-alyst performance for the H2O2direct synthesis. The Catalyst Wet Pretreatment Method was applied in different metha-nolic solutions containing H2O2, NaBr, and H3PO4, either as single modifiers or as a mixture. The catalyst wascharacterized by Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. It was concluded that themodified catalysts give rise to higher selectivities compared to the pristi ne reference catalyst thus opening a possibilityto exclude the addit ion of the undesirable selectivity enhancers in the reaction medium. This work provides original evi-dence on the role of promoter s, especially bromide, allowing the formulation of a new reaction mechanism for one ofthe most challenging reactions recognized by the world.
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| 13. |
- Boily, Jean-Francois, et al.
(author)
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X-ray photoelectron spectroscopy of fast-frozen hematite colloids in aqueous solutions. 2. tracing the relationship between surface charge and electrolyte adsorption
- 2010
-
In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:6, s. 2613-2616
-
Journal article (peer-reviewed)abstract
- Colloidal-sized hematite spheroids exposed to aqueous NaCl solutions were investigated by X-ray photoelectron spectroscopy using the fast-frozen technique. The O 1s region provided evidence for (de)protonation reactions of surface (hydr)oxo groups of OH-enriched/O-depleted hematite Surfaces. These results were also correlated to changes in sodium (Na 1s) and chloride (Cl 2p) contents with pH. Electrolyte ion surface loadings were successfully predicted using a classic thermodynamic adsorption model normalized for surface site density. These efforts pointed to ion-specific inner-Helmholtz plane capacitances.
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| 14. |
- Borah, Raju Kumar, et al.
(author)
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Copper Oxide Nanoparticles as a Mild and Efficient Catalyst for N-Arylation of Imidazole and Aniline with Boronic Acids at Room Temperature
- 2017
-
In: Synlett. - : Georg Thieme Verlag KG. - 0936-5214 .- 1437-2096. ; 28:10, s. 1177-1182
-
Journal article (peer-reviewed)abstract
- The present work describes the excellent catalytic activity of copper(II) oxide nanoparticles (NPs) towards N-arylation of aniline and imidazole at room temperature. The copper(II) oxide NPs were synthesized by a thermal refluxing technique and characterized by FT-IR spectroscopy; powder XRD, SEM, EDX, TEM, TGA, XPS, BET surface area analysis, and particle size analysis. The size of the NPs was found to be around 12 nm having a surface area of 164.180 m(2) g(-1). The catalytic system was also found to be recyclable and could be reused in subsequent catalytic runs without a significant loss of activity.
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| 15. |
- Bottone, Anna, et al.
(author)
-
Sodium hypochlorite as an oxidizing agent for removal of soil organic matter before microplastics analyses
- 2021
-
In: Journal of Environmental Quality. - : John Wiley & Sons. - 0047-2425 .- 1537-2537. ; 51:1, s. 112-122
-
Journal article (peer-reviewed)abstract
- The omnipresence of microplastics (MPs) across Earth's surface has raised concerns about their environmental impact and created an urgent need for methods to identify them in complex soil and sedimentary matrices. However, detecting MPs in the O horizons of soils is difficult because plastic polymers share many physical and chemical properties with natural soil organic matter (SOM). In this study, we assessed whether sodium hypochlorite (NaOCl), a reagent that can oxidize SOM and simultaneously preserve mineral constituents, can be used for MP analysis and characterization in soil environments. In addition, we scrutinized how factors such as MP size, polymer type, extraction methods, and soil matrix affect the recovery of microplastic particles. We used both hydrophobic and density-dependent separation methods to assess the effects of our oxidation treatment on the recovery of MP. We observed that NaOCl effectively removed SOM without greatly altering the surface properties of resistant MP polymers (polypropylene, polylactic acid, low-density polyethylene, and polyethylene terephthalate), which were characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy after SOM removal. The NaOCl treatment caused some chlorination and formation of additional C–OH bonds on polymer surfaces, which likely contributed to the reduced efficiency of the hydrophobic-based (oil) extraction. We conclude that NaOCl treatment can improve detection of MPs in SOM-rich soil and that recovery of MPs from soils is influenced by MP size, polymer type, extraction method, and soil type, which makes it challenging to develop a universal analytical method.
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| 16. |
- Bukhanko, Natalia, et al.
(author)
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Continuous gas phase synthesis of 1-ethyl chloride from ethyl alcohol and hydrochloric acid over Al2O3-based catalysts: the ‘green’ route
- 2013
-
In: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 1:8, s. 883-893
-
Journal article (peer-reviewed)abstract
- The synthesis of 1-ethyl chloride in the gas-phase mixture of ethanol and hydrochloric acid over ZnCl2/Al2O3 catalysts was studied in a continuous reactor using both commercial and tailor-made supports. The catalytic materials were characterized by the means of structural (XPS, TEM, XRD, and BET) and catalytic activity (selectivity and conversion) measurements. The reaction parameters such as temperature, pressure, and feedstock flow rates were optimized for the conversion of ethanol to ethyl chloride. The new tailor-made highly porous Al2O3-based catalyst outperformed its commercial counterpart by exhibiting high conversion and selectivity (98%) at the temperature of 325 °C. Long-term stability tests (240 h) confirmed the excellent durability of the tailor-made alumina catalysts. The process demonstrated here poses an efficient and economic “green” large-scale on-site synthesis of this industrially important reactant in industry, where bioethanol is produced and 1-ethyl chloride is necessary, e.g., for ethylation of cellulose and synthetic polymer products. On-site in situ production of ethyl chloride avoids the problems associated with the transportation and storage of toxic and flammable 1-ethyl chloride.
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| 17. |
- Bukhanko, Natalia, et al.
(author)
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Gas phase synthesis of isopropyl chloride from isopropanol and HCl over alumina and flexible 3-D carbon foam supported catalysts
- 2017
-
In: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 542:25, s. 212-225
-
Journal article (peer-reviewed)abstract
- Isopropyl chloride synthesis from isopropanol and HCl in gas phase over ZnCl2 catalysts supported on Al2O3 as well as flexible carbon foam was studied in a continuous reactor. A series of catalytic materials were synthesised and characterised by BET, XPS, SEM, TEM, XRD and NH3-TPD methods. Catalytic activity tests (product selectivity and conversion of reactants) were performed for all materials and optimal reaction conditions (temperature and feedstock flow rates) were found. The results indicate that the highest yield of isopropyl chloride was obtained over 5 wt.% ZnCl2 on commercial Al2O3 (No. II) (95.3%). Determination of product mixture compositions and by-product identification were done using a GC-MS method. Carbon foam variant catalyst, 5 wt.% ZnCl2/C, was found to perform best out of the carbon-supported materials, achieving ∼75% yield of isopropyl chloride. The kinetic model describing the process in a continuous packed bed reactor was proposed and kinetic parameters were calculated. The activation energy for the formation of isopropyl chloride reaction directly from isopropanol and HCl was found to be ∼58 kJ/mol.
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| 18. |
- Cano, A., et al.
(author)
-
Contribution to the coordination chemistry of transition metal nitroprussides : a cryo-XPS study
- 2019
-
In: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 43:12, s. 4835-4848
-
Journal article (peer-reviewed)abstract
- The series of coordination polymers under investigation was formed by the assembly of a pentacyanonitrosylferrate(ii) anionic block, [Fe(CN)(5)NO](2-), through monovalent and divalent transition metal ions, e.g. Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+. For divalent ions, the resulting materials have a 3D porous framework with attractive features for applications in gas storage and separation, as electroactive solids, light-driven molecular magnets, and so on; in this study, we report the results obtained for a series of coordination polymers using the cryogenic X-ray photoelectron spectroscopy (cryo-XPS) data; comprehensive details regarding their coordination chemistries were obtained from the acquired spectra in addition to their comparison with the structural and spectroscopic information obtained from other techniques. The results discussed herein are original and contribute towards the understanding of the electronic structures and related properties for this family of coordination polymers. This series of solids was found to be highly susceptible to strong damage induced by X-ray beams throughout the conventional XPS experiment; therefore, the analysis was conducted under cryogenic conditions.
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| 19. |
- Cano, A., et al.
(author)
-
Intercalation of pyrazine in layered copper nitroprusside : synthesis, crystal structure and XPS study
- 2019
-
In: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 273, s. 1-10
-
Journal article (peer-reviewed)abstract
- Hybrid inorganic–organic solids form an interesting family of functional materials, where their functionalities are determined by both, the inorganic and organic building blocks. This study reports the intercalation of pyrazine in 2D copper nitroprusside, the crystal structure of the resulting hybrid solid and explores the scope of cryogenic X-ray photoelectron spectroscopy (XPS) to shed light on its electronic structure. In this material, the pyrazine molecule appears coordinated to Cu atoms from neighboring layers, to form the columns in the resulting 3D porous framework. Its crystal structure was solved and refined from the corresponding XRD powder pattern. XPS data, recorded under cryogenic conditions, provided fine details on the electronic structure of this hybrid solid. The binding energy values for the ligand atoms and the involved metals show a definite correlation with the structural data and FT-IR spectra. When XPS spectra were recorded at room temperature, a significant sample decomposition was observed. Three possible mechanisms for the sample damage during the XPS experiment are considered. The hybrid material under study is representative of a wide series of nanoporous solids obtained by intercalation of organic pillars between 2D inorganic solids.
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| 20. |
- Cant, David J. H., et al.
(author)
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Cryo-XPS for surface characterization of nanomedicines
- 2023
-
In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:39, s. 8220-8227
-
Journal article (peer-reviewed)abstract
- Nanoparticles used for medical applications commonly possess coatings or surface functionalities intended to provide specific behavior in vivo, for example, the use of PEG to provide stealth properties. Direct, quantitative measurement of the surface chemistry and composition of such systems in a hydrated environment has thus far not been demonstrated, yet such measurements are of great importance for the development of nanomedicine systems. Here we demonstrate the first use of cryo-XPS for the measurement of two PEG-functionalized nanomedicines: a polymeric drug delivery system and a lipid nanoparticle mRNA carrier. The observed differences between cryo-XPS and standard XPS measurements indicate the potential of cryo-XPS for providing quantitative measurements of such nanoparticle systems in hydrated conditions.
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| 21. |
- Cheng, Wei, et al.
(author)
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Nanoscale hydration in layered manganese oxides
- 2021
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:2, s. 666-674
-
Journal article (peer-reviewed)abstract
- Birnessite is a layered MnO2 mineral capable of intercalating nanometric water films in its bulk. With its variable distributions of Mn oxidation states (MnIV, MnIII, and MnII), cationic vacancies, and interlayer cationic populations, birnessite plays key roles in catalysis, energy storage solutions, and environmental (geo)chemistry. We here report the molecular controls driving the nanoscale intercalation of water in potassium-exchanged birnessite nanoparticles. From microgravimetry, vibrational spectroscopy, and X-ray diffraction, we find that birnessite intercalates no more than one monolayer of water per interlayer when exposed to water vapor at 25 °C, even near the dew point. Molecular dynamics showed that a single monolayer is an energetically favorable hydration state that consists of 1.33 water molecules per unit cell. This monolayer is stabilized by concerted potassium–water and direct water–birnessite interactions, and involves negligible water–water interactions. Using our composite adsorption–condensation–intercalation model, we predicted humidity-dependent water loadings in terms of water intercalated in the internal and adsorbed at external basal faces, the proportions of which vary with particle size. The model also accounts for additional populations condensed on and between particles. By describing the nanoscale hydration of birnessite, our work secures a path for understanding the water-driven catalytic chemistry that this important layered manganese oxide mineral can host in natural and technological settings.
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| 22. |
- Chernyschova, Irina V., et al.
(author)
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Mechanism of adsorption of long-chain alkylamines on silicates : a spectroscopic study. 2. Albite
- 2001
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:3, s. 775-785
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Journal article (peer-reviewed)abstract
- Using FTIR (DRIFTS and IRRAS) and XPS spectroscopy, ζ potential measurements, and Hallimond flotation tests, we confirmed that long-chain primary amines are adsorbed on silicates at pH 6-7 through the 2D-3D precipitation mechanism. The orientation and packing of dodecyl- and hexadecylammonium acetate and chloride adsorbed on albite in the different regions of the adsorption isotherm were determined. It was shown that these characteristics depend strongly on the substrate. Coadsorption of the counterion was not revealed, but the counterion was found to affect indirectly the adsorption at concentrations above the concentration of the bulk amine precipitation
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| 23. |
- Chernysova, Irina V., et al.
(author)
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Mechanism of adsorption of long-chain alkylamines on silicates. A spectroscopic study. 1. Quartz
- 2000
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 16:21, s. 8071-8084
-
Journal article (peer-reviewed)abstract
- The mechanism of adsorption of long-chain alkylamines at pH 6-7 onto quartz was studied using FTIR and XPS spectroscopy. The spectroscopic data were correlated with ζ potential and Hallimond flotation results. For the first time it was shown that (1) amine cation in the first monolayer is H-bonded with surface silanol group and this H-bond becomes stronger after the break in the adsorption characteristics (isotherm, ζ potential, floatability); (2) at the break the origin of the adsorbed amine species changes qualitatively, and along with alkylammonium ion attached to deprotonated silanol group, molecular amine appears at the surface and, as a result, monolayer thick patches of well-oriented and densely packed adsorbed amine species form rendering the surface highly hydrophobic; and (3) at higher amine concentration, bulk precipitation of molecular amine takes place. The counterion was found to influence both these steps. A model of successive two-dimensional and three-dimensional precipitation was suggested to explain amine adsorption on a silicate surface.
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| 24. |
- Courtois, Julien, et al.
(author)
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A study of surface modification and anchoring techniques used in the preparation of monolithic microcolumns in fused silica capillaries.
- 2006
-
In: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 29:1, s. 14-24
-
Journal article (peer-reviewed)abstract
- Based on a survey of the literature on pretreatment of fused silica capillaries, 3 etching procedures and 11 silanization protocols based on the vinylic silane 3-((trimethoxysilyl)propyl) methacrylate (gamma-MAPS) were found to be most representative as a means of ensuring attachment of in situ prepared vinylic polymers. These techniques were applied to fused silica capillaries and the success in establishing the intended surface modification was assessed. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state of the surface, providing information regarding presence of the reagent bound to the capillary. Wetting angles were measured and correlated with the XPS results. An adherence test was done by photopolymerization of a 2 mm long plug of 1,6-butanediol dimethacrylate in the prepared capillaries and evaluation of its ability to withstand applied hydraulic pressure. SEM was also performed in cases where the plug was released or other irregularities were observed. Finally, the roughness of the etched surface, considered to be of importance, was assessed by atomic force microscopy. Alkaline etching at elevated temperature provided a surface roughness promoting adhesion. The commonly used silanization protocols involving water in the silanization or washing steps gave inadequate surface treatment. The best silanization procedure was based on toluene as a solvent.
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| 25. |
- Danishevskiĭ, A M, et al.
(author)
-
Clusters of sulfur and selenium in nanoporous carbon
- 2007
-
In: Physics of the Solid State. - : MAIK Nauka/Interperiodica distributed exclusively by Springer Science+Business Media LLC.. ; 49:3, s. 571-9
-
Journal article (peer-reviewed)abstract
- The results of x-ray diffraction, x-ray photoelectron spectroscopy, electrical, and galvanomagnetic studies of nanoporous carbon with sulfur and selenium nanoclusters introduced into pores are analyzed. Conclusions are drawn concerning the short-range order in the introduced clusters and their interaction with carbon.
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| 26. |
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| 27. |
- Davidovich, P. B., et al.
(author)
-
Synthesis and structure of dinitrosyl iron complexes with secondary thiolate bridging ligands [Fe-2(mμ-SCHR2)(2)(NO)(4)], R = Me, Ph
- 2015
-
In: Polyhedron. - : Elsevier. - 0277-5387 .- 1873-3719. ; 90, s. 197-201
-
Journal article (peer-reviewed)abstract
- New dinitrosyl iron complexes of binuclear structure [Fe-2(mu-SCHMe2)(2)(NO)(4)] and [Fe-2(mu-SCHPh2)(2)(NO)(4)] were first synthesized employing new method from Fe(CO)(5), corresponding thiol, and EtONO. Complexes structures were determined by XRD technique. DFT calculations were performed to probe the cis-conformer structures in gas and solution phases. NO donor ability of the complex with isopropyl thiolate ligand was studied.
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| 28. |
- Davidovich, P. B., et al.
(author)
-
Synthesis, structure, biochemical, and docking studies of a new dinitrosyl iron complex [Fe-2(mu-SC4H3SCH2)(2)(NO)(4)]
- 2015
-
In: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1092, s. 137-142
-
Journal article (peer-reviewed)abstract
- A new dinitrosyl iron complex of binuclear structure [Fe-2(mu-S-2-methylthiophene)(2)(NO)(4)] was first synthesized and structurally characterized by XRD and theoretical methods. Using caspase-3 as an example it was shown that [Fe-2(mu-S-2-methylthiophene)(2)(NO)(4)] and its analog [Fe-2(mu-S-2-methylfurane)(2)(NO)(4)] can inhibit the action of active site cysteine proteins; the difference in inhibitory activity was explained by molecular docking studies. Biochemical and in silico studies give grounds that the biological activity of dinitrosyl iron complexes is a mu-SR bridging ligand structure function. Thus the rational design strategy of [Fe-2(mu-SR)(2)(NO)(4)] complexes can be applied to make NO prodrugs with high affinity to therapeutically significant targets involved in cancer and inflammation.
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| 29. |
-
Dehydroisomerization of α-pinene over metal supported Si-SBA-15 mesoporous molecular sieves
- 2013
-
Editorial proceedings (peer-reviewed)abstract
- The effective dispersion of active metal species on mesoporous Si-SBA-15 is acquired by means of deposition-precipitation method. In order to achieve this, the surface of Si-SBA-15 was first modified with TiO2 via grafting method, followed by deposition-precipitation method (DP) to obtain a fine dispersion of metallic nanoparticles over TiO2 modified Si-SBA-15. The structural features of the synthesized materials were characterized by means of X-ray diffraction (XRD), nitrogen sorption (BET), XPS and HR-TEM. A valuable platform chemical, p-cymene, was produced over the prepared catalyst by dehydroisomerization of α-pinene under vapour-phase conditions. A stable catalyst for one-spot synthesis of renewable p-cymene from α-pinene was developed.
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| 30. |
- Domashevskaya, E. P., et al.
(author)
-
Electronic structure of undoped and doped SnOx nanolayers
- 2013
-
In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 537, s. 137-144
-
Journal article (peer-reviewed)abstract
- Results of electronic structure investigations for tin oxide nanolayers obtained by tin magnetron sputtering and their following oxidation in air at different temperatures are presented. Using X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy techniques it was shown that at the 240 degrees C anneal a predominant phase in the sample surface layers is tin monoxide. With the annealing temperature increase up to 450 degrees C the phase composition corresponds to tin dioxide. Rather high sorption sensitivity for the samples oxidized at 450 degrees C was found. The compositional model of the gap structure based on XANES and XPS data matching for SnOx nanolayers revealed occurrence of the crossed transitions with the energy of similar to 3.7 eV in the presence of two phases: the SnO and the SnO2 or SnOx with vacancies. Under surface doping of SnO2 nanolayers with palladium PdO and PdO2 is observed where PdO is the most intensive component. O-2 and H-2 multiple alternate exposures resulted in the disappearance of palladium dioxide and PdO recovery to the metallic Pd. Under Pd bulk doping of nanolayers PdO and PdO2 were observed in the surface layers. In this case PdO2 was presented by two types of particles different in size, one of them having the greatest binding energy of Pd 3d(5/2) (339.0 eV). (C) 2013 Elsevier B.V. All rights reserved.
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| 31. |
- Domashevskaya, EP, et al.
(author)
-
XPS and XANES studies of SnOx nanolayers
- 2008
-
In: Journal of Structural Chemistry. - New York : Springer. - 0022-4766 .- 1573-8779. ; 49:Suppl 1, s. 80-91
-
Journal article (peer-reviewed)abstract
- This paper presents the results of our XPS (X-ray photoelectron spectroscopy) and XANES (X-ray absorption near edge structure) Studies of tin oxide nanolayers obtained by magnetron spraying of the metal and its further oxidation in air at different temperatures. It was shown that at 240 degrees C (annealing temperature), tin monoxide was dominant in the surface layer of the samples. When the temperature was increased to 450 degrees C, the phase composition corresponded to tin dioxide. Increased sorption ability was found for the samples oxidized at 450 degrees C. The band structure model of SnOx nanolayers obtained by superposition of the XANES and XPS data revealed cross transitions with energy similar to 3.7 eV in the presence of the SnO and SnO, phases. Surface doping of nanolayers with palladium gave the Pd, PdO, and PdO2 components, among which PdO was most intense. Alternate treatments with O-2 and H-2 gases led to the disappearance of palladium dioxide and the reduction of PdO to the Pd metal. After the volume doping of nanoplayers with palladium, the surface layer contained PdO and PdO2; the latter was represented by two types of particles with different sizes.
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| 32. |
- Ekspong, Joakim, et al.
(author)
-
Stabilizing Active Edge Sites in Semicrystalline Molybdenum Sulfide by Anchorage on Nitrogen-Doped Carbon Nanotubes for Hydrogen Evolution Reaction
- 2016
-
In: Advanced Functional Materials. - : Wiley-VCH Verlagsgesellschaft. - 1616-301X .- 1616-3028. ; 26:37, s. 6766-6776
-
Journal article (peer-reviewed)abstract
- Finding an abundant and cost-effective electrocatalyst for the hydrogen evolu-tion reaction (HER) is crucial for a global production of hydrogen from water electrolysis. This work reports an exceptionally large surface area hybrid catalyst electrode comprising semicrystalline molybdenum sulfi de (MoS 2+ x) catalystattached on a substrate based on nitrogen-doped carbon nanotubes (N-CNTs), which are directly grown on carbon fiber paper (CP). It is shown here that nitrogen-doping of the carbon nanotubes improves the anchoring of MoS 2+ xcatalyst compared to undoped carbon nanotubes and concurrently stabilizes a semicrystalline structure of MoS 2+ x with a high exposure of active sites for HER. The well-connected constituents of the hybrid catalyst are shown to facilitate electron transport and as a result of the good attributes, the MoS 2+ x/N-CNT/CPelectrode exhibits an onset potential of −135 mV for HER in 0.5 M H2SO4, a Tafel slope of 36 mV dec −1, and high stability at a current density of −10 mA cm −2.
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| 33. |
- Eriksson, Johan, et al.
(author)
-
Binding of 2,4,6-Trinitrotoluene, Aniline, and Nitrobenzene to Dissolved and Particulate Soil Organic Matter
- 2004
-
In: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 38:11, s. 3074-80
-
Journal article (peer-reviewed)abstract
- The distribution of TNT* (the sum of TNT and its degradation products), aniline, and nitrobenzene between particulate organic matter (POM), dissolved soil organic matter (DOM), and free compound was studied in controlled kinetic (with and without irradiation) and equilibrium experiments with mixtures of POM and DOM reflecting natural situations in organic rich soils. The binding of TNT* to POM was fast, independent of irradiation, and adsorption isotherms had a great linear contribution (as determined by a mixed model), indicative of a hydrophobic partitioning mechanism. The binding of TNT* to DOM was slower, strongly enhanced under nonirradiated conditions, and adsorption isotherms were highly nonlinear, indicative of a specific interaction between TNT derivatives and functional groups of DOM. Nitrobenzene was associated to both POM and DOM via hydrophobic partitioning, whereas aniline binding was dominated by specific binding to POM and DOM functional groups. On the basis of nitrobenzene and TNT* adsorption parameters determined by a mixed Langmuir + linear model, POM had 2-3 times greater density of hydrophobic moieties as compared to DOM. This difference was reflected by a greater (O + N)/C atomic ratio for DOM. The sum of C-C and C-H moieties, as determined by X-ray photoelectron spectroscopy (XPS), and the sum of aryl-C and alkyl-C, as determined by solid-state cross-polarization magic-angle spinning (CP-MAS) 13C NMR, could only qualitatively account for differences in adsorption parameters. Aliphatic C was found to be more important for the hydrophobic partitioning than aromatic C. On the basis of nonlinear adsorption parameters, the density of functional groups reactive with aniline and TNT derivatives was 1.3-1.4 times greater in DOM than in POM, which was in fair agreement with 13C NMR and XPS data for the sum of carboxyl and carbonyl groups as potential sites for electrostatic and covalent bonding. We conclude that in contaminated soils characterized by continuous leaching of DOM, formation of TNT derivatives (via biotic and abiotic reductive degradation) and their preference for specific functional groups in DOM may contribute to a significant transportation of potentially toxic TNT compounds into surface waters and groundwaters.
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| 34. |
- Fischer, A I, et al.
(author)
-
Crystal and molecular structures of mixedvalence octanuclear cobalt(II,III) propionate and butyrate with an etagerelike core
- 2012
-
In: Russian chemical bulletin. - : Springer Science+Business Media B.V.. - 1066-5285 .- 1573-9171. ; 61:4, s. 821-827
-
Journal article (peer-reviewed)abstract
- The new mixed-valence octanuclear cobalt carboxylate complexes [CoII4CoIII4(μ4-O)4-(μ3-OMe)4(μ-O2CR)6(O2CR)2(H2O)6]·4H2O, where R = Et (3) or n-Pr (4), were investigated by X-ray diffraction analysis. Complexes 3 and 4 have a molecular octanuclear structure, and they are valence trapped, and contain four cobalt atoms Co3+ in the central cubane fragment with four cobalt atoms Co2+ at the periphery of the molecules. The molecules of the complexes are stabilized by four intramolecular hydrogen bonds and are linked, together with water solvent molecules, by intermolecular hydrogen bonds to form a three-dimensional supramolecular system.
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| 35. |
- Fisher, AI, et al.
(author)
-
The first example of cobalt(III) mu-oxoacetate with water molecules in apical positions
- 2008
-
In: Russian journal of general chemistry. - New York : Maik Nauka/Interperiodica. - 1070-3632 .- 1608-3350. ; 78:11, s. 2006-2012
-
Journal article (peer-reviewed)abstract
- Oxidation of Co(MeCOO)(2)center dot 4H(2)O with ozone in acetic acid followed by the treatment with nitric acid results in the formation of the trinuclear oxo-centered acetate complex [Co(III) (3)(mu(3)-O)(mu-O(2)CMe)(6)(OH(2))(3)] NO(3)center dot MeCOOH ([I]NO(3)center dot MeCOOH). Reasons of a decrease in the idealized symmetry of molecular structure (D (3h) -> D (3)) of the complex cation [I](+) were analyzed by means of quantum-chemical calculations. The complex does not retain its structure in solutions (in water, methanol, and ethanol).
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| 36. |
- Frankki, Sofia, et al.
(author)
-
Partitioning of chloroaromatic compounds between the aqueous phase and dissolved and particulate soil organic matter at chlorophenol contaminated sites
- 2007
-
In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 148:1, s. 182-90
-
Journal article (peer-reviewed)abstract
- The retention and mobility of hydrophobic organic contaminants (HOCs) in soil is mainly determined by hydrophobic partitioning to dissolved and particulate organic matter (DOM and POM, respectively). The aqueous phase, DOM, and POM fractions were extracted and separated from soils at three sites contaminated with technical chlorophenol formulations. Concentrations of chlorophenols (CP), polychlorinated phenoxyphenols (PCPP), polychlorinated diphenyl ethers (PCDE) and polychlorinated dibenzo-p-dioxins and furans (PCDD/F) were determined. The partitioning to POM, in relation to DOM, increased in all three soils with increasing hydrophobicity in the order CP < PCPP PCDE PCDF < PCDD. Differences in partitioning to DOM (log KDOC) and POM (log KPOC) could not be explained by differences in gross organic C chemistry. Black carbon did not contribute significantly to the sorption of PCDDs, whereas >70% wood fibre in one soil resulted in a decrease of log KPOC of 0.5 units for CPs and PCDDs. We conclude that log KOC for both DOM and POM need to be explicitly determined when the retention and mobility of HOCs is described and modelled in soils.Increasing hydrophobicity of organic compounds increases the partitioning to particulate natural organic matter relative to dissolved natural organic matter.
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| 37. |
- Gemo, Nicola, et al.
(author)
-
The influence of catalyst amount and Pd loading on the H2O2 synthesis from hydrogen and oxygen
- 2015
-
In: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 5:7, s. 3545-3555
-
Journal article (peer-reviewed)abstract
- Palladium catalysts with an active metal content from 0.3 to 5.0 wt.% and supported on a strongly acidic, macroporous resin were prepared by ion-exchange/reduction method. H2O2 direct synthesis was carried out in the absence of promoters (acids and halides). The total Pd amount in the reacting environment was varied by changing A) the catalyst concentration in the slurry and B) the Pd content of the catalyst. In both cases, smaller amounts of the active metal enhance the selectivity towards H2O2, at any H-2 conversion, with option B) better than A). In case A), the Pd(II)/Pd(0) molar ratio (XPS) in the spent catalysts was found to decrease at lower catalyst Pd content. With these catalysts and this experimental set-up the dynamic H-2(1)/Pd molar ratio, the metal loading and the metal particle size were the key factors controlling the selectivity, which reached 57% at 60% H-2 conversion, and 80% at lower conversion.
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| 38. |
- Gemo, Nicola, et al.
(author)
-
TiO2 nanoparticles vs. TiO2 nanowires as support in hydrogen peroxide direct synthesis : the influence of N and Au doping
- 2016
-
In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 6:105, s. 103311-103319
-
Journal article (peer-reviewed)abstract
- The performance of Pd on titania support were evaluated in the direct synthesis of hydrogen peroxide. The equipment used was a high pressure, semi-batch apparatus equipped with a special injection system. Pd (1 wt%) catalysts on TiO2 materials with different nature were prepared by wet impregnation method. Three aspects were investigated: (a) the structure of the support (nanoparticles vs. nanowires); (b) the addition of a second active metal (Au); (c) the influence of N-doping of the support. All samples were characterized by means of XPS, TEM and XRD analyses. TiO2 nanoparticle supported catalyst demonstrated higher H2O2 selectivity and higher turnover frequency (TOF) than the catalysts based on TiO2 nanowires. The addition of Au to the Pd TiO2 nanowire catalyst improved the H2O2 selectivity due to altered particle size and electronic effects. Both N-doped versions of the catalysts gave rise to higher H2O2 selectivity than the parent non-doped ones. The synthetic procedure was the source of this observation: larger mean Pd nanoparticles were present, thus favouring the formation of H2O2 as the primary product.
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| 39. |
- Gojkovic, Zivan, et al.
(author)
-
Cryogenic X-ray photoelectron spectroscopy determines surface composition of algal cells and gives insights into their spontaneous sedimentation
- 2020
-
In: Algal Research. - : Elsevier. - 2211-9264. ; 47
-
Journal article (peer-reviewed)abstract
- The flotation properties of two green microalgal species isolated from Northern Sweden, Chlorella vulgaris 13-1 and Coelastrella sp. 3-4, were investigated. C. vulgaris 13-1 is a flotating alga that remains suspended in solution during culturing, while Coelastrella sp. 3-4 is readily sedimenting in the stationary growth phase. We were the first to use cryogenic X-ray photoelectron spectroscopy (Cryo-XPS) to gain information on the chemical composition of the algal cell surface and added to these data results obtained from diffuse reflectance - Fourier Transform infrared spectroscopy (DR-FTIR) and classical chemical extractions of carbohydrates, lipids and proteins. Based on the Cryo-XPS data the surface of the sedimenting Coelastrella sp. 3-4 strain is rich in proteins and lipids, while the cell surface of non-flocculating C. vulgaris 13-1 is predominated by carbohydrates, but is poor in lipids. The Zeta-potential of both strains was equally negative. Cell size and the amount of carbohydrates on the algal cell surface, but not the negative surface charge, therefore indicate colloidal stability of microalgae in solutions and can be applied to predict flotation properties of green microalgae.
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| 40. |
- Golyakov, A. M., et al.
(author)
-
Electrochemical and spectral properties of the polymer form of Cu(II) complex with N,N '-bis(salicylidene)-1,3-propylenediamine
- 2013
-
In: Russian journal of general chemistry. - 1070-3632 .- 1608-3350. ; 83:3, s. 423-429
-
Journal article (peer-reviewed)abstract
- A conductive polymer based on the Cu(II) complex with N,N'-bis(salicylidene)-1,3-propylenediamine was obtained electrochemically. The optimal mode of the synthesis of the polymer under potentiostatic conditions was found. We determined the charge diffusion coefficient and activation barrier and elucidated the nature of the limiting step of the charge transfer in the polymer bulk in the electrolyte medium. The azomethine base, Cu(II) complex, and its polymer form in the oxidized and reduced states were characterized by X-ray photoelectron spectroscopy and electron absorption spectroscopy.
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| 41. |
- Golyakov, A M, et al.
(author)
-
Electrochemical Synthesis and Spectroscopy of the Polymeric Form of N,N '-Bis(3-methoxysalicylidene)-1,3-propylenediamine
- 2011
-
In: Russian journal of applied chemistry. - : Springer. - 1070-4272 .- 1608-3296. ; 84:2, s. 317-324
-
Journal article (peer-reviewed)abstract
- Electrochemical oxidation of N,N '-bis(3-methoxysalicylidene)-1,3-propylenediamine leads to the formation of a conducting polymer on the electrode surface. The diffusion coeffi cient and activation barrier of the charge transfer in the bulk of the polymer in an electrolyte medium were determined. The Schiff base and its polymeric form in the oxidized and reduced states were characterized by IR, X-ray photoelectron, and electronic absorption spectroscopy. Reversible changes in the polymer structure, accompanying its electrochemical oxidation–reduction, are substantiated.
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| 42. |
- Gracia-Espino, Eduardo, et al.
(author)
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Understanding the Interface of Six-Shell Cuboctahedral and Icosahedral Palladium Clusters on Reduced Graphene Oxide : Experimental and Theoretical Study
- 2014
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:18, s. 6626-6633
-
Journal article (peer-reviewed)abstract
- Studies on noble-metal-decorated carbon nanostructures are reported almost on a daily basis, but detailed studies on the nanoscale interactions for well-defined systems are very rare. Here we report a study of reduced graphene oxide (rGOx) homogeneously decorated with palladium (Pd) nanoclusters with well-defined shape and size (2.3 +/- 0.3 nm). The rGOx was modified with benzyl mercaptan (BnSH) to improve the interaction with Pd clusters, and N,N-dimethylformamide was used as solvent and capping agent during the decoration process. The resulting Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are fully consistent with six-shell cuboctahedral and icosahedral clusters containing similar to 600 Pd atoms, where 45% of these are located at the surface. According to X-ray photoelectron spectroscopy analysis, the Pd clusters exhibit an oxidized surface forming a PdOx shell. Given the well-defined experimental system, as verified by electron microscopy data and theoretical simulations, we performed ab initio simulations using 10 functionalized graphenes (with vacancies or pyridine, amine, hydroxyl, carboxyl, or epoxy groups) to understand the adsorption process of BnSH, their further role in the Pd cluster formation, and the electronic properties of the graphene-nanoparticle hybrid system. Both the experimental and theoretical results suggest that Pd clusters interact with fiinctionalized graphene by a sulfur bridge while the remaining Pd surface is oxidized. Our study is of significant importance for all work related to anchoring of nanoparticles on nanocarbon-based supports, which are used in a variety of applications.
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| 43. |
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| 44. |
- Gustafson, Karl P. J., et al.
(author)
-
Chemoenzymatic Dynamic Kinetic Resolution of Primary Benzylic Amines using Pd-0-CalB CLEA as a Biohybrid Catalyst
- 2019
-
In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 25:39, s. 9174-9179
-
Journal article (peer-reviewed)abstract
- Herein, we report on the use a biohybrid catalyst consisting of palladium nanoparticles immobilized on cross-linked enzyme aggregates of lipase B of Candida antarctica (CalB CLEA) for the dynamic kinetic resolution (DKR) of benzylic amines. A set of amines were demonstrated to undergo an efficient DKR and the recyclability of the catalysts was studied. Extensive efforts to further elucidate the structure of the catalyst are presented.
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| 45. |
- Gälman, Veronika, 1969-, et al.
(author)
-
The role of iron and sulfur in the visual appearance of lake sediment varves
- 2009
-
In: Journal of Paleolimnology. - : Springer Netherlands. - 0921-2728 .- 1573-0417. ; 42:1, s. 141-153
-
Journal article (peer-reviewed)abstract
- Easily discernible sediment varves (annual laminations) may be formed in temperate zone lakes, and reflect seasonal changes in the composition of the accumulating material derived from the lake and its catchment (minerogenic and organic material). The appearance of varves may also be influenced by chemical processes. We assessed the role of iron (Fe) and sulfur (S) in the appearance of varves in sediments from Lake Nylandssjön in northern Sweden. We surveyed Fe in the lake water and established whether there is internal transport of Fe within the sediment. We used a unique collection of seven stored freeze cores of varved sediment from the lake, collected from 1979 to 2004. This suite of cores made it possible to follow long-term changes in Fe and S in the sediment caused by processes that occur in the lake bottom when the sediment is ageing. We compared Fe and S concentrations using X-ray fluorescence spectroscopy (XRF) in specific years in the different cores. No diagenetic front was found in the sediment and the data do not suggest that there is substantial vertical transport of Fe and S in the sediment. We also modeled Fe and S based on thermodynamic, limnological, and sediment data from the lake. The model was limited to the five components H+, e-, Fe3+, SO42-, H2CO3 and included the formation of solid phases such as Fe(OH)3 (amorphous), FeOOH (aged, microcrystalline), FeS and FeCO3. Modeling showed that there are pe (redox) ranges within which either FeS or Fe(OH)3/FeOOH is the only solid phase present and there are pe ranges within which the two solid phases co-exist, which supports the hypothesis that blackish and grey-brownish layers that occur in the varves were formed at the time of deposition. This creates new possibilities for deciphering high-temporal-resolution environmental information from varves.
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| 46. |
- Halonen, Niina, et al.
(author)
-
Low-temperature growth of multi-walled carbon nanotubes by thermal CVD
- 2011
-
In: Physica status solidi. B, Basic research. - Malden : Wiley-Blackwell. - 0370-1972 .- 1521-3951. ; 248:11, s. 2500-2503
-
Journal article (peer-reviewed)abstract
- Low-temperature thermal chemical vapor deposition (thermal CVD) synthesis of multi-walled carbon nanotubes (MWCNTs) was studied using a large variety of different precursor compounds. Cyclopentene oxide, tetrahydrofuran, methanol, and xylene: methanol mixture as oxygen containing heteroatomic precursors, while xylene and acetylene as conventional hydrocarbon feedstocks were applied in the experiments. The catalytic activity of Co, Fe, Ni, and their bi-as well as tri-metallic combinations were tested for the reactions. Low-temperature CNT growth occurred at 400 degrees C when using bi-metallic Co-Fe and tri-metallic Ni-Co-Fe catalyst (on alumina) and methanol or acetylene as precursors. In the case of monometallic catalyst nanoparticles, only Co (both on alumina and on silica) was found to be active in the low temperature growth (below 500 degrees C) from oxygenates such as cyclopentene oxide and methanol. The structure and composition of the achieved MWCNTs products were studied by scanning and transmission electron microscopy (SEM and TEM) as well as by Raman and X-ray photoelectron spectroscopy (XPS) and by X-ray diffraction (XRD). The successful MWCNT growth below 500 degrees C is promising from the point of view of integrating MWCNT materials into existing IC fabrication technologies. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 47. |
- Hu, Guangzhi, et al.
(author)
-
Small palladium islands embedded in palladium-tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction
- 2014
-
In: Nature Communications. - : Macmillan Publishers Ltd.. - 2041-1723. ; 5, s. Article number: 5253-
-
Journal article (peer-reviewed)abstract
- The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world. Here we demonstrate an efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium: tungsten = 1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium-tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are similar to 1 nm in diameter, and contain 10-20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.
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| 48. |
- Ivanova, T M, et al.
(author)
-
X-ray photoelectron spectra of heterometallic 3d-metal carboxylate complexes
- 2011
-
In: Russian Journal of Inorganic Chemistry. - : Maik Nauka/Interperiodica. - 0036-0236 .- 1531-8613. ; 56:1, s. 104-109
-
Journal article (peer-reviewed)abstract
- The electronic structure and magnetic states in the heterometallic hexanuclear complex Mn4II Fe2III (μ4-O)2(Piv)10 · MeCN4 have been studied by X-ray photoelectron spectroscopy (XPS). The substitution of two Mn atoms for two Fe atoms in the hexanuclear complex was found to have an effect on the patterns of iron and manganese X-ray photoelectron spectra. XPS data are evidence of the high-spin paramagnetic state of MnII and FeIII atoms, as well as of the ligand-metal charge transfer upon complex formation. In the heteroatomic complex, the degree of bond covalence increased for both the manganese and iron atoms. The results obtained are in good agreement with X-ray diffraction data.
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| 49. |
- Ivanova, TM, et al.
(author)
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XPS study of the electronic structure of binuclear 3d transition metal pivalate complexes
- 2012
-
In: Russian Journal of Inorganic Chemistry. - 0036-0236 .- 1531-8613. ; 57:11, s. 1484-1489
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Journal article (peer-reviewed)abstract
- Binuclear pivalate complexes of 3d transition metals (manganese, iron, cobalt, and nickel) with the same ligand environment and a lantern structure have been studied by X-ray photoelectron spectroscopy. The M2p, M3s, C1s, O1s, and N1s X-ray photoelectron spectra have been examined. A redistribution of electron density in the OCO group has been revealed. It has been shown that the theory fits the experimental data on the energy separation between the high- and low-spin components in the M3s spectra and between the spin doublet components in the M2p spectra. It has been demonstrated that the iron, cobalt, and nickel complexes are paramagnetic at room temperature, whereas the manganese complex exhibits antiferromagnetic properties. There is a correlation between the size of the 3d subshell of the transition metal atom and the M-O and M-N bond lengths.
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- Jonsson, Sofi, 1984-, et al.
(author)
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Mercury methylation rates for geochemically relevant HgII species in sediments
- 2012
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 46:21, s. 11653-11659
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Journal article (peer-reviewed)abstract
- Monomethylmercury (MeHg) in fish from freshwater, estuarine and marine environments are a major global environmental issue. Mercury levels in biota are mainly controlled by the methylation of inorganic mercuric mercury (HgII) to MeHg in water, sediments and soils. There is, however, a knowledge gap concerning the mechanisms and rates of methylation of specific geochemical HgII species. Such information is crucial for a better understanding of variations in MeHg concentrations among ecosystems and, in particular, for predicting the outcome of currently proposed measures to mitigate mercury emissions and reduce MeHg concentrations in fish. To fill this knowledge gap we propose an experimental approach using HgII isotope tracers, with defined and geochemically important adsorbed and solid HgII forms in sediments, to study MeHg formation. We report HgII methylation rate constants, km, in estuarine sediments which span over two orders of magnitude depending on chemical form of added tracer: metacinnabar (β-201HgS(s)) < cinnabar (α-199HgS(s)) < HgII reacted with mackinawite (≡FeS-202HgII) < HgII bonded to natural organic matter (NOM-196HgII) < a typical aqueous tracer (198Hg(NO3)2(aq)). We conclude that a combination of thermodynamic and kinetic effects of HgII solid-phase dissolution and surface desorption control the HgII methylation rate in sediments and causes the large observed differences in km-values. The selection of relevant solid-phase and surface adsorbed HgII tracers will therefore be crucial to achieving biogeochemically accurate estimates of ambient HgII methylation rates.
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