| 1. |
- Akbarkermani, Mohammadreza, et al.
(författare)
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Eutectic freeze crystallization in the boric acid–water system
- 2023
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Ingår i: Chemické zvesti. - : Springer Nature. - 0366-6352 .- 1336-9075. ; 77:10, s. 5881-5891
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Tidskriftsartikel (refereegranskat)abstract
- Boron compounds are widely used in various industries. Current high rates of boron production/usage generate significant wastes. As an ecologically friendly technology, eutectic freeze crystallization (EFC) has the potential to treat boron wastewater ponds for mineral recovery; however, its feasibility has not been examined before. Here, we determined the eutectic point of boric acid (a major boron compound)-water system to be -0.79 °C and 2.5 ± 0.05 wt%. At the eutectic point, ice and boric acid crystals were isolated from the aqueous solution. The nucleation rate and growth rate of boric acid were considered, as well as the boron content in ice crystals. Our results show that it is feasible to separate boric acid and water from boron waste streams by EFC.
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| 2. |
- Bekhradnia, Ahmadreza R., et al.
(författare)
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1,3-dipolar cycloaddition between substituted phenyl azide and 2,3-dihydrofuran
- 2014
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Ingår i: Chemical Papers. - : Springer Science and Business Media LLC. - 0366-6352 .- 1336-9075. ; 68:2, s. 283-290
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical study was performed on the 1,3-dipolar cycloaddition between 2,3-dihydrofuran and substituted phenyl azide using Density Functional Theory (DFT) in combination with a 6-311++G(d,p) basis set. The optimum geometries for reactant, transition state and product, as well as the kinetic data, rate constants and reaction constant (rho) were investigated to rationalise the substitution effects and reaction rates of the 1,3-dipolar cycloaddition process in various solvents. The DFT calculation and Frontier Molecular Orbital (FMO) theory as well as the atomic Fukui indices show that the electron-withdrawing substituents enhance the reaction constant (rho > 0), especially in polar aprotic solvents. Consequently, small changes in the rate constant of the reaction in various solvents and geometric similarity between reactants and transition state structures were suggested as the early transition state mechanism for electron-withdrawing substituents. In addition, the slope of the Hammett plot and susceptibility of the reaction to electron-withdrawing substituents in various solvents confirmed the mechanism. (C) 2013 Institute of Chemistry, Slovak Academy of Sciences
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| 3. |
- Bortoluzzi, Marco, et al.
(författare)
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Luminescent lanthanide complexes with phosphoramide and arylphosphonic diamide ligands
- 2020
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Ingår i: Chemické zvesti. - : Springer. - 0366-6352 .- 1336-9075. ; 74:11, s. 3693-3704
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Tidskriftsartikel (refereegranskat)abstract
- The sensitization of Eu(III) luminescence by the phosphoramide and arylphosphonic diamide ligands OP(NMe2)2Ind, OP(NMe2)2Cbz, OP(NMe2)2Ph, OP(NMe2)2(1-Naph) and OP(NMe2)2(2-Naph) (Ind = indol-1-yl; Ph = phenyl; Cbz = carbazol-9-yl; 1-Naph = naphtalen-1-yl; 2-Naph = naphtalen-2-yl) was verified by coordination to the [Eu(NO3)3] metal fragment. The emission spectra of the corresponding complexes showed only the 5D0 → 7FJ transitions of the metal centre, with the exception of the carbazolyl derivative. Some of the ligands were also able to sensitize Tb(III) luminescence, in agreement with the triplet state energies estimated from the phosphorescence spectra of the analogous Gd(III) nitrates. On the basis of the photoluminescence results achieved using nitrate as ancillary ligand, heptacoordinate Eu(III) complexes having general formula [Eu(β-dike)3L] (β-dike = dibenzoylmethanate, tenoyltrifluoroacetonate; L = phosphoramide or arylphosphomic diamide ligand) were prepared and characterized. All the complexes exhibited bright red emission upon excitation with near-UV and violet-blue light, with intrinsic quantum yields ranging between 18 and 36%.
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| 4. |
- Bortoluzzi, Marco, et al.
(författare)
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The conjugate base of malonaldehyde as antenna-ligand towards trivalent europium and terbium ions
- 2018
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Ingår i: Chemické zvesti. - : Springer. - 0366-6352 .- 1336-9075. ; 72:4, s. 809-819
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Tidskriftsartikel (refereegranskat)abstract
- Coordination compounds having formulae [M(MA)3]n and M(MA)(Me2Tp)2 (M = Y, Eu, Tb; MA = conjugate base of malonaldehyde; Me2Tp = tris(3,5-dimethyl-pyrazol-1-yl)borate) were synthesized and characterized. The photoluminescence features of the europium and terbium derivatives were investigated. By comparing the herein reported photoluminescence data with those relative to analogous nitro- and bromomalonaldehyde derivatives, it appears that the conjugate base of malonaldehyde is a more efficient antenna-ligand for the sensitization of Tb(III) luminescence. The experimental data were rationalized on the basis of DFT calculations. Tb(MA)(Me2Tp)2 was used as dopant for the preparation of luminescent plastic materials based on poly(methyl methacrylate).
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| 5. |
- Gutierrez-Sanchez, Cristina, et al.
(författare)
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Third-generation oxygen amperometric biosensor based on Trametes hirsuta laccase covalently bound to graphite electrode
- 2015
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Ingår i: Chemické zvesti. - : Slovak Academic Press. - 0366-6352 .- 1336-9075. ; 69:1, s. 237-240
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Tidskriftsartikel (refereegranskat)abstract
- The response of low-density graphite electrodes hosting Trametes hirsuta laccase in a direct electron transfer regime is presented for real-time analysis of O2 concentrations. The use of contrasting immobilisation methods developed for biocathodes affords good reproducibility and reliability of the amperometric biosensor, which shows a limit of detection below 1 µM and a sensitivity slightly higher than 60 nA cm−2 M.
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| 6. |
- Johansson, Ted, et al.
(författare)
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Characterization of LaRhO3 perovskites for dry (CO2) reforming of methane (DRM)
- 2014
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Ingår i: Chemické zvesti. - : Springer Science and Business Media LLC. - 0366-6352 .- 1336-9075. ; 68:9, s. 1240-1247
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Tidskriftsartikel (refereegranskat)abstract
- This work reports on the characterization of LaRhO3 perovskite as a catalyst for dry reforming of methane. The catalyst was studied using CH4-temperature programmed reduction (TPR), H-2-TPR, and temperature programmed surface reaction (TPSR), and the changes in the crystal structure of the catalyst due to these treatments were studied by X-ray diffraction (XRD). XRD pattern of the freshly calcined perovskites showed the formation of highly crystalline LaRhO3 and La2O3 phases. H-2-TPR of the fresh calcined catalyst showed a shoulder at 342A degrees C and a broad peak at 448A degrees C, suggesting that the reduction of Rh in perovskite occurs in multiple steps. XRD pattern of the reduced catalyst suggests complete reduction of the LaRhO3 phase and the formation of metallic Rh and minor amounts of La(OH)(3). The CH4-TPR data show qualitatively similar results as H-2-TPR, with a shoulder and a broad peak in the same temperature range. Following the H-2-TPR up to 950A degrees C, the same batch of catalyst was oxidized by flowing 5 vol. % O-2/He up to 500A degrees C and a second H-2-TPR (also up to 950A degrees C) was conducted. This second H-2-TPR differed significantly from that of the fresh calcined catalyst. The single sharp peak at 163A degrees C in the second H-2-TPR suggests a significant change in the catalyst, probably causedby the transformation of about 90 % of the perovskite into Rh/La2O3. This was confirmed by the XRD studies of the catalyst reduced after the oxidation at 500A degrees C. TPSR of the dry reforming reaction on the fresh calcined catalyst showed CO and H-2 formation starting at 400A degrees C, with complete consumption of the reactants at 650A degrees C. The uneven consumption of reactants between 400A degrees C and 650A degrees C suggests that reactions other than DRM occur, including reverse water gas shift (RWGS) and the Boudouard reaction (BR), probably as a result of in-situ changes in the catalyst, consistent with the H-2-TPR results. TPSR, after a H-2-TPR up to 950A degrees C, showed that the dry reforming reaction did not light off until 570A degrees C, which is much higher temperature than the one observed using fresh calcined catalyst. This shows that the uniform sites produced during the 950A degrees C H-2-TPR are catalytically less active than those of the fresh calcined catalyst, and that no significant side reactions such as RWGS or the Boudouard reaction occur. This suggests that reduction leads to the formation of a single type of sites which do not catalyze simultaneous side reactions.
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| 7. |
- Molaei, Arman, 1988-, et al.
(författare)
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New low-cost, flow-through carbon electrodes characterized in brackish water
- 2023
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Ingår i: Chemické zvesti. - : Slovenskâa akadâemia vied; Springer. - 0366-6352 .- 1336-9075. ; 77, s. 1941-1950
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Tidskriftsartikel (refereegranskat)abstract
- We propose a simple and low-cost flow-through electrode for electrochemical cells used for instance in capacitive desalination. We have coated macro-porous carbon fiber papers with various loads of carbon microporous particles to combine both a high surface area and an open structure for good fluid dynamics. In this first study, we restrict our investigation to the charging/discharging behavior, the identification of side reactions, and the effect of geometry on the diffusion of ions. The electrochemical performance was first investigated by cyclic voltammetry and galvanic charge-discharge techniques. The specific capacitance increases by three orders of magnitude upon adding the carbon particles. Then, electrochemical impedance spectroscopy revealed the presence of charge transfer phenomena and modification in the mass transport by the diffusion process for the coated electrode.
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| 8. |
- Moretti, Elisa, et al.
(författare)
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Luminescent Eu-doped GdVO4 nanocrystals as optical markers for anti-counterfeiting purposes
- 2017
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Ingår i: Chemical Papers. - : Springer. - 0366-6352 .- 2585-7290 .- 1336-9075. ; 71:1, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- Luminescent Eu:GdVO4 nanoparticles, with an average size of 60 nm, were deposited first on monocrystalline silicon wafers, then on four different natural stone materials, by a spray-coating technique and a silica layer was subsequently deposited by atmospheric pressure plasma jet to protect the luminescent layer and improve its adhesion to the substrate. The luminescent films were characterized by photoluminescence excitation and emission, while the surface morphology was examined by FEG-SEM microscopy and spectroscopic ellipsometry to determine the coating thickness. The optical appearance of the coatings was also evaluated by colorimetric measurements and the efficacy of the fixing action of the silica layer was estimated by PL measurements performed before and after a Scotch™ tape peeling test. The proposed methodology, easily applied on the surface of stone supports, has led to the realization of a luminescent film displaying good mechanical properties, transparent and undetectable in the presence of visible light, but easily activated by UV light source, indicating that the Eu:GdVO4 nanophosphors could be used as luminescent nanotags for a reliable anti-counterfeiting technology.
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| 9. |
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| 10. |
- Suzaei, F. M., et al.
(författare)
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Recent molecularly imprinted polymers applications in bioanalysis
- 2023
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Ingår i: Chemické zvesti. - : Springer Nature. - 0366-6352 .- 1336-9075. ; 77:2, s. 619-655
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Tidskriftsartikel (refereegranskat)abstract
- Molecular imprinted polymers (MIPs) as extraordinary compounds with unique features have presented a wide range of applications and benefits to researchers. In particular when used as a sorbent in sample preparation methods for the analysis of biological samples and complex matrices. Its application in the extraction of medicinal species has attracted much attention and a growing interest. This review focus on articles and research that deals with the application of MIPs in the analysis of components such as biomarkers, drugs, hormones, blockers and inhibitors, especially in biological matrices. The studies based on MIP applications in bioanalysis and the deployment of MIPs in high-throughput settings and optimization of extraction methods are presented. A review of more than 200 articles and research works clearly shows that the superiority of MIP techniques lies in high accuracy, reproducibility, sensitivity, speed and cost effectiveness which make them suitable for clinical usage. Furthermore, this review present MIP-based extraction techniques and MIP-biosensors which are categorized on their classes based on common properties of target components. Extraction methods, studied sample matrices, target analytes, analytical techniques and their results for each study are described. Investigations indicate satisfactory results using MIP-based bioanalysis. According to the increasing number of studies on method development over the last decade, the use of MIPs in bioanalysis is growing and will further expand the scope of MIP applications for less studied samples and analytes.
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| 11. |
- Van Wyk, Shane C., et al.
(författare)
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Bimetallic nickel and palladium complexes for catalytic applications
- 2016
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Ingår i: Chemical Papers. - : Springer Science and Business Media LLC. - 0366-6352 .- 1336-9075. ; 70:8, s. 1003-1023
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Forskningsöversikt (refereegranskat)abstract
- South Africa is a mineral-rich country and one area in which minerals can be very important is catalysis. Over an extended period of time, homogeneous catalysis has grown to become very useful, particularly in the chemical and pharmaceutical industries. The organometallic compounds required in the catalysis industry have advanced from metallocenes to an alternative in the form of α-diimines. Most α-diimines are prepared from iminopyridyl moieties and are most active with nickel and palladium transition metals. This review providesa history of homogeneous catalysis and a discussion on iminopyridines, with the main focus on the nickel and palladium complexes formed from them. There follows a discussion of the bimetallic nickel and palladium complexes in various catalytic applications such as Suzuki and Heck coupling, with the main focus on ethylene polymerisation. The limitations are addressed and possible solutions presented to overcome those challenges. Several reviews in the related topics are to be found in the literature but not the α-diimine with iminopyridines and bimetallic nickel and palladium metals.
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| 12. |
- Bayat, Mohammad, et al.
(författare)
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An experimental study for finding the best condition for PHI zeolite synthesis using Taguchi method for gas separation
- 2018
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Ingår i: Chemical papers. - : Springer. - 2585-7290 .- 1336-9075. ; 72:5, s. 1139-1149
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Tidskriftsartikel (refereegranskat)abstract
- Phillipsite zeolite particles and membranes were successfully synthesized at different operational and environmental conditions. Using an L9 orthogonal array of the Taguchi method, effects of experimental condition—synthesis temperature (130–150 °C), synthesis time (2–3 days), number of synthesized layers (1–3), and seeding suspension percentage—for membrane preparation with respect to CO2/CH4 ideal selectivity were investigated. The results showed that the ideal selectivity was improved up to 4.20 from 1.15 by increasing the number of synthesized layers, synthesis temperature, and seed solution concentration and by decreasing synthesis time. Moreover, the best synthesis conditions were defined based on the Taguchi method results and the membrane was synthesized with the highest ideal selectivity which was around 4.40. In addition, it was shown that T zeolite is formed beside PHI zeolite at low temperature even with long synthesis time.
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| 13. |
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| 14. |
- Safaei, Fariba, et al.
(författare)
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Preparation of an acrylic acid-based superabsorbent composite : investigation of synthesis parameters
- 2020
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Ingår i: Chemical Papers. - : Institute of Chemistry, Slovak Academy of Sciences. - 2585-7290 .- 1336-9075. ; 74:3, s. 939-949
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Tidskriftsartikel (refereegranskat)abstract
- This research was an attempt to investigate the influence of polymerization parameters including monomer concentration, neutralization percent, initiator concentration, the presence of porogen agent and Perlite content on the swelling properties of acrylic-based hydrogels and their composites. With regard to water absorbency, the conclusion drawn was that the highest levels occurred in the following conditions: monomer concentration of 6.127 M, neutralization percentage of 75, initiator concentration of 0.197 M and sodium bicarbonate, as a porogen agent, of 0.375 M. The research was also focused on the absorbency under load (AUL) of the prepared hydrogel composites (acrylic acid/Perlite) at different amounts of Perlite. The composite with Perlite content of 8.33 wt% showed maximum water absorbency under load. The chemical structure of Perlite, hydrogel and their composite was studied using Fourier transform infrared spectroscopy (FTIR). Furthermore, field-emission scanning electron microscopy (FESEM) was used to evaluate the morphology of the prepared hydrogel; while, the energy-dispersive X-ray (EDS) was used to investigate the dispersion of the Perlite in the composite. The FTIR test results confirmed the presence of both components of hydrogel and Perlite in the composite. In addition, the FESEM images and EDS results confirmed induced porous structure after incorporating Perlite particles to the hydrogel, considering an acceptable dispersion.
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