Enhanced carbon dioxide adsorption performance and kinetic study of K and Al co-doped Li4SiO4

Effective K and Al incorporation in Li₄SiO₄ leads to the broadened adsorption temperature range and enhanced carbon dioxide adsorption performance.     

A new method of one-pot synthesis of dicarboxylic acid derivatives and diketones containing quaternary carbon atom and remote functional groups from linear acyl halides

The one-pot, regioselective synthesis of branched diacid derivatives – diesters, dithioesters, diamides [YC(O)O(CH₂)_mC(Me)₂OC(O)Y] and diketones of aromatic and heteroaromatic series, [ArCO(CH₂)_mC(Me)₂C(O)Ar,) from available linear acyl halides, C_nH_2 n+1COCl (n = 7–9), CO (1 at) and various nucleophiles (YH = EtOH, CF₃CH₂OH, H(CF₂)₂CH₂OH, thiophene, anisole, Et₂NH, aniline, and morpholine) in the presence of the superelectrophilic complex, CBr₄·2AlBr₃ has been performed for the first time. This method provides access to new and promising groups of dicarboxylic acid derivatives and diketones containing quaternary carbon atom and remote functional groups.     

Catalytic conversion of CO2–CH4 mixture into synthetic gas—Effect of electron-beam radiation

The radiolysis of methane (0.7 MeV electron beam) was studied as a function of its concentration at two doses: 5 and 20 kGy. In both cases the G (–CH₄) value raised with the increase of the substrate concentration. Thereby the yields observed at 20 kGy are much lower, because of recombination processes. Results are also reported on the conversion of the gas mixture CH₄:CO₂:He=1:1:1 into synthetic gas (H₂/CO) at 500 °C, using two catalysts : (N5) and (N20), containing 5 wt% Ni and 20 wt% Ni, respectively, supported on γ-Al₂O₃. In an experimental series the catalysts (N5) and (N20) were treated by irradiation (4 MGy dose) before use. The highest conversion yields (above 35%) were observed by implementation of N5 and N20 catalyst at 500 °C under the influence of electron beam radiation.     

Impurity and vacancy clustering at the Σ3(1 1 1)[1 −1 0] grain boundary in strontium titanate

The interaction of selected point defects and the Σ3(1 1 1)[1 −1 0] symmetrical twin boundary in SrTiO₃ is investigated by density-functional band-structure calculations. The pristine boundary is SrO₃-terminated and exhibits electronic properties which are comparable with the pure bulk phase. Both the mirror-symmetric twin and some laterally shifted structures have low grain boundary energies, thus they may coexist in a real crystal if external stress is applied. With varying chemical potential of the electrons, the TiO₃ sublattice of the pristine boundary is destabilised by both electron enrichment and electron depletion. These results may explain, why different translation states can be observed by electron microscopy within the same bicrystal.Substitutional doping of the Ti columns next to the boundary plane with formally 3+ cations yields a contraction compared with the pure boundary. The same result, accompanied by more pronounced local geometry changes, is obtained for the translation state in the presence of O vacancies. Neutral O vacancies in the boundary plane are the most stable species followed by positively charged O vacancies in the neighbouring Sr/O plane parallel to the boundary. The Fermi level is shifted either upward to metal-derived states by substitutional doping or downward into the O-2p manifold for O vacancies. These findings may rationalise both the observed low, mainly electronic, grain boundary conductivity of SrTiO₃ boundaries and the changes in local potential found at the grain boundary by tunnelling and force microscopy experiments.     

Forced proximity of nitroxide groups in pincer compounds with a xanthene spacer

We designed bisnitroxide compounds where the radical sites are located close to each other in a molecule. Two new pincer-type bisnitroxide compounds have been synthesized, involving xanthene-4,5-diyl as a spacer and tert-butyl phenyl nitroxides as arms. From the X-ray crystal structure analysis, the shortest intramolecular interatomic N?O and O?O distances respectively are 5.074(6) and 5.258(6) Å for the m,m′-derivative and 3.624(3) and 3.771(3) Å for the p,p′-derivative. The N?O distance in the latter satisfies the empirical criterion for possible dimerization/degradation reaction accompanied by dia-/paramagnetic transition. However, the magnetic study clarified paramagnetic behavior in all the temperature range. According to a singlet-triplet model, antiferromagnetic couplings were characterized with 2J/k_B = ?7.71(2) and ?8.83(4) K for the m,m′ and p,p′-derivatives, respectively. The present result suggests that a more flexible spacer is required for realization of possible dia-/paramagnetic transition.     

Assembly of succinic acid and isoxazolidine motifs in a single entity to mitigate CO2 corrosion of mild steel in saline media

Inhibition of CO₂ corrosion of mild steel in 0.5 M NaCl under atmospheric pressure at 40 °C as well as high pressure (10 bar) at 120 °C by 2-[2-methyl-4(or 5)-alkylisoxazolidin-5(or 4)-yl)methyl]succinic acids, a new class of molecules having inhibitive motifs of succinic acid, isoxazolidine and hydrophobic alkyl chain assembled in a single entity, has been examined by gravimetric and electrochemical methods. Inhibitor molecule containing CH₃(CH₂)₈ outperformed its counterpart with a shorter hydrophobe CH₃(CH₂)₄ and two other commercial imidazoline-based inhibitors. The effectiveness of these new inhibitors was also evaluated by electrochemical impedance spectroscopy. The inhibition efficiency by EIS was found to be 75%, 91% and 98% in the presence of 1, 5 and 20 ppm, respectively, at 40 °C. The potentiodynamic polarization studies indicated that the new inhibitors act as anodic inhibitors. The adsorption of the synthesized inhibitors follows Temkin adsorption isotherm model with favorable high values of –ΔG°_ads and −ΔH°_ads pointing the inhibitors adsorbed on the metal surface by chemisorption process. The XPS study confirmed the adsorption of the inhibitors on the metal surface.     

Adsorption of CO2 and CH4 on a magnesium-based metal organic framework

A magnesium-based metal organic framework (MOF), also known as Mg-MOF-74, was successfully synthesized, characterized, and evaluated for adsorption equilibria and kinetics of CO₂ and CH₄. The Mg-MOF-74 crystals were characterized with scanning electron microscopy for crystal structure, powder X-ray diffraction for phase structure, and nitrogen adsorption for pore textural properties. Adsorption equilibrium and kinetics of CO₂ and CH₄ on the Mg-MOF-74 adsorbent were measured in a volumetric adsorption unit at 278, 298, and 318 K and pressures up to 1 bar. It was found that the Mg-MOF-74 adsorbent prepared in this work has a median pore width of 10.2 Å, a BET specific surface area of 1174 m²/g, CO₂ and CH₄ adsorption capacities of 8.61 mmol g^?1 (37.8 wt.%) and 1.05 mmol g^?1 (1.7 wt.%), respectively, at 298 K and 1 bar. Both CO₂ and CH₄ adsorption capacities are significantly higher than those of zeolite 13X under similar conditions. The pressure-dependent equilibrium selectivity of CO₂ over CH₄ (q_CO2/q_CH4) in the Mg-MOF-74 adsorbent showed a trend similar to that of zeolite 13X and the intrinsic selectivity of Mg-MOF-74 at zero adsorption loading is 283 at 298 K. The initial heats of adsorption of CO₂ and CH₄ on the Mg-MOF-74 adsorbent were found to be 73.0 and 18.5 kJ mol^?1, respectively. The adsorption kinetic measurements suggest that the diffusivities of CO₂ and CH₄ on Mg-MOF-74 were comparable to those on zeolite 13X. CH₄ showed relatively faster adsorption kinetics than CO₂ in both adsorbents. The diffusion time constants of CO₂ and CH₄ in the Mg-MOF-74 adsorbent at 298 K were estimated to be 8.11 × 10^?3 and 4.05 × 10^?2 s^?1, respectively, showing a modest kinetic selectivity of about 5 for the separation CH₄ from CO₂.     

Nanospace geometry-sensitive molecular assembly

Interaction of a molecule with micropore walls strongly depends on the micropore width. Molecules confined in the micropore tend to form an intermolecular structure inherent to each molecule/pore system in order to lower the whole molecular energy. Supercritical NO is adsorbed in micropores of zolite or activated carbon fiber in the form of a dimer at 303 K. The NO dimerization varies with the micropore width. CCl₄ molecules only in pore of pore width =1.0 nm at 303 K form a plastic crystalline structure which is observed at 246–250 K in the bulk phase. H₂O molecules are associated with each other to form an ordered assembly in carbon micropores at 303 K; the smaller the pore width, the more ordered the assembly structure. The presence of preadsorbed H₂O noticeably enhances adsorption of supercritical CH₄ in carbon micropores at 303 K due to methane nanohydrate formation, which has an optimum pore width of 1 nm.     

About the co-product of the OH radical in the reaction of acetyl with O2 below atmospheric pressure

Recent studies have shown that the reaction between acetyl radicals and O₂ at low pressures leads to the direct fast formation of OH radical, but the nature of co-products is controversial. Laser photolysis coupled to TDLAS (10–200 Torr, 298 K) has been employed to directly monitor two possible co-products of this reaction, CO and formaldehyde. Only CH₂O has been detected in yield of 0.29 ± 0.13, but with time constants much slow than the OH formation under these conditions; the observed CH₂O-time profiles are compatible with the known mechanism of peroxyacetyl secondary reactions.     

Computational study of the molecular hydrogen physisorption in some of the corannulene derivatives as a carbon nanostructure

Substitution of the peripheral H atoms in the corannulene molecule as a carbon nanostructure by OH, CH₃, NH₂ and NO₂ groups on the molecular hydrogen physisorption was evaluated at MP2/6-31G(d) level of theory. Two orientations of hydrogen were used on the concave and convex sides of corannulene. It was seen that binding to the concave face is favored relative to the convex face. The average binding energy was calculated and corrected for the basis set superposition error (BSSE) using the counterpoise method. Results showed that binding energy varies depending upon the site and side of absorption. The electronic density, charge transfer and spatial prohibition of the substituted groups affects the binding energy. The increment of the electronic density because of the substitution of electron donor groups facilitates hydrogen adsorption and leads to larger binding energies than when H atoms are substituted by electron acceptor groups. Substitution of H atoms with each of the considered groups leads to decreasing of the HOMO–LUMO energy gap and so decreasing of the kinetic stability and increasing of the reactivity. The energy gap and binding energy for corannulene derivatives decreases in the order of: CH₃ > OH > NH₂ > NO₂.     

Vapour pressures,densities, and viscosities of the (water + lithium bromide + potassium acetate) system and (water + lithium bromide + sodium lactate) system

Measurements of thermophysical properties (vapour pressure, density, and viscosity) of the (water + lithium bromide + potassium acetate) system LiBr:CH₃COOK = 2:1 by mass ratio and the (water + lithium bromide + sodium lactate) system LiBr:CH₃CH(OH)COONa = 2:1 by mass ratio were measured. The system, a possible new working fluid for absorption heat pump, consists of absorbent (LiBr + CH₃COOK) or (LiBr + CH₃CH(OH)COONa) and refrigerant H₂O. The vapour pressures were measured in the ranges of temperature and absorbent concentration from T = (293.15 to 333.15) K and from mass fraction 0.20 to 0.50, densities and viscosities were measured from T = (293.15 to 323.15) K and from mass fraction 0.20 to 0.40. The experimental data were correlated with an Antoine-type equation. Densities and viscosities were measured in the same range of temperature and absorbent concentration as that of the vapour pressure. Regression equations for densities and viscosities were obtained with a minimum mean square error criterion.     

Phase transfer catalysis: Synthesis of monodispersed FePt nanoparticles and its electrocatalytic activity

Using dibenzo-24-crown-8-ether (DB24C8) as phase transfer catalyst, the monodispersed iron–platinum (FePt) alloy nanoparticles with size of ∼17 nm were synthesized by reduction of H₂PtCl₆·6H₂O and FeCl₂·4H₂O in the solvothermal system. The structure, magnetic property and electrocatalytic activity of FePt nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction system (XRD), vibration sample magnetometer (VSM) and CHI 820 electrochemical analyser (three electrodes system, the reference electrode is saturated calomel electrode (SCE), the counter electrode is platinum electrode and the glassy carbon electrode is used as working electrode (GCE)), respectively. The results show that the as-synthesized FePt nanoparticles have a chemically disordered fcc structure and can be transformed into chemically ordered fct structure after annealing treatment above 400 °C, simultaneously accompanying with the coercivity changed from 5 to 2400 Oe. CVs of 0.5 M H₂SO₄/0.5 M CH₃OH on GCE modified with FePt nanoparticles monolayer illustrate that the as-synthesized FePt nanoparticles have strong electrocatalytic activity toward the oxidation of CH₃OH in aqueous solution.     

An expedient approach to ferrocenyl thioamides via Fischer carbenes

Oxidative demetalation of Fischer ferrocenyl ethoxy carbene complexes (1a–c, M = Cr, Mo, W) and new Fischer ferrocenyl R-amino carbene complexes [2–5 (a–c), 11–15 (a–c), and 21–22 (a–c); M = Cr, Mo, W; R = H, CH₃, C₂H₅, C₃H₇, (CH₂)₂OH, (CH₂)₃OH, (CH₂)₂(OMe)₂, (CH₂)₃N(Me)₂, CH₂CHCH₂, (CH₂)₂OSi(CH₃)₃, (CH₂)₃OSi(CH₃)₃] with elemental sulfur–NaBH₄ were carried out under mild conditions, obtaining O-ethyl ferrocenecarbothioate (6) and novel ferrocenyl thioamides (7–10 and 16–20) in excellent yields.     

Methanol adsorption on γ-irradiated SiO2 surface

The adsorption of methanol on γ-irradiated and un-irradiated SiO₂ surfaces pretreated at 473 K was investigated by Fourier transform infrared spectroscopy, temperature programmed desorption (TPD) and pulse methods. Methanol adsorbed only in molecular form on the un-irradiated sample. Treating the pre-irradiated silica surface with methanol at room temperature formaldehyde and hydrogen were formed. The methanol adsorbed on the irradiated silica transformed to formyl groups during a longer time at room temperature and desorbed as formaldehyde simultaneously with CH₃OH (T_max=395 K) on the TPD.     

Signal enhancement in solution-cathode glow discharge — optical emission spectrometry via low molecular weight organic compounds

HCOOH, CH₃COOH, and CH₃CH₂OH were used as chemical modifiers in a solution-cathode glow discharge. Emission was measured directly from the discharge, without a gas–liquid separator or a secondary excitation source. Emission from Ag, Se, Pb, and Hg was strongly enhanced, and the detection limits (DL) for these elements were improved by up to an order of magnitude using a combination of HCOOH and HNO₃ compared to using HNO₃ alone. The DL was measured for Mg (1 μg/L), Fe (10 μg/L), Ni (6 μg/L), Cu (6 μg/L), Pb (1 μg/L), Ag (0.1 μg/L), Se (300 μg/L), and Hg (2 μg/L). Coefficients of determination (R²) were between 0.9986 and 0.9999. A voltage of 1 kV was used, which produced a current of approximately 70 mA.     

New all-cis-tetra(p-tolyl)cyclotetrasiloxanetetraol and its functionalization

New all-cis-tetra(p-tolyl)cyclotetrasiloxanetetraol and its derivatives with Si(CH = CH₂)Me and Si(H)Me₂ groups have been prepared and characterized by IR and NMR spectroscopy, GPC, mass spectrometry, TGA and DSC. Molecular and crystalline structures of the tetraol and its derivative with four Si(CH = CH₂)Me groups have been determined by single-crystal X-ray diffraction.     

Mono- and dinitroxide radicals from 9,9′(10H,10′H)-spirobiacridine: An approach to a D2d triplet biradical

Oxidation of 9,9′(10H,10′H)-spirobiacridine with m-chloroperbenzoic acid gave a dinitroxide biradical derivative, SBDO, together with a monoradical, SBO. Their molecular and crystal structures were determined by X-ray crystallographic analysis. Magnetic measurements on a polycrystalline sample of SBDO revealed the presence of dominant antiferromagnetic interaction, which can be ascribed mainly to intermolecular interaction due to close contacts between two nitroxide groups. The intermolecular N–O distances were 3.176(2) and 3.184(2) Å. The diluted ESR experiments and the DFT calculation on a single molecule of SBDO indicated the ground triplet state. We also found that SBO worked as a versatile host for organic solvent molecules (CH₂Cl₂, CHCl₃, CH₃CN, ClC₆H₅, CH₃OH, etc.).     

Evidence of an odd–even effect on the thermodynamic parameters of odd fluorotelomer alcohols

A phase transition study, including vapour pressure determinations of odd fluorotelomer alcohols {oFTOH; CF₃(CF₂)_nCH₂OH, with n = 5 to 9}, is reported in order to explore the effect of the successive introduction of –CF₂– groups into the molecule on the thermodynamic properties related to (solid + liquid, solid + gas, and liquid + gas) equilibria. An odd–even effect on the thermodynamic parameters of fusion and sublimation was observed in the homologous series of odd fluorotelomer alcohols indicating an increase of the stability in the crystal packing for the members with an odd number of carbon atoms. The vaporization parameters of o-FTOH were compared with the literature data for their alkane analogues and the results showed a higher volatility of liquid fluorotelomer alcohols than their congeners. The higher molecular conformation restriction of perfluorinated alcohols and/or the higher molar mass seems to contribute to their higher entropy of vaporization which drives the volatility of the 1H,1H-perfluorinated alcohols.     

(Liquid + liquid) equilibria of the (water + butyric acid + dodecanol) ternary system

(Liquid + liquid) equilibrium (LLE) data for the (water + butyric acid + dodecanol) ternary system have been determined experimentally at T = (298.2, 308.2 and 318.2) K. Complete phase diagrams were obtained by determining binodal curves and tie lines. The reliability of the experimental tie lines was confirmed by using the Othmer–Tobias correlation. The UNIFAC method was used to predict the phase equilibrium in the ternary system using the interaction parameters determined from experimental data of CH₃, CH₂, COOH, OH and H₂O functional groups. Distribution coefficients and separation factors were evaluated for the immiscibility region.