Electrorheological behavior of copper phthalocyanine-doped MCM-41 suspensions

A type of anhydrous electrorheological (ER) material of copper phthalocyanine (CuPC)-doped MCM-41 was synthesized by in situ micelle-assisted incorporation of CuPC during MCM-41 synthesis. The ER behavior of the suspensions of CuPC-doped MCM-41 particles in paraffin liquid with a 30 wt.% was investigated under an applied electric field. It is found that the ER effect increased with increasing the CuPC-doping ratio. The dopants of CuPC molecules within the mesochannel of MCM-41 mesoporous sieve improved the conductivity of the particles, and produced a proper conductivity of 10⁻⁷ S m⁻¹. Dielectric spectra of the fluids were also measured to examine their possible correlation with the ER behavior, and the results were explained based on Ikazaki's criterion that the relaxation frequency must be in the range 100–10⁵ Hz and the difference in the dielectric constant must be large below and above the relaxation frequency for an appreciable ER effect.     

Electrorheological behavior of copper phthalocyanine-doped mesoporous TiO2 suspensions

A type of anhydrous electrorheological (ER) material of copper phthalocyanine (CuPC)-doped mesoporous TiO2 was synthesized by in situ micelle-assisted incorporation CuPC during mesoporous TiO2 synthesis. TEM, XRD and the nitrogen adsorption-desorption isotherms demonstrated that the material had mesoporous structure and an anatase framework. The ER behavior of the suspensions of CuPC-doped mesoporous TiO2 in silicone oil with the different volume fractions was investigated under an applied electric field. It is found that the suspensions showed visible electrorheological behavior which were compared with that of pure TiO2. The dopants of CuPC molecules within the mesochannel of TiO2 mesoporous sieve improved the conductivity of the particles and produced a proper conductivity of approximately 10(-7) S m(-1). Dielectric spectra of the ER fluid were measured to examine the peak of epsilon' should appear in the frequency range of 10(2)-10(5) Hz and have a large Deltaepsilon' in this frequency range. Therefore, the both properties may make a conjunct effect on electrorheological behavior.     

Determination of absorptivity and formation constant of a chalcone association complex

A UV spectrometric method was developed to determine the molar absorptivity (_C) and formation constant (K_c) of the association complex of unsubstituted chalcone in cyclohexane, in the concentration range from 4.00·10⁻⁴ to 2.00·10⁻² mol dm⁻³. The thermodynamic and spectroscopic magnitudes such as K_c and _C contribute to the understanding of the physicochemical behavior of several ,β-unsaturated carbonylic compounds, of low solubility in water, as it is the case of numerous flavonoids of chemical and biological importance. The studied association complex, formed by two chalcone molecules, is characterized by the constants _C (300.8 nm)=4.98·10⁴ dm³ mol⁻¹ cm⁻¹ and K_c=5.58·10³. The method proposed is convenient for the study of solute–solute molecular associations particularly those due to dipole–dipole interactions.     

Photocatalytic removal of the insecticide fenitrothion from water sensitized with TiO2

The photocatalytic removal of the insecticide fenitrothion (IUPAC name: O,O-dimethyl O-4-nitro-m-tolyl phosphorothioate), C₉H₁₂NO₅PS, from water suspension of TiO₂, was investigated by following the disappearance of the original substance along with the formation and disappearance of intermediates via recording NMR (¹H and ³¹P) and UV spectra, as well as by pH measurements. Based on the obtained data, a possible reaction mechanism was proposed. It was found that ³¹P-NMR spectrometry can be successfully used to follow the kinetics of transforming organic into inorganic phosphorus in the course of the degradation (k_a=9.2×10⁻⁷ mol dm⁻³ min⁻¹, r=0.980 for the illumination period after 15 h). The rate of fenitrothion aromatic ring decomposition was followed by UV spectrometry during the illumination (k_a=3.1×10⁻⁶ mol dm⁻³ min⁻¹, r=0.989). The complete mineralization was attained after about 66 h of irradiation.     

Photocatalytic oxidation of the herbicide (4-chloro-2-methylphenoxy)acetic acid (MCPA) over TiO2

The photocatalytic decomposition of the herbicide (4-chloro-2-methylphenoxy)acetic acid (MCPA), C₉H₉ClO₃, in aqueous suspensions containing TiO₂ was investigated by following the formation of intermediates via recording proton NMR spectra. One of theoretically possible intermediates, 4-chloro-2-methylphenolmethanoate, was synthesized by a modified esterification procedure. Based on the data obtained a possible reaction mechanism was proposed. The rate of MCPA aromatic ring decomposition was followed by pH changes during illumination. As a result, apparent reaction rate constant was found to be 7.0×10⁻⁶ mol dm⁻³ min⁻¹. The complete mineralization was attained after about 15 h of illumination.     

Kinetic study of a thermal dechlorination and oxidation of neodymium oxychloride

This study investigated the kinetics of a thermal dechlorination and oxidation of neodymium oxychloride (NdOCl) by using a non-isothermal thermogravimetric (TG) analysis under various oxygen partial pressures. The results of the isoconversional analysis of the TG data suggests that the dechlorination and oxidation of NdOCl follows a single step reaction and the observed activation energy was determined as 228.3 ± 6.1 kJ mol⁻¹. A kinetic rate equation was derived for a conversion of the NdOCl into Nd₂O₃ with a power law model, f() = 2/3^−1/2. The oxygen power dependency and the pre-exponential factor were determined as 0.315 and 3.55 × 10⁵ s⁻¹ Pa^−0.315, respectively.     

First steps in radiation-induced hydrogel synthesis: radical formation and oligomerization in dilute aqueous N-isopropylacrylamide solutions

The reactions of hydroxyl radical, hydrogen atom and hydrated electron intermediates of water radiolysis with N-isopropylacrylamide (NIPAAm) were studied by pulse radiolysis in dilute aqueous solutions. OH, H and e_aq⁻ react with NIPAAm with rate coefficient of (6.9±1.2)×10⁹, (6.6±1)×10⁹, and (1.0±0.2)×10¹⁰ mol⁻¹ dm³ s⁻¹. In OH and H radical addition to the double bond mainly -carboxyalkyl type radicals form, (OHCH₂CH^√C(N-i-C₃H₇)O and CH₃CH^√C(N-i-C₃H₇)O). In reaction of e_aq⁻ oxygen atom centered radical anion is produced (CH₂CHC^√(N-i-C₃H₇)O⁻), the anion undergoes reversible protonation with pK_a=8.7. There is also an irreversible protonation on the β-carbon atom that produces the same radical as forms in H atom reaction (CH₃CH^√C(N-i-C₃H₇)O). The -carboxyalkyl type radicals at low NIPAAm concentration (0.1–1 mmol dm⁻³) mainly disappear in self-termination reactions, 2k_t,m=8.4×10⁸ mol⁻¹ dm³ s⁻¹. At higher concentrations the decay curves reflect the competition of the self-termination and radical addition to monomer (propagation). The termination rate coefficient of oligomer radicals containing a few monomer units is 2k_t≈2×10⁸ mol⁻¹ dm³ s¹.     

Micellar effects on photoinduced redox reactions of Fe(bpy)2(CN)2

Excitation of solutions of Fe(bipy)₂(CN)₂ by a 266-nm laser pulse produces a hydrated electron and the oxidized complex, Fe(bipy)₂ (CN)₂⁺, in the primary photochemical step, in homogeneous aqueous solution as well as in aqueous solutions containing cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) micelles. In all cases nascent hydrated electrons react with ground state Fe(bipy)₂(CN)₂ to form Fe(bipy)₂(CN)₂⁻, and comparison of the decay constants in the three media (H₂O: k = 2.8 × 10¹⁰ M⁻¹ s⁻¹; CTAB: k = 2.9 × 10¹⁰ M⁻¹ s⁻¹; SDS: k = 5.5 × 10⁹ M⁻¹ s⁻¹), shows that the reaction is essentially unaffected by CTAB micelles but is much slower in SDS solution. Similar micellar effects were found for the back reaction between e_aq⁻ and Fe(bpy)₂(CN)₂⁺. Rate constants for the scavenging of the photogenerated hydrated electrons by methyl viologen (MV²⁺) cations and NO₃⁻ anions were measured in the three systems, and the results indicate that for scavenging by MV²⁺ the rate constants are decreased in the micelle systems (k in H₂O, 8.4 × 10¹⁰; CTAB, 3.5 × 10¹⁰ and SDS, 1.58 × 10¹⁰ M⁻¹ s⁻¹), whereas for NO₃⁻ the CTAB micelle decreases while the SDS micelle enhances the scavenging compared to water solution (k in H₂O, 8.3 × 10⁹; CTAB, 7 × 10⁸; and SDS, 2.05 × 10¹⁰ M⁻¹ s⁻¹). For the comproportionation reaction between Fe(bipy)₂(CN)₂⁺ and Fe(bipy)₂(CN)₂⁻ both micelles reduce the rate (k in H₂O, 3.3 × 10¹⁰; CTAB, 2.3 × 10¹⁰; and SDS, 1.05 × 10¹⁰ M⁻¹s⁻¹), but while the reaction of Fe(bipy)₂(CN)₂⁺ with MV⁺ is increased in CTAB compared to water, it is slowed in SDS (k in H₂O, 2.4 × 10¹⁰; CTAB, 8.9 × 10¹⁰; and SDS, 1.8 × 10¹⁰ M⁻¹s⁻¹). All effects observed in these microheterogeneous systems can be uniformly interpreted in terms of Coulombic interactions between the actual reactants and the charged surface of the micelles.     

Novel CO2 selectively permeating membranes containing PETEDA dendrimer

Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy. The composite membranes for selectively permeating CO₂ were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO₂ and CH₄ gases and the gas mixture containing 10 vol.% CO₂ and 90 vol.% CH₄, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO₂ permeance of 8.14 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO₂ permeance reaches 3.56 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity is 19. For the gas mixture, the membrane has a CO₂ permeance of 6.94 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO₂ permeance of 3.29 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO₂/CH₄ gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO₂ permeance and CO₂/CH₄ selectivity increase and CH₄ permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS).     

Direct crystallisation of a hydroxy sodalite membrane without seeding using a conventional oven

A double layered hydroxy sodalite membrane was synthesised directly onto a tubular -alumina support without seeding using a conventional hot-air oven. The effect of different synthesis parameters including the water content, ageing period, synthesis time and temperature, on the purity and continuity of the membrane was investigated. The water content was an important factor in controlling the presence of contaminating zeolite phases in the membrane. The optimised membrane which was contaminant free was characterised by XRD, SEM and single gas permeation using He, N₂ and SF₆. The permeance of the three gases through the membrane ranged from 0.8 to 8 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹. The selectivity ( = 2.5–2.7) compared well to the Knudsen diffusion ratio for He/N₂.     

Surface modification of mesoporous membranes by fluoro-silane coupling reagent for CO2 separation

The potential of hybrid organic–inorganic membranes for separating organic molecules from air, based on solubility selective mechanism, was evaluated. Alumina and titana membranes with average pore size near 4 nm were surface modified using trimethoxysilane fluorinated coupling reagent. The permeabilities to helium, nitrogen, methane, ethane, propane, butane and carbon dioxide were evaluated at feed pressures lying between (1.5 × 10⁵ and 3.5 × 10⁵ Pa) 1.5 and 3.5 bar and permeate outlet near 1 × 10⁵ Pa (1 bar). The permeabilities of the grafted membranes generally decreased by about two to three orders of magnitude compared with the untreated membranes. The CO₂/N₂ permselectivity increased significantly in the case of the TiO₂ grafted membrane. The membranes performances were compared and the TiO₂ grafted membrane exhibits higher permselectivity and permeability, so that, it is a good candidate for CO₂ to N₂ separation and CO₂ to hydrocarbon separation.     

Photocatalytic bleaching of p-nitrosodimethylaniline in TiO2 aqueous suspensions: A kinetic treatment involving some primary events photoinduced on the particle surface

The photocatalytic bleaching of p-nitrosodimethylaniline (P) has been investigated in aqueous suspensions of TiO₂. It was found that both charge carriers (hole and electron) were reactive to P to result in a bleaching. The roles of O₂ and several hole scavengers (HCOO⁻, EDTA, I⁻) have also been examined. A reaction mechanism has been proposed with consideration of several primary processes photoinduced on TiO₂ surface. The results of the kinetic analysis fit fairly well to those of the experiments. The rate constant (k^h_p) of the reaction between P and the adsorbed hydroxyl radical was estimated to be in the order 10¹⁰ M⁻¹ s⁻¹, which is in good agreement with that obtained from the homogeneous reaction of P with free OH radicals. Of particular interest is the pH dependence of the photobleaching rate. Around both pK_a of P and pH_ZPC of TiO₂, the photobleaching of P was steeply enhanced. This can be reasonably attributed to the mutual interaction (repulsion versus attraction) between P and TiO₂ particles in different pH ranges.     

Membrane reactor performance of steam reforming of methane using hydrogen-permselective catalytic SiO2 membranes

Hydrogen production by steam reforming of methane using catalytic membrane reactors was investigated first by simulation, then by experimentation. The membrane reactor simulation, using an isothermal and plug-flow model with selective permeation from reactant stream to permeate stream, was conducted to evaluate the effect of permselectivity on membrane reactor performance – such as methane conversion and hydrogen yield – at pressures as high as 1000 kPa. The simulation study, with a target for methane conversion of 0.8, showed that hydrogen yield and production rate have approximately the same dependency on operating conditions, such as reaction pressure, if the permeance ratio of hydrogen over nitrogen ((H₂/N₂)) is larger than 100 and of H₂ over H₂O is larger than 15. Catalytic membrane reactors, consisting of a microporous Ni-doped SiO₂ top layer and a catalytic support, were prepared and applied experimentally for steam reforming of methane at 500 °C. A bimodal catalytic support, which allows large diffusivity and high dispersion of the metal catalyst, was prepared for the enhancement of membrane catalytic activity. Catalytic membranes having H₂ permeances in the range of 2–5 × 10⁻⁶ m³ m⁻² s⁻¹ kPa⁻¹, with H₂/N₂ of 25–500 and H₂/H₂O of 6–15, were examined for steam reforming of methane. Increased performance for the production of hydrogen was experimentally obtained with an increase in reaction-side pressure (as high as 500 kPa), which agreed with the theoretical simulation with no fitting parameters.     

Photoinduced electron transfer dynamics in porphyrin donor dyads

Intramolecular photoinduced electron transfer (PET) processes occurring in dyads with a free base porphyrin-tetraazaanthracene donor (P) and either a tetracyanonaphthoquinidodimethane (TCQ) or benzoquinone (BQ) acceptor linked by a rigid six σ-bond polynorbornane bridge ([6]) have been investigated. For P[6]BQ, PET in the polar solvent benzonitrile (_s = 25.9) occurs with a rate constant (k_PET) of 1.6 × 10⁸ s⁻¹ but is not evident in solvents less polar than tetrahydrofuran (_s = 7.52). For P[6]TCQ, highly efficient forward PET occurs in both polar and non-polar solvents (k_PET > 2 × 10¹⁰ s⁻¹). For P[6]TCQ the lifetime of the resulting charge-separated state decreases markedly with increasing solvent polarity. The results are discussed in the context of the likely mechanisms for electronic coupling and current theories for PET processes in such linked molecular systems.     

Comment on "Electrorheological behavior of copper phthalocyanine-doped mesoporous TiO2 suspensions"

We comment on the electrorheological (ER) behavior of copper phthalocyanine (CuPC)-doped mesoporous TiO(2) suspensions. Our Cole-Cole plot not only fits the dielectric spectra of the two CuPC-doped mesoporous TiO(2) templated ER fluids with CuPC/cetyltrimethylammonium (CTAB) molar ratios of 0.10 and 0.15, respectively, but also provides a better explanation of their polarizability by differentiating their ER performance.     

Hydrothermally stable silica–alumina composite membranes for hydrogen separation

A thin layer (30–40 nm) of a dual-element silica–alumina composition was deposited on a porous alumina support by chemical vapor deposition (CVD) in an inert atmosphere at high temperature. Prior to CVD, an intermediate layer of γ-alumina was coated on the macroporous alumina support. The intermediate layer was prepared by the dip-coating and calcination of boehmite sols of different sizes to give a graded structure that was substantially free of defects. The resulting supported composite membrane had high permeance for hydrogen in the order of 2–3 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 873 K with selectivities of H₂ over CH₄, CO and CO₂ of 940, 700 and 590, respectively. The membrane operated by a hopping mechanism involving jumps of permeating molecules between solubility sites. The presence of aluminum improved the hydrothermal stability of the membranes for periods in excess of 500 h at 873 K in 16% steam, allowing the permeance to remain above 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹, although with decreased selectivities.     

Molecular motion and phase transition in perovskite-type (CH3)nNH4−nSnCl3 (n=1–4) studied by proton NMR spin–lattice relaxation

Powder X-ray diffraction, ¹¹⁹Sn NMR spectra, and ¹H NMR spin–lattice relaxation times, T₁, were measured for (CH₃)_nNH_4−nSnCl₃ (n=1–4). From the Rietveld analysis, it is shown that all four compounds crystallize into deformed perovskite-type structures at room temperature. The temperature dependence of ¹H T₁ was analyzed in terms of the CH₃ reorientation and other motions of the whole cation. Except for the phase transition in CH₃NH₃SnCl₃, which is from monoclinic to rhombohedral at 331 K, ¹H T₁ was continuously changed at other phase transitions in this compound as well as in the n=2–4 compounds, suggesting that the transitions are not caused by the change of the motional state of the cation but by an instability of the [SnCl₃]_nⁿ⁻ perovskite lattice.     

The molecular structure and the puckering potential function of silacyclobutane as determined by gas electron diffraction and relaxation constraints from ab initio calculations

Gas electron diffraction is applied to determine the geometric parameters of the silacyclobutane molecule using a dynamic model where the ring puckering was treated as a large amplitude motion. The structural parameters and the parameters of the potential function were refined taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the MP2/6-311+G(d, p) level of theory. The potential function has been described as V() = V₀[(/_e)² − 1]² with the following parameters V₀ = 0.82 ± 0.60 kcal/mol and _e = 33.5 ± 2.7°, where is a puckering angle of the ring.

The geometric parameters at the minimum V() (r_a in Å, in degrees and uncertainties given as three times the standard deviations including a scale error) are: r(Si–H_ax) = 1.467(96), r(Si–H_eq) = 1.468(96), r(Si–C) = 1.885(2), r(C–C) = 1.571(3), r(C–H) = 1.100(3), CSiC = 77.2(9), HSiH = 108.3, SiCH_eq = 123.5(16), SiCH_ax = 111.9(16), CC₅H_eq = 118.4(24), CC₅H_ax = 112.3(24), HC₃H = 107.7, δ(HSiH) = 6.6, δ(HC₃H) = 7.0, where the tilts δ, HSiH, and HC₃H are estimated from ab initio constraints. The structural parameters are compared with those obtained for related compounds.     

Potentiometric Cd-selective electrode with a detection limit in the low ppt range

A recently introduced model describing the response curves of polymer membrane ion-selective electrodes (ISEs) is used here to optimize a Cd²⁺-ISE with a view to achieve very low detection limits. In a first step, the selectivity behavior is determined for two membranes based on the ionophore, N,N,N′,N′-tetradodecyl-3,6-dioxaoctanedithioamide (ETH 5435), but having different concentrations of the ionophore and ion-exchanger. Based on these data, the optimal response curves are calculated with a model that takes into account the ion fluxes induced by interfering ions. The experimental results with different ionic backgrounds correspond very well with the predicted effects. The best lower detection limit of 10⁻¹⁰ M or 11 ppt Cd²⁺ is achieved at pH 7 with an ionic background of 10⁻⁴ M NaNO₃.     

Synthesis, structure and non-linear optical property of a copper(II) thiocyanate three-dimensional supramolecular compound

A novel copper(II) thiocyanate complex [Cu(im)₂(NCS)₂] 1 (im=imidazole) has been prepared and characterized by spectroscopic analysis and crystallographic method. This supramolecular compound exhibits a three-dimensional solid state structure constituted by N–HS hydrogen bonds and π–π stacking interactions. The compound in DMF solutions has a very strong third-order non-linear optical (NLO) behavior with absorption coefficient and refractive index ₂=1.18×10⁻¹¹ mw⁻¹, n₂=−9.00×10⁻¹⁶ m²w⁻¹, respectively, and third-order NLO susceptibility χ⁽³⁾ of 7.00×10⁻¹⁰ esu.