Evaluation of the microporosity of pillared [Fe(CN)6]–MgAl–LDHs

Layered double hydroxides (LDHs) containing Mg²⁺ and Al³⁺ in the basic layers and NO⁻₃ as an interlayer anion were synthesized by the method of coprecipitation (pH 10). By changing the Mg²⁺/Al³⁺ ratio (1.5–4.5), the charge density on the (NO₃)–MgAl–LDH sheets was varied. After pillaring with Fe(CN)³⁻₆, which was based on an anion exchange process, the interlayer space became accessible. This was reflected in the large created surface areas and micropore volumes. The applied models for the calculation of the micropore size distributions (Maes–Zhu–Vansant and Horvath–Kawazoe) gave matching results, revealing narrow distributions for all the samples, with the majority of the pores smaller than 0.71 nm. A correlation was found between the Mg²⁺/Al³⁺ ratio and the resulting microporosity after pillaring. The optimal ratio was situated around 3.3, resulting in a pillared [Fe(CN)₆]–MgAl–LDH with a Langmuir surface area of 499 m²/g and a micropore volume between 0.158 ml/g (μPV_min) and 0.177 ml/g (μPV_max). As an alternative, direct coprecipitation of the pillared LDHs was evaluated. This one-step mechanism proved to be a method producing similar results. Taking all this into consideration, one can conclude that hexacyanoferrate(III) complexes form ideal anionic pillars for the creation of microporous layered double hydroxides.     

Rapid discharge performance of composite electrode of hydrated sodium manganese oxide and acetylene black

Hydrated sodium manganese oxide was synthesized by reducing permanganate ion using ethanol by a sol–gel method. By including acetylene black in the synthetic reaction, we obtained composite materials in which sodium manganese oxide hydrate particles were small and mixed well with the acetylene black. We evaluated those composites as a lithium battery cathode and found that they showed 170 mA h g⁻¹ under 5 mA g⁻¹ and 117 mA h g⁻¹ under 5 A g⁻¹ on the basis of composite weight. This rapid discharge performance was probably caused by the favorable contact condition of the composite constituents.     

Experimental investigation of sheet flexibility of layered double hydroxides: One-pot morphosynthesis of inorganic intercalates

The sheet flexibility of layered double hydroxides (LDHs) has been investigated experimentally using co-precipitation and urea hydrolysis methods in an aqueous solution of long-chain anion surfactant in this work. Using dodecylsulfate (DS) anion as morphology-controlling agent, layer-bended or contorted Mg/Al-LDH is obtained successfully. The morphology of bent layers is retained during either in situ decomposition of interlayer DS to SO₄²⁻ or ion exchange of interlayer DS by CO₃²⁻. The direct synthesis of the layer-distorted LDHs intercalated with small inorganic anions is quite difficult. It has been achieved using layer-bended LDHs pillared with bulky organic anions as precursors in this paper. The morphosynthesis is expanded to Co/Al and Ni/Al-LDHs, indicative of the general flexibility of this kind of anionic clays.     

Synthesis and characterization of Zn/Al and Pt/Zn/Al layered double hydroxides obtained by the sol–gel method

The influence of the nature of the Zn, Al and Pt precursors, and of the temperature of precipitation and aging have been studied in connection with the preparation of Zn/Al and Pt/Zn/Al layered double hydroxides (LDH) by the sol–gel method. Whatever the precursors the XRD analysis shows that LDH is formed at the expense of ZnO when the precipitation and aging temperatures decrease from 353 K to 273 K. Moreover, chemical composition and TG analysis suggest the presence of weak amounts of hydrozincite, hydrozincite-like and Al(OH)₃ phases. When the precursors are Zn acetate-2-hydrate or Al acetylacetonate the amount of LDH reaches a maximum of 50 mol% at 273 K. At variance, about 90 mol% of LDH is obtained when using Zn acetylacetonate and Al isopropoxide as precursors, which are precipitated at 273 K. This proportion is slightly improved for the Pt-containing sample prepared under the same conditions. The specific surface areas of the different samples obtained after calcination at 723 K increase with their LDH content, reaching values of 110–120 m² g⁻¹. They make them particularly attractive for catalytic applications.     

Influence of the surface area of the support on the activity of gold catalysts for CO oxidation

In the preparation of 1% Au/TiO₂ catalysts supported on either Degussa P-25 or anatase (90 m² g⁻¹) by deposition–precipitation, the gold content passes through a maximum at about the isoelectric point (pH 6), but maximum specific rates occur at pH 8–9 because the Au particle size becomes smaller as the pH is further increased. The gold uptake increases with the surface area of the support (anatase, rutile, P-25) and is complete above 200 m² g⁻¹; adsorption of the gold precursor at pH 9 is shown to be equilibrium-limited. Highest activities are found with supports of 50 m² g⁻¹. Catalysts made with high-area anatase (240 or 305 m² g⁻¹) are least active but show least deactivation.With Au/SnO₂ catalysts, gold uptake does not depend on the area of the support, and is highest at pH 7–8; very active catalysts (T₅₀ = 230–238 K) are obtained using SnO₂ of 47 m² g⁻¹. Storing a catalyst at 258 K for 1 week dramatically improves its stability. Results for Au/CeO₂ and Au/ZrO₂ catalysts confirm that moderate support areas give the most active catalysts, and suggest that surface area is often more important than chemical composition.     

Electrochemical properties of anatase TiO2 nanotubes as an anode material for lithium-ion batteries

Titanium oxides with a one-dimensional nanostructure are of great significance in electrochemical lithium insertion due to their high specific surface area and pore volume. In this paper, anatase TiO₂ nanotubes with diameters of about 10 nm and lengths of 200–400 nm were synthesized by a hydrothermal process. The phase structure and morphology were analyzed by X-ray diffraction, Raman scattering, and transmission electron microscopy. The electrochemical properties were investigated by constant current discharge–charge and cyclic voltammetry. There is a potential plateau at 1.73 and 1.88 V in the process of Li insertion and extraction, and the initial Li insertion/extraction capacity is 290 and 238 mAh g⁻¹ at 36 mA g⁻¹, respectively. The Li insertion capacity at the potential plateau of 1.73 V in the first cycle is about 150 mAh g⁻¹. In the 20th cycle, the reversible capacity still remains at about 200 mAh g⁻¹, and the coulombic efficiency is approximately 98%, exhibiting excellent cycling stability. The discharging capacity is about 168 mAh g⁻¹ in the 30th cycle at 210 mA g⁻¹, demonstrating a good high-rate performance. Anatase TiO₂ nanotubes might be a promising negative material for lithium-ion batteries.     

铁铝柱撑酸化蒙脱土催化剂的表征及催化性能

为改善柱撑蒙脱土的催化活性,对蒙脱土进行酸预处理,并采用离子交换法制备铁铝柱撑酸化蒙脱土(Fe-Al-酸化土)催化剂,通过XRD、BET、ICP和FI-IR对其进行表征。结果表明,蒙脱土经酸化预处理制备Fe-Al酸化土催化剂比表面积为157.3 m~2·g~(-1),层间距d001为1.787 nm,铁铝柱撑剂进入酸化蒙脱土层间域形成均一稳定的Si—O—Fe结构,在2 930 cm-1处出现尖锐的吸收峰,在协同过氧化氢降解废水实验中表现出较高的活性和稳定性。     

Surfactant-mediated synthesis of metal substituted hexaaluminate from alumina sol

Manganese substituted hexaaluminate has been prepared using environmentally benign surfactants such as Triton X-100, under ambient condition with a commercial alumina sol and metal acetate precursors. The surface area of the pure alumina can be controlled to 10–70 m² g⁻¹ using cetyltrimethylammonium chloride after heating in oxygen flow at 1200°C for 6 h. The crystal structure of the obtained alumina was high purity θ-Al₂O₃. Incorporation of La and Mn leads to the formation of the high purity manganese substituted hexaaluminate with a surface area of 30–40 m² g⁻¹ which is also controllable using organic additives such as urea. The catalytic activity of the manganese substituted hexaaluminate was comparable to the sol–gel derived hexaaluminate catalyst from metal alkoxides.     

High-quality, oriented and mesostructured organosilica monolith as a potential UV sensor

We synthesized high-quality and oriented periodic mesoporous organosilica (PMO) monoliths through a solvent evaporation process using a wide range of mole ratios of the components: 0.17–0.56 1,2-bis(triethoxysilyl)ethane (BTSE): 0.2 cetyltrimethylammonium chloride (CTACl): 0–1.8 × 10⁻³ HCl: 0–80 EtOH: 5–400 H₂O. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images indicated that the mesoporous channels within the monolith samples were oriented parallel to the flat external surface of the PMO monolith and possessed a hexagonal symmetry lattice (p6mm). The PMO monolith synthesized from a reactant composition of 0.35 BTSE: 0.2 CTACl: 1.8 × 10⁻⁶ HCl: 10 EtOH: 10 H₂O had a pore diameter, pore volume, and surface area – obtained from an N₂ sorption isotherm – of 25.0 Å, 0.96 cm³ g⁻¹ and 1231 m² g⁻¹, respectively. After calcination at 280 °C for 2 h in N₂ flow, the PMO monolith retained monolith-shape and mesostructure. Pore diameter and surface area of the calcined PMO monolith sample were 19.8 Å, 0.53 cm³ g⁻¹ and 1368 m² g⁻¹, respectively. We performed ²⁹Si and ¹³C CP MAS NMR spectroscopy experiments to confirm the presence of Si–C bonding within the framework of the PMO monoliths. We investigated the thermal stability of the PMO monoliths through thermogravimetric analysis (TGA). In addition, rare-earth ions (Eu³⁺, Tb³⁺ and Tm³⁺) were doped into the monoliths. Optical properties of those Eu³⁺, Tb³⁺ and Tm³⁺-doped PMO monoliths were investigated by photoluminescence (PL) spectra to evaluate their potential applicability as UV sensors.     

Removal of metal ions in aqueous solutions by organic polymers: use of a polydiphenylamine resin

Adsorption of Ni(II), Cu(II), Zn(II), Pb(II) and Cd(II) ions on a polydiphenylamine resin prepared at a strongly oxidizing controlled potential of 3.2 V (vs. ECS) was studied in aqueous solutions. The optimum sorption conditions were determined. The optimum pH for the removal of metal ions was between 4 and 6 for Ni(II), 6 for Cu(II) and Pb(II) and 5 for Zn(II) and Cd(II). The total sorption capacity of the resin was 57.3 mg g⁻¹ for Ni(II), 23 mg g⁻¹ for Cu(II), 36.9 mg g⁻¹ for Zn(II), 19 mg g⁻¹ for Pb(II) and 24.5 mg g⁻¹ for Cd(II). The sorption capacity was compared with other conventional chelating polymers. The sorption kinetics was fairly rapid, as apparent from the loading half time (t_1/2) values, indicating a better accessibility of the chelating sites. The study of the selectivity of the metal ions in the binary solutions shows that the resin presents a higher affinity for the ions of nickel (II).     

Synthesis of a novel super-microporous layered material and its catalytic application in the vapor-phase Beckmann rearrangement of cyclohexanone oxime

A novel well-ordered super-microporous layered material, silica-pillared niobic acid, was synthesized by a guest-exchange route and structurally characterized by powder X-ray diffraction (XRD), infrared absorption spectroscopy (IR), thermogravimetric and differential thermal analysis (TG/DTA), transmission electron micrographs (TEM), nitrogen adsorption method and ammonia-temperature-programmed desorption (NH₃-TPD). The obtained silica-pillared layered niobic acid had a supergallery of 1.78 nm, a large BET surface area of 250 m² g⁻¹, and a high thermal stability exceeding 973 K.The pillared layered material was also found to be an efficient solid acid catalyst for the vapor-phase Beckmann rearrangement of cyclohexanone oxime. When 1-hexanol was fed with cyclohexanone oxime, this solid catalyst exhibited a 100% conversion of the oxime with a selectivity of ε-caprolactam beyond 85% at a reaction temperature of 613 K and a WHSV of 0.17 h⁻¹ in terms of cyclohexanone oxime, and there was no significant change of the conversion and selectivity within 6 h.     

Fractal analysis of gas adsorption on Syncrude coke

Fractal dimension is an intrinsic, quantitative measure of surface irregularity and provides a convenient parameter for comparing surface physical properties. Several particle size ranges of Syncrude coke were studied by nitrogen and carbon dioxide adsorption. The apparent surface area, A, was observed to increase from 1 to 15 m² g⁻¹ for N₂ and from 65 to 300m² g⁻¹ for CO₂ data with decreased particle size. The fractal dimension, D, was determined from the proportionality: A∝R^D-3, where the surface area is determined by BET or D-P (Dubinin-Polanyi) theories, R is the particle radius and 2D3. The value of D for Syncrude coke was determined to be 2.48 from both N₂ and CO₂ results.     

Oxygen sorptivity of mesoporous aluminosilicate modified by Co-salen complex

Mesoporous aluminosilicate, FSM-16 (Al-FSM-16(n)), was functionalized by Co-salen modification. The Si/Al ratio, n, was varied from 12.8 to 60.0, and inclusion of Co-salen (N,N^′-bis(salicylidene)ethylenediaminocobalt(II)) was carried out by a novel preparative method comprising Co²⁺ ion exchange in a nonaqueous solution of cobalt(II) acetate and chelation with salen-H₂ (N,N^′-bis(salicylidene)ethylenediamine). Prominent O₂ sorptivity was imparted to this mesoporous material and the amount of O₂ sorbed on Co-salen-Al-FSM-16(60.0) was 0.275 mmol g⁻¹ at 298 K, significantly larger than that on Al-FSM-16(60.0) itself (0.085 mmol g⁻¹). The O₂ sorption on Co-salen-Al-FSM-16(60.0) remarkably proceeded under a pressure around 20 kPa at 298 K, which was similar to powdery, free Co-salen. The maximum O₂/Co-salen ratio for Co-salen included in mesopores was seven times as large as that for neat Co-salen. The pore structure of Al-FSM-16(n) with a high n value was retained through the modification as evidenced by XRD, TEM and N₂ adsorption measurements, but that of Al-FSM-16(12.8) was partly collapsed.     

Investigation of pyridine sorption in USY and Ce/USY zeolites by liquid phase microcalorimetry and thermogravimetry studies

USY (ultrastabilized Y) and Ce/USY (5 wt.% supported) zeolite acidities were characterized by microcalorimetric and adsorption studies of pyridine using liquid phase (Cal-Ad), thermogravimetry, and infrared analysis. The average adsorption enthalpies determined by microcalorimetry were −125.0 kJ mol⁻¹ for USY and −97.2 kJ mol⁻¹ for Ce/USY. A heterogeneous distribution of acid sites with heats of adsorption ranging from −134.0 (maximum heat value for USY) to −73.5 (minimum heat value for Ce/USY) kJ mol⁻¹ was found for both zeolites. A two-site model was best fitted by the Cal-Ad method for HUSY (n₁ = 0.1385 mmol g⁻¹ with ΔH₁ = −134.0 kJ mol⁻¹, and n₂ = 0.7365 mmol g⁻¹ with ΔH₂ = −101.5 kJ mol⁻¹) and Ce/HUSY (n₁ = 0.0615 mmol g⁻¹ with ΔH₁ = −117.6 kJ mol⁻¹, and n₂ = 0.7908 mmol g⁻¹ with ΔH₂ = −83.6 kJ mol⁻¹). DRIFTS measurements after pyridine adsorption showed that USY zeolite possesses only Brønsted acidity and that cerium impregnation leads to the appearance of Lewis sites. Based on these results, three families of acid strength were distinguished: (i) strong Brønsted sites (ΔH > −130 kJ mol⁻¹); (ii) Brønsted sites with intermediate strength (−100 < ΔH < −130); and (iii) weak Brønsted and Lewis sites (ΔH < −100). Thermogravimetric analysis showed that the strongest sites were able to retain pyridine up to 800 °C and that cerium incorporation leads to a more stable zeolite. A loss of strength was observed after impregnation. The total number of sites desorbed after gas adsorption (0.88 and 0.95 mmol for HUSY and Ce/HUSY, respectively) supports the Cal-Ad results (0.88 and 1.19 mmol for HUSY and Ce/HUSY, respectively) and indicates that not all Al sites are available to pyridine. The methodology used in this work for solid acid characterization (Cal-Ad) proved to be efficient in the evaluation of acid strength, total number and distribution of acid sites. XRPD, ICP-AES, ²⁷Al NMR, and FTIR were used for additional structural characterization.     

Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2  of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<680 mL g⁻¹; the intrinsic viscosity, 130<[η]<550 mL g⁻¹. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000<M<240 000 g mol⁻¹. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [η] were: [η]=5.58×10⁻³ M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen k_s values for these substances is discussed.     

Untersuchung über die anionenadsorption mit hilfe markierter ionen

From previous work, the adsorption of anions is regarded as an essential factor for the different corrosion behaviour of metals in solutions containing different anions. Adsorption is measured by means of ³⁶Cl⁻, ⁸²Br⁻, ¹⁸ F⁻, ³⁶ClO₄⁻, ³⁵O₄²⁻, H³⁵S⁻ and ¹⁴CN⁻ on Pt, Ni and Fe in the form of sheets and evaporated films. Besides the determination of the adsorption after dipping into the solution, a method has been developed for the measurement of adsorption in contact with the solution and for the determination of its kinetics. The method can also be applied to O₂-free metal surfaces produced under vacuum. In this case, however, very rapid adsorption is observed, whereas normally saturation is reached only after many hours. It is concluded that, in general, exchange between oxygen on the metal and the anion takes place rather than simple adsorption.

The distribution of the anions adsorbed on the metal surface has been studied by autoradiography; adsorption takes place preferentially at the grain boundaries and increases when the crystal size decreases.

These results confirm the interpretation of passivation as a competition between various processes: metal dissolution, coverage by a passivating oxide film, and displacement of oxygen by anions.     

Microporous polyurethane-acrylamide film cured by electron beam irradiation

The morphology and aggregation structure of electron beam (EB)-cured microporous polyurethane-acrylamide film was investigated. The urethane-acrylamide prepolymer was synthesized by the reaction of poly(butylene adipate)diol, 4,4′-diphenylmethane diisocyanate, and N-(hydroxymethyl)acrylamide. It was found from scanning electron microscopy that the urethane-acrylamide film, which was prepared by using a methyl ethyl ketone and dimethylformamide (3:1 v/v) mixture as casting solvent, had a microporous structure with pore size of several micrometres, and that the morphology was fixed by EB irradiation. The pore volume of the EB-cured microporous film was determined to be about 460 mm³ g⁻¹ by mercury porosimetry. The micropores were not destroyed even after immersing in solvent, possibly because the cured film had high crystallinity and dense crosslinking. Moreover, it was found by X-ray photoelectron spectroscopy that terminal portions of urethane-acrylamide were localized at the film surface.     

Polypyrrole materials doped with weakly coordinating anions: influence of substituents and the fate of the doping anion during the overoxidation process

The influence of weakly coordinating anions with different shapes and substituents has been studied to get the overoxidation resistance limit of the material, ORL. The anions utilized are derivatives of [Co(C₂B₉H₁₁)₂]⁻, [B₁₂H₁₂]²⁻ and [B₁₂H₁₁NH₃]⁻. The following tendencies have been established (1) boron cluster monoanions are to date the anions that offer the highest stability to overoxidation of PPy doped materials (2) the ORL stability of the material can not be attributed only to the shape of the cluster (3) monoanionic clusters are far superior than dianionic to get an ORL rise (4) cluster charge density reduction results in ORL rise as has been observed in [Co(C₂B₉H₁₁)₂]⁻ after incorporation of electron-withdrawing substituents with no electron back-donation (5) globular, rigid and large monoanions are less suitable for enhanced ORL values than elongated and non-rigid species (6) adequate anion's substitution produce a rise in the ORL of the material, thus polyether side-arms are beneficial with [Co(C₂B₉H₁₁)₂]⁻, whereas, T-shaped methylaryl groups are appealing in [B₁₂H₁₁NH₃]⁻ based materials, respectively, (7) substituents on the anions usually imply higher difficulty in the materials' growth. The high boron contents in these materials has permitted to learn on the fate of the doping anions during the overoxidation process. There is a built-up of the concentration of the doping anion in the electrolyte near surface area, whereas, a depletion is observed in the nearest inner layers.     

Effect of pH, inorganic ions, organic matter and H2O2 on E. coli K12 photocatalytic inactivation by TiO2: Implications in solar water disinfection

The effect of different chemical parameters on photocatalytic inactivation of E. coli K12 is discussed. Illumination was produced by a solar lamp and suspended TiO₂ P-25 Degussa was used as catalyst. Modifications of initial pH between 4.0 and 9.0 do not affect the inactivation rate in the absence or presence of the catalyst. Addition of H₂O₂ affects positively the E. coli inactivation rate of both photolytic (only light) and photocatalytic (light plus TiO₂) disinfection processes. Addition of some inorganic ions (0.2 mmol/l) like HCO₃⁻, HPO₄²⁻, Cl⁻, NO₃⁻ and SO₄²⁻ to the suspension affects the sensitivity of bacteria to sunlight in the presence and in absence of TiO₂. Addition of HCO₃⁻ and HPO₄²⁻ resulted in a meaningful decrease in photocatalytic bactericidal effect while it was noted a weak influence of Cl⁻, SO₄²⁻ and NO₃⁻. The effect of counter ion (Na⁺ and K⁺) is not negligible and can modify the photocatalytic process as the anions. Bacteria inactivation was affected even at low concentrations (0.2 mmol/l) of SO₄²⁻ and HCO₃⁻, but the same concentration does not affect the resorcinol photodegradation, suggesting that disinfection is more sensitive to the presence of natural anions than photocatalytic degradation of organic compounds. The presence of organic substances naturally present in water like dihydroxybenzenes isomers shows a negative effect on photocatalytic disinfection. The effect of a mixture of chemical substances on photocatalytic disinfection was also studied by adding to the bacterial suspension nutrient broth, phosphate buffer and tap water.     

Sorption kinetics of ammonia and ammonium ions on gel and macroporous sulphonic acid cation exchangers

Diffusion of ammonia and ammonium ions in sulphonic acid cation exchangers (gel Purolite SGC 100 × 10 MBH and macroporous Purolite C 160 MBH) from the solutions, representing the composition of “caustic condensate” (waste of nitrogen fertilizers production) is affected by pH of initial solution and structure of the matrix of cation exchanger. In gel matrix the effective intraparticle diffusivity (D_ef) depends greatly on the solution pH because of shrinkage in alkaline and swelling in acidic medium: on decreasing the initial concentration of ammonia from 0.214 to 0.003 and increasing that of ammonium nitrate from 0 to 0.214 mol l⁻¹ instead, the effect of ion exchange leads to a decrease in pH, resulting in swelling and increase in D_ef from 0.1 to 0.34 × 10⁻¹⁰ for gel Purolite SGC 100 × 10 MBH and variation of 0.18–0.11 × 10⁻¹⁰ m² s⁻¹ for macroporous Purolite C 160 MBH (resistant to shrinkage and swelling).

In Purolite C 160 MBH both macropore diffusivity (0.07–0.29 × 10⁻¹⁰ m² s⁻¹) and gel (solid phase) diffusivity (0.06–0.19 × 10⁻¹⁰ m² s⁻¹) are higher than micropore diffusivity (0.28–0.56 × 10⁻¹⁸ m² s⁻¹).

With respect to the effective intraparticle diffusivity, resistance to nitric acid, used for the regeneration, and high concentration of ammonium nitrate in eluate (up to 110 g l⁻¹), Purolite C 160 MBH has been installed for the conversion of ammonia and ammonium ions to ammonium nitrate reusable in the fertilizers production. This allows minimizing the economic loss and preventing the environmental contamination.