Hydrogen adsorption on activated carbons prepared from olive waste: effect of activation conditions on uptakes and adsorption energies

Two series of activated carbon samples have been prepared from olive waste, using ZnCl₂ and H₃PO₄ as chemical activation agents. The porous structure characteristics of all samples are determined by nitrogen adsorption at ?196 °C. Hydrogen adsorption at ?196 °C is followed using both manometry and calorimetry. The results show that the highest areas are observed for the samples prepared with larger diameter of precursors and that the hydrogen uptake is strongly influenced by the available BET area. Furthermore, the adsorption energies do not vary significantly for any activation protocol and therefore seem to play only a minor role to the hydrogen adsorption behavior. However, the chemical activation does have a strong role on hydrogen uptake. Samples prepared with H₃PO₄ show a greater hydrogen uptake per unit area such that comparable uptakes are observed for the samples prepared with larger diameter of precursor even though the sample prepared with ZnCl₂ shows a 30 % higher BET area. This work highlights the non-trivial role of each activation protocol on hydrogen uptake.     

Shear bond strength to dentine of dental adhesives containing hydroxyapatite nano-fillers

The aim of this study was to compare the effect of hydroxyapatite (HAP) nano-rods (HAP_rods) and HAP nano-sticks (HAP_sticks) added to commercial adhesives on the macro-shear bond strength (SBS) to dentine and morphology of the adhesive–dentine interface. HAP was added to Single Bond Universal (SBU, 3M ESPE) and Te-Econom Bond (TeE; Ivoclar Vivadent), in the form of water suspensions to avoid agglomeration of nano-particles and to achieve HAP concentrations of 0.5, 1.0 and 1.5 wt%. Following a ‘total-etch’ or a ‘self-etch’ protocol, the adhesives were applied to flat dentine surface of 162 intact human, third molars (N = 6/group). Composite (Z250, 3M ESPE) was built-up using a split stainless steel mould, 3 mm in diameter. SBS was tested using a universal testing machine at 1 mm/min until fracture. Data were statistically analysed using two-way and one-way analysis of variance with Tukey’s post-test (α = 0.05). HAP_rods had no significant effect on SBS of the tested adhesives while HAP_sticks improved bond strength to dentine only of adhesives applied following the ‘total-etch’ total-etch protocol. SBS values of SBU containing 1% HAP_sticks (15.10 ± 2.96 MPa) and TeE containing 0.5% HAP_sticks applied following the total-etch protocol (12.96 ± 4.48 MPa) were higher than those of their respective control groups (10.36 ± 2.68 and 7.97 ± 3.64 MPa). Samples with higher SBS showed more ‘mixed’ failures. HAP nano-fillers may improve bond strength of total-etch adhesives without an adverse effect on adhesive dispersion on dentine and its ability to infiltrate dentinal tubules.     

A Synergic Blend of Newly Isolated <Emphasis Type="Italic">Pseudomonas mandelii</Emphasis> KJLPB5 and [hmim]Br for Chemoselective 2° Aryl Alcohol Oxidation in H<Subscript>2</Subscript>O<Subscript>2</Subscript>: Synthesis of Aryl Ketone or Aldehydes via Sequential Dehydration-Oxidative C=C Cleavage

Abstract  

Pseudomonas mandelii KJLPB5 is reported for the oxidation of aryl alcohols in ionic liquid [hmim]Br (1-hexyl-3-methyl imidazolium bromide) with H₂O₂. With a slight alteration of reaction conditions, the developed protocol leads either to (i) chemoselective oxidation of 2° aryl alcohols over 1° and aliphatic counterparts or (ii) direct one pot-two step sequential conversion of 2° aryl alcohols into corresponding one or two carbons shorter aryl aldehydes through oxidative cleavage pathway, thus providing a new facet to metal-free oxidations. The key operational parameters such as substrate concentration, incubation temperature, incubation time, ionic liquid type and ionic liquid concentration are also optimized.     

Structural composites formed by reaction injection moulding Interlaminar fracture properties of glass fibre mat-copoly(urea/isocyanurate) resin composites

Abstract

Structural (SRIM) composites, comprising up to 40% by volume of random continuous glass fibres in a specially developed copoly(urea/isocyanurate) (PUrI) matrix, have been formed via reaction injection moulding (RIM). The two stage polymerisation process of the PUrI matrix provided low initial viscosity during mould filling followed by a 'snap cure' to give tough composite materials in <30 s. Characterisation by DMTA confirmed the two phase morphology of the rubber toughened glassy matrix. Mode I and mode II interlaminar fracture tests, carried out in accordance with the ESIS protocol, gave values of G _Ic and G _IIc in the ranges 1·4-2·8 kJ m^-2 and 3·3-5·0 kJ m^{- 2}, respectively, and were an order of magnitude greater than those determined for unidirectional carbon fibre-epoxy composites. The G _Ic values for the SRIM composites are a factor of 2-3 greater than that (0·8 kJ m^-2) for the unreinforced PUrI matrix and show significant variation due to extensive fibre bridging during crack propagation.     

High cell density fermentation of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> GS2 for selenium-enriched yeast production

This paper describes a fed-batch fermentation protocol about production of selenium-enriched yeast. Saccharomyces cerevisiae GS2 was selected because of its high tolerance to selenium. The strain GS2 was tested and 122±0.5 g·l ⁻¹ dry cell weight was obtained after 30 h cultivation through feed back control of feed rate of glucose according to the concentration of ethanol and dissolved oxygen. Furthermore, the optimal pattern of Na₂SeO₃ addition was 9 mg Na₂SeO₃ against 1 g DCW at late exponential phase. With the combination of glucose feeding and Na₂SeO₃ addition, the final dry cell biomass reached 102±0.4 g·l ⁻¹ and a Se uptake level of 2,020±13 mg·Kg⁻¹ was achieved in a 5 l fermentor after 38 h cultivation.     

Improving the Stability and Catalyst Lifetime of the Halogenase RebH By Directed Evolution

We previously reported that the halogenase RebH catalyzes selective halogenation of several heterocycles and carbocycles, but product yields were limited by enzyme instability. Here, we use directed evolution to engineer an RebH variant, 3‐LR, with a T_opt over 5 °C higher than that of wild‐type, and 3‐LSR, with a T_m 18 °C higher than that of wild‐type. These enzymes provided significantly improved conversion (up to fourfold) for halogenation of tryptophan and several non‐natural substrates. This initial evolution of RebH not only provides improved enzymes for immediate synthetic applications, but also establishes a robust protocol for further halogenase evolution.     

Oxime Palladacycle‐Catalyzed Suzuki–Miyaura Alkenylation of Aryl,Heteroaryl, Benzyl,and Allyl Chlorides under Microwave Irradiation Conditions

A simple new protocol for the palladium‐catalyzed Suzuki–Miyaura cross‐coupling of organic chlorides under microwave irradiation is presented. Deactivated aryl and heteroaryl chlorides are efficiently cross‐coupled with alkenylboronic acids and potassium alkenyltrifluoroborates using the 4,4′‐dichlorobenzophenone oxime‐derived palladacycle 1b as precatalyst in 0.1 to 0.5 mol% palladium loading, tris(tert‐butyl)phosphonium tetrafluoroborate {[HP(t‐Bu)₃]BF₄} as ligand, tetra‐n‐butylammonium hydroxide as cocatalyst, and potassium carbonate as base in N,N‐dimethylformamide at 130 °C under microwave irradiation conditions. Under these conditions, styrenes, stilbenes, and alkenylarenes are obtained in good to high yields, and with high regio‐ and diastereoselectivities in only 20 min. The reported protocol is also very efficient for the regioselective alkenylation of benzyl and allyl chlorides to afford allylarenes and 1,4‐dienes.     

ZrOCl2·8H2O as an efficient,environmentally friendly and reusable catalyst for synthesis of benzoxazoles,benzothiazoles, benzimidazoles and oxazolo[4,5-b]pyridines under solvent-free conditions

A new and efficient method for the preparation of benzoxazoles, benzothiazoles, benzimidazoles and oxazolo[4,5-b]pyridines from reactions of orthoesters with o-substituted aminoaromatics and 2-amino-3-hydroxypyridine in the presence of catalytic amounts of the moisture stable, inexpensive ZrOCl₂·8H₂O under solvent-free conditions is presented. This new protocol has the advantages of easy availability, easy handling, stability, reusability and eco-friendly of the catalyst, high yields, very short reaction times, solvent-free reaction conditions, simple experimental and work-up procedure.     

A novel hydrothermal releasing synthesis of modified SiO<Subscript>2</Subscript> material and its application in phenol removal process

A modified SiO₂ material (MSM) was successfully synthesized by using Na₂SiO₃ and a novel CO₂SM in the presence of CTAB through an innovative hydrothermal releasing treatment protocol. The MSM was systemically characterized using several techniques, including N₂ adsorption-desorption isotherm, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The CO₂SM as a platform for CO₂ capturing and releasing can be reversibly used for multiple cycles without significant loss of capabilities. The optimum conditions for the preparation of MSM were identified as follows: Na₂SiO3 concentration, 0.2mol/L; hydrothermal temperature, 120 °C; CO₂SM dosage, 6 g; CTAB concentration, 24 g/L, reaction time, 12 h. Additionally, the MSM exhibited high efficiency for the removal of phenol from aqueous solution: it showed a phenol adsorption capacity of 91.29mg/g when shaken with the aqueous phenol solution at 180 rpm for 1 h at 25 °C.     

Establishment and maintenance of an optimal chiral surface in cinchona-modified 1% Pt/Al2O3 for enantioselective hydrogenation of α-keto esters

An optimal chiral surface in the cinchona-modified Pt/Al₂O₃ catalytic system is established for fast enantioselective hydrogenation of ethyl pyruvate. A makeup protocol is used to compensate for the destructive hydrogenation of the chiral modifier, thus maintaining the optimal chiral surface over the course of the hydrogenation reaction. Hydrogenation over the optimal surface (Pt_surface/modifier = 5–12) results in high enantioselectivity (94% ee) under mild conditions (5.8 bar and 17^°C) with high turnover frequency (4 s^-1) and turnover numbers (pyruvate/modifier>28,000, pyruvate/Pt_surface>5,500). This revised version was published online in June 2006 with corrections to the Cover Date.     

Fabrication and H2 flux measurement of asymmetric La27W3.5Mo1.5O55.5-δ − La0.87Sr0.13CrO3-δ membranes

Novel asymmetric hydrogen permeable membranes consist of a dense ceramic–ceramic (cercer) composite layer of La_0.87Sr_0.13CrO_3-δ and La₂₇W_3.5Mo_1.5O_55.5-δ deposited on a tubular porous support of the latter composition. The membranes were produced by extrusion and dip-coating with various thermal cycles required for adjusting the thermal shrinkage of the different layers and obtaining gas tight membrane layers. The produced asymmetric membranes have a dense cercer layer thicknesses ranging from 25 to 50 μm on supports exhibiting a porosity of up to 40 vol%. The effect of processing parameters, such as volume of pore former, coating steps, sintering temperature and soaking time on the microstructure of the membranes is discussed to highlight critical steps in the manufacturing protocol. Hydrogen fluxes were measured as a function of temperature with both wet and dry Ar sweep gas. Results are discussed with respect to membrane architectures and materials properties.     

A glutamic acid-based polymer keeping intact the integrity of all the three original functionalities of the amino acid

Dimethyl glutamate, on treatment with allyl bromide, afforded dimethyl N,N-diallylglutamate which upon alkaline ester hydrolysis followed by acidification with aqueous HCl gave N,N-diallylglutamic acid hydrochloride [(CH₂=CH–CH₂)₂NH⁺CH(CO₂H)(CH₂)₂CO₂H Cl^?] I. Using Butler’s cyclopolymerization protocol, new monomer I underwent ammonium persulfate-initiated polymerization to give pyrrolidine ring-embedded linear cyclopolymer II i.e. ?[?CH₂(C₄H₆)NH⁺{CH(CO₂H)(CH₂)₂CO₂H Cl^?}CH₂?]?_n retaining the integrity of all the three functionalities of glutamic acid. Under the influence of pH, the repeating units of triprotic acid (+) in II were equilibrated to those of water-insoluble diprotic polyzwitterionic acid (±) III, water-soluble monoprotic poly(zwitterion-anion) (±?) IV, and its conjugate base polydianion (=) V. The critical salt concentration required to promote water solubility of (±) III has been determined to be 0.548 M NaCl, 0.271 M NaBr, 0.133 M NaI. The basicity constants of the carboxyl groups and trivalent nitrogen in (=) V have been determined. A 5 ppm and 20 ppm concentrations of III are effective in inhibiting the precipitation of CaSO₄ from its supersaturated solution with a ≈100% scale inhibition efficiency at 40 °C for a duration of over 3 and 16 h, respectively.     

Processing and properties of Bi0.98R0.02FeO3 (R = La,Sm, Y) ceramics flash sintered at ~650°C in <5 s

We show that flash sintering produces single-phase, nanograin-sized polycrystals of isovalent-substituted multiferroic ceramics of complex compositions. Single-phase polycrystals of Bi_0.98R_0.02FeO₃ (R = La, Sm, Y) were produced at a furnace temperature of ~650°C in a few seconds by the application of an electric field of 50 V cm⁻¹, with the current limit set to 40 mA mm⁻². The dielectric and insulating properties compared favorably with expected values. Impedance spectroscopy suggests electrically homogenous microstructure, except for the sample Bi_0.98La_0.02FeO₃ that shows a small grain boundary contribution to the impedance. These results reinforce the enabling nature of flash sintering for ceramics which pose difficulties in conventional sintering because they contain low melting constituents or develop secondary phases during the sintering protocol.     

Unusual heating rates,dose responses and kinetic parameters detected on thermoluminescence from YAl3(BO3)4:Sm3+ phosphors

This study focused on the thermoluminescence (TL) characteristics of YAl₃(BO₃)₄ (YAB) phosphors modified with various contents of Sm³⁺ ions. The TL response of the YAB: Sm³⁺ phosphors exposed to beta irradiation was measured across the temperature range of 25–500 °C, exhibiting three TL maxima at 70, 235, and 408 °C. Preheating protocol was also carried out to remove the low temperature TL peak followed by further experiments with the two-remaining high-temperature peaks. In the TL measurements conducted with variable heating rates (HR) between 0.1 and 5 °Cs^-1, an anomalous heating rate behaviour was observed. A semi-localized transition model was used to address this feature. There was a standard deviation of less than 5% in the reusability measurements. The results of the kinetic parameters obtained by initial rise (IR) and various heating rate (VHR) methods were compared with those obtained by glow curve deconvolution (GCD) method. T_m-T_stop analysis revealed a continuous distribution of trap levels with a trap depth ranging from 1.35 to 2.20 eV. Through the use of GCD, the glow curve was found to demonstrate general order kinetics and consist of seven superimposed traps. The values of the kinetic parameters obtained for the glow curve agreed with those obtained by other methods excluding the VHR method encountering an anomalous impact. The results obtained from these tests showed that the sample could be successfully used for TL dosimetry applications.     

From selective dissolution to crystal chemistry of brownmillerite in sulfate resisting cement

The aim of this study is to extract brownmillerite from sulfate resisting Portland cement (SRPC) in order to determine its crystal chemistry and the effects of dissolution protocols. Brownmillerites (C₄AF) from four SRPC were extracted and systematically studied by X-ray diffraction (XRD), electron probe microanalysis (EPMA), and X-ray fluorescence spectroscopy. Two extraction steps were used. The first is the salicylic acid/methanol (SAM) protocol that leaves a residue rich in ferrite, C₃A and sulfates. Precipitated hydrated sulfate minerals are also observed for clinker with high molar SO₃/Na₂O_eq ratio. The second, developed in this paper, uses acetic acid (AcA) extraction to dissolve C₃A and sulfates. The Rietveld refinements showed that all brownmillerites of this study crystallize in Ibm2 space group. Two families of brownmillerite were identified by their aluminum content and cell parameters, related to the presence of C₃A in the clinker. EPMA indicated that ferrites from SR0 and SR3 cements have Al/Fe ratios about 0.7 and 0.8–1.0, respectively. XRD allows to predict the (Al+Mg+Si)/Fe ratio in brownmillerite in good agreement with EPMA. The SAM protocol is the best way to study crystal chemistry of brownmillerite and the AcA protocol is recommended to dissolve sulfates and C₃A for further reactivity studies.     

The System Bi2O,—B2O3

The phase diagram for the system Bi₂O₃-B₂O₃ has been determined experimentally. The melting point of Bi₂O₃ has been redetermined as 825° C with an estimated overall uncertainty of about ±3°C, and the molal heat of fusion of Bi₂O₃, calculated from the slope of the liquidus curve, is 2050 cal per mole. The system contains a body-centered cubic phase of approximate composition 12Bi₂O₃·B₂O₃, which melts incongruently at 632°C. Four congruently melting compounds exist in the system: 2Bi₂O₃· B₂O₃·5B₂O₃, Bi₂O₃·3B₂O₃, and Bi₂O₃·4B₂O₃, with melting points, respectively, of 675°, 722°, 708°, and 715°C. The Bi₂O₃·4B₂O₃ compound exhibits a sluggish transformation at 696°C. Compositions containing up to 97.5 wt% (85 mole %) Bi₂O₃ can be partly or totally quenched to glass. Indices of the quenched glasses are greater than 1.74. A region of liquid immiscibility extends at 709°C from almost pure B₂O₃ to 19.0 mole % Bi₂O₃. The extent of immiscibility theoretically calculated agrees with the experimentally determined value when 1.20 A is used for the ionic radius of Bi³⁺.     

SOME METHODS FOR ANALYSIS OF SOLVENT EXTRACTION DATA AND THEIR APPLICATIONS

Abstract

Three programs develpoed to analyze data for liquid-liquid extraction of metal have been applied to the calculation of the stability constants of aqueous cadmium(II)-thiocyanato complexes by using the data for the extraction of tricaprylmethylammonium salt in benzene. The resulting stability constants of the aqueous thiocyanato complexes determined were: for the trial and error method log β₁ = 2·97, log β₂ = 3·70, log β₃ =3·50 and log β₄ =3·28; for the Gauss method log β₁ = 2·91, log β₂ = 3·70, log β₃ =3·35 and log β₄ = 3·29; for the Newton-Gauss method for log β₁ = 2·47, log β₂ =3·24, log β₃ =2·29 and log β₄ = 2·85     

Dehydration,Water Vapor Adsorption and Desorption Behavior of Zn[B3O3(OH)5] · H2O and Zn[B3O4(OH)3]

The dehydration behaviors of two different hydrated zinc borate species, Zn[B₃O₃(OH)₅] · H₂O and Zn[B₃O₄(OH)₃], which are industrially important flame retardants, were studied by thermal gravimetric(TG) analysis and in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Dehydration onset temperatures of Zn[B₃O₃(OH)₅] · H₂O and Zn[B₃O₄(OH)₃] were 129 and 320°C, respectively, at a 10°C/min ramp rate. A very small amount of boric acid was volatilized in addition to water vapor when both samples were heated at 250°C. A significant amount of water vapor was adsorbed by Zn[B₃O₃(OH)₅] · H₂O from air at 25°C. However, Zn[B₃O₄(OH)₃] adsorbed a very small amount of water under the same conditions. Both zinc borates did not have a tendency to cake during storage.     

PREPARATION AND THERMAL EXPANSION OF FE2-xYxW3O12 POWDER BY CITRATE SOL-GEL PROCESS

Fe_2-xY_xW₃O₁₂ powder has been synthesized by the citrate sol-gel process. A model was proposed to calculate the concentration of species in a citric solution. The calculated results could provide valuable information for determining the optimal molar ratio of cation to citric acid and pH value of solution for Fe_2-xY_xW₃O₁₂ preparation. The predicted parameters derived from this model are in good agreement with the experimental results. The prepared gel and the Fe_2-xY_xW₃O₁₂ powder were characterized by X-ray diffraction (XRD) and differential thermal analysis-thermogravimetry (DTA-TG). The results show that it is very difficult to obtain pure Fe₂W₃O₁₂ powder by the citrate sol-gel process in the temperature range 500°–1000°C, however, Y₂W₃O₁₂ can easily be prepared even at 500°C. Y₂W₃O₁₂ annealed at 1000°C for 10 h is favorable for absorbing moisture in air to form Y₂W₃O₁₂·3.3H₂O. The thermal expansion coefficients of Y₂W₃O₁₂·3.3H₂O are: α_a = ? 8.01 × 10^?6°C^?1, α_b = ? 2.51 × 10^?7°C^?1, and α_c = ? 5.55 × 10^?6°C^?1 in 473–1173 K.     

Stability of calcium substituted lanthanum chromites used as SOFC anodes for methane oxidation

La_0·7Ca_0·32CrO₃, La_0·75Ca_0·15Sr_0·1Cr_0·95Mg_0·05O₃, La_0·85Ca_0·15CrO₃ and La_0·85Ca_0·15Cr_0·9Mg_0·1O₃ compounds were studied in reducing atmospheres containing hydrogen, methane and CO/CO₂. They were found to exhibit liquid phase sintering except for La_0·85Ca_0·15CrO₃. Mg enhanced the densification of stoichiometric LaCrO₃. Current was found to affect the stability of the heavily doped samples, whereas the reducing atmospheres did not have a detectable impact. Calcium and or strontium and chromium enriched secondary phases were detected on current treated La_0·7Ca_0·32CrO₃ and La_0·75Ca_0·15Sr_0·1Cr_0·95Mg_0·05O₃ samples. La_0·85Ca_0·15Cr_0·9Mg_0·1O₃ did not degrade under current, at least for 100 h. A current enhanced demixing could be responsable for the segregation. The solubility limit of calcium in LaCrO₃ is thought to be low at 800°C (around 15%).