Papers by Keyword: Hydrotalcite

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Authors: Dong Jin Wan, Dan Qu, Hua Xiao, Yong De Liu, Ting Lu, Wen Qing Xu
Abstract: Hydrotalcites (HT-X) of different Mg/Al ratio (X is Mg/Al molar ratio, 3 and 4) was synthesized by co-precipitation method. Calcined HTLCs (CHT-X) at 500°C have been shown to recover their original layered structure by taking up chloride ion from aqueous solution. Adsorption of chloride by CHT-X was investigated in batch mode. The kinetics study showed that the pseudo-second-order kinetics model could be used to describe the adsorption process satisfactorily. The equilibrium isotherm showed that the Langmuir model gave a better fit to the experimental data than the Freundlich model. The maximum adsorption capacity of CHT-3 was 83.33 mg/g; CHT-4 was 90.09 mg/g .The samples of different Mg/Al ratio have different crystallite size, thus showing different adsorption capacity. As the Mg/Al ratio increases from 3 to 4; the electric charge density between the layers becomes weaker; the interlayer spacing increases; the sample shows greater adsorption capacity. The HT-X where characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDX).
Authors: Min Hong Xu, Ma Li Zhu
Abstract: Rhodamine B is one of biodegradable azo dyes. In this thesis, the CoPc-LDHs were prepared by applying cobalt phthalocyanine on the Mg-Al hydrotalcites, and catalytic oxidation decolorization of rhodamine B (RhB) was studied. The results shown that compared with H2O2, CoPc-LDHs play a key role in catalytic oxidation of RhB. The optimal conditions about CoPc-LDHs/H2O2 system were H2O2 (30% w/w) 1.50 mL, pH 7 and 62.5°C. The catalytic oxidation decolorization effect of RhB reduced with the increase of initial concentration of RhB.
Authors: Margarita del Arco, Daniel Carriazo, Cristina Martín, Amalia M. Pérez Grueso, Vicente Rives
Abstract: PXRD (powder x-ray diffraction), FT-IR (Fourier Transform infrared), N2 adsorption at - 196 °C and TG/DTA (thermogravimetric and differential thermal analyses) techniques have been used for characterisation of MgAl- and ZnAl-CrO4 LDHs, which had been prepared by the ion exchange method from the corresponding chloride LDH (layered double hydroxides) precursors. The results indicates that the oxometalate intercalation in both systems produces interlayer microporosity and a basal spacing of 8.7 Å; This gallery height decreases when the samples are calcined in the temperature range 100-300 °C, due to a grafting process. A larger thermal stability is detected for MgAl-CrO4 sample than for the zinc-containing one.
Authors: Patricia Benito, Maria Herrero, Francisco Martin Labajos, Vicente Rives
Abstract: The synthesis and characterization of Co,Al Layered Double Hydroxides (LDHs) containing carbonate is reported. The solids have been submitted to several thermal treatments, hydrothermal and microwave-hydrothermal, modifying both the treatment time and temperature, with the main aim of studying their influence on the crystallinity of the solids and on the stabilization of divalent cobalt oxidation state. The results show that whichever the temperature and time used the only phase detected was the hydrotalcite, and that the cobalt cations keep the divalent oxidation state.
Authors: D. Álvarez, A. Collazo, Miguel Hernández, Xosé R. Nóvoa, C. Pérez
Abstract: Hydrotalcite-like compound that belongs to anionic clay family was prepared by classical co-precipitation method using magnesium and aluminium nitrates as precursors. Different weight percentages of hydrotalcite with Mg/Al ratio of 2.5 was added (1, 5 and 10 % wt.) to hybrid sols prepared by copolymerization of 3-Glycydoxypropyltrimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (TPOZ). The aim of this work was to study the effect of the hydrotalcite incorporation to hybrid sol-gel coatings on aluminium alloys as substitution of chromate inhibitors. Hybrid sol-gel coatings were deposited by dip coating method on AA2024-T3 substrates. By Scanning Electron Microscopy (SEM) and mechanic profilometry it was possible to see the distribution of HTCP agglomerates which varies from nanometres to micrometers. The corrosion performance was evaluated by the accelerated test salt fog spray chamber (SSFC) and by Electrochemical Impedance Spectroscopy (EIS). The obtained results show the corrosion resistance improvement at higher weight percentages of HTCP.
Authors: Dantiele W.S. Albuquerque, Elisângela S. Costa, Jussara L. de Miranda, Rosana Drumond Gonçalves, Luiza Cristina de Moura
Abstract: Several compounds are being investigated for CO2 capture, besides alkolamines, including solid materials as activated charcoal, zeolites, metal organic frameworks, metal oxides and hydrotalcites. Hydrotalcites, also called layered double hydroxides (LDHs), present some characteristics that are very interesting for CO2 capture, including their speed to achieve equilibrium and their high regeneration. These compounds can be represented by the general formula [M1-x2+Mx3+(OH)2]x+ [(An-)x/n.yH2O]x, where M2+ and M3+ are divalent metals and trivalent cations, respectively, and An- is an anion of valency n which occupies the interlayer region, and maintains electrical neutrality of these materials. In the present work, we have synthesized specific LDHs, thermally modified for CO2 sorption. LDH’s were synthesized intercalated with carbonate anions employing the heterogeneous precipitation method, also known as co precipitation method. After LDH's calcination at different temperatures, the formation of oxides was observed with different surface areas and therefore a varied adsorption capacity. The products were characterized by X-ray diffraction, infrared absorption spectroscopy and thermo gravimetric analysis. The maximum efficiency of CO2 adsorption was observed at reduced pressure with the calcined sample of LDH-CO3, Mg2Al which indicates that the material maintained stable and with a high crystallinity. These properties presented for LDH-CO3, Mg2Al synthesized in this work indicate that these materials can be good and also cheap candidates for CO2 capture.
Authors: A.J. Coleman, H.N. McMurray, G. Williams, Andreas Afseth, Geoff M. Scamans
Abstract: High levels of surface shear experienced during rolling, grinding or machining can cause 6000 series aluminium to develop an ultra-fine grained surface layers which dramatically increase susceptibility to filiform corrosion (FFC) under paint films. In-situ Scanning Kelvin Probe (SKP) measurements in humid air are used to compare the kinetics and mechanism of FFC on abraded and lacquer-coated samples of high copper containing AA6111 and low level copper AA6016. FFC is initiated by applying a small volume of aqueous HCl to a penetrative defect on polyvinylbutyral (PVB) coated alloy samples prior to placement in a chamber maintained at constant humidity and temperature. The SKP is then repeatedly scanned over a fixed surface area to produce a time-lapse animation showing the dynamic evolution of localized free corrosion potential patterns. The spatial distribution of potential variation provides insight into the FFC mechanism and the numerical integration of areas of dissimilar potential provides a measure of the time-dependent area of coating delamination. Various possible FFC inhibition strategies are investigated for use under circumstances where removal of the surface layer prior to application of an organic (paint) coating is not feasible. The two strategies shown in this paper are the use of an anti-corrosion pigments based on an intrinsically conducting polymer called polyaniline. An anion-exchange pigment called hydrotalcite is also used.
Authors: Yoshiyuki Yokogawa, Hiroya Sano, Shota Namba, Kazuo Fujii, Yuki Morita, Masato Hotta, Yutaka Doi
Abstract: Many people worldwide assess themselves as having halitosis, often caused by bio-film and microbial putrefaction of the debris in the mouth, leading to the production of mal-odorous compounds, volatile sulfur compounds (VSC) such as hydrogen sulfide (H2S), methyl mercaptan and dimethyl sulfide. Some desulfurizing agents such as CaO and Na2CO3 in the industry are widely used, but there are few dental desulfurizing agents or adsorbents for removal of VSC. Ag ion exchanged zeolite material showed a high adsorptive property of H2S in aqueous solution (H2S water), however Ag sulfides were formed in aqueous solution. The VSC adsorption capabilities of layered double hydroxides, of which composition is A1-xAlx(OH)2Bx/n·mH2O, where A is Mg and/or Zn and B is CO32-, in aqueous medium was studied by FPD/GC. The concentration of H2S fell to 0% in 2 h when the Zn hydrotalcite was used, while that decreased to 20% in 18 h when the Mg hydrotalcite heated at 500 °C was used. The zinc ion was not detected in the H2S water after soaking for 18 hours.The Zn hydtotalcite is expected to be likely adsorbent for the fast removal of VSC from the mouth.
Authors: Doris Homsi, Samer Aouad, Cedric Gennequin, Antoine Aboukaïs, Edmond Abi-Aad
Abstract: Co6Al2 oxide was prepared using the hydrotalcite route. The obtained solid was thermally stabilized at 500°C and then impregnated with 5 wt.% copper or 1 wt.% ruthenium nitrate solution followed by calcination at 500°C under an air flow. X-ray diffraction results showed that the calcination of the impregnated solids led to the formation of various oxides (CuO, RuO2, Co3O4, CoAl2O4, CoAl2O4). The different impregnated and non impregnated solids were tested in the methane steam reforming reaction (MSR). Methane conversion did not exceed 5% at 800°C in the case of the non impregnated solid, whereas the impregnation strongly enhanced the reactivity: ~89% and ~92% conversions were reached at 600°C for Cu and Ru respectively. The good reactivity of ruthenium impregnated catalyst was attributed to the formation of easily reducible ruthenium and cobalt oxide species at the surface of the support. The addition of ruthenium made the reduction of surface and bulk cobalt oxides possible at lower temperatures.
Authors: Inés Reyero, Gurutze Arzamendi, Luis M. Gandía
Abstract: This chapter aims at providing an overview of the potential of layered double hydroxides (LDHs) or hydrotalcite-like compounds (HTs) for contributing to the catalysis of the synthesis of biodiesel through the transesterification of triglycerides. First, the main methods of preparation of HTs and the most relevantfeatures of these materials are presented, with emphasis on their basic properties. Afterwards, the literature on the use of HTs as catalysts, catalysts precursors, and supports of transesterification catalysts is reviewed. HTs are promising materials for the synthesis of biodiesel from refined and waste vegetable oils, showing reasonable resistance to water and free fatty acids but an improvement of the chemical stability under the desired reaction conditions is still necessary.
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