Synthesis and CO2 adsorption properties of hydrotalcite-like compounds prepared from aluminum saline slag wastes

[EN]This study describes the synthesis of hydrotalcite-like materials by the co-precipitation method using aluminum extracted from saline slags wastes. Saline slags were chemically treated with 2 mol/dm3 aqueous solutions of NaOH for 2 h using a reflux system. The aluminum aqueous solutions were used as precursors with cobalt, magnesium and nickel nitrates, and Na2CO3, to obtain hydrotalcite-like materials with two mole M2+/Al3+ ratios, 2:1 and 4:1. The resulting solids were characterized by X-ray diffraction, termogravimetric analyses, nitrogen adsorption at −196 °C and scanning electron microscopy. After thermal treatment at 200 °C, the CO2 adsorption at 50, 100 and 200 °C was evaluated under dry conditions. The results showed a remarkable sorption capacity of 5.26 mmol/g at a pressure of 80 kPa and at a temperature of 50 °C for the MgAl-2:1 sample, with sorption capacities considerably higher than those reported in the literature for hydrotalcites under similar conditions. The Henry’s law constants were obtained directly from the adsorption isotherms at low pressures and the values found are between 0.01 and 4.20 mmol/kPa·g. The isosteric heats of CO2 adsorption found, using the Clausius-Clapeyron equation, were in the range of 5.2 to 16.8 kJ/mol.The authors are grateful for financial support from the Spanish Ministry of Economy, Industry and Competitiveness (AEI/MINECO), and the European Regional Development Fund (ERDF

Saline slag waste as an aluminum source for the synthesis of Zn–Al–Fe–Ti layered double-hydroxides as catalysts for the photodegradation of emerging contaminants

In this work, aluminum extracted from saline slag waste is valorized to create a layered double-hydroxide series containing zinc and various proportions of aluminum/titanium. Materials were synthesized by the co-precipitation method with an Me2+/Me3+ molar ratio of 3:1 and tested for the removal of diclofenac and salicylic acid from water under UV radiation. The incorporation of 5 wt% iron by wet impregnation is evaluated. In addition, another series of zinc, aluminum/iron materials with and without 5 wt% impregnated titanium are tested as catalysts for comparison. Structural characterization and comparison of the two series was performed by powder X-ray diffraction (PXRD), nitrogen adsorption at 77 K, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) measurements. The uncalcinated samples had a typical hydrotalcite structure with a high crystallinity; the presence of ZnO, ZnFe2O4 or Fe3O4 was found after calcination. The specific surface areas of the dried samples ranged from 78 to 199 m2/g, being highest for Zn6Al0.5Ti1.5. Overall, the results showed that the ZnAlTi series were more effective catalysts than ZnAlFe for photodegradation of the emerging contaminants diclofenac and salicylic acid, under UV light at 298 K, considering two concentrations of the organic molecules (5 and 50 μmol/dm3

Progress in the removal of pharmaceutical compounds from aqueous solution using layered double hydroxides as adsorbents: A review

Emerging contaminants and, among them, pharmaceutical compounds, have a significant impact on water ecosystems. Layered Double Hydroxides (LDH), being easy to synthesize and cheap materials, have recently gained attention as adsorbents in aqueous solutions. This work describes the latest research performed in the adsorption capacity of LDH towards both antibiotics and Non-Steroidal Anti-Inflammatory Drugs (NSAID) describing and analyzing the synthesis conditions (Me2+:Me3+ molar ratio, calcination temperature, choice of metals for the memory effect), kinetics and isotherm models used, use of support (more practical in a 3D over a 2D form), temperature effect and several techniques for the recovery of the adsorbents. LDH exhibited great performance and potential as clean adsorbents for these emerging contaminant

A review on characterization of pillared clays by specific techniques

[EN]The use of specific characterization techniques, namely Thermal Analysis, Near Infrared Spectroscopy, Ultraviolet–Visible Spectroscopy, Electron Paramagnetic Resonance, Mössbauer Spectroscopy and Neutron Scattering, in the characterization of pillared clays is reviewed. Special emphasis is placed in the information provided by each of these techniques in the characterization of pillared clays

Synthesis and characterization of organosaponites. Thermal behavior of their poly(vinyl chloride) nanocomposites

[EN]The aim of this work was to synthesize and characterize the structural properties of the materials resulting from the combination of a synthetic saponitewith several organicmolecules, namely, Arquad 2HT-75, octadecylamine, 3-aminopropyltriethoxysilane, trimethyloctadecylammonium bromide and tetraethoxysilane, or combinations of them, and with or without the addition of HCl during synthesis. The ratios organic molecule/saponite and HCl/organic molecule were considered as synthesis variables. Structural characterization was based on X-ray diffraction (XRD), simultaneous thermogravimetric/differential thermal analysis (TG/DTA) and infrared spectroscopy (FTIR). The chemical composition of the materials was determined through X-ray fluorescence (XRF) and atomic absorption spectroscopy (AAS), and theirmorphologywas analyzed through scanning electron microscopy (SEM). The values obtained for the basal spacings were a function of the type and amount of the organic molecule. Otherwise, HCl did not significantly influence the basal spacing, but it had the capacity to significantly modify the morphology and the chemical composition of the samples. From the results found, the solids modified with tetraethoxysilane and 3-aminopropyltriethoxysilane were selected to incorporate various titaniumprecursors. These neworgano-modified saponiteswere used in the formulation of PVC nanocomposites and their thermal behavior was evaluated at two temperatures (70 and 180 °C).This work was funded by the Spanish Ministry of Science and Innovation (MICINN) and the European Regional Development Fund (FEDER)IPT-420000-2010-01

Structural, textural and acidic properties of Cu-, Fe- and Cr-doped Ti-pillared montmorillonites

Montmorillonite has been treated with Ti-based solutions, alone or doped with Cu2 +, Fe3 + or Cr3 + cations, yielding new intercalated solids, which have been calcined at various temperatures to test the stability of the so-formed pillars. The solids calcined at 500 °C were fully characterized by chemical analysis, X-ray diffraction, FT-IR spectroscopy, thermal analyses, nitrogen adsorption and acidity evaluation. The evolution of the specific surface area, porosity and acidic properties is discussed, analysing the effect of pillaring and doping procedures on these propertie

Effect of dopants on the structure of titanium oxide used as a photocatalyst for the removal of emergent contaminants

Photocatalysts composed of titanium dioxide modified with B, F, N and P have been synthesized, characterized and applied to the degradation of caffeine, diclofenac, ibuprofen and salicylic acid. The modified TiO2 samples were prepared by the sol–gel technique starting from titanium(IV) isopropoxide and using H3BO3, NH4F, N(C2H5OH)3 and H3PO4 as precursors of the modifiers, with the content varying between 0 and 5 wt%. Structural characterization was based on nitrogen physisorption at −196 °C, powder X-ray diffraction (PXRD), simultaneous thermogravimetric/differential thermal analysis (TG/DTA) and X-ray photoelectron spectroscopy (XPS). The structural properties of the modified TiO2 solids were significantly different depending on the nature and amount of modifiers and the calcination temperature. TiO2 in the anatase phase was obtained in all cases and was stable upon calcination at 400 °C. The photocatalytic degradation of caffeine, diclofenac, ibuprofen and salicylic acid by modified TiO2 was investigated under ultraviolet irradiation at 25 °C. The photocatalytic degradation behavior followed the order: caffeine > diclofenac = ibuprofen > salicylic acid. B-doped TiO2 was the most efficient catalyst in the degradation of these selected emerging contaminants

Rapid microwave-assisted synthesis of saponites and their use as oxidation catalysts

Saponites containing divalent Mg, Ni, or Fe as octahedral cations and trivalent Al and Fe substituting Si in the tetrahedral sheet were synthesized using microwave radiation. Saponite with a high specific surface area was obtained in all the syntheses, although Fe-Al saponite crystallized was impurified by Fe2O3 and analcime. The catalytic activity of the solids for the epoxidation of (Z)-cyclooctene by hydrogen peroxide was tested, the solids obtained being highly active (conversion up to 8.8%, and 100% selectivity to the epoxide

Effect of chemical modification of palygorskite and sepiolite by 3-aminopropyltriethoxisilane on adsorption of cationic and anionic dyes

[EN]A study has been performed on the removal of representative cationic and anionic dyes, methylene blue and metanil yellow, from aqueous solutions using fibrous clay minerals grafted with amine groups using (3- aminopropyl)triethoxysilane as functionalizing agent. Parameters affecting dye uptake, including contact time and dye concentration, the desorption process, pH and the recovery of both the dyes and the adsorbents, were evaluated. The adsorption capacities were 49.48 and 47.03 mg/g for grafted palygorskite and 60.00 and 59.78 mg/g for grafted sepiolite, for methylene blue and metanil yellow dyes, respectively. Adsorption of the anionic dye was enhanced by the grafting process. Grafted clay mineral adsorbents proved to be efficient to remove the contaminants from a real wastewater from textile industry within 30 min. Both adsorbents showed good reusability and the maximum adsorption capacity was maintained stable after a 2-cycle test. Thus, hybrid adsorbents based on fibrous clay minerals can efficiently be applied in adsorption/desorption cycles for removal of dye

Analysis of the Structure of Alumina-Pillared Clays by Nitrogen and Carbon Dioxide Adsorption

Nitrogen and carbon dioxide adsorption methods were used to study the structural properties developed by a series of alumina-pillared clays. The solids were prepared by varying the Al/clay ratio and the calcination temperature of a montmorillonite intercalated with solutions of aluminium. Equilibrium data for CO 2 adsorption by these materials were analyzed using the Langmuir, Freundlich and Toth isotherm models. The fitting parameters for these models demonstrated the heterogeneous nature of the materials studied and that CO 2 interaction with the surface was influenced by the calcination temperature