Open Access
Microwave-assisted pillaring of a montmorillonite with al-polycations in concentrated media
(MDPI, 2017) González, Beatriz; Pérez, Alba Helena; Trujillano, Raquel; Gil Bravo, Antonio; Vicente, Miguel Ángel; Química Aplicada; Kimika Aplikatua
A montmorillonite has been intercalated with Al3+ polycations, using concentrated solutions and clay mineral dispersions. The reaction has been assisted by microwave radiation, yielding new intercalated solids and leading to Al-pillared solids after their calcination at 500 °C. The solids were characterized by elemental chemical analysis, X-ray diffraction, FTIR spectroscopy, thermal analyses, and nitrogen adsorption. The evolution of the properties of the materials was discussed as a function of the preparation conditions. Microwave treatment for 2.5 min provided correctly pillared solids.
Open Access
Hydrocalumite-TiO2 hybrid systems synthesized from aluminum salt cake for photodegradation of ibuprofen
(Elsevier, 2024) Rebollo, Beatriz; Jiménez, Alejandro; Trujillano, Raquel; Rives, Vicente; Gil Bravo, Antonio; Vicente, Miguel Ángel; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Synthesis of hydrocalumite–TiO2 hybrid systems and their use in photodegradation of ibuprofen is reported for the first time. Hydrocalumite was prepared with Al3+ recovered from an aluminum slag (circular economy), TiO2 was deposited on hydrocalumite by hydrolysis of titanium(IV) isopropoxide, and the solids thus obtained were calcined at 400 and 750 ºC. The solid calcined at 400 ºC was essentially amorphous, showing the presence of calcite due to the fixation of atmospheric CO2, while the solid calcined at 750 ºC was composed of mayenite, perovskite and rutile. The calcined solids were used for catalytic degradation of ibuprofen (50 ppm in aqueous solutions) under UV irradiation, obtaining better results than when using commercial TiO2–P25 from Degussa. Under the specific conditions used, the degradation took place in the initial steps of the process, mainly giving rise to species with higher molecular mass than initial ibuprofen.
Open Access
Synthesis strategies of alumina from aluminum saline slags
(Elsevier, 2023) Grande López, Lucía; Vicente, Miguel Ángel; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Aluminum saline slags is a waste of the metallurgical industry that presents serious environmental problems since it needs very extensive areas for its disposal, the toxicity it causes in the atmosphere and groundwater, in addition to high transportation costs. The valorization of this residue by the synthesis of alumina, a compound widely used in the chemical industry, generates a high impact and great interest. In this work, the strategies for synthesizing alumina from aluminum saline slags are reviewed in a context of growing demand for this metal and environmental crisis. The first sections present the aluminum production processes, both from natural bauxite (primary process) and from the recycling of materials with a high aluminum content (secondary process); paying attention to the waste generated and what environmental problems they produce. The main investigations that have allowed to address the recovery of the waste generated are described below, focusing on the processes of recovery/extraction of the aluminum present in its composition. The aluminum in these residues can be found as a metal or forming other compounds such as simple or mixed oxides. Chemical processes are the most relevant, especially those that deal with the acid and alkaline extraction of the metal. The most important section of the work reports on the methods of synthesis of Al2O3, highlighting the methods of precipitation, sol-gel, hydrothermal synthesis, and combustion, among others. The work ends with a summary and conclusions section.
Open Access
Removal of heavy metals from aqueous solutions by adsorption on zeolites synthesized from aluminum saline slags
(Elsevier, 2024-10-31) Jiménez, Alejandro; Trujillano, Raquel; Rives, Vicente; Vicente, Miguel Ángel; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Three heavy metals (Cu2+, Cd2+ and Pb2+) were removed from aqueous solutions using zeolites prepared from saline slags, a very important waste generated during aluminum recycling. Zeolites were characterized by powder X-ray diffraction, thermal analysis, Fourier transform infrared spectroscopy, X-ray microfluorescence, element chemical analysis, nitrogen adsorption at -196 °C and electron microscopy. The textural and structural properties of X-type faujasite zeolite convert it in a promising adsorbent in aqueous streams. Removal of the heavy metals was evaluated in batch mode, studying the adsorbent dose, the initial concentration of the heavy metal, the selectivity of the solid in case of mixtures with various metal cations and the recyclability of the solid. The kinetic and equilibrium results were evaluated using both pseudo-first- and pseudo-second-order kinetics, and Langmuir, Freundlich and Toth equation isotherms for the equilibrium. The time needed to reach equilibrium was between 10 and 20 min. Faujasite was highly effective in removing Cu2+, Cd2+ and Pb2+ from aqueous solutions, much higher than analcime and pollucite, other two zeolites recently synthesized by us from aluminum slags, and used in this work for comparison purposes. The maximum adsorption capacity was 591 mg/g for Pb2+, 304 mg/g for Cu2+ and 279 mg/g for Cd2+.
Open Access
Photocatalytic degradation of trimethoprim on doped Ti-pillared montmorillonite
(Elsevier, 2019) González, Beatriz; Trujillano, Raquel; Vicente, Miguel Ángel; Rives, Vicente; Korili, Sophia A.; Gil Bravo, Antonio; Institute for Advanced Materials and Mathematics - INAMAT2
Montmorillonite pillared with titanium and doped with Cr3+ or Fe3+ has been tested for the photo-degradation of the antibiotic trimethoprim (trimethoxybenzyl-2,4-pyrimidinediamine) under different conditions, namely, in the dark or in UV light, with or without catalyst, finding excellent catalytic performance under photocatalytic conditions. The degradation by-products were preliminary analysed by mass spectrometry. The results suggested that the molecule broke in two halves, corresponding to its two existing rings. The process continued with the breakage of new fragments from the trimethoxybenzene half, these fragments later reacted with the methoxy groups in this part of the molecule, giving species with m/z values higher than that for the starting molecule, and with the breakage of new fragments.
Open Access
Effect of high pressure on the reducibility and dispersion of the active phase of Fischer-Tropsch catalysts
(MDPI, 2019) Yunes, Simón; Vicente, Miguel Ángel; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
The effect of high pressure on the reducibility and dispersion of oxides of Co and Fe supported on -Al2O3, SiO2, and TiO2 has been studied. The catalysts, having a nominal metal content of 10 wt.%, were prepared by incipient wetness impregnation of previously calcined supports. After drying at 60 °C for 6 h and calcination at 500 °C for 4 h, the catalysts were reduced by hydrogen at two pressures, 1 and 25 bar. The metal reduction was studied by temperature-programmed reduction up to 750 °C at the two pressures, and the metal dispersion was measured by CO chemisorption at 25 °C, obtaining values between 1% and 8%. The physicochemical characterization of these materials was completed by means of chemical analysis, X-ray diffraction, N2 adsorption-desorption at -196 °C and scanning electron microscopy. The high pressure lowered the reduction temperature of the metal oxides, improving their reducibility and dispersion. The metal reducibility increased from 42%, in the case of Fe/Al2O3 (1 bar), to 100%, in the case of Fe/TiO2 (25 bar).
Open Access
Synthesis of pollucite and analcime zeolites by recovering aluminum from a saline slag
(Elsevier, 2021) Jiménez, Alejandro; Misol, Alexander; Morato, Álvaro; Rives, Vicente; Vicente, Miguel Ángel; Gil Bravo, Antonio; Institute for Advanced Materials and Mathematics - INAMAT2
This work describes a valorization procedure for one of the most important wastes generated during aluminum recycling, namely, saline slag. This procedure was divided in two steps: a) recovery of aluminum or its compounds in various fractions, and b) the use of one of those fractions in the synthesis of two zeolites: analcime (NaAlSi2O6 center dot H2O) and pollucite (CsAlSi2O6 center dot nH(2)O). Saline slag was ground, sieved (1 mm), washed and separated into two fractions of different sizes, one larger and another smaller than 0.4 mm. The fraction smaller than 0.4 mm was treated under reflux conditions with NaOH or CsOH solutions. The extraction liquor contained aluminum and alkali metal cations; after adding the necessary amount of Si, hydrothermal synthesis was carried out, obtaining the zeolitic materials. Characterization of the solids obtained was carried out by powder X-ray diffraction, thermal analysis, FT-IR spectroscopy, element chemical analysis and electron microscopy. The valorization procedure proposed in this work showed that a high percentage of Al (close to 45 wt%) can be recovered from the fraction smaller than 0.4 mm and that the liquors extracted with NaOH or CsOH can be used as a source for the hydrothermal synthesis (200 degrees C for 24 h) of two zeolites of the analcime family, obtaining in both cases pure and crystalline solids.
Open Access
Preparation of Ca2Al1–mFem(OH)6Cl 2H2O-doped hydrocalumites and application of their derived mixed oxides in the photodegradation of ibuprofen
(MDPI, 2022) Jiménez, Alejandro; Valverde, Marta; Misol, Alexander; Trujillano, Raquel; Gil Bravo, Antonio; Vicente, Miguel Ángel; Institute for Advanced Materials and Mathematics - INAMAT2
Aluminum from saline slags generated during the recycling of this metal, extracted under reflux conditions with aqueous NaOH, was used in the synthesis of hydrocalumite-type solids with the formula Ca2Al1–mFem(OH)6Cl 2H2O. The characterization of the obtained solids was carried out by powder X-ray diffraction, infrared spectroscopy, thermal analysis, element chemical analysis, N2 adsorption-desorption at -196ºC and electron microscopy. The results showed the formation of Layered Double Hydroxide-type compounds whose characteristics varied as the amount of incorporated Fe3+ increased. These solids were calcined at 400ºC and evaluated for the catalytic photodegradation of ibuprofen, showing promising results in the elimination of this drug by advanced oxidation processes. The CaAl photocatalyst (without Fe) showed the best performance under UV light for the photodegradation of ibuprofen.
Open Access
Progress and perspectives on pillared clays applied in energetic and environmental remediation processes
(Elsevier, 2020) Gil Bravo, Antonio; Vicente, Miguel Ángel; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
Pillared interlayered clays (PILCs) are materials that show a two-dimensional layered porous structure with properties that could be interesting alternatives to zeolites and other microporous solids. Some of the properties that make these materials interesting are specific surface area, high exchange capacity, low permeability, swelling ability, relatively good heat resistance stability, high acidic properties, and relatively low price. PILCs have attracted intense research among several years in relation to the possible control of these properties and environmental applications. The current short work is devoted to the tendencies and new insights in to the last five years of PILCs as adsorbents and heterogeneous catalysts. The work finishes considering the future application prospects.
Open Access
Effective degradation of methylene blue in aqueous solution using Pd-supported Cu-doped Ti-pillared montmorillonite catalyst
(Elsevier, 2019) Joseph, Annu; Vellayan, Kannan; González, Beatriz; Vicente, Miguel Ángel; Gil Bravo, Antonio; Institute for Advanced Materials and Mathematics - INAMAT2
The effluents from the textile, paper and food industries contain organic dyes that are strongly colored and reveal harmful effect on living systems. In order to reduce water pollution, the degradation of dye into non toxic form is desirable. Methylene blue is one such organic dye, discharged from textile industries. In this work, the catalytic degradation of methylene blue was investigated using a montmorillonite supported trimetallic catalyst, prepared by supporting Pd on a Cu-doped Ti pillared montmorillonite. The catalyst exhibited excellent performance to reduce methylene blue, in the presence of NaBH4. The decolorization was appreciable and the results indicated that methylene blue could be successfully decolorized and degraded using the catalyst under room conditions. Almost complete degradation was achieved within 20 min. The results obtained were better than those reported for other catalysts. © 2018 Elsevier B.V.