Influence of activation atmosphere used in the chemical activation of almond shell on the characteristics and adsorption performance of activated carbons

7 pages, 5 figures, 5 tables.The aim of this work was to compare the effect of different activating atmospheres on the final properties and adsorption performance of activated carbons. Almond shell based activated carbons have been obtained by chemical activation with phosphoric acid. Two sets of activated carbons were prepared. First set was prepared under inert atmosphere at different impregnation ratios, temperatures and times of activation. Second set of activated carbons was prepared at the same activating conditions except the activating atmosphere using an oxidant one. Activated carbons prepared under both activation atmospheres were characterized by elemental analysis (EA), thermogravimetry (TGA), temperature programmed desorption (TPD), point zero charge (PZC), Boehm titration and N 2 physisorption. To study the adsorption performance of the activated carbons toluene adsorption – desorption isotherms were determined gravimetrically. The results obtained con fi rm that the activating atmosphere has a strong in fl uence on the fi nal characteristics of the activated carbons. Activated carbons with higher oxygen content and more negative surface charge have been obtained by changing the activatingatmospherebyanoxidantone.Surfaceareaisalsohigherforactivatedcarbonspreparedunderoxidant atmosphere. However toluene adsorption capacity is lower for activated carbons prepared under oxidant atmo- sphere due to their surface chemistry. © 2013 Elsevier B.V. All rights reserved.The financial support from Spanish Ministry of Environment (contracts 439/2006/3- 11.2 and B030/2007/2-11.2) is duly recognized.Peer reviewe

Aplicaciones de la espectroscopia fotoelectronica de rayos X en la caracterización de materiales funcionales

El objetivo principal de esta Tesis es la aplicación de la espectroscopía XPS al estudio de distintos tipos de materiales inorgánicos y orgánicos, que tienen aplicaciones de interés en diferentes procesos medioambientales, energéticos y farmacéuticos. En alguno de los materiales analizados, además de realizar un estudio químico general de su superficie, también se ha utilizado espectroscopía fotoelectrónica de ángulo resuelto o perfiles de profundidad con desbastado iónico, para establecer el posible efecto de contaminación superficial. La mayor parte de las muestras analizadas son membranas comerciales de distintos materiales y características, con aplicación en diferentes procesos de separación. El hecho de que las membranas seleccionadas sean de tipo comercial, va a permitir conocer la composición química de sus superficies, que no siempre coincide con la indicada por los suministradores debido a factores que se pueden considerar “ambientales” (depósito de contaminantes, oxidación temporal,…) o asociados a la propia fabricación de las membranas. Además, algunas de esas muestras han sido modificadas posteriormente, con el fin de variar alguna de sus propiedades, lo que puede mejorar el transporte o algún otro parámetro característico de la membrana, en relación a una aplicación determinada. Junto con las membranas, también se ha estudiado por XPS la superficie de otros dos materiales funcionales, uno inorgánico y otro orgánico, con aplicaciones como catalizador y dispositivo para la difusión de fármacos o activos, respectivamente, así como dos líquidos iónicos a temperatura ambiente basados en el catión imidazolio

Nanoporous Alumina Support Covered by Imidazole Moiety–Based Ionic Liquids: Optical Characterization and Application

This work analyzes chemical surface and optical characteristics of a commercial nanoporous alumina structure (NPAS) as a result of surface coverage by different imidazolium-based ionic liquids (1-butyl-3-metylimidazolium hexafluorophosphate, 3-methyl-1-octylimidazolium hexafluorophosphate, or 1-ethyl-3-methylimidazolium tetrafluoroborate). Optical characteristics of the IL/NPAS samples were determined by photoluminescence (at different excitation wavelengths (from 300 nm to 400 nm), ellipsometry spectroscopy, and light transmittance/reflectance measurements for a range of wavelengths that provide information on modifications related to both visible and near-infrared regions. Chemical surface characterization of the three IL/NPAS samples was performed by X-ray photoelectron spectroscopy (XPS), which indicates almost total support coverage by the ILs. The IL/NPAS analyzed samples exhibit different photoluminescence behavior, high transparency (<85%), and a reflection maximum at wavelength ~380 nm, with slight differences depending on the IL, while the refractive index values are rather similar to those shown by the ILs. Moreover, the illuminated I–V curves (under standard conditions) of the IL/NPAS samples were also measured for determining the efficiency energy conversion to estimate their possible application as solar cells. On the other hand, a computational quantum mechanical modeling method (DFT) was used to establish the most stable bond between the ILs and the NPAS support.Partial funding for open access charge: Universidad de Mála

Modification of the Physical Properties of a Nafion Film Due to Inclusion of n-Dodecyltriethylammonium Cation: Time Effect.

This study investigates the effects of modifying commercial Nafion-212 thin films with dodecyltriethylammonium cation (DTA+) on their electrical resistance, elastic modulus, light transmission/reflection and photoluminescence properties. The films were modified through a proton/cation exchange process for immersion periods ranging from 1 to 40 h. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the crystal structure and surface composition of the modified films. The electrical resistance and the different resistive contributions were determined via impedance spectroscopy. Changes in the elastic modulus were evaluated using stress–strain curves. Additionally, optical characterization tests, including light/reflection (250–2000 nm) and photoluminescence spectra, were also performed on both unmodified and DTA+-modified Nafion films. The results reveal significant changes in the electrical, mechanical and optical properties of the films, depending on the exchange process time. In particular, the inclusion of the DTA+ into the Nafion structure improved the elastic behavior of the films by significantly decreasing the Young modulus. Furthermore, the photoluminescence of the Nafion films was also enhanced. These findings can be used to optimize the exchange process time to achieve specific desired properties.Partial funding for open access charge: Universidad de Málag

Nanoporous alumina support covered by imidazole moiety-based ionic liquids: optical characterization and application

This work analyzes chemical surface and optical characteristics of a commercial nanoporous alumina structure (NPAS) as a result of surface coverage by different imidazolium-based ionic liquids (1-butyl-3-metylimidazolium hexafluorophosphate, 3-methyl-1-octylimidazolium hexafluorophosphate, or 1-ethyl-3-methylimidazolium tetrafluoroborate). Optical characteristics of the IL/NPAS samples were determined by photoluminescence (at different excitation wavelengths (from 300 nm to 400 nm), ellipsometry spectroscopy, and light transmittance/reflectance measurements for a range of wavelengths that provide information on modifications related to both visible and near-infrared regions. Chemical surface characterization of the three IL/NPAS samples was performed by X-ray photoelectron spectroscopy (XPS), which indicates almost total support coverage by the ILs. The IL/NPAS analyzed samples exhibit different photoluminescence behavior, high transparency (<85%), and a reflection maximum at wavelength ~380 nm, with slight differences depending on the IL, while the refractive index values are rather similar to those shown by the ILs. Moreover, the illuminated I–V curves (under standard conditions) of the IL/NPAS samples were also measured for determining the efficiency energy conversion to estimate their possible application as solar cells. On the other hand, a computational quantum mechanical modeling method (DFT) was used to establish the most stable bond between the ILs and the NPAS support.M.A. thanks the SpanishMinistry of Science and Innovation (MCIN/AEI/10.13039/ 501100011033) through project PID2021-122613OB-I00

Optical and physicochemical characterizations of a cellulosic/CdSe-QDs@S-DAB5 film

CdSe quantum dots nanoparticles were coated with the thiolated (DiAminoButane based dendrimer) DAB dendrimer of fifth generation (S-DAB(5)) and embedded in a highly hydrophilic regenerated cellulose (RC) film by simple dip-coating method (immersion in QD-dendrimer aqueous solution) as a way to get a flexible nano-engineered film (RC-4/CdSe-QDs@S-DAB(5)) with high transparency and photoluminescence properties for different applications. Optical changes in the RC film associated with QDs inclusion were determined by spectroscopic ellipsometry (SE) measurements, which provide information on changes caused in the refraction index and the extinction coefficients of the film, as well as by light transmittance/reflectance curves and photoluminescence (PL) spectra. Impedance spectroscopy (IS) and other typical physicochemical techniques for material characterization (TEM, SEM and XPS) have also been used in order to have more complete information on film characteristics. A comparison of RC-4/CdSe-QDs@S-DAB(5) film optical characteristics with those exhibited by other RC-modified films depending on the type of dendrimer was also carried out

Influence of TiO2-Coating Layer on Nanoporous Alumina Membranes by ALD Technique

Geometrical, chemical, optical and ionic transport changes associated with ALD of TiO2-coating on the porous structure of two nanoporous alumina membranes (NPAMs), which were obtained by the two-step aluminum anodization method but with different pore size and porosity, are presented. Chemical and morphological changes were determined by analyzing XPS spectra and SEM images, showing practically total coverage of the NPAMs surface and leading to a reduction in the geometrical parameters of both samples, while SAED and high resolution TEM measurements allowed us to determine the crystalline structure and thickness of the TiO2-coating, with the latter confirmed by depth-profile XPS analysis. Spectroscopic ellipsometry measurements were also carried out in order to detect changes in characteristic optical parameters (refractive index, n, and extinction coefficient, k), due to the TiO2-coating of NPAMs. Considering the common application of NPAMs in solute/ion diffusion processes, the effect of the TiO2-coverage on electrochemical parameters was analyzed by measuring the concentration potential with a typical model electrolyte (KCl solutions), leading to an increase of the electropositive character for both kinds of samples

Development of activated carbons from lignocellulosic wastes for toluene and n-hexane adsorption and recovery

El objetivo principal de esta investigación es desarrollar carbones activados a partir de cáscara de almendra para la adsorción y recuperación de dos compuestos orgánicos volátiles, tolueno y n-hexano, en baja concentración en corrientes de gas. Se ha optimizado la metodología se obtención de los carbones activados a partir de cáscara de almendra mediante activación química con H3PO4, a partir de un diseño experimental simplex, con las siguientes variables: temperatura de activación, tiempo de activación, ratio de impregnación y dos atmosferas de activación, inerte y oxidante. Los carbones activados obtenidos poseen altas áreas específicas (mayores de 1100 m2/g en muchos casos) y una gran cantidad de grupos funcionales oxigenados ácidos. Se ha aplicado la metodología de superficies de respuesta que permite optimizar las condiciones de preparación de los carbones activados para maximizar diferentes características de los mismos, y por tanto la obtención de carbones activados “a medida” para aplicaciones concretas. Las isotermas de adsorción de tolueno y n-hexano han permitido obtener las capacidades máximas de adsorción, resultando superiores al 60% en peso para el tolueno y superiores al 40% en peso para el n-hexano. Mediante adsorciones dinámicas en lecho fijo a bajas concentraciones (500 y 1000 ppm). Las capacidades de adsorción obtenidas son mayores del 20% en peso para tolueno y superiores al 10% en peso para n-hexano, esta diferencia se debe principalmente a la mayor presión relativa equivalente del tolueno obtenida en modo estático. Mediante adsorciones dinámicas de ambos compuestos en presencia de vapor de agua (3%) se ha comprobado que el vapor de agua reduce las capacidades de adsorción obtenidas, indicando que se establece una competencia entre ambos adsorbatos. Las reducciones en la capacidad de adsorción son mayores para n-hexano, debido a su menor afinidad con el carbón y a las propiedades del compuesto. Se han realizado experimentos de adsorción de mezclas multicomponente de tolueno y n-hexano en ausencia y presencia de vapor de agua, con una concentración inicial de 250 ppm de cada compuesto y, en su caso, 3% de vapor de agua. Las curvas de ruptura de la mezcla en ausencia de humedad muestran un desplazamiento del n-hexano adsorbido por parte del tolueno, denominado efecto roll-up, debido a la mayor afinidad del tolueno con la superficie del carbón y su menor volatilidad. En presencia de vapor de agua se mantiene este efecto y la capacidad de adsorción de la mezcla disminuye. Se han realizado ciclos de adsorción-desorción en modo estático de los carbones activados y las capacidades de adsorción de tolueno y n-hexano se mantienen. Simulando una aplicación práctica, se han realizado ciclos de adsorción en modo dinámico a 25ºC y desorción a 150ºC para tolueno, n-hexano y su mezcla, manteniéndose las capacidades de adsorción a lo largo de varios ciclos, por lo que resultan aptos para su aplicación industrial. La consecución de este trabajo permite la elección de las condiciones de preparación de los carbones activados, obtenidos a partir de cáscara de almendra, maximizando una característica determinada de los mismos o una combinación de características apropiada para su uso final, en el caso presente, la adsorción de tolueno y n-hexano.Peer reviewe

Chemical Surface, Thermal and Electrical Characterization of Nafion Membranes Doped with IL-Cations

Surface and bulk changes in a Nafion membrane as a result of IL-cation doping (1-butyl-3-methylimidazolium tetrafluoroborate or BMIM+BF4 and phenyltrimethylammonium chloride or TMPA+Cl−) were studied by X-ray photoelectron spectroscopy (XPS), contact angle, differential scanning calorimetry (DSC) and impedance spectroscopy (IS) measurements performed with dry samples after 24 h in contact with the IL-cations BMIM+ and TMPA+. IL-cations were selected due to their similar molecular weight and molar volume but different shape, which could facilitate/obstruct the cation incorporation in the Nafion membrane structure by proton/cation exchange mechanism. The surface coverage of the Nafion membrane by the IL-cations was confirmed by XPS analysis and contact angle, while the results obtained by the other two techniques (DSC and IS) seem to indicate differences in thermal and electrical behaviour depending on the doping-cation, being less resistive the Nafion/BMIM+ membrane. For that reason, determination of the ion transport number was obtained for this membrane by measuring the membrane or concentration potential with the samples in contact with HCl solutions at different concentrations. The comparison of these results with those obtained for the original Nafion membrane provides information on the effect of IL-cation BMIM+ on the transport of H+ across wet Nafion/BMIM+ doped membranes

Adsorption of toluene and toluene–water vapor mixture on almond shell based activated carbons

The aim of work is to study the adsorption of a common volatile organic compound such as toluene using activated carbons prepared by chemical activation with phosphoric acid of a lignocellulosic precursor, almond shell, under different conditions. The Impregnation ratio, temperature and time of activation were modified to obtain activated carbons with different characteristics. Regarding the characteristics of the activated carbons, the effects of porous structure and surface chemistry on the toluene adsorption capacity from toluene isotherms have been analysed. Results show that the control of properties of the activated carbons, particularly porous structure, highly dependent on the preparation conditions, plays a decisive role on the toluene adsorption capacity of the activated carbons. Concerning the experiments of toluene adsorption conducted in dynamic mode, activated carbons prepared at low temperatures of activation show higher breakthrough times than those obtained for activated carbons prepared at higher activation temperatures. The amount of toluene adsorbed in presence of water vapor in the gas stream lead to a decrease ranging from 33 to 46 % except for carbons prepared at higher temperatures activated that show only a slight decrease in the amount of toluene adsorbed. Activated carbons can be regenerated with soft heat treatment showing a slight decrease in the adsorption capacity. The high toluene adsorption capacities as well as the high breakthrough times obtained in presence of water vapor make these activated carbons suitable for commercial applicationsSpanish Ministry of Environment (contracts 439/2006/3-11.2 and B030/2007/2-11.2)Peer reviewe