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Adsorption: Journal of the International Adsorption Society (v.17, #3)

Guest editorial by Joaquín Silvestre-Albero; Antonio Sepúlveda-Escribano (pp. 411-412).

Activated carbon cloth as adsorbent and oxidation catalyst for the removal of amitrole from aqueous solution by C. Moreno-Castilla; M. A. Fontecha-Cámara; M. A. Álvarez-Merino; M. V. López-Ramón; F. Carrasco-Marín (pp. 413-419).

Removal of amitrole from water was studied by adsorption on an activated carbon cloth and by oxidation with hydrogen peroxide using the same activated carbon cloth as catalyst. Study variables included the solution pH, ionic strength, and temperature in the adsorption process and the solution pH and the surface chemistry of the activated carbon cloth in the oxidation process. Results showed that amitrole adsorption on activated carbon cloth was not adequate to remove amitrole from water due to the high solubility and low aromaticity of the herbicide, which reduced its adsorption on the carbon. A higher amitrole removal rate was obtained with the activated carbon/H₂O₂ system. The best results were obtained on basic activated carbon surfaces at pH 7–10, when hydroxyl radical formation is favored, achieving the removal of 35–45% of the AMT, compared with 20–25% under the best adsorption conditions. Importantly, oxygen fixed on the carbon surface during AMT oxidation must be removed by heat treatment in order to regenerate the surface basicity of the carbon before its reutilization in another oxidation cycle.

Keywords: Amitrole adsorption; Amitrole oxidation; Activated carbon cloth

Reactive adsorption of penicillin on activated carbons by Conchi O. Ania; Joaquina G. Pelayo; Teresa J. Bandosz (pp. 421-429).

A series of activated carbons with varied surface chemistry, obtained by wet oxidation and thermal treatment, was used for the removal of penicillin from low concentration aqueous solution. It was found that the carbon surface chemistry favors the degradation of the antibiotic, giving rise to various intermediates detected both in solution and in the adsorbed phase (deposited with the pore structure of the activated carbons). The confinement of penicillin molecules entrapped in the nanopores of activated carbons of acidic nature accelerates their degradation compared to that one in the bulk solution, which can be linked the strong local pH fall inside the pores. Degradation also takes place in activated carbons of basic pH, although the nature and partition of the intermediates formed differ from those in the acidic carbons. In both cases most of the breakdown products do not present therapeutic activity.

Keywords: Activated carbon; Reactive adsorption; Penicillin; Antibiotics

Adsorption of dyes on carbon xerogels and templated carbons: influence of surface chemistry by J. L. Figueiredo; J. P. S. Sousa; C. A. Orge; M. F. R. Pereira; J. J. M. Órfão (pp. 431-441).

The removal of textile dyes by adsorption onto carbon materials with extended mesoporosity is addressed in the present work. Two types of high surface area carbon adsorbents were prepared, namely a carbon xerogel and a templated carbon. Both materials were subsequently subjected to appropriate treatments in order to modify their surface chemistries, while keeping their textural properties relatively unchanged. The carbon adsorbents were extensively characterized by different techniques in order to correlate their adsorption performances with the corresponding surface properties. The behavior of the different materials was evaluated by determining equilibrium adsorption isotherms of two anionic dyes (Reactive Red 241 and Acid Blue 113) at different pH values. The results are compared with data previously obtained with commercial activated carbons subjected to the same treatments, and discussed in terms of the carbon surface chemistry and the interaction between the dye molecules and the adsorbent surface (dispersive and electrostatic interactions).

Keywords: Adsorption; Templated carbons; Carbon xerogels; Surface chemistry; Dyes

Pressure swing adsorption for CO₂ capture in Fischer-Tropsch fuels production from biomass by Ana M. Ribeiro; João C. Santos; Alírio E. Rodrigues (pp. 443-452).

Environmental concerns and oil price rises and dependency promoted strong research in alternative fuel sources and vectors. Fischer-Tropsch products are considered a valid alternative to oil derivatives having the advantage of being able to share current infrastructures. As a renewable source of energy, synthesis gas obtained from biomass gasification presents itself as a sustainable alternative. However, prior to hydrocarbon conversion, the bio-syngas must be conditioned, which includes the removal of carbon dioxide for subsequent sequestration and capture. A pressure swing adsorption cycle was developed for the removal and concentration of CO₂ from the bio-syngas stream. Activated carbon was chosen as adsorbent. The simulation results showed that it was possible to produce a (H₂ + CO) product with a H₂/CO stoichiometric ratio of 2.14 (suitable as feed stream for the Fischer-Tropsch reactor) and a CO₂ product with a purity of 95.18%. A CO₂ recovery of 90.3% was obtained. A power consumption of 3.36 MW was achieved, which represents a reduction of about 28% when compared to a Rectisol process with the same recovery.

Keywords: PSA; Fischer-Tropsch; CO₂ capture; Biomass; Biosyngas

Activation and structural and adsorption features of activated carbons with highly developed micro-, meso- and macroporosity by V. M. Gun’ko; V. V. Turov; O. P. Kozynchenko; V. G. Nikolaev; S. R. Tennison; S. T. Meikle; E. A. Snezhkova; A. S. Sidorenko; F. Ehrburger-Dolle; I. Morfin; D. O. Klymchuk; S. V. Mikhalovsky (pp. 453-460).

Three sets of activated carbons (ACs) were prepared with the same precursor but activated differently (by CO₂ or water vapour) with various burn-off levels. The ACs demonstrate increased deviation of the pore shape from the slitshaped model with increasing burn-off and contributions of pores of different sizes depending on the activation type. Significant re-arrangement of adsorption complexes, especially of the Van der Waals type characteristic for nonpolar or weakly polar adsorbates (H₂, CH₄, CH₂Cl₂, CHCl₃), occurs in both micropores and mesopores of ACs with decreasing temperature. The behaviour of their mixtures with water and DMSO can strongly differ from that of individual adsorbates.

Keywords: Activated carbons; CO₂ activation; H₂O activation; Structural characteristics; Particle morphology; Interfacial behaviour

Soft-templating synthesis and adsorption properties of mesoporous carbons with embedded silver nanoparticles by Jerzy Choma; Katarzyna Jedynak; Joanna Górka; Mietek Jaroniec (pp. 461-466).

Mesoporous carbons containing silver nanoparticles have been successfully synthesized under acidic conditions by employing resorcinol and formaldehyde as carbon precursors and triblock copolymer EO₁₀₁PO₅₆EO₁₀₁ (Lutrol F127) as a soft template. Silver nanoparticles of ∼90 nm were added to the synthesis mixture to achieve 10 wt% and 20 wt% of Ag loading in the carbon. Also, tetraethyl orthosilicate (TEOS) was introduced to the system in order to improve adsorption properties of the silver-carbon composites and to reinforce its structure. The resulting carbons with incorporated silver nanoparticles featured high surface areas, large total pore volumes and primary mesopores in the range between ∼6–7 nm.

Keywords: Soft-template method; Mesoporous carbons; Silver nanoparticles; Adsorption properties

Carbon materials as electrodes for electrosorption of NaCl in aqueous solutions by Isabel Villar; David J. Suarez-De la Calle; Zoraida González; Marcos Granda; Clara Blanco; Rosa Menéndez; Ricardo Santamaría (pp. 467-471).

Different porous carbons (MWCNT, a carbon aerogel, an activated carbon cloth and a chemically activated carbon) were evaluated as electrode material for the electrosorption of NaCl. The results obtained from the chronoamperometric experiments were correlated to the surface area and the size of the pores present in each carbon. These results indicate that all the surfaces are equivalent for the electrosorption process, demonstrating that both, mesopores and micropores, are equally effective. Nevertheless, the kinetics of the process is influenced by the pore size distribution of the carbon, although it is rather fast for all the carbons studied. The chemically activated carbon seems to be the most suitable carbon material for electrosorption of NaCl due to the combination of a high surface area and an appropriate pore size distribution.

Keywords: Electrosorption; Activated carbon; MWCNT; Carbon aerogel

Benzene and toluene adsorption at low concentration on activated carbon fibres by M. A. Lillo-Ródenas; D. Cazorla-Amorós; A. Linares-Solano (pp. 473-481).

The present study analyses the preparation of activated carbon fibres (ACFs) by the so-called “physical” activation method with steam or carbon dioxide and their application for benzene and toluene adsorption at low concentration (200 ppmv). ACFs have been scarcely studied for the adsorption of these pollutants at low concentration in gaseous phase, despite their interesting features regarding adsorption kinetics, bed pressure drop, possibility of conformation and others. Our results have shown that the preparation method used is suitable to produce ACFs with high adsorption capacities for benzene and toluene at the low concentration used. The fibre morphology of the ACFs does not enhance their performance, which results to be similar to other non-fibrous activated carbons such as granular, pellets and powders. Such good performance of the ACFs, leading to benzene and toluene adsorption capacities as large as 31 g benzene/100 g ACF or 53 g toluene/100 g ACF, can be explained due to their large volume of narrow micropores (<0.7 nm) developed upon activation and their low content in surface oxygen groups. Our results have also shown very good agreement between the adsorption results derived from dynamic adsorption experiments and from adsorption isotherms. As the relative pressure of the organic compound increases the corresponding fraction of narrow micropore volumes filled by benzene and toluene increases. For a given low and comparable relative pressure, toluene always occupies a larger fraction of narrow micropores than benzene.

Keywords: Activated carbon fibres; Adsorption; Volatile organic compounds; Porosity; Surface chemistry

Phenol adsorption from water solutions over microporous and mesoporous carbon surfaces: a real time kinetic study by Eva Castillejos; Inmaculada Rodríguez-Ramos; Maria Soria Sánchez; Vicenta Muñoz; Antonio Guerrero-Ruiz (pp. 483-488).

This study illustrates the effect of the adsorbent porosity (activated carbon and high surface area graphite) on the phenol adsorption kinetics. We have developed an experimental system where on line analysis of the solution is carried out by an optic fiber probe introduced in the water solution and directly connected with the UV spectrometer. This experimental setup permits to be more precise in determining kinetic parameters, considering that measurements are taken each 20 seconds. Our results show that the choice of the particle diameter of the adsorbent is critical in the control of the adsorption process kinetic, while the porosity of the carbon materials appears to be less relevant.

Keywords: Activated carbon; Graphite; Kinetic; Adsorption; Phenol

Adsorption of arsenic (V) from a water solution onto a surfactant-modified zeolite by Jovita Mendoza-Barrón; Araceli Jacobo-Azuara; Roberto Leyva-Ramos; Ma. Selene Berber-Mendoza; Rosa Ma. Guerrero-Coronado; Laura Fuentes-Rubio; J. Merced Martínez-Rosales (pp. 489-496).

In this study a surfactant-modified zeolite (SMZ) was prepared by adsorbing the cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide on a clinoptilolite. The adsorption of the surfactant modified the surface properties of the clinoptilolite and enhanced the anionic capacity of the SMZ. The adsorption equilibrium data of As(V) from the water solution on the SMZ were obtained in a batch adsorber, and the Langmuir isotherm matched the data reasonably well. The As(V) adsorption capacity of the SMZ was 12.5 times greater than that of the clinoptilolite. The adsorption of As(V) on SMZ was mainly due to the interactions between the anionic sites of the SMZ and the As(V) anions in water solution. The adsorption capacity of the SMZ was dependent on the solution pH. The adsorption capacity was increased and decreased by augmenting the pH from 5 to 7 and from 7 to 12, respectively. This unusual behavior was due to the fact that the affinity of the As(V) for the SMZ was dependent on the As(V) species that were present in solution. The adsorption capacity of the SMZ was slightly favored by decreasing the temperature from 25 to 15 °C. The heat of adsorption was estimated to be ΔH _ads=−46.82 KJ/mol, indicating that the adsorption was exothermic and the As(V) was chemisorbed on the SMZ.

Keywords: Adsorption; Arsenic (V); HDTMA; Surfactant-modified zeolite

CO₂ adsorption on binderless activated carbon monoliths by Diana Paola Vargas; Liliana Giraldo; Joaquín Silvestre-Albero; Juan Carlos Moreno-Piraján (pp. 497-504).

A series of activated carbon monoliths have been prepared by chemical activation of two lignocellulosic precursors, coconut shell (CACM) and African palm stones (PACM). The incorporation of a conforming step between the impregnation with H₃PO₄ and the activation step allows the successful development of disc-shape monoliths without the use of a binder. Textural characterization results using N₂ adsorption at 77 K show that the effect of the activating agent highly depends on the nature of the carbon precursor used. While chemical activation with phosphoric acid has mainly no effect when using coconut shell, a large development of both micro- and mesoporosity is observed for African palm stones. Large concentrations of the activating agent produce the partial shrinkage of the narrow microporous structure independently of the precursor used. Concerning the adsorption of CO₂ at atmospheric pressure and 273 K, both series of activated carbon monoliths exhibit an improved adsorption behaviour with the activation degree up to an optimum value around ∼164 mg CO₂/g, for sample CACM-32, and ∼162 mg CO₂/g, for sample PACM-28, the amount adsorbed decreasing thereafter. Apparently, the total amount of CO₂ adsorbed under these experimental conditions is defined by the volume of narrow micropores (V n).

Keywords: Activated carbon monoliths; CO₂ adsorption; H₃PO₄ ; Coconut shell; African palm stones

The removal and kinetic study of Mn, Fe, Ni and Cu ions from wastewater onto activated carbon from coconut shells by Juan Carlos Moreno-Piraján; Vanessa S. Garcia-Cuello; Liliana Giraldo (pp. 505-514).

Activated carbon from coconut shells (ACCS) was synthesised and used for the removal of metal ions (manganese, iron, nickel and copper) from aqueous solutions. Two different adsorption models were used for analysing the data. Adsorption capacities were determined: copper ions exhibited the greatest adsorption on activated carbon obtained from coconut shells because of their size and pH conditions. Adsorption capacity varied as a function of the pH. Adsorption isotherms from aqueous solutions of heavy metals on ACCS were determined and were found to be consistent with Langmuir’s adsorption model. Adsorbent quantity and immersion enthalpy were studied. The results were compared with other adsorbents used in a prior study.

Keywords: Activated carbon; Immersion enthalpy; Adsorption; Heavy metals; Coconut shell

Adsorption of lead(II) from aqueous solution onto several types of activated carbon fibers by R. Leyva-Ramos; M. S. Berber-Mendoza; J. Salazar-Rabago; R. M. Guerrero-Coronado; J. Mendoza-Barron (pp. 515-526).

In this work, the adsorption of Pb(II) from aqueous solution was investigated on various types of activated carbon fibers (ACFs) manufactured from polyacrylonitrile and phenolic resin. The textural and physicochemical properties of the ACFs were determined by the N₂-BET method and acid-base titration. The experimental adsorption equilibrium data of Pb(II) on the ACFs were obtained in a batch adsorber, and the Langmuir isotherm model better fitted the experimental data. The effects of the type of ACF and precursor of ACF, solution pH and temperature upon the adsorption of Pb(II) on the ACFs were examined in detail. The adsorption capacity was highly dependent upon the precursor of ACF. The Pb(II) adsorption capacity of the ACFs augmented when the solution pH and temperature were increased from 2 to 4 and from 288 to 308 K, respectively. The effect of the pH was attributed to the interactions between the surface of the ACF and Pb²⁺ ions present in the water solution. The Pb(II) adsorption capacity of the ACFs was enhanced by oxidation with HNO₃ solution and the enhancement factor was between 1.1 and 1.4. The reversibility of the adsorption of Pb(II) was investigated by first adsorbing Pb(II) on an ACF and then desorbing the Pb(II). It was noticed that Pb(II) was substantially desorbed from ACF while reducing the solution pH to 2. It was concluded that the Pb(II) was mainly adsorbed on the ACFs by chemisorption, electrostatic interactions and ion exchange.

Keywords: Activated carbon fiber; Adsorption; Desorption; Mechanism; Pb(II)

Preparation, characterization and catalytic applications of ZrO₂ supported on low cost SBA-15 by Álvaro Reyes-Carmona; Ramón Moreno-Tost; Josefa Mérida-Robles; José Santamaría-González; Pedro J. Maireles-Torres; Antonio Jiménez-López; Elisa Moretti; Maurizio Lenarda; Enrique Rodríguez-Castellón (pp. 527-538).

This work presents some applications of ZrO₂ supported over SBA-15 silica as promoter of sulfated zirconia and as support from CuO/CeO₂ catalytic system for preferential oxidation of CO to CO₂ in hydrogen rich streams, used as feed for proton exchange membrane fuel cells (PEMFC). Different amounts of ZrO₂, from 10 to 30 wt.% were incorporated. These prepared materials were characterized by powder XRD, adsorption-desorption of N₂ at 77 K, transmission and scanning electron microscopy (TEM and SEM) and X-rays photoelectron spectroscopy (XPS). The acidity was studied by thermo-programmed desorption of ammonia (NH₃-TPD). These materials were tested, after treatment with H₂SO₄, by 2-propanol dehydration and 1-butene isomerization catalytic tests. The samples were found quite good catalyst with strong acid sites, the sample with 20 wt.% of ZrO₂ being the better performing sample. Finally this material was successfully used as support for a CuO/CeO₂ system, with 6 wt.% of Cu and 20 wt.% of Ce. The resulting catalyst was tested in the preferential oxidation of CO (CO-PROX) attaining conversions close to 100% and high selectivity to CO₂.

Keywords: SBA-15; ZrO₂ ; Sulfated zirconia; CuO/CeO₂ ; PROX

Adsorption of oxygen-containing aromatics used in petrochemical, pharmaceutical and food industries by means of lignin based active carbons by L. M. Cotoruelo; M. D. Marqués; A. Leiva; J. Rodríguez-Mirasol; T. Cordero (pp. 539-550).

The adsorption processes of three aromatic chemicals onto activated carbons (ACs) from aqueous solutions have been studied. Eucalyptus kraft lignin obtained from cellulose industry as a residual biomass has been used to prepare activated carbons by physical activation with CO₂. The influences of the activation time on the surface areas and pore volumes of the ACs were analyzed. The physicochemical properties and the surface chemical structure of the adsorbents have been studied by means of N₂ and CO₂ adsorption, ultimate analysis, XPS, TPD and SEM. XPS and TPD spectra of the ACs have suggested the presence of aromatic rings and carbon-oxygen functional groups in the solid surfaces. The potential use of the ACs for the removal of acetaminophen (paracetamol), salicylic acid and benzoic acid has been investigated at different pH, temperature and contact time. The adsorption equilibrium data have been correlated to Langmuir isotherm model. The thermodynamic study has been developed, the values of ΔH, ΔG, and ΔS have been calculated and they indicated that the processes are endothermic for acetaminophen and exothermic for salicylic and benzoic acids. The analysis of the kinetic experiments showed that the effective diffusivities are low; 10⁻¹² to 10⁻¹¹ cm²/s, and they are the corresponding to intraparticle mass transfer, which appears as the controlling step for the net adsorption processes.

Keywords: Lignin; Aromatic compounds; Activated carbons; Adsorption; Isotherm

Evaluation of a mixed geometry model for the characterization of activated carbons by J. P. Toso; R. H. López; D. C. S. de Azevedo; C. L. Cavalcante Jr.; M. J. Prauchner; F. Rodríguez-Reinoso; G. Zgrablich (pp. 551-560).

The predictions of the Pure Slit Geometry Model (PSGM) and the Mixed Geometry Model (MGM) for the characterization of activated carbons (AC) are compared and tested against the behavior of the textural properties of series of AC obtained from coconut shells by varying the concentration of the chemical activation agent over a wide range. Through the analysis of results it is concluded that the MGM can be regarded as reliable as the PSGM, with an apparently more consistent description of the behavior as a function of the degree of chemical activation and superior consistency between the results for different adsorbates, like N₂ and CO₂.

Keywords: Activated carbon; Pore size distribution; Slit pores; Triangular pores

Characterization of Supported Ionic Liquid Phase (SILP) materials prepared from different supports by Jesus Lemus; Jose Palomar; Miguel A. Gilarranz; Juan J. Rodriguez (pp. 561-571).

Supported ionic liquid phase (SILP) materials are a recent concept where a film of ionic liquid (IL) is immobilized on a solid phase, combining the advantages of ILs (non volatility, high solvent capacity, etc.) with those of heterogeneous support materials. In this work, new SILP materials were prepared using a series of supports with different porosity and chemical nature. An imidazolium-based IL, 1-methyl-3-octylimidazolium hexafluorophosphate (OmimPF₆), was confined at variable contents (5–60% w/w) in three different activated carbons (ACs), silica (SiO₂), alumina (Al₂O₃) and titania (TiO₂).For the first time, a systematic characterization of different SILP systems has been carried out applying a variety of analytical and spectroscopic techniques to provide information of interest on these materials. Elemental analysis (EA), adsorption–desorption isotherms of N₂ at 77 K, mercury porosimetry, termogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM) and energy dispersive X-ray (EDX) were conducted to explore confinement effects. The results demonstrate that EA is a useful tool for quantifying the amount of imidazolium-based IL incorporated on support, independently of the nature of the solid. An excellent correlation has been obtained between the percentage of elemental nitrogen and the IL loaded on the support. The combination of nitrogen adsorption–desorption isotherms at 77 K and mercury porosimetry measurements was used to characterize the pore structure of both supports and SILP materials. It was found that depending on the available pores in the solid support, the IL tends to fill micropores firstly, then mesopores and lately in macropores. Thermal properties of SILP materials were studied herein by using both TGA and DSC methods, evidencing that the stability of SILP materials and the decomposition mechanism are strongly dependent on the surface chemistry of the solid support. SEM and EDX provided evidences of external surface coverage by ILs and filling of macropores at high IL load.

Keywords: Ionic liquids; SILP; Supported ionic liquid phase; Characterization; Activated carbon; Porous structure; Thermal stability

Synthesis, characterization and in vitro cytotoxicity of Pt-TiO₂ nanoparticles by T. López; M. Alvarez; R. D. González; M. J. Uddin; J. Bustos; S. Arroyo; A. Sánchez (pp. 573-581).

The adverse toxicological profile of cisplatin (cis-dichlorodiammineplatinum (II)), characterized by nephrotoxicity and neurotoxicity is the main factor that limit the clinical usefulness of this antineoplastic drug, specifically the possibility of applying it in effective high-dose regimens. In order to overcome these disadvantages, many efforts in the search for new drugs have been made. Due to this particularity, we obtained via sol–gel process Pt(acac)₂–TiO₂ (NPt) nanostructured materials with antitumoral activity to be used as an alternative in the treatment of cancer tumors. The biocatalysts were prepared by the sol–gel route using the complex Pt(acac)₂. Sol–gel parameters were controlled in order to obtain high platinum dispersion and particles in the nano-size range. TEM, FTIR, N₂ adsorption and XPS characterization studies of the samples were carried out. In order to investigate interactions between the biocatalyst and DNA, agarose gel electrophoresis was performed, and we observed the formation of DNA adducts. 45 minutes after contact, NPt completely degraded the DNA (cisplatin 120 minutes). These results demonstrate that using a metal supported and dispersed over an inorganic biocompatible oxide, can be effectively used in the treatment of localized tumors.

Keywords: Sol–gel process; Nanomedicine; Glioblastoma multiforme; DNA electrophoresis

Characterisation of hybrid xerogels synthesised in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as precursors by Xabier Rios; Paula Moriones; Jesús C. Echeverría; Asunción Luquín; Mariano Laguna; Julián J. Garrido (pp. 583-593).

The mild synthetic conditions provided by the sol-gel process and the versatility of the colloidal state allow for the mixing of inorganic and organic components at the nanometre scale in virtually any ratio for the preparation of hybrid materials. Our interest in hybrid xerogels focuses on combining their porosity with other properties to prepare optic-fibre sensors. The specific aim of this paper is to synthesise hybrid xerogels in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as silica precursors and to investigate the effect of the MTEOS molar ratio on the structure and porous texture of xerogels. Gelation time exponentially increased as the MTEOS molar ratio increased. Increasing the MTEOS molar ratio yielded xerogels with lower density and lower particle size. The incorporation of MTEOS resulted in new FTIR bands at 1276 and 791 cm⁻¹, which was attributed to vibrational modes of methyl group. The band around 1092 cm⁻¹ associated with siloxane bonds shifted to lower wavenumbers and split into two bands. The ²⁹Si spectra only showed the Q n (n=2, 3, 4) signal in xerogels with 0% MTEOS and the T n (n=2, 3) signal in xerogels with 100% MTEOS; hybrid xerogels showed both Q and T signals. From XRD peaks at 2θ around 9°, we inferred that xerogels (>70% MTEOS) consisted of nanocrystalline CH₃–SiO_3/2 species. Increasing the MTEOS molar ratio produced xerogels with lower pore volumes and lower average pore size. The integration of methyl groups on the surface decreased the surface polarity and, in turn, the characteristic energy.

Keywords: Hybrid xerogels; Structure; Porous texture; TEOS; MTEOS

Nitromethane-water competitive adsorption over modified activated carbon by L. Gonzalo-Chacón; A. Arcoya; I. Rodríguez-Ramos; E. Gallegos-Suárez; A. Guerrero-Ruiz (pp. 595-602).

Modifications of texture and surface properties of a commercial activated carbon (Norit GF-40) were performed by several treatments in order to study their effects on the selective adsorption of nitromethane from nitromethane/water vapor mixtures. Characterisation of the samples by nitrogen adsorption and thermal analysis showed that HNO₃ treatments produce important losses of porosity and surface area, accompanied of an increase of oxygenated functional groups on the surface of carbon, which are progressively removed by heating at temperatures between 573 and 1073 K. All this leads to a drastic decrease of the adsorption capacity per gram of adsorbent with respect to the raw carbon, which offers, on the other hand, the best adsorptive performance. Oxidation by H₂O₂ does not practically affect its textural properties and introduces an important amount of oxygen functional groups at the surface, but changes in the adsorptive properties of carbon are insignificant. Sample oxidised by H₂O₂ and subsequently treated by diethylentriamine shows a decrease in adsorption capacity, without any relevant loss of surface area. The raw carbon treated at high temperature that exhibits the highest surface area and where surface functional groups are absent, showed the greatest adsorption capacity for nitromethane, being much more selective for nitromethane than for water, in nitromethane-water mixtures. Adsorption capacity values for nitromethane on the different samples are related to the extent of the surface area, while water vapour adsorption seems to depend on the population of functional groups at the surface, which may work as adsorption sites.

Keywords: Nitromethane; Activated carbon; Selective adsorption; Adsorption capacity

Mercury removal from aqueous solution by adsorption on activated carbons prepared from olive stones by A. Wahby; Z. Abdelouahab-Reddam; R. El Mail; M. Stitou; J. Silvestre-Albero; A. Sepúlveda-Escribano; F. Rodríguez-Reinoso (pp. 603-609).

The textural characterization of a series of activated carbons prepared from olive stones, by carbonization at different temperatures (400, 550, 700 and 850 °C) and thermal activation with CO₂, has been investigated using N₂ adsorption at −196 °C and CO₂ adsorption at 0 °C. The effect of pre-oxidation of the carbonized precursor has also been studied, using temperature-programmed decomposition (TPD), to evaluate the effect of oxygen content of the chars in the performance of the obtained activated carbons for mercury removal. The adsorption of Hg(II) cations from aqueous solutions at room temperature by the prepared activated carbons was studied. Experimental results show that all samples exhibit a large microporosity (pore diameter below 0.56 nm). The amount of surface oxygen groups increased after pre-oxidation treatment, this enhancing the Hg(II) uptake (up to 72%). It can be concluded that these groups make the support more hydrophilic, thus providing a more efficient adsorption of Hg(II). The formation of a great amount of surface oxide groups such as carboxyl, phenol and lactone alters the surface charge properties of the carbon, this enhancing the surface-Hg(II) interaction.

Keywords: Mercury removal; Adsorption; Activated carbon; Surface oxygen groups

Adsorbent-adsorbate interactions in the adsorption of organic and inorganic species on ozonized activated carbons: a short review by José Rivera-Utrilla; Manuel Sánchez-Polo (pp. 611-620).

This objective of this work was to summarize the main results obtained in previous papers related to the adsorbent-adsorbate interactions involved in the adsorption of naphthalenesulphonic acids and heavy metals (Cd(II) or Hg(II)) by modified activated carbons. The adsorption of organic compounds (1-naphthalenesulphonic acid, 1,5-naphthalenedisulphonic acid and 1,3,6-naphthalenetrisulphonic acid) and inorganic species (Cd(II) and Hg(II)) was studied on a series of ozonized activated carbon in aqueous phase. Commercial activated carbon (Filtrasorb 400) was treated with different ozone doses to study the effect of ozone treatment on its surface properties and investigate the behavior of the treated carbon samples in the above adsorption processes. After ozonation, carbonyl- and carboxyl-type groups were generated on the carbon surface. The action of ozone also affected the textural characteristics of the carbon; thus, the surface area diminished due both to the ozone attack and to the increase in oxygenated groups, which prevented the diffusion of nitrogen by obstructing micropore entrances. The capacity of activated carbon to adsorb naphthalenesulphonic acids sharply decreased with a greater number of sulphonic groups in the aromatic rings of these acids. As the concentration of oxygenated electron-withdrawing groups on the carbon surface increased, a significant reduction in adsorption capacity was observed. In all cases, the adsorption uptake decreased with higher solution pH. The adsorption of metallic ions, Cd(II) and Hg(II), by this series of ozonized activated carbons was also studied. In the case of Cd(II), the adsorption capacity and affinity of the adsorbents increased with a higher concentration of acid oxygenated groups on the activated carbon surface. In the case of Hg(II), the adsorption diminished with an increase in the degree of oxidation of the activated carbon. The adsorption of 1,3,6-naphthalenetrisulphonic acid on the ozonized carbons was also studied in the presence of Cd(II) and Hg(II). The presence of Cd(II)) in the medium enhanced the sulphonic acid uptake, mainly for the most ozonized activated carbon sample, whereas the presence of Hg(II) had no significant effect on the adsorption.

Keywords: Adsorption; Metal species; Organic micropollutants; Activated carbon surface; Interactions

Development of activated carbon from vine shoots by physical and chemical activation methods. Some insight into activation mechanisms by M. Ruiz-Fernández; M. Alexandre-Franco; C. Fernández-González; V. Gómez-Serrano (pp. 621-629).

Activated carbons (ACs) are prepared from vine shoots (VS) by the method of physical activation in air, CO₂ and steam atmospheres and by the method of chemical activation with H₃PO₄, ZnCl₂ and KOH aqueous solutions. The ACs were characterized texturally by N₂ adsorption at −196 °C, mercury porosimetry, and density measurements. The method of chemical activation has been proved to be more effective than the method of physical activation to prepare ACs with a well-developed porosity. ACs with high micro- and mesopore volumes are prepared with ZnCl₂ and H₃PO₄. Using ZnCl₂, the volume of micropores is 0.62 cm³ g⁻¹ and the volume of mesopores is 0.81 cm³ g⁻¹. A greater development of macroporosity is obtained by KOH activation. The volume of macropores is as high as 1.13 cm³ g⁻¹ for the resulting AC. Yield of the process of preparation of the ACs is low for the method of chemical activation. Some insights into the performance of the activating agents in the activation process are provided.

Keywords: Vine shoots; Activated carbon; Textural characterization

Preparation, characterization and catalytic activity towards green reactions of sulfonic functionalized SBA-15 by Elena I. Basaldella; M. Soledad Legnoverde; Ignacio Jiménez-Morales; Enrique Rodríguez-Castellón; Bruno O. Dalla Costa; Carlos A. Querini (pp. 631-641).

Acidic heterogeneous catalysts based on the anchorage of sulfonic groups on SBA-15 mesoporous silica were synthesized. In a first synthesis step, samples containing mercapto groups were prepared by co-condensation of tetraethylorthosilicate with 3-mercaptopropyltrimethoxysilane, in presence of ethylene-propylene block copolymer as mesoporous silica structure director. In other samples, mercapto groups were introduced by post-functionalization of the traditional calcined SBA-15. In a second step, these mercapto groups were oxidized in order to get sulfonic acid groups on the surface. Characterization of the samples was carried out by N₂ adsorption-desorption, FTIR, XPS and acid-base titration. Spectroscopic techniques showed that the effective incorporation of sulfonic groups depends on the synthesis methodology used. In turn, the SBA-15 post-synthesis functionalization produces changes in structural characteristics like a decrease in BET surface and changes in the pore size distribution. The as-prepared materials were tested as acid catalysts in the alkylation of isobutane with 1-butene, and in the esterification of free fatty acids with methanol. The results obtained show a lack of activity in the alkylation reaction which can be associated with the formation and stabilization of the intermediate carbocation species.

Keywords: Mesoporous silica; SBA-15; Functionalization; Sulfonation; Acid catalysts; Alkylation; Esterification

Effect of nanoscale curvature sign and bundle structure on supercritical H₂ and CH₄ adsorptivity of single wall carbon nanotube by M. Yamamoto; T. Itoh; H. Sakamoto; T. Fujimori; K. Urita; Y. Hattori; T. Ohba; H. Kagita; H. Kanoh; S. Niimura; K. Hata; K. Takeuchi; M. Endo; F. Rodríguez-Reinoso; K. Kaneko (pp. 643-651).

The adsorptivities of supercritical CH₄ and H₂ of the external and internal tube walls of single wall carbon nanotube (SWCNT) were determined. The internal tube wall of the negative curvature showed the higher adsorptivities for supercritical CH₄ and H₂ than the external tube wall of the positive curvature due to their interaction potential difference. Fine SWCNT bundles were prepared by the capillary force-aided drying treatment using toluene or methanol in order to produce the interstitial pore spaces having the strongest interaction potential for CH₄ or H₂; the bundled SWCNT showed the highest adsorptivity for supercritical CH₄ and H₂. It was clearly shown that these nanostructures of SWCNTs are crucial for supercritical gas adsorptivity.

Keywords: Carbon nanotube; Capillary force; Nanoscale curvature; Nanoporosity; Hydrogen adsorption; Methane adsorption

Assessing surface chemistry and pore structure of active carbons by a combination of physisorption (H₂O, Ar, N₂, CO₂), XPS and TPD-MS by M. Thommes; C. Morlay; R. Ahmad; J. P. Joly (pp. 653-661).

In order to address open questions concerning the surface chemistry and pore structure characterization of nanoporous carbons, we performed extensive experiments by combining various experimental techniques on a series of commercially available activated carbons which exhibit diverse surface chemistry characteristics. Pore size analysis was performed on Ar (87 K), N₂ (77 K) and CO₂ (273 K) adsorption isotherms using state-of-the art methods based on density functional theory, including the recently developed quenched solid density functional theory (QSDFT). A detailed study of the surface chemistry was obtained by applying temperature programmed desorption coupled with mass spectrometry (TPD-MS) as well as XPS (X-Ray-Photoelectron Scattering). This information together with the pore structure information leads to a reliable interpretation of systematic water adsorption measurements obtained on these materials. Our results clearly suggest that water adsorption is indeed a sensitive tool for detecting differences in surface chemistry between chemically and physically activated active carbon materials with comparable ultramicropore structure. The occurrence of sorption hysteresis associated with the filling of micro- and narrow mesopores (in a range where nitrogen and argon isotherms are reversible) provides additional structural information, complementary to the insights from argon/nitrogen/carbon dioxide adsorption.

Keywords: Activated carbon; Pore size analysis; Water adsorption; Carbon dioxide adsorption; Nitrogen adsorption; Quenched solid density functional theory (QSDFT); TPD-MS; XPS; Surface chemistry

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Adsorption: Journal of the International Adsorption Society (v.17, #3)

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Adsorption: Journal of the International Adsorption Society (v.17, #3)