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Adsorption: Journal of the International Adsorption Society (v.15, #3)

Facile synthesis of the cubic mesoporous material MCM-48. Detailed study of accompanying phase transformations by Wieslaw J. Roth (pp. 221-226).

The synthesis of cubic mesoporous material MCM-48 has been simplified and can be accomplished via facile hydrothermal synthesis using convenient commercial reagents. The cubic structure evolves from the initially formed hexagonal MCM-41 and undergoes slow conversion to the lamellar MCM-50 precursor. The system was sampled at 1 hr intervals and the intermediate products characterized by elemental analysis, X-ray powder diffraction and adsorption. The results are discussed from the standpoint of possible mechanisms of MCM-48 generation.

Keywords: MCM-48 facile synthesis; MCM-48 phase conversions; MCM-41; M41 family

Functionalized hexagonal mesoporous silica monoliths with hydrophobic azo-chromophore for enhanced Co(II) ion monitoring by Sherif A. El-Safty (pp. 227-239).

We introduce here new optical strips for the colorimetric monitoring of Co(II) ions in an aqueous solution. The optical nanosensors were designed by direct immobilizing azo-chromophore with long hydrophobic tails onto hexagonal mesoporous silica monoliths (HOM-2). Although, azo-dye probe was used as signaling reporter for selective detection of the Co(II) analyte up to 10⁻⁶ mol/dm³ in solution, the tailoring of the Co(II) ion-sensing functionality was successfully manipulated up to 10⁻⁹ mol/dm³ with the incorporation of azo-chromophore into hexagonal mesoporous silica monoliths (HOM-2), which led to small, easy-to-use optical sensor strips. However, our simple design of colorimetric sensors is based on a physical adsorption of chemically responsive dyes onto HOM materials followed by stronger dye-analyte interactions in aqueous sensing systems. No elution of the probe molecules was evident with the addition of Co(II) analyte ions during the sensing process. The binding of Co(II) ions with probes led to the color change of nanosensors corresponding to the formation of the metal-chelate [Co(II)-Probe] n⁺ complexes. Results indicated that hexagonal nanosensors offer one-step and simple sensing procedures for both quantification and visual detection of Co(II) ions without the need for sophisticated instruments. However, the solid HOM-2 materials immobilized by the these indicator dyes, in principle, could be used as preconcentrators to yield high adsorption capacity and preconcentration efficiency, leading to simultaneously visual inspection and simple detection over a wide, adjustable range of Co(II) ions even at trace levels. For Co(II) ion selectivity assays, negligible changes in either the developed color or the reflectance intensities of the [Co-Probe] n⁺ complex were observed, despite the addition of competitive cations. Moreover, the hexagonal nanosensors are reversible and have the efficient potential to serve for multiple analyses. Hexagonal optical strips for the colorimetric monitoring of Co(II) ions in an aqueous solution was successfully fabricated. This strip enabled to create ion-sensitive responses with revisable, selective and sensitive recognitions of a wide range of detectable Co(II) ions down to sub-nanomolar (∼15×10⁻⁹ M) in rapid sensing responses (in the order of minutes)

Keywords: Co(II) ions; Detection; Optical sensor; Hexagonal monoliths; Azo-chromophore

Effects of surface structure on the molecular projection area. Adsorption of argon and nitrogen onto defective surfaces by L. F. Herrera; D. D. Do (pp. 240-246).

This paper studies the effects of surface structure (defective surfaces) on the molecular projection area of argon and nitrogen at 77 K. The determination of the molecular projection area is based on choice of the surface area of the structure studied and the adsorption data obtained from the GCMC simulation. Two methods were used to determine the surface area: the flat surface area that are commonly used in the literature and the geometrical surface area. The molecular projection areas of argon and nitrogen at 77 K vary with pressure over the recommended range for BET plot (reduced pressures from 0.05 to 0.3) and also they varies with the percentage of defects on the surface. Additionally, it is seen that the geometrical surface area method gives molecular projection area of defective surfaces values that are in accordance with the experimental value reported in the literature.

Keywords: Adsorption; Projection area; Simulation

Studies on mesoporous niobosilicates synthesized using F127 triblock copolymer by Agnieszka Feliczak-Guzik; Agata Wawrzynczak; Izabela Nowak (pp. 247-253).

A detailed characterization of cage-like mesoporous SBA-16 niobosilicate with tailored features of the structure is reported. The materials were synthesized in a EO₁₀₆PO₇₀EO₁₀₆(F127)-water system under acidic conditions and the pore diameters were tuned by varying the hydrothermal treatment temperature and time. The effects of the synthesis parameters on the structural/textural properties of the cubic Im3m niobosilicates have been investigated systematically. We show that the total pore volume, pore diameter, and micro-/mesopores ratio can be controlled very efficiently by changing the synthesis parameters.

Keywords: NbSBA-16; Cage-like structure; Characterization; Structural/textural properties; Niobium source

Dynamics of monolayer films formed on a substrate of square symmetry by A. Patrykiejew; W. Rżysko; S. Sokołowski (pp. 254-263).

The paper discusses the ground state properties and dynamics of monolayer films formed by atomic adsorbates on a square lattice, being the (100) plane of a face centered cubic crystal. The vibrations of films ordered into the commensurate c(2×2) as well as into the recently discovered ordered phase exhibiting a distorted Archimedean tiling of the type (3².4.3.4) are considered. The dispersion relations and the densities of states are determined and discussed.

Keywords: Monolayers; Lattice dynamics; Archimedean tiling

Isosteric heats of adsorption of carbon dioxide on zeolite MCM-22 modified by alkali metal cations by Arnošt Zukal; Justyna Pawlesa; Jiří Čejka (pp. 264-270).

Adsorption isotherms of carbon dioxide were measured on cation-exchanged (Li⁺, Na⁺, K⁺, Cs⁺) MCM-22 zeolite with the molar ratio of Si/Al=15 and series of Na-MCM-22 of Si/Al molar ratios varying in the range from 15 to 40 at 273, 293, 313 and 333 K. Based on the known temperature dependence of CO₂ adsorption, isosteric heats of adsorption were calculated. The obtained dependences of isosteric heats related to the amount of CO₂ adsorbed have provided detailed insight into the interaction of carbon dioxide molecule with alkali metal cations.

Keywords: MCM-22 zeolite; Alkali metal cation exchange; CO₂ adsorption; Isosteric heat of adsorption

Adsorption of methane in activated carbons obtained from coconut shells using H₃PO₄ chemical activation by Rafael B. Rios; F. Wilton M. Silva; A. Eurico B. Torres; Diana C. S. Azevedo; Célio L. Cavalcante Jr. (pp. 271-277).

Activated carbon samples from coconut shells (Brazilian coconut species “Coco da Baía”) were prepared by chemical activation with phosphoric acid as the activating agent. Samples were characterized by nitrogen adsorption isotherms at 77 K. Some samples were randomly chosen in order to perform methane adsorption experiments under pressures between 1 and 60 bar at 303 K. A close relationship between surface area, micropore volume and methane adsorption capacity for carbons prepared from the same starting material was observed. The highest methane storage capacity in the tested samples was found to be 95 v/v at 303 K and 35 bar, which is comparable to results obtained for commercial samples indicated for this application. A moderate concentration of phosphoric acid (around 35%) seems to favor high surface areas, micropore volumes and, hence, gas storage capacity. The inclusion of an acid wash step before carbonization and the use of inert gas flow during carbonization also seem to enhance the development of porosity. This result suggests that activated carbons prepared from “Coco da Baía” by chemical activation with phosphoric acid have potential to be used as a storage media for natural gas.

Keywords: Chemical activation; N₂ isotherms; Carbon; Adsorption; Gravimetric measurements; Methane

Synthesis, structure and adsorption properties of nanoporous SBA-15 materials with framework and surface functionalities by M. Barczak; S. Pikus; Barbara Skrzydło-Radomańska; A. Dąbrowski (pp. 278-286).

Highly ordered SBA-15 nanoporous silica containing ethylene, phenylene bridges or/and amine, thiol, vinyl and phenyl surface groups were synthesized by using amphiphilic block copolymer as the structure-directing agent. The XRD data shows high degree of the order of the final structures. Obtained materials have well-developed porous structure—values of specific surface area are in the range 700–1050 m²/g and the sizes of cylindrical mesopores are in the range 6.5–9.5 nm. It was determined that size of the mesopores strongly depends even on small amounts of co-monomers co-condensing with TEOS. A new technique to introduce some amount of pendant amine groups by co-condensation of proper monomers has been proposed. Tetragonal structure was obtained when small amount of vinyl groups was introduced to the system. A new approach of determining pore size based only on the XRD measurements was compared with KJS method, confirming full usefulness of the former for calculation of the size of mesopores in SBA-15 materials.

Keywords: Adsorption; Functionalization; Sol-gel method; Hybrid materials; Ordered mesoporous materials; Nanoporous materials; Porosity; SBA-15; XRD

Controlling adsorption and release of drug and small molecules by organic functionalization of mesoporous materials by Tewodros Asefa; Amy N. Otuonye; Gang Wang; Elizabeth A. Blair; Rajyalakshmi Vathyam; Kelley Denton (pp. 287-299).

A series of mesoporous nanosphere materials that are functionalized with various terminal and bridging organic groups were synthesized. They have improved adsorption capacity and different release properties for drug and small molecules. The materials contained terminal vinyl, 3-mercaptopropyl, 3-aminopropyl, and secondary amine functional groups and bridging ethane, ethene, and benzene groups within their mesopore channel walls. The samples containing mercaptopropyl and vinyl groups showed greater adsorption capacity and better controlled release behavior for rhodamine 6G molecules. On the other hand, mesoporous matrices containing amine functional groups showed higher adsorption capacity and better release properties for ibuprofen molecules. Further studies revealed that the bridging organic groups in the mesopore channel walls also improved the adsorption capacity and release properties of the materials compared to the corresponding samples containing no bridging organic groups. Such improved adsorption and controlled release properties of molecules by simple changes of functional groups on mesoporous materials are important for the development of nanomaterial drug delivery vehicles and for controlled release of drugs over long time periods at specific targeted sites in the body. By judicious choice of organic groups and by systematic design and synthetic approaches, nanoporous materials having different adsorption capacity and release properties for many other drug molecules can also be achieved.

Keywords: Multifunctional mesoporous materials; Drug delivery; Periodic mesoporous organosilica; Controlled drug release; Organofunctional mesoporous materials

Study of structure properties of organized silica sorbents synthesized on polymeric templates by Adam W. Marczewski; Anna Derylo-Marczewska; Iwona Skrzypek; Stanislaw Pikus; Maciej Kozak (pp. 300-305).

Mesoporous silica materials were synthesized by applying Pluronic type polymers as pore creating agents. The composition of a reacting mixture and the process conditions were changed in a synthesis procedure. These changes differentiated the characteristics of porous structure of obtained sorbents. The parameters characterizing the pore structure were estimated and the changes of pore arrangement of obtained materials being a result of different synthesis conditions were investigated. The small-angle XRD results indicate that F cubic structure was formed what confirms the cage-like ordering of the synthesized silicas.

Keywords: Mesoporous silicas; Kinetics of adsorption from solution

Synthesis monitoring of SBA-15 nanostructured materials by Antonio S. Araujo; Solange A. Quintella; Ana Carla S. L. S. Coutinho (pp. 306-311).

The SBA-15 materials were synthesized by the hydrothermal method using tetraethyl orthosilicate as silica source and P123 as template agent. The synthesis process was accomplished varying the time during the hydrothermal processing. For the synthesis monitoring, a small amount of sample was removed at different times, and analyzed by thermal analysis in order to determine the temperature ranges related to water desorption, template decomposition and silanol condensation for the SBA-15 nanostructured materials, as well as to estimate their quality. The samples were characterized by X-ray diffraction, infrared absorption spectroscopy, scanning electron microscopy, BET surface area and pore size distribution. The activation energy relative to decomposition of P123 template was determined from TG curves, using multiple heating rates and applying the model free kinetics. From the obtained data, it is possible to monitor the hydrothermal synthesis of SBA-15 in order to control the properties and conditions to prepare ordered materials.

Keywords: Adsorbents; Synthesis techniques; Characterization of properties; Activation; Measurement properties

Boron substituted graphene: energy landscape for hydrogen adsorption by L. Firlej; B. Kuchta; C. Wexler; P. Pfeifer (pp. 312-317).

We have analyzed the modifications of interaction energy between a molecule of hydrogen and graphene layers partially substituted by boron. We show that the presence of boron modifies the symmetry of the energy landscape. It is due to both the larger boron size (with respect to carbon) and its stronger interaction with hydrogen molecules. The changes of energy surface are not confined to the neighborhood of substituted sites but extend over several graphene carbon sites, making the surface more heterogeneous. We show that the average increase of adsorption energy could meet DOE targets for hydrogen storage if a partial charge transfer between boron and hydrogen occurs during adsorption.

Keywords: Adsorption; Hydrogen; Boron

Effect of pore expansion and amine functionalization of mesoporous silica on CO₂ adsorption over a wide range of conditions by Youssef Belmabkhout; Abdelhamid Sayari (pp. 318-328).

Adsorption of CO₂ was investigated over a wide range of conditions on a series of mesoporous silica adsorbents comprised of conventional MCM-41, pore-expanded MCM-41 silica (PE-MCM-41) and triamine surface-modified PE-MCM-41 (TRI-PE-MCM-41). The isosteric heat of adsorption, calculated from adsorption isotherms at different temperatures (298–328 K), showed a significant increase in CO₂–adsorbent interaction after amine functionnalization of PE-MCM-41, consistent with the high CO₂ uptake in the very low range of CO₂ concentration. The CO₂ adsorption isotherm and kinetics data showed the high potential of TRI-PE-MCM-41 material for CO₂ removal in gas purification and separation applications. With TRI-PE-MCM-41, the CO₂ selectivity over N₂ was drastically improved over a wide range of conditions compared to pure mesoporous silica. Moreover, the adsorption was reversible and fast, and the adsorbent was thermally stable and tolerant to moisture.

Keywords: CO₂ adsorption; N₂ adsorption; Pore-expanded MCM-41; Amine modified pore-expanded MCM-41; CO₂ adsorption selectivity; CO₂ removal; Tolerance to moisture

Water stability of a cheap sol-gel-based adhesive by Janne Puputti; Mika Lindén (pp. 329-335).

The humidity and water tolerance of a sol-gel derived binder prepared using a cheap, multicomponent precursor has been studied. The sol was prepared by dissolving the precursor in water under acidic conditions using either formic acid or a mixture of formic acid and citric acid for pH adjustments. It is shown that a post-treatment temperature of 400 °C or higher is needed in order to achieve full binder stability under excess water conditions, as thermal decomposition of metal carboxylates leads to a pronounced decrease in water solubility of the gels. The mesoporous gel can be made hydrophobic by post-treatments with either a silane or an organophosphonate, showing that both silica and metal oxides are exposed on the surface of the binder. Surface functionalization is especially effective for gels heat-treated at higher temperatures where the metal carboxylates have decomposed to the corresponding oxides or carbonates. The results are expected to be of great importance for the use of this cheap binder in large scale industrial applications.

Keywords: Silica precursor; Inorganic binder; Water adsorption; Green chemistry

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Adsorption: Journal of the International Adsorption Society (v.15, #3)

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Adsorption: Journal of the International Adsorption Society (v.15, #3)