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The sorption mechanisms in porous materials have been of long standing interest and debate. Concretely, the involved hysteresis during nitrogen adsorption–desorption processes and its interpretation has represented an important challenge for experimentalists and theoreticians. Moreover, a better understanding of the different observed hysteretic behaviors and the elapsed are as is still remaining. Such a scenario has motivated us to study the pore connectivity and pore size distribution effects upon the hysteresis in nitrogen adsorption–desorption isotherms of a porous solid. Our simulation has been carried out over the entire range of connectivity assuming three-dimensional pores randomly inscribed in a two-dimensional lattice with different occupation probabilities, related with pore connectivity, including the percolation threshold. The adsorption and desorption curves as a function of pressure have been simulated taking into account the monolayer–multilayer formation process and the capillary condensation–evaporation phenomena by using the Broekhoff de Boer and Kelvin equations, respectively. Results show that the employed methodology allows reproducing different types of hysteresis experimentally observed where the hysteretic behavior is strongly dependent upon both connectivity and the broadening of the pore size distribution. Specifically, the hysteresis loop area exhibits a maximum at the percolation threshold and then it decreases monotonically above the threshold.

The use of a reaction mixture, characterized by high dilution (H2O/TEOS = 495), low to medium acid concentration (0.4–1.6 M HCl) and the presence of a cosurfactant (CTMABr), allows the synthesis of micron-sized particles of SBA-16 type mesoporous silica with different morphologies and structural characteristics. With a F127/TEOS molar ratio around 0.005 and a temperature between 70 °C and 95 °C, perfect rhombododecahedra (∅ 2–8 μm) are obtained. High acid concentration (1.6 M HCl) and/or temperature higher than 100 °C produce a smoothening of the edges and lead to the formation of spherical particles. This morphology is also favoured by low F127/TEOS molar ratios and corresponds to a disordered mesoporous structure. At a temperature of 40 °C or lower, the gel-like particles with poorly organized mesostructure are difficult to transform into well-organized materials. High F127/TEOS molar ratios lead to the same result. These different behaviours can be rationalized taking into account the strength of the interactions between the surfactant and the silica species which depends on the conformation of the hydrophilic poly-ethylene-oxide chains. Temperature and acid concentration are the main parameters to modify the conformation. But these two parameters are also responsible of the degradation of the Pluronic F127.

Spherical particles (∅>3 μm, with 5–10 nm pore size) of SBA15-type mesoporous silica, usable as stationary phase for HPLC, were prepared with tetraethoxysilane (TEOS) as silica source, triblock copolymer Pluronic P123 (EO20PO70EO20) as surfactant S0 and cetyltrimethylammonium bromide (CTMABr) as co-surfactant S+. The synthesis mechanism involves a surfactant-silica species self-assembly process in acidic medium under quiescent conditions, where S0H3O+X−I+ and S+X−I+ interactions occur. The syntheses were carried out using two procedures: (a) with one heating step and (b) with two heating steps. Synthesis conditions, such as the dilution, temperature and acidity of the reaction mixture and the temperature and duration of the reaction, influence the porous characteristics as well as the morphology and size of the particles. Spherical particles were obtained with one heating step under conditions that weaken the surfactants-silicate interactions such as high dilution, high temperature and low acidity. The modification of the micelle volume with the temperature and acidity allowed the adjustment of the pore size.

Chitosan was derivatized by two methodologies for analyzing their effect on chitosan physicochemical characteristics and its applicability as carrier for Bacillus circulans b-galactosidase immobilization. Glutaraldehyde (GA) and epichlorohydrin (EPI) were used for crosslinking and activation of chitosan, producing the corresponding supports (C-GA and C-EPI-EPI) after a one-step and a two- step process, respectively. The spherical shape and mean diameter of chitosan particles was not significantly affected by polymer derivati- zation, while Fourier transform infrared analysis showed that in both cases, chitosan polymer was chemically modified. TGA analysis indicated that C-EPI-EPI was the most thermally stable. The high degree of activation of C-EPI-EPI (586 lmol of aldehydes/g) resulted in the highest loss of activity during immobilization; hence a support with 100 lmol of aldehydes/g was produced (C-EPI-EPI100). The highest expressed activity (89.3 IU/g) was obtained with the enzyme immobilized in C-GA, while the biocatalyst with highest thermal stability at 60 � C was obtained with C-EPI-EPI100 (half-life was 84-fold higher than the one of the soluble enzyme). The best compro- mise between biocatalyst expressed activity and thermal stability corresponded to b-galactosidase immobilized in C-EPI-EPI100. Accord- ing to this study, chitosan derivatized with EPI is a thermally stable carrier appropriate for producing highly stable immobilized B. circulans b-galactosidase. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40171.

β-galactosidase from Kluyveromyces lactis was covalently immobilised on a Glyoxyl Sepharose (GS) support by multi-point attachment. The enzyme immobilisation process was very efficient; the supports immobilised almost all the protein responsible for the catalytic activity in a short period of time, retaining approximately 82% of the activity in the case of the optimal immobilised preparations. Stability of the GS derivatives varied as a function of enzyme-support incubation time. The optimal immobilised preparation was produced after 2 h of incubation with the support at alkaline pH. This derivative, obtained by multi-point covalent attachment, was 100-fold more stable at pH 7 and 50 °C than the cyanogen bromide Sepharose derivative obtained by a one-point covalent immobilisation method. Stabilisation was also observed under a wide range of experimental conditions. This method allowed the immobilisation of 9000 IU enzyme g−1 of support, resulting in highly active and stable derivatives suitable for industrial processes., We thank COLCIENCIAS, Municipio de Rionegro and Universidad de Antioquia for financial support through the program “Becas doctorales 2007 en el convenio de cooperación # 030-2006”. We also thank the Spanish Ministry of Science for financial support through intramural projects (2008801058) and project No. (AGL-2009- 07625).

International audience; The formation mechanism of large defect cavities (∅ 11-23 nm) beside the MCM41 mesopores (∅ ∼ 2.3 nm), was studied from mixtures of sodium silicate, cetyl trimethyl ammonium bromide (CTAB) and ethyl acetate (EtAc) with the molar composition 1 SiO2; 1 Na2O; x CTAB; y EtAc: 237 H2O (with x = 0.33 or 0.65, y = 3, 6, 9 or 15). The silica flocculation and polycondensation were obtained by decreasing the pH using the hydrolysis of different amounts of EtAc. The reaction was carried out in two steps at 25 and 80 °C. The samples were characterized by SEM, TEM, XRD, nitrogen adsorption and TGA. The CTA/SiO2 molar ratio, which forms complete silica layers covering the micelles in the MCM41 structure, was estimated from the area covered by the CTA cations in the micelles head and the silica tetrahedron area in the layers. The number of silicate anions needed to compensate the CTA cations charge was determined in function of the pH from the anions ionization constants. From these two parameters, a model, showing the percentage of missing tetrahedra in the silica layers, was established in function of the pH and the CTA/SiO2 molar ratio, and used to propose a mechanism which explains the formation of large defect cavities. Their size was discussed taking into account the pH decrease rate, which is function of the EtAc amount. The particles morphology, varying from long and curved prismatic rods to isometric particles of strongly bended short rods, is due to their softness, which results of the presence of the numerous defect cavities.

Monomodal or bimodal porous silicas with large mesopores, constituted by particles or having a monolithic (block type) morphology, respectively, are synthesized using sodium silicate as siliceous species source, cetyltrimethylammonium bromide (CTAB) as pore template and ethyl acetate (EtAc) as pH modifier. The monomodal porosity is represented by 20-30 nm pores and the bimodal one by these pores and also macropores. These characteristics are modulated in function of the CTAB and EtAc concentrations as well as the pH and hydrothermal treatment. The role of these reagents upon the porosity is rationalized. The presence of high CTAB concentration and a rather low pH decreasing rate (function of EtAc concentration and hydrothermal treatment) are essential for having the already known bimodal mesoporous silicas (BMS). On the contrary a rather high pH decreasing rate promotes the formation of the new bimodal mesoporous-macroporous silicas (BMMS) synthesized in this work, where the EtAc also plays the role of emulsion forming agent. The hydrolytic stability of the synthesized silica under aqueous conditions, at different pH values, makes these silicas good candidates for application in different areas of catalysis, especially in the enzymatic one.

The use of hard templates is one of the best ways for obtaining ordered mesoporous carbons (OMC) with well controlled morphology and porosity, characteristics that are very important for their use in many technological applications. Since the SBA-16 type mesoporous silica has a 3D connected mesostructure and can be synthesized with different morphologies, we select this material as a hard template and study the influence of its pore (cavities and entrances) size and hydrothermal stability on the qualities of the OMC replicas obtained by liquid impregnation of sucrose.

The evolution of the species in acidic solutions, prepared from tetraethoxysilane (TEOS), surfactant (Cetyltrimethylammonium bromide, Pluronic P123 or Pluronic F127) and HCl, was followed by visual observation and Dynamic Light Scattering (DLS) measurements between 25 and 90°C until their precipitation. The nature of the precipitated phases was studied by optical microscopy (in-situ in the reaction mixtures) and by SEM (after filtration and drying). In all cases, the first stage corresponds to the formation of micelles coated by siliceous species (composite colloids). In a second stage the modification of their colloidal characteristics leads to their aggregation with a phase separation into micron-sized liquid particles. In the third stage, the progress of the polycondensation transforms the latter into solid particles of mesoporous silica. The final morphology depends on the polycondensing degree of the silica before the phase separation and on the prevailing synthesis parameters (temperature and pH).

The synthesis of micro-sized spherical core-shell particles with a thin mesoporous silica shell is shown in this work. The dense silica used as the core is prepared by calcination of a mesoporous SBA-3-type silica, in the form of micron-sized spherical particles. The shell is formed by polycondensation, upon the core particles of: a) tetraethylortosilicate in the presence of a triblock copolymer Pluronic (P123 or F127) in acidic medium (CSA samples) or b) Silicic species, which are generated by partial dissolution of the core in basic medium (NH 4 OH) in the presence of cetyltrimethylammonium bromide (CSB samples). Conditions that improve the interaction between the nuclei and the shell precursors in order to form mesoporous shells are discussed. The results of the evaluation of some of these samples as stationary phases in normal HPLC show the interest of these materials for this application.

Procedures reported in the literature to modify the silanol content of mesoporous silica are applied to a material prepared with the triblock copolymer Pluronic F127 in acidic medium under quiescent conditions, in order to adapt it for silylation reaction. These include: calcination at relatively high temperature and rehydroxylation in presence of NH4OH. The nature and content of silanol groups in these materials is measured by following the pyridine interaction with them through the infrared specific absorptions at 1595 and 1446 cm−1 assigned to pyridine interacting with hydrogen-bonded and free silanol groups respectively. In order to render these SBA-16-type mesoporous silica hydrophobic, a silylation reaction is effected in which its efficiency depends mainly on the nature and concentration of silanol groups. To follow the degree of silylation a method based on infrared transmission spectroscopy (FTIR) is designed in this work. With this method, unlike solid state 29Si-NMR, it is possible to measure the relative concentrations of the organic groups bonded to silica when two silylating reagents are used, and to qualify in an indirect way how the weak silanol groups change during the different post synthesis treatments of a mesoporous silica.

The relations between the morphology (particle shape and size) of SBA-15 and SBA-16 mesoporous silica and the synthesis parameters (composition of the reaction mixtures, nature of the triblock surfactant, fluoride anions, synthesis procedure) were established. This allowed defining the conditions for the formation of materials with micro-sized isometric particles suitable for HPLC applications. The presence of fluoride anions favors the formation of spherical shaped particles, with probably higher weak acidic silanol groups content to give higher hydrophobic materials after silylation, which is an advantage for their use as HPLC reverse phases. The different materials were evaluated in HPLC tests (separation of mixtures of aromatic and polynuclear aromatic molecules).

Mesoporous silica is used as filler for styrene-butadiene rubber (SBR); filler-polymer interactions are compared with those exhibited when Ultrasil silica (VN3) is used. A silane coupling agent is added to improve filler dispersion and its influence on the bound-rubber formation is also investigated. The bound-rubber content is higher for the mesoporous silica and increases further for the sample containing silane. The increase is explained by chemical interactions between filler and rubber and penetration of the rubber chains into the mesopores. This is confirmed by 13C solid-state NMR, IR spectroscopy and differential scanning calorimetry. Dynamic mechanical thermal analysis shows higher storage modulus for the rubber filled with mesoporous silica.