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The macroscopic modeling of gas transport in mixed-matrix membranes (MMMs) made of a Polymer of Intrinsic Microporosity (PIM-1) and silicalite1 (MFI) is compared to the experimental results presented in a previous paper, which shows unexpectedly large gas separation factors, although the silicalite-1 filler is practically nonselective. The mismatch between the predictions of the Maxwell model and the experiments is zeroed by the recognition of nonideal effects, the extent of which is evaluated. The good performance of the PIM-1 MMM is explained by non-covalent cross-linking of the PIM-1 matrix. Cross-linking results from π-π stacking interactions between the 2-phenylethyl grafts on the outer surface of the MFI crystals and the aromatic ladder segments of PIM-1, in agreement with the current explanation of the good transport performance of PIM-1 MMMs containing porous aromatic fillers (e.g., PAF-1).

Carbon capture, utilization, and storage (CCUS) is one of the key promising technologies that can reduce GHG emissions from those industries that generate CO2 as part of their production processes. Compared to other effective CO2 capture methods, the adsorption technique offers the possibility of reducing the costs of the process by setting solid sorbent with a high capacity of adsorption and easy regeneration and, also, controlling the performance of gas-solid contactor. In this work, an amine-functionalized mesoporous sorbent was used to capture CO2 emissions in a confined-fluidized bed. The adoption of a confined environment allows the establishment of a homogeneous expansion regime for the sorbent and allows to improve the exchange of matter and heat between gas and solid phase. The results illustrate how the different concentration of the solution adopted during the functionalization affects the adsorption capacity. That, measured as mg of CO2 per g of sorbent, was determined by breakthrough curves from continuous adsorption tests using different concentrations of CO2 in air. Mesoporous silica functionalized with a concentration of 20% of APTES proves to be the best viable option in terms of cost and ease of preparation, low temperature of regeneration, and effective use for CO2 capture.

Hyper-cross-linked porous polymers (HCPs) are proposed as sorbents for the removal of aromatic volatile pollutants by using toluene as a representative of the BTX family. The hierarchical (micro and meso) porous architecture of the HCPs has been established by N2 physisorption at 77 K while the toluene adsorption capacities were determined by volumetric adsorption at 308 K. The HCPs display very high toluene uptakes, reaching adsorption capacities as high as 154% in weight for the polymer obtained with a tetraphenylmethane (TPM) and a formaldehyde dimethyl acetal (FDA) ratio of 1/16, whereas only very low uptakes were observed for aliphatic molecules such as n-hexane. HCP materials experience swelling effects evaluated by comparing the volume assessed via N2 physisorption with the volume occupied by toluene molecules in volumetric adsorption experiments. A multispectroscopic approach involving FT-IR and solid-state NMR techniques gave direct proof of the close spatial proximity between the polymeric host ...

In this work, different mesoporous silicas were studied as potential sorbents for toluene, selected as a model molecule of aromatic organic fuel-based pollutants. Three siliceous materials with different textural and surface properties (i.e., fumed silica and mesoporous Santa Barbara Amorphous (SBA)-15 and Mobil Composition of matter (MCM)-41 materials) were considered and the effect of their physico-chemical properties on the toluene adsorption process was studied. In particular, FT-IR spectroscopy was used to qualitatively study the interactions between the toluene molecule and the surface of silicas, while volumetric adsorption analysis allowed the quantitative determination of the toluene adsorption capacity. The combined use of these techniques revealed that textural properties of the sorbents, primarily porosity, are the driving forces that control the adsorption process. Considering that, under real conditions of usage, the sorbents are soaked in water, their hydrothermal stability was also investigated and toluene adsorption by both the gas and aqueous phase on hydrothermally pre-treated samples was studied. The presence of ordered porosity, together with the different pore size distribution and the amount of silanol groups, strongly affected the adsorption process. In toluene adsorption from water, SBA-15 performed better than MCM-41.

This manuscript deals with the thermal and chemical modification of a natural kaolinite that shows excellent performance in the capture of a cationic organic pollutant from the aqueous phase. Kaolinite was calcined at 700 °C and treated with HCl to remove aluminium and to obtain a siliceous material. The structural changes and the physico-chemical properties of the materials at different stages of thermal and chemical modification were investigated with several techniques, including XRPD, MAS-NMR, SEM-EDX, FT-IR, and N2 physisorption at 77 K. The ability of the parent kaolinite and siliceous material to capture the organic dye, Rhodamine B, from the aqueous phase was investigated by means of UV-Vis spectroscopy. The siliceous material exhibited better adsorption capacity with respect to the parent kaolinite. Finally, the functional stability of the siliceous material was tested over three cycles of regeneration and adsorption.

Defect-free mixed matrix membranes (MMMs) for natural gas separation obtained by adding SAPO-34 crystals to Hyflon® AD60X, a perfluoropolymer resistant to plasticization and tolerant to condensable hydrocarbons, are more permeable and selective (CO2/CH4 40 vs. 22) than the polymer. The experimental characterization of MMMs containing permeable and impermeable crystals of different size, shape and aspect ratio, and the macroscopic modeling of gas fluxes, allow to understand the mass transport phenomena at work. Polymer free volume increases at the interface, and barriers to the transport of gas are evidenced in the interior or on the surface of SAPO-34.

Versatile materials for oxidizing As(III) into less hazardous As(V) species has triggered increasing attention. In this work, 7% anatase TiO2 was coated on pre-formed SBA-15 by means of impregnation to produce Ti-SBA-15. The materials were characterized by XRD, Raman, FTIR, N2 adsorption, DRS and TEM techniques. Photo-oxidation tests at different pHs were carried out. In the dark, the As(III) adsorption equilibrium on Ti-SBA-15 was reached, showing a moderated adsorption capacity at pHs 4, 7, and 9 (7%, 11%, and 30%, respectively), being more evident at alkaline conditions. This fact was attributed to the presence of surface hydroxyl groups on the deposited TiO2, which promotes the formation of surface monodentate As(III) complexes on Ti-SBA-15. Moreover, Ti-SBA-15 showed to be an efficient photocatalyst in all pHs, being more than 98% of As(III) photo-oxidized into As(V). Results demonstrated that the oxidation process is induced by reactive oxygen species, including •OH and 1O2, generated onto the TiO2 nanoparticles loaded on SBA-15 during the irradiation. SBA-15 instead showed a negligible impact on adsorption and photo-oxidation, indicating that these processes are the effect of the presence of TiO2 deposited on it. However, the use of SBA-15 as support promotes an adequate dispersion of TiO2, favoring these processes. Thus, a mechanism for the adsorption and photo-oxidation of As(III) on Ti-SBA-15 was proposed. Finally, despite the fact that TiO2 covers only a few percent of the overall Ti-SBA-15 surface it showed an unprecedented photocatalytic behavior, demonstrating to be a prominent photocatalyst for the removal of arsenic from water.

Two requirements of a porous filler for Mixed Matrix Membranes [MMMs] are a good adhesion to the polymer and the openness of its pores. The surface of SAPO-34 has been grafted with moieties containing amino groups, aromatic rings, and fluorinated chains, for a good adhesion to glassy polyimides, aromatic polymers and perfluoropolymers. The controlled excess of the modification agent – preferably trichlorosilanes – in hydrophobic solvents and the strict control of moisture in the reaction environment prevent the growth of thick layers of grafts around the crystals. XPS confirms the success of the derivatizations and indicates a homogeneous and thin coverage of the surface. The negligible reduction of the surface area suggests that the modification of the surface does not plug the micropores. The counter-intuitive faster adsorption of n-heptane in silicalite-1 after modification with bulky fluorinated grafts indicates the openness of the pores even for large molecules, and the reduction of the resistance to the transport of mass across the surface of the molecular sieves, thanks to the reduced amount of water adsorbed on the hydrophobic outer surface of the crystals.

Mixed matrix membranes (MMMs) are considered a viable solution for coupling the outstanding gas separation performances of inorganic porous materials with the ease of fabrication of polymeric membranes. It is known that the heterogeneous system may include a polymer shell of modified permeability surrounding the filler particles. In addition to that, modifications of the filler were evidenced from the comparison of the permeability of selective perfluoropolymer/SAPO-34 MMMs with existing extended Maxwell-like model calculations. This is in agreement with experimental and theoretical evidences of the presence of barriers to gas transport in the filler. A 4-phase approach for the transport of gas through MMMs is proposed here to quantitatively describe the modified layers, both within the Maxwell model and by finite element analysis. The four phases are: bulk and modified polymer and bulk and modified filler. The latter explicitly accounts for the barriers to mass transport. The changes in the modified layers are quantitatively determined by numerical optimization procedures based on Maxwell’s effective medium analytical formula and a finite element solution of the transport differential equations. The new approach is applied to the minimization of the residuals between each model and an extensive set of experimental permeability data (He, H 2 , CO 2 , N 2 ) through Hyflon AD60X/SAPO-34 MMMs, including different filler particle sizes (0.2, 1.5 and 2 μm), aspect ratios (2, 3 and 9) and loadings (20, 30, 35 and 44 vol%). A MMM subset containing impermeable fillers gives information on the transport properties of the sole matrix. Both the effective medium and the microscopic 4-phase approaches yield physically sound descriptions of the permeability trends, but FEM simulations also provide spatially resolved gas flows and concentrations throughout the systems. The focus on the real physical phenomena makes the four-phase approach a powerful tool for understanding the MMM transport and improving membrane design.

Stoichiometric triethylamine in methanol produces sub-micron ZIF-90 in 98% yield with the largest gas uptakes ever measured. Micropore volume and surface area are compatible with an empty pore network and with crystallographic data, but the occurrence of crystal defects, such as missing ligands or Zn2+ ions, although improbable, can not be ruled out.

The good affinity of TiO2 surface for hydrogen sorption has prompted in the past the synthesis of high specific surface area, Ti-doped mesoporous silicas. Since most TiO2 is buried in the pore walls of the silicas, such materials did not express their full potential H2 uptake. In order to overcome this limitation, different amounts of titania were deposited on the pore surface of a pre-formed SBA-15 of 704 m2/g, and the resulting oxides were calcined at 300 or 500 °C. The hydrogen sorption–desorption isotherms of the materials prepared in this study, at 77.4 K and up to 100 kPa, reveal that a small amount of titania doubles the hydrogen storage capacity of SBA-15, provided that the materials are calcined at least at 300 °C. Reproducible H2 uptakes up to 1.4 wt.% at 77.4 K and 100 kPa have been measured. The optimal amount of TiO2 is 4.5% in moles, leading to a uniform dispersion in the mesopores. A higher loading (7.3%) brings about the formation of large titania particles that tend to block the lumen of the mesopores, with no gain in the H2 sorption capacity.

Amorphous and glassy polyhexafluoropropylene (PHFP) has been used for the first time as the matrix of mixed matrix membranes (MMMs). The preparation and the gas transport modeling of defect-free MMMs based on PHFP and 200 nm SAPO-34 crystals are described. By grafting SAPO-34 with perfluorinated tails the filler was well dispersed in the polymer and a good interfacial adhesion was guaranteed. The nano-particles determine a marked increase in gas permeability and a modest enhancement of the CO2/CH4 permselectivity with respect to the neat polymer. Unexpectedly, the increase of permeability of the MMMs is not monotonous with the amount of SAPO-34. Following a recent approach, unrestricted gas diffusivity and solubility in SAPO-34 and PHFP are the inputs of the four-phase macroscopic modelling of gas transport through the MMMs. A four-phase approach to MMM modelling is dictated by the evidences of two distinct interfacial changes with respect to the ideal, nominal two phase MMM made of bulk-like SAPO-34 particles embedded in the pristine PHFP polymer matrix: a modified polymer phase of larger free volume (increasing permeability), which surrounds SAPO-34 particles, and barriers to the transport of gas (making the filler less permeable than PHFP), in the interior or on the surface of SAPO-34. The four-phase modelling, which delivers total gas transport features in excellent agreement with the experiments, is carried out by means of numerical optimization procedures based on a) Maxwell's effective medium analytical formulas, and b) a finite element solution of the transport differential equations. The latter approach reveals additional details, with respect to the first one, by delivering the different paths of gases through or around the SAPO-34 crystals in the MMMs. This work demonstrates the need to identify the real phenomena at work for a fruitful modelling of mass transport in MMMs, by overcoming the simplistic assumptions of MMMs obtained by the mere addition of the two original components.

The adsorption and the thermal desorption of hydrogen in as-made and surface-modified silicalite-1 (MFI) loose crystals has been studied to shed light on the relation between the outer surface barrier and the transport of mass through it. The four different surface modifications can be probed by the change in the contact angle of water, but do not produce any apparent change in the morphology and the structure of the crystals. The H 2 adsorption isotherms in a Sievert's-type apparatus at 77 K and up to 8 MPa on the pristine and the modified silicalite-1 samples are almost overlapping, showing that the modifications involve the external surface of the samples. However the diffusion coefficients of H 2 , as derived from the sorption kinetics, evidence different sorption rates of H 2 into the different silicalite-1 samples. In particular the unmodified silicalite-1 sample presents the lowest diffusion coefficient and yields the highest H 2 desorption temperature in Thermal Desorption Spectra acquired at 0.03 K/s. The observed phenomena have been attributed to the surface silanols on the outer surface of the as-made silicalite-1 crystals, which are either eliminated or greatly reduced in number by the modifying agents. Polar and hydrophilic silanol groups bind frozen water molecules on the outer surface of as-made crystals which hinder the diffusion of hydrogen, and interact more strongly with the H 2 molecules. This provides sorption sites with higher potential energy barriers, and at the same time physically obstructs the pore entrances of the molecular sieve. The surface modification of porous fillers is of interest for the manufacture of mixed matrix membranes, for the improvement of the performance of pressure swing adsorption processes, and for gas storage applications.

In this paper we report the preparation of catalytic polymeric membranes having the complex [( N,N ′- bis (3- tert -butyl-5-(heptadecafluorooctyl)salicylidene)- trans -1,2-cyclohexanediamine)Co] embedded into Hyflon AD60X, PES and PSf and their use in the cyclopropanation reaction of olefins with ethyl diazoacetate (EDA). A study of the reaction in the homogeneous phase was also performed. The kinetics of the cyclopropanation reaction is first-order in the diazoacetate and the catalyst and zero order in the olefin, but we observed a more complex dependence on the additive, NMI ( N -methylimidazole). The positive effect of the additive is completely reversed at NMI concentration higher than 6·10 −2 M.

In this work, the use of PVDF flat membranes as contactors for direct solvent-free biphasic oxidation of cyclohexene to adipic acid has been reported. The oxidation has been carried out using 30% H2O2 and ammonium molybdate ((NH4)6Mo7O24) in the presence of succinic acid. The effect of different membranes as interfaces between the organic phase, containing cyclohexene, and the aqueous phase, with the oxidant and catalyst, has been studied and related to conversion and selectivity.

In the last years membrane processes for gas separation are gaining a larger acceptance in industry and in the market are competing with consolidated operations such as pressure swing absorption and cryogenic distillation. The key for new applications of membranes in challenging and harsh environments (e.g., petrochemistry) is the development of new tough, high performance materials. The modular nature of membrane operations is intrinsically fit for process intensification, and this versatility might be a decisive factor to impose membrane processes in most gas separation fields, in a similar way as today membranes represent the main technology for water treatment. This review highlights the most promising areas of research in gas separation, by considering the materials for membranes, the industrial applications of membrane gas separations, and finally the opportunities for the integration of membrane gas separation units in hybrid systems for the intensification of processes.

The research of new polymeric materials for membrane application in the field of nanofiltration is of great interest. PEEKWC, a modified polyetheretherketone with a cardo group, is a polymer characterized by high thermal, chemical and mechanical properties and then useful for application in the nanofiltration field. In this work, the preparation and characterization of different PEEKWC membranes by non-solvent induced phase inversion for nanofiltration of aqueous solutions containing Azur B and maltose were discussed. Interesting results in terms of retention and relative flux were obtained compared to the performance of two commercial membranes, N30F and NFTFC50. Tuning the preparation conditions, size of pores and roughness of the PEEKWC membranes can be varied with consequent effects on the membrane performance.

The synthesis of zeolite membranes and thin films using the secondary growth process is briefly described. In this process colloidal zeolite particles (sols) are prepared hydrothermally and then subsequently deposited on substrates to produce uniform layers of controlled thickness, as illustrated with silicalite and zeolite-A. The formation and growth of the zeolite sols has been investigated in situ by small angle neutron scattering (SANS). SANS measurements on silicalite sols at progressively higher concentrations have provided details of the colloid interactions which lead to zeolite gel-layer structures which are uniform and free of defects.

A thermodynamic analysis of the CO2 hydrogenation to methanol where competitive reactions take place is presented for a membrane reactor (MR) where methanol was selectively removed. A non-isothermal mathematical model was written to simulate a micro-porous MR. Zeolite membranes with different values of the CH3OH and H2O permeances were considered in the MR modelling. The effect of temperature, pressure and species permeation on the conversion, selectivity and yield was analysed. A higher CO2 conversion and CH3OH selectivity can be reached by the use of an MR. An increased CH3OH yield allows to reduce the consumption of reactant and also to operate at lower pressures and higher temperatures, a fact, which favours the kinetics reducing the residence time and the reactor volume. The MR with the highest CH3OH/H2O permeance ratio resulted in better selectivity and yield of CH3OH with respect to the other MR characterised by a higher conversion.

The self-diffusion of some organic molecules in silicone rubber and of water and water-ethanol mixtures in sodium alginate membranes was investigated to obtain information on the transport behavior in these systems. The temperature dependence of self-diffusion was examined by the pulsed field gradient NMR technique. The experimental data confirm the homogeneous amorphous nature of PDMS and the affinity of silicone rubber to apolar solvents. The interrelations between solvent and polymer structures of the sodium alginate membrane varying the temperature have been obtained using differential scanning calorimetric. The results have been compared with the trend of self-diffusion coefficients, and structure modifications of the membranes have been evidenced. The overall results confirm the potentialities of the technique used in measuring transport parameter in polymeric membranes.

In a previous work, sodium alginate dense membranes demonstrated a good combination of selectivity and permeation flux for dehydrating organic solvents by pervaporation. In this article, the pervaporation performances of alginate composite membranes has been investigated to find out the best condition of membrane formation and the optimum operating conditions. Some ultrafiltration membranes made of poly-(vinylidene fluoride), polyacrylonitrile, and hydrolyzed polyacrylonitrile—either commercially available or prepared in our laboratories—were used as supports for the composite membranes. Sodium alginate dense membranes, modified through ion exchange of sodium with multivalent metal ions (such as Al3+, Cr3+, Fe3+, and Mg2+) have also been prepared, and their permselectivities have been tested for the water–ethanol mixture. An interesting stability of the modified membranes in long-term operation is expected. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 959–968, 1998

Gas permeability (Pi) and diffusion (Di) coefficients in respect to several gases (H2, O2, N2, CO, CO2, CH4) have been measured for poly(2,6-dimethylphenylene oxide) (PMPO), poly(2,6-diphenylphenylene oxide) (PPPO), and phenylene oxide copolymers containing methyl, phenyl, and allyl radicals as side groups. X-ray diffraction study shows that both homopolymers are semicrystalline materials, whereas all the copolymers are completely amorphous. The results show that a replacement of methyl by phenyl groups in PMPO/PPPO pair is accompanied by decrease in the P values. A transition from semicrystalline PMPO to amorphous copolymers results in a decrease in permeability and solubility coefficients and not in a growth of these parameters as can be expected on the basis of the behavior of other semicrystalline polymers (e.g. polyolefins). It is supposed that the crystallites of PMPO, and possibly of PPPO are packed loosely and, hence, take part in sorption and gas transport. This assumption is in agreement with numerous X-ray data as well as the results of positron annihilation study of these polymers.

A resource-intensive industrial development, particularly in some Asian countries, characterized the last century. Its main causes can be ascribed to the significant elongation of life expectation, and to the overall increase in the standards characterizing the quality of life. The drawback of these positive aspects is the emergence of problems related to the industrial development: water stress, the environmental pollution, and the increase of CO2 emissions into the atmosphere.

The preparation and characterization of new, tailor-made polymeric membranes using poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers for gas separation are reported. Structural differences in the copolymer membranes, obtained by manipulation of the self-assembly of the block copolymers in solution, are characterized using atomic force microscopy, transmission electron microscopy, and the transport properties of three gases (CO2, N2, and CH4). The CH4/N2 ideal selectivity of 7.2, the highest value ever reported for block copolymers, with CH4 permeability of 41 Barrer, is obtained with a membrane containing the higher amount of polybutadiene (79 wt%) and characterized by a hexagonal array of columnar polystyrene cylinders normal to the membrane surface. Membranes with such a high separation factor are able to ease the exploitation of natural gas with high N2 content. The CO2/N2 ideal selectivity of 50, coupled with a CO2 permeability of 289 Barrer, makes SBS a good candidate for the preparation of membranes for the post-combustion capture of carbon dioxide.

In the present work the effect of the nanoscale morphology on the transport of ethanol/water mixtures through SBS block copolymer membranes is reported. In particular, the ethanol selectivity and overall flux can be optimized by varying the nanostructure of the SBS membranes. Membranes with well controlled nanostructure, characterized by AFM and TEM, have been prepared by selecting the casting solvent on the basis of interaction parameters ( χ ) with polybutadiene (PB) and polystyrene (PS) blocks and the amount of PS in the copolymer.

This chapter describes the preparation, characterization and transport properties containing zeolite crystals dispersed in a perfluorinated polymer

In this work the use of poly(vinylidene) fluoride based membrane as interfaces for the biphasic oxidation of benzyl alcohol to benzaldheyde has been reported. The membranes have been prepared by means of dry-wet phase inversion. Membranes with different surface characteristics have been selected for the oxidation reaction.

A series of dense membranes for gas separation based on poly[bis(phenoxy)phosphazene] (PPOP) were prepared in flat sheet configurations. They were characterized by viscosimetry, differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Permeation tests of O 2 , N 2 , He and CO 2 were made at five different temperatures below the T (1) transition of PPOP, which gave results that proved to be stable and reversible with temperature. The Arrhenius plots of permeabilities were linear, and showed that the faster permeability of CO 2 with respect to He was due to a larger solubility. Interesting O 2 to N 2 selectivity ratios were obtained.

A thin MFI zeolite membrane was synthesised on a porous α-Al 2 O 3 tubular support by in situ nucleation and secondary growth. Single gas permeances (CH 4 , H 2 , N 2 , CO, CO 2 ) were measured through the MFI membrane according to the pressure drop method, from room temperature to 280 °C, with pressure differences between 0.1 and 0.4 bar. The membrane combines high permeances (1.6–8.0 μmol m −2 s −1 Pa −1 ) and also good separation properties (the H 2 /SF 6 permselectivity value is equal to 24 at room temperature). The membrane has been tested also in the pervaporation of an ethanol/water mixture, showing high fluxes (2.1 kg m −2 h −1 ) and low selectivity.

The 129 Xe-NMR method was used for evaluation of the sizes of free volume elements in amorphous glassy materials—random copolymers of tetrafluoroethylene and perfluorodioxoles of different structures. 129 Xe chemical shifts were measured at different pressures up to 1060 Torr. The zero pressure chemical shifts obtained by extrapolation were used for calculation of the diameters of microcavities having spherical and cylindrical shapes. The sizes of microcavities are consistent with those found by means of positron annihilation lifetimes and inverse gas chromatography methods.

PEEK-WC is an amorphous polyetheretherketone with high chemical stability, excellent thermal resistance and significant solubility in various solvents. It has been used to prepare flat membranes by the phase inversion technique. The water vapour permeability through a porous PEEK-WC film was 1350 g/m2 day at 26 °C and its liquid entry pressure (LEP) of water equivalent to a column of 2.0 m. These values were remarkably improved by addition of an aliphatic ether polyurethane (PU) into the PEEK-WC/DMF dopes: the water vapour flux was increased up to 2000 g/m2 day and the LEP was equivalent to 12.5 m. This improvement is correlated to the different structure of the membranes: a spongy, porous and almost symmetric structure for the PEEK-WC/PU membranes, and an asymmetric structure with fingers for PEEK-WC membrane. The presence of PU influences also the mechanical properties of the blend membranes. The role of the PU on the resulting membrane morphology is rationalised on the basis of the mechanism of phase separation.

The synthesis of zeolite membranes and thin films using the secondary growth process is briefly described. In this process colloidal zeolite particles (sols) are prepared hydrothermally and then subsequently deposited on substrates to produce uniform layers of controlled thickness. In order to optimise this process, an understanding of the nature of the sols and an insight into the structure of the consolidated layer so formed, is required. Such studies are illustrated here with silicalite and zeolite A. The formation and growth of silicalite sols has been investigated in situ by small angle neutron scattering (SANS). SANS measurements on sols at progressively higher concentrations have provided details of the colloid interactions which lead to zeolite gel-layer structures which are uniform and free of defects. Several techniques (XRD, small angle X-ray scattering (SAXS), and nitrogen adsorption isotherms) have also been used to characterize colloidal species extracted by ultracentrifugation at progressive stages from solutions during the hydrothermal synthesis of zeolite LTA.

Tubular MFI zeolite membranes have been prepared in two steps with a modification of the secondary growth method. The first synthetic step is only devoted to the in situ nucleation of the molecular sieve, directly on the surface of the tubular ceramic UF support, and the bulk of the membrane is then grown on it under different conditions. The right choice of the synthetic parameters (composition of the synthetic clear solutions, temperature) enables one to obtain membranes with high gas permeability and sustained selectivity. The preliminary gas transport results and the morphology are compared with the ones from a membrane obtained in one step: permeability increases by almost one order of magnitude. SEM observations indicate the presence of a very thin (1–2 μm) MFI zeolite layer on the tubular support. The method illustrated in this work is an easy way to skip the deposition of pre-formed nano-sized crystals on tubular supports before the secondary growth of the MFI membrane.

Sorption and permeability measurements have been performed to determine the transport parameters of carbon dioxide through dense homogeneous PEEKWC membranes. The enthalpy of solution of CO2 is exothermic. The concentration dependence of diffusion has been measured. Permeability coefficients obtained from sorption data have been compared with the experimental values, obtaining a good agreement.

We report on our latest studies on alignment of chromonic liquid crystals, a special class of molecules which recently attracted the attention of researchers. In particular, we show a detailed study of planar anchoring of disodium cromoglycate (DSCG) and, for the first time in the literature, a stable homeotropic alignment, achieved using a surface property of the alignment layer, i.e. the hydrophobicity. Excellent candidates from this point of view are pure polybutadiene (PB) and polydimethylsiloxane (PDMS). In fact, for the former the homeotropic anchoring stabilizes after one day, while for the latter stabilization occurs soon after cooling from the isotropic phase. After a long time both types of alignments (planar and homeotropic) evolve into thermodynamically stable configurations, i.e. ribbon structures. An explanation of the behaviour is given.

Poly(phenylene oxide) (PPO) composite membranes have been prepared on a polysulfone (PSf) ultrafiltration support, which was previously coated with highly permeable polydimethylsiloxane (PDMS). The PDMS gutter layer was used in order to: plug the pores of the support; minimise the thickness of the separating PPO deposit; and reduce the tortuosity of the path of the gas molecules to the pores of the support. Composite membranes with high fluxes and good selectivities for gas separations have been obtained with an amorphous and cross-linkable phenylene oxide co-polymer.