Terminal Silanol Research Articles

Atom-Economic Synthesis of Zeolites.

Zeolites are typically synthesized in the presence of strong alkaline or fluoride species, which is not atom-economic for zeolite synthesis due to the high solubility of strong alkaline and fluoride species to silica. One of the solutions for this issue is to reduce solubility of silica in the zeolite synthesis, but it is challenging. Herein, we show that nucleation and growth of zeolites can occur under near neutral conditions, giving an atom-economical synthesis of zeolites with almost full silica utilization due to very low silica solubility. Compared to conventional hydrothermal synthesis, this work both enhances the zeolite yield and reduces waste emissions, even water zero emission. Particularly, structural defects (terminal silanols) in zeolites are obviously lowered, thus giving high thermal and hydrothermal stabilities and good performance in the Beckmann rearrangement.

Intracrystalline diffusion regulation of Au/hierarchical TS-1 for simultaneously enhanced stability and selectivity in propene epoxidation with H2 and O2

Regulation of intracrystalline diffusion plays a pivotal role in ensuring the catalytic stability of metal-supported zeolite catalysts. Herein, we successfully achieved precise modulation of intracrystalline diffusion in Au-loaded hierarchical TS-1 catalysts by two-step recrystallization approach. This modulation was achieved by manipulating the length of mesoporogens, characterized by the hierarchical factor (HF). The HF could be used as the descriptor to reveal the reaction stability and deactivation process including blocking degree (VAu: gold volume / Vna: volume not accessible for N2) by the Au nanoparticles and coke formation in fresh and used catalysts, respectively. In addition, the enhanced selectivity was attributed to the improved hydrophobicity of Au/hierarchical TS-1 with gradually decreased terminal silanols by two-step recrystallization approach. This work not only provides the new strategy for the regulation of zeolite intracrystalline diffusion, but also could shed new lights on the industrial process of direct propene epoxidation with H2 and O2.

A Study of the Degradation Mechanism of Ladder-like Polyhedral Oligomeric Silsesquioxane via Fourier Transform Infrared Spectroscopy

As a result of global warming, fire outbreaks are becoming a common occurrence. There is, therefore, the need for an effective, low-cost and environmentally friendly fire-retardant material. Amine-terminated polyhedral oligomeric silsesquioxane, ATL-POSS, is a low-cost, water-soluble, fire-retardant material based on aminosilane coupling agents. Because of its solubility in water, it can serve as a general-purpose fire retardant. The ATL-POSS nanoparticles reported in this paper have high char retentions of about 75 and 54% in nitrogen and air atmospheres, respectively. Differential scanning calorimetry (DSC) was used to determine the phase transition temperatures. It was shown that ATL-POSS is an amorphous material. The thermal stability and rate of decomposition of POSS was determined by using thermogravimetric analysis (TGA). The TGA derivative curves (DTA) show that the degradation of ladder-like POSS occurred in multiple stages and that the rate of degradation is affected by the heating rate. The mechanism of decomposition of ATL-POSS was determined by using Fourier transform infrared spectroscopy, FTIR. The FTIR technique was chosen for this study because of its accessibility and ability to distinguish ladder-like POSS from the cage-type POSS structures. The FTIR spectra showed that the -Si-O-Si- cyclic structure was the predominant structure of POSS. By analyzing the FTIR spectra of the thermally treated POSS residues, obtained at the specified test temperatures, the detailed degradation mechanism of POSS was inferred. It was shown that the terminal silanol group was degraded at test temperatures below 400 °C. Silica was shown to be the final product of the pyrolysis of POSS. The presence of the FTIR transmission peaks at 1000 and 1100 cm−1, due to asymmetric vertical and horizontal stretching vibrations of the Si-O-Si, respectively, was the key evidence used to infer the ladder-like structure of POSS.

Modulating the Microenvironment of Silanols in Pure-Silicon Zeolites for Boosting Vapor-phase Beckmann Rearrangement of Cyclohexanone Oxime.

Vapor-phase Beckmann rearrangement of cyclohexanone oxime (CHO) to ε-caprolactam (CPL) is still difficult to commercialize at the industrial scale due to its relatively low catalytic activity and poor lifetime. Herein, we synthesized a series of pure-silicon zeolites (including MFI, MEL, and -SVR) with three-dimensional 10-member-ring topolgies, diverse silanol status, and hierarchical porosity to investigate the synergistic effects of inner diffusivity and reactivity. S-1 zeolite of MFI-type topology with plentiful silanol nests exhibits a more preferable catalytic performance in terms of CHO conversion (99.7%) and CPL selectivity (89.7%), much higher than those of MEL- and -SVR-type zeolites mainly due to their diverse silanol distribution. With the construction of hierarchical porosity, S-1-P shows improved CPL selectivity of 94.1% owing to the enhanced diffusivity to shorten the retention time of the reactant and product molecules. The reaction mechanism and network have been further revealed by density functional theory (DFT) calculations and experimental designs, which indicate that silanol nests are major active sites due to their suitable interaction with CHO rather than terminal silanols. Particularly, the microenvironments of silanols can be modulated by alcohol solvents, ascribed to their different charge transfer and steric hindrance. Consequently, S-1-P shows superior CPL selectivity of 97.3% in ethonal solvents, which have higher adsorb energy of -0.627 eV with silanol nests than other alcohols. The present study not only provides a fundamental guide for the design of zeolite catalysts but also provides a reference for modulating the microenvironment of active sites according to the catalytic mechanism.

Molecularly Capped Omniphobic Polydimethylsiloxane Brushes with Ultra-Fast Contact Line Dynamics.

Droplet friction is common and significant in any field where liquids interact with solid surfaces. This study explores the molecular capping of surface-tethered, liquid-like polydimethylsiloxane (PDMS) brushes and its substantial effect on droplet friction and liquid repellency. By exchanging polymer chain terminal silanol groups for methyls using a single-step vapor phase reaction, the contact line relaxation time is decreased by three orders of magnitude-from seconds to milliseconds. This leads to a substantial reduction in the static and kinetic friction of both high- and low-surface tension fluids. Vertical droplet oscillatory imaging confirms the ultra-fast contact line dynamics of capped PDMS brushes, which is corroborated by live contact angle monitoring during fluid flow. This study proposes that truly omniphobic surfaces should not only have very small contact angle hysteresis, but their contact line relaxation time should be significantly shorter than the timescale of their useful application, i.e., a Deborah number less than unity. Capped PDMS brushes that meet these criteria demonstrate complete suppression of the coffee ring effect, excellent anti-fouling behavior, directional droplet transport, increased water harvesting performance, and transparency retention following the evaporation of non-Newtonian fluids.

Adsorption of As(V) at Humic Acid-Kaolinite-Bacteria Interfaces: Kinetics, Thermodynamics, and Mechanisms

The immobilization and transformation of arsenic at the mineral-organic interface in soil environments ultimately depend on the soil components and their interactions. Herein, the effect of humic acid (HA) and a typical bacterium (a Gram-positive Bacillus subtilis) coating on the adsorption of arsenate As(V) to kaolinite (Kao) mineral was investigated. The As(V) adsorption reaction kinetics, isotherms, thermodynamics, and mechanism on the clay mineral-organic composites of kaolinite-Bacillus subtilis (Kao-B.s) and humic acid-kaolinite-Bacillus subtilis (Kao-HA-B.s) were investigated. The As(V) adsorption on the composites was better fitted to pseudo-second-order kinetics and the Freundlich model. The adsorption capacity of As(V) followed the order of Kao-HA-B.s > Kao-B.s > B.s > Kao-HA > Kao. The positive ΔH (31.44, 5.87 kJ mol−1) and ΔG (0.10–0.96 kJ mol−1) values confirmed that the adsorption of As(V) by all composites was nonspontaneous and endothermic in character at room temperature. The FT-IR, XRD, and thermodynamic results revealed that the adsorption mechanism of As(V) on the kaolinite–organic interfaces could be attributed to the electrostatic forces between the terminal aluminum or silanol groups of kaolinite and As(V) and the complexation between HA, bacteria, and As(V), which formed an inner-sphere complex and surface complex, respectively. The experimental results showed that the adsorption of As(V) on the Kao-HA or Kao-bacteria system was accompanied by significant additive interactions, while the ternary Kao-HA-bacteria system had a significant inhibitory effect on As(V) binding at a higher HA content due to the shielding effect, with the promotion effect shown at a lower concentration for dispersion effect for HA on the kaolinite particles.

Efficient esterification over hierarchical Zr-Beta zeolite synthesized via liquid-state ion-exchange strategy

The eco-friendly zeolite-based solid acid catalysts constitute an important alternative to the liquid acid catalyst for the production of plasticizer tributyl citrate (TBC), due to their non-corrosive, high hydrothermal stability and easiness to recycle. Herein, a simple acid treatment to the H-Beta zeolite and subsequent incorporation of ZrIV ions into the vacated Al sites were conducted by liquid-state ion-exchange of ZrO(NO3)2 aqueous solution. The ZrIV ions were incorporated into the framework by the expand of the unit cell size, verified by XRD patterns, the emerging new band at ∼198 nm on UV–vis spectra, the enhanced binding energies of the Zr 3d5/2 and Zr 3d3/2 on XPS spectra, as well as the variations of isolated terminal silanol groups (Si-OH) by FTIR and the change of integrated intensity ratio of Q3/Q4 by 29Si MAS NMR. It was illustrated that the Lewis acid sites was the main active sites for esterification reaction and the produced abundant mesopores in the Zr-Beta-x catalysts would facilitate the transportation of TBC. The maximum conversion of citric acid as high as 80 % was obtained on Zr-Beta-128 (SiO2/ZrO2 molar ratio = 128) catalyst with the highest Lewis acid amount. Furthermore, the Zr-Beta-128 zeolite exhibited high stability without any detectable deactivation after 6 cycles with the 100 % selectivity to TBC. The efficient Zr-Beta catalyst could supply a novel possibility for the development of an environmentally-friendly solid acid catalyst with good performance for the TBC production.

A significant support effect on RuSn catalysts for carboxylic acid transformation to hydrocarbons

The ever-increasing demand for substitute energy sources encourages the usage of biofuels as transportation fuel; however, the unstable properties and low calorific value of biofuels caused by high oxygen content limits their direct application. In this study, we report the upgrading of a model biofuel in octanoic acid by hydrodeoxygenation (HDO) using RuSn supported on SiO2-doped Al2O3 (SiAl). The presence of SiO2 on Al2O3 was crucial for the formation of Ru3Sn7 alloy phase because SiO2 modified the metal-support interaction between RuSn and Al2O3. The alloy phase conferred significant hydrogenation activity to convert octanoic acid to octanol and minimized carbon loss by reducing decarbonylation activity. The deposition of SiO2 also resulted in improved acidity, which increased with increasing SiO2 loading from 10 to 30 %, due to the formation of isolated terminal silanols (Si-OH). The presence of the silanol groups was important for dehydration of octanol to octane, since the silanols retained octenes longer on the support, facilitating over-hydrogenation. The cooperative metal-support activity on RuSn/SiAl enables high and selective hydrogenation and dehydration activity for upgrading fatty acids in biofuel to hydrocarbons.

Function of Brønsted and Lewis acid sites in xylose conversion into furfural.

In this work, the xylose conversion and the selectivity to furfural were assessed over mesoporous sulfonic silica SBA-15-(X)SO3H catalysts doped with metal ions (X = Al(iii), Ti(iv) or Zr(iv)). The type and amount of acid sites were analyzed by adsorption of pivalonitrile. The SBA-15-(X)SO3H materials show Lewis acid sites (LAS) and two types of Brønsted acid sites (BAS) with different strengths. Type I (BAS I) belongs to terminal silanol groups, type II (BAS II) is ascribed to hydroxyl groups bonded to sulfur or transition metal, and the LAS is related to M-O bonds. Optimal reaction conditions for the most active catalyst (SBA-15-(Zr)SO3H) were 120 minutes of reaction at 160 °C, 20 wt% of catalyst, and 2.5% of xylose/solvent. Additionally, a kinetic study was carried out to calculate the rate constants, the activation energy, and the pre-exponential factor for the xylose dehydration reaction. It was found that the selectivity to furfural in sulfonic silica SBA-15-(X)SO3H catalysts was directly related to the BAS II fraction. While LAS negatively impacts the selectivity to furfural leading to the undesired reaction between furfural and xylose obtaining humins as secondary products.

Effect of desilication on the catalytic activity of Fe-FER for direct, selective, partial oxidation of methane

The effect of desilication on the physic-chemical properties of ferrierite zeolite was investigated using spectroscopic and solid characterisation techniques including N2-adsorption, XRD, SEM, H2-TPR, NH3-TPD and in situ FTIR. Stability of active oxygen species formed from N2O over the Fe-FER catalysts and the catalytic activity for direct conversion of methane to value-added products at temperatures between 300 °C and 400 °C were studied.Ferrierite zeolites, pre-treated with 0.1 M, 0.2 M and 0.3 M NaOH solutions preserved the crystal structure of the ferrierite zeolite but their textural properties were significantly modified, leading to an increase in mesopore area and creating a greater concentration of terminal Si-OH groups, concomitant with increase in the amount of extra-framework Al and reduction in the number of bridging Si-OH-Al species.Batch-mode catalytic reaction studies of methane with N2O conducted in an in situ FTIR cell demonstrate that the methoxy groups formed on extraframework iron sites followed by the migration of these species to silicon defect sites, which resulted in a decline in the intensity of terminal Si-OH groups bands in the IR spectra.N2O-TPD experiments confirm that N2O is converted to N2, O2 and NO over Fe-FER catalysts at 350 °C. The decline in the desorption temperature of these products observed over Fe-FER catalysts treated with alkaline solution is consistent with a significant increase in the mesopore surface area from 28.3 m2/g to 102.4 m2/g. The peak areas of desorbed O2 and NO were estimated, and the different ratios of O2/NO observed on these catalysts appears to be related to the difference stabilities of surface oxygen species.Studies under continuous reaction conditions demonstrate that, at a similar level of methane conversion (ca. 2.8 %), Fe-FER catalysts prepared with the moderately alkaline solution (0.2 M NaOH) results the highest yield of methanol, dimethyl ether and formaldehyde. It is asserted that this enhanced selectivity is the result of the comparatively high concentrations of terminal silanol groups, Brønsted-acid sites, stability of active oxygen species and mesopore volume.

Optically Transparent Polydimethylsiloxane-Ethylene Oxide-Propylene Oxide Multiblock Copolymers Crosslinked with Isocyanurates as Organic Compound Sorbents.

New crosslinked (polydimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate multiblock copolymers (MBCs) were synthesized, and their supramolecular structure and sorption characteristics were studied. It was found that the interaction of PPEG and D4 leads to polyaddition of D4 initiated by potassium-alcoholate groups. The use of the amphiphilic silica derivatives associated in an oligomeric medium (ASiPs) leads to structuring of the MBC due to the transetherification reaction of the terminal silanol groups of the MBC with ASiPs. It was established that the supramolecular structure of an MBC is built according to the “core-shell” structure. The obtained polymers were tested as sorbents for the development of new methods for the concentration and determination of inorganic compounds. The efficiency of sorption of reagents increased with an increase in the “thickness” of the polydimethylsiloxane component of the “shell” and with a decrease in the size of the polyisocyanurate “core”. The use of the obtained polymers as adsorbents of organic reagents is promising for increasing the efficiency of field methods of chemical testing and inorganic analysis, including the determination of the elemental composition and the detection of traces of contamination.

Investigation of the active centers and structural modifications for TS-1 in catalyzing the Beckmann rearrangement

The Beckmann rearrangement (BR) of cyclohexanone oxime (CHO) to produce caprolactam (CPL) has been studied over various titanosilicates. TS-1 showed superior catalytic performance, compared to Ti-MWW, Ti-Beta and Ti-MOR. Based on the close relationship between Ti content and CHO conversion, and the Na+-exchange experiments, the silanol groups, adjacent to the “open” Ti sites, were proved to be the active centers for the BR reaction of CHO to produce CPL, in addition to those generated by defects including terminal silanols, hydrogen-bonded silanols and silanol nests. Moreover, monolithic TS-1 (M-TS-1) microspheres showed higher catalytic activity than the conventional TS-1. The diffusion properties of M-TS-1 were further enhanced via the chemical modifications to achieve longer lifetime for the Beckmann rearrangement under optimized reaction conditions.

The crystal structure of mineral magadiite, Na2Si14O28(OH)2∙8H2O

Abstract Magadiite from Lake Magadi was structurally analyzed based on X-ray powder diffraction data. The idealized chemical composition of magadiite is Na16[Si112O224(OH)16]∙64H2O per unit cell. The XRD powder diffraction pattern was indexed in orthorhombic symmetry with lattice parameters a0 = 10.5035(9) Å, b0 = 10.0262(9) Å, and c0 = 61.9608(46) Å. The crystal structure was solved from a synthetic magadiite sample in a complex process using 3D electron diffraction combined with model building as presented in an additional paper. A Rietveld refinement of this structure model performed on a magadiite mineral sample in space group F2dd (No. 43) converged to residual values of RBragg = 0.031 and RF = 0.026 confirming the structure model. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of magadiite contains two enantiomorphic silicate layers of, so far, unknown topology. The dense layers exhibit no porosity or micro-channels and have a thickness of 11.5 Å (disregarding the van der Waals radii of the terminal O atoms) and possess a silicon Q4 to Q3 ratio of 2.5. 16 out of 32 terminal silanol groups are protonated, and the remaining groups compensate for the charge of the hydrated sodium cations. Bands of edge-sharing [Na(H2O)6/1.5] octahedra are intercalated between the silicate layers extending along (110) and (110). The water molecules are hydrogen bonded to terminal silanol groups with O···O distances of 2.54–2.91 Å. The structure of magadiite is slightly disordered, typical for hydrous layer silicates (HLS), which possess only weak interactions between neighboring layers. In this respect, the result of the structure refinement represents a somewhat idealized structure. Nevertheless, the natural magadiite possesses a higher degree of structural order than any synthetic magadiite sample. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds between the terminal O atoms (silanol/siloxy groups), confirmed by 1H MAS NMR and DRIFT spectroscopy. The surface zone of the silicate layers, as well as the interlayer region containing the [Na(H2O)6/1.5] octahedra, are closely related to the structure of Na-RUB-18.

Condensation and growth of amorphous aluminosilicate nanoparticles via an aggregation process.

The precipitation of zeolite nanoparticles involves the initial formation of metastable precursors, such as amorphous entities, that crystallize through non-classical pathways. Here, using reactive force field-based simulations, we reveal how aluminosilicate oligomers grow concomitantly to the decondensation of silicate entities during the initial step of the reaction. Aluminate clusters first form in the solution, thus violating the Loewenstein rule in the first instant of the reaction, which is then followed by their connection with silicate oligomers at the terminal silanol groups before reorganization to finally diffuse within the silicate oligomers to form stable amorphous aluminosilicate nanoparticles that do obey the Loewenstein rule. Our results clearly indicate that aluminate does not serve as the nucleation center for the growth of aluminosilicates in a nucleation-like process but rather proceeds via an aggregation process. The coexistence of aluminosilicate oligomers and small silicate entities induces a phase separation that promotes the precipitation of zeolites with aging.

The crystal structure of synthetic kenyaite, Na2Si20O40(OH)2·8H2O

A synthetic kenyaite sample possessing the chemical composition Na16[Si160O320(OH)16]·64H2O per unit cell was structurally analysed using X-ray powder data. The powder pattern was indexed based on space group symmetry Fdd2 (No. 43) with lattice parameters a0 ​= ​10.080(1) Å, b0 ​= ​79.383(8) Å, c0 ​= ​10.604(1) Å. The crystal structure was solved by model building based on the unit cell parameters, the results of a general characterisation of the material and the comparison with the closely related structures of RUB-6, Na-RUB-18 and magadiite. A Rietveld refinement of this structure model converged to residual values of χ2 ​= ​3.1, RF ​= ​0.020 and RBragg ​= ​0.025, confirming the structure model. Physico-chemical characterisation using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of kenyaite contains thick silicate layers with a thickness of 15.9 ​Å (ignoring the van der Waals radii of the terminal oxygen atoms). The dense layers possess the same topology as the layers of RUB-6, exhibit no porosity and have a silicon Q4 to Q3 ratio of 4.0. 16 out of 32 terminal silanol groups are protonated while 16 siloxy groups (≡Si–O–) compensate the charge of the sodium cations. RUB-6 and kenyaite differ, however, with respect to the cation intercalated and to the stacking arrangement of layers. Bands of edge-sharing [Na(H2O)6/1.5] octahedra are intercalated between the silicate layers extending along [110] and [1¯10]. The equatorial water molecules of the octahedra are hydrogen bonded to terminal silanol groups with O⋯O distances of 2.5 ​Å to 2.6 ​Å. The structure of kenyaite is slightly disordered typical for hydrous layer silicates which possess only weak interactions between neighbouring silicate layers. In this respect, the result of the structure refinement represents a somewhat idealised structure. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds (d(O⋯O) ≈ 2.5 ​Å) between the terminal O atoms (silanol/siloxy groups) confirmed by 1H MAS NMR spectroscopy. The surface zone of the silicate layers as well as the inter-layer region containing the edge-sharing [Na(H2O)6/1.5] octahedra are closely related to the structures of Na-RUB-18 and magadiite.

Beneficiation of ponded coal ash through chemi-mechanical grinding

Four samples of low quality ponded coal ash were subjected to a chemi-mechanical beneficiation technique to test improvements to traditional grinding methods. The addition of water into this beneficiation process can further increase the reactivity of the subjected materials. Changes to the reactivity of these ponded ashes and their structure were analyzed utilizing ATR spectroscopy, X-Ray Diffraction, and Scanning Electron Microscopy. The results show a drop in structural order, smaller particle size, and a 7 to 70 percent increase in amorphous content. These improvements are in contrast to an increase in crystallinity observed with the more traditional dry grinding technique. ATR IR spectroscopy confirms the formation of additional terminal silanol groups after the chemi-mechanical grinding process suggesting a further increase in pozzolanic reactivity. These results suggest that the proposed modification to the beneficiation process does not interfere with the ash improvements observed with traditional grinding but further improves the ash reactivity due to the formation of additional silanol groups. Additionally, ponded ashes (being hydrated) are the ideal source material for this beneficiation process, allowing for a larger quantity of this material to be reutilized efficiently.

Density Functional Theory Study on the Morphology Evolution of Hydroxylated β-Cristobalite Silica and Desilication in the Presence of Methanol

In the present work, the hydroxylation process of three low-index β-cristobalite silica surfaces, that is, C(100), C(101), and C(011) surfaces under different hydroxyl coverages has been investigated using density functional theory (DFT) calculations. The surface hydroxylation process is described as consecutively dissociative adsorption of water molecules on the hypothetically pristine crystalline silica surfaces, resulting in Q2 terminal silanols and Q3 H-bonded silanols. Based on the calculated Gibbs surface free energies at different hydroxylation conditions, the evolution of the β-cristobalite nanoparticle morphology and the exposed hydroxylated surface structure ratios are predicted using the Wulff construction principle. The fully hydroxylated C(100) and C(101) surfaces are two exposed structures of the rodlike β-cristobalite silica until 1000 K, while the fully dehydroxylated C(101) surface becomes the only exposed surface structure on the octahedral β-cristobalite silica when the temperature reaches over 1700 K. The surface desilication of three fully hydroxylated β-cristobalite structures in the presence of methanol via the formation of tetramethyl orthosilicate was also studied. Compared with the fully hydroxylated C(100) and C(101) surfaces in which the surface desilication is thermodynamically and kinetically hindered, the fully hydroxylated C(011) surface is unstable with the plausible desilication process.

Separation of an aqueous mixture of 6-kestose/sucrose with zeolites: A molecular dynamics simulation

Extra-large pore zeolites are a small subset (21) among the whole list of 253 zeolites available. The discovery of new low-glycemic sugars is very attractive as new healthy additives in the food field. This is the case of the 6-kestose. In the present case, it appears in a mixture in aqueous solution together with sucrose, the separation of the mixture being necessary. For this, we have focused on using certain zeolites with adequate pore sizes that allow the separation of this mixture, considering that since the molecular size of 6-kestose is greater than sucrose, it is necessary to promote the sorption of the latter, so that the first can be purified. After a computational screening of micropores of the 253 IZA zeolites, 11 zeolites were selected. Of these, 3 extra-large pore zeolites (AET, DON, ETR) have been proposed, which were analyzed in-depth through a molecular dynamics study considering the external surface. The results show that DON presents the most promising theoretical results for a selective sucrose/6-kestose separation. • Separation of dissacharide/trissacharide mixtures is important for agroalimentary process. • With 7.5/9.1 Å size of these sugars, extra-large pore zeolites might be used for separation. • Molecular dynamics of sucrose/kestose have been made on extra-large pore zeolites. • Models include large unit cells with: water, sugar, zeolite layers and reservoir (membranes). • Effects considered: external surface, terminal silanols, pore size, temperature, water.

Amphiphilic Poly(dimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate Cross-Linked Block Copolymers in a Membrane Gas Separation.

Amphiphilic poly(dimethylsiloxane-ethylene-propylene oxide)-polyisocyanurate cross-linked block copolymers based on triblock copolymers of propylene and ethylene oxides with terminal potassium-alcoholate groups (PPEG), octamethylcyclotetrasiloxane (D4) and 2,4-toluene diisocyanate (TDI) were synthesized and investigated. In the first stage of the polymerization process, a multiblock copolymer (MBC) was previously synthesized by polyaddition of D4 to PPEG. The usage of the amphiphilic branched silica derivatives associated with oligomeric medium (ASiP) leads to the structuring of block copolymers via the transetherification reaction of the terminal silanol groups of MBC with ASiP. The molar ratio of PPEG, D4, and TDI, where the polymer chains are packed in the “core-shell” supramolecular structure with microphase separation of the polyoxyethylene, polyoxypropylene and polydimethylsiloxane segments as the shell, was established. Polyisocyanurates build the “core” of the described macromolecular structure. The obtained polymers were studied as membrane materials for the separation of gas mixtures CO2/CH4 and CO2/N2. It was found that obtained polymers are promising as highly selective and productive membrane materials for the separation of gas mixtures containing CO2, CH4 and N2.

Gas-sieving zeolitic membranes fabricated by condensation of precursor nanosheets.

The synthesis of molecular-sieving zeolitic membranes by the assembly of building blocks, avoiding the hydrothermal treatment, is highly desired to improve reproducibility and scalability. Here we report exfoliation of the sodalite precursor RUB-15 into crystalline 0.8-nm-thick nanosheets, that host hydrogen-sieving six-membered rings (6-MRs) of SiO4 tetrahedra. Thin films, fabricated by the filtration of a suspension of exfoliated nanosheets, possess two transport pathways: 6-MR apertures and intersheet gaps. The latter were found to dominate the gas transport and yielded a molecular cutoff of 3.6 Å with a H2/N2 selectivity above 20. The gaps were successfully removed by the condensation of the terminal silanol groups of RUB-15 to yield H2/CO2 selectivities up to 100. The high selectivity was exclusively from the transport across 6-MR, which was confirmed by a good agreement between the experimentally determined apparent activation energy of H2 and that computed by ab initio calculations. The scalable fabrication and the attractive sieving performance at 250-300 °C make these membranes promising for precombustion carbon capture.