Silica Sodalite Research Articles

Effect of Silica Sodalite Loading on SOD/PSF Membranes during Treatment of Phenol-Containing Wastewater.

In this study, silica sodalite (SSOD) was prepared via topotactic conversion and different silica sodalite loadings were infused into the polysulfone (PSF) for application in phenol-containing water treatment. The composite membranes were fabricated through the phase inversion technique. Physicochemical characteristics of the nanoparticles and membranes were checked using a Scanning Electron Microscope (SEM), Brunauer Emmett–Teller (BET), and Fourier Transform Infrared (FTIR) for surface morphology, textural properties, and surface chemistry, respectively. A nanotensile test, Atomic Force Microscopy (AFM), and contact angle measurement were used to check the mechanical properties, surface roughness, and hydrophilicity of the membranes, respectively. SEM results revealed that the pure polysulfone surface is highly porous with large evident pores. However, the pores decreased with increasing SSOD loading. The performance of the fabricated membranes was evaluated using a dead-end filtration device at varying feed pressure during phenol-containing water treatment. The concentration of phenol in water used in this study was 20 mg/L. The pure PSF displayed the maximum phenol rejection of 95 55% at 4 bar, compared to the composite membranes having 61.35% and 64.75% phenol rejection for 5 wt.% SSOD loading and 10 wt.% SSOD loading, respectively. In this study, a novel Psf-infused SSOD membrane was successfully fabricated for the treatment of synthetic phenol-containing water to alleviate the challenges associated with it.

Effect of Silica Sodalite Functionalization and PVA Coating on Performance of Sodalite Infused PSF Membrane during Treatment of Acid Mine Drainage.

In this study, silica sodalite (SSOD) nanoparticles were synthesized by topotactic conversion and functionalized using HNO3/H2SO4 (1:3). The SSOD and functionalized SSOD (fSSOD) nanoparticles were infused into a Polysulfone (Psf) membrane to produce mixed matrix membranes. The membranes were fabricated via the phase inversion method. The membranes and the nanoparticles were characterized using Scanning Electron Microscopy (SEM) to check the morphology of the nanoparticles and the membranes and Fourier Transform Infrared to check the surface chemistry of the nanoparticles and the membranes. Thermal stability of the nanoparticles and the membranes was evaluated using Themogravimetry analysis (TGA) and the degree of hydrophilicity of the membranes was checked via contact angle measurements. The mechanical strength of the membranes and their surface nature (roughness) were checked using a nanotensile instrument and Atomic Force Microscopy (AFM), respectively. The textural property of the nanoparticles were checked by conducting N2 physisorption experiments on the nanoparticles at 77 K. AMD-treatment performance of the fabricated membranes was evaluated in a dead-end filtration cell using a synthetic acid mine drainage (AMD) solution prepared by dissolving a known amount of MgCl2, MnCl2·4H2O, Na2SO4, Al(NO3)3, Fe(NO3)3·9H2O, and Ca2OH2 in deionized water. Results from the N2 physisorption experiments on the nanoparticles at 77 K showed a reduction in surface area and increase in pore diameter of the nanoparticles after functionalization. Performance of the membranes during AMD treatment shows that, at 4 bar, a 10% fSSOD/Psf membrane displayed improved heavy metal rejection >50% for all heavy metals considered, expect the SSOD-loaded membrane that showed a rejection <13% (except for Al3+ 89%). In addition, coating the membranes with a PVA layer improved the antifouling property of the membranes. The effects of multiple PVA coating and behaviour of the membranes during real AMD are not reported in this study, these should be investigated in a future study. Therefore, the newly developed functionalized SSOD infused Psf membranes could find applications in the treatment of AMD or for the removal of heavy metals from wastewater.

Synthesis and Evaluation of HSOD/PSF and SSOD/PSF Membranes for Removal of Phenol from Industrial Wastewater.

Phenol is regarded as a major pollutant, as the toxicity levels are in the range of 9–25 mg/L for aquatic life and humans. This study embedded silica sodalite (SSOD) and hydroxy sodalite (HSOD) nanoparticles into polysulfone (PSF) for enhancement of its physicochemical properties for treatment of phenol-containing wastewater. The pure polysulfone membranes and sodalite-infused membranes were synthesized via phase inversion. To check the surface morphology, surface hydrophilicity, surface functionality, surface roughness and measure the mechanical properties of the membranes, characterization techniques such as Scanning Electron Microscope (SEM), contact angle measurements, Fourier Transform Infrared, Atomic Force Microscopy (AFM) nanotensile tests were used, respectively. The morphology of the composite membranes showed incorporation of the sodalite crystals decreased the membrane porosity. The results obtained showed the highest contact angle of 83.81° for pure PSF as compared to that of the composite membranes. The composite membranes with 10 wt.% HSOD/PSF and 10 wt.% SSOD/PSF showed mechanical enhancement as indicated by a 20.96% and 19.69% increase in ultimate tensile strength, respectively compared to pure PSF. The performance evaluation of the membranes was done using a dead-end filtration cell at varied feed pressure. Synthetic phenol-containing wastewater was prepared by dissolving one gram of phenol crystals in 1 L of deionized water and used in this study. Results showed higher flux for sodalite infused membranes than pure PSF for both pure and phenol-containing water. However, pure PSF showed the highest phenol rejection of 93.55% as compared to 63.65% and 64.75% achieved by 10 wt.% HSOD/PSF and 10 wt.% SSOD/PSF, respectively. The two sodalite infused membranes have shown enhanced mechanical properties and permeability during treatment of phenol in synthetic wastewater.

Evaluation of silica sodalite infused polysulfone mixed matrix membranes during H2/CO2 separation

Global warming and environmental degradation have stimulated the drive towards the capture of large point source carbon emissions and reducing high energy intensity of industrial processes. Mixed membranes infused with high porosity silica sodalite are potential useful for pre-combustion CO2 capture. However, development of high quality mixed matrix membranes is a challenge. In this study, silica sodalite (SSOD) infused polysulfone (PSF) membranes were developed and evaluated for pre-combustion CO2 capture. The SSOD was obtained via topotactic conversion of layered silicates; and the membrane was prepared using the phase inversion method. The physicochemical nature of the SSOD and the SSOD/PSF was checked using XRD, SEM, and N2 physisorption at 77 K. Single gas permeation used to check membrane quality. N2 physisorption shows that the SSOD possesses higher surface area of 56.56 m2/g and pore volume of 0.181 cm3/g, when compared to that of the hydrothermally-synthesized hydroxy sodalite (HSOD) crystals (surface area: 27.43 m2/g; pore volume: 0.084 cm3/g). The SSOD/PSF membrane is asymmetric with higher mechanical strength than the ordinary PSF. Loading the PSF with SSOD enhanced its H2 permeance from 4.9 × 10−7 mol/m2·s·Pa but with a decrease in H2/CO2 separation factor from 2.2 to 0.6. While the enhanced H2 permeance is attributed to the enhanced porosity of the SSOD, the ideal selectivity is low but still within the values reported in literature. Increasing the SSOD loading up to 10 wt% enhanced the quality and performance of the PSF membrane, displaying H2 permeance of 6.5 × 10−7 mol/m2·s·Pa and a separation factor of 1.1. Though results reported in this study are promising, a robust synthesis protocol that will further enhance both the H2 selectivity and H2 permeance of the membrane is required. Furthermore, more studies are required on the process optimization and techno-economic feasibility for pre-combustion CO2 capture.

Encapsulation of Cu nanoparticles in nanovoids of plate-like silica sodalite through interlayer condensation of Cu2+ ion-exchanged layered silicate RUB-15.

The interlayer condensation of layered silicates is a unique method for synthesizing zeolites and is effective for the introduction of metal species into platy zeolite frameworks. Layered silicate RUB-15 is a useful starting material because metal ions can be introduced between the layers and zeolite frameworks (all-silica SOD-type zeolite; silica sodalite) can be formed through interlayer condensation. In this study, Cu ions were intercalated into layered silicate RUB-15, and metal Cu nanoparticles were formed in the nanovoids of silica sodalite by a simple heat treatment in an inert atmosphere. Both interlayer condensation and the reduction of Cu2+ ions were confirmed by in situ XRD analysis performed during the heat treatment. The residual interlayer tetramethylammonium ions played two roles: the control of stacking sequence in the interlayer condensation and the reduction of Cu2+ ions. The formed Cu nanoparticles were stable in air atmosphere because of their confinement in the nanovoids of the sodalite frameworks.

Topotactic conversion of layered silicate RUB-15 to silica sodalite through interlayer condensation in N-methylformamide.

Silica sodalite was obtained using topotactic conversion of layered silicate RUB-15 through stepwise processes that consisted of the control of stacking sequence of the layers, interlayer condensation by refluxing, and elimination of intercalated guest species. The interlayer condensation of RUB-15, in which acetic acid was pre-intercalated between the layers to control the stacking sequence, afforded a sodalite framework containing organic guest species by refluxing in N-methylformamide (NMF). The pre-intercalated acetic acid molecules were largely replaced with NMF. This formation process of silica sodalite containing large amounts of intercalated organic guest species is in clear contrast to the previously reported process that used direct calcination of an intercalation compound of layered RUB-15 accommodating acetic acid between the layers. Calcination of the condensed product provided sodalite with fewer defects than the directly calcined product, thus indicating the advantage of the stepwise process. The method reported here is useful for the preparation of pure silica sodalite with relatively low defects and plate-like morphology.

Hydrous layer silicates as precursors for zeolites obtained through topotactic condensation: a review

In the search for new synthesis routes of zeolites, the topotactic condensation of hydrous layer silicates shows promising results in generating novel zeolite materials with distinct framework types which might have new, interesting properties as, e.g ., molecular sieves or form-selective catalysts. In order to manipulate and optimise the condensation process detailed knowledge of the crystal structures is essential. The layer silicates considered here are of a special type and can be designated as high-silica hydrous layer silicates , HLSs. The structures consist of a tetrahedral layer of interconnected [SiO4]-units containing equal numbers of terminal silanol/siloxy groups on either side of the layer and of an inter-layer region where cations of low charge density (predominantly organic cations) and water molecules are located. A topotactic condensation of the layers performed at temperatures of around 500°C with simultaneous expulsion of the inter-layer constituents is able to form fully condensed, uninterrupted framework silicates. The topotactic conversion has so far been described rarely in comparison to the classical hydrothermal synthesis of zeolites. Nevertheless, several hydrous layer silicates with different layer topologies were successfully converted into zeolites of different framework types using this synthesis route: CAS (type material: EU-20, EU-20b), CDO (type material: CDS-1), FER (type material: siliceous ferrierite), MWW (type material: MCM-22), NSI (type material: NU-6(2)), RRO (type material: RUB-41), RWR (type material: RUB-24), SOD (type material: guest-free silica sodalite). Thereby, four new zeolite framework types were obtained which have not been synthesized, so far, by direct hydrothermal synthesis (CDO, NSI, RRO, RWR). This review gives an overview on the hydrous layer silicates being structurally characterized in detail, on the condensation process and on some properties of the resulting zeolite materials.

The unusual thermal expansion of pure silica sodalite probed by in situ time-resolved synchrotron powder diffraction

The thermal behaviour of a pure silica sodalite containing trioxane was studied using the in situ synchrotron X-ray powder-diffraction technique. Rietveld refinements show that temperature-induced transformations can be schematized into three main steps: (1) The relaxation of the host–guest interactions between trioxane and the surrounding framework in the 25–200 °C temperature range determines a regularization in the 6-membered rings and, consequently, a process of expansion. (2) The cell volume remains constant until 380 °C and then starts to contract when template molecule decomposition occurs. (3) When the trioxane molecule decomposition and expulsion process is completed at above 760 °C, unit cell volume contraction cannot be fully justified by the negligible mass loss observed on the TG curves, thus suggesting a negative thermal expansion (NTE) process. This behaviour is unusual for sodalite-type materials which typically show positive thermal expansion upon heating, thus indicating that the presence of organic molecules instead of metal ions in the zeolite cages strongly controls the thermal expansion mechanism.

Role of Acidic Pretreatment of Layered Silicate RUB-15 in Its Topotactic Conversion into Pure Silica Sodalite

Topotactic conversion of crystalline layered silicates into zeolite provides an opportunity to create new chemical compositions, framework types, and macroscopic morphologies that are difficult to achieve by conventional hydrothermal synthesis. We have recently reported the successful synthesis of pure silica sodalite with a unique sheet-like morphology from layered silicate RUB-15 occluding interlayer TMA+ cations. Pretreatment of RUB-15 with acetic acid was found to be crucial for topotactic dehydration–condensation between the silicate layers upon heating. In this study, a homologous series of carboxylic acids of varying concentrations is examined for their capability to generate an ordered intermediate state, and important factors for topotactic conversion are determined. Both length of the alkyl chains and concentration of the carboxylic acids strongly affected the crystallinity of the products, and well-crystallized sodalite was obtained using either acetic or propionic acid. Transmission electron m...

Synthesis and characterization of mesoporous silicon directly from pure silica sodalite single crystal

Mesoporous silicon granules with high surface area were synthesized directly from pure silica sodalite single crystals, with the starting shape retained. The sodalite single crystals were reduced by a magnesiothermal process in vacuum at 630 °C. The X-ray diffraction patterns indicate the presence of crystal silicon. Transmission electron microscopy studies reveal that the obtained silicon granules are composed of a monocrystalline surface with an island-like mesoporous internal structure. The results of N2 adsorption and desorption analysis indicate that the surface area is around 308 m2 g−1 and the single point pore volume is 0.37 cm3 g−1. The photoluminescence emission centered at 2.7 eV may be due to both an oxidized surface and quantum confinement effects. These results reveal that the silicon granules possess a different microstructure from those of etched silicon films. The present synthetic design correlates the microporous zeolite and mesoporous silicon together and gives a new way for enlarging the structural diversity of porous silicon crystal.

The Synthesis, Full Characterisation and Utilisation of Template‐Free Silica Sodalite, a Novel Polymorph of Silica

Empty glass: Subjecting ethylene glycol silica sodalite to heat (680 degrees C) under a nitrogen atmosphere (i) successfully removes the templating agent to give cubic silica sodalite, which, upon consequent heating under an oxygen atmosphere (ii), transforms into a rhombohedral form of the empty sodalite, in effect a novel polymorph of silica.

Silica Sodalite without Occluded Organic Matters by Topotactic Conversion of Lamellar Precursor

Novel pure silica sodalite with hollow sodalite-cages has been synthesized for the first time by topotactic conversion of layered silicate (RUB-15) precursor. This success has been achieved by stepwise syntheses from silicate monomers, through clusters and layers, to microporous crystals. The pretreatment of layered silicate with small carboxylic acids before conversion is a crucial step. The obtained sodalite possesses accessible micropores, as confirmed by physical adsorption of hydrogen molecules. This plate-like silica sodalite would be very promising as fillers in mixed-matrix membranes for hydrogen separation.

Preparation and characterization of sodium-free nanocrystalline sodalite

Zeolitic membranes based on the sodalite structure are of special interest for the separation of very small atoms and molecules (He, H 2, H 2O, NH 3). The two-step technique for the preparation of zeolitic membranes requires first the synthesis of suitable nanocrystals which act as seed crystals in the second step, the preparation of membrane. This work deals with the possibilities of synthesizing crystalline nanoparticles of pure silica sodalites and of aluminosilicate sodalites with a high Si:Al ratio. In the case of silica sodalites prepared with different neutral organic molecules as structure-directing agents, preparation of nanocrystals proved difficult and was possible only with low yields in a tedious process. With the tetramethylammonium cation (TMA) as structure-directing agent, aluminosilicate sodalite with idealized framework Si:Al ratio of 5:1 can be obtained as colloidal suspensions of nanocrystalline sodalite from a clear solution. By changing the reaction conditions from hydrothermal to an open reaction system, it is possible to generate sodalite nanocrystals in high yield. The characterization of these nanoparticles was done via dynamic light scattering, X-ray powder diffraction and high resolution scanning electron microscopy. The aluminosilicate sodalite nanocrystals thus produced can be used as seed crystals in the preparation of silica sodalite crystals with varying Si:Al ratios.

Solvothermal synthesis of germanosilicate-sodalite and silica-sodalite: Effects of water, germanium and fluoride

The crystallization of silica-sodalite ( SOD) in ethylene glycol solutions at 453 K has been investigated in the absence and presence of water, germanium dioxide and ammonium fluoride. In the systems studied, water at small amounts acts as an additional solvation agent to ethylene glycol, and does not significantly affect sodalite crystallization. At high contents that exceed the molar values equivalent to SiO 2, water privileges a formation of the most dense crystalline silica phase, α-quartz. In contrast, presences of germanium and fluoride species favor the crystallization of silica-based materials having the SOD framework structure, which possesses a lower framework density than quartz. An interplaying relationship of these three species has been found and discussed.

Normal mode approach for predicting the mechanical properties of solids from first principles: Application to compressibility and thermal expansion of zeolites

We present a method for analyzing the mechanical properties of solids, based on normal modes and their coupling to lattice strains. This method was used to study elastic compression and thermal expansion of zeolites, with parameters calculated from density functional theory. We find in general that the bulk modulus can be divided into two contributions: a positive term arising from compression without internal relaxation, and a negative term from coupling between compression and internal vibrational modes. For silica polymorphs, the former term varies little among the phases studied, reflecting the intrinsic rigidity of $\mathrm{Si}{\mathrm{O}}_{4}$ tetrahedra. In contrast, the latter term varies strongly from one polymorph to the next, because each polymorph exhibits different symmetry constraints on internal vibrations and their couplings to lattice strains. Typically only a few normal modes contribute to the bulk modulus. To facilitate parametrization of this normal mode model, we constructed a simplified classical spring-tetrahedron model for silica. After fitting to properties of silica sodalite, this model reproduces cell volumes and predicts bulk moduli of $\ensuremath{\alpha}$-cristobalite and silica zeolites CHA, LTA, and MFI. We incorporated anharmonic effects into the theory, allowing the calculation of the thermal expansion coefficient. The resulting expression provides a generalization of classical Gr\"uneisen theory, taking into account additional anharmonicities. This method was used to study thermal expansion of fcc aluminum and an aluminosilica sodalite, yielding good agreement with experiment.

Effect of cation distribution on self-diffusion of molecular hydrogen in Na3Al3Si3O12 sodalite: A molecular dynamics study

The diffusion of hydrogen in sodium aluminum sodalite (NaAlSi-SOD) is modeled using classical molecular dynamics, allowing for full flexibility of the host framework, in the temperature range 800-1200 K. From these simulations, the self-diffusion coefficient is determined as a function of temperature and the hydrogen uptake at low equilibrium hydrogen concentration is estimated at 573 K. The influence of the cation distribution over the framework on the hydrogen self-diffusion is investigated by comparing results employing a low energy fully ordered cation distribution with those obtained using a less ordered distribution. The cation distribution is found to have a surprisingly large influence on the diffusion, which appears to be due to the difference in framework flexibility for different cation distributions, the occurrence of correlated hopping in case of the ordered distribution, and the different nature of the diffusion processes in both systems. Compared to our previously reported calculations on all silica sodalite (all-Si-SOD), the hydrogen diffusion coefficient of sodium aluminum sodalite is higher in the case of the ordered distribution and lower in case of the disordered distribution. The hydrogen uptake rates of all-Si-SOD and NaSiAl-SOD are comparable at high temperatures (approximately 1000 K) and lower for all-Si-SOD at lower temperatures (approximately 400 K).

Density Functional Theory Study of Silica Zeolite Structures: Stabilities and Mechanical Properties of SOD, LTA, CHA, MOR, and MFI

We have investigated various silica zeolites using density functional theory with periodic supercells, plane waves, and pseudopotentials. These zeolitic phases include silica sodalite, chabazite, mordenite, silica LTA, and silicalite. Atom-level geometries, elastic properties, and cohesive energies are presented. Although the zeolites exhibit a wide range of Si−O−Si angles and densities, the cohesive energies remain nearly constant. The elastic properties vary significantly from one phase to another, and in some cases, large elastic anisotropies are observed.

Diffusion of inert gases in silica sodalite: Importance of lattice flexibility

It is known that some zeolites are able to adsorb sorbates with diameters larger than their pore size. This ability is usually explained by the flexibility of zeolite lattices. In this paper we quantify this explanation by incorporating lattice flexibility into transition state theory to compute transport rates of inert gas molecules (Ne, Ar and Kr) through narrow windows of silica sodalite cages. We find that the diffusion rates obtained with the flexible zeolite lattice are in much better agreement with experiment than those with a rigid lattice, as stretching of the zeolite window considerably reduces the activation barrier.

An in situ infrared spectroscopic investigation of the pyrolysis of ethylene glycol encapsulated in silica sodalite

The thermal stability and pyrolysis of ethylene glycol (EG) encapsulated in the sodalite cages of all-silica sodalite were studied by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and transmission infrared spectroscopy. Evidence for the presence of encapsulated CO 2 formed as a result of partial decomposition of EG molecules was observed starting at about 600 K. Complete, irreversible pyrolysis of the EG occurred between 675 and 775 K. After treatment at 775 K, the CO 2 remained encapsulated in the sodalite framework, even though there were spectroscopic indications that the pyrolysis caused a disordering of the sodalite framework. There appeared to be a temperature dependence of the conformational interactions of the EG OH groups up to 600 K, which was mainly manifested as a weakening of intramolecular hydrogen bonding. The only detectable encapsulated products of the EG decomposition in an inert (N 2 or Ar) environment were CO 2 and a carbonaceous (coke- or soot-like) residue. There was no evidence of other encapsulated products, such as CO, H 2, H 2O, or light hydrocarbons.

Compression mechanism of cubic silica sodalite [Si12O24]: a first principles study of theIm3̅mtoI4̅3mphase transition

AbstractThe high pressure behaviour of cubic silica sodalite has been investigated byab initiocalculations based on density functional theory. The experimentally observed phase transition from the fully-expanded ideal sodalite framework (space groupIm3̅m) to a collapsed framework with space groupI4̅3mcould be successfully reproduced to appear at 0.12 GPa. This transition is discontinuous. The mechanism of the transition can be understood in terms of a tilt of the framework and of deformations of the SiO4-tetrahedra. Discontinuities of the enthalpy, cell volume, Si-O bond lengths and angles at 1.15 and 3.01 Gpa point at further possible pressure-induced iso-symmetric phase transitions in the space groupI4̅3m.