Silicate Framework Research Articles

Inorganic Polymers From CaO-FeOx-SiO2 Slag: The Start of Oxidation of Fe and the Formation of a Mixed Valence Binder

Belonging to the family of alternative cementitious materials, inorganic polymers are rising in importance because of the drive to decrease CO2 emissions of concrete production. A synthetic Fe-rich slag resembling industrial copper or lead slags, was mixed with a sodium silicate activating solution. 57Fe Mossbauer spectra analyses indicate that the oxidation reactions are taking place simultaneously with the polymerization reactions. The slag contains Fe2+ states and a small amount of Fe3+. During polymerization a new octahedral Fe2+ state is formed, while oxidation is manifested through the appearance of an additional Fe3+ state. The reactions continue after setting, lowering the relative contributions of the slag in the Mossbauer and FTIR spectra of the samples. The Na+/Fe3+ molar ratio in the mixture that makes up the binder after 28 days is approximately 1, suggesting the participation of tetrahedral Fe3+ in the silicate framework, charge balanced by Na+.

Ceramic Mineral Waste-Forms for Nuclear Waste Immobilization.

Crystalline ceramics are intensively investigated as effective materials in various nuclear energy applications, such as inert matrix and accident tolerant fuels and nuclear waste immobilization. This paper presents an analysis of the current status of work in this field of material sciences. We have considered inorganic materials characterized by different structures, including simple oxides with fluorite structure, complex oxides (pyrochlore, murataite, zirconolite, perovskite, hollandite, garnet, crichtonite, freudenbergite, and P-pollucite), simple silicates (zircon/thorite/coffinite, titanite (sphen), britholite), framework silicates (zeolite, pollucite, nepheline /leucite, sodalite, cancrinite, micas structures), phosphates (monazite, xenotime, apatite, kosnarite (NZP), langbeinite, thorium phosphate diphosphate, struvite, meta-ankoleite), and aluminates with a magnetoplumbite structure. These materials can contain in their composition various cations in different combinations and ratios: Li–Cs, Tl, Ag, Be–Ba, Pb, Mn, Co, Ni, Cu, Cd, B, Al, Fe, Ga, Sc, Cr, V, Sb, Nb, Ta, La, Ce, rare-earth elements (REEs), Si, Ti, Zr, Hf, Sn, Bi, Nb, Th, U, Np, Pu, Am and Cm. They can be prepared in the form of powders, including nano-powders, as well as in form of monolith (bulk) ceramics. To produce ceramics, cold pressing and sintering (frittage), hot pressing, hot isostatic pressing and spark plasma sintering (SPS) can be used. The SPS method is now considered as one of most promising in applications with actual radioactive substances, enabling a densification of up to 98–99.9% to be achieved in a few minutes. Characteristics of the structures obtained (e.g., syngony, unit cell parameters, drawings) are described based upon an analysis of 462 publications.

Theoretical study of the effect of isomorphous substitution by $$\hbox {Al}^{3+}$$ and/or $$\hbox {Fe}^{3+}$$ cations to tetrahedral positions in the framework of a zeolite with erionite topology

The isomorphous substitution of $$\hbox {Al}^{3+}$$ and/or $$\hbox {Fe}^{3+}$$ cations into the erionite zeolite framework were studied through periodic density functional theory computations. Taking as reference the Mulliken charges for siliceous framework computed in previous work (Antunez-Garcia et al. in J Mol Struct 1059:232–238, 2014), the present results show that the basicity of ERI zeolite increases when those cations are introduced into the framework. It was also observed that when at least two $$\hbox {Si}^{4+}$$ cations are isomorphically substituted by $$\hbox {Fe}^{3+}$$ in the unit cell of the erionite zeolite, it acquires magnetic properties. The results show that a specific net-spin polarization (up or down) could be correlated with particular configurations of erionite zeolite, containing ferric iron.

Synthesis and characterization of MFI-type zincosilicate zeolites with high zinc content using mechanochemically treated Si–Zn oxide composite

Modification of zeolites by the incorporation of divalent Zn in the silicate framework is attracting extensive attention because it results in higher anionic charge density and creates new active acid sites. However, it is a great challenge to incorporate Zn into the framework of highly siliceous MFI-type zeolites without Al. In this study, ball milling, a mechanochemical method, was employed to prepare Si–Zn oxide composites from mixtures of fumed silica and ZnO as the starting materials for the zeolite synthesis. The dispersion of Zn on an atomic level inside the silica matrix was realized by mechanical forces. Then, the Si–Zn oxide composites were subjected to hydrothermal treatment in the presence of an additional Si source and a structure-directing agent to synthesize MFI-type zincosilicate zeolites with high Zn contents (Si/Zn = 36.9–13.4) but negligible Al impurity (Si/Al>900). The successful incorporation of Zn into the zeolite framework was confirmed by several characterization techniques. Ion exchange experiments showed the superior selectivity and capacity of MFI-type zincosilicate zeolites for divalent cations (Co2+ as a model cation) as compared with those of aluminosilicate analogs. The mechanochemically treated Si–Zn oxide composite plays a crucial role in the synthesis of MFI-type zincosilicate zeolites with high Zn contents and minor extra-framework Zn species.

Photoluminescence and energy transfer in transparent glass-ceramics based on GdF3:RE3+ (RE = Tb, Eu) nanocrystals

In the present work, the transparent oxyfluoride glass-ceramic samples containing GdF3:RE3+ (RE = Tb, Eu) nanocrystals (nGCs) were fabricated via controlled heat-treatment of precursor xerogels prepared using a sol-gel method. The formation of GdF3 nanocrystalline phase from gadolinium(III) trifluoroacetate was verified based on XRD measurements. The average crystal sizes calculated from Scherrer formula were estimated to ∼10 nm as well as ∼6 nm for Tb3+- and Eu3+-doped samples, respectively. The optical behavior of prepared sol-gel samples was evaluated based on photoluminescence excitation (PLE) and emission spectra (PL) as well as luminescence decay analysis. Obtained samples exhibit the 5D4 → 7FJ (J = 6–3, Tb3+) and the 5D0 → 7FJ (J = 0–4, Eu3+) emission bands recorded within the visible spectral area under excitation at near-UV (393 nm (Eu3+), 351, 369, 378 nm (Tb3+)) as well as middle-UV illumination (273 nm (Gd3+)). Additionally, based on recorded decay curves, the luminescence lifetimes (τm) for the 5D4 (Tb3+) and the 5D0 (Eu3+) excited states were also evaluated. In general, recorded luminescence spectra and double-exponential character of decay curves for nGCs indicate a successful migration of Tb3+ and Eu3+ dopant ions from amorphous silicate framework to low-phonon energy GdF3 nanocrystal phase.

Use of Microwaves to Activate Bentonite in the Processes of Sorption of Nickel Ions from Concentrated Aqueous Solutions

The physicochemical parameters of the process of sorption water purification from compounds of Nickelwith clay sorbent in static conditions are studied. The absorption isotherm of ions of this metal from concentratedaqueous solutions on samples of bentonite using ultrahigh-frequency irradiation (microwave) is analyzed. Mostcorrectly, it is described by the linear equation of Langmuir. It is shown that irradiation of this sorbent bymicrowaves in the process of nickel ion sorting almost 2 times increases the value of the marginal sorptioncapacity for this metal (in comparison with the method of "stimulation" - preliminary washing of bentonite withpure water under the action of microwaves). The results of the study of spent bentonite by scanning electronmicroscopy, energy dispersion and X-ray diffraction analysis indicate that the metal under action of themicrowave is deposited on the surface of the bentonite not only in the form of an adsorbed monolayer of ions, butalso in the form of a separate crystalline phase, nickel silicate. Changes in the acidity of the medium duringsorption purification under the action of microwave are observed: from pH ≈ 5.7 ... 6.5 (before exposure) to pH ≈6.7 ... 7.1 (after irradiation). Confirmed assumption about that under the action of microwaves in the aqueousmedium there is a partial destruction of the silicate framework of clay sorbents with the release of silicon ionsSiO32-. These ions undergo hydrolysis, as a result of which the pH of the solution increases. Also, the directdiscontinuity of the Si-O bonds in the near-surface groups ≡Si-OH is not excluded, which leads to an increase inthe number of "free" hydroxyl groups.

Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

This study presents the synthesis, characteristics and catalytic reactivity of sustainable bifunctional heterogeneous catalysts derived from coal fly ash-based geopolymer, particularly those with a high Ca content (C-class) fly ash. The developed catalysts were synthesized at room temperature and pressure in a simple ecologically-benign procedure and their reactivity was evaluated in the Friedel-Crafts acylation of various arenes. These catalysts can be produced with multilevel porous architecture, and a combination of acidic and redox active sites allowing their use as bifunctional catalysts. The acidic sites (Lewis and Brønsted acidic sites) were generated within the catalyst framework by ion-exchange followed by thermal treatment, and redox sites that originated from the catalytically reactive fly ash components. The developed catalysts demonstrated higher reactivity than other commonly used solid catalysts such as Metal-zeolite and Metal-mesoporous silicate, heteropolyacids and zeolite imidazole frameworks (ZIF).

Syngas production via CO2 reforming of CH4 over Ni-based SBA-15: Promotional effect of promoters (Ce, Mg, and Zr)

The promotional effect of different types of metals (Ce, Mg, and Zr) over Ni/SBA-15 which synthesized using ultrasonic co-impregnation technique were scientifically evaluated via CO2 reforming of CH4 (CRM). Characterizations including XRD, BET, FTIR, CO2-TPD were done to examine their physical attributes, metal-support interactions, and basicity properties. XRD results suggested that NiO particles were not distributed homogeneously within the confined framework of SBA-15 for Ni-Ce/SBA-15. Nevertheless, Mg and Zr promoters could effectively improve Ni dispersion over the SBA-15's siliceous framework and controlled the NiO crystallize sizes. The smallest NiO crystallite size of 9.3 nm was obtained by Ni-Zr/SBA-15. BET results verified the alteration of pore structure without changing the ordered structure of SBA-15 upon promoter addition. FTIR results suggested the partial transformation of Si–OH groups to the Si–O–X bond (X = Ce, Mg and Zr), whereas, CO2-TPD results confirmed the moderate basic sites present in Ni-Zr/SBA-15. H2-TPR evidenced the strongest metal-support interaction in Ni-Zr/SBA-15 owing to its high temperature reduction behaviour. At operating condition of P = 1.0 bar and WHSV = 15,000 mLg−1h−1, catalytic performance and stability ascended the trend of un-promoted < Ce-promoted < Mg-promoted < Zr-promoted Ni/SBA-15, in which Zr-promoted Ni/SBA-15 manifested the best catalytic activity (CO2 conversion = 93.8%; CH4 conversion = 88.3%; H2/CO ratio = 0.82). The ascendency catalytic activity and stability of Ni-Zr/SBA-15 catalyst were attributed to its favourable properties such as strong Si–O–Zr bond formation, smallest NiO crystallite size and a moderate amount of basic sites, which crucial for sintering restriction of NiO particles and carbon deposition, thus facilitated CRM reaction.

Highly dispersed molybdenum containing mesoporous silicate (Mo-TUD-1) for olefin metathesis

Abstract Employing a one-pot sol-gel synthesis technique, molybdenum with variable loadings (2–14 wt%), was successfully incorporated into a mesoporous TUD-1 silicate framework. Diffuse reflectance UV–vis and Raman spectra of samples dehydrated at reaction temperatures (450 °C) revealed the dominant presence of highly dispersed tetrahedral di-oxo (Si-O)2Mo(=O)2 species. Neither bulk nor crystalline MoO3 was evident at Mo loadings from 2 to 7 wt.% from complementary analytical techniques suggesting that a high dispersion of MoOx species is achieved by this synthesis method. Mo L-edge XANES of catalyst samples at ambient conditions and Mo K-edge XAS of catalyst samples dehydrated at the reaction temperature (450 °C) further confirm the existence of mixed tetrahedral and octahedral Mo sites. The relative population of dioxo Mo species observed in Mo-TUD-1 catalysts at various Mo loadings correlate well with the Lewis acidity and apparent TOFs (mmol propene/mol Mo/s) observed with these samples. These observations confirm that the dioxo Mo species are the active site precursors, as also reported previously with other Mo-based catalyst formulations. Compared to Mo-impregnated SiO2 (Mo/SiO2) catalyst, the Mo-TUD-1 catalysts (2–7 wt% Mo loadings) provide higher apparent TOFs. At higher Mo loadings, the fraction of MoO3 species that are Bronsted acidic in nature increases, resulting in decreased TOFs and increased catalyst deactivation due to the formation of heavier hydrocarbons that deposit on the catalyst surface. However, the metathesis activity is fully restored after simple air regeneration of the catalyst.

A study of possible extra-framework cation ordering in Pbca leucite structures with stoichiometry RbCsX2+Si5O12 (X = Mg, Ni, Cd)

Leucites are silicate framework structures with some of the silicon framework cations partially replaced by divalent or trivalent cations. A monovalent extraframework alkali metal cation is also incorporated to balance the charges. We have previously reported Pbca leucite structures with the stoichiometries Cs2X2+Si5O12 (X = Mg, Mn, Co, Ni, Cu, Zn, Cd) and Rb2X2+Si5O12 (X = Mg, Mn, Ni, Cd). These orthorhombic leucite structures have all the silicon and non-silicon framework cations completely ordered onto separate crystallographic sites. This structure has five distinct Si sites and 1 X site; there are also two distinct sites for the extra-framework Cs or Rb. We have recently synthesised leucite analogues with two different extra-framework cations, these have the stoichiometry RbCsX2+Si5O12 (X = Mg, Ni, Cd). The initial Rietveld refinements assumed 50% Cs and 50% Rb on each of the two extra-framework cation sites. The refined structures for X = Ni and Cd have (within error limits) complete extra-framework cation site disorder. However, for X = Mg there is partial ordering of the extra-framework cation sites, the site occupancies are:- Cs1 0.37(3), Rb1 0.63(3), Cs2 0.63(3), Rb2 0.37(3).

Bubble-Manipulated Local Drug Release from a Smart Thermosensitive Cerasome for Dual-Mode Imaging Guided Tumor Chemo-Photothermal Therapy.

Thermosensitive liposomes have demonstrated great potential for tumor-specific chemotherapy. Near infrared (NIR) dyes loaded liposomes have also shown improved photothermal effect in cancer theranostics. However, the instability of liposomes often causes premature release of drugs or dyes, impeding their antitumor efficacy. Herein, we fabricated a highly stable thermo-responsive bubble-generating liposomal nanohybrid cerasome with a silicate framework, combined with a NIR dye to achieve NIR light stimulated, tumor-specific, chemo-photothermal synergistic therapy.Methods: In this system, NIR dye of 1,1'-Dioctadecyl-3,3,3',3'- Tetramethylindotricarbocyanine iodide (DiR) with long carbon chains was self-assembled with a cerasome-forming lipid (CFL) to encapsulate ammonium bicarbonate (ABC), which was further used for actively loading doxorubicin (DOX), affording a thermosensitive and photosensitive DOX-DiR@cerasome (ABC).Results: The resulting cerasome could disperse well in different media. Upon NIR light mediated thermal effect, ABC was decomposed to generate CO2 bubbles, resulting in a permeable channel in the cerasome bilayer that significantly enhanced DOX release. After intravenous injection into tumor-bearing mice, DOX-DiR@cerasome (ABC) could be efficiently accumulated at the tumor tissue, as monitored by DiR fluorescence, lasting for more than 5 days. NIR light irradiation was then performed at 36h to locally heat the tumors, resulting in immediate CO2 bubble generation, which could be clearly detected by ultrasound imaging, facilitating the monitoring process of controlled release of the drug. Significant antitumor efficacy could be obtained for the DOX-DiR@cerasome (ABC) + laser group, which was further confirmed by tumor tissue histological analysis.

Meteoric Water and Salt-Dome-Related Diagenesis in Tertiary Turbidite Reservoirs from the EspÍrito Santo Basin, Brazil

Abstract Quantitative petrography and stable-isotope and fluid-inclusion analysis revealed that the diagenetic evolution of two Tertiary turbidite sandstone reservoirs from the offshore part of the Espirito Santo Basin, eastern Brazil, was influenced by the flow of meteoric water and salt-dome-related fluids, which had different impacts on their quality. Influx of meteoric water during early burial, in response to relative sea-level fall, resulted in extensive kaolinization and dissolution of framework silicate grains. Mesogenetic compactional fluids were progressively modified by the proximity of salt domes, which led to ubiquitous feldspar albitization and localized quartz, calcite, and saddle-dolomite precipitation. Fluid inclusions in quartz overgrowths indicate that the precipitating fluids had salinities predominantly in the range 8–13 wt% NaCl equivalent and temperatures largely in the 100–155°C range (higher than present-day formation temperatures—105° up to 115°C). The distribution of feldspar albitization suggests that the fracture systems along the margins of the salt domes acted as preferential pathways for such hot brines. However, the influence of the salt domes on the diagenetic processes of the reservoirs was relatively mild, despite their proximity, because pore-filling neoformed illite is absent, and occurrence of quartz cement is limited in the sandstones, which may be related to the late burial of the reservoirs and the intermittent behavior of the salt-dome-associated fracture systems as effective conduits for reactive fluids. We expect that this paper may contribute to the understanding and prediction of diagenesis and reservoir properties of turbidite sandstones influenced by meteoric and salt-dome-related fluids in offshore Espirito Santo Basin and in other similar areas.

A structure hierarchy for silicate minerals: sheet silicates

AbstractThe structure hierarchy hypothesis states thatstructures may be ordered hierarchically according to the polymerisation of coordination polyhedra of higher bond-valence. A hierarchical structural classification is developed for sheet-silicate minerals based on the connectedness of the two-dimensional polymerisations of (TO4) tetrahedra, where T = Si4+plus As5+, Al3+, Fe3+, B3+, Be2+, Zn2+and Mg2+. Two-dimensional nets and oikodoméic operations are used to generate the silicate (sensu lato) structural units of single-layer, double-layer and higher-layer sheet-silicate minerals, and the interstitial complexes (cation identity, coordination number and ligancy, and the types and amounts of interstitial (H2O) groups) are recorded. Key aspects of the silicate structural unit include: (1) the type of plane net on which the sheet (or parent sheet) is based; (2) the u (up) and d (down) directions of the constituent tetrahedra relative to the plane of the sheet; (3) the planar or folded nature of the sheet; (4) the layer multiplicity of the sheet (single, double or higher); and (5) the details of the oikodoméic operations for multiple-layer sheets. Simple 3-connected plane nets (such as 63, 4.82and 4.6.12) have the stoichiometry (T2O5)n(Si:O = 1:2.5) and are the basis of most of the common rock-forming sheet-silicate minerals as well as many less-common species. Oikodoméic operations, e.g. insertion of 2- or 4-connected vertices into 3-connected plane nets, formation of double-layer sheet-structures by (topological) reflection or rotation operations, affect the connectedness of the resulting sheets and lead to both positive and negative deviations from Si:O = 1:2.5 stoichiometry. Following description of the structural units in all sheet-silicate minerals, the minerals are arranged into decreasing Si:O ratio from 3.0 to 2.0, an arrangement that reflects their increasing structural connectivity. Considering the silicate component of minerals, the range of composition of the sheet silicates completely overlaps the compositional ranges of framework silicates and most of the chain-ribbon-tube silicates.

Understanding the Stability of Salt-Inclusion Phases for Nuclear Waste-forms through Volume-based Thermodynamics

Formation enthalpies and Gibbs energies of actinide and rare-earth containing SIMs with silicate and germanate frameworks are reported. Volume-based thermodynamics (VBT) techniques complemented by density functional theory (DFT) were adapted and applied to these complex structures. VBT and DFT results were in closest agreement for the smaller framework silicate structure, whereas DFT in general predicts less negative enthalpies across all SIMs, regardless of framework type. Both methods predict the rare-earth silicates to be the most stable of the comparable structures calculated, with VBT results being in good agreement with the limited experimental values available from drop solution calorimetry.

Tunable mesoporosity and hydrophobicity of natural rubber/hexagonal mesoporous silica nanocomposites

Polymer/silica nanocomposites with diverse mesoporosity and hydrophobic properties have actual and potential applications in the area of catalysis, adsorption and drug delivery. The present work reports a simple but efficient approach to tune the mesostructure and hydrophobicity of natural rubber (NR)/hexagonal mesoporous silica (HMS) nanocomposites synthesized via the in situ sol-gel technique in the presence of different primary amines (C n H 2 n +1 NH 2 , n = 8, 10, 12, 14 and 16) as structural templating agents. The change in the mesostructure ordering and textural properties of the NR/HMS nanocomposites with different template sizes was similar to that for the pure silica HMS series. Powder X-ray diffraction and transmission electron microscopy analyses revealed an expansion of the hexagonal unit cell and channel wall thickness of the nanocomposites due to the incorporated rubber molecules. Using amine templates with longer alkyl chains provided NR/HMS materials with a higher NR content at 13.7–15.6 wt% but decreased the rubber phase dispersion and hydrophobic properties. X-ray photoelectron spectroscopy indicated that the amount of NR exposed at the composite's surface was 7.99–9.48 wt%, while the remaining NR was incorporated into the mesostructured silicate framework and/or entrapped in the mesopores. The hydrophobic interaction between the NR molecules and the alkyl chains of primary amine template was probably a crucial factor that determined the rubber phase dispersion, and so the hydrophobic character, in the NR/HMS nanocomposites. • A series of NR/HMS nanocomposites were synthesized via in situ sol-gel method. • Their mesoporosity and hydrophobicity varied with type of primary amine template. • Using longer amine templates enhanced the rubber content but lowered dispersion. • Using shorter amine templates gave the materials with more hydrophobic surface.

Evidence of shock‐induced vaporization of matrix to form porosity in Baszkówka, a porous L5 chondrite

AbstractBaszkówka is an equilibrated, apparently low‐shock, unusually porous chondrite. Some earlier studies were undertaken to understand whether the porosity in Baszkówka, and similar porous chondrites, is a relic of a primordial feature or rather the effect of atypical reprocessing on the parent body. Neither of the studies reconstructed the accurate thermal and deformational evolution of chondrites, however, while it is known that shock‐induced compaction is the main means to affect chondritic porosity. Here we use a combination of 3‐D and 2‐D petrographic examination to understand how the evolution of pores correlates with thermal and shock history recorded in the Baszkówka chondrite. The grain framework silicates in Baszkówka contain healed shock fractures—a clear recorder of significant shock process and postshock annealing. Simultaneously, metal grains do not exhibit any preferred orientation or fabric, which would be expected to develop in response to the deformation as recorded by silicates. We interpret this as evidence for re‐agglomeration and annealing of shocked material. Pore spaces in Baszkówka are connected and decorated by fine‐grained plagioclase‐dominated mass and bulky euhedral olivine crystals, which exhibit growth steps on crystal surfaces. The euhedral olivine must have formed owing to the condensation of a vapor, while plagioclase most likely crystallized from melted chondritic matrix. During the shock event, fine‐grained matrix in Baszkówka was melted and vaporized. Vapor expansion added to ballistic velocity led to ejection and opening of the pore spaces. After re‐agglomeration in a hot ejecta blanket the rock was annealed, melted material circulated in created pore spaces and vapor condensed.

Novel ionic liquid-templated ordered mesoporous aluminosilicates: Synthesis, characterization and catalytic properties

Abstract Highly crystalline ordered mesoporous aluminosilicates with hexagonal AlIITM-41 and cubic AlIITM-48 pore symmetries with varying silicon-to-aluminium ratios were hydrothermally synthesized, for the first time, using long-chain ionic-liquid (IL) such as 1-hexadecyl-3-methylimidazolium chloride (HDMIC), as structure directing agent. The prepared materials were systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, BET, TEM and XRF. In addition, the extent of aluminium incorporation and the nature of acid sites were deduced from 27 Al MAS-NMR and NH 3 -TPD measurements. The structural and physico-chemical properties of both AlIITM-41 and AlIITM-48 were compared with analogous AlMCM-41 and AlMCM-48, respectively prepared using hexadecyltrimethylammonium bromide (CTAB). It was found that all the ionic liquid-templated materials, viz., AlIITM-41 and AlIITM-48, and exhibited large surface area, high crystallinity and thicker pore walls. The observed superior orderness of AlIITM-41 and AlIITM-48 could attribute to a well distributed positive charge and π-π stacking of aromatic imidazolium head group of ionic-liquid. In addition, it also assisted in the incorporation of all the aluminium species exclusively in the tetrahedral silicate framework even after the calcination as confirmed by 27 Al MAS NMR. AlIITM-41 and AlIITM-48 possess more medium and strong Bronsted acid sites due to their thicker walls, high crystallinity and presence of tetrahedral aluminium in the framework, due to which they exhibited higher catalytic activity towards tertiary butylation of phenol with a good Para tertiary butyl phenol selectivity compared to commonly used aluminosilicates, H-AlMCM-41 and H-AlMCM-48.

Mechanochemically assisted hydrothermal synthesis of Sn-substituted MFI-type silicates

ABSTRACTSubstitution of Al atoms in a zeolite framework by catalytic metal atoms has attracted considerable attention because the catalytic behavior can be tuned by the substituted atoms. In the present study, Sn-substituted MFI-type silicates were synthesized using a hydrothermal reaction of an amorphous Si-O-Sn precursor prepared by mechanochemical grinding of SiO2 and Sn(OH)4. The mechanochemical treatment was found to be a key technique for obtaining the amorphous Si-O-Sn precursor, where tetrahedral Sn4+ species were incorporated into the amorphous matrix. The Sn content in the framework of the MFI-type silicates was successfully controlled by the initial HCl/Si molar ratio of the hydrothermal procedures. Optical reflectance measurements revealed that the Sn4+ ions were dispersedly incorporated into the silicate framework while preserving the initial tetrahedrally coordinated species. Infrared results imply that the resulting Sn-substituted MFI-type silicate has Brønsted acid character. Precise control of the Brønsted and Lewis acid properties by Sn doping is a promising approach to the development of novel types of zeolite-based catalytic materials.

Novel two-step process for synthesising β-SiC whiskers from coal fly ash and water glass

Highly crystalline, high-purity β-SiC whiskers were successfully synthesised from a mixed sol of coal fly ash (CFA) and water glass (a silicon resource), and activated carbon (a carbon source) in a carbothermic reduction. The efficiency of the process is over 70%. The alkali activation effects of the water glass on CFA were characterised by FTIR and MAS-NMR. In the activation reaction, silicate frameworks of water glass and CFA became connected to form a large network, producing a stable, uniform sol system. Experiments and thermodynamic analyses were used to study the effects of Na2O, Al2O3, and Fe2O3 on the synthesis of β-SiC whiskers, revealing that Na2O does not affect the synthesis process while Al2O3 and Fe2O3 promote the elongation of the SiC whiskers. The results of this study may not only help to reduce the production cost of SiC whiskers but also allow value to be extracted from waste.

Implications of meso- to micro-scale deformation for fault sealing capacity: Insights from the Lenghu5 fold-and-thrust belt, Qaidam Basin, NE Tibetan Plateau

As faults can be barriers to or conduits for fluid flow, it is critical to understand fault seal processes and their effects on the sealing capacity of a fault zone. Apart from the stratigraphic juxtaposition between the hanging wall and footwall, the development of fault rocks is of great importance in changing the sealing capacity of a fault zone. Therefore, field-based structural analysis has been employed to identify the meso-scale and micro-scale deformation features and to understand their effects on modifying the porosity of fault rocks. In this study, the Lenghu5 fold-and-thrust belt (northern Qaidam Basin, NE Tibetan Plateau), with well-exposed outcrops, was selected as an example for meso-scale outcrop mapping and SEM (Scanning Electron Microscope) micro-scale structural analysis. The detailed outcrop maps enabled us to link the samples with meso-scale fault architecture. The representative rock samples, collected in both the fault zones and the undeformed hanging walls/footwalls, were studied by SEM micro-structural analysis to identify the deformation features at the micro-scale and evaluate their influences on the fluid flow properties of the fault rocks. Based on the multi-scale structural analyses, the deformation mechanisms accounting for porosity reduction in the fault rocks have been identified, which are clay smearing, phyllosilicate-framework networking and cataclasis. The sealing capacity is highly dependent on the clay content: high concentrations of clay minerals in fault rocks are likely to form continuous clay smears or micro- clay smears between framework silicates, which can significantly decrease the porosity of the fault rocks. However, there is no direct link between the fault rocks and host rocks. Similar stratigraphic juxtapositions can generate fault rocks with very different magnitudes of porosity reduction. The resultant fault rocks can only be predicted only when the fault throw is smaller than the thickness of a faulted bed, in which scenario self-juxtaposition forms between the hanging wall and footwall.