Aluminosilicate Framework Research Articles

Study on the Inhibition Effect of Fly Ash on Alkali–SilicaReaction and Its Influence on Building Energy Performance

Abstract: Cracks and other defects in concrete will affect its durability, thermal insulation effect, and energy consumption. ASR is one of the common causes of concrete cracks. In this study, mortar specimens modified with fly ash were prepared using the mortar bar rapid method, and the inhibition effect of ASR in two alkali environments and the building energy efficiency characteristics were comparatively analyzed. SEM, EDS, and XRD were used to analyze the microstructure, elemental distribution, and products in the specimens’ interfacial transition zone comparatively. The results show that a replacement amount of 20–30% fly ash can restrain ASR expansion and maintain high mechanical strength. In both alkaline environments, K and Al are enriched in the interface transition zone and combine with SiO2 and Al2O3 to form a stable framework aluminosilicate mineral. In addition to the inhibition effect of fly ash on ASR, the external wall heat dissipation flux decreased from 132.6 W/m2 to 117.6 W/m2, a decrease of 11.3%, and the overall envelope heat dissipation flux decreased by 9.2%, significantly reducing building energy consumption. This study provides a new perspective for the development of building energy-saving materials and helps green buildings and sustainable development.

MER Zeolite with Remarkable Pb2+ and Cd2+ Removal Capability Cost-Effectively Synthesized from Postprocessed Natural Stellerite.

MER zeolite, a low-silica zeolite with an 8-membered ring aluminosilicate framework, has been recognized as a promising material in sorption, separation, and ion-exchange applications. Herein, we developed a cost-effective and rapid method to convert parent zeolite H-STI, which was derived from natural stellerite, into MER zeolite through interzeolite conversion with a crystallization time of 8 h. This MER zeolite exhibits high efficiency in removing Pb2+ and Cd2+ from simulated heavy metal wastewater over a pH range of 3-8. It also shows excellent selectivity in the presence of competitive cations, including Na+, K+, Ca2+, Mg2+, Zn2+, Cu2+, and Co2+. At 25 °C, with a MER-S dosage of 1/3000 g·mL-1 for Pb2+ and 1/500 g·mL-1 for Cd2+, the removal efficiencies were 99.7 and 99.9%, respectively. The distribution coefficients were 1097 L·g-1 for Pb2+ and 550 L·g-1 for Cd2+, and the sorption capacities reached 513 mg·g-1 for Pb2+ and 171 mg·g-1 for Cd2+, indicating that the product MER zeolite is one of the highest sorbents for Pb2+ and Cd2+ reported for zeolitic materials. The sorption for Pb2+ and Cd2+ both follows the chemisorption-dominated mechanism, driven by the ion-exchange process between the K+ in the channels MER-S and the Pb2+ or Cd2+ in solution. This work highlights the potential of rapidly synthesized MER zeolite for the effective removal of heavy metal cations, emphasizing its performance and practical applicability.

Effect of temperature and extraframework cation type on CHA framework flexibility

The sorption properties of zeolites are controlled by several factors, i.e. Si/Al ratio of the aluminosilicate framework [AlSiO4]-, the type and position of the extraframework (EF) cations, and the applied temperature. Here we investigate the flexibility of CHA framework as a function of EF cation-content and temperature (20–350 °C). Two CHA forms (Na- and Cu-CHA) with Si/Al = 2 were analysed. The main objectives were: (i) to shed light on the HT behaviour of Na-CHA, for which contrasting results exist in literature; (ii) define the role of temperature and EF cation-type in the response to the heating stimuli. We show that at 75 °C, Na-CHA undergoes a severe contraction of the unit-cell volume (-12%) accompanied by a symmetry lowering (R-3m to I2/m). The transformation is reversible, if the dehydrated Na-CHA is exposed to ambient conditions. In contrast, Cu-CHA experiences a significant different dehydration path, which involves minor changes of the CHA framework, and a net positive thermal-expansion after dehydration. The implications of the observed transformations for gas separation processes are finally discussed.

Crystal Chemistry and Refined Formula of Tounkite

New data on the crystal structure and isomorphism of extra-framework components in the cancrinite-group mineral tounkite have been obtained using chemical and single-crystal X-ray diffraction data, as well as infrared, Raman, ESR, UV–Vis–near-IR absorption and photoluminescence spectroscopy methods. The crystal structure of tounkite is based on the aluminosilicate framework formed by the САСАСВСВСАСВ stacking sequence with ordered Si and Al atoms The framework hosts Losod and liottite cages as well as columns of cancrinite cages. It is shown that tounkite is characterized by wide variations of the chemical composition. Its simplified crystal–chemical formula is (Na+3.89–5.18K+0.15–1.64Ca2+2.30–2.58(Al6Si6O24)(SO42−,S52−,S4) 2−x (Cl−, HS−)1+y·nH2O (x, y, n < 1). The S2⦁− and S3⦁− radical anions may occur in some tounkite samples in minor amounts. These crystal–chemical features indicate that tounkite crystallizes under highly reducing conditions. All studied tounkite samples were polysynthetic twins. A large 10-layed cage formed at the border between twin components, connected by a rotation of 180° around the [001] axis, which may host the large S52− anion.

Negative Temperature Coefficient Properties of Natural Clinoptilolite

Negative temperature coefficient (NTC) materials are usually based on ceramic semiconductors, and electrons are involved in their transport mechanism. A new type of NTC material, adequate for alternating current (AC) applications, is represented by zeolites. Indeed, zeolites are single charge carrier ionic conductors with a temperature-dependent electrical conductivity. In particular, electrical transport in zeolites is due to the monovalent charge-balancing cations, like K+, capable of hopping between negatively charged sites in the aluminosilicate framework. Owing to the highly non-linear electrical behavior of the traditional electronic NTC materials, the possibility to have alternative types of materials, showing linearity in their electrical behavior, is very desirable. Among different zeolites, natural clinoptilolite has been selected for investigating NTC behavior since it is characterized by high zeolite content, a convenient Si/Al atomic ratio, good mechanical strength due to its compact microstructure, and low toxicity. Clinoptilolite has shown a rapid and quite reversible impedance change under heating, characterized by a linear dependence on temperature. X-ray diffraction (XRD) has been used to identify the natural zeolite, to establish all types of crystalline phases present in the mineral, and to investigate the thermal stability of these phases up to 150 °C. X-ray photoelectron spectroscopy (XPS) analysis was used for the chemical characterization of this natural clinoptilolite sample, providing important information on the cationic content and framework composition. In addition, since electrical transport takes place in the zeolite free-volume, a Brunauer–Emmett–Teller (BET) analysis of the mineral has also been performed.

Study of the adsorption of copper, nickel and zinc ions on a zeolite-containing sorbent synthesized from thermal power plant waste

The study investigated the possibility of using ash and slag waste from thermal power plants as an alternative raw material source to obtain an inexpensive zeolite-containing sorbent, which was synthesized by hydrothermal synthesis by adding 20% sodium hydroxide at a temperature of 120оC for 24 hours. Using X-ray diffraction, it was established that the synthesized material mainly consists of the framework aluminosilicate mineral hydrosodalite. Using the obtained material, the sorption of copper, zinc, and nickel cations from aqueous media was studied using the Langmuir, Freundlich, and Dubinin-Radushkevich models. The constants of these equations were determined, the values of the isobaric-isothermal potential and the free energy of ion adsorption were calculated. It has been established that the sorption of metal ions is of a physical nature. It was found that the Dubinin–Radushkevich equation better describes the process of adsorption of zinc and nickel, and the Langmuir equation better describes the sorption of copper ions. The decrease in the degree of affinity of sorbed ions to the surface of the synthesized zeolite-containing sorbent was determined as follows: . Thus, based on the obtained values of sorption of copper, zinc, and nickel ions, the fundamental possibility of using ash and slag waste as a raw material source for obtaining inexpensive and effective zeolite-containing sorbents for extracting the above metal ions from aqueous media was established.

Metal ion effect on pore size reduction in Mesoporous Aluminosilicate in the presence of TETA as a template and its catalytic performance of CO2 decomposition at lower temperature

AbstractMesoporous AlSiO4‐33 and Co2+ incorporated Co‐AlSiO4‐15 catalysts are synthesized at room temperature using Triethylenetetramine (TETA) as a template for the purpose of CO2 decomposition. The prepared materials are characterized by FT‐IR, XRD, UV‐DRS, BET, TGA, 27Al NMR and TEM. Based on XRD data, the materials are crystalline in nature. The mesoporosity of the materials with pore sizes of 33 nm (AlSiO4) and 15 nm (Co‐AlSiO4) are confirmed by BET analysis. Consequently, we designated AlSiO4 and Co‐AlSiO4 as AlSiO4‐33 and Co‐AlSiO4‐15. This lowered diameter value for Co‐AlSiO4‐15 may be due to the octahedral coordination of Co2+ ion. In the tetrahedral aluminosilicate framework, the template directs the Co2+ towards octahedral coordination. Due to the octahedral coordination, the bond angle between Si−O−Co is reduced. Due to this reduction, the pore size reduced from 33 nm (AlSiO4‐33) to 15 nm (Co‐AlSiO4‐15). These two catalysts are applied for CO2 decomposition. AlSiO4‐33 is active at 100 °C while Co‐AlSiO4‐6 is active at 150 °C. Co‐AlSiO4‐15 has produced more oxygen than AlSiO4‐33. It may be due to the Co‐AlSiO4‐15 has more bronsted acidic sites than the AlSiO4‐33. Co‐AlSiO4‐15 is reduced the activation energy 67 % while AlSiO4‐33 is reduced 78 % for CO2 decomposition at lower temperatures compare to conventional methods.

Modulating acid sites in Y zeolite for valorisation of furfural to get γ-valerolactone.

Furfural is a biomass-derived platform molecule that can be converted into a variety of useful products. Catalysts having appropriate balance between Lewis and Brønsted acid sites are suitable for valorisation of furfural. Lewis acidic metal ion incorporated zeolites were studied for this purpose. However, incorporating Lewis acidic metal ions into an alumino-silicate framework of a zeolite is a cumbersome process. Hence, an attempt has been made in this work to modulate the acid sites of Y zeolite via thermal treatment to effect controlled dealumination and use it for valorisation of furfural using isopropyl alcohol, which is a cascade transformation. The thermal treatment of zeolites changed the distribution of acid sites and increased the weak plus moderate to strong acid site ratio. Among the thermally dealuminated Y, beta and mordenite zeolites, with SiO2/Al2O3 ratio 5.2, 25 and 20, only Y zeolite could yield γ-valerolactone, the final product of the aimed cascade transformation. Complete conversion of furfural and 52% γ-valerolactone yield could be achieved under the optimized conditions using NH4Y zeolite thermally dealuminated at 700 °C (TY700). The better catalytic activity of TY700 could be correlated to a combination different factors such as framework structure, suitable weak plus moderate to strong acid site ratio, presence of both penta-coordinated and octahedral Al sites and balance between Brønsted and Lewis acid sites.

Modification of Zeolite Morphology via NH4F Etching for Catalytic Bioalcohol Conversion

AbstractVarious commercial zeolites, including FER, MOR, ZSM‐5, BEA, and FAU frameworks, were treated with NH4F aqueous solutions to study the effects of fluoride etching on different zeolite frameworks. NH4F‐treated small‐medium pore FER, MOR, and ZSM‐5 samples showed much higher mesoporosities than the untreated ones without alteration of the structural compositions and acidic properties. On the other hand, the 12‐membered ring zeolites BEA and FAU showed severe dissolution of the framework aluminosilicate structure after NH4F etching due to the high accessibility of fluoride species into the framework structures. The effect of NH4F concentration on the fluoride treatment of H‐ZSM‐5 zeolite was specifically studied. From the results, we observed that structural etching with 20 wt % NH4F was optimal for fabricating open‐pore H‐ZSM‐5 zeolite and resulted in a high mesoporosity with comparable relative crystallinity and acidity with respect to the untreated H‐ZSM‐5. The catalytic activities of the open‐pore H‐ZSM‐5 were evaluated with acid‐catalyzed methanol and bioethanol conversions. Remarkably, the hierarchical open‐pore H‐ZSM‐5 zeolite fabricated via fluoride etching exhibited an enhanced catalytic performance in bioethanol conversion with >85 % conversion over 34 h TOS and a higher catalytic stability in methanol conversion than the parent H‐ZSM‐5 (~50 % of bioethanol conversion at 34 h TOS).

Mechanism of Cs Immobilization within a Sodalite Framework: The Role of Alkaline Cations and the Si/Al Ratio

Conditioning of radioactive waste generated from the operation of medical institutions, nuclear cycle facilities, and nuclear facilities is important for the safety of the environment. One of the most hazardous radionuclides is radioactive cesium. There is a need for more effective solutions to contain radionuclides, especially cesium (Cs+). Geopolymers are promising inorganic materials that can provide a large active surface area with adjustable porosity and binding capacity. The existence of nanosized zeolite-like structures in aluminosilicate gels was shown earlier. These structures are candidates for immobilizing radioactive cesium (Cs+). However, the mechanisms of their interactions with the aluminosilicate framework related to radionuclide immobilization have not been well studied. In this work, the influence of alkaline cations (Na+ or K+) and the aluminosilicate framework structure on the binding capacity and mechanism of interaction of geopolymers with Cs+ is explored in the example of a sodalite framework. The local structure of the water molecules and alkaline ions in the equilibrium state and its behavior when the Si/Al ratio was changed were studied by DFT.

Interfacial Effect-Induced Electrocatalytic Activity of Spinel Cobalt Oxide in Methanol Oxidation Reaction.

In this study, spinel cobalt oxide (Co3O4) nanoparticles without combining with any other metal atoms have been decorated through the influence of two hard templating agents, viz., zeolite-Y and carboxy-functionalized multiwalled carbon nanotubes (COOH-MWCNT). The adornment of the Co3O4 nanoparticles, through the combined impact of the aluminosilicate and carbon framework has resulted in quantum interference, causing the reversal of signatory Raman peaks of Co3O4. Apart from the construction of small Co3O4 nanoparticles at the interface of the two matrices, the particles were aligned along the direction of COOH-MWCNT. The catalyst Co3O4-Y-MWCNT exhibited excellent catalytic activity toward the methanol oxidation reaction (MOR) in comparison to Co3O4-Y, Co3O4-MWCNT, and bared Co3O4 with the current density of 0.92 A mg-1 at an onset potential of 1.33 V versus RHE. The material demonstrated persistent electrocatalytic activity up to 300 potential cycles and 20,000 s without substantial current density loss. High surface area of zeolite-Y in combination with the excellent conductivity of the COOH-MWCNT enhanced the electrocatalytic performance of the catalyst. The simplicity of synthesis, scale-up, and remarkable electrocatalytic activity of the catalyst Co3O4-Y-MWCNT provided an effective way toward the development of anode materials for direct methanol fuel cells.

Investigation of Brønsted acidity in zeolites through adsorbates with diverse proton affinities

Understanding the adsorption behavior of base probes in aluminosilicates and its relationship to the intrinsic acidity of Brønsted acid sites (BAS) is essential for the catalytic applications of these materials. In this study, we investigated the adsorption properties of base probe molecules with varying proton affinities (acetonitrile, acetone, formamide, and ammonia) within six different aluminosilicate frameworks (FAU, CHA, IFR, MOR, FER, and TON). An important objective was to propose a robust criterion for evaluating the intrinsic BAS acidity (i.e., state of BAS deprotonation). Based on the bond order conservation principle, the changes in the covalent bond between the aluminum and oxygen carrying the proton provide a good description of the BAS deprotonation state. The ammonia and formamide adsorption cause BAS deprotonation and cannot be used to assess intrinsic BAS acidity. The transition from ion-pair formation, specifically conjugated acid/base interaction, in formamide to strong hydrogen bonding in acetone occurs within a narrow range of base proton affinities (812–822 kJ mol−1). The adsorption of acetonitrile results in the formation of hydrogen-bonded complexes, which exhibit a deprotonation state that follows a similar trend to the deprotonation induced by acetone. This allows for a semi-quantitative comparison of the acidity strengths of BAS within and between the different aluminosilicate frameworks.

Tuning Al sites in Y-zeolite for selective production of ϒ-valerolactone from levulinic acid

Converting biomass derived levulinic acid (LA) to γ-valerolactone (GVL) through catalytic transfer hydrogenation, using Lewis acidic catalysts and alcohols as hydrogen donors, is an important route for biomass valorization. Zeolites containing Lewis acidic metal ions have been widely studied for catalytic transfer hydrogenation of LA. On the other hand, zeolites themselves have Al-Lewis acid sites, inherent to their aluminosilicate framework, and these sites can be generated and tuned through simple post-synthesis methods. The present study shows that properly tuned Al sites in Y zeolites can catalyze LA to GVL conversion, and the key requirement for this conversion is creating more penta-coordinated Al sites in the catalyst. In order to establish this, a series of thermally-treated (500–800 °C) and steam-treated (500 and 700 °C) Y zeolites were prepared, characterized by X-ray diffraction, N2 adsorption, temperature programmed desorption of NH3, 27Al MAS NMR spectroscopy and pyridine adsorption – FTIR spectroscopy and then tested for LA to GVL conversion. Thermal dealumination of NH4Y zeolite at 700 °C (TY700) gave the highest percentage (21%) of penta-coordinated Al and it was found to be more selective (∼94%) in forming GVL than other catalysts studied under the optimized conditions. The turnover frequency of formation GVL, (TOFGVL) from isopropyl levulinate (IPL) on TY700 was three times higher than that of TY500 (NH4Y thermally treated at 500 °C). During the reaction, acid sites of the zeolite catalyze esterification of LA with isopropyl alcohol and hence LA is readily converted to isopropyl levulinate and then Meerwein–Ponndorf–Verley (MPV) reduction of IPL leads to the formation of isopropyl 4-hydroxy pentanoate, which undergoes lactonization to form GVL. Based on the experimental results, a plausible reaction mechanism involving the penta-coordinated Al Lewis acid sites and -Al-OH group was proposed.

A novel integrated multiphase crystal system of Kavlite for the effective and instantaneous removal of cationic and anionic dyes

Textile dye effluent pollution is one of the major threats to the environment in this generation. Various techniques have emerged to remove the textile dye effluent, but adsorption is the best process for effective removal. Aluminosilicate is one of the universal adsorbents to remove textile effluents from wastewater because of its large surface area and large availability of active/acid sites. But it shows a higher affinity for the cationic dyes alone. This limits the usage for the removal of both cationic and anionic dyes. Moreover, it takes a longer time to attain equilibrium. Herein, we invented an integrated multiphase crystal system of Kavlite (NiO@AS) is nothing but multiphase nickel aluminosilicate. This is prepared by one-pot sol-gel method at room temperature and atmospheric pressure for the effective removal of Victoria Blue (VB) and Metanil Yellow (MY) within a short span of time. It is characterized by XRD, FTIR and HRTEM. Integration of nickel oxide into the aluminosilicate framework creates more active/acid sites in the framework, as evidenced by XRD analysis. Furthermore, XRD results revealed the formation of 6 different phases with 3 different crystal systems in the framework. This could also additionally induce the adsorption performance. This resulted in a faster adsorption rate of VB and MY within 10 and 35 min respectively, with 83% removal. The adsorption capacity of VB is higher than that of MY (Experimental Qe = 113.32 mg/g for VB and 20.92 mg/g for MY). This is because of the large availability of possible interaction sites in VB. This work provides a deep insight into understanding the interaction possibilities between the adsorbent and adsorbate interface based on the XRD, adsorption kinetics, isotherms and thermodynamic study.

Bystrite, Na7Ca(Al6Si6O24)S52–Cl–: formula redefinition and relationships with other four-layer cancrinite-group minerals

AbstractBystrite is redefined as a four-layer cancrinite-group mineral with the four-layer Losod-type framework and the end-member formula Na7Ca(Al6Si6O24)S52–Cl–. The mineral is known only at the Malo–Bystrinskoe gem lazurite deposit, Baikal Lake area, Siberia, Russia. The associated minerals are calcite, lazurite, sodalite, fluorapatite, phlogopite, diopside, dolomite and plagioclase. Bystrite is brittle, with the Mohs hardness of 5 and distinct cleavage on {10$\bar{1}$0}. The yellow colour of bystrite is due to the presence of S52– anions occurring in Losod (LOS) cages of the aluminosilicate framework with the ABAC stacking sequence. Measured and calculated density is, respectively, 2.43(1) and 2.412 g cm–3 for the holotype and 2.42(1) and 2.428 g cm–3 for the cotype sample. Bystrite is uniaxial (+), ɛ = 1.660(2) and ω = 1.584(2). The mineral was characterised by infrared and Raman spectra. The empirical formulae of the holotype and cotype samples are Na6.97K0.04Ca0.98(Si6.03Al5.97O24)(S52–)0.93[(SO42–)0.15Cl0.83] and Na6.75K0.04Ca1.11(Si6.09Al5.91O24)(S52–)1.04[(HS–)0.17Cl0.85], respectively. Bystrite is trigonal, space group P31c. The unit-cell parameters are: a = 12.8527(6) Å, c = 10.6907(5) Å, V = 1529.4(1) Å3 and Z = 2. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 4.821 (32) (102), 3.915 (38) (211), 3.712 (100) (300), 3.307 (50) (212), 2.782 (18) (400), 2.692 (22) (401), 2.673 (30) (004) and 2.468 (23) (402). Isomorphism and genesis of bystrite-type minerals is discussed. Bystrite and its K,HS-analogue sulfhydrylbystrite, Na5K2Ca(Al6Si6O24)S52–(HS)–, are indicators of highly reducing conditions.

Construction of flower-like nanoassembly P-doped MOF-derived MoS2/Co9S8 grown on hexagonal microporous alumino-silicate framework for overall water splitting in alkaline media

Water splitting is a noteworthy process in the field of hydrogen and oxygen gas production. MoS2 has emerged as an effective material for catalyzing water splitting; however, its low electronic conductivity and oxidative corrosion in environmental conditions suppress its practical applications in electrolyzers. Herein, we constructed a new hetero-nanostructure composed of MoS2 and Co9S8 phases, which is assembled onto the hexagonal microporous alumino-silicate (HMS) structure. Different combinations ratios of Mo and Co elements in hetero-nanostructures offered tremendous opportunities for morphology control and, further, modification of chemical and physical properties to enhance the overall water splitting process. HMS/MoS2/Co9S8-31 (with the mole ratio of 3:1 for Mo:Co) showed synergistically enhanced electrocatalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with overpotentials of −127 and 280 mV at 10 mA cm−2, respectively. In the next step, phosphorization of HMS/MoS2/Co9S8-31 was performed via a simple one-step route (HMS/MoS2/Co9S8/P-31), so the overpotentials were reduced to −85 and 200 mV, which shows dramatic improvement in the overall water splitting performance of electrocatalyst. In addition, for a symmetrical electrolyzer, a current density of 10 mA cm−2 was obtained at a quite low cell voltage of 1.56 V. Systematic studies on HMS/MoS2/Co9S8/P-31 and a set of finely designed control catalysts suggest that the enhanced electrocatalytic behavior should be related to electronic coupling effect and modulation between MoS2 and Co9S8 and the advantage of the ordered HMS architecture. In addition, phosphorus doping can modify the electronic properties of hetero-nanostructure and facilitates electron transfer between MoS2 and Co9S8 hetero-phases.

In Ukrainian

In this paper it is discussed the colloidal-chemical method of synthesis of dispersed composite bentonite-ferromagnetic powders that are stable to oxidation. It is shown that for this purpose it is advisable to use acid-activated bentonite clay with a high content of clay mineral - montmorillonite. Modified bentonite is a slightly amorphized silica product that serves as a porous matrix for crystallization of goethite α-FeOOH. The formation of goethite occurs at the centers of crystallization - particles of ferrihydrite stabilized by activated bentonite (Fh) during precipitation with an ammonia solution from a ferrum(ІІІ) hydroxide FeO(OH)×nH2O colloidal solution. In the resulting composite, goethite particles are cemented in the aluminosilicate framework of activated dispersed clay as a result of the interpenetration of the structures of the double layered hydroxide and activated bentonite. Further recrystallization of goethite with the formation of mainly magnetite and possibly maghemite in the structure of activated bentonite is provided by thermal firing of composite goethite powder with the addition of metallic iron powder. The methods of IR spectroscopy, X-ray structural analysis, electron microscopy and the study of magnetic properties showed that the obtained composite powder is environmentally friendly and exhibits the properties of a soft magnetic material. Such powders are promising for use as sorbents for environmental cleaning, as well as for biomedical purposes due to their low toxicity and high value of saturation magnetization.

Importance of the Nature of Acidic Sites of Different Aluminosilicates on Fixation of Carbon Dioxide with Styrene Oxide.

The nature of acidic sites in commercially available aluminosilicates, zeolite Na-Y, zeolite NH4 + -ZSM-5, and as-synthesized Al-MCM-41 have been investigated by employing them as catalysts for capturing CO2 by styrene oxide. The catalysts, in tandem with tetrabutylammonium bromide (TBAB), produce styrene carbonate, and the yield of the product is observed to be governed by the acidity of the catalysts and hence, the Si/Al ratio. All these aluminosilicate frameworks have been characterized by IR, BET, TGA, and XRD. XPS, NH3 -TPD, and 29 Si solid-state NMR studies have been carried out to analyze the Si/Al ratio and the acidity of these catalysts. According to TPD studies, the number of weak acidic sites of these materials follow an order as NH4 + -ZSM-5 < Al-MCM-41 < zeolite Na-Y, which is just in accordance with their Si/Al ratios and the yield of the cyclic carbonates obtained, i. e., 55.3 %, 68 %, and 75.4 % respectively. The TPD data and the yield of the product carried out with calcined zeolite Na-Y indicate that not only the weak acidic sites but also the role of strong acidic sites might appear crucial in the cycloaddition reaction.

Synthesis of Hollow Mesoporous Silica Nanospheroids with O/W Emulsion and Al(III) Incorporation and Its Catalytic Activity for the Synthesis of 5-HMF from Carbohydrates

Controlling the particle size as well as porosity and shape of silica nanoparticles is always a big challenge while tuning their properties. Here, we designed a cost-effective, novel, green synthetic method for the preparation of perforated hollow mesoporous silica nanoparticles (PHMS-1) using a very minute amount of cationic surfactant in o/w-type (castor oil in water) emulsion at room temperature. The grafting of Al(III) through post-synthetic modification onto this silica framework (PHMS-2, Si/Al ~20 atomic percentage) makes this a very efficient solid acid catalyst for the conversion of monosaccharides to 5-HMF. Brunauer–Emmett–Teller (BET) surface area for the pure silica and Al-doped mesoporous silica nanoparticles (MSNs) were found to be 866 and 660 m2g−1, respectively. Powder XRD, BET and TEM images confirm the mesoporosity of these materials. Again, the perforated hollow morphology was investigated using scanning electron microscopic analysis. Al-doped hollow MSNs were tested for acid catalytic-biomass conversion reactions. Our results show that PHMS-2 has much higher catalytic efficiency than contemporary aluminosilicate frameworks (83.7% of 5-HMF yield in 25 min at 160 °C for fructose under microwave irradiation).

Structural composition of antibacterial zinc-doped geopolymers.

Elucidating the structural composition of a three-dimensional amorphous sodium-aluminosilicate-hydrate (Na2O-Al2O3-SiO2-H2O, N-A-S-H) gel in geopolymers is a prerequisite for its prevailing application in biomaterials, construction, waste management, and climate change mitigation. An unsolved challenge in geopolymer science is the clear structural understanding of amorphous N-A-S-H doped with desired metals. Here, we uncover the molecular structure of (Zn)-N-A-S-H, confirming the tetrahedral coordination of Zn with O and the presence of Si-O-Zn bonds. The Zn-Si distance of ∼3.0-3.1 Å proves the connection of the corners of ZnO42- tetrahedra and SiO4 tetrahedra by slight twisting. The stoichiometric formula of the ZnO-doped geopolymer is quantified as (Na0.19Zn0.02AlSi1.74O5.095)·0.19H2O. The remarkable antimicrobial efficacy of the Zn modified-geopolymer in inhibiting the formation of biofilms by the sulphur-oxidising bacteria Acidithiobacillus thiooxidans and inhibiting biogenic acidification is evidenced. The biodegradation process of the geopolymer featuring the rupture of the Si-O-Al and Si-O-Zn bonds of the networks leads to the expelling of tetrahedral AlO4- and ZnO42- from the aluminosilicate framework and the eventual formation of the siliceous structure. This work demonstrates that the (Zn)-N-A-S-H structure of our new geopolymer provides a solution to optimising geopolymer materials and provides further possibilities for designing novel geopolymer composites for use in construction materials, antibacterial biomaterials in dental or bone surgery, and management of hazardous and radioactive waste.