Silicate Structure Research Articles

MODIFICATION OF ZEOLITE-Y CATALYST BY ADDITION OF SELECTED TRANSITION METAL IONS (ZN &CU IONS)

Zeolite is a microporous nanomaterial with alumina and silicate structure which can be used to crack heavy petroleum fraction to yield lighter components. Recent studies suggest that zeolite can be used for sugar conversion to fuel and value-added chemicals with proper modification. In this study, fresh zeolite -y catalyst was subjected to initial characterization, Brunauser Emmett Teller (BET), X-Ray Diffractometer (XRD), X-Ray Flourescence (XRF) and Scanning Electron Microscope (SEM) and modified. 50ml of prepared standard solution of zinc and copper chloride each was added to 5g of fresh zeolite catalyst and mixed thoroughly for 1 hour at room temperature. The mixture was dried at 110 0C for 24 hours using dry oven. The crystalline solid obtained was calcined at 500 0C for 2 hours in a muffle furnace. The modified catalyst was finally characterized (BET, XRD, XRF and SEM) and the results obtained were compared with the fresh catalyst characterized results. BET results shows that the pore volume, pore diameter and surface area of the modified catalyst increase from 0.309cc/g, 2.105nm, and 627.998m2/g to 0.365cc/g, 2.446nm and 746.062m2/g respectively. Similarly, from the XRD result, the modified catalyst has all the crystalline peaks at Bragg angle (2θ) present in the fresh catalyst with additional peaks formed. The additional crystalline peaks formed show the increase in mechanical strength of the modified catalyst. The SEM results show the change in surface texture of the fresh catalyst from smooth and uniform to rough and agglomerated. Keywords: Zeolite, Catalyst, Transition metals. Modification, Crude, ions.

The Application of Mineral Kaolinite for Environment Decontamination: A Review

Kaolinite clay mineral with a layered silicate structure is an abundant resource in China. Due to its advantages of excellent stability, high specific surface area and environmental friendliness, kaolinite is widely used in environment decontamination. By using kaolinite as a carrier, the photocatalytic technology in pure photocatalysts of poor activities, narrow spectral responses, and limited electron transport can be overcome, and the nano-Ag disinfectant’s limitation of the growth and aggregation of nanoparticles is released. Moreover, pure kaolinite used as an adsorbent shows poor surface hydroxyl activity and low cation exchange, leading to the poor adsorption selectivity and easy desorption of heavy metals. Current modification methods including heat treatment, acid modification, metal modification, inorganic salt modification, and organic modification are carried out to obtain better adsorption performance. This review systematically summarizes the application of kaolinite-based nanomaterials in environmental decontamination, such as photocatalytic pollutant degradation and disinfection, nano silver (Ag) disinfection, and heavy metal adsorption. In addition, applications on gas phase pollutant, such as carbon dioxide (CO2), capture and the removal of volatile organic compounds (VOCs) are also discussed. This study is the first comprehensive summary of the application of kaolinite in the environmental field. The review also illustrates the efficiency and mechanisms of coupling naturally/modified kaolinite with nanomaterials, and the limitation of the current use of kaolinite.

Ring Silicates Cs4Tm2[Si4O12](OH)2 and Cs4(Tm,Tb)2[Si4O12](OH)2 As Merohedral Twins

New ring silicates Cs4Tm2[Si4O12](OH)2 and Cs4(Tm,Tb)2[Si4O12](OH)2 have been synthesized by the hydrothermal method. A structural analogy is revealed between them and the previously studied silicates K4Sc2(OH)2(Si4O12) and K2Sc[Si2O6]F. Their crystal structures are identified as orthorhombic merohedral twins by the lost element of tetragonal symmetry. The structures of new ring silicates are related to those of fresnoite and tetragonal melilite.

A review on borate bioactive glasses (BBG): effect of doping elements, degradation, and applications.

Because of their excellent biologically active qualities, bioactive glasses (BGs) have been extensively used in the biomedical domain, leading to better tissue-implant interactions and promoting bone regeneration and wound healing. Aside from having attractive characteristics, BGs are appealing as a porous scaffold material. On the other hand, such porous scaffolds should enable tissue proliferation and integration with the natural bone and neighboring soft tissues and degrade at a rate that allows for new bone development while preventing bacterial colonization. Therefore, researchers have recently become interested in a different BG composition based on borate (B2O3) rather than silicate (SiO2). Furthermore, apatite synthesis in the borate-based bioactive glass (BBG) is faster than in the silicate-based bioactive glass, which slowly transforms to hydroxyapatite. This low chemical durability of BBG indicates a fast degradation process, which has become a concern for their utilization in biological and biomedical applications. To address these shortcomings, glass network modifiers, active ions, and other materials can be combined with BBG to improve the bioactivity, mechanical, and regenerative properties, including its degradation potential. To this end, this review article will highlight the details of BBGs, including their structure, properties, and medical applications, such as bone regeneration, wound care, and dental/bone implant coatings. Furthermore, the mechanism of BBG surface reaction kinetics and the role of doping ions in controlling the low chemical durability of BBG and its effects on osteogenesis and angiogenesis will be outlined.

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.

Insight into the role of excess hydroxide ions in silicate condensation reactions.

The formation of silicate oligomers in the early stages is key to zeolite synthesis. The pH and the presence of hydroxide ions are important in regulating the reaction rate and the dominant species in solutions. This paper describes the formation of silicate species, from dimers to 4-membered rings, using ab initio molecular dynamics simulations in explicit water molecules with an excess hydroxide ion. The thermodynamic integration method was used to calculate the free energy profile of the condensation reactions. The hydroxide group's role is not only to control the pH of the environment, but also to actively participate in the condensation reaction. The results show that the most favorable reactions are linear-tetramer and 4-membered-ring formation, with overall barriers of 71 kJ mol-1 and 73 kJ mol-1, respectively. The formation of trimeric silicate, with the largest free-energy barrier of 102 kJ mol-1, is the rate-limiting step under these conditions. The excess hydroxide ion aids in the stabilization of the 4-membered-ring structure over the 3-membered-ring structure. Due to a relatively high free-energy barrier, the 4-membered ring is the most difficult of the small silicate structures to dissolve in the backward reaction. This study is consistent with the experimental observation that silicate growth in zeolite synthesis is slower in a very-high-pH environment.

Study of the thermal behaviour of a derivative based on a zirconium agent (modified montmorillonite) and determination of the physical characteristics

In this research, untreated Algerian maghnite has been used to develop two types of modified clays: the first one is a homo-ionic sodium clay (Na-Mag) which is a support to develop a montmorillonite by insertion of zirconium hydroxyl cations. The different series of techniques, including thermogravimetric analysis (TGA), differential thermal analysis (DTA), dynamic light scattering (DLS), and zeta potential (ζ), have been used to define the physical characteristics of the clays by studying their particle size distribution as well as the thermal profile. In addition, the pillar-shaped montmorillonite (Maghnite) exhibit a negative charge even when its pH reach 2.8. This large negative surface charge of montmorillonite suggests optimal removal of organic molecule particles present in the aqueous medium. The results obtained by Fourier transform infrared (FT-IR) analysis show that the bands characterizing the presence of intercalating agents are visible. Thermography of the zirconium pillar species shows an improvement in the thermal stability of the silicate structure with two well differentiated zones. Adsorbed organic cations result in a reduction of the surface load, that is, a decrease of its negativity, as well as a cancellation of the charge.

The behavior of aluminum sites in H-[Al]-RUB-18 catalysts: A theoretical-experimental investigation

Functional acidic sites can be generated in the structure of layered silicates by the isomorphic substitution of silicon by aluminum atoms, leading to suitable heterogeneous catalysts. H-[Al]-RUB-18 samples were synthesized with Si/Al molar ratios of 15, 30, and 60. Experimental characterizations showed that two different aluminum sites were obtained: one tetrahedrally coordinated (framework-Al), very similar to those found in microporous zeolites; and the other octahedrally coordinated, analogous to silanol groups (hydrated aluminol sites). Computational simulations based on Density Functional Theory (DFT) were used to test the atomic positions of these aluminum sites and confirmed, in terms of electronic energies, the tetrahedral and octahedral positions already predicted in the experimental characterizations. In addition, ethanol dehydration reaction was used to probe the acidic sites and evaluate the performance of the different [Al]-RUB-18 samples. Although a widely known reaction for zeolites and other porous solids, the chemical analysis in this work indicated that the Al-substituted layered silicates are promising candidates to be used in heterogeneous catalysis. The experimental catalytic data showed that the presence of aluminum atoms improved the reaction conversion. Moreover, MEP calculations also presented, in each step of ethanol dehydration, Alframework sites with the lowest electronic energy barriers.

Softening of sand mixtures on a liquid-glass binder as a result of thermal-oxidative destruction of a combined carbon-containing additive. Part 1

The chemical and physical processes that occur during high-temperature heating of carbon-containing additives are studied in order to develop an effective composition, whose components destruction will lead to a violation of the integrity of the binder film and a decrease in the residual strength of liquid-glass mixtures, and hence an improvement in the knock-out of molds and cores in the conditions of obtaining castings from alloys of ferrous metals. Carboncontaining materials used in foundry production, the destruction of which proceeds in different temperature ranges, have been studied. The methods of thermogravimetric and differential thermal analyzes have been used to study the processes that tale place with materials under study when heated to temperatures comparable to the actual operating conditions of casting cores in direct contact with liquid and solidifying metal in the mold. As a result of the analysis of the considered carbon-containing materials, the temperature intervals of destruction were revealed, which made it possible to predict their effect on the structure of sodium silicate (binder) on the refractory filler and the residual strength of mixtures in order to improve the knock-out of steel castings. Obtaining high-quality casting molds and cores depends on the technological, hydraulic and mechanical characteristics of the mixture, therefore, additional studies were carried out, the results of which revealed the compliance of the determined properties of the studied samples with the requirements for molding and core sand mixtures on a liquid-glass binder.

Role of P2O5 in the viscous behavior and structure of yellow phosphorus slag

To clarify the role of P2O5 in the fluidity of yellow phosphorus slag during the centrifugal granulation process, the viscosity and structure of slag with various P2O5 contents were researched. It showed that increasing P2O5 content from 1.38wt% to 5.80wt% enhanced the slag viscosity and activation energy for viscous flow, which reduced the slag fluidity. P2O5 in slag existed as QP0 and QP1 units whose proportions were about 0.89 and 0.11, respectively, irrespective of the P2O5 contents. The introduced P2O5 promoted the polymerization of silicate structure because the metal cations coordinated by non-bridging oxygens in silicate structure became connected with the phosphate structure. P2O5 addition encouraged the conversion of [AlO4] units into [AlO5] units and reduced the polymerization degree of aluminate structure. The variations in the polymerization degree of silicate and aluminate structure played a competitive role in determining the slag viscosity, and the silicate structure was the dominant factor.

Molecular dynamics simulations to structure-properties relationship of MgO−BaO−CaO−Al2O3−B2O3−SiO2 glass-ceramic for intermediate temperature solid oxide fuel cell

The mechanism of MgO inhibiting phase precipitation and phase transformation of BaAl2Si2O8 in MgO−BaO−CaO−Al2O3−B2O3−SiO2 glass-ceramic is systematically investigated and analyzed. The molecular dynamics simulation results show that the addition of MgO makes the transformation of [BO3] to [BO4], bridge oxygen to non-bridge oxygen, and Qn distribution of [SiO4] tetrahedrons from Q3 to Q1, which is confirmed by infrared and Raman spectroscopy analysis of melt-quenched glass. Consequently, the precipitation process of the BaAl2Si2O8 phase is inhibited by the silicate structure transformation from metasilicate (SiO3)2− to pyrosilicate (Si2O7)6− to protosilicate (SiO4)4−, resulting in the BaAl2Si2O8 phase is gradually replaced with MgSiO3, Mg2SiO4, BaMgSiO4, Ba2MgSi2O7 and BaCa2Mg(SiO4)2 phase with increment of the MgO in the MBCASB glass. It means that the Mg ions are more competitive reacting with silicate structure to form the new crystalline phase than Al and Ba ions.

Preparation and Characterization of LCT/SPEEK Composite Membrane for PEMFC Application

AbstractA novel SPEEK‐based blends proton exchange membrane doping liquid crystal polymer intercalated montmorillonite (LCT) were prepared by solution casting technology. FT‐IR, XRD and POM proved that SPEEK contained sulfonic acid group and LCT which had liquid crystal intercalated into SPEEK matrix. LCT/SPEEK composite membrane with 1.0 wt% had higher swelling rate and proton conductivity than those membranes. It was also shown that the proton conductivity of LCT/SPEEK composite membrane decreased, but reached 0.137 S/cm when LCT was 1.0 wt%, and the swelling rate of SPEEK membrane was significantly decreased 6.19 % to 3.38 %. The layer silicate structure in LCT promotes its dimensional stability, and the sulfonic group forms hydrogen bond network in SPEEK matrix to promote proton transfer. These results propose the composite membranes as a potential candidate for PEMFC at 25 °C making SPEEK composite membrane.

The Study of Clay with Waste from Khovu-Aksy Dump Samples Composition for the Production of Ceramic Products

The composition of samples based on krasno-yarsk clay with sludge and dearsenization cake of the Khovu-Aksy dump was considered. It was found that already at the stage of drying at room temperature there are changes in the structure and composition of the samples. There is a decrease in arsenic content in the materials of the samples, which further creates the prerequisites for their use in the production of ceramic products. Significant changes in the phase composition of the samples were found: they lack calcite, dolomite, a number of silicate and aluminosilicate structures, instead of them a new phase – albite – is formed. A significant amount of albite (up to 52 %) was observed in the samples fired at 850 °C.

Influence of electropulsing treatment on crystallization and structure of calcium silicate-based melt

Electropulsing treatment (EPT) is a promising technology for controlling the phase transition during the solidification of melts owing to its electric and thermal effects. In this study, the influence of EPT on the crystallization and melt structure of a calcium silicate-based mold flux was investigated. The results showed that the morphology of crystals that precipitated in the mold flux changed from elongated columnar to block shape, and the equivalent grain diameter of the crystals increased with increasing voltage from 0 to 20 V. The mass fraction of Ca4Si2O7F2 precipitated in the mold flux decreased with increasing impulse voltage, whereas that of Ca2Mg0.75Al0.5Si1.75O7 increased. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses suggest that the network structure of both silicate and aluminate was simplified by electropulsing because the simpler structural units of Q0, Q1, [AlO6]9+, etc., increased with increasing impulse voltage, whereas the complex structural units of Q2, Q3, and [AlO4]5+ decreased. The extra electric field force is the repulsion force between two oppositely charged ions, which was the root of the network structure simplification and crystallization promotion. The results obtained in this study provide an innovative method for locally controlling the crystallization behavior of mold flux in a mold.

The investigation of dynamic heterogeneity in lead silicate liquid via molecular dynamic simulation

The structure and dynamics of liquid lead silicate with a wide range of PbO ratio are done by molecular dynamics methods. The simulated result shows that the pair radial distribution functions (PRDFs) are in good agreement with the results of previous studies. Our calculated data indicates that the system exists regions of fast and slow atoms determined via the mean square displacement (MSD) in the same interval. The exhibition of dynamical heterogeneity (DH) is also found in this paper.

Long-term sulfate resistance of synthesized cement systems with variable C3A/C4AF ratio at low temperature or ambient conditions: Insights into the crystalline and amorphous phase assemblage

Synthesized cement systems made with variable C3A/C4AF ratios, containing C3S, gypsum and, optionally, calcite, were stored long-term at humid conditions at 5 or 20 °C, without any protection against atmospheric carbonation. Analytical techniques able to assess both the crystalline and amorphous phases were used. Experimental results were compared with thermodynamic simulations. The systems with C3A/C4AF < 1 better preserved the soundness of the CSH phase, which hosted iron, and prevented thaumasite formation. The addition of calcite in these systems inhibited carbonation. When occurred (mixtures without calcite), the carbonation was significantly more intense at ambient temperature. In the systems that underwent extensive deterioration, cross-linking of silicate structures, AFt decomposition, and iron release from the deteriorating CSH, occurred, while Al-incorporating amorphous silica, calcium carbonate polymorphs and hydrous iron oxide formed. The presence of unreacted C3A in the systems with C3A/C4AF = 1, suggested that CSH decomposition was contributed by available sulfates.

Application of Geopolymer in Stabilization/Solidification of Hazardous Pollutants: A Review.

Geopolymers, as a kind of inorganic polymer, possess excellent properties and have been broadly studied for the stabilization/solidification (S/S) of hazardous pollutants. Even though many reviews about geopolymers have been published, the summary of geopolymer-based S/S for various contaminants has not been well conducted. Therefore, the S/S of hazardous pollutants using geopolymers are comprehensively summarized in this review. Geopolymer-based S/S of typical cations, including Pb, Zn, Cd, Cs, Cu, Sr, Ni, etc., were involved and elucidated. The S/S mechanisms for cationic heavy metals were concluded, mainly including physical encapsulation, sorption, precipitation, and bonding with a silicate structure. In addition, compared to cationic ions, geopolymers have a poor immobilization ability on anions due to the repulsive effect between them, presenting a high leaching percentage. However, some anions, such as Se or As oxyanions, have been proved to exist in geopolymers through electrostatic interaction, which provides a direction to enhance the geopolymer-based S/S for anions. Besides, few reports about geopolymer-based S/S of organic pollutants have been published. Furthermore, the adsorbents of geopolymer-based composites designed and studied for the removal of hazardous pollutants from aqueous conditions are also briefly discussed. On the whole, this review will offer insights into geopolymer-based S/S technology. Furthermore, the challenges to geopolymer-based S/S technology outlined in this work are expected to be of direct relevance to the focus of future research.

Assessment of Pozzolanic Activity of Ground Scoria Rocks under Low- and High-Pressure (Autoclave) Steam Curing.

Two sources of natural scoria rocks were procured and ground for use in concrete as natural pozzolans (NP1 and NP2). The evaluation of their pozzolanic reactivity is carried out using different techniques and approaches. The primary goal of employing these techniques is to monitor the amount of portlandite (CH=Ca(OH)2) consumed during steam curing at low or high pressure. The pozzolanicity of NP powders is determined either directly by monitoring CH variation or indirectly by compressive strength and microstructure development. Autoclave curing is known to stimulate the pozzolanicity of the inert siliceous and aluminosiliceous materials under its high-pressure steam conditions. Both steam-curing conditions were applied in this investigation. In this study, X-ray diffraction, scanning electron microscope, thermogravimetric, Fourier transform infrared, and isothermal analyzers were used. It is concluded that the nature and types of minerals in SR determine their pozzolanic reactivity as either low-pressure steam-reactive or high-pressure steam-reactive cementitious materials. Due to the nature of their silicate structures, notably single-chain or 3D-framework structures, plagioclase feldspars (albite-anorthite) minerals are high-pressure steam-reactive minerals, whereas pyroxene (enstatite and diopside) minerals are low-pressure steam-reactive minerals. Using high-pressure steam curing, varied replacement levels of up to 60% were achieved in NP1, with a consistent strength activity index (SAI) of 99%, while an SAI of 79% was obtained with NP2. During low-pressure steam curing, NP1 and NP2 consumed around 72 and 80% of portlandite, respectively, demonstrating their relative pozzolanic reactivity. When compared to the control concrete mix, the strength activity indices of NP1, NP2, and class F fly ash in their normal concrete mixes reached 74.3, 82, and 73.7%, respectively, after 56 days of normal curing conditions.

Effect of B2O3 content on viscosity and structure of SiO2−MgO−FeO-based slag

The effect of B2O3 content on the viscosity of SiO2−MgO−FeO-based molten slag system was investigated using the rotating cylinder method. The evolution process of the melt structure under different contents of B2O3 was comprehensively studied via FTIR spectroscopy and a model for calculating the degree of polymerization was developed. The results showed that the viscosity of the molten slag decreased with the addition of B2O3, which had a slight effect when its content exceeded 3 wt.%. As the addition of B2O3 increased from 0 to 4 wt.%, the break temperature of the slags decreased from 1152 to 1050 °C and the apparent activation energy decreased from 157.90 to 141.84 kJ/mol. The addition of B2O3 to the molten slag destroyed the chain silicate structure to form a more cyclic borosilicate structure. The Urbain model was improved to calculate the viscosity of the SiO2−MgO−FeO-based slags, and the values were in good agreement with the experimentally measured values.

Luminescence studies of Eu3+ doped calcium magnesium silicate phosphor prepared at different annealing temperatures for fine color tunability

This research article explores the possibility of fine-tuning of the color monochromaticity of Eu3+ doped calcium magnesium silicate: CaMgSi2O6: Eu3+, Ca3MgSi2O8: Eu3+, and Ca2MgSi2O7: Eu3+ (CMS: Eu3+) phosphor by introducing a crystal field effect in the luminescence emission spectra. The effect of Eu doping and annealing temperature on modifying the morphology, crystal structure, bonding nature, luminescent properties, and color monochromaticity of calcium magnesium silicate; CaMgSi2O6, Ca3MgSi2O8, and Ca2MgSi2O7 (CMS) phosphor is analyzed in detail. CMS and CMS: Eu3+ were separately prepared by the sol-gel method, employing five different annealing temperatures. Morphological analysis using FESEM confirmed agglomerated porous structures at annealing temperatures of 800 °C, 900 °C, and 1000 °C, whereas clear particle formation was observed at 1100 °C and 1200 °C, both in CMS and CMS: Eu3+. An increase in the particle size with temperature and reduction in the growth kinetics with Eu3+ doping was noticed. The non-stoichiometric composition identified during the chemical analysis was in agreement with the XRD findings of the formation of merwinite, diopside, and akermanite phases in CMS and CMS: Eu3+. The XRD analysis further confirmed that Eu3+ doping favor merwinite over diopside structure. The structural modifications in the CMS due to the presence of Eu3+ appeared as blue and redshift in the vibrational wavenumbers of Ca–O and Mg–O in FTIR studies. Luminescence studies confirmed an increase in the peak splitting with the annealing temperature in the excitation and the emission spectra due to the crystal field effect. The possible reasons for the peak splitting are the formation of multiple phases with multiple site occupancy, preferably with the octahedral coordination, and the J mixing due to the effective charge balancing expected due to higher oxygen capture occurring at the higher annealing temperature. With the increase in annealing temperature, color chromaticity coordinates varied from (0.61, 0.39) to (0.63, 0.37) due to better charge compensation which is in agreement with the luminescence studies.