Silicate Precursor Research Articles

Vitreous silica supported metal catalysts for direct non-oxidative methane coupling

Direct non-oxidative methane coupling (NMC) transforms methane into valuable chemicals and hydrogen, which is a promising pathway to boost industrial decarbonization. The reaction, however, is challenged by high C-H bond activation temperature, catalyst coking, and low selectivity towards hydrocarbon products. Here we studied the efficacy of five vitreous silica supported 3d transition metal (Mn, Fe, Co, Ni, and Cu) catalysts (denoted as M/SiO2-v) for NMC. These catalysts were prepared by flame fusion of mixtures of quartz and metal silicate precursors. The metal species in the as-synthesized catalysts were fully or partially oxidized, with their stability following the order of Mn > Fe ≈ Co > Ni > Cu in the NMC reaction. The Cu species has low methane reaction rate, due to the high adsorption and dissociation energies of methane. The Mn and Ni species have high methane reaction and coke formation rates, which is supported by easy kinetics of methane deep dehydrogenation to carbon. In contrast, Fe and Co species showed the best hydrocarbon product selectivity. Particularly, the Co species emerged as the optimal catalyst for NMC, showcasing a balanced methane activation, hydrocarbon formation, and low coke yield. The relationship between the evolved metal species under reaction conditions and their NMC performance was discussed. The present study screens and provides effective catalyst formulations for NMC reactions.

Integrating phase change materials and spontaneous emulsification: In-situ particle formation at oil–water interfaces

The properties of interfaces between two immiscible fluids, as engineered by interfacial materials, are crucial in various processes, including printing, coating, and multiphase flow in porous media. Interfacial materials, such as surface-active molecules and particles can be adsorbed from the bulk fluid phases to the interface or formed in-situ at the interface. In this study, we develop a methodology to form stiff silica-based particles in situ at the oil–water interface through coupling of phase change materials and spontaneous emulsification. This process is demonstrated by introducing a heptane micellar solution that spontaneously generates a microemulsion phase when in contact with an aqueous phase. Micron-sized droplets, consisting of an aqueous silicate precursor mixture, undergo a sol–gel reaction, leading to the generation of colloidal-sized particles. SEM micrographs and confocal images of dried samples, taken from the aqueous-heptane interface, reveal the formation of particles post-gelation. The in-situ formation of stiff particles can be characterized through the dynamics of evaporation, where a significant reduction in the heptane evaporation rate is observed. This particle generation method, utilizing phase change materials and emulsion templates, is spontaneous, energy-efficient, and enables particle formation at the interface at a predetermined time. Our findings offer valuable insights for the fabrication of interfacial materials with tailored properties and controlled timing.

SYNTHESIS AND CHARACTERIZATION OF NANOSILICA (SiO2) VOLCANIC ROCK OF MOUNT BATUR IN BALI

This research was conducted to synthesize and characterize silica minerals (SiO2) from volcanic rocks in the active volcano in Bali, namely Mount Batur. The synthesis carried out on five different color variants of this rock sample is by the coprecipitation method which begins with the process of taking rock samples on Mount Batur, crushing the rock until it becomes powder with a size of 100 mesh, washing with distilled water and drying, immersing the rock powder in the solution. 2 M HCl for 12 hours, then the results of the soaking were reacted again with 7 M NaOH solution as a hydrolysis process to obtain pure SiO2 in the sample. In the form of sodium silicate precursor (Na2SiO3), the sample was titrated with a 2 M HCl solution to obtain silica gel which was then washed and dried until amorphous silica powder was produced. The results of the XRF analysis showed that the SiO2 mineral content in the sample after going through the synthesis process was 94.9% and the Si element was 89.9%. The XRD characterization results show that the phase formed from the sample has a quartz structure with the highest peak at an angle of 2θ = 23.07o, then decreases and levels out at an angle of 2θ = 32.94o which is characteristic of an amorphous structure and with a silica grain size of 8.47 nm – 8.65 nm.

Silica Biomineralization with Lignin Involves Si-O-C Bonds That Stabilize Radicals.

Plants undergo substantial biomineralization of silicon, which is deposited primarily in cell walls as amorphous silica. The mineral formation could be moderated by the structure and chemistry of lignin, a polyphenol polymer that is a major constituent of the secondary cell wall. However, the reactions between lignin and silica have not yet been well elucidated. Here, we investigate silica deposition onto a lignin model compound. Polyphenyl propanoid was synthesized from coniferyl alcohol by oxidative coupling with peroxidase in the presence of acidic tetramethyl orthosilicate, a silicic acid precursor. Raman, Fourier transform infrared, and X-ray photoelectron spectroscopies detected changes in lignin formation in the presence of silicic acid. Bonds between the Si-O/Si-OH residues and phenoxyl radicals and lignin functional groups formed during the first 3 h of the reaction, while silica continued to form over 3 days. Thermal gravimetric analysis indicated that lignin yields increased in the presence of silicic acid, possibly via the stabilization of phenolic radicals. This, in turn, resulted in shorter stretches of the lignin polymer. Silica deposition initiated within a lignin matrix via the formation of covalent Si-O-C bonds. The silica nucleants grew into 2-5 nm particles, as observed via scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. Additional silica precipitated into an extended gel. Collectively, our results demonstrate a reciprocal relation by which lignin polymerization catalyzes the formation of silica, and at the same time silicic acid enhances lignin polymerization and yield.

Effect of defect-healing treatment on layered silicate precursors toward well-defined crosslinked frameworks.

The synthesis of zeolites from two-dimensional layered precursors through interlayer crosslinking of the layers is a promising avenue for realizing meticulously designed synthesis routes. However, the presence of defective silanol species in the precursors hinders the achievement of desirable synthesis outcomes. This study focuses on PREFER-a layered precursor for FER-type zeolites-which was synthesized and subjected to a liquid-mediated defect-healing treatment that we recently developed. The defect-healing process involves the use of fluoride compounds for reconstruction and organic pore fillers to stabilize the framework. The effects of the treatment on the structure, composition, and iron insertion behavior of PREFER were examined. Characterization results revealed a reduction in the number of intralayer silanol defects, whereas interlayer silanols were unaffected by the defect-healing treatment. Furthermore, the subsequent alterations observed in the crosslinking behavior with iron atoms indicated that the defect-healing treatment may enhance the insertion of iron species between the layers in more homogeneous environments compared with the untreated precursor. These findings provide valuable insights into the prospects of controlled interlayer linkage in two-dimensional zeolite materials.

Oxygen isotope study of the Asuka-881020 CH chondrite II: Porphyritic chondrules

Oxygen isotope ratios and elemental compositions of porphyritic chondrules and olivine and pyroxene fragments in the Asuka-881020 CH chondrite were analyzed. The oxygen isotope ratios inside individual porphyritic chondrules are homogeneous within the uncertainty, except for relict grains of olivine and low-Ca pyroxene that have distinct oxygen isotope ratios. The average oxygen isotope ratios of the individual chondrules plot along and above the primitive chondrule mineral (PCM) line with Δ17O (=δ17O – 0.52 × δ18O) values from −4.7 ‰ to +4.1 ‰. The olivine and pyroxene fragments, which have Δ17O values ranging from −2.1 ‰ to +3.2 ‰, are likely to be fragments of the porphyritic chondrules.Unlike the non-porphyritic chondrules in CH and CB chondrites and chondrules in other carbonaceous chondrites, the type I and II chondrules do not show a systematic difference in the Δ17O values. Furthermore, the Δ17O values of the type I chondrules increase from −4.7 ‰ to +4.1 ‰ with increasing Mg# (=molar [MgO]/[MgO + FeO] × 100) from 96 to 99. We argue that the positive Δ17O-Mg# trend is explained by an addition of 16O-poor carbon-rich organics as a reducing agent to the relatively 16O-rich precursor silicate, which is a new environment for chondrule formation. This hypothesis is supported by the two lines of evidence observed in the present study. (1) The chondrules and fragments with higher Δ17O values show larger deviations from the PCM line towards low δ18O, suggesting oxygen isotope mass fractionation between the chondrule melt and CO or CO2. (2) Olivine phenocrysts in the chondrules with high Δ17O values contain Ni-poor Fe-metal particles surrounded by silica-rich glass, which may be reduction products during the chondrule formation. Thus, it is suggested that the porphyritic chondrules in CH and CB chondrites have different origins from chondrules in any other chondrite types, even from the non-porphyritic chondrules in CH and CB chondrites.

Synthesis and characterization of zeolite Y from agricultural and municipal wastes: A waste management approach

Here in, we reported the utilization of guinea corn husk (an agricultural waste) and aluminium can (a municipal waste) for low-cost and sustainable means of zeolite Y preparation. Sodium silicate and sodium aluminate precursors were prepared from guinea corn husk and aluminium wastes respectively. The obtained solutions of the precursors were directly and hydrothermally converted to zeolite Y at 100 °C crystallization temperature for 24 h. The resulting zeolitic material was characterized by its properties. In comparison with collected standard data and commercially available zeolite Y, zeolite Y was successfully prepared from the waste resources. The result of X-ray Diffraction (XRD) indicated zeolite Y with good crystallinity, especially at the characteristic 2θ of 6.23°, 10.9° and 11.86°. The elemental compositions observed from Energy Dispersive X-ray (EDX) are in appropriate proportion and also confirmed the product. The Fourier Transform Infrared (FTIR) spectra showed the major characteristic absorption bands of zeolite in the mid-infrared region. It can be concluded that re-using agricultural and municipal wastes for the preparation of zeolite Y was achieved. This is a sustainable means of preparation of zeolite Y through a waste management approach for potential applications in adsorption, catalysis and ion exchange.

Renewing the potential of rice crop residues as value-added products in the cosmetics industry

Purpose of this study is to explore the extraction of potentially valuable cosmetic ingredients from rice crop residues, aiming to mitigate their environmental impact. MethodsWe employed AOAC methods to analyze the fat, protein, ash, fiber, soluble, and insoluble carbohydrate content in these residues. To identify sugars rich in galactose and acidic sugars, a total soluble carbohydrate extraction was performed. Cellulose, as part of the insoluble carbohydrates, was isolated through alkaline and acid hydrolysis, while sodium silicate was derived from the ash. Characterization of insoluble cellulose and silicate involved techniques like FTIR, DSC, PXRD, microphotography, porosity assessments, and water absorption studies. For proteins, alkaline solubilization and precipitation at the isoelectric point were utilized, with quantification via BCA and amino acid profiling through gas chromatography. Evaluation of radical scavenging capacity using DPPH led to the calculation of apparent molecular weight via SDS-PAGE. ResultsThe results revealed low levels of gum, mucilage, and pectin in both residues, contrasting with a high concentration of insoluble polysaccharides. Among these, Iβ cellulose displayed potential attributes for cosmetic applications due to its oil and water adsorption characteristics. However, silicates obtained from the ashes did not exhibit direct use potential. In terms of protein extraction, we observed antioxidant properties, with enhanced performance through enzymatic hydrolysis, achieving a hydrolysis degree of 30.41% and a DPPH radical absorption rate exceeding 70%. ConclusionRice residues, particularly husk and straw, shown valuable substances suitable for potential cosmetic applications, encompassing cellulose, hydrolyzed proteins, and ash as a silicate precursor.

Development of a novel extrusion device to improve the printability of 3D printable geopolymer concrete

This study explores the printability of 3D geopolymer concrete using a novel extrusion device. Geopolymer, known for its eco-friendliness and rapid curing, offers an eco-friendly alternative to conventional cement in 3D printing. A novel extrusion device, integrating mixing and stirring functions, was developed to blend sodium silicate powder and precursor slurry effectively. Systematic experiments on mixing ratio, time, and speed revealed optimal conditions for geopolymer concrete printability. The precursor slurry remained pumpable for 90 min and displayed rapid reactivity in the new device. The extruded geopolymer concrete exhibited exceptional buildability, reaching a remarkable yield strength growth rate of 931.69 Pa/s. Actual printing tests resulted in a 154-layer hollow cylinder, 1840 mm tall, printed in just 26.87 min. Increasing mixing time enhanced compressive strength and reduced porosity, showcasing the potential of this set-on-demand approach and the novel extrusion device in 3D printable geopolymer concrete applications.

Amine-functionalized porous silica production via ex- and in-situ method using silicate precursors as a selective adsorbent for CO2 capture applications

A comparison of the amine-modified silica particle’s characteristics via ex- and in-situ routes and their application as a CO2 gas adsorbent is reported. Modifying silica particles via ex-situ involves two separate steps: forming porous silica particles with sodium lauryl sulfate (SLS) as a template and impregnation using ultrasound assistance. In contrast to ex-situ modification, in-situ modification of silica particles is carried out in one step by mixing directly between the silica source and the modifying agent. Controlling the characteristics of modified silica particles via in-situ is carried out by adding an SLS template removed simultaneously with particle formation to increase the surface area and porosity. Increasing the SLS template concentration shows a linear relationship between increasing particle surface area and amine loading. However, two different modification routes exert a direct influence on aminopropyl distribution. Silanization via in-situ which involves a simultaneous condensation reaction produces a higher amine loading reaching 1.2845 mmol/g of silica than via ex-situ which is only 0.9610 mmol/g of silica. The amount of aminopropyl that can be grafted on the silica surface shows a linear relationship to the quantity of CO2 gas adsorption capacity. Amine-modified silica particles obtained the highest adsorption capability via the in-situ route with an SLS 3 CMC template of 2.32 mmol/g silica at an operating pressure of 6 bar.

Designable Synthesis of Layered Silicates and Tunable Interlayer Expanded to Zeolites.

Layered zeolitic silicates and corresponding interlayer-expanded porous materials exhibit attractive application potential in wide fields. Nonetheless, designable synthesis and structure analysis of layered silicates remain challenging. Herein, two kinds of layered silicates are synthesized using different di-quaternary ammonium-type organic structure-directing agents (OSDAs). Their crystal structures are analyzed and verified by 3D electron diffraction (3D ED) and high-resolution TEM imaging. The suitable configurations of OSDA can lead to desirable interlayer states. Additionally, two new zeolite structures both with 12-membered ring (MR) channels intersected by 8 MR channels and larger interlayer spaces are constructed from layered silicate precursors by interlayer silylation. The new zeolitic material exhibits potential application in adsorption of organic pollution and catalytic reaction. This study is expected to develop versatile ways for the design and synthesis of layered silicates even zeolites and provide references in characterizing layered materials and zeolites as well.

An efficient and template‐free synthesis of mesoporous silica from coal fly ash

AbstractIn the study, the desilication liquids and acid‐leached residues derived from the “alumina extraction process” of coal fly ash (CFA) were used as raw materials to prepare sodium silicate precursor. Then, the mesoporous silica with controllable pore structure properties was synthesized by an efficient, template‐free process from obtained sodium silicate. The effect of the sodium silicate properties and synthesis conditions on the pore structure properties of disordered mesoporous silica were investigated. The resulting material was characterized by N2 adsorption–desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) and tested as an adsorbent for removal of lead ions (Pb2+). The results showed that the precursor with high modulus (3.0) and concentration (60 g·L−1) was beneficial for the synthesis of mesoporous silica with high specific surface area. The mesoporous silica with specific surface area of 690 m2·g−1 and pore volume of 1.28 cm3·g−1 was synthesized at mild aging temperature (40°C) and pH value of 8. Moreover, the materials possessed an adsorption capacity of 303 mg·g−1 for lead ions after amino modification. The adsorption efficiencies for lead ions were maintained at ~90% after five recovery cycles. Overall, the utilization efficiency of SiO2 in CFA reached up to 93%.

Chemorheology of a Si/Al > 3 Alkali Activated Metakaolin Paste through Parallel Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA).

Although geopolymers, as structural materials, should have superior engineering properties than traditional cementitious materials, they often need to improve their final characteristics' reproducibility due to the need for more control of the complex silico-aluminate decomposition and polymerisation stages. Thermosetting of a reactive geopolymeric paste involves tetrahedral Silicate and Aluminate precursor condensation into polyfunctional oligomers of progressively higher molecular weight, transforming the initial liquid into a gel and a structural solid. Viscosity and gelation control become particularly critical when the geopolymer is processed with 3D printing additive technology. Its physical state modification kinetics should match the flow and setting characteristics required by the deposition process. The reaction kinetics and the elastic and viscous characteristics preceding gelation and hardening have been investigated for an alkali-activated Metakaolin/Sodium Silicate-Sodium Hydroxide paste with a Si/Al ratio > 3. A chemoreological approach has been extended to these inorganic polymerisable systems, as already utilised for organic thermosetting polymers. Differential scanning calorimetry and Oscillatory DMA were carried out to monitor the advancement of the polymerisation reaction and the associated variations of the rheological viscoelastic properties. Dynamic thermal scans were run at 1 °C/min and a frequency of 10 Hz for the dynamic mechanical tests. The observed kinetics of polymerisation and variations of the elastic and viscous components of the complex viscosities and shear moduli are described in terms of polycondensation of linear and branched chains of oligomeric macromolecules of increasing complexity and molecular weight up to gelation (Gel1) and cross-linking of the gelled macrostructure (Gel2) and final glassy state. Geopolymerization can be allocated into two main behavioural zones: a viscoelastic liquid paste below 32.5% of reaction advancement and a viscoelastic solid above. Initial complex viscosities range from 2.3 ± 0.9 × 10-5 MPa*s to 6.8 ± 0.9 × 10-2 in the liquid-like state and from 1.9 ± 0.1 MPa to 9.6 ± 2.1 × 102 MPa in the solid-like state.

Up-conversion color tunable and red luminescence of Ho3+/Yb3+ co-doped glass ceramics containing NaLaSiO4 crystals

By using the melt-annealing method, silicate precursor glasses were prepared. Optimal heat treatment conditions for glass ceramics at 610 °C for 90 min were established through a series of tests. Glass ceramics containing NaLaSiO4 crystals with β-K2SO4 structure were successfully synthesized after heat treatment. XRD patterns of glass ceramics were successfully fitted using Rietveld refinement, with rare earth ions entering the lattice by replacing sites of La resulting in a reduction in cell volume. A tunable emission from green light to red light was achieved by varying the Yb3+ doping concentration. By varying the concentration of Ho3+, the intensity of the up-conversion emission was significantly increased while maintaining high color purity in red light. The optimal concentration of Ho3+ was 0.4%, when the red light color purity was 98.9%. These results indicate that glass ceramics containing NaLaSiO4 crystals co-doped with Ho3+-Yb3+ could be used for up-conversion color-tunable emission and red luminescence.

Characterization of new modified mesostructured silica nanocomposites fabricated for effective removal of aromatic acids

Santa Barbara Amorphous-15 (SBA-15) is a mesoporous molecular sieve with a large surface area and is extensively applied in purification, separation, and catalytic procedures. In this study, an SBA-15 was prepared from a sodium silicate precursor, and pentaethylene hexamine was anchored to its surface. A composite named N-SBA-15 was characterized using several experimental techniques. FTIR and XPS measurements confirmed that amino groups were conjugated on the surface of SBA-15. XRD and TEM confirmed that N-SBA-15 comprised highly ordered, hexagonal mesopore structures, which were not destroyed by the addition of amino groups. After functionalization, the surface area, pore volume, and pore size of the composite were 188 m2/g, 0.303 cm3/g, and 5.0 nm, respectively. N-SBA-15 was applied in the adsorption of aromatic acids, namely tannic acid (TA), acid red 1 (AR-1), and acid blue 40 (AB-40). The influence of various adsorption conditions such as dye concentration, adsorbent dosage, solution pH, and solution temperature was investigated. For AB-40 dye, the N-SBA-15 composite exhibited 40 times higher adsorption capacity than pure SBA-15. The highest adsorption capacities of N-SBA-15 for TA, AB-40, and AR-1 were 869, 818, and 308 mg/g, respectively. Thermodynamic studies were conducted to evaluate the exothermic property of the adsorption process and spontaneous behavior. The adsorptive data fitted well with pseudo-second-order and Langmuir isotherm models. Results confirmed that amino-modified SBA-15 material is a promising adsorbent for the elimination of aromatic acids form aqueous solution.

Construction of spontaneously polarized ceramic via synergistic mechanical activation‒Biomimetic mineralization for activating air and water

Spontaneously polarized crystals with intrinsic electric dipole moment have attracted immense interest as excellent functional materials for extensive applications. It is of great significance to engineer sustainable spontaneously polarized materials with fascinating characteristics and performance for activating air and water. Herein, a novel strategy based on the synergy of mechanical activation (MA) and biomimetic mineralization (BM) was created to construct spontaneously polarized ceramic. MA induced the structural damage of clay and promoted the dissolution of ions and the release of free proteins, contributing to the formation of silicate precursor in BM process. After high temperature firing, the silicate precursor in clay was converted to form KCa3AlCa3Si4O16 (hexagonal crystal system, L6 symmetry type, and P63 space group) in the resulting spontaneously polarized ceramic. The non-centrosymmetric structure of KCa3AlCa3Si4O16 and the high intrinsic electric dipole moments contributed by K(1) polyhedrons resulted in high spontaneous polarization (0.2322 μC/cm2) and far-infrared emissivity (0.951) of spontaneously polarized ceramic. In air, spontaneously polarized ceramic can activate H2O and O2 molecules to form negative air ions owing to surface electric field. In water, spontaneously polarized ceramic can disaggregate large water clusters to form small water clusters ascribed to surface electric field and far-infrared emission; water pH can be regulated from weak acidity to approximate neutrality via the capture of electrons by H+ ions to produce releasable hydrogen gas. This work provides great promise for rational design and synthesis of spontaneously polarized materials for functional applications.

Size‐controlled synthesis of mesoporous silica nanoparticles using rice husk by microwave‐assisted sol–gel method

AbstractMesoporous silica nanoparticles with distinct characteristics like particle size, tunable pores, and high surface area have received much interest for environmental remediation, energy conversion, and biological applications. In this work, we synthesized spherical silica nanoparticles with tunable particle size and mesoporous properties using a low‐cost silica source (rice husk) and polyethylene glycol (PEG) via microwave‐assisted sol–gel synthesis. The formation of an amorphous silica structure was found using XRD and FTIR analysis. FESEM analysis showed that altering the PEG concentration from .01 to .005 M produced spherical silica nanoparticles with 100–500 nm in size. Nitrogen adsorption–desorption demonstrated that silica nanoparticles obtained with .005, .007, and .01 M of PEG had unique pore sizes and distributions, with specific surface areas of 51.475, 62.367, and 84.251 m2/g, respectively. These results might be due to PEG molecules’ capping effect, which acts as a soft template to regulate particle size, pore size, and dispersion by interacting with sodium silicate precursor. Hence, this approach can be a facile and cost‐effective method to prepare mesoporous silica nanoparticles with controllable nanoscale characteristics for suitable applications.

Europium-Doped Calcium Silicate Nanoparticles as High-Quantum-Yield Red-Emitting Phosphors.

Europium ion-activated calcium silicate phosphors (Ca2SiO4:Eu3+) with sharp red-light emission were fabricated via the hydrothermal method. The size of Ca2SiO4:Eu3+ phosphors was controlled between 20 and 200 nm by precursor silicate particle sizes. Systematic studies to determine morphology, crystal phase, and photoluminescence (PL) were carried out for all the phosphors, and their optical efficiencies were compared. We found that the luminescence intensity and emission wavelength of Ca2SiO4:Eu3+ phosphors depend on their particle sizes. Particularly, the Ca2SiO4:Eu3+ synthesized with 20 nm silica seed contains the most intense red emission, high color purity, and high PL quantum yield. For the 20 nm-sized Ca2SiO4:Eu3+ phosphor, PL quantum yields are measured to be above 87.95% and high color purity of 99.8%. The unusually high intensity of 5D0 → 7F4 emission (712 nm) is explained by structural distortion arising from silicate particle size reductions. We show that the obtained phosphor is a suitable candidate for solid-state lighting as a red component through CIE chromaticity coordinate and color purity measurements. Furthermore, the Ca2SiO4:Eu3+ particles are examined for their validity as promising bio-imaging probes through cell labeling and imaging experiments and biodegradability studies.

Systematic investigation on preparation and characterization of silica shell microencapsulated phase change materials based on sodium silicate precursor

A kind of paraffin@silica (Pn@SiO2) microencapsulated phase change materials (MEPCM) were prepared by sol-gel method using sodium silicate as silica precursor. The investigation of this synthesis technique demonstrates that pH value and core/shell ratio play key role in optimizing the morphology and microstructure of Pn@SiO2 microcapsules to achieve optimal thermal storage properties. Therefore, we systematically investigated the effects of pH value and core/shell ratio on the microstructure, crystallization behavior and phase transition properties of Pn@SiO2. It was determined that at pH 3 and Pn/SiO2 ratio of 5:1, the synthesized Pn@SiO2 exhibited well-defined core-shell structure and regularly spherical morphology. The encapsulation rate reached 74.14 % with latent heat of about 186.4 J/g due to the formation of perfect microstructure and morphology. In addition, Pn@SiO2 presents excellent heat storage capacity, high thermal stability and good shape stability, and shows reliable and durable phase-change performance. In summary, sodium silicate was used as the SiO2 precursor for the first synthesis of MEPCM with high encapsulation rate and regularly spherical morphology.

The effect of synthesis parameters on pore diameter of superhydrophobic silica aerogel prepared at ambient pressure

Silica aerogels were prepared by the sol-gel method and dried at ambient pressure with sodium silicate precursor. The prepared aerogel is superhydrophobic. The effect of various synthesis conditions on pore structure and diameter was investigated. The results of N2 adsorption-desorption isotherms, BET theory, BJH method, and field emission scanning electron microscopy images showed that by changing the surface modification method, the porosity of the samples changes. The order of increasing the average pore diameter for different protic solvents is isopropanol < methanol < ethanol. The specific surface area and total pore volume also increase with the increasing concentration of citric acid citric. The sample surface modified with HMDZ has smaller average pore diameters and total pore volume than the sample surface modified with TMCS. With increasing temperature, the average pore diameter and total pore volume increase, and the BET surface decreases.