•Thermal properties of window containing PCM and silica aerogel were investigated.•A numerical model is established and verified.•Effects of thermal conductivity, density, specific heat and thickness ...were analyzed.•The most significant parameters are thickness and conductivity of silica aerogel.•The optimum silica aerogel thickness is 20–30 mm.
This paper investigates the thermal performance of glass window composed of glass, silica aerogel and phase change material (PCM), which concurrently provides storage and restitution of heat, super thermal insulation and daylighting to the interior environment. To assess the glass window thermal behavior, a numerical model describing the heat transfer mechanisms occurring in the PCM layer in combination with the other transparent wall layers was established and verified. Then, the influence of factors such as thermal conductivity, density, specific heat and thickness of silica aerogel on the thermal performance of the glass window was analyzed. The results show that the most significant controlling parameters are the thermal conductivity and thickness of silica aerogel, while the impact of density and specific heat of silica aerogel on the thermal performance of glazing unit is marginal. A proper thickness of aerogel that maximizes the exploitation of latent heat of PCM should be identified, which is between20 and 30 mm for the studied climatic conditions. It was concluded that integrating silica aerogel insulation into PCM-glass window system is an effective technology in cold regions, solving the problem that PCM cannot effectively exploit latent heat, while retaining the advantages of PCM in winter.
In order to inhibit the serious damage of pore structure of silica template during the conventional hydrothermal method to prepare Ni-phyllosilicate material, a solvothermal method using double ...solvent, a small amount of water and a large amount of hydrophobic n-pentane, was proposed to synthesize FDU-12 derived Ni-phyllosilicate in this work. Water can infiltrate the inside channels of FDU-12 owing to more hydrophilic silica hydroxyl groups, and the hydrophobic n-pentane tends to surround the outside of FDU-12. The growth of Ni-phyllosilicate occured only inside channels rather than surface, and the addition of urea could improve its formation at 180 °C in 12 h. As a result, the optimal catalyst retained the pore structure of FDU-12 and obtained fine Ni particle size of 1.5 nm after 750 °C reduction in H.sub.2 flow, which exhibited CO.sub.2 conversion of 77.0% and CH.sub.4 selectivity of 94.7% at 450 °C, 60 L·g.sup.-1·h.sup.-1. In addition, this catalyst showed high long-term stability in a 100 h-lifetime test with high anti-sintering property derived from Ni-phyllosilicate.
Three mesoporous silica materials (MCM-41, MSN and BMMs) possessing different morphologies but similar hexagonal arranged mesopores with almost the same pore size (2-3 nm) were functionalized by Zn ...and 1-(trimethoxysilyl)propyl-3-methylimidazolium ionic liquid (ILs) via post-grafting treatment. The ILs grafted mesoporous silicas were then characterized by porosity, microscopy and SAXS techniques, and the successful loading of Zn and ILs, as well as the different distribution of functional groups in different supports were shown. Furthermore, the cycloaddition reaction of CO.sub.2 with epoxide was employed to evaluate the influences of the ILs distribution, which was proved to be caused mainly by varying morphologies of different supports. All the catalysts showed good catalytic activities. Interestingly, at low temperature, the inter particle supported ILs in BMMs had the highest catalytic efficiency, while the aggregation grafting ILs on MCM-41 present the lowest activity. However, the mesoporous silicas with ordered arranged nanopores present the superiority at higher temperature. The results highlight the crucial role played by the morphology of the supports.
Silica aerogel, a kind of nanoporous material, is regarded as a desired drug carrier for its low toxicity, high specific surface area, and excellent biocompatibility. Using silica aerogel in a drug ...carrier may be an appropriate method to improve the performance of pure resveratrol. In this study, resveratrol-loaded silica aerogel (RSA) as a drug delivery system was prepared by the sol-gel method. Before gelling, resveratrol was added into the hydrolyzed tetraethyl orthosilicate (TEOS) ethanol solution then dispersed by stir and ultrasound. The results showed that RSA has a high loading rate of 19% with low cost and excellent biocompatibility. The SEM images showed that silica aerogel wraps up outside the resveratrol. Sustained releasing effect could be observed in RSA after 1 h, while pure resveratrol did not display this. The release of RSA lasted for over 6 h, and the release amount reached over 90% and 80% in either simulated gastric fluid (pH = 2.0) or phosphate-buffered saline (pH = 7.4) at 37 °C. Preliminary in vitro toxicity test revealed RSA to be biocompatible and stable; and when coupled with the anti-inflammatory effects of resveratrol, showed good potential for osteoarthritis treatment.
The synthesis of C.sub.2 oxygenates including ethanol directly from coal-derived syngas is significant from both academic and practical points of view and SiO.sub.2 supported Rh-based catalysts are ...very effective for this conversion. However, the high price of Rh requires the improvement of its dispersion to maximize Rh efficiency. The adjustment of impregnation solution pH value can modify effectively the metal dispersion over the support. Herein, we reported the pH effect on catalytic performance of Rh-Mn-Li/SiO.sub.2 for CO hydrogenation to C.sub.2 oxygenates for the first time. A series of catalysts were prepared from different pH values of impregnation solutions, and were characterized by various techniques. With the increasing of solution pH value above zero point of charge (ZPC) of silica, Rh particle sizes increased with much wider size distribution and reduction of Rh species was restrained over the prepared catalysts owing to the stronger interaction between Rh and support. As a result, the active sites for CO insertion, especially for CO or H.sub.2 dissociation was lowered, leading to the depletion of the activity for the formation of C.sub.2 oxygenates from CO hydrogenation, and larger Rh particle size with wider size distribution favors the production of long chain hydrocarbons. On the contrary, when the catalyst was prepared using solution with pH below ZPC of silica, the dispersion and the reduction of Rh were promoted due to suitable Rh-support interaction, and in the CO hydrogenation reaction, the space time yield and selectivity of C.sub.2 oxygenates reached 679.4 g/kg-cat/h and 73.3%, respectively. Graphic The pH value of impregnating solution regulate the metal-support interaction and thus Rh particle sizes and its reduction, which effects strongly CO hydrogenation activity and selectivity.
Pretreated silica sand labeling using varying concentrations of tin(II) fluoride and chloride as reducing agents and different times labeling was performed in order to develop a methodology for ...labeling silica sand with .sup.99mTc for using as solid radiotracer. Influence of different sand pretreatment parameters on the sorption yield (R.sub.ret%) was statistically evaluated. The effectiveness of the methods used to reduce pertechnetate (.sup.99mTcO.sub.4.sup.-) by ascending paper chromatography was confirmed. Results show relatively high values of .sup.99mTc sorption yields on silica sand. It was possible to establish a methodology for obtaining solid .sup.99mTc labeled radiotracers in support of silica sand.
Niobium–silica mesoporous catalysts can be easily prepared via solventless dry impregnation from niobocene dichloride. They showed good activity, excellent chemoselectivity and unexpected ...regioselectivity in the liquid-phase epoxidation of limonene with aqueous hydrogen peroxide as oxidant. Display omitted
► Preparation of niobium–silica mesoporous catalysts via solventless dry impregnation. ► Good activity and excellent selectivity in liquid-phase epoxidation with aqueous H2O2. ► Good yield in limonene epoxide production with unexpected regioselectivity.
A series of niobium catalysts for the selective epoxidation was synthesised by post-synthesis modification of a commercial silica, starting from niobocene dichloride through solventless organometallic precursor dry impregnation (OM-DI) or conventional liquid-phase grafting technique. OM-DI showed to be cheaper, more versatile, less time-consuming and avoided the use of environmentally unfriendly chlorinated solvents. Nb–SiO2 catalysts displayed an excellent performance in the epoxidation of limonene, using aqueous hydrogen peroxide as oxidant. Niobium–silica catalysts were obtained via OM-DI for the first time in this occasion. They showed conversions up to 78% and chemoselectivity to epoxide of 98%. An unexpected regioselectivity to exocyclic epoxide was also observed.
The literatures about superhydrophobic coatings (SHCs) are increasing every year, however, undesirable chemicals including organic solvents and fluorinated compounds are intensively used in the ...existing preparation methods, which seriously hinder their large scale production and practical applications. Herein, a simple approach for preparation of totally waterborne, fluorine-free and durable SHCs is reported. First, a waterborne suspension of hexadecyl polysiloxane modified SiO
(SiO
@HD-POS) was prepared via HCl-catalyzed hydrolytic condensation of hexadecyltrimethoxysilane (HDTMS) and tetraethoxysilane with SiO
nanoparticles. The SHCs with high water contact angles (CA = 163.9°) and low sliding angles (SA = 3.7°) were prepared simply by sequentially spray-coating a polyurethane (PU) waterborne solution and the SiO
@HD-POS waterborne suspension onto glass slides. The influences of SiO
, HDTMS, reaction time and fabrication temperature on superhydrophobicity were investigated. The SHCs can withstand 80 m of reciprocating abrasion against A4 paper at 4.5 kPa and impacting of at least 50 g of sand microparticles with 30 cm release height. Moreover, the coatings also show exceptional thermostability in boiling water. The SHCs showed promising applications in various areas including oil/water separation and preventing scald, as the method is environmental benign and the coatings are applicable onto various substrates.
Morphology, glass transition and molecular dynamics of polydimethylsiloxane (PDMS) adsorbed onto three types of silica nanoparticles, namely Stöber, fumed-pyrogenic, and silica gel, were studied ...employing scanning electron microscopy (SEM), isothermal nitrogen adsorption–desorption, calorimetry (DSC) and broadband dielectric spectroscopy (BDS) techniques. The initial Stöber particles (specific surface area SBET ∼240 m2/g) form a quite loose silica network with mainly textural pores of ∼12 nm in size. Fumed silica (SBET ∼260 m2/g) demonstrates denser aggregation and increased textural porosity (∼11 nm), while silica gel (SBET ∼850 m2/g) exhibits tremendous intraparticle porosity (tubular-like pores of ∼6 nm). On adsorption of PDMS (at ∼20 and ∼30 wt%), the glass transition temperature (Tg) decreases as compared to the bulk, while the glass transition step broadens. Results suggest loosened molecular packing of the polymer chains accompanied by a broadening of the range of relaxation times in the composites as compared to the neat polymer. On the other hand, the heat capacity step at glass transition is significantly suppressed in the composites, suggesting the formation of a rigid polymer fraction (RAF) at the interfaces with nanoparticles due to strong physical interaction (hydrogen bonding). RAF increases in the order Stöber < fumed (A300) < silica gel, this increase following that of SBET, in agreement with results in previous work on silica/PDMS systems. Next to the segmental dynamics (α relaxation) of the bulk-like polymer related to the glass transition, BDS allowed the detection of a separate segmental-like relaxation of the polymer in the interfacial silica-PDMS zone. In terms of timescale the interfacial relaxation is almost identical for Stöber and A300, and slightly faster for silica gel. Comparison of the results of the present work with previous results obtained with similar nanocomposites based on low molecular weight PDMS and silica, provides additional support to recently proposed ‘SBET–interfacial dynamics’ and ‘chain packing–polymer dynamics’ correlations.
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•Specific surface area of initial silicas Stöber (240 m2/g)<fumed (260 m2/g)<silica gel (850 m2/g).•In silica/PDMS composites Tg decreases and range of relaxation times increases.•Indications for rigid amorphous fraction (RAF) in the interfacial layer by DSC.•Retarded mobility of the interfacial polymer by BDS, αint relaxation next to α of the bulk.•RAF and interfacial dynamics governed by specific surface area (SBET).
In this paper, we discuss the unique challenges posed by Silicaf/Silica composite while measuring their thermal conductivity by using Transient Plane Source (TPS) method and specific heat by ...Differential Scanning Calorimeter (DSC). The measured thermal conductivity values were found reaching a plateau followed by a reduction at temperatures 800 °C and above. Thermal expansion characteristics as measured in Thermomechanical Analyzer (TMA) exhibited strong dependency on static force applied during experiments. Keeping in view the real life application of the developed Silicaf/Silica composite, a novel method of sample preparation was implemented which restricted the sample compression at elevated temperatures during TPS experiments. Experiments utilizing DSC under linear and step heating with sample placement in alumina crucible yielded inconsistent values of specific heat (Cp). With further experimentation, the combination of step heating and direct placement of sample in platinum crucible was found most appropriate for accurate measurement of specific heat of Silicaf/Silica.
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