Search Results (17)

The interaction between carbon dioxide and molecularly confined pharmaceutical compounds can result in CO₂ retention that exceeds that achieved through conventional physical adsorption. This study investigates CO₂ retention following sorption in hydrophilic and hydrophobic silica aerogels containing the fenamates mefenamic acid and flufenamic acid. The Thermal stability of the retained CO₂ was characterized using temperature-programmed oxidation and temperature-programmed desorption measurements. Concurrently, single-point nitrogen adsorption measurements monitored relative changes in the apparent accessible surface area of the porous matrix. Untreated silica aerogels did not exhibit a significant CO₂ desorption peak at elevated temperatures. In contrast, all composites containing fenamates exhibited an additional high-temperature desorption step beginning at approximately 225 °C, indicating enhanced CO₂ retention after sorption once the external CO₂ layer was removed. This characteristic persisted following preliminary thermal treatment, suggesting it is not solely attributable to residual volatile substances. Surface-area measurements indicated minimal changes in the original aerogels after the CO₂ cycle, whereas composites with flufenamic acid demonstrated more pronounced alterations. Considering previous nuclear magnetic resonance, spectroscopic, and computational studies, these findings suggest a combined effect of nanoconfinement, surface-dependent interfacial phenomena, and specific interactions involving the fenamate-containing phase. Reversible chemical interactions may contribute to the observed retention, although the current measurements do not allow for quantitative separation of their effects from those of physical confinement. Full article

Hydrophobic and salt-storage functionalization can impart anti-icing capability to asphalt, but the associated changes in rheological behavior should be evaluated concurrently. In this study, silica aerogel and potassium acetate-loaded diatomite were incorporated as hydrophobic and salt-storage components, respectively. Contact angle and leachate conductivity were used to characterize surface wettability and ion-release response, while temperature sweep, frequency sweep, multiple-stress creep and recovery, bending-beam rheometer, and linear amplitude sweep tests were conducted to evaluate rheological performance. A compromise formulation was subsequently selected using multi-objective evaluation and the response surface methodology. The hydrophobic component increased the contact angle of asphalt, whereas the salt-storage component generated a time-dependent aqueous ion-release response. Composite modification improved high-temperature deformation resistance but increased low-temperature creep stiffness and reduced stress-relaxation capacity and fatigue life, indicating a clear rheological trade-off associated with functionalization. The selected formulation contained an 8% hydrophobic component and a 14.6% salt-storage component. At the mixture scale, this formulation reduced ice accumulation by 48.3%, lowered the freezing temperature of a 1 mm water film by approximately 2.8 °C, and decreased the apparent ice–pavement shear strength at −10 °C from 0.71 to 0.45 MPa relative to the control. These results indicate that hydrophobic and salt-storage components contribute differently to anti-icing behavior while jointly altering the rheological response of asphalt. Full article

Silica aerogel–incorporated cementitious composites possess low density and thermal conductivity. Their thermal conductivity is influenced by the interplay of mix composition, pore structure, mineral admixtures, and environmental testing conditions. In this study, a literature-derived database containing 208 data records was established for thermal conductivity prediction. Eight variables were utilized as inputs: aerogel content, water-to-cement ratio (W/C), sand content, foam content, silica fume content, fly ash content, testing temperature, and testing relative humidity. Thermal conductivity was designated as the output. The models developed for this study included XGBoost, random forest (RF), support vector regression (SVR), and their counterparts optimized using particle swarm optimization (PSO), which were subsequently compared. Among the optimized models, PSO–SVR showed the most balanced predictive performance, with test-set R², RMSE, and MAE values of 0.9306, 0.1005, and 0.0658, respectively. SHAP analysis identified sand content as the most important variable, followed by W/C and aerogel content. Mechanistically, silica aerogel reduces effective thermal conductivity by introducing low-conductivity phases, weakening solid heat–transfer networks, increasing heat–flow tortuosity, and accumulating interfacial thermal resistance. This study provides a data–driven and interpretable approach for thermal conductivity prediction and low–conductivity mix design of silica aerogel–incorporated cementitious composites. Full article

Facing the increasingly severe energy challenges and environmental problems, the development of thermally stable, lightweight, and thermal insulating materials is critical. Herein, we report an organic-inorganic composite strategy combined with a high-temperature carbonization step to fabricate aerogel-containing composites synergistically reinforced with chopped glass fibers and hollow glass microspheres. By systematically varying the ratio of acrylic emulsion to potassium silicate solution, we investigated the effects on the forming behavior, microstructure, hydrophobicity, thermal stability, and thermal insulation performance. Increasing the acrylic emulsion fraction substantially enhanced hydrophobicity, yielding a maximum water contact angle of 129.3°. Concurrently, the apparent density decreased from 0.18 g/cm³ to 0.09 g/cm³ and the thermal conductivity dropped from 57.9 mW/(m·K) to 29.0 mW/(m·K). Mechanical testing revealed that the compressive Young’s modulus decreased with increasing acrylic content, from 3.6 MPa for the purely inorganic sample to 0.55 MPa at 70% acrylic content, reflecting a trade-off between stiffness and organic-derived porosity. Microstructural characterization revealed a hierarchical porous network in which uniformly dispersed hollow glass microspheres and the aerogel-derived silica network form an efficient thermal barrier system. Thermogravimetric analysis demonstrated excellent thermal stability, with total weight loss below 5% up to 800 °C. Infrared thermography analysis showed that, after unilateral heating at 300 °C and 400 °C for 10 min, the backside surface temperature of the composites decreased as the acrylic emulsion content increased. At 300 °C, the temperature decreased from 176.1 °C for AP-1 to 151.0 °C for AP-4, while at 400 °C, it decreased from 228.5 °C to 199.3 °C. These results indicate that the composites exhibit effective thermal insulation and maintain structural stability under high-temperature exposure. Taken together, this facile and scalable approach yields these aerogel-containing composites that combine low density, low thermal conductivity, robust structural integrity, and good environmental resistance, as evidenced by a water contact angle of 129.3°, making them promising candidates for aerospace, building, and industrial high-temperature insulation applications. Full article

Porous silica gel powders, doped with gold nanoparticles (AuNPs), were obtained by heating silica gels containing 1-dodecanethiol and tetrachloroauric acid at temperatures of 450 °C, 700 °C and 900 °C, and characterized using X-ray diffraction, TEM/EDS studies, UV/Vis reflectance spectroscopy and DTA/TG investigations. The color and microstructure of the obtained samples with a composition SiO₂:AuNPs (about 0.03% Au) depend on the heating temperature. The UV/Vis reflection spectra of the samples are explained using Mie’s theory. The thermal stability of the obtained samples, as well as the processes occurring in the sol–gel matrix upon heating, were monitored by DTA/TG. The textural properties of the obtained materials were described based on adsorption–desorption isotherms. The obtained nanocomposites are promising pigments for ceramic glazes, similar to the Purple of Cassius. The textural properties of certain samples, S_BET = 200–350 m²/g, a mean pore diameter (D_AV) of approximately 10 nm and a specific pore volume (V_t) between 0.5 and 0.8 cm³/g, make them promising candidates for catalytic applications, comparable to aerogel-like materials. Full article

Aerogel fibers, characterized by their ultra-low density and ultra-low thermal conductivity, are an ideal candidate for personal thermal management as they hold the potential to effectively reduce the energy consumption of room heating and significantly contribute to energy conservation. However, most aerogel fibers have weak mechanical properties or require complex manufacturing processes. In this study, simple continuous silk fibroin–agarose composite aerogel fibers (SCAFs) were prepared by mixing agarose with silk fibroin through wet spinning and rapid gelation, followed by solvent replacement and supercritical carbon dioxide treatment. Among them, the rapid gelation of the SCAFs was achieved using agarose physical methods with heat-reversible gel properties, simplifying the preparation process. Hydrophobic silk fibroin–agarose composite aerogel fibers (HSCAFs) were prepared using a simple chemical vapor deposition (CVD) method. After CVD, the HSCAFs’ gel skeletons were uniformly coated with a silica layer containing methyl groups, endowing them with outstanding radial elasticity. Moreover, the HSCAFs exhibited low density (≤0.153 g/cm³), a large specific surface area (≥254.0 m²/g), high porosity (91.1–94.7%), and excellent hydrophobicity (a water contact angle of 136.8°). More importantly, they showed excellent thermal insulation performance in low-temperature (−60 °C) or high-temperature (140 °C) environments. The designed HSCAFs may provide a new approach for the preparation of high-performance aerogel fibers for personal thermal management. Full article

Both cyclodextrin (CD) and porous silica possess interesting properties of adsorption and release. A silica–CD hybrid, therefore, could synergically merge the properties of the two components, giving rise to a material with appealing properties for both environmental and pharmaceutical applications. With this aim, in the present study, a first hybrid is obtained through one-pot sol–gel synthesis starting from CD and tetramethyl orthosilicate (TMOS) as a silica precursor. In particular, methyl-β-cyclodextrin (bMCD) is selected for this purpose. The obtained bMCD–silica hybrid is a dense material containing a considerable amount of bMCD (45 wt.%) in amorphous form and therefore represents a promising support. However, since a high specific surface area is desirable to increase the release/adsorption properties, an attempt is made to produce the hybrid material in the form of an aerogel. Both the synthesis of the gel and its drying in supercritical CO₂ are optimized in order to reach this goal. All the obtained samples are characterized in terms of their physico-chemical properties (infra-red spectroscopy, thermogravimetry) and structure (X-ray diffraction, electron microscopy) in order to investigate their composition and the interaction between the organic component (bMCD) and the inorganic one (silica). Full article

Water pollution caused by heavy metal ions has attracted worldwide attention. In this work, gold tailings were used as raw materials and the sol–gel method combined with the atmospheric pressure drying method were used to achieve the low-cost preparation of a silica aerogel. (3-Aminopropyl) triethoxysilane (APTES), ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), and chitosan were used to modify the silica aerogel, which was then used as an adsorbent for the adsorption of copper ions in wastewater. The adsorbent type, adsorption time, copper ion concentration, and pH value were investigated as variables to explore the best adsorption conditions. The adsorption mechanism was also elaborated on. The crystal structure, surface morphology, surface functional groups, chemical composition, and specific surface area of the aerogels and the modified aerogels were characterized by various physiochemical characterizations such as XRD, SEM, FT-IR, XRF, and BET. The results showed that the prepared silica aerogel contained 91.1% SiO₂, mainly amorphous SiO₂, and amino and carboxyl groups. Other functional groups were successfully grafted onto the silica aerogels. The original silica aerogels and modified silica aerogels had a large specific surface area, total pore volume, and pore diameter. When copper ions were adsorbed by the chitosan-modified silica aerogels, the adsorption capacity of the copper ions was the highest (33.51 mg/g) under the conditions of a copper ion concentration of 100 mg/L, a pH value of 7, and an adsorption time of 2 h. The adsorption of Cu²⁺ was mainly due to the ion exchange and electrostatic gravity. Full article

Silica aerogel composites with recycled tire rubber have been synthesized and evaluated for their potential use for thermal protection in buildings. The present work describes for the first time the preparation of silica-based aerogel composites containing recycled rubber tires reinforced with polyvinyl butyral (PVB) by hot pressing. The developed composite was extensively characterized regarding its physical, morphological, thermal and mechanical features, and the results showed their properties were relevant, leading to composites with different properties/performances. The obtained bulk density values were satisfactory, down to 474 kg·m⁻³, and very good thermal properties were achieved, namely, thermal conductivity as low as 55 mW·m⁻¹·K⁻¹ for composites with silica aerogel, recycled tire rubber and PVB. The most promising composites were those based on low bulk density and thermal conductivity values, and they were thermally stable, indicating their suitability for thermal insulation applications. Full article

Blown films based on low-density polyethylene (LDPE)/linear low-density polyethylene (LLDPE) and silica aerogel (SA; 0, 0.5, 1, and 1.5 wt.%) were obtained at the pilot scale. Good particle dispersion and distribution were achieved without thermo oxidative degradation. The effects of different SA contents (0.5–1.5 wt.%) were studied to prepare transparent-heat-retention LDPE/LLDPE films with improved material properties, while maintaining the optical performance. The optical characteristics of the composite films were analyzed using methods such as ultraviolet–visible spectroscopy and electron microscopy. Their mechanical characteristics were examined along the machine and transverse directions (MD and TD, respectively). The MD film performance was better, and the 0.5% composition exhibited the highest stress at break. The crystallization kinetics of the LDPE/LLDPE blends and their composites containing different SA loadings were investigated using differential scanning calorimetry, which revealed that the crystallinity of LDPE/LLDPE was increased by 0.5 wt.% of well-dispersed SA acting as a nucleating agent and decreased by agglomerated SA (1–1.5 wt.%). The LDPE/LLDPE/SA (0.5–1.5 wt.%) films exhibited improved infrared retention without compromising the visible light transmission, proving the potential of this method for producing next-generation heat retention films. Moreover, these films were biaxially drawn at 13.72 MPa, and the introduction of SA resulted in lower draw ratios in both the MD and TD. Most of the results were explained in terms of changes in the biaxial crystallization caused by the process or the influence of particles on the process after a systematic experimental investigation. The issues were strongly related to the development of blown nanocomposites films as materials for the packaging industry. Full article

β-Tricalcium phosphate was combined with silica aerogel in composites prepared using the sol–gel technique and supercritical drying. The materials were used in this study to check their biological activity and bone regeneration potential with MG63 cell experiments. The composites were sintered in 100 °C steps in the range of 500–1000 °C. Their mechanical properties, porosities, and solubility were determined as a function of sintering temperature. Dissolution studies revealed that the released Ca-/P molar ratios appeared to be in the optimal range to support bone tissue induction. Cell viability, ALP activity, and type I collagen gene expression results all suggested that the sintering of the compound at approximately 700–800 °C as a scaffold could be more powerful in vivo to facilitate bone formation within a bone defect, compared to that documented previously by our research team. We did not observe any detrimental effect on cell viability. Both the alkaline phosphatase enzyme activity and the type I collagen gene expression were significantly higher compared with the control and the other aerogels heat-treated at different temperatures. The mesoporous silica-based aerogel composites containing β-tricalcium phosphate particles treated at temperatures lower than 1000 °C produced a positive effect on the osteoblastic activity of MG63 cells. An in vivo 6 month-long follow-up study of the mechanically strongest 1000 °C sample in rat calvaria experiments provided proof of a complete remodeling of the bone. Full article

Rigid polyurethane foams (RPUFs) are widely used in many fields, but they are easy to burn and produce a lot of smoke, which seriously endangers the safety of people’s lives and property. In this study, tetraethyl(1,5–bis(bis(2–hydroxypropyl)amino)pentane–1,5–diyl)bis(phosphonate) (TBPBP), as a phosphorus–nitrogen–containing reactive–type flame retardant, was successfully synthesized and employed to enhance the flame retardancy of RPUFs, and silica aerogel (SA) powder was utilized to reduce harmful fumes. Castor oil–based rigid polyurethane foam containing SA powder and TBPBP was named RPUF–T45@SA20. Compared with neat RPUF, the obtained RPUF–T45@SA20 greatly improved with the compressive strength properties and the LOI value increased by 93.64% and 44.27%, respectively, and reached the V–0 rank of UL–94 testing. The total heat release (THR) and total smoke production (TSP) of RPUF–T45@SA20 were, respectively, reduced by 44.66% and 51.89% compared to those of the neat RPUF. A possible flame–retardant mechanism of RPUF–T45@SA20 was also proposed. This study suggested that RPUF incorporated with TBPBP and SA powder is a prosperous potential composite for fire and smoke safety as a building insulation material. Full article

Polyurethane foam (PUF) has generally been used in liquefied natural gas (LNG) carrier cargo containment systems (CCSs) owing to its excellent mechanical and thermal properties over a wide range of temperatures. An LNG CCS must be designed to withstand extreme environmental conditions. However, as the insulation material for LNGC CCSs, PUF has two major limitations: its strength and thermal conductivity. In the present study, PUFs were synthesized with various weight percentages of porous silica aerogel to reinforce the characteristics of PUF used in LNG carrier insulation systems. To evaluate the mechanical strength of the PUF-silica aerogel composites considering LNG loading/unloading environmental conditions, compressive tests were conducted at room temperature (20 °C) and a cryogenic temperature (−163 °C). In addition, the thermal insulation performance and cellular structure were identified to analyze the effects of silica aerogels on cell morphology. The cell morphology of PUF-silica aerogel composites was relatively homogeneous, and the cell shape remained closed at 1 wt.% in comparison to the other concentrations. As a result, the mechanical and thermal properties were significantly improved by the addition of 1 wt.% silica aerogel to the PUF. The mechanical properties were reduced by increasing the silica aerogel content to 3 wt.% and 5 wt.%, mainly because of the pores generated on the surface of the composites. Full article

The present work describes for the first time the preparation of silica-based aerogel composites containing tetraethoxysilane (TEOS) and vinyltrimethoxysilane (VTMS) reinforced with Kevlar^® pulp. The developed system was extensively investigated, regarding its physical, morphological, thermal and mechanical features. The obtained bulk density values were satisfactory, down to 208 kg·m⁻³, and very good thermal properties were achieved—namely a thermal conductivity as low as 26 mW·m⁻¹·K⁻¹ (Hot Disk^®) and thermal stability up to 550 °C. The introduction of VTMS offers a better dispersion of the polyamide fibers, as well as a higher hydrophobicity and thermal stability of the composites. The aerogels were also able to withstand five compression-decompression cycles without significant change of their size or microstructure. A design of experiment (DOE) was performed to assess the influence of different synthesis parameters, including silica co-precursors ratio, pulp amount and the solvent/Si molar ratio on the nanocomposite properties. The data obtained from the DOE allowed us to understand the significance of each parameter, offering reliable guidelines for the adjustment of the experimental procedure in order to achieve the optimum properties of the studied aerogel composites. Full article

Silica aerogel-based materials exhibit a great potential for application in many industrial applications due to their unique porous structure. In the framework of this study, carbon fiber and nickel coated carbon fiber–silica aerogel nanocomposites were proposed as effective electromagnetic shielding material. Herein, the initial oxidation of the surface of carbon fibers allowed the deposition of a durable Ni metallic nanolayer. The fibers prepared in this way were then introduced into a silica aerogel structure, which resulted in obtaining two nanocomposites that differed in terms of fiber volume content (10% and 15%). In addition, analogous systems containing fibers without a metallic nanolayer were studied. The conducted research indicated that carbon fibers with a Ni nanolayer present in the silica aerogel structure negatively affected the structural properties of the composite, but were characterized by two-times higher electrical conductivity of the composite. This was because the nickel nanolayer effectively blocked the binding of the fiber surface to the silica skeleton, which resulted in an increase of the density of the composite and a reduction in the specific surface area. The thermal stability of the material also deteriorated. Nevertheless, a very high electromagnetic radiation absorption capacity between 40 and 56 dB in the frequency range from 8 to 18 GHz was obtained. Full article