Ambient Pressure Drying Research Articles

Fabrication of super-elastic graphene aerogels by ambient pressure drying and application to adsorption of oils

Three-dimensional graphene-based aerogels have promising applications in oil adsorption and environmental restoration. However, current research of graphene-based aerogels is often hindered by high preparation cost, poor mechanical properties and low recycling efficiency. Here, super-elastic graphene aerogel (SGA) was prepared through one-step freezing and twice hydrothermal reduction followed by drying under ambient pressure. The simple atmospheric drying provides a possibility for large-scale preparation of high performance graphene-based aerogels. The prepared SGA not only has the ability of highly repeatable compression rebound, but also exhibits excellent oil adsorption performance. And the overall performance of SGA is better than most of graphene-based aerogels prepared by freeze drying. After the SGA was cyclically compressed with 70% strain for 300 times, it can return to the original shape and height substantially. SGA retained about 90% of the initial adsorption capacity after 50 cycles of adsorption and compression regeneration for cyclohexane.

Silica-Based Aerogel Composites Reinforced with Reticulated Polyurethane Foams: Thermal and Mechanical Properties.

In this work, silica aerogel composites reinforced with reticulated polyurethane (PU) foams have been manufactured having densities in the range from 117 to 266 kg/m3 and porosities between 85.7 and 92.3%. Two different drying processes were employed (ambient pressure drying and supercritical drying) and a surface modification step was applied to some of the silica formulations. These composites, together with the reference PU foam and the monolithic silica aerogels, were fully characterized in terms of their textural properties, mechanical properties and thermal conductivities. The surface modification with hexamethyldisilazane (HMDZ) proved to improve the cohesion between the reticulated foam and the silica aerogels, giving rise to a continuous network of aerogel reinforced by a polyurethane porous structure. The samples dried under supercritical conditions showed the best interaction between matrixes as well as mechanical and insulating properties. These samples present better mechanical properties than the monolithic aerogels having a higher elastic modulus (from 130 to 450 kPa), a really exceptional flexibility and resilience, and the capacity of being deformed without breaking. Moreover, these silica aerogel-polyurethane foam (Sil-PU) composites showed an excellent insulating capacity, reaching thermal conductivities as low as 14 mW/(m·K).

Facile preparation of nano-SiO2 composites with excellent high-temperature thermal insulation performance

Inorganic thermal insulation materials can greatly reduce heat loss from high-temperature equipment, thereby supporting energy-saving technologies. Among these nano-SiO2 composites have promising application potential, which is limited by their existing preparation methods. This study aims to develop a low-cost high-performance thermal insulator. Nano-SiO2 composites were prepared by the wet impregnation of glass fibre felt with nano-SiO2 aqueous slurry and ambient pressure drying. The density of the composite linearly increased from 0.17 to 0.24 g/cm3 when the solid content of the slurry was increased from 5% to 15%. As the density of the composite increased, the thermal conductivity at 300–700 °C decreased. The introduction of SiC to the composites significantly improved their thermal insulation performance. The composite with SiC exhibited a thermal conductivity of 0.1334 W/(m·K) at 700 °C, which is better than its commercial counterpart of SiO2 aerogel felt. The rear surface temperatures of the composites at 700 °C with different pressures of 0.01–0.1 MPa were investigated to comprehensively understand the thermal insulation performances. Overall, a facile, efficient, safe, and eco-friendly preparation for nano-SiO2 composites have good prospect in the field of industrial energy saving.

Transparent, robust, and machinable hybrid silica aerogel with a “rigid-flexible” combined structure for thermal insulation, oil/water separation, and self-cleaning

Silica aerogel has many attractive properties, but poor mechanical properties severely limit its practical applications. Many reinforcement strategies have been implemented, however, most of which usually impair other properties of aerogel. Herein, we report a hybrid silica aerogel with excellent comprehensive performance using methyltriethoxysilane (MTES) and multi-alkoxy polyhedral oligomeric silsesquioxane (POSS) with a “rigid-flexible” combined structure as co-precursors by ambient pressure drying. The resulting hybrid aerogel has high strength (compressive strength of 16.25 MPa), low density (0.23 g·cm−3), uniform mesopores (10–30 nm), high specific surface area (815 m2·g−1), low thermal conductivity(28.6 mW·m−1·k−1), good thermal stability (>470 °C), high transparency (>80%) and superhydrophobicity (water contact angle of 152°) with excellent oil/water separation capability and self-cleaning properties. Moreover, the hybrid aerogel shows superb compressive resilience (up to 70% strain) and exceptional fatigue resistance (at the strain of 40% for 30 times). Benefiting from outstanding mechanical properties, the hybrid aerogel is machinable and can be cut into various shapes with a knife. The multifunctional hybrid aerogel holds great promise for the practical applications of transparent energy-saving building, thermal insulation, and oil/water separation.

Oxygen self-doped carbon aerogels: A solid-phase microextraction fiber coating for the extraction and detection of trace phthalate esters

ABSTRACT In this study, an oxygen self-doped carbon aerogel (ODCA), synthesized via ambient pressure drying and carbonization, was employed as solid-phase microextraction (SPME) coating material for phthalate esters (PAEs) detection in water samples by gas chromatography (GC) coupled with a flame ionization detector (FID). The materials were obtained by incomplete carbonization of the phenolic aerogel at a controlled temperature of 950°C, which leads to a certain amount of oxygen self-doping in the carbon aerogel. The ODCA-coated fiber exhibited fascinating extraction properties for PAEs mainly due to its oxygen active sites, π-π interaction, high surface area, and porosity of carbon aerogel. This as-proposed fiber showed wide linearity ranges (0.5–500, 1.0–500, 1.0–1000, 2.0–500 μg L−1, respectively), and provided low limits of detection (LOD, 0.17–0.83 μg L−1) for PAEs analysis under the optimal conditions. The single fiber and fiber-to-fiber relative standard deviations at 100 μg L−1 were observed in the range of 5.31%–10.37% and 9.17%–16.65%, respectively. Moreover, this method was also used for the determination of five PAEs in real water samples.

Springback effect and structural features during the drying of silica aerogels tracked by in-situ synchrotron X-ray scattering

The springback effect during ambient pressure drying of aerogels is an interesting structural phenomenon, consisting of a severe shrinkage followed by almost complete re-expansion. The drying of gels causes shrinkage, whereas re-expansion is believed to be linked to repelling forces on the nanoscale. A multi-scale structural characterization of this significant volume change is key in controlling aerogel processing and properties. In this work, hydrophobic, monolithic silica aerogels with high specific surface areas were synthesized by modification with trimethylchlorosilane and ambient pressure drying. Here, we report a multi-method approach focusing on in-situ X-ray scattering to observe alterations of the nanostructured material during the drying of surface-modified and unmodified silica gels. Both show a porous fractal nanostructure, which partially collapses during drying and only recovers in surface-modified samples during the springback effect. Distinct changes of the X-ray scattering data were reproducibly associated with the shrinkage, re-expansion and drying of the gel network. Our findings may contribute to tailor aerogels with specific functionality, as the springback effect has a direct influence on properties (e.g., porosity, pore size distribution), which is directly affected by the degree of re-expansion.

Core shell Fe3O4@TiO2/silica aerogel nanocomposite; synthesis and study of structural, magnetic and photocatalytic properties

In this work, magnetic Fe3O4@TiO2 nanospheres supported by a mesoporous silica aerogel substrate were synthesized using simple combining procedure of sol-gel and ultrasound assisted reflux technique for photocatalytic activity. The characteristics study of the as-synthesized ternary nanocomposite showed highly dispersion and covering of the Fe3O4@TiO2 nanoparticles on the silica aerogel. The hydrophobic porous silica aerogel was prepared using industrial diatomite earth (DE) as a silica source by a sol-gel procedure under ambient pressure drying. The specifications results of the resulting silica aerogel revealed a fine particulate morphology with an average size of 26 nm, a low density of about 0.85 g/cm3 and a good degree of porosity with a BET surface area of 572 m2/g. In addition, the structural and morphological studies of the prepared Fe3O4@TiO2 also represented the formation of a pure Fe3O4@TiO2 phase with a core shell spherical morphology and an average particle size of 22 nm. The introduction of the Fe3O4@TiO2 on the silica aerogel nanoparticles led to increase the particle size to 38 nm and decrease of BET surface area to 347 m2/g confirming the formation of Fe3O4@TiO2/silica aerogel nanocomposite. The photocatalytic activity of the prepared ternary nanocomposite was also studied for the removal of tetracycline (TC) as an organic pollutant from water under visible light in details.

Synthesis of porous polyimide films with low dielectric constant and excellent mechanical properties by ambient pressure drying

Synthesis of porous polyimide films with low dielectric constant and excellent mechanical properties by ambient pressure drying

Preparation of monolithic amorphous silica aerogel through promising valorization of silicomanganese slag

Monolithic silica aerogels were successfully synthesized from silicomanganese slag by a highly efficient hydrometallurgical extraction process followed by solvent exchanges and ambient pressure drying. The silica content of the silicomanganese slag was first extracted by a facile and economical acid digestion-gelation process. The extracted silica hydrogel was then converted to silica aerogel through three-step solvent exchange, aging, and ambient pressure drying. No surface modifier was used. The characterization results revealed that the obtained silica aerogel had an amorphous structure having a low bulk density of ∼0.08 g/cm3, high specific surface area (∼509 m2/g), large pore volume (∼0.97 cm3/g), and an average pore diameter of ∼7.5 nm. Overall, the results showed that the proposed valorization process is a promising method to prepare monolithic silica aerogel from a cheap silica resource under ambient pressure drying without the use of any surface modification.

Monolithic carbon aerogels within foam framework for high-temperature thermal insulation and organics absorption

Carbon aerogels exhibit high porosity, good electrical conductivity, and low thermal conductivity, but their practical applications are greatly hindered by their tedious preparation and inherent structure brittleness. Herein, monolithic carbon aerogels (MCAs) with low density and large size are prepared via a facile sol-gel polymerization of phenolic resin within melamine foam (MF), followed by ambient pressure drying and co-carbonization. During ambient pressure drying process, the MF matrix can deliver supporting force to counteract against the solvent evaporation surface tension, thus inhibiting volume shrinkage and shape deformation. Upon co-carbonization process, the MF matrix and organic aerogel could pyrolyze and shrink cooperatively, which could effectively prevent the brittle fracture of monolith. Therefore, large-sized MCAs (up to 250 × 250 × 20 mm) with low densities of 0.12–0.22 g·cm−3 are obtained. The as-obtained MCAs possess high compressive strength (2.50 MPa), ultra-low thermal conductivity (0.051 W·m−1·K−1 at 25 °C and 0.111 W·m−1·K−1 at 800 °C), and high-volume organic absorption capability (77.3–88.0%, V/V). This facile and low-cost method for the fabrication of large-sized monolithic carbon aerogels with excellent properties could envision enormous potential for high-temperature thermal insulation and organics absorption.

High-efficiency capture of ammonia using hierarchically porous Zr-MOF nanoarchitectures under ambient conditions: Thermodynamics, kinetics, and mechanisms

Zirconium-based metal–organic frameworks (Zr-MOFs) have emerged as a promising candidate for efficiently eliminating toxic chemicals under ambient conditions. Herein, we demonstrate the remarkable ammonia capture capabilities of the hierarchically porous MOF-808 xerogel (G808) macrostructure and its amino-functionalized analogue (G808-NH2), which were constructed through a sol–gel-based strategy combined with convenient ambient pressure drying. Static isotherm measurements and dynamic breakthrough tests using engineered Zr-MOF xerogel granules were conducted to illuminate the thermodynamic and kinetic characteristics for ammonia sorption. The G808 and G808-NH2 xerogels manifest substantially higher ammonia uptake, intensified interfacial interactions, and enhanced irreversible retention toward ammonia compared with the state-of-the-art activated carbon-based materials, particularly at the low-concentration region. Moreover, these hierarchical Zr-MOF nanoarchitectures exhibit extraordinary ammonia removal performance as well as excellent environmental robustness under simulated respirator canister/protection filter circumstances, with the breakthrough capacities of G808-NH2 being individually more than two and one orders of magnitude greater than those for the pristine and metal-amine impregnated carbons. The kinetic ammonia adsorption behaviors can be well delineated by the pseudo-first-order Wheeler-Jonas model. An in-depth discussion on the ammonia sorption regime, detailing five binding patterns besides reversible physisorption with a special focus on the impacts of polar amino groups and humidity, was proposed based on multiple characterizations and Grand Canonical Monte Carlo simulation.

Highly efficient catalytic derived synthesis process of carbon aerogel for hydrogen storage application

For the present work, resorcinol-formaldehyde (R–F) aerogels were synthesized through both acid (nitric acid) and base (sodium carbonate) catalyzed sol-gel process followed by supercritical drying (SCD) as well as ambient pressure drying (APD). RF aerogels were carbonized at high temperatures to form carbon aerogels. The effect of the catalyst type and drying methods on the final characteristics were studied in detail. Microstructural and textural characteristics were evaluated through XRD, SEM, BET, RAMAN, FTIR, and TEM techniques. It was found that the combination of base catalysis and SCD delivered a higher micropore density and more uniform pore distribution. The CAs prepared under such conditions displayed a hydrogen uptake of 0.80 wt% at room temperature and 2.85 wt% at liquid nitrogen temperature (77 K).

Synthesis and Characterization of High Surface Area Transparent SiOC Aerogels from Hybrid Silicon Alkoxide: A Comparison between Ambient Pressure and Supercritical Drying.

In this article, highly porous and transparent silicon oxycarbide (SiOC) gels are synthesized from Bis(Triethoxysilyl) methane (BTEM). The gels are synthesized by the sol-gel technique followed by both ambient pressure and supercritical drying. Then, the portion of wet gels have been pyrolyzed in a hydrogen atmosphere at 800 and 1100 °C. The FT-IR spectroscopy analysis and nitrogen sorption results indicate the successful synthesis of Si-O-Si bonds and the formation of mesopores. From a hysteresis loop, the SiOC ceramics showed the H1 type characteristic with well-defined cylindrical pore channels for the aerogel and the H2 type for the ambigel samples, indicating that the pores are distorted due to the capillary stress. The produced gels are mesoporous materials having high surface areas with a maximum of 1140 m2/g and pore volume of 2.522 cm3/g obtained from BTEM aerogels. The pyrolysis of BTEM aerogels at 800 °C results in the production of a bulk and transparent sample with a slightly pale white color, while BTEM xerogels are totally transparent and colorless at the same temperature. At 1100 °C, all the aerogels become opaque brown, confirming the formation of free carbon and crystalline silicon.

Ultrasound-promoted synthesis of high-porosity silica aerogels using embedded recycled PET fibers

Silica aerogel is fabricated through replacement of solvent by the air, so that this stage is of high relevance to achieve appropriate physical properties. Although, evaporation under ambient pressure is considered as simplest drying technique, but leads to irreversible shrinkage and collapse of gel network. Here, we improve the efficiency of ambient pressure drying via increasing the strength of gel network through physically reinforcement of the gel network using recycled polyethylene terephthalate (rPET) fibers. The polymeric phase of rPET was then removed from structure using thermal treatment. Also, the effect of using four different sonication time, from 5 to 35 min, on enhancement of aerogel properties was also investigated. the prepared silica aerogels exhibit a high surface area and porosity and using more sonication time was led to better properties. According to results, surface area and porosity were increased from 593 m 2 /g and 93% up to 691 m 2 /g and 96% by enhancing sonication time from 5 min to 35 min, respectively. The reason is thought to be related to create further dispersion among silanol groups and fibers surface. As well, the fabricated silica aerogels showed mesopores structure along with a narrow and uniform pore size. These results indicate the high efficiency of proposed method for synthesize of silica aerogel. Improvement of the ambient pressure drying of wet gel to produce the silica aerogel via increasing the strength of gel network by recycled PET fibers reinforcement. • Development of a cost-effective and eco-friendly approach to silica aerogel preparation based on ambient pressure drying. • Improve the efficiency of drying through reinforcing the gel network using embedding the PET fibers into gel matrix. • Investigate the effect of ultrasonic and dispersion degree on aerogel properties using two different sonication time. • Obtaining the high specific surface area, low density and high porosity based on the proposed approach.

Manufacturing silica aerogel and cryogel through ambient pressure and freeze drying.

Achieving a mesoporous structure in superinsulation materials is pivotal for guaranteeing a harmonious relationship between low thermal conductivity, high porosity, and low density. Herein, we report silica-based cryogel and aerogel materials by implementing freeze-drying and ambient-pressure-drying processes respectively. The obtained freeze-dried cryogels yield thermal conductivity of 23 mW m−1 K−1, with specific surface area of 369.4 m2 g−1, and porosity of 96.7%, whereas ambient-pressure-dried aerogels exhibit thermal conductivity of 23.6 mW m−1 K−1, specific surface area of 473.8 m2 g−1, and porosity of 97.4%. In addition, the fiber-reinforced nanocomposites obtained via freeze-drying feature a low thermal conductivity (28.0 mW m−1 K−1) and high mechanical properties (∼620 kPa maximum compressive stress and Young's modulus of 715 kPa), coupled with advanced flame-retardant capabilities, while the composite materials from the ambient pressure drying process have thermal conductivity of 28.8 mW m−1 K−1, ∼200 kPa maximum compressive stress and Young's modulus of 612 kPa respectively. The aforementioned results highlight the capabilities of both drying processes for the development of thermal insulation materials for energy-efficient applications.

Scalable and robust silica aerogel materials from ambient pressure drying

A scalable thermal insulation aerogel composite sheet using recycled cellulose materials.

Synthesis of silica-cellulose aerogel derived from bagasse through impregnation and ambient pressure drying methods as thermal insulator

The trend of research and development of technological advancement in thermal insulators involves using renewable materials, selecting manufacturing processes that require the lowest possible energy, or using waste materials that may help subdue the reduction of petroleum reserves. This review discusses the potential substitution of petroleum by natural materials in thermal insulation manufacturing. This review presents an overview of the definition, properties, materials, and methods that can be used in the manufacture of thermal insulators based on results reported in the literature. Many materials are currently being investigated to produce thermal insulator such as cellulose. Cellulose fiber has a big potential to be used in the manufacture of thermal insulators because cellulose possesses many advantageous properties over petroleum-based polymers, i.e. biocompatibility, biodegradability, thermal stability, chemical stability, and low cost. Another material that may be used is silica, as it has high temperature resistance and low thermal expansion. Bagasse containing high cellulose and silica with the composition of 32-44% cellulose and 55.5%-70% silica. Therefore, bagasse proves appealing to be processed into thermal insulator. Aerogels are among the best thermal insulating materials known. This review proposes the impregnation method followed by the ambient pressure drying (APD) method to synthesize cellulose-silica aerogel. The impregnation of silica into cellulose aerogel will increase mechanical strength, flexibility, and the resulting silica-cellulose aerogel will be transparent with a very low thermal conductivity.

Transparent thermal insulation ceramic aerogel materials for solar thermal conversion.

Thermal management in energy-efficient solar thermal energy conversion and transparent windows requires advanced materials with low thermal conductivity and high transparency, such as transparent silica aerogel materials. However, the large scatter domains in porous silica materials would deteriorate their optical transparency. Herein, we report transparent silica aerogels by controlling hydrolyzation and meanwhile silylation modification to enhance the integrity of the microstructure under ambient pressure drying. The transparent silica aerogel materials show a broad-spectrum transparency of 70% from 400 nm and 800 nm, showing promising applications in transparent windows and solar thermal energy conversion systems. The scalability for transparent windows could be achieved with a composite material by incorporating transparent polymeric materials. The solar receiver coupled with a transparent silica aerogel could reach 122 °C within 12 min at a solar irradiance of 1 Sun, ∼200% higher than that in the ambient atmosphere. The engineered structure of the transparent porous silica backbone provides a pathway for solar thermal systems and transparent window applications.

A New Schiff Base Organically Modified Silica Aerogel-Like Material for Metal Ion Adsorption with Ni Selectivity

Nickel has several industrial uses and is a valuable metal, making its selective separation and recycling a priority goal. A novel adsorbent, a Schiff base organically modified silica (ORMOSIL) aerogel, was prepared, for selective nickel removal from wastewater with other metal ions, by including a salen ionophore in the silica-based network. The newly developed adsorbent takes advantage of the salen’s selectivity and of the high porosity of silica aerogels. The aerogel-like adsorbent was prepared via sol-gel chemistry, using a coprecursor approach and ambient pressure drying. The inclusion of the Schiff base in the silica network was accomplished by reacting an amine-containing silica precursor with an aldehyde and confirmed by nuclear magnetic resonance (NMR) analysis. The adsorbent shrunk only 10% after evaporative drying, which resulted in a highly porous material (85% porosity, 4 cm3 g−1 specific pore volume). The low surface area of 28 m2 g-1 was due to the predominantly macroporous structure of the material (mean pore diameter of 563 nm). Adsorption isotherms and kinetic curves with single and binary mixtures of cations at room temperature were used to assess the selectivity of the adsorbent. The adsorption follows a BET (Brunauer-Emmett-Teller) trend. Due to the proximity of the oxygen and nitrogen atoms in the salen and steric hindrance from their neighboring atoms, it is likely that only the smallest hydrated cations can act as a coordination center and interact with both donor atoms. Thus, nickel was fairly removed (50 mg g-1), while other cations barely interacted with the adsorbent (cadmium adsorption maximum of 5 mg g-1). The estimated selectivity coefficient for nickel ranges from 1.8, in relation to copper, to 9.4 relatively to cadmium, which can be relevant for the separation of nickel in several industrial contexts, for instance, from electroplating sludge.

High‐performance thermal insulator based on polymer foam and silica xerogel

AbstractIn this work, methyltrimethoxysilane (MTMS) was used as a precursor, n‐hexadecyltrimethylammonium bromide (CTAB) as a surfactant, and EtOH/H2O as a co‐solvent, while 10 mM HCl and urea were used as acid and base catalysts to prepare silica xerogels and xerogel inside the cells of a polyethylene (PE) foam via a sol–gel process combined with ambient pressure drying. The xerogels and PE‐silica xerogel foams were characterized by scanning electron microscope (SEM), Brunauer–Emmett–Teller method (BET), and thermal conductivity. The results indicate that the xerogels have a three‐dimensional nanoporous structure, and the specific surface areas of the SiO2 xerogel and PE‐xerogel foam are 536 and 377 m2/g, respectively. The PE‐xerogel foam exhibited very low thermal conductivity (22–24 mW/m.K) compared with conventional insulation materials on the market (30–50 mW/m.K). The thermal insulation properties of PE‐silica xerogels were increased by 45% and 49% compared with neat PE foam. Additionally, the compressive modulus and density of the PE‐xerogel foam was increased by the presence of the silica xerogel. These PE‐xerogel foams are believed to be excellent candidates for thermal insulation applications in terms of cost/performance.