A mesoporous NiaAl2O3aZrO2 aerogel (NiaAZ) catalyst was prepared by a single-step epoxide-driven sol-gel method and a subsequent supercritical CO2 drying method. For comparison, a mesoporous ...Al2O3aZrO2 aerogel (AZ) support was prepared by a single-step epoxide-driven sol-gel method, and subsequently, a mesoporous Ni/Al2O3aZrO2 aerogel (Ni/AZ) catalyst was prepared by an incipient wetness impregnation method. The effect of preparation method on the physicochemical properties and catalytic activities of NiaAZ and Ni/AZ catalysts was investigated. Although both catalysts retained a mesoporous structure, Ni/AZ catalyst showed lower surface area than NiaAZ catalyst. From TPR, XRD, and H2aTPD results, it was revealed that NiaAZ catalyst retained higher reducibility and higher nickel dispersion than Ni/AZ catalyst. In the hydrogen production by steam reforming of ethanol, both catalysts showed a stable catalytic performance with complete conversion of ethanol. However, NiaAZ catalyst showed higher hydrogen yield than Ni/AZ catalyst. Superior textural properties, high reducibility, and high nickel surface area of NiaAZ catalyst were responsible for its enhanced catalytic performance in the steam reforming of ethanol.
Silica aerogels are very light and highly porous materials that are intriguingly and complexly networked with large internal surface area, high hydrophobicity with extremely low density and thermal ...conductivity. These features make them ideal choice for applications as thermal and acoustics insulators or as optical, electrical, and energy storing devices. However, their exploitation for structural applications is primarily inhibited by their brittleness. The brittleness of the silica aerogels makes their processing and handling difficult. Volumetric shrinkage occurs, which becomes more apparent at elevated temperatures. While there are hybrid silica aerogels doped with materials such as polymer, ceramics, metals in the market, the improvements in the mechanical properties are compromised with tremendous increase in density and reduction in the insulation performance. Post-synthesis binding treatment of silica aerogels composites are not extensively explored due to the chemically inert trimethylsilyl (TMS) terminal groups on the surface of the hydrophobic silica aerogels. This paper discusses a unique fabrication method of developing a ductile silica aerogel composite solid via post-synthesis binding treatment. Gelatinasilica aerogel (GSA) and GSAasodium dodecyl sulfate (SDS) composite blocks were produced by mixing hydrophobic aerogel granulates in a gelatinaSDS foamed solution by frothing method. The entire fabrication process and grounds for using a controlled % of gelatin as the main binder and SDS as an additive are explained. The compression testing of the blocks is presented. The associated strain recoveryaan unusual phenomenon with brittle silica aerogels, observed upon unloading is highlighted and studied. The microstructure and surface characterization of these composites was examined via FESEM/EDX and XPS/ESCA, respectively. The dependency of process variables involved were analyzed through analysis of variance (ANOVA) model. Empirical models that relate the composition of gelatin, aerogel, and SDS to achieve the optimal strain recovery with the associated compressive modulus and strength and density are established. The transition from brittleness to ductility is measured in terms of compressive stress versus strain behavior for various mass fractions of gelatin and SDS. The test data presented indicate analogous behavior of these to creep-like behavior of a material typically identified as the primary, secondary, and tertiary stages. The rationale and mechanisms behind such creep-like three stages are explained using schematic diagrams.
Nanoconfinement of 2LiBH4aMgH2aTiCl3 in resorcinolaformaldehyde carbon aerogel scaffold (RFaCAS) for reversible hydrogen storage applications is proposed. RFaCAS is encapsulated with approximately ...1.6ANBwt. % TiCl3 by solution impregnation technique, and it is further nanoconfined with bulk 2LiBH4aMgH2 via melt infiltration. Faster dehydrogenation kinetics is obtained after TiCl3 impregnation, for example, nanoconfined 2LiBH4aMgH2aTiCl3 requires similar to 1 and 4.5ANBh, respectively, to release 95% of the total hydrogen content during the 1st and 2nd cycles, while nanoconfined 2LiBH4aMgH2 ( similar to 2.5 and 7ANBh, respectively) and bulk material ( similar to 23 and 22ANBh, respectively) take considerably longer. Moreover, 95a98.6% of the theoretical H2 storage capacity (3.6a3.75ANBwt. % H2) is reproduced after four hydrogen release and uptake cycles of the nanoconfined 2LiBH4aMgH2aTiCl3. The reversibility of this hydrogen storage material is confirmed by the formation of LiBH4 and MgH2 after rehydrogenation using FTIR and SR-PXD techniques, respectively.
Food-grade aerogels are solid materials possessing high surface area, high porosity, and ultra-low density. Until today, numerous aerogels have been fabricated from polysaccharides, proteins, and ...seed mucilages which fulfill the requirements for food applications. Meanwhile, food industries have placed higher priority on the development of healthy foods through the incorporation of functional ingredients. However, the protection of these sensitive ingredients from adverse conditions is highly challenging. Therefore, the fabrication of food-grade aerogels and impregnating them with desired functional ingredients is the rapidly emerging trend.
The objective of the current review is to highlight the influence of various production conditions on the end structural properties of each food-grade aerogels. The recent findings on the impregnation method, impregnation efficiency, and controlled release properties of food-grade aerogels loaded with various functional ingredients are noteworthy. Therefore, the study was framed to discuss relevant research reports in four sections viz-polysaccharide aerogels, protein aerogels, seed mucilage aerogels, and their role as a carrier matrix of functional ingredients for food applications.
The end structural properties significantly differ between each food-grade aerogels based on the production parameters and methods employed. Food-grade aerogel as a carrier matrix of functional ingredients protects the micronutrients, healthy oils, and bioactive compounds from degradation, enhances their bioavailability, and controls their release into the target site. However, the challenges associated with the incorporation of impregnated food-grade aerogels into real food systems must be addressed.
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•Food-grade aerogels are derived from polysaccharides, proteins, and seed mucilages.•Their end properties can be tuned by optimizing various production parameters.•Food-grade aerogels serve as a potential carrier matrix of functional ingredients.•Incorporation of food-grade aerogels into real food systems is highly challenging.•Further studies on their application in food products could answer various queries.
The unremitting pursuit of high-performance and multifunctional materials has consistently propelled modern industries forward, stimulating research and motivating progress in related fields. In such ...materials, polybenzoxazine (PBz) aerogel, which combines the virtues of PBz and aerogel, has attracted salient attention recently, emerging as a novel research focus in the realm of advanced materials. In this review, the preparation scheme, microscopic morphology, and fundamental characteristics of PBz aerogels are comprehensively summarized and discussed in anticipation of providing a clear understanding of the correlation between preparation process, structure, and properties. The effective strategies for enhancing the performance of PBz aerogels including composite fabrication and hybridization are highlighted. Moreover, the applications of PBz-based aerogels in various domains such as adsorption (including wastewater treatment, CO2 capture, and microwave adsorption), thermal insulation, energy storage as well as sensors are covered in detail. Furthermore, several obstacles and potential directions for subsequent research are delineated with a view to surmounting the prevailing constraints and achieving a realization of the shift from experimental exploration to practical applications.
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•Polybenzoxazine (PBz) aerogels present a wide-ranging potential for applications as emerging high-performance materials.•Elaborate summaries of preparation routes for PBz aerogels.•The microscopic morphology of PBz aerogels can be modulated through colloid chemistry principles.•Comprehensive introduction of composite and hybrid materials based on PBz aerogels.•Challenges and potential development directions faced by PBz aerogels.
Benefiting from the inherent properties of ultralight weight, ultrahigh porosity, ultrahigh specific surface area, adjustable thermal/electrical conductivities, and mechanical flexibility, aerogels ...are considered ideal supporting alternatives to efficiently encapsulate phase change materials (PCMs) and rationalize phase transformation behaviors. The marriage of versatile aerogels and PCMs is a milestone in pioneering advanced multifunctional composite PCMs. Emerging aerogel-based composite PCMs with high energy storage density are accepted as a cutting-edge thermal energy storage (TES) concept, enabling advanced functionality of PCMs. Considering the lack of a timely and comprehensive review on aerogel-based composite PCMs, herein, we systematically retrospect the state-of-the-art advances of versatile aerogels for high-performance and multifunctional composite PCMs, with particular emphasis on advanced multiple functions, such as acoustic–thermal and solar–thermal–electricity energy conversion strategies, mechanical flexibility, flame retardancy, shape memory, intelligent grippers, and thermal infrared stealth. Emphasis is also given to the versatile roles of different aerogels in composite PCMs and the relationships between their architectures and thermophysical properties. This review also showcases the discovery of an interdisciplinary research field combining aerogels and 3D printing technology, which will contribute to pioneering cutting-edge PCMs. This review aims to arouse wider research interests among interdisciplinary fields and provide insightful guidance for the rational design of advanced multifunctional aerogel-based composite PCMs, thus facilitating the significant breakthroughs in both fundamental research and commercial applications.
Aerogels are highly porous structures produced by replacing the liquid solvent of a gel with air without causing a collapse in the solid network. Unlike conventional fabrication methods, additive ...manufacturing (AM) has been applied to fabricate 3D aerogels with customized geometries specific to their applications, designed pore morphologies, multimaterial structures, etc. To date, three major AM technologies (extrusion, inkjet, and stereolithography) followed by a drying process have been proposed to additively manufacture 3D functional aerogels. 3D‐printed aerogels and porous scaffolds showed great promise for a variety of applications, including tissue engineering, electrochemical energy storage, controlled drug delivery, sensing, and soft robotics. In this review, the details of steps included in the AM of aerogels and porous scaffolds are discussed, and a general frame is provided for AM of those. Then, the different postprinting processes are addressed to achieve the porosity (after drying); and mechanical strength, functionality, or both (after postdrying thermal or chemical treatments) are provided. Furthermore, the applications of the 3D‐printed aerogels/porous scaffolds made from a variety of materials are also highlighted. The review is concluded with the current challenges and an outlook for the next generation of 3D‐printed aerogels and porous scaffolds.
3D‐printed aerogels and porous scaffolds made from a variety of materials have promising properties for electrochemical energy storage, electrical energy generation, sensors and soft actuators, biomedical, and environmental applications. This review discusses the details of 3D printing processes along with drying and other postprocesses. A comprehensive summary for applications is also provided.
Elastic graphene aerogels are lightweight and offer excellent and electrical performance, expanding their significance in many applications. Recently, elastic graphene aerogels have been fabricated ...via various methods. However, for most reported elastic graphene aerogels, the fabrication processes are complicated and the applications are usually limited by the brittle mechanical properties. Thus, it still remains a challenge to explore facile processes for the fabrication of graphene aerogels with low density and high compressibility. Herein, arbitrary‐shaped, superelastic, and durable graphene aerogels are fabricated using melamine foam as sacrificial skeleton. The resulting graphene aerogels possess high elasticity under compressive stress of 0.556 MPa and compressive strain of 95%. Thanks to the superelasticity, high strength, excellent flexibility, outstanding thermal stability, and good electrical conductivity of graphene aerogels, they can be applied in sorbents and pressure/strain sensors. The as‐assembled graphene aerogels can adsorb various organic solvents at 176–513 g g−1 depending on the solvent type and density. Moreover, both the squeezing and combustion methods can be adopted for reusing the graphene aerogels. Finally, the graphene aerogels exhibit stable and sensitive current responses, making them the ideal candidates for applications as multifunctional pressure/strain sensors such as wearable devices.
Superelastic, arbitrary‐shaped, and durable graphene aerogels can be fabricated using melamine foam as a sacrificial skeleton. The resulting graphene aerogels exhibit superelasticity, high strength, excellent flexibility, outstanding thermal stability, and good electrical conductivity, making them the ideal candidates for applications as promising sorbents for the removal of pollutants and multifunctional pressure/strain sensors such as wearable devices.
Noise reduction remains an important priority in the modern society, in particular, for urban areas and highly populated cities. Insulation of buildings and transport systems such as cars, trains, ...and airplanes has accelerated the need to develop advanced materials. Various porous materials, such as commercially available foams and granular and fibrous materials, are commonly used for sound mitigating applications. In this review, a special class of advanced porous materials, aerogels, is examined, and an overview of the current experimental and theoretical status of their acoustic properties is provided. Aerogels can be composed of inorganic matter, synthetic or natural polymers, as well as organic/inorganic composites and hybrids. Aerogels are highly porous nanostructured materials with a large number of meso‐ and small macropores; the mechanisms of sound absorption partly differ from those of traditional porous absorbers possessing large macropores. The understanding of the acoustic properties of aerogels is far from being complete, and experimental results remain scattered. It is demonstrated that the structure of the aerogel provides a complex three‐dimensional architecture ideally suited for promising high‐performance materials for acoustic mitigation systems. This is in addition to the numerous other desirable properties that include low density, low thermal conductivity, and low refractive index.
Aerogels are highly porous nanostructured materials with a large number of meso‐ and small macropores; their complex three‐dimensional architecture is ideally suited for promising high‐performance materials for acoustic mitigation systems.
Aerogels owe their high thermal insulation and other unique properties to their nanostructure configuration. However, controlling the aerogels' morphology is always a scientific challenge. In this ...study, double dianhydride backbone (double backbone) polyimide aerogels with tailored nanostructure assembly are created for the first time. This is achieved by controlled polymerization reaction of oligomers with distinct dianhydride monomers. Combining the two oligomers through a controlled polymerization reaction is a successful strategy for tailoring the aerogels nanostructure assembly as well as other properties. The fabricated double backbone aerogel presents 40% reduced thermal conductivity of 19.7 mW mK−1 over previously studied polyimide aerogels along with the compression modulus of 1.64 MPa at a relatively low density of 0.068 g cm−3. Such low thermal conductivity is comparable with the inorganic counterparts. Light in weight and high thermally insulated polyimide aerogels with suitable mechanical properties and high service temperature are an appropriate replacement for current fireproof insulation materials.
This study presents double backbone polyimide aerogels with tailored nanostructure assembly. By combining two oligomers with distinct dianhydride monomers, a successful strategy in tailoring the aerogels nanostructure is presented. The fabricated aerogel presents compression modulus of 1.64 MPa at a low density of 0.068 g cm−3 and a very low thermal conductivity of 19.7 mW mK−1, comparable to inorganic counterparts.
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