Aerogel Hybrids and Nanocomposites

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Chemistry and Physics".

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 26096

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Debreceni Egyetem, Department of Inorganic and Analytical Chemistry, University of Debrecen, 4032 Debrecen, Hungary
Interests: aerogel synthesis; hybrid aerogels; catalytic and photocatalytic activity; fluorescent aerogels; analytical applications; supercritical adsorption; tissue engineering; bone substitution
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Department of Chemical Engineering, Cyprus University of Technology, 3603 Limassol, Cyprus
Interests: nanoparticles; aerogel synthesis; aerogel properties; materials synthesis; physicochemical characterization; crystallography; nanomaterials
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Dear Colleagues,

Aerogels are amazing lightweight solids, and the most beautiful ones have the rightly deserved name of solid smoke. They vary widely in their composition and can be of inorganic or organic origin. Due to their extremely low density, huge specific surface area, and open mesoporous structure, single-component aerogels have already claimed dozens of applications.

The Special Issue “Aerogel Hybrids and Nanocomposites” would like to focus on any aspect of the synthesis, production, structure, properties, and any applications of such complex aerogel materials while paying special attention to the cooperation between the hybrid matrix components and the guest particles.

Both original papers and reviews dealing with the synthesis, properties, and applications of inorganic, organic, or organic–inorganic aerogel hybrids or nanocomposites are welcome.

Dr. István Lázár
Dr. Melita Menelaou
Guest Editors

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Keywords

  • aerogel
  • hybrid material
  • nanocomposite
  • matrix-guest interaction
  • reinforcement
  • adsorption
  • supercritical extraction
  • catalytic activity
  • biomedical applications

Published Papers (11 papers)

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Editorial

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4 pages, 217 KiB  
Editorial
Editorial for the Special Issue: “Aerogel Hybrids and Nanocomposites”
by István Lázár and Melita Menelaou
Gels 2023, 9(10), 812; https://doi.org/10.3390/gels9100812 - 12 Oct 2023
Viewed by 837
Abstract
Aerogel materials are porous ultralight solid materials obtained from gels, wherein a gas, commonly air, replaces the liquid component [...] Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)

Research

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20 pages, 6671 KiB  
Article
Chitosan-Silica Hybrid Biomaterials for Bone Tissue Engineering: A Comparative Study of Xerogels and Aerogels
by Antonio Pérez-Moreno, Manuel Piñero, Rafael Fernández-Montesinos, Gonzalo Pinaglia-Tobaruela, María V. Reyes-Peces, María del Mar Mesa-Díaz, José Ignacio Vilches-Pérez, Luis Esquivias, Nicolás de la Rosa-Fox and Mercedes Salido
Gels 2023, 9(5), 383; https://doi.org/10.3390/gels9050383 - 5 May 2023
Cited by 10 | Viewed by 1638
Abstract
Chitosan (CS) is a natural biopolymer that shows promise as a biomaterial for bone-tissue regeneration. However, because of their limited ability to induce cell differentiation and high degradation rate, among other drawbacks associated with its use, the creation of CS-based biomaterials remains a [...] Read more.
Chitosan (CS) is a natural biopolymer that shows promise as a biomaterial for bone-tissue regeneration. However, because of their limited ability to induce cell differentiation and high degradation rate, among other drawbacks associated with its use, the creation of CS-based biomaterials remains a problem in bone tissue engineering research. Here we aimed to reduce these disadvantages while retaining the benefits of potential CS biomaterial by combining it with silica to provide sufficient additional structural support for bone regeneration. In this work, CS-silica xerogel and aerogel hybrids with 8 wt.% CS content, designated SCS8X and SCS8A, respectively, were prepared by sol-gel method, either by direct solvent evaporation at the atmospheric pressure or by supercritical drying in CO2, respectively. As reported in previous studies, it was confirmed that both types of mesoporous materials exhibited large surface areas (821 m2g−1–858 m2g−1) and outstanding bioactivity, as well as osteoconductive properties. In addition to silica and chitosan, the inclusion of 10 wt.% of tricalcium phosphate (TCP), designated SCS8T10X, was also considered, which stimulates a fast bioactive response of the xerogel surface. The results here obtained also demonstrate that xerogels induced earlier cell differentiation than the aerogels with identical composition. In conclusion, our study shows that the sol-gel synthesis of CS-silica xerogels and aerogels enhances not only their bioactive response, but also osteoconduction and cell differentiation properties. Therefore, these new biomaterials should provide adequate secretion of the osteoid for a fast bone regeneration. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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19 pages, 2240 KiB  
Article
Photocatalytic Hydrogen Production Using Porous 3D Graphene-Based Aerogels Supporting Pt/TiO2 Nanoparticles
by Márta Kubovics, Cláudia G. Silva, Ana M. López-Periago, Joaquim L. Faria and Concepción Domingo
Gels 2022, 8(11), 719; https://doi.org/10.3390/gels8110719 - 7 Nov 2022
Cited by 3 | Viewed by 1918
Abstract
Composites involving reduced graphene oxide (rGO) aerogels supporting Pt/TiO2 nanoparticles were fabricated using a one-pot supercritical CO2 gelling and drying method, followed by mild reduction under a N2 atmosphere. Electron microscopy images and N2 adsorption/desorption isotherms indicate the formation [...] Read more.
Composites involving reduced graphene oxide (rGO) aerogels supporting Pt/TiO2 nanoparticles were fabricated using a one-pot supercritical CO2 gelling and drying method, followed by mild reduction under a N2 atmosphere. Electron microscopy images and N2 adsorption/desorption isotherms indicate the formation of 3D monolithic aerogels with a meso/macroporous morphology. A comprehensive evaluation of the synthesized photocatalyst was carried out with a focus on the target application: the photocatalytic production of H2 from methanol in aqueous media. The reaction conditions (water/methanol ratio, catalyst concentration), together with the aerogel composition (Pt/TiO2/rGO ratio) and architecture (size of the aerogel pieces), were the factors that varied in optimizing the process. These experimental parameters influenced the diffusion of the reactants/products inside the aerogel, the permeability of the porous structure, and the light-harvesting properties, all determined in this study towards maximizing H2 production. Using methanol as the sacrificial agent, the measured H2 production rate for the optimized system (18,800 µmolH2h−1gNPs−1) was remarkably higher than the values found in the literature for similar Pt/TiO2/rGO catalysts and reaction media (2000–10,000 µmolH2h−1gNPs−1). Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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13 pages, 4060 KiB  
Article
Features of Luminescent Properties of Alginate Aerogels with Rare Earth Elements as Photoactive Cross-Linking Agents
by Vladislav Kaplin, Aleksandr Kopylov, Anastasiia Koryakovtseva, Nikita Minaev, Evgenii Epifanov, Aleksandr Gulin, Nadejda Aksenova, Peter Timashev, Anastasiia Kuryanova, Ilya Shershnev and Anna Solovieva
Gels 2022, 8(10), 617; https://doi.org/10.3390/gels8100617 - 27 Sep 2022
Cited by 1 | Viewed by 1661
Abstract
Luminescent aerogels based on sodium alginate cross-linked with ions of rare earth elements (Eu3+, Tb3+, Sm3+) and containing phenanthroline, thenoyltrifluoroacetone, dibenzoylmethane, and acetylacetone as ligands introduced into the matrix during the impregnation of alginate aerogels (AEG), were [...] Read more.
Luminescent aerogels based on sodium alginate cross-linked with ions of rare earth elements (Eu3+, Tb3+, Sm3+) and containing phenanthroline, thenoyltrifluoroacetone, dibenzoylmethane, and acetylacetone as ligands introduced into the matrix during the impregnation of alginate aerogels (AEG), were obtained for the first time in a supercritical carbon dioxide medium. The impregnation method used made it possible to introduce organically soluble sensitizing ligands into polysaccharide matrices over the entire thickness of the sample while maintaining the porous structure of the aerogel. It is shown that the pore size and their specific area are 150 nm and 270 m2/g, respectively. Moreover, metal ions with content of about 23 wt.%, acting as cross-linking agents, are uniformly distributed over the thickness of the sample. In addition, the effect of sensitizing ligands on the luminescence intensity of cross-linked aerogel matrices is considered. The interaction in the resulting metal/ligand systems is unique for each pair, which is confirmed by the detection of broad bands with individual positions in the luminescence excitation spectra of photoactive aerogels. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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12 pages, 2737 KiB  
Article
Efficient Removal of Polyvalent Metal Ions (Eu(III) and Th(IV)) from Aqueous Solutions by Polyurea-Crosslinked Alginate Aerogels
by Efthalia Georgiou, Ioannis Pashalidis, Grigorios Raptopoulos and Patrina Paraskevopoulou
Gels 2022, 8(8), 478; https://doi.org/10.3390/gels8080478 - 29 Jul 2022
Cited by 12 | Viewed by 1792
Abstract
The removal of polyvalent metal ions Eu(III) and Th(IV) from aqueous solutions using polyurea-crosslinked calcium alginate (X-alginate) aerogels has been investigated by batch-type experiments under ambient conditions and pH 3. The material presents relatively high sorption capacity for Eu(III) (550 g kg−1 [...] Read more.
The removal of polyvalent metal ions Eu(III) and Th(IV) from aqueous solutions using polyurea-crosslinked calcium alginate (X-alginate) aerogels has been investigated by batch-type experiments under ambient conditions and pH 3. The material presents relatively high sorption capacity for Eu(III) (550 g kg−1) and Th(IV) (211 g kg−1). The lower sorption capacity for Th(IV) compared to Eu(III) is attributed to the net charge of the dominant species in solution under the given experimental conditions, which is Eu3+ for Eu(III), and Th(OH)22+ and Th(OH)3+ for Th(IV). Generally, the sorption is an endothermic and entropy-driven process, and it follows the Langmuir isotherm model. According to the FTIR spectra, sorption occurs via formation of inner-sphere complexes between the surface functional groups and the f-metal cationic species. The presence of europium and thorium in the adsorbent material was confirmed and quantified with EDS analysis. To the best of our knowledge, this is the first report of an aerogel material used as an adsorbent for Eu(III). Compared to other materials used for the sorption of the specific ions, which are mostly carbon-based, X-alginate aerogels show by far the highest sorption capacity. Regarding Th(IV) uptake, X-alginate aerogels show the highest capacity per volume (27.9 g L−1) among the aerogels reported in the literature. Both Eu(III) and Th(IV) could be recovered from the beads by 65% and 70%, respectively. Furthermore, Th(VI) could also be quantitatively removed from wastewater, while Eu(III) could be removed by 20%. The above, along with their stability in aqueous environments, make X-alginate aerogels attractive candidates for water treatment and metal recovery applications. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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15 pages, 2448 KiB  
Article
Preparation of Vancomycin-Loaded Aerogels Implementing Inkjet Printing and Superhydrophobic Surfaces
by Patricia Remuiñán-Pose, Clara López-Iglesias, Ana Iglesias-Mejuto, Joao F. Mano, Carlos A. García-González and M. Isabel Rial-Hermida
Gels 2022, 8(7), 417; https://doi.org/10.3390/gels8070417 - 4 Jul 2022
Cited by 6 | Viewed by 2641
Abstract
Chronic wounds are physical traumas that significantly impair the quality of life of over 40 million patients worldwide. Aerogels are nanostructured dry porous materials that can act as carriers for the local delivery of bioactive compounds at the wound site. However, aerogels are [...] Read more.
Chronic wounds are physical traumas that significantly impair the quality of life of over 40 million patients worldwide. Aerogels are nanostructured dry porous materials that can act as carriers for the local delivery of bioactive compounds at the wound site. However, aerogels are usually obtained with low drug loading yields and poor particle size reproducibility and urges the implementation of novel and high-performance processing strategies. In this work, alginate aerogel particles loaded with vancomycin, an antibiotic used for the treatment of Staphylococcus aureus infections, were obtained through aerogel technology combined with gel inkjet printing and water-repellent surfaces. Alginate aerogel particles showed high porosity, large surface area, a well-defined spherical shape and a reproducible size (609 ± 37 μm). Aerogel formulation with vancomycin loadings of up to 33.01 ± 0.47 μg drug/mg of particle were obtained with sustained-release profiles from alginate aerogels for more than 7 days (PBS pH 7.4 medium). Overall, this novel green aerogel processing strategy allowed us to obtain nanostructured drug delivery systems with improved drug loading yields that can enhance the current antibacterial treatments for chronic wounds. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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20 pages, 5303 KiB  
Article
Environment-Friendly Catalytic Mineralization of Phenol and Chlorophenols with Cu- and Fe- Tetrakis(4-aminophenyl)-porphyrin—Silica Hybrid Aerogels
by Enikő Győri, Ádám Kecskeméti, István Fábián, Máté Szarka and István Lázár
Gels 2022, 8(4), 202; https://doi.org/10.3390/gels8040202 - 23 Mar 2022
Cited by 2 | Viewed by 2348
Abstract
Fenton reactions with metal complexes of substituted porphyrins and hydrogen peroxide are useful tools for the mineralization of environmentally dangerous substances. In the homogeneous phase, autooxidation of the prophyrin ring may also occur. Covalent binding of porphyrins to a solid support may increase [...] Read more.
Fenton reactions with metal complexes of substituted porphyrins and hydrogen peroxide are useful tools for the mineralization of environmentally dangerous substances. In the homogeneous phase, autooxidation of the prophyrin ring may also occur. Covalent binding of porphyrins to a solid support may increase the lifetime of the catalysts and might change its activity. In this study, highly water-insoluble copper and iron complexes of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin were synthesized and bonded covalently to a very hydrophilic silica aerogel matrix prepared by co-gelation of the propyl triethoxysilyl-functionalized porphyrin complex precursors with tetramethoxysilane, followed by a supercritical carbon dioxide drying. In contrast to the insoluble nature of the porphyrin complexes, the as-prepared aerogel catalysts were highly compatible with the aqueous phase. Their catalytic activities were tested in the mineralization reaction of phenol, 3-chlorophenol, and 2,4-dichlorophenol with hydrogen peroxide. The results show that both aerogels catalyzed the oxidation of phenol and chlorophenols to harmless short-chained carboxylic acids under neutral conditions. In batch experiments, and also in a miniature continuous-flow tubular reactor, the aerogel catalysts gradually reduced their activity, due to the slow oxidation of the porphyrin ring. However, the rate and extent of the degradation was moderate and did not exclude the possibility that the as-prepared catalysts, as well as their more stable derivatives, might find practical applications in environment protection. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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10 pages, 4197 KiB  
Article
Thermal Gelation for Synthesis of Surface-Modified Silica Aerogel Powders
by Kyoung-Jin Lee, Jae Min Lee, Ki Sun Nam and Haejin Hwang
Gels 2021, 7(4), 242; https://doi.org/10.3390/gels7040242 - 29 Nov 2021
Cited by 11 | Viewed by 3017
Abstract
A spherical silica aerogel powder with hydrophobic surfaces displaying a water contact angle of 147° was synthesized from a water glass-in-hexane emulsion through ambient pressure drying. Water glass droplets containing acetic acid and ethyl alcohol were stabilized in n-hexane with a surfactant. [...] Read more.
A spherical silica aerogel powder with hydrophobic surfaces displaying a water contact angle of 147° was synthesized from a water glass-in-hexane emulsion through ambient pressure drying. Water glass droplets containing acetic acid and ethyl alcohol were stabilized in n-hexane with a surfactant. Gelation was performed by heating the droplets, followed by solvent exchange and surface modification using a hexamethyldisilazane (HMDS)/n-hexane solution. The pH of the silicic acid solution was crucial in obtaining a highly porous silica aerogel powder with a spherical morphology. The thermal conductivity, tapped density, pore volume, and BET surface area of the silica aerogel powder were 22.4 mW·m−1K−1, 0.07 g·cm−3, 4.64 cm3·g−1, and 989 m2·g−1, respectively. Fourier transform infrared (FT–IR) spectroscopy analysis showed that the silica granule surface was modified by Si-CH3 groups, producing a hydrophobic aerogel. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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13 pages, 3400 KiB  
Article
Robust Silica-Bacterial Cellulose Composite Aerogel Fibers for Thermal Insulation Textile
by Huazheng Sai, Meijuan Wang, Changqing Miao, Qiqi Song, Yutong Wang, Rui Fu, Yaxiong Wang, Litong Ma and Yan Hao
Gels 2021, 7(3), 145; https://doi.org/10.3390/gels7030145 - 17 Sep 2021
Cited by 27 | Viewed by 3661
Abstract
Aerogels are nanoporous materials with excellent properties, especially super thermal insulation. However, owing to their serious high brittleness, the macroscopic forms of aerogels are not sufficiently rich for the application in some fields, such as thermal insulation clothing fabric. Recently, freeze spinning and [...] Read more.
Aerogels are nanoporous materials with excellent properties, especially super thermal insulation. However, owing to their serious high brittleness, the macroscopic forms of aerogels are not sufficiently rich for the application in some fields, such as thermal insulation clothing fabric. Recently, freeze spinning and wet spinning have been attempted for the synthesis of aerogel fibers. In this study, robust fibrous silica-bacterial cellulose (BC) composite aerogels with high performance were synthesized in a novel way. Silica sol was diffused into a fiber-like matrix, which was obtained by cutting the BC hydrogel and followed by secondary shaping to form a composite wet gel fiber with a nanoscale interpenetrating network structure. The tensile strength of the resulting aerogel fibers reached up to 5.4 MPa because the quantity of BC nanofibers in the unit volume of the matrix was improved significantly by the secondary shaping process. In addition, the composite aerogel fibers had a high specific area (up to 606.9 m2/g), low density (less than 0.164 g/cm3), and outstanding hydrophobicity. Most notably, they exhibited excellent thermal insulation performance in high-temperature (210 °C) or low-temperature (−72 °C) environments. Moreover, the thermal stability of CAFs (decomposition temperature was about 330 °C) was higher than that of natural polymer fiber. A novel method was proposed herein to prepare aerogel fibers with excellent performance to meet the requirements of wearable applications. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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11 pages, 2486 KiB  
Communication
Reduction of PVA Aerogel Flammability by Incorporation of an Alkaline Catalyst
by Zhi-Han Cheng, Mo-Lin Guo, Xiao-Yi Chen, Ting Wang, Yu-Zhong Wang and David A. Schiraldi
Gels 2021, 7(2), 57; https://doi.org/10.3390/gels7020057 - 8 May 2021
Cited by 4 | Viewed by 2652
Abstract
Sodium hydroxide was used as a base catalyst to reduce the flammability of poly(vinyl alcohol) (PVA) aerogels. The base-modified aerogels exhibited significantly enhanced compressive moduli, likely resulting in decreased gallery spacing and increased numbers of “struts” in their structures. The onset of decomposition [...] Read more.
Sodium hydroxide was used as a base catalyst to reduce the flammability of poly(vinyl alcohol) (PVA) aerogels. The base-modified aerogels exhibited significantly enhanced compressive moduli, likely resulting in decreased gallery spacing and increased numbers of “struts” in their structures. The onset of decomposition temperature decreased for the PVA aerogels in the presence of the base, which appears to hinder the polymer pyrolysis process, leading instead to the facile formation of dense char. Cone calorimetry testing showed a dramatic decrease in heat release when the base was added. The results indicate that an unexpected base-catalyzed dehydration occurs at fire temperatures, which is the opposite of the chemistry normally observed under typical synthesis conditions. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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Review

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40 pages, 1970 KiB  
Review
Aerogel-Based Materials in Bone and Cartilage Tissue Engineering—A Review with Future Implications
by István Lázár, Ladislav Čelko and Melita Menelaou
Gels 2023, 9(9), 746; https://doi.org/10.3390/gels9090746 - 13 Sep 2023
Cited by 5 | Viewed by 2294
Abstract
Aerogels are fascinating solid materials known for their highly porous nanostructure and exceptional physical, chemical, and mechanical properties. They show great promise in various technological and biomedical applications, including tissue engineering, and bone and cartilage substitution. To evaluate the bioactivity of bone substitutes, [...] Read more.
Aerogels are fascinating solid materials known for their highly porous nanostructure and exceptional physical, chemical, and mechanical properties. They show great promise in various technological and biomedical applications, including tissue engineering, and bone and cartilage substitution. To evaluate the bioactivity of bone substitutes, researchers typically conduct in vitro tests using simulated body fluids and specific cell lines, while in vivo testing involves the study of materials in different animal species. In this context, our primary focus is to investigate the applications of different types of aerogels, considering their specific materials, microstructure, and porosity in the field of bone and cartilage tissue engineering. From clinically approved materials to experimental aerogels, we present a comprehensive list and summary of various aerogel building blocks and their biological activities. Additionally, we explore how the complexity of aerogel scaffolds influences their in vivo performance, ranging from simple single-component or hybrid aerogels to more intricate and organized structures. We also discuss commonly used formulation and drying methods in aerogel chemistry, including molding, freeze casting, supercritical foaming, freeze drying, subcritical, and supercritical drying techniques. These techniques play a crucial role in shaping aerogels for specific applications. Alongside the progress made, we acknowledge the challenges ahead and assess the near and far future of aerogel-based hard tissue engineering materials, as well as their potential connection with emerging healing techniques. Full article
(This article belongs to the Special Issue Aerogel Hybrids and Nanocomposites)
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