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Gels
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Aerogels—Preparation and Properties
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Aerogels—Preparation and Properties

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

Deadline for manuscript submissions: 30 June 2025 | Viewed by 14079

Special Issue Editors

Prof. Dr. Stoyan Gutzov

E-Mail Website
Guest Editor
Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”, 1164 Sofia, Bulgaria
Interests: aerogels; optical materials; sol-gel; luminescence; solid state
Special Issues, Collections and Topics in MDPI journals
Dr. Xiaodong Wang

E-Mail Website
Guest Editor
School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Interests: aerogels; optical coatings; sol-gel; Raman spectroscopy; SERS; CDI; solid state physics

Special Issue Information

Dear Colleagues,

A new challenge in materials science is aerogels—a class of porous solids with extremely valuable material properties and different chemistry, including organic materials, carbon, ceramic oxides and even metals.

The valuable properties of aerogels based on their unique structure, such as low density, thermal insulation properties and transparency, make them attractive in many research areas. Aerogels are included as part of NASA's projects for the development of materials applicable in space, in aircrafts, insulation equipment, astronaut suits, blankets, etc.

A promising direction is the search for new modified aerogel materials that combine the advantages of the matrix and the properties of the new component embedded into their structure: for example, reinforced silica aerogels with a polymer component incorporated into the matrix. Another new research direction for hybrid composite-based aerogels is the incorporation of optical active components into aerogel granules and powders. In this way, aerogel composite materials, which combine the properties both of the aerogel matrix and the embedded complex, are developed.

The present Special Issue, “Aerogels—Preparation and Properties”, focuses on several topics, including but not limited to the following:

  1. The preparation–structure–property relationships of aerogels;
  2. Aerogel composites;
  3. Specific applications of aerogels and their composites, etc.

Original articles, reviews, short communications and perspectives are all suitable types of papers for submission.

Prof. Dr. Stoyan Gutzov
Dr. Xiaodong Wang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • aerogels
  • aerogel composites
  • aerogel hybrids
  • nano-aerogels
  • supercritical drying
  • subcritical drying
  • optical properties
  • electrical properties
  • magnetic properties
  • mechanical properties

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Published Papers (10 papers)

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Research

23 pages, 7619 KiB  
Article
Development of Porous Silicon(Si) Anode Through Magnesiothermic Reduction of Mesoporous Silica(SiO2) Aerogel for All-Solid-State Lithium-Ion Batteries
by Pratik S. Kapadnis, Kangsanin Kim, Kisun Nam, Yongseon Kim, Hyung-Ho Park and Haejin Hwang
Gels 2025, 11(4), 304; https://doi.org/10.3390/gels11040304 - 21 Apr 2025
Viewed by 421
Abstract
All-solid-state lithium-ion batteries (ASSLBs) are attractive energy storage devices because of their excellent gravimetric and volumetric capacity and ability to supply high power rates. Porous silicon (Si) is a promising material for an anode in lithium-ion batteries due to its high capacity and [...] Read more.
All-solid-state lithium-ion batteries (ASSLBs) are attractive energy storage devices because of their excellent gravimetric and volumetric capacity and ability to supply high power rates. Porous silicon (Si) is a promising material for an anode in lithium-ion batteries due to its high capacity and low discharge potential. However, Si anodes cause significant problems due to strong volume growth during the lithiation and delithiation processes, which results in rapid capacity fading and poor cycle stability. To overcome this problem, we developed mesoporous silica (SiO2) aerogels into porous silicon (Si) anodes using a magnesiothermic reduction (MTR) process. By effectively preserving the porous structure, this approach enables the material to endure volume fluctuations while maintaining its structural integrity during cycling. In our study, we demonstrated a feasible approach to fabricate the porous silicon (Si) from hydrophobic and hydrophilic silica (SiO2) aerogel and magnesium powder (Mg) through the MTR process at 600~900 °C. The sample obtained after the reduction process was treated with hydrochloric acid (HCl) to remove byproducts. As prepared, Si was characterized using various techniques, including XRD, XRF, FT-IR, XPS, SEM, and BET, which confirmed the successful production, chemical purity, and structural retention of Si. Furthermore, the coin cell was fabricated using Si as an anode, and the electrochemical performance was analyzed. The charge/discharge cycling tests at 1 C and 0.02~2 V (vs. the Li condition) revealed the effects of silicon content, wettability, and interfacial compatibility on electrode performance. Conversely, for better understanding, a long-term cycling test was conducted at 1 C rate, 0–1.5 V (vs. Li) to evaluate capacity retention. Our findings highlight the potential application of silicon (Si) aerogels produced from silica (SiO2) aerogels by magnesiothermic reduction to improve lithium-ion battery performance. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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12 pages, 2949 KiB  
Article
Preliminary Investigation into the Use of Amino-Acid-Derived Ionic Liquids for Extracting Cellulose from Waste Biomass to Prepare Cellulose Aerogel Adsorbents
by Yun Deng, Qiusheng Zhao, Shuai Nian, Ziyan Sha, Lin Fu, Ian Beadham, Xiaolan Xiao and Changbo Zhang
Gels 2025, 11(3), 210; https://doi.org/10.3390/gels11030210 - 16 Mar 2025
Viewed by 771
Abstract
To investigate the feasibility of cellulose extraction from lignocellulosic waste biomass using ionic liquids—a sustainable and efficient approach—for preparing cellulose aerogel adsorbents, we employed a fully green amino acid-derived ionic liquid, cysteine nitrate ([Cys][NO3]), for cellulose separation from diverse biomass sources. [...] Read more.
To investigate the feasibility of cellulose extraction from lignocellulosic waste biomass using ionic liquids—a sustainable and efficient approach—for preparing cellulose aerogel adsorbents, we employed a fully green amino acid-derived ionic liquid, cysteine nitrate ([Cys][NO3]), for cellulose separation from diverse biomass sources. The extracted cellulose, with a purity range of 83.8–93.9%, was processed into cellulose aerogels (CAs) via a conventional aerogel preparation protocol. The resulting CA exhibited promising adsorption capacities, including 0.2–11.6 mg/g for Na+, 4.4–19.9 mg/g for Ca2+, 4.15–35.6 mg/g for Mg2+, and 1.85–13.3 mg/g for Cd2+, as well as 9.7–17.7 g/g for engine oil. These results demonstrate the presence of effective mass transfer channels in the CA, proving that the cellulose’s fibrillation capacity was preserved in the pre-treatment. This study illuminates the potential of this green, straightforward method for preparing aerogels from cellulose derived from waste biomass, with promising applications in wastewater treatment and material recovery. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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19 pages, 19913 KiB  
Article
Thermal Reverse-Engineered Synthesis and Catalytic Activity of Nanogold-Containing Silica Aerogels
by Hanna Judit Csupász-Szabó, Boglárka Döncző, Máté Szarka, Lajos Daróczi and István Lázár
Gels 2025, 11(2), 87; https://doi.org/10.3390/gels11020087 - 23 Jan 2025
Viewed by 1083
Abstract
Silica aerogels are extensively used as catalyst supports due to their mesoporous structure and chemical inertness. In this study, SiO2–AuNP aerogels containing gold nanoparticles (AuNPs) were synthesized using the sol-gel method followed by supercritical CO2 drying. The inclusion of polyvinyl [...] Read more.
Silica aerogels are extensively used as catalyst supports due to their mesoporous structure and chemical inertness. In this study, SiO2–AuNP aerogels containing gold nanoparticles (AuNPs) were synthesized using the sol-gel method followed by supercritical CO2 drying. The inclusion of polyvinyl pyrrolidone (PVP) as a stabilizing agent preserved the gold particle sizes during the gelation process. In contrast, aerogels synthesized without PVP contained enlarged AuNP aggregates, resulting in a shift in the plasmon resonance color from red to bluish or blue–grey. Thermal treatment of these bluish-colored aerogels at high temperatures restored their red coloration, visually indicating the breakdown of large gold clusters into individual nanoparticles. Both types of aerogels were characterized using SEM, TEM, 3D optical microscopy, UV–vis and ATR-IR spectroscopy, and N2 porosimetry, with their properties analyzed as a function of annealing temperature. Their catalytic activity was evaluated through the reduction of 4-nitrophenol with sodium borohydride, and both aerogel types demonstrated catalytic activity. This thermal conversion of large clusters into individual nanoparticles within an aerogel matrix introduces a new and promising approach for creating catalytically active nanogold-containing aerogel catalysts. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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12 pages, 2456 KiB  
Article
Exploration of Key Factors in the Preparation of Highly Hydrophobic Silica Aerogel from Rice Husk Ash Assisted by Machine Learning
by Yun Deng, Ziyan Sha, Xingxing Wang, Ke Duan, Weijie Xue, Ian Beadham, Xiaolan Xiao and Changbo Zhang
Gels 2025, 11(1), 74; https://doi.org/10.3390/gels11010074 - 17 Jan 2025
Viewed by 1056
Abstract
To expand the applications of hydrophobic silica aerogels derived from rice husk ash (HSA) through simple traditional methods (without adding special materials or processes), this paper employs machine learning to establish mathematical models to identify optimal conditions for extracting water glass and investigates [...] Read more.
To expand the applications of hydrophobic silica aerogels derived from rice husk ash (HSA) through simple traditional methods (without adding special materials or processes), this paper employs machine learning to establish mathematical models to identify optimal conditions for extracting water glass and investigates how preparation conditions and heat treatment temperatures affect properties such as the porosity and hydrophobicity of HSA. The results indicate that the decision tree regression model provides the most accurate predictions for the extraction rate and modulus of water glass. Notably, the water contact angle of HSA produced using nitric acid as a catalyst can reach as high as 159.5°, classifying it as a superhydrophobic material. Additionally, while moderately increasing the concentration of the hydrophobic modifier enhances HSA’s hydrophobicity, it concurrently reduces its porosity. The HSA maintained hydrophobicity until 500 °C. The pore structure of HSA collapsed gradually with the increase in heat temperature. After treatment at 700 °C, HSA lost its hydrophobicity and the porous structure was severely damaged. Compared with silica aerogel using traditional silicon sources, the damage to pore structure and the crystallization occurred at lower temperatures, but the hydrophobicity remained at higher temperatures. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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15 pages, 3574 KiB  
Article
Machine Learning Models for Predicting Thermal Properties of Radiative Cooling Aerogels
by Chengce Yuan, Yimin Shi, Zhichen Ba, Daxin Liang, Jing Wang, Xiaorui Liu, Yabei Xu, Junreng Liu and Hongbo Xu
Gels 2025, 11(1), 70; https://doi.org/10.3390/gels11010070 - 16 Jan 2025
Cited by 1 | Viewed by 1005
Abstract
The escalating global climate crisis and energy challenges have made the development of efficient radiative cooling materials increasingly urgent. This study presents a machine-learning-based model for predicting the performance of radiative cooling aerogels (RCAs). The model integrated multiple parameters, including the material composition [...] Read more.
The escalating global climate crisis and energy challenges have made the development of efficient radiative cooling materials increasingly urgent. This study presents a machine-learning-based model for predicting the performance of radiative cooling aerogels (RCAs). The model integrated multiple parameters, including the material composition (matrix material type and proportions), modification design (modifier type and content), optical properties (solar reflectance and infrared emissivity), and environmental factors (solar irradiance and ambient temperature) to achieve accurate cooling performance predictions. A comparative analysis of various machine learning algorithms revealed that an optimized XGBoost model demonstrated superior predictive performance, achieving an R2 value of 0.943 and an RMSE of 1.423 for the test dataset. An interpretability analysis using Shapley additive explanations (SHAPs) identified a ZnO modifier (SHAP value, 1.523) and environmental parameters (ambient temperature, 1.299; solar irradiance, 0.979) as the most significant determinants of cooling performance. A feature interaction analysis further elucidated the complex interplay between the material composition and environmental conditions, providing theoretical guidance for material optimization. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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23 pages, 7544 KiB  
Article
Lignin Polyurethane Aerogels: Influence of Solvent on Textural Properties
by Razan Altarabeen, Dmitri Rusakov, Erik Manke, Lara Gibowsky, Baldur Schroeter, Falk Liebner and Irina Smirnova
Gels 2024, 10(12), 827; https://doi.org/10.3390/gels10120827 - 14 Dec 2024
Viewed by 1702
Abstract
This study explores the innovative potential of native lignin as a sustainable biopolyol for synthesizing polyurethane aerogels with variable microstructures, significant specific surface areas, and high mechanical stability. Three types of lignin—Organosolv, Aquasolv, and Soda lignin—were evaluated based on structural characteristics, Klason lignin [...] Read more.
This study explores the innovative potential of native lignin as a sustainable biopolyol for synthesizing polyurethane aerogels with variable microstructures, significant specific surface areas, and high mechanical stability. Three types of lignin—Organosolv, Aquasolv, and Soda lignin—were evaluated based on structural characteristics, Klason lignin content, and particle size, with Organosolv lignin being identified as the optimal candidate. The microstructure of lignin polyurethane samples was adjustable by solvent choice: Gelation in DMSO and pyridine, with high affinity to lignin, resulted in dense materials with low specific surface areas, while the use of the low-affinity solvent e.g acetone led to aggregated, macroporous materials due to microphase separation. Microstructural control was achieved by use of DMSO/acetone and pyridine/acetone solvent mixtures, which balanced gelation and phase separation to produce fine, homogeneous, mesoporous materials. Specifically, a 75% DMSO/acetone mixture yielded mechanically stable lignin polyurethane aerogels with a low envelope density of 0.49 g cm−3 and a specific surface area of ~300 m2 g−1. This study demonstrates a versatile approach to tailoring lignin polyurethane aerogels with adjustable textural and mechanical properties by simple adjustment of the solvent composition, highlighting the critical role of solvent–lignin interactions during gelation and offering a pathway to sustainable, high-performance materials. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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Graphical abstract

13 pages, 2102 KiB  
Article
Machine Learning Techniques to Analyze the Influence of Silica on the Physico-Chemical Properties of Aerogels
by Hamdi Chaouk, Emil Obeid, Jalal Halwani, Jack Arayro, Rabih Mezher, Omar Mouhtady, Eddie Gazo-Hanna, Semaan Amine and Khaled Younes
Gels 2024, 10(9), 554; https://doi.org/10.3390/gels10090554 - 27 Aug 2024
Viewed by 1289
Abstract
This study explores the application of machine learning techniques, specifically principal component analysis (PCA), to analyze the influence of silica content on the physical and chemical properties of aerogels. Silica aerogels are renowned for their exceptional properties, including high porosity, large surface area, [...] Read more.
This study explores the application of machine learning techniques, specifically principal component analysis (PCA), to analyze the influence of silica content on the physical and chemical properties of aerogels. Silica aerogels are renowned for their exceptional properties, including high porosity, large surface area, and low thermal conductivity, but their mechanical brittleness poses significant challenges. The study initially utilized cross-correlation analysis to examine the relationships between key properties such as the Brunauer–Emmett–Teller (BET) surface area, pore volume, density, and thermal conductivity. However, weak correlations prompted the application of PCA to uncover deeper insights into the data. The PCA results demonstrated that silica content has a significant impact on aerogel properties, with the first principal component (PC1) showing a strong positive correlation (R2 = 94%) with silica content. This suggests that higher silica levels correspond to lower thermal conductivity, porosity, and BET surface area, while increasing the density and elastic modulus. Additionally, the analysis identified the critical role of thermal conductivity in the second principal component (PC2), particularly in samples with moderate to high silica content. Overall, this study highlights the effectiveness of machine learning techniques like PCA in optimizing and understanding the complex inter-relationships among the physico-chemical properties of silica aerogels. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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13 pages, 4147 KiB  
Article
Synthesis of Flexible Polyamide Aerogels Cross-Linked with a Tri-Isocyanate
by Daniel A. Scheiman, Haiquan Guo, Katherine J. Oosterbaan, Linda McCorkle and Baochau N. Nguyen
Gels 2024, 10(8), 519; https://doi.org/10.3390/gels10080519 - 7 Aug 2024
Cited by 1 | Viewed by 1341
Abstract
A new series of flexible polyamide (PA) aerogels was synthesized using terephthaloyl chloride (TPC), 2,2′-dimethylbenzidine (DMBZ) and cross-linked with an inexpensive, commercially available tri-isocyanate (Desmodur N3300A) at polymer concentrations of 6–8 wt.% total solids and repeating units, n, from 30 to 60. [...] Read more.
A new series of flexible polyamide (PA) aerogels was synthesized using terephthaloyl chloride (TPC), 2,2′-dimethylbenzidine (DMBZ) and cross-linked with an inexpensive, commercially available tri-isocyanate (Desmodur N3300A) at polymer concentrations of 6–8 wt.% total solids and repeating units, n, from 30 to 60. The cross-linked DMBZ-based polyamide aerogels obtained, after supercritically drying using liquid CO2, had shrinkages of 19–27% with densities ranging from 0.12 g/cm3 to 0.22 g/cm3, porosity and surface areas up to 91% and 309 m2/g, respectively, and modulus values ranging from 20.6 to 109 MPa. Evidence suggests that a higher flexibility could be achieved using DMBZ in the polyamide backbone with N3300A as a cross-linker, when compared to previously reported TPC-mPDA-BTC PA aerogels, N3300A-polyimide aerogels, and N3300-reinforced silica aerogels. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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14 pages, 8775 KiB  
Article
Facile Synthesis of Surface-Modified Hollow-Silica (SiO2) Aerogel Particles via Oil–Water–Oil Double Emulsion Method
by Pratik S. Kapadnis, Ki-Sun Nam, Hyun-Young Kim, Hyung-Ho Park and Haejin Hwang
Gels 2024, 10(6), 380; https://doi.org/10.3390/gels10060380 - 2 Jun 2024
Cited by 1 | Viewed by 2351
Abstract
Due to their high surface area and low weight, silica aerogels are ideally suited for several uses, including drug delivery, catalysis, and insulation. Oil–water–oil (OWO) double emulsion is a simple and regulated technique for encasing a volatile oil phase in a [...] Read more.
Due to their high surface area and low weight, silica aerogels are ideally suited for several uses, including drug delivery, catalysis, and insulation. Oil–water–oil (OWO) double emulsion is a simple and regulated technique for encasing a volatile oil phase in a silica shell to produce hollow silica (SiO2) aerogel particles by using hydrophilic and hydrophobic emulsifiers. In this study, the oil–water–oil (OWO) double emulsion method was implemented to synthesize surface-modified hollow silica (SiO2) aerogel particles in a facile and effective way. This investigation mainly focused on the influence of the N-hexane-to-water glass (OW) ratio (r) in the first emulsion, silica (water glass) content concentration (x), and surfactant concentration (s) variations. Furthermore, surface modification techniques were utilized to customize the aerogel’s characteristics. The X-ray diffraction (XRD) patterns showed no imprints of impurities except SiO2. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images highlight the hollow microstructure of silica particles. Zeta potential was used to determine particle size analysis of hollow silica aerogel particles. The oil–water–oil (OWO) double emulsion approach was successfully employed to synthesize surface-modified hollow silica (SiO2) aerogel particles, providing precise control over the particle characteristics. By the influence of the optimization condition, this approach improves the aerogel’s potential applications in drug delivery, catalysis, and insulation by enabling surface modifications. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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14 pages, 4795 KiB  
Article
Enhancing Water Resistance in Foam Cement through MTES-Based Aerogel Impregnation
by Zhi Li, Shengjie Yao, Guichao Wang, Xi Deng, Fang Zhou, Xiaoxu Wu and Qiong Liu
Gels 2024, 10(2), 118; https://doi.org/10.3390/gels10020118 - 1 Feb 2024
Cited by 4 | Viewed by 2051
Abstract
The propensity of foamed concrete to absorb water results in a consequential degradation of its performance attributes. Addressing this issue, the integration of aerogels presents a viable solution; however, their direct incorporation has been observed to compromise mechanical properties, attributable to the effects [...] Read more.
The propensity of foamed concrete to absorb water results in a consequential degradation of its performance attributes. Addressing this issue, the integration of aerogels presents a viable solution; however, their direct incorporation has been observed to compromise mechanical properties, attributable to the effects of the interface transition zone. This study explores the incorporation of MTES-based aerogels into foamed cement via an impregnation technique, examining variations in water–cement ratios. A comprehensive analysis was conducted, evaluating the influences of MTES-based aerogels on the thermal conductivity, compressive strength, density, chemical composition, and microstructure of the resultant composites across different water–cement ratios. Our findings elucidate that an increment in the water–cement ratio engenders a gradual regularization of the pore structure in foamed concrete, culminating in augmented porosity and diminished density. Notably, aerogel-enhanced foamed concrete (AEFC) exhibited a significant reduction in water absorption, quantified at 86% lower than its conventional foamed concrete (FC) counterpart. Furthermore, the softening coefficient of AEFC was observed to surpass 0.75, with peak values reaching approximately 0.9. These results substantiate that the impregnation of MTES-based aerogels into cementitious materials not only circumvents the decline in strength but also bolsters their hydrophobicity and water resistance, indirectly enhancing the serviceability and longevity of foamed concrete. In light of these findings, the impregnation method manifests promising potential for broadening the applications of aerogels in cement-based materials. Full article
(This article belongs to the Special Issue Aerogels—Preparation and Properties)
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