Gels | Special Issue : Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application

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21 pages, 5655 KiB

Open AccessArticle

Radially and Axially Oriented Ammonium Alginate Aerogels Modified with Clay/Tannic Acid and Crosslinked with Glutaraldehyde

by Lucía G. De la Cruz, Tobias Abt, Noel León and Miguel Sánchez-Soto

Gels 2024, 10(8), 526; https://doi.org/10.3390/gels10080526 - 10 Aug 2024

Viewed by 746

Abstract

Lightweight materials that combine high mechanical strength, insulation, and fire resistance are of great interest to many industries. This work explores the properties of environmentally friendly alginate aerogel composites as potential sustainable alternatives to petroleum-based materials. This study analyzes the effects of two [...] Read more.

Lightweight materials that combine high mechanical strength, insulation, and fire resistance are of great interest to many industries. This work explores the properties of environmentally friendly alginate aerogel composites as potential sustainable alternatives to petroleum-based materials. This study analyzes the effects of two additives (tannic acid and montmorillonite clay), the orientation that results during casting, and the crosslinking of the biopolymer with glutaraldehyde on the properties of the aerogel composites. The prepared aerogels exhibited high porosities between 90% and 97% and densities in the range of 0.059–0.191 g/cm³. Crosslinking increased the density and resulted in excellent performance under loading conditions. In combination with axial orientation, Young’s modulus and yield strength reached values as high as 305 MPa·cm³/g and 7 MPa·cm³/g, respectively. Moreover, the alginate-based aerogels exhibited very low thermal conductivities, ranging from 0.038 W/m·K to 0.053 W/m·K. Compared to pristine alginate, the aerogel composites’ thermal degradation rate decreased substantially, enhancing thermal stability. Although glutaraldehyde promoted combustion, the non-crosslinked aerogel composites demonstrated high fire resistance. No flame was observed in these samples under cone calorimeter radiation, and a minuscule peak of heat release of 21 kW/m² was emitted as a result of their highly efficient graphitization and fire suppression. The combination of properties of these bio-based aerogels demonstrates their potential as substituents for their fossil-based counterparts. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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15 pages, 8365 KiB

Open AccessArticle

Ceramic Fiber-Reinforced Polyimide Aerogel Composites with Improved Shape Stability against Shrinkage

by Wanlin Shi, Mengmeng Wan, Yating Tang and Weiwang Chen

Gels 2024, 10(5), 327; https://doi.org/10.3390/gels10050327 - 10 May 2024

Cited by 2 | Viewed by 1088

Abstract

Polyimide (PI) aerogels, renowned for their nano-porous structure and exceptional performance across a spectrum of applications, often encounter significant challenges during fabrication, primarily due to severe shrinkage. In this study, we innovatively incorporated ceramic fibers of varying diameters into the PI aerogel matrix [...] Read more.

Polyimide (PI) aerogels, renowned for their nano-porous structure and exceptional performance across a spectrum of applications, often encounter significant challenges during fabrication, primarily due to severe shrinkage. In this study, we innovatively incorporated ceramic fibers of varying diameters into the PI aerogel matrix to enhance the shape stability against shrinkage. The structure of the resulting ceramic fiber-reinforced PI (CF-PI) aerogel composites as well as their performance in thermal decomposition, thermal insulation, and compression resistance were characterized. The results revealed that the CF-PI aerogel composites dried by supercritical ethanol achieved greatly reduced shrinkage as low as 5.0 vol.% and low thermal conductivity ranging from 31.2 mW·m⁻¹·K⁻¹ to 35.3 mW·m⁻¹·K⁻¹, showcasing their excellent performance in shape stability and thermal insulation. These composites also inherited the superior residue-forming ability of ceramic fibers and the robust mechanical attributes of PI, thereby exhibiting enhanced thermal stability and compression resistance. Besides, the effects of different drying conditions on the structure and properties of CF-PI aerogels were also discussed. The coupling use of supercritical ethanol drying with the addition of ceramic fibers is preferred. This preferred condition gives birth to low-shrinkage CF-PI aerogel composites, which also stand out for their integrated advantages include high thermal stability, low thermal conductivity, and high mechanical strength. These advantages attribute to CF-PI aerogel composites substantial potential for a wide range of applications, particularly as high-performance thermal insulation materials for extreme conditions. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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13 pages, 6355 KiB

Open AccessArticle

Cellulose Diacetate Aerogels with Low Drying Shrinkage, High-Efficient Thermal Insulation, and Superior Mechanical Strength

by Sizhao Zhang, Kunming Lu, Yangbiao Hu, Guangyu Xu, Jing Wang, Yanrong Liao and Shuai Yu

Gels 2024, 10(3), 210; https://doi.org/10.3390/gels10030210 - 21 Mar 2024

Cited by 1 | Viewed by 1330

Abstract

The inherent characteristics of cellulose-derived aerogels, such as their natural abundance and environmental friendliness, make them highly interesting. However, its significant shrinkage before and after the supercritical drying procedure and low mechanical strength limit its potential application. Here, we propose a strategy to [...] Read more.

The inherent characteristics of cellulose-derived aerogels, such as their natural abundance and environmental friendliness, make them highly interesting. However, its significant shrinkage before and after the supercritical drying procedure and low mechanical strength limit its potential application. Here, we propose a strategy to prepare cellulose diacetate aerogels (CDAAs) with low drying shrinkage, exceptional thermal insulation, and superior mechanical strength. The low drying shrinkage (radial drying shrinkage of 1.4%) of CDAAs is attributed to their relative strong networking skeletons, which are greatly formed by tert-butanol solvent exchange in exerting the interaction of reducing the surface tension force. In this case, CDAAs are eventually endowed with the low bulk density of 0.069 g cm⁻³ as well. Additionally, as-prepared CDAAs possess an abundant three-dimensional networking structure whose pore size is concentrated in the diameter range of ~50 nm, and the result above is beneficial for improving the thermal insulation performance (thermal conductivity of 0.021 W m⁻¹ K⁻¹ at ambient environmental and pressure conditions). On the other hand, the optimal compressive stresses of CDAAs at 3% and 5% strain are 0.22 and 0.27 MPa respectively, indicating a mechanically well robustness. The above evidence demonstrates indeed the exceptional thermal insulation and superior compressive properties of CDAAs. This work may provide a new solution for developing a kind of high-performance cellulose-derived aerogel in the future. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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13 pages, 3309 KiB

Open AccessArticle

A Novel, Controllable, and Efficient Method for Building Highly Hydrophobic Aerogels

by Shu-Liang Li, Yu-Tao Wang, Shi-Jun Zhang, Ming-Ze Sun, Jie Li, Li-Qiu Chu, Chen-Xi Hu, Yi-Lun Huang, Da-Li Gao and David A. Schiraldi

Gels 2024, 10(2), 121; https://doi.org/10.3390/gels10020121 - 2 Feb 2024

Viewed by 1573

Abstract

Aerogels prepared using freeze-drying methods have the potential to be insulation materials or absorbents in the fields of industry, architecture, agriculture, etc., for their low heat conductivity, high specific area, low density, degradability, and low cost. However, their native, poor water resistance caused [...] Read more.

Aerogels prepared using freeze-drying methods have the potential to be insulation materials or absorbents in the fields of industry, architecture, agriculture, etc., for their low heat conductivity, high specific area, low density, degradability, and low cost. However, their native, poor water resistance caused by the hydrophilicity of their polymer matrix limits their practical application. In this work, a novel, controllable, and efficient templating method was utilized to construct a highly hydrophobic surface for freeze-drying aerogels. The influence of templates on the macroscopic morphology and hydrophobic properties of materials was investigated in detail. This method provided the economical and rapid preparation of a water-resistant aerogel made from polyvinyl alcohol (PVA) and montmorillonite (MMT), putting forward a new direction for the research and development of new, environmentally friendly materials. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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Full article ">Figure 1
The FTIR spectra of the MMT, PMA, and HPMA. Full article ">Figure 2
SEM images of the surfaces of PMA before and after hydrophobic modification (named HPMA) (left). Pore size distribution of PMA and PVA aerogels (named PAs) (right). Full article ">Figure 3
Images of water contact angle measurements of HPMA. Full article ">Figure 4
A 3D roughness reconstruction of PMAs treated with different sandpapers. Full article ">Figure 5
SEM images of the surfaces for PMAs treated with different sandpaper. Full article ">Figure 6
SEM images of the internal cross-section for HPMA and HPMA-2000. Full article ">Figure 7
Images of water contact angle measurements of HPMA with sandpaper templating. Full article ">Scheme 1
The preparation of HPMAs via a freeze-drying and vapor chemical deposition method. Full article ">

17 pages, 8366 KiB

Open AccessArticle

Meso-Microporous Carbon Nanofibrous Aerogel Electrode Material with Fluorine-Treated Wood Biochar for High-Performance Supercapacitor

by Md Faruque Hasan, Kingsford Asare, Shobha Mantripragada, Victor Charles, Abolghasem Shahbazi and Lifeng Zhang

Gels 2024, 10(1), 82; https://doi.org/10.3390/gels10010082 - 22 Jan 2024

Cited by 4 | Viewed by 2113

Abstract

A supercapacitor is an electrical energy storage system with high power output. With worldwide awareness of sustainable development, developing cost-effective, environmentally friendly, and high-performance supercapacitors is an important research direction. The use of sustainable components like wood biochar in the electrode materials for [...] Read more.

A supercapacitor is an electrical energy storage system with high power output. With worldwide awareness of sustainable development, developing cost-effective, environmentally friendly, and high-performance supercapacitors is an important research direction. The use of sustainable components like wood biochar in the electrode materials for supercapacitor uses holds great promise for sustainable supercapacitor development. In this study, we demonstrated a facile and powerful approach to prepare meso-microporous carbon electrode materials for sustainable and high-performance supercapacitor development by electrospinning polyacrylonitrile (PAN) with F-treated biochar and subsequent aerogel construction followed by stabilization, carbonization, and carbon activation. The resultant carbon nanofibrous aerogel electrode material (ENFA-FBa) exhibited exceptional specific capacitance, attributing to enormously increased micropore and mesopore volumes, much more activated sites to charge storage, and significantly greater electrochemical interaction with electrolyte. This electrode material achieved a specific capacitance of 407 F/g at current density of 0.5 A/g in 1 M H₂SO₄ electrolyte, which outperformed the state-of-the-art specific capacitance of biochar-containing electrospun carbon nanofibrous aerogel electrode materials (<300 F/g). A symmetric two-electrode cell with ENFA-FBa as electrode material showed an energy density of 11.2 Wh/kg at 125 W/kg power density. Even after 10,000 cycles of charging-discharging at current density of 10 A/g, the device maintained a consistent coulombic efficiency of 53.5% and an outstanding capacitance retention of 91%. Our research pointed out a promising direction to develop sustainable electrode materials for future high-performance supercapacitors. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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17 pages, 3641 KiB

Open AccessArticle

Self-Assembled Aminated and TEMPO Cellulose Nanofibers (Am/TEMPO-CNF) Aerogel for Adsorptive Removal of Oxytetracycline and Chloramphenicol Antibiotics from Water

by Rabia Amen, Islam Elsayed, Gregory T. Schueneman and El Barbary Hassan

Gels 2024, 10(1), 77; https://doi.org/10.3390/gels10010077 - 20 Jan 2024

Cited by 1 | Viewed by 2657

Abstract

Antibiotics are used for the well-being of human beings and other animals. Detectable levels of antibiotics can be found in pharmaceutical, municipal, and animal effluents. Therefore, the treatment of antibiotic contaminated water is of great concern. In this study, we fabricated a sustainable [...] Read more.

Antibiotics are used for the well-being of human beings and other animals. Detectable levels of antibiotics can be found in pharmaceutical, municipal, and animal effluents. Therefore, the treatment of antibiotic contaminated water is of great concern. In this study, we fabricated a sustainable aminated/TEMPO cellulose nanofiber (Am/TEMPO-CNF) aerogel to remove oxytetracycline (OTC) and chloramphenicol (CAP) from synthetic wastewater. The prepared aerogel was characterized using different analytical techniques such as elemental analysis, FTIR, TGA, SEM-EDS, and N₂ adsorption–desorption isotherms. The characterization techniques confirmed the presence and interaction of quaternary amine -[NR₃]⁺ and -COOH groups on Am/TEMPO-CNF with OTC and CAP, which validates the successful modification of Am/TEMPO-CNF. The adsorption process of the pollutants was examined as a function of solution pH, concentrations, reaction time, and temperatures. The maximum adsorption capacity was 153.13 and 150.15 mg/g for OTC and CAP, respectively. The pseudo-second order (PSO-2) was well fitted to both OTC and CAP, confirming the removal is via chemisorption. Hydrogen bonding and electrostatic attraction have been postulated as key factors in facilitating OTC and CAP adsorption according to spectroscopic studies. Energetically, the adsorption was spontaneous and endothermic for both pollutants. In conclusion, the efficient removal rate and excellent reusability of Am/TEMPO-CNF indicate the strong potential of the adsorbent for antibiotics’ removal. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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Figure 1

Figure 1
(a) Am/TEMPO-CNF nitrogen adsorption–desorption isotherm, (b) Am/TEMPO-CNF pore size distribution, (c) FTIR spectra of TEMPO-CNF, Am-CNF, and Am/TEMPO-CNF, and (d) TGA-DTG thermograph of TEMPO-CNF, Am-CNF, and Am/TEMPO-CNF. Full article ">Figure 2
Fe-SEM micrograph of (a) Am-CNF, (b) Am/TEMPO-CNF, and (c–f) Electron image and EDS of Am/TEMPO-CNF. Full article ">Figure 3
(a) Effect of pH on the adsorption capacity, (b) point of zero charge (PZC), (c) OTC structure with pH-dependent speciation curve, and (d) CAP structure with pH-dependent speciation curve. Full article ">Figure 4
The adsorption kinetics curves of OTC and CAP using Am/TEMPO-CNF at room temperature: (a) OTC pseudo-second order non-linear fit, (b) OTC pseudo-second order linear fit, (c) CAP pseudo-second order non-linear fit, and (d) CAP pseudo-second order linear fit. Full article ">Figure 5
The adsorption isotherm curves of OTC and CAP using Am/TEMPO-CNF at different temperatures: (a) OTC Langmuir non-linear fit, (b) OTC Langmuir linear fit, (c) CAP Langmuir non-linear fit, and (d) CAP Langmuir linear fit. Full article ">Figure 6
Removal mechanism of OTC and CAP using Am/TEMPO-CNF. Full article ">Figure 7
Regeneration cycles of Am/TEMPO-CNF for OTC and CAP. Full article ">Scheme 1
Synthesis mechanism of Am/TEMPO-CNF aerogel. Full article ">

12 pages, 1485 KiB

Open AccessArticle

Uncovering Key Factors in Graphene Aerogel-Based Electrocatalysts for Sustainable Hydrogen Production: An Unsupervised Machine Learning Approach

by Emil Obeid and Khaled Younes

Gels 2024, 10(1), 57; https://doi.org/10.3390/gels10010057 - 12 Jan 2024

Cited by 3 | Viewed by 1426

Abstract

The application of principal component analysis (PCA) as an unsupervised learning method has been used in uncovering correlations among diverse features of aerogel-based electrocatalysts. This analytical approach facilitates a comprehensive exploration of catalytic activity, revealing intricate relationships with various physical and electrochemical properties. [...] Read more.

The application of principal component analysis (PCA) as an unsupervised learning method has been used in uncovering correlations among diverse features of aerogel-based electrocatalysts. This analytical approach facilitates a comprehensive exploration of catalytic activity, revealing intricate relationships with various physical and electrochemical properties. The first two principal components (PCs), collectively capturing nearly 70% of the total variance, attested the reliability and efficacy of PCA in unveiling meaningful patterns. This study challenges the conventional understanding that a material’s reactivity is solely dictated by the quantity of catalyst loaded. Instead, it unveils a complex perspective, highlighting that reactivity is intricately influenced by the material’s overall design and structure. The PCA bi-plot uncovers correlations between pH and Tafel slope, suggesting an interdependence between these variables and providing valuable insights into the complex interactions among physical and electrochemical properties. Tafel slope stands to be positively correlated with PC₁ and PC₂, showing an evident positive correlation with the pH. These findings showed that the pH can have a positive correlation with the Tafel slope, however, it does not necessarily reflect a direct positive correlation with the overpotential. The impact of pH on current density (j)and Tafel slope underscores the importance of adjusting pH to lower overpotential effectively, enhancing catalytic activity. Surface area (from 30 to 533 m² g⁻¹) emerges as a key physical property, inclusively inverse correlation with overpotential, indicating its direct role in lowering overpotential and increasing catalytic activity. The introduction of PC₃, in conjunction with PC₁, enriches the analysis by revealing consistent trends despite a slightly lower variance (60%). This reinforces the robustness of PCA in delineating distinct characteristics of graphene aerogels, affirming their potential implications in diverse electrocatalytic applications. In summary, PCA proves to be a valuable tool for unraveling complex relationships within aerogel-based electrocatalysts, extending insights beyond catalytic sites to emphasize the broader spectrum of material properties. This approach enhances comprehension of dataset intricacies and holds promise for guiding the development of more effective and versatile electrocatalytic materials. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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19 pages, 2663 KiB

Open AccessArticle

Sustainable Tannin Gels for the Efficient Removal of Metal Ions and Organic Dyes

by Ann-Kathrin Koopmann, Caroline Ramona Ehgartner, Daniel Euchler, Martha Claros and Nicola Huesing

Gels 2023, 9(10), 822; https://doi.org/10.3390/gels9100822 - 17 Oct 2023

Cited by 1 | Viewed by 1819

Abstract

The usage of a highly efficient, low-cost, and sustainable adsorbent material as an industrial wastewater treatment technique is required. Herein, the usage of the novel, fully sustainable tannin-5-(hydroxymethyl)furfural (TH) aerogels, generated via a water-based sol–gel process, as compatible biosorbent materials is presented. In [...] Read more.

The usage of a highly efficient, low-cost, and sustainable adsorbent material as an industrial wastewater treatment technique is required. Herein, the usage of the novel, fully sustainable tannin-5-(hydroxymethyl)furfural (TH) aerogels, generated via a water-based sol–gel process, as compatible biosorbent materials is presented. In particular, this study focusses on the surface modification of the tannin biosorbent with carboxyl or amino functional groups, which, hence, alters the accessible adsorption sites, resulting in increased adsorption capacity, as well as investigating the optimal pH conditions for the adsorption process. Precisely, highest adsorption capacities are acquired for the metal cations and cationic dye in an alkaline aqueous environment using a carboxyl-functionalized tannin biosorbent, whereas the anionic dye requires an acidic environment using an amino-functionalized tannin biosorbent. Under these determined optimal conditions, the maximum monolayer adsorption capacity of the tannin biosorbent ensues in the following order: Cu²⁺ > RB > Zn²⁺ > MO, with 500, 244, 192, 131 mg g⁻¹, respectively, indicating comparable or even superior adsorption capacities compared to conventional activated carbons or silica adsorbents. Thus, these functionalized, fully sustainable, inexpensive tannin biosorbent materials, that feature high porosity and high specific surface areas, are ideal industrial candidates for the versatile adsorption process from contaminated (heavy) metal or dye solutions. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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Review

Jump to: Research

24 pages, 2950 KiB

Open AccessReview

Enhancing Photocatalytic Properties of TiO₂ Photocatalyst and Heterojunctions: A Comprehensive Review of the Impact of Biphasic Systems in Aerogels and Xerogels Synthesis, Methods, and Mechanisms for Environmental Applications

by Lizeth Katherine Tinoco Navarro and Cihlar Jaroslav

Gels 2023, 9(12), 976; https://doi.org/10.3390/gels9120976 - 13 Dec 2023

Cited by 7 | Viewed by 2300

Abstract

This review provides a detailed exploration of titanium dioxide (TiO₂) photocatalysts, emphasizing structural phases, heterophase junctions, and their impact on efficiency. Key points include diverse synthesis methods, with a focus on the sol-gel route and variants like low-temperature hydrothermal synthesis (LTHT). [...] Read more.

This review provides a detailed exploration of titanium dioxide (TiO₂) photocatalysts, emphasizing structural phases, heterophase junctions, and their impact on efficiency. Key points include diverse synthesis methods, with a focus on the sol-gel route and variants like low-temperature hydrothermal synthesis (LTHT). The review delves into the influence of acid-base donors on gelation, dissects crucial drying techniques for TiO₂ aerogel or xerogel catalysts, and meticulously examines mechanisms underlying photocatalytic activity. It highlights the role of physicochemical properties in charge diffusion, carrier recombination, and the impact of scavengers in photo-oxidation/reduction. Additionally, TiO₂ doping techniques and heterostructures and their potential for enhancing efficiency are briefly discussed, all within the context of environmental applications. Full article

(This article belongs to the Special Issue Recent Progress and Development of Advanced Aerogels: Latest Processing Methods, Improved Properties and Application)

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