Gels | Special Issue : Preparation and Application of Aerogel and its Composite Materials

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16 pages, 11625 KiB

Open AccessArticle

Aramid Pulp Reinforced Clay Aerogel Composites: Mechanical, Thermal and Combustion Behavior

by Xiaowu Wang, Yang Wang, Mengtian Sun, Guichao Wang, Qiong Liu, Ming Li, Yury M. Shulga and Zhi Li

Gels 2022, 8(10), 654; https://doi.org/10.3390/gels8100654 - 14 Oct 2022

Cited by 4 | Viewed by 1865

Abstract

In this work, we reported that aramid pulps (AP) reinforced clay aerogel composites with improved mechanical strength, good thermal insulation and fire resistance based on the combination of AP, Poly(vinyl alcohol) (PVA) and sodium montmorillonite (MMT), which present a promising prospect in the [...] Read more.

In this work, we reported that aramid pulps (AP) reinforced clay aerogel composites with improved mechanical strength, good thermal insulation and fire resistance based on the combination of AP, Poly(vinyl alcohol) (PVA) and sodium montmorillonite (MMT), which present a promising prospect in the thermal insulation application. The PVA-MMT-AP_x (x: denotes the mass content of AP) aerogel composites present an isotropic “lamella-honeycomb” porous structure, which endows them with excellent comprehensive performance. With the AP content increasing, the extremely low density is kept, ranging between 67–73 mg/cm³, and the low thermal conductivity is maintained within 40.9–47.9 mW·m⁻¹·K⁻¹. The mechanical strength is significantly improved with the maximum compressive modulus increasing from 2.95 to 5.96 MPa and the specific modulus rising from 44.03 to 81.64 MPa∙cm³/g. Their detailed heat transfer process has been analyzed, which provides a deep understanding to the low thermal conductivity of the PVA-MMT-AP_x aerogel composites. Based on the combination of thermogravimetric analysis and combustion behavior, the PVA-MMT-AP_x aerogel composites are demonstrated to possess improved thermal stability and fire resistance. This study puts forward a facile approach to utilizing AP to reinforce clay aerogel composites, which provides new insight into the development of thermal-insulating, fire-safe and high-strength thermal insulation materials. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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17 pages, 6028 KiB

Open AccessArticle

In-Situ Synthesis of Layered Double Hydroxide/Silica Aerogel Composite and Its Thermal Safety Characteristics

by Mengtian Sun, Yang Wang, Xiaowu Wang, Qiong Liu, Ming Li, Yury M. Shulga and Zhi Li

Gels 2022, 8(9), 581; https://doi.org/10.3390/gels8090581 - 13 Sep 2022

Cited by 11 | Viewed by 2047

Abstract

To adjust the thermal safety of hydrophobic silica aerogel, layered double hydroxide (LDH)/silica aerogel (SA) composites were prepared by an in-situ sol-gel process at ambient pressure. This study found the physical combination of SA and MgAl-LDH based on the FTIR spectra and phase [...] Read more.

To adjust the thermal safety of hydrophobic silica aerogel, layered double hydroxide (LDH)/silica aerogel (SA) composites were prepared by an in-situ sol-gel process at ambient pressure. This study found the physical combination of SA and MgAl-LDH based on the FTIR spectra and phase composition of LDH/SA. The N₂ sorption analysis confirms that the introduction of MgAl-LDH does not change the mesoporous attribution of LDH/SA significantly. With the increase in MgAl-LDH addictive content, the low density (0.12–0.13 g/cm³), low thermal conductivity (24.28–26.38 mW/m/K), and large specific surface area (730.7–903.7 m²g) of LDH/SA are still maintained, which can satisfy the requirements of thermal insulation. The TG-DSC analysis demonstrates that the endothermic effects and metal oxides formed during the MgAl-LDH decomposition are beneficial to the improvement of the thermal stability of LDH/SA composites. In addition, it was found that the gross calorific values of LDH/SA composites decrease with an increase in MgAl-LDH addictive content, all of which are lower than that of the pure SA. The research outcomes indicate that the thermal safety of LDH/SA composites is enhanced significantly by doping MgAl-LDH without impairing too many of the excellent properties, which benefits their expansion in the thermal insulation field. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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9 pages, 37472 KiB

Open AccessCommunication

Aerogel Assembled by Two Types of Carbon Nanoparticles for Efficient Removal of Heavy Metal Ions

by Xue-Chun Yang, Song Gao, Sha-Qi Fu, Xuan Yao, Zheng Jiao, Jing-Tai Zhao, Zhi-Jun Zhang and Ling-Li Cheng

Gels 2022, 8(8), 459; https://doi.org/10.3390/gels8080459 - 22 Jul 2022

Cited by 2 | Viewed by 1558

Abstract

Both sodium alginate and polyethyleneimine (PEI) have a good ability to adsorb heavy metal ions. PEI and sodium alginate were used as important precursors to synthesize positively charged carbon nanoparticles (p-CNDs) with hydroxyl and carboxyl, and negatively charged carbon nanoparticles (n-CNDs) with amino, [...] Read more.

Both sodium alginate and polyethyleneimine (PEI) have a good ability to adsorb heavy metal ions. PEI and sodium alginate were used as important precursors to synthesize positively charged carbon nanoparticles (p-CNDs) with hydroxyl and carboxyl, and negatively charged carbon nanoparticles (n-CNDs) with amino, respectively. The carbon nanoparticles (CNDs) aerogel with a large specific surface area and rich functional groups were constructed by self-assembled p-CNDs and n-CNDs via electrostatic attraction for adsorption of heavy metal ions in water. The results show that CNDs aerogel has good adsorption properties for Pb²⁺ (96%), Cu²⁺ (91%), Co²⁺ (86%), Ni²⁺ (82%), and Cd²⁺ (78%). Furthermore, the fluorescence emission intensity of CNDs aerogel will gradually decrease with the increase in the adsorption rate, indicating that it can detect the adsorption process synchronously. In addition, the cytotoxicity test reveals that CNDs have good biocompatibility and will not cause secondary damage to biological cells. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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14 pages, 3845 KiB

Open AccessArticle

Composite Aerogel Comprised of Sodium Alginate and Bentonite via Supercritical CO₂ Drying: An Efficient Adsorbent for Lysozyme

by Jie Zhao, Liqin Cao and Yong Dong

Gels 2022, 8(6), 359; https://doi.org/10.3390/gels8060359 - 8 Jun 2022

Cited by 2 | Viewed by 2206

Abstract

To meet the demand for the separation of specific substances, the construction of porous composite aerogels with a high specific surface area and a strong adsorption capacity is still a challenge. Herein, a sodium alginate/bentonite composite aerogel was efficiently prepared through supercritical fluid [...] Read more.

To meet the demand for the separation of specific substances, the construction of porous composite aerogels with a high specific surface area and a strong adsorption capacity is still a challenge. Herein, a sodium alginate/bentonite composite aerogel was efficiently prepared through supercritical fluid drying. The aerogel’s volume shrank less during supercritical drying, maintaining its original three-dimensional mesh structure. The resulting aerogel had a large specific surface area (445 m²/g), a low density (0.059 g/cm³), and a large pore volume (3.617 cm³/g). Due to the fixation and intercalation effects, bentonite was uniformly dispersed in the sodium alginate matrixes. The adsorption of lysozyme by the composite aerogel was evaluated, and the results showed that the optimal adsorption pH was 8 when the pH of the phosphoric acid buffer solution was between pH = 5 and 8.5. The time for adsorption to reach equilibrium was 8 h. The adsorption capacity increased with the increase in bentonite content, and when the initial concentration of lysozyme was from 0.2 to 1.2 g/L, the adsorption capacity first increased and then stabilized, and the maximum adsorption amount was 697 mg/g. The adsorption behavior was simulated in the isothermal region, and the linear correlation coefficient of Langmuir isothermal adsorption fitting was found to be 0.997. Thus, this composite aerogel with strong adsorption capacity can be used as a good alternative to enzymatic adsorbents or immobilized materials. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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15 pages, 11616 KiB

Open AccessEditor’s ChoiceArticle

Improvement of the Thermal Insulation Performance of Silica Aerogel by Proper Heat Treatment: Microporous Structures Changes and Pyrolysis Mechanism

by Zhiyi Lun, Lunlun Gong, Zhongxin Zhang, Yurui Deng, Yong Zhou, Yuelei Pan and Xudong Cheng

Gels 2022, 8(3), 141; https://doi.org/10.3390/gels8030141 - 23 Feb 2022

Cited by 8 | Viewed by 3924

Abstract

A simple heat treatment method was used to optimize the three-dimensional network structure of the hydrophobic aerogel, and during the heat treatment process at 200–1000 °C, the thermal conductivity of the aerogel reached the lowest to 0.02240 W/m·K between 250 °C and 300 [...] Read more.

A simple heat treatment method was used to optimize the three-dimensional network structure of the hydrophobic aerogel, and during the heat treatment process at 200–1000 °C, the thermal conductivity of the aerogel reached the lowest to 0.02240 W/m·K between 250 °C and 300 °C, which was mainly due to the optimization of microstructure and pyrolysis of surface groups. Further Fluent heat-transfer simulation also confirmed the above results. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to finely measure the pyrolysis process of aerogels, and the pyrolysis process of aerogel was divided into four stages. (I) Until 419 °C, as the temperature continued to rise, surface methyl groups were oxidized to form hydroxyl. (II) As the temperature reached to 232 °C, the oxidation proceeded. In addition, inside the aerogel, because of lacking oxygen, the reaction produced CH₄ and C–Si bonds would form. (III) After 283 °C, Si–OH groups began to condense to form Si–O–Si, which optimized the three-dimensional network structures to be beneficial to improve the thermal insulation performance of silica aerogel. (IV) When it reached 547 °C, the chemical reaction was terminated, and all the primary particles gradually fused into secondary particles and sintered to form clusters. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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13 pages, 3724 KiB

Open AccessArticle

Mechanically Strong and Tailorable Polyimide Aerogels Prepared with Novel Silicone Polymer Crosslinkers

by Zhongxin Zhang, Yurui Deng, Zhiyi Lun, Xiao Zhang, Mingyuan Yan, Pan He, Caihong Li and Yuelei Pan

Gels 2022, 8(1), 57; https://doi.org/10.3390/gels8010057 - 12 Jan 2022

Cited by 2 | Viewed by 2877

Abstract

Polyimide (PI) aerogels were prepared using self-designed silicone polymer cross-linkers with multi-amino from low-cost silane coupling agents to replace conventional small-molecule cross-linkers. The long-chain structure of silicone polymers provides more crosslinking points than small-molecule cross-linkers, thus improving the mechanical properties of polyimide. To [...] Read more.

Polyimide (PI) aerogels were prepared using self-designed silicone polymer cross-linkers with multi-amino from low-cost silane coupling agents to replace conventional small-molecule cross-linkers. The long-chain structure of silicone polymers provides more crosslinking points than small-molecule cross-linkers, thus improving the mechanical properties of polyimide. To investigate the effects of amino content and degree of polymerization on the properties of silicone polymers, the different silicone polymers and their cross-linked PI aerogels were prepared. The obtained PI aerogels exhibit densities as low as 0.106 g/cm³ and specific surface areas as high as 314 m²/g, and the maximum Young’s modulus of aerogel is up to 20.9 MPa when using (T-20) as cross-linkers. The cross-linkers were an alternative to expensive small molecule cross-linkers, which can improve the mechanical properties and reduce the cost of PI aerogels. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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13 pages, 4584 KiB

Open AccessArticle

Novel Solvent–Latex Mixing: Thermal Insulation Performance of Silica Aerogel/Natural Rubber Composite

by Chayanan Boonrawd, Supan Yodyingyong, Lazhar Benyahia and Darapond Triampo

Gels 2022, 8(1), 7; https://doi.org/10.3390/gels8010007 - 22 Dec 2021

Cited by 6 | Viewed by 4326

Abstract

In this work, the novel natural rubber latex (NRL) mixing was approached. The mixing process was carried out by using n-hexane as the dispersed phase of silica aerogel which acted as thermal insulation filler prior to NRL mixing. The silica aerogel/NR composites were [...] Read more.

In this work, the novel natural rubber latex (NRL) mixing was approached. The mixing process was carried out by using n-hexane as the dispersed phase of silica aerogel which acted as thermal insulation filler prior to NRL mixing. The silica aerogel/NR composites were prepared with different silica aerogel contents of 20, 40, 60, 80, and 100 parts per hundred rubber (phr). The morphology of the 40 phr composite showed the NR macropore formation with silica aerogel intercalated layers. The optimal content of silica aerogels and n-hexane were the key to obtaining the NR macropore. The thermal insulation performance of silica aerogel/NR composites was investigated because of their porous structures. The thermal conductivity of the composites were lower than that of the neat NR sheet and decreased from 0.081 to 0.055 W m⁻¹·K⁻¹ with increasing silica aerogel content. The lower densities of the composites than that of the NR sheet were revealed noticeably. In addition, the silica aerogel/NR composites exhibited a higher heat retardant ability than that of the NR sheet, and the comparable glass transition temperatures (T_g) of the composites and the neat NR indicated the maintained flexibility at ambient temperature or higher, which can benefit various temperature applications. The overall results demonstrated that the silica aerogel/NR composites from the novel NRL mixing preparation could be a promising technique to develop the porous materials and be utilised as thermal insulation products and building constructions. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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Review

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17 pages, 3971 KiB

Open AccessReview

Aerogels for Biomedical, Energy and Sensing Applications

by Muhammad Tayyab Noman, Nesrine Amor, Azam Ali, Stanislav Petrik, Radek Coufal, Kinga Adach and Mateusz Fijalkowski

Gels 2021, 7(4), 264; https://doi.org/10.3390/gels7040264 - 14 Dec 2021

Cited by 30 | Viewed by 6215

Abstract

The term aerogel is used for unique solid-state structures composed of three-dimensional (3D) interconnected networks filled with a huge amount of air. These air-filled pores enhance the physicochemical properties and the structural characteristics in macroscale as well as integrate typical characteristics of aerogels, [...] Read more.

The term aerogel is used for unique solid-state structures composed of three-dimensional (3D) interconnected networks filled with a huge amount of air. These air-filled pores enhance the physicochemical properties and the structural characteristics in macroscale as well as integrate typical characteristics of aerogels, e.g., low density, high porosity and some specific properties of their constituents. These characteristics equip aerogels for highly sensitive and highly selective sensing and energy materials, e.g., biosensors, gas sensors, pressure and strain sensors, supercapacitors, catalysts and ion batteries, etc. In recent years, considerable research efforts are devoted towards the applications of aerogels and promising results have been achieved and reported. In this thematic issue, ground-breaking and recent advances in the field of biomedical, energy and sensing are presented and discussed in detail. In addition, some other perspectives and recent challenges for the synthesis of high performance and low-cost aerogels and their applications are also summarized. Full article

(This article belongs to the Special Issue Preparation and Application of Aerogel and its Composite Materials)

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