Advances on Dimensional Structure Designs and Functional Applications of Aerogels

A Review of High-Temperature Aerogels: Composition, Mechanisms, and Properties

High-temperature aerogels have garnered significant attention as promising insulation materials in various industries such as aerospace, automotive manufacturing, and beyond, owing to their remarkable thermal insulation properties coupled with low density. With advancements in manufacturing techniques, the thermal resilience of aerogels has considerable improvements. Notably, polyimide-based aerogels can endure temperatures up to 1000 °C, zirconia-based aerogels up to 1300 °C, silica-based aerogels up to 1500 °C, alumina-based aerogels up to 1800 °C, and carbon-based aerogels can withstand up to 2500 °C. This paper systematically discusses recent advancements in the thermal insulation performance of these five materials. It elaborates on the temperature resistance of aerogels and elucidates their thermal insulation mechanisms. Furthermore, it examines the impact of doping elements on the thermal conductivity of aerogels and consolidates various preparation methods aimed at producing aerogels capable of withstanding temperatures. In conclusion, by employing judicious composition design strategies, it is anticipated that the maximum tolerance temperature of aerogels can surpass 2500 °C, thus opening up new avenues for their application in extreme thermal environments.

Wearable Aerogels for Personal Thermal Management and Smart Devices

Extreme climates have become frequent nowadays, causing increased heat stress in human daily life. Personal thermal management (PTM), a technology that controls the human body's microenvironment, has become a promising strategy to address heat stress. While effective in ordinary environments, traditional high-performance fibers, such as ultrafine, porous, highly thermally conductive, and phase change materials, fall short when dealing with harsh conditions or large temperature fluctuations. Aerogels, a third-generation superinsulation material, have garnered extensive attention among researchers for their thermal management applications in building energy conservation, transportation, and aerospace, attributed to their extremely low densities and thermal conductivity. While aerogels have historically faced challenges related to weak mechanical strength and limited secondary processing capacity, recent advancements have witnessed notable progress in the development of wearable aerogels for PTM. This progress underscores their potential applications within extremely harsh environments, serving as self-powered smart devices and sensors. This Review offers a timely overview of wearable aerogels and their PTM applications with a particular focus on their wearability and suitability. Finally, the discussion classifies five types of PTM applications based on aerogel function: thermal insulation, heating, cooling, adaptive regulation (involving thermal insulation, heating, and cooling), and utilization of aerogels as wearable smart devices.

Bioinspired Multilayer Structures for Energy-Free Passive Heating and Thermal Regulation in Cold Environments

Passive thermal regulation has attracted increasing interest owing to its zero-energy consumption capacity, which is expected to alleviate current crises in fossil energy and global warming. In this study, a biomimetic multilayer structure (BMS) comprising a silica aerogel, a photothermal conversion material (PTCM), and a phase change material (PCM) layer is designed inspired by the physiological skin structure of polar bears for passive heating with desirable temperature and endurance. The transparent silica aerogel functions as transparent hairs and allows solar entry and prevents heat dissipation; the PTCM, a glass plate coated with black paint, acts as the black skin to convert the incident sunlight into heat; and the PCM composed of n-octadecane microcapsules stores the heat, regulating temperature and increasing endurance. Impressively, outdoor and simulated experiments indicate efficient passive heating (increment of 60 °C) of the BMS in cold environments, and endurance of 157 and 92 min is achieved compared to a single aerogel and PTCM layer, respectively. The uses of the BMS for passive heating of model houses in winter show an increase of 12.1 °C. COMSOL simulation of the BMSs in high latitudes indicates robust heating and endurance performance in a -20 °C weather. The BMS developed in this study exhibits a smart thermal regulation behavior and paves the way for passive heating in remote areas where electricity and fossil energy are unavailable in cold seasons.

Evaluation of Aerogel Spheres Derived from Salix psammophila in Removal of Heavy Metal Ions in Aqueous Solution

Heavy metal wastewater treatment is a huge problem facing human beings, and the application degree of Salix psammophila resources produced by flat stubble is low. Therefore, it is very important to develop high-value products of Salix psammophila resources and apply them in the removal heavy metal from effluent. In this work, we extracted the cellulose from Salix psammophila, and cellulose nanofibers (CNFs) were prepared through TEMPO oxidation/ultrasound. The aerogel spheres derived from Salix psammophila (ASSP) were prepared with the hanging drop method. The experimental results showed that the Cu(II) adsorption capacity of the ASSP composite (267.64 mg/g) doped with TOCNF was significantly higher than that of pure cellulose aerogel spheres (52.75 mg/g). The presence of carboxyl and hydroxyl groups in ASSP enhanced the adsorption capacity of heavy metals. ASSP is an excellent heavy metal adsorbent, and its maximum adsorption values for Cu(II), Mn(II), and Zn(II) were found to be 272.69, 253.25, and 143.00 mg/g, respectively. The abandoned sand shrub resource of SP was used to adsorb heavy metals from effluent, which provides an important reference value for the development of forestry in this sandy area and will have a great application potential in the fields of the adsorption of heavy metals in soil and antibiotics in water.

Study on swelling and drug releasing behaviors of ibuprofen-loaded bimetallic alginate aerogel beads with pH-responsive performance

Bimetallic alginate aerogel beads were prepared by ionotropic gelation method with Ca²⁺-Ba²⁺ bimetallic solution and ibuprofen was loaded as a model drug. The swelling and drug releasing behaviors of the beads, especially the influence of barium, were investigated in artificial gastric and intestinal fluids. The results showed that these beads presented higher encapsulation efficiency due to the special structure of aerogel, and barium was beneficial for the more stable structure and drug releasing behavior. The lower swelling capacity of bimetallic beads was observed than monometallic beads. A rapid high-level releasing of ibuprofen was achieved in artificial intestinal fluid, which was up to 96.9% within 1 h, while ibuprofen releasing was avoided in artificial gastric fluid effectively. The drug releasing mechanism of these beads was explored in detail. In the bimetallic crosslinking system, Ba²⁺ presented a special effect on alginate beads with more sensitive pH response performance. Thus, these beads had more widely potential as a site-specific delivery system, especially for intestinal therapy.

Ultralight hybrid silica aerogels derived from supramolecular hydrogels self-assembled from insoluble nano building blocks

Supramolecular hydrogels are a type of hydrogel cross-linked by non-chemical bonds and they have been widely applied in the field of smart systems, sensors, tissue engineering, and controlled drug delivery. Most supramolecular hydrogels are formed by soluble molecules, polymers, and metal ions. In this work, supramolecular hydrogels self-assembled between two insoluble nano building blocks (ISNBBs), graphene oxide (GO) and amino-functionalized silica nanoparticles (SiO₂-NH₂), have been discovered and synthesized. The gelation conditions of the two ISNBBs have been investigated. A step further, ultralight hybrid silica aerogels are obtained by supercritical drying of the physical hydrogels. No visible volume shrinkage is observed, due to the fact that the hydrogel networks are formed by rigid ISNBBs. Thus the hybrid aerogels possess ultralow density (down to 7.5 mg cm^-3), high specific surface areas (178.6 m² g^-1), and extremely high porosity (99.6%). The present work shows an alternative strategy to design and synthesize supramolecular hydrogels and aerogels using predetermined building blocks, together with designable morphology and physical properties for the target aerogels.