Hierarchical Aerogel Research Articles

Nanocellulose-based cobalt(II) coordinated malonic acid hybrid aerogels exhibiting reversible thermochromism and moisture sensor properties

The emergence of sustainable polymers and technologies has led to the development of innovative materials with minimal carbon emissions which find extensive applications in wearable electronics, biomedical sensors, and Internet of Things (IoT)-based monitoring systems. Nanocellulose which can be generated from abundant biomass materials has been widely recognized as a sustainable alternative for a diverse range of applications due to its remarkable properties and eco-friendly nature. By making use of the unique and easily accessible coordination transformation property of Co(II) ions and associated visible light absorption changes, we report a novel Co(II) cation-incorporated nanocellulose/malonic acid hybrid aerogel material that exhibits reversible thermochromism induced by thermal stimulus in the presence of atmospheric moisture. This effect is accentuated by the highly porous nature of the nanocellulose aerogel material we have developed. Besides the reversible thermochromic property which Co(II) ions exhibit, the metal ions act as very efficient reinforcing units contributing significantly to the structural stability and rigidity of the hierarchical aerogels by coordinative cross-linking through carboxylate moieties present in the TEMPO-oxidized cellulose nanofibers (TCNF) and additionally adding malonic acid to provide sufficient COO− for cross-linking. Thorough characterization and detailed investigation of as-prepared hybrid aerogels was conducted to evaluate their overall properties including reversible thermochromism and moisture sensor behaviour. Further, an Android mobile-based application was developed to demonstrate the real-world application of the aerogels for atmospheric humidity sensing.

Hierarchical aerogels based on cellulose nanofibers and long-chain polymers for enhancing oil–water separation efficiency

The hydrophobic chain length of biomass-based aerogels used for oil–water separation was evaluated as a major parameter influencing the aerogels’ hydrophobicity. The properties of the porous structure were enhanced by the hierarchical assembly of the aerogels with biopolymeric structural units and polymer mineralization. The cellulose network was strengthened through silanization, and the nanocellulose network was further enhanced through coating with mineralizers containing long-chain hydrophobic molecules. Interfacial engineering was employed to establish multiscale interactions through the freeze-drying-induced modification of cellulose nanofibers and mineralized coatings of long-chain alkyl polymers. The resulting hierarchically structured aerogel exhibits low density (11.4 kg/m3), excellent mechanical compression properties across a wide temperature range (capable of enduring 100 cycles of compression), high porosity (99.2%), superhydrophobicity (152°), and recyclability. It maintains a 57.9% adsorption rate even after 40 adsorption–desorption tests, while also preserving its shape integrity. Moreover, it can be recycled and reused. At a temperature of 700 °C, the mass loss was only 44.47%, with excellent thermal stability. The aerogel can reduce oil pollutants in the ocean by adsorption, recover oil resources, and protect the natural environment. The assembly and optimization of nanofibrous matrix interfaces through the mineralization of long-chain polymers enhanced the performance of functionalized cellulose-based aerogels.

S defect-rich MoS2 aerogel with hierarchical porous structure: Efficient photocatalysis and convenient reuse for removal of organic dyes

To avoid the difficulty of separating solids from liquids when reusing powder photocatalysts, 3D stereoscopic photocatalysts were constructed. In this study, three-dimensional S defect-rich MoS2 hierarchical aerogel was prepared by chemical cross-linking of functional ultrathin 2D MoS2. Its phase, micro-morphology and structure were characterized, and it was used in the study of photocatalytic degradation of organic pollutants. Of the samples tested, MS@CA-3 (i.e., defect-rich 3D MoS2 aerogel with a loading of 30 mg of defect-rich MoS2) exhibited the best photocatalytic activity due to its suitable load, good light transmission, and a degradation rate of up to 91.0% after 3 h. In addition, MS@CA-3 aerogel offers high recyclability and structural stability, and the degradation rate of the organic pollutant methylene blue decreases only 9.8% after more than ten cycles of photocatalytic degradation. It combines the high catalytic performance of S defect-rich 2D MoS2 and the convenient reusability of hierarchical porous aerogel. This study provides valuable data and a reference for the practical promotion and application of photocatalytic technology in the field of environmental remediation.

Hierarchical superstructure aerogels for in situ biofluid metabolomics.

High-throughput biofluid metabolomics analysis for screening life-threatening diseases is urgently needed. However, the high salt content of biofluid samples, which introduces severe interference, can greatly limit the analysis throughput. Here, a new 3-D interconnected hierarchical superstructure, namely a "plasmonic gold-on-silica (Au/SiO2) double-layered aerogel", integrating distinctive features of an upper plasmonic gold aerogel with a lower inert silica aerogel was successfully developed to achieve in situ separation and storage of inorganic salts in the silica aerogel, parallel enrichment of metabolites on the surface of the functionalized gold aerogel, and direct desorption/ionization of enriched metabolites by the photo-excited gold aerogel for rapid, sensitive, and comprehensive metabolomics analysis of human serum/urine samples. By integrating all these unique advantages into the hierarchical aerogel, multifunctional properties were introduced in the SALDI substrate to enable its effective utilization in clinical metabolomics for the discovery of reliable metabolic biomarkers to achieve unambiguous differentiation of early and advanced-stage lung cancer patients from healthy individuals. This study provides insight into the design and application of superstructured nanomaterials for in situ separation, storage, and photoexcitation of multi-components in complex biofluid samples for sensitive analysis.

Liquid Metal‐MXene‐Based Hierarchical Aerogel with Radar‐Infrared Compatible Camouflage

AbstractAs military power advances in the realm of information warfare, stealth technology has become a critical area of research for its effectiveness to evade detection. However, achieving high performance of compatible stealth across different functional mode bands remains a significant challenge. In this study, drawing inspiration from plant bionics, concepts of the directional freezing process are applied to develop a liquid metal‐MXene‐based hierarchical aerogel with radar‐infrared compatible camouflage. With a density of only 4.4 mg cm−3, the maximum reflection loss can reach −73.2 dB, and the absorption bandwidth can be adjusted up to 7 GHz. Following a thermal camouflage durability test, the sample successfully lowers the target's temperature from 400 to ≈160 °C. Remarkably, this temperature remains stable even after 180 days of exposure. Additionally, the material's ease of machining enables shape‐shifting camouflage capabilities, allowing objects to transform and resemble harmless items, thereby blending seamlessly with their surroundings. This breakthrough in compatibility performance signifies a substantial leap forward in multifunctional stealth technology development. It not only introduces innovative concepts, but also provides technical support, catalyzing further advancement in this field.

Structural Engineering of Hierarchical Aerogels Hybrid Networks for Efficient Thermal Comfort Management and Versatile Protection (Small 25/2023)

Hierarchical Aerogels Hybrid Networks Silica nanofiber aerogels functionalized P(VDF-HFP) membrane (SFP membrane), inspired by constructional engineering is constructed. As the host material for thermal comfort management and versatile protection, the SFP membrane features a large surface area, porous structure, and a robust skeleton that can render excellent mechanical properties. Additionally, the SFP membrane exhibits exceptional solar reflectivity (0.95) and strong mid-infrared emittance (0.98). More details can be found in article number 2301164 by Qinghua Zhang and co-workers.

Hierarchical SiC-Graphene Composite Aerogel-Supported Ni-Mo-S Nanosheets for Efficient pH-Universal Electrocatalytic Hydrogen Evolution.

MoS2 exhibits good prospects in electrocatalytic hydrogen evolution. Whereas, the electrocatalytic property of MoS2 is restrained by its insufficient active sites, low electrical conductivity, and slow water dissociation processes. Herein, an aerogel composed of silicon carbide (SiC) and graphene (SiCnw-RGO) was constructed by growing SiC nanowires (SiCnw) in the graphene aerogel (RGO) via the CVD method, and then Ni-Mo-S nanosheets were hydrothermally synthesized on the SiCnw-RGO composite aerogel to develop an efficient pH-universal electrocatalyst. Ni-Mo-S nanosheets supported on SiCnw-RGO (Ni-Mo-S@SiCnw-RGO) exhibit an interesting hierarchical three-dimensional interconnected structure of composite aerogel. The optimal Ni-Mo-S@SiCnw-RGO electrocatalyst exhibits excellent catalytic performance with low Tafel slopes of 60 mV/dec under acidic conditions and 90 mV/dec under alkaline conditions. Density functional theory calculations demonstrate a composite catalyst exhibits advantageous hydrogen adsorption free energy and water dissociation energy barrier. This study provides a reference to design an efficient hierarchical aerogel electrocatalyst.

Carbon Dot-Modified TiO2@SiO2 Aerogel as an Anode for Lithium-Ion Batteries

Titanium oxides have been considered promising anode materials for lithium-ion batteries (LIBs). However, the poor conductivity and low specific capacity of bulk titanium oxides limit their application. In this study, a carbon dot-modified TiO2@SiO2 aerogel was successfully fabricated through a facile ambient pressure drying strategy and used as an anode material of LIBs. Benefiting from the crosslinking of carbon dots and the surface modification of SiO2, the as-prepared hierarchical aerogel exhibited a high initial discharge capacity of 974 mAh g−1 and maintained a capacity of 299 mAh g−1 after 100 cycles at 0.1 A g−1. It also retained a discharge capacity of 111 mAh g−1 with a CE of 99.9% at 3 A g−1. The carbon dot-modified cross-linking skeleton contributes to the structural integrity of the TiO2@SiO2 aerogel during repeated insertion/extraction of lithium ions, guaranteeing outstanding cycling and high-rate performance. This ambient pressure drying strategy provides a facile and feasible way to produce high-performance aerogel anode materials for lithium-ion storage.

Temperature-adaptable pressure sensors based on MXene-coated GO hierarchical aerogels with superb detection capability

With the broader application of intelligent sensors in various complex conditions, sensing materials with better mechanical and conductive properties as well as higher temperature adaptability are required. For this purpose, a GO/PVA/MXene (GPM) composite aerogel was designed and prepared via a two-step strategy, including self-assembly and vacuum-assisted dip-coating processes. The as-prepared GPM has a unique structure composed of hierarchical GO network skeleton and MXene coating, endowing it with high Young's modulus (11.2 kPa) and compressibility (90%). Demonstrated with the finite element (FE) simulation, the elasticity and toughness of the GPM are originated from the hierarchical microstructure and the improved thickness of shells. Besides, the GPM exhibits a long-term durability of 5,000 compression cycles at 50% strain, a high sensitivity of 1.744 kPa−1, and a rapid response time of 4.5 ms. Further application examples reveal that the pressure sensor based on GPM has superior physiological signal capture capability, realizing fingertip pulse and temporal artery detections. Moreover, the GPM aerogel possesses high thermal insulation efficiency, resulting in good temperature adaptability in harsh environments from −196 °C to 300 °C. The sensitive pressure sensors should have the potential application in many fields of intelligent factories, complex militaries, and space discoveries.

Rationally designed multifunctional Ti3C2 MXene@Graphene composite aerogel integrated with bimetallic selenides for enhanced supercapacitor performance and overall water splitting

In this work, multifunctional Ti3C2 MXene@Graphene composite aerogel fabricated with bimetallic NiCo2Se4 (denoted as NCSe@MGA) have been prepared by hydrothermal method with the assistance of wet-chemical approach. 3D spatial arrangement of NCSe microspheres in hierarchical aerogel structure improved the exposed electroactive surface area. High surface to volume ratio and luxuriant 3D porous framework of aerogel enabled fast multi-dimensional ion-phase transport. Ti3C2 MXene@Graphene composite aerogel act as flexible skeleton to facilitate strain release and restrained the pulverization of NCSe during electrochemical tests. As a result, NCSe@MGA exhibited high specific capacity of 352.4 mAh g − 1 at 1 A g − 1 with 99.6% initial coulombic efficiency, and maintained capacity retention rate to 91.5% after 5000 consecutive cycles at 12 A g − 1. In case of electrocatalytic water splitting, NCSe@MGA realized 10 mA cm−2 current at significantly low overpotentials of 78 and 201 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The value of Tafel slope was as low as 55 mV dec−1 (HER) and 79 mV dec−1 (OER), demonstrating fast kinetics. For both half reactions, no significant decay of current density was observed during 10 h electrolysis test. The synergistic effects stemming from intimate contact among NCSe, MXene and Graphene ultimately boosted the electrochemical activity of NCSe@MGA in comparison to NCSe and NCSe@GA. This study proposes a feasible strategy to design 3D electrode materials with optimal properties for multi-range technological applications.

Hierarchical aerogels with hollow Co3O4 nanoparticles and graphitized carbon vesicles embedded in multi-channel carbon nanofibers for high-performance asymmetric supercapacitors

Low ionic diffusivity, sluggish charge transfer kinetics, and volume shrinkage/expansion during charging/discharging of transition metal oxides and conductive carrier materials seriously reduce capacity and damage cycle stability of electrodes. Herein, we demonstrate an in situ structural transformation strategy for fabricating hierarchical aerogels with hollow Co3O4 (H-Co3O4) nanoparticles embedded in multi-channel carbon nanofibers (MCNFs) by electrospinning polyacrylonitrile/polystyrene/metal organic framework mixtures, freeze-drying, carbonization and oxidation. The positive electrode prepared with MCNF@H-Co3O4 aerogel as the active material exhibits high specific capacity of 244.5 mA h g−1 (1600.6 F g−1) at 1 A g−1, and ultra-long cycle life of retaining 90.5 % of its initial specific capacity after 30,000 cycles at 20 A g−1. Furthermore, N and O co-doped hollow MCNF (NO-HMCNF) aerogels with hollow carbon vesicles embedded in the MCNFs are also prepared by acid-etching. The negative electrode prepared with the NO-HMCNF aerogel as the active material exhibits a high specific capacitance of 362.5 F g−1 at 0.3 A g−1, and retains 95.5 % of its initial specific capacitance after 30,000 cycles at 5 A g−1. The assembled MCNF@H-Co3O4//NO-HMCNF asymmetric supercapacitor provides a high energy density of 51.9 W h kg−1 (750.3 W kg−1) and retains 90.1 % of its initial specific capacity after 5000 cycles at 5 A g−1. The “double-void” structure plays crucial roles in exposing active sites and accommodating volume changes for enhancing capacity and cycling of the electrodes.

Multi-scale structure synergistic strategy: A transpiration inspired hierarchical aerogel evaporator for highly efficient solar-driven clean water production

Solar-driven evaporation has been recognized as a great candidate for freshwater production and has received growing interest as a practical approach to cope with global water scarcity and energy crisis. However, evaporation design with low heat loss, high photothermal conversion and sustainable water supply is still challenging for practical application. In this work, inspired by the transpiration of plants, we reported a high photothermal chitosan (CS)/cellulose nanofiber (CNF) based aerogel evaporator with a hierarchical light-absorbing structure by introducing PPy cross-linked network as light-absorber, which realize the synergistic integration of light absorption, heat location and water transportation. The integration of microstructure for light-absorbing and macroporous structure inside aerogel leads to strong water transportation via capillary action and vapor escape. Moreover, the hierarchical porous structure contributes to the low sunlight reflection (under 10%). Interestingly, the integrated evaporation system not only shows high efficiency (94.3%) and evaporation rate (1.67 kg m−2 h−1) but also achieves satisfactorily self-disinfection. We believed that this work could provide new insights into the development of solar-driven low-energy water purification/harvesting and sustainable cleaner production.

Temperature-Adaptable Pressure Sensors Based on Mxene-Coated Go Hierarchical Aerogels with Superb Detection Capability

Temperature-Adaptable Pressure Sensors Based on Mxene-Coated Go Hierarchical Aerogels with Superb Detection Capability

The construction of bio-inspired hierarchically porous graphene aerogel for efficiently organic pollutants absorption

Three-dimensional graphene aerogel shows a wide application in many frontier domains, which have attracted extensive research interest owing to its large specific surface area and high porosity. However, it is still a great challenge to construct the ideal hierarchical pore structure while guaranteeing excellent absorption and mechanical performance. In this paper, inspired by the bio-based porous material, a hierarchical graphene aerogel with inter-connected micro-/nano-scale pore structure was constructed. The micro and nano-scale pores are generated by the bubble and nanoparticles (NPs) template, respectively. The resulting graphene aerogel (GA) presents low density, increased interfacial areas, high mechanical performance, and excellent absorption performance towards a mass of organic solvents. In combination with its high compressibility, a diverse organic solvent can be absorbed efficiently and recycled by extrusion conveniently. Besides, owing to the scattered hydrophilic sites of functional groups and NPs on the surface of GA-b/NP, it shows high adhesion properties for water droplets, thus presents great potential in high-efficiency fog collecting materials. In a word, the proposed approach presents a novel strategy for the construction of the hierarchical aerogel with light-weight and elasticity, as well as the achievement of efficient functionalization, which has great potential for the preparation of diverse functional composites.

Structural Engineering of Hierarchical Aerogels Comprised of Multi-dimensional Gradient Carbon Nanoarchitectures for Highly Efficient Microwave Absorption

HighlightsThe delicate “3D helix–2D sheet–1D fiber–0D dot” hierarchical aerogels were successfully synthesized.The graphene sheets are uniformly intercalated by helical carbon nanocoils, which endow the as-obtained aerogel with abundant porous structures and better dielectric properties.By adjusting the growth parameters of 0D core-shell structured particles and 1D carbon nanofibers, the tunable electromagnetic properties and excellent impedance matching are achieved.

Gradient fibrous aerogel conjugated with chemokine peptide for regulating cell differentiation and facilitating osteochondral regeneration

Despite many advanced efforts have been made in osteochondral tissue engineering, it remains challenging to rehabilitate cartilage-to-bone interface complex through three-dimensional (3D) scaffolding treatment. Inspired by extracellular matrix (ECM) fibrous structure and heterogeneous osteochondral interface, herein, a novel 3D fibrous aerogel (gradient aerogel, A-G) with composition and mechanical gradients was designed with three layers based on electrospun poly(L-lactide)/gelatin composite fibers and controlled biomineralization technique. The A-G aerogel, briefly, contained glycosaminoglycan in its top layer and apatite in its middle/bottom layers. In vitro results indicated that this hierarchical aerogel could induce bone marrow mesenchymal stromal cells (BMSCs) to exhibit zone-specific morphology and bi-directionally differentiate into chondrogenic or osteogenic phenotypes. A cell affinity peptide, E7-peptide, was grafted onto the A-G aerogel to endow it with improved capacity in enhancing cell migration and recruiting BMSCs for in vivo applications. The E7-conjugated gradient aerogel (A-E7G) was implanted into an osteochondral defect (4 mm × 4 mm) created in rabbit knee for 12 weeks. Compared to the aerogel without composition gradient and the A-G aerogel, the A-E7G aerogel reconstructed the osteochondral interfacial tissue with hierarchically mature structure and clear tidemark more efficiently in an enhanced mode. These results indicated that the E7-peptide modified gradient aerogel could be a promising candidate in the osteochondral tissue engineering in the way of no growth factor addition.

Carbon/Sulfur Aerogel with Adequate Mesoporous Channels as Robust Polysulfide Confinement Matrix for Highly Stable Lithium-Sulfur Battery.

The ability to restrict the shuttle of lithium polysulfide (LiPSn) and improve the utilization efficiency of sulfur represents an important endeavor toward practical application of lithium-sulfur (Li-S) batteries. Herein, we report the crafting of a robust 3D graphene-wrapped, nitrogen-doped, highly mesoporous carbon/sulfur (G-NHMC/S) hierarchical aerogel as an effective polysulfide confinement matrix for a highly stable Li-S battery. Rich polar sites of NHMC firmly anchor LiPSn on the matrix surface. Porous NHMC provides ample space for accommodating sulfur and cushioning its volume expansion. Moreover, graphene wrapped on NHMC/S not only physically hinders the LiPSn shuttle but also interconnects the isolated NHMC/S, thus increasing electron transfer rate. Taken together, triple confinement of G-NHMC/S aerogel synergistically retains the soluble LiPSn and displays a specific capacity of 1322 mAh g-1 and 1000-cycle life. As such, rationally designed 3D carbon/sulfur aerogel affords a unique platform to impart high energy density and stable electrodes for energy storage devices.

In situ fabrication of hierarchical iron oxide spheres@N-doped 3D porous graphene aerogel for superior lithium storage

To improve the electronic conductivity and dramatic volume change of iron oxide as anode for lithium-ion batteries, we finally fabricate a hierarchical aerogel composite of FeOx spheres encapsulated in porous N-doped three-dimensional graphene (FeOx@N-3DG) via a facile in situ electrostatic self-assembly strategy assisted with hydrothermal. In the hierarchical architecture, the distributed FeOx spheres that consist of Fe2O3 and Fe3O4 crystals are intimately wrapped by N-3DG acting as protective elastomer to buffer the volume change during cycling. Moreover, the integrally interconnected porous structure is beneficial for fast electron transfer and penetration of the electrolyte. More importantly, the abundant grain boundaries of Fe2O3 and Fe3O4 crystals inside FeOx spheres provide smooth channels for fast lithium-ion transport and increase lithium storage sites. Therefore, FeOx@N-3DG anode material exhibits high specific capacity (1100 mAh g−1 after 200 cycles at 0.5 A g−1), excellent rate performance (550 mAh g−1 at 5 A g−1) and outstanding long cycling stability (81.6% of capacity retention after 1000 cycles at 1 A g−1), which is attributed to the superior surface capacitance behavior in the hierarchical architecture during charging and discharging. Thus, the hierarchical FeOx@N-3DG aerogel has potential to be an advanced anode material for lithium-ion batteries.

Aerobijels: Ultralight Carbon Monoliths from Cocontinuous Emulsions

AbstractBijels are used to develop a new class of ultralight hierarchically porous aerogels exhibiting multimodal porosity across multiple length scales. Through in situ functionalization of a particle‐laden liquid interface wherein binary liquid pairs are kinetically trapped out of equilibrium through interfacial jamming, monolithic and freestanding carbon electrodes are produced with prescribed bulk densities down to ≈2 mg cm−3. Exemplary electrokinetic experiments indicate that the bicontinuity of the pore structure is essential for enhancing transport to and from the active electrode surfaces, demonstrating that these materials possess a superior ability to accumulate and transport charge when compared to analogous systems with restricted pore connectivity and fluid throughput. This approach offers a new synthetic route to bicontinuous and hierarchical aerogel materials with nested multimodal porosities. The flexibility of this scheme can address critical issues related to transport‐limited behaviors that arise in many technological fields, ranging from energy and catalysis research to remediation and sensing applications.

Emerging Hierarchical Aerogels: Self-Assembly of Metal and Semiconductor Nanocrystals.

Aerogels assembled from colloidal metal or semiconductor nanocrystals (NCs) feature large surface area, ultralow density, and high porosity, thus rendering them attractive in various applications, such as catalysis, sensors, energy storage, and electronic devices. Morphological and structural modification of the aerogel backbones while maintaining the aerogel properties enables a second stage of the aerogel research, which is defined as hierarchical aerogels. Different from the conventional aerogels with nanowire-like backbones, those hierarchical aerogels are generally comprised of at least two levels of architectures, i.e., an interconnected porous structure on the macroscale and a specially designed configuration at local backbones at the nanoscale. This combination "locks in" the inherent properties of the NCs, so that the beneficial genes obtained by nanoengineering are retained in the resulting monolithic hierarchical aerogels. Herein, groundbreaking advances in the design, synthesis, and physicochemical properties of the hierarchical aerogels are reviewed and organized in three sections: i) pure metallic hierarchical aerogels, ii) semiconductor hierarchical aerogels, and iii) metal/semiconductor hybrid hierarchical aerogels. This report aims to define and demonstrate the concept, potential, and challenges of the hierarchical aerogels, thereby providing a perspective on the further development of these materials.