Ultralight Density Research Articles

Ultralight M5 aerogels with superior thermal stability and inherent flame retardancy.

Ultra-lightweight materials often face the formidable challenge of balancing their low density, high porosity, high mechanical stiffness, high thermal and environmental stability, and low thermal conductivity. This study introduces an innovative method for synthesizing high-performance polymer aerogels to address the challenge. Specifically, we detail the production of poly (2,5-dihydroxy-1,4-phenylene pyridine diimidazole) (PIPD or M5) aerogels. This process involves chemically stripping M5 "super" fibers into nanofibers, undergoing a Sol-Gel transition, followed by freeze-drying and subsequent thermal annealing. The M5 aerogels excel beyond existing polymer aerogels, boasting an ultralight density of 6.03 mg cm-3, superior thermal insulation with thermal conductivity at 32 mW m-1 K-1, inherent flame retardancy (LOI = 50.3%), 80% compression resilience, a high specific surface area of 462.1 m2 g-1, and outstanding thermal stability up to 463 °C. These multi-faceted properties position the M5 aerogel as a front-runner in lightweight insulation materials, demonstrating the strategic use of high-performance polymer assembly units in aerogel design.

An overview of patents of noise reduction in buildings

Noise is an unwanted sound in urban areas. Natural and or recycled acoustic absorbing or insulation materials are invented to reduce air and or impact sounds in buildings. Yet, they are not widely and commercially available. This review presented an overview of relevant studies on natural materials particularly on cotton and rubber using Scopus search engine and of the patents registered and granted using Espacenet and Google Patents search engines on noise reduction in buildings from the years 1996 to 2023. The 18% and 68% (out of 32 articles) relevant articles, respectively, were written on cotton and rubber and other recycled natural material e.g., consumed teabags, rubber crumb, indicating a clear vision for experimentation and modeling of natural materials e.g., to investigate their sound absorption coefficients at lower frequencies (below 250 Hz) for (recycled) cotton sound absorbing materials and for producing ultralight density with high sound absorption materials (0.56) using recycled rubber material. There were found 31 patents registered and granted, in total. Natural materials, namely, cotton, rubber, glass wool and rock wool were applied in 29% of patents registered and granted from 1996 to 2022. Yet, 93% of patents registered and granted lacked data on sound absorption index of materials they invented. LDA models estimated 29% of Espacenet and Google Patents patents registered and granted having an increased trend of patent innovations for example, in method, structure and building materials in the last decade.

Multiphase Symbiotic Engineered Elastic Ceramic-Carbon Aerogels with Advanced Thermal Protection in Extreme Oxidative Environments.

Elastic aerogels can dissipate aerodynamic forces and thermal stresses by reversible slipping or deforming to avoid sudden failure caused by stress concentration, making them the most promising candidates for thermal protection in aerospace applications. However, existing elastic aerogels face difficulties achieving reliable protection above 1500°C in aerobic environments due to their poor thermomechanical stability and significantly increased thermal conductivity at elevated temperatures. Here, a multiphase sequence and multiscale structural engineering strategy is proposed to synthesize mullite-carbon hybrid nanofibrous aerogels. The heterogeneous symbiotic effect between components simultaneously inhibits ceramic crystalline coarsening and carbon thermal etching, thus ensuring the thermal stability of the nanofiber building blocks. Efficient load transfer and high interfacial thermal resistance at crystalline-amorphous phase boundaries on the microscopic scale, coupled with mesoscale lamellar cellular and locally closed-pore structures, achieve rapid stress dissipation and thermal energy attenuation in aerogels. This robust thermal protection material system is compatible with ultralight density (30mg cm-3), reversible compression strain of 60%, extraordinary thermomechanical stability (up to 1600°C in oxidative environments), and ultralow thermal conductivity (50.58mW m-1 K-1 at 300 °C), offering new options and possibilities to cope with the harsh operating environments faced by space exploration.

Highly Porous ZnO/CNT Hybrid Microclusters for Superior UV Photodetection.

The formation of nanoscale junctions among nanoparticles in self-assembled nanostructures is crucial for improving both interfacial conductivity and structural integrity. However, the inherent reliance on weak van der Waals forces to hold nanoparticles together poses challenges in developing commercially viable devices due to their inefficient carrier transport characteristics. This study presents the successful integration of carbon nanotubes (CNTs) into highly porous nanomicrocluster arrays of ZnO, resulting in the formation of cohesive and crack-free highly porous ZnO/CNT heterojunction films. This integration marks a significant improvement in UV photodetection performance, demonstrating a record-high photocurrent to dark current ratio of 3.3 × 106 and an exceptional responsivity of 18.5 A/W at a low bias of 0.5 V and under an ultra low light density of 25 μW/cm2. These findings underscore the efficacy of this high-performance structure as a versatile and scalable platform technology for the rapid, cost-effective fabrication of hybrid photodetectors in wearable and portable devices.

Multifunctional graphene/Ti3C2Tx MXene aerogel inlaid with Ni@TiO2 core-shell microspheres for high-efficiency electromagnetic wave absorption and thermal insulation

The demand for high-performance electromagnetic wave absorbing (EMA) materials featured with strong attenuation ability, extended absorption bandwidth and ultralight property is imperative yet remains challenging. Herein, a three-dimensional hierarchically porous reduced graphene oxide (rGO)/Ti3C2Tx MXene aerogel embedded with Ni@TiO2 core–shell microspheres was prepared via directional freeze-drying followed by a mild annealing process. The divergence in structure and multicomponent dielectric/magnetic features bring about optimized impedance matching characteristic, multiple polarization and loss pathways, collectively contributing to the excellent absorption performance. As a result, the Ni@TiO2/MXene/rGO (NTMRG-2) aerogel exhibits optimized EMA capability with a maximal effective absorption bandwidth (EABmax) of 6.48 GHz at a lower loading level of 5 wt% in the supporting matrix, covering the whole Ku band. Additionally, it achieves a minimum reflection loss (RLmin) of −71.4 dB with a matching thickness of 2.04 mm. Moreover, the aerogel also exhibits an ultra-light density of 5.58 mg cm−3, superior thermal insulation capacity (close to air) and hydrophobicity, underscoring its potential for multiple applications in various scenarios.

Multifunctional and magnetic MXene composite aerogels for electromagnetic interference shielding with low reflectivity

Lightweight and multifunctional compressible aerogels with low reflectivity are highly demanded to protect electronic devices from increasingly serious electromagnetic interference and radiation. Although simply incorporating magnetic particles can reduce the strong electromagnetic (EM) reflection caused by the high conductivity of MXene, high density, inhomogeneous dispersion and weak interfacial interactions may impede the potential applications. Here, we report the fabrication of three-dimensional magnetic MXene/Fe3O4@acidified-MWCNT (aMWCNT) composite aerogel by a directional freezing and subsequent freeze-drying process, and the shielding effectiveness of composite aerogel can be tuned from 32.5 to 51.6 dB in the X-band. At the same time, since the Fe3O4 nanoparticles are pre-decorated onto aMWCNTs, the heterogeneous interface polarization and magnetic loss are enhanced at low loadings. Therefore, the reflected power coefficient of the aerogel is as low as 0.31 with an ultra-light density of only 10 mg cm-3. Moreover, the good reversible compressibility, fatigue resistance, excellent heat insulation, and infrared stealth grant the aerogels great application prospects for anti-infrared detection and green shielding materials.

Superhydrophobic cellulose-based aerogel derived from Phormium tenax (harakeke) for efficient oil sorption

Oil removal and recovery solutions are essential in our modern world, and discovering eco-friendly, highly efficient oil sorbents is of paramount importance. In this study, a straightforward method was designed to create reusable, superhydrophobic cellulose nanofiber-based aerogels derived from harakeke, a native New Zealand flax plant. By employing chemical purification and ultrasonication techniques, cellulose nanofibers (CNFs) were extracted from raw harakeke fibers, and nanocellulose-based aerogels were formed through freeze-drying. The resulting harakeke-derived cellulose nanofiber aerogels (HNAs) exhibited remarkable porosity (98.98–99.73%) and an ultralight density (3.91–15.13 mg/cm3). Among the various cellulose aerogels produced, the 1.2 wt% CNF aerogel demonstrated the highest Young's modulus of 39.45 kPa. Subsequent surface modification with methyltriethoxysilane (MTES) transformed the aerogels into superhydrophobic materials (s-HNA), with a water contact angle of 153°. The oil sorption capacity of s-HNA ranged from 90 to 146 g/g for various oils and solvents. The oil sorption of s-HNAs obeys the pseudo-second order kinetic model, with sorption constant rate of 0.00525 g∙g−1∙s−1.

Ultralight, robust, and high Prussian blue-loading polyacrylonitrile aerogel: Preparation, characterization and efficient adsorption/removal of Cs+

Highly efficient and selective adsorption/removal of Cs+ is greatly essential for both resource utilization and radioactive pollution control. To overcome the poor water stability of Prussian blue (PB), a highly selective Cs+ adsorbent, PB-based polyacrylonitrile (PAN) aerogel was prepared using PB-loaded PAN nanofibers. Pre-doping of Fe3+ in PAN nanofibers through electrospinning provides abundant and evenly distributed active sites for the in-situ growth of PB, thus endowing resultant PAN/PB aerogel with much higher PB-loading capacity than reported PB-based composite adsorbents. Systematic structure characterization and property investigation show that as-prepared PAN/PB aerogel has interconnected porous structure, ultralight density, greatly improved water stability, increased thermal stability, robust mechanical elasticity, high hydrophilicity, excellent Cs+ adsorption selectivity. Its practical application potential was well demonstrated by the excellent performances in highly efficient, rapid and selective adsorption/removal of Cs+ from simulated seawater and salt lake brine. The maximum Cs+ adsorption amount of PAN/PB aerogel reached up to 152.67 mg∙g−1 within 1 min. In this work, co-spinning active groups (e.g., Fe3+) in PAN nanofibers is demonstrated to be an effective strategy for increasing the PB-loading of aerogel, which not only provides an excellent Cs+ adsorbent, but also paves a promising way for preparing high-performance aerogels.

Characterization of cellulose nanocrystals prepared by different delignification methods and application of ultra-light, hydrophobic aerogels as oil absorbent in food systems

In this study, cellulose nanocrystals (CNCs) were isolated and characterized from sugarcane pith (SP), a renewable, low-cost agro-industrial residue. The effects of bleaching methods on CNCs morphology and physicochemical properties were investigated. Then, an ultralight and hydrophobic nanocellulose-based aerogel was fabricated as an oil absorbent for food systems. The results showed that hydrogen peroxide bleached CNC retained its good characteristics (a whisker-like shape, L/D 38, CrI 72.1%, zeta potential −29.97 ± 0.05 mV) and the typical shear-thinning rheological behavior, an eco-friendly delignification. In addition, the obtained MTMS-modified aerogels exhibited ultralight density (0.031–0.053 g/cm3), high porosity (96.45–97.44%), lipophilicity (water contact angle as high as 130.2 ± 5.8°), and reusability. Furthermore, their absorption capacity was up to 49.8 g/g, with a wide range of catering oils and organic solvents. This study provides insight into the high value-added utilization of agro-industrial residues and the application of nanocellulose-based aerogels for oil-water separation in food systems.

Multi-modal piezoresistive sensor based on cotton fiber aerogel/PPy for sound detection and respiratory monitoring

At present, most wearable flexible sensors can satisfy the requirements of sensitivity and wide response range. However, how to prepare sensors with good sensing performance and integration functions is still an urgent problem to be solved. Herein, the multimodel piezoresistive sensor integrating sound recognition, airflow detection and respiration monitoring was manufactured by vapor deposition of polypyrrole on cotton fiber aerogel (CA@PPy). The sensor exhibits wide response range (0–122.50 kPa), high stability (over 4500 cycles), high pressure resolution (0.2%) and ultra-light density (27.5 mg/cm3). Besides detecting normal human motion signals, it can also capture biological/abiotic sound signals with excellent sensitivity (minimum detection limit is 56 dB). Moreover, the sensor can also be used to detect the air flow rate with the minimum flow rate of 0.09 m/s, providing real-time respiratory monitoring for patients with respiratory diseases. We believe that this integrated multimode sensor will have great application potential in flexible electronics and bring great convenience to people's lives.

CMF/Cu@CuS as photothermal conversion material for solar-driven water evaporation in wet sand systems

Solar-driven water evaporation (WE) is a promising strategy to directly extract freshwater from different water source. Carbonized melamine foam (CMF) was employed as the substrate for loading Cu@CuS with plasma effect and visible-near-infrared light absorption performance as photothermal conversion material (PCM) for WE in the wet sand systems. The porous microstructure, wettability, ultra-light density, and WE property of the obtained CMF/Cu@CuS were characterized and measured. CMF/Cu@CuS has good WE rate and photothermal conversion efficiency (PCE) whether in the wet xalsonte or fine sand system. The WE rate can reach 1.917 kg m−2h−1, with a PCE of 91.75 % in the wet xalsonte system. This work gives a new perspective to expand the application of solar-driven WE technology, especially in the inland and remote areas.

Study on preparation and performance of advanced aerogel foamed concrete with ultra-light aerogel

Aerogel foamed concrete has been acknowledged as one of the most promising energy efficient building materials with high thermal insulation performance and low density in applications of green buildings and nearly zero energy buildings. However, the practical economy of aerogel foamed concrete is still relatively poor because of the greater amount of high-price ultra-insulating aerogel additive needed in the foamed concrete. Therefore, based on the premise of maintaining the high thermal insulation performance and low density of foamed concrete, reducing the amount of aerogel additive has become a key issue to improve the economy and promote the application of high-performance aerogel foamed concrete. This study proposed an equal volume replacement method based on using an ultra-light SiO2 aerogel instead of conventional SiO2 aerogel to reduce the amount of aerogel additive in foamed concrete while maintaining a high thermal insulation performance and low density. Two kinds of aerogel foamed concrete were prepared by filling light density (170 kg/m3) and ultra-light density (75 kg/m3) adiabatic aerogel powder into foamed concrete. An experiment was conducted to study the influence of different aerogel densities on the thermal conductivity, compressive strength and density of foamed concrete. The research results indicate that the density and thermal conductivity can be effectively reduced by filling ultra-light aerogel powder compared with traditional aerogel foamed concrete with an acceptable compressive strength. The results also show that the mass dosage of aerogel can be significantly reduced by using ultra-light aerogel powder. Specifically, for a foam volume ratio of 70 % and aerogel volume ratio of 13 %, the density and thermal conductivity of the ultra-light aerogel foamed concrete were reduced by approximately 10 %, which resulted in a cost reduction of 49 %. By applying the ultra-light aerogel foamed concrete in the construction of an exterior wall of a building, the heat loss through the wall can be reduced by 9 %. This study provides a significant reference for the preparation of high-performance foamed concrete and accelerates the application of super adiabatic aerogels in the building energy conservation industry.

PDMS – Coated pomelo peel carbon aerogel: Synthesis, characterization, and oil removal application

AbstractRaw pomelo peel (RPP) has been widely reported as a potential eco‐friendly adsorbent due to its porous structure. In this work, pomelo peel‐derived carbon aerogel (PCA) was synthesized by approaching simple methods: Hydrothermal treatment and freeze‐drying technique. The obtained PCA from RPP exhibits an abundance of honeycomb‐like open porous structure, ultralight density of 0.03 g/cm3, and porosity of 99.23 %. To enhance the hydrophobicity and selectivity for removal of oil in water, PCA was coated with Poly(dimethylsiloxane) (PDMS) by facile dip‐coating method. The as‐prepared hydrophobic PDMS‐coated pomelo peel carbon aerogel (PDMS/PCA) exhibits the water resistance ability via the water contact angle of 101.6 o and good adsorption capacity of 11.672 and 7.691 g/g for used cooking and lubricating oils, respectively. Furthermore, the pseudo‐first‐order and pseudo‐second‐order models were approached to predict the adsorption behavior of PDMS/PCA for both used cooking and lubricating oils. The obtained results illustrate the potential application of RPP for synthesizing eco‐friendly and low‐cost adsorbents for the removal of oil in water.

Hierarchical SiC fiber aerogel toward microwave attenuation and thermal insulation application

Materials with structural hierarchy have drawn great attenuation due to their fascinating physical and mechanical properties given by the unique microstructures. In this study, hierarchical SiC fiber aerogel was successfully developed via a simple method by using carbonized silk fiber mat as a template and subsequent in-situ growth of SiC nanowires array through carbothermal reduction at high temperature. The formation mechanisms of hierarchical SiC fiber aerogel based on a vapor-solid-liquid process were discussed. Owing to the highly porous structure supported by SiC nanowires, the aerogel could show an ultralight density of 0.04 g/cm 3 and a compression fatigue resistance of 10 cycles at 40% strain with small and stable energy loss coefficients. The electromagnetic (EM) investigation suggests that the aerogel could serve as a wideband microwave attenuator with a minimal reflection loss (RL) of − 68 dB and a maximum effective attenuation bandwidth (EAB, RL<−10 dB) of 7.2 GHz when embedded in silicone matrix at 10 wt% loading ratio. Additionally, the hierarchical SiC fiber aerogel reveals remarkably low thermal conductivity of 0.027 W/m·K, suggesting enormous potential for thermal insulation. • Hierarchical SiC fiber aerogel have been fabricated by in-situ grown synthesis method. • Lightweight, wideband microwave absorber with low thermal conductivity is obtained. • The effects of hierarchical structure on the enhanced performance are elaborated.

Synthesis of cellulose aerogels as promising carriers for drug delivery: a review

Cellulose is an important raw material used for the preparation of aerogel materials in life sciences. Cellulose aerogel's excellent biocompatibility, biodegradability, and nontoxicity combined with its multiple chemical functions make it an ideal carrier for drug delivery. Cellulose aerogels offer high porosity, large specific surface area, and ultra-light density. They can be used as drug carriers to improve bioavailability and drug loading. We reviewed the methods used to prepare cellulose aerogels with nanocellulose, renewable cellulose, and cellulose derivatives as raw materials. In addition, we described cellulose aerogels as a drug delivery carrier to inspire work in new drug delivery systems that intelligently use cellulose aerogels. Finally, we described the application prospects of intelligent and responsive cellulose aerogels in drug delivery systems.

Ultra-light 3D fabric Reinforced Composite with Distinct Thermal Insulation and Superior Sound-absorbing Properties

Research on lightweight advanced materials that combine heat insulation and sound isolation becomes more attractive day by day. In this study, a 3D spacer structural Kevlar/polyimide composite (3DSSK/PIC) with light weight, heat insulation and sound absorbing properties was prepared by a combination of structural design, hand paste resin method and hot-pressing process. The fabricated 3DSSK/PIC possesses more than 80% of void as well as the ultra-light density (0.2 g/cm3). Consequently, the thermal insulation performance of 3DSSK/PIC (34%) is superior to that of polystyrene foam (adiabatic ratio ΔT ~20%) and similar to that of wood block (ΔT ~35%). Furthermore, the sound absorption coefficient of the 3DSSK/PIC is higher than 0.2 in the range of 600 ~ 2500 Hz, demonstrating its super sound absorption performance. In addition, compressive tests and SEM images were conducted to characterize the mechanical and structural performance. Therefore, the ultra-light 3D fabric reinforced composite with ultra-high thermal insulation and sound-absorbing properties justify a great potential in a wide variety of applications in the industry engineering, automobile, or aerospace.

Carbon fibers assisted 3D N-doped graphene aerogel on excellent adsorption capacity and mechanical property

In order to improve structural stability of aerogel, supported N-doped reduced graphene oxide aerogels are prepared by introducing fiber materials (biomass cellulose and carbon fibers) via self-assembly method. Thereinto, N-doped carbon fibers/reduced graphene oxide aerogel exhibits ultra-light density (7.19 mg/cm3), high specific surface area (329.6 m2/g), excellent superhydrophobicity, high adsorption capacity (206.38 g/g), which is superior to most reported cellulose aerogels. Moreover, regardless of multiple heating or squeezing cycles, adsorption capacity of this aerogel is also more than 90 %. In addition, N-doped carbon fibers/reduced graphene oxide aerogel shows good mechanical compressive property and thermal stability, which contributes to high-valued utilization in practice.

Rice straw agri-waste for water pollutant adsorption: Relevant mesoporous super hydrophobic cellulose aerogel

A simplistic synthesis approach for fabrication of ultra-light density (2.2 to 24 mg. cm−3), highly porous (98.4%–99.8%), and cross-linked natural cellulose aerogel from rice straw was developed via a freeze-drying process. The obtained natural cellulose aerogels exhibited porous network structure with specific areas of 178.8 m2. g-1 and mesopore volumes of 0.8 cm3. g-1. The cellulose aerogel with 1.3 wt% displayed the highest Young’s modulus and compressive strength. Subsequent hydrophobic coating with methyltrimethoxysilane, the super-hydrophobic and oleophilic cellulose aerogel (water contact angle as high as 151 ± 7°) were capable of adsorbing a wide range of organic solvents and oils with adsorption capacities up to 170 g. g-1 based on the density of the liquids. Furthermore, the adsorbed organic solvent could be desorbed by means of simple mechanical squeezing. These results suggested that the super-hydrophobic natural cellulose aerogel can be used as a precious sorbents for adsorption of oil and organic solvents.

Facile synthesis 3D porous MXene Ti3C2Tx@RGO composite aerogel with excellent dielectric loss and electromagnetic wave absorption

3D porous materials with ultralight density, thin thickness, strong, and broadband absorption are attracting attention as promising candidates as novel microwave absorbents. Herein, a unique 3D porous MXene Ti3C2Tx@RGO hybrid aerogel was fabricated via a hydrothermal method and freeze-drying treatment. The network-like 3D heterostructure, which combines 2D MXene and RGO sheets, can reduce stacked nanosheets, and provides an efficient interface structure, which benefits electromagnetic (EM) energy attenuation. More significantly, their microwave absorption properties have been quite efficiently enhanced over pristine 2D Ti3C2Tx nanosheets. Only with 15 wt% filler loading, the minimum reflection loss of the Ti3C2Tx@RGO composite aerogel reaches −31.2 dB at 8.2 GHz, and the effective frequency bandwidth (below −10 dB) achieves up to 5.4 GHz at a thickness of only 2.05 mm. The illustrated EM wave response mechanism indicates that the highly conductive network, interface polarization, dipole polarization, and multiple scattering contribute importantly to its EM wave absorption. Therefore, the synthesized MXene Ti3C2Tx@RGO composite aerogel offers a sufficient foundation for utilization as a perfect absorbent and in the design of other lightweight microwave absorbers.

Graphene-based 3D lightweight cellular structures: Synthesis and applications

Ultralight three-dimensional (3D) cellular architectures are both a challenge and an opportunity for those academic and industrial applications involved with high performance material design. The challenges have been accessed by employing a variety of materials. Accordingly, graphene has shown greatest potential by virtue of its unique chemical, thermal, electronic, and mechanical properties for applications ranging from structural materials to energy storage/conversion devices. In this review, we highlight recent efforts and advances made in the implementation of graphene-based 3D cellular architectures, especially focusing on the ultralight density region (<10 mg·cm−3). First, we reviewed the synthetic approaches for generating graphene-based 3D lightweight cellular structures according to the criteria of closed-cellular structures (CCSs) or open-cellular structures (OCSs) whether cell faces between constituent unit cells exist or not, respectively. These structural differences could lead to discerning physical properties, such as in mass transport across pores, heat/electron transfer through graphene framework, and various modes in mechanical deformation. We then collectively introduce recent achievements for representative applications utilizing different types of cellular structures such as flexible electronics, energy storage/conversion systems, fluid absorption, mechanical dampers, and sensors. Finally, we highlight the future perspectives of graphene-based lightweight cellular structures to surpass existing technological challenges.