Aerogel Network Research Articles

Light/electro-thermal conversion of carbonized sweet potato 3D grid-supported PEG shape-stable phase change materials for thermal management applications

Phase change materials (PCMs) are functional energy-storage materials that achieve reversible heat storage and release through phase transition processes. They have extensive applications in the thermal management and solar energy industries. However, their low electrical and thermal conductivities and poor stability often fail to meet application requirements. In this study, we utilised an abundant biomass-derived carbon source, sweet potatoes, to prepare a three-dimensional network of carbon aerogels. By simply vacuum-impregnating polyethylene glycol (PEG), the PCM was embedded in the carbon aerogel. The obtained PEG/carbon aerogel composite material exhibited high enthalpy (158.1 J/g) and good thermal and shape stability. They also demonstrated efficient photothermal (88.47 %) and electrothermal conversion (94.02 %). This research has significant potential for applications in solar energy storage and utilisation, building energy storage, space–ground thermal energy storage, and electronic device thermal management. This study provides a novel approach for the preparation and photothermal applications of bio-based PCMs.

Controlled porosity intelligent aerogel based on chitosan nanofiber, anthocyanins and starch nanoparticles: Preparation, characterization and application in monitoring food spoilage

The aim of this study was to design a food freshness colorimetric aerogel with controlled porosity based on chitosan nanofibers (CHNF), Ixiolirion tataricum anthocyanins (ITA), and starch nanoparticles (SNPs). Two size-controlled SNPs were produced via nanoprecipitation (133.3 nm; SNP-A) and H2SO4 hydrolysis methods (86.2 nm; SNP-B) and were used for controlling the porosity and morphological characteristics of aerogel solid support. According to FE-SEM images, the porosity of smart aerogels improved after SNPs incorporation, and SNP-B was able to decrease the disrupting effect of ITA on 3D porous network of aerogels. The formation of hydrogen bonds between the CHNF and ITA molecules was confirmed by FT-IR analysis and the absence of obvious change in the FT-IR spectra approved the physical entrapment of SNPs. The improvement in the crystallinity and thermal stability of the aerogels after SNPs loading was confirmed by the XRD and TGA tests, respectively. The SNPs loaded aerogels showed color variation from red to green over the pH range of 2–12. In addition, the SNP-B-incorporated aerogel exhibited high sensitivity to ammonia vapor and good color response reversibility. The CHNF/SNP-B/ITA aerogel with the best porosity and sensitivity was used for monitoring food spoilage and could differentiate minced beef into three stages: fresh, medium fresh, and spoiled, facilitating simple observation of freshness-spoilage progression. This research opens a new insight to develop advanced and highly sensitive indicators capable of monitoring freshness/spoilage in protein-based food products.

Robust-flexible and highly-thermostable polyimide-silica aerogels with adjustable fiber skeleton structure for efficient aerospace thermal protection

The rapid growth of the aerospace industry presents significant challenges in developing lightweight and flexible thermal protective materials for spacecraft and related equipment. One longstanding challenge has been the preparation of high-thermostable and highly flexible aerogels, which limits their practical application in flexible thermal protection. In this work, through a rational 'chain-sphere' dual-combination structure design, polyimide-silica aerogels with integrated properties of the adjustable aerogel-fiber skeleton structure, robust flexibility and high thermostable have been prepared. By incorporating 2,2-dimethylbenzidine (DMBZ), we achieve a more solid aerogel network. The aerogel membrane retains its original shape without creases or cracks even after undergoing 500 folding and unfolding tests. Additionally, the silicon nanoparticles surrounding the aerogel exhibit superior performance at high temperatures. The unique structure and components of the composite enable it to possess lightweight (0.075–0.11 g/cm−3), low thermal shrinkage (300℃∼6 %), excellent thermostability (95 % weight retention at 474℃∼557℃), and promising thermal insulating performance below 600℃. The integrated performances of the aerogel make it suitable for high-temperature thermal protection applications that require both efficient thermal insulation and robust flexibility.

Structural properties and barrier performance of low-cost aerogel composites for building insulation

The high cost and weak mechanical properties of silica-based aerogel seriously affect its wide application in the field of building insulation. In this paper, low-cost SiO2 aerogel (WSA) was prepared based on water glass/water system, and the modulation of aerogel network structure was achieved under the dual effect of sodium methylsilicate (SMS) and pH. WSA exhibits extremely low density (∼88.5 kg/m3) and thermal conductivity (0.02114 W/(m·K)) as well as high hydrophobicity (150°). The cost of WSA is 53 % lower compared to atmospheric pressure drying and 21.5 % lower than commercial aerogel. On this basis, rock wool fiber felt (RWF) and ultrafine glass fiber wool felt (UGFW) were modified with WSA. The effect of fiber arrangement on the force-thermal coupling property of WSA@RWF was investigated. Meanwhile, the addition of WSA reduced the volumetric water absorption of RWF by 85.1 % and 91.4 %. Since the sandwich structure, the thermal conductivity of WSA@UGFW can be as low as 0.01168 W/(m·W), which is 44.7 % and 44.4 % lower than that of UGFW and WSA. It features a low density of 45.7 kg/m3 and a high hydrophobicity angle of 155.87°. In addition, the compressive strength of WSA@UGFW is increased by 16.5 times. Therefore, the aerogel materials prepared in this paper have great application potential as fire-proof building insulation materials.

Polydopamine Enhanced Interactions of Graphene Nanosheets to Fabricate Graphene/Polydopamine Aerogels with Effectively Clear Organic Pollutants.

Graphene/polydopamine aerogels (GPDXAG, where X represents the weight ratio of DA·HCl to GO) were prepared by the chemical reduction of graphene oxide (GO) using dopamine (DA) and l-ascorbic acid as reducing agents. During the gelation process, DA was polymerized to form polydopamine (PDA). The introduction of PDA in the gelation of aerogels led to a deeper reduction of GO and stronger interactions between graphene nanosheets forced by covalent cross-linking and noncovalent bonding including π-π stacking and hydrogen bonding. The weight ratio of DA·HCl to GO influencing the formation and morphology of GPDXAG was explored. With the increasing content of DA in gelation, the reduction of GO and the cross-linking degree of graphene nanosheets were enhanced, and the resulting GPDXAG had a more regular pore distribution. Additionally, introducing PDA into GPDXAG improved its hydrophobicity because of the adhesion of PDA to a network of aerogels. GPDXAG exhibited a higher removal efficiency for organic pollutants than the controlled graphene aerogels (GAG). Specifically, the adsorption capacity of GPDXAG for organic solvents was superior to that of GAG, and organic solvent was completely separated from the oil/water mixture by GPDXAG. The equilibrium adsorption capacity of GPDXAG for malachite green (MG) was measured to be 768.50 mg/g, which was higher than that for methyl orange (MO). In MG/MO mixed solutions, aerogels had obvious adsorption selectivity for the cationic dye. The adsorption mechanism of aerogels for MG was also discussed by simulating adsorption kinetic models and adsorption isothermal models.

Bidirectional anisotropic bacterial cellulose/polyvinyl alcohol/MXene aerogel phase change composites for photothermal conversion enhancement

The issues of inherent low thermal conductivity, slow heat transport rate and easy leakage are critical challenges for accelerating solar-thermal energy harvesting and storage for organic solid-liquid phase change materials (PCMs). Aerogel carriers with thermal conductivity enhancement based on ice temple methods show favorable potential for PCMs solar thermal applications. Comparing with disordered and unidirectional freezing, bidirectional freezing can assemble efficiently in multiple dimensions and result in long-range ordered structures. In this paper, bacterial cellulose/polyvinyl alcohol/MXene aerogels were constructed by bidirectional freezing. The anisotropic PCMs composites were from vacuum impregnation PEG into aerogel networks. By controlling crystallization and growth of ice crystals through the dual temperature gradients, the PCMs composites obtained enhanced heat transfer efficiency in horizontal and vertical directions. Bidirectional aligned PCMs with PDMS wedge angle of 0° and 20° exhibit high thermal conductivity of 0.716 W m−1 K−1 and 0.768 W m−1 K−1, which were 184% higher than that of PEG, and photothermal conversion efficiency of 55.17% and 76.91%. Remarkably, the PCMs composites with a 20° PDMS wedge angle also exhibited a high PCM loading capacity (96.3%) and a high enthalpy (157.7 J/g). The results show that bidirectional anisotropic PCMs composites have excellent overall performance and are expected to improve solar thermal application.

Tailoring hierarchical structures in cellulose carbon aerogels from sugarcane bagasse using different crosslinking agents for enhancing electrochemical desalination capability

Sugarcane bagasse is one of the most common Vietnamese agricultural waste, which possesses a large percentage of cellulose, making it an abundant and environmentally friendly source for the fabrication of cellulose carbon aerogel. Herein, waste sugarcane bagasse was used to synthesize cellulose aerogel using different crosslinking agents such as urea, polyvinyl alcohol (PVA) and sodium alginate (SA). The 3D porous network of cellulose aerogels was constructed by intermolecular hydrogen bonding, which was confirmed by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption/desorption. Among the three cellulose aerogel samples, cellulose – SA aerogel (SB-CA-SA) has low density of 0.04 g m−3 and high porosity of 97.38%, leading to high surface area of 497.9 m2 g−1 with 55.67% micropores of activated carbon aerogel (SB-ACCA-SA). The salt adsorption capacity was high (17.87 mg g−1), which can be further enhanced to 31.40 mg g−1 with the addition of CNT. Moreover, the desalination process using the SB-ACCA-SA-CNT electrode was stable even after 50 cycles. The results show the great combination of cellulose from waste sugarcane bagasse with sodium alginate and carbon nanotubes in the fabrication of carbon materials as the CDI-utilized electrodes with high desalination capability and good durability.

Nanocomposite Aerogel Network Featuring High Surface Area and Superinsulation Properties

Nanocomposite Aerogel Network Featuring High Surface Area and Superinsulation Properties

Novel soy protein isolate/sodium alginate-based functional aerogel for efficient uptake of organic dye from effluents

In response to the increasing global concern regarding water pollution, there is a growing demand for the development of novel adsorbents capable of effectively eliminating hazardous organic pollutants from effluents. In this study, we present a functional soy protein isolate (SPI)/sodium alginate (ALG)/polyethyleneimine (PEI) aerogel prepared via a facile chemical crosslinking process as a novel adsorbent with excellent capabilities for removing toxic methyl blue (MB) dye from effluents. Thanks to the synergistic dense oxygen and nitrogen-containing functional groups in the networks, the ALG/SPI/PEI (ASP) aerogel displayed high adsorption capacity for MB (106.3 mg/g) complying the adsorption kinetics and isotherm with the pseudo-second-order and Langmuir models, respectively. Remarkably, the MB adsorption capability of the ASP aerogel surpasses that of its pristine counterpart and outperforms recently reported adsorbents. Moreover, the aerogel maintained >80% of initial adsorption capability in the fourth regenerative cycle, indicating excellent reusability. The superior MB adsorbability coupled with high-efficiency regenerability in this study reveal the significant potential of ASP aerogel in efficiently eliminating organic dye from wastewater.

Divalent metal-ions blowing strategy achieved 3D luffa aerogels heterostructure for lightweight broadband microwave absorber

Explicitly, effective dispersion configuration and hierarchical network construction are two practicable measures to develop the broadband and lightweight absorbers. Based on the newly developed sugar blowing art, 3D Luffa aerogels heterostructure have been successfully developed through metal ion assisted caramel blowing (MCB) strategy. The Luffa foam hierarchical configuration with those dielectric, magnetic, and porous interfaces can be all achieved. Such hierarchical 3D lightweight aerogels are facilitated to building effective impedance matching networks (2.4 wt%) and exhibit an optimized polarization relaxation. Thus, the effective absorbing bandwidth (EAB) of the Luffa aerogel can be broadened up to 8.0 GHz. Moreover, the MCB strategy can be applicable to a wide range of divalent metal ions (Co2+, Ni2+, Mn2+, Zn2+ et al.). This study provides a new method for efficient synthesis of aerogel network structures and opens a way to realize lightweight and broadband electromagnetic wave absorbing (EWA) materials.

Partially oxidized inter-doped RuNi alloy aerogel for the hydrogen evolution reaction in both alkaline and acidic media.

A facile reduction and doping process is employed with the supercritical ethanol drying method to form RuNi alloy aerogels. The optimized heterostructure comprising RuNi metal, RuO2, and NiO phases is synthesized through partial oxidation. When applied to the surface of Ni foam, the multiphase aerogels form a morphology of highly porous 0D colloidal aerogel networks on the surface. RuNi alloy-Ni foam oxidized at 350 °C (RuNi-350@NF) has an overpotential of 89 and 61 mV in 1 M KOH and 0.5 M H2SO4 media at 50 mA cm-2, as well as satisfactory long-term stability. Additionally, the Tafel slopes in alkaline and acidic media are found to be 34 and 30.9 mV dec-1, respectively. Furthermore, it exhibits long-term stability (35 h) in alkaline and acidic media at high current densities of 50 mA cm-2, respectively. This study presents a novel strategy for developing exceptionally efficient and free-standing 3D porous aerogel electrocatalysts with potential applications in hydrogen production.

Micro structural design and macro synthesis of aerogel networks with gradient stiffness properties

Conductive aerogels have received extensive attention in a variety of application fields such as structural engineering and electrochemistry due to their lightweight, porous and conductive properties. The stiffness of aerogel is a key factor affecting its performance. So compared with conventional single stiffness aerogels, the preparation of conductive aerogels with gradient stiffness properties is expected to achieve better stiffness matching and greater performance. Here, we develop a theoretical model of the gradient stiffness carbon nanotube (CNT) network and analyze the factors affecting the stiffness of the model from several perspectives, including spatial configuration and intrinsic parameters. Then, according to the guidance of the simulation results, actual CNT aerogels with gradient stiffness properties are successfully synthesized which have an ultra-wide range of stiffness variations. The unique lightweight gradient stiffness conductive aerogels are expected to show outstanding performance in many stiffness-dominated application fields.

Graphene encapsulated MnO2 nanorods boosts interfacial polarization for microwave absorption

The lightweight and efficient electromagnetic wave (EMW) absorption materials have been a popular research topic. In this work, MnO2 @graphene (MnGr) nanofibers with core-shell structure were synthesized by a one-step hydrothermal method. This one-dimensional linear structure was further self-assembled into a three-dimensional hierarchical MnGr aerogel network structure due to the interlayer forces of graphene sheets. The addition of graphene greatly enhances the interfacial polarization. The significant differences in electronic structure and work function between the outer graphene layer and the inner MnO2 layer greatly enhance the interfacial polarization. The formation of 3D hierarchical MnGr aerogel network structure constructs more fast electron transport channels. With the addition of graphene oxide at 7.5 wt% of the theoretical yield of MnO2, MnGr-7.5 exhibits excellent wave absorption properties. The effective absorption bandwidth (EAB) can reach 6.40 GHz at 2.2 mm. And the minimum reflection loss (RLmin) is − 41.3 dB at 1.8 mm and 17.36 GHz. Finite element physical simulation is used to simulate the response of 3D conductive network to electromagnetic wave. Through calculation, it is found that the inter-lap network structure is beneficial to enhance the loss. The low-cost MnO2 compounded with a small amount of graphene has excellent wave absorption performance and a great application prospect.

Ultrafine Pd nanoparticles-decorated TiO2 three-dimensional (3D) hybrid aerogel with large specific surface areas and highly interconnected porous networks for hydrogen sensing

A hybrid aerogel structure for hydrogen sensing was produced and tested, which consists of Pd nanoparticles decorated on a TiO2 aerogel skeleton structure with large specific surface areas and high porosity. The effects of decorated with different contents of Pd nanoparticles on the microstructure of anatase TiO2 aerogel and the hydrogen response characteristics were investigated. The contribution of the doping of Pd nanoparticles to the specific selectivity of the anatase phase TiO2 aerogel for hydrogen sensing was investigated. Benefiting from highly interconnected porous networks of aerogel, ultra-large specific surface area, and homogeneous Pd nanoparticles dispersion, the resulting Pd nanoparticle-decorated TiO2 3D hybrid aerogel hydrogen sensors express high hydrogen sensing performance. The response was 4.8 toward 100 ppm hydrogen at the optimal working temperature of 325 °C, with a short response time (<2 s), short recovery time (<22 s), and high selectivity and long-term stability. A hydrogen-sensitive mechanism is proposed in which metal atom doping causes more oxygen defects in metal oxide semiconductor lattice. The approach of constructing aerogel network structures by decorating metal nanoparticles on metal oxide semiconductors provides a new way to develop gas sensors.

Effect of molar concentration and drying methodologies on monodispersed silica sol for synthesis of silica aerogels with temperature-resistant characteristics

A variety of hierarchical nanoporous silica aerogels with diversified particle distributions were synthesized from well-dispersed silica sols by a traditional sol–gel method. Among the six particle sizes of aerogels, the silica aerogel with 0.4 M TEOS/MTMS surface modification and supercritical drying attains 11.61 ± 2.96 nm constituent part with well slender size particle dissemination, high-temperature confrontation and low thermal conductivity. In association with the outmoded two-step acid-base dilution of silica sols, the well-diffused form of silica sols with surface alteration also provides a low thermal conductivity of 0.01865 W.m−1 K−1 with greater thermal resistance. In addition, the drying shrinkage can be minimized with surface modification by properly silylation with TMCS. The concentrations of well-diffused silica sol were adjusted to achieve higher surface area, low density, large pore size and structure, and temperature resilience with the help of controlling the sol–gel reaction. The resilient skeleton structure developed from the assembly of tiny particles can efficiently restrict the glutinous heat dissipation between aerogel networks without collapsing a porous network up to a higher temperature of 900 °C. However, this network retains a similar pattern up to 1000 °C with only 32 % volume contraction after 2hr of heat treatments. At an elevated temperature of 1100–1200 °C, the viscid heat flow between nanoparticles and the porous network cannot be meritoriously suppressed and starts to collapse after a shorter duration. The enormous results of silica aerogels will help design suitable thermal insulation with higher resilience and low thermal conductivity.

Hydrosilylation Adducts to Produce Wide-Temperature Flexible Polysiloxane Aerogel under Ambient Temperature and Pressure Drying.

Despite incorporation of organic groups into silica-based aerogels to enhance their mechanical flexibility, the wide temperature reliability of the modified silicone aerogel is inevitably degraded. Therefore, facile synthesis of soft silicone aerogels with wide-temperature stability remains challenging. Herein, novel silicone aerogels containing a high content of Siare reported by using polydimethylvinylsiloxane (PDMVS), a hydrosilylation adduct with water-repellent groups, as a "flexible chain segment" embedded within the aerogel network. The poly(2-dimethoxymethylsilyl)ethylmethylvinylsiloxane (PDEMSEMVS) aerogelis fabricated through a cost-effective ambient temperature/pressure drying process. The optimizedaerogel exhibits exceptional performance, such as ultra-low density (50mg cm-3), wide-temperature mechanical flexibility, and super-hydrophobicity, in comparison to the previous polysiloxane aerogels. A significant reduction in the density of these aerogels is achieved while maintaining a high crosslinking density by synthesizing gel networks with well-defined macromolecules through hydrolytic polycondensation crosslinking of PDEMSEMVS. Notably, the pore/nanoparticle size of aerogels can be fine-tuned by optimizing the gel solvent type. The as-prepared silicone aerogels demonstrate selective absorption, efficient oil-water separation, and excellent thermal insulation properties, showing promising applications in oil/water separation and thermal protection.

Aerogel-glass fiber composite filter media for effective separation of emulsified water droplets from diesel fuel

This work evaluates several mechanisms of separation of surfactant-stabilized emulsified water droplets from diesel fuel using high surface area (50–370 m2/g) and high porosity (>90 %) filter media fabricated by combining aerogels and glass fiber mats. Specifically, high surface area, porous gels of syndiotactic polystyrene (sPS) and silica are developed inside glass fiber mats via dip coating in corresponding sol followed by sol–gel transition. The resultant materials are supercritically dried to obtain aerogel-coated separation media. The abundant meso- and macropores of the aerogel network and the different surface energy of sPS and silica produce cooperative functioning of the mechanisms of size exclusion, coalescence filtration, surfactant adsorption, and volumetric water absorption for removal of emulsified water droplets from ultralow sulfur diesel fuel under continuous flow conditions. The role of each separation mechanism is elucidated in this paper. The results reveal high water separation efficiency of ∼92 % compared to ∼30 % for the glass fiber mats.

Title High Solar-Thermal Conversion Aerogel for Efficient Atmospheric Water Harvesting.

The shortage of freshwater is a global problem, however, the gel that can be used for atmospheric water harvesting (AWH) in recent years studying, suffer from salt leakage, agglomeration, and slow water evaporation efficiency. Herein, a solar-driven atmospheric water harvesting (SAWH) aerogel is prepared by UV polymerization and freeze-drying technique, using poly(N-isopropylacrylamide) (PNIPAm), hydroxypropyl cellulose (HPC), ethanolamine-decorate LiCl (E-LiCl) and polyaniline (PANI) as raw materials. The PNIPAm and HPC formed aerogel networks makes the E-LiCl stably and efficiently loaded, improving the water adsorption-desorption kinetics, and PANI achieves rapid water vapor evaporation. The aerogel has low density ≈0.12-0.15gcm-3, but can sustain a weight of 1000 times of its own weight. The synergist of elements and structure gives the aerogel has 0.46-2.95gg-1 water uptake capability at 30-90% relative humidity, and evaporation rate reaches 1.98kgm-2h-1 under 1 sun illumination. In outdoor experiments, 88% of the water is harvesting under natural light irradiation, and an average water harvesting rate of 0.80gwater gsorbent -1day-1. Therefore, the aerogel can be used in arid and semi-arid areas to collect water for plants and animals.

Development of a low-cost photocatalytic aerogel based on cellulose, carbon nanotubes, and TiO2 nanoparticles for the degradation of organic dyes

A hybrid ultra-light and porous cellulose aerogel was prepared by extracting cellulose fibers from white paper, alkali/urea as a crosslinker agent, and functionalized with CNTs and pure anatase TiO2 nanoparticles. Since CNTs work as mechanical reinforcement for aerogels, physical and mechanical properties were measured. Besides, since TiO2 acts as a photocatalyst for degrading dyes (rhodamine B and methylene blue), UV–Vis spectroscopy under UV light, visible light, and darkroom was used to evaluate the degradation process. XRD, FTIR, and TGA were employed to characterize the structural and thermal properties of the composite. The nanostructured solid network of aerogels was visualized in SEM microscopy confirming the structural uniformity of cellulose and TiO2-CNTs onto fibers. Moreover, CLSM was used to study the nano-porous network distribution of cellulose fibers and porosity, and the functionalization process in a detailed way. Finally, the photocatalytic activity of aerogels was evaluated by degradation of dye aqueous solutions, with the best photocatalytic removal (>97 %) occurring after 110 min of UV irradiation. In addition, HPLC-MS facilitated the proposed mechanism for the degradation of dyes. These results confirm that cellulose aerogels coupled with nanomaterials enable the creation of economic support to reduce water pollution with higher decontamination rates.

Optimization of Mass and Light Transport in Nanoparticle-Based Titania Aerogels.

Aerogels composed of preformed titania nanocrystals exhibit a large surface area, open porosity, and high crystallinity, making these materials appealing for applications in gas-phase photocatalysis. Recent studies on nanoparticle-based titania aerogels have mainly focused on optimizing their composition to improve photocatalytic performance. Little attention has been paid to modification at the microstructural level to control fundamental properties such as gas permeability and light transmittance, although these features are of fundamental importance, especially for photocatalysts of macroscopic size. In this study, we systematically control the porosity and transparency of titania gels and aerogels by adjusting the particle loading and nonsolvent fraction during the gelation step. Mass transport and light transport were assessed by gas permeability and light attenuation measurements, and the results were related to the microstructure determined by gas sorption analysis and scanning electron microscopy. Mass transport through the aerogel network was found to proceed primarily via Knudsen diffusion leading to relatively low permeabilities in the range of 10-5-10-6 m2/s, despite very high porosities of 96-99%. While permeability was found to depend mainly on particle loading, the optical properties are predominantly affected by the amount of nonsolvent during gelation, allowing independent tuning of mass and light transport.