Superhydrophobic Aerogel Research Articles

Low temperature-resistant superhydrophobic and elastic cellulose aerogels derived from seaweed solid waste as efficient oil traps for oil/water separation

Aerogel has excellent application potential in adsorption, heat preservation, and other areas due to its typical advantages of low density and high porosity. However, there are several issues with the use of aerogel in oil/water separation, including weak mechanical qualities and challenges in eliminating organic contaminants at low temperature. Inspired by cellulose Iα, which has excellent performance at low temperature, this study used cellulose Iα nanofibers extracted from seaweed solid waste as the skeleton, through covalent cross-linked with ethylene imine polymer (PEI) and hydrophobic modification of 1, 4-phenyl diisocyanate (MDI), supplemented by freeze-drying technology to form three-dimensional sheet, and successfully obtained cellulose aerogels derived from seaweed solid waste (SWCA). The compression test shows that the maximum compressive stress of SWCA is 61 kPa, and the initial performance still maintains 82% after 40 cryogenic compression cycles. In addition, the contact angles of water and oil on the surface of the SWCA were 153° and 0°, respectively, and the stable hydrophobic time in simulated seawater is more than 3 h. By combining the elasticity and superhydrophobicity/superoleophilicity, the SWCA with an oil absorption capacity of up to 11–30 times its mass, might be utilized repeatedly for the separation of an oil/water mixture.

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.

Efficient recovery of highly viscous crude oil spill by superhydrophobic ocean biomass-based aerogel assisted with solar energy

The crude oil spills is one of the crucial ocean environmental disaster. The low fluidity of high-viscosity crude oil poses significant challenges for its penetration into conventional porous adsorption materials. Fortunatelly, the viscosity of crude oil is especially temperature-sensitive, leading to the extensive research on porous materials that utilize solar heat for heat generation. In this work, we propose a biodegradable marine bio-based aerogel (PDMS-Ink@CS) with aligned channel structure via directional freeze casting technique, primarily composed of chitosan and cuttlefish ink. The PDMS-Ink@CS demonstrates excellent photothermal conversion and oil adsorption performance. We systematically investigated the effects of sunlight intensity and pore structure on the viscosity-reduction and adsorption rate of crude oil. Under simulated sunlight intensity of 1 kW m−2, the surface temperature of PDMS-Ink@CS aerogel reaches approximately 70 ℃ within 60 s, allowing to absorb crude oil 18 times its weight and recover via extrusion. When combined with a vacuum pump device, the PDMS-Ink@CS aerogel realizes the continuous recovery of crude oil from the seawater surface. Moreover, the separation efficiency of PDMS-Ink@CS aerogel for W/O emulsions can reach 99 %, which greatly broadens its range of applications. Particularly noteworthy is the fact that the PDMS-Ink@CS aerogel biodegrades within 30 days without causing environmental pollution. Thus, this super-hydrophobic ocean biomass-based chitosan aerogel exhibits vast potential for oil spill recovery applications.

Facile construction of a degradable and renewable superhydrophobic indole-based hemiaminal aerogel for efficient oil–water separation

Facile construction of a degradable and renewable superhydrophobic indole-based hemiaminal aerogel for efficient oil–water separation

Biomass Chitosan-Based Tubular/Sheet Superhydrophobic Aerogels Enable Efficient Oil/Water Separation.

Water pollution, which is caused by leakage of oily substances, has been recognized as one of the most serious global environmental pollutions endangering the ecosystem. High-quality porous materials with superwettability, which are typically constructed in the form of aerogels, hold huge potential in the field of adsorption and removal of oily substances form water. Herein, we developed a facile strategy to fabricate a novel biomass absorbent with a layered tubular/sheet structure for efficient oil/water separation. The aerogels were fabricated by assembling hollow poplar catkin fiber into chitosan sheets using a directional freeze-drying method. The obtained aerogels were further wrapped with -CH3-ended siloxane structures using CH3SiCl3. This superhydrophobic aerogel (CA ≈ 154 ± 0.4°) could rapidly trap and remove oils from water with a large sorption range of 33.06-73.22 g/g. The aerogel facilitated stable oil recovery (90.07-92.34%) by squeezing after 10 sorption-desorption cycles because of its mechanical robustness (91.76% strain remaining after 50 compress-release cycles). The novel design, low cost, and sustainability of the aerogel provide an efficient and environmentally friendly solution for handling oil spills.

Development of superhydrophobic hybrid silica-cellulose aerogel as promising thermal insulation and sound absorption

AbstractA cost-effective and facile synthesis method is developed for hybrid aerogels using recycled cellulose fiber concentration of 1–4 wt.% and methoxytrimethylsilane (MTMS). The developed hybrid aerogel was modified with surface hydroxyl groups to achieve superhydrophobic behavior with a contact angle as high as 163.4°. This excellent three-dimensional reticular structure with various cellulose concentrations provides a thermal conductivity of 0.039–0.041 W m−1 K−1. However, the thermal degradation of the hybrid aerogels exhibits a superior improvement with minimum weight loss. A comparatively good sound absorption coefficient of 0.392–0.504 was achieved with the inclusion of cellulose fiber concentration from 1 to 4 wt.% in comparison with silica aerogels (0.303–0.512). The experimental results also show an increase in compressive Young’s modulus of hybrid aerogels up to 96%, with an increase in cellulose concentration. This work delivers a facile approach to developing hybrid aerogels with an industrial application to replace polymer-based insulations.

Bionic Aerogel with a Lotus Leaf-like Structure for Efficient Oil-Water Separation and Electromagnetic Interference Shielding.

Increasing pollution from industrial wastewater containing oils or organic solvents poses a serious threat to both the environment and human health. Compared to complex chemical modifications, bionic aerogels with intrinsic hydrophobic properties exhibit better durability and are considered as ideal adsorbents for oil-water separation. However, the construction of biomimetic three-dimensional (3D) structures by simple methods is still a great challenge. Here, we prepared biomimetic superhydrophobic aerogels with lotus leaf-like structures by growing carbon coatings on Al2O3 nanorod-carbon nanotube hybrid backbones. Thanks to its multicomponent synergy and unique structure, this fascinating aerogel can be directly obtained through a simple conventional sol-gel and carbonization process. The aerogels exhibit excellent oil-water separation (22 g·g-1), recyclability (over 10 cycles) and dye adsorption properties (186.2 mg·g-1 for methylene blue). In addition, benefiting from the conductive porous structure, the aerogels also demonstrate outstanding electromagnetic interference (EMI) shielding capabilities (~40 dB in X-band). This work presents fresh insights for the preparation of multifunctional biomimetic aerogels.

Full Bio-Based Aerogel Incorporating Lignin for Excellent Flame Retardancy, Mechanical Resistance, and Thermal Insulation

Aerogels have drawn a lot of interest as prospective insulation materials in the construction industry due to their low thermal conductivity. However, the combination of excellent mechanical properties and flame retardancy is a fundamental issue with the majority of bio-based aerogels. By utilizing the ability of the alginate solution to gel in mildly acidic environments, sodium alginate (SA)/sodium lignosulfonate (LS)/phytic acid (PA) aerogels were fabricated in a quick and facile method. To solve the issue of inorganic additives being incompatible with the bio-based substrate, we introduced lignin to it as a structural reinforcer and char-forming agent, significantly improving the mechanical strengths of the aerogels, which has increased their compressive modulus by nearly 30 times. The inclusion of lignin dramatically boosted the ability of aerogels to suppress smoke while simultaneously reducing its fire index and then providing outstanding fire resistance. A superhydrophobic flame-retardant aerogel with a water contact angle of 150° was then obtained by chemical vapor deposition of methyltrichlorosilane (MTCS), further broadening its application potential. This work offers a fresh idea for the high-value utilization of lignin, and the obtained aerogels have enormous application potential in the fields of construction and transportation.

Facile fabrication of superhydrophobic wood aerogel by vapor deposition method for oil-water separation

With the increasing deterioration of natural environment caused by industrial sewage and oil leak, superhydrophobic materials for oil-water separation have attracted considerable attention. However, most of the superhydrophobic materials are petroleum-based and difficult to be degraded, which will bring secondary pollution for natural environment. Herein, a facile vapor deposition method is reported to fabricate a superhydrophobic methyltrimethoxysilane (MTMS) modified wood aerogel (M-WA) for oil-water separation from natural renewable balsa wood. Firstly, to construct micro-nano roughness and enough pores, balsa wood was chemically treated to remove lignin and hemicellulose. Secondly, MTMS was vapor-deposited on the skeleton surface of the treated balsa wood to form a crosslinked network and provide low surface energy through hydrolysis-condensation reaction. The obtained superhydrophobic M-WA showed a high water contact angle (WCA) of 151.8°. The M-WA was able to selectively absorb oils from oil-water mixtures and the adsorption capacity for methylene chloride reached 25.1 times of its own weight. Furthermore, the M-WA was utilized as a filter to continuously separate oil-water mixtures and the separation efficiency reached 99.1%. Even after 20 cycles, the separation efficiency still maintained 98.5%, demonstrating excellent recyclability. The method to prepare the superhydrophobic M-WA is facile and highly efficient, no fluorinated chemical is involved, and the M-WA has natural and renewable characteristics, which is very beneficial for environment safety and protection. Our findings conceivably develop a new strategy to prepare environment-friendly superhydrophobic materials for the treatments of spill accidents and industrial sewage emissions.

Anisotropic superhydrophobic graphene aerogel with radial superelasticity and axial superstiffness for efficient on-demand oil–water separation

Graphene aerogels possess unique advantages for treating oil–water mixtures, but their fragile mechanical properties hinder further development, and their separation mechanisms remain unclear.

Dynamics of Droplets Impacting on Aerogel, Liquid Infused, and Liquid-Like Solid Surfaces.

Droplets impacting superhydrophobic surfaces have been extensively studied due to their compelling scientific insights and important industrial applications. In these cases, the commonly reported impact regime was that of complete rebound. This impact regime strongly depends on the nature of the superhydrophobic surface. Here, we report the dynamics of droplets impacting three hydrophobic slippery surfaces, which have fundamental differences in normal liquid adhesion and lateral static and kinetic liquid friction. For an air cushion-like (super)hydrophobic solid surface (Aerogel) with low adhesion and low static and low kinetic friction, complete rebound can start at a very low Weber (We) number (∼1). For slippery liquid-infused porous (SLIP) surfaces with high adhesion and low static and low kinetic friction, complete rebound only occurs at a much higher We number (>5). For a slippery omniphobic covalently attached liquid-like (SOCAL) solid surface, with high adhesion and low static friction similar to SLIPS but higher kinetic friction, complete rebound was not observed, even for a We as high as 200. Furthermore, the droplet ejection volume after impacting the Aerogel surface is 100% across the whole range of We numbers tested compared to other surfaces. In contrast, droplet ejection for SLIPs was only observed consistently when the We was above 5-10. For SOCAL, 100% (or near 100%) ejection volume was not observed even at the highest We number tested here (∼200). This suggests that droplets impacting our (super)hydrophobic Aerogel and SLIPS lose less kinetic energy. These insights into the differences between normal adhesion and lateral friction properties can be used to inform the selection of surface properties to achieve the most desirable droplet impact characteristics to fulfill a wide range of applications, such as deicing, inkjet printing, and microelectronics.

Superhydrophobic aerogel blanket with magnetic and solar heating effect enables efficient continuous cleanup of highly viscous crude oil

Rapid cleanup of highly-viscous oil spills the sea is eagerly desired while still remains a great challenge. Hydrophobic and lipophilic adsorbents are regarded as ideal candidate for oil spill remediation. However, traditional adsorbents are not suitable for viscous crude oil, which would block the porous structure and lead to poor adsorption efficiency. In this work, a non-contact responsive superhydrophobic SiO2 aerogel blankets (SAB) with excellent magnetic and solar heating effect for efficient removal of viscosity oils under harsh environments was developed, via assembled MXene and Fe3O4/polydimethylsiloxane layer-by-layer along the SAB skeleton (Fe3O4/MXene@SAB). The Fe3O4/MXene@SAB exhibited excellent compression tolerance (compression stress 70.69 kPa), superhydrophobic performance (water contact angle 166°), and corrosion resistance (weak acid/strong base). Due to high water repellency and stable porous structure, the Fe3O4/MXene@SAB could successfully separate oil-water mixture, while with remarkable separation flux (1.50–3.19 × 104 L m−2 h−1), and separation efficiency (99.91–99.98 %). Furthermore, the responsive Fe3O4/MXene@SAB also showed outstanding magnetic-heating and solar-heating conversion efficiency, which could continuously separate high viscosity crude oil from seawater by pump even under relatively low magnetic fields and mild sun. The superhydrophobic blankets hold great promise for efficient treatment of heavy oil spills.

Study on Silica Aerogel Modified by Trimethylchlorosilane

The mechanical properties of SiO2 aerogel prepared under atmospheric pressure are poor, so it is difficult to prepare large pieces of materials for practical engineering. In this paper, trimethylchlorosilane (TMCS) was used as a surface modifier to transform hydrophilic substances with higher surface activity into hydrophobic groups, to improve the network strength of SiO2 aerogel. Super-hydrophobic SiO2 aerogel was prepared by the sol-gel method under atmospheric pressure. The effects of trimethylchlorosilane on the structure and properties of SiO2 aerogel were characterized by a specific surface area analyzer, Fourier transform infrared spectrometer, thermal conductivity meter, static contact angle meter, and scanning electron microscope. The results show that the SiO2 aerogel prepared when n (Si):n (TMCS) is 1 has the best performance. Its density is as low as 0.0759 g/cm3, the porosity is as high as 96.5%, the specific surface area is as high as 723.08 m2/g, and the contact angle is 163.8°. It has good hydrophobic properties.

Super-hydrophobic cotton aerogel with ultra-high flux and high oil retention capability for efficient oil/water separation

Natural biodegradable cotton-based materials are one of the promising materials for oil/water separation. However, the high oil retention ability of the oil/water separation materials benefiting oil transportation and storage is often ignored, and the separation flux of these cotton-based materials is usually unsatisfactory, hindering their applications. In this work, a super-hydrophobic cotton aerogel was prepared through a facile and mild dipping-heating process for oil/water separation. The obtained super-hydrophobic cotton aerogel with high porosity (about 94%), and super-hydrophobic surface (water contact angle as high as 152.7° ± 1.1°, and sliding angle as low as 9.2° ± 0.2°) showed excellent structural strength, allowing them to get an ultra-high separation flux (about 37,000 L m−2 h−1) as well as a high oil retention ability. This work provides a facile approach to fabricating cost-effectively and environment-friendly materials for efficient oil/water separation.

Self-cleaning superhydrophobic aerogels from waste hemp noil for ultrafast oil absorption and highly efficient PM removal

Environmental pollution and resource waste are two major concerns with the development of civilization. During hemp fiber separation short fiber noil is produced as a waste. This paper demonstrates the reuse of waste hemp noil by dissolution in a precooled NaOH/urea system to form porous aerogels. After hydrophobization, the hemp aerogels exhibited self-cleaning ability and could be used for oil adsorption and air purification. The superhydrophobic hemp aerogels exhibited elastic behavior with 75 % recoverable strain after 10 cycles of compression. The high porosity and compressibility endowed hemp aerogels with excellent oil absorption capacity and reusability. With a fiber concentration of 1.5 %, the hemp aerogel could achieve an oil removal of 29.4 times of its own weight, whilst 85.4 % of the initial absorption capacity remained after 10 absorption/desorption cycles. The ultrafast oil absorption was completed within 0.048 s. The oil contaminated hemp aerogel could be self-cleaned in an ethanol solution. The hemp aerogels also had high removal efficiencies of particulate materials (PM) such as PM2.5 and PM10 at both 94 %. The remodeled waste hemp noil showed great potential in environmental governance and recycling of natural resources.

Ultralight and shape recovery bio-based aerogel for oil-water separation

Elastic superhydrophobic aerogels have attracted significant attention to treat increasingly serious oil pollution because of their recycling performance. Using chitosan (CS) and cellulose nanofibrillated fiber (CNF) as raw materials, ultralight and elastic aerogels with the highly-oriented wavy structures were prepared by bidirectional freezing, chemical crosslinking, and chemical vapor deposition (CVD) for oil-water separation. Both the chemical crosslinking and CVD made the aerogels possess good mechanical strength at low density. The aerogel exhibited excellent shape recovery, maintaining more than 88% of its original compressive strength after 50 cycles of compression-release testing, with a high recovery rate of 96.6%. The shape memory property of the bio-based aerogels was improved with a decrease in density. The adsorption capacities of various organic solvents are more than 100 g/g, especially that of chloroform up to 232 g/g. After 10 simple and convenient adsorption-extrusion cycles, the adsorption retention rate of the aerogel can still reach 87.5%. This type of bio-based aerogel with excellent recycling performance has broad application prospects in the field of oil-water separation.

Reduced graphene aerogels as energy efficient selective oil sorbents

Graphene aerogels are widely used in the oil–water system as they possess high internal surface area and super-oleophilic properties. However, they tend to absorb water along with oil, and to overcome this problem; surface coatings are generally employed using expensive fluoro-silane compounds. It leads to an increase in production costs and environmental concerns. Herein, we report super-hydrophobic 3D graphene aerogels as selective oil sorbent for oil–water​ separation. The reduction of oxygen-containing functional groups on the surface of graphene aerogels has been studied and characterized with FTIR. The thermal treatment of up to 700 °C was carried out using an in-house flow system. The gases used to reduce graphene oxide aerogel are H2 and N2 with an optimized ratio of 5:95. The presence of H2 significantly decreased the oxygen-containing functional groups in graphene aerogel. The increase in the C/O ratio results in higher uptake capacity due to higher surface area and pore volume. The thermal reduction yields a C/O ratio of 24:1, slightly higher than most reported values.

Preparation of peanut shell cellulose nanofibrils and their superhydrophobic aerogels and their application on cotton fabrics

Nowadays, the application range of biomass materials is more and more extensive. In this work, peanut shell powder was used as the raw material. The cellulose nanofibrils was extracted from it by chemical mechanical method. Then, using the sol-gel method, methyltrimethoxysilane (MTMS) was added to the peanut shell cellulose nanofibrils suspension to modify it. Finally, the nano-cellulose superhydrophobic aerogel was prepared by freeze-drying method. The nano-cellulose aerogel and polydimethylsiloxane (PDMS) were coated on the cotton fabric by spraying method, and the superhydrophobic aerogel and superhydrophobic cotton fabric were analyzed and characterized respectively. The results shown that the prepared nanocellulose aerogel had a three-dimensional sheet-like structure with superhydrophobicity. The hydrophobic property and water contact angle (WCA) of cotton fabrics were significantly improved after superhydrophobic finishing. The WCA can reached 160°, the finished fabric has good antifouling performance and self-cleaning performance, and the oil-water separation efficiency can reach 82.2%.

Comparative Analysis of Superhydrophobic Elastic Polymethylsilsesquioxane Aerogels Prepared at Atmospheric Pressure and under Supercritical Conditions

Comparative Analysis of Superhydrophobic Elastic Polymethylsilsesquioxane Aerogels Prepared at Atmospheric Pressure and under Supercritical Conditions

Superelastic, Highly Conductive, Superhydrophobic, and Powerful Electromagnetic Shielding Hybrid Aerogels Built from Orthogonal Graphene and Boron Nitride Nanoribbons.

Three-dimensional (3D) elastic aerogels enable diverse applications but are usually restricted by their low thermal and electrical transfer efficiency. Here, we demonstrate a strategy for fabricating the highly thermally and electrically conductive aerogels using hybrid carbon/ceramic structural units made of hexagonal boron nitride nanoribbons (BNNRs) with in situ-grown orthogonally structured graphene (OSG). High-aspect-ratio BNNRs are first interconnected into a 3D elastic and thermally conductive skeleton, in which the horizontal graphene layers of OSG provide additional hyperchannels for electron and phonon conduction, and the vertical graphene sheets of OSG greatly improve surface roughness and charge polarization ability of the entire skeleton. The resulting OSG/BNNR hybrid aerogel exhibits very high thermal and electrical conductivity (up to 7.84 W m-1 K-1 and 340 S m-1, respectively) at a low density of 45.8 mg cm-3, which should prove to be vastly advantageous as compared to the reported carbonic and/or ceramic aerogels. Moreover, the hybrid aerogel possesses integrated properties of wide temperature-invariant superelasticity (from -196 to 600 °C), low-voltage-driven Joule heating (up to 42-134 °C at 1-4 V), strong hydrophobicity (contact angel of up to 156.1°), and powerful broadband electromagnetic interference (EMI) shielding effectiveness (reaching 70.9 dB at 2 mm thickness), all of which can maintain very well under repeated mechanical deformations and long-term immersion in strong acid or alkali solution. Using these extraordinary comprehensive properties, we prove the great potential of OSG/BNNR hybrid aerogel in wearable electronics for regulating body temperature, proofing water and pollution, removing ice, and protecting human health against EMI.