Cellulose-based Aerogels Research Articles

Subtle devising of electro-induced shape memory behavior for cellulose/graphene aerogel nanocomposite

Herein, a cellulose-based aerogel, containing graphene-oxide (GO), chemically-reduced-GO (CrGO), and thermally-reduced-GO (TrGO), has been facile prepared to investigate mechanical and electrical properties as well as meso-(nano)structure features. The effect of reduction processes on the cellulose/GO aerogel was tracked by FT-IR spectroscopy and EDS analysis, confirming the accomplishment of reduction processes—carbon/oxygen (C/O) ratio asserted it evidently. The formation of porous structure has been declared using SEM micrographs, and then, Mercury-porosimetry and BET tests revealed meso-(nano)structure of aerogels. The improvement of mechanical behavior with the increment of Young modulus has been seen by raising C/O ratio. Low thermal and moderate electrical conductivity was measured for the reduced aerogels concerning the addition of different conductive fillers. With introducing a novel method for studying shape memory properties, the best shape recovery rate was obtained for thermally reduced aerogel in an aqueous situation by simultaneously applying mechanical force and an electrical field (various voltages).

Preparation and adsorption properties of hyperbranched polyethyleneimine-cellulose nanofiber aerogel

A novel cellulose-based aerogel was prepared by a chemical cross-linking reaction and hydrogen bonding between cellulose nanofibers (CNF), polyethylene glycol diglycidyl ether (PEGDE), and hyperbranched polyethyleneimine (HPEI).

Lignocellulosic nanofibril aerogel via gas phase coagulation and diisocyanate modification for solvent absorption

Cellulose-based aerogels are considered to be carriers that can absorb oils and organic solvents owing to the merits of low density and high surface area. However, the natural hydrophility and poor mechanical strength often obstruct their widespread applications. In this work, Miscanthus-based dual cross-linked lignocellulosic nanofibril (LCNF) aerogels were prepared by gas phase coagulation and methylene diphenyl dissocyanate (MDI) modification. Due to physical and chemical cross-linking strategies, the optimally 4 M-LCNF aerogels had high surface area of 157.9 m2/g, water contact angle of 138.1°, and enhanced compression properties. Moreover, the modified aerogels exhibited absorption performance for various organic solvents, and the maximal absorption capacity of chloroform was 42 g/g aerogel. Because LCNF was directly produced from Miscanthus without using bleaching reagents, this research provided a more sustainable methodology to utilize lignocelluloses to design robust aerogels to deal with the leakage of oil and organic solvents in industrial applications.

Fabrication of cellulose-based aerogel for thermal and acoustic insulation applications

A method to prepare aerogels from rice straw and polyvinyl alcohol in the presence of fiberglass and glutaraldehyde is herein reported. The morphology, pore structure and physical properties of the aerogels were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), thermal conductivity, water contact angle (WCA) measurements, oil adsorption and sound absorption measurements. The obtained aerogels should be considered as a promising material for upcoming applications, since it has high porosity (up to 93.72%), low density (0.083-0.127 g/cm3), super low thermal conductivity (0.032-0.048 W/mK), high Young modulus (0.201-1.207 MPa), high sound absorption (absorption coefficient of 0.87) and a good oil adsorption capacity (4.8 g/g).

Green Fabrication of Bio-based Aerogels from Coconut Coir for Heat Insulation and Oil Removal

Each year, the global annual production of coconut fibre (CF) is around 350×103 t, while they are utilized for fine art, fertilization, and animal feed. However, there have not seen many engineering applications to utilize these materials. The coir with high cellulose content of over 40 % has potential for high-value engineering applications like fabricating cellulose-based aerogels. Recently, the cellulose aerogel from CF was formed using a sol-gel method in an NaOH/Urea solution, with an anticipated completion time of 7 d due to the time required for gelation and solvent exchange, which might take up to 4 d. This demonstrates that the present approach is subject to several time limitations. To improve this, for the first time, a novel fabrication of aerogels from the CF with chemical pre-treatment in advance has been successfully developed by using polyvinyl alcohol (PVA) and xanthan gum (XTG) as biodegradable binders. The treated CFs are dispersed homogeneously into a PVA/XTG solution, followed by freeze-drying to remove water, leaving behind a highly porous called CF aerogel. The influences of CF content on CF aerogels' physical and mechanical characteristics, as well as oil adsorption and thermal conductivity, have all been thoroughly investigated. For oil removal, the fabricated CF aerogels are surface-modified with methyltrimethoxysilane (MTMS) to enhance their hydrophobicity. This method required 2 times less time and used fewer chemicals while retaining the same oil adsorption capabilities of up to 20 g/g as previous CF aerogel and demonstrating additional good insulation of 0.040 W/(m·K). Thus, this study provides a new novel approach to synthesize an oil-absorbing and insulating CF aerogel.

Highly compressible nanocellulose aerogels with a cellular structure for high-performance adsorption of Cu(II)

Cellulose-based aerogels have considerable potential for various application due to renewable, low cost, and high availability. However, mechanical robustness and functionalization remain major challenges. Here, we synthesized a compressible, recoverable cellulose nanofiber (CNF)/carboxymethyl cellulose (CMC)/branched polyethyleneimine (BPEI) aerogel via electrostatic-modulated interfacial covalent crosslinking and freeze-drying process. The porous BPEI@CNF/CMC aerogel possessed excellent mechanical compression and high-density metal-chelating groups, which exhibited fast adsorption kinetics and high adsorption capacity (452.49 mg g−1) in static copper adsorption process. Furthermore, BPEI@CNF/CMC aerogels displayed excellent recyclability and could still reach 85% after 10 cycles. The integrated analyses of ATR-FTIR and XPS suggested that the predominant adsorption mechanism included electrostatic interaction, ion-exchange and chelation. This strategy provides a sustainable route to fabricate efficient biomass-based adsorbents for selective copper removal from water.

Sustainable cellulose-based aerogels fabricated by directional freeze-drying as excellent sound-absorption materials

Sustainable cellulose-based aerogels fabricated by directional freeze-drying as excellent sound-absorption materials

3D freeze-printed cellulose-based aerogels: Obtaining truly 3D shapes, and functionalization with cross-linking and conductive additives

Cellulose is the most abundant natural polymer existing on earth and nanomaterials derived from cellulose have been used in variety of applications. There is a great research interest in aerogels based on cellulosic nanomaterials due to their ultra-low thermal conductivity, modulus, sonic velocity, refractive index, dielectric constant, high specific surface area, and adjustable density. 3D printing of cellulose-based aerogels provided an ability to fabricate complex geometries with designed pore morphologies, which can be advantageous for various applications. Yet, the complexity of the geometry still has a limitation due to the lack of support material that can be removed from the structure without using harsh and tedious chemical / thermal processes that may affect the cellulosic material. In this study, by using water as support material, we have fabricated the first cellulose-based aerogels having truly 3D geometries with overhang features via the 3D freeze printing method incorporating a drop on demand-based materials deposition approach. The support material was removed from the main structure by a freeze-drying process, which is already a regular step in 3D printing process of aerogels. Fabricated aerogels possessed a highly ordered microstructure, in which the micropores were aligned along the freezing direction. We have investigated the effects of this anisotropy in the mechanical properties of the final aerogels. All the samples exhibited an excellent strain memory effect, and after 100 cyclic compression up to 25% strain, the obtained stress decay values were ~30% and ~16% in axial and radial directions, respectively. We further investigated the cross-linking of the fabricated aerogels to enhance their stability for making them feasible for applications such as biomedical or tissue engineering that requires wet environment. Finally, we functionalized the 3D printed cellulose-based aerogels with PEDOT:PSS, and evaluated their performance in piezoresistive sensing applications.

Virus pH-Dependent Interactions with Cationically Modified Cellulose and Their Application in Water Filtration.

Norovirus and Rotavirus are among the pathogens causing a large number of disease outbreaks due to contaminated water. These viruses are nanoscale particles that are difficult to remove by common filtration approaches which are based on physical size exclusion, and require adsorption-based filtration methods. This study reports the pH-responsive interactions of viruses with cationic-modified nanocellulose and demonstrates a filter material that adsorbs nanoscale viruses and can be regenerated by changing the solution's pH. The bacteria viruses Qbeta and MS2, with diameters below 30nm but different surface properties, are used to evaluate the pH-dependency of the interactions and the filtration process. Small angle X-ray scattering, cryogenic transmission electron microscopy, and ζ-potential measurements are used to study the interactions and analyze changes in their nanostructure and surface properties of the virus upon adsorption. The virus removal capacity of the cationic cellulose-based aerogel filter is 99.9% for MS2 and 93.6% for Qbeta, at pH = 7.0; and desorption of mostly intact viruses occurs at pH = 3.0. The results contribute to the fundamental understanding of pH-triggered virus-nanocellulose self-assembly and can guide the design of sustainable and environmentally friendly adsorption-based virus filter materials as well as phage and virus-based materials.

Anisotropic cellulose nanofiber/chitosan aerogel with thermal management and oil absorption properties

Attributed to low cost, renewable, and high availability, cellulose-based aerogels are desirable materials for various applications. However, mechanical robustness and functionalization remain huge challenges. Herein, we synthesized a recoverable, anisotropic cellulose nanofiber (CNF) / chitosan (CS) aerogel via directional freeze casting and chemical cross-link process. The chitosan was performed as strength polymers to prohibits the shrinkage and retains the structural stability of 3D cellulose nanofiber skeleton, endowing the composite aerogel with satisfactory deformation recovery ability (without loss under 60 % stress cycled 100 times). The CNF/CS composite aerogel has ultralow density (∼8.4 mg/cm3), high temperature-invariant (above 300 °C) and high porosity (98 %). The CNF/CS aerogel demonstrates anisotropic thermal insulation properties with low thermal conductivity (28 mWm−1 K−1 in rational direction and 36 mW m−1 K−1 in the axial direction). Moreover, the composite aerogel (water contact angle ∼148°) exhibited outstanding oil/water selectivity and high absorption capacity (82–253 g/g) for various oils and organic solvents. Therefore, the multifunctional CNF/CS composite aerogels are potential materials for thermal management and oil absorption applications.

Nanofibrillated Cellulose-Based Aerogels Functionalized with Tajuva (Maclura tinctoria) Heartwood Extract.

Aerogels are 3-D nanostructures of non-fluid colloidal interconnected porous networks consisting of loosely packed bonded particles that are expanded throughout their volume by gas and exhibit ultra-low density and high specific surface area. Cellulose-based aerogels can be obtained from hydrogels through a drying process, replacing the solvent (water) with air and keeping the pristine three-dimensional arrangement. In this work, hybrid cellulose-based aerogels were produced and their potential for use as dressings was assessed. Nanofibrilated cellulose (NFC) hydrogels were produced by a co-grinding process in a stone micronizer using a kraft cellulosic pulp and a phenolic extract from Maclura tinctoria (Tajuva) heartwood. NFC-based aerogels were produced by freeze followed by lyophilization, in a way that the Tajuva extract acted as a functionalizing agent. The obtained aerogels showed high porosity (ranging from 97% to 99%) and low density (ranging from 0.025 to 0.040 g·cm−3), as well a typical network and sheet-like structure with 100 to 300 μm pores, which yielded compressive strengths ranging from 60 to 340 kPa. The reached antibacterial and antioxidant activities, percentage of inhibitions and water uptakes suggest that the aerogels can be used as fluid absorbers. Additionally, the immobilization of the Tajuva extract indicates the potential for dentistry applications.

Recycling of Pineapple Leaf and Cotton Waste Fibers into Heat-insulating and Flexible Cellulose Aerogel Composites

Pineapple leaf and cotton waste fibers known as abundant by-products in the agriculture and textile industry are combined for the first time to produce thermal insulating and flexible cellulose-based aerogel composites via an environmentally friendly and cost-effective freeze-drying process. The effect of total fiber content and the ratio of pineapple leaf fibers (PF) to cotton waste fibers (CF) on the density, porosity, morphology, durability, and thermal properties of aerogel composites are comprehensively investigated. The as-fabricated aerogel composites show an exceedingly low density of 0.019–0.046 g cm−3 with high porosity of more than 96%. Because of the porous structure inside, our aerogel composites exhibit outstanding heat insulation with extraordinarily low thermal conductivity of 0.039–0.043 W m−1 K−1 that is comparable to commercial insulation materials (mineral wool, fiberglass, polystyrene) and previous cellulose-based aerogels from recycled cellulose fibers, sugarcane bagasse, and rice straw. Interestingly, the combination of those fibers has remarkably improved the flexibility of our previous aerogels from pineapple leaf fibers only, in particular, the compressive modulus of aerogel composites (11.33–44.63 kPa) is 6 times higher than that of PF aerogels (5.73 kPa). The sheet of aerogel composite with a dimension of 28 × 28 cm which is rolled up shows no crack on its surface, demonstrating its excellent mechanical strength. The research results increase the possibility of applying the developed aerogel composites from biomass into practical insulation.

Highly compressible and durable superhydrophobic cellulose aerogels for oil/water emulsion separation with high flux

Nowadays high porosity aerogels are widely applied in wastewater purification, while the fragility and unversatility of nascent cellulose aerogels limited the application in oil/water filtering separation. Here, highly compressible, elastic, superhydrophobic cellulose/poly(vinyl alcohol) (PVA) composite aerogels were fabricated via combination of chemical cross-linking, freeze drying and silanization. The obtained cellulose/PVA aerogels exhibited durable superhydrophobicity with WCA of 156.6 °, even maintaining 155.0 ° after 30 days. Synergistic effects of physical entanglement, chemical cross-linking and H-bond network between cellulose and PVA molecular chains endowed the aerogels with excellent compressibility and recoverability. The aerogels exhibited maximum compressive stress of 490.7 kPa at 90% strain, even without reduction in mechanical strength under 70% compressive strain for 10 cycles. More importantly, the strengthened aerogels exhibited remarkable separation performances for both immiscible oil/water mixtures and surfactant-stabilized water-in-oil emulsions. Fascinating permeation flux of up to 7176.3 L m−2 h−1 and total separation amount as high as 4550.6 L m−2 with separation efficiency of 98.5% for water-in-cyclohexane emulsion were harvested. Thus, this work provides a green, sustainable and mass-producible cellulose-based aerogel for high-efficiency oily wastewater remediation.

Antibacterial cellulose-based aerogels for wound healing application: A review

Aerogels have been steadily developed since its first invention to become one of the most promising materials for various medical and non-medical applications. It has been prepared from organic and inorganic materials, in pure forms or composites. Cellulose-based aerogels are considered one of the promising materials in biomedical applications due to their availability, degradability, biocompatibility and non-cytotoxicity compared to conventional silica or metal-based aerogels. The unique properties of such materials permit their utilization in drug delivery, biosensing, tissue engineering scaffolds, and wound dressing. This review presents a summary of aerogel development as well as the properties and applications of aerogels. Herein, we further discuss the recent works pertaining to utilization of cellulose-based aerogels for antibacterial delivery.

Investigation of Cellulose-Based Aerogels for Oil Spill Removal

Oil pollution caused by heavy shipping traffic in the Baltic Sea could be removed by the help of highly porous aerogels made from the waste. These could be produced from environmentally friendly cellulose, e.g., from paper waste, but would have to be hydrophobized for oil sorption. Such a cellulose aerogel was investigated in this research work. Six types of aerogel with 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 wt% cellulose with porosities in the range of 96–98% stabilized by unsaturated polyester as cross-linker have been produced. Aerogel’s sorption capacity as well as its regeneration for sorption of crude oil, marine diesel oil, and biodiesel sorption from water surface and mechanical strength has been estimated. It was found out that crude oil sorption capacity reach 29.67 ± 0.39 g g−1, biodiesel—29.07 ± 0.26 g g−1, while marine diesel oil—26.26 ± 0.39 g g−1. The aerogel with 0.5 wt% cellulose shows the best sorption properties after 10 cycles of the sorption.

Cellulose II Aerogel-Based Triboelectric Nanogenerator.

Cellulose-based triboelectric nanogenerators (TENGs) have gained increasing attention. In this study, a novel method is demonstrated to synthesize cellulose-based aerogels and such aerogels are used to fabricate TENGs that can serve as mechanical energy harvesters and self-powered sensors. The cellulose II aerogel is fabricated via a dissolution-regeneration process in a green inorganic molten salt hydrate solvent (lithium bromide trihydrate), where. The as-fabricated cellulose II aerogel exhibits an interconnected open-pore 3D network structure, higher degree of flexibility, high porosity, and a high surface area of 221.3 m2 g-1. Given its architectural merits, the cellulose II aerogel-based TENG presents an excellent mechanical response sensitivity and high electrical output performance. By blending with other natural polysaccharides, i.e., chitosan and alginic acid, electron-donating and electron-withdrawing groups are introduced into the composite cellulose II aerogels, which significantly improves the triboelectric performance of the TENG. The cellulose II aerogel-based TENG is demonstrated to light up light-emitting diodes, charge commercial capacitors, power a calculator, and monitor human motions. This study demonstrates the facile fabrication of cellulose II aerogel and its application in TENG, which leads to a high-performance and eco-friendly energy harvesting and self-powered system.

Facile and novel ambient pressure drying approach to synthesis and physical characterization of cellulose-based aerogels

In this study, highly porous and ultralight cellulose aerogel (CA) was successfully synthesized via a novel and facile ambient pressure drying technique. In this drying method, naphthalene (NPH) as the porous-making agent occupied space between cellulose fibers and controlled structural collapse and severe shrinkage of samples successfully. By sublimation of NPH crystals at the end of procedure, ultimate CA was obtained. This technique can be considered as a fast, safe and cost-effective drying method. CA samples illustrated appropriate physical characteristics including: low densities (0.058 g cm−3), high porosity (> 96.5%), low thermal conductivity (0.0417 W m−1 K−1), appropriate mechanical strength and negligible shrinkage (< 10%) during the drying procedure. hydrophobic cellulose aerogel (HCA) and carbonized cellulose aerogel (CCA) were also obtained and the oil/water separation efficiency of these samples were investigated. Contact angle test reveled highly hydrophobicity with angle equal to 137° and 126° for HCA and CCA, respectively. Investigation of oils and organic solvents adsorption capacity illustrated that samples adsorbed oils and organic solvents in range from 1200 to 1800% of their weight. Regeneration ability of HCA and CCA was studied in five cycles. Depending on type of adsorbate, regeneration study showed various regeneration capacity from 30 to 98%.

Kinetic, isotherm, and thermodynamic studies of the adsorption of dye from aqueous solution by propylene glycol adipate-modified cellulose aerogel

Cellulose-based aerogel is widely concerned as a new type of adsorption material. However, due to its low mechanical strength and small adsorption capacity in practical applications, it is necessary to enhance its mechanical strength through certain means. In this study, poly(propylene glycol adipate) (PPA)-modified cellulose aerogel materials were prepared with direct mixing method, and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results suggested that the modified cellulose aerogel (PCA) had a more stable network structure and more uniform pore size. The adsorption ability of the aerogel was measured by Congo red (CR), an azo dye, as an adsorbate. Analysis of the adsorption amounts, kinetics and thermodynamics towards Congo Red further confirmed the CR removal capacity of PCA, which can reach 120 mg g-1. According to the research results, the use of PPA as a modifier can effectively improve the mechanical strength of cellulose aerogel and has great potential in the treatment of printing and dyeing wastewater.

Top-Down Approach Making Anisotropic Cellulose Aerogels as Universal Substrates for Multifunctionalization.

Highly porous, strong aerogels with anisotropic structural properties are of great interest for multifunctional materials for applications including insulators in buildings, filters for oil cleanup, electrical storage devices, etc. Contemporary aerogels are mostly extracted from fossil resources and synthesized from bottom-up techniques, often requiring additional strategies to obtain high anisotropy. In this work, a universal approach to prepare porous, strong, anisotropic aerogels is presented through exploiting the natural hierarchical and anisotropic structure of wood. The preparation comprises nanoscale removal of lignin, followed by dissolution–regeneration of nanofibers, leading to enhanced cell wall porosity with nanofibrillated networks occupying the pore space in the cellular wood structure. The aerogels retain structural anisotropy of natural wood, exhibit specific surface areas up to 247 m2/g, and show high compression strength at 95% porosity. This is a record specific area value for wood aerogels/foams and even higher than most cellulose-based aerogels for its assigned strength. The aerogel can serve as a platform for multifunctional composites including scaffolds for catalysis, gas separation, or liquid purification due to its porous matrix or as binder-free electrodes in electronics. To demonstrate the multifunctionality, the aerogels are successfully decorated with metal nanoparticles (Ag) and metal oxide nanoparticles (TiO2) by in situ synthesis, coated by the conductive polymer (PEDOT:PSS), and carbonized to yield conductive aerogels. This approach is found to be a universal way to prepare highly porous anisotropic aerogels.

High loading cotton cellulose-based aerogel self-standing electrode for Li-S batteries

Lithium-sulfur (Li-S) batteries have attracted considerable attention due to their high energy density (2600 Wh kg−1). However, its commercialization is hindered seriously by the low loading and utilization rate of sulfur cathodes. Herein, we designed the cellulose-based graphene carbon composite aerogel (CCA) self-standing electrode to enhance the performance of Li-S batteries. The CCA contributes to the mass loading and utilization efficiency of sulfur, because of its unique physical structure: low density (0.018 g cm−3), large specific surface area (657.85 m2 g−1), high porosity (96%), and remarkable electrolyte adsorption (42.25 times). Compared to Al (about 49%), the CCA displayed excellent sulfur use efficiency (86%) and could reach to high area capacity of 8.60 mAh cm−2 with 9.11 mg S loading. Meanwhile, the CCA exhibits the excellent potential for pulse sensing applications due to its flexibility and superior sensitivity to electrical response signals.