High-strength and morphology-controlled aerogel based on carboxymethyl cellulose and graphene oxide

Mechanically Strengthened Aerogels through Multiscale, Multicompositional, and Multidimensional Approaches: A Review

In recent decades, aerogels have attracted tremendous attention in academia and industry as a class of lightweight and porous multifunctional nanomaterial. Despite their wide application range, the low mechanical durability hinders their processing and handling, particularly in applications requiring complex physical structures. "Mechanically strengthened aerogels" have emerged as a potential solution to address this drawback. Since the first report on aerogels in 1931, various modified synthesis processes have been introduced in the last few decades to enhance the aerogel mechanical strength, further advancing their multifunctional scope. This review summarizes the state-of-the-art developments of mechanically strengthened aerogels through multicompositional and multidimensional approaches. Furthermore, new trends and future directions for as prevailed commercialization of aerogels as plastic materials are discussed.

Cellulose/GO monolith covered with Pd-Pt bimetallic nanocrystals for continuous-flow catalytic reduction of hexavalent chromium

Cellulose monolith materials have interconnected open porous structures with very high porosity, making them attractive structures for use as support materials in heterogeneous catalysis applications. In this study, we developed a highly efficient and reusable continuous-flow reactor for Cr(VI) remediation by combining the advantageous features of cellulose monoliths with suitable reinforcement techniques. We fabricated a porous monolithic cellulose/graphene oxide (GO) composite with a continuous three-dimensional skeletal framework using the thermally induced phase separation technique. Pd nanocrystals were synthesized in situ on the surface of the composite monolith, and then converted to porous Pd-Pt bimetallic nanocrystals through a galvanic replacement reaction. This approach eliminated the need for additional reductants and stabilizers, making the process simpler and more environmentally friendly. Under carefully optimized conditions, the cellulose/GO/Pd-Pt nanocomposite monolith exhibited outstanding performance in continuous-flow reactions for Cr(VI) reduction, achieving a maximum conversion rate of 98 %. Moreover, the nanocomposite monolith-based heterogeneous catalyst exhibited remarkable long-term stability, maintaining its catalytic activity even after extended periods of storage in the dried state. These findings highlight the potential of cellulose-based composite monoliths as versatile and robust support materials for heterogeneous catalysis.

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.

Nanocellulose-graphene composites: Preparation and applications in flexible electronics

In recent years, the pursuit of high-performance nano-flexible electronic composites has led researchers to focus on nanocellulose-graphene composites. Nanocellulose has garnered widespread interest due to its exceptional properties and unique structure, such as renewability, biodegradability, and biocompatibility. However, nanocellulose materials are deficient in electrical conductivity, which limits their applications in flexible electronics. On the other hand, graphene boasts remarkable properties, including a high specific surface area, robust mechanical strength, and high electrical conductivity, making it a promising carbon-based nanomaterial. Consequently, research efforts have intensified in exploring the preparation of graphene-nanocellulose flexible electronic composites. Although there have been studies on the application of nanocellulose and graphene, there is still a lack of comprehensive information on the application of nanocellulose/graphene in flexible electronic composites. This review examines the recent developments in nanocellulose/graphene flexible electronic composites and their applications. In this review, the preparation of nanocellulose/graphene flexible electronic composites from three aspects: composite films, aerogels, and hydrogels are first introduced. Next, the recent applications of nanocellulose/graphene flexible electronic composites were summarized including sensors, supercapacitors, and electromagnetic shielding. Finally, the challenges and future directions in this emerging field was discussed.

MXene/Graphene modified cellulose aerogel for photo-electro-assisted all-weather cleanup of high-viscous crude oil from spill

The frequent occurrence of oil spills has led to serious environmental pollution and ecological issues. Given the high-viscosity of crude oil, it is essential to develop sorbents with efficient viscosity reduction and sorption capacity in various environmental conditions. Herein, a superhydrophobic carboxymethyl cellulose (CMC) aerogel co-modified by MXene and graphene jointly (M-Mxene/Gr CA) with aligned channels structure was prepared. The aligned channels structure can effectively improve the longitudinal thermal conductivity and reduce the sorption resistance. Through the modification of MXene and graphene, the aerogel realized efficient photo/electro-thermal conversion, thus ensuring its adaption to various working environments. The rapid heat generation can significantly reduce the viscosity of crude oil, achieving rapid recovery. Under one sun illumination (1.0 kW/m2), the surface temperature of M-Mxene/Gr CA can reach 72.6 °C and its sorption capability for high-viscous crude oil reaches 18 g/g. Combining photo-thermal and electro-thermal (0.5 kW/m2 and 23 V), the average sorption rate of crude oil can reach 1.3 × 107 g m-3 s-1. Finally, we present a continuous sorption system to recover offshore oil spills under the assistance of a pump. This work provides a new option for tackling high-viscous offshore oil spills due to its environmental friendliness and fast sorption capacity.

"Rigid-Flexible" Anisotropic Biomass-Derived Aerogels with Superior Mechanical Properties for Oil Recovery and Thermal Insulation

Aerogels with low density, high mechanical strength, and excellent elasticity have a wide potential for applications in wastewater treatment, thermal management, and sensors. However, the fabrication of such aerogels from biomass materials required complex preparation processes. Herein, a sustainable and facile strategy was reported to construct lignin/cellulose aerogels (LCMA) with three-dimensional interconnected structures by introducing homologous lignin with a polyphenyl propane structure as a structural enhancer through a top-down directional freezing approach, prompting a 2036% enhancement in compressive modulus and an 8-12-fold increase in oil absorption capacity. In addition, the hydrophobic aerogels with superelasticity were achieved by combining the aligned polygon-like structure and flexible silane chains, which exhibited remarkable compressional fatigue resistance and superhydrophobicity (WCA = 168°). Attributed to its unique pore design and surface morphology control, the prepared aerogel exhibited excellent performance in immiscible oil-water separation and water-in-oil emulsion separation. Due to the ultra-low density (8.3 mg·cm-3) as well as high porosity (98.87%), the obtained aerogel showed a low thermal conductivity (0.02565 ± 0.0024 W·m-1·K-1), demonstrating a potential in insulation applications. The synthetic strategy and sustainability concept presented in this work could provide guidance for the preparation of advanced biomass-based aerogels with unique properties for a wide range of applications.

Improving the comprehensive properties of chitosan-based thermal insulation aerogels by introducing a biobased epoxy thermoset to form an anisotropic honeycomb-layered structure

Naturally-derived aerogels have attracted considerable attention owing to their good biocompatibility, biodegradability and sustainability, but their weak mechanical properties largely limit their applications in various fields. Herein, we proposed the use of a directional freeze-drying method to prepare an anisotropic honeycomb three-dimensional porous aerogel with water-soluble chitosan (CS) as a rigid skeleton and water-soluble biobased epoxy resin as cross-linked hard segments, which had low volume shrinkage and density of 13.9 % and 34.3 mg/cm3, respectively. The resultant aerogel had anisotropic mechanical properties, such as rigidity in the axial direction with a maximum axial modulus of 6.71 MPa, which was 51.6 times larger than that of the pure chitosan aerogel, demonstrating a good compressive elasticity in the radial direction. It also had anisotropic thermal management properties, with a lower thermal conductivity in the radial direction than in the axial direction, down to 0.029 W/mK. The introduction of biobased epoxy resin improved the overall thermal stability, flame retardancy, and increased the biomass content in the aerogel, reducing the carbon footprint of the material. This study paves the way for the construction of a special graded porous, structurally and functionally integrated thermal insulation aerogel, which is of great significance for the development of new thermal insulation materials.

Multifunctional microwave absorption materials of multiscale cobalt sulfide/diatoms co-doped carbon aerogel

Microwave absorption materials (MAMs) have attracted much attention for their potential applications in stealth technology and prevention of electromagnetic pollution problems. Multifunctional MAMs are highly demanded because they can be applied in harsh environments. Hence, based on multiscale manipulation of atomic engineering, nanostructure and microstructure, a multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel was preparedthrough the physical crosslinking of divalent ions, unidirectional freezing, kirkendall effect, and heteroatomic doping. The aerogel with a low density of 13.1 mg/mm³ has a unique "lamellar-pillar" network structure due to the growth of ice crystals during the preparation process. With the assistance of thiourea, the doping of N, S atoms and the construction of hollow cobalt sulfide are accomplished simultaneously. The ingenious integration facilitates the synergistic effect of conductive loss, defect polarization, interfacial polarization, and multiple scattering. The multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel had a maximum reflection loss of -51.96 dB and an effective absorption bandwidth of 6.4 GHz, which is higher than that of other reported MAMs. It is further verified through finite element simulation and experiments that the aerogel has an excellent microwave absorption properties. In addition, the aerogel has excellent thermal insulation and flame retardant properties. Therefore, the development of this aerogel can help to use MAMs in complex applications.

Aramid nanofibers supported metal-organic framework aerogel for protection of chemical warfare agent

Protective fabrics containing Zr-Based Metal-Organic Frameworks (Zr-MOFs) show great potential in the detoxification of chemical warfare agents (CWAs). However, the current studies still face the challenges of complicated fabrication processes, limited MOF loading mass, and insufficient protection. Herein, we developed a lightweight, flexible and mechanical robust aerogel by in situ growth of UiO-66-NH₂ onto aramid nanofibers (ANFs) and assembly of UiO-66-NH₂ loaded ANFs (UiO-66-NH₂@ANFs) into 3D hierarchically porous architecture. The UiO-66-NH₂@ANF aerogels feature high MOF loading of 261 %, high surface area of 589.349 m² g^-1, open and interconnected cellular structure, which provide efficient transfer channels and promote catalytic degradation of CWAs. As a result, the UiO-66-NH₂@ANF aerogels demonstrate high 2-chloroethyl ethyl thioether (CEES) removal rate at 98.9 % and a short half-life of 8.15 min. Moreover, the aerogels present good mechanical stability (recovery rate of 93.3 % after 100 cycles under 30 % strain), low thermal conductivity (λ of 25.66 mW m^-1 K^-1), high flame resistance (LOI of 32 %) and good wearing comfortableness, indicating promising potential in multifunctional protection against CWAs.

Ambient Pressure Drying to Construct Cellulose Acetate/Benzoxazine Hybrid Aerogels with Flame Retardancy, Excellent Thermal Stability, and Superior Mechanical Strength Resistance to Cryogenic Temperature

Cellulose aerogels are highly attractive candidates in various applications, such as thermal insulation, adsorption separation, biomedical field, and as carriers, due to their intrinsic merits of low density, high porosity, biodegradability, and renewability. However, the expensive cost of the supercritical drying process and poor mechanical properties limit their practical applications. Herein, a new method was presented to fabricate cellulose acetate/benzoxazine hybrid aerogels (CBAs) with low cost, low drying shrinkage, excellent mechanical properties under cryogenic condition (-196 °C), outstanding thermal insulation, flame retardancy, and good thermal stability by ambient pressure drying. In more detail, the weighted drying shrinkage rate of CBAs-T2 can be controlled to 6.8% (the average value along the radial and axial directions), mainly due to the enhanced skeleton, by introducing polybenzoxazine networking chains. The resultant CBAs-T2 exhibit outstanding mechanical properties at room temperature because of the presence of the polybenzoxazine hybrid in the cellulose networking system. CBAs-T2 still have good mechanical properties even after subjecting them to liquid nitrogen treatment. In addition, the optimal value of thermal conductivity (0.033 W m^-1 K^-1) is gained easily because of the uniform cross-linking networking structure and small pore size. A superior flame retardance of CBAs-T2 is endowed to achieve self-extinguishment after ignition, which is attributed to the presence of the aromatic ring in the backbone structure. Moreover, the good thermal stability of CBAs-T2 is attributed to the fact that polybenzoxazine components could resist the decomposition of cellulose acetate and inhibit heat release during the combustion process. Our study would provide a novel method for obtaining biomass aerogels including the cellulose-based materials system with low drying shrinkage and superior mechanical properties despite bearing a cryogenic environment by the low-cost ambient pressure drying approach.

Graphene oxide modified with carboxymethyl cellulose for high adsorption capacities towards Nd(III) and Ce(III) from aqueous solutions

This work addresses a simple method to functionalize graphene oxide with sodium carboxymethyl cellulose using tetraethyl orthosilicate as a linker for rapid and significant removal of Nd(III) and Ce(III) from aqueous solutions. The prepared composite (GO–CMC) was characterized by different techniques to confirm the modification and adsorption process. The sorption performance of the GO–CMC was evaluated using Nd(III) and Ce(III) as absorbent materials. The experimental results demonstrated that the sorption process was excellently fitted by the pseudo-second-order kinetic model. The adsorption results were also analyzed by different isotherm models. According to the Langmuir isotherm model, the experimental sorption capacities at pH 3.0 was 661.21 and 436.55 mg/g for Nd(III) and Ce(III), respectively. The thermodynamic results indicated that the sorption process of the two examined metal ions was endothermic and spontaneous. The regenerated GO–CMC composite has a similar removal percentage to the original composite. These results confirmed that the prepared composite (GO–CMC) could be used as an effective adsorbent for Nd(III) and Ce(III) from certain multielement solutions.

Fabrication and mechanical properties of different types of carbon fiber reinforced polyetheretherketone: A comparative study

OBJECTIVES

To find alternative non-metallic materials as dental implants for clinical application, different types of carbon fiber reinforced polyetheretherketone were fabricated and investigated.

METHODS

Continuous carbon fiber reinforced polyetheretherketone fabrics were fabricated with polyetheretherketone fibers and carbon fibers. Different kinds of carbon fiber reinforced polyetheretherketone were synthesized by setting specific experiment parameters of injection or hot press molding. Various mechanical tests were performed to determine the mechanical properties of different carbon fiber reinforced polyetheretherketone, pure polyetheretherketone and pure titanium.

RESULTS

Polyetheretherketone composites presented outstanding mechanical and thermal properties after incorporating carbon fiber. The bending and tensile strength of short carbon fiber reinforced polyetheretherketone were close to human bone, and the bending strength of continuous carbon fiber reinforced polyetheretherketone reached 644 MPa, even higher than that of pure titanium.

CONCLUSIONS

The mechanical properties of polyetheretherketone composites are more similar to bone tissue than titanium, and the stress shielding phenomenon may be inhibited. They may become promising materials as substitutions for titanium and prospective materials in bone tissue engineering.

Mechanically durable green aerogel composite based on agricultural lignocellulosic residue for organic liquids/oil sorption

Various oil spill cleanup sorbents have good hydrophobicity and oil separation efficiency, but their practical use has been limited due to the difficult and costly fabrication procedure. The research aims towards material development using the consumption of lignocellulosic agricultural residue for isolating cellulose nanofiber and its forward use to construct a 3D porous structure. A simple freeze-drying technique was used to assemble low-density porous structure. The biodegradable polylactic acid coating was used to alter the wettability from hydrophilic to hydrophobic and the maximum water contact angle value was around 120°. The prepared coated samples were testified for a series of oil/organic solvents-water mixtures. The sorption capacity was in the range of 28-70 g/g. The prepared aerogels were efficiently reused for at least 10 cycles. Developed material was used in continuous oil-water separation to remove oil from the water's surface. The cost analysis was estimated for scaleup production in the future.

Proton Donor-Regulated Mechanically Robust Aramid Nanofiber Aerogel Membranes for High-Temperature Thermal Insulation

High-performance thermal insulators are urgently desired for energy-saving and thermal protection applications. However, the creation of such materials with synchronously ultralow thermal conductivity, lightweight, and mechanically robust properties still faces enormous challenges. Herein, a proton donor-regulated assembly strategy is presented to construct asymmetric aramid nanofiber (ANF) aerogel membranes with a dense skin layer and a high-porous nanofibrous body part. The asymmetric structure originates from the otherness of the structural restoration of deprotonated ANFs and the resulting ANF assembly due to the diversity of available proton concentrations. Befitting from the synergistic effect of the distinct architectures, the resulting aerogel membranes exhibit excellent overall performance in terms of a low thermal conductivity of 0.031 W·m^-1·K^-1, a low density of 19.2 mg·cm^-3, a high porosity of 99.53%, a high tensile strength of 11.8 MPa (16.5 times enhanced), high heat resistance (>500 °C), and high flame retardancy. Furthermore, a blade-scraping process is further proposed to fabricate the aerogel membrane in a continuous and scalable manner, as it is believed to have potential applications in civil and military fields.

Preparation of carboxymethyl cellulose/graphene composite aerogel beads and their adsorption for methylene blue

Carboxymethyl cellulose/ graphene composite aerogel beads (CMC/GAs) were prepared by the easily scaling-up method, i.e., wet spinning- environmental pressure drying method. The influences of the type and concentration of coagulating bath on the formation of aerogel beads were discussed, and the forming mechanism was analyzed. The CMC/GAs was characterized through SEM, XRD, FI-IR, Raman, XPS, electronic universal testing machine and other methods. The CMC/GAs-30 has an average particle size and a mean pore diameter of 3.83 mm and 82 μm, respectively. The analysis results indicated that the adsorption mechanisms of CMC/GAs on methylene blue (MB) are mainly through the electrostatic interaction. The adsorption process conforms to the Langmuir model (R² = 0.9964) and pseudo-second-order kinetic model (R² is higher than 0.99). When the particle size of CMC/GAs-30 decreases, the equilibrium adsorption capacity for MB increases. Under the experimental conditions explored, the Langmuir maximum adsorption capacity of CMC/GAs-30 for MB is 222.72 mg.g^-1. The CMC/GAs-30 show good recycle performance in MB adsorption. The removal rate of MB from water by CMC/GAs-30 remained at about 90% after 30-times adsorption- regeneration cycles.

A pulp foam with highly improved physical strength, fire-resistance and antibiosis by incorporation of chitosan and CPAM

Bio-inspired borate cross-linked pulp foam (PF) with high porosity and low density can be widely used in many fields. However, PF is flammable, and lack of mechanical strength and antibacterial activity. To solve these issues, an ultra-strong PF was prepared by incorporation of chitosan and cationic polyacrylamide (CPAM). Results showed that the obtained PF exhibited highly improved mechanical properties (the compressive strength (485 kPa at a strain of 50%) was over 6 times higher compared with the borate cross-linked PF without chitosan and CPAM, and it was even higher than most of the reported cellulose-based porous materials). Also, the prepared PF has good performance on fire-retardance (hard to light), thermal insulation, antibiosis and sound absorption, due to the synergistic actions of borate, chitosan and CPAM. Additionally, spent liquor in preparing PF could be fully recycled, and thus this sustainable approach has potential for large-scale production of high-performance PF.

Fruit waste-derived cellulose and graphene-based aerogels: Plausible adsorption pathways for fast and efficient removal of organic dyes

A wide range of organic pollutants in industrial effluents, agricultural runoff, and domestic discharges are exacerbating water scarcity, leading to water-borne ailments, and adversely affecting the marine ecosystem and biodiversity. The efficient, sustainable, and cost-effective materials need to be addressed urgently for the removal of organic pollutants. Herein, ultra-light (0.018 g.cm^-3) and highly porous (96.4%) composite aerogel is prepared by gelatinization of graphene oxide with fruit waste-derived cellulose. The macroscopic porosity generated by interconnecting cellulosic skeleton and graphene oxide sheets via hydrogen bonding network provided ample avenues for transport and diffusion of organic dyes-enriched wastewater throughout the cellulose-graphene oxide composite aerogel (CGA). Consequently, organic dyes are efficiently adsorbed by easily accessible surface sites distributed throughout the CGA. The size, charge, and chemical structure of organic dyes along with textural features and accessible surface active sites of CGA governed the adsorption process. The spectroscopic analyses based on FTIR, Raman, and XPS measurements suggest electrostatic, n-π, π-π, cation-π interactions, dipole-dipole hydrogen, and Yoshida hydrogen linkages as major interactive pathways for the adsorption of organic dyes by the CGA. Moreover, the composite aerogel furnished an excellent recyclability for the adsorptive removal of organic pollutants from wastewater. The present work promises the potential of 2D nanostructured layered materials and fruit-waste-derived composite aerogels for sustainable utilization in wastewater treatment, which can be an excellent step towards water security.

Fabrication, Structure, Performance, and Application of Graphene-Based Composite Aerogel

Graphene-based composite aerogel (GCA) refers to a solid porous substance formed by graphene or its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), with inorganic materials and polymers. Because GCA has super-high adsorption, separation, electrical properties, and sensitivity, it has great potential for application in super-strong adsorption and separation materials, long-life fast-charging batteries, and flexible sensing materials. GCA has become a research hotspot, and many research papers and achievements have emerged in recent years. Therefore, the fabrication, structure, performance, and application prospects of GCA are summarized and discussed in this review. Meanwhile, the existing problems and development trends of GCA are also introduced so that more will know about it and be interested in researching it.

Preparation and Characterization of Nanocellulose/Chitosan Aerogel Scaffolds Using Chemical-Free Approach

Biopolymer-based aerogels are open three-dimensional porous materials that are characterized by outstanding properties, such as a low density, high porosity and high surface area, in addition to their biocompatibility and non-cytotoxicity. Here we fabricated pure and binary blended aerogels from cellulose nanofibers (CNFs) and chitosan (CS), using a chemical-free approach that consists of high-pressure homogenization and freeze-drying. The prepared aerogels showed a different porosity and density, depending on the material and mixing ratio. The porosity and density of the aerogels ranged from 99.1 to 90.8% and from 0.0081 to 0.141 g/cm³, respectively. Pure CNFs aerogel had the highest porosity and lightest density, but it showed poor mechanical properties and a high water absorption capacity. Mixing CS with CNFs significantly enhance the mechanical properties and reduce its water uptake. The two investigated ratios of aerogel blends had superior mechanical and thermal properties over the single-material aerogels, in addition to reduced water uptake and 2-log antibacterial activity. This green fabrication and chemical-free approach could have great potential in the preparation of biopolymeric scaffolds for different biomedical applications, such as tissue-engineering scaffolds.

Cellulose-Based Hybrid Aerogels: Strategies toward Design and Functionality

The brittle nature of early aerogels developed from inorganic precursors fueled the discovery of their organic counterparts. Prominent among these organics are cellulose aerogels because of their natural abundance, biocompatibility, sustainable precursors, and tunable properties. The hierarchical structure of cellulose, from polymers to nano/microfibers, further facilitates fabrication of materials across multiple length scales with added applicability. However, the inherent flammability, structural fragility, and low thermal stability have limited their use. Recently developed cellulose-based hybrid aerogels offer strong potential owing to their tunability and enhanced functionality brought about by combining the inherent properties of cellulose with organic and inorganic components. A survey of the historical background and scientific achievements in the design and development of cellulose-based hybrid aerogel materials is encompassed here. The impacts of incorporating organic and inorganic ingredients with cellulose and the corresponding synergistic effects are discussed in terms of their design and functionality. The underlying principles governing the structural integration and functionality enhancement are also analyzed. The latest developments of cellulose-based hybrid aerogels fabricated from nontraditional incipient aerogels, such as fibrous webs, are also explored. Finally, future opportunities that could make these materials achieve even greater impacts through improved scalability, rationally designed synthesis, and multifunctional properties are discussed.

In situ nanoarchitectonics of magnesium hydroxide particles for property regulation of carboxymethyl cellulose/poly(vinyl alcohol) aerogels

Carboxymethyl cellulose (CMC)-based aerogels with low density, low thermal conductivity, and biodegradability are promising candidates for environmentally friendly heat-insulating materials. However, the application of CMC-based aerogels as insulation materials in building exterior walls is limited by the high water sensitivity, poor mechanical properties and high flammability of these aerogels. In this work, a simple hydration method was used to generate magnesium hydroxide (MH) directly from CMC/polyvinyl alcohol (PVA) mixed sol with active MgO obtained by calcined magnesite as the raw material. A series of composite aerogels with different MH contents were prepared through the freeze-drying method. Scanning electron microscopy showed that nanoflower-like MH was successfully synthesised in situ in the 3D porous polymer aerogel matrix. Compared with the mechanical properties and water resistance of the original CMC/PVA composite aerogels, those of the composite aerogels were significantly improved. In addition, the flame retardancy of the CMC/PVA composite aerogels was greatly enhanced by the introduction of MH into the polymer matrix, and the limiting oxygen index reached 35.5% when the MH loading was 60%.

Flame retardant efficiency of magnesium hydroxide in cellulose aerogels improved by in situ formation.

Elastic Recovery Properties of Ultralight Carbon Nanotube/Carboxymethyl Cellulose Composites

Ultralight materials exhibit superelastic behavior depending on the selection, blending, and carbonization of the materials. Recently, ultimate low-density materials of 5 mg/cm³ or less have attracted attention for applications such as sensors, electrodes, and absorbing materials. In this study, we fabricated an ultralight material composed of single-walled carbon nanotubes (CNT) and sodium carboxymethyl cellulose (CMC), and we investigated the effect of density, composition, and weight average molecular weight of CMC on elastic recovery properties of ultralight CNT/CMC composites. Our results showed that the elastic recovery properties can be improved by reducing the density of the composite, lowering the mass ratio of CNTs, and using CMC with small molecular weight.

Fabrication of Reusable Carboxymethyl Cellulose/Graphene Oxide Composite Aerogel with Large Surface Area for Adsorption of Methylene Blue

A highly efficient adsorbent for methylene blue (MB) adsorption was developed by combination of carboxymethyl cellulose (CMC) and graphene oxide (GO) via a simple one-step hydrothermal method. The as-synthesized CMC/GO composite aerogel has a mesoporous structure with an average pore diameter of 30 nm and a high specific surface area of 800.85 m²·g⁻¹. Moreover, the CMC/GO composite aerogel demonstrates a significant selectivity for the dye adsorption, especially for MB, where its adsorption capacity can reach 244.99 mg·g⁻¹ with an excellent recyclability for more than nine times. Thus, the prepared CMC/GO composite aerogel would be an effective adsorbent for dyes adsorption, owing to the merits of high efficiency, reusability, and eco-friendliness.

Polysaccharide-based aerogels for thermal insulation and superinsulation: An overview

To reduce energy losses due to the insufficient thermal insulation is one of the current "hot" topics. Various commercial porous materials are used with the best conductivity around 0.03-0.04 W/(m·K). Aerogels are the only known materials with "intrinsic" thermal superinsulating properties, i.e. with thermal conductivity below that of air in ambient conditions (0.025 W/(m·K)). The classical thermal superinsulating aerogels are based on silica and some synthetic polymers, with conductivity 0.014-0.018 W/(m·K). Aerogels based on natural polymers are new materials created at the beginning of the 21st century. Can bio-aerogels possess thermal superinsulating properties? What are the bottlenecks in the development of bio-aerogels as new high-performance thermal insulationing materials? We try to answer these questions by analyzing thermal conductivity of bio-aerogels reported in literature.

Performance of the highly sensitive humidity sensor constructed with nanofibrillated cellulose/graphene oxide/polydimethylsiloxane aerogel via freeze drying

A kind of capacitive humidity sensor with high sensitivity constructed with nanofibrillated cellulose (NFC), graphene oxide (GO) and polydimethylsiloxane (PDMS) is presented in this work, via a simple ultrasonic dispersion and freeze drying technology. The NFC and GO with a strong adsorption for water molecules were used as a substrate for the promotion of capacitive response of the humidity sensor. Moreover, anhydrous ethanol was added to inhibit the generation of big cracks in the humidity sensor in the freeze drying process, so as to obtain a regular network porous structure, then providing a great deal of conduction channels and active sites for molecular water. Also, the addition of PDMS can effectively enhance the flexibility and stability of its porous structure. The results confirmed that the humidity sensor with 30 wt% GO showed an excellent humidity sensitivity (6576.41 pF/% RH), remarkable reproducibility, low humidity hysteresis characteristic in 11-97% relative humidity (RH) at 25 °C, and short response/recovery times (57 s/2 s). In addition, the presented sensor exhibited small relative deviation of the measured relative humidity value compared with the commercial hygrometer. The realization of the high sensitivity can be attributed to the theories about interaction of the hydrophilic group, proton transfer of water molecules and the three-dimensional network transport structure model. Therefore, the NFC/GO/PDMS humidity sensor finally realizes stable, reproducible and fast humidity sensing via an eco-friendly process, exhibiting promising potential for wide practical application.

Directionally-Grown Carboxymethyl Cellulose/Reduced Graphene Oxide Aerogel with Excellent Structure Stability and Adsorption Capacity

A novel three-dimensional carboxymethyl cellulose (CMC)/reduced graphene oxide (rGO) composite aerogel crosslinked by poly (methyl vinyl ether-co-maleic acid)/poly (ethylene glycol) system via a directional freezing technique exhibits high structure stability while simultaneously maintaining its excellent adsorption capacity to remove organic dyes from liquid. A series of crosslinked aerogels with different amounts of GO were investigated for their adsorption capacity of methylene blue (MB), which were found to be superb adsorbents, and the maximum adsorption capacity reached 520.67 mg/g with the incorporation of rGO. The adsorption kinetics and isotherm studies revealed that the adsorption process followed the pseudo-second-order model and the Langmuir adsorption model, and the adsorption was a spontaneous process. Furthermore, the crosslinked aerogel can be easily recycled after washing with dilute HCl solution, which could retain over 97% of the adsorption capacity after recycling five times. These excellent properties endow the crosslinked CMC/rGO aerogel’s potential in wastewater treatment and environment protection.

Aerogel doped by sulfur-functionalized graphene oxide with convenient separability for efficient patulin removal from apple juice

Patulin (PAT) contaminant causes severe food safety issue throughout apple industry. Although adsorption is the feasible approach to remove PAT, the limited adsorption capacity and separation difficulty of most adsorbent is the major drawback that remains to be overcome. Here GO-SH doped aerogel was prepared and used for removal PAT from apple juice. The intrinsic porous of the aerogel and abundant active sites including -COOH, -NH₂ and -SH offered the PAT adsorption capacity of 24.75 μg/mg that superior to most reported adsorbents. Furthermore, it could reduce 89 ± 1.23% PAT in real apple juice without juice quality deterioration and cytotoxicity. Importantly, the aerogel with good mechanical strength and structure stability could endure the complex juice solution so that there was no any residue after convenient separation of the aerogel, which proved that the proposed aerogel was a promising adsorbent to be applied to apple juice industry for PAT removal.

Electrospinning Nanofiber-Reinforced Aerogels for the Treatment of Bone Defects

Objective: Application of aerogels in bone tissue engineering is an emerging field, while the reports of electrospinning nanofiber-reinforced aerogels are limited. This research aimed at fabricating the nanofiber-reinforced aerogels and evaluating their physiochemical and biological properties. Approach: The chitosan (CS) aerogels incorporated with cellulose acetate (CA) and poly (ɛ-caprolactone) (PCL) nanofibers were fabricated via ball milling and freeze-drying techniques. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrum, X-ray photoelectron spectroscopy (XPS), compressive experiment, and in vitro experiment were conducted to assess their physiochemical properties and biological behavior. Results: The SEM examination showed that satisfying morphology was attained in the CA/PCL/CS aerogels with incorporation of CA/PCL nanofibers and CS solution. The results of FT-IR and XPS indicated the perfect incorporation of CA, PCL, and CS. A compressive experiment confirmed that the CA/PCL/CS aerogels enhanced the compressive modulus of the pure CS aerogel. For in vitro experiment, the CA/PCL/CS composite scaffolds were proven to possess better cytocompatibility compared with the pure CS. Also, cells on the CA/PCL/CS showed well-extended morphology and could infiltrate into a porous scaffold. Furthermore, confocal experiment revealed that the CA/PCL/CS could also promote the osteogenic differentiation of MC3T3-E1 cells. Innovation: This study fabricated the nanofiber-reinforced aerogels mainly to optimize the cell/material interaction of the pure CS scaffold. Conclusion: The CA/PCL nanofibers not only improved the mechanical property of the CS aerogel to some extent but also facilitated cell adhesion and osteogenic differentiation. Thus, it could be considered a promising candidate for bone tissue engineering.

Lightweight, Anisotropic, Compressible, and Thermally-Insulating Wood Aerogels with Aligned Cellulose Fibers

The growing demand for lightweight, renewable, and excellent thermal insulation materials has fueled a search for high performance biomass materials with good mechanical compressibility and ultralow thermal conductivity. We propose a fabrication method for making a lightweight, anisotropic, and compressible wood aerogel with aligned cellulose fibers by a simple chemical treatment. The wood aerogel was mainly composed of highly aligned cellulose fibers with a relative crystallinity of 77.1%. The aerogel exhibits a low density of 32.18 mg/cm³ and a high specific surface area of 31.68 m²/g due to the removal of lignin and hemicellulose from the wood. Moreover, the multilayer structure of the aerogel was formed under the restriction of wood rays. Combined with a nanoscale pore, the aerogel presents good compressibility and an ultralow thermal conductivity of 0.033 W/mK. These results show that the wood aerogel is a high quality biomass material with a potential function of thermal insulation through optimizing structures.

Bacterial cellulose/graphene oxide aerogels with enhanced dimensional and thermal stability

We present a novel method for processing bacterial cellulose/graphene oxide (BC/GO) aerogels with multifunctional properties. The addition of a small amount of dimethyl sulfoxide (DMSO) to the aqueous dispersion of the nanomaterials during the gelification process affected the water freezing temperature of the system and thereby affecting the porous structure of the aerogel obtained after liophilization. The possibility to obtain small and elongated pore with axial orientation allowed a significant improvement of the structural stability of the aerogels. Moreover, the aerogels reduction by thermal treatment with ammonia gas induced crosslinking between the different nanophases, thus given an incremental factor for the mechanical performance of the aerogels under harsh conditions. The resulting aerogels also showed significant improvements in terms of thermal stability and electrical conductivity. These multifunctional BC/GO aerogels present high potential as sustainable and ecological alternative materials for lightweight packaging, filters for atmosphere and water treatment, or energy applications.

Fabrication and Application of Carboxymethyl Cellulose-Carbon Nanotube Aerogels

In this study, composite aerogels with excellent mechanical properties were prepared by using carboxymethyl cellulose (CMC) as raw materials, with carboxylic carbon nanotubes (CNTs) as reinforcement. By controlling the mass fraction of CNTs, composite aerogels with different CNTs were prepared, and the surface morphology, specific surface area, compressive modulus, density and adsorption capacities towards different oils were studied. Compared to the pure CMC aerogel, the specific surface areas of CMC/CNTs were decreased because of the agglomeration of CNTs. However, the densities of composite aerogels were lower than pure CMC aerogel. This is because the CNTs were first dispersed in water and then added to CMC solution. The results indicated that it was easy for the low CMC initial concentration to be converted to low density aerogel. The compressive modulus was increased from 0.3 MPa of pure CMC aerogel to 0.5 MPa of 5 wt % CMC/CNTs aerogel. Meanwhile, the prepared aerogels showed promising properties as the adsorption materials. Because of the high viscosity, liquid possesses strong adhesion to the pore wall, the adsorption capacity of the CMC aerogel to the liquid increases as the viscosity of the liquid increases.

Effects of Sodium Montmorillonite on the Preparation and Properties of Cellulose Aerogels

In this study, first, a green and efficient NaOH/urea aqueous solution system was used to dissolve cellulose. Second, the resulting solution was mixed with sodium montmorillonite. Third, a cellulose/montmorillonite aerogel with a three-dimensional porous structure was prepared via a sol-gel process, solvent exchange and freeze-drying. The viscoelastic analysis results showed that the addition of montmorillonite accelerated the sol-gel process in the cellulose solution. During this process, montmorillonite adhered to the cellulose substrate surface via hydrogen bonding and then became embedded in the pore structure of the cellulose aerogel. As a result, the pore diameter of the aerogel decreased and the specific surface area of the aerogel increased. Furthermore, the addition of montmorillonite increased the compressive modulus and density of the cellulose aerogel and reduced volume shrinkage during the preparation process. In addition, the oil/water adsorption capacities of cellulose aerogels and cellulose/montmorillon aerogels were investigated.

Insights into the phosphate adsorption behavior onto 3D self-assembled cellulose/graphene hybrid nanomaterials embedded with bimetallic hydroxides

3D self-assembled cellulose/graphene hybrids (3D cell/GO hybrids) were used as the host for encapsulating the Zr and La hydroxides, forming the Zr/La-cell/GO hybrids. After phosphate adsorption, the crystallization peaks of LaPO₄·xH₂O in saturated Zr/La-cell/GO hybrids were observed and they were reduced with the increase in pHs. Especially, a low crystallization was observed at pH 10.0 as compared with those at pH 3.0 and 6.0; this also corresponded well to the varied adsorption capacity as a function of pHs. The increased humic acid (HA) amounts (150 mg/L) only resulted in a low capacity loss (16.3%) in phosphate uptake from 25.3 to 21.2 mg/g. A noticeable La leach (2.1 mg/L) was observed at the HA level of 150 mg/L but no Zr leach was detected, and therefore, complexation of La with HA seemed a potential explanation for the increased La leaching. The interference of different coexisting anions on phosphate uptake followed the order as F^- > SiO₃^2- > HCO₃^- > SO₄^2- > NO₃^- > Cl^-. Phosphate uptake by Zr/La-cell/GO hybrids was significantly reduced at the co-existing fluoride partially due to the stronger electro-negativity of fluoride to combine with the protonated Zr/La hydroxides. In addition, Ca²⁺ laden on the Zr/La-cell/GO hybrids significantly enhanced the adsorption of phosphate by Zr/La-cell/GG hybrids due to the formation of calcium phosphate precipitation in framework of Zr/La-cell/GG hybrids.

Conductive Polymer Composites from Renewable Resources: An Overview of Preparation, Properties, and Applications

This article reviews recent advances in conductive polymer composites from renewable resources, and introduces a number of potential applications for this material class. In order to overcome disadvantages such as poor mechanical properties of polymers from renewable resources, and give renewable polymer composites better electrical and thermal conductive properties, various filling contents and matrix polymers have been developed over the last decade. These natural or reusable filling contents, polymers, and their composites are expected to greatly reduce the tremendous pressure of industrial development on the natural environment while offering acceptable conductive properties. The unique characteristics, such as electrical/thermal conductivity, mechanical strength, biodegradability and recyclability of renewable conductive polymer composites has enabled them to be implemented in many novel and exciting applications including chemical sensors, light-emitting diode, batteries, fuel cells, heat exchangers, biosensors etc. In this article, the progress of conductive composites from natural or reusable filling contents and polymer matrices, including (1) natural polymers, such as starch and cellulose, (2) conductive filler, and (3) preparation approaches, are described, with an emphasis on potential applications of these bio-based conductive polymer composites. Moreover, several commonly-used and innovative methods for the preparation of conductive polymer composites are also introduced and compared systematically.

Aerogel-based materials for adsorbent applications in material domains

Aerogels are considered to be promising materials in various applications due to their exclusive properties. Over the last decades, the potential of organic, inorganic, or hybrid aerogels has been practically exploited in different fields of use. Some aerogel compositions have been patented recently but their application in the area of adsorption remains limited. This review intends to discuss the potential of aerogels as adsorbents, which is summarised from the more recent progressive research and their capabilities. Furthermore, the potential of aerogels as viable absorbents for environmental remediation is also discussed. After a short introduction covering the aerogel properties, preparation procedures, and their possible classification options, the review is structured based on their possible use as adsorbents.

Ultralight, hydrophobic, anisotropic bamboo-derived cellulose nanofibrils aerogels with excellent shape recovery via freeze-casting

Cellulose aerogels have shown outstanding potential as renewable functional materials; however, their practical applications are still limited by inherent hydrophilicity and weak mechanical properties. To overcome hydrophilicity and fragility issues of aerogels, in this study, silylated bamboo-derived cellulose nanofibrils (CNF) aerogels with aligned porous structures were achieved by directionally freeze-casting a mixture of CNF suspension and methyltrimethoxysilane sol. The silylated CNF aerogels exhibited distinct aligned lamellar structures and significantly anisotropic mechanical properties. They had improved strength and stiffness in the axial direction (along the freezing direction) and excellent rapid shape recovery ability in the radial direction (perpendicular to the freezing direction) with a significant high shape recovery ratio of 92% after 100 cycles at 80% compression. Owing to their ultra-low density, hydrophobicity, and high compressive recoverability, the silylated CNF aerogels can be potentially used in a wide range of industrial applications, such as hydrophobic polymer nanocomposites, absorbents, and biomedical scaffolds.

Hydrothermal Synthesis of Ultra-Light Coal-Based Graphene Oxide Aerogel for Efficient Removal of Dyes from Aqueous Solutions

A novel carboxymethyl cellulose (CMC)-supported graphene oxide aerogel (CGOA) was fabricated from a cost-effective and abundant bituminous coal by a mild hydrothermal process and freeze-drying treatment. Such an aerogel has cross-linked graphene oxide layers supported by CMC, and therefore, displays high mechanical strength while having ultra-low density (8.257 mg·cm-3). The CGOA has a 3D interconnected porous structure, beneficial graphene framework defects and abundant oxygen-containing functional groups, which offer favorable diffusion channels and effective adsorption sites for the transport and adsorption of dye molecules. The adsorption performance of rhodamine B by an optimized CGOA shows a maximum monolayer adsorption capacity of 312.50 mg·g-1, as determined by Langmuir isotherm parameters. This CGOA exhibited a better adsorption efficiency (99.99%) in alkaline solution, and satisfactory stability (90.60%) after three cycles. In addition, adsorption experiments on various dyes have revealed that CGOA have better adsorption capacities for cationic dyes than anionic dyes.