Cellulose Aerogels Research Articles

Preparation of ambient-dried multifunctional cellulose aerogel by freeze-linking technique

Ambient drying is currently the cheapest and most efficient way to prepare aerogels, but it is invisible for the preparation of cellulose aerogels. In this paper, we describe a method of preparing cellulose aerogels that can be dried under atmospheric pressure by freeze-linking technique. The amino silane coupling agent forms an amino-rich polymer layer on the bacterial cellulose surface during the freezing process. And, the cross-linked network constructed by Schiff base reaction can strengthen the fiber skeleton in the process of solvent exchange. Due to the double cross-linked network structures, the cellulose ethanol gel can be dried directly under atmospheric pressure at 60 °C and the volume shrinkage can be as low as 3.3 %±1.4 %. In the process of solvent exchange, the loss of some polysiloxane causes defects in the aerogel, which not only reduces its thermal conductivity but also increases its specific surface area. And the water resistance, thermal performance, and dye adsorption performance of the aerogel are also significantly improved. This study provides a low-cost and high-efficiency solution for the manufacture of cellulose aerogels and promotes their wide applications.

3D Tea-Residue Microcrystalline Cellulose Aerogel with Aligned Channels for Solar-Driven Interfacial Evaporation Co-generation.

Solar-driven interfacial evaporation co-generation (SIE-CG) technology is of great significance in solving the problem of water and energy shortage. Herein, we report the ionic liquid-assisted alignment of waste biomass tea residue-based microcrystalline cellulose for aerogels (abbreviated as TPPA-5) with aligned channels for solar-driven interfacial evaporation co-generation. In the ionic liquid, strong H-bonding is formed between the pyranoid rings of cellulose combined with the slow freezing technique, resulting in the microcrystalline cellulose being reoriented, which allowed TPPA-5 to form abundant aligned channels after solvent replacement and freeze-drying. These aligned channels enable the brine to form a localized circulating flow, which is conducive to the improvement of the TPPA's evaporation rate and salt resistance. The salinity gradient is naturally formed in the channel of TPPA, which enables TPPA-5 to show excellent power generation performance. The evaporation rate of TPPA-5 can reach 3.39 kg m-2 h-1 under 1 kW m-2. With methanol as a highly polar proton solvent, the maximum output voltage obtained was 67.534 mV due to the overlapping electric double-layer effect formed by hydrogen protons on the TPPA surface, and the energy utilization efficiency is 95.95%. Moreover, TPPA-5 can purify pesticide-containing wastewater, which has the advantages of being recyclable and environmentally friendly, showing potential application value in the field of seawater desalination and steam co-generation.

Hydrophobic microcrystalline cellulose/polyethyleneimine composite aerogel for effective sound absorption

A hydrophobic and ultralight cellulose aerogel (CA) was reinforced by polyethyleneimine (PEI) and functionalized by methyltrimethoxysilane (MTMS). Adding PEI improved the mechanical strength and the elastic resilience of the resulting material due to the flexibility enhancement of the cellulose chains, which prevented the collapse of the pore structure and contributed to the uniform pore size distribution. The hydrophobic property of the aerogels with the functionalization of MTMS was improved, which can prevent the pore structure from collapsing due to the absorption of water. The maximum compression modulus of aerogel reached 1.1 MPa at the strain of 80%, and its hydrophobic water contact angle was up to 112°. The hydrophobic composite aerogels exhibited ultrahigh efficiency in sound absorption across a wide frequency range from 500 to 6300 Hz, and their average absorption coefficient was greater than 0.74. The light weight, high porosity, and environmentally friendly aerogels presented in this work are promising for efficient sound absorption. They have potential applications in noise pollution treatment.

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.

A gentle strategy to design amine-functionalized cellulose aerogel with tunable graft density for urea adsorption

The development of efficient adsorbent materials to remove urea from dialysate is an effective way to solve the bottleneck limiting the development of a wearable artificial kidney. Three methods were used to fabricate amine-functionalized cellulose aerogels aiming to screen for excellent structures favorable for urea adsorption. The influence of APTES addition on the structure and adsorption performance of the adsorption materials was investigated. The kinetics and thermodynamics of urea adsorption were evaluated, and adsorption mechanisms were also discussed. Results indicate that the material prepared by the gentle method was still able to maintain a large specific surface area, large pore volume and low crystallinity. Amine-functionalized cellulose aerogels retain the original hydroxyl adsorption sites, and the amino or silanol hydroxyl as new adsorption active sites are also introduced. Furthermore, proper APTES graft density plays a critical role in the urea adsorption. The equilibrium adsorption capacity of urea on HA-N-NCA-10 is increased by 156%.

Enhanced oil removal by graphene oxide/N,N′-methylene bisacrylamide modified magnetite-cellulose aerogel derived from ramie stem waste: Adsorption performance, kinetics, and economical analysis

Oil spills in the sea pose grave environmental and health risks. The discovery of novel methods to remove oil from water has been the focus of numerous investigations, however they are having trouble scaling up. This study focuses on a modified adsorbent made from graphene oxide (GO) and N,N′-methylene bisacrylamide (MBA) sourced from waste ramie stems, designed for oil-seawater mixtures with high-capacity and reusable aerogels. A synthesized aerogel included ramie pulp dissolution in NaOH-urea, with additions of Fe3O4, potassium peroxydisulfate, GO, and MBA at 1–13 g/L concentrations. Treatments involved ultrasonication, coagulation, solvent exchange, and coating, resulting in a hydrophobic aerogel with a 117.46° contact angle. A maximum 5.81 g/g adsorption capacity was observed at 13 g/L MBA. MBA improved pore count and size, raising adsorption. MBA increased aerogel porosity from 0.873 to 0.898 and decreased density from 0.193 to 0.159 g·cm−3. GO bolstered aerogel structure, rendering it reusable for two cycles. This sustainable, cost-effective, magnetite cellulose aerogel could offer a biodegradable cellulose-based sorbents for oil spill challenges.

Biomass aerogel composite containing BaTiO3 nanoparticles and MXene for highly sensitive self-powered sensor and photothermal antibacterial applications

Biomass aerogel materials are increasingly attracting researchers’ attention because of good biocompatibility of biomass materials and multiple functional features of aerogel materials. Herein, novel biomass aerogel composite was fabricated by doping hydroxylated barium titanate (BT-OH) nanoparticles and MXene in chitosan/bacterial cellulose (CB) aerogel by simple methods containing chemical modification, physical mixture and lyophilization. The novel aerogel composite named CB/BT-OH/MXene showed favorable piezoelectric properties and excellent photothermal antibacterial properties. The aerogel composite-based piezoelectric sensor displayed short response time (0.4 s), high response sensitivity (800 mV/N), and long cycle stability (over 1000 cycles), which could monitor various body movements, including fingers bending, speaking, wrist bending, elbow bending, smiling, and walking. Moreover, the aerogel composite possessed satisfactory photothermal conversion ability, which could reach 55 ℃ by 10 s of near-infrared irradiation (808 nm, 0.2 W/cm2), successfully achieving complete sterilization effect towards S. aureus and E. coli. The novel biomass aerogel composite may find its potential applications in wearable or implantable self-powered sensors with satisfactory antibacterial performance.

3D lanthanum modified cellulose aerogel based on filter paper with excellent adsorption performance for phosphate

3D lanthanum modified cellulose aerogel based on filter paper with excellent adsorption performance for phosphate

NANOFIBRILLATED CELLULOSE AEROGEL FROM KHAT (CATHA EDULIS) WASTE: FABRICATION AND CHARACTERIZATIONS

Cellulose fiber was extracted from khat waste (KW) using the chlorine free method and an aerogel was prepared by freeze drying of nanofibrillated cellulose of KW. The aerogel was loaded with a model drug, diclofenac sodium. The drug loaded aerogel (LA), drug unloaded aerogel (ULA), as-extracted cellulose (Cel) and KW were characterized using different instrumental techniques. Nanofibrillation of the cellulose fiber for 4 h gave 83.06% nanofiber. ULA had lower crystallinity index, as compared to Cel (53.89% vs 65.22%), but had higher thermal stability than LA and Cel. The drug loading capacity of the aerogel was 11.7 mg of pure drug per 100 mg of the nanofiber. The in vitro drug release from LA was less than one-third of the loaded drug (i.e., 31.4%) within 6 h. The findings highlight that nanofibrillated cellulose aerogel can be prepared from KW and may have potential applications in areas such as drug delivery.

Bioinspired Thermochromic Textile Based on Robust Cellulose Aerogel Fiber for Self-Adaptive Thermal Management and Dynamic Labels.

Aerogel fiber has emerged recently for incorporation in personal thermal management textiles due to its flexibility, scalability, and ultrahigh porosity, which allows the body to keep warm via thermal isolation without energy consumption. However, the functionalization and intellectualization of cellulose-based aerogel fibers have not yet been fully developed. Herein, we propose a biomimicking design inspired by polar bear and Siamese cat hair that combines porous cellulose aerogel fiber (CAF) with reversible thermochromic microcapsules to mimic biological sensory and adaptive thermoregulation functions. The produced CAF has a controllable pore structure, a large specific surface area (230 m2/g), and excellent mechanical strength (∼15 MPa). Low-temperature darkening microcapsules have been incorporated into the robust CAF to spontaneously adjust color by perceiving the ambient temperature. The functional aerogel fiber fabric achieves high thermal insulation and photothermal modulation simultaneously at temperatures below 18 °C. The temperature of the thermochromic fabric was higher by 6 °C than that of the sample without the microcapsules at a light intensity of 0.2 W/cm2. In addition, the aerogel fibers mixed with two types of thermochromic microcapsules exhibit three color switches with fast response, a color-control precision of 0.2 °C, and good cycling performance. This smart aerogel fibers hold great promise for self-adaptive thermal management, temperature indication, information transfer, and anticounterfeiting in textiles.

Strong, Lightweight, and Shape-Memory Bamboo-Derived All-Cellulose Aerogels for Versatile Scaffolds of Sustainable Multifunctional Materials.

Strong, lightweight, and shape-memory cellulose aerogels have great potential in multifunctional applications. However, achieving the integration of these features into a cellulose aerogel without harsh chemical modifications and the addition of mechanical enhancers remains challenging. In this study, a strong, lightweight, and water-stimulated shape-memory all-cellulose aerogel (ACA) is created using a combination strategy of partial dissolution and unidirectional freezing from bamboo. Benefiting from the firm architecture of cellulose microfibers bridging cellulose nanofibers /regenerated cellulose aggregated layers and the bonding of different cellulose crystal components (cellulose Iβ and cellulose II), the ACA, with low density (60.74mg cm-3 ), possesses high compressive modulus (radial section: 1.2MPa, axial section: 0.96MPa). Additionally, when stimulated with water, the ACA exhibits excellent shape-memory features, including highly reversible compression-resilience and instantaneous fold-expansion behaviors. As a versatile scaffold, ACA can be integrated with hydroxyapatite, carboxyl carbon nanotubes, and LiCl, respectively, via a simple impregnation method to yield functionalized cellulose composites for applications in thermal insulation, electromagnetic interference shielding, and piezoresistive sensors. This study provides inspiration and a reliable strategy for the elaborately structural design of functional cellulose aerogels endows application prospects in various multifunction opportunities.

Ionic Liquid Directed Spinning of Cellulose Aerogel Fibers with Superb Toughness for Weaved Thermal Insulation and Transient Impact Protection.

Aerogel fibers, combining the nanoporous characteristics of aerogels with the slenderness of fibers, have emerged as a rising star in nanoscale materials science. However, endowing nanoporous aerogel fibers with good strength and high toughness remains elusive due to their high porosity and fragile mechanics. To address this challenge, this paper reports supertough aerogel fibers (SAFs) initially started from ionic-liquid-dissociated cellulose via wet-spinning and supercritical drying in sequence. The supertough nanoporous aerogel fibers assembled with cellulose nanofibers exhibit a high specific surface area (372 m2/g), good mechanical strength (30 MPa), and large elongation (107%). Benefiting from their high strength and elongation, the resultant cellulose nanoporous aerogel fibers show ultrahigh toughness up to 21.85 MJ/m3, much outperforming the known aerogel materials in the literature. Moreover, the toughness of this nanoporous aerogel fiber is 7.4 times higher than that of human knee ligaments, and its specific toughness is comparable to that of commonly used solid polyester fibers. In addition, we also verified the weavability, desirable thermal insulation performance, and supertoughness to resist the transient impact of SAFs. The long-sought strategy to simultaneously resolve the strength and toughness of nanoporous aerogel fibers, in combination with the biodegradable nature of the cellulose, provides multifaceted opportunities for broad potential applications, including lightweight wearable textiles and beyond.

Nata de coco as an abundant bacterial cellulose resource to prepare aerogels for the removal of organic dyes in water

A hydrogel-like product of the bacterial fermentation of coconut water is well-known as nata de coco which contains low-cost and high-quality bacterial cellulose. In this work, nata de coco was applied for the facile preparation of lightweight bacterial cellulose aerogels upon grinding and subsequent freeze-drying. The obtained aerogels possessed the three-dimensional network containing bacterial cellulose fibers with high crystallinity and porosity. The experimental results proved the high affinity of the bacterial cellulose network to the cationic dyes with adsorption capacities from 25 to 81 mg/g. By contrast, the aerogel was inefficient with most of the tested anionic dyes except for congo red which afforded a significant adsorption capacity of 145 mg/g. The promising results were obtained without any further chemical modification being applied to the bacterial cellulose aerogels and notably comparable to the previous performances of biomass-based sorbents. This biomaterial showed a great potential in environmentally-friendly treating organic dyes-polluted wastewater.

Bacterial Cellulose Aerogels Derived from Pineapple Peel Waste for the Adsorption of Dyes.

Valorization of pineapple peel waste is an attractive research topic because of the huge quantities of this byproduct generated from pineapple processing industries. In this study, the extract from pineapple waste was collected to produce a hydrogel-like form containing bacterial cellulose fibers with a three-dimensional structure and nanoscale diameter by the Acetobacter xylinum fermentation process. The bacterial cellulose suspension was subsequently activated by freeze-drying, affording lightweight aerogels as potential adsorbents in wastewater treatment, in particular the adsorptive removal of organic dyes. Intensive tests were carried out with the adsorption of methylene blue, a typical cationic dye, to investigate the influence of adsorption conditions (temperature, pH, initial dye concentration, time, and experiment scale) and aerogel-preparation parameters (grinding time and bacterial cellulose concentration). The bacterial cellulose-based aerogels exhibited high adsorption capacity not only for methylene blue but also for other cationic dyes, including malachite green, rhodamine B, and crystal violet (28-49 mg/g). However, its activity was limited for most of the anionic dyes, such as methyl orange, sunset yellow, and quinoline yellow, due to the repulsion of these anionic dyes with the aerogel surface, except for the case of congo red. It is also an anionic dye but has two amine groups providing a strong interaction with the hydroxyl group of the aerogel via hydrogen bonding. Indeed, the aerogel has a substantially large congo red-trapping capacity of 101 mg/g. Notably, the adsorption process exhibited similar performances, upscaling the solution volume to 50 times. The utilization of abundant agricultural waste in the simple aerogel preparation to produce a highly efficient and biodegradable adsorbent is the highlight of this work.

The Effect of Fe3O4 Addition on the Density and Porosity of Cellulose Nanofiber Aerogel Extracted by Oil Palm Trunk

This study investigates the influence of Fe3O4 addition on cellulose nanofiber aerogels' density and porosity characteristics. The cellulose nanofiber aerogels were synthesized with varying concentrations of Fe3O4: 0%, 0.25%, 0.5%, 0.75%, and 1%. The characterization of the cellulose nanofiber aerogels included physical tests to determine density and porosity and Fourier transform infrared (FTIR) analysis for functional group analysis. The results reveal a progressive increase in density from the lowest to the highest Fe3O4 concentrations: 0.115 g/cm3, 0.135 g/cm3, 0.162 g/cm3, 0.163 g/cm3, and 0.241 g/cm3 for Fe3O4 concentrations of 0%, 0.25%, 0.5%, 0.75%, and 1%, respectively. Similarly, the porosity of the cellulose nanofiber aerogels exhibited a trend of decreasing values from the lowest to the highest Fe3O4 concentrations: 90.808%, 89.499%, 88.064%, 87.764%, and82.844% for Fe3O4 concentrations of 0%, 0.25%, 0.5%, 0.75%, and 1%, respectively. Furthermore, FTIR analysis indicated that the structural integrity of the cellulose aerogels remained unchanged even after the incorporation of Fe3O4 . While no new functional groups emerged, a discernible shift in wave numbers suggests the formation of bonds between the polymer network and Fe3O4 . So, adding Fe3O4 to cellulose nanofiber aerogels led to notable alterations in density and porosity, while FTIR analysis confirmed the establishment of bonds between the polymer network and Fe3O4 without causing significant structural changes.

(Digital Presentation) Electrocatalytic and Conductive Vanadium Oxide on Carbonized Bacterial Cellulose Aerogel for the Sulfur Cathode in Li-S Batteries

Li-S chemistry is regarded as promising next-generation battery technology. However, its complex redox process and long-chain lithium polysulfides shuttling are hindering the development of practical Li-S battery technology. To address these problems, many transition-metal-oxide-based catalysts have been investigated to chemically bind soluble lithium polysulfides and accelerate their redox kinetics. However, the intrinsic poor electrical conductivities of these oxides restrict their catalytic performance, consequently limiting the sulfur utilization and the rate performance of Li-S batteries. Herein, we report a freestanding electrocatalytic sulfur host consisting of hydrogen-treated VO2 nanoparticles (H-VO2) anchored on nitrogen-doped carbonized bacterial cellulose aerogels (N-CBC). The hydrogen treatment enables the formation and stabilization of the rutile VO2(R) phase with metallic conductivity at room temperature, significantly enhancing its catalytic capability compared to the as-synthesized insulative VO2(M) phase. We characterized the electrocatalytic performance of this unique H-VO2@N-CBC structure using several methods and found that the activation energy between S8 and polysulfides and the one between polysulfides and Li2S are largely reduced by 28.2 and 43.3 kJ/mol, respectively. Accordingly, the Li-S battery performance is greatly improved, with a high initial specific capacity of 1347 mAh g−1 at 0.1 C and remarkable cycling stability with a capacity of 758 mAh g-1 after 300 cycles at 1 C. This work provides an effective strategy for designing and fabricating conductive oxide catalysts to promote the electrochemical performance of Li-S batteries.

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.

Bacterial cellulose derived carbon nanofiber aerogel assembled with redox active hydrogel and alpha-MoO3 nanoplate for high-performance supercapacitors

Dual-asymmetric supercapacitors (DASCs) with high capacitive performance were developed in this work through carefully design and configuration of all the capacitor components. Free-standing carbon aerogel was directly utilized as the positive electrode, which was fabricated by pyrolyzing bacterial cellulose (BC) aerogel. Its porous structure afforded it excellent interface with the redox active electrolyte. Redox active hydrogel electrolyte based on mixed-valence iron ions (PVA/H2SO4/Fe3+/2+) was prepared with a freezing-thawing method and combined with the carbon aerogel to form the positive compartment of the capacitors. Meanwhile, α-MoO3 nanoplates were fabricated by hydrothermal method and used for the fabrication of negative electrodes, which were assembled with conventional PVA/H2SO4 hydrogel electrolyte to form the negative compartment. The as-assembled DASCs showed a specific capacitance of 560.8 F g−1 at 1 A g−1 and energy density of 131.6 Wh kg−1, indicating its remarkable capacitive performance. Moreover, the optimized DASC displayed a remarkable long-term cycling stability. This work on the design and assembly of the battery-like supercapacitor with carbon aerogel electrodes combined with their corresponding hydrogel electrolytes afforded a new configuration to fabricate the devices with high performance.

Synthesis and Characterisation of Carbon Aerogel Derived from Carboxymethyl Cellulose as Hydrogen Storage Material

A direct, simple and low-cost approach to synthesising carbon aerogelmagnesium (CA-Mg) composites has been demonstrated in this research. It is conducted by carbonising sodium carboxymethyl cellulose (CMC) aerogels via a sol-gel and freezedrying process. Mg is used as an enhancer for CA in the preparation step and as a selective candidate for the hydrogen storage device. Note that the structure and morphology of CA-Mg composites are characterised using field emission scanning electron microscopy (FESEM), fourier transforms infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. The ability of CA-Mg composites to act as a hydrogen storage device is analysed by utilising Brunauer-Emmett-Teller (BET) and temperature-programmed desorption analysis. The CA-Mg composites comprise porous structures with a high specific surface area of 101.4407 m2 /g, and 0.002 mol of Mg2+ is the optimum concentration for synthesising CA-Mg composites. As a potential candidate for a hydrogen storage device, the CA-Mg composites show an initial dehydrogenation temperature of 377.22°C, where they desorbed the maximum amount of hydrogen gas. This study emphasises the potential for using CA as a hydrogen storage device, which fulfils the seventh goal of the Sustainable Development Goals (SDGs), affordable and clean energy, as well as Department of Energy (DOE)’s goal of using carbon-based materials.

Bacterial cellulose composite aerogel with high elasticity and adjustable wettability for dye absorption and oil–water separation

Recently, cellulose-based biomass aerogel, as a high performance adsorption material, has received considerable attention. However, it remains a huge challenge to prepare cellulose aerogels with outstanding mechanical properties by simple and environmentally-friendly strategies. Here, we describe a green one-pot method to prepare a versatile bacterial cellulose/γ-(2,3-epoxypropoxy) propytrimethoxysilane trimethoxysilane composite aerogel (BK aerogel). The elasticity of BK aerogel is significantly improved and up to 96.4% after compression under 80% strain. Further, the elastic recovery can reach 87.8% over 50 times compressions at a set strain of 80 %, implying the obtained composite aerogel possesses strong fatigue resistance. BK aerogel could be soaked in water to adsorb cationic dyes and reused without being damaged. In addition, the prepared BK aerogel is rich in hydroxyl and epoxy groups, so its surface chemistry can be further adjusted. Taking hydrophobic modification as an example, the prepared aerogel can be used for oil–water separation and reused by mechanical squeezing. This study paves a simple and green solution for developing high elastic cellulose nanofiber aerogel with adjustable surface chemistry to meet diverse applications.