Cellulose Nanofibril Aerogel Research Articles

Near-infrared analysis of nanofibrillated cellulose aerogel manufacturing

Biomaterial aerogel fabrication by freeze-drying must be further improved to reduce the costs of lengthy freeze-drying cycles and to avoid the formation of spongy cryogels and collapse of the aerogel structures. Residual water content is a critical quality attribute of the freeze-dried product, which can be monitored in-line with near-infrared (NIR) spectroscopy. Predictive models of NIR have not been previously applied for biomaterials and the models were mostly focused on the prediction of only one formulation at a time. We recorded NIR spectra of different nanofibrillated cellulose (NFC) hydrogel formulations during the secondary drying and set up a partial least square regression model to predict their residual water contents. The model can be generalized to measure residual water of formulations with different NFC concentrations and the excipients, and the NFC fiber concentrations and excipients can be separated with the principal component analysis. Our results provide valuable information about the freeze-drying of biomaterials and aerogel fabrication, and how NIR spectroscopy can be utilized in the optimization of residual water content.

Fire‐Retardant and Thermal‐Insulating Cellulose Nanofibril Aerogel Modified by In Situ Supramolecular Assembly of Melamine and Phytic Acid

The widespread utilization of cellulose nanofibril (CNF) has been significantly hindered by its inherent flammability. To explore the potential of using CNF aerogel as sustainable material with good fire‐retardant and thermal‐insulating properties, CNF aerogel is modified by in situ supramolecular assembly of melamine (MEL) and phytic acid (PA). This strategy addresses CNF's flammability and avoids the environment issues associated with the incorporation of traditional fire‐retardant. The modified aerogel exhibits highly porous honeycomb structure with low density and good mechanical properties. After modification with MEL–PA, the aerogel exhibits highly improved shape integrity during burning, higher thermal stability, and favorable combustion behavior for fire retardancy. The heat transfer of the modified aerogel is well hindered, which demonstrated effective thermal insulation performance. In view of the excellent thermal and fire‐retardant properties, the MEL–PA/CNF composite aerogel can be a potential fire‐retardant and thermal‐insulating material for applications such as clothing, building, and electronic devices.

Facile and Green Synthesis of Pd-Decorated Alginate/ Nanofibrillated Cellulose Aerogel for Simultaneous Dye Degradation, Oil/Water Separation and Oil Collection

Facile and Green Synthesis of Pd-Decorated Alginate/ Nanofibrillated Cellulose Aerogel for Simultaneous Dye Degradation, Oil/Water Separation and Oil Collection

3-D Porous Cellulose Nanofibril Aerogels with a Controllable Copper Nanoparticle Loading as a Highly Efficient Non-Noble-Metal Catalyst for 4-Nitrophenol Reduction

3-D Porous Cellulose Nanofibril Aerogels with a Controllable Copper Nanoparticle Loading as a Highly Efficient Non-Noble-Metal Catalyst for 4-Nitrophenol Reduction

Liquid Transport and Real-Time Dye Purification via Lotus Petiole-Inspired Long-Range-Ordered Anisotropic Cellulose Nanofibril Aerogels.

Nowadays, large-scale oriented functional porous materials have been sought after by researchers. However, regulation of the long-range uniform and oriented structures of the material remains a challenge. Herein, ultralong anisotropic cellulose nanofibril (CNF) aerogels with uniformly ordered structures of pore walls inspired by lotus petioles were constructed by applying external speeds to counterbalance the growth driving forces of ice crystals. Based on the growth law of ice crystals, the ice crystals grew at a stable rate when the applied external speed was 0.04 mm/s, ensuring the consistent orientation of the large-scale CNF aerogel. The aerogel exhibited a rapid long-range directional transport ability to different liquid solvents, delivering ethanol up to 40 mm from bottom to top within 50 s. Moreover, by introducing rectorites with good cation-exchange properties, the resulting long-range composite possessed an enhanced adsorption capacity for methylene blue. Furthermore, aerogel successfully achieved real-time dye purification at a long distance, such as fast dye adsorption or selective adsorption. This flexible and straightforward strategy of fabricating ultralong oriented CNF aerogel materials is expected to promote the development of functional aerogels in directional liquid transport and sewage treatment.

Highly Efficient Iron Oxide Nanoparticles Immobilized on Cellulose Nanofibril Aerogels for Arsenic Removal from Water.

The application and optimal operation of nanoparticle adsorbents in fixed-bed columns or industrial-scale water treatment applications are limited. This limitation is generally due to the tendency of nanoparticles to aggregate, the use of non-sustainable and inefficient polymeric resins as supporting materials in fixed-bed columns, or low adsorption capacity. In this study, magnesium-doped amorphous iron oxide nanoparticles (IONPs) were synthesized and immobilized on the surface of cellulose nanofibrils (CNFs) within a lightweight porous aerogel for arsenic removal from water. The IONPs had a specific surface area of 165 m2 g−1. The IONP-containing CNF aerogels were stable in water and under constant agitation due to the induced crosslinking using an epichlorohydrin crosslinker. The adsorption kinetics showed that both As(III) and As(V) adsorption followed a pseudo second-order kinetic model, and the equilibrium adsorption isotherm was best fitted using the Langmuir model. The maximum adsorption capacities of CNF-IONP aerogel for As(III) and As(V) were 48 and 91 mg As g-IONP−1, respectively. The optimum IONP concentration in the aerogel was 12.5 wt.%, which resulted in a maximum arsenic removal, minimal mass loss, and negligible leaching of iron into water.

Synthesis of Copper Nanoparticles from Cu2+-Spiked Wastewater via Adsorptive Separation and Subsequent Chemical Reduction.

Copper in ionic form (Cu2+) should be removed from wastewater because of its harmful effects on human health. Meanwhile, Cu-metal nanoparticles (Cu0 NPs) are widely used in various applications such as catalysts, optical materials, sensors, and antibacterial agents. Here, we demonstrated the recovery of Cu2+ from wastewater and its subsequent transformation into Cu0 NPs, a value-added product, via continuous adsorption followed by chemical reduction by hydrazine. To separate and enrich Cu2+ from wastewater, a biosorbent that exhibits excellent selectivity and adsorption capacity toward Cu2+, i.e., polyethyleneimine-grafted cellulose nanofibril aerogel (PEI@CNF), was packed into a column and used to treat 20 mg/L Cu2+ wastewater at a flow rate of 5 mL/min. The Cu2+ adsorption reached equilibrium at 72 h, and the Cu2+-saturated column was eluted using 0.1 M of HCl. After five consecutive elutions of Cu2+ from the adsorbent column, a Cu2+-enriched solution with a concentration of 3212 mg/L was obtained. The recovered Cu2+ concentrate was chemically reduced to obtain Cu0 NPs by reaction with hydrazine as a reductant in the presence of sodium dodecyl sulfate (SDS) as a stabilizer. The solution pH and hydrazine/Cu2+ ratio strongly affected the reduction efficiency of Cu2+ ions. When 0.1 M of SDS was used, spherical 50–100 nm Cu0 NPs were obtained. The results demonstrate that Cu2+-spiked wastewater can be converted into Cu0 NPs as a value-added product via adsorption followed by chemical reduction.

Modified cellulose nanofibril aerogel: Tunable catalyst support for treatment of 4-Nitrophenol from wastewater

4-Nitrophenol (4-NP) is a hazardous aromatic compound widely used for various industries. Catalytic reduction of 4-NP using metal nanoparticles (NPs) is a highly effective method to treat 4-NP from waste effluent. Even though lots of methods have investigated to prepare efficient metal NPs composites, the nano and/or micro size of composites makes it hard to recover after wastewater treatment, limiting its practical use. Here, we fabricate 3-dimensional polyethylene imine grafted cellulose nanofibril (CNF-PEI) aerogel as a porous support material for platinum (Pt) NPs to practically and effectively treat 4-NP from wastewater. The Pt NPs are formed in-situ mode on cylindrical CNF-PEI aerogel by adsorption reaction with amine groups of PEI and subsequently reduction with NaBH4. Control of PEI grafting density and the initial concentration of Pt ions allows manipulation of the loading mass, size, and distribution of Pt NPs on 3D scaffold of CNF-PEI aerogel. The composite aerogel shows high catalytic activity for conversion of 4-NP. The 4-NP conversion activity is strongly affected by the size of Pt NPs and effective surface area of aerogels. The 2.74 nm size Pt NPs with even distribution in the aerogel show fast reaction kinetics (k = 0.12 min−1). Finally, 4-NP reduction efficiency does not decrease during 5 times reuse cycle of Pt NPs loaded CNF-PEI aerogel. This CNF-PEI aerogel loaded with Pt NPs is recovered easily from wastewater after treatment, so it is reusable and offers high potential as a practical recyclable environmental catalyst.

"Robust-Soft" Anisotropic Nanofibrillated Cellulose Aerogels with Superior Mechanical, Flame-Retardant, and Thermal Insulating Properties.

Advanced thermal insulation materials with low thermal conductivity and robustness derived from regenerative resources are badly needed for building energy conservation. Among them, nanofibrillated cellulose aerogels have huge application potential in the field of thermal insulation materials, but it is still a challenge to prepare cellulose aerogels of excellent comprehensive properties in a simple way. Herein, we demonstrate a unidirectional freeze-drying strategy to develop a novel "robust-soft" anisotropic nanofibrillated cellulose aerogel (NFC-Si-T) by integrating nanofibrillated cellulose (NFC) and Si-O-Si bonding networks under the catalytic dehydration of p-toluenesulfonic acid (TsOH). The anisotropic structure endows the NFC-Si-T with high flexibility that can be easily bent or even tied with a knot, and in addition, it possesses high Young's modulus (1-3.66 MPa) that can resist the compression weight of 10,000 times of its own weight without deformation. Furthermore, the NFC-Si-T aerogels exhibit anisotropic thermal insulation performances with a low average thermal conductivity (0.028-0.049 W m-1 K-1). More importantly, the limited oxygen index of the NFC-Si-T reaches up to 42.6-51%, showing excellent flame-retardant performance. Therefore, the "robust-soft" anisotropic NFC-Si-T aerogels can be used as an advanced thermal insulation material for building thermal insulation applications.

Fabrication of cylindrical 3D cellulose nanofibril(CNF) aerogel for continuous removal of copper(Cu2+) from wastewater

Heavy metal contamination in wastewater is a serious problem due to its high toxicity. In this study, three-dimensional porous and flexible polyethylene imine grafted cellulose nanofibril aerogel (PEI@CNF aerogel) is synthesized as a highly efficient biosorbent for continuous treatment of wastewater containing copper (Cu2+). The synthesized PEI@CNF aerogel efficiently separates Cu2+ from wastewater and exhibits outstanding selectivity for Cu2+ in the presence of other metal ions. The amine groups in polyethylene imine (PEI) grafted onto the porous cellulose nanofibrils (CNFs) scaffold form chelates with Cu2+ thereby effectively adsorbing Cu2+. The combination of a flexible CNF scaffold and rigid PEI results in a durable elastic matrix of the aerogel providing excellent wet stability, shape recovery property and recycle ability of PEI@CNF aerogel. Finally, in the column test, the PEI@CNF aerogel treats 88 bed volumes of wastewater containing Cu2+(∼20 mg/L). This result demonstrates that PEI@CNF aerogels are practically viable and highly efficient bio-sorbents for the treatment of wastewater containing Cu2+.

Zinc oxide-filled polyvinyl alcohol–cellulose nanofibril aerogel nanocomposites for catalytic decomposition of an organic dye in aqueous solution

This paper discusses the preparation of polyvinyl alcohol/cellulose nanofibril (PVA–CNF) aerogel nanocomposites loaded with zinc oxide (ZnO) particles via the freeze-thaw process, followed by subsequent in-situ synthesis of ZnO particles using zinc chloride and ammonium solution. Aerogel samples were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and Brunauer–Emmet–Teller analysis. The aerogels were used for decoloration of methylene blue (MB) in aqueous solution via simultaneous adsorption and catalytic degradation with sodium borohydride. The adsorption behavior of MB on the aerogel was investigated with the aid of kinetics and isotherm models and found to fit a Langmuir model, which suggested monolayer adsorption of dye with maximum adsorption capacity of 24.53 mg/g. The presence of ZnO particles in the stable and reusable crosslinked PVA–CNF aerogel has improved the removal of MB as high as two folds after ten cycles of treatment.

Sponge-like polypyrrole–nanofibrillated cellulose aerogels: synthesis and application

Polypyrrole–nanofibrillated cellulose aerogel.

Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Summary Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating ice-templated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m−1 K−1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.

Development of eco-friendly CO2-responsive cellulose nanofibril aerogels as “green” adsorbents for anionic dyes removal

A novel CO2-responsive cellulose nanofibril aerogel as a “green” adsorbent derived from poly(methacrylic acid-co-2-(dimethylamino) ethyl methacrylate) and carboxylated cellulose nanofibrils was successfully prepared via stepwise cation-induced gelation and freeze drying method. This aerogel exhibited CO2-triggered adsorption behavior towards anionic dyes with a rapid adsorption rate and a high adsorption capacity, as well as satisfactory mechanical properties. Upon CO2 stimulation, the charged aerogel can selectively adsorb anionic dyes from aqueous solutions based on an electrostatic interaction. The maximum adsorption capacities of this aerogel towards methyl blue (MB), naphthol green B (NGB), and methyl orange (MO) were 598.8, 621.1 and 892.9 mg g−1, respectively, accompanied by fast adsorption equilibriums towards MB and NGB within 7 min, and MO within 12 min. Meanwhile, the adsorption isotherms and the kinetics of the CO2-responsive adsorbents followed the Freundlich isotherm and the pseudo-second-order model, respectively. Furthermore, the resulting CO2-responsive adsorbent exhibited outstanding recyclability, as its adsorption performance can still be maintained even after twenty cycles. Accordingly, the resultant CO2-responsive cellulose nanofibril aerogel could be a promising adsorbent material for the removal of anionic dyes in wastewater remediation.

Flexible and Super Thermal Insulating Cellulose Nanofibril/Emulsion Composite Aerogel with Quasi-Closed Pores.

Because of the prevailing environment and energy challenges, there has been a growing interest in biobased materials for thermal insulation application. Although cellulose aerogel has been considered as an excellent thermal insulating material, its thermal conductivity is generally negatively affected by the interconnected internal pores. Herein, it is demonstrated that a cellulose nanofibril (CNF)/emulsion composite aerogel with quasi-closed internal pores can be facilely fabricated by Pickering emulsion templating and solvent exchange methods. The CNF-stabilized oil-in-water Pickering emulsion (with an average diameter of 1.3 μm) can be converted into quasi-closed pores by sequential solvent exchange to acetone and tert-butanol (TBA), followed by freeze-drying from TBA to suppress the formation of large ice crystals. The presence of quasi-closed pores from emulsion templating is verified by both confocal microscopy and scanning electron microscopy images and is confirmed to reduce thermal conductivity to as low as 15.5 mW/(m K). Compared to the CNF aerogel, increasing emulsion content can lead to better volume retention with significantly reduced density (11.4 mg/cm3), increased mesoporosity, and enhanced specific modulus (18.2 kPa/(mg/cm3)) and specific yield strength (1.6 kPa/(mg/cm3)). In addition, the CNF/emulsion composite aerogel also demonstrates superb flexibility and infrared shielding performance.

Optimizing material and manufacturing process for PEGDA/CNF aerogel scaffold

Cellulose nano fibril (CNF) aerogel, which is provided with high porosity, ultralow density and biodegradable ability, is a promising material for tissue engineering scaffold. Restricted by its poor mechanical properties, common CNF aerogel is unable to make scaffold with customized 3D structures. In order to make it useful in tissue engineering, the synthetic polymer Poly(ethylene glycol) diacrylate (PEGDA) has been chosen to mix with CNF solution to form a kind of composite bio-resin, which is ready for stereolithography. Our former study has proved the printability of the bio-resin and the biocompatibility of the CNF aerogel scaffold. But the relationship among its properties, material component and manufacturing condition has not been systematically studied. Thus an attempt is made to study and optimize the process factors that govern the aerogel scaffold’s property by using Taguchi experiment design in this work, where four main factors of material and fabrication process: the content of PEGDA, the content of CNF, the size of CNF and the pre-freeze temperature have been chosen to make a discussion of their effect on the aerogel scaffold’s properties including its porosity, mechanical property, micro-structure and so on. An orthogonal array of experiment is developed. It has the least number of experimental runs with desired process factor settings. The results analyzed by the tool of Analysis of Variance (ANOVA) show that different factor has various degrees of effect on different properties. Finally the optimized factors are acquired by screening the experiments data.

Facile fabrication of an effective nanocellulose-based aerogel and removal of methylene blue from aqueous system

Water pollution caused by organic dyes is becoming a critical global environmental concern. Here, we designed a novel and green aerogel by freeze-drying composed of cellulose nanofibril (CNF) and graphene oxide-silica (GO-silica), which could efficiently remove organic dyes from contaminated water and solve the recycle of nanohybrid materials. Subsequently, the as-synthesized aerogels were evaluated for the adsorption of methylene blue (MB) form aqueous solution. The results showed that GO-silica particles were synthesized successfully and displayed a low degree of crystallinity. And compared to pure CNF aerogels, the composite aerogels exhibited superior adsorption performances, with the maximum value of 608.4 mg/g. Furthermore, the adsorption kinetic and isotherm MB on the composite aerogels obeyed the pseudo-second-order and the Langmuir model, respectively. The Langmuir model fitting yielded a maximum adsorption capacity of 623.9 mg/g for MB. According to the results of the mean free energy (E) and the Elovich isotherm model, the decolorization applying CNF and composite aerogels was occurred chemically. This aerogel introduced here is easy to fabricate, efficient, and biodegradable, which makes it a potential alternative for wastewater treatment.

Carbon nanofibril composites with high sulfur loading fabricated from nanocellulose for high-performance lithium-sulfur batteries

Owing to the low cost, high theoretical specific energy density and environmentally friendly, Lithium-sulfur (Li-S) batteries have become one of the most promising candidates for electrical energy storage systems. However, some technical obstacles of lithium sulfur batteries are still addressed, such as the volume expansion, non-conductivity and shuttle effect of polysulfides. Herein, we have described a simple method for preparing carbon nanofiber aerogel (CNFA) via carbonization of the 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized cellulose nanofibril (TOCN) aerogel. Special three-dimensional (3D) net-like carbon@sulfur (C@S) composite was then successfully fabricated based on CNFA with high porosity, which dramatically alleviates the volume expansion during charging and discharging process of lithium-sulfur battery, improves the conductivity of polysulfide and suppresses the diffusion and dissolution of polysulfide generated during the charge and discharge process. The results showed that the composite material exhibited an extremely high reversible capacity of 590 mA h g−1 and had a great loaded performance of 390 mA h g−1 with high load 2.9 mg/cm2 over 200 cycles at 0.5 C. Compared with other biomass carbon materials, we have omitted the complicated high-temperature activation pore-forming process. In addition, the high sulfur loading carbon nanofibril composite aerogel also provides a way for the high-quality needs of electronic products.

Cellulose nanofibril-based aerogel derived from sago pith waste and its application on methylene blue removal

Sago pith cellulose nanofibril (SPCNF) aerogel derived from sago pith waste (SPW) was successfully produced through three consecutive steps, namely dewaxing and delignification, ultra-sonication and homogenization and freeze drying. The aerogel was characterized using field emission scanning electron microscopy (FE-SEM), Fourier-transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Results of the analyses collectively showed that lignin & hemicellulose were absent in the SPCNF aerogel product which has a high crystallinity index of 88%. The diameters of individual nanofibril constituents of the SPCNF were between 15 and 30 nm and aspect ratios >1000 were observed. The SPCNF aerogel, with a density measured at 2.1 mg/cm3, was efficient in methylene blue (MB) removal with a maximum MB adsorption of 222.2 mg/g at 20 °C. The adsorption of MB onto the SPCNF aerogel was rapid and found to follow a pseudo-second-order kinetic model with the adsorption isotherm being in congruence with the Langmuir model. The SPCNF aerogel exhibited outstanding MB removal efficacies with 5 mg and 20 mg of SPCNF capable of removing over 90% and almost 99% MB, respectively. The optimized pH value and temperature for MB adsorption were determined as pH 7 and 20 °C.

Cellulose nanofibril (CNF) based aerogels prepared by a facile process and the investigation of thermal insulation performance

Herein, a facile method on fabricating aerogels with hierarchical porous structures was created by freeze-drying the cellulose nanofibril (CNF)/methyltrimethoxysilan (MTMS)/fumed silica (FS) suspension. FS was introduced for its porous structure, which could improve the thermal insulation performance of freeze-dried aerogels. The as-prepared aerogels were hydrophobic with improved mechanical properties (elastic recovery rate was up to 99.7%) and reduced thermal conductivity (0.027 Wm−1 K−1 at 25 °C). Most importantly, the addition of FS was proved to improve the thermal insulation stability of cellulose aerogels efficiently in different values of relative humidity (RH) and temperatures. The thermal conductivity of pure CNF aerogel conditioned at 25 °C and 95% RH was 196% higher than that of the fully-dried one, while the increase was 56% for the composite aerogel. Besides, at 30% RH, the thermal conductivity increased by 24% for the pure CNF aerogel when tested from 20 to 60 °C while only a 2% increase for the composite aerogel. Moreover, when tert-butanol was used as the solvent to optimize the distribution of the pores of freeze-dried aerogels, their thermal insulation performance was further improved. Our work provides easily available CNF/MTMS/FS ternary aerogels, which are stable in thermal conductivity in the changing environment.