pH-Dependent Morphology Control of Cellulose Nanofiber/Graphene Oxide Cryogels

Highly Permeable and Regenerative Microhoneycomb Filters

Allergic reactions can profoundly influence the quality of life. To address the health risks posed by allergens and overcome the permeability limitations of the current filter materials, this work introduces a novel microhoneycomb (MH) material for practical filter applications such as masks. Through a synthesis process integrating ice-templating and a gas-phase post-treatment with silane, MH achieves unprecedented levels of moisture resistance and mechanical stability while preserving the highly permeable microchannels. Notably, MH is extremely elastic, with a 92% recovery rate after being compressed to 80% deformation. The filtration efficiency surpasses 98.1% against pollutant particles that simulate airborne pollens, outperforming commercial counterparts with fifth-fold greater air permeability while ensuring unparalleled user comfort. Moreover, MH offers a sustainable solution, being easily regenerated through back-flow blowing, distinguishing it from conventional nonwoven fabrics. Finally, a prototype mask incorporating MH is presented, demonstrating its immense potential as a high-performance filtration material, effectively addressing health risks posed by allergens and other harmful particles.

The regulation of CuSNPs' interface for further enhancing mechanical and photothermal conversion properties of chitosan/@CuSNPs hybrid fibers

Our previous study has demonstrated that the microstructure of copper sulfide nanoparticles (CuSNPs) can be controlled to enhance mechanical and photothermal conversion properties of chitosan (CS)/CuSNPs hybrid fibers. However, achieving optimal dispersion and compatibility of CuSNPs within a CS matrix remains a challenge, this study aims to improve dispersion and compatibility by modifying the CuSNPs' interface, thereby enhancing mechanical and photothermal conversion properties of hybrid fibers. The interfaces of @CuSNPs (CuS@Xylan NPs, CuS@SA NPs, and CuS@PEG NPs) contain hydroxyl groups, facilitating the hydrogen bonds formation with the CS matrix. The dispersibility is further enhanced by the synergistic effect of xylan and SA's anionic charges with cationic chitosan. Notably, the viscosity of the CS/@CuSNPs hybrid spinning solution is significantly enhanced, resulting in improved breaking strength for initial hybrid fibers. Specifically, the breaking strength of CS/CuS@Xylan NPs hybrid fibers reaches 1.4 cN/dtex, exhibiting a 42.86 % and 20.6 % increase over CS and CS/CuSNPs hybrid fibers. Simultaneously, the CS/CuS@Xylan NPs hybrid fibers exhibit exceptional photothermal conversion performance, surpassing that of CS fibers by 5.2 times and CS/CuSNPs hybrid fibers by 1.4 times. The regulation of interface modification is an efficient approach to enhance the tensile strength and photothermal conversion properties of CS/CuSNPs hybrid fibers.

Electrochemical Regeneration of Highly Stable and Sustainable Cellulose/Graphene Adsorbent Saturated with Dissolved Organic Dye

Electrochemical regeneration of adsorbents presents a cost-effective and environmentally friendly approach. Yet, its application to 3D structured adsorbents such as cellulose/graphene-based aerogels remains largely unexplored. This study introduces a method for producing these aerogels, highlighting their significant adsorption capacity for dissolved organic pollutants and resilience during electrochemical regeneration. By adjusting the ratio of hydrophobized cellulose nanofibers to graphene, the aerogels demonstrate a tunable adsorption capacity, ranging from 56 to 228 mg/g. Hydrophobization using oleic acid is vital for maintaining the aerogels' structural stability in water. Notably, the aerogels maintain structural integrity and efficiency over at least 18 electrochemical regeneration cycles, underscoring their potential for long-term environmental applications. The increase in adsorption capacity observed after regeneration cycles, approximately 10-20% by the fifth cycle, is attributed to electrochemical surface roughening and the creation of new adsorption sites. The tunability and durability of these aerogels offer a sustainable solution for adsorption with electrochemical regeneration technology.

Directional-Freezing-Enabled MXene Orientation toward Anisotropic PVDF/MXene Aerogels: Orientation-Dependent Properties of Hybrid Aerogels

Polymer hybrid materials that contain reinforcements with a preferred orientation have received growing attention because of their unique properties and promising applications in multifunctional fields. Herein, anisotropic poly(vinylidene fluoride) (PVDF)/MXene hybrid aerogels with highly ordered delaminated MXene nanosheets and anisotropic porous structures were successfully fabricated by unidirectional freezing of thermoreversible gels followed by a freeze-drying process. The strong interfacial interactions between PVDF chains and abundant functional groups on the surface of MXene enabled the orientation of MXene nanosheets at the boundaries of ice crystals as the semicrystalline PVDF and delaminated MXene nanosheets are squeezed along the freezing direction. These aerogels display distinct properties along the freezing and perpendicular to the freezing (transverse) directions. These anisotropic aerogels are flexible and flame-retardant and possess an anisotropic compression performance, heat transfer, electrical conductivity, and electromagnetic interference (EMI) shielding. Further, by increasing the MXene loadings, the electrical conductivity and EMI shielding performances of hybrid aerogels were significantly improved. The PVDF aerogel showed sticky hydrophobicity with a contact angle of 139°, whereas the contact angle increased significantly in hybrid aerogels (153°) with low water adhesion, making them suitable as self-cleaning materials. The combination of the above characteristics makes these hybrid aerogels potential candidates for a wide range of electronic applications.

Nanoarchitectonics of RGO-Wrapped CNF/GO Aerogels with Controlled Pore Structures by PVA-Assisted Freeze-Casting Approach for Efficient Sound and Microwave Absorption

Acoustic absorption materials play an important role in eliminating the negative effects of noise. Herein, a polyvinyl alcohol (PVA)-assisted freeze-casting was developed for controllably fabricating reduced graphene oxide wrapped carbon nanofiber (RGO@CNF)/graphene oxide composite aerogel. During the freeze-casting, PVA was used as an icing inhibitor to control the size of ice crystals. While the concentration of PVA increased from 0 to 15 mg ⋅ ml^-1 , the average pore size of the aerogel was reduced from 154 to 45 μm. Due to the modulation of the pore size and composition, the propagation path and friction loss for sound were optimized, especially at low frequency. For instance, the normalized sound absorption coefficient of RGO@CNF/GO-10 achieves 0.79 (250-6300 Hz). The sample also exhibits a desirable microwave absorbing property whose maximum reflection loss is -47.3 dB (9.44 GHz, d=3.0 mm). Prospectively, this synthetic strategy can be extended to develop other forms of elastic aerogel with a controlled pore size.

Cellulose nanofibrils-graphene hybrids: recent advances in fabrication, properties, and applications

With the fast-developing social economy and the acceleration of industrialization, seeking effective renewable, sustainable, and environmentally friendly resources that show promising properties is an urgent task and a crucial means to achieve sustainable progress in the face of the growing depletion of non-renewable resources and the deterioration of environmental issues. Cellulose nanofibrils (CNFs) are natural polymeric nanomaterials with excellent biocompatibility, biodegradability, good mechanical features, high strength, low density, high specific surface area, and tunable chemistry. Their combination with other nanomaterials, such as graphene derivatives (GNMs), has been demonstrated to be effective since they produce hybrids with outstanding physicochemical properties, tailorable functionality, and high performance. In this review, recent advances in the preparation, modification, and emerging application of CNFs/GNMs hybrids are described and discussed using the latest studies. First, the concise background of nanocellulose and graphene derivatives is provided, followed by the interfacial interactions between CNFs and GNMs. The different hybrids exhibit great promise in separation, adsorption, optics, flexible electronics, energy storage, thermal management, barrier and packaging, and electromagnetic shielding. The main challenges that inhibit the applicability of these hybrids are finally highlighted, and some perspectives for future research directions are provided.

Aqueous Dispersion of Carbon Nanomaterials with Cellulose Nanocrystals: An Investigation of Molecular Interactions

Dispersing carbon nanomaterials in solvents is effective in transferring their significant mechanical and functional properties to polymers and nanocomposites. However, poor dispersion of carbon nanomaterials impedes exploiting their full potential in nanocomposites. Cellulose nanocrystals (CNCs) are promising for dispersing and stabilizing pristine carbon nanotubes (pCNTs) and graphene nanoplatelets (pGnP) in protic media without functionalization. Here, the underlying mechanisms at the molecular level are investigated between CNC and pCNT/pGnP that stabilize their dispersion in polar solvents. Based on the spectroscopy and microscopy characterization of CNCpCNT/pGnP and density functional theory (DFT) calculations, an additional intermolecular mechanism is proposed between CNC and pCNT/pGnP that forms carbonoxygen covalent bonds between hydroxyl end groups of CNCs and the defected sites of pCNTs/pGnPs preventing re-agglomeration in polar solvents. This work's findings indicate that the CNC-assisted process enables new capabilities in harnessing nanostructures at the molecular level and tailoring the performance of nanocomposites at higher length scales.

Tuning liquid aggregation of zwitterionic chitin nanocrystals by graphene oxide planar catchers via electrostatic regulation

As important structural units, biomass nanomaterials have exhibited great potentials to construct high-performance macroscopic materials for broad applications by liquid assembly. However, the liquid aggregation of nanomaterials was less investigated. Here, we demonstrate that the one-dimensional (1D) zwitterionic chitin nanocrystals (ZChNCs) can be reversibly captured and released by two-dimensional (2D) planar catchers of graphene oxide (GO) sheets. The dominant electrostatic regulation strategy by pH variation drives that there are three reversible changes for the liquid aggregation of ZChNCs and GO, which were the isolated dispersion state (pH > 7), homogeneous hybridization state (7 ≥ pH ≥ 5), and partially stacked hybridization state (pH < 5), respectively. We found there are no sedimentation during the change of liquid aggregation with the higher absolute Zeta potentials (almost>30 mV). Moreover, the ZChNCs-GO nanohybrids have reached a maximum Zeta potential up to -80 mV, which can be explained by the ionization of excess carboxyl groups on the surface of ZChNCs. Besides, the electrostatic regulation endows the nanohybrids with rheological behavior, which is beneficial to the macro assembly of liquid nanomaterials. This work provides a new class of hybrid colloidal nanomaterials, opens the structural design dimension of macro assembly and holds great potentials in high-performance biodegradable material.

Mechanically Strong Electrically Insulated Nanopapers with High UV Resistance Derived from Aramid Nanofibers and Cellulose Nanofibrils

Aramid nanofibers (ANFs) have great potential for civil and military applications due to their remarkable mechanical modulus, excellent chemical reliability, and superior thermostability. Unfortunately, the weak combination of neighboring ANFs limits the mechanical properties of ANF-based materials owing to their inherent rigidity and chemical inertness. Herein, high-performance nanopapers are fabricated by introducing a tiny amount of cellulose nanofibrils (CNFs) to serve as reinforcing blocks via vacuum filtration. As a result of the formation of nanosized building blocks and hydrogen-bonding interaction of CNFs, the resultant ANF/CNF nanopaper yields a record-high tensile strength (406.43 ± 16.93 MPa) and toughness (86.13 ± 5.22 MJ m^-3), which are 1.8 and 4.3 times higher than those of the pure ANF nanopaper, respectively. When normalized by weight, the specific tensile strength of the nanopaper is as high as 307.90 MPa·g^-1·cm³, which is even significantly superior to that of titanium alloys (257 MPa·g^-1·cm³). The ANF/CNF nanopaper also possesses excellent dielectric strength (53.42 kV mm^-1), superior UV-shielding performance (≥99.999% absorption for ultraviolet radiation), and a favorable thermostability (T_onset = 530 °C). This study proposes a new design strategy for developing ultrathin ANF-based nanopapers combined with high reliability and thermostability for application in high-end electrical insulation fields, such as 5G communication, wearable electronics, and artificial intelligence.

Helically aligned fused carbon hollow nanospheres with chiral discrimination ability

While the functions of carbon materials with precisely controlled nanostructures have been reported in many studies, their chiral discriminating abilities have not been reported yet. Herein, chiral discrimination is achieved using helical carbon materials devoid of chiral attachments. A Fe₃O₄ nanoparticle template with ethyl cellulose (carbon source) is self-assembled on dispersed multiwalled carbon nanotubes (MWCNTs) fixed in a lamellar structure, with helical nanoparticle alignment induced by the addition of a binaphthyl derivative. Carbonization followed by template removal produces helically aligned fused carbon hollow nanospheres (CHNSs) with no chiral molecules left. Helicity is confirmed using vacuum-ultraviolet circular dichroism spectroscopy. Chiral discrimination, as revealed by the electrochemical reactions of binaphthol and a chiral ferrocene derivative in aqueous and nonaqueous electrolytes, respectively, is attributable to the chiral space formed between the CHNS and MWCNT surfaces.

Recent advances in the hybridization of cellulose and carbon nanomaterials: Interactions, structural design, functional tailoring, and applications

Due to the good biocompatibility and flexibility of cellulose and the excellent optical, electronic, as well as mechanical properties of carbon nanomaterials (CNMs), cellulose/CNM hybrid materials have been widely synthesized and used in energy storage, sensors, adsorption, biomedicine, and many other fields. In this review, we present recent advances (2016-current) in the design, structural design, functional tailoring and various applications of cellulose/CNM hybrid materials. For this aim, first the interactions between cellulose and CNMs for promoting the formation of cellulose/CNM materials are analyzed, and then the hybridization between cellulose with various CNMs for tailoring the structures and functions of hybrid materials is introduced. Further, abundant applications of cellulose/CNM hybrid materials in various fields are presented and discussed. This comprehensive review will be helpful for readers to understand the functional design and facile synthesis of cellulose-based nanocomposites, and to promote the high-performance utilization and sustainability of biomass materials in the future.

Fabrication of graphene-based porous materials: traditional and emerging approaches

The anisotropic nature of ‘graphenic’ nanosheets enables them to form stable three-dimensional porous materials. The use of these porous structures has been explored in several applications including electronics and batteries, environmental remediation, energy storage, sensors, catalysis, tissue engineering, and many more. As method of fabrication greatly influences the final pore architecture, and chemical and mechanical characteristics and performance of these porous materials, it is essential to identify and address the correlation between property and function. In this review, we report detailed analyses of the different methods of fabricating porous graphene-based structures – with a focus on graphene oxide as the base material – and relate these with the resultant morphologies, mechanical responses, and common applications of use. We discuss the feasibility of the synthesis approaches and relate the GO concentrations used in each methodology against their corresponding pore sizes to identify the areas not explored to date.

Due to their anisotropic nature, graphene nanosheets can be used to form 3-dimensional porous materials using template-free and template-directed methodologies. These fabrication strategies are found to influence the properties of the final structure.