With the increasing demand for wearable electronics (such as smartwatch equipment, wearable health monitoring systems, and human–robot interface units), flexible energy storage systems with ...eco‐friendly, low‐cost, multifunctional characteristics, and high electrochemical performances are imperative to be constructed. Nanocellulose with sustainable natural abundance, superb properties, and unique structures has emerged as a promising nanomaterial, which shows significant potential for fabricating functional energy storage systems. This review is intended to provide novel perspectives on the combination of nanocellulose with other electrochemical materials to design and fabricate nanocellulose‐based flexible composites for advanced energy storage devices. First, the unique structural characteristics and properties of nanocellulose are briefly introduced. Second, the structure–property–application relationships of these composites are addressed to optimize their performances from the perspective of processing technologies and micro/nano‐interface structure. Next, the recent specific applications of nanocellulose‐based composites, ranging from flexible lithium‐ion batteries and electrochemical supercapacitors to emerging electrochemical energy storage devices, such as lithium‐sulfur batteries, sodium‐ion batteries, and zinc‐ion batteries, are comprehensively discussed. Finally, the current challenges and future developments in nanocellulose‐based composites for the next generation of flexible energy storage systems are proposed.
Recent advances on nanocellulose‐based composites consisting of nanocellulose and other electrochemical materials for emerging flexible energy‐storage devices are comprehensively discussed, with a focus on structure–property–application relationships to optimize their performance. The current challenges and future developments regarding design and fabrication of nanocellulose‐based composites for the next generation of energy‐storage systems are discussed and proposed.
In recent decades, flexible and wearable devices have been extensively investigated due to their promising applications in portable mobile electronics and human motion monitoring. MXene, a novel ...growing family of 2D nanomaterials, demonstrates superiorities such as outstanding electrical conductivity, abundant terminal groups, unique layered‐structure, large surface area, and hydrophilicity, making it to be a potential candidate material for flexible and wearable devices. Numerous pioneering works are devoted to develop flexible MXene‐based composites with various functions and designed structures. Therefore, the latest progress of the flexible MXene‐based composites for wearable devices is summarized in this review, focusing on the preparation strategies, working mechanisms, performances, and applications in sensors, supercapacitors, and electromagnetic interference shielding materials. Moreover, the current challenges and future outlooks are also discussed.
This is a comprehensive review of flexible MXene‐based composites for various applications as wearable devices in sensors, supercapacitors, and electromagnetic interference shielding materials. The preparation strategies, working mechanisms, performances, and applications of flexible MXene‐based composites are highlighted. Additional work is suggested to be conducted to improve the performance of the flexible MXene‐based composites for wearable devices.
Lignin, as the most abundant aromatic biopolymer in nature, has attracted great attention due to the complexity and richness of its functional groups for value‐added applications. The yield of ...production of lignin and the reactivity of prepared lignin are very important to guarantee the study and development of lignin‐based chemicals and materials. Various fractionation techniques have been developed to obtain high yield and relatively high‐purity lignin as well as carbohydrates (hemicelluloses and celluloses) and to reduce the condensed and degraded nature of conventional biorefinery lignin. Herein, novel and efficient biomass fractionation and lignin fractionation towards lignin valorization are summarized and discussed.
How to fractionate efficiently: Efficient fractionation strategies for lignin are the key and basis for the subsequent transformation into value‐added products. Herein, efficient approaches of lignin fractionation towards lignin valorization are reviewed.
Due to the similarity in chemical structure, lignin has presented great potential in the synthesis of bio-based phenolic resin. Herein, a facile and scalable synthesis strategy for a novel cage-like ...lignin-based phenolic resin was proposed through direct spray drying of the mixture of phenolic resin and unmodified lignin. The as-prepared lignin-based phenolic resin was pre-carbonized and carbonized using KOH to produce mesoporous carbon materials (LPRAC) that were further employed as supercapacitor electrodes. The results revealed that the lignin addition led to the noticeable change of the resin shape from perfect sphere to cage-like structure owing to the surfactivity and hydrophilicity of lignin. The cage-like structure promoted the KOH-activated pore generation and expansion in the carbonization process, resulting in the significantly increased specific surface area of the phenolic carbon and the intensified mesoporous formation. The electrochemical performance determination indicated that the specific capacitance of LPRAC-20% (20% lignin addition) was 217.3 F/g at 0.5 A/g, which was considerably higher than that of the lignin-free phenolic carbon (122.6 F/g). Moreover, the LPRAC-20% also exhibited preferable capacitance retention and excellent cycling stability. Accordingly, the present work offers a simple and scalable approach to prepare cage-like mesoporous carbon with excellent electrochemical performance from lignin-based phenolic resin and thus provides a promising route for lignin valorization in energy storage materials.
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The recent strategies in preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were described. CNCs and CNFs are two types of nanocelluloses (NCs), and they possess various ...superior properties, such as large specific surface area, high tensile strength and stiffness, low density, and low thermal expansion coefficient. Due to various applications in biomedical engineering, food, sensor, packaging, and so on, there are many studies conducted on CNCs and CNFs. In this review, various methods of preparation of CNCs and CNFs are summarized, including mechanical, chemical, and biological methods. The methods of pretreatment of cellulose are described in view of the benefits to fibrillation.
Highlights
Preparation strategies of cellulose nanopaper were elaborated.
Functionalization of cellulose nanopaper and its advanced applications were summarized.
Prospects and challenges of cellulose ...nanopaper were discussed.
Cellulose nanopaper has shown great potential in diverse fields including optoelectronic devices, food packaging, biomedical application, and so forth, owing to their various advantages such as good flexibility, tunable light transmittance, high thermal stability, low thermal expansion coefficient, and superior mechanical properties. Herein, recent progress on the fabrication and applications of cellulose nanopaper is summarized and discussed based on the analyses of the latest studies. We begin with a brief introduction of the three types of nanocellulose: cellulose nanocrystals, cellulose nanofibrils and bacterial cellulose, recapitulating their differences in preparation and properties. Then, the main preparation methods of cellulose nanopaper including filtration method and casting method as well as the newly developed technology are systematically elaborated and compared. Furthermore, the advanced applications of cellulose nanopaper including energy storage, electronic devices, water treatment, and high-performance packaging materials were highlighted. Finally, the prospects and ongoing challenges of cellulose nanopaper were summarized.
Highlights
Hyperelastic and superlight multifunctional MXene/nanocellulose composite aerogels with high conductivity are designed by constructing biomimetic texture.
The MXene/nanocellulose aerogels ...as flexible pressure sensors exhibit appealing linear sensitivity performance (817.3 kPa
−1
).
The as-prepared compressible supercapacitor with MXene/nanocellulose electrodes reveals superior electrochemical performance (849.2 mF cm
−2
at 0.8 mA cm
−2
).
Multifunctional architecture with intriguing structural design is highly desired for realizing the promising performances in wearable sensors and flexible energy storage devices. Cellulose nanofiber (CNF) is employed for assisting in building conductive, hyperelastic, and ultralight Ti
3
C
2
T
x
MXene hybrid aerogels with oriented tracheid-like texture. The biomimetic hybrid aerogels are constructed by a facile bidirectional freezing strategy with CNF, carbon nanotube (CNT), and MXene based on synergistic electrostatic interaction and hydrogen bonding. Entangled CNF and CNT “mortars” bonded with MXene “bricks” of the tracheid structure produce good interfacial binding, and superior mechanical strength (up to 80% compressibility and extraordinary fatigue resistance of 1000 cycles at 50% strain). Benefiting from the biomimetic texture, CNF/CNT/MXene aerogel shows ultralow density of 7.48 mg cm
−3
and excellent electrical conductivity (~ 2400 S m
−1
). Used as pressure sensors, such aerogels exhibit appealing sensitivity performance with the linear sensitivity up to 817.3 kPa
−1
, which affords their application in monitoring body surface information and detecting human motion. Furthermore, the aerogels can also act as electrode materials of compressive solid-state supercapacitors that reveal satisfactory electrochemical performance (849.2 mF cm
−2
at 0.8 mA cm
−2
) and superior long cycle compression performance (88% after 10,000 cycles at a compressive strain of 30%).
•Solid acid catalytic phenolation (SACP) is applied to treat enzymatic hydrolysis lignin (EHL).•EHL is depolymerized significantly during SACP treatment without condensation.•Phenol is incorporated ...into EHL by a nucleophilic reaction that stops lignin condensation.•Treated EHL shows increased phenolic hydroxyl content and reactivity with formaldehyde.•50% phenol is substituted by treated EHL to prepare phenolic foam with satisfactory properties.
Lignin valorization offers a significant opportunity for the commercial operation of a cellulosic ethanol-derived biorefinery. In this work, a novel solid acid catalytic phenolation (SACP) process was employed to treat enzymatic hydrolysis lignin (EHL) and the obtained product was further applied to prepare lightweight phenolic foams (ρ = 30–40 kg/m3). The changes of the molecular weight and structure of lignin under the SACP treatment were investigated by GPC, Py-GCMS, and 2D-NMR analyses. The results indicated that under the optimized SACP conditions (140 °C, 4% HZSM-5, and 2 h), the molecular weight (M¯w) of EHL sharply decreased from 6695 to 2418 g/mol without condensation. The Py-GCMS and 2D-NMR analyses suggested that phenol was incorporated at the Cα position through a nucleophilic reaction and this reaction inhibited the lignin condensation during the acidic treatment. Due to the simultaneous depolymerization and phenolation, the treated lignin showed noticeable increase in phenolic hydroxyl content and reactivity with formaldehyde. The further characterization of lignin-based phenolic foams showed that the treated lignin could replace 50% phenol to prepare phenolic foams with satisfactory thermal insulation and compression strength properties. Consequently, this work demonstrates that SACP is effective to depolymerize and activate lignin for high lignin content phenolic foam preparation and offers a value-added way of lignin application as heat-insulating foam materials.
Bacterial cellulose (BC) and its derivatives are a rich source of renewable natural ingredients, which are of great significance for biomedical and medical applications but have not yet been fully ...exploited. BC is a high-purity, biocompatible, and versatile biomaterial that can be used alone or in combination with other ingredients such as polymers and nanoparticles to provide different structural organization and function. This review briefly introduces the research status of BC hydrogels, focusing on the preparation of BC-based composite hydrogels and their applications in the field of biomedicine, particularly the wound dressings, tissue engineering scaffolds, and drug delivery.
By reviewing the most recent literature on this subject, we summarized recent advances in the preparation of BC-based composite hydrogels and their advances in biomedical applications, including wound dressings, tissue engineering, and drug delivery.
BC composite hydrogels have broadened the field of application of BC and developed a variety of BC-based biomaterials with excellent properties. BC-based hydrogels have good biocompatibility and broad application prospects in the biomedical field.
BC-based composite hydrogels with the advantages of 3D structure, nontoxicity, high purity, and good biocompatibility, have great prospects in the development of sustainable and multifunctional biomaterials for biomedical applications.
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