Progress, Challenge, and Perspective of Fabricating Cellulose.

Cellulose as the most abundant biopolymers on Earth, presents appealing performance in mechanical properties, thermal management, and versatile functionalization. Developing fabrication methods to design functional materials and open new application areas. However, cellulose is hard to be dissolved or melt due to its recalcitrant property. Herein, the recent progress of fabricating cellulose is summarized. First, the unique hierarchical structure of cellulose is fully investigated and the resulted processability is analysed in directions of down to nanocellulose, dissolution, and thermoplastic processing. Then, the reported fabrication methods are summarized in three aspects: (1) self-assembly from nano/micro cellulose suspensions, especially the formation of cellulose nanocrystals; (2) dissolution-regeneration-drying, covering spinning and solvent infusion processing; and (3) thermoplastic processing, focusing on the setup and the morphology changes of the prepared products. In each aspect, the flowchart of the fabrication method, the mechanism, fabricated products, and effects of processing parameters are explored. Finally, this review provides a perspective on the further direction of fabricating cellulose, especially the challenges toward mass production.

Rapid Synthesis of High-Entropy Oxide Microparticles.

High-entropy nanoparticles have received notable attention due to their tunable properties and broad material space. However, these nanoparticles are not suitable for certain applications (e.g., battery electrodes), where their microparticle (submicron to micron) counterparts are more preferred. Conventional methods used for synthesizing high-entropy nanoparticles often involve various ultrafast shock processes. To increase the size thereby achieving high-entropy microparticles, longer reaction time (e.g., heating duration) is usually used, which may also lead to undesired particle overgrowth or even densified microstructures. In this work, an approach based on Joule heating for synthesizing high-entropy oxide (HEO) microparticles with uniform elemental distribution is reported. In particular, two key synthesis conditions are identified to achieve high-quality HEO microparticles: 1) the precursors need to be loosely packed to avoid densification; 2) the heating time needs to be accurately controlled to tens of seconds instead of using milliseconds (thermal shock) that leads to nanoparticles or longer heating duration that forms bulk structures. The utility of the synthesized HEO microparticles for a range of applications, including high-performance Li-ion battery anode and water oxidation catalyst. This study opens up a new door toward synthesizing high-entropy microparticles with high quality and broad material space.

Scalable Synthesis of High Entropy Alloy Nanoparticles by Microwave Heating.

High entropy alloy nanoparticles (HEA-NPs) are reported to have superior performance in catalysis, energy storage, and conversion due to the broad range of elements that can be incorporated in these materials, enabling tunable activity, excellent thermal and chemical stability, and a synergistic catalytic effect. However, scaling the manufacturing of HEA-NPs with uniform particle size and homogeneous elemental distribution efficiently is still a challenge due to the required critical synthetic conditions where high temperature is typically involved. In this work, we demonstrate an efficient and scalable microwave heating method using carbon-based materials as substrates to fabricate HEA-NPs with uniform particle size. Due to the abundant functional group defects that can absorb microwave efficiently, reduced graphene oxide is employed as a model substrate to produce an average temperature reaching as high as ∼1850 K within seconds. As a proof-of-concept, we utilize this rapid, high-temperature heating process to synthesize PtPdFeCoNi HEA-NPs, which exhibit an average particle size of ∼12 nm and uniform elemental mixing resulting from decomposition nearly at the same time and liquid metal solidification without diffusion. Various carbon-based materials can also be employed as substrates, including one-dimensional carbon nanofibers and three-dimensional carbonized wood, which can achieve temperatures of >1400 K. This facile and efficient microwave heating method is also compatible with the roll-to-roll process, providing a feasible route for scalable HEA-NPs manufacturing.

Continuous Synthesis of Hollow High-Entropy Nanoparticles for Energy and Catalysis Applications.

Mixing multimetallic elements in hollow-structured nanoparticles is a promising strategy for the synthesis of highly efficient and cost-effective catalysts. However, the synthesis of multimetallic hollow nanoparticles is limited to two or three elements due to the difficulties in morphology control under the harsh alloying conditions. Herein, the rapid and continuous synthesis of hollow high-entropy-alloy (HEA) nanoparticles using a continuous "droplet-to-particle" method is reported. The formation of these hollow HEA nanoparticles is enabled through the decomposition of a gas-blowing agent in which a large amount of gas is produced in situ to "puff" the droplet during heating, followed by decomposition of the metal salt precursors and nucleation/growth of multimetallic particles. The high active sites per mass ratio of such hollow HEA nanoparticles makes them promising candidates for energy and electrocatalysis applications. As a proof-of-concept, it is demonstrated that these materials can be applied as the cathode catalyst for Li-O2 battery operations with a record-high current density per catalyst mass loading of 2000 mA gcat. -1 , as well as good stability and durable catalytic activity. This work offers a viable strategy for the continuous manufacturing of hollow HEA nanomaterials that can find broad applications in energy and catalysis.

Rapid Processing of Whole Bamboo with Exposed, Aligned Nanofibrils toward a High-Performance Structural Material.

Lightweight structural materials are critical in construction and automobile applications. In past centuries, there has been great success in developing strong structural materials, such as steels, concrete, and petroleum-based composites, most of which, however, are either too heavy, high cost, or nonrenewable. Biosourced composites are attractive alternatives to conventional structural materials, especially when high mechanical strength is presented. Here we demonstrate a strong, lightweight bio-based structural material derived from bamboo via a two-step manufacturing process involving partial delignification followed by microwave heating. Partial delignification is a critical step prior to microwave heating as it makes the cell walls of bamboo softer and exposes more cellulose nanofibrils, which enables superior densification of the bamboo structure via heat-driven shrinkage. Additionally, microwave heating, as a fast and uniform heating method, can drive water out of the bamboo structure, yet without destroying the material's structural integrity, even after undergoing a large volume reduction of 28.9%. The resulting microwave-heated delignified bamboo structure demonstrates outstanding mechanical properties with a nearly 2-times improved tensile strength, 3.2-times enhanced toughness, and 2-times increased bending strength compared to natural bamboo. Additionally, the specific tensile strength of the modified bamboo structure reaches 560 MPa cm3 g-1, impressive given that its density is low (1.0 g cm-3), outperforming common structural materials, such as steels, metal alloys, and petroleum-based composites. These excellent mechanical properties combined with the resource abundance, renewable and sustainable features of bamboo, as well as the rapid, scalable manufacturing process, make this strong microwave-processed bamboo structure attractive for lightweight, energy-efficient engineering applications.

High-strength cellulose films obtained by the combined action of shear force and surface selective dissolution.

Cellulose is a promising and advantageous material because it is low-cost, abundant and biodegradable. Nonetheless, dealing with this material is extremely challenging because cellulose cannot dissolve in most solvents or melt at any temperature or pressure in the air owing to strong hydrogen-bonding networks. In this work, a surface selective dissolution with shear force process was proposed to prepare cellulose films with high strength from microcrystalline cellulose powders. The tensile strength reached 94 MPa and the thermal decomposition temperature improved by 64 °C compared with that of regenerated cellulose. A mechanism of surface dissolution and reconnection was proposed to explain the process. The outstanding mechanical property attributes to tight reconnection of the undissolved cores via dissolved surfaces in cellulose powders, and the improved thermal decomposition temperature is due to preserved cellulose Ⅰ crystalline structure of microcrystalline cellulose. We believe that this cost-effective and facile method holds promise for industrial-scaleproduction of cellulose materials.