Stable Na Electrodeposition Enabled by Agarose-Based Water-Soluble Sodium Ion Battery Separators

A label-free fluorescent-hydrogel sensor for heparin detection in diluted whole blood

Heparin is a widely used blood anticoagulant and its monitoring in blood is essential during surgery. Unavoidable interference factors such as blood color and luminescence can interfere with the fluorescence visualization of heparin. Herein, we found a ratiometric fluorescence probe consisting of SYBR green and cresyl violet responsive to heparin mainly based on electrostatic interactions. A simple sensor was further embedded in an agarose hydrogel, exhibiting an obvious color change from orange to green without complex pretreatment of blood, which overcomes the susceptibility of fluorescence sensors toward biological samples.

Advances in agar-based composites: A comprehensive review

This review article explores the developments and applications in agar-based composites (ABCs), emphasizing various constituents such as metals, clay/ceramic, graphene, and polymers across diversified fields like wastewater treatment, drug delivery, food packaging, the energy sector, biomedical engineering, bioplastics, agriculture, and cosmetics. The focus is on agar as a sustainable and versatile biodegradable polysaccharide, highlighting research that has advanced the technology of ABCs. A bibliometric analysis is conducted using the Web of Science database, covering publications from January 2020 to March 2024, processed through VOSviewer Software Version 1.6.2. This analysis assesses evolving trends and scopes in the literature, visualizing co-words and themes that underscore the growing importance and potential of ABCs in various applications. This review paper contributes by showcasing the existing state-of-the-art knowledge and motivating further development in this promising field.

Porous Agarose Layered Magnetic Graphene Oxide Nanocomposite for Virus RNA Monitoring in Wastewater

The detection of virus RNA in wastewater has been established as a valuable method for monitoring Coronavirus disease 2019. Carbon nanomaterials hold potential application in separating virus RNA owing to their effective adsorption and extraction capabilities. However, carbon nanomaterials have limited separability under homogeneous aqueous conditions. Due to the stabilities in their nanostructure, it is a challenge to efficiently immobilize them onto magnetic beads for separation. Here, we develop a porous agarose layered magnetic graphene oxide (GO) nanocomposite that is prepared by agglutinating ferroferric oxide (Fe3O4) beads and GO with agarose into a cohesive whole. With an average porous size of approximately 500 nm, the porous structure enables the unhindered entry of virus RNA, facilitating its interaction with the surface of GO. Upon the application of a magnetic field, the nucleic acid can be separated from the solution within a few minutes, achieving adsorption efficiency and recovery rate exceeding 90% under optimized conditions. The adsorbed nucleic acid can then be preserved against complex sample matrix for 3 days, and quantitatively released for subsequent quantitative reverse transcription polymerase chain reaction (RT-qPCR) detection. The developed method was successfully utilized to analyze wastewater samples obtained from a wastewater treatment plant, detecting as few as 10 copies of RNA molecules per sample. The developed aMGO-RT-qPCR provides an efficient approach for monitoring viruses and will contribute to wastewater-based surveillance of community infections.

Enabling Further Organic Electrolyte Infiltration of Cellulose-Based Separators via Defect-Rich Polypyrrole Modification for High Sodium Ion Transport in Sodium Metal Batteries

Sodium metal batteries (SMBs) have high-density and cost-effective characteristics as one of the energy storage systems, but uncontrollable dendrite growth and poor rate performance still hinder their practical applications. Herein, a nitrogen-rich modified cellulose separator with released abundant ion transport tunnels in organic electrolyte was synthesized by in situ polymerization of polypyrrole, which is based on the high permeability of cellulose in aqueous solution and the interfacial interaction between cellulose and polypyrrole. Meanwhile, the introduction of abundant structural defects such as branch chains, oxygen-containing functional groups, and imine-like structure to disrupt polypyrrole conjugation enables the utilization of conductive polymers in composite separator applications. With the electrolyte affinity surface on, the modified separator exhibits reinforced electrolyte uptake (254%) and extended electrolyte wettability, thereby leading to accelerated ionic conductivity (2.77 mS cm-1) and homogeneous sodium deposition by facilitating the establishment of additional pathways for ion transport. Benefiting from nitrogen-rich groups, the polypyrrole-modified separator demonstrates selective Na+ transport by the data of improved Na+ transference number (0.62). Owing to the above advantages, the battery assembled with the modified separators exhibits outstanding rate performance and prominent capacity retention two times that of the pristine cellulose separator at a high current density under the condition of fluorine-free electrolyte.

Chitin Nanofibrils from Fungi for Hierarchical Gel Polymer Electrolytes for Transient Zinc-Ion Batteries with Stable Zn Electrodeposition

Rechargeable batteries play an integral role toward carbon neutrality. Environmentally sustainable batteries should consider the trade-offs between material renewability, processability, thermo-mechanical and electrochemical performance, as well as transiency. To address this dilemma, we follow circular economy principles to fabricate fungal chitin nanofibril (ChNF) gel polymer electrolytes (GPEs) for zinc-ion batteries. These biocolloids are physically entangled into hierarchical hydrogels with specific surface areas of 49.5 m2 ·g-1 . Ionic conductivities of 54.1 mS·cm-1 and a Zn2+ transference number of 0.468 are reached, outperforming conventional non-renewable/non-biodegradable glass microfibre separator-liquid electrolyte pairs. Enabled by its mechanically elastic properties and large water uptake, a stable Zn electrodeposition in symmetric Zn|Zn configuration with a lifespan above 600 h at 9.5 mA·cm-2 is obtained. At 100 mA·g-1 , the discharge capacity of Zn/α-MnO2 full cells increases above 500 cycles when replacing glass microfiber separators with ChNF GPEs, while the rate performance remains comparable to glass microfiber separators. To make the battery completely transient, the metallic current collectors are replaced by biodegradable polyester/carbon black composites undergoing degradation in water at 70 °C. This work demonstrates the applicability of bio-based materials to fabricate green and electrochemically competitive batteries with potential applications in sustainable portable electronics, or biomedicine.

Bottom-Up Design of a Green and Transient Zinc-Ion Battery with Ultralong Lifespan

Transient batteries are expected to lessen the inherent environmental impact of traditional batteries that rely on toxic and critical raw materials. This work presents the bottom-up design of a fully transient Zn-ion battery (ZIB) made of nontoxic and earth-abundant elements, including a novel hydrogel electrolyte prepared by cross-linking agarose and carboxymethyl cellulose. Facilitated by a high ionic conductivity and a high positive zinc-ion species transference number, the optimized hydrogel electrolyte enables stable cycling of the Zn anode with a lifespan extending over 8500 h for 0.25 mA cm^-2 - 0.25 mAh cm^-2 . On pairing with a biocompatible organic polydopamine-based cathode, the full cell ZIB delivers a capacity of 196 mAh g^-1 after 1000 cycles at a current density of 0.5 A g^-1 and a capacity of 110 mAh g^-1 after 10 000 cycles at a current density of 1 A g^-1 . A transient ZIB with a biodegradable agarose casing displays an open circuit voltage of 1.123 V and provides a specific capacity of 157 mAh g^-1 after 200 cycles at a current density of 50 mA g^-1 . After completing its service life, the battery can disintegrate under composting conditions.

Hierarchical Nanocellulose-Based Gel Polymer Electrolytes for Stable Na Electrodeposition in Sodium Ion Batteries

Sodium ion batteries (NIBs) based on earth-abundant materials offer efficient, safe, and environmentally sustainable solutions for a decarbonized society. However, to compete with mature energy storage technologies such as lithium ion batteries, further progress is needed, particularly regarding the energy density and operational lifetime. Considering these aspects as well as a circular economy perspective, the authors use biodegradable cellulose nanoparticles for the preparation of a gel polymer electrolyte that offers a high liquid electrolyte uptake of 2985%, an ionic conductivity of 2.32 mS cm^-1 , and a Na⁺ transference number of 0.637. A balanced ratio of mechanically rigid cellulose nanocrystals and flexible cellulose nanofibers results in a mesoporous hierarchical structure that ensures close contact with metallic Na. This architecture offers stable Na plating/stripping at current densities up to ±500 µA cm^-2 , outperforming conventional fossil-based NIBs containing separator-liquid electrolytes. Paired with an environmentally sustainable and economically attractive Na₂ Fe₂ (SO₄ )₃ cathode, the battery reaches an energy density of 240 Wh kg^-1 , delivering 69.7 mAh g^-1 after 50 cycles at a rate of 1C. In comparison, Celgard in liquid electrolyte delivers only 0.6 mAh g^-1 at C/4. Such gel polymer electrolytes may open up new opportunities for sustainable energy storage systems beyond lithium ion batteries.

Rational Design of Cellulose Nanofibrils Separator for Sodium-Ion Batteries

Cellulose nanofibrils (CNF) with high thermal stability and excellent electrolyte wettability attracted tremendous attention as a promising separator for the emerging sodium-ion batteries. The pore structure of the separator plays a vital role in electrochemical performance. CNF separators are assembled using the bottom-up approach in this study, and the pore structure is carefully controlled through film-forming techniques. The acid-treated separators prepared from the solvent exchange and freeze-drying demonstrated an optimal pore structure with a high electrolyte uptake rate (978.8%) and Na⁺ transference number (0.88). Consequently, the obtained separator showed a reversible specific capacity of 320 mAh/g and enhanced cycling performance at high rates compared to the commercial glass fiber separator (290 mAh/g). The results highlight that CNF separators with an optimized pore structure are advisable for sodium-ion batteries.