Nanocellulose for Sustainable Water Purification

Nanocellulose-Based Materials for Water Pollutant Removal: A Review

Cellulose in the nano regime, defined as nanocellulose, has been intensively used for water treatment. Nanocellulose can be produced in various forms, including colloidal, water redispersible powders, films, membranes, papers, hydrogels/aerogels, and three-dimensional (3D) objects. They were reported for the removal of water contaminants, e.g., heavy metals, dyes, drugs, pesticides, pharmaceuticals, microbial cells, and other pollutants from water systems. This review summarized the recent technologies for water treatment using nanocellulose-based materials. A scientometric analysis of the topic was also included. Cellulose-based materials enable the removal of water contaminants, and salts offer advanced technologies for water desalination. They are widely used as substrates, adsorbents, and catalysts. They were applied for pollutant removal via several methods such as adsorption, filtration, disinfection, coagulation/flocculation, chemical precipitation, sedimentation, filtration (e.g., ultrafiltration (UF), nanofiltration (NF)), electrofiltration (electrodialysis), ion-exchange, chelation, catalysis, and photocatalysis. Processing cellulose into commercial products enables the wide use of nanocellulose-based materials as adsorbents and catalysts.

In situ Electrical Impedance Tomography for Visualizing Water Transportation in Hygroscopic Aerogels

The global water crisis demands immediate attention, and atmospheric water harvesting (AWH) provides a viable alternative. However, studying the real-time subtle relationship between water absorption, diffusion, and internal structure for hygroscopic materials is challenging. Herein, a dynamic visualization technique is proposed that utilizes an in situ electrical impedance tomography (EIT) system and a precise reconstruction algorithm to achieve real-time monitoring of the water sorption process within aerogels from an internal microstructural perspective. These results can be inferred that composites' pore sizes affecting the kinetics of their moisture absorption. In addition, the diffusion path of moisture absorption and the distribution of stored moisture inside aerogels exhibit intrinsic self-selective behavior, where the fiber skeleton of the aerogel plays a crucial role. In summary, this work proposes a generic EIT-based technique for the in situ and dynamic monitoring of the hygroscopic process, pointing to an entirely new approach regarding research on AWH materials.

A review on the potential of cellulose nanomaterials for the development of thin film composite polyamide membranes for water treatment

Membrane-based separation technologies have drawn significant interest because of their compactness, low energy consumption, and ability to be easily integrated with existing processes. There has been significant interest in the utilization of natural materials derived from sustainable and renewable resources for membrane fabrication. Cellulose is one of the promising polymers which has been extensively studied in membrane fabrication and modification due to its abundant availability, non-toxicity and biodegradability. While there have been several reviews in recent years separately on TFC membranes and cellulose-based materials for different applications, reviews exclusively focusing on cellulosic nanomaterials-based TFC membranes are still lacking. This review provides an overview of the types of cellulose nanomaterials exploited for the development and modification of TFC membranes, particularly those used for desalination and wastewater treatment. We have presented a brief description of cellulose-based nanomaterials followed by a detailed discussion of different studies addressing each cellulose nanomaterial separately. In addition, we have summarized the performance of different studies in the literature, paying particular attention to the enhancement achieved by the incorporation of cellulose nanomaterial in the membrane.

Efficient cellulose dissolution and derivatization enabled by oxalic/sulfuric acid for high-performance cellulose films as food packaging

The performance of cellulose-based materials is highly dependent on the choice of solvent systems. Exceptionally, cellulose dissolution and derivatization by efficient solvent have been considered as a key factor for large-scale industrial applications of cellulose. However, cellulose dissolution and derivatization often requires harsh reaction conditions, high energy consumption, and complex solubilizing, resulting in environmental impacts and low practical value. Here we address these limitations by using a low-temperature oxalic acid/sulfuric acid solvent to enable cellulose dissolution and derivatization for high-performance cellulose films. The dissolution and derivatization mechanism of the mixed acid is studied, demonstrating that cellulose is firstly socked by oxalic acid, then more hydrogen bonds ionized by sulfuric acid break cellulose chain, and finally the esterification reaction between oxalic acid and cellulose is catalyzed by sulfuric acid. Solutions containing 8 %-10 % cellulose are obtained and can be stored for a long time at -18 °C without significant degradation. Moreover, the cellulose film exhibits a higher tensile strength of up to 66.1 MPa, thermal stability, and degree of polymerization compared to that fabricated by sulfuric acid. These unique advantages provide new paths to utilize renewable resources for alternative food packaging materials at an industrial scale.

Fabrication of flame-retardant and water-resistant nanopapers through electrostatic complexation of phosphorylated cellulose nanofibers and chitin nanocrystals

Biogenic, sustainable two-dimensional architectures, such as films and nanopapers, have garnered considerable interest because of their low carbon footprint, biodegradability, advanced optical/mechanical characteristics, and diverse potential applications. Here, bio-based nanopapers with tailored characteristics were engineered by the electrostatic complexation of oppositely charged colloidal phosphorylated cellulose nanofibers (P-CNFs) and deacetylated chitin nanocrystals (ChNCs). The electrostatic interaction between anionic P-CNFs and cationic ChNCs enhanced the stretchability and water stability of the nanopapers. Correspondingly, they exhibited a wet tensile strength of 17.7 MPa after 24 h of water immersion. Furthermore, the nanopapers exhibited good thermal stability and excellent self-extinguishing behavior, triggered by both phosphorous and nitrogen. These features make the nanopapers sustainable and promising structures for application in advanced fields, such as optoelectronics.

Cellulose Membranes: Synthesis and Applications for Water and Gas Separation and Purification

Membranes are a selective barrier that allows certain species (molecules and ions) to pass through while blocking others. Some rely on size exclusion, where larger molecules get stuck while smaller ones permeate through. Others use differences in charge or polarity to attract and repel specific species. Membranes can purify air and water by allowing only air and water molecules to pass through, while preventing contaminants such as microorganisms and particles, or to separate a target gas or vapor, such as H2 and CO2, from other gases. The higher the flux and selectivity, the better a material is for membranes. The desirable performance can be tuned through material type (polymers, ceramics, and biobased materials), microstructure (porosity and tortuosity), and surface chemistry. Most membranes are made from plastic from petroleum-based resources, contributing to global climate change and plastic pollution. Cellulose can be an alternative sustainable resource for making renewable membranes. Cellulose exists in plant cell walls as natural fibers, which can be broken down into smaller components such as cellulose fibrils, nanofibrils, nanocrystals, and cellulose macromolecules through mechanical and chemical processing. Membranes made from reassembling these particles and molecules have variable pore architecture, porosity, and separation properties and, therefore, have a wide range of applications in nano-, micro-, and ultrafiltration and forward osmosis. Despite their advantages, cellulose membranes face some challenges. Improving the selectivity of membranes for specific molecules often comes at the expense of permeability. The stability of cellulose membranes in harsh environments or under continuous operation needs further improvement. Research is ongoing to address these challenges and develop advanced cellulose membranes with enhanced performance. This article reviews the microstructures, fabrication methods, and potential applications of cellulose membranes, providing some critical insights into processing-structure-property relationships for current state-of-the-art cellulosic membranes that could be used to improve their performance.

Aluminum-Crosslinked Nanocellulose Scaffolds for Fluoride Removal

Anionic carboxylated cellulose nanofibers (CNF) are effective media to remove cationic contaminants from water. In this study, sustainable cationic CNF-based adsorbents capable of removing anionic contaminants were demonstrated using a simple approach. Specifically, the zero-waste nitro-oxidization process was used to produce carboxylated CNF (NOCNF), which was subsequently converted into a cationic scaffold by crosslinking with aluminum ions. The system, termed Al-CNF, is found to be effective for the removal of fluoride ions from water. Using the Langmuir isotherm model, the fluoride adsorption study indicates that Al-CNF has a maximum adsorption capacity of 43.3 mg/g, which is significantly higher than that of alumina-based adsorbents such as activated alumina (16.3 mg/g). The selectivity of fluoride adsorption in the presence of other anionic species (nitrate or sulfate) by Al-CNF at different pH values was also evaluated. The results indicate that Al-CNF can maintain a relatively high selectivity towards the adsorption of fluoride. Finally, the sequential applicability of using spent Al-CNF after the fluoride adsorption to further remove cationic contaminant such as Basic Red 2 dye was demonstrated. The low cost and relatively high adsorption capacity of Al-CNF make it suitable for practical applications in fluoride removal from water.

Nanocellulose-Bovine Serum Albumin Interactions in an Aqueous Medium: Investigations Using In Situ Nanocolloidal Probe Microscopy and Reactive Molecular Dynamics Simulations

As a versatile nanomaterial derived from renewable sources, nanocellulose has attracted considerable attention for its potential applications in various sectors, especially those focused on water treatment and remediation. Here, we have combined atomic force microscopy (AFM) and reactive molecular dynamics (RMD) simulations to characterize the interactions between cellulose nanofibers modified with carboxylate or phosphate groups and the protein foulant model bovine serum albumin (BSA) at pH 3.92, which is close to the isoelectric point of BSA. Colloidal probes were prepared by modification of the AFM probes with the nanofibers, and the nanofiber coating on the AFM tip was for the first time confirmed through fluorescence labeling and confocal optical sectioning. We have found that the wet-state normalized adhesion force is approximately 17.87 ± 8.58 pN/nm for the carboxylated cellulose nanofibers (TOCNF) and about 11.70 ± 2.97 pN/nm for the phosphorylated ones (PCNF) at the studied pH. Moreover, the adsorbed protein partially unfolded at the cellulose interface due to the secondary structure's loss of intramolecular hydrogen bonds. We demonstrate that nanocellulose colloidal probes can be used as a sensitive tool to reveal interactions with BSA at nano and molecular scales and under in situ conditions. RMD simulations helped to gain a molecular- and atomistic-level understanding of the differences between these findings. In the case of PCNF, partially solvated metal ions, preferentially bound to the phosphates, reduced the direct protein-cellulose connections. This understanding can lead to significant advancements in the development of cellulose-based antifouling surfaces and provide crucial insights for expanding the pH range of use and suggesting appropriate recalibrations.

Introducing terminal alkyne groups at the reducing end of cellulose nanocrystals by aldimine condensation for further click reaction

In recent years, click reactions with cellulose nanocrystals (CNC) participation have gradually become a research hotspot. Carboxylamine condensation is the most used method to introduce terminal alkyne groups at the reducing end of CNC as reaction sites for click reactions. However, hydroxyl groups on CNC surface would be slightly oxidized during the carboxyamine condensation process, inducing the potential positions of introduced alkynes would be not only at the reducing end but also on CNC surface. Here, aldimine condensation was proposed to introduce terminal alkyne groups just at the reducing end of CNC, and a systematic comparison analysis was conducted with carboxylamine condensation. Firstly, the selectivity and extent of alkynylation were characterized by XPS and EA. Secondly, the end aldehyde content in these CNC samples was measured by the BCA method, which quantitatively explained the grafting efficiency of aldimine condensation and further verified its feasibility. Thirdly, the clickability of the modified CNC samples was confirmed through XPS analysis of the products after a pre-designed click reaction. In sum, aldimine condensation was proven to be a simple and effective strategy for introducing terminal alkyne groups at the reducing end of CNC, which could be used as reaction sites for further click reactions.

Fabrication of Loose Nanofiltration Membrane by Crosslinking TEMPO-Oxidized Cellulose Nanofibers for Effective Dye/Salt Separation

Dye/salt separation has gained increasing attention in recent years, prompting the quest to find cost-effective and environmentally friendly raw materials for synthesizing high performance nanofiltration (NF) membrane for effective dye/salt separation. Herein, a high-performance loose-structured NF membrane was fabricated via a simple vacuum filtration method using a green nanomaterial, 2,2,6,6-tetramethylpiperidine-1-oxide radical (TEMPO)-oxidized cellulose nanofiber (TOCNF), by sequentially filtrating larger-sized and finer-sized TOCNFs on a microporous substrate, followed by crosslinking with trimesoyl chloride. The resulting TCM membrane possessed a separating layer composed entirely of pure TOCNF, eliminating the need for other polymer or nanomaterial additives. TCM membranes exhibit high performance and effective dye/salt selectivity. Scanning Electron Microscope (SEM) analysis shows that the TCM membrane with the Fine-TOCNF layer has a tight layered structure. Further characterizations via Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed the presence of functional groups and chemical bonds of the crosslinked membrane. Notably, the optimized TCM-5 membrane exhibits a rejection rate of over 99% for various dyes (Congo red and orange yellow) and 14.2% for NaCl, showcasing a potential candidate for efficient dye wastewater treatment.

Biomass-derived cellulose nanocrystals modified nZVI for enhanced tetrabromobisphenol A (TBBPA) removal

Nano zero-valent iron (nZVI) is an advanced environmental functional material for the degradation of tetrabromobisphenol A (TBBPA). However, high surface energy, self-agglomeration and low electron selectivity limit degradation rate and complete debromination of bare nZVI. Herein, we presented biomass-derived cellulose nanocrystals (CNC) modified nZVI (CNC/nZVI) for enhanced TBBPA removal. The effects of raw material (straw, filter paper and cotton), process (time, type and concentration of acid hydrolysis) and synthesis methods (in-situ and ex-situ) on fabrication of CNC/nZVI were systematically evaluated based on TBBPA removal performance. The optimized CNC-S/nZVI(in) was prepared via in-situ liquid-phase reduction using straw as raw material of CNC and processing through 44 % H2SO4 for 165 min. Characterizations illustrated nZVI was anchored to the active sites at CNC interface through electrostatic interactions, hydrogen bonds and FeO coordinations. The batch experiments showed 0.5 g/L CNC-S/nZVI(in) achieved 96.5 % removal efficiency at pH = 7 for 10 mg/L initial TBBPA. The enhanced TBBPA dehalogenation by CNC-S/nZVI(in), involving in initial adsorption, reduction process and partial detachment of debrominated products, were possibly attributed to elevated pre-adsorption capacity and high-efficiency delivery of electrons synergistically. This study indicated that fine-tuned fabrication of CNC/nZVI could potentially be a promising alternative for remediation of TBBPA-contaminated aquatic environments.

Nanocellulose-stabilized nanocomposites for effective Hg(II) removal and detection: a comprehensive review

Mercury pollution, with India ranked as the world's second-largest emitter, poses a critical environmental and public health challenge and underscores the need for rigorous research and effective mitigation strategies. Nanocellulose is derived from cellulose, the most abundant natural polymer on earth, and stands out as an excellent choice for mercury ion remediation due to its remarkable adsorption capacity, which is attributed to its high specific surface area and abundant functional groups, enabling efficient Hg(II) ion removal from contaminated water sources. This review paper investigates the compelling potential of nanocellulose as a scavenging tool for Hg(II) ion contamination. The comprehensive examination encompasses the fundamental attributes of nanocellulose, its diverse fabrication techniques, and the innovative development methods of nanocellulose-based nanocomposites. The paper further delves into the mechanisms that underlie Hg removal using nanocellulose, as well as the integration of nanocellulose in Hg detection methodologies, and also acknowledges the substantial challenges that lie ahead. This review aims to pave the way for sustainable solutions in mitigating Hg contamination using nanocellulose-based nanocomposites to address the global context of this environmental concern.

Cellulose nanocrystals intercalated clay biocomposite for rapid Cr(VI) removal

The application of bentonite (Bt) as an adsorbent for heavy metals has been limited due to its hydrophobicity and insufficient surface area. Herein, we present cellulose nanocrystal (CNC) modified Bt composite (CNC@Bt) with enhanced efficiency for Cr(VI) removal. CNC@Bt exhibited an increased specific surface area and a porous structure, while maintaining the original crystal structure of Bt. This was achieved through a synergistic function of ion exchange, hydrogen bonding, electrostatic interactions, and steric hindrance. The adsorption of Cr(VI) by CNC@Bt followed the pseudo-second-order kinetic and Langmuir isotherm adsorption model. Moreover, the process was endothermic and spontaneous. At an initial Cr(VI) concentration of 20 mg/L and pH = 4.0, 10 g/L CNC@Bt achieved a removal rate of 92.7%, and the adsorption capacity was 1.85 mg/g, significantly higher than bare Bt (37.9% and 0.76 mg/g). The removal efficiency remained consistently above 80% over a wide pH range, indicating the potential practical applicability of CNC@Bt. With its fast adsorption rate, pH adaptability, and stable performance, CNC@Bt presents promising prospects for the rapid treatment of Cr-contaminated wastewater.

Carboxyl-modified nanocellulose (cNC) enhances the stability of cNC/pullulan bio-nanocomposite hard capsule against moisture variation

The quality of polysaccharide-based films and hard capsules is often affected by changes in relative humidity, manifesting as unstable water content, and changes in mechanical strength that make them brittle or soft. Herein, carboxyl-modified nanocellulose (cNC) was prepared and used as a new component to successfully improve the moisture resistance of cNC/pullulan/high-acyl gellan bio-nanocomposite hard capsules (NCPGs). Homogenously dispersed cNC in the pullulan/high-acyl gellan matrix could render the formation of more hydrogen bonds that provided additional water-binding sites and limited the free movement of pullulan and high-acyl gellan molecular chains within NCPGs. This contributed to a decreased amount of pooling adsorption water and an increased amount of Langmuir adsorption water in NCPGs, as compared to pullulan/high-acyl gellan hard capsules (PGs) without cNC. Therefore, the equilibrium moisture content (EMC) values of NCPGs decreased at 83 % relative humidity and increased at 23 % relative humidity compared to those of PGs. Together with enhanced mechanical and barrier properties, NCPGs effectively protected encapsulated amoxicillin and probiotic powder from changes in the outside humidity. Additionally, NCPGs exhibited faster drug release. This study presents a new mechanism and strategy for fabricating films and hard capsules with enhanced stability against moisture variation.

Fundamental investigation of micro-nano cellulose and lignin interaction for transparent paper: Experiment and electrostatic potential calculation

Plastic has significant negative consequences for the environment and human health, demanding greener alternatives. Lignocellulose is a sustainable biomass material, and its paper has been considered as a potential material to replace plastics. Micro-nano lignocellulose, derived from natural plants, possesses a small size and abundant hydrogen bonding capacity. However, there is no clear explanation for the interactions between lignin and micro-nano cellulose, and little understanding of how the interaction can affect the papers' structure and optical properties. Electrostatic potential calculation is a reliable tool to explain non-covalent interactions, and can explore the binding between lignin and micro-nano cellulose. In this paper, kenaf - a non-wood fiber raw material - was employed to prepare micro-nano lignocellulose. The resulting slurry facilitated the production of transparent paper via a simple casting method. The prepared transparent micro-nano paper exhibited high transparency (~90 %), UVA resistance (~80 %), and hydrophobicity (~114°). More importantly, the electrostatic potential calculation demonstrates the inherent relationship between structure and performance, providing practical knowledge for constructing film materials.

The Missing Chalcogen Bonding Donor: Strongly Polarized Oxygen of Water

A biscyclen molecular cabin, synthesized by connecting two cyclen macrocycles with four linkages, entraps a Li+···H2O···Li+ trimer with a water molecule clamped by two Li+ ions. This configuration results in strongly polarized water, characterized by a water proton resonance shift of up to 10.00 ppm. The arrangement facilitates unprecedented O-centered chalcogen bonds between the lone pairs of pyridinyl nitrogen atoms and polarized water oxygen, as confirmed by X-ray crystallography, NMR spectroscopy, and theoretical calculations. Further observation of O-centered chalcogen bonding in a H2O·(LiCl)2 cluster suggests its widespread presence in hydrated salt systems.

Cellulose modification for sustainable polymers: overcoming problems of solubility and processing

Two new water-soluble cellulose derivatives were prepared by a two-step transformation with 1,3-propane sultone, followed by either maleic or succinic anhydride, thereby converting cellulose into a more easily processable form. It was found that the solubility was dependent on both the degree of substitution and the chemical properties of the substituents. The water-soluble cellulose has a molecular weight greater than 100 000 g mol-1 and both the morphology and molecular weight can be tuned by varying the reaction conditions. Furthermore, the flexible, two-step nature of the process allows for expansion of this methodology in order to prepare cellulose analogues for different applications.

Fabrication of cellulose nanocrystals/carboxymethyl cellulose/zeolite membranes for methylene blue dye removal: understanding factors, adsorption kinetics, and thermodynamic isotherms

This study introduces environmentally-friendly nanocellulose-based membranes for AZO dye (methylene blue, MB) removal from wastewater. These membranes, made of cellulose nanocrystals (CNCs), carboxymethyl cellulose (CMC), zeolite, and citric acid, aim to offer eco-friendly water treatment solutions. CNCs, obtained from sugarcane bagasse, act as the foundational material for the membranes. The study aims to investigate both the composition of the membranes (CMC/CNC/zeolite/citric acid) and the critical adsorption factors (initial MB concentration, contact time, temperature, and pH) that impact the removal of the dye. After systematic experimentation, the optimal membrane composition is identified as 60% CNC, 15% CMC, 20% zeolites, and 5% citric acid. This composition achieved a 79.9% dye removal efficiency and a 38.3 mg/g adsorption capacity at pH 7. The optimized membrane exhibited enhanced MB dye removal under specific conditions, including a 50 mg adsorbent mass, 50 ppm dye concentration, 50 mL solution volume, 120-min contact time, and a temperature of 25°C. Increasing pH from neutral to alkaline enhances MB dye removal efficiency from 79.9% to 94.5%, with the adsorption capacity rising from 38.3 mg/g to 76.5 mg/g. The study extended to study the MB adsorption mechanisms, revealing the chemisorption of MB dye with pseudo-second-order kinetics. Chemical thermodynamic experiments determine the Freundlich isotherm as the apt model for MB dye adsorption on the membrane surface. In conclusion, this study successfully develops nanocellulose-based membranes for efficient AZO dye removal, contributing to sustainable water treatment technologies and environmental preservation efforts.

Recent advances in TEMPO-oxidized cellulose nanofibers: Oxidation mechanism, characterization, properties and applications

Cellulose is the richest renewable polymer source on the earth. TEMPO-mediated oxidized cellulose nanofibers are deduced from enormously available wood biomass and functionalized with carboxyl groups. The preparation procedure of TOCNFs is more environmentally friendly compared to other cellulose, for example, MFC and CNCs. Due to the presence of functional carboxyl groups, TOCNF-based materials have been studied widely in different fields, including biomedicine, wastewater treatment, bioelectronics and others. In this review, the TEMPO oxidation mechanism, the properties and applications of TOCNFs are elaborated. Most importantly, the recent advanced applications and the beneficial role of TOCNFs in the various abovementioned fields are discussed. Furthermore, the performances and research progress on the fabrication of TOCNFs are summarized. It is expected that this timely review will help further research on the invention of novel material from TOCNFs and its applications in different advanced fields, including biomedicine, bioelectronics, wastewater treatment, and the energy sector.

Robust synthesis of free-standing films comprising conjugated microporous polymers nanotubes for water disinfection

Water environmental pollution especially caused by bacteria, viruses and other microorganisms always would accelerate the spread of infectious diseases and has been one of the issues highly concerned by the World Health Organization for a long time. The development of novel antibacterial materials with high activity for water cleanness was of great importance for public health and ecological sustainable development. In this work, we developed two really free-standing conjugated microprous polymers (CMPs) film with large size and processibility by a simple and convenient solid surface-assisted polymerization between bromo- and aryl-acetylene monomers. With the solid interfacial orientation from silica nanofibers, the resulting CMPs film exhibited nanotube-liked morphology with BET surface area of 379.5 m2 g-1 and 480.1 m2 g-1. The introduction of antibacterial isocyanurate and acetanilide group into polymer skeleton brings the resulting CMPs film intrinsically antimicrobial capability and durability. The growth of E. coli can be completely inhibited by the resulting CMPs film even after several cycles. Our work was suggested to provide a new route for rational design of CMPs film or membrane with antibacterial activity for water treatment and sterilization.

Enhanced Photothermal Property of NDI-Based Conjugated Polymers by Copolymerization with a Thiadiazolobenzotriazole Unit

Solar steam generation (SSG) is a promising photothermal technology to solve the global water storage issue. The potential of π-conjugated polymers as photothermal materials is significant, because their absorption range can be customized through molecular design. In this study, naphthalenediimide (NDI) and thiadiazolobenzotriazole (TBZ) were employed as bifunctional monomers to produce conjugated polymers. There are two types of polymers, P1 and P2. P1 is based on NDI, while P2 is a copolymer of NDI and TBZ in a ratio of 9:1. Both polymers had high molecular weights and sufficient thermal stability. UV-vis-near-infrared (NIR) absorption spectra revealed that both polymers have large extinction coefficients ascribed to the NDI and TBZ chromophores. Notably, the absorption spectrum of P2 exhibited a significant red shift compared to P1, resulting in a narrow optical bandgap and absorption in the NIR range. This result suggested that P2 has a higher light absorption than P1. Photoluminescence (PL) spectra were measured to elucidate the conversion of the absorbed light into thermal energy. It was found that P2 has a reduced fluorescence quantum yield as a result of the TBZ unit, signifying a proficient conversion of the photothermal energy. Based on the results, it appears that the P2 film has a greater photothermal property compared to that of the P1 film. The surface temperature of the P2 film reached approximately 50 °C under the investigated conditions. In addition, copolymer P2 exhibited an impressive SSG efficiency of 72.4% under 1 sun (1000 W/m2) irradiation. All the results suggested that narrow bandgap conjugated polymers containing the TBZ unit are highly effective materials for achieving optimal performance in SSGs.

Nanocelluloses fine-tuned polyvinylidene fluoride (PVDF) membrane for enhanced separation and antifouling

To mitigate membrane fouling and address the trade-off between permeability and selectivity, we fabricated nanocellulose (NC) fine-tuned polyvinylidene fluoride (PVDF) porous membranes (NC-PVDFs) using phase inversion method through blending NCs with varied aspect ratios, surface charges and grafted functional groups. NC-PVDF presented rougher surface (increased by at least 18.3 %), higher porosity and crystallinity compared to PVDF membrane. Moreover, cellulose nanocrystals incorporated PVDF (CNC-PVDF) elevated membrane surface charge and hydrophilicity (from 74.3° to 71.7°), while 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers modified PVDF (TCNF-PVDF) enhanced the porosity (from 25.0 % to 40.3 %) and tensile strength (63.6 % higher than PVDF). For separation performance, NC improved flux, rejection and fouling resistance due to facilitation of phase transition thermokinetics as pore-forming agent and increased hydrophilicity at both interface and pore wall. For water flux, NC-PVDFs (139-228 L·m-2·h-1) resulted in increased permeability compared to bare PVDF. CNC-PVDF membrane exhibited the highest water flux because of improved porosity, roughness and hydrophilicity. For bovine serum albumin (BSA) rejection, the removal rates of all NC-PVDFs were all above 90 %. Notably, TCNF-PVDF exhibited the most remarkable elevation of BSA rejection (95.1 %) owing to size exclusion and charge repulsion in comparison with PVDF.

MOF-derived Co-Ni layered double hydroxides/polyethyleneimine modified chitosan micro-nanoreactor for high-efficiency capture of uranium from seawater

The preparation of powder adsorbent into microsphere adsorbent is one of the effective methods for the industrialization of uranium extraction from seawater. Herein, a MOF-derived Co-Ni layered double hydroxides/polyethyleneimine modified chitosan micro-nanoreactor (DNPM) was prepared by a simple method in this work. The microstructure and chemical structure of DNPM were comprehensively characterized. The pH value, adsorption time, initial solution concentration, temperature, competitive ions, regeneration performance, and bed column heights were investigated for the adsorption performance of DNPM by batch adsorption and fixed-bed column continuous adsorption experiments. When the contact time was 8 h, the initial concentration was 150 mg/L, and the pH value was 6, the adsorption capacity of DNPM was 334.67 mg/g. The uranium adsorption by DNPM fits with the pseudo-second-order kinetic and Langmuir models, which was a spontaneous and endothermic process. In addition, DNPM has good adsorption selectivity and reusability. The fixed-bed column continuous adsorption experiment shows that the adsorption capacity increased with the increase of bed column height. The adsorption mechanism can be attributed to coordination chelation and electrostatic interaction. In general, this work provides an effective strategy for developing environmentally friendly uranium adsorbent that can be industrially used.

Function-Led Design of Covalent-Organic-Framework Membranes for Precise Ion Separation

Insufficient access to clean water and resources has emerged as one of the most pressing issues affecting people globally. Membrane-based ion separation has become a focal point of research for the generation of fresh water and the extraction of energy elements. This Review encapsulates recent advancements in the selective ion transport of covalent organic framework (COF) membranes, accomplished by strategically pairing diverse monomers to create membranes with various pore sizes and environments for specific purposes. We first discuss the merits of using COF materials as a basis for fabricating membranes for ion separation. We then explore the development of COF membranes in areas such as desalination, acid recovery, and energy element extraction, with a particular emphasis on the fundamental principles of membrane design. Lastly, we address both theoretical and practical challenges, as well as potential opportunities in the targeted design of ion-selective membranes. The goal of this Review is to stimulate future investigative efforts in this field, which is of significant scientific and strategic importance.

Fixed-bed column adsorption modeling using Zr biocomposites for fluoride removal

This research involved conducting continuous adsorption experiments to assess fluoride elimination from drinking water achieved by utilizing biocomposites created from the peels of oranges and apples, which were impregnated with zirconium (Zr), to form BOP-Zr and BAP-Zr, respectively. The findings from the experimental data indicate that BOP-Zr and BAP-Zr are effective biosorbents with a solid ability to remove fluoride selectively. Additionally, these biosorbents were found to be stable, as they do not release Zr into the treated water. Notably, these environmentally friendly biosorbents are derived from renewable sources and enhance the value of waste materials. The study employed various empirical models, including Bohart-Adamas, Thomas, Yoon-Nelson, BDST, Clark, Yan, and Woolborska, to elucidate the mechanisms and crucial parameters involved in fluoride adsorption within packed bed columns. The Yan model demonstrated the highest correlation among these models, indicating a chemical adsorption process with kinetics following a pseudo-second-order pattern. BOP-Zr and BAP-Zr exhibited a maximum adsorption capacity of 59.3 and 47.5 mg/g, respectively, under a flow rate of 4 mL/min and an inlet fluoride concentration of 25 mg/L. The analysis of mass transfer coefficients revealed that the primary step governing the adsorption procedure was diffusion through pores. Consequently, the study conclusively establishes that BOP-Zr and BAP-Zr biocomposites, originating from lignocellulosic biomass remains, present a practical and competitive choice for eliminating fluoride from water. These materials surpass waste materials in performance and rival more expensive options in efficiency and performance.

Controlling the nanocellulose morphology by preparation conditions

Nanocellulose (NC) is the desired building block for novel biomaterials. The morphology of NC is one of the core parameters impacting the functionality and property of engineered functional materials. This work aims to reveal the relationship between the product morphology and sulfuric acid hydrolysis conditions (including acid concentration, temperature and time), and to realize morphological regulation of obtained NC. Three representative products were obtained from microcrystalline cellulose via sulfuric acid hydrolysis, which are cellulose nanocrystals with broad size distribution (W-CNC, 383.9 ± 131.7 nm in length, 6 ± 2.1 nm in height) obtained by 61 % H2SO4, 55 °C and 90 min, cellulose nanospheres (CNS, 61.3 ± 15.9 nm in diameter) obtained by 64 % H2SO4, 35 °C and 75 min, and CNC with narrow size distribution (N-CNC, 276.1 ± 28.7 nm in length, 4.1 ± 0.6 nm in height), obtained by 64 % H2SO4, 45 °C and 45 min. The results showed that the crystallographic form of W-CNC and N-CNC are cellulose I, while cellulose I and II coexist in CNS. Only W-CNC and N-CNC can form chiral nematic structures through evaporation-induced self-assembly strategy and reflected light with specific wavelengths. In addition, the formation mechanism of CNS with cellulose I/II was proposed, which provided a better understanding of NC morphology regulation.

High Freshwater Flux Solar Desalination via a 3D Plasmonic Evaporator with an Efficient Heat-Mass Evaporation Interface

Passive solar desalination with interfacial heating is a promising technique to utilize solar energy to convert seawater into fresh water through evaporation and condensation. However, the current freshwater flux of solar desalination is much below industrial requirements (> 20 L m-2  h-1 ). Herein, it is demonstrated that a 3D plasmonic evaporator with an efficient heat-mass evaporation interface (HM-EI) achieves a freshwater flux of 29.1 L m-2  h-1 for 3.5 wt.% NaCl, which surpasses the previous solar evaporators and approaches the level of reverse osmosis (the highest installed capacity in industrial seawater desalination technology). The realization of high freshwater flux solar desalination comes from the efficient HM-EI comprising a grid-like plasmonic macrostructure for enhanced energy utilization in heat properties and a large-pore microstructure for accelerated ion transport in mass properties. This work provides a new direction for designing next-generation solar evaporators with high freshwater flux for industrial requirements.

Coconut coir-derived nanocellulose as an efficient adsorbent for removal of cationic dye safranin-O: a detailed mechanistic adsorption study

Coconut (Cocos nucifera) coir is an abundant agricultural waste prevalent worldwide. Utilization of this waste has been carried out in this study by obtaining nanocellulose (NC) fibres for wastewater remediation purposes. Nanocellulose was obtained from coconut coir using bleaching and acid-alkali treatments followed by ultrasonication and lyophilization. The structural, compositional, surface and thermal properties of the synthesized material were identified using transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, differential thermal (DT) and derivative thermogravimetric (DTG) analyses. These analyses confirmed the synthesized NC with enhanced thermal stability and porosity which was further used for adsorption process. After synthesis, NC was used for the removal of cationic dye safranin-O from water under ambient conditions through batch adsorption studies. The batch adsorption studies revealed that at 10 ppm of dye concentration, above 99% removal was achieved by 100 mg dosage of NC within 4.5 h at room temperature with qe (maximum adsorption capacity at equilibrium) value of around 83 mg g-1. The corresponding adsorption process fitted well with Langmuir isotherm and pseudo-second order kinetics. The primary mode of adsorption from the thermodynamic studies was found to be chemisorption. The adsorption process was achieved through response surface methodology (RSM) study which revealed that at optimized conditions of temperature 35 °C with a dose of 137.50 mg and contact time of 180 min, above 99% of dye (conc. 0.01 mg mL-1) was removed. In addition, the adsorbent can be recycled up to six cycles without any significant loss of its adsorption capacity. The present comprehensive study revealed that a greener eco-friendly synthesis of NC from waste material coconut coir was an effective nanoadsorbent for dye removal with high efficacy. This surely opens up opportunities to develop sustainable protocols for efficient environmental remediation.

Green synthesize of copper nanoparticles on the cotton fabric as a self-regenerating and high-efficient plasmonic solar evaporator

Harvesting solar energy, as a clean and abundant resource, in the photothermal process, is the winning point of solar steam generation (SSG) systems. Herein, copper plasmonic nanoparticles were synthesized through a green method via red sanders extraction on the cotton fabric as the reducing matrix. The prepared fabrics were analyzed using FESEM, EDS, XRD, PL, Raman, and contact angle. The treated fabric on the stitched PU foam with cotton yarns with bio-inspired jellyfish structure was used for heat localization and water transmission, simultaneously. The evaporation rate, enhancement, and conversion efficiency of the plasmonic SSG were 1.73 kg m-2 h-1, 179%, and ~ 98%, under one sun irradiation, respectively. The quality of the collected water was investigated via induced coupled plasma which presents the proper solar desalination (> 99.83% for filtration of Na+ ion). Regenerating features of the treated fabric along with the simple and cost-effective preparation method promises viable aspects of our system for large-scale applications.

Current and Potential Applications of Green Membranes with Nanocellulose

Large-scale applications of nanotechnology have been extensively studied within the last decade. By exploiting certain advantageous properties of nanomaterials, multifunctional products can be manufactured that can contribute to the improvement of everyday life. In recent years, one such material has been nanocellulose. Nanocellulose (NC) is a naturally occurring nanomaterial and a high-performance additive extracted from plant fibers. This sustainable material is characterized by a unique combination of exceptional properties, including high tensile strength, biocompatibility, and electrical conductivity. In recent studies, these unique properties of nanocellulose have been analyzed and applied to processes related to membrane technology. This article provides a review of recent synthesis methods and characterization of nanocellulose-based membranes, followed by a study of their applications on a larger scale. The article reviews successful case studies of the incorporation of nanocellulose in different types of membrane materials, as well as their utilization in water purification, desalination, gas separations/gas barriers, and antimicrobial applications, in an effort to provide an enhanced comprehension of their capabilities in commercial products.

Preparation of cellulose nanocrystals from commercial dissolving pulp using an engineered cellulase system

There is increasing attention to the production of cellulose nanocrystals (CNCs) from lignocellulosic biomass by enzymatic hydrolysis with cellulase. In this study, the feasibility of the application of a cellulase system from engineered strain Penicillium oxalicum cEES in the production of CNCs was assessed. Using commercial eucalyptus dissolving pulp (EDP) as substrate, the CNCs were successfully obtained by enzymatic hydrolysis with the cellulase cEES, and the total yields of CNCs reached 15.7% through three-step enzymatic hydrolysis of total 72 h (24 h for each step). The prepared CNCs were characterized and found that their crystallinity and thermal stability were higher than that of EDP. In the later stage of enzymatic hydrolysis, the process efficiency of enzymatic preparation of CNCs greatly decreased because of the high crystallinity of cellulosic substrate, and a simple homogenization treatment can promote the enzymatic hydrolysis, as well as produce fusiform CNCs with more uniform size and more fermentable sugar that could be further converted into fuels and bulk chemicals through fermentation. This study provides a feasible enzymatic preparation process for CNCs with engineered cellulase and commercial cellulosic materials.

Carbon dots, cellulose nanofiber, and essential oil from Torreya grandis aril added to fish scale gelatin film for tomato preservation

In this study, carbon dots (CDs), cellulose nanofibers (CNF) and essential oil nanoemulsion (EON) were extracted from the aril waste of Torreya grandis following nuts production. These three nanomaterials were formulated for the preparation of a composite film to be employed for postharvest tomato storage. Visual, microscopical and physicochemical properties of the prepared nanocomposite films were analyzed at different levels of CDs and CNF for optimization purposes. The UV absorption and antioxidant capacity of gelatin film with 10 % CDs (G/10CD) were enhanced compared with gelatin (G) film, concurrent with a reduction in water barrier capacity, water contact angle (WCA) and tensile strength (TS). Compared with G/10CD film, the WCA of gelatin film after incorporation of 10 % CDs and 3 % CNF (G/10CD/3CNF) was significantly increased by 14.5°at 55 s. In contrast, TS increased by 1.26 MPa, as well as the significant enhancement in water barrier capacity. The above composite film mixed with NEO (G/10CD/3CNF/EON) exerted further antimicrobial effects against Escherichia coli. G/10CD/3CNF/EON coating effectively extended tomato shift life compared with the control group. Therefore, this new eco-friendly film presents several advantages of biodegradability, sustainability as well as multifunctional properties posing it as potential packaging material for food applications.

Covalent Crosslinking Cellulose/Graphene Aerogels with High Elasticity and Adsorbability for Heavy Metal Ions Adsorption

With the fast development of modern industry, heavy metal contaminant became more severe. How to remove heavy metal ions in water in a green and efficient way is a prominent problem in current environmental protection. The adsorption of cellulose aerogel as a novel heavy metal removal technology has many advantages, including abundant resources, environmental friendly, high specific surface, high porosities and without second pollution, which means it has a wide application prospect. Here, we reported a self-assembly and covalent crosslinking strategy to prepare elastic and porous cellulose aerogels using PVA and graphene and cellulose as precursor. The resulting cellulose aerogel had a low density of 12.31 mg cm^-3 and excellent mechanical properties, which can recover to its initial form at 80% compressive strain. Meanwhile, the cellulose aerogel had strong adsorption capacity of Cu²⁺ (80.12 mg g^-1), C_d²⁺ (102.23 mg g^-1), Cr³⁺ (123.02 mg g^-1), Co²⁺ (62.38 mg g^-1), Zn²⁺ (69.55 mg g^-1), and Pb²⁺ (57.16 mg g^-1). In addition, the adsorption mechanism of the cellulose aerogel was investigated using adsorption kinetics and adsorption isotherm, and the conclusion was that the adsorption process was mainly controlled by chemisorption mechanism. Therefore, cellulose aerogel, as a kind of green adsorption material, has a very high application potential in future water treatment applications.

One-pot synthesis of magnetic cellulose nanocrystal and its post-functionalization for doxycycline adsorption

The composite of magnetite (Fe₃O₄) and cellulose nanocrystal (CNC) is considered a potential adsorbent for water treatment and environmental remediation. In the current study, a one-pot hydrothermal procedure was utilized for magnetic cellulose nanocrystal (MCNC) development from microcrystalline cellulose (MCC) in the presence of ferric chloride, ferrous chloride, urea, and hydrochloric acid. The x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and Fourier-transform infrared spectroscopy analysis confirmed the presence of CNC and Fe₃O₄, while transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis verified their respective sizes (< 400 nm and ≤ 20 nm) in the generated composite. To have an efficient adsorption activity for doxycycline hyclate (DOX), the produced MCNC was post-treated using chloroacetic acid (CAA), chlorosulfonic acid (CSA), or iodobenzene (IB). The introduction of carboxylate, sulfonate, and phenyl groups in the post-treatment was confirmed by FTIR and XPS analysis. Such post treatments decreased the crystallinity index and thermal stability of the samples but improved their DOX adsorption capacity. The adsorption analysis at different pHs revealed the increase in the adsorption capacity by reducing the basicity of the medium due to decreasing electrostatic repulsions and inducing strong attractions.

Spray-assisted LBL assembly of chitosan/nanocellulose as coatings of commercial membranes for oil-in-water emulsion separation

Owing to the limitation of their wettability and pore size, lab filter membrane could not separate oil/water emulsions. Herein, we present surface modification of commercial membranes with chitosan/nanocellulose coatings via a spray-assisted layer-by-layer (LBL) assembly technology. By alternate spraying chitosan (CS) solution and TEMPO-oxidized tunicate cellulose nanofiber (TCNF) suspension, (CS/TCNF)_n multilayers were obtained, where n denotes the number of bilayers. The (CS/TCNF)₆ coated membrane possessed superhydrophilicity, underwater superoleophobicity, and outperforming anti-oil-fouling properties, which could effectively separate various oil-in-water emulsions. Importantly, the (CS/TCNF)₆ coated membrane not only had stable permeate flux with nearly 100 % recovery ratio for the separation of pump oil-in-water emulsion, but also exhibited good harsh-environment-tolerant property. This work provided a novel strategy for designing and preparing stable anti-oil-fouling membranes for oily wastewater treatment.

Designing Highly Photoactive Hybrid Aerogels for In-Flow Photocatalytic Contaminant Removal Using Silica-Coated Bacterial Nanocellulose Supports

This study explores the use of silica-coated bacterial nanocellulose (BC) scaffolds with bulk macroscopic yet nanometric internal pores/structures as functional supports for high surface area titania aerogel photocatalysts to design flexible, self-standing, porous, and recyclable BC@SiO₂-TiO₂ hybrid organic-inorganic aerogel membranes for effective in-flow photo-assisted removal of organic pollutants. The hybrid aerogels were prepared by sequential sol-gel deposition of the SiO₂ layer over BC, followed by coating of the resulting BC@SiO₂ membranes with a porous titania aerogel overlayer of high surface area using epoxide-driven gelation, hydrothermal crystallization, and subsequent supercritical drying. The silica interlayer between the nanocellulose biopolymer scaffold and the titania photocatalyst was found to greatly influence the structure and composition, particularly the TiO₂ loading, of the prepared hybrid aerogel membranes, allowing the development of photochemically stable aerogel materials with increased surface area/pore volume and higher photocatalytic activity. The optimized BC@SiO₂-TiO₂ hybrid aerogel showed up to 12 times faster in-flow photocatalytic removal of methylene blue dye from aqueous solution in comparison with bare BC/TiO₂ aerogels and outperformed most of the supported-titania materials reported earlier. Moreover, the developed hybrid aerogels were successfully employed to remove sertraline drug, a model emergent contaminant, from aqueous solution, thus further demonstrating their potential for water purification.

Boron Adsorption Kinetics of Microcrystalline Cellulose and Polymer Resin

Tailoring boron-polysaccharide interactions is an important strategy for developing functional soft materials such as hydrogels, fire retardants, and sorbents for environmental remediation, for example, using lignocellulosic biomass. For such applications to be realized, it is paramount to understand the adsorption kinetics of borate anions on cellulose and their local structures. Here, the kinetic aspects of boron adsorption by microcrystalline cellulose, lignin, and polymeric resin are investigated and compared. Borate anions interact with the vicinal diols in the glucopyranoside moieties of cellulose to yield chemisorbed boron chelate complexes. In contrast to cellulose, technical lignin contains fewer cis-vicinal diols, and it does not have a tendency to form such chelate complexes upon treatment with the aqueous boric acid solution. The formation kinetics and stability of these chelate complexes strongly depend on nanoscale structures, as well as reaction conditions such as pH and concentration of the sorbate and sorbent. Specifically, insights into the distinct boron adsorption sites were obtained by solid-state one-dimensional (1D) ¹¹B magic-angle spinning NMR and the local structures and intermolecular interactions in the vicinities of boron chelate complexes are elucidated by analyzing two-dimensional (2D) ¹H-¹³C and ¹¹B-¹H heteronuclear correlation NMR spectra. The total boron adsorption capacity of cellulose is estimated to be in the 1.3-3.0 mg range per gram of sorbent, which is lower than the boron adsorption capacity of a polystyrene-based resin, ∼17.2 mg of boron per gram of Amberlite IRA 743. Our study demonstrates that the local backbone and side chain flexibility as well as the structures of polyol groups play a significant role in determining the kinetic and thermodynamic stability of chelate complexes, yielding to different boron adsorption capabilities of lignocellulosic polymers.

Sustainable, Insoluble, and Photonic Cellulose Nanocrystal Patches for Calcium Ion Sensing in Sweat

Self-assembly of cellulose nanocrystals (CNCs) is invaluable for the development of sustainable optics and photonics. However, the functional failure of CNC-derived materials in humid or liquid environments inevitably impairs their development in biomedicine, membrane separation, environmental monitoring, and wearable devices. Here, a facile and robust method to fabricate insoluble hydrogels in a self-assembled CNC-polyvinyl alcohol (PVA) system is reported. Due to the reconstruction of inter- or intra-molecular hydrogen bond interactions, thermal dehydration makes an optimized CNC/PVA photonic film form a stable hydrogel network in an aqueous solution rather than dissolve. Notably, the resulting hydrogel exhibits superb mechanical performance (stress up to 3.3 Mpa and tough up to 0.73 MJ m^-3 ) and reversible conversion between dry and wet states, enabling it convenient for specific functionalization. Sodium alginate (SA) can be adsorbed into the CNC photonic structure by swelling dry CNC/PVA film in a SA solution. The prepared hydrogel showcases the comprehensive properties of freezing resistance (-20°C), strong adhesion, satisfactory biocompatibility, and highly sensitive and selective Ca²⁺ sensing. The material could act as a portable wearable patch on the skin for the continuous analysis of calcium trends during different physical exercises, facilitating their development in precision nutrition and health monitoring.

Tailored Sky-Parking Architectures of 3D Graphene Oxide Towards Highly-Efficient Water Purification

The widespread use of chemicals has brought serious water pollution threatening human health and environment, which requires green, fast, and low-cost purification urgently. Here, we build up a novel material family of sky-parking-like 3D structured graphene oxides (SP-GOs) with adjustable interlayer-space of 0.8-1.7 nm via the insertion of different sized diamine compounds as support pillars between GO layers. The assembled 3D SP-GOs exhibit superior adsorption capacity and short removal time for various aromatic organic compounds in water, achieving record-breaking maximum adsorption capacity of 535.79 mg g^-1 toward the most common water-pollutant bisphenol A (BPA) at ambient conditions as well as significantly improved removal of other organic pollutants including sulfapyridine, carbamazepine, ketoprofen and 2-naphthol. The construction of SP-GO provides a simple approach for evolving the GO material from 2D to 3D and a new avenue for the decontamination of pollutants in environmental remediation.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Bioactive polymer-enabled conformal neural interface and its application strategies

Neural interface is a powerful tool to control the varying neuron activities in the brain, where the performance can directly affect the quality of recording neural signals and the reliability of in vivo connection between the brain and external equipment. Recent advances in bioelectronic innovation have provided promising pathways to fabricate flexible electrodes by integrating electrodes on bioactive polymer substrates. These bioactive polymer-based electrodes can enable the conformal contact with irregular tissue and result in low inflammation when compared to conventional rigid inorganic electrodes. In this review, we focus on the use of silk fibroin and cellulose biopolymers as well as certain synthetic polymers to offer the desired flexibility for constructing electrode substrates for a conformal neural interface. First, the development of a neural interface is reviewed, and the signal recording methods and tissue response features of the implanted electrodes are discussed in terms of biocompatibility and flexibility of corresponding neural interfaces. Following this, the material selection, structure design and integration of conformal neural interfaces accompanied by their effective applications are described. Finally, we offer our perspectives on the evolution of desired bioactive polymer-enabled neural interfaces, regarding the biocompatibility, electrical properties and mechanical softness.

Preparation of nanocellulose grafted molecularly imprinted polymer for selective adsorption Pb(II) and Hg(II)

Heavy metal pollution has become a major problem in environmental pollution. Ion imprinted polymers with specific identification and wide practicality have gradually become an important tool for wastewater treatment. In this work, ion-imprinted polymer-grafted modified nanocellulose was designed as an adsorbent for the serious hazard of Pb(II) and Hg(II) in wastewater. This work used medical cotton wool as raw material to prepare a nanocellulose suspension by acid-catalyzed hydrolysis. The high reactivity of carbonyl diimidazole (CDI) was utilized to react with acrylic acid (AA) to generate reactive intermediates, which then reacted with nanocellulose to form activated nanocellulose (AA-CDI-NC). Crown ether was used as functional monomers to synthesize Pb(II) ion-imprinted polymers and grafted onto the AA-CDI-NC surface (Pb(II)-MIP-NC). Meanwhile, Hg(II) ion-imprinted polymer was synthesized and grafted onto the AA-CDI-NC surface (Hg(II)-MIP-NC) using thymine as a functional monomer. The experimental results showed that Pb(II)-MIP-NC and Hg(II)-MIP-NC could effectively adsorb Pb(II) and Hg(II), respectively. Their adsorption behaviors for Pb(II) and Hg(II) were consistent with the secondary kinetic model and Langmuir adsorption isotherm model. The adsorption capacities of Pb (II)-MIP-NC and Hg (II)-MIP-NC for Pb (II) and Hg (II) were 27.55 mg/g and 161.31, respectively.

Mechanically strong nanopapers based on lignin containing cellulose micro- and nano-hybrid fibrils: Lignin content-fibrils morphology-strengthening mechanism

Lignin-containing cellulose nanopapers are emerging multifunctional materials in the fields of coatings, films, and packaging. However, the forming mechanism and properties of nanopapers with various lignin content have not been thoroughly studied. In this work, a mechanically strong nanopaper was fabricated based on lignin-containing cellulose micro- and nano-hybrid fibrils (LCNFs). The influence of lignin content and fibrils morphology on the formation process of nanopapers was investigated to understand the strengthening mechanism of nanopapers. LCNFs with high lignin content provided nanopapers with intertwined micro- and nano-hybrid fibrils layers with small layer spacing, while LCNFs with low lignin content offered nanopapers interlaced nanofibrils layers with large layer spacing. Although lignin was expected to interfere with hydrogen bonds between fibrils, the uniformly distributed lignin contributed to the stress transfer between fibrils. Due to the good coordination between microfibrils, nanofibrils and lignin (as network skeleton, filler and natural binder, respectively), the well-designed LCNFs nanopapers with lignin content of 14.5 % showed excellent mechanical properties, including tensile strength (183.8 MPa), Young's modulus (5.6 GPa) and elongation (9.2 %). This work deeply reveals the relationship between lignin content, morphology and strengthening mechanism of nanopapers, and providing theoretical guidance for employing LCNFs as structural and reinforcing materials to design robust composites.

The versatility of nanocellulose, modification strategies, and its current progress in wastewater treatment and environmental remediation

Deterioration in the environmental ecosystems through the depletion of nonrenewable resources and the burden of deleterious contaminants is considered a global concern. To this end, great interest has been shown in the use of renewable and environmentally-friendly reactive materials dually to promote environmental sustainability and cope with harmful contaminants. Among the different available options, the use of nanocellulose (NC) as an environmentally benign and renewable natural nanomaterial is an attractive candidate for environmental remediation owing to its miraculous physicochemical characteristics. This review discusses the intrinsic properties and the structural aspects of different types of NC, including cellulose nanofibrils (CNFs), cellulose nanocrystals (CNCs), and bacterial cellulose (BC) or bacterial nanocellulose (BNC). Also, the different modification strategies involving the functionalization or hybridization of NC by using different functional and reactive materials aimed at wastewater remediation have been elaborated. The modified or hybridized NC has been explored for its applications in the removal or degradation of aquatic contaminants through adsorption, filtration, coagulation, catalysis, photocatalysis, and pollutant sensing. This review highlights the role of NC in the modified composites and describes the underlying mechanisms involved in the removal of contaminants. The life-cycle assessment (LCA) of NC is discussed to unveil the hidden risks associated with its production to the final disposal. Moreover, the contribution of NC in the promotion of waste management at different stages has been described in the form of the five-Rs strategy. In summary, this review provides rational insights to develop NC-based environmentally-friendly reactive materials for the removal and degradation of hazardous aquatic contaminants.

Preparation, Characterization and Antibacterial Property Analysis of Cellulose Nanocrystals (CNC) and Chitosan Nanoparticles Fine-Tuned Starch Film

To improve the mechanical and antibacterial properties of traditional starch-based film, herein, cellulose nanocrystals (CNCs) and chitosan nanoparticles (CS NPs) were introduced to potato starch (PS, film-forming matrix) for the preparation of nanocomposite film without incorporation of additional antibacterial agents. CNCs with varied concentrations were added to PS and CS NPs composite system to evaluate the optimal film performance. The results showed that tensile strength (TS) of nanocomposite film with 0, 0.01, 0.05, and 0.1% (w/w) CNCs incorporation were 41, 46, 47 and 41 MPa, respectively. The elongation at break (EAB) reached 12.5, 10.2, 7.1 and 13.3%, respectively. Due to the reinforcing effect of CNCs, surface morphology and structural properties of nanocomposite film were altered. TGA analysis confirmed the existence of hydrogen bondings and electrostatic attractions between components in the film-forming matrix. The prepared nanocomposite films showed good antibacterial properties against both E. coli and S. aureus. The nanocomposite film, consist of three most abundant biodegradable polymers, could potentially serve as antibacterial packaging films with strong mechanical properties for food and allied industries.

Sustainable Plant-Based Biopolymer Membranes for PEM Fuel Cells

Carboxycellulose nanofibers (CNFs) promise to be a sustainable and inexpensive alternative material for polymer electrolyte membranes compared to the expensive commercial Nafion membrane. However, its practical applications have been limited by its relatively low performance and reduced mechanical properties under typical operating conditions. In this study, carboxycellulose nanofibers were derived from wood pulp by TEMPO oxidation of the hydroxyl group present on the C6 position of the cellulose chain. Then, citric acid cross-linked CNF membranes were prepared by a solvent casting method to enhance performance. Results from FT-IR spectroscopy, ¹³C NMR spectroscopy, and XRD reveal a chemical cross-link between the citric acid and CNF, and the optimal fuel cell performance was obtained by cross-linking 70 mL of 0.20 wt % CNF suspension with 300 µL of 1.0 M citric acid solution. The membrane electrode assemblies (MEAs), operated in an oxygen atmosphere, exhibited the maximum power density of 27.7 mW cm^-2 and the maximum current density of 111.8 mA cm^-2 at 80 °C and 100% relative humidity (RH) for the citric acid cross-linked CNF membrane with 0.1 mg cm^-2 Pt loading on the anode and cathode, which is approximately 30 times and 22 times better, respectively, than the uncross-linked CNF film. A minimum activation energy of 0.27 eV is achieved with the best-performing citric acid cross-linked CNF membrane, and a proton conductivity of 9.4 mS cm^-1 is obtained at 80 °C. The surface morphology of carboxycellulose nanofibers and corresponding membranes were characterized by FIB/SEM, SEM/EDX, TEM, and AFM techniques. The effect of citric acid on the mechanical properties of the membrane was assessed by tensile strength DMA.