Nanocelluloses as sustainable membrane materials for separation and filtration technologies: Principles, opportunities, and challenges

Nanocellulose-based functional materials towards water treatment

Water resources are important ecological resources for human survival. To date, advanced water purification technology has become one of the focus of global attention due to the continuous deterioration of the environment and the serious shortage of freshwater resources. Recently, nanocellulose, as a kind of sustainable and carbon-neutral biopolymer, has not only the properties of cellulose, but also the important nature of nanomaterials, including large specific surface area, tailorable surface chemistry, excellent mechanical flexibility, biodegradability, and environmental compatibility. Herein, this review covers several methods of extraction and preparation of nanocellulose and the functional modification strategies. Subsequently, we systematically review the application and latest research progress of nanocellulose-based functional material towards water treatment, from micro/nanoparticles filtration, dyes/organics adsorption/degradation, heavy metal ions adsorption/detection and oil-water separation to seawater desalination. Furthermore, scalable and low-cost nanocellulose synthesis strategies are discussed. Finally, the challenges and opportunities of nanocellulose water purification substrate in industrial application and emerging directions are briefly discussed. This review is expected to provide new insights for the application of advanced functional materials based on nanocellulose in water treatment and environmental remediation, and promote rapid cross-disciplinary development.

Structure-property relations in rheology of cellulose nanofibrils-based hydrogels

Hydrogels prepared from self-assembled cellulose nanofibrils (CNFs) are widely used in biomedicine, electronics and environmental technology. Their ability to serve as inks for extrusion-based 3D printing is conventionally evaluated by means of rheological tests. A model is developed that describes the response of CNF gels in small- and large-amplitude oscillatory tests in a unified manner. The model involves a reasonably small number of material parameters, ensures good agreement between results of simulation and observations in oscillatory tests and correctly predicts the stress-strain Lissajous curves, experimental data in hysteresis loop tests, and measurements of the steady-state viscosity. The model is applied to analyze how composition and preparation conditions for CNF gels affect transition from shear thinning to weak strain overshoot in large-amplitude shear oscillatory tests. Based on the model, simple relations are derived for the fractal dimension of CNF clusters and the storage modulus of gels prepared in aqueous solutions of multivalent salts. The validity of these equations is confirmed by comparison of their predictions with observations in independent tests.

State-of-the-Art Synthesis of Porous Polymer Materials and Their Several Fantastic Biomedical Applications: a Review

Porous polymers, including hydrogels, covalent organic frameworks (COFs), and hyper crosslinked polymers (HCPs), have become essential in biomedical research for their tunable pore architectures, large surface areas, and functional versatility. This review provides a comprehensive overview of their classification and updated synthesis mechanisms, such as 3D printing, electrospinning, and molecular imprinting. Their pivotal roles in drug delivery, tissue engineering, wound healing, and photodynamic/photothermal therapies, focusing on how pore size, distribution, and architecture impact drug release, cellular interactions, and therapeutic outcomes, are explored. Key challenges, including biocompatibility, mechanical strength, controlled degradation, and scalability, are critically assessed alongside emerging strategies to enhance clinical potential. Finally, recent challenges and future perspectives, emphasizing the broader biomedical applications of porous polymers, are addressed. This work provides valuable insights for advancing next-generation biomedical innovations through these materials.

Versatile synthesis of cellulose film with excellent electrothermal/photothermal dual responsiveness by introducing MXene and small molecule self-assembled nanosphere

Plant-derived biomaterials have great application prospects in solving environmental pollution and sustainable resource utilization, but the insufficient mechanical strength and lack of functional responsiveness often limit their further development. Inspired by natural small molecules functionalization, a vacuum-assisted filtration nanofibrillated cellulose (NFC)-based film with excellent antibacterial properties, mechanical strength, and electrothermal/photothermal dual-responsiveness was fabricated. As a natural bioactive molecule, antibacterial cinnamaldehyde (CA) is grafted onto tannic acid (TA) rich in pyrogallols via a small molecule self-assembly strategy, and then co-assembled with zinc acetate (ZA) through ion crosslinking to synthesize the functional TACA@ZA nanospheres. After incorporating the MXene and TACA@ZA, an inorganic-organic 3D network system was established in the NFC matrix through dynamic intermolecular hydrogen bonding and strong ionic cross-linking. The mechanical strength and toughness of hybrid composites are remarkably improved by 83.6 % and 418.9 %, respectively. Due to the synergistic effects of MXene and TACA@ZA, the designed NFC-based film also shows significantly enhanced antibacterial activity, UV-blocking ability, as well as photothermal and electrothermal performance. This bioinspired small molecule functionalization strategy opens an innovative design concept for the fabrication of multirole NFC-based biomaterials, which has great application prospects in the commercial fields of multifunctional adhesives, electronic devices, UV shielding coatings, and antibacterial materials.

A review of valorization of agricultural waste for the synthesis of cellulose membranes: Separation of organic, inorganic, and microbial pollutants

Agricultural waste presents a significant environmental challenge due to improper disposal and management practices, contributing to soil degradation, biodiversity loss, and pollution of water and air resources. To address these issues, there is a growing emphasis on the valorization of agricultural waste. Cellulose, a major component of agricultural waste, offers promising opportunities for resource utilization due to its unique properties, including biodegradability, biocompatibility, and renewability. Thus, this review explored various types of agricultural waste, their chemical composition, and pretreatment methods for cellulose extraction. It also highlights the significance of rice straw, sugarcane bagasse, and other agricultural residues as cellulose-rich resources. Among the various membrane fabrication techniques, phase inversion is highly effective for creating porous membranes with controlled thickness and uniformity, while electrospinning produces nanofibrous membranes with high surface area and exceptional mechanical properties. The review further explores the separation of pollutants including using cellulose membranes, demonstrating their potential in environmental remediation. Hence, by valorizing agricultural residues into functional materials, this approach addresses the challenge of agricultural waste management and contributes to the development of innovative solutions for pollution control and water treatment.

A feasibility study on femtosecond laser texturing of sprayed nanocellulose coatings

Nanocelluloses are emerging as natural materials with favourable properties for coating industry and can be applied by state-of-the-art spraying technology. While additional functionalities are commonly introduced through chemical modification, the surface microstructuring of nanocellulose coatings with high throughput methods remains unexplored. Here, a femtosecond laser is used for texturing spray-coated coatings made of cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC). For coating thickness of 1.5 to 8 μm, processing limits were determined with maximum ablation energy linearly increasing with coating thickness and minimum ablation energy decreasing or increasing depending on the apparent coating density. Within applicable processing window of pulse rate and power setting, the operational ranges were determined for creating one-dimensional and two-dimensional surface patterns, requiring a higher laser energy for CNC compared to CNF coatings and yielding thinnest possible resolved patterns of 17 μm as determined by the laser spot diameter. The laser ablation under low energy corresponds to an increase in surface roughness and intensifies surface hydrophilicity, while the line patterns are able to pin water droplets with rising water contact angles up to 90°. Present feasibility study opens future possibilities for managing surface properties of nanocellulose coatings in applications where tuning of surface hydrophilicity is required.

Transparent, thermal stable, water resistant and high gas barrier films from cellulose nanocrystals prepared by reactive deep eutectic solvents

Nanocellulose-based film, as a novel new type of film mainly made of nanosized cellulose, has demonstrated an ideal combination of renewability and enhanced or novel properties. Considerable efforts have been made to enhance its intrinsic properties or create new functions to expand its applications, such as in food packaging, water treatment or flexible electronics. In this paper, two different types of deep eutectic solvents (guanidine sulfamate-glycerol and guanidine sulfamate-choline chloride) were formulated and applied to prepare cellulose nanocrystals with dialdehyde cellulose (DAC). The effects of reaction conditions including time, temperature and cellulose-DES ratio on the grafting degree and yield were studied. After ultrasonication, two types of CNCs, with an average diameter of 3-5 nm and an average length of 140.7-204.2 nm, were obtained. The synthesized CNCs displayed an enhanced thermal stability compared to pristine cellulose. Moreover, highly transparent (light transmittance higher than 90 %) and water stable nanocellulose based films (a wet tensile strength of higher than 30 MPa after immersing in water for 24 h) were fabricated. Besides, the obtained films exhibited low oxygen transmission rate, showing a good potential application in food packaging.

Approaches for the Efficient Removal of Fluoride from Groundwater: A Comprehensive Review

Contamination of groundwater with fluoride represents a significant global issue, with high concentrations posing serious public health threats. While fluoride is a critical element in water, excessive levels can be detrimental to human health and potentially life-threatening. Addressing the challenge of removing fluoride from underground water sources via nanotechnological approaches is a pressing concern in environmental science. To collate relevant information, extensive literature searches were conducted across multiple databases, including Google Scholar, PubMed, Scopus, Web of Science, the American Chemical Society, Elsevier, Springer, and the Royal Society of Chemistry. VOS Viewer software version 1.6.20 was employed for a systematic review. This article delivers an exhaustive evaluation of various groundwater fluoride removal techniques, such as adsorption, membrane filtration, electrocoagulation, photocatalysis, and ion exchange. Among these, the application of nanoparticles emerges as a notable method. The article delves into nano-compounds, optimizing conditions for the fluoride removal process and benchmarking their efficacy against other techniques. Studies demonstrate that advanced nanotechnologies-owing to their rapid reaction times and potent oxidation capabilities-can remove fluoride effectively. The implementation of nanotechnologies in fluoride removal not only enhances water quality but also contributes to the safeguarding of human health.

Recent advances in membrane technologies applied in oil-water separation

Effective treatment of oily wastewater, which is toxic and harmful and causes serious environmental pollution and health risks, has become an important research field. Membrane separation technology has emerged as a key area of investigation in oil-water separation research due to its high separation efficiency, low costs, and user-friendly operation. This review aims to report on the advances in the research of various types of separation membranes around emulsion permeance, separation efficiency, antifouling efficiency, and stimulus responsiveness. Meanwhile, the challenges encountered in oil-water separation membranes are examined, and potential research avenues are identified.

Innovative ionic liquid pretreatment followed by wet disk milling treatment provides enhanced properties of sugar palm nano-fibrillated cellulose

In order to accommodate the increased demand for innovative materials, intensive research has focused on natural resources. In pursuit of advanced substances that exhibit functionality, sustainability, recyclability, and cost-effectiveness, the present work attempted an alternative study on cellulose nanofibers derived from sugar palm fiber. Leveraging an innovative approach involving ionic liquid (IL) pre-treatment, bleaching, and wet disc mill technique, nano-fibrillated cellulose (NFC) was successfully obtained from the sugar palm fiber source. Remarkably, 96.89% of nanofibers were extracted from the sugar palm fiber, demonstrating the process's efficacy and scalability. Further investigation revealed that the sugar palm nano-fibrillated cellulose (SPNFC) exhibited a surface area of 3.46 m2/g, indicating a significant interface for enhanced functionality. Additionally, the analysis unveiled an average pore size of 4.47 nm, affirming its suitability for various applications that necessitate precise filtration. Moreover, the surface charge densities of SPNFC were found to be -32.1 mV, offering opportunities for surface modification and enhanced interactions with various materials. The SPNFC exhibit remarkable thermal stability, enduring temperatures of up to 360.5 °C. Additionally, the isolation process is evident in a significant rise in the crystallinity index, escalating from 50.97% in raw fibers to 61.62% in SPNFC. These findings shed light on the vast potential and distinct features of SPNFC, opening the path for its application in a wide array of industries, including but not limited to advanced materials, biomedicine, and environmental engineering.

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.

Next-Generation Water Treatment: Exploring the Potential of Biopolymer-Based Nanocomposites in Adsorption and Membrane Filtration

This review article focuses on the potential of biopolymer-based nanocomposites incorporating nanoparticles, graphene oxide (GO), carbon nanotubes (CNTs), and nanoclays in adsorption and membrane filtration processes for water treatment. The aim is to explore the effectiveness of these innovative materials in addressing water scarcity and contamination issues. The review highlights the exceptional adsorption capacities and improved membrane performance offered by chitosan, GO, and CNTs, which make them effective in removing heavy metals, organic pollutants, and emerging contaminants from water. It also emphasizes the high surface area and ion exchange capacity of nanoclays, enabling the removal of heavy metals, organic contaminants, and dyes. Integrating magnetic (Fe2O4) adsorbents and membrane filtration technologies is highlighted to enhance adsorption and separation efficiency. The limitations and challenges associated are also discussed. The review concludes by emphasizing the importance of collaboration with industry stakeholders in advancing biopolymer-based nanocomposites for sustainable and comprehensive water treatment solutions.