Self-Assembled TEMPO Cellulose Nanofibers: Graphene Oxide-Based Biohybrids for 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.

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.

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.

Controllable Drug-Release Ratio and Rate of Doxorubicin-Loaded Natural Composite Films Based on Polysaccharides: Evaluation of Transdermal Permeability Potential

In drug delivery systems, it is crucial to develop a drug carrier capable of regulating both the drug-release rate and the drug-release ratio. This study proposes a method for controlling the drug-release ratio/rate using doxorubicin-loaded natural composite films composed of polysaccharides (cellulose, chitin, chitosan, or cellulose nanocrystal) and mineral substances (MMT: montmorillonite). We succeeded in controlling the doxorubicin release ratio from 25 to 88% depending on the natural polysaccharide. Likewise, the reduction rate differed depending on the type of natural polysaccharide, whereas the reduction in release was achieved by mixing MMT. Cellulose had the largest reduction in the drug release ratio, approximately 30%, and cellulose nanocrystals showed little change. Furthermore, we conducted a skin permeation test on the natural polysaccharide film with the highest release rate to confirm its transdermal permeability potential. The polysaccharide doxorubicin-loaded film sustainably released doxorubicin for 2 days, which indicated the potential of a carrier for DDS applications.

A review of carbon nanomaterials/bacterial cellulose composites for nanomedicine applications

Carbon nanomaterials (CNMs) mainly include fullerene, carbon nanotubes, graphene, carbon quantum dots, nanodiamonds, and their derivatives. As a new type of material in the field of nanomaterials, it has outstanding physical and chemical properties, such as minor size effects, substantial specific surface area, extremely high reaction activity, biocompatibility, and chemical stability, which have attracted widespread attention in the medical community in the past decade. However, the single use of carbon nanomaterials has problems such as self-aggregation and poor water solubility. Researchers have recently combined them with bacterial cellulose to form a new intelligent composite material to improve the defects of carbon nanomaterials. This composite material has been widely synthesized and used in targeted drug delivery, biosensors, antibacterial dressings, tissue engineering scaffolds, and other nanomedicine fields. This paper mainly reviews the research progress of carbon nanomaterials based on bacterial cellulose in nanomedicine. In addition, the potential cytotoxicity of these composite materials and their components in vitro and in vivo was discussed, as well as the challenges and gaps that need to be addressed in future clinical applications.

In-situ biofabrication of bacterial nanocellulose (BNC)/graphene oxide (GO) nano-biocomposite and study of its cationic dyes adsorption properties

In the present study, bacterial nanocellulose/graphene oxide nano-biocomposites (BNC-GO-NBCs) were fabricated by Komagataeibacter saccharivorans NUWB1 using an in-situ method involving three time-dependent approaches. Physicochemical studies showed that the chosen dried BNC-GO-NBC possessed a three-dimensional interconnected porous structure of BNC with GO layers embedded within the BNC fibrils. BNC-GO-NBC had a crystallinity index of 74.21 %, higher thermostability up to 380 °C and could withstand a tensile load of 84.72 MPa. N2 adsorption-desorption isotherm of the BNC-GO-NBC was found to be of type IV, suggesting a mesoporous type structure with a total pore volume and surface area of 6.232e-04 cc g-1 and 10.498 m2. BNC-GO-NBC exhibited remarkable adsorption capacity for two cationic dyes, Rhodamine B (RhB) and Acridine Orange (AO), and the adsorption data conformed well to the Langmuir isotherm (R2 = 0.99) and pseudo-second-order model. Thermodynamic studies indicated that the adsorption process was spontaneous and endothermic. Additionally, the BNC-GO-NBC displayed the potential for regeneration, with the ability to be recycled up to five times. Further, the antibacterial activity, cell cytotoxicity and oxidative stress assays of the BNC-GO-NBC revealed its non-cytotoxic nature. The findings of the present investigation evidently suggest the potentiality of BNC-GO-NBC in the application of dye adsorption and other environmental applications.

TEMPO-Oxidized Cellulose Nanofibril Films Incorporating Graphene Oxide Nanofillers

To design a new system of novel TEMPO-oxidized cellulose nanofibrils (TOCNs)/graphene oxide (GO) composite, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was utilized. For the better dispersion of GO into the matrix of nanofibrillated cellulose (NFC), a unique process combining high-intensity homogenization and ultrasonication was adopted with varying degrees of oxidation and GO percent loadings (0.4 to 2.0 wt%). Despite the presence of carboxylate groups and GO, the X-ray diffraction test showed that the crystallinity of the bio-nanocomposite was not altered. In contrast, scanning electron microscopy showed a significant morphological difference in their layers. The thermal stability of the TOCN/GO composite shifted to a lower temperature upon oxidation, and dynamic mechanical analysis signified strong intermolecular interactions with the improvement in Young's storage modulus and tensile strength. Fourier transform infrared spectroscopy was employed to observe the hydrogen bonds between GO and the cellulosic polymer matrix. The oxygen permeability of the TOCN/GO composite decreased, while the water vapor permeability was not significantly affected by the reinforcement with GO. Still, oxidation enhanced the barrier properties. Ultimately, the newly fabricated TOCN/GO composite through high-intensity homogenization and ultrasonification can be utilized in a wide range of life science applications, such as the biomaterial, food, packaging, and medical industries.

Sugarcane leave-derived cellulose nanocrystal/graphene oxide filter membrane for efficient removal of particulate matter

The goal of this study is to isolate cellulose nanocrystals (CNC) from sugarcane leaves (SCL) and fabricate filter membranes. Filter membranes consisting of the CNC and varying amount graphene oxide (GO) were fabricated using vacuum filtration technique. The α-cellulose content increased from 53.56 ± 0.49 % in untreated SCL to 78.44 ± 0.56 % and 84.99 ± 0.44 % in steam-exploded and bleached fibers, respectively. Atomic force microscopy (AFM) and transmission electron microscope (TEM) of CNC isolated from SCL indicated nanosized particles in the range of 7.3 nm and 150 nm for diameter and length, respectively. Morphologies of the fiber and CNC/GO membranes were determined by scanning electron microscopy (SEM) and crystallinity by X-ray diffraction (XRD) analysis of crystal lattice. The crystallinity index of CNC decreased with the addition of GO into the membranes. The CNC/GO-2 recorded the highest tensile index of 3.001 MPa. The removal efficiency increases with increasing GO content. The highest removal efficiency of 98.08 % was recorded for CNC/GO-2. CNC/GO-2 membrane reduced growth of Escherichia coli to 65 CFU compared to >300 CFU of control sample. SCL is a potential bioresource for isolation of cellulose nanocrystals and fabrication of high-efficiency filter membrane for particulate matter removal and inhibition of bacteria.

Review on Hybrid Reinforced Polymer Matrix Composites with Nanocellulose, Nanomaterials, and Other Fibers

The use of composite materials has seen many new innovations for a large variety of applications. The area of reinforcement in composites is also rapidly evolving with many new discoveries, including the use of hybrid fibers, sustainable materials, and nanocellulose. In this review, studies on hybrid fiber reinforcement, the use of nanocellulose, the use of nanocellulose in hybrid forms, the use of nanocellulose with other nanomaterials, the applications of these materials, and finally, the challenges and opportunities (including safety issues) of their use are thoroughly discussed. This review will point out new prospects for the composite materials world, enabling the use of nano- and micron-sized materials together and creating value-added products at the industrial scale. Furthermore, the use of hybrid structures consisting of two different nano-materials creates many novel solutions for applications in electronics and sensors.

Nanoscale structural and electronic properties of cellulose/graphene interfaces

The development of electronic devices based on the functionalization of (nano)cellulose platforms relies upon an atomistic understanding of the structural and electronic properties of a combined system, cellulose/functional element. In this work, we present a theoretical study of the nanocellulose/graphene interfaces (nCL/G) based on first-principles calculations. We find that the binding energies of both hydrophobic/G (nCL^phob/G) and hydrophilic/G (nCL^phil/G) interfaces are primarily dictated by the van der Waals interactions, and are comparable with those of their 2D interface counterparts. We verify that the energetic preference of nCL^phob/G has been reinforced by the inclusion of an aqueous medium via an implicit solvation model. Further structural characterization was carried out using a set of simulations of the carbon K-edge X-ray absorption spectra to identify and distinguish the key absorption features of the nCL^phob/G and nCL^phil/G interfaces. The electronic structure calculations reveal that the linear energy bands of graphene lie in the band gap of the nCL sheet, while depletion/accumulation charge density regions are observed. We show that external agents, i.e., electric field and mechanical strain, allow for tunability of the Dirac cone and charge density at the interface. The control/maintenance of the Dirac cone states in nCL/G is an important feature for the development of electronic devices based on cellulosic platforms.

Effect of decoration route on the nanomechanical, adhesive, and force response of nanocelluloses-An in situ force spectroscopy study

Although cellulose derivatives are widely applied in high-tech materials, the relation between their force responses and their surface chemical properties in a biological environment as a function of pH is unknown. Here, interaction forces of surface modified cellulose nanocrystals (CNCs), lignin residual cellulose nanocrystals (LCNCs), and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibres (TCNFs) with OSO3-, COO- and lignin chemical groups were measured using in situ peak force quantitative nanomechanical mapping and force spectroscopy in salt solution at two pH values. We found that the forces acting between the tip and CNC or LCNC are steric dominated showing long range and slow decay as a result of their low surface charge density. High Mw lignin contributed to the increased repulsion range for LCNCs compared to CNCs. The repulsion measured for TCNFs at the very short range was electrostatic force dominating showing a steep decay attributed to its high surface charge density. In the case of TCNFs, electrostatic double layer force was also evidenced by the attraction measured at secondary minima. In all the three cases the electro steric interactions are pH dependent. Dissipation maps verified that the force behavior for each material was related to structural conformation restriction of the groups at compression. The slow decayed repulsion of CNCs or LCNCs is related to a weak restriction of conformational change due to small surface groups or high molecular weight bound polymers forming flat layers, whereas the steep repulsion of TCNFs is attributed to a strong conformation restriction of carboxylic groups occurred by forming extended structure. Our results suggest that the force responses of the materials were dominated by surface charges and structural differences. TCNFs showed superior nanomechanical and repulsion properties over CNCs or LCNCs at neutral pH.

Recent advances and future perspective on nanocellulose-based materials in diverse water treatment applications

Over the past few years, nanocellulose and its derivatives have drawn attention as promising bio-based materials for water treatment applications due to their high surface area, high strength, and renewable, biocompatible nature. The abundance of hydroxyl functional groups on the surfaces of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) enables a broad range of surface modifications which results in propitious nanocomposites with tunable characteristics. In this context, this review describes the continuously developing applications of nanocellulose-based materials in the areas of adsorption, catalysis, filtration, and flocculation, with a special emphasis on the removal of contaminants such as heavy metals, dyes, and pharmaceutical compounds from diverse water systems. Recent progresses in the diverse forms of application of nanocellulose adsorbents (suspension, hydrogel, aerogel, and membrane) are also highlighted. Finally, challenges and future perspectives on emerging nanocellulose-based materials and their possible industrial applications are presented and discussed.

Coupling of 3-Aminopropyl Sulfonic Acid to Cellulose Nanofibers for Efficient Removal of Cationic Dyes

A novel anionic nanostructured cellulose derivate was prepared through the coupling of TEMPO-oxidized cellulose nanofibers with 3-aminopropyl sulfonic acid (3-APSA). 3-APSA grafting was variously investigated by FT-IR spectroscopy and transmission electron microscopy (TEM) analysis, confirming a high reaction degree. The surface morphology investigated via scanning electron microscopy (SEM) revealed a more uniform organization of the nanofibers after the 3-APSA coupling, with improvements in terms of fiber packing and pore interconnectivity. This peculiar morphology contributes to improving methylene blue (MB) adsorption and removal efficiency at different operating conditions (pH, initial time, and initial concentration). The results indicated a maximum adsorption capacity of 526 mg/g in the case of 3-APSA grafted nanofibers, over 30% more than that of non-grafted ones (370 mg/g), which confirm a relevant effect of chemical modification on the adsorbent properties of cellulose nanofibers. The adsorption kinetics and isotherms of the current adsorbents match with the pseudo-second-order kinetic and Langmuir isotherm models. This study suggests the use of chemical grafting via 3-APSA is a reliable and facile post-treatment to design bio-sustainable and reusable nanofibers to be used as high-performance adsorbent materials in water pollutant remediation.

Prospecting cellulose fibre-reinforced composite membranes for sustainable remediation and mitigation of emerging contaminants

Many environmental pollutants caused by uncontrolled urbanization and rapid industrial growth have provoked serious concerns worldwide. These pollutants, including toxic metals, dyes, pharmaceuticals, pesticides, volatile organic compounds, and petroleum hydrocarbons, unenviably compromise the water quality and manifest a severe menace to aquatic entities and human beings. Therefore, it is of utmost importance to acquaint bio-nanocomposites with the capability to remove and decontaminate this extensive range of emerging pollutants. Recently, considerable emphasis has been devoted to developing low-cost novel materials obtained from natural resources accompanied by minimal toxicity to the environment. One such component is cellulose, naturally the most abundant organic polymer found in nature. Given bio-renewable sources, natural abundance, and impressive nanofibril arrangement, cellulose-reinforced composites are widely engineered and utilized for multiple applications, such as wastewater decontamination, energy storage devices, drug delivery systems, paper and pulp industries, construction industries, and adhesives, etc. Environmental remediation prospective is among the fascinating application of these cellulose-reinforced composites. This review discusses the structural attributes of cellulose, types of cellulose fibrils-based nano-biocomposites, preparatory techniques, and the potential of cellulose-based composites to remediate a diverse array of organic and inorganic pollutants in wastewater.

Cellulose nanofibrils-graphene hybrids: recent advances in fabrication, properties, and applications

With the fast-developing social economy and the acceleration of industrialization, seeking effective renewable, sustainable, and environmentally friendly resources that show promising properties is an urgent task and a crucial means to achieve sustainable progress in the face of the growing depletion of non-renewable resources and the deterioration of environmental issues. Cellulose nanofibrils (CNFs) are natural polymeric nanomaterials with excellent biocompatibility, biodegradability, good mechanical features, high strength, low density, high specific surface area, and tunable chemistry. Their combination with other nanomaterials, such as graphene derivatives (GNMs), has been demonstrated to be effective since they produce hybrids with outstanding physicochemical properties, tailorable functionality, and high performance. In this review, recent advances in the preparation, modification, and emerging application of CNFs/GNMs hybrids are described and discussed using the latest studies. First, the concise background of nanocellulose and graphene derivatives is provided, followed by the interfacial interactions between CNFs and GNMs. The different hybrids exhibit great promise in separation, adsorption, optics, flexible electronics, energy storage, thermal management, barrier and packaging, and electromagnetic shielding. The main challenges that inhibit the applicability of these hybrids are finally highlighted, and some perspectives for future research directions are provided.

Selective Oxidation of Cellulose—A Multitask Platform with Significant Environmental Impact

Raw cellulose, or even agro-industrial waste, have been extensively used for environmental applications, namely industrial water decontamination, due to their effectiveness, availability, and low production cost. This was a response to the increasing societal demand for fresh water, which made the purification of wastewater one of the major research issue for both academic and industrial R&D communities. Cellulose has undergone various derivatization reactions in order to change the cellulose surface charge density, a prerequisite condition to delaminate fibers down to nanometric fibrils through a low-energy process, and to obtain products with various structures and properties able to undergo further processing. Selective oxidation of cellulose, one of the most important methods of chemical modification, turned out to be a multitask platform to obtain new high-performance, versatile, cellulose-based materials, with many other applications aside from the environmental ones: in biomedical engineering and healthcare, energy storage, barrier and sensing applications, food packaging, etc. Various methods of selective oxidation have been studied, but among these, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) (TEMPO)-mediated and periodate oxidation reactions have attracted more interest due to their enhanced regioselectivity, high yield and degree of substitution, mild conditions, and the possibility to further process the selectively oxidized cellulose into new materials with more complex formulations. This study systematically presents the main methods commonly used for the selective oxidation of cellulose and provides a survey of the most recent reports on the environmental applications of oxidized cellulose, such as the removal of heavy metals, dyes, and other organic pollutants from the wastewater.

Fabrication of graphene-based porous materials: traditional and emerging approaches

The anisotropic nature of ‘graphenic’ nanosheets enables them to form stable three-dimensional porous materials. The use of these porous structures has been explored in several applications including electronics and batteries, environmental remediation, energy storage, sensors, catalysis, tissue engineering, and many more. As method of fabrication greatly influences the final pore architecture, and chemical and mechanical characteristics and performance of these porous materials, it is essential to identify and address the correlation between property and function. In this review, we report detailed analyses of the different methods of fabricating porous graphene-based structures – with a focus on graphene oxide as the base material – and relate these with the resultant morphologies, mechanical responses, and common applications of use. We discuss the feasibility of the synthesis approaches and relate the GO concentrations used in each methodology against their corresponding pore sizes to identify the areas not explored to date.

Due to their anisotropic nature, graphene nanosheets can be used to form 3-dimensional porous materials using template-free and template-directed methodologies. These fabrication strategies are found to influence the properties of the final structure.

Cellulose-Based Materials for Water Remediation: Adsorption, Catalysis, and Antifouling

Cellulose-based materials have been advanced technologies that used in water remediation. They exhibit several advantages being the most abundant biopolymer in nature, high biocompatibility, and contain several functional groups. Cellulose can be prepared in several derivatives including nanomaterials such as cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidized cellulose nanofibrils (TOCNF). The presence of functional groups such as carboxylic and hydroxyls groups can be modified or grafted with organic moieties offering extra functional groups customizing for specific applications. These functional groups ensure the capability of cellulose biopolymers to be modified with nanoparticles such as metal-organic frameworks (MOFs), graphene oxide (GO), silver (Ag) nanoparticles, and zinc oxide (ZnO) nanoparticles. Thus, they can be applied for water remediation via removing water pollutants including heavy metal ions, organic dyes, drugs, and microbial species. Cellulose-based materials can be also used for removing microorganisms being active as membranes or antibacterial agents. They can proceed into various forms such as membranes, sheets, papers, foams, aerogels, and filters. This review summarized the applications of cellulose-based materials for water remediation via methods such as adsorption, catalysis, and antifouling. The high performance of cellulose-based materials as well as their simple processing methods ensure the high potential for water remediation.

Biopolymer-Based Membrane Adsorber for Removing Contaminants from Aqueous Solution: Progress and Prospects

The demand for energy-efficient water treatment as well as the limitation in adsorption of existing membranes has motivated the pursuit of membranes that can break the selectivity-permeability trade-off and provide high selective adsorption for chemicals of interest. The membrane adsorbers have received a lot of attention for removing contaminants from aqueous solution due to combine both advantages of adsorption and membrane separation. Membrane adsorbers constructed by biopolymer with many functional groups are widely used in water purification, because the biopolymers are easily available from biomass materials in nature, degradable, and low-cost. This paper summarizes the characteristics and important development direction of these types of biomass-based membrane adsorption materials to adsorb organic/inorganic contaminants of water and analyzes the preparation methods of natural biomacromolecule cellulose, chitosan, sodium alginate, and protein to construct the membrane adsorption materials, as well as the application of pollutant removal from aqueous solutions. According to the current problems and shortcomings in the research of biopolymer-based membrane adsorbers, it is proposed to improve the understanding of the adsorption mechanism of biopolymer-based membrane adsorbers and accelerate the development of practical applications as the focus of future research.

Nanocellulose-Based Materials for Water Treatment: Adsorption, Photocatalytic Degradation, Disinfection, Antifouling, and Nanofiltration

Nanocelluloses are promising bio-nano-materials for use as water treatment materials in environmental protection and remediation. Over the past decades, they have been integrated via novel nanoengineering approaches for water treatment processes. This review aims at giving an overview of nanocellulose requirements concerning emerging nanotechnologies of waster treatments and purification, i.e., adsorption, absorption, flocculation, photocatalytic degradation, disinfection, antifouling, ultrafiltration, nanofiltration, and reverse osmosis. Firstly, the nanocellulose synthesis methods (mechanical, physical, chemical, and biological), unique properties (sizes, geometries, and surface chemistry) were presented and their use for capturing and removal of wastewater pollutants was explained. Secondly, different chemical modification approaches surface functionalization (with functional groups, polymers, and nanoparticles) for enhancing the surface chemistry of the nanocellulose for enabling the effective removal of specific pollutants (suspended particles, microorganisms, hazardous metals ions, organic dyes, drugs, pesticides fertilizers, and oils) were highlighted. Thirdly, new fabrication approaches (solution casting, thermal treatment, electrospinning, 3D printing) that integrated nanocelluloses (spherical nanoparticles, nanowhiskers, nanofibers) to produce water treatment materials (individual composite nanoparticles, hydrogels, aerogels, sponges, membranes, and nanopapers) were covered. Finally, the major challenges and future perspectives concerning the applications of nanocellulose based materials in water treatment and purification were highlighted.

GO-based antibacterial composites: Application and design strategies

Graphene oxide (GO), for its unique structure with high biocompatibility and designability, is widely used in the antibacterial field. Various strategies have been designed to fabricate GO-based composites with antibacterial properties. This review summarized these strategies, divided them into three types and interpreted their antibacterial mechanisms: (i) "GO*/non-GO" type in which GO acts as the single antibacterial core, (ii) "GO*/non-GO*" type in which GO and non-GO components function synergistically as dual antibacterial cores, (iii) "GO/non-GO*" type in which non-GO acts as the single antibacterial core, while GO component plays a supportive, not a dominant role in antibiosis. Besides, the fields suiting their applications and factors influencing their antibacterial properties were analyzed. Finally, the limitations and prospects in the current researches were discussed. In summary, GO-based composites have revolutionized antibacterial strategies. This review may serve as a reference to inspire further research on GO-based antibacterial composites.

Ultra-thin graphene oxide membrane deposited on highly porous anodized aluminum oxide surface for heavy metal ions preconcentration

Analyte extraction using graphene oxide (GO) can be challenging owing to the stochastic behavior of the permeation of water molecules and heavy metal ions, imperfect pore structures, and irregular distribution of multi-layer sheets. We prepared a free standing, through-hole graphene oxide membrane deposited on porous anodic aluminum oxide (AAO) substrate. The hydrophilicity of the GO membrane was improved via oxygen plasma treatment. The resulting AAO-GO membrane was used as novel adsorbent for the heavy metal ions preconcentration prior to their determination using inductively coupled plasma optical emission spectroscopy. This sub-micrometer-thick membrane allowed unimpeded permeation of water molecules via two-dimensional capillaries formed across the pores and in between the closely spaced GO sheets. The proposed method shows good detection limit of 1.2 ng L^-1, and the co-existing ions did not affect the extraction efficiency of the adsorbent. The accuracy of the method was assessed by analyzing standard reference materials, where the Student's t-test values were less than the critical Student's t-value of 4.303 (95% confidence level). Good precision was achieved, as coefficients of variation ranged between 4% and 5%. The developed SPE adsorbent is a promising alternative for bulk adsorbents owing to the wide variety of available 2D materials and deposition methods.

Production of Bacterial Cellulose from Acetobacter Species and Its Applications – A Review

Bacterial cellulose (BC) is a natural polymer secreted as a protective cell covering of certain bacterial species. In contrary to plant cellulose, BC possesses some unique features like high moisture-holding capacity, high durability, high liquid absorbing capabilities, biostability, and biodegradability, makes BC an excellent raw material in wide-ranging areas like biomedical, food, agriculture, paper, textile industries and electronics. The main objective of this review is to discuss various aspects of BC production (different sources for bacterial strain isolation, culture media and, its alternatives also major culture techniques). In addition, various applications of BC are also reviewed.

Ultrafiltration Process in Disinfection and Advanced Treatment of Tertiary Treated Wastewater

The paper presents the results of research on the use of ultrafiltration, using membranes of 200 and 400 kDa separation, for disinfection of municipal treated wastewater. The research was conducted on a fractional technical scale using real municipal treated wastewater from two large wastewater treatment plants treating most of the wastewater over the one-million polycentric Gdańsk agglomeration (1.2 million inhabitants). UF 200 kDa and UF 400 kDa processes enabled further improvement of the physical and chemical parameters of treated wastewater. Total phosphorus (to below 0.2 mg/L–UF 200 kDa, 0.13 mg/L–UF 400 kDa) and turbid substances (to below 0.2 mg/L, both membranes) were removed in the highest degree. COD was reduced efficiently (to below 25.6 mgO₂/L–UF 200 kDa, 26.8 mgO₂/L–UF 400 kDa), while total nitrogen was removed to a small extent (to 7.12 mg/L–UF 200 kDa and 5.7 mg/L–UF 400 kDa. Based on the reduction of indicator bacteria; fecal coliforms including E. coli (FC) and fecal enterococci (FE) it was found that the ultrafiltration is an effective method of disinfection. Not much indicator bacterial were observed in the permeate after processes (UF 200 kDa; FC—5 CFU/L; FE—1 CFU/L and UF 400 kDa; FC—70 CFU/L; FE—10 CFU/L. However, microscopic analysis of prokaryotic cells and virus particles showed their presence after the application of both membrane types; TCN 3.0 × 10² cells/mL–UF 200 kDa, 5.0 × 10³ cells/mL–UF 400 kDa, VP 1.0 × 10⁵/mL. The presence of potentially pathogenic, highly infectious virus particles means that ultrafiltration cannot be considered a sufficient disinfection method for treated wastewater diverted for reuse or discharged from high load wastewater treatment plants to recreational areas. For full microbiological safety it would be advisable to apply an additional disinfection method (e.g., ozonation).

Liquid-Exfoliated Mesostructured Collagen from the Bovine Achilles Tendon as Building Blocks of Collagen Membranes

Mesoscaled assemblies are organized in native collagen tissues to achieve remarkable and diverse performance and functions. In this work, a facile, low-cost, and controllable liquid exfoliation method was applied to directly extract these collagen mesostructures from bovine Achilles tendons using a sodium hydroxide (NaOH)/urea aqueous system with freeze-thaw cycles and sonication. A series of collagen fibrils with diameters of 26-230 nm were harvested using this process, and in situ observations under polarizing microscopy (POM) and using molecular dynamics simulations revealed the influence of the NaOH/urea system on the tendon collagen. FTIR and XRD results confirmed that these collagen fibrils preserved typical structural characteristics of type I collagen. These isolated collagen fibrils were then utilized as building blocks to fabricate free-standing collagen membranes, which exhibited good stability in solvents and outstanding mechanical properties and transparency, with potential for utility in optical and electronic sensors. Moreover, in vitro and vivo evaluations demonstrated that these new resulting collagen membranes had good cytocompatibility, biocompatibility, and degradability for potential applications in biomedicine. This work provides a new approach for collagen processing by liquid exfoliation with utility for the formation of robust collagen materials that consist of native collagen mesostructures as building blocks.

A nanocomposite paper comprising calcium silicate hydrate nanosheets and cellulose nanofibers for high-performance water purification

Removal of soluble organic and inorganic contaminants from wastewater to produce clean water has received much attention recently. However, the simultaneous enhancement of water permeability and removal efficiency is still a challenge for filtration membranes. Here, we present a new kind of nanocomposite paper (CSH/CNF) consisting of calcium silicate hydrate (CSH) nanosheets and cellulose nanofibers (CNFs), and demonstrate the rapid water filtration and highly efficient contaminant (e.g., dyes, proteins, and metal ions) adsorption properties. The CNFs can serve as the bridging material to connect the CSH nanosheets to form a porous network structure and vital channels in the CSH/CNF paper for rapid water transportation. The weight ratio of CSH nanosheets in the paper is up to 75–85%. The weight ratio of CSH nanosheets has a significant effect on the water permeability and removal efficiency. The water permeability of the CSH/CNF paper with 82.5 wt% CSH nanosheets reaches as high as 312.7 L m⁻² h⁻¹ bar⁻¹, which is about 14.7 times that of the CSH/CNF paper with 75 wt% CSH nanosheets. Because of the high specific surface area and abundant adsorption sites of CSH nanosheets, the CSH/CNF paper with 82.5 wt% CSH nanosheets exhibits high adsorption capacities and removal efficiencies for methyl blue (242.6 mg g⁻¹, 97.3%), bovine serum albumin (289.2 mg g⁻¹, 98.5%) and Pb²⁺ ions (366.2 mg g⁻¹, 98.2%). The CSH/CNF nanocomposite paper holds great potential for application in environmental wastewater purification.

A nanocomposite paper with high water permeability and removal efficiency was prepared for the removal of organic and inorganic contaminants by filtration.

Carboxylated cellulose cryogel beads via a one-step ester crosslinking of maleic anhydride for copper ions removal

In this study, we developed a one step protocol to prepare highly carboxylated and chemically crosslinked cellulose nanofibril (CNF) cryogel beads using maleic anhydride (MA). Fourier transform infrared spectroscopy (FTIR) and conductometric-potentiometric titration results confirmed the presence of carboxyl groups and ester linkages produced simultaneously during the ring open reaction of MA, yielding a carboxylic content of up to 2.78 mmol/g. The effect of CNF concentration on the morphology and wet mechanical strength of the crosslinked cryogel beads were also investigated, and results suggested that higher CNF concentration yielded a compact network that displayed a maximum compressive stress of 2800 Pa at 60 % strain. In addition, the heavy metal ions (i.e., Cu (II)) removal capacity, kinetics, mechanism as well as the recyclability of the resulted CNF-MA cryogel beads were examined.

Separation and preconcentration of arsenite and other heavy metal ions using graphene oxide laminated with protein molecules

The graphene oxide surface was laminated with bovine serum albumin (BSA) followed by the directional flow through a membrane to prepare a free-standing PLGO (protein laminated GO) composite. BSA immobilization increased the interlayer spacing of GO and led to the formation of capillaries. The column packed with PLGO adsorbent permeated water faster as much as ca. 5 fold as compared to only GO packed column. The PLGO composite was used to develop a solid phase extraction method for the selective preconcentration of As(III) in the presence of As(V), prior to their determination. As(III) binding to sulfhydryl groups of BSA in PLGO plays a key role in the speciation. The coexisting heavy metal ions did not hinder the recovery of trace As(III). The method was advantageously employed for the preconcentration of As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) from water and food samples. A 3 mL of 1 M hydrochloric acid would be adequate for the complete desorption (recovery > 99%) of the adsorbed metal ions. The preconcentration limit achieved for As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) were 1.7, 2.0, 2.0, 2.0, 1.8 and 2.0 μg L^-1 respectively, with an optimized sample flow rate of 10 mL min^-1.

Applications of Nanocellulose/Nanocarbon Composites: Focus on Biotechnology and Medicine

Nanocellulose/nanocarbon composites are newly emerging smart hybrid materials containing cellulose nanoparticles, such as nanofibrils and nanocrystals, and carbon nanoparticles, such as "classical" carbon allotropes (fullerenes, graphene, nanotubes and nanodiamonds), or other carbon nanostructures (carbon nanofibers, carbon quantum dots, activated carbon and carbon black). The nanocellulose component acts as a dispersing agent and homogeneously distributes the carbon nanoparticles in an aqueous environment. Nanocellulose/nanocarbon composites can be prepared with many advantageous properties, such as high mechanical strength, flexibility, stretchability, tunable thermal and electrical conductivity, tunable optical transparency, photodynamic and photothermal activity, nanoporous character and high adsorption capacity. They are therefore promising for a wide range of industrial applications, such as energy generation, storage and conversion, water purification, food packaging, construction of fire retardants and shape memory devices. They also hold great promise for biomedical applications, such as radical scavenging, photodynamic and photothermal therapy of tumors and microbial infections, drug delivery, biosensorics, isolation of various biomolecules, electrical stimulation of damaged tissues (e.g., cardiac, neural), neural and bone tissue engineering, engineering of blood vessels and advanced wound dressing, e.g., with antimicrobial and antitumor activity. However, the potential cytotoxicity and immunogenicity of the composites and their components must also be taken into account.

Graphene oxide coated meshes with stable underwater superoleophobicity and anti-oil-fouling property for highly efficient oil/water separation

Developing underwater superoleophobic filtration materials with robust stability and excellent anti-oil-fouling performance in harsh environments is desired for high efficiency oil/water separation. In this work, irregular hydrophilic graphene oxide (GO) was adopted as a coating material to modify oxidized copper mesh with desired hierarchical surface roughness and hydrophilic composition through a novel in situ copper ion induced crosslinking method. The combination of microscale copper wires and nanoscale hydrophilic GO sheets endowed the resultant GO coated oxidized copper mesh (GO@CuO) with unique underwater superoleophobicity and excellent anti-oil-fouling property. Moreover, the mesh exhibited excellent stability in corrosive solutions with no apparent variations in wetting properties, indicating its good stability. The as-prepared GO@CuO mesh can be applied to separate oil/water mixtures with high efficiency (>99.49%) and good reusability. Due to the excellent anti-oil-fouling property, high separation efficiency, and good stability, the as-prepared underwater superoleophobic mesh could find broad applications in oil/water separations.

Graphene Oxide/Carbon Nanotube Membranes for Highly Efficient Removal of Metal Ions from Water

Graphene oxide (GO) has an excellent adsorption capacity toward metal ions. Therefore, it is widely recognized as an auspicious material for fabrication of membranes applied in metal ion separation. However, GO membranes are not stable in aqueous solution because of electrostatic repulsion between GO nanosheets which are negatively charged. This paper shows that stable GO membranes can be easily obtained by the noncovalent interaction of GO with oxidized carbon nanotubes (CNTs). The experiment also shows that the GO/CNTs membranes can be used for the effective adsorption of metal ions. The kinetic data, adsorption isotherms, competitive adsorption experiment, and X-ray photoelectron spectroscopy indicate that the adsorption of metal ions is based on chemisorption. The membranes are remarkably durable in acidic, neutral, and basic solutions. Although the significant stabilization of the membranes by CNTs is observed, they strongly influence the adsorption process. Our study reveals that even a small amount of CNTs (GO/CNTs in the ratio 8:1) significantly reduces adsorption capacities of the membranes which were as follows: 37, 40, 50, 42, 48, and 98 mg g^-1 for Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II), respectively. The reduction of the membrane adsorption capacities results from the creation of micro- and nanochannels formed by entangled CNTs. Durability and adsorptive properties of studied membranes indicate their potential use for the removal of metals from water.

Multifunctional graphene oxide loaded nanofibrous membrane for removal of dyes and coliform from water

In this study, we fabricated a trifunctional polyurethane (PU)/graphene oxide (GO) electrospun membrane for adsorption of organic dyes such as methylene blue (MB) and rhodamine B (RB). Moreover, the prepared membrane showed antifouling property and inhibition against bacteria. The GO modified PU nanofiber shows a maximum adsorption capacity of 109.88  mg/g and 77.15 mg/g towards MB and RB respectively. Theoretical studies confirmed that the dye adsorption is followed pseudo-second-order kinetics and the Langmuir adsorption isotherm. The superhydrophilic PU/10GO membrane exhibits high water flux of 17,706 lm^-2hr^-1. This membrane also exhibits good antifouling property for separating oil-in-water emulsions with 99.99% separation efficiency. The Mechanism of antifouling was investigated using Hermia model. The results showed that PU/GO membranes also have antibacterial activity against Gram-negative and Gram-positive bacterias. Thus a superhydrophilic nanofibrous antifouling membrane that can reject both organic dye molecule and bacteria from contaminated water is developed using simple electrospinning technique.

Mechanically robust high flux graphene oxide - nanocellulose membranes for dye removal from water

Ultrathin graphene oxide (GO) layer was fabricated on cellulose nanofiber (CNF) membrane to achieve robust crosslinker free layered membrane with synergistic water flux and separation performance. Unlike pristine cellulosic or GO membranes, GO-CNF hybrid membranes exhibited significantly improved mechanical stability in both dry and wet states. All membranes showed negative surface zeta potential. GO: CNF membrane (1:100) exhibited significantly high water flux (18,123 ± 574 Lm^-2 h^-1 bar^-1); higher than that of CNF membrane or the hydrophilic commercial reference membrane with comparable pore structure (Nylon 66, 0.2 μm). We hypothyse that a unique surface structure of "standing inserted GO nanosheets" observed at low concentrations of GO contributes enormously to its ultrafast water permeability through creation of numerous water transport nanochannels. The aniosptropic layered membranes exhibited >90% rejection of positively and negatively charged dyes through a combination of electrostatic interaction, hydrophobic interactions and molecular size exclusion. Construction of an ultrathin GO layer on CNF offers a unique and efficient way to prepare highly functional, economical and scalable water purification membranes having significant advantage with respect to flux, mechanical stability and rejection of dyes compared to isotropic membrane with GO nanosheets randomly dispersed in the cellulose nanofibrous network.

Design of ultrathin hybrid membranes with improved retention efficiency of molecular dyes

Nanocellulose–graphene oxide ultrathin coatings for water purification membranes with excellent swelling resistance, permeability and dyes retention are presented.

Bimetallic Fe-Cu Nanocomposites on Sand Particles for the Inactivation of Clinical Isolates and Point-of-Use Water Filtration

Bimetallic Fe-Cu nanocomposites with an average size of 26.4 ± 4.7 nm were prepared on the surface of fine sand particles by modified coprecipitation and the chemical reduction method and were applied as an in vitro broad spectrum antimicrobial agent and recyclable hand-held water filter to sieve bacteria and metals. The size of the nanocomposites could be further reduced to 11.8 ± 1.6 nm when prepared after ball milling the sand particles, keeping the antimicrobial property intact. The results showed that the chemical nature and morphology of the nanocomposites had a great effect on both Gram-positive and Gram-negative bacteria with a minimum inhibitory concentration of 10.6 μg/mL and 13.8 μg/mL of copper, whereas the minimum bactericidal concentration was found to be 15.9 μg/mL and 21.2 μg/mL. The nanocomposites exhibited antimicrobial activity against multidrug-resistant bacteria as well as fungus isolated from different human biological samples like blood, urine, pus, and wound swabs. The nanocomposites were also capable of filtering a wide range bacteria like Acinetobacter baumannii, Escherichia coli, Salmonella typhi, Bacteroides fragilis, Salmonella paratyphi, Shigella dysenteriae, and Enterococcus faecalis, which are predominantly responsible for waterborne diseases. Further, the nanocomposites were used for the removal of hazardous metals like nickel, zinc, and lead. Leaching of copper and iron from the nanocomposites was within the permissible limit as per Bureau of Indian Standards (BIS) for Drinking Water (IS-10500-2012, second revision) as well as the International Standards for Drinking Water.

Nanocellulose, a Versatile Green Platform: From Biosources to Materials and Their Applications

With increasing environmental and ecological concerns due to the use of petroleum-based chemicals and products, the synthesis of fine chemicals and functional materials from natural resources is of great public value. Nanocellulose may prove to be one of the most promising green materials of modern times due to its intrinsic properties, renewability, and abundance. In this review, we present nanocellulose-based materials from sourcing, synthesis, and surface modification of nanocellulose, to materials formation and applications. Nanocellulose can be sourced from biomass, plants, or bacteria, relying on fairly simple, scalable, and efficient isolation techniques. Mechanical, chemical, and enzymatic treatments, or a combination of these, can be used to extract nanocellulose from natural sources. The properties of nanocellulose are dependent on the source, the isolation technique, and potential subsequent surface transformations. Nanocellulose surface modification techniques are typically used to introduce either charged or hydrophobic moieties, and include amidation, esterification, etherification, silylation, polymerization, urethanization, sulfonation, and phosphorylation. Nanocellulose has excellent strength, high Young's modulus, biocompatibility, and tunable self-assembly, thixotropic, and photonic properties, which are essential for the applications of this material. Nanocellulose participates in the fabrication of a large range of nanomaterials and nanocomposites, including those based on polymers, metals, metal oxides, and carbon. In particular, nanocellulose complements organic-based materials, where it imparts its mechanical properties to the composite. Nanocellulose is a promising material whenever material strength, flexibility, and/or specific nanostructuration are required. Applications include functional paper, optoelectronics, and antibacterial coatings, packaging, mechanically reinforced polymer composites, tissue scaffolds, drug delivery, biosensors, energy storage, catalysis, environmental remediation, and electrochemically controlled separation. Phosphorylated nanocellulose is a particularly interesting material, spanning a surprising set of applications in various dimensions including bone scaffolds, adsorbents, and flame retardants and as a support for the heterogenization of homogeneous catalysts.

Biopolymer nanofibrils: structure, modeling, preparation, and applications

Biopolymer nanofibrils exhibit exceptional mechanical properties with a unique combination of strength and toughness, while also presenting biological functions that interact with the surrounding environment. These features of biopolymer nanofibrils profit from their hierarchical structures that spun angstrom to hundreds of nanometer scales. To maintain these unique structural features and to directly utilize these natural supramolecular assemblies, a variety of new methods have been developed to produce biopolymer nanofibrils. In particular, cellulose nanofibrils (CNFs), chitin nanofibrils (ChNFs), silk nanofibrils (SNFs) and collagen nanofibrils (CoNFs), as the four most abundant biopolymer nanofibrils on earth, have been the focus of research in recent years due to their renewable features, wide availability, low-cost, biocompatibility, and biodegradability. A series of top-down and bottom-up strategies have been accessed to exfoliate and regenerate these nanofibrils for versatile advanced applications. In this review, we first summarize the structures of biopolymer nanofibrils in nature and outline their related computational models with the aim of disclosing fundamental structure-property relationships in biological materials. Then, we discuss the underlying methods used for the preparation of CNFs, ChNFs, SNF and CoNFs, and discuss emerging applications for these biopolymer nanofibrils.

Hierarchical Assembly of Nanocellulose-Based Filaments by Interfacial Complexation

In the present study, interfacial complexation spinning of oppositely charged cellulose-materials is applied to fabricate hierarchical and continuous nanocellulose based filaments under aqueous conditions by using cationic cellulose nanocrystals with different anionic celluloses including soluble sodium carboxymethyl cellulose and insoluble 2,2,6,6-tetramethylpiperidinyl-1-oxy radical-oxidized cellulose nanofibers and dicarboxylated cellulose nanocrystals (DC-CNC). The morphologies of the wet and dry nanocellulose based filaments are further investigated by optical and electron microscopy. All fabricated continuous nanocellulose based filaments display a hierarchical structure similar to the natural cellulose fibers in plant cells. As far as it is known, this is not only the first report about the fabrication of nanocellulose based filaments by interfacial complexation of cationic CNCs with anionic celluloses but also the first demonstration of fabricating continuous fibers directly from oppositely charged nanoparticles by interfacial nanoparticle complexation (INC). This INC approach may provide a new route to design continuous filaments from many other oppositely charged nanoparticles with tailored characteristics.

Current State and New Trends in the Use of Cellulose Nanomaterials for Wastewater Treatment

Nanotechnology has been identified as having great potential for improving the efficiency of water prevention and purification while reducing costs. In this field, two applications of nanocellulose have generated attention and have proven to be a sound strategy as an adsorbent and as a membrane for the removal of contaminants. This potential is attributed to its high aspect ratio, high specific surface area, high capacity retention, and environmental inertness. In addition to the aforementioned advantages, the presence of active sites allows the incorporation of chemical moieties that may enhance the binding efficiency of pollutants to the surface. This review paper intends to understand how nanocellulose affects the adsorption behavior of water pollutants, e.g., heavy metal ions, microbes, dyes, and organic molecules, and is divided in two parts. First, a general overview of the different strategies for the preparation of nanocellulose is described, and its specific properties are reported. The second section reports some of its application as adsorbent nanomaterial or separation membrane. It appears that the use of nanocellulose for these applications is very promising for wastewater treatment industries.