Chitosan biopolymer for fuel cell applications

Improved Proton Conductivity of Chitosan-Based Composite Proton Exchange Membrane Reinforced by Modified GO Inorganic Nanofillers

Non-fluorinated chitosan-based proton exchange membranes (PEMs) have been attracting considerable interest due to their environmental friendliness and relatively low cost. However, low proton conductivity and poor physicochemical properties have limited their application in fuel cells. In this work, a reinforced nanofiller (sulfonated CS/GO, S-CS/GO) is accomplished, for the first time, via a facile amidation and sulfonation reaction. Novel chitosan-based composite PEMs are successfully constructed by the incorporation of the nanofiller into the chitosan matrix. Additionally, the effects of the type and amount of the nanofillers on physicochemical and electrochemical properties are further investigated. It is demonstrated that the chitosan-based composite PEMs incorporating an appropriate amount of the nanofillers (9 wt.%) exhibit good membrane-forming ability, physicochemical properties, improved proton conductivity, and low methanol permeability even under a high temperature and low humidity environment. When the incorporated amounts of S-CS/GO are 9 wt.%, the proton conductivity of the composite PEMs was up to 0.032 S/cm but methanol permeability was decreased to 1.42 × 10-7 cm2/s. Compared to a pristine CS membrane, the tensile strength of the composite membrane is improved by 98% and the methanol permeability is reduced by 51%.

Atomistic Modeling of Quaternized Chitosan Head Groups: Insights into Chemical Stability and Ion Transport for Anion Exchange Membrane Applications

The chemical stability and ion transport properties of quaternized chitosan (QCS)-based anion exchange membranes (AEMs) were explored using Density Functional Theory (DFT) calculations and all-atom molecular dynamics (MD) simulations. DFT calculations of LUMO energies, reaction energies, and activation energies revealed an increasing stability trend among the head groups: propyl trimethyl ammonium chitosan (C) < oxy propyl trimethyl ammonium chitosan (B) < 2-hydroxy propyl trimethyl ammonium chitosan (A) at hydration levels (HLs) of 0 and 3. Subsequently, all-atom MD simulations evaluated the diffusion of hydroxide ions (OH-) through mean square displacement (MSD) versus time curves. The diffusion coefficients of OH- ions for the three types of QCS (A, B, and C) were observed to increase monotonically with HLs ranging from 3 to 15 and temperatures from 298 K to 350 K. Across different HLs and temperatures, the three QCS variants exhibited comparable diffusion coefficients, underlining their effectiveness in vehicular transport of OH- ions.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

A sustainable and eco-friendly approach for environmental and energy management using biopolymers chitosan, lignin and cellulose - A review

Biopolymers are a naturally occurring alternative to synthetic polymers that are linked by covalent bonds, which includes cellular components such as proteins, nucleotides, lipids, and polysaccharides. Based on the extensive literature review it was found that chitosan, lignin, and cellulose were predominantly used in the energy and environmental sectors. Due to their vast array of qualities, including the adsorption, flocculation, anticoagulation, and furthermore, have made them useful for treating wastewater and pollutant removal. Chitosan and lignin have been used as a proton exchange membrane in the energy storage device of fuel cells. As these biopolymers develop strong coordination connections with metal surfaces, they act as an anticorrosive agent, which inhibiting the corrosion. Besides, there are a lot of recent developments in the application of biopolymers for energy and environmental fields. The present review provides a concise summary of recent developments in membrane-based biopolymers role in energy and environmental field. In addition, this review is drawn to a conclusion with a discussion of future trends in the real application of biopolymers in a variety of different industries, as well as the financial significance of these future trends.

Recent Advances in the Development of Sustainable Composite Materials used as Membranes in Microbial Fuel Cells

MFC can have dual functions; they can generate electricity from industrial and domestic effluents while purifying wastewater. Most MFC designs comprise a membrane which physically separates the cathode and anode compartments while keeping them electrically connected, playing a significant role in its efficiency. Popular commercial membranes such as Nafion, Hyflon and Zifron have excellent ionic conductivity, but have several drawbacks, mainly their prohibitive cost and non-biodegradability, preventing the large-scale application of MFC. Fabrication of composite materials that can function better at a much lower cost while also being environment-friendly has been the endeavor of few researchers over the past years. The current review aims to apprise readers of the latest trends of the past decade in fabricating composite membranes (CM) for MFC. For emphasis on environmental-friendly CM, the review begins with biopolymers, moving on to the carbon-polymer, polymer-polymer, and metal-polymer CM. Lastly, critical analysis towards technology-oriented propositions and realistic future directives in terms of strengths, weakness, opportunities, challenges (SWOC analysis) of the application of CM in MFC have been discussed for their possible large-scale use. The focus of this review is the development of hybrid materials as membranes for fuel cells, while underscoring the need for environment-friendly composites and processes.

Morphology and Transport Study of Acid-Base Blend Proton Exchange Membranes by Molecular Simulations: Case of Chitosan/Nafion

Blending a basic polymer (e.g., chitosan) with Nafion can modify some membrane properties in direct methanol fuel cell applications, e.g., controlling methanol crossover, by regulating the morphology of hydrophilic channels. Unraveling the mechanisms by which the channel morphology is modified is essential to formulate design strategies for acid-base blend membrane development. Thus, we use molecular simulations to analyze the morphological features of a blend membrane (at 75/25 chitosan/Nafion wt %), i.e., (i) water/polymer phase organizations, (ii) number and size of water clusters, and (iii) quantitative morphological measures of hydrophilic channels, and compare them to the pure Nafion in a wide range of water contents. It is found that the affinity of water to different hydrophilic groups in the blend membrane can result in more distorted and dispersed hydrophilic phase and fewer bulk water-like features compared to pure Nafion. Also, the width of the hydrophilic network bottleneck, i.e., pore limiting diameter (PLD), is found to be almost five times smaller for the blend membrane compared to Nafion at their maximum water contents. Moreover, by changing the chitosan/Nafion weight ratio from 75/25 to 0/100, we show that as Nafion content increases, all channel morphological characteristics alter monotonically except PLD. This is mainly due to the strong acid-base interactions between Nafion and chitosan, which hinder the monotonic growth of PLD. Interestingly, water and methanol diffusion coefficients are strongly correlated with PLD, suggesting that PLD can be used as a single parameter for tailoring the blending ratio for achieving the desired diffusion properties of acid-base membranes.

Review: chitosan-based biopolymers for anion-exchange membrane fuel cell application

Chitosan (CS)-based anion exchange membranes (AEMs) have gained significant attention in fuel cell applications owing to their numerous benefits, such as environmental friendliness, flexibility for structural alteration, and improved mechanical, thermal and chemical durability. This study aims to enhance the cell performance of CS-based AEMs by addressing key factors including mechanical stability, ionic conductivity, water absorption and expansion rate. While previous reviews have predominantly focused on CS as a proton-conducting membrane, the present mini-review highlights the advancements of CS-based AEMs. Furthermore, the study investigates the stability of cationic head groups grafted to CS through simulations. Understanding the chemical properties of CS, including the behaviour of grafted head groups, provides valuable insights into the membrane's overall stability and performance. Additionally, the study mentions the potential of modern cellulose membranes for alkaline environments as promising biopolymers. While the primary focus is on CS-based AEMs, the inclusion of cellulose membranes underscores the broader exploration of biopolymer materials for fuel cell applications.

Chitosan Polysaccharides from a Polarizable Multiscale Approach

We report simulations of chitosan polysaccharides in the aqueous phase, at infinite dilute conditions and zero ionic strength. Those simulations are performed by means of a polarizable multiscale modeling scheme that relies on a polarizable all atom force field to model solutes and on a polarizable solvent coarse grained approach. Force field parameters are assigned only from quantum chemistry ab initio data. We simulate chitosan monomer units, dimers and 50-long chains. Regarding the 50-long chains we simulate three sets of ten randomly built chain replica at three different pH conditions (corresponding to different chain protonation states, the chain degree of deacetylation is 85%). Our simulations show the persistence length of 50-long chitosan chains at strong acidic conditions (pH <5) to be 24 ± 2 nm (at weak/negligible ionic strength conditions), and to be 1 order of magnitude shorter at usual pH conditions. Our simulation data support the most recent simulation and experimental studies devoted to chitosan polysaccharides in the aqueous phase.

Structural diversity, functional versatility and applications in industrial, environmental and biomedical sciences of polysaccharides and its derivatives - A review

Recent efforts on the expansion of sustainable and commercial primal matters are essential to enhance the knowledge of their hazards and noxiousness to humans and their environments. For example, polysaccharide materials are widely utilized in food, wound dressing, tissue engineering, industry, targeted drug delivery, environmental, and bioremediation due to their attractive degradability, nontoxicity and biocompatibility. There are numerous easy, quick, and efficient ways to manufacture these materials that include cellulose, starch, chitosan, chitin, dextran, pectin, gums, and pullulan. Further, they exhibit distinctive properties when combined favourably with raw materials from other sources. This review discusses the synthesis and novel applications of these carbohydrate polymers in industrial, environmental and biomedical sciences.

Fabrication and Characterization of Eco-Friendly Thin Films as Potential Optical Absorbers for Efficient Multi-Functional Opto-(Electronic) and Solar Cell Applications

The necessity for reliable and efficient multifunctional optical and optoelectronic devices is always calling for the exploration of new fertile materials for this purpose. This study leverages the exploitation of dyed environmentally friendly biopolymeric thin films as a potential optical absorber in the development of multifunctional opto-(electronic) and solar cell applications. Uniform, stable thin films of dyed chitosan were prepared using a spin-coating approach. The molecular interactivity between the chitosan matrix and all the additive organic dyes was evaluated using FTIR measurements. The color variations were assessed using chromaticity (CIE) measurements. The optical properties of films were inspected using the measured UV-vis-NIR transmission and reflection spectra. The values of the energy gap and Urbach energy as well as the electronic parameters and nonlinear optical parameters of films were estimated. The prepared films were exploited for laser shielding as an attenuated laser cut-off material. In addition, the performance of the prepared thin films as an absorbing organic layer with silicon in an organic/inorganic heterojunction architecture for photosensing and solar energy conversion applicability was studied. The current-voltage relation under dark and illumination declared the suitability of this architecture in terms of responsivity and specific detectivity values for efficient light sensing applications. The suitability of such films for solar cell fabrications is due to some dyed films achieving open-circuit voltage and short-circuit current values, where Saf-dyed films achieved the highest V_oc (302 mV) while MV-dyed films achieved the highest J_sc (0.005 mA/cm²). Finally, based on all the obtained characterization results, the engineered natural cost-effective dyed films are considered potential active materials for a wide range of optical and optoelectronic applications.

Synthesis of biodegradable antimicrobial pH-sensitive silver nanocomposites reliant on chitosan and carrageenan derivatives for 5-fluorouracil drug delivery toward HCT116 cancer cells

The current research relies on a one-pot green biosynthesis of silver nanoparticles (SNPs) with various ratios of silver (Ag) in the existence of N, N, N-trimethyl chitosan chloride (TMC) and carboxymethyl kappa-carrageenan (CMKC), to investigate the effectiveness of the synthesized silver nanocomposites (SNCs) as pH sensitive biodegradable carrier for orally intestinal delivery of 5-fluorouracil (5-FU) drug. FTIR, XRD, TEM and FE-SEM/EDX methods were utilized to demonstrate the structure of the prepared polyelectrolyte complex PEC (TMC/CMKC) and SNCs (TMC/CMKC/Ag). The results showed that the 5-FU encapsulation effectiveness inside all of the prepared SNCs samples was improved by increasing the concentration of Ag, reaching 92.16 ± 0.57 % with 3 % Ag. In vitro release behavior of 5-FU loaded SNC 3 % (TMC/CMKC/Ag 3 %), displayed slow and sustained release reaching 96.3 ± 0.81 % up to 24 h into pH 7.4 medium. The successful release of 5-FU from the loaded SNC 3 % was confirmed through occurrence of strong cytotoxicity, with an IC₅₀ value of 31.15 μg/ml, and high % of apoptotic cells (30.66 %) within the treated HCT116 cells. Besides, SNC 3 % showed good biodegradability and antimicrobial properties against different bacterial strains. Overall, SNC 3 % can be suggested as an effective system for both controlled drug delivery and antibacterial action.

Chitosan-Urushiol nanofiber membrane with enhanced acid resistance and broad-spectrum antibacterial activity

Due to the large specific surface area and rich pore structure, chitosan nanofiber membrane has many advantages over conventional gel-like or film-like products. However, the poor stability in acidic solutions and relatively weak antibacterial activity against Gram-negative bacteria severely restrict its use in many industries. Here, we present a chitosan-urushiol composite nanofiber membrane prepared by electrospinning. Chemical and morphology characterization revealed that the formation of chitosan-urushiol composite involved the Schiff base reaction between catechol and amine groups and the self-polymerization of urushiol. The unique crosslinked structure and multiple antibacterial mechanisms endowed the chitosan-urushiol membrane with outstanding acid resistance and antibacterial performance. After immersion in HCl solution at pH 1, the membrane maintained its intact appearance and satisfactory mechanical strength. In addition to its good antibacterial performance against Gram-positive Staphylococcus aureus (S. aureus), the chitosan-urushiol membrane exhibited synergistic antibacterial activity against Gram-negative Escherichia coli (E. coli) that far exceeded that of neat chitosan membrane and urushiol. Moreover, cytotoxicity and hemolysis assays revealed that the composite membrane had good biocompatibility similar to that of neat chitosan. In short, this work provides a convenient, safe, and environmentally friendly method to simultaneously enhance the acid resistance and broad-spectrum antibacterial activity of chitosan nanofiber membranes.

Recent progress and future directions of membranes green polymers for oily wastewater treatment

The preparation, modification and application of green polymers such as poly-lactic acid (PLA), chitosan (CS), and cellulose acetate (CA) for oily wastewater treatment is summed up in this review. Due to the low environmental pollution, good chemical resistivity, high hydrophobicity, and good capacity for water-oil emulsion separation of the presented polymers, it then highlights the various membrane production methods and their role in producing effective membranes, with a focus on recent advances in improving membrane properties through the addition of various Nano materials. As a result, the hydrophilic/hydrophobic properties that are critical in the oil separation mechanism are highlighted. Finally, it looks at the predictions and challenges in oil/water separation and recovery. These ideas are discussed with a focus on modern production methods and oil separation proficiency.

Sulfamic acid grafted to cross-linked chitosan by dendritic units: a bio-based, highly efficient and heterogeneous organocatalyst for green synthesis of 2,3-dihydroquinazoline derivatives

In this work, novel cross-linked chitosan by the G1 dendrimer from condensation of melamine and toluene-2,4-diisocyante terminated by sulfamic acid groups (CS-TDI-Me-TDI-NHSO₃H), as a bio-based and heterogeneous acidic organocatalyst, was designed and prepared. Also, the structure of the prepared organocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and thermogravimetric analysis/derivative thermogravimetry (TGA/DTA). Subsequently, the catalytic performance of the biobased and dendritic CS-TDI-Me-TDI-NHSO₃H, as a multifunctional solid acid, was evaluated for the preparation of 2,3-dihydroquinazoline derivatives through a three-component reaction by following green chemistry principles. Some of the advantages of this new protocol include high to excellent yields and short reaction times as well as easy preparation and remarkable catalyst stability of the introduced acidic organocatalyst. The CS-TDI-Me-TDI-SO₃H catalyst can be used for up to five cycles for the preparation of quinazoline derivatives with a slight decrease in its catalytic activity.

Characteristics and performance studies of a composite polymer electrolyte membrane based on chitosan/glycerol-sulfosuccinic acid modified montmorillonite clay

In this study, chitosan (CS) doped sulphosuccinic acid (SSA)-glycerol (Gly) and modified montmorillonite clay (MMT) were successfully fabricated. The membranes were prepared using the solution casting method. Analysis of morphology and topography using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the composite membrane with 3 wt% MMT filler, namely CS/MMT-1, possessed the most adequate surface roughness compared to the other fabricated membranes. Furthermore, mechanical characterization of the CS/MMT-1 composite membrane showed that the membrane achieved satisfactory mechanical strength with a value of 39.23 MPa. Proton conductivity of the composite membranes increased as the temperature was increased. The proton conductivity of the CS/MMT-1 composite membrane increased from 1.75 × 10-2 S cm-1 at 25 °C up to 3.57 × 10-2 S cm-1 at 80 °C. The CS/MMT-1 composite membrane also exhibited a methanol permeability value that was significantly lower than that of pristine CS, namely 1.22 × 10-7 cm2 s-1 and 12.49 × 10-7 cm2 s-1, respectively. The results of this study show that the fabricated composite membrane can be used as an alternative polymer electrolyte membrane (PEM) for DMFC applications.

Efficient and Eco-Friendly Perspectives for C-H Arylation of Benzothiazole Utilizing Pd Nanoparticle-Decorated Chitosan

In this contribution, an eco-friendly, sustainable, and efficient palladium nanoparticle-decorated chitosan (Pd@Chitosan) catalyst was synthesized by a simple impregnation method. The synthesized material was utilized as a heterogeneous catalyst for the C-H arylation of benzothiazole under ultrasonic irradiation. The Pd@Chitosan catalyst efficiently catalyzed the conversion of aryl iodides and bromides to 1-(4-(benzothiazol-2-yl)phenyl)ethan-1-one selectively. A single product of 83–93% yield was obtained in N,N-dimethylformamide solvent at 80 °C for 2.5h. This study reveals that Pd@Chitosan is an efficient catalyst, which catalyzes the C-H arylation with good reaction yields. The activity of the Pd@Chitosan is due to the presence of highly dispersed Pd(0) nanoparticles on the surface of the chitosan and Pd2+; a tentative mechanism was proposed based on the XPS results of the fresh catalyst and spent catalyst.

Use of Chitosan as Copper Binder in the Continuous Electrochemical Reduction of CO2 to Ethylene in Alkaline Medium

This work explores the potential of novel renewable materials in electrode fabrication for the electrochemical conversion of carbon dioxide (CO₂) to ethylene in alkaline media. In this regard, the use of the renewable chitosan (CS) biopolymer as ion-exchange binder of the copper (Cu) electrocatalyst nanoparticles (NPs) is compared with commercial anion-exchange binders Sustainion and Fumion on the fabrication of gas diffusion electrodes (GDEs) for the electrochemical reduction of carbon dioxide (CO₂R) in an alkaline medium. They were tested in membrane electrode assemblies (MEAs), where selectivity to ethylene (C₂H₄) increased when using the Cu:CS GDE compared to the Cu:Sustainion and Cu:Fumion GDEs, respectively, with a Faradaic efficiency (FE) of 93.7% at 10 mA cm^-2 and a cell potential of -1.9 V, with a C₂H₄ production rate of 420 µmol m^-2 s^-1 for the Cu:CS GDE. Upon increasing current density to 90 mA cm^-2, however, the production rate of the Cu:CS GDE rose to 509 µmol/m²s but the FE dropped to 69% due to increasing hydrogen evolution reaction (HER) competition. The control of mass transport limitations by tuning up the membrane overlayer properties in membrane coated electrodes (MCE) prepared by coating a CS-based membrane over the Cu:CS GDE enhanced its selectivity to C₂H₄ to a FE of 98% at 10 mA cm^-2 with negligible competing HER. The concentration of carbon monoxide was below the experimental detection limit irrespective of the current density, with no CO₂ crossover to the anodic compartment. This study suggests there may be potential in sustainable alernatives to fossil-based or perfluorinated materials in ion-exchange membrane and electrode fabrication, which constitute a step forward towards decarbonization in the circular economy perspective.

IL versus DES: Impact on chitin pretreatment to afford high quality and highly functionalizable chitosan

Chitin is mainly extracted from crustaceans, but this resource is seasonally dependent and can represent a major drawback to satisfy the traceability criterion for high valuable applications. Insect resources are valuable alternatives due to their lower mineral content. However, the deacetylation of chitin into chitosan is still an expensive process. Therefore, we herein compare the impact of both DES/IL-pretreatments on the efficiency of the chemical deacetylation of chitin carried out over two insect sources (Bombyx eri, BE and Hermetia illucens, HI) and shrimp shells (S). The results showed that chitosans obtained from IL-pretreated chitins from BE larva, present lower acetylation degrees (13-17%) than DES-pretreated samples (18-27%). A selective N-acylation reaction with oleic acid has also been performed on the purest and most deacetylated chitosans leading to high substitution degrees (up to 27%). The overall approach validates the proper chitin source and processing methodology to achieve high quality and highly functionalizable chitosan.

Natural biopolymers as proton conductors in bioelectronics

Bioelectronic devices sense or deliver information at the interface between living systems and electronics by converting biological signals into electronic signals and vice-versa. Biological signals are typically carried by ions and small molecules. As such, ion conducting materials are ideal candidates in bioelectronics for an optimal interface. Among these materials, ion conducting polymers that are able to uptake water are particularly interesting because, in addition to ionic conductivity, their mechanical properties can closely match the ones of living tissue. In this review, we focus on a specific subset of ion-conducting polymers: proton (H⁺ ) conductors that are naturally derived. We first provide a brief introduction of the proton conduction mechanism, and then outline the chemical structure and properties of representative proton-conducting natural biopolymers: polysaccharides (chitosan and glycosaminoglycans), peptides and proteins, and melanin. We then highlight examples of using these biopolymers in bioelectronic devices. We conclude with current challenges and future prospects for broader use of natural biopolymers as proton conductors in bioelectronics and potential translational applications.

3D nanoflower-like layered double hydroxide modified quaternized chitosan/polyvinyl alcohol composite anion conductive membranes for fuel cells

To solve the trade-off problem among ionic conductivity, mechanical and chemical stability of anion exchange membranes (AEMs), quaternized chitosan (QCS) was first prepared and then was blended with polyvinyl alcohol (PVA) to improve mechanical strength of QCS. Afterwards, three-dimensional (3D) hierarchical flower-like layered double hydroxides (LDHs) were prepared via one-pot ethylene glycol-assisted solvothermal method, and then were incorporated into QCS/PVA blend matrix to fabricate composite AEMs. By constructing 3D hierarchical structure, the active sites of LDH nanosheets are fully exposed, thus impressive ion conductivity, alkali and fuel resistant ability of LDH nanosheets can be rationally utilized. The composite membrane displayed the maximum OH^- conductivity of 25.7 mS cm^-1, which was 48.6 % higher than that of the pristine membrane. Alkaline stability measurement proved that the composite membranes kept residual ionic conductivity of as high as 92 % after immersion in a 2 M KOH for 100 h. Due to the decreased methanol permeability and increased conductivity, the composite membrane with 6% LDHs content exhibited a peak power density of 73 mW cm^-2 at 60 °C, whereas the pristine membrane demonstrated only 40 mW cm^-2.

Applications of chitosan in environmental remediation: A review

Environmental biotechnology is the use of biotechnology to develop and regulate biological systems for the remediation of environmental contamination. Nature has gifted ample material for remediation of its resources, among which chitosan is one of the most important and largely available biomaterial globally. Chitosan is a biopolymer obtained by deacetylation of chitin extracted from marine waste and its applications from drug delivery to food additives are broadly available. Chitosan exhibit several properties such as availability, low cost, high biocompatibility, and biodegradability. These properties make it biologically and chemically acceptable for use in various fields. Due to some limitations of pure chitosan, there has been a growing interest in modifying the chitosan in order to improve the original properties and widen the applications of pure phase chitosan. Various modified forms of chitosan and their associated applications are reviewed here with emphasis on their use in environmental remediation. The demand of chitosan in the global industrial market is growing which is briefly explained in this paper. Chitosan is used for water purification since a long time and still progress is going on for making it more efficient in the removal process. It can be used as a flocculent and coagulant, as an adsorbent for removing the contaminants like heavy metals, dyes, pesticides, antibiotics, biological contaminants from wastewater. Soil remediation using chitosan material is explained in this review. Various other applications such as drug delivery, food additives, tissue engineering are thoroughly reviewed.

Efficient Chitosan/Nitrogen-Doped Reduced Graphene Oxide Composite Membranes for Direct Alkaline Ethanol Fuel Cells

Herein, we prepared a series of nanocomposite membranes based on chitosan (CS) and three compositionally and structurally different N-doped graphene derivatives. Two-dimensional (2D) and quasi 1D N-doped reduced graphene oxides (N-rGO) and nanoribbons (N-rGONRs), as well as 3D porous N-doped graphitic polyenaminone particles (N-pEAO), were synthesized and characterized fully to confirm their graphitic structure, morphology, and nitrogen (pyridinic, pyrrolic, and quaternary or graphitic) group contents. The largest (0.07%) loading of N-doped graphene derivatives impacted the morphology of the CS membrane significantly, reducing the crystallinity, tensile properties, and the KOH uptake, and increasing (by almost 10-fold) the ethanol permeability. Within direct alkaline ethanol test cells, it was found that CS/N rGONRs (0.07 %) membrane (Pmax. = 3.7 mWcm-2) outperformed the pristine CS membrane significantly (Pmax. = 2.2 mWcm-2), suggesting the potential of the newly proposed membranes for application in direct ethanol fuel cells.

Ionotropic Gelation of Chitosan Flat Structures and Potential Applications

The capability of some polymers, such as chitosan, to form low cost gels under mild conditions is of great application interest. Ionotropic gelation of chitosan has been used predominantly for the preparation of gel beads for biomedical application. Only in the last few years has the use of this method been extended to the fabrication of chitosan-based flat structures. Herein, after an initial analysis of the major applications of chitosan flat membranes and films and their usual methods of synthesis, the process of ionotropic gelation of chitosan and some recently proposed novel procedures for the synthesis of flat structures are presented.

Quaternized Chitosan-Based Anion Exchange Membrane Composited with Quaternized Poly(vinylbenzyl chloride)/Polysulfone Blend

An efficient and effective process for the production of high-performance anion exchange membranes (AEMs) is necessary for the commercial application of fuel cells. Therefore, in this study, quaternized poly vinylbenzyl chloride (QVBC) and polysulfone were composited with glycidyltrimethylammonium-chloride-quaternized chitosan (QCS) at different ratios (viz., 1 wt %, 5 wt %, and 10 wt %). The structure and morphology of the membranes were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Further, the water uptake, swelling ratio, and ionic conductivities of the composite membrane at different wt % of QCS were evaluated. The membrane with 5% QCS exhibited an ionic conductivity of 49.6 mS/cm and 130 mS/cm at 25 °C and 70 °C, respectively.

Recent Progress in Conducting Polymers for Hydrogen Storage and Fuel Cell Applications

Hydrogen is a clean fuel and an abundant renewable energy resource. In recent years, huge scientific attention has been invested to invent suitable materials for its safe storage. Conducting polymers has been extensively investigated as a potential hydrogen storage and fuel cell membrane due to the low cost, ease of synthesis and processability to achieve the desired morphological and microstructural architecture, ease of doping and composite formation, chemical stability and functional properties. The review presents the recent progress in the direction of material selection, modification to achieve appropriate morphology and adsorbent properties, chemical and thermal stabilities. Polyaniline is the most explored material for hydrogen storage. Polypyrrole and polythiophene has also been explored to some extent. Activated carbons derived from conducting polymers have shown the highest specific surface area and significant storage. This review also covers recent advances in the field of proton conducting solid polymer electrolyte membranes in fuel cells application. This review focuses on the basic structure, synthesis and working mechanisms of the polymer materials and critically discusses their relative merits.

Composite Proton Exchange Membranes Based on Chitosan and Phosphotungstic Acid Immobilized One-Dimensional Attapulgite for Direct Methanol Fuel Cells

In order to obtain biopolymer chitosan-based proton exchange membranes with excellent mechanical properties as well as high ionic conductivity at the same time, natural attapulgite (AT) with one-dimensional (1D) structure was loaded with a strong heteropolyacid and also a super proton conductor, phosphotungstic acid (PWA), using a facial method. The obtained PWA anchored attapulgite (WQAT) was then doped into the chitosan matrix to prepare a series of Chitosan (CS)/WQAT composite membranes. The PWA coating could improve the dispersion and interfacial bonding between the nano-additive and polymer matrix, thus increasing the mechanical strength. Moreover, the ultra-strong proton conduction ability of PWA together with the interaction between positively charged CS chains and negatively charged PWA can construct effective proton transport channels with the help of 1D AT. The proton conductivity of the composite membrane (4 wt.% WQAT loading) reached 35.3 mS cm⁻¹ at 80 °C, which was 31.8% higher than that of the pure CS membrane. Moreover, due to the decreased methanol permeability and increased conductivity, the composite membrane with 4% WQAT content exhibited a peak power density of 70.26 mW cm⁻² fed at 2 M methanol, whereas the pure CS membrane displayed only 40.08 mW cm⁻².

Novel N-p-carboxy benzyl chitosan/poly (vinyl alcohol/functionalized zeolite mixed matrix membranes for DMFC applications

The novel N-p-carboxy benzyl chitosan (CBC)/ poly (vinyl alcohol) (PVA) based mixed matrix membranes (MMMs) filled with surface-modified zeolite have been prepared using the dissolution casting technique. The applicability of prepared MMMs for direct methanol fuel cell (DMFC) was investigated in terms of water uptake, methanol permeation, and proton conductivity by changing filler content (10-50 wt. %). The zeolite was modified by silane coupling agent, 3-mercaptopropyltrimethoxysilane (MPTMS). The resultant modified zeolite (MZ) was incorporated into CBC/PVA blend to obtain mixed matrix PEMs. The functional group, structural properties, morphological and topographical investigation of MMMs were examined using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Scanning electron microscopy (SEM) respectively. The prepared MMMs exhibited a remarkable decrease in methanol permeability of 2.3 × 10^-7  cm²/s with C-CPMZ50. The maximum value of proton conductivity of 0.0527 Scm^-1, was shown by C-CMPZ10. The prepared PEMs also displayed good stability during long term operating time.

Structure and properties of thermomechanically processed chitosan/carboxymethyl cellulose/graphene oxide polyelectrolyte complexed bionanocomposites

Bionanocomposites of chitosan and chitosan/carboxymethyl cellulose (CMC) polyelectrolyte complexed materials with graphene oxide (GO) or reduced graphene oxide (rGO) were prepared by thermomechanical processing with excellent levels of dispersion. While GO has a greater affinity with the chitosan polycation, rGO had a more pronounced effect on properties resulting in increased tensile strength, Shore D hardness, and thermal stability of both matrices. Although GO is more hydrophilic than rGO, the former increased more effectively the surface hydrophobicity of the biocomposites regardless of matrix type. GO and rGO changed the α-transition of the biocomposites in a similar manner. The electrochemical properties of the biocomposites were influenced by both nanofiller type and matrix. This research revealed that inclusion of 2D carbon nanomaterials can alter biopolymer interactions and that the phase structure of the biopolymer blend may play a more important role than nanofiller-matrix interactions in determining the overall properties of these bionanocomposites.

Development of a Simple Reversible-Flow Method for Preparation of Micron-Size Chitosan-Cu(II) Catalyst Particles and Their Testing of Activity

A simple flow system employing a reversible-flow syringe pump was employed to synthesize uniform micron-size particles of chitosan-Cu(II) (CS-Cu(II)) catalyst. A solution of chitosan and Cu(II) salt was drawn into a holding coil via a 3-way switching valve and then slowly pumped to drip into an alkaline solution to form of hydrogel droplets. The droplets were washed and dried to obtain the catalyst particles. Manual addition into the alkaline solution or employment of flow system with a vibrating rod, through which the end of the flow line is inserted, was investigated for comparison. A sampling method was selected to obtain representative samples of the population of the synthesized particles for size measurement using optical microscopy. The mean sizes of the particles were 880 ± 70 µm, 780 ± 20 µm, and 180 ± 30 µm for the manual and flow methods, without and with the vibrating rod, respectively. Performance of the flow methods, in terms of rate of droplet production and particle size distribution, are discussed. Samples of 180 µm size CS-Cu(II) particles were tested for catalytic reduction of 0.5 mM p-nitrophenol to p-aminophenol by 100-fold excess borohydride. The conversion was 98% after 20 min, whereas without the catalyst there was only 14% conversion.