Hybrid Composite Membrane of Phosphorylated Chitosan/Poly (Vinyl Alcohol)/Silica as a Proton Exchange Membrane

Chitosan-based Schiff bases: Promising materials for biomedical and industrial applications

There is plenty of scope for modifying chitosan, an only polycationic natural polysaccharide, owing to its reactive functional groups, namely hydroxyl and amino groups. Although innumerable numbers of chitosan derivatives have been synthesized by modifying these groups and reported elsewhere, in this review article, an attempt has been exclusively made to demonstrate the syntheses of various chitosan-based Schiff bases (CSBs) simply by allowing the reactions of reactive amino groups of chitosan with different aldehydes/ketones of interest. Due to their very peculiar and unique characteristics, such as biodegradability, biocompatibility, metal-binding capability, etc., they are found to be very useful for diversified applications. Thus, we have also attempted to showcase their very specific biomedical fields, including tissue engineering, drug delivery, and wound healing, to name a few. In addition, we have also discussed the utilization of CSBs for industrial applications such as wastewater treatment, catalysis, corrosion inhibition, sensors, etc.

Investigating the Sulfonated Chitosan/Polyvinylidene Fluoride-Based Proton Exchange Membrane with fSiO2 as Filler in Microbial Fuel Cells

Chitosan (CS), a promising potential biopolymer with exquisite biocompatibility, economic viability, hydrophilicity, and chemical modifications, has drawn interest as an alternative material for proton exchange membrane (PEM) fabrication. However, CS in its original form exhibited low proton conductivity and mechanical stability, restricting its usage in PEM development. In this work, chitosan was functionalized (sulfonic acid (-SO3H) groups)) to enhance proton conductivity. The sulfonated chitosan (sCS) was blended with polyvinylidene fluoride (PVDF) polymer, along with the incorporation of functionalized SiO2 (-OH groups), for fabricating chitosan-based composite proton exchange membranes to enhance microbial fuel cell (MFC) performances. The results show that adding functionalized inorganic fillers (fSiO2) into the membrane enhances the mechanical, thermal, and anti-biofouling behavior. From the results, the PVDF/sCS/fSiO2 composite membrane exhibited enhanced proton conductivity 1.0644 × 10-2 S cm-1 at room temperature and increased IEC and mechanical and chemical stability. Furthermore, this study presents a revolutionary way to generate environmentally friendly natural polymer-based membrane materials for developing PEM candidates for enhanced MFC performances in generating bioelectricity and wastewater treatment.

Polyelectrolyte membranes based on phosphorylated-PVA/cellulose acetate for direct methanol fuel cell applications: synthesis, instrumental characterization, and performance testing

Designing and synthesis of cost-effective and improved methanol permeable and proton conductive membranes are the main challenges for preparation of polymeric electrolyte membrane (PEM). Herein, a cost-effective PEM membrane based on phosphorylated polyvinyl alcohol (PVA)-grafted-cellulose acetate (CA) was prepared by a solution-casting technique. Water and methanol uptakes of phosphorylated PVA/CA membranes were characterized as function with the molar ratio of CA. Additionally, structure and morphology of phosphorylated PVA/CA (Ph-PVA/CA) membranes were verified by FT-IR analysis, SEM investigation. Furthermore, ion exchange capacity (IEC), proton conductivity and methanol permeation of Ph-PVA/CA membranes were examined based on the concentration of OPA basically. The results manifested a perceptible improvement in proton conductivity from 0.035 to 0.05 S/cm at 25 and 70 °C, respectively using 600 μL of OPA, and IEC of 2.1 meq/g using 400 μL of OPA at ambient temperature. On the other hand, methanol permeability (P = 1.08 × 10-10 cm2/s) was lower than Nafion 117 admirably. The optimum OPA concentration was 200 μL according to conductivity measurements (at 10% PVA, 150 μL GA, and CA 7%). Finally, prepared Ph-PVA/CA membranes exhibited enhancement in critical natures such as proton conductivity and IEC combined with its low-cost materials, which make them excellent candidate as PEM for DMFCs application.

Fabrication of Cellulose Acetate-Based Proton Exchange Membrane with Sulfonated SiO2 and Plasticizers for Microbial Fuel Cell Applications

Developing a hybrid composite polymer membrane with desired functional and intrinsic properties has gained significant consideration in the fabrication of proton exchange membranes for microbial fuel cell applications. Among the different polymers, a naturally derived cellulose biopolymer has excellent benefits over synthetic polymers derived from petrochemical byproducts. However, the inferior physicochemical, thermal, and mechanical properties of biopolymers limit their benefits. In this study, we developed a new hybrid polymer composite of a semi-synthetic cellulose acetate (CA) polymer derivate incorporated with inorganic silica (SiO₂) nanoparticles, with or without a sulfonation (-SO₃H) functional group (sSiO₂). The excellent composite membrane formation was further improved by adding a plasticizer (glycerol (G)) and optimized by varying the SiO₂ concentration in the polymer membrane matrix. The composite membrane's effectively improved physicochemical properties (water uptake, swelling ratio, proton conductivity, and ion exchange capacity) were identified because of the intramolecular bonding between the cellulose acetate, SiO₂, and plasticizer. The proton (H⁺) transfer properties were exhibited in the composite membrane by incorporating sSiO₂. The composite CAG-2% sSiO₂ membrane exhibited a higher proton conductivity (6.4 mS/cm) than the pristine CA membrane. The homogeneous incorporation of SiO₂ inorganic additives in the polymer matrix provided excellent mechanical properties. Due to the enhancement of the physicochemical, thermal, and mechanical properties, CAG-sSiO₂ can effectively be considered an eco-friendly, low-cost, and efficient proton exchange membrane for enhancing MFC performance.

Preparation and Characterization of Chitosan/LDH Composite Membranes for Drug Delivery Application

In this study, composite membranes based on chitosan (CS), layered double hydroxide (LDH), and diclofenac were prepared via dispersing of LDH and diclofenac (DCF) in the chitosan matrix for gradual delivery of diclofenac sodium. The effect of using LDH in composites was compared to chitosan loaded with diclofenac membrane. LDH was added in order to develop a system with a long release of diclofenac sodium, which is used in inflammatory conditions as an anti-inflammatory drug. The prepared composite membranes were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope Analysis (SEM), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA) and UV-Vis Spectroscopy. The results of the FTIR and XPS analyses confirmed the obtaining of the composite membrane and the efficient incorporation of diclofenac. It was observed that the addition of LDH can increase the thermal stability of the composite membrane and favors the gradual release of diclofenac, highlighted by UV-Vis spectra that showed a gradual release in the first 48 h. In conclusion, the composite membrane based on CS-LDH can be used in potential drug delivery application.

Nanocomposite Membranes for PEM-FCs: Effect of LDH Introduction on the Physic-Chemical Performance of Various Polymer Matrices

This is a comparative study to clarify the effect of the introduction of layered double hydroxide (LDH) into various polymer matrices. One perfluorosulfonic acid polymer, i.e., Nafion, and two polyaromatic polymers such as sulfonated polyether ether ketone (sPEEK) and sulfonated polysulfone (sPSU), were used for the preparation of nanocomposite membranes at 3 wt.% of LDH loading. Thereafter, the PEMs were characterized by X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) for their microstructural and thermomechanical features, whereas water dynamics and proton conductivity were investigated by nuclear magnetic resonance (PFG and T₁) and EIS spectroscopies, respectively. Depending on the hosting matrix, the LDHs can simply provide additional hydrophilic sites or act as physical crosslinkers. In the latter case, an impressive enhancement of both dimensional stability and electrochemical performance was observed. While pristine sPSU exhibited the lowest proton conductivity, the sPSU/LDH nanocomposite was able to compete with Nafion, yielding a conductivity of 122 mS cm^-1 at 120 °C and 90% RH with an activation energy of only 8.7 kJ mol^-1. The outcome must be ascribed to the mutual and beneficial interaction of the LDH nanoplatelets with the functional groups of sPSU, therefore the choice of the appropriate filler is pivotal for the preparation of highly-performing composites.

Nata de Cassava Type of Bacterial Cellulose Doped with Phosphoric Acid as a Proton Exchange Membrane

This work aims to encourage the use of natural materials for advanced energy applications, such as proton exchange membranes in fuel cells. Herein, a new conductive membrane produced from cassava liquid waste was used to overcome environmental pollution and the global crisis of energy. The membrane was phosphorylated through a microwave-assisted method with different phosphoric acid, (H₃PO₄) concentrations (10-60 mmol). Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), dynamic mechanical analysis (DMA), swelling behavior test, and contact angle measurement were carried out on the membrane doped with different H₃PO₄ levels. The phosphorylated NdC (nata de cassava) membrane doped with 20 mmol (NdC20) H₃PO₄ was successfully modified and significantly achieved proton conductivity (maximum conductivity up to 7.9 × 10^-2 S cm^-1 at 80 °C). In addition, the fabricated MEA was assembled using an NdC20 membrane with 60 wt% Pt/C loading of 0.5 mg cm^-2 for the anode and cathode. Results revealed that a high power density of 25 mW cm^-2 was obtained at 40 °C operating temperature for a single-cell performance test. Thus, this membrane has the potential to be used as a proton exchange membrane because it is environment-friendly and inexpensive for fuel cell applications.

Preparation and Characterization of Chitosan/TiO2 Composite Membranes as Adsorbent Materials for Water Purification

As it is used in all aspects of human life, water has become more and more polluted. For the past few decades, researchers and scientists have focused on developing innovative composite adsorbent membranes for water purification. The purpose of this research was to synthesize a novel composite adsorbent membrane for the removal of toxic pollutants (namely heavy metals, antibiotics and microorganisms). The as-synthesized chitosan/TiO₂ composite membranes were successfully prepared through a simple casting method. The TiO₂ nanoparticle concentration from the composite membranes was kept low, at 1% and 5%, in order not to block the functional groups of chitosan, which are responsible for the adsorption of metal ions. Nevertheless, the concentration of TiO₂ must be high enough to bestow good photocatalytic and antimicrobial activities. The synthesized composite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and swelling capacity. The antibacterial activity was determined against four strains, Escherichia coli, Citrobacter spp., Enterococcus faecalis and Staphylococcus aureus. For the Gram-negative strains, a reduction of more than 5 units log CFU/mL was obtained. The adsorption capacity for heavy metal ions was maximum for the chitosan/TiO₂ 1% composite membrane, the retention values being 297 mg/g for Pb²⁺ and 315 mg/g for Cd²⁺ ions. These values were higher for the chitosan/TiO₂ 1% than for chitosan/TiO₂ 5%, indicating that a high content of TiO₂ can be one of the reasons for modest results reported previously in the literature. The photocatalytic degradation of a five-antibiotic mixture led to removal efficiencies of over 98% for tetracycline and meropenem, while for vancomycin and erythromycin the efficiencies were 86% and 88%, respectively. These values indicate that the chitosan/TiO₂ composite membranes exhibit excellent photocatalytic activity under visible light irradiation. The obtained composite membranes can be used for complex water purification processes (removal of heavy metal ions, antibiotics and microorganisms).