Polyaniline Membranes for Separation and Purification of Gases, Liquids, and Electrolyte Solutions

Novel polyaniline-polyethersulfone nanofiltration membranes: effect of in situ polymerization time on structure and desalination performance

In this research, novel polyaniline-layered nanofiltration membranes were prepared by phase inversion of base polyethersulfone (PES) membranes and subsequent in situ solution-phase deposition of polyaniline as a thin surface layer. In these composite membranes, the impact of the polyaniline deposition time on steric hindrance and electrostatic interactions during permeation was elucidated. The chemical structure, thermal stability, and mechanical properties of the PES and PANI-PES membranes were investigated using Fourier-transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA), respectively. The membranes' porosity and pore size decreased as PANI deposition time increased. As PANI deposition time increased, PANI layered nanofiltration membranes exhibited improved thermal stability but deteriorated mechanical characteristics due to free radical destruction from prolonged exposure to the oxidant. These PANI-PES membranes showed 43% rejection (NaCl) at 1.7 bar coupled with a flux of 11.59 L h-1 m2 that is quite promising when comparing with similar Nanofilteration (NF) membranes in the literature and commercial NF membranes, as well. As the deposited layer, PANI is partially doped; hence, permeation results have been interpreted in terms of steric hindrance and electrostatic repulsion by electrochemical PANI layering.

Progressive Intercalation and Exfoliation of Clay in Polyaniline–Montmorillonite Clay Nanocomposites and Implication to Nanocomposite Impedance

Conducting polymers, such as polyaniline (PANi) and polypyrrole (PPy), and their nanocomposites, are desired in a wide range of applications, including supercapacitors, lithium ion battery, chemical sensors, biosensors, barrier thin films, and coatings, because of their interesting electrical and electrochemical properties. It is well known that the properties of polymer nanocomposites depend on their chemical structure, as well as their microstructure, yet scientists and engineers have not fully understood how to properly control the structure of polymer nanocomposites. In this study, it is shown that the structure of polyaniline–montmorillonite clay nanocomposites (PACN) can be controlled by varying the ammonium persulfate (APS, oxidant) concentration. The structure of polyaniline and Cloisite 20A clay are, therefore, profoundly affected during the synthesis of PACN nanocomposites. The thickness of polyaniline crystal decreased with increasing oxidant concentration. Fourier transform infrared spectroscopy (FTIR) was used to determine the oxidation state of PANi. The structure of the nanocomposites was studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS). Electrochemical impedance spectroscopy (EIS) analysis of polyimide nanocomposite coatings containing PACN with varying levels of intercalation and exfoliation indicate that the coating impedance decreased with exposure time for some coating systems. It is shown that polyimide–PACN nanocomposite coating containing highly intercalated clay was more durable and maintained constant impedance after 20 weeks of exposure in a corrosive medium.

Linking the Tuneability and Defouling of Electrically Conductive Polyaniline/Exfoliated Graphite Composite Membranes

Stimuli responsive membranes, which are able to respond to environmental stimuli, are attracting ever-increasing interests. In this study, we blended exfoliated graphite (EG) into the polyaniline (PANI) and developed PANI/EG composite membranes. The properties of the new generated membranes, especially the stimuli response properties (e.g., electrical tuneability, deformation), were studied. The fouling removal ability of the membrane under applied electrical potential was also investigated by using bovine serum albumin (BSA) as a model foulant. A flat membrane with defect-free surface and good adhesion to the support layer was formed by non-solvent induced phase separation method. The electrical conductivity of the formed PANI/EG composite membrane was (5.10 ± 0.27) ×10^-4 S cm^-1. The dynamic droplet penetration rate through the membranes showed an increase under applied electrical potential, which gives a preliminary quantitative indication of the electrical tuneability of the membranes. The membrane deformation appeared at a fast response under applied potential and recovered to its original position immediately when removing the applied potential. The application of electrical potential led to the removal of BSA foulant from the membrane surface as indicated by the increase in permeance of the fouled membrane on cleaning with 46.2% flux recovery ratio and increased BSA concentration in the wash solution. The electrically conductive PANI/EG composite membranes are able to respond to electrical stimuli, enabling a new range of potential applications including externally tuneability and in situ removal and control of fouling.

Dye Separation and Antibacterial Activities of Polyaniline Thin Film-Coated Poly(phenyl sulfone) Membranes

We fabricated a nanofiltration membrane consisting of a polyaniline (PANI) film on a polyphenylsulfone (PPSU) substrate membrane. The PANI film acted as a potent separation enhancer and antimicrobial coating. The membrane was analyzed via scanning electron microscopy and atomic force microscopy to examine its morphology, topography, contact angle, and zeta potential. We aimed to investigate the impact of the PANI film on the surface properties of the membrane. Membrane performance was then evaluated in terms of water permeation and rejection of methylene blue (MB), an organic dye. Coating the PPSU membrane with a PANI film imparted significant advantages, including finely tuned nanometer-scale membrane pores and tailored surface properties, including increased hydrophilicity and zeta potential. The PANI film also significantly enhanced separation of the MB dye. The PANI-coated membrane rejected over 90% of MB with little compromise in membrane permeability. The PANI film also enhanced the antimicrobial activity of the membrane. The bacteriostasis (B R) values of PANI-coated PPSU membranes after six and sixteen hours of incubation with Escherichia coli were 63.5% and 95.2%, respectively. The B R values of PANI-coated PPSU membranes after six and sixteen hours of incubation with Staphylococcus aureus were 70.6% and 88.0%, respectively.

An Efficient Method to Determine Membrane Molecular Weight Cut-Off Using Fluorescent Silica Nanoparticles

Membrane processes have revolutionized many industries because they are more energy and environmentally friendly than other separation techniques. This initial selection of the membrane for any application is based on its Molecular Weight Cut-Off (MWCO). However, there is a lack of a quantitative, liable, and rapid method to determine the MWCO of the membrane. In this study, a methodology to determine the MWCO, based on the retention of fluorescent silica nanoparticles (NPs), is presented. Optimized experimental conditions (Transmembrane pressure, filtration duration, suspension concentration, etc.) have been performed on different membranes MWCO. Filtrations with suspension of fluorescent NPs of different diameters 70, 100, 200 and 300 nm have been examined. The NPs sizes were selected to cover a wide range in order to study NPs diameters larger, close to, and smaller than the membrane pore size. A particle tracking analysis with a nanosight allows us to calculate the retention curves at all times. The retention rate curves were shifted over the filtration process at different times due to the fouling. The mechanism of fouling of the retained NPs explains the determined value of the MWCO. The reliability of this methodology, which presents a rapid quantitative way to determine the MWCO, is in good agreement with the value given by the manufacturer. In addition, this methodology gives access to the retention curve and makes it possible to determine the MWCO as a function of the desired retention rate.

Adsorption of methylene blue onto electrospun nanofibrous membranes of polylactic acid and polyacrylonitrile coated with chloride doped polyaniline

This study presents the preparation of membranes of polylactic acid (PLLA), polyacrylonitrile (PAN) and their corresponding membranes coated with polyaniline (PANI) for the adsorption of methylene blue (MB). Scanning electron microscopy micrographs reveal that all the membranes exhibit nanofibrous morphology. The adsorption capacity and the removal efficiency of the membranes are studied as a function of (initial adsorbate concentration, pH of the medium, temperature, contact time and adsorbent dosage). Coated membranes with PANI showed better adsorption performance and their DC conductivities were correlated to MB concentrations. Adsorption isotherms have also been performed and the adsorption process has been tested according to Langmuir and Freundlich models. The regeneration and reuse of the prepared membranes to re-adsorb MB were also investigated. The enhancement in adsorption performance and reusability of PANI-coated membranes in comparison with non-coated ones are fully discussed.

Membrane-based separation of potential emerging pollutants

The potential emerging pollutants (PEPs) such as hazardous chemicals, toxic metals, bio-wastes, etc., pose a severe threat to human health, hygiene and ecology by way of polluting the environment and water sources. The PEPs are originated from various industrial effluent discharges including pharmaceutical, food and metal processing industries. These PEPs in contact with water may pollute the water and disturb the aquatic life. Innumerable methods have been used for the treatment of effluents and separating the toxic chemicals/metals. Of these methods, membrane-based separation processes (MBSPs) are effective over the conventional techniques for providing clean water from wastewater streams at an affordable cost with minimum energy requirement. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) methods as well as hybrid technologies are discussed citing the published results of the past decade.

Electrocatalysis of Lindane Using Antimony Oxide Nanoparticles Based-SWCNT/PANI Nanocomposites

This work describes the chemical synthesis of antimony oxide nanoparticles (AONPs), polyaniline (PANI), acid functionalized single-walled carbon nanotubes (fSWCNTs), and the nanocomposite (AONP-PANI-SWCNT) as catalyst for the trace detection of lindane. Successful synthesis of the nanomaterials was confirmed by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, x-ray diffraction (XRD) spectroscopy, and scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for investigating the electrochemical behavior of the modified electrodes in the ferrocyanide/ferricyanide ([Fe(CN)₆]⁴⁻/[Fe(CN)₆]³⁻) redox probe. GCE-AONP-PANI-SWCNT exhibited faster electron transport properties as well as higher electroactivity as compared to bare-GCE, GCE-AONPs, GCE-PANI, and GCE-SWCNT electrodes. Electrocatalytic studies further showed that GCE-AONP-PANI-SWCNT modified electrode was stable (after 20 scans) with only a small current drop in lindane (0.57%). The GCE-AONP-PANI-SWCNT electrode with low detection limit of 2.01 nM performed better toward the detection of lindane as compared to other studies in literature. The GCE-AONP-PANI-SWCNT electrode is highly selective toward the detection of lindane in the presence of various organic and inorganic interfering species. Real sample analysis of river water and tap water samples using the developed sensor gave satisfactory percentage recoveries therefore confirming the potential of the proposed sensor for practical application.

Structural and electrochemical studies of heterogeneous ion exchange membranes based on polyaniline-coated cation exchange resin particles

Polyaniline was deposited on polystyrene sulfonated divinyl benzene resin by varying polymerization time to fabricate heterogeneous PVC matrix membranes.

A novel process of alcohol promoted polymerization of aniline to form a nanofibrous, fluorescent and highly crystalline polyaniline salt

Use of acid was replaced by alcohol in the polymerization of aniline to a highly crystalline, nanofibrous, fluorescent and conducting polyaniline salt.

X-Ray Photoelectron Spectroscopy Characterization of Polyaniline-Cellulose Ester Composite Membranes

X-ray photoelectron spectroscopy (XPS) is a promising technique employed for the study of conducting polymers and their composites. XPS was used to study the surface chemistry of polyaniline-mixed cellulose ester (PANI-ME) composite membranes prepared by various chemical oxidative polymerization techniques such as insitu solution, vapour phase polymerizations and aniline polymerization using a two-compartment permeation cell. Hydrolytic degradation of surface deposited PANI and scission of cellulosic chains due to x-ray irradiation inside the XPS chamber influenced the quantification of polyaniline deposition levels as well as oxidation and doping states in PANI-ME membranes. N1s core level spectra allowed characterization of the PANI deposition level, its oxidation state and x-ray induced cellulosic ring cleavage. C1s and O1s core level spectra revealed PANI hydrolysis at the membrane surface. These degradation phenomena influence the performance of PANI composite membranes used specifically in electrodiffusion applications. It was shown that successful quantification of PANI deposition levels and its oxidation state on microporous mixed cellulose ester membranes using XPS could be realized by incorporating the degradation effects in the characterization results.