Rapid and Efficient Removal of Anionic Dye in Water Using a Chitosan-Coated Iron Oxide-Immobilized Polyvinylidene Fluoride Membrane.

Anionic dyes are one of the most serious contaminants in water as these molecules are known to be toxic to many living organisms. Herein, we report the development of functionalized polyvinylidene fluoride membranes modified with chitosan-coated iron oxide nanomaterials (Fe-PVDF) for the efficient treatment of anionic dye-contaminated water. Aqueous solutions of anionic dyes could be captured rapidly by passing through the functionalized membrane under reduced pressure. Under neutral conditions, Fe-PVDF showed a maximum removal capacity of 74.6 mg/g for Evans blue (EB) through the adsorption process. In addition, the adsorption capacity was significantly enhanced up to 434.78 mg/g under acidic conditions. The adsorption process for EB matched well with the Langmuir model, indicating monolayer adsorption of the dye to the membrane surface. Moreover, Fe-PVDF can be reusable by a simple washing step in an alkaline solution, and thus, the composite membrane was applied several times without a significant decrease in its adsorption performance. The same composite membrane was further applied to the removal of five other different anionic dyes with high efficiencies. The adsorption mechanism can be explained by the electrostatic interaction between the positively charged chitosan and the negatively charged dye as well as the affinity of the sulfate groups in dye molecules for the surface of the iron oxide nanoparticles. The easy preparation and rapid decolorization procedures make this composite membrane suitable for efficient water treatment.

Polyacrylamide Functionalized Graphene Oxide/Alginate Beads for Removing Ciprofloxacin Antibiotics.

Ciprofloxacin (CPX), a widely used antibiotic, was removed by synthesizing graphene oxide/calcium alginate-polyacrylamide (GO/Ca-Alg2-PAM) beads, a three-dimensional double-network complex. The synthesis of GO/Ca-Alg2-PAM beads was performed by crosslinking and cation exchange mechanisms with graphene oxide (GO), sodium alginate (Na-Alg), and polyacrylamide (PAM). The properties of GO/Ca-Alg2-PAM beads were confirmed using field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and a thermogravimetric analysis. Furthermore, isothermal adsorption experiments were performed and fitted using three isothermal adsorption models (Langmuir, Freundlich, and Temkin). The adsorption isotherm experimental data fit well with the Langmuir isotherm model with a qm value of 6.846 mg/g. In addition, the spontaneous reaction of the CPX adsorption using GO/Ca-Alg2-PAM was confirmed by temperature-dependent experiments.

Removal of Hexavalent Chromium(VI) from Wastewater Using Chitosan-Coated Iron Oxide Nanocomposite Membranes.

Chromium is a toxic and carcinogenic heavy metal that originates from various human activities. Therefore, the effective removal of chromium from aqueous solutions is an extremely important global challenge. Herein, we report a chitosan-coated iron oxide nanoparticle immobilized hydrophilic poly(vinylidene) fluoride membrane (Chi@Fe2O3-PVDF) which can potentially be used for efficient removal of hexavalent chromium(VI) by a simple filtration process. Membrane filtration is an easy and efficient method for treating large volumes of water in a short duration. The adsorption experiments were conducted by batch and continuous in-flow systems. The experimental data showed rapid capture of hexavalent chromium (Cr(VI)) which can be explained by the pseudo-second-order kinetic and Langmuir isotherm model. The nanocomposite membrane exhibited high adsorption capacity for Cr(VI) (14.451 mg/g in batch system, 14.104 mg/g in continuous in-flow system). Moreover, its removal efficiency was not changed significantly in the presence of several competing ions, i.e., Cl-, NO3-, SO42-, and PO43-. Consequently, the Chi@Fe2O3-PVDF-based filtration process is expected to show a promising direction and be developed as a practical method for wastewater treatment.

Copper ferrocyanide chemically immobilized onto a polyvinylidene fluoride hollow-fibre membrane surface for the removal of aqueous cesium.

A method of chemically bonding copper ferrocynide (CuFC) to the surface of a PVDF hollow-fibre membrane (PVDF-CuFC) was designed and the resulting PVDF-CuFC was applied to the effective removal of aqueous cesium (Cs). In order to chemically immobilize CuFC on the surface of the PVDF hollow-fibre membrane, carboxyl groups were introduced onto the membrane surface (PVDF-COOH) to peptide bond with amine groups from CuFC. The introduction of the carboxyl group onto the surface of the PVDF hollow-fibre membrane was confirmed by Fourier-transform infrared spectroscopy (FT-IR), while the immobilization of CuFC was confirmed by scanning electron microscopy with energy dispersed spectroscopy, FT-IR, and thermogravimetric analysis. The PVDF-CuFC showed higher Cs adsorption kinetics and adsorption capacity than PVDF-COOH. Moreover, as the initial pH increased, the amount of Cs adsorption by PVDF-CuFC also increased. However, the amount of Cs adsorption at pH 10 was slightly less. The applicability of PVDF-CuFC as a filter type adsorbent for the treatment of a Cs-contaminated water source is demonstrated by continuous filtration experiments.

Synthesis of Silver-Impregnated Magnetite Mesoporous Silica Composites for Removing Iodide in Aqueous Solution.

Mag@silica-Ag composite has a high sorption ability for I- in aqueous solution due to its high surface area and strong affinity for the studied anion. The material adsorbed I- rapidly during the initial contact time (in 45 min, η = 80%) and reached adsorption equilibrium after 2 h. Moreover, mag@silica-Ag proved to selectively remove I- from a mixture of Cl-, NO3- and I-. The adsorption behavior fitted the Langmuir isotherm perfectly and the pseudo-second-order kinetic model. Based on the Langmuir isotherm, the maximum adsorption capacity of mag@silica-Ag was 0.82 mmol/g, which is significantly higher than previously developed adsorbents. This study introduces a practical application of a high-capacity adsorbent in removing radioactive I- from wastewaters.

Simultaneous selective removal of cesium and cobalt from water using calcium alginate-zinc ferrocyanide-Cyanex 272 composite beads.

Composite beads consisting of Ca alginate mixed with zinc ferrocyanide (ZnFC) and Cyanex 272 were synthesized in order to selectively adsorb Cs+ and Co2+ from water. Their physicochemical properties of the synthesized composite beads were characterized using various techniques, including FESEM, EDX, FTIR, and TGA. The ZnFC/Cyanex 272/alginate (ZCA) composite beads were then tested as an adsorbent for the selective removal of Cs+ and Co2+ from an aqueous solution. The adsorption capacity increased with increasing ZnFC and Cyanex 272 contents. The adsorption process followed the Langmuir model and pseudo-second-order kinetics. The ZCA composite beads exhibited excellent selectivity toward Cs+ and Co2+ even in the presence of competitive cations (K+, Na+, Fe2+, and Ni2+). The adsorption capacity of the ZCA composite beads for Cs+ and Co2+ was almost maintained after three times of adsorption-desorption process.

Ecofriendly, selective removal of radioactive strontium ions in aqueous solutions using magnetic banana peels.

Radionuclide Sr2+ in aqueous solution was removed using a large amount of banana peel (BP). Magnetized BP, mag@BP, was synthesized for recovery after the adsorption process. The synthesis was a very simple process of precipitation of BP with a magnetic substance. The synthesized adsorbent was thoroughly examined by performing Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction analysis, and vibration sample magnetometer analysis. Moreover, mag@BP has a Sr2+ maximum adsorption capacity of 23.827 mg/g according to isothermal adsorption, which is the best fit for the Langmuir isotherm model. In the pH effect experiment, the highest Sr2+ adsorption capacity was found at pH 9, and it has a spontaneous adsorption mechanism through experiments on temperature, time, and selectivity, and it reaches adsorption equilibrium within a short time and has high selectivity through competitive adsorption with Na+. In addition, an adsorption mechanism accompanied by ion exchange with K+ on the surface of BP, bonding with various functional groups, and electrical attraction were established. Therefore, mag@BP is suitable for use an environmentally friendly, low cost, and recoverable adsorbent for magnetic removal of Sr2+ from aqueous solutions. Further, unlike other carbon-based adsorbents, it does not cause cytotoxicity.

Improved Electrochemical and Mechanical Properties of Poly(vinylpyrrolidone)/Nafion® Membrane for Fuel Cell Applications.

A novel blend of membranes made of Nafion® and poly(vinylpyrrolidone) (PVP) was prepared and characterized to investigate its applicability in proton exchange membrane fuel cells (PEMFCs). In addition to being effectively proton conductive, the membranes exhibited better mechanical strength, chemical stability, and adequate water retention ability, as well as ion exchange capacity comparable to that of cast Nafion® membrane. The data obtained from an electrochemical impedance spectroscopy (EIS) fitting of the fuel cells revealed the membrane electrode assemblies (MEAs) made of 0.5 wt.% PVP/Nafion® had lower ohmic and charge transfer resistance compared with that of the Nafion® membrane. The intermolecular interactions and morphology of these membranes were assessed using Fourier-transform infrared spectroscopy and field-emission scanning electron microscopy. The results of the performance curve indicate that the introduction of PVP as a modifier played a vital role in improving membrane performance. Accordingly, this solution-casted polymer electrolyte membrane with suitable PVP content offers a simple way to improve electrochemical, mechanical, and chemical properties, and thereby promises the prospect of use in low-temperature PEMFCs.

Synthesis of Metal-Organic Framework ZnO x -MOF@MnO2 Composites for Selective Removal of Strontium Ions from Aqueous Solutions.

A Zn(II)-based metal-organic framework (MOF) compound and MnO2 were used to prepare ZnO x -MOF@MnO2 composites for selective Sr2+ removal in aqueous solutions. The ZnO x -MOF@MnO2 composites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller surface area analysis. The functional groups, morphologies, thermal stabilities, and specific surface areas of the composites were suitable for Sr2+ adsorption. A maximum adsorption capacity of 147.094 mg g-1 was observed in batch adsorption experiments, and the sorption isotherms were fit well by the Freundlich model of multilayer adsorption. Adsorption reached equilibrium rapidly in kinetic experiments and followed the pseudo-second-order kinetic model. The adsorption capacity of the ZnO x -MOF@MnO2 composite with the highest MnO2 content was high over a wide pH range, and the composite was highly selective toward Sr2+ in solutions containing coexisting competing ions. Also, it has a good reusability for removing Sr2+.

Selective separation of Cs-contaminated clay from soil using polyethylenimine-coated magnetic nanoparticles.

We evaluated the feasibility of using magnetic nanoparticles (MNPs) coated with polyethylenimine (PEI), a cationic polymer, to remediate radioactive contaminated soil by separating Cs-contaminated clay from the soil. The influences of the solution pH, PEI-to-MNPs mass ratio, and the PEI-MNPs dose on the magnetic separation performance were systematically examined. The highest SE% of illite from solution through electrostatic attraction was approximately 100% at a mass ratio of 0.04 g-PEI-MNPs/g-clay. The PEI coating clearly enhanced the adhesion between MNPs and clay minerals by increasing the quantity of functional amine groups available for adsorbing negatively charged clay minerals. In separation experiments using a soil mixture, the PEI-coated MNPs selectively separated clay- and silt-sized fine particles smaller than 0.038 mm even in the presence of a large amount of sand when used at a low dose (mass ratio of 0.05 g-PEI-MNPs/g-clay) and without pH control. We also used the PEI-MNPs to separate 137Cs-contaminated illite from soil under an external magnetic field. After magnetic separation, the highest removal efficiency achieved for 137Cs removal from the treated soil was 81.7% at a low nanoparticle dosage, which resulted in satisfying the reduction of radioactivity and waste volume. The results clearly demonstrate that the selective separation of Cs-contaminated clay using PEI-coated MNPs is a promising technique for remediating radioactive soil.

Imparting High Proton Conductivity to Nafion® Tuned by Acidic Chitosan for Low-Temperature Proton Exchange Membrane Fuel Cell Applications.

A successful polymer electrolyte membrane for fuel cell application must have efficient proton conductivity as well as good water retention capability. The viability of using composite membranes prepared by blending 85% deacetylated chitosan (CS) and Nafion® in proton exchange membrane fuel cells (PEMFCs) was investigated based on the concept of hydrophilicity and the water uptake characteristics of CS. These membranes were characterized by infrared spectroscopy and field-emission scanning electron microscopy to investigate their intermolecular interactions and morphology, respectively. Absorption studies were carried out to evaluate the interactions of the membranes with water. Titrimetric ion exchange capacity analysis indicated the availability of active sites in the membrane. The CS/Nafion® blend was found to be suitable for PEMFC applications because of its relatively high proton conductivity compared to that of regular Nafion®. Above all, the cost-effectiveness and simple fabrication of such composite membranes make their use in low-temperature PEMFCs very attractive and economical.

Computational Design of Functional Amyloid Materials with Cesium Binding, Deposition, and Capture Properties.

Amyloid materials are gaining increasing attention as promising materials for applications in numerous fields. Computational methods have been successfully implemented to investigate the structures of short amyloid-forming peptides, yet their application in the design of functional amyloid materials is still elusive. Here, we developed a computational protocol for the design of functional amyloid materials capable of binding to an ion of interest. We applied the protocol in a test case involving the design of amyloid materials with cesium ion deposition and capture properties. As part of the protocol, we used an optimization-based design model to introduce mutations at non-ß-sheet residue positions of an amyloid designable scaffold. The designed amino acids introduced to the scaffold mimic how amino acids bind to cesium ions according to experimentally resolved structures and also aim at energetically stabilizing the bound conformation of the pockets. The optimum designs were computationally validated using a series of simulations and structural analysis to select the top designed peptides, which are predicted to form fibrils with cesium ion binding properties for experimental testing. Experiments verified the amyloid-forming properties of the selected top designed peptides, as well as the cesium ion deposition and capture properties by the amyloid materials formed. This study demonstrates the first, to the best of our knowledge, computational design protocol to functionalize amyloid materials for ion binding properties and suggests that its further advancement can lead to novel, highly promising functional amyloid materials of the future.

Highly Proton Conductive Poly(vinyl acetate)/Nafion® Composite Membrane for Proton Exchange Membrane Fuel Cell Application.

A novel blend of membranes made of cast Nafion® and poly(vinyl acetate) (PVAc) was prepared and its proton conductivity and ion exchange capacity (IEC) were characterized to investigate its applicability in proton exchange membrane fuel cells (PEMFCs). The intermolecular interactions and morphology of these membranes were assessed using Fourier-transform infrared spectroscopy (FT-IR) and field-emission scanning electron microscopy (FE-SEM). A twofold increase in the proton conductivity is observed for the PVAc/Nafion® composite membrane (2 × 10-2 Scm-1) compared to that of cast Nafion® (1.1 × 10-2 Scm-1). In addition to that, the composite membranes exhibited better mechanical strength and adequate water retention ability as well as IEC comparable to that of cast Nafion®. The thermal property and chemical degradation property were also investigated. The results indicate that the introduction of PVAc as a modifier played a vital role in improving the membrane performance. Accordingly, these polymer electrolyte membranes with suitable PVAc contents have prospect for use in low-temperature PEMFCs.

Proton-Conducting Polymer Membrane Consisting of Cross-Linked Poly(2-hydroxyethyl methacrylate) with Nafion® for Fuel Cell Application.

To increase the water retention and proton-conducting ability of Nafion®, we prepared a cross-linked polymer consisting of poly(2-hydroxyethyl methacrylate) (pHEMA) and Nafion®. pHEMA was chosen as a cross-linking polymer because it produces a water-insoluble but water-swellable polymer. Although it is hydrophobic, its water-swellable characteristic means that water will not be excluded from the polymer. Introduction of pHEMA into Nafion® prevents polymer solubility and provides structural stability and rigidity, which should in turn reduce the methanol permeability. Moreover, convenient permeability of pHEMA to cations makes it a good candidate for a hydrocarbon proton-conducting polymer tuned with Nafion®.

Copper Ferrocyanide Functionalized Core-Shell Magnetic Silica Composites for the Selective Removal of Cesium Ions from Radioactive Liquid Waste.

The copper ferrocyanide functionalized core-shell magnetic silica composite (mag@silica-CuFC) was prepared and was found to be easily separated from aqueous solutions by using magnetic field. The synthesized mag@silica-CuFC composite has a high sorption ability of Cs owing to its strong affinity for Cs as well as the high surface area of the supports. Cs sorption on the mag@silica-CuFC composite quickly reached the sorption equilibrium after 2 h of contact time. The effect of the presence of salts with a high concentration of up to 3.5 wt% on the efficiency of Cs sorption onto the composites was also studied. The maximum sorption ability was found to be maintained in the presence of up to 3.5 wt% of NaCl in the solution. Considering these results, the mag@silica-CuFC composite has great potential for use as an effective sorbent for the selective removal of radioactive Cs ions.

Sulfated Titania-Silica Reinforced Nafion Nanocomposite Membranes for Proton Exchange Membrane Fuel Cells.

Sulfated titania-silica (SO4(2-)-/TiO2-SiO2) composites were prepared by a sol-gel method with sulfate reaction and characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The nanometric diameter and geometry of the sulfated titania-silica (STS) was investigated by transmission electron microscopy (TEM). A small amount of the STS composite in the range of 0.5-3 wt% was then added as reinforcing into the Nafion membrane by water-assisted solution casting method to prepare STS reinforced Nafion nanocomposite membranes (STS-Nafion nanocomposite membranes). The additional functional groups, sulfate groups, of the nanocomposite membrane having more surface oxygenated groups enhanced the fuel cell membrane properties. The STS-Nafion nanocomposite membranes exhibited improved water uptake compared to that of neat Nafion membranes, whereas methanol uptake values were decreased dramatically improved thermal property of the prepared nanocomposite membranes were measured by thermogravimetric analysis (TGA). Furthermore, increased ion exchange capacity values were obtained by thermoacidic pretreatment of the nanocomposite membranes.

Efficient Immobilization of Ammonium Tungstophosphate at the Mesoporous Silica Support for the Removal of Cs Ion.

The ammonium salt of phosphotugstic acid (NH4PTA) deposited on the surface of mesoporous silica (SBA-15) support was prepared and characterized using several analytical techniques. The spectroscopic results showed that the NH4PTA was evenly dispersed on the internal and external silica surfaces. The ion exchange capacity tests demonstrated that the specific activity for Cs removal increased with insertion of the NH4PTA phase on the silica surface. The results showed that the ion exchange capacity of Cs increased with increasing the PTA loading. The NH4PTA at a loading of 50 wt% supported on silica showed the highest ion exchange capacity for Cs ion among the loading range of 20-50 wt%. The effects of co-existing cations and nitric acid on the Cs sorption efficiency onto the composites were also studied.

High-Performance of PEI/Nafion/ox-MWCNT Composite Membranes Based on Semi-Interpenetrating Polymer Networks for PEMFCs.

Polymer electrolyte membrane fuel cells (PEMFCs) are an up-and-coming technology for green and efficient power generation and offer a clean alternative to current technologies that use hydrocarbon fuel sources. In this paper, a reinforcing membrane was fabricated by Polyethylenimine polymer. Oxidized multiwalled carbon nanotube was dispersed into the PEI/Nafion membranes to achieve additional strength. The membranes were acidified via absorption of phosphoric acid from aqueous solution to make semi-interpenetrating polymer network (s-IPNs) which increases the proton conductivity by producing proton channel in the membrane. The PEI/Nafion/ox-MWCNT composite membranes show excellent phosphoric acid retention and high humidity, which impart a high ion exchange capacity (IEC) as well as improved proton conductivity. The surface morphologies and cross-sections of the resulting H3PO4 treated PEI/Nafion/ox-MWCNT composite membranes were observed using optical microscopy and scanning electron microscopy (SEM). The improvements in the thermal properties of the prepared PEI/Nafion/ox-MWCNT composite membranes were determined using thermogravimetric analysis (TGA). These performance results combined with the low inexpensive synthetic approach substantiate the potential for the new membrane to be used in PEMFCs.

Passive approach for the improved dispersion of polyvinyl alcohol-based functionalized multi-walled carbon nanotubes/Nafion membranes for polymer electrolyte membrane fuel cells.

Multi-walled carbon nanotubes (MWCNTs) are regarded as ideal fillers for Nafion polymer electrolyte membranes (PEMs) for fuel cell applications. The highly aggregated properties of MWCNTs can be overcome by the successful cross-linking with polyvinyl alcohol (PVA) into the MWCNTs/Nafion membrane. In this study, a series of nanocomposite membranes were fabricated with the PVA-influenced functionalized MWCNTs reinforced into the Nafion polymer matrix by a solution casting method. Several different PVA contents were blended to f-MWCNTs/Nafion nanocomposite membranes followed by successful cross-linking by annealing. The surface morphologies and the inner structures of the resulting PVA-MWCNTs/Nafion nanocomposite membranes were then observed by optical microscopy and scanning electron microscopy (SEM) to investigate the dispersion of MWCNTs into the PVA/Nafion composite membranes. After that, the nanocomposite membranes were characterized by thermo-gravimetric analysis (TGA) to observe the thermal enhancement caused by effective cross-linking between the f-MWCNTs with the composite polymer matrixes. Improved water uptake with reduced methanol uptake revealed the successful fabrication of PVA-blended f-MWCNTs/Nafion membranes. In addition, the ion exchange capacity (IEC) was evaluated for PEM fuel cell (PEMFC) applications.

Non-covalent bonding interaction of surfactants with functionalized carbon nanotubes in proton exchange membranes for fuel cell applications.

Dispersion of functionalized multiwalled carbon nanotubes (MWCNTs) in proton exchange membranes (PEMs) was conducted via non-covalent bonding between benzene rings of various surfactants and functionalized MWCNTs. In the solution casting method, dispersion of functionalized MWCNTs in PEMs such as Nafion membranes is a critical issue. In this study, 1 wt.% pristine MWCNTs (p-MWCNTs) and oxidized MWCNTs (ox-MWCNTs) were reinforced in Nafion membranes by adding 0.1-0.5 wt.% of a surfactant such as benzalkonium chloride (BKC) as a cationic surfactant with a benzene ring, Tween-80 as a nonanionic surfactant without a benzene ring, sodium dodecylsulfonate (SDS) as an anionic surfactant without a benzene ring, or sodium dodecylben-zenesulfonate (SDBS) as an anionic surfactant with a benzene ring and their effects on the dispersion of nanocomposites were then observed. Among these surfactants, those with benzene rings such as BKC and SDBS produced enhanced dispersion via non-covalent bonding interaction between CNTs and surfactants. Specifically, the surfactants were adsorbed onto the surface of functionalized MWCNTs, where they prevented re-aggregation of MWCNTs in the nanocomposites. Furthermore, the prepared CNTs reinforced nanocomposite membranes showed reduced methanol uptake values while the ion exchange capacity values were maintained. The enhanced properties, including thermal property of the CNTs reinforced PEMs with surfactants, could be applicable to fuel cell applications.