Water stability of high‐molecular‐weight (HMW) syndiotacticity‐rich poly(vinyl alcohol) (PVA)/HMW atactic PVA/iodine complex blend films

To precisely identify the effect of blend ratios of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA)/atactic PVA (a‐PVA) on the water stability of s‐PVA/a‐PVA/iodine complex blend films, we prepared two PVAs with similar number‐averaged degrees of polymerization of 4000 and degrees of saponification of 99.9% and with different syndiotactic diad contents of 58.5 and 53.5%, respectively. The desorption behavior of iodine in s‐PVA/a‐PVA/iodine complex films in water was investigated in terms of the solubility of s‐PVA/a‐PVA blend films in water. The degree of solubility of s‐PVA/a‐PVA blend films with s‐PVA content over 50% in water at 70°C was limited to about 10–20%, whereas that of s‐PVA/a‐PVA blend films with s‐PVA content of 10% was 85% under the same conditions. The degree of iodine desorption of complex blend films decreased with increasing s‐PVA content. The degree of iodine desorption of s‐PVA/a‐PVA drawn film with s‐PVA content of 90% was limited to 7%, regardless of the soaking temperature from 30 to 70°C. The desorption of iodine in water was strongly affected by the dissolution of blends. Moreover, the stability of iodine in the drawn s‐PVA/a‐PVA/iodine blend films in hot water was far superior to that of the undrawn film. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1435–1439, 2004     

Ag+ ions imprinted cryogels for selective removal of silver ions from aqueous solutions

ABSTRACT

The removal of heavy metal ions from aquatic media or any conditions is crucial. Silver ions turn out to be the important example of this problem on earth when these are released to the environment. In the present study, silver ions (Ag⁺) imprinted poly(hydroxyethyl methacrylate) (PHEMA)-based cryogels were prepared using N-methacryloyl-L-cysteine as functional monomer, to be chelated with Ag⁺ ions. The maximum adsorption capacity of Ag⁺-imprinted polymeric cryogel was found to be 49.27 mg/g from aqueous solutions. To investigate the affinity of Ag⁺-imprinted PHEMAC cryogel column, photographic film material from the natural silver ion source was used. The recovery results were 72.8% for the Ag⁺-imprinted PHEMAC cryogel and 0.62% for the non-imprinted PHEMAC cryogels. These values clearly showed the selectivity of the Ag⁺-imprinted PHEMAC cryogel column. The adsorption–desorption cycle was performed more 10 times with use of the same Ag⁺-imprinted PHEMAC cryogel for the determination of reuse. These molecularly imprinted cryogels were used in adsorption process for a long time with no significant loss.     

Synthesis and application of ion‐imprinted resin based on modified melamine–thiourea for selective removal of Hg(II)

A novel Hg(II) ion‐imprinted resin based on thiourea‐modified melamine was manufactured for selective elimination of Hg²⁺ from aqueous solutions. The polymerizable thiourea–melamine ligand together with its Hg(II) complex were extensively investigated using elemental analysis, Fourier transform infrared (FTIR) and ¹H NMR spectroscopies. The Hg(II) complex was used in a condensation polymerization in the presence of formaldehyde crosslinker and then the Hg(II) ions were leached out from the crosslinked polymeric network to finally leave the ion‐imprinted Hg‐PMTF resin. Both ion‐imprinted Hg‐PMTF and non‐imprinted resins were examined utilizing scanning electron microscopy and FTIR spectroscopy. The potential of the prepared resin for selective separation of Hg(II) ions from aqueous solutions was then evaluated by performing a series of batch experiments. Hg‐PMTF displayed an obvious rapid removal of Hg(II) ions with a pseudo‐second‐order kinetic pattern. In addition, the Langmuir adsorption isotherm model exhibited the best fit with the experimental data with comparatively high maximum adsorption capacity (360.5 mg g^?1). © 2015 Society of Chemical Industry     

Synthesis of azo‐functionalized ion‐imprinted polymeric resin for selective extraction of nickel(II) ions

The work presented involved the fabrication and evaluation of an ion‐imprinted azo‐functionalized phenolic resin for selective extraction of Ni²⁺ ions from aqueous media. The azo‐containing ligand was first synthesized by coupling of a p‐aminophenol diazonium salt with resorcinol. The ligand was coordinated with Ni²⁺ ion template before condensation polymerization with formaldehyde and resorcinol was performed. The Ni²⁺ ions were extracted from the crosslinked resin matrix to finally afford the Ni²⁺ ion‐imprinted Ni‐PARF adsorbent. The synthetic steps were extensively investigated using elemental analysis and Fourier transform infrared, NMR and energy‐dispersive X‐ray spectroscopies. Also, the surface morphologies along with the surface areas of the adsorbent resin were evaluated using scanning electron microscopy and Brunauer–Emmett–Teller techniques, respectively. Batch experiments indicated that the pseudo‐second‐order kinetic equation provided the best fit with the experimentally obtained kinetic data and equilibrium was reached after 40 min. The isotherm studies were also in a good fit with the Langmuir model and the maximum adsorption capacities of Ni²⁺ ions with respect to both Ni‐PARF and control non‐imprinted C‐PARF adsorbents were around 260 and 100 mg g^?1, respectively. In the presence of Co²⁺, Cu²⁺, Zn²⁺ and Pb²⁺ as competing coexisting ions, the relative selectivity coefficients of Ni‐PARF for Ni²⁺ were, respectively, 84.91, 44.97, 30.41 and 32.20. Regeneration experiments indicated that after eight adsorption/desorption cycles, the Ni‐PARF adsorbent still maintained around 97% of its initial efficiency. © 2018 Society of Chemical Industry     

pH‐controlled uphill transport of boric acid through a poly(vinyl alcohol) (PVA) membrane

The uphill transport of boric acid in aqueous solutions through a thermal‐crosslinked poly(vinyl alcohol) (PVA) membrane was investigated. A normal permeation caused by the concentration difference of the boron along the PVA membrane was observed for equal pH conditions at both sides of the membrane, and higher flux was observed under an acidic condition at pH = 5.0 than under a basic condition at pH = 10.0. When the pH of one side is kept pH = 5.0 (acid side) and the other side was kept at pH = 10.0 (base side), uphill transport of boric acid from the acid side to the base side was observed under an equal initial concentration of both sides. Such an uphill transport was also observed against the concentration difference under the condition in which the initial concentration of the base side was higher than that of the acid side. The uphill transport could be explained by the difference in the permeation rates through the PVA membrane between B(OH)₃, the dominant form under lower pH, and B(OH)₄^?, the dominant form under higher pH, which makes a complex with diols in PVA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1451–1455, 2007     

Preparation and characterization of monovalent ion‐selective poly(vinyl chloride)‐blend‐poly(styrene‐co‐butadiene) heterogeneous anion‐exchange membranes

New types of composite anion‐exchange membranes were prepared by blending of suspension‐produced poly(vinyl chloride) (S‐PVC) and poly(styrene‐co‐butadiene), otherwise known as styrene–butadiene rubber (SBR), as binder, along with anion‐exchange resin powder to provide functional groups and activated carbon as inorganic filler additive. Also, an ultrasonic method was used to obtain better homogeneity. In solutions with mono‐ and divalent anions, the effect of activated carbon and sonication on the morphology, electrochemical properties and selectivity of these membranes was elucidated. For all solutions, ion‐exchange capacity, membrane potential, permselectivity, transport number, ionic permeability, flux and current efficiency of the prepared membranes initially increased on increasing the activated carbon concentration to 2 wt% in the casting solution and then began to decrease. Moreover, the electrical resistance and energy consumption of the membranes initially decreased on increasing the activated carbon loading to 2 wt% and then increased. S‐PVC‐blend‐SBR membranes with additive showed a decrease in water content and a slight decrease in oxidative stability. Also, these membranes showed good monovalent ion selectivity. Structural images of the prepared membranes obtained using scanning optical microscopy showed that sonication increased polymer‐particle interactions and promoted the compatibility of particles with binder. Copyright © 2010 Society of Chemical Industry     

Separation of small organic ions from salts by ion‐exchange membrane in electrodialysis

Electrodialysis (ED) can be applied in the food and fermentation industry for separating inorganic salts and organic ions from other fractions. However, the separation efficiency for small organic ions should be understood in detail. In this article, the membrane selectivity and transport mechanism of small organic ions from mixed salts by ion‐exchange membranes are theoretically and experimentally investigated. First of all, the influence of current density on the solute flux (organic ions and inorganic ions) and on membrane selectivity (between organic ions and inorganic ions and between different organic ions) in ED has been studied. The selectivity was shown to be influenced by changing the applied current density. It was observed that separation of inorganic ions from organic solutes was feasible, but the selectivity was dependent on the size, charge, and functional groups of the organic ions. Furthermore, results imply that binary organic anions with larger molar mass (>130, i.e., aspartate and tartrate) can be adsorbed onto the membrane free volume and hence form a charged double layer, which affects membrane selectivity. Finally, competition between small organic and inorganic ions is discussed by comparison of the concentration profiles and current efficiencies of the different anions. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Pervaporation separation of water/isopropanol mixtures through crosslinked carboxymethyl chitosan/polysulfone hollow‐fiber composite membranes

Carboxymethyl chitosan (CMCS)/polysulfone (PS) hollow‐fiber composite membranes were prepared through glutaraldehyde (GA) as the crosslinking agent and PS hollow‐fiber ultrafiltration membrane as the support. The permeation and separation characteristics for dehydration of isopropanol were investigated by the pervaporation method. Pure chitosan, carboxymethyl chitosan, and crosslinked carboxymethyl chitosan membranes were characterized by Fourier transform infrared (FT‐IR) spectroscopy and X‐ray diffraction (XRD) to study the crosslinking reaction mechanism and degree of crystallinity, respectively. The effects of feed composition, crosslinking agent, membrane thickness, and feed temperature on membrane performance were investigated. The results show that the crosslinked CMCS/PS hollow‐fiber composite membranes possess high selectivity and promising permeability. The permeation flux and separation factor for isopropanol/water is 38.6 g/m²h and 3238.5, using 87.5 wt % isopropanol concentration at 45°C, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1959–1965, 2007     

Binding behavior of Fe3+ ions on ion‐imprinted polymeric beads for analytical applications

We used a molecular imprinting approach to achieve specific metal binding utilizing N‐methacryloyl‐(L )‐cysteine methyl ester (MAC) as a metal‐complexing ligand. MAC was synthesized using methacryloyl chloride and cysteine methyl ester. Then, Fe³⁺ was complexed with MAC monomer. Fe³⁺‐imprinted poly(hydroxyethyl methacrylate‐N‐methacryloyl‐(L )‐cysteine methyl ester) [poly(HEMA‐MAC)] beads with average size of 63–140 μm were produced by suspension polymerization. After that, the template ions (i.e. Fe³⁺ ions) were removed by 0.1M HCl. Fe³⁺‐imprinted beads were characterized by swelling studies, FTIR, and elemental analysis. The Fe³⁺‐imprinted beads with a swelling ratio of 72%, and containing 3.9 mmol MAC/g were used in the binding of Fe³⁺ ions from aqueous solutions, tap water, certified reference serum sample, and real serum sample. Maximum binding capacity, optimum pH, and equilibrium binding time were 107 μmol/g, pH 3.0, and 30 min, respectively. It was observed that even in the presence of other ions, Fe³⁺‐imprinted beads selectively bound Fe³⁺ ions with 97% efficiency. Removal of Fe³⁺ ions from certified reference serum sample was approximately found to be 33%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3520–3528, 2006     

Hexamethylene diisocyanate crosslinking 2‐hydroxypropyltrimethyl ammonium chloride chitosan/poly(acrylonitrile) composite nanofiltration membrane

The effects of membrane preparation conditions on membrane properties were studied in detail. The results suggested that composite nanofiltration (NF) membrane from 2.0 wt % 2‐hydroxypropyltrimethyl ammonium chloride chitosan (HACC) vaporized for 2.5 h at 50°C, and then crosslinked for 9 h at 50°C with hexamethylene diisocyanate (HDI)/ethanol (0.45/50 wt/wt) were found to have optimal performance. The resultant membrane was called HACC/PAN [poly(acrylonitrile)] NF membrane. The characteristics of this membrane such as pure water permeability, molecular weight cut‐off, rejection of salts, and swelling were investigated. And its cut‐off molecular weight (MWCO) was ～520 Da. At 25°C and 1.0 MPa, the permeability of water was 17.24 L/h m² MPa. Swelling in water decreased and rejection of salts increased with increasing HDI concentration, indicating pore contraction and increase in hydrophobicity as well as pore tortuosity due to crosslinking. The order of rejection to different salt solutes followed the decreasing of CaCl₂, MgCl₂, NaCl, KCl, and Na₂SO₄, suggesting that this membrane was positively charged. The rejections to MgCl₂ and CaCl₂ were more than 0.90; therefore, this membrane can be used for hardness removal in water treatment process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007.     

Pervaporation separation of water–ethanol mixtures using metal‐ion‐exchanged poly(vinyl alcohol) (PVA)/sulfosuccinic acid (SSA) membranes

Poly(vinyl alcohol)/sulfosuccinic acid (PVA/SSA) membranes in the hydrogen form were converted to monovalent metal ion forms Li⁺, Na⁺, and K⁺. The effect of exchange with metal ions was investigated by measuring the swelling of water–ethanol (10/90) mixtures at 30 °C and by the pervaporative dehydration performance test for aqueous ethanol solutions with various ethanol concentrations at 30, 40, and 50 °C. In addition, electron spectroscopy for chemical analysis (ESCA) analysis was carried out to study the quantity of metal ions in membranes. From the ESCA analysis, the lithium ion quantity in the resulting membranes is greater than that of any other metal ions in question because of the easy diffusion of a smaller metal ion into the membrane matrix. The swelling ratio was in the following order: PVA/SSA‐Li⁺ > PVA/SSA‐Na⁺ > PVA/SSA‐K⁺ membranes. For pervaporation, the PVA/SSA‐Na⁺ membrane showed the lowest flux and highest separation factor for all aqueous ethanol solutions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1867–1873, 2002     

Towards a new strategy of a chitosan‐based molecularly imprinted membrane for removal of 4‐nitrophenol in real water samples

The issue of water contaminants, which affects human and environmental health, is not trivial. It is thus paramount to find new cheap and user friendly ways to detect and remove them from the environment. Here, the synthesis of a green chitosan (CS ) based molecularly imprinted membrane for the detection and quantification of 4‐nitrophenol (4‐NO₂Ph ) in aqueous media is proposed. The concentration of 4‐NO₂Ph in a water solution was measured by HPLC analysis. CS as a functional polymer, 4‐NO₂Ph as template, 4‐[(4‐hydroxy)phenylazo]benzenesulfonic acid as ligand, and glutaraldehyde as crosslinker in the presence of polyethylene glycol as porogen were used. The membrane was characterized by SEM and Fourier transform IR analyses, which confirmed the CS and polyethylene glycol backbone of the membrane. Kinetic studies of the detection system were performed by using pseudo‐first‐order and pseudo‐second‐order models. Then, the binding efficiency between 195.33 µmol L^?1 and 9235.55 µmol L^?1 of 4‐NO₂Ph was evaluated, finding a maximum adsorption of 723.25 µmol 4‐NO₂Ph per gram of membrane consistent with the Q _max calculated from the Langmuir isotherm. The selectivity of the membrane versus three phenolic competitor molecules, sharing very similar molecular structure to 4‐NO₂Ph , was demonstrated. Finally, the applicability of the membrane to real‐world samples was evaluated, by using drinking water spiked with 7.19 µmol L^?1 of 4‐NO₂Ph , obtaining a removal efficiency of 70.6%. © 2017 Society of Chemical Industry     

Preparation and characterization of CMCS/PVA blend membranes and its sorption and pervaporation performance (I)

Novel pervaporation (PV) membranes for ethanol dehydration were prepared by blend poly(vinyl alcohol) (PVA) and carboxymethyl chitosan (CMCS), followed by the crosslinking reaction with glutaraldehyde; the structure and miscibility of the blend membranes were characterized by Fourier transform infrared, X‐ray diffraction, and differential scanning calorimetry; the results indicated that the blends were miscible. The effect of feed concentration, operation temperature, crosslinking agent content, etc. on sorption performance and PV performance of the blend membrane is investigated. The membrane of CMCS/PVA blend ratio of 8 : 2 exhibited a high separation factor of 2959 with a reasonably high water flux value of 0.14 kg m^?2h^?1 at the azeotropic feed composition (95 wt % of ethanol) at a temperature of 45°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of a PVA/HAP composite polymer membrane for a direct ethanol fuel cell (DEFC)

A novel PVA/Hydroxyapatite (HAP) composite polymer membrane was prepared by the direct blend process and solution casting method. The characteristic properties of the PVA/HAP composite polymer membranes were investigated using thermal gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-Raman spectroscopy and the AC impedance method. An alkaline direct ethanol fuel cell, consisting of an air cathode with MnO₂ carbon inks based on Ni-foam, an anode with PtRu black on Ni-foam, and the PVA/HAP composite polymer membrane, was assembled and investigated. It was found that the alkaline direct ethanol fuel cell comprising of a novel cheap PVA/HAP composite polymer membrane showed an improved electrochemical performance in ambient temperature and air. As a result, the maximum power density of the alkaline DEFC, using a PtRu anode based on Ni-foam (10.74 mW cm⁻²), is higher than that of DEFC using an E-TEK PtRu anode based on carbon (7.56 mW cm⁻²) in an 8M KOH + 2M C₂H₅OH solution at ambient temperature and air. These PVA/HAP composite polymer membranes are a potential candidate for alkaline DEFC applications.     

Pervaporation of tertiary butanol/water mixtures through chitosan membranes cross‐linked with toluylene diisocyanate

Membranes made from 84% deacetylated chitosan biopolymer were cross‐linked by a novel method using 2,4‐toluylene diisocyanate (TDI) and tested for the separation of t‐butanol/water mixtures by pervaporation. The unmodified and cross‐linked membranes were characterized by Fourier transform infra red (FTIR) spectroscopy, X‐ray diffraction (XRD) studies and sorption studies in order to understand the polymer–liquid interactions and separation mechanisms. Thermal stability was analyzed by differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) while tensile strength measurement was carried out to assess mechanical strength. The membrane appears to have good potential for breaking the aqueous azeotrope of 88.2 wt% t‐butanol by giving a high selectivity of 620 and substantial water flux (0.38 kg m^?2 hr^?1). The effects of operating parameters such as feed composition, membrane thickness and permeate pressure on membrane performance were evaluated. Copyright © 2005 Society of Chemical Industry     

Modification of tetraethylorthosilicate crosslinked poly(vinyl alcohol) membrane using chitosan and its application to the pervaporation separation of water–isopropanol mixtures

Tetraethylorthosilicate crosslinked poly(vinyl alcohol) membrane was modified by varying the amounts of chitosan. The resulting membranes were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. The effects of chitosan content and feed composition on the pervaporation performance of the membranes were analyzed. The modified membranes exhibit simultaneous increase of both flux and selectivity. The membrane containing 15 mass % of chitosan shows the highest separation selectivity of 2991, with a flux of 2.39 × 10^?2 kg/(m² h) at 30°C for 10 mass % of water in the feed. The total flux and flux of water are almost overlapping each other, manifesting that the membranes could be used effectively to break the azeotropic point of water–isopropanol mixture, so as to remove water from the isopropanol. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (E_pw) are significantly lower than those of isopropanol permeation (E_pIPA), suggesting that the membranes developed here have higher separation ability for water–isopropanol system. In addition, difference was negligibly small between the activation energy values of total permeation (E_p) and water permeation (E_pw), indicating that coupled transport is minimal because of a higher selective nature of membranes. The E_p and E_D values ranged between 40.92 and 52.60, and 39.58 and 52.47 kJ/mol, respectively. The positive heat of sorption (ΔH_s) values observed in all the membranes suggests that Henry's mode of sorption is predominant. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1380–1389, 2006     

Preparation of functionalized ion‐imprinted phenolic polymer for efficient removal of copper ions

In this work, an ion‐imprinted polymeric material based on functionalized phenolic resin was developed for the efficient selective removal of Cu²⁺ ions from aqueous solution. p‐Aminophenol‐isatin Schiff base ligand (HPIS) was first synthesized and combined with Cu²⁺ ions to prepare the corresponding complex [Cu(PIS)₂]. The Schiff base ligand along with its copper complex was fully investigated and characterized before anchoring in a base‐catalyzed condensation copolymerization with formaldehyde and resorcinol. The Cu²⁺ ions were removed from the obtained resin construction and the resulting Cu²⁺ ion‐imprinted material (Cu‐PIS) was employed for the selective extraction of Cu²⁺ ions under different pH values, initial concentrations and contact time conditions. The optimum pH for the removal process was chosen as 6 and the maximum adsorption capacity was 187 ± 1 mg g^–1. Also, the kinetics showed a better fit with the pseudo‐second‐order equations. The selectivity of the prepared Cu‐PIS was also evaluated in a multi‐ionic species containing Ni²⁺, Cd²⁺, Pb²⁺, Co²⁺ besides Cu²⁺ ions and the determined parameters confirmed a superior recognition capability toward the imprinted Cu²⁺ ions. © 2019 Society of Chemical Industry     

Oxidation of hydroquinone to p‐benzoquinone catalyzed by Cu(II) supported on chitosan flakes

Copper (sorbed on chitosan flakes) was used as a catalyst for the oxidation of hydroquinone, with dioxygen (from air) and hydrogen peroxide as oxidizing agents. The supported catalyst was very efficient at oxidizing hydroquinone into p‐benzoquinone. With hydrogen peroxide at pH 5.8, drastic oxidizing conditions led to the formation of subproducts. With a short contact time, together with the use of a low hydrogen peroxide concentration and a small amount of the catalyst, the formation of subproducts could be minimized. The influence of the catalyst/substrate and hydrogen peroxide/substrate ratios was investigated to determine optimum experimental conditions for a high initial oxidation rate and a high production of p‐benzoquinone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3034–3043, 2006