Experimental design and batch experiments for optimization of Cr(VI) removal from aqueous solutions by hydrous cerium oxide nanoparticles

Hydrous cerium oxide (HCO) was synthesized by intercalation of solutions of cerium(III) nitrate and sodium hydroxide and evaluated as an adsorbent for the removal of hexavalent chromium from aqueous solutions. Simple batch experiments and a 2⁵ factorial experimental design were employed to screen the variables affecting Cr(VI) removal efficiency. The effects of the process variables; solution pH, initial Cr(VI) concentration, temperature, adsorbent dose and ionic strength were examined. Using the experimental results, a linear mathematical model representing the influence of the different variables and their interactions was obtained. Analysis of variance (ANOVA) demonstrated that Cr(VI) adsorption significantly increases with decreased solution pH, initial concentration and amount of adsorbent used (dose), but slightly decreased with an increase in temperature and ionic strength. The optimization study indicates 99% as the maximum removal at pH 2, 20 °C, 1.923 mM of metal concentration and a sorbent dose of 4 g/dm³. At these optimal conditions, Langmuir, Freundlich and Redlich–Peterson isotherm models were obtained. The maximum adsorption capacity of Cr(VI) adsorbed by HCO was 0.828 mmol/g, calculated by the Langmuir isotherm model. Desorption of chromium indicated that the HCO adsorbent can be regenerated using NaOH solution 0.1 M (up to 85%). The adsorption interactions between the surface sites of HCO and the Cr(VI) ions were found to be a combined effect of both anion exchange and surface complexation with the formation of an inner-sphere complex.     

All solid-state polymer electrolytes prepared from a hyper-branched graft polymer using atom transfer radical polymerization

We propose an all solid-state (liquid free) polymer electrolyte (SPE) prepared from a hyper-branched graft copolymer. The graft copolymer consisting of a poly(methyl methacrylate) main chain and poly(ethylene glycol) methyl ether methacrylate side chains was synthesized by atom transfer radical polymerization changing the average chain distance between side chains, side chain length and branched chain length of the proposed structure of the graft copolymer. The ionic conductivity of the SPEs increases with increasing the side chain length, branched chain length and/or average distance between the side chains. The ionic conductivity of the SPE prepared from POEM₉ whose POEM content = 51 wt% shows 2 × 10⁻⁵ S/cm at 30 °C. The tensile strength of the SPEs decreases with increases the side chain length, branched chain length and/or average distance between the side chains. These results indicate that a SPE prepared from the hyper-branched graft copolymer has potential to be applied to an all-solid polymer electrolyte.     

Preparation and characterization of new anhydrous, conducting membranes based on composites of ionic liquid trifluoroacetic propylamine and polymers of sulfonated poly (ether ether) ketone or polyvinylidenefluoride

A novel ionic liquid of trifluoroacetic propylamine, i.e., [CH₃CH₂CH₂NH₃⁺] [CF₃COO⁻] (TFAPA), was synthesized from trifluoroacetic acid and propylamine. The ionic liquid of TFAPA was used to prepare anhydrous, conducting membranes based on polymers of sulfonated poly (ether ether) ketone (SPEEK) or polyvinylidenefluoride (PVDF). The ionic conductivity and mechanical strength of the composite membranes were investigated at elevated temperatures and under anhydrous conditions. Conductivity of 0.030 S/cm was achieved with TFAPA at 180 °C, and of 0.019 S/cm with a membrane containing 70% (wt) TFAPA in SPEEK with a sulfonation degree of 86% at 160 °C. Increasing either ionic liquid content or temperature reduced the mechanical strength of the composite membrane. Efforts were made to improve the strength of TFAPA/SPEEK composite membranes by cross-linking the SPEEK, which led to some strength enhancement at 110 °C and 130 °C.     

Effect of ionic strength on the foam fractionation of BSA with existence of antifoaming agent

Foam fractionation is an economical and effective technology for protein concentration and separation. However, the presence of antifoaming agent in the fermentation broth restricts the application of this technology. In this paper surfactant-assisted foam process was conducted with a mimic system using bovine serum albumin (BSA) as target protein, polyoxypropylene polyoxyethylene glylerin ether (PGE) as antifoaming agent and cetyltrimethyl ammonium bromide (CTAB) as surfactant, putting emphasis on study of the effect of ionic strength on the separation process. The experimental results showed that with ionic strength increasing, the mixed-system foaming ability gradually increased. Under the conditions of C_BSA 100 mg/L, C_CTAB 20 mg/L, C_PGE 8 mg/L and pH 7.4, feed liquid 250 mL, air flow rate 100 mL/min at 25 °C, the maximum enrichment ratio of BSA reached 27 when the ionic strength was 0.0500 mol/kg and the maximum recovery of BSA reached 80.5% when the ionic strength was 0.1696 mol/kg. Furthermore, K⁺ had better separate efficiency than Na⁺ under the same ionic strength.     

Synthesis and self-assembly of amphiphilic poly(acrylic acid-b-dl-lactide) to form micelles for pH-responsive drug delivery

An amphiphilic diblock copolymer of poly(acrylic acid-b-dl-lactide) (PAAc-b-PDLLA) was synthesized by ring-opening polymerization of dl-lactide initiated by hydroxyl-terminated polyacrylic acid (PAAc-OH). The critical micelle concentration (CMC) of PAAc-b-PDLLA in aqueous solution, determined by fluorescence spectroscopy using pyrene as a probe, was found about 80 mg L⁻¹. A solution of PAAc-b-PDLLA in tetrahydrofuran (THF) was dialyzed against pure water to form pH-responsive micelles. Transmission electron microscopy (TEM) measurement showed that the micelles exhibited regular spherical morphology and the diameters of particles were in the range from 40 to 90 nm. The micelles were stable at a pH above 3 or at an ionic strength below 1.0, however, they aggregated and precipitated in the solutions when further decreasing pH or increasing ionic strength. Prednisone acetate, as a model hydrophobic drug, was loaded into the polymeric micelles. In vitro release of prednisone acetate from polymeric micelles showed that the release kinetics was strongly pH-dependent. Hydrophobic drug displayed “burst” release at pH 7.4, while only a small part of loaded drug released at pH 1.4. This provides a new choice to design delivery system for the gastrointestinal tract (GI tract), where the pH environment is strongly acidic in stomach and basic in intestine. The cytotoxicity measurement by MTT assay indicated that PAAc-b-PDLLA was low toxic in HeLa cells with an IC50 value of 2.8 mg mL⁻¹, which suggests that PAAc-b-PDLLA could be used as a safe candidate for pH-responsive drug delivery.     

The effect of ionic strength and pH on the stability of tannic acid-facilitated carbon nanotube suspensions

Carbon nanotubes (CNTs) are prone to aggregation and precipitation in water due to their high hydrophobicity and aspect ratio. However, the addition of dissolved organic matter (DOM) has been reported to disperse and stabilize certain CNTs, suggesting the potential transport and bioavailability of CNTs in natural aqueous environments. For a better understanding of the CNT-DOM interaction, five multiwalled CNTs with outer diameters of <10 (MWCNT10), 10-20 (MWCNT20), 20-40 (MWCNT40), 40-60 (MWCNT60), and 60-100 nm (MWCNT100) were used to investigate their sorptive and suspension behavior in tannic acid (TA, as a DOM surrogate) solution; the effects of ionic strength and pH on the TA-CNT interaction were examined. Suspension of MWCNTs sharply improved with increasing TA concentration and leveled off at an initial TA concentration ca. 20 mg/L. Suspension of MWCNTs was in the order of MWCNT40 > MWCNT60 > MWCNT20 > MWCNT100 > MWCNT10. The TA-stabilized CNTs were stable within pH 5-11, while they quickly precipitated at pH < 5. Different ions (Na⁺, Mg²⁺, Ca²⁺, or La³⁺) aggregated the stabilized CNTs, with a critical coagulation concentration exponentially correlated to ionic valence. Changes of steric repulsion and electrostatic interaction with the added TA could account for the variation of CNT stability.     

Preparation and characterisation of a poly(acrylamidoglycolic acid-co-acrylamide) hydrogel for selective binding of Cu and application to diffusive gradients in thin films measurements

A poly(acrylamidoglycolic acid-co-acrylamide) [poly(AAGA-co-AAm)] hydrogel was prepared by copolymerising 2-acrylamidoglycolic acid (AAGA) with acrylamide (AAm). The copolymer hydrogel composition and structure was characterised by FTIR spectroscopy and elemental microanalysis and found to contain 3.5 AAGA monomer units for each AAm monomer unit. This was similar to the monomer ratios used in the synthesis. The metal ion binding properties of the hydrogel were characterised for a range of metal ions (Cu²⁺, Cd²⁺, K⁺, Na⁺, Mg²⁺ and Ca²⁺) under varying conditions of pH, ionic strength, metal concentration and time. The hydrogel was shown to bind Cu²⁺ and Cd²⁺ strongly under non-competitive binding conditions, with binding capacities of 5.3 and 5.1 μmol cm⁻², respectively. The binding capacity of each metal decreased, under competitive binding conditions (with a range of metal ions present at 17.8 μN), to 1.3 and 0.17 μmol cm⁻², respectively, indicating stronger selectivity for Cu²⁺. The metal ions were readily recovered (>94%) by eluting with 2 M nitric acid solution for 24 h. The binding capacities for Cu²⁺ and Cd²⁺ were also found to decrease with increasing ionic strength and at pH values <5. The copolymer was found to have an equilibrium swelling ratio (q_w) of over 500 at a maxima of pH 5.4 and at low ionic strengths. Finally, the copolymer hydrogel was tested as a binding phase with the diffusive gradients in thin films technique. A linear mass vs. time relationship was observed for Cu²⁺ in synthetic Windermere water with a recovery of approximately 100%.     

Synthesis and dual response of ionic nanocomposite hydrogels with ultrahigh tensibility and transparence

Ionic nanocomposite hydrogels cross-linked by hectorite Laponite XLS with high tensile strength and ultrahigh tensibility were successfully synthesized for the first time via in situ copolymerization of N-isopropylacrylamide (NIPAm) and sodium methacrylate (SMA). The pH and temperature response, transparency, and mechanical properties of the ionic hydrogels were investigated. The results showed that the addition of only 2 mol% of SMA endowed the nanocomposite hydrogels with pH response, while the temperature response remained in the whole pH range. All the as-prepared hydrogels, even with 10 mol% of SMA, demonstrated transparency higher than 75%. The tensile strength evidently decreased from 60 kPa to 45 kPa when the SMA content was higher than 6 mol%. The elongation at break increased with increasing SMA content and 2800% was achieved for the sample containing 10 mol% of SMA. The effective network chain density was estimated from the tensile stress at elongation of 200% and the equilibrium storage modulus. The low chain density was the intrinsic origin of the ultrahigh tensibility for these ionic NC gels. This work provides a new way to prepare dual responsive hydrogels with ultrahigh tensibility and high transparency.     

Ionic conductivity of chitosan membranes

Chitosan membranes with various degrees of deacetylation and different molecular weights (MW) were prepared by film casting with aqueous solutions of chitosan and acetic acid. Ultraviolet (UV) spectrometry and infrared (IR) spectrometry were used to determine the degree of deacetylation (DDA) of chitosan. The viscosity-average MW of chitosan was measured in an aqueous solvent system of 0.25 M CH₃COOH/0.25 M CH₃COONa. The intrinsic ionic conductivities of the hydrated chitosan membranes were investigated using impedance spectroscopy. It was found that the intrinsic ionic conductivity was as high as 10⁻⁴ S cm⁻¹ after hydration for 1 h. The tensile strength and breaking elongation of the membranes were evaluated according to standard ASTM methods. The crystallinity and swelling ratio of the membranes were examined. A tentative mechanism for the ionic conductivity of chitosan membranes is also suggested.     

Effect of methylsisesquioxane filler on the properties of ionic liquid based polymer electrolyte

Composite electrolyte comprising methylsisesquioxane (MSQ) filler and 1-butyl-3-methyl-imidazolium-tetrafluoroborate (BMImBF₄) ionic liquid (IL) in poly(2-hydroxyethyl methacrylate) (PHEMA) matrix had been prepared. The polymer matrix was formed by free radical polymerization of HEMA macromer, and MSQ was produced in situ from methyl-trimethoxysilane by the sol-gel method. Infrared spectroscopy and dynamic mechanical analysis were employed to give insight into the interactions among the methylsisesquioxane filler, BMImBF₄ and the PHEMA polymer matrix. The PHEMA-IL-MSQ hybrids and the PHEMA-IL electrolyte without MSQ were investigated regarding their ionic conductivity and thermal and electrochemical properties. BMImBF₄ increased the thermal stability of the polymer and provided the ion conductivity; MSQ filler as the additive increased the mechanical strength of the polymer and provided the ion conductive pathway. The electrolyte with MSQ at the 10 wt% showed the highest ionic conductivity of 5×10⁻⁴ S cm⁻¹ which was five times higher than that of the electrolyte without MSQ, and the electrochemical window was up to 3.6 V.     

Preparation of poly(acrylonitrile-butyl acrylate) gel electrolyte for lithium-ion batteries

Poly(acrylonitrile-butyl acrylate) gel polymer electrolyte was prepared for lithium ion batteries. The preparation started with synthesis of poly(acrylonitrile-butyl acrylate) by radical emulsion polymerization, followed by phase inversion to produce microporous membrane. Then, the microporous gel polymer electrolytes (MGPEs) was prepared with the microporous membrane and LiPF₆ in ethylene carbonate/diethyl carbonate. The dry microporous membrane showed a fracture strength as high as 18.98 MPa. As-prepared gel polymer electrolytes presented ionic conductivity in excess of 3.0 × 10⁻³ S cm⁻¹ at ambient temperature and a decomposition voltage over 6.6 V. The results showed that the as-prepared gel polymer electrolytes were promising materials for Li-ion batteries.     

Synthesis of novel copolymers containing tri(ethylene oxide) segments and bithiazole rings on the backbone and magnetic properties of their complexes

Two novel copolymers containing bithiazole rings and ethylene oxide on the skeleton (PPOBTz and PNOBTz) were synthesized via Schiff reaction and Ullmann reaction, respectively. The copolymers were characterized by FTIR, ¹H NMR. Their polymeric complexes with Cu²⁺ and Nd²⁺ were prepared. The magnetic behavior of these polymeric complexes was measured as a function of magnetic field strength (0-60 kOe) at 4 K and as a function of temperature (4-300 K) at a magnetic field strength of 30 kOe, indicating that they all exhibited features of soft ferromagnet.     

Effect of surface modified porous inorganic-organic hybrid polyphosphazene nanotubes on the properties of polyethylene oxide based solid polymer electrolytes

2-(2-methyloxyethoxy)ethanol modified poly (cyclotriphosphazene-co-4,4′-sufonyldiphenol) (PZS) nanotubes were synthesized and solid composite polymer electrolytes based on the surface modified polyphosphazene nanotubes added to PEO/LiClO₄ model system were prepared. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) were used to investigate the characteristics of the composite polymer electrolytes (CPE). The ionic conductivity, lithium ion transference number and electrochemical stability window can be enhanced after the addition of surface modified PZS nanotubes. The electrochemical investigation shows that the solid composite polymer electrolytes incorporated with PZS nanotubes have higher ionic conductivity and lithium ion transference number than the filler SiO₂. Maximum ionic conductivity values of 4.95 × 10⁻⁵ S cm⁻¹ at ambient temperature and 1.64 × 10⁻³ S cm⁻¹ at 80 °C with 10 wt % content of surface modified PZS nanotubes were obtained and the lithium ion transference number was 0.41. The good chemical properties of the solid state composite polymer electrolytes suggested that the inorganic-organic hybrid polyphosphazene nanotubes had a promising use as fillers in solid composite polymer electrolytes and the PEO₁₀-LiClO₄-PZS nanotubes solid composite polymer electrolyte can be used as a candidate material for lithium polymer batteries.     

Preparation and characterization of charcoals that contain dispersed aluminum oxide as adsorbents for removal of fluoride from drinking water

Charcoals adsorbents that contain dispersed aluminum and iron oxides have been synthesized by impregnating wood with salt solutions followed by carbonization at 500 °C, 650 °C or 900 °C. The adsorbents were characterized and their performance for fluoride removal from aqueous solution was evaluated. Aluminum and iron oxides were well dispersed into the porous charcoals. The carbons were amorphous and highly porous. XRD of the adsorbents showed crystalline iron oxide but did not show any form of crystalline aluminum oxides. All the adsorbents showed acidic surface properties. The efficiency of defluoridation was found to depend on the carbonization temperature, the pH of point of zero charge (pHPZC), and the co-existing ions. Substrates prepared at 650 °C with aluminum and iron oxides exhibited the best efficiency with a fluoride sorption capacity of 13.64 mg g⁻¹. More than 92% removal of fluoride was achieved within 24 h from a 10 mg L⁻¹ solution at neutral pH. Fluoride adsorption kinetic was well fitted by a pseudo-second order model. The amounts of residual Al and Fe in treated solution were pH dependant. At neutral pH, the amounts of dissolved Al and Fe were found to be 0.67 and 1.8 mg L⁻¹, respectively.     

Improved ionic conductivity of nitrile rubber/ionic liquid composites

Polymer electrolytes with high ionic conductivity and good elasticity were prepared by mixing nitrile rubber (poly(acrylonitrile-co-butadiene) rubber; NBR) with ionic liquid, N-ethylimidazolium bis(trifluoromethanesulfonyl)imide (EImTFSI). The NBR/EImTFSI composites were obtained as homogeneous and transparent films when the ionic liquid content was less than 60 wt%. Raman spectroscopy suggested the interaction between nitrile group of NBR and TFSI anion. Sample with ionic liquid content of 50 wt% showed the ionic conductivity of 1.2×10⁻⁵ S cm⁻¹ at 30 °C. Addition of lithium salt to this NBR/EImTFSI composite further enhanced the ionic conductivity to about 10⁻⁴ S cm⁻¹ without spoiling mechanical properties. DSC studies showed two glass transition temperatures for composites indicating microphase separation.     

Sulfonated poly(ether ether ketone) membranes for electric double layer capacitors

Sulfonated poly(ether ether ketone) (S-PEEK) with different degree of sulfonation (DS) has been prepared and evaluated as a proton conducting membrane for electric double layer capacitor (EDLC). The polymer electrolytes prepared with S-PEEK membrane exhibited ionic conductivities about 1.2 × 10⁻³-4.5 × 10⁻³ S cm⁻¹ at room temperature, which depended on both soaking solvent and degree of sulfonation. The quasi-solid-state EDLCs consisted of activated carbon electrodes and S-PEEK membrane were assembled, and their electrochemical characteristics were studied by cyclic voltammetry and charge-discharge cycle tests. The effect of DS on the electrochemical performances of EDLCs has been investigated.     

Synthesis and electrochemical characterization of PEO-based polymer electrolytes with room temperature ionic liquids

New gel polymer electrolytes containing 1-butyl-4-methylpyridinium bis(trifluoromethanesulfonyl)imide (BMPyTFSI) ionic liquid are prepared by solution casting method. Thermal and electrochemical properties have been determined for these gel polymer electrolytes. The addition of BMPyTFSI to the P(EO)₂₀LiTFSI electrolyte results in an increase of the ionic conductivity, and at high BMPyTFSI concentration (BMPy⁺/Li⁺ = 1.0), the ionic conductivity reaches the value of 6.9 × 10⁻⁴ S/cm at 40 °C. The lithium ion transference numbers obtained from polarization measurements at 40 °C were found to decrease as the amount of BMPyTFSI increased. However, the lithium ionic conductivity increased with the content of BMPyTFSI. The electrochemical stability and interfacial stability for these gel polymer electrolytes were significantly improved due to the incorporation of BMPyTFSI.     

Electrochemical behavior of ionically crosslinked polyampholytic gel electrolytes

An ionic complex of anionic and cationic monomers was obtained by protonation of (N,N-diethylamino)ethylmethacrylate (DEA) with acrylic acid (AAc). Free radical copolymerization of the ionic complex and acrylamide (AAm), yielded the ionically crosslinked polyampholytic gel electrolytes [poly(AAc-DEA-AAm), designated as PADA] using two types of organic solvents containing a lithium salt. The PADA gel electrolyte exhibited good thermal stability shown by the DSC thermogram. The impedance analysis at temperatures ranging from −30 to 75 °C indicated that the ionic conductivities of the PADA gel electrolytes were rather close to those of liquid electrolytes. The temperature dependence of the ionic conductivities was found to be in accord with the Arrhenius equation. Moreover, the ionic conductivities of PADA gel electrolytes increased with an increase of the molar ratios of cationic/anionic monomers. The ionic conductivities of PADA gels prepared in solvent mixtures of propylene carbonate, ethyl methyl ether and dioxolane (3:1:1, v/v) were higher than those of PADA gels prepared in propylene carbonate only. Significantly, the ionic conductivities of two kinds of PADA gel electrolytes were in the range of 10⁻³ and 10⁻⁴ S cm⁻¹ even at −30 °C. The electrochemical windows of PADA gel electrolytes measured by cyclic voltammetry were in the range from −1 V to 4.5 V.     

Microstructure and ionic conductivity properties of gadolinia doped ceria (GdxCe1−xO2−x/2) electrolytes for intermediate temperature SOFCs prepared by the polyol method

Gd_0.1Ce_0.9O_1.95 and Gd_0.2Ce_0.8O_1.9 powders were prepared through the polyol process without using any protective agent. Microstructural and physical properties of the samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG) and impedance analysis methods. The results of the thermogravimetry/differential thermal analysis (TG/DTA) and XRD indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 500 °C. The XRD patterns of the samples revealed that the crystallite size of the samples increased as calcination temperatures increased. The sintering behavior and ionic conductivity of pellets prepared from gadolinia doped ceria (GDC) powders, which were calcined at 500 °C, were also investigated. The relative densities of the pellets, which were sintered at temperatures above 1300 °C, were higher than 95%. The results of the impedance spectroscopy revealed that the GDC-20 sample that was sintered at 1400 °C exhibited an ionic conductivity of 3.25×10⁻² S cm⁻¹ at 800 °C in air. This result clearly indicates that GDC powder with adequate ionic conductivity can be prepared through the polyol process at low temperatures.     

Preparation of a microporous polymer electrolyte based on poly(vinyl chloride)/poly(acrylonitrile-butyl acrylate) blend for Li-ion batteries

Poly(acrylonitrile-co-butyl acrylate) (P(AN-co-BuA))/poly(vinyl chloride) (PVC) blend-based gel polymer electrolyte (BGPE) was prepared for lithium-ion batteries. The P(AN-co-BuA)/PVC BGPE consists of an electrolyte-rich phase, which is mainly composed of P(AN-co-BuA) and liquid electrolyte, acting as a conducting channel and a PVC-rich phase that provides mechanical strength. The dual phase was just simply developed by the difference of miscibility properties in solvent, PC, between P(AN-co-BuA) and PVC. The mechanical strength of this new blend electrolyte was found to be much higher, with a fracture stress as high as 29 MPa in dry membrane and 21 MPa in gel state, than that of a previously reported P(AN-co-BuA)-based gel polymer electrolyte. The blended gel polymer electrolyte showed ionic conductivity of higher than 1.5 × 10⁻³ S cm⁻¹ and electrochemical stability up to at least 4.8 V. The results showed that the as-prepared gel polymer electrolytes were promising materials for lithium-ion batteries.