Recovery of hydrochloric acid using positively-charged nanofiltration membrane with selective acid permeability and acid resistance.

An acid-recovering nanofiltration (NF) membrane with both acid resistance and selective acid permeability was fabricated via a water-based coating process for the recovery of hydrochloric acid. To achieve this, a thermally cross-linked branched-polyethyleneimine (b-PEI) layer was introduced to a loose polyethersulfone NF membrane by dip-coating of b-PEI and an epoxy linker and heat treatment in a sealed oven with a high-humidity atmosphere. The resulting membrane displayed a positive surface charge with a zeta potential, and exhibited a rejection performance order of MgCl2> MgSO4> NaCl > Na2SO4 characteristic of positive-charge-separation membranes. Mg rejection and Cl permeation experiments showed that the selective permeation of hydrochloric acid was achieved with Mg rejection above 95% and Cl permeation above 70%, and this allowed the acid to be recovered by obtaining permeate at the same pH as the feed. Moreover, the NF membrane maintained selective separation performance and flow rate for a month.

Recovery of sulfuric acid aqueous solution from copper-refining sulfuric acid wastewater using nanofiltration membrane process.

We used a nanofiltration (NF) membrane process to produce purified aqueous sulfuric acid from copper-refining sulfuric acid wastewater. Wastewater generated from a copper-refining process was used to explore the membrane performances and acid stabilities of six commercial NF membranes. A combination of permeate flux, sulfate permeation, and metal ion rejection clearly showed that two polyamide membranes and a polyacrylonitrile-based membrane achieved recovery of a purified sulfuric acid solution. Acid-stability and long-term performance tests showed that the polyamide membranes were unsuitable for copper-refining wastewater treatment because of their low acid stabilities. In contrast, the polyacrylonitrile-based composite membrane showed excellent acid stability, and gave greater than 90% metal ion rejection, with the exception of calcium ions, for 430 d. We also evaluated the recovery performance in 1 ton/d pilot-scale process using wastewater from copper-refining process; 90% metal ion rejection was achieved, with the exception of calcium ions, even at 95% recovery rate.

Hydrophilic and positively charged polyethylenimine-functionalized mesoporous magnetic clusters for highly efficient removal of Pb(II) and Cr(VI) from wastewater.

We develop mesoporous magnetic clusters (MMCs) functionalized with hydrophilic branched polyethylenimine (b-PEI), later called b-MG, and MMCs functionalized with positively charged b-PEI (p-MG). These materials efficiently remove Pb(II) and Cr(VI) from wastewater. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and nitrogen adsorption-desorption analysis results clearly indicate that hydrophilic b-PEI and positively charged b-PEI are successfully attached to the MMC surfaces. Wide-angle X-ray diffraction, high-resolution transmission electron microscopy, and field-emission scanning electron microscopy analyses confirm that the crystal structures and morphologies of the MMCs are maintained well even when wet chemical modification processes are used to introduce hydrophilic b-PEI and positively charged b-PEI to the MMC surfaces. Langmuir and Sips isotherm models are applied to describe Pb(II) adsorption behavior of the b-MG and Cr(VI) adsorption behavior of the p-MG. The isotherm models indicate that the maximum adsorption capacities of b-MG and p-MG, respectively, are 216.3 and 334.1 mg g-1, respectively. These are higher than have previously been found for other adsorbents. In reusability tests, using magnetic separation and controlling the pH, the Pb(II) recovery efficiency of the b-MG is 95.6% and the Cr(VI) recovery efficiency of the p-MG is 68.0% even after the third cycle.

Structurally Enhanced Self-Plasticization of Poly(vinyl chloride) via Click Grafting of Hyperbranched Polyglycerol.

A highly self-plasticized poly(vinyl chloride) (PVC) is demonstrated for the first time via click grafting of hyperbranched polyglycerol (HPG). The plasticizing effect of the grafted HPG on PVC is systematically investigated by various analytical methods. The amorphous and bulky dendritic structure of HPG efficiently increases the free volume of the grafted PVC, which leads to a remarkably lower glass transition temperature comparable to that of the conventional plasticized PVC. Viscoelastic analysis reveals that HPG considerably improves the softness of the grafted PVC at room temperature and promotes the segmental motion in the system. The HPG-grafted PVC films exhibit an exceptional stretchability unlike the mixture of PVC and HPG because the covalent attachment of HPG to PVC allows it to maintain its homogeneous and well-organized architecture under tensile stretching. The work provides valuable insights into the design of highly flexible and stretchable polymeric materials by means of introducing hyperbranched side chains.

Physical state of cellulose in BmimCl: dependence of molar mass on viscoelasticity and sol-gel transition.

In this work, we investigated the correlation between the molar mass and the rheological properties of cellulose/1-butyl-3-methylimidazolium chloride (BmimCl) solutions, and provided the depolymerization kinetics of cellulose in BmimCl. Gel permeation chromatography was used to track the change in molar mass and kinetics as a function of the dissolution time. The molar mass of cellulose in BmimCl decreased significantly as the dissolution time increased, following a zeroth order rate law. The decrease of inter-chain friction induced by depolymerization resulted in a lower viscosity, shorter relaxation time, and lower activation energy. The activation energies for flow were distinctly different above and below the critical molar mass, which indicates that the relaxation mechanisms were not identical above and below the critical molar mass. The transition behavior of liquid crystalline phase also changed at the critical molar mass, which strongly demonstrated the effect of chain length on the formation of cholesteric phase. The exponents of Mark-Houwink-Sakurada and the radius of gyration showed that cellulose in BmimCl existed as a Gaussian chain in a theta solvent.

Probing the Role of Side-Chain Interconnecting Groups in the Structural Hydrophobicity of Comblike Fluorinated Polystyrene by Solid-State NMR Spectroscopy.

In order to probe the role of side-chain interconnecting groups (-O-, -S-, and -SO2- linkages between the polystyrene (PST) main chain and fluorooctyl side chain) in the hydrophobicity of the comblike fluorinated polystyrenes, the molecular motion and structure of polymers are explored using the spin-lattice relaxation times (T1 and T1ρ) by solid-state (1)H and (19)F nuclear magnetic resonance spectroscopy. The chain-end motions of the polystyrene main chain and the fluorooctyl side chain are homogeneous, regardless of the interconnecting groups, which means that the chain-end motions of the main chain and the side chain maintain consistency, and these are irrelevant to each other. However, the local dynamic of the main chain shows the structural heterogeneity composed of the mobile and rigid regions, attributed to the rigidity of the side chain. The mobile dynamic portions of the main chain for PST-O and PST-S increase, and their rigid dynamic portions decrease as the temperature increases, whereas the ratio of structural heterogeneity for PST-SO2 is maintained despite increasing temperature. The activation energies (Ea) corresponding to the local motion of fluorooctyl side chains for PST-O and PST-S are drastically increased on the fast motion side compared to the slow motion side, suggesting the motional transformation of side chains for PST-O and PST-S from the small local motion into the large-scale movements related to a cooperative segmental motion when heated. Also, the local motion of the fluorooctyl side chain for PST-SO2 has similar Ea values on both sides, indicating that the relaxation time of PST-SO2 does not change with temperature. Therefore, PST-SO2 is structurally more stable than PST-O or PST-S, which can be attributed to the densely packed fluorooctyl side chain structure caused by the large dipole moment of the sulfone interconnecting group.

Adsorption-assisted photocatalytic activity of nitrogen and sulfur codoped TiO2 under visible light irradiation.

Applying post thermal treatment on the doped TiO2 at high temperature is mostly regarded as an indispensable process, although it has negative effects on the photocatalytic activity of doped TiO2. Herein, we synthesized the N- and S-codoped TiO2 (NSTs) with an anatase phase using a simple solvothermal treatment and investigated their visible light photocatalytic activity associated with the thermal behavior of dopants in NSTs. We found that the as-synthesized NST (NST-As) has better visible light photocatalytic activity and adsorptivity than the commercially available P25 and the thermally treated NSTs. The S dopants effectively assist the surface reaction by adsorbing cations of organic dyes on the NST-As surface. The N dopants increase the absorbance at visible light region of NST-As by forming a delocalized state at the band gap of NST-As. However, the photocatalytic activity of NSTs gradually weakens with the post thermal treatment, because S dopants on the NST-As surface are transformed from sulfide to sulfate during the thermal treatment and N dopants move out during the crystallization of TiO2. The adsorption-assisted photocatalytic activity of NST-As under visible light irradiation is an attractive feature for environmental and photonic technologies.

Nylon nanoweb with TiO2 nanoparticles as a solid matrix for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RATIONALE: The solid matrices used for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) enable the analysis of small molecules by preventing fragmentations of organic matrix molecules in the low mass-to-charge ratio (m/z) range. In this work, a nylon nanoweb with TiO(2) particles was developed as a solid matrix for MALDI-TOFMS to improve the low intensities of mass peaks, narrow detection ranges and low signal-to-noise levels. METHODS: The nylon nanoweb with TiO(2) particles was prepared by simultaneously electrospinning a nylon nanoweb and electrospraying TiO(2) nanoparticles measuring 25 nm in diameter to form TiO(2) spheres 300 nm in diameter. RESULTS: MS of multiple analytes was demonstrated in the low molecular weight range using eight amino acids. Additionally, leucine-enkephalin (555.6 g/mol) and cyclic citrullinated peptide (1668 g/mol) were used as model analytes to test the feasibility of a nylon nanoweb containing TiO(2) particles as a solid matrix for MALDI-TOFMS. CONCLUSIONS: The nylon nanoweb with TiO(2) particles can be applied for the detection of volatile small molecule analytes in the m/z ratio range of small molecules.

Role of electrical conductivity of spinning solution on enhancement of electrospinnability of polyamide 6,6 nanofibers.

Optimal conditions for electrospinning of uniform polyamide 6,6 (PA66) nanofibers were determined by the control of various parameters, such as polymer solution concentration, flow rate, tip-to-collector distance (TCD), applied voltage, and electrical conductivity of the polymer solution. An organic salt, benzyl trimethyl ammonium chloride (C10H16CIN, BTMAC), was added to the solutions for increase of electrical conductivity. When no salt was added to the PA66 solution, the uniform nanofibers were electrospun only at limited conditions, such as flow rate of 0.5 mL/h and electric fields greater than 2.0-3.5 kV/cm. In contrast, by the addition of BTMAC, range of optimal conditions for uniform nanofibers was expanded; uniform nanofibers were obtained at flow rate of 0.5-1.5 mL/h and electric fields greater than 1.3-1.6 kV/cm. This means that the electrospinnability of the nanofibers is improved by increasing electrical conductivity of the solutions. Furthermore, the addition of BTMAC affected the increasing of number average diameters and standard deviation of the nanofibers. On the other hand, the process variables, such as flow rate, TCD, and applied voltage, exerted little influence on the increase of diameters.

Frontal polymerization-triggered simultaneous ring-opening metathesis polymerization and cross metathesis affords anisotropic macroporous dicyclopentadiene cellulose nanocrystal foam.

Multifunctionality and effectiveness of macroporous solid foams in extreme environments have captivated the attention of both academia and industries. The most recent rapid, energy-efficient strategy to manufacture solid foams with directionality is the frontal polymerization (FP) of dicyclopentadiene (DCPD). However, there still remains the need for a time efficient one-pot approach to induce anisotropic macroporosity in DCPD foams. Here we show a rapid production of cellular solids by frontally polymerizing a mixture of DCPD monomer and allyl-functionalized cellulose nanocrystals (ACs). Our results demonstrate a clear correlation between increasing % allylation and AC wt%, and the formed pore architectures. Especially, we show enhanced front velocity (vf) and reduced reaction initiation time (tinit) by introducing an optimal amount of 2 wt% AC. Conclusively, the small- and wide-angle X-ray scattering (SAXS, WAXS) analyses reveal that the incorporation of 2 wt% AC affects the crystal structure of FP-mediated DCPD/AC foams and enhances their oxidation resistance.

Facile Sonochemical Synthesis of Flexible Fe-Based Metal-Organic Frameworks and Their Efficient Removal of Organic Contaminants from Aqueous Solutions.

An iron-based metal-organic framework, MIL-53(Fe), was synthesized via the simple sonochemical method, which is a facial and fast strategy, and their adsorption performance for organic contaminants removal from aqueous solutions was studied. The crystal structure and morphology analysis indicate that the sonochemical synthesis of MIL-53(Fe) particles was faster than the solvothermal preparation method, showing high crystallinity with a downsized hexagonal bipyramid shape. Furthermore, the prepared MIL-53(Fe) exhibited enhanced adsorption capability for the organic dyes compared to metal-organic framework prepared via the solvothermal method and showed excellent maximum adsorption capability for the methyl orange removal from aqueous solutions. Based on the superior adsorption properties and facile synthesis, MIL-53(Fe) prepared by ultrasound irradiation has a potential application for an efficient, economic, and ecofriendly wastewater purification process.

Mechanochemically Synthesized Prussian Blue for Efficient Removal of Cesium Ions from Aqueous Solutions.

The adsorptive removal of radioactive cesium [Cs(I)] is important for ensuring a clean aquatic environment. In this work, the adsorption of Cs(I) was carried out using Prussian blue (PB) prepared by mechanochemical synthesis. X-ray diffraction, Fourier-transform infrared spectroscopy, and field-emission scanning electron microscopy results indicated that PB had been successfully synthesized by mechanochemical synthesis. Thermogravimetric analysis, contact angle analysis, inductively coupled plasma atomic emission spectrometry, elemental analysis, and electrophoretic light scattering spectrophotometry confirmed that several defects were formed, explaining the principal mechanism for the efficient adsorption over PB prepared by mechanochemical synthesis. The superior adsorption properties toward Cs(I) make PB prepared by mechanochemical synthesis an attractive candidate material for the efficient, economical, and eco-friendly processes for purifying radioactive wastewater.

Enhancement of tensile toughness of poly(lactic acid) (PLA) through blending of a polydecalactone-grafted cellulose copolymer: The effect of mesophase transition on mechanical properties.

Increasing the toughness of poly(lactic acid) (PLA), i.e., simultaneously increasing both the tensile strength and ductility, remains a major challenge. In this study, fully bio-based PLA blends with polydecalactone (PDL)-grafted cellulose copolymer (CgPD) were prepared and comprehensively analyzed to enhance the toughness of the PLA matrix. The blends were found by FT-IR and solid-state 1H NMR to be physically intact and miscible at the sub-twenty-nanometer scale. The WXRD and DSC analyses indicated that the addition of the alkyl-branched CgPD imparts a more structurally disordered PLA mesophase state to the prepared PLA_CgPD bio-blends. UTM analysis was used to characterize the macroscopic mechanical properties of the PLA_CgPD bio-blends. Both the tensile strength and elongation properties were simultaneously improved with the addition of 1 wt% CgPD loading amount to PLA (PLA_CgPD1). This study experimentally demonstrates that the enhanced mechanical properties of PLA_CgPD1 are closely related to the existence of more ordered PLA mesophases induced by the introduction of an optimal amount of CgPD into the PLA matrix.

Remarkable thermoplasticity of branched cellulose copolymers: Graft-chain-dependent structural transition and thermoplasticity.

In this study, we designed novel methods to prepare a cellulose graft copolymer series (Cell-g-PDLs) with varied graft chain lengths, via direct ring-opening polymerization (ROP) of unmodified cellulose with alkyl-branched lactones. With increasing alkyl-branched graft chain length of the Cell-g-PDLs, the crystalline phase of cellulose became increasingly weakened, while the glass transition temperature significantly decreased. The latter was attributed to the extended free volume derived from the increased chain end-group concentrations of the branched graft chains. These results suggested that the incorporation of a highly alkyl-branched graft chain into unmodified cellulose is an effective way to improve its thermo-plasticity. Notably, the Cell-g-PDL with the longest graft chain (Cell-g-PDL9) was demonstrative of highly sufficient thermo-plasticity, owing to the enhanced molecular mobility resulting from the reduced frictional forces between the cellulose molecules.

Iron-induced cyclodextrin self-assembly into size-controllable nanospheres.

Iron-induced self-assembly of beta-cyclodextrin, beta-CD, into size controllable nanospheres with a well-defined spherical morphology and a relatively narrow size distribution was formed when acetone was added to a solution of beta-CD with iron(II) acetate, Fe(OAc)(2), in DMF. Thermogravimetric analysis, inductively coupled plasma atomic emission spectroscopy, and high resolution transmission electron microscopy showed that the irons were present as a well-dispersed state in the beta-CD nanospheres. In the (1)H NMR spectrum of the beta-CD/Fe(OAc)(2), beta/Fe, solution before adding acetone, the peaks corresponding to beta-CD were broadened and their spin-spin splitting had disappeared. In particular, the beta/Fe solutions were found to remain in a clean solution state at 1 week after solution preparation. These findings indicate the isolation of individual iron ions caused by the surrounding of each ion with the beta-CD molecules in the solution before the addition of acetone. X-ray crystal structure analysis, morphological observations, and N(2) adsorption and desorption experiments showed that the beta-CD nanospheres were generated by the formation of iron-embedded beta-CD primary particles with disordered cage type structure and simultaneous spherical assembly of the primary particles during the addition of acetone to the beta/Fe solution with appropriate mole ratio between beta-CD and Fe(OAc)(2). Interestingly, the size of the beta-CD nanospheres could be simply controlled by changing the speed at which acetone was added to the solution, with higher acetone addition speeds yielding smaller particles.

Manganese oxides with hierarchical structures derived from coordination polymers and their enhanced catalytic activity at low temperature for selective catalytic reduction of NOx.

Hierarchical manganese oxides with enhanced catalytic performance have been successfully synthesized via simple thermal annealing of manganese coordination polymer precursors, which is a facile, cost-effective, and environmentally benign preparation method. The resultant manganese oxide particles formed hierarchical structures with a starfish-like morphology and exhibited enhanced low-temperature SCR performance below 200 °C without dopants or supporting materials. In addition, the morphology, chemical states, crystal structure and acidity of manganese oxide catalysts prepared at different calcination temperatures were investigated. It is elucidated that enhanced SCR catalytic performance was strongly dependent on the hierarchical morphology of the catalysts.

Mn-Doped Maghemite (γ-Fe2O3) from Metal-Organic Framework Accompanying Redox Reaction in a Bimetallic System: The Structural Phase Transitions and Catalytic Activity toward NOx Removal.

Mn-doped maghemite (γ-Fe2O3) particles were generated from a binary metal (Fe,Mn)-based metal-organic framework (MOF) via thermal decomposition under air. The X-ray photoelectron spectroscopy analysis revealed that the synthesis of Fe/Mn-MOF accompanied the reduction of the metal ions. The existence of Mn ions in this synthetic process leads to thermally stable maghemite particles under air. A temperature-induced structural phase transition from γ-Fe2O3 to α-Fe2O3 was observed through a mixed phase with another structure. Mn-doped γ-Fe2O3 and α-Fe2O3 exhibit superparamagnetic behavior. The sample annealed at 600 °C showed a mixed magnetic hysteresis loop indicating the existence of an intermediate structural phase between γ-Fe2O3 and α-Fe2O3 during the phase conversion from FeMn-MOF. The constructed Mn-doped iron oxides are active toward reducing nitric oxide with NH3. The NO conversion is 97% over Mn-doped γ-Fe2O3 calcined at 320 °C.

Ionic cluster size distributions of swollen nafion/sulfated beta-cyclodextrin membranes characterized by nuclear magnetic resonance cryoporometry.

Nafion/sb-CD membranes were prepared by mixing 5 wt% Nafion solution with H+-form sulfated beta-cyclodextrin (sb-CD), and their water uptakes, ion exchange capacities (IECs), and ionic cluster size distributions were measured. Gravimetric and thermogravimetric measurements showed that the water uptake of the membranes increased with increases in their sb-CD content. The IECs of the membrane were measured with acid-base titration and found to increase with increases in the sb-CD content, reaching 0.96 mequiv/g for NC5 ("NCx" denotes a Nafion/sb-CD composite membrane containing x wt% of sb-CD). The cluster-correlation peaks and ionic cluster size distributions of the water-swollen membranes were determined using small-angle X-ray scattering (SAXS) and 1H nuclear magnetic resonance (NMR) cryoporometry, respectively. The SAXS experiments confirmed that increases in the sb-CD content of the membranes shifted the maximum SAXS peaks to lower angles, indicating an increase in the cluster correlation peak. NMR cryoporometry is based on the theory of the melting point depression, Delta Tm, of a liquid confined within a pore, which is dependent on the pore diameter. The melting point depression was determined by analyzing the variation of the NMR signal intensity with temperature. Our analysis of the intensity-temperature (IT) curves showed that the ionic cluster size distribution gradually became broader with increases in the membrane sb-CD content due to the increased water content, indicating an increase in the ionic cluster size. This result indicates that the presence of sb-CD with its many sulfonic acid sites in the Nafion membranes results in increases in the ionic cluster size as well as in the water uptake and the IEC. We conclude that NMR cryoporometry provides a method for determining the ionic cluster size on the nanometer scale in an aqueous environment, which cannot be obtained using other methods.

Synthesis and photocatalytic activity of mesoporous TiO(2) with the surface area, crystallite size, and pore size.

Mesoporous TiO(2) materials with various pore-size distributions were synthesized by using diblock copolymers via a sol-gel process in aqueous solution. The properties of these materials were characterized by FE-SEM, HR-TEM, XRD, DRS, BET, and BJH analysis. All particles have spherical morphology with a diameter range of 1-3 mum. The mesoporous TiO(2) materials calcined at 400 degrees C were found to have different specific surface areas - 186, 210, and 192 m(2) g(-1) - and average pore sizes depending on the type of diblock copolymer-5.1, 6.1, and 6.4 nm-and their crystallite sizes were found to be 8.1, 8.3, and 8.8 nm. The photocatalytic activity of each sample was investigated by measuring the photodecomposition of methylene blue (MB), and the small crystallite size, large surface area, and small pore size were found to exhibit better photocatalytic activities. In addition, the photocatalytic activities of all the mesoporous TiO(2) materials were found to be better than that of commercial TiO(2).

Flexible Poly(vinyl chloride) Nanocomposites Reinforced with Hyperbranched Polyglycerol-Functionalized Graphene Oxide for Enhanced Gas Barrier Performance.

Herein, we describe the preparation of flexible poly(vinyl chloride) (PVC) containing hyperbranched polyglycerol (HPG)-functionalized graphene oxide (HGO) as a reinforcing filler and reveal that the obtained composites exhibit greatly improved gas barrier properties. Moreover, we show that HGO, synthesized by surface-initiated ring-opening polymerization of glycidol followed by esterification with butyric anhydride, exists as individual exfoliated nanosheets possessing abundant functional groups capable of interacting with PVC. A comparative study of butyl-terminated graphene oxide (BGO) reveals that functionalization with HPG is of key importance for achieving a uniform dispersion of HGO in the PVC matrix and results in strong interfacial interactions between HGO and PVC. As a result, flexible PVC/HGO nanocomposite films exhibit significantly enhanced tensile strength and toughness compared to those of neat plasticized PVC while maintaining its inherent stretchability. Furthermore, the two-dimensional planar structure and homogeneous distribution of HGO in PVC/HGO nanocomposites make gas molecules follow a highly tortuous path, resulting in remarkably reduced oxygen permeability, which is more than 60% lower than that of neat plasticized PVC. Consequently, HGO is demonstrated to be promising component of flexible and gas-impermeable PVC films for a wide range of applications.