Coverage Of Pores Research Articles

Tuning charge density in tethered electrolyte active-layer membranes for enhanced ion-ion selectivity

Efforts toward developing membranes for aqueous separations beyond desalination have intensified, in attempts to achieve zero liquid discharge and a circular economy. Treatment of unconventional wastewaters and brines as well as recovery of valuable species require separation of solutes and ions. Recently, tethered electrolyte active-layer membranes (TEAMs) with dense ionizable brush polymers grafted from cellulose ultrafiltration supports were introduced as a robust, highly controllable membrane platform for these aqueous separations. In this study, we investigate crosslinking of single-block TEAMs to increase the effective charge density and coverage of pores by the active layer, and to possibly tap into size-based exclusion mechanisms. We also determine if crosslinking multiblock TEAMs comprising block copolymers of both negative and positive charge can better align blocks, thereby improving ion rejection. Single-block TEAMs with relatively short crosslinkers proved to have the highest divalent co-ion rejection in dilute solutions, at ∼85–95%. NaCl was rejected ∼55 and 80% by crosslinked negatively- and positively-charged TEAMs, respectively. Anion monovalent selectivity, Cl−/SO42−, was as high as ∼25 for negative TEAMs, while the maximum Na+/Ca2+ ratio achieved by positive TEAMs was ∼9.5. This work reinforces the value of ultrathin brush active-layer membranes and TEAMs as important tools to understand fundamental transport through membranes and better control synthesis for targeted selectivity.

Investigation on the lead adsorption capacity of Iranian natural zeolite: modifications, structural effects, adsorption isotherms, kinetics, and mechanism studies

ABSTRACT Clinoptilolite (NZ) as a natural and cost-effective adsorbent, modified with two different methods. At the first stage, by sodium chloride solution to obtain NaCl-modified natural zeolite (NaCl-MNZ), then sodium dodecyl sulfate (SDS) was used to modify NaCl-MNZ (SDS-MNZ). Along with NZ, NaCl-MNZ, and SDS-MNZ, commercial NaY zeolite was also used for removing lead cations from synthesized wastewater. The adsorption of SDS molecules on the outer surface of zeolite was confirmed by FTIR and the specific surface area of the SDS-MNZ was decreased due to the coverage of smaller pores by anionic surfactant molecules. The zeta potential measurements also revealed that the modification process has decreased the surface charge of the zeolite significantly, which was favorable for the adsorption of Pb2+ cations and improved clinoptilolite performance. The non-linear adsorption kinetics and isotherms are best described by the pseudo-first-order and Sips model, respectively. The maximum adsorption capacity of lead ions were 25.8435, 39.5992, 38.5454, and 101.0240 (mg/g) for NZ, NaCl-MNZ and SDS-MNZ and NaY, respectively. The results indicated that the adsorption capacity of natural zeolites modified with NaCl and SDS were approximately 35% and 33% higher than that of the clinoptilolite alone.

Effects of open pores on grinding performance of porous metal-bonded aggregated cBN wheels during grinding Ti–6Al–4V alloys

Porous metal-bonded wheels coupled with the aggregated cubic boron nitride (cBN) grains and water-soluble carbamide particles as pore-forming agents were fabricated, aiming to the improvement of grinding wheel performance and ground surface quality in grinding of Ti–6Al–4V alloys. Grinding forces and force ratio, ground surface roughness and microhardness were investigated to evaluate wheel performance. In addition, the wear evolutions of cBN grains and macropores were performed as the material removal volume increases during wheel wear tests. Findings show that the dynamic changing behavior of the coverage and exposure of open pores attributes to the improvement of grinding performance and ground surface quality of porous AcBN wheels. Meanwhile, the promising self-sharpening property of wheels can be guaranteed in basis of dynamic wear variations of multiple cBN abrasive grains layer by layer.

Investigation of slagging characteristics and anti-slagging applications for Indonesian coal gasification

The phase diagram characteristics of Indonesian coal ash were studied with thermodynamic equilibrium calculations and the Na2O-Al2O3-SiO2 ternary system. Baikuang coal was selected as the blended coal, and the blending ratio was optimized. Gasification experiments were carried out in a horizontal tube furnace system; the microstructure, mineral crystalline phases and chemical compositions of residues were analyzed; and the retention ratios of sodium and potassium were calculated. The particles underwent three stages, namely, (1) internal crushing and quick pore growth, (2) the formation of dense layers on the surface, and (3) the coverage and blockage of pores. These three stages corresponded to the release of the internal gas phases, the formation of silicates and aluminosilicates, and the low-temperature co-melting with other metallic elements (Ca, Mg, Fe), respectively. The main crystalline phases in the residues were converted from SiO2 to NaAlSiO4. During the reaction, the chemical form of Na changed from H2O-soluble to insoluble and HCl-soluble. The gasification temperature had a pronounced effect on the sodium conversion rate and the conversion degree, and the retention ratio of sodium and potassium was significantly reduced as the temperature was increased. After coal blending, the slagging tendency was significantly alleviated, the peak of NaAlSiO4 decreased, and the crystal phase of mullite (3Al2O3·2SiO2) was determined. In addition, the sodium content in the ash was remarkably reduced. Adjusting the coal ash components by coal blending was an effective way to alleviate or even avoid slagging of Indonesian coal, and a mixing ratio of 25% was optimal.

Electrical conductivity and physiological comfort of silver coated cotton fabrics

The objective of present study was to develop multifunctional and wearable electrically conductive fabrics with acceptable comfort properties by in-situ deposition of silver particles. The effect of silver nitrate concentration and number of dips was investigated for change in electrical conductivity, EMI shielding, and antimicrobial properties of coated fabrics. The dynamic light scattering and SEM analysis were employed to study the morphology of deposited silver particles. The EMI shielding was found to increase with increase in concentration of silver particles. Later, the comfort and mechanical properties were studied. No significant decrease in air permeability and water vapor permeability was observed due to partial coverage of fabric pores by coating of silver particles. Moreover, the coated fabrics also showed promising behavior toward antimicrobial properties. When the durability of coated fabrics was examined against washing, the application of binder provided good retention of silver particles without loss of electrical conductivity of coated fabrics.

Antifouling enhancement of PVDF membrane tethered with polyampholyte hydrogel layers

The preparation and property of antifouling poly(vinylidene fluoride) (PVDF) membrane tethered with polyampholyte hydrogel layers were described in this work. In fabricating these membranes, the [2‐(methacryloyloxy)ethyl] trimethylammonium chloride and 2‐acrylamide‐2‐methyl propane sulfonic acid monomers were grafted onto the alkali‐treated PVDF membrane to yield polyampholyte hydrogel layers via radical copolymerization with N,N′‐methylenebisacrylamide as crosslinking agent. The analyses of fourier transform infrared attenuated total reflection spectroscopy and X‐ray photoelectron spectroscopy confirm the covalent immobilization of polyampholyte hydrogel layer on PVDF membrane surface. The grafting density of polyampholyte hydrogel layer increases with the crosslinking agent growing. Especially for the membrane with a high grafting density, a hydrogel layer can be observed obviously, which results in the complete coverage of membrane pores. Because of the hydrophilic characteristic of grafted layer, the modified membranes show much lower protein adsorption than pristine PVDF membrane. Cycle filtration tests indicate that both the reversible and irreversible membrane fouling is alleviated after the incorporation of polyampholyte hydrogel layer into the PVDF membrane. This work provides an effective pathway of covalently tethering hydrogel onto the hydrophobic membrane surface to achieve fouling resistance. POLYM. ENG. SCI., 55:1367–1373, 2015. © 2015 Society of Plastics Engineers

High Pt Utilization Electrodes for Polymer Electrolyte Membrane Fuel Cells by Dispersing Pt Particles Formed by a Preprecipitation Method on Carbon “Polished” with Polypyrrole

Pt utilization on carbon black (CB) has been significantly improved by initially utilizing polypyrrole (PPy) as a moiety to polish the carbon surface and subsequently by dispersing Pt particles formed by a preprecipitation process to minimize their migration into the geometrically restricted areas of the carbon surface. This process strategy has helped to significantly extend the triple-phase boundary as a greater number of Pt particles comes in direct contact with Nafion, leading to a substantial improvement in the overall catalyst utilization. Preliminary analyses such as IR, thermogravimetric analysis, and N 2 sorption confirmed the presence of PPy on the surface. Approximately 50% reduction in the surface area of CB after the controlled in situ polymerization of pyrrole monomer on the carbon surface indicated preferential filling and coverage of pores and other geometrically restricted pockets of carbon surface. On the other hand, by converting Pt into colloids in the preprecipitation method prior to their reduction, the platinum particles are forced to stay on the hybrid support; a major part of which otherwise would have been migrated into the surface pores and defect sites. Platinum particle size on these hybrid supports is 2 times higher than the catalyst prepared by polyol process. However, the electroactive surface area and mass activity are 2 times higher than that of the Pt particles prepared by polyol on hybrid material and are also significantly higher than that of the conventional electrocatalysts prepared by the polyol method. At 0.8 V, the kinetic current density (j k ) of Pt/C-PPy-Pre obtained from the Koutecky-Levich plot is 1.5 and 2.5 times higher than that of catalysts prepared by the polyol method on PPy-coated carbon and Vulcan XC-72 carbon, respectively. Almost 210 and 160 mW cm -2 improvement for the maximum power density, respectively with oxygen and air, was obtained with the modified system in comparison to the conventional system when the single cell evaluations were carried out at 60 °C with a Pt loading of 0.5 mg cm -2 in the anode and cathode sides. This enhancement in the cell performance under the two different oxygen partial pressure conditions clearly emphasizes the improved oxygen reduction reaction (ORR) and mass-transfer characteristics of the hybrid electrode material compared to the other catalysts.

Influence of particle size and antacid on release and stability of plasmid DNA from uniform PLGA microspheres

PLGA microspheres are attractive DNA delivery vehicles due to their controlled release capabilities. One major problem with PLGA microspheres is that they develop an acidic microclimate as the polymer degrades, lowering the intraparticle pH, and potentially damaging the DNA. Antacids have recently shown promise in buffering this acidic microclimate and enhancing protein stability. We manufactured uniform plasmid DNA-encapsulating PLGA microspheres of two sizes (47, 80 μm diameter) and antacid concentrations (0, 3% Mg(OH) 2). Microspheres with antacid had a homogeneous surface coverage of small pores, which resulted in a significant reduction of the burst effect. The 47 μm microspheres exhibited complete release of plasmid DNA over the course of two months. Incomplete release was observed from 80 μm spheres, though microspheres with 3% Mg(OH) 2 showed a higher cumulative release, suggesting that the antacid at least partially aids in increasing the stability of DNA. SEM was used to visualize the surface pore evolution and cross-sectional microsphere structure over time. Subsequent image analysis was used to quantify the increase of surface pore sizes. Cross-sectional images showed increasing internal degradation and erosion, which resulted in a hollowing-out of microspheres. Our studies show that the incorporation of antacid into the microsphere structure has potential in addressing some of the major problems associated with DNA encapsulation and release in PLGA microspheres.

Preparation of novel composite membranes: Reactive coating on microporous poly(ether imide) support membranes

Poly(ether imide) asymmetric membranes can be covalently functionalized with aminic modifiers. When poly(ethylene imine), i.e., a polyvalent high molecular weight modifier, is used, the functionalization is connected with the support membrane pore-filling in a very thin layer. The poly(ethylene imine) layer is, however, not stables at increased temperatures and does not fill completely large pores. The layer can be stabilized by crosslinking with oligomeric poly(ethylene glycol) diglycidyl ether (PEGDGE), but this does not improve the coverage of large pores. The poly(ethylene imine) functionalized membrane can be stabilized, however, by reactive coating with copolymers of methacrolein with 1-vinylpyrrolidone instead stabilization with PEGDGE with a coverage of the large pores. The copolymers having various ratios of both polymeric units were prepared by free radical polymerization. The methacrolein units of copolymers, which comprised predominantly 1-vinyl-2-pyrrolidone units, had aldehyde groups in a free reactive form. These aldehyde groups react readily with the amine groups of the poly(ethylene imine) layer, while 1-vinylpyrrolidone units render the coating hydrophilic. The membranes coated under optimal conditions had nanofiltration separation properties at high water fluxes. Good adhesion between the coating layer and the support membrane, which results from the covalent binding, should allow separations under harsh conditions.

Passivation of the calcite surface with phenylmalonate and benzylmalonate ions

We explored the affinity of calcite to adsorbed organic molecules as an approach to the conservation of cultural heritage built of marble and limestone. The utilization of phenylmalonic and benzylmalonic acids provided a hydrophobic adsorptive interface, adequate to prevent processes of aqueous weathering. Samples of marble powder (polycrystalline calcite) were impregnated with solutions of phenylmalonic and benzylmalonic acid at three concentrations ( 5 × 10 −2 , 5 × 10 −3 , and 5 × 10 −4 M ) and different pH values (6.00, 7.00, and 8.00). The surface charge of the calcite suspensions was determined by potentiometric measurements under equilibrium conditions at room temperature in aqueous solution of the dicarboxylic acids, in order to understand the influence of the electrokinetic potential in the surface association. The adsorbed amounts were determined by calculation of the thermodynamic equilibria of solutions. The presence of the organic interface on the mineral surface was corroborated by Raman spectroscopy and small-angle X-ray scattering (SAXS). The results indicate effective adsorption of both dicarboxylic acids as a function of the concentration and pH, and several other conditions that favors coulombic interaction, an absence of electrophoretic mobility or surface electroneutrality related to the solid surface potentials. The coverage of pores by dicarboxylic adsorbate modified the geometrical pore shape and the pore size distribution, filling all the pores of larger than 80 Å diameter, giving as a result a mesoporous structure. This change in the surface morphology by organic adsorbates constitutes a modification in the diffusional processes of the environment on the mineral surface.

Surface modification of graphite by coke coating for reduction of initial irreversible capacity in lithium secondary batteries

Surface modification of graphite to reduce the irreversible capacity loss during the first charging period of graphite anodes is described. For the surface modification, artificial graphite (Lonza KS44) is dispersed in a tetrahydrofuran/acetone solution which contains coal tar pitch. The solvent is then evaporated. The loaded pitch component is converted to coke by a heat treatment at 1000°C in argon atmosphere. The resulting coke-coated graphite has a smaller surface area than that of the pristine one. The reduction of surface area, which is due to the coverage of pores of <10 nm by the coke component, causes a decrease in the irreversible capacity on the first cycle. The extent of electrolyte decomposition, gas evolution and surface film growth is also less with the coke-coated graphite electrode.