Porous Cellulose Acetate Membranes Research Articles

Influence of citric acid concentrations on the porosity and performance of cellulose acetate-based porous membranes: A comprehensive study

This study investigates the influence of citric acid concentration on the fabrication of porous cellulose acetate (CA) membranes using the Non-Solvent Induced Phase Separation (NIPS) method. A notable aspect is the precise control over membrane properties, particularly pore size and porosity, achieved solely through the adjustment of citric acid concentration, serving as the additive. Higher concentrations of citric acid increase pore size by rendering polymer chains more pliable, whereas lower concentrations lead to smaller, denser pores due to improved dispersion in the CA matrix and altered water interactions during phase separation. A decrease in porosity and Gurley values with reducing citric acid concentrations (from 5 × 10−2 to 1 × 10−3 M ratios) indicates less plasticization of CA chains. However, at very low concentrations (1 × 10−4 and 1 × 10−5), porosity increases, despite the presence of smaller pores, and Gurley values approach those of pure CA in terms of gas permeability. Fourier Transform Infrared (FT-IR) spectroscopy confirms the presence of citric acid and its interaction with carbonyl groups, consistent with the pore size observations from Scanning Electron Microscopy (SEM). Spectral data deconvolution reveals weakened carbonyl bonds due to the reduced presence of citric acid, correlating with the smaller pores observed in SEM. Thermal Gravimetric Analysis (TGA) demonstrates that composite membranes are more thermally stable than pure CA, attributed to the citric acid-induced crosslinking within the polymer chains. Stability increases with decreasing citric acid concentration, with some anomalies at the lowest levels. In conclusion, this study highlights the capability of adjusting citric acid concentration to tailor membrane properties, offering valuable insights for the creation of porous materials across diverse industrial applications.

A combination of nonsolvent and thermally induced phase separation (N-TIPS) technique for the preparation of highly porous cellulose acetate membrane as lithium-ion battery separators

A combination of nonsolvent and thermally induced phase separation (N-TIPS) technique for the preparation of highly porous cellulose acetate membrane as lithium-ion battery separators

Gap Confinement Effect of a Tandem Nanochannel System and Its Application in Salinity Gradient Power Generation.

As an important nanofluidic device, an artificial ion nanochannel could selectively transport ions inside its nanoconfinement space and the surface charge of the pore wall. Here, confinement effects were realized by tandem nanochannel units, which kept their cascade gaps less than 500 nm. Within these gaps, ionic conductance was governed by the surface charge density of the channel unit. Cations could be sufficiently selected and enriched within this confined space, which improves the cation transfer number of the system. Therefore, the tandem nanochannel system could greatly improve the diffusion potential and energy conversion efficiency in the salinity gradient power generation process. Poisson-Nernst-Planck equations were introduced to numerically simulate the ionic transport behavior and confirmed the experimental results. Finally, the gap confinement effect was introduced in the porous cellulose acetate membrane tandem nanochannel system, and a high output power density of 4.72 W/m2 and energy conversion efficiency of 42.22% were achieved under stacking seven channel units.

Processes to enhance the sensitivity of sensor for 2‐n‐octyl‐4‐isothiazolin‐3‐one as biocide

AbstractIn this study, hydraulic treatment was performed to fabricate porous cellulose acetate (CA) membranes for application as adsorbents for impurities. For this purpose, porous CA membranes were prepared by applying a water pressure of 8 bar on CA dissolved in a mixed solvent of acetone and water. These porous polymers could separate impurities from 2‐n‐octyl‐4‐isothiazolin‐3‐one (OIT) by providing adsorption surfaces for the suspended impurities and allowed pure OIT to filter through the membrane; the filtered OIT may subsequently be used for octyl‐group quantification. After impurity adsorption, the degree of OIT permeation in the CA membrane and the adsorption mechanism of CA were investigated by Fourier transform infrared spectroscopy and water‐adsorption studies. Further, we analyzed the porous characteristics and behavior of CA by scanning electron microscopy and conducted thermogravimetric analysis to observe the physical and chemical changes occurring in the polymers.

Moist-Induced Electricity Generation by Electrospun Cellulose Acetate Membranes with Optimized Porous Structures.

Harvesting energy from moist in the atmosphere has recently been demonstrated as an effective manner for a portable power supply to meet the ever-increasing demands of energy consumption. Porous materials are shown to have great potential in moist-induced electricity generation. Herein, we report moist-induced electricity generation by electrospun cellulose acetate (CA) membranes with optimized porous structures. We show that the pore size and porosity of CA membranes can be readily tuned via a facile compression and annealing process, and the effect of pore features on the output voltages can thus be investigated systematically. We find that, at a relatively high porosity, the electricity-generation performance can be further enhanced by constructing a smaller pore to form more nanochannels. Porous CA membranes, with an optimized porosity of 52.6% and a pore diameter less than 250 nm, are prepared to construct moist-induced electricity generators, which can be applied as breath sensors and can power up calculator operation. The current study provides insights for the construction of porous materials with different pore characteristics for moist-induced electricity generation, especially in the exploration of more efficient and low-cost porous materials for large-scale practical application of the portable power supply.

Porous cellulose acetate membranes prepared by water pressure-assisted process for water-treatment

We fabricated membranes by adding the inorganic additive, Ni(NO3)2∙6H2O, to cellulose acetate (CA) polymer. When subjected to water pressure, the polymer chain was weakened by the plasticizing effect of Ni(NO3)2∙6H2O contained in the CA. The water pressure was varied by applying a range of distilled water pressure from 0 to 10bar and well-formed pores were confirmed by SEM images. When water-pressure was applied for pore-generation, the flux of distilled water was about 50LMH at a maximum pressure of 8bar. In addition, the water treatment performance in terms of separation of a 200ppm sodium alginate solution was 75% or more for all the membranes prepared, from 3 to 10bar; the maximum salt rejection was 89% at 7bar. The physical and chemical properties of the membranes were investigated using TGA and FT-IR. The porosity of the membrane was also confirmed using a porosimeter.

Rapid Production of a Porous Cellulose Acetate Membrane for Water Filtration using Readily Available Chemicals

A chemistry laboratory experiment using everyday items and readily available chemicals is described to introduce advanced high school students and undergraduate college students to porous polymer membranes. In a three-step manufacturing process, a membrane is produced at room temperature. The filtration principle of the membrane is then illustrated by filtering solutions containing pigmentary watercolor or food coloring. A comparison of the filtration results shows that insoluble watercolor pigments are too large to pass the pores of the membrane and are successfully rejected by the membrane, whereas the food coloring is completely soluble in water and easily passes the membrane. The laboratory experiment can be performed in a 2 h activity and serves the purpose of (1) exposing students to a new and interesting field of material science. It (2) makes them familiar with porous membranes for the production of safe drinking water and (3) introduces them to a template-removal technique utilizing acid/base the...

공유결합으로 다공성 막에 고정화된 PLD에 의한 포스퍼티딕산 생산

Phospholipase D (PLD) was immobilized on a submicro-porous membrane through covalent immobilization. The immobilization was conducted on the porous membrane surface with the treatment of polyethyleneimine, glutaraldehyde, and the anhydrase, in sequence. The immobilization was confirmed using X-ray photon spectrometer. The pH values of phosphatidylcholine (PC) dispersion solution with buffer were monitored with respect to time to calculate the catalytic activities of PC for free and immobilized PLD. The catalytic rate constant values for free PLD, immobilized PLD on polystyrene nanoparticles, and im- mobilized PLD on a porous cellulose acetate membrane were 0.75, 0.64, and 0.52 s -1 , respectively. Reusability was studied up to 10 cycles of PC hydrolysis. The activity for the PLD immobilized on the membrane was kept to 95% after 10 cycles, and com- parable to the PLD on the nanoparticles. The stabilities for heat and storage were also investigated for the three cases. The results suggested that the PLD immobilized on the membrane had the least loss rate of the activity compared to the others. From these studies, the porous membrane was feasible as a carrier for the PLD immobilization in the production of phosphatidic acid.

Preparation of Saccharide Exchange Membrane Modified by Phenylboronic Acid Azoprobe/Polyamidoamine (PAMAM) Dendrimer

Phenylboronic acid azoprobe (B-Azo-Cb) for saccharide recognition was synthesized. B-Azo-Cb/polyamidoamine (PAMAM) complex was synthesized by the condensation reaction of terminal carboxylic group of B-Azo-Cb and surface amine of PAMAM dendrimer. Thin porous cellulose acetate membrane embedded with B-Azo-Cb/PAMAM dendrimer complex was prepared from cellulose acetate, formamide, acetone, and B-Azo-Cb/PAMAM dendrimer complex by casting on the glass plate at various temperatures. The saccharide transportability was evaluated by measuring the amount of saccharide in receiving solution. The amount of saccharide transport of porous cellulose acetate membrane embedded with B-Azo-Cb/PAMAM dendrimer complex was higher at low temperature-treated membrane, and low pH of receiving solution. In contrast, the saccharide transportabilities through non-treated cellulose acetate membrane were the same at any pH of receiving solution. Saccharide transportability was in the order of galactose > glucose > fructose (B-Azo-Cb/PAMAM G4 modified membrane), and glucose > galactose > fructose (B-Azo-Cb/PAMAM G5 modified membrane). These orders were the same of the saccharide response in solution. These results indicated that the saccharide transport of B-Azo-Cb/PAMAM-embedded membrane is successfully mediated by the phenylboronic acid.

공유결합으로 다공성 막에 고정화된 효소에 의한 이산화탄소 포집

Bovine Carbonic anhydrase (BCA) was immobilized on a submicro-porous membrane through covalent immobilization. The immobilization was conducted on the porous membrane surface with the treatment of polyethyleneimine, glutaraldehyde, and the anhydrase, in sequence. The immobilization was confirmed using X-ray photon spectrometer. The pH values of carbon-dioxide saturated solution with buffer were monitored with respect to time to calculate the catalytic activities of hydration of carbon-dioxide for free and immobilized CA. The catalytic rate constant values for free CA, immobilized CA on polystyrene nanoparticles, and immobilized CA on a porous cellulose acetate membrane were 0.79, 0.67, and 0.56 <TEX>$s^{-1}$</TEX>, respectively. Reusability was studied up to 10 cycles of <TEX>$CO_2$</TEX> sequestration. The activity for the CA immobilized on the membrane was kept to 95% after 10 cycles, and comparable to the CA on the nanoparticles. The stabilities for heat and storage were also investigated for the three cases. The results suggested that the CA immobilized the membrane had the least loss rate of the activity compared to the others. From this study, the porous membrane was feasible as a carrier for the CA immobilization in hydration and sequestration of carbon-dioxide.

Concentration of Bio-Ethanol through Cellulose Ester Membranes during Temperature-Difference Controlled Evapomeation

To evaluate the high-performance of membrane materials in the concentration of an aqueous solution of dilute bioethanol under temperature-difference controlled evapomeation (TDEV), asymmetric porous cellulose nitrate (CN) and cellulose acetate (CA) membranes were prepared by a phase inversion method. In the concentration of dilute ethanol under TDEV, these membranes showed a high permeation rate and high ethanol/water selectivity. In membranes with almost the similar pore size, the ethanol/water selectivity was considerably higher for the CN membrane than the corresponding CA membrane. This result suggested that the affinity between the membrane material and the permeant is an important factor in the separation selectivity.

Preparation and study of cellulose acetate membranes modified with linear polymers covalently bonded to Starburst polyamidoamine dendrimers

AbstractNovel ion‐selective membranes were prepared by means of the noncovalent modification of a cellulose acetate (CA) polymer with either poly(ethylene‐alt‐maleic anhydride) or poly(allylamine hydrochloride) chains covalently linked to Starburst amine‐terminated polyamidoamine (PAMAM) dendrimers generations 4 and 3.5, respectively. Linear polymer incorporation within the porous CA membrane was performed with mechanical forces, which resulted in modified substrates susceptible to covalent adsorption of the relevant dendritic materials via the formation of amide bonds with a carbodiimide activation agent. The membranes thus prepared were characterized by chemical, physical, and spectroscopic measurements, and the results indicate that the dendrimer peripheral functional groups were the species that participated in the ion‐exchange events. The prepared materials were also evaluated for their ion‐exchange permeability with sampled current voltammetry experiments involving cationic and anionic species {[Ru(NH3)6]3+ and [Fe(CN6)]3−, respectively} as redox probe molecules under different pH conditions. As expected, although permeability was favored by opposite charges between the dendrimer and the electroactive probe, a clear blocking effect took place when the charge in the dendritic polymer and the electroactive complex was the same. Electrochemical impedance spectroscopy measurements, on the other hand, showed that the PAMAM‐modified membranes were characterized by good selectivity and low resistance values for multivalent ions compared to a couple of commercial ion‐exchange membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Adsorption and Surface Properties of Vladipor Cellulose Acetate and Polysulfonamide Membranes

Surface and adsorption characteristics of porous cellulose acetate (UAM) and polysulfonamide (UPM) membranes with pore diameters from 0.015 to 0.1 µm are compared. The specific surface areas of UPM membranes are 130 and 150 cm2/cm2, whereas those of UAM membranes vary from 80 to 360 cm2/cm2 of the membrane area. The density of negative charges on the pore surface is 5 × 10− 8 and about 20 × 10−8 C/cm2 for UAM and UPM membranes, respectively. The adsorption of basic and acidic substances, proteins (cytochrome C and ovalbumin) and dyes (rhodamine 6G and Acid Orange), from aqueous solutions is studied. Far stronger hydrophobic interactions are observed for the UPM than for UAM membranes. The adsorption of basic substances is markedly higher than that of acidic substances because of acidic properties of the membrane surface. The distribution constants for the adsorption of Acid Orange and cytochrome C on the UPM membrane with a pore diameter of 0.1 µm are 50- and 100-fold higher than for the UAM membrane of the same pore diameter and specific surface area.

Permeation rates of low molecular weight gases through a plasma synthesized allyl alcohol membrane

Gas separation membranes were produced from the pulsed plasma deposition of poly(allyl alcohol). It was discovered that only low duty cycle, pulsed plasma deposition (1 ms on/30 ms off, 300 W peak power) produced membranes of sufficient uniformity to permit permeation studies. The membranes, deposited on porous ceramic filters, were found to permeate common gases through a combination of porous flow and the flow of adsorbed gases on the inner surface of the pores. The degree of surface transport was correlated with the critical temperature of the gas under test. The amount of surface transport for all gases tested increased strongly with applied pressure. The poly(allyl alcohol) films were compared with published data for porous cellulose acetate membranes; it was found that the poly(allyl alcohol) membranes had greatly enhanced surface transport compared to the cellulose acetate membranes.

Porous cellulose acetate membrane prepared by thermally induced phase separation

AbstractMicroporous cellulose acetate membranes were prepared by a thermally induced phase separation (TIPS) process. Two kinds of cellulose acetate with acetyl content of 51 and 55 mol % and two kinds of diluents, such as 2‐methyl‐2,4‐pentandiol and 2‐ethyl‐1,3‐hexanediol, were used. In all polymer‐diluent systems, cloud points were observed, which indicated that liquid–liquid phase separation occurred during the TIPS process. The growth of droplets formed after the phase separation was followed using three cooling conditions. The obtained pore structure was isotropic, that is, the pore size did not vary across the membrane. In addition, no macrovoids were formed. These pore structures were in contrast with those usually obtained by the immersion precipitation method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3951–3955, 2003

Effect of organic solvents on membrane formation by phase separation with supercritical CO 2

Porous cellulose acetate membranes were prepared by phase separation with supercritical CO 2 as a non-solvent. Four kinds of organic solvents were used and the effect of the solvent on the membrane structure was investigated. As the mutual affinity between solvent and supercritical CO 2 decreased, the membrane porosity and the average pore size near the center position increased. In all cases, macrovoid was not formed, although the phase separation occurred instantaneously after CO 2 was introduced. The membrane performances such as solute rejection coefficient and water permeability were measured for the obtained porous membrane.

Chemical Modification of Cellulose Acetate with Titanium Isopropoxide

This study describes the chemical modification of cellulose acetate (CA) using titanium isopropoxide (TiP) in a sol-gel process for the formation of an organic/inorganic hybrid (OIH) material. The hydrolysis and condensation reactions that characterize this process result in CA cross-linking and formation of inorganic oxide particles. TiP-modified CA gels and membrane materials are characterized by solubility and swelling measurements, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC) and ultrasonic time-domain reflectometry. Whereas the solubility of the CA significantly decreased with increasing TiP exposure consistent with high levels of cross-linking, unambiguous spectroscopic evidence for cross-linking could not be determined. In addition, DSC measurements indicated no significant change in CA glass-transition temperature as a function of TiP exposure. On the other hand, TiP treatment dramatically improved the creep behavior of treated porous CA membranes, whereby the total compressive strain decreases by as much as 70% relative to the untreated materials. Overall, the results suggest that TiP treatment can be used as a post-fabrication processing step to create OIH-modified CA membranes with improved chemical and mechanical stability.

Preparation and Characterization of Novel Weak Amphoteric Charged Membrane Containing Cysteine Residues

Novel weak amphoteric charged membranes having cysteine residues were prepared. Cysteine (Cys) is one of the amino acids and has an amphoteric ion pair, which consists of an amino group and a carboxyl group. The poly(ethylene glycol) derivatives, with cysteine residues added to their side chains (PEG–Cys), were graft-polymerized onto a porous cellulose acetate (CA) membrane. The zeta potential was measured using a streaming potential method at various pH values ranging from 2.5 to 10 to investigate the behavior of the charge groups on the pore surface of these membranes. The zeta potential of this PEG–Cys-grafted membrane was pH-dependent, and the zeta potential/pH profile showed a plateau which was characteristic of an amphoteric ion pair in the range pH 4/9. The apparent surface charge density on these membranes was obtained from the zeta potential. The experimental results could be well explained by a calculated value using a site dissociation model including the contribution of not only the amphoteric ion pairs on the grafted polymer chains but also the negative charge groups originating from the base CA membrane.

Measurements of self-diffusion coefficients of water in porous membranes by PFG-NMR

Self-diffusion coefficients of water in inhomogeneous materials — porous cellulose acetate membranes (MF: average pore sizes 0.025, 0.8 and 8.0 μm) and ceramic membrane (CM: average pore size 4.4 μm) — were measured as a function of diffusion time using PFG-NMR. The relationship between the water diffusion coefficient and the membrane structure, as determined by SEM, was examined. The magnitude of the water diffusion coefficient is in the order of MF8 > MF0.8 > CM > MF0.025. These were well explained by the restricted diffusion theory of Tanner. According to this theory, the diffusion coefficients depend on the pore size and thickness of the membrane matrix. Results show that the decrease in the diffusion coefficient is affected not only by a decrease in the pore diameter but also by an increase in the membrane matrix size.

Preconcentration of quinolones by dialysis on-line coupled to high-performance liquid chromatography

The parameters influencing dialytic separation of ciprofloxacin (CF) fluoroquinolone were investigated. Dialysis with a porous cellulose acetate membrane was on-line coupled with HPLC and the analysis of dialysate was made by isocratic ion-pairing liquid chromatography using a reversed-phase analytical column and fluorescence detection. Optimisation of the experimental conditions for selective dialytic enrichment are described and explanations of some phenomena affecting dialysis efficiency discussed. By the use of a neutral donor (pH≈7) and acidic acceptor solution (pH<4) a substantial enrichment of quinolones was achieved. Accumulation of CF in the acidic acceptor phase is based on the protonation of the analyte in the acceptor compartment. Continuous-flow of donor solution and a stagnant acceptor solution gave high dialysis efficiency in 5–15 min. Effects of interfering substances present in real samples on the variation of dialysis efficiency can be minimised by successive dialysis runs of the original and spiked samples.