Hydrolyzed Polyacrylonitrile Membrane Research Articles

Effects of polyacrylonitrile carboxylation on pore structure and performance of thermally crosslinked organic solvent nanofiltration membrane

In this work, polyacrylonitrile (PAN) membranes were hydrolyzed with NaOH solution, and then hydrolyzed PAN (HPAN) membranes were used to prepare organic solvent nanofiltration (OSN) membranes with thermal crosslinking method. The chemical structure and pore structure evolutions of membrane during hydrolysis and thermal crosslinking were systematically investigated. The influences of hydrolysis carboxylation on permeation performances of membranes were studied in detail. Benefiting from the carboxylic groups generated by hydrolysis reaction of nitrile groups, the cyclization reaction of HPAN molecular chains was more easily initiated by ionic mechanism at a lower temperature, and the pore structure fusion of thermally crosslinked membranes was effectively inhibited. The permeances of the thermally crosslinked membranes derived from HPAN membranes were greatly improved. Furthermore, the thermally crosslinked membrane showed stable OSN performance due to the generation of ladder structure during thermal crosslinking. Therefore, the OSN membranes prepared in this work have great potential for practical applications.

Hydrolyzed polyacrylonitrile UF-membrane for surface and TAP water treatment: Influence on DBPs formation and removal

The integration of pre-treatment methods with low pressure-driven ultrafiltration (UF) has been found effective for reducing the formation of disinfection by-products (DBPs) in drinking water. In this study, a low dose peroxone (H2O2/O3) assisted alkaline hydrolyzed polyacrylonitrile (HPAN) UF-membrane system was explored, to determine its performance efficiency against two dissolved organic matter (DOM) sources and TAP water, specifically focusing the formation and removal of regulated DBPs. Increased hydrophilicity, enhanced incorporation of carboxyl groups, and decreased surface porosity were observed for the PAN membrane as a function of increased hydrolysis time. Filtration experiments involving humic acid (HA) and samples of real DOM sources displayed a high flux recovery (>90%) with the HPAN membrane. The initial flux for the optimized HPAN was found to be twice than that of the NF-3 membrane, irrespective of the DOM source. However, a relatively comparable removal efficiency was observed for both HPAN and NF-3 membranes in terms of organic matter and DBPs formation potential. Additionally, the H2O2/O3-HPAN system significantly reduced the aromatic and fluorescent content of the DOM by upto 70–80%, as represented by the DOC, UV254 and parallel factor analysis (PARAFAC) components. The fluorescence ratio C1/C2 showed a relatively greater reduction for soil-derived organic matter (SOM) as compared to the Olympic Lake (OL) water. Post-chlorination was found highly effective for the degradation of the humic-like DOM component (C1) than that of the fulvic and protein-like components. Moreover, the integration of H2O2/O3 with HPAN was able to remove 80% of the THMs and HAAs formation for both OL and SOM samples, together with a comparable reduction in DBP cytotoxicity. Interestingly, the HPAN membrane by reducing the TAP water DBPs upto 50%, fulfills the criteria of USEPA maximum contaminant level for drinking water.

Photocatalytic self-cleaning membrane with polyaniline/NH2-MIL-125 heterojunction for highly oil-water/seawater separation and bacterial inactivation

Emulsified oils and microbial contaminations in water environments have posed huge risks to human health and ecological balance. In this work, we fabricated a polyaniline/NH2-MIL-125 (PANI/MIL) heterojunction decorated hydrolyzed polyacrylonitrile (HPAN) membrane with photocatalytic self-cleaning property for oil–water separation and bacterial inactivation. In which, PAN membrane was prepared by electrospinning and then HPAN membrane was obtained by alkaline hydrolysis. The photo-responsive PANI/MIL heterojunction was immobilized on HPAN membrane by vacuum-assisted assembly using protocatechuic acid (PCA) as the binder. The resultant PANI/MIL@HPAN composite membrane has a wettability of in-air superamphilicity and underwater superoleophobicity as well as surface nano-micro heterostructure. The composite membrane showed good separation efficiency (above 99.4%) and high flux (1446–3744 L m−2h−1) in a series of oil-in-water/seawater emulsions separation. In particular, the membrane can effectively deal with viscous oil fouling under visible light to achieve a desired flux recovery ratio (FRR) after separating crude oil from water, which was ascribed to the self-cleaning capacity originating from the surface coating photocatalyst. Meanwhile, the multifunctional composite membrane showed 100% photocatalytic inactivation efficiency against pathogenic Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus (6 log units) in water under visible light with low power intensity. The oil–water separation performance as well as photocatalytic inactivation efficiency of PANI/MIL@HPAN are superior to MIL@HPAN. The studies on the wettability, photothermal properties and photoelectric properties suggested that the coupling of conductive polymer PANI can simultaneously enhance the underwater superoleophobicity of the composite membrane, as well as improve the photocatalytic activity by creating a type II heterojunction to promote the separation of charge carriers and amplifying the photothermal effect, making the PANI/MIL@HPAN multifunctional membrane achieve the improved oil/water separation performance and antibacterial activity synergistically. This work provides a new strategy for developing effective self-cleaning membranes both toward oil/water separation and bacterial inactivation applications based on MIL metal–organic framework coupling with conductive polymers.

Brine desalination via pervaporation using kaolin-intercalated hydrolyzed polyacrylonitrile membranes

Polyacrylonitrile (PAN) has been mostly used as a base polymer for asymmetric membrane synthesis with the aim of pervaporation (PV) applications, since it has a superior hydrophilicity and the ability to become hydrolyzed with an alkaline solution. Nonetheless, PAN and hydrolyzed PAN membranes have shown moderate permeate fluxes along with a mechanical softness. In this study, we aimed to improve the PV performance by exploring the possible effect of the hydrolysis of a novel mixed matrix membrane based on PAN and kaolin. Specifically, 15% PAN was used as a dope solution along with varying concentrations (2, 5, 7, and 10%) of kaolin to synthesize mixed matrix membranes using a non-solvent-induced phase separation technique. The 2% kaolin addition maximized the hydrophilicity and water sorption capacity of the membrane by developing well-organized, deep channel structures with increased porosity, membrane thickness, and surface roughness. The tensile strength was also the highest with the 2% kaolin addition. Further hydrolysis of the 2% kaolin-embedded PAN caused an extra enhancement of its hydrophilicity with a decrease of pore size due to the amplified carboxylic group density. PV performance tests under different salt concentrations confirmed that the hydrolyzed PAN membrane with a 2% kaolin intercalation had an outstanding permeation flux of 82 kg m-2h−1 and 59 kg m-2h−1 as well as a salt rejection of 99.93% and 99.91% with a 3.5% and 10% NaCl solution, respectively, at a 65 °C feed temperature.

Separation and antifouling properties of hydrolyzed PAN hybrid membranes prepared via in-situ sol-gel SiO2 nanoparticles growth

In this work, a novel approach of hydrolysis followed by in-situ sol-gel of tetraethyl orthosilicate (TEOS) was developed to modify the polyacrylonitrile (PAN) porous membrane prepared via non-solvent induced phase separation technique for improved separation and antifouling properties. PAN/SiO2 hybrid membranes prepared using different contents of TEOS were characterized through ATR-FTIR, XPS, SEM, EDS, water contact angle measurement, cross-flow permeation test, static protein adsorption test and dynamic cross-flow protein fouling experiment. It was found that the sol-gel of TEOS took placed both on membrane surface and within membrane pore and the generated SiO2 particles affected both membrane surface and permeation properties through the roles of surface deposition and pore-filling, respectively. The in-situ sol-gel of TEOS could efficiently improve membrane separation property through tuning pore size and narrowing pore size distribution. Compared with the base and hydrolyzed PAN membranes of same water permeability, the PAN/SiO2 hybrid membrane exhibited a much lower molecular weight cut-off and thus enhanced rejection performance. Furthermore, both static protein adsorption and dynamic cross-flow fouling experiments with bovine serum albumin aqueous solution demonstrated that the surface deposition of SiO2 could appreciably improve membrane antifouling property through making membrane surface more hydrophilic, negatively charged and enriched with hydroxyl groups.

Ultrafiltration membrane for effective removal of chromium ions from potable water

The objective of the present work was to investigate the efficacy of indigenously developed polyacrylonitrile (PAN) based ultrafiltration (UF) membrane for chromium ions removal from potable water. The hydrolyzed PAN membranes effectively rejected chromium anions in the feed ranging from 250 ppb to 400 ppm and a rejection of ≥90% was achieved for pH ≥ 7 at low chromate concentration (≤25 ppm) in feed. The rejection mechanism of chromium ions was strongly dependent on Donnan exclusion principle, while size exclusion principle for UF did not play a major role on ions rejection. Feed pH played a vital role in changing porosity of membrane, which influenced the retention behavior of chromate ions. Cross-flow velocity, pressure did not play significant role for ions rejection at low feed concentration. However, at higher feed concentration (≥400 ppm), concentration polarization became important and it reduced the chromate rejection to 32% at low cross flow and high pressure. Donnan steric-partitioning pore and dielectric exclusion model (DSPM-DE) was applied to evaluate the chromate ions transport through PAN UF membrane as a function of flux by using optimized model parameters and the simulated data matched well with experimental results.

Branched and ionic β-Cyclodextrins multilayer assembling onto polyacrylonitrile membranes for removal and controlled release of triclosan

The present study summarizes the formation and characterization of multilayers of polyacrylonitrile (PAN) membranes with β-cyclodextrin derivatives in order to be potentially interesting for triclosan (TR) controlled delivery with antibacterial purposes, as well as, for the removal of TR from wastewater. With this object, cationic and anionic branched β-cyclodextrins (bβCDs) were incorporated by layer-by-layer (LbL) process onto previously synthesized and hydrolyzed PAN membranes. FTIR, XPS and labelling with fluoresceinamine (FA) let to study the formation and stability of the prepared multilayered systems. TR is a widely used antibacterial and antifungal agent with proven ability to inhibit bacterial growth that, however, recently has shown a potential toxicity. The ability of obtained bβCDs/PAN multilayered membranes to retain TR in water was evaluated by two different loading procedures. The delivery kinetic profile of TR from loaded membranes was also analyzed showing the maximum release in the first 24h.

Fabricating graphene oxide-based ultrathin hybrid membrane for pervaporation dehydration via layer-by-layer self-assembly driven by multiple interactions

Graphene oxide (GO)-based ultrathin hybrid membranes with thicknesses less than 115nm were fabricated via layer-by-layer (LbL) self-assembly driven by multiple interactions. Gelatin (GE) and GO were alternately deposited on hydrolyzed polyacrylonitrile (H-PAN) ultrafiltration membranes through electrostatic attraction, hydrogen bond, and hydrophobic interaction to obtain hybrid multilayer membranes. The incorporation of GO favored the coverage of nanopores on H-PAN membrane, which greatly reduced the required deposition cycles for acceptable permselectivity of membrane, and then simplified the membrane-fabrication procedure. Enhanced thermal stability of GE molecules was obtained for as-fabricated hybrid multilayer membranes compared with GE/H-PAN pristine membrane. In membrane separation experiments, the hybrid multilayer membrane achieved synchronous enhancement in permeation flux and separation factor for pervaporation dehydration of ethanol aqueous solution in comparison with GE/H-PAN pristine membrane. The pH value of 4.0 was determined as the optimal condition of self-assembly process in terms of separation performance. The optimized separation performance of hybrid multilayer membranes with the bilayer number 10.5 was obtained with the permeation flux of 2275g/m2h and water content in permeate of 98.7wt% under the conditions of 350K and water content in feed of 20wt%. Desirable operation stability was acquired in the long-term membrane separation experiment.

Polyacrylonitrile-based zwitterionic ultrafiltration membrane with improved anti-protein-fouling capacity

The adhesion of proteins to the surface and pores of ultrafiltration membrane is one of the most important causes of membrane fouling, consequently lead to deterioration of membrane performance. In the present study, a polyacrylonitrile (PAN)-based zwitterionic ultrafiltration membrane was developed to improve its anti-protein-fouling capacity. 3-Dimethylaminopropylamine was first grafted onto the hydrolyzed PAN membrane by activation. Subsequently, carboxylic zwitterions were produced on the membrane surface by quaternization with 3-bromopropionic acid. The zwitterionic membranes were rigorously characterized in terms of chemical composition, morphology, and surface properties indicating that the zwitterion could successfully be bonded onto the PAN membrane without having significant effects on the membrane morphology. The anti-protein-fouling properties of the membrane were tested using static protein adsorption and dynamic-filtration experiments. The experimental results show that, although the hydrophilicity of the zwitterionic membrane decreased, the flux recovery rate of the zwitterion-grafted membrane was much higher than that of the hydrolyzed PAN membrane. Therefore, the formation of zwitterionic hydration layer may effectively prevent the adsorption interaction between protein and membrane surface, which is beneficial for the improvement of the anti-protein-fouling capacity.

Solvent Resistant Hydrolyzed Polyacrylonitrile Membranes

We have studied the solvent resistance of polyacrylonitrile membranes hydrolyzed by NaOH. The hydrolyzed polyacrylonitrile membranes provide a candidate material for either the selective layer or the supporting layer for the solvent resistant composite membrane. The origin of this solvent resistance is summarized. Polyacrylonitrile (PAN) cation-exchange NF membranes were prepared from ultrafiltration (UF) membranes through a convenient way developed recently by us. Several explanations for the difference of various solvent permeability coefficients of the cation-exchange PAN NF membrane were also suggested. Relatively high permeability was observed for the solvents with a benzene ring structure. Furthermore, products of their viscosities and permeability, , are close to a constant.

Hydrolysis differences of polyacrylonitrile support membrane and its influences on polyacrylonitrile-based membrane performance

As polyacrylonitrile (PAN)-based membrane plays an important role in the processes of pervaporation, bioproduct purification and water treatment, this study aims at better understanding the hydrolysis differences by using different alkaline species, and how the hydrolysis degree affect the subsequent modification of hydrolyzed PAN membranes. The ATR-FTIR spectra and the measurements of ion exchange capacity (IEC) demonstrated the differences of hydrolysis degree among the KOH, NaOH and LiOH hydrolyzed PAN membranes. The microtopographical changes on membrane surfaces were characterized by atomic force microscopy. It was found that the membrane surface roughness decreased with the increase in the hydrolysis degree. The molecular weight cut-off (MWCO) of the hydrolyzed membranes was determined by filtration studies using poly(ethylene glycol) and Cytochrome C solutions. It was noted that the MWCO of the PAN membranes decreased from 20,000 to 6000 after hydrolysis with 2 N NaOH or 2 N KOH for 1 h at 65°C. Subsequently, the polyethyleneimine (PEI) was deposited on the top surface of the hydrolyzed PAN membrane to form a composite membrane. The pervaporation performance and ions rejection property of the PAN/PEI composite membrane clearly demonstrated that the hydrolysis difference had a great influence on subsequent modification of the PAN-based membrane.