Polydopamine mediated self-cleaning of high-flux pH-responsive isoporous membranes for filtration applications

A major challenge in membrane filtration is fouling which reduces the membrane performance. The fouling is mainly due to the adhesion of foulants on the membrane surfaces. In this work, we studied the fouling behavior of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) isoporous membrane and the mussel inspired polydopamine/L-Cysteine isoporous zwitterionic membrane. The polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) isoporous membrane was fabricated via self-assembly and non-solvent induced phase separation.1 Subsequently, the isoporous membrane was modified through a mild mussel-inspired polydopamine (PDA) coating by retaining the isoporous morphology and water flux.2 Furthermore, zwitterionic L-Cysteine was anchored on the PDA layer coated membranes via Michael addition reaction at neutral pH and 50oC. The membranes were thoroughly characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and zeta potential measurements. The contact angle and dynamic scanning calorimetry (DSC) measurements were carried out to examine their hydrophilicity. The pH-responsive behaviour of the modified membrane remains unchanged and the antifouling ability after PDA/L-Cysteine functionalization was improved. The modified and unmodified isoporous membranes were tested using humic acid and natural organic matter contaminated solutions at 0.5 bar feed pressure. References Peinemann, K.-V.; Abetz, V.; Simon, P. F. W. Asymmetric Superstructure Formed in a Block Copolymer via Phase Separation. Nat. Mater. 2007, 6, 992–996. Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science. 2007, 318, 426–430

Novel adsorptive ultrafiltration membranes derived from polyvinyltetrazole-co-polyacrylonitrile for Cu(II) ions removal

Novel adsorptive ultrafiltration membranes based on polyvinyltetrazole-co-polyacrylonitrile polymer were manufactured for an efficient copper removal. [Display omitted] •Polyvinyltetrazole (PVT)-co-PAN based ultrafiltration membranes were fabricated.•PVT segment played a significant role for copper adsorption.•The binding capacity of PVT–PAN membranes for Cu(II) ions exceeded 130mgg−1.•Copper loaded membranes could be regenerated with 0.25mM EDTA solution. Novel adsorptive ultrafiltration membranes were manufactured from synthesized polyvinyltetrazole-co-polyacrylonitrile (PVT-co-PAN) by nonsolvent induced phase separation (NIPS). PVT-co-PAN with various degree of functionalization (DF) was synthesized via a [3+2] cycloaddition reaction at 60°C using a commercial PAN. PVT-co-PAN with varied DF was then explored to prepare adsorptive membranes. The membranes were characterized by surface zeta potential and static water contact angle measurements, scanning electron microscopy as well as atomic force microscopy (AFM) techniques. It was shown that PVT segments contributed to alter the pore size, charge and hydrophilic behavior of the membranes. The membranes became more negatively charged and hydrophilic after addition of PVT segments. The PVT segments in the membranes served as the major binding sites for adsorption of Cu(II) ions from aqueous solution. The maximum adsorption of Cu(II) ions by the membranes in static condition and in a continuous ultrafiltration of 10ppm solution was attained at pH=5. The adsorption data suggest that the Freundlich isotherm model describes well Cu(II) ions adsorption on the membranes from aqueous solution. The adsorption capacity obtained from the Freundlich isotherm model was 44.3mgg−1; this value is higher than other membrane adsorption data reported in the literature. Overall, the membranes fabricated from PVT-co-PAN are attractive for efficient removal of heavy metal ions under the optimized conditions

CO2-Philic Thin Film Composite Membranes: Synthesis and Characterization of PAN-r-PEGMA Copolymer

In this work, we report the successful fabrication of CO2-philic polymer composite membranes using a polyacrylonitrile-r-poly(ethylene glycol) methyl ether methacrylate (PAN-r-PEGMA) copolymer. The series of PAN-r-PEGMA copolymers with various amounts of PEG content was synthesized by free radical polymerization in presence of AIBN initiator and the obtained copolymers were used for the fabrication of composite membranes. The synthesized copolymers show high molecular weights in the range of 44–56 kDa. We were able to fabricate thin film composite (TFC) membranes by dip coating procedure using PAN-r-PEGMA copolymers and the porous PAN support membrane. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to analyze the surface morphology of the composite membranes. The microscopy analysis reveals the formation of the defect free skin selective layer of PAN-r-PEGMA copolymer over the porous PAN support membrane. Selective layer thickness of the composite membranes was in the range of 1.32–1.42 μm. The resulting composite membrane has CO2 a permeance of 1.37 × 10−1 m3/m2·h·bar and an ideal CO2/N2, selectivity of 65. The TFC membranes showed increasing ideal gas pair selectivities in the order CO2/N2 > CO2/CH4 > CO2/H2. In addition, the fabricated composite membranes were tested for long-term single gas permeation measurement and these membranes have remarkable stability, proving that they are good candidates for CO2 separation

Scalable Synthesis of Amphiphilic Copolymers for CO2- and Water-Selective Membranes: Effect of Copolymer Composition and Chain Length

Dehumidification is a critical energy-intensive and crucial process for several industries (e.g., air conditioning and gas dehydration). Polymeric membranes with high water vapor permeability and selectivity are needed to achieve an energy-efficient water vapor removal. Herein, we demonstrate high-performance water vapor transport membranes based on novel amphiphilic tercopolymers. A series of amphiphilic tercopolymers comprising polyacrylonitrile, poly­(ethylene glycol) methyl ether methacrylate (PEGMA), and poly­(N,N-dimethylamino ethyl methacrylate) (PDMAEMA) segments are synthesized via an economical and facile free radical polymerization. The water vapor permeability increases with the increase in PEGMA chain length and the content of PEGMA segments. The best performing membrane (i.e., PEGMA-9502) achieved a water vapor permeability of 174 kBarrer. By optimizing the content and chain length of the PEGMA segments, the membranes could be tuned for carbon capture applications. The optimized membranes tested for CO2 separation showed a high CO2 permeability of 47 Barrer along with CO2/N2 and CO2/CH4 selectivities of 67 and 23, respectively. This work presents a simple and economic amphiphilic tercopolymer for the fabrication of membranes with excellent gas and water vapor separation performance

Rapid Size-Based Protein Discrimination inside Hybrid Isoporous Membranes

Owing to their unique morphology, isoporous membranes derived from block copolymers (BCPs) have rapidly advanced the process of macromolecular separation. In such separations, fouling is the most daunting challenge, affecting both the permeability and selectivity of high-performance isoporous membranes. To overcome this, we increase the hydrophilicity of nanostructured BCP isoporous membranes by incorporating hydrophilic polymer-grafted graphene oxide nanosheets into them. Due to the synergy of these two highly functional components, the hybrid isoporous membranes show pH-responsive and alcohol-gating behaviors, along with improved bactericidal capabilities. Leveraging the high permeability and selectivity behavior of BCP isoporous membranes together with the antifouling capabilities imparted by the polymer-grafted graphene oxide nanosheets, we achieved the highest separation factor (33) ever obtained during the ultrafiltration of the common blood proteins bovine serum albumin and immunoglobulin. This was accompanied by a 60% enhanced flux compared to that of the pristine BCP membranes during this challenging size-based separation of a protein mixture. We surmise that such fouling-resistant hybrid isoporous membranes with rationally functionalized filler materials can be used to replace existing membranes for specific energy-efficient bioseparation applications with improved performance

Highways for water molecules: Interplay between nanostructure and water vapor transport in block copolymer membranes

Water vapor removal is a crucial process for several industries (e.g., air conditioning systems, flue gas dehydration, compressed air drying etc.). An effective dehumidification has the potential to drastically reduce the energy consumption and the overall cost of a process stream. Membranes with high water permeance and selectivity are promising candidates to achieve an energy-efficient water removal. We propose self-assembled membranes with interconnected and ordered hydrophilic domains that act as extremely fast water transport highways (water channels). We used a commercial amphiphilic pentablock copolymer (Nexar™), which has the ability to form long-range, self-ordering nanoscale morphologies with rigid end-blocks and a flexible molecular network where polar and non-polar solvents regulated the final morphologies of the membranes. Our results demonstrate how well-defined periodic morphology allow for molecular level control in effective removal of water vapor. The membranes with ordered hydrophilic nanochannels present a 6-fold improvement in water vapor permeability and a 14-fold increase in water vapor/N2 selectivity compared to Nexar™ membranes with disordered domains. Molecular dynamics stimulations are carried out on the self-assembly behavior of block copolymer solution in different solvents. In addition, sorption and desorption kinetics studies for Nexar™ films were correlated to the different morphologies imaged by transmission electron, atomic force and environmental scanning electron microscopy. Block copolymer membranes with ordered and disordered nanostructure showing highways for water molecules. [Display omitted] •The Nexar nanoscale morphology was optimized for maximum water permeance.•The water vapor permeance of commercial Nexar films could be increased by 500%.•The water vapor selectivity could be increased 14 fold by optimizing the morphology.•Performance enhancement is explained using molecular dynamics simulations

Polyanionic pH-responsive polystyrene-b-poly(4-vinyl pyridine-N-oxide) isoporous membranes

Recently isoporous block copolymer (BCP) membranes obtained by non-solvent induced phase separation gained a lot of attention due to their highly ordered surface layer, high flux and superior separation properties. These polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP) based membranes showed a strong flux dependence of pH; pores closed at low pH and opened at high pH. The pH-response could now be reversed by a simple post modification; pores are now opening at low pH and closing at high pH. The original membrane was transformed into a polyanionic pH responsive membrane in a one step chemical modification without affecting the isoporous surface morphology. A polystyrene-b-poly-4-vinylpyridine-N-oxide (PS-b-P4VPN-oxide) membrane is obtained by selective oxidation of the PS-b-P4VP membrane. The in situ generated peracid obtained by reacting acetic acid and hydrogen peroxide is employed for oxidation. Surprisingly not only the asymmetric membrane structure with the isoporous skin was retained, but also the mechanical and chemical membrane stability was improved significantly. The modified membranes are insoluble in solvents like DMF, NMP and DMSO. Two kinds of PS-b-P4VP based isoporous membranes are available now with reverse flux response to pH. This opens the door to new interesting charge based fractionations. [Display omitted] •Polyanionic pH-responsive isoporous block copolymer membranes were prepared.•The membranes were synthesized by a chemical post-modification of PS-b-P4VP membranes.•The membrane pores are opening at low pH and closing at high pH.•The post-modification improved the mechanical and chemical stability of the membranes