Synthesis and Characterization of Micro-Patterned Thin Film Composite (TFC) Membranes for Water Treatment

Thin film composite (TFC) membranes, mostly used in reverse osmosis and nanofiltration are critical for water treatment and provide clean and desalinated water to millions on daily basis. The two main limitations: fouling and low permeance of these membranes greatly affect their performance and sustainability. Several measures have been taken for membrane fouling mitigation including chemical, physical and hydrodynamic methods. Recently, patterned membranes have been evolved as an innovative tool for fouling mitigation. However, the synthesis procedure for patterned membranes has not been developed at a scale-up level. Lately, Prof. Vankelecom’s research group (KU Leuven) has introduced a non-solvent spray assisted phase inversion (s-NIPS) as an efficient synthesis procedure for patterned membranes. s-NIPS makes the use of a patterned casting knife combined with modified non-solvent spray assisted phase inversion process. It overcomes the limitations of previously used methods such as phase separation micromolding (PSμM) and imprinting lithography (IL) as phase separation induces from the pattern side and no reduction in pore size is observed. Previous studies for patterned TFC membranes have only managed to create a top selective layer above patterned UF supports with heights in the range of 160 nm to 5 μm which limits the potential advantages of such membranes. s-NIPS patterned supports can significantly enhance the intrinsic low permeance of such NF/RO membranes by producing UF supports with higher pattern heights up to 180 μm. Hence, in this study, a defect-free thin film polyamide layer was developed over s-NIPS micro-patterned supports through interfacial polymerization (IP). In order to achieve this, several parameters were explored including effect of monomer concentrations, effect of pattern height, removal of excess monomer solution from the valleys before IP, effect of UF polymer support and spin assisted layer by layer thin film deposition. It was found that the 1, 2 and 3 layered TFC membrane could give a maximum of ca. 85, 96 and 97 % MgSO4 retention respectively at enhanced permeance. Furthermore, 2 layered spin assisted IP with 2 wt% MPD and 0.1 wt% TMC concentration was found to be optimum for PSf500 supports (polysulfone supports prepared using casting knife with pattern height 500 μm) with 94% MgSO4 retention at the permeance of 1.66 LMH/bar.<br /

Study of synthesis parameters and active layer morphology of interfacially polymerized polyamide-polysulfone membranes

Thin film composite (TFC) polyamide membranes were prepared on a polysulfone support membrane and the effect of various synthesis conditions on the active layer morphology, the physicochemical properties and the membrane performance was investigated. The support membrane porosity factor had a significant effect on the TFC membrane performance. A polyamide top layer was formed within 15 s of reaction. Prolonging the reaction time, although resulting in a thicker active layer, only had a minor influence on the membrane performance. This highlights the importance of the incipient layer of the polyamide structure on its performance. The addition of both a surfactant and a base to the amine solution resulted in a change of the active layer morphology and an improved performance. The effect of additives was attributed to changes in the polymerization mechanism. In addition, it was demonstrated that curing at 50°C resulted in an improved membrane performance, due to more cross-linking of the active layer. Curing at higher temperatures deteriorated the structure of the support membrane. This research shows that the TFC membrane performance is well correlated with the changes in the active layer morphology, measured using SEM, AFM and TEM; whereas only minor changes in the physicochemical characteristics of the membranes were detected by zeta potential and ATR-FTIR spectroscopy when the same synthesis parameters were varied.status: publishe

Applicability of organic carbonates as green solvents for membrane preparation

Common polar aprotic solvents, like N,N-dimethylformamide (DMF), 1,4-dioxane, N,N-dimethylacetamide (DMA) and tetrahydrofuran (THF), are excellent for membrane preparation. However, due to their toxicity or volatile nature, it would be useful to replace them by “greener” solvents for environmental and health reasons. In this work, organic carbonates, obtainable through carbon dioxide fixation, were selected as green solvents to find possible use in membrane preparation. Polymer solubility experiments were performed to screen their applicability in the phase inversion process to create porous membrane with appropriate structures and selectivities. Hansen solubility parameters were used to rationalize the solubility results. Membrane morphology and pore structure were characterized using scanning electron microscopy (SEM), while the performance of the membrane was determined by applying a 35 μM aqueous feed solution of rose bengal (RB, MW = 1017 Da) to screen the potential of these polymer/organic carbonate systems toward nanofiltration application

UV-cured polysulfone-based membranes: Effect of co-solvent addition and evaporation process on membrane morphology and SRNF performance

Membranes consisting of a semi-interpenetrating network of polysulfone (PSU) and cross-linked polyacrylate were synthesized via non-solvent induced phase inversion followed by UV-treatment. Tetrahydrofuran (THF) or 1,4-dioxane (DIO) was added as co-solvent to the N,N-dimethylformamide (DMF)-based polymer solutions and cast films were subjected to evaporation prior to coagulation. Effects of synthesis variables on the membrane morphology and solvent resistant nanofiltration (SRNF) performance were investigated by using a Rose Bengal solution in isopropanol. By increasing the evaporation time from 0 to 100 s for the membranes prepared with THF and DIO as co-solvent respectively, rejections increased from 65.3% to 94.2% and 60.1–89.1%, while permeances decreased from 0.29 to 0.01 l/m2 h bar and 0.41–0.08 l/m2 h bar. A similar effect was observed when the co-solvent/solvent ratio was increased from 0/100 to 100/0: rejections increased from 63.1% to 94.9% and 59.2–90.6%, while permeances decreased from 0.43 to 0.01 l/m2 h bar for THF-based membranes and to 0.07 l/m2 h bar for DIO-based membranes respectively. A post-treatment was performed to increase the flux by immersing UV-cured PSU-based films in DMF for 48 h. The resultant membranes showed higher permeances and lower rejections, making them especially useful as potential candidates for stable supports to apply selective layers upon, such as e.g. in thin film composite (TFC) membranes. As observed in scanning electron microscopy, higher evaporation times and lower initial co-solvent concentrations resulted in less or even no macrovoids

Solvent-resistant nanofiltration for product purification and catalyst recovery in Click chemistry reactions

The quickly developing field of "click" chemistry Would undoubtedly benefit from the availability of an easy and efficient technology for product purification to reduce the potential health risks associated with the presence of copper in the final product. Therefore. solvent-resistant nanofiltration (SRNF) membranes have been developed to selectively separate "clicked" polymers from the copper catalyst and solvent. By using these solvent-stable cross-linked polyimide membranes in diafiltration, up to 98% of the initially present copper could be removed through the membrane together with the DMF solvent, the polymer product being almost completely retained. This paper also presents the first SRNF application in which the catalyst permeates through the membrane and the reaction product is retained

Doped ordered mesoporous carbons as novel, selective electrocatalysts for the reduction of nitrobenzene to aniline

Ordered mesoporous carbons (OMCs) doped with nitrogen, phosphorus or boron were synthesised through a two-step nanocasting method and studied as electrocatalysts for the reduction of nitrobenzene to aniline in a half-cell setup. The nature of the dopant played a crucial role in the electrocatalytic performance of the doped OMCs, which was monitored by LSV with a rotating disk electrode setup. The incorporation of boron generated the electrocatalysts with the highest kinetic current density, whereas the incorporation of phosphorus led to the lowest overpotential. Doping with nitrogen led to intermediate behaviour in terms of onset potential and kinetic current density, but provided the highest selectivity towards aniline, thus resulting in the most promising electrocatalyst developed in this study. Density functional theory calculations allowed explaining the observed difference in the onset potentials between the various doped OMCs, and indicated that both graphiticN and pyrdinic N can generate active sites in the N-doped electrocatalyst. A chronoamperometric experiment over N-doped OMC performed at -0.75 V vs. Fc/Fc(+) in an acidic environment, resulted in a conversion of 61% with an overall selectivity of 87% to aniline. These are the highest activity and selectivity ever reported for an electrocatalyst for the reduction of nitrobenzene to aniline, making N-doped OMC a promising candidate for the electrochemical cogeneration of this industrially relevant product and electricity in a fuel cell setup

Influence of the Composition and Preparation of the Rotating Disk Electrode on the Performance of Mesoporous Electrocatalysts in the Alkaline Oxygen Reduction Reaction

We report a systematic study of the influence of the composition and preparation method of the electrocatalyst layer deposited on the rotating (ring) disk electrodes (RDE/RRDE) employed in the alkaline oxygen reduction reaction (ORR). To investigate and rationalize the generally underestimated role of these factors on the ORR performance of mesoporous electrocatalysts, we studied the activity and selectivity of nitrogen-doped ordered mesoporous carbon as a function of the loading of electrocatalyst and of binder, of the type of binder, and of the addition order of the components onto the electrode. The use of an anion-exchange polymer (Fumion FAA-3 (R)) as the binder instead of the commonly employed Nafion (R) increased the selectivity towards H2O2 and led to a lower kinetic current density. In addition, higher selectivity towards H2O was observed when increasing the loading of the catalyst and of the binder, although the latter resulted in a decreased kinetic current density. These results prove the crucial effect of the composition and preparation method of the layer deposited on the electrode on the ORR performance of the mesoporous electrocatalyst and can provide useful guidelines in view of the translation of the results of RDE studies to an alkaline fuel-cell setup

Effect of operational parameters on the performance of a magnetic responsive biocatalytic membrane reactor

In this work, the performance of an innovative magnetic responsive biocatalytic membrane reactor (BMRSP) has been investigated under various operational parameters. In particular, feed concentrations, flow rates across the bed, temperature and amount of biocatalytic bead were varied to probe the flow-dependent transport and kinetic properties of the reaction and the subsequent hydrolytic performance of the BMRSP. The rate of fouling for the BMRSP was always lower than a corresponding control system. For a given enzymatic concentration, a constant foulant hydrolyzing capacity is identified. At 3 g/m2 pectinase containing bionanocomposites, the BMRSP hydrolytic efficiency was 1.5 g/m2 h. This efficiency was further increased by increasing the amount of bionanocomposites per membrane area. This further allowed the BMRSP to hydrolyze higher loads of foulants while keeping a low if not zero increase in TMP over time at constant flux. Identification of an optimal operating condition laid the platform for continuous operation of the BMRSP over 200 h, without visible transmembrane pressure drift while maintaining constant flux. Product assay in the permeate gave constant value in the entire duration, i.e., no enzymatic activity decay owing to stable enzyme immobilization and no leakage through the pores of the membrane owing to the synergistic magnetic interaction between the magnetic membrane and magnetic bionanocomposites. The obtained stability over a broad range of operational parameters and sustainable performance over long period gives a high prospect to the newly developed BMRSP to be utilized in continuous biocatalysis and separation, thereby significantly improved process efficiency

Pectinases immobilization on magnetic nanoparticles and their anti-fouling performance in a biocatalytic membrane reactor

Enzyme immobilization on commercial superparamagnetic nanoparticles (NPSP) was performed using covalent bonding. The biofunctionalized NPSP was then immobilized on the surface of the membrane using an external magnetic field to form a magneto-responsive biocatalytic membrane reactor (BMRSP). The magnetically formed smart nanolayer can be easily re-dispersed and recovered from the membrane when the enzyme is deactivated or whenever cleaning is required due to substrate over-accumulation. The system was used to hydrolyze pectin contained in different streams. Results are supported with complementary data from hydrodynamic, kinetic and morphological characterization in a flow-through reactive filtration. Wavelength-dispersive X-ray spectroscopy (WDS) elemental mapping revealed that the NPSP are uniformly dispersed on the surface of the membrane forming a thin biocatalytic layer. Both results of hydrodynamic studies and SEM micrographs of the membrane with the enzyme layer under various operating conditions, show that the immobilized enzyme effectively reduced membrane–foulant interaction. Comparison of filtration data using this commercial NPSP reveals good agreement with our previously used home-made NPSP. This implies that the scaling-up and commercialization of the developed BMRSP can be straightforward