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

Significant Quantitative and Qualitative Transition in Pituitary Stem / Progenitor Cells Occurs during the Postnatal Development of the Rat Anterior Pituitary

We reported recently that a pituitary-specific transcription factor PROP1 is present in SOX2-positive cells and disappears at the early stage of the transition from progenitor cell to committed cell during the embryonic development of the rat pituitary. In the present study, we examined the localisation and identification of SOX2-positive and PROP1/SOX2-positive cells in the neonatal and postnatal rat pituitaries by immunohistochemistry. Quantitative analysis of immunoreactive cells demonstrated that SOX2-positive pituitary stem/progenitor cells are not only predominantly localised in the marginal cell layer, but also are scattered in the parenchyma of the adult anterior lobe. In the marginal cell layer, the number of PROP1/SOX2-positive cells significantly decreased after postnatal day 15, indicating that a significant quantitative transition is triggered in the marginal cell layer during the first postnatal growth wave of the anterior pituitary. By contrast, other phenotypes of SOX2-positive stem/progenitor cells that express S100β appeared in the postnatal anterior pituitary. These data suggested that quantitative and qualitative transition occurs by acquisition of a novel mechanism in terminal differentiation in the postnatal development of the anterior pituitary

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

Dynamic response of ultrathin highly dense ZIF-8 nanofilms

Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for nonequilibrium organic polymers

Study of different titanosilicate (TS-1 and ETS-10) as fillers for Mixed Matrix Membranes for CO2/CH4 gas separation applications

Three titanosilicate zeolites were used as fillers for Mixed Matrix Membranes: (i) ETS-10, TS-1 having Si/Ti=100 and (iii) TS-1 using Si/Ti=25. Zeolite samples were characterized by X-Ray Diffraction, Scanning Electron Microscopy, Atomic Emission Spectroscopy, X-Ray Photoelectron Spectroscopy, and CO2 and CH4 adsorption isotherms. TS-1 particles showed a narrow size distribution ranging from 200 nm to 400 nm. In the case of ETS-10, the size distribution was broader ranging from 400 nm to 800 nm. Mixed Matrix Membranes were prepared using Matrimid (R) polyimide as continuous phase and filler loadings of 10, 20, and 30 wt%. Membranes were characterized by Thermogravimetric Analysis, Differential Scanning Calorimetry, and Scanning Electron Microscopy. The performances was measured at 8 bars of transmembrane pressure for CO2/CH4 mixed gases system at 50/50 vol/vol. concentration. Membranes using TS-1 (Si/Ti=25) as filler showed a maximum increase of 89.1% of CO2 permeability and 23.9% increase in separation factor. In the case of TS-1 (Si/Ti=100) only permeability increased significantly, with a maximum increase of 90.1%. Regarding the ETS-10 membranes, both permeability and separation factor increased slightly with respect to the reference polymeric membrane (22.5% in CO2 permeability and 7.8% in the separation factor). In conclusion, TS-1 (Si/Ti=25) is the most suitable filler for the use in Mixed Matrix Membranes for gas separation applications among the titanosilicate studied in this work

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

Round ligament varicocele

A 24-year-old pregnant woman (at 25 weeks gestation) was referred to our department because of a painless swelling in the left groin which she was feeling for one week. The swelling was more apparent in the upright position and when coughing. The swelling was reducible. Ultrasound demonstrated an anechoic structure with intralesional septa at the left inguinal area (Fig. A, longitudinal ultrasound image). The lesion augmented with the Valsalva manoeuvre and in standing position. Power Doppler confirmed the presence of venous flow (Fig. B). Inverted venous flow was seen after Valsalva (Fig. C, arrow)