Track-etched membrane as a thin substrate with straight pores to fabricate polyamide forward osmosis membrane

Controlling the internal concentration polarization in forward osmosis (FO) membranes by minimizing the substrate thickness is critical to enhancing the water flux. This study aimed to achieve the fabrication of an ultra-thin FO membrane by forming the polyamide (PA) active layer on a thin and straight-bore film, a so-called track-etched (TE) membrane. The polycarbonate TE membrane had a uniform pore size of 0.22 µm and a thickness of 25 µm. The PA active layer was successfully formed only by creating a thin m-phenylenediamine solution layer on the smooth TE membrane surface before interfacial polymerization. The TE- FO membrane with low porosity (14 %) provided a water flux of 21 L/m2h and a reverse salt flux of 8.0 g/m2h when evaluated with a 1.0 M NaCl draw solution. Further evaluations showed the potential of increasing water flux by increasing the TE substrate porosity (14 %) and reducing the apparent PA active layer thickness (504 nm). These results suggest the potential of achieving a high-water flux FO membrane using a thin TE substrate and ultimately improving the validity of FO membrane-based water treatment.Journal of Membrane Science Letters, 4(1), art. no. 100068; 202

Development of high-integrity reverse osmosis membranes for enhanced removal of microorganisms

Improved integrity of reverse osmosis (RO) membranes for pathogenic microorganisms can enhance the microbiological safety of potable water reuse. This study aimed to produce a high-integrity RO membrane that is less prone to defects or failures of the polyamide skin layer. The commercial track-etched (TE) microfiltration membranes with uniform pore sizes of 0.2 μm were adopted as a robust support layer. The polyamide skin layer was successfully formed by creating a thin m-phenylenediamine (MPD) layer using a spin coater before the interfacial polymerization. The best TE-based RO membranes had a pure water permeability of 1.1 L/m2 hbar and a salt rejection of 97 %. The field emission scanning electron microscopy revealed that the skin layer thickness of the TE-based membrane (approx. 31 nm) was equivalent to a commercial RO membrane. The removal of bacteria-sized particles (0.5 μm fluorescent microspheres) by the fabricated TE-based membrane (8.6-log) was greater than that by the commercial RO membrane taken out from an RO membrane element (7.8-log). Although complete removal of bacteria-sized particles was not achieved with small TE-based RO membrane coupons, this study established a viable protocol for producing a high-integrity RO membrane by forming the polyamide skin layer on the TE support layer.Desalination, 572, art. no. 117155; 202

Impact of heat modification conditions on the removal of N-nitrosodimethylamine by polyamide reverse osmosis membranes

Advanced wastewater treatment using a reverse osmosis (RO) membrane is a key separation process for ensuring the removal of chemical hazards so that treated wastewater can be used for potable purposes. This study systematically assesses the effects of heat modification conditions of three commercial RO membranes on the removal of a challenging chemical of emerging concern?N-nitrosodimethylamine (NDMA). The RO membranes were modified in pure water at the heat treatment temperature between 70 and 100 °C; 90?100 °C achieved the highest NDMA rejection during separation tests. A lower pH during heat treatment generally resulted in higher NDMA rejection, however a solution pH lower than four can reduce NDMA rejection depending on the presence of a protective layer on the RO membrane surface. Overall, a linear tradeoff between NDMA rejection and water permeance was commonly observed among the heat-treated RO membranes. The stability of a heat-modified membrane in water permeance and NDMA rejection was demonstrated over a week-long test using treated wastewater. The enhanced removal of NDMA by heat-treated RO membranes was speculated to occur due to the shrinking of the passage of solutes?free-volume holes. This study demonstrates the importance of heat modification conditions on RO membranes to achieve a high NDMA rejection

Solvent-Induced Reversed Stereoselectivity in Reciprocal Resolutions of Mandelic Acid and <i>erythro</i>-2-Amino-1,2-diphenylethanol

Solvent-induced chirality switching in reciprocal optical resolution between mandelic acid (<b>1</b>) and <i>erythro</i>-2-amino-1,2-diphenylethanol (<b>2</b>) has been demonstrated. The stereochemistry of the deposited salts was controlled by changing the crystallization solvent from 1-PrOH or 1-BuOH to 1,4-dioxane. It was revealed from ¹H NMR spectra, thermogravimetric analysis, and X-ray crystallography of the salts that an equimolar amount of the crystallization solvent was incorporated in each diastereomeric salt. On the basis of the crystal structures, it was found that both the hydrogen-bonding ability and the size of the solvent molecule played an important role. Differences in the formed hydrogen-bonding networks (columnar or sheetlike structure) and their packing manner were found to be crucial for the reversed stereoselectivity. Furthermore, pseudopolymorphic salt crystals that incorporated 1,4-dioxane were obtained during the enantioseparation of racemic <b>2</b>, and their solid-state properties were examined by measurement of their IR spectra. This solvent-induced dual stereocontrol technique was successfully applied to the successive resolution process, eliminating the need to change the resolving agent for access to both enantiomers of <b>1</b> and <b>2</b>

Solvent-Induced Reversed Stereoselectivity in Reciprocal Resolutions of Mandelic Acid and <i>erythro</i>-2-Amino-1,2-diphenylethanol

Solvent-induced chirality switching in reciprocal optical resolution between mandelic acid (<b>1</b>) and <i>erythro</i>-2-amino-1,2-diphenylethanol (<b>2</b>) has been demonstrated. The stereochemistry of the deposited salts was controlled by changing the crystallization solvent from 1-PrOH or 1-BuOH to 1,4-dioxane. It was revealed from ¹H NMR spectra, thermogravimetric analysis, and X-ray crystallography of the salts that an equimolar amount of the crystallization solvent was incorporated in each diastereomeric salt. On the basis of the crystal structures, it was found that both the hydrogen-bonding ability and the size of the solvent molecule played an important role. Differences in the formed hydrogen-bonding networks (columnar or sheetlike structure) and their packing manner were found to be crucial for the reversed stereoselectivity. Furthermore, pseudopolymorphic salt crystals that incorporated 1,4-dioxane were obtained during the enantioseparation of racemic <b>2</b>, and their solid-state properties were examined by measurement of their IR spectra. This solvent-induced dual stereocontrol technique was successfully applied to the successive resolution process, eliminating the need to change the resolving agent for access to both enantiomers of <b>1</b> and <b>2</b>

Solvent-Induced Reversed Stereoselectivity in Reciprocal Resolutions of Mandelic Acid and <i>erythro</i>-2-Amino-1,2-diphenylethanol

Solvent-induced chirality switching in reciprocal optical resolution between mandelic acid (<b>1</b>) and <i>erythro</i>-2-amino-1,2-diphenylethanol (<b>2</b>) has been demonstrated. The stereochemistry of the deposited salts was controlled by changing the crystallization solvent from 1-PrOH or 1-BuOH to 1,4-dioxane. It was revealed from ¹H NMR spectra, thermogravimetric analysis, and X-ray crystallography of the salts that an equimolar amount of the crystallization solvent was incorporated in each diastereomeric salt. On the basis of the crystal structures, it was found that both the hydrogen-bonding ability and the size of the solvent molecule played an important role. Differences in the formed hydrogen-bonding networks (columnar or sheetlike structure) and their packing manner were found to be crucial for the reversed stereoselectivity. Furthermore, pseudopolymorphic salt crystals that incorporated 1,4-dioxane were obtained during the enantioseparation of racemic <b>2</b>, and their solid-state properties were examined by measurement of their IR spectra. This solvent-induced dual stereocontrol technique was successfully applied to the successive resolution process, eliminating the need to change the resolving agent for access to both enantiomers of <b>1</b> and <b>2</b>

Solvent-Induced Reversed Stereoselectivity in Reciprocal Resolutions of Mandelic Acid and <i>erythro</i>-2-Amino-1,2-diphenylethanol

Solvent-induced chirality switching in reciprocal optical resolution between mandelic acid (<b>1</b>) and <i>erythro</i>-2-amino-1,2-diphenylethanol (<b>2</b>) has been demonstrated. The stereochemistry of the deposited salts was controlled by changing the crystallization solvent from 1-PrOH or 1-BuOH to 1,4-dioxane. It was revealed from ¹H NMR spectra, thermogravimetric analysis, and X-ray crystallography of the salts that an equimolar amount of the crystallization solvent was incorporated in each diastereomeric salt. On the basis of the crystal structures, it was found that both the hydrogen-bonding ability and the size of the solvent molecule played an important role. Differences in the formed hydrogen-bonding networks (columnar or sheetlike structure) and their packing manner were found to be crucial for the reversed stereoselectivity. Furthermore, pseudopolymorphic salt crystals that incorporated 1,4-dioxane were obtained during the enantioseparation of racemic <b>2</b>, and their solid-state properties were examined by measurement of their IR spectra. This solvent-induced dual stereocontrol technique was successfully applied to the successive resolution process, eliminating the need to change the resolving agent for access to both enantiomers of <b>1</b> and <b>2</b>

Solvent-Induced Reversed Stereoselectivity in Reciprocal Resolutions of Mandelic Acid and <i>erythro</i>-2-Amino-1,2-diphenylethanol

Solvent-induced chirality switching in reciprocal optical resolution between mandelic acid (<b>1</b>) and <i>erythro</i>-2-amino-1,2-diphenylethanol (<b>2</b>) has been demonstrated. The stereochemistry of the deposited salts was controlled by changing the crystallization solvent from 1-PrOH or 1-BuOH to 1,4-dioxane. It was revealed from ¹H NMR spectra, thermogravimetric analysis, and X-ray crystallography of the salts that an equimolar amount of the crystallization solvent was incorporated in each diastereomeric salt. On the basis of the crystal structures, it was found that both the hydrogen-bonding ability and the size of the solvent molecule played an important role. Differences in the formed hydrogen-bonding networks (columnar or sheetlike structure) and their packing manner were found to be crucial for the reversed stereoselectivity. Furthermore, pseudopolymorphic salt crystals that incorporated 1,4-dioxane were obtained during the enantioseparation of racemic <b>2</b>, and their solid-state properties were examined by measurement of their IR spectra. This solvent-induced dual stereocontrol technique was successfully applied to the successive resolution process, eliminating the need to change the resolving agent for access to both enantiomers of <b>1</b> and <b>2</b>

Solvent-Induced Reversed Stereoselectivity in Reciprocal Resolutions of Mandelic Acid and <i>erythro</i>-2-Amino-1,2-diphenylethanol

Solvent-induced chirality switching in reciprocal optical resolution between mandelic acid (<b>1</b>) and <i>erythro</i>-2-amino-1,2-diphenylethanol (<b>2</b>) has been demonstrated. The stereochemistry of the deposited salts was controlled by changing the crystallization solvent from 1-PrOH or 1-BuOH to 1,4-dioxane. It was revealed from ¹H NMR spectra, thermogravimetric analysis, and X-ray crystallography of the salts that an equimolar amount of the crystallization solvent was incorporated in each diastereomeric salt. On the basis of the crystal structures, it was found that both the hydrogen-bonding ability and the size of the solvent molecule played an important role. Differences in the formed hydrogen-bonding networks (columnar or sheetlike structure) and their packing manner were found to be crucial for the reversed stereoselectivity. Furthermore, pseudopolymorphic salt crystals that incorporated 1,4-dioxane were obtained during the enantioseparation of racemic <b>2</b>, and their solid-state properties were examined by measurement of their IR spectra. This solvent-induced dual stereocontrol technique was successfully applied to the successive resolution process, eliminating the need to change the resolving agent for access to both enantiomers of <b>1</b> and <b>2</b>