Recent Advancements in Metal-Organic Framework-Based Membranes for Hydrogen Separation: A Review.

Metal-organic frameworks (MOFs) are promising porous materials that have huge potential for gas separation when put in the membrane configuration. MOFs have huge potential due to certain salient features of the MOFs such as excellent pore size, ease of tuning the pore chemistry, higher surface area, and chemical and thermal stabilities. MOFs have been explored for various gas separation and storage applications. This review discusses various approaches for fabricating MOFs-based membranes for the separation of H2 gas from a variety of feeds having various gases CO2 , CO, N2 , and CH4 as impurities. The emphasis has been put on three types of membranes for H2 separation which include MOFs-based hollow fibrous/tubular/disk membranes, MOFs-based mixed matrix membranes (MMMs), and MOFs-based stand-alone membranes. In addition, various challenges such as reducing inhomogeneity between MOFs and polymeric matrices have also been discussed. Similarly, the approaches to successfully decorating MOFs on different supports in different configurations have been explained. The possible ways of improving the MOFs-based membranes for H2 have also been discussed.

Decoration of ß-Cyclodextrin and Tuning Active Layer Chemistry Leading to Nanofiltration Membranes for Desalination and Wastewater Decontamination.

Given the huge potential of thin film composite (TFC) nanofiltration (NF) membranes for desalination and micro-pollutant removal, two different sets of six NF membranes were synthesized. The molecular structure of the polyamide active layer was tuned by using two different cross-linkers, terephthaloyl chloride (TPC) and trimesoyl chloride (TMC), reacted with tetra-amine solution containing ß-Cyclodextrin (BCD). To further tune the structure of the active layers, the time duration of interfacial polymerization (IP) was varied from 1 to 3 min. The membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA), attenuated total reflectance Fourier transform infra-red (ATR-FTIR) spectroscopy, elemental mapping and energy dispersive (EDX) analysis. The six fabricated membranes were tested for their ability to reject divalent and monovalent ions followed by rejection of micro-pollutants (pharmaceuticals). Consequently, terephthaloyl chloride turned out to be the most effective crosslinker for the fabrication of membrane active layer with tetra-amine in the presence of ß-Cyclodextrin using interfacial polymerization reaction for 1 min. The membrane fabricated using TPC crosslinker (BCD-TA-TPC@PSf) showed higher % rejection for divalent ions (Na2SO4 = 93%; MgSO4 = 92%; MgCl2 = 91%; CaCl2 = 84%) and micro-pollutants (Caffeine = 88%; Sulfamethoxazole = 90%; Amitriptyline HCl = 92%; Loperamide HCl = 94%) compared to the membrane fabricated using TMC crosslinker (BCD-TA-TMC@PSf). For the BCD-TA-TPC@PSf membrane, the flux was increased from 8 LMH (L/m2.h) to 36 LMH as the transmembrane pressure was increased from 5 bar to 25 bar.

Removal of pharmaceutically active compounds from water sources using nanofiltration and reverse osmosis membranes: Comparison of removal efficiencies and in-depth analysis of rejection mechanisms.

Trace organic compounds from effluent streams are not completely removed by conventional purification techniques and hence, contaminating groundwater sources. Herein, we report the removal efficiency and rejection mechanisms of three common pharmaceutically active compounds (PhACs); caffeine (CFN), omeprazole (OMZ), and sulfamethoxazole (SMX), using commercial nanofiltration (NF) and reverse osmosis (RO) membranes with different surface characteristics. The RO membranes showed near-complete removal of all PhACs with rejection rates >99%. On the other hand, retention capabilities for the NF membranes varied and were influenced by the characteristics of the PhACs, membranes, and the feed solution. In general, during long-term testing, the rejection did not show much variation and followed a trend compatible with the size exclusion (steric hindrance) mechanism. When a real matrix was used, the rejection of CFN by the more tight NF membranes, HL TFC and NFW decreased by ∼10%, whereas the removal of SMX by the loose NF membrane, XN45, increased by the same ratio. In short-term testing, the rejection of negatively charged SMX increased significantly (∼20-40%) at a higher pH of ∼8 and in the presence of salts. Fouling by the PhACs was more severe on the high-flux NF membranes, HL TFC and XN45, as witnessed by the significant change in Contact angle (CA) values (∼25-50°) as well as the flux decline (∼15%) during long-term testing. To summarize, the removal of PhACs by membranes is a complex phenomenon and depends upon a combination of several factors.

NH2-CuO-MCM-41 covalently cross-linked multipurpose membrane for applications in water treatment: Removal of hazardous pollutants from water, water desalination and anti-biofouling performance.

The current study was planned to fabricate a new set of membranes to target multiple application areas such as desalting, removal of micropollutants and antibiofouling performance. In-situ incorporated copper oxide to MCM-41 (CuO-MCM-41) was synthesized and amine (-NH2) functionalized by reacting with N1-(3-trimethoxy silylpropyl) diethylenetriamine (NTSDETA) yielding NH2-CuO-MCM-41. Different concentrations of NH2-CuO-MCM-41 were covalently cross-linked in polyamide active layer during interfacial polymerization (IP) between N, N'-bis(3-aminopropyl)ethylenediamine and terephthaloyl chloride (TPC) on polysulfone/poly ester terephthalate (PS/PET) support. The membranes were extensively characterized by Water Contact Angle (WCA), Scanning Electron Microscopy (SEM), Fourier Transform Infra-red (FTIR) spectroscopy, Energy Dispersive X-ray (EDX) analysis, Elemental mapping and Powder X-ray Diffraction (PXRD). From among the different versions of X-CuO-MCM-41/PA@PS/PET membranes, the 0.05%-CuO-MCM-41/PA@PS/PET membrane showed best performance in terms of rejecting a variety of salts, micropollutants and antibiofouling. The 0.05%-CuO-MCM-41/PA@PS/PET showed >98% rejection of MgCl2 and 78% rejection of caffeine with a permeate flux of 16 LMH at 25 bar. The 0.1-NH2-CuO-MCM-41inhibited S. aureus growth by 51.7%. Hence, the current strategy of membrane fabrication proved to be highly efficient for multipurpose applications in water treatment.

Yttria-based sol-gel coating for capillary microextraction online coupled to high-performance liquid chromatography.

This work about the development of yttria-based polymeric coating using [bis(hydroxyethyl) amine] terminated polydimethylsiloxanes and yttrium trimethoxyethoxide inside the capillary. The coated capillary was utilized for online capillary microextraction and high-performance liquid chromatography analysis. The prepared coating material was characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectrometry, and thermogravimetric analysis. The coated capillary with polymer presented better extraction efficiency compared with the pure yttria-based coated capillary with applicability in extreme pH environments (pH 0-pH 14). Excellent extraction towards polyaromatic hydrocarbons, aldehydes, ketones, alcohols, phenols, and amides was observed with limit of detection ranging from 0.18 to 7.35 ng/mL (S/N = 3) and reproducibility in between 0.6 and 6.8% (n = 3). Capillary-to-capillary extraction analysis has presented reproducibility between 4.1 and 9.9%. The analysis provided linear response for seven selected phenols in the range of 5-200 ng/mL with R2 values between 0.9971 and 0.9998. The inter-day, intra-day, and capillary-to-capillary reproducibility for phenols was also <10%. Real sample analysis by spiking 5, 50, and 200 ng/mL of phenols in wastewater and pool-water produced recovery between 84.7 and 94.3% and reproducibility within 7.6% (n = 3).

4-phenyl-1,2,3-triazole functionalized mesoporous silica SBA-15 as sorbent in an efficient stir bar-supported micro-solid-phase extraction strategy for highly to moderately polar phenols.

A simple and effective strategy for the extraction of highly to moderately polar phenols in water samples was developed by synthesizing a series of 4-phenyl-1,2,3-triazole functionalized SBA-15 sorbents (xN3-Ph-SBA-15; x = 2 - 10 wt%) via two steps: azide functionalization of SBA-15 and its click reaction with phenylacetylene. The formed sorbents, which have a blend of both polar (1,2,3-triazole) and non-polar (long chain alkyl groups) sites were characterized using magic angle spinning NMR, surface area, pore size/pore volume N2 adsorption-desorption isotherms, scanning electron microscopy, and Fourier transform infrared spectroscopy. The surface area and pore size/pore volume were seen to decrease with increasing loading of 4-phenyl-1,2,3-triazole. The sorbents were used in a stir bar-supported micro-solid-phase extraction (SB-µ-SPE) for seven selected phenols in 10 mL water samples, and in combination with gas chromatography - mass spectrometry (GC-MS). A wide number of parameters were studied in the method optimization: 10N3-Ph-SBA-15 was the best sorbent which performed better using 20 mg dosage; 15 min extraction time; 300 µL of ethyl acetate as desorption solvent, 20 min desorption time; and ionic strength set at 0.5 g NaCl. The approach provided the desired linearity range for all tested phenols with R2 value up to 0.9989 and detection limit (LOD) of 0.23-0.37 ng mL-1. Relative standard deviation (RSD) and relative recovery experiments were tested using phenols spiked at 1, 100 and 400 ng mL-1. RSD values were calculated in the range of 2.3-7.5% and the relative recoveries in the wastewater matrix successfully presented a range of 88.5-99.2%.

Urea functionalized surface-bonded sol-gel coating for on-line hyphenation of capillary microextraction with high-performance liquid chromatography.

Sol-gel urea functionalized-[bis(hydroxyethyl)amine] terminated polydimethylsiloxane coating was developed for capillary microextraction-high performance liquid chromatographic analysis from aqueous samples. A fused silica capillary is coated from the inside with surface bonded coating material and is created through in-situ sol-gel reaction. The urea-functionalized coating was immobilized to the inner surface of the capillary by the condensation reaction of silanol groups of capillary and sol-solution. The characterization of the coating material was successfully done by using X-ray photoelectron spectroscopy, thermogravimetric analysis, field emission scanning electron microscope, and energy dispersive X-ray spectrometer. To make a setup of online capillary microextraction-high performance liquid chromatography, the urea functionalized capillary was installed in the HPLC manual injection port. The analytes of interest were pre-concentrated in the coated sampling loop, desorbed by the mobile phase, chromatographically separated on C-18 column, and analyzed by UV detector. Sol-gel coated capillaries were used for online extraction and high-performance liquid chromatographic analysis of phenols, ketones, aldehydes, and polyaromatic hydrocarbons. This newly developed coating showed excellent extraction for a variety of analytes ranging from highly polar to non-polar in nature. The analysis using sol-gel coating showed excellent overall sensitivity in terms of lower detection limits (S/N = 3) for the analytes (0.10 ng mL-1-14.29 ng mL-1) with acceptable reproducibility that is less than 12.0%RSD (n = 3). Moreover, the capillary to capillary reproducibility of the analysis was also tested by changing the capillary of the same size. This provided excellent%RSD of less than 10.0% (n = 3).

Bis(1,3-benzothia-zole-2-thiol-ato)[(Z)-methyl 2-(2-amino-1,3-thia-zol-4-yl)-2-(methoxy-imino)acetate]nickel(II).

In the title compound, [Ni(C(7)H(4)NS(2))(2)(C(7)H(9)N(3)O(3)S)], the Ni(II) ion is in a slightly distorted N(4)S(2) octa-hedral coordination environment. The two benzothia-zole-2-thiol-ate ligands chelate via their thia-zole N and thiol-ate S atoms while the methyl 2-(2-amino-thia-zol-4-yl)-2-(methoxy-imino)acetate also acts as a chelate ligand binding through the thia-zole and imino N atoms. Intra-molecular N-H⋯N, C-H⋯N and C-H⋯O inter-actions contribute to the mol-ecular conformation. In the crystal structure, inter-molecular N-H⋯O hydrogen bonds produce R(1) (2)(6) rings and generate chains along the c axis. An extensive one-dimensional supra-molecular network of N-H⋯O hydrogen bonds and C-H⋯π inter-actions is responsible for the crystal structure stabilization.