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Abstract:Membrane support properties influence the performance of thin-film composite nanofiltration membranes. We fabricated several polysulfone (PSf) supports. The physicochemical properties of PSf were altered by adding polyethylene glycol (PEG) of varying molecular weights (200-35,000 g/mol). This alteration facilitated the formation of a thin polyamide layer on the PSf surface during the interfacial polymerization reaction involving an aqueous solution of piperazine containing 4-aminobenzoic acid and an organic solution of trimesoyl chloride. Attenuated total reflectance-Fourier transform infrared validated the presence of PEG in the membrane support. Scanning electron microscopy and atomic force microscopy illustrated that the thin-film polyamide layer morphology transformed from a rough to a smooth surface. A cross-flow filtration test indicated that a thin-film composite polyamide membrane comprising a PSf support (TFC-PEG20k) with a low surface porosity, small pore size, and suitable hydrophilicity delivered the highest water flux and separation efficiency (J = 81.1 ± 6.4 L·m −2 ·h −1 , R Na2SO4 = 91.1% ± 1.8%, and R NaCl = 35.7% ± 3.1% at 0.60 MPa). This membrane had a molecular weight cutoff of 292 g/mol and also a high rejection for negatively charged dyes. Therefore, a PSf support exhibiting suitable physicochemical properties endowed a thin-film composite polyamide membrane with high performance.

Mixed matrix membranes (MMMs) were synthesized from poly­(amide-b-ethylene oxide) (Pebax) and mixed-ligand zeolitic imidazolate framework (ZIF-8–90­(x)). The separation performance and microstructure of the membranes with different organic linker fractions and ZIF-8–90­(x) loadings were characterized. Energy-dispersive X-ray microanalysis and field-emission scanning electron microscopy showed excellent adhesion between Pebax and ZIF-8–90­(x), and no voids or clusters were observed. Single gas permeation measurements on MMMs revealed that the CO2/N2 selectivity of the membranes with ZIF-8–90­(x) was better than that of the membrane with ZIF-8. Permeation analysis showed that the membranes with mixed ZIF-8 and ZIF-90 offers a tight microstructure. Overall, this study demonstrated that the gas separation behavior of the Pebax membrane was significantly changed by ZIF-8–90­(x) loading. The ZIF-8–90­(x)/Pebax membranes can be a good candidate for CO2 capture applications.

We applied Simmons–Balluffi methods, positron measurements, and neutron diffraction to estimate the vacancy of CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs) using Cu as a benchmark. The corresponding formation enthalpies and associated entropies of the HEAs and Cu were calculated. The vacancy-dependent effective free volumes in both CoCrFeNi and CoCrFeMnNi alloys are greater than those in Cu, implying the easier formation of vacancies by lattice structure relaxation of HEAs at elevated temperatures. Spatially resolved synchrotron X-ray measurements revealed different characteristics of CoCrFeNi and CoCrFeMnNi HEAs subjected to quasi-equilibrium conditions at high temperatures. Element-dependent behavior revealed by X-ray fluorescence (XRF) mapping indicates the effect of Mn on the Cantor Alloy.