The potential of pristine and cobalt-incorporated AlPO4-5 zeotype fillers in the separation enhancement and organic fouling mitigation of polyethersulfone ultrafiltration membranes

Abstract

In this study, novel ultrafiltration (UF) membranes were prepared via blending AlPO4-5(100), AlPO4- 5(400), 2.5CoAPO-5(100), 2.5CoAPO-5(400), 5.0CoAPO-5(100), and 5.0CoAPO-5(400) into polyethersulfone (PES) membrane to improve their selectivity for separation of bovine serum albumin (BSA) from water, as well as antifouling properties. Each filler had a distinct morphology (plate-like – 100H2O: 1 Al2O3, and hexagonal columnar – 400H2O: 1 Al2O3), and extent of cobalt loading (0, 2.5, and 5 mol%) that influenced the membrane performance differently. All hybrid membranes were fabricated with nonsolvent induced phase inversion (NIPS) technique. Prior to composite membrane fabrication, the fillers were hydrothermally synthesized, and were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), and fourier transform infra-red spectroscopy (FTIR) to confirm the AFI crystalline framework, morphology, and successful cobalt isomorphous substitution of AlPO4-5, respectively. Next, the PES/2.5CoAPO-5(100) blend membranes were optimized by varying the filler concentration from 0 to 10 wt.% in the casting solution. The membranes were characterized using surface zeta potential, porosity and mean pore size testing, contact angle measurements, atomic force microscopy (AFM), thermal gravimetric analysis (TGA), tensile strength testing, FTIR, and SEM. The surface charges, topology, and wettability were altered due to the incorporation of 2.5CoAPO-5(100). The hybrid membrane's pure water flux and rejection was greatly dependent on the amount of 2.5CoAPO-5(100) incorporated within the membrane matrix. The maximum water flux (563 L m-2 h -1 bar-1 (540 ℃)), obtained using the membrane with 2 wt.% 2.5CoAPO-5(100), was almost 36% higher than that membrane without 2.5CoAPO-5(100) (414 L m-2 h -1 bar-1 (540 ℃)). The fouling resistance and BSA retention capabilities of the membranes were examined through dead-end UF tests of 50 ppm synthetic BSA solution at 1 bar feed pressure and neutral pH. The hybrid membrane with 6 wt.% 2.5CoAPO-5(100) loading exhibited remarkable improvement over the pristine one, rejecting more that 88%, and recovering 93% of its initial water flux after washing. Another set of hybrid membrane were fabricated, at a fixed filler loading of 6 wt.% that were calcined at 540 ℃ to investigate the effect of crystal morphology and cobalt loading on the antifouling and performance of the membranes. The membranes were analogously characterized as the first set of composite membranes. Performance-wise the incorporation of the moderately hydrophilic AlPO4-5(400) filler of cylindrical structure has overall improved the PWF (688.7 L m-2 h -1 bar-1 ), which surpass the pristine PES flux (487.2 L m-2 h -1 bar-1 ). The plate-like structure blend membrane of narrower pores resulted in a lower value (467 L m-2 h -1 bar-1 ). Crystal structures with cobalt ion has introduced new hydrophilic sites (negatively charged, Bronsted-acid sites) that not necessarily affected the PWF, instead improved the BSA rejection. The maximum BSA rejection of 99.4% was noted for the 5CoAPO(400) membrane, whereas the 5CoAPO(100) membrane rejected 96.8% of the BSA in the feed.

Date of Award	May 2021
Original language	American English