Enhancing nanofiltration in thin film nanocomposite membranes using Bi-Metal modified biochar nanofillers

The advancement in the development of nanofillers for thin-film nanocomposite (TFN) membranes, particularly those derived from eco-friendly sources, has gained increasing recognition. This is largely due to their potential to markedly improve both permeation and selectivity. However, the investigation of biochar (BC), a by-product of biomass pyrolysis, as a distinctive nanofiller remains limited. This study investigates the incorporation of porous iron/zinc (Fe/Zn) modified biochar (MBC) into a polyamide active layer for the purpose of fabricating TFN membranes on a polyethersulfone (PES) substrate via interfacial polymerisation (IP). Imaging confirmed the formation of metal nanoparticles dispersed uniformly throughout the porous BC substrate. Further crystallinity and surface analysis suggest strong interactions between metal and BC substrate, with a surface area of 117.99 m2/g and high nanofiller pore volume of 7.72 cm3/g. The effects of incorporating MBC into both the membrane substrate and polyamide (PA) layers on the physicochemical properties, permeation, and rejection of salts and dye were examined. Scanning Electron Microscopy (SEM) imaging has shown that the incorporation of MBC in both the substrate and PA layer results in the seamless formation of a finger-like structure spanning both layers. This incorporation also causes a minor increase in the surface roughness of the PA layer. Fourier transform Infra-Red (FT-IR) spectroscopy shows an enhancement in hydrophilic functional groups (–OH and –COOH) on the membrane surface, as evidenced by the reduced contact angle value of 55°. Permeation and rejection testing indicate that M5, where MBC was incorporated in both substrate and thin film structure, was the best performing membrane, with water permeance from the feeds of water, MO, MgSO4 and NaCl solutions of 46.55 ± 0.08, 44.49 ± 0.28, 37.43 ± 0.36, and 21.55 ± 0.03 Lm2h-1bar−1, respectively. Rejection of MO, MgSO4 and NaCl were recorded to be 99.53 ± 0.02, 99.25 ± 0.09 and 46.99 ± 0.69 %. This study provides a compelling perspective on the application of green-derived BC as a nanofiller in the fabrication of TFN membranes for desalination, resulting in enhanced water product quality.