Polyethersulfone ultrafiltration membranes embedded with Zn-Cr LDH with improved hydrophilicity and dye separation performance

This study reports the synthesis of zinc-chromium layered double hydroxide (Zn-Cr LDH) via a co-precipitation technique and the incorporation of the resulting LDH into polyethersulfone (PES) membranes to improve the filtration performance. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis confirmed layered morphology for the synthesized Zn-Cr LDH. The phase inversion method was used to fabricate membranes with various LDH particle contents (0–1 wt%). The morphology studies of the prepared membranes revealed an asymmetric structure, including small pores on the top layer and larger, finger-like pores and macro-voids in the sublayer. The porosity of the Zn-Cr LDH blended PES membranes increased with higher LDH content, reaching a maximum at 0.75 wt% LDH, with a porosity of 51.6 % and a mean pore size of 9.8 nm. Contact angle measurements revealed that incorporating Zn-Cr LDH decreased the contact angle, improving the hydrophilicity of the membranes. The addition of 0.5 wt% Zn–Cr LDH increased the pure water flux from 135.6 L/m²·h for the unmodified PES membrane to 222.3 L/m²·h, demonstrating significantly enhanced permeability. Flux recovery ratio analysis demonstrated superior antifouling properties for the Zn-Cr LDH modified membranes compared with unmodified membranes. Additionally, the Zn–Cr LDH/PES blended membranes exhibited higher efficiency in separating the anionic dyes Reactive Red 195 and Direct Yellow 12, with the membrane containing 1 wt% LDH achieving 92.90 % rejection of Reactive Red 195, and the 0.5 wt% LDH-modified membrane showing the highest rejection of 77.72 % for Direct Yellow 12.