Improved Salts Transportation of a Positively Charged Loose Nanofiltration Membrane by Introduction of Poly(ionic liquid) Functionalized Hydrotalcite Nanosheets

Basically, commercialized nanofiltration membranes exhibit a salt (NaCl) rejection of >30%, which are difficult to accomplish the separation of low-molecular-weight organics from their salts-containing wastewater. To solve this problem, in this study, a facile and novel loose nanofiltration membrane was developed by the embedment of modified hydrotalcite (mHT) in poly(ether sulfone) (PES) membrane matrix upon a phase inversion method. Membrane performance was characterized by scanning electron microscopy (SEM), water contact angle, transmission electron microscopy (TEM), atomic force microscopy (AFM), water uptake, tensile strength and percentage elongation, and thermal stability. Nanofiltration tests were performed using a series of salts (MgCl₂, MgSO₄, NaCl, and Na₂SO₄, 0.5 g/L) and dyes (reactive black 5 and reactive red 49, 1 g/L) aqueous solutions to evaluate membrane permeation properties. The resulted membrane showed higher surface hydrophilicity, enhanced mechanical and thermal stability, as well as higher dyes retention (above 95% for reactive black 5 and around 90% for reactive red 49) and near-zero salts rejection properties. Moreover, the short-term operation test demonstrated the stability of flux and rejection of mHT mixed PES membrane for dyes desalination. Therefore, this loose nanofiltration membrane may have potential applications in separation of dyes from salts-containing wastewater.