Effect of ceramic substrate pore size on the structure and performance of polyamide nanofiltration membrane via interfacial polymerization

Abstract

Thin-film composite (TFC) membranes prepared by interfacial polymerization (IP) have been widely used in wastewater treatment. The substrate pore size plays a critical role on the polyamide (PA) membrane performance. Herein, a variety of PA nanofiltration (NF) membranes on ceramic substrate with different pore size (5 nm (CM-5), 20 nm (CM-20), 50 nm (CM-50), and 200 nm (CM-200)) are successfully prepared via IP. The results depict that substrates with smaller pores have less absorption capacity of the aqueous monomer (piperazine). Reducing ceramic substrate pore size from 200 nm to 5 nm, the formed PA layer transforms from cracked “ridge-and-valley" structure to continuous film. Cross-sectional FESEM images further demonstrate that the PA layer thickness decreases from 106 nm to 29 nm. The pore size of the polyamide membrane on CM-20 is 0.17 nm with a water permeance of 27.3 L m⁻² h⁻¹ bar⁻¹ and Na₂SO₄ rejection of ∼96 %. A smaller pore size of the ceramic substrate might reduce the available space for monomer movement, increasing the collision and reaction between the monomers, which leads to an elevated cross-linking degree of PA (a denser PA layer). Based on the nanofiltration performance, a ceramic substrate with pore size of 20 nm is optimal for the TFC membrane preparation. The obtained membrane keeps stable performance during 72 h operation. The obtained membrane also demonstrates excellent stability in high-temperature environment and in organic solvent. Overall, ceramic substrate with pore size of 20 nm is selected for the preparation of PA NF membrane via IP. The obtained membrane has broad applications in desalination and environmental remediation.