Double Polyamide Layers with CaCO3 Nanoparticles as Scaffolds for High Performance Nanofiltration Membranes

Nanofiltration (NF) membranes commonly with a single polyamide (PA) barrier layer play a significant role in the fields of separation and purification. Herein, an NF membrane with double PA layers was successfully fabricated through interfacial polymerization (IP) of a diamine with trimesoyl chloride, and CaCO3 nanoparticles were used as scaffolds. The upper PA layer grounded on the nano-CaCO3 aggregates was incomplete with multidefects. Trimesoyl chloride solution could permeate through the multidefect PA layer to continue IP reaction with diamine underneath the multidefect PA layer to form a bottom defect-free PA layer. The double PA layers almost fitted together, and additional nanovoids were left after removing nano-CaCO3 particles by HCl. The NF membranes with double PA layers exhibited a high water permeance of 34.1 L·m–2·h–1·bar–1, 3.4-fold that of the control sample without sacrificing selectivity. This was attributed to the enhancement of the hydrophilicity and effective filtration area and decrease in PA layer thickness, as well as additional nanovoids to reduce transport resistance. The antifouling performance of the NF membrane was found to be superior to that of the control sample possibly because the upper thin PA layer as a protective layer reduced the contamination to the separation layer.