LBL assembled polyelectrolyte nanofiltration membranes with tunable surface charges and high permeation by employing a nanosheet sacrificial layer

Abstract

Polyelectrolyte membranes provide a highly promising platform for an efficient and sustainable nanofiltration (NF) process. The challenge is to prepare polyelectrolyte NF membranes with high permeation. Herein, we report a novel strategy to fabricate a polyelectrolyte membrane via a layer-by-layer (LBL) self-assembly technique with a Ni(OH)₂ nanosheet sacrificial layer for a fast NF process. The sacrificial layer helps to deposit a LBL assembled polyelectrolyte layer directly on a microfiltration (MF) substrate and thus results in the formation of a membrane with tiny filtration resistance. Meanwhile, the surface charges and thickness of the membranes can be adjusted facilely by the number of assembled layers. The resultant membranes show excellent NF performances with a high water flux of up to 466 L m⁻² h⁻¹ bar⁻¹, perfect rejection for organic dye molecules and moderate salt rejection (88.2% MgSO₄). Typically, the 570 nm-thick membrane has the water flux of 198 L m⁻² h⁻¹ bar⁻¹, 98% rejection for dyes (M_w 373.9) and 81.3% rejection for MgCl₂. Furthermore, the membrane has a good rejection and anti-fouling ability for organic molecules with similar charges. The newly developed strategy has wide application in the fabrication of highly permeable polyelectrolyte membranes.