Self‐Assembly in “Matrix‐Free” Functionalized Boron Nitride Sheets as Free‐Standing Thin Film Sieves for Stable Forward Osmosis and Robust Dye Removal Applications

Abstract

AbstractHerein, a facile “matrix‐free” thin film membrane strategy is reported that exploits polymer brushes grafted hydroxyl‐functionalized hexagonal boron nitride nanosheets (h‐BNOH) toward forward osmosis desalination and dye rejection application. The functionalized nanosheets are characterized using Fourier transform infrared spectroscopy (FTIR), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), Nuclear magnetic resonance (NMR), UV–visible spectrophotometry, and thermogravimetric analysis (TGA). Covalently functionalized nanosheets of poly methyl methacrylate (PMMA) termed as boron nitride grafted PMMA (BN‐g‐PMMA) obtained via RAFT polymerization are deployed toward “matrix‐free” nanocomposite membranes.  The membranes exhibit ≈5260 L /m−2 h−1 at a moderate pressure of 0.21 MPa in cross‐flow mode and a 70% of flux retention ratio against bovine serum albumin as protein foulant. The matrix‐free membranes exhibit ≈93% salt rejection for NaCl and >99% rejection for MgCl2 and Ca(NO3)2·4H2O for 2000 ppm draw solution (water TDS benchmark for domestic purifiers) while 90% NaCl, and >96% rejection for MgCl2 and Ca(NO3)2·4H2O for 5000 ppm draw. In simulated domestic water salinity, 97.8% rejection is observed for 2000 ppm and 94.5% for 5000 ppm draw solution, respectively. The matrix‐free membranes also achieve almost 100% dye rejection for eight model dye pollutants at 1 ppm and >96.6% for 10 ppm concentrations, respectively.