Efficient removal of fluoride ion by the composite forward osmosis membrane with modified cellulose nanocrystal interlayer

Abstract

In this paper, the performance of three-layer film composite (TFC) forward osmosis (FO) membrane for the retention of fluoride ions was investigated. A cellulose nanocrystal (CNC) interlayer was introduced on the porous substrate by coating method to enhance the hydrophilicity and retention capacity of the FO membrane. In order to improve the dispersibility of CNC, boric acid (BA) and (3-aminopropyl)triethoxysilane (APTES) were used for chemical modification, respectively. The characterization results demonstrated the successful introduction of CNC, BA/CNC and APTES/CNC–CNC interlayers. The introduction of the interlayer enhanced the hydrophilicity of the membrane and increased the negative surface charge, which facilitated the transport of water molecules and the retention of fluoride ions. The FO tests indicated that the water flux of TFC/CNC membrane was increased by 46.4% compared to the original TFC membrane, and the water flux of TFC/APTES-CNC and TFC/BA-CNC membranes were higher than that of TFC/CNC membranes by 5.9% and 13.0%, respectively. 97.0% and 97.6% of the fluoride ions of TFC/BA-CNC and TFC/APTES-CNC could be retained. Based on the molecular simulation of adsorption, it was demonstrated that BA-CNC interlayer was more favorable for the adsorption of water molecules than CNC and APTES-CNC interlayer. This study contributes to the development of high-performance TFC-FO membrane for the treatment of wastewater containing fluoride.