Effects of locations of cellulose nanofibers in membrane on the performance of positively charged membranes

Cellulose nanofibers (CNFs) with high hydrophilicity and huge specific surface area have great prospect for upgrading the performance of thin-film composite (TFC) membranes, but the optimal location for their incorporation in the membrane is still unclear. Herein, we studied and compared the effects of nanomaterials locations: i) embedded in the active separation layer (Embedded-CNFs), and ii) as an interlayer between the support layer and the active separation layer (Interlayered-CNFs) on the performance of positively charged membrane. The effects of CNFs locations on the TFC membrane's structure, morphology, physicochemical properties and performance were investigated by a series of characterizations. Compared with the Control membrane, both the Embedded-CNFs membrane and Interlayered-CNFs membrane had improved separation performance. Specifically, the Interlayered-CNFs membrane achieved a significantly improved water flux of 270% (53.1 Lm−2h−1 at 4 bar) with high MgCl2 rejection while the Embedded-CNFs membrane had an increased flux of 135%. Our work provides insights and directions for designing and constructing of high-performance positively charged composite membranes using environmentally friendly CNFs.