The role of carboxylated cellulose nanocrystals placement in the performance of thin-film composite (TFC) membrane

Nanomaterials have been used in the formulation of thin-film composite (TFC) membranes to improve membrane performance and reduce environmental impact. Here we investigate the role of nanomaterial placement in the active layer versus the support layer of the TFC using carboxylated cellulose nanocrystals (C–CNCs) with high hydrophilicity, aspect ratio, excellent mechanical strength and sustainability. Placement of the C–CNCs in the active layer of the membrane (ALC) yielded a higher permeate flux, while incorporation of these materials in the support layer of the membrane (SLC) improved salt rejection. With different incorporation positions of C–CNCs, the dominant mechanism for salt rejection was different for the ALC and SLC membranes. Surface characterization by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy confirmed the successful incorporation of C–CNCs into ALC and SLC membranes. ALC membrane exhibited higher hydrophilicity and more negatively charged surfaces, while SLC membrane displayed thicker and denser polyamide layers. In addition, the enhancement of the mechanical properties of the SLC membrane was superior to that of the ALC membrane due to better compatibility between C–CNCs and the polyethersulfone ultrafiltration support. Significantly, this comparison between the different incorporation positions of nanomaterials provides new insights into the targeted construction of TFC membranes for water treatment.