Functionalised carbon nanotube thin film nanocomposite membranes: A comparison study on the role of backbone monomers and hydraulic pressure on membrane's performance and fouling

Abstract

Thin film nanocomposite (TFN) reverse osmosis (RO) and nanofiltration (NF) membranes have attracted considerable attention for industrial applications in recent years. Among recent nanomaterials used in the fabrication of TFN membranes, carbon nanotubes (CNTs) have gained significant interest due to their unique structure (e.g., tubular shape, mechanical strength, porosity, etc.). Here, the effects of multi-walled carbon nanotubes (MWCNTs) with different functional groups as one of the well proven nanchannel structures and their interaction with two typical monomers, MPD and PIP, were thoroughly investigated. All fabricated membranes were analysed using SEM, FTIR, AFM and contact angle analyzer. Pressure variation significantly affected the performance of membranes over 24 hours of testing. The membranes incorporated with polypyrrole (PPy) modified MWCNTs showed promising results with nearly 37 % and 99 % water flux improvement for the TFN-RO and NF membranes, respectively, compared to the bare (unmodified) TFC RO/NF membranes. Specifically, the water flux of the RO OX-MWCNTs-PPy membrane increased from 18.9 to 25.5 L.m−2.h−1, while the NF OX-MWCNTs-PPy membrane's water flux rose from 45.2 to 90.1 L.m−2.h−1. The salt rejection of RO and NF remained relatively high, with over 90 % salt rejection against NaCl and Na2SO4 for RO and NF membranes. The NF OX-MWCNTs-PPy membrane exhibited a 98.2 % rejection rate for Na2SO4, and the RO OX-MWCNTs-PPy membrane showed around a 98.8 % rejection rate for NaCl. The TFN membranes showed less fouling tendency compared to the TFC membranes. In general, the integration of MWCNTs with various functional groups significantly enhanced the water flux and salt rejection properties of these membranes. Specifically, the modified membranes showed considerable improvements in water flux and maintained high salt rejection rates. Additionally, the interaction between MWCNTs and PIP monomers in TFN-NF membranes exhibited a stronger affinity compared to MPD monomers in TFN-RO membranes, indicating a more promising performance for NF applications. The findings suggest that TFN-NF membranes incorporating MWCNTs hold great promise for future industrial use, offering enhanced performance and reduced fouling rates.