Humic acid non-covalent functionalized multi-walled carbon nanotubes composite membrane and its application for the removal of organic dyes

It was the first time that humic acid (HA) was used to non-covalent functionalize multi-walled carbon nanotubes (MWCNTs). The MWCNT and HA-MWCNT was characterized by X-ray photoelectron spectroscopy (XPS), infrared spectra (IR) and transmission electron microscopy (TEM). Then, a HA non-covalent functionalized multi-walled carbon nanotubes (HA-MWCNTs) membrane was prepared by vacuum filtration and used to remove organic dyes. To investigate the removal mechanism of organic dyes by HA-MWCNTs membrane, the dynamic filtration effectiveness of HA-MWCNTs membrane was compared with the adsorption ability of HA-MWCNTs. The results proved that HA-MWCNTs membrane had a higher effectiveness for the removal of dyes as it had shorter filtration time compared with the static adsorption experiment. Especially, the HA-MWCNTs membrane had a higher removal efficiency for cationic dye methylene blue (MB) than the raw MWCNTs (P-MWCNTs) membrane. The electrostatic interaction played an important role on the removal of MB, and the functionalization of MWCNTs with HA increased the surface electronegativity of MWCNTs membrane, and promoted the removal of MB during filtration process. As for RB19, in addition to π–π stacking interaction, electrostatic interaction also influenced its removal by MWCNTs membrane. Compared with P-MWCNTs membrane, HA-MWCNTs membrane slightly decreased the effectiveness of RB19 removal during filtration due to the increased electrostatic repulsion. Generally, the dynamic membrane filtration based on MWCNTs composite membrane could avoid the ecological risk caused by the release of MWCNTs. It provided a new idea for the further innovation of low-pressure membrane technology in the field of dye wastewater treatment. • Compared with static adsorption, MWCNTs composite membrane had a higher effectiveness for the removal of organic dyes. • HA non-covalent functionalized MWCNTs composite membrane promoted the removal of cationic dyes. • The MWCNTs dynamic membrane filtration could avoid the ecological risk caused by the release of MWCNTs.