Low-pressure carbon nanotube membrane with different surface properties for the removal of organic dyes and PPCPs

Low-pressure carbon nanotube membranes (CNT membranes) was prepared with multi-walled carbon nanotubes (MWCNTs), carboxyl functionalized MWCNTs (COOH-MWCNTs) and single-walled carbon nanotubes (SWCNTs). Surface properties of MWCNTs and SWCNTs were further altered by their non-covalent functionalization with Humic acid (HA), Sodium dodecyl sulfate (SDS), Sodium alginate (SA) and Polyethylene glycol (PEG). The CNT membranes with different surface properties were then used for the removal of organic dyes and pharmaceuticals and personal care products (PPCPs). The results revealed that HA/SDS/SA non-covalent functionalized MWCNTs membrane significantly promoted the removal of cationic dye MB, while it slightly interfered the removal of anionic dye RB19. During the dynamic filtration process, a 20∼30% increase of MB removal was promoted by HA/SDS/SA-MWCNTs membrane compared with the MWCNTs membrane, while the HA/SDS/SA-MWCNTs membrane significantly deteriorated the removal of PPCPs. The specific surface area of CNTs played a very important role in the dynamic filtration process of CNT membranes. The removal rate of PPCPs by SWCNTs membranes was almost all above 70% after 120 min’s filtration, and a further 10% increase was promoted by SA-SWCNTs membrane. HA and SDS non-covalent functionalization only slightly deteriorate the removal of PPCPs, and the removal rate of majority of PPCPs by HA-SWCNTs membrane and SDS-SWCNTs membrane remained over 60% and 30%. This work present new insight for the effectiveness of low-pressure CNT membranes in actual application, where the impact of competitive background organic materials on the removal of Low-MW organic pollutants were sometimes overestimated.