TREATMENT OF SALINE WATER BY NANOFILTRATION PROCESS WITH A MODIFIED POLYAMIDE MEMBRANE MULTI-WALLED CARBON NANOTUBES

The object of this paper is the synthesis and modification of piperazine-polyamide NF membranes using MWCNTs to improve flux of the membranes and to reduce the fouling which is the main concern of the similar studies. Multi-walled carbon nanotubes (MWCNTs) were exposed to acid solution containing HNO3 and H2SO4 to synthesis of oxidized MWCNTs and used for preparation of piperazine-based polyamide thin film nanocomposite nanofiltration membrane. Both raw and oxidized MWCNTs were applied in the fabrication of the membranes with four different concentrations of 0.001, 0.002, 0.005, and 0.01 wt% in the piperazine solution. Salt rejection, permeation, and antifouling properties of unfilled, raw and oxidized MWCNTs embedded membranes were investigated. Water flux for 0.005 wt% oxidized MWCNTs was 65.7 L/m2h which increased significantly due to this fact that membrane hydrophilicity improved as a result of functionalization of MWCNTs. Contact angle measurements confirmed the improvement of hydrophilicity by adding oxidized MWCNTs to the membranes. Surface SEM images illustrated that the MWCNTs made surface of the membranes smoother and macro-voids enlargement leads to water flux enhancement. The antifouling properties were investigated using bovine serum albumin (BSA)/salt solution. The results showed that the membranes with a smoother surface had a better resistance against the fouling. The salt rejection performance exhibited that by embedding of the raw MWCNTs and oxidized MWCNTs, improvement in rejecting of Na2SO4 salt can be observed. Rejection for 0.005 wt% oxidized MWCNTs was 97.9% which was the highest among all of the membranes. It can be stated that the addition of raw and oxidized MWCNTs could enhance the performance of the nano filtration membranes in all characteristics of fouling, salt rejection and flux. Moreover, the addition of oxidized MWCNTs could improve the flux rate without any depletion in the salt rejection and also with an improvement in the antifouling properties.