Modification of a Highly Permeable Thin-Film-Based Nanofiltration Membrane (PVC) to Increase Efficiency and Separation by Air Plasma Treatment

In this research, considering the superhydrophobic properties of nanofiltration (NF) membranes with very high permeability based on polyvinyl chloride (PVC), its surface modification by plasma and its effect on membrane performance have been investigated. To make membranes, PVC polymer was used as the base polymer, dimethylacetamide, and tetrahydrofuran in the ratio of 15:85 as a solvent. The surface modification of thin-film NF membranes under the effect of Air plasma in a plasma cleaner device applied with the power of 20, 40, and 60 W has been investigated. The best power to achieve the hydrophilic surface in irradiation for 5 min at a pressure of 80 mTorr in the chamber is 60 W, and the contact angle of 12° is obtained in this case. The results of the FTIR spectrum definitely confirmed the formation of amide and amine functional groups on the surface of the modified membrane compared to the control membrane, due to the formation of these polar functional groups, the modified surface became hydrophilic. Scanning electron microscopy (SEM) images showed that the surface of the membrane changed after plasma treatment and the plasma-treated membranes had a smoother surface than the control membrane. The surface roughness in AFM analysis was found to be 32.85 nm for the control membrane and 12.83 nm for the membrane modified by the plasma method. The results of CA showed a significant decrease in the contact angle from 101° to 12°, this change in contact angle clearly indicates the increase in the hydrophilicity of the surface of the modified membranes. The water flux increased with increasing applied power, and an opposite trend was observed for salt rejection. Salt rejection was measured at 76% for plasma-treated membranes and 85% for the control membrane. The computational results from the MATLAB code program, for example, water flux 29.0523 (L/ $\text{m}^{2}~\cdot $ h) close to laboratory results 31 (L/ $\text{m}^{2}~\cdot $ h), were obtained.