Fabrication of superhydrophilic/underwater superoleophobic functionalized-nanoparticles/PVDF-supported thin film composite polyamide membranes for efficient water purification

Abstract

For water treatment, membrane-based separation methods are very essential owing to long-term efficiency, high mechanical stability and durability. The filtration process with polymer-inorganic and organic composite is an outstanding strategy that enhances the properties of both inorganic materials such as thermal and mechanical stability and organic material including flexibility and processability of the membranes. Therefore, the surface wettability of the membranes is vital for pollutants separation. Here, the high hydrophobic behavior of polyvinylidene fluoride (PVDF) membranes is altered to superhydrophilicity and underwater superoleophobicity via single-step coating. This PVDF membrane has high molecular separation due to the ultrathin thickness and good controllable interlayer. In this study, the PVDF membrane was by interfacial polymerization coated with a polyamide (PAm) layer, modified alumina nanoparticles (Al-NPs), (aminopropyl)triethoxysilane (APTES), and folic acid (FA) through a chemical grafting reaction. The influence of the PAm and Al-APTES-FA content on the morphology, structure, antifouling, and superhydrophilicity of the PVDF-g-PAm@Al-APTES-FA membrane has been investigated which has enhanced the oil and salt rejection as well as filtration performance. Fourier Transform Infrared (FTIR) spectroscopy showed the specific functional groups from the obtained results indicating the successful preparation. Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX), and AFM (Atomic Force Microscope) techniques were conducted to observe the membrane surface morphology, roughness, and elemental adsorption after the filtration process. Furthermore, this modified PVDF membrane exhibited an excellent superoleophobicity with underwater oil contact angle (OCA~145°), and superhydrophilic visualization with water contact angle (WCA ~ 0°) after being functionalized. Additionally, the parameters of membrane performance such as permeate flux, heavy metal ions, oil and salts rejection, were assessed. The modified material on the PVDF membrane enhanced the membrane efficiency under high operating pressure of 10 bar with 53 LMH (L.m−2 h−1, while it is ≈0 for PVDF membrane), permeate flux, over 90 % salt rejection, and almost 100 % hydrocarbons and heavy metal ions rejection, owing to membrane surface changes, hydrophilicity, and roughness. This research will provide new insights on porous surface transformation to improve the separation and antifouling properties of PVDF membranes used in water purification.