Fabrication of aramid-coated asymmetric PVDF membranes towards acidic and alkaline solutions concentration via direct contact membrane distillation

An asymmetric membrane for direct contact membrane distillation (DCMD) was first prepared with the ability to concentrate strongly acidic and alkaline solutions. The membrane was fabricated by a simple coating and non-solvent phase separation process. The successful preparation of the aramid-coated polyvinylidene fluoride (PVDF) asymmetric membrane was demonstrated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) characterization. Furthermore, it was verified via contact angle measurements that this modified membrane had better acid and alkali resistance than the pristine PVDF membrane at an elevated temperature. During the DCMD process, the pH of the permeate side did not fluctuate significantly when solutions with different pH values were used as the feed solutions, thus also demonstrating the excellent separation efficiency of the modified PVDF membrane. Moreover, the modified PVDF membrane exhibited a higher concentration factor for acidic and alkaline solutions than the pristine membrane. Therefore, it is believed that the modified membrane has great potential for application in DCMD process with the concentration of acidic and alkaline solutions.