Tunable separation via chemical functionalization of polyvinylidenefluoride membranes using piranha reagent

Polyvinylideneflouride (PVDF) has considerable usage in different disciplines including sensors, piezoelectric materials, biomedical application as well as membranes. In this paper, facile and effective method for the activation of inert PVDF surface and molecular grafting of this material is presented. Mild concentration of piranha reagent used to generate hydroxyl groups on the surface of the polymer through a free radical reaction. Functionalization was investigated as a function of reaction time and concentration. For characterization, various analytical methods and techniques were employed including infrared spectroscopy, scanning electron microscopy, X-ray diffraction, atomic-force microscopy, and contact goniometry. Physicochemical properties including contact angle, surface free energy, surface tension, work of adhesion as well as morphological properties (e.g. pore size distribution and roughness) were evaluated. Subsequently, membranes were tested for desalination, volatile organic compounds removal, and apple juice concentration in various modes of membrane distillation. Significant increase in pore size (53%), surface roughness (43%), and flux (from ca. 8 kg m^-2 h^-1 to 10.5 kg m^-2 h^-1) were found. Fouling mitigation was also noticed in comparison to unmodified membranes. Flux decline was equal to 37.5% and 5.1% for unmodified PVDF and PVDF membrane activated for 1 min by 20% Piranha reagent, respectively.