Hydrophobic Montmorillonite/PVDF Membrane: Experimental Investigation of Membrane Synthesis toward Wetting Characterization and Performance via DCMD

High wetting resistance membranes are developed to reduce wetting issues during membrane distillation (MD). Functionalization agents are used to improve the wetting characteristics of the prepared membranes. In this study, two pristine membranes of polyvinylidene fluoride with different solvents (N-methyl-2-pyrrolidone and triethyl phosphate) were prepared to compare their wetting characteristics. The polyvinylidene fluoride/triethyl phosphate (PTEP) membrane exhibited a high liquid entry pressure (LEP) of 2.63 bar, while the polyvinylidene fluoride/N-methyl-2-pyrrolidone membrane obtained a lower LEP of 0.30 bar. In this work, an ideal natural water repellent was introduced to synthesize a high wetting resistance membrane with comparison of fluoroalkyl silane. The selected PTEP membrane was improved by adding functionalized montmorillonite (Mt) with 1H, 1H, 2H, 2H-perfluorooctyl-trichlorosilane (FOTS, f_s-Mt) and carnauba wax (f_w-Mt). The addition of f_s-Mt and f_w-Mt particles to the PTEP membrane significantly increased the LEP and contact angle (CA) of the prepared membranes. The Pf_w-Mt membrane obtained the highest LEP value (4.10 bar) with a CA of 124°. The permeate flux of Pf_s-Mt and Pf_w-Mt membranes improved to 6.86 and 4.12 L/m²h, respectively, after 16 h of separation. Field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy proved the absence of Na and Cl elements in the inner morphology of Pf_w-Mt membranes after 24 h of direct contact membrane distillation. Hence, Pf_w-Mt membrane can be an alternative MD membrane for salt removal in long-term operation due to the self-cleaning effect that prevents membrane fouling.