F-MWCNTs/AgNPs-coated superhydrophobic PVDF nanofibre membrane for organic, colloidal, and biofouling mitigation in direct contact membrane distillation

Abstract

While membrane distillation (MD) is considered a promising cost-effective and efficient desalination process, it remains severely affected by membrane fouling that compromises the quantity and quality of water recovered. In this study, superhydrophobic PVDF membranes modified with organically-functionalised silica (f-SiO2) nanoparticles (NPs) were synthesized. Silica nanoparticles (SiO2NPs) were functionalised with three different silane reagents, namely: octadecyltrimethoxysilane (OTMS), N-octadecyltrichlorosilane (ODTS), and chlorodimethyl-octadecyl silane (Cl-DMOS), and finally embedded on polyvinylidene fluoride (PVDF) nanofibre membranes using an in-situ electrospinning technique. The resulting superhydrophobic membranes were coated with a thin layer containing carboxylated multiwalled carbon nanotubes (f-MWCNTs) and silver nanoparticles (AgNPs) to reduce membrane fouling. Fouling tests were conducted using sodium alginate, colloidal silica, and thermophilic bacteria effluent as model organic, inorganic, and bio-foulants, respectively, in direct contact membrane distillation (DCMD). The uncoated membranes were characterized by flux decays ranging from 30 to 90% and salt rejection decays of 1.4–6.1 %. Membrane coating reduced the flux and salt rejection decays to 10–24 % and 0.07–0.75 %, respectively. The hydrophilic coating layer of the nanofibre membrane induced a decrease in the initial water flux (i.e., from 36-42 LMH to 16–17 LMH). However, this coating layer also proved to be efficient in maintaining high salt rejection and resistance to flux decline. This approach is a suitable one-step solution for fouling mitigation in DCMD