Metal-organic frameworks/graphene oxide nanohybrids to control pore wetting in membrane distillation
Andoni Moriones, Lucía Cano-Herranz, José Miguel Luque‐Alled, Carlos Téllez, Patricia Gorgojo
Abstract
Membrane distillation (MD) is an emerging technology in the field of water desalination due to its high-energy efficiency and the fact that is not affected by feed salt concentration. As an alternative to feed water pre-treatment, membrane surface modification aims at changing different properties to make it less prone to fouling. This work addresses the mitigation of the most concerning membrane degradation effects in MD, such as pore wetting and fouling, by modifying the membrane surface. This work takes advantage of the adsorption properties of metal-organic frameworks (MOF)@graphene oxide (GO) nanohybrids to create sacrificial sites (located zones where adsorption of foulants is facilitated) on the membrane surface. MOF@GO nanohybrids are embedded between two polydopamine (PDA) layers that are deposited on top of commercial polyethylene (PE) membranes. Two types of MOF@GO nanohybrids were evaluated, one containing UiO-66-NH 2 and the other one ZIF-8. Air gap membrane distillation (AGMD) experiments using highly concentrated foulant solutions to accelerate the effects of membrane degradation, showed that surface modification effectively extended membrane life. The selective foulant adsorption delayed pore wetting and allowed to retain most of the membrane flux. Pore wetting occurred after 109 h for the membrane containing ZIF-8@GO (500 mg·m −2 ), compared to 4–5 h for the unmodified commercial membrane. Due to their high adsorption properties, the presence of MOFs is essential to ensure the formation of sacrificial sites and to maintain the initial flux, thus higher fluxes were observed for MOF@GO membranes (13 kg·m −2 ·h −1 ), compared to those containing only GO (5 kg·m −2 ·h −1 ). • Metal-organic frameworks-graphene oxide nanohybrids were synthesised. • The incorporation of nanohybrids delayed pore-wetting in membrane distillation. • Control membrane showed adequate salt rejection for 4.5 h. • Nanohybrid membranes maintaied very high salt rejection over 100 h. • Adsorption properties of metal-organic frameworks were key to prevent membrane failure.