Graphene oxide membranes for lactose-free milk

Abstract

Because of the increasing demand for lactose-free milk, the dairy industry requires lactose separation membranes with effective antiorganic fouling. Here, we demonstrate that graphene oxide (GO) membranes exhibit higher lactose permeation flux (2.87 kg m−2 day−1) than commercial nanofiltration (0.57 kg m−2 day−1) and ultrafiltration (1.61 kg m−2 day−1) membranes, and display excellent water flux recovery (0.89) after milk filtration. Molecular dynamics (MD) simulations demonstrate that lactose exhibits mainly weak van der Waals interactions with GO layers, which allows lactose to diffuse through the nanochannels in GO membranes, whereas fat and proteins are preserved in milk. Fouling on membranes can be initiated via protein adsorption on the membrane surface, which diminishes the filtration performance. Hence, we performed MD calculations and experimental observations, which indicated that protein adsorption was dominated by Coulomb interactions. From milk filtration experiments, the fouling layers on GO membranes were porous, facilitating higher permeation flux and water flux recovery, whereas commercial nanofiltration and ultrafiltration membranes exhibited dense layers and lower water flux recovery. The unique lactose separation and water flux recovery of our novel GO membranes are ideal for food industry, wastewater treatment, medicine, and other related applications.