Superhydrophobic Cellulosic Membranes for Membrane Distillation

Membrane distillation (MD) offers robust drinking water solutions to off-grid global communities. However, synthetic polymer-based MD membranes often hamper this goal due to the relative high cost and nondegradable nature. In this study, we demonstrate a composite cellulosic membrane system, using neat microfibrillated cellulose (MFC) as a scaffold and its composite as a barrier layer, in which MFC can be extracted from any lignocellulose biomass source. The membranes exhibited superhydrophobicity (water contact angle >150°), high porosity, and high wet mechanical strength. The superhydrophobicity was induced by the surface microstructure of the barrier layer containing hydrophobic inorganic fillers (precipitated calcium carbonate) dispersed in a cross-linked MFC scaffold treated by a hydrophobic sizing agent. The wet strength and high porosity were achieved by the cross-linking reaction between MFC fibers, which maintained as hydrophilic but water-resistant. The best performing cellulosic membrane was tested for desalination of simulated blackish water and seawater (8 g/L NaCl solution to 35 g/L NaCl solution) using the direct contact membrane distillation (DCMD) method and exhibited high-water flux and high salt rejection ratio, comparable to the performance of commercial polytetrafluoroethylene (PTFE) membranes. The demonstrated composite cellulosic membrane system, manufactured by using typical papermaking ingredients and procedures, offers promising features that can replace synthetic polymeric membranes for sustainable MD operations.