In Situ Growth of MOF-303 Membranes onto Porous Anodic Aluminum Oxide Substrates for Harvesting Salinity-Gradient Energy

As an emerging metal-organic framework (MOF) material in recent years, the MOF-303 membrane has shown great potential applications in seawater desalination, dehydration, and atmospheric water harvesting. Herein, we report on a dense and uniform MOF-303 membrane fabricated by a facile in situ hydrothermal synthesis approach in the presence of an anodized aluminum oxide (AAO) channel membrane acting as the only Al source and substrate. Interestingly, the MOF-303 isomer can be obtained due to an insufficient amount of organic ligand caused by the less hydrophilic and larger pore size of the AAO substrate. The MOF-based composite membranes possessed surface-charge-governed ionic transport behavior. Moreover, the MOF-303/AAO membrane yielded an output power density of 1.87 W/m² under a 50-fold KCl concentration gradient. Under a 50-fold gradient of artificial seawater and river water, a maximum power density of 1.46 W/m² can be obtained. After 30 days of stability testing, the composite membrane still maintained the power output, and the power density was higher than 1.20 W/m². This work provides a facile and effective strategy for constructing Al-based MOF composite membranes and boosts their applications in harvesting salinity-gradient energy.