Two-dimensional hybrid membranes with tunable nanochannels for the ultrafast recovery of precious metals from seawater

The design of advanced membranes for achieving energy-efficient applications such as clean energy harvesting, water purification, environmental remediation and resource recove...ery from seawater have attracted tremendous attentions in recent years [1-4]. In particular, high performance molecular-sieving membranes have been designed strategically for potable water production [5, 6]. By the stacking of graphene oxide nanosheets, membrane assembly with high water permeance and molecular sieving characteristics were fabricated [7-9]. However, the redispersion of the GO membranes due to the hydrophilic functional groups on the surface often result in poor durability, thus limiting their applications [10, 11]. Meanwhile, the partial reduction of the GO nanosheets to form the reduced GO membrane resulted in the formation of compact laminar channels with high durability [12, 13]. This strategy, although a significant improvement on the existing GO membranes, often results in a compromise of water flux by the creation of tight interlamellar spacings across the membrane. Thus, the design of interlocked network structures within the 2D channels is considered a better strategy to prevent the redispersion of the GO membrane and achieve high molecular separations [14-16]. Recent studies have shown that hybrid ultrathin transition metal dichalcogenides/graphene nanosheets have achieved high-rate energy applications for the fast intercalation/de-intercalation of Li+/Na+ ions [17]. By combining this approach with the carefully controlled inter-layer grafting of ion-sieving molecules such as the crown ethers, a new class of hybrid 2D membranes with tunable nanochannels for the ultrafast recovery of precious metal ions from seawater and desalination brines can be fabricated. We thus propose a strategy for the fabrication of hybrid 2D membranes with tunable nanochannels for the recovery of precious metals from seawater. The hybrid membranes shall comprise of 2D layered TMDs and high carrier mobility materials such as graphene and hexagonal boron nitride, cross-linked through crown ether grafting. The grafted crown ethers of shall prevent the restacking of the 2D layers, provide sufficient hydrophilicity and create suitable nanochannels for ion-diffusion. It is believed that this study shall pave the way for the fabrication of next generation of membranes with high ion-conductivity for resource recovery and clean water and energy applications.