Membranes have an increasingly important role in alleviating water scarcity and the pollution of aquatic environments. Promising molecular-level design approaches are reviewed for membrane materials, focusing on how these materials address the urgent requirements of water treatment applications.
Chemistry at the nexus of water and energy
Our ability to harness reactions that absorb or release energy is often contingent on water as a mediator. We can appreciate this simply by considering the steam that drives our electricity-generating turbines, the rivers that flow through our hydroelectric plants, and the freshwater–saltwater interface from which we can harvest blue energy. Whether we split water (as plants do), make it (as a product of combustion) or just drink it, this compound is inexorably tied to energy. Chemistry is at the heart of these topics and this collection brings together content from across Nature Research that focuses on the chemistry of energy production and water treatment.
Cations are used to control the interlayer spacing of graphene oxide membranes, enabling efficient and selective sieving of hydrated cations.
Few-layered, vertically aligned MoS2 films can efficiently harvest visible light for photocatalytic water disinfection, allowing >99.999% bacteria to be rapidly inactivated.
Ion permeation and selectivity of graphene oxide membranes with sub-nm channels dramatically alters with the change in interlayer distance due to dehydration effects whereas permeation of water molecules remains largely unaffected.
Scalable graphene-based membranes reject more than 80% NaCl under aggressive shear for more than 20 h and exhibit chlorine resistance.
Electro-oxidation of CNT Joule heaters can be eliminated through the application of sufficiently high a.c. frequencies, which enables their use as self-heating membranes in membrane distillation.
Solar energy can be used to evaporate water and generate steam, however this usually requires expensive optical concentrators. Ni et al. demonstrate a low-cost solar receiver based on thermal concentration that generates steam at 100 ∘C without the need for optical concentration.
Water treatment processes mostly rely on the use of membranes and filters, which have high pumping costs and require periodic replacement. Here, the authors describe an efficient membraneless method that induces directed motion of suspended colloidal particles by exposing the suspension to CO2.
Nanoparticles can act as absorbent materials for environmental clean-up due to their high surface-to-volume ratio, but subsequent removal can be difficult. Here, the authors report nanoparticles that aggregate upon UV radiation, allowing them to absorb pollutants from water and subsequently be removed in the aggregated state.
Carbon nanotubes have been proposed for many forms of water treatment, although ultrafiltration nanotube-based membranes with very high flow rates remain rare. Here, the authors fabricate a membrane delivering water permeability close to 30,000 litres per square meter per hour at 1 bar.
Spider-silk-mimicking microfibers often suffer from low efficiency and durability in water collection. Here, the authors fabricate robust microfibers with spindle cavity-knots and different topological fiber-networks with improved water-collecting performance