(507f) All-in-One, Robust, Ready-to-Use, 3D Interconnected Hydrogels for Efficient Water Desalination

Water scarcity is one of the most pressing challenges facing human society, especially in remote rural areas. Solar evaporation and capacitive deionization (CDI) using porous hydrogels have demonstrated efficient desalination performance to ensure an affordable clean water supply. However, it remains challenging to realize low-cost, ready-to-use, and 3D interconnected porous materials with tunable physicochemical properties for rapid and energy-efficient water desalination. Here, a simple yet effective electro-formation method is adopted as an advanced platform technology to fabricate mechanically durable, ready-to-use, and low-cost hydrogels with abundant internal capillary channels composed of a hydrophilic polymer framework (sodium alginates, SA) and solar absorber (Ti₃C₂Tx MXene nanosheets) (referred to as M-hydrogels). First, the M-hydrogels with 3D cone configurations can be applied directly for solar evaporation. The SA can significantly facilitate water evaporation because of the reduced water evaporation enthalpy in the hydrogel network. The MXene nanosheets penetrating into the polymeric network enable efficient solar-thermal energy conversion. The M-hydrogels exhibit a highly interconnected porous structure with low tortuosity, enabling fast water transport. The abundant air in the unique 3D hollow tubular hydrogel acts as an excellent natural thermal barrier and facilitates heat localization on the top surface of the evaporator, which has a positive impact on the evaporation rates. In addition, our 3D hollow tubular hydrogel can absorb energy from the environment because the lateral surface temperature of the hydrogel absorber is lower than the ambient temperature during operation. With excellent mechanical properties, the 3D M-hydrogels are easy to process without damage during solar evaporation operation. As a result, the 3D M-hydrogels show highly efficient and stable evaporation with an evaporation rate of 3.4 kg m^-2 h^-1 and ~ 94% solar-to-vapor efficiency. The hydrogel-based solar evaporator also shows excellent antifouling properties, enabling long-term stable water desalination without the need for maintenance. Second, after a freeze-drying process, the M-hydrogels become lightweight, electrochemically active M-aerogels, which are applied as the CDI electrodes. The M-aerogels demonstrate high salt adsorption capacity (33.3 mg g^−1) and long-term operation reliability (over 30 cycles), showing an outstanding desalination performance compared to previously reported results. It is expected that this simple yet effective electroforming strategy, which does not involve complex and expensive 3D printing technology, will accelerate the industrialization of gel-based desalination devices for practical applications.