Hierarchically aligned reduced graphene oxide/MXene foam enabling Marangoni-driven salt-resistant desalination via bidirectional ion reflux.

Interfacial solar desalination has emerged as a sustainable pathway for treating high-salinity brines, but the non-equilibrium phase transition at the evaporation frontier inevitably induces self-amplifying crystallization to reduce purification efficiency. Herein, a hierarchically aligned reduced graphene oxide/MXene (Mr) foam is fabricated to optimize ion transport channels while reducing optical scattering interfaces that enhance solar energy utilization. The aligned layered structure with interconnected anisotropic microchannels is built under dual temperature gradients with the ice crystal exclusion, which significantly shortens the water transport path and facilitates diffusion and reflux of salt ions. The finite element simulations validate the exceptional photon-to-thermal energy efficiency of Mr foam coupled with inherently low thermal conductivity, synergistically suppressing heat dissipation through thermal localization strategy. The steep thermal gradient originating from the liquid-vapor interface propagates through the subsurface aqueous phase, establishing a localized surface tension differential that activates spontaneous Marangoni convection currents, which drives self-sustaining hydrodynamic patterns to suppress salt accumulation. Consequently, the Mr foam achieves a water evaporation rate of 2.04 kg m h under 1 sun irradiation. Importantly, it maintains a stable evaporation rate of 1.76 kg m h over 100 h in 25 wt% NaCl solution, which demonstrates a great potential for efficient and long-term solar desalination.