Easy and resilient spatio-temporal water-salt separation and collection via hydrothermal all-in-one cubic biomass

Biomass-derived materials for solar-driven interfacial evaporation hold great potential as an environmentally sustainable solution to global water scarcity. However, a trade-off persists between the highly efficient evaporation rate and salt deposition in biomass-based materials for future practical application. To address this issue, we demonstrated an all-in-one, constantly recycled cubic biomass evaporator material via simple hydrothermal carbonization, capable of efficient solar water evaporation and controlled localized salt crystallization, thereby enabling the simultaneous separation and harvesting of salt. Then exploring the structure design of biomass, confirmed the suitable practical configuration for balancing the evaporator evaporation rates and salt collection performance. Hydrothermal carbonization treatment preserved the vertical channels of biomass while precisely adjusting pore size and wettability, enabling the evaporator to achieve a stable evaporation rate of ∼2.64 kg m^-2 h^-1(under one Sun irradiation) and reach an energy conversion efficiency of 96.35%. Through the structure design of biomass, spontaneous local salt deposition endows the evaporator with salt collection capabilities. After comparison, the cone-shaped and T-shaped ends of the evaporator provide salt collection capabilities. Reasonable separation of fresh water and salt from high salinity through condensation and gravity assistance, thus avoiding the impact of salt clogging. This straightforward approach to transform waste biomass into efficient separation materials offers potential for sustainable and cost-effective wastewater purification coupled with salt recovery simultaneously.