Tailor‐Made Solar Desalination and Salt Harvesting from Diverse Saline Water Enabled by Multi‐Material Printing

Solar-powered interfacial evaporation offers a sustainable, low-carbon solution to freshwater scarcity. Aerogels, hydrogels, and foams are common photothermal materials, yet their isotropic 3D structures from conventional fabrication constrain performance optimization, integrated functionality, and user-defined applications. Herein, photothermal matrices are fabricated via multi-material 3D printing, precisely depositing diverse photothermal inks at designated spatial locations. Synergistic engineering of ink formulations, cation-modulated cross-linking, printing fidelity, hierarchical porosity, and matrix integration enables compositional, structural, and functional heterogeneity for high-performance solar desalination and solute separation across a broad salinity range (3.5-25%). Under 1 sun, 3D steam generators (SGs) attain the highest water evaporation rate of 17.9 kg m^-2 h^-1 in seawater under 2 m s^-1 airflow - 10.5% higher than in freshwater and over six times that under calm air. Even in 25% brine, evaporation rates of 6.6 kg m^-2 h^-1 are retained. Strategic rearrangement of matrix units further produces 3D solar crystallizers (SCs) for localized salt harvesting. The work demonstrates, for the first time, the use of multi-material printing for the flexible fabrication of both SGs and SCs, delivering application-specific photothermal materials that not only enhance evaporation in seawater compared to freshwater, but also operate effectively under extreme salinity with record-level performance.