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

Abstract 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.