Hierarchically integrated photothermal core-shell matrices for tailored solar interfacial desalination

Solar-powered interfacial evaporation represents a sustainable, low-carbon paradigm for addressing global freshwater scarcity. While photothermal porous materials are widely used, their isotropic, statistically averaged architectures inherent to conventional fabrication generally constrain hierarchical multiscale integration, spatially varying properties, and user-defined scalability. Herein, architected 3D photothermal matrices are developed via coaxial multi-material printing. By engineering distinct core-shell ink formulations, this coaxial strategy enables precise encapsulation of a mechanically robust core within a hierarchically porous shell, generating Janus-like filaments with tunable compositional and structural heterogeneity. Synergistic engineering of ink chemistry, lattice geometry, multiscale hierarchical porosity, vertical aspect ratios and zwitterion-mediated salt resistance yields spatially resolved functionalities within the 3D core-shell matrices across multiple length scales. In seawater, a 6 cm-tall matrix achieves an outstanding evaporation rate of 3.04 kg m^-2 h^-1 (1 sun without airflow) and 11.79 kg m^-2 h^-1 (1 sun and 1 m s^-1 airflow) under laboratory conditions, and a peak rate of 16.40 kg m^-2 h^-1 under real sky conditions-ranking among the top-performing solar evaporation systems. Gratifyingly, a 69% reduction in raw material consumption, a unit cost as low as $1.3, and a payback period of 155 days underscore the economic viability of these matrices. Our work demonstrates the flexible and precise fabrication of patterned photothermal materials integrating tailored surface geometries, spatial anisotropy, topological design, and hierarchical void architectures, enabling high-performance, customizable, and economically viable solar desalination.