Traditional Ink/Paper-Based Grid Evaporator: Solar-Ambient Synergy for Sustainable Desalination

Interfacial solar desalination is often hindered by complex fabrication, high cost, and the “low-cost vs high-performance” trade-off. However, beyond material cost, a fundamental challenge lies in achieving the coordinated regulation of heat localization, water transport, and vapor diffusion within simple and scalable systems. Herein, we report a grid-structured paper-based solar evaporator using traditional Chinese ink, an eco-friendly, low-cost photothermal material composed of nanoscale carbon black and gelatin binder. Commercial filter paper is folded into a three-dimensional (3D) grid architecture. Only the outer surface of grid is coated with ink prepared by grinding traditional ink sticks. This architecture spatially decouples photothermal conversion from internal water transport pathways by confining heat generation to the external surface, while preserving rapid capillary-driven water supply within the uncoated paper-based network. The grid structure further promotes lateral vapor diffusion and establishes spatially distributed evaporation interfaces, thereby enabling coordinated regulation of heat and mass transfer processes. This enables synergistic solar-ambient energy harvesting: solar energy contributes ∼84.6%, ambient energy ∼15.4%, and total heat loss ∼9.7%. Under 1 sun illumination, the evaporator achieves a high evaporation rate of 3.12 kg m–2 h–1, with a salt-rejection rate >99.9% (meets WHO standards). It maintains stable operation over 14 consecutive cycles in 3.5 wt % NaCl solution. Notably, the material cost per device is <1 US cent, with no specialized equipment or hazardous chemicals required. This work proposes a design strategy based on “functional partitioning and three-dimensional structural regulation,” within which material distribution, water transport, and thermal management are integrally optimized on a simple paper-based platform. This framework provides a scalable and mechanism-driven pathway for achieving high-performance interfacial solar desalination.