Ink‐Stained Chalk: A Low‐Cost 3D Evaporator for Efficient and Stable Solar Desalination

Solar‐driven steam generation is considered one of the most promising techniques to obtain fresh water. Under the same projection area, a 3D evaporator has a larger evaporation area and can get more energy from the environment, resulting into better evaporation performance. 3D evaporators are often hindered by complex and dangerous fabrication processes, special and expensive equipment, and costly raw materials. Herein, a simple method to prepare a low‐cost and highly efficient 3D solar evaporator using chalk and ink that are common in classrooms is proposed. This method does not involve expensive raw materials and any equipment, and the manufacturing process is simple and fast, especially suitable for less developed regions. Thanks to the excellent hydrophilicity of chalk and the strong sunlight absorption of black ink, the ink‐stained chalk (ISC) shows up to 20.49 kg m−2 h−1 of the evaporation rate under one sun illumination. When treating a real seawater sample, ISC prepared from broken or used chalks show highly efficient (8.97–19.91 kg m−2 h−1) and stable (24 h) solar desalination. The ISC presented in this work offers a new avenue to develop 3D solar evaporator for low‐cost and high‐efficient seawater desalination, which is especially attractive for remote and less developed areas.