Tannic Acid-Induced\nPolypyrrole Photothermal Coating\nfor Efficient Solar-Driven Water Evaporation with Salt Resistance\nthrough the Roof-Structure Water Transfer Model

Solar-driven evaporation has received widespread attention\nin obtaining\nfresh water from seawater and wastewater. However, a major challenge\nin this process is maintaining a high evaporation rate, while preventing\nsalt accumulation. Herein, a hydrophilic tannic acid (TA)-induced\npolypyrrole (PPy) coating layer with a controllable thickness was\ndeveloped on nonwoven fabric using a layer-by-layer (LbL) assembly\ntechnique. TA along with pyrrole (Py) molecules was first deposited\non the substrate surface through noncovalent interactions. Then, Fe<sup>3+</sup> was bonded with TA through metal coordination, acting as\nan oxidant for the polymerization of Py molecules. After the LbL cycle\nprocess, a uniform TA/PPy coating was formed on the fabric surface,\nexhibiting excellent hydrophilicity and solar absorption performance.\nThe roof-structure evaporation system was then built by placing the\nfabric on the roof-structure support, ensuring that seawater flows\nfrom top to bottom. This structure helps to remove the concentrated\nbrine from the fabric at the bottom of the evaporator, thereby preventing\nthe accumulation of salt crystals. This design results in a high evaporation\nrate of 2.67 kg m<sup>–2</sup> h<sup>–1</sup> and a\ncomparable evaporation efficiency of 89.6% under 1 sun irradiation.\nIt is possible to achieve rapid and continuous evaporation even with\nhigh-concentration saline water containing 21% NaCl. Therefore, this\nstudy provides a simple construction of TA/PPy coatings suitable for\ndifferent substrates and demonstrates the design of a roof-structure\nevaporation system for efficiently producing fresh water from seawater\nand high-salinity wastewater.