Tannic Acid-Induced Polypyrrole Photothermal Coating for Efficient Solar-Driven Water Evaporation with Salt Resistance through the Roof-Structure Water Transfer Model

Solar-driven evaporation has received widespread attention in obtaining fresh water from seawater and wastewater. However, a major challenge in this process is maintaining a high evaporation rate, while preventing salt accumulation. Herein, a hydrophilic tannic acid (TA)-induced polypyrrole (PPy) coating layer with a controllable thickness was developed on nonwoven fabric using a layer-by-layer (LbL) assembly technique. TA along with pyrrole (Py) molecules was first deposited on the substrate surface through noncovalent interactions. Then, Fe3+ was bonded with TA through metal coordination, acting as an oxidant for the polymerization of Py molecules. After the LbL cycle process, a uniform TA/PPy coating was formed on the fabric surface, exhibiting excellent hydrophilicity and solar absorption performance. The roof-structure evaporation system was then built by placing the fabric on the roof-structure support, ensuring that seawater flows from top to bottom. This structure helps to remove the concentrated brine from the fabric at the bottom of the evaporator, thereby preventing the accumulation of salt crystals. This design results in a high evaporation rate of 2.67 kg m–2 h–1 and a comparable evaporation efficiency of 89.6% under 1 sun irradiation. It is possible to achieve rapid and continuous evaporation even with high-concentration saline water containing 21% NaCl. Therefore, this study provides a simple construction of TA/PPy coatings suitable for different substrates and demonstrates the design of a roof-structure evaporation system for efficiently producing fresh water from seawater and high-salinity wastewater.