Ionic Dye Based Covalent Organic Frameworks for Photothermal Water Evaporation

Conversion of solar energy into heat for water evaporation is of great significance to provide clean and sustainable technology for water purification by using inexhaustible sunlight. In this field, one of the challenges comes from the design of high-performance photothermal materials powerful in light harvesting, light-to-heat conversion, and water activation. Herein, it is demonstrated that rationalization of the ionic covalent organic framework (iCOF) can simultaneously satisfy these multiple requirements and a new iCOF STTP is constructed through the Schiff base chemistry in a rapid microwave-assisted solvothermal route by using a hydrophilic dye molecule safranineT as the ionic building block. The integrated dye-related ionic moieties greatly strengthen the light absorbance (>97%) throughout the entire solar spectrum from UV–vis to the infrared region. The framework ionic moieties provide strong polarization to reduce the exciton dissociation energy for enhanced photothermal effect, and in addition, promote sufficient water activation to decrease the water evaporation enthalpy. As an outcome, the STTP driven solar water evaporator affords a fast water evaporation rate of 3.55 kg h⁻¹ m⁻² and high solar-to-vapor efficiency of 95.8%. This study highlights the potential of designing iCOF materials for photothermal applications.