A cationic radical metal–organic framework enabling low water evaporation enthalpy and high photothermal conversion efficiency for solar-driven water purification

Abstract

Solar vapor generation is a promising and sustainable strategy to purify seawater and contaminated water sources. However, achieving efficient integration between solar energy capture and desalination remains a critical challenge. In this context, we have developed an innovative solar evaporator that integrates Cu foam and a hierarchical cationic radical MOF (PFC-771) photothermal absorber component for the rapid and efficient solar energy-driven water evaporation. The highly ordered arrangement guarantees an adequate shielding effect to protect radicals from bleaching; therefore, PFC-771 exhibits outstanding stability in various solvents and under ambient conditions. Notably, the persistent radical characteristic of PFC-771 broadens its light absorption spectrum, enhancing sunlight absorption and photothermal conversion efficiency. Additionally, the excellent hydrophilic hierarchical pore structure of the PFC-771/Cu film and the ionic framework significantly lowered the evaporation enthalpy from 2430 kJ kg⁻¹ to 1724 kJ kg⁻¹, resulting in a fast water evaporation rate of 1.33 kg m⁻² h⁻¹ under 1 sun illumination. The design principle of integrating radical linkers in ionic MOFs not only improves photothermal efficiency but also addresses critical challenges in solar-driven desalination. This work paves the way for future advancements in designing low-enthalpy, high-performance water evaporators, highlighting the pivotal role of MOFs in a sustainable water purification solution.