Bandgap Engineering on UiO–66 Metal‐Organic Framework Derivatives for Solar‐Driven Seawater Desalination

The growing scarcity of freshwater, driven by climate change and pollution, necessitates the development of efficient and sustainable desalination technologies. Solar-powered interfacial water evaporation has emerged as a promising solution; however, its practical implementation is hindered by the limited availability of efficient and stable photothermal materials. Herein, a bandgap engineering strategy via linker modification to enhance the photothermal conversion capability of metal-organic frameworks (MOFs) is reported toward efficient solar-driven desalination. By systematically introducing functional groups with varying electron-donating and electron-withdrawing abilities, the energy bandgap of UiO-66-X (X = ─F, ─H, ─OH, ─NH₂, ─(NH₂)₂) is finely tuned. Density functional theory (DFT) calculations and femtosecond transient absorption (fs-TA) spectroscopy reveal that stronger electron-donating functional groups narrow the bandgap of the MOFs, thereby improving their photothermal conversion efficiency. The optimized UiO-66-(NH₂)₂ material reaches a peak surface temperature of 58.7 °C when exposed to simulated sunlight at ≈1 kW·m^-2 with a photothermal conversion efficiency of 86.50% and an evaporation rate of 2.34 kg·m^-2·h^-1 with an evaporation efficiency of 97.40%. This study presents a novel approach for fine-tuning the bandgap in photothermal materials, offering a pathway toward advanced solar desalination technologies to address the global water scarcity crisis.