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.