Surface Hydrophobic Treatment of Water-Sensitive DUT-4 Metal–Organic Framework To Enhance Water Stability for Hydrogen Storage

Water stability in acidic, neutral, and basic aqueous solutions is quite important for the potential application of metal–organic frameworks. As evidenced by X-ray diffraction and scanning electron microscopy results, the pristine DUT-4 is extremely water sensitive to acidic, neutral, and basic aqueous solutions and undergoes crystal structure and morphology transformation. The pristine DUT-4 nearly loses its porosity and H2 uptake capacity after being exposed for 6 d. A facile solution-immersion approach was employed to deposit a hydrophobic layer on the DUT-4 surface without significant loss of surface area. This layer could effectively protect DUT-4 from water molecule attack and greatly enhance water stability. After the same exposure to aqueous solutions, the hydrophobic-treated DUT-4 could basically retain their crystal structure, morphology, surface area, and H2 uptake capacity. This approach could be explored to broaden the scope of practical applications of DUT-4 and other metal–organic frameworks under water-containing environments.