Water sorption studies with mesoporous multivariate monoliths based on UiO-66.

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) offer tunable porosity for various applications.
• Enhancing pore size and surface area in monolithic MOFs is crucial for performance.
• Hierarchical linker thermolysis is a known method for powder MOFs.

Purpose of the Study:

• To apply hierarchical linker thermolysis to monolithic MOFs for the first time.
• To investigate the effect of thermolabile linker decomposition on MOF porosity.
• To evaluate the water sorption performance of the modified monolithic MOFs.

Main Methods:

• Synthesis of monolithic UiO-66-based MOFs with mixed linkers, including 2-aminoterephthalic acid (BDC-NH2).
• Thermolysis of the BDC-NH2 linker at approximately 350 °C to induce mesopore formation.
• Nitrogen and water sorption analysis to quantify changes in porosity and uptake capacity.

Main Results:

• Thermolysis successfully created mesopores in the monolithic MOFs.
• Gas uptake increased by over 200 cm³ g⁻¹, with enhanced pore volume and mean pore width.
• The modified MOF exhibited a maximum water vapor uptake of 61.0 wt%, outperforming parent materials, while a highly mesoporous version showed lower uptake (36.2 wt%).

Conclusions:

• Hierarchical linker thermolysis is effective in enhancing porosity of monolithic MOFs.
• The presence of hydrophilic functional groups, like -NH2, is vital for high water uptake.
• This study extends a known technique to a new material format, demonstrating its potential for tailored MOF properties.