Tunable Low-Pressure Water Adsorption in Stable Multivariate Metal-Organic Frameworks for Boosting Water-Based...

Area of Science:

• Materials Science
• Chemical Engineering
• Sustainable Energy

Background:

• Adsorption refrigeration using water as a refrigerant is a key strategy for near-zero-carbon cooling.
• Existing metal-organic frameworks (MOFs) often show limited water uptake below P/P₀ = 0.2, hindering cooling performance.
• Improving low-pressure water uptake is crucial for enhancing the coefficient of performance (COP) in refrigeration.

Purpose of the Study:

• To develop multivariate MOFs (MTV-MOFs) that enhance low-pressure water uptake for improved refrigeration.
• To design and synthesize novel MTV-MOFs by modifying the MIL-125-NH₂ structure.
• To evaluate the performance of these MTV-MOFs in water-based adsorption refrigeration systems.

Main Methods:

• Ligand exchange was employed to modify the pristine MIL-125-NH₂ MOF, creating MTV-MOFs with bare nitrogen sites.
• Water uptake capacity was measured at 298 K and varying relative pressures (P/P₀).
• Adsorption refrigeration performance, including COP and working capacity, was evaluated under an ultralow-driven temperature of 65 °C.

Main Results:

• The synthesized MIL-125-NH₂/MD-5% exhibited a significantly enhanced water uptake of 0.39 g g⁻¹ at P/P₀ = 0.2, three times higher than the pristine MOF.
• This MTV-MOF demonstrated comparable water uptake to benchmark materials like KMF-1 and MIP-200.
• MIL-125-NH₂/MD-5% achieved a high COP of 0.8 and a working capacity of 0.24 g g⁻¹, outperforming other MOFs under ultralow-driven temperatures.

Conclusions:

• The developed MTV-MOFs, particularly MIL-125-NH₂/MD-5%, effectively boost low-pressure water uptake for adsorption refrigeration.
• These materials offer excellent stability, fast sorption kinetics, and low-temperature regeneration capabilities.
• MIL-125-NH₂/MD-5% represents a highly efficient adsorbent for practical, ultralow-temperature-driven green cooling applications.