Particle size-dependent flexibility in DUT-8(Cu) pillared layer metal-organic framework

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) exhibit tunable properties based on their constituent metals.
• The DUT-8(M) family, featuring various metals (Ni, Zn, Co, Cu), demonstrates size-dependent flexibility and responsiveness.
• Understanding metal's role is crucial for designing MOFs with specific adsorption and gate-opening behaviors.

Purpose of the Study:

• To investigate the influence of copper (Cu) on the flexibility and responsiveness of DUT-8 MOFs.
• To compare the behavior of DUT-8(Cu) with other DUT-8(M) analogues (M=Ni, Zn, Co).
• To elucidate the distinct desolvation and guest adsorption responses of DUT-8(Cu) across different particle sizes.

Main Methods:

• Synthesis of isostructural DUT-8(M) compounds with Ni, Zn, Co, and Cu.
• Desolvation of macro-sized and submicron-sized crystals.
• In situ powder X-ray diffraction analysis.
• Gas adsorption studies (CO2 at 195 K).

Main Results:

• Unlike Ni, Zn, and Co analogues, DUT-8(Cu) does not form a closed-pore (cp) phase upon desolvation, regardless of crystal size.
• Macro-sized desolvated DUT-8(Cu) crystals exhibit breathing behavior upon CO2 adsorption at 195 K.
• Submicron-sized DUT-8(Cu) particles remain rigid and nonresponsive after desolvation.

Conclusions:

• Copper incorporation into the DUT-8 framework fundamentally alters its flexible behavior compared to Ni, Zn, and Co.
• DUT-8(Cu) presents a unique case of metal-induced flexibility, showing breathing but not a complete phase transition to a cp state.
• Particle size remains a critical factor, with macro-crystals showing responsiveness while submicron particles are rigid.