Scientists have discovered new "local flexible" materials

On January 25th, a study published in the journal Science used metal-organic framework (MOF) materials, a highly engineered structural platform, to incorporate temperature response on the cage walls of rigid skeleton MOFs. Dynamic "switching" controls the diffusion of gas molecules in the porous material by controlling the perturbation of the pore walls.

Gu Cheng, the first author of the paper and a researcher at the State Key Laboratory of Luminescent Materials and Devices of South China University of Technology, told the Journal of Chinese Academy of Sciences: “The new material has temperature-controlled adsorption characteristics. This unique adsorption property not only allows the material to be at a higher temperature. Dynamic screening of similar gases can also be carried out to achieve physical storage of gases at ambient temperature and pressure."

According to the laws of thermodynamics, as the temperature increases, the amount of adsorption of the porous material to the gas decreases. However, the MOF material has almost no adsorption near the boiling temperature of various gases. As the temperature increases, the gas adsorption amount gradually increases and reaches a maximum value, and then the gas adsorption amount gradually decreases with increasing temperature. The researchers found that this is the result of a thermodynamically controlled framework-gas interaction and kinetic controlled diffusion-limited interaction.

The researchers designed a butterfly-type ligand that introduces oxidized phenothiazine at the 5-position of isophthalic acid, a unit that is effective for thermal vibration. The perturbation caused by the thermal vibration of the oxidized phenothiazine is sufficient to open the "gate" for the diffusion of gas molecules. Since the MOF material introduces kinetic control, the "gate" opening amplitude is also different at different temperatures.

The researchers filled the MOF material into a separation column and tested the separation of oxygen/argon and ethylene/ethane. The results show that in the case of 180K, the oxygen content of the mixture is only 5%, the purification ratio of MOF material to oxygen can still reach 95%. In the case where the ethylene content in the mixture at 273 K is only 5%, the purification ratio can still reach 80%.