It is well known that zirconium (Zr) metal–organic frameworks (MOFs) are the most stable of all MOFs. Can the best be even better? What new applications would be opened up with more stable Zr-MOFs?

In a study published in Adv. Mater., the research groups led by Prof. LIN Qipu and ZHANG Jian at Fujian Institute of Research on the Structure of Matter of Chinese Academy of Sciences reported a family of tetragonal Zr-polyphenolate-porphyrin frameworks (ZrPP-n, n = 1, 2) that are initially computationally designed and then subsequently synthesized.

Among these materials, ZrPP-1 reveals the largest range of pH resistance among all MOFs, retaining its framework integrity against the attack of HCl (pH = 1) and even the saturated NaOH solution (ca. 20 M).

Another important aspect of this study is that highly stable Zr-oxide chains could be able to couple highly stable Zr-oxide chain with light-harvesting porphyrinic units, as well as catalytically active metal centers, all in one uniformly integrated heterometallic crystalline material.

As a result of this potent design strategy, ZrPP-1 exhibits not only high CO₂ trapping capability (ca. 90 cm³·g^-1 at 1 atm, 273 K), but also high photocatalytic activity for reduction of CO₂ into CO (ca. 14 μmol·g^-1h^-1) and the highest selectivity for CO over CH₄ (>96%) under visible-light irradiation (λ > 420 nm).

It is noteworthy that ZrPP-1 has the strong chemical resistance in extreme alkali conditions, which is particularly advantageous for reactions that require harsh conditions. Such advantages have been demonstrated by showing these catalysts can be recycled multiple times without appreciable loss of activity.

The structures of ZrPP-n and their photoreduction CO₂-to-CO process under visible light irradiation (Image by Prof. LIN’s Group)