Metal-organic framework (MOF) materials have considerable potential for practical applications in solid-phase separation technology. However, the application of MOFs for zirconium and hafnium separation remains unexplored.

In a study published in ACS Applied Materials & Interfaces, a research group led by Prof. YANG Fan from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences constructed a MIL-101-diglycolic acid (DGA) (MOF) coupling the betaine hydrochloride system, and enabled green and efficient zirconium and hafnium separation under low-acid conditions.

Researchers employed MIL-101-NH₂ as the matrix material and synthesized MIL-101-DGA by incorporating DGA functional groups through a single-step ring-opening reaction. This modification endowed the MOF with tridentate coordination ability and excellent binding affinity for zirconium ions. 

In addition, betaine hydrochloride was introduced as a competitive ligand that preferentially forms water-soluble complexes with hafnium ions. This strategy establishes a "push-pull" mechanism which significantly improves the efficiency of zirconium and hafnium separation under low acid conditions. At a pH of 0.50, the separation factor (β_Zr/Hf) reached 19.7, and at a pH of 1.46, the separation factor (β_Zr/Hf) was 8.2.

Moreover, researchers introduced L-aspartic acid as a desorption enhancer. In a traditional single sulfuric acid system, the desorption of zirconium and hafnium was difficult. However, by combining 0.2 mol/L L-aspartic acid with 0.2 mol/L sulfuric acid, the desorption efficiencies of zirconium and hafnium were significantly increased to 87% and 90%, respectively. This approach realized efficient desorption of zirconium and hafnium at low acid concentrations.

The MIL-101-DGA material demonstrated excellent cycling and immersion stability, with a loss of physicochemical properties of less than 7% after multiple adsorption/desorption cycles. After immersion for seven days in betaine hydrochloride solutions with pH values ranging from 0.50 to 2.00, as well as in a mixed solution of 0.2 mol/L L-aspartic acid and 0.2 mol/L sulfuric acid, the material demonstrated excellent stability in the separation environment.

This study not only addresses the high toxicity and acidity issues of traditional separation methods, but also broadens the scope of solid-phase separation materials, paving the way for the application of MOFs in the field of separation.