Probing the Critical Metal Node and Ligand Concentrationsfor MOF Nucleation on a Substrate

Determining the critical concentrations of metal nodes and ligands required for metal–organic framework (MOF) nucleation on a substrate remains a fundamental challenge. Here we propose an electrochemical method to address this issue by integrating in situ surface mass change analysis with in situ surface pH measurement during a cathodic deposition process. Taking UTSA-280 ([Ca(C₄O₄)]_n) as an example, the critical metal ion (c(Ca²⁺)) and deprotonated ligand (c(C₄O₄^2–)) concentrations for UTSA-280 nucleation on a gold substrate are determined. It is found that the values of c(Ca²⁺) × c(C₄O₄^2–) in different electrolytes with varied bulk Ca²⁺ concentrations are similar, which can be seen as an analogue of the solubility product of UTSA-280 considering its chemical formula. Also, a simple yet previously overlooked strategy to shorten the incubation time for MOF nucleation in cathodic deposition is proposed and verified. The presented method can be applied to other MOFs.