Chelation-Assisted Selective Etching Construction of Hierarchical Polyoxometalate-Based Metal–Organic Framework

A chelation-assisted selective etching (CASE) strategy is developed to construct a hierarchical polyoxometalate-based metal–organic framework (POM@MOF). The selected chelator, ethylenediaminetetraacetic dianion (EdtaH22–), can bind protons of the acid etchant to provide a low initial proton concentration. The dwindling protons are more controllable when localized at specific positions (e.g., polar crystal facets) of POM@MOF to initiate selective etching. Subsequently, with the liberated metal ions being chelated, the bound protons are gradually released in situ. The secondary release of protons results in a local high proton concentration (i.e., enrichment effect), thereby further enhancing the etch selectivity. When the amount of EdtaH22– is controlled, POM@MOFs with different morphologies and pore structures are fabricated by selective etching. The on-demand storage and release of protons overcomes the traditional uncontrollability caused by direct proton addition. The CASE strategy provides a feasible way to design diverse hierarchical MOFs because of the universal chelation between EdtaH22– and metal ions.