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.