Site-selective etching and conversion of bismuth-based Metal–Organic frameworks by oxyanions enables efficient and selective adsorption via robust coordination bonding

Abstract

Anisotropic etching and conversion of MOF micro/nanostructures results in innovative structures and regulates properties. However, the anisotropic higher-order construction of MOFs remains a major challenge. Here, for the first time, we report the preparation of two unprecedented Bi-MOF (CAU-17) derivative structures via facile chemical etching and simultaneous conversion on solid CAU-17 microrods by reaction with Te- and Se-containing oxyanions. The TeOx2−-mediated hollow tubular structures are obtained via unique splitting, self-welding, and dissolution processes, a tube-forming mechanism never before seen in MOFs. In comparison, SeOx2− ions tend to etch CAU-17 into hierarchical sponge-like structures assembled from fine nanoparticles. DFT calculations, XANES modeling, and EXAFS fittings suggest that the site-selective coordination of oxyanions with Bi-O bonds in the Bi-MOF forms robust Bi-O-Te/Se bonds, which in turn leads to an anisotropic structural transition of CAU-17. More interestingly, benefiting from the coordination bond-dominated conversion, CAU-17 is shown to be a superior adsorbent for the selective and irreversible capture of highly radiotoxic oxyanions containing Te and Se from wastewater. These findings provide new insights into the anisotropic etching and conversion mechanism of MOFs by oxyanions and a fundamental understanding for designing advanced MOF-based guest oxyanion adsorbents.