A growing demand of boric acid has been forecasted with the rapid development of industries while the world is suffering the consequence from boron-containing wastewater. Metal–organic frameworks (MOFs) with exceptional stability and remarkable surface area have been preliminarily identified as effective boron adsorbents, adsorption mechanism has yet been elucidated though. Herein isostructural MOFs based on diverse metal centers were studied for boron removal from water where considerable amount of boron was captured per metal cluster through a spontaneous endothermic process with fast kinetics by means of chemisorption. It has been observed that metal species with weaker electronegativity and larger atomic radii could be favorable for stronger boron-metal bonding, leading to higher boron adsorption capacity of MOFs. The increased binding energy of metal and oxygen as well as reduced binding energy of boron by the X-ray photoelectron spectroscopy suggested the interaction between electron-deficient boron and the multinuclear metal clusters. Owing to the crystalline nature of MOFs, the boron binding sites were precisely elucidated by single crystal X-ray diffraction where boric acid was attached to the available coordinative sites on the metal clusters through the M−O−B(OH)<sub>2</sub> connection.

Unveiling the nature of boric acid adsorption by isostructural metal−organic frameworks

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