Chromium speciation in Zirconium-based metal–organic frameworks for environmental remediation

Abstract

Acute Cr(VI)water pollution due to anthropogenic activities is an increasing worldwide concern. The high toxicity and mobility of Cr(VI)makes it necessary to develop dual adsorbent/ion-reductive materials that are able to capture Cr(VI)and transform it efficiently into the less hazardous Cr-III. An accurate description of chromium speciation at the adsorbent/ion-reductive matrix is key to assessing whether Cr(VI)is completely reduced to Cr-III, or if its incomplete transformation has led to the stabilization of highly reactive, transient Cr(V)species within the material. With this goal in mind, a dual ultraviolet-visible and electron paramagnetic spectroscopy approach has been applied to determine the chromium speciation within zirconium-based metal-organic frameworks (MOFs). Our findings point out that the generation of defects at Zr-MOFs boosts Cr(VI)adsorption, whilst the presence of reductive groups on the organic linkers play a key role in stabilizing it as isolated and/or clustered Cr(III)ions.