Suchergebnisse

The presence of hexavalent chromium water pollution is a growing global concern. Among the currently applied technologies to remove Cr-VI, its adsorption and photocatalytic reduction to Cr-III less mobile and toxic forms are the most appealing because of their simplicity, reusability, and low energy consumption. However, little attention has been paid to bifunctional catalysts, that is, materials that can reduce Cr-VI to Cr-III and retain both hexavalent and trivalent chromium species at the same time. In this work, the dual Cr-VI adsorption-reduction capacity of two iconic photoactive water-stable zirconium and titanium-based metal-organic frameworks (MOFs) has been investigated: UiO-66-NH2 and MIL-125. The bifunctionality of photoactive MOFs depends on different parameters, such as the particle size in MIL-125 or organic linker functionalization/defective positions in UiO-66 type sorbents. For instance, the presence of organic linker defects in UiO-66 has shown to be detrimental for the chromium photoreduction but beneficial for the retention of the Cr-III phototransformed species. Both compounds are able to retain from 90 to 98% of the initial chromium present at acidic solutions as well as immobilize the reduced Cr-III species, demonstrating the suitability of the materials for Cr-VI environmental remediation. In addition, it has been demonstrated that adsorption can be carried out also in a continuous flux mode through a diluted photoactive MOF/sand chromatographic column. The obtained results open the perspective to assess the bifunctional sorption and photoreduction ability of a plethora of MOF materials that have been applied for chromium capture and photoreduction purposes. In parallel, this work opens the perspective to develop specific chemical encoding strategies within MOFs to transfer this bifunctionality to other related water remediation applications. ; Spanish Ministry of Economy and Competitiveness (MINECO) MAT2016-76739-R MAT2016-76039C4-3-R European Commission Basque Government Industry and Education Department under the ELKARTEK (LION, ACTIMAT) Basque Government Industry and Education Department under the HAZITEK (SIMAN) Basque Government Industry and Education Department under the PIBA PIBA-2018-06 European Commission Research & Innovation H2020-MSCA-RISE-2017 INDESMOF project 778412 ; Versión publicada - versión final del editor

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. ; Spanish Ministry of Economy and Competitiveness (MINECO) (AEI/FEDER, UE) (FEDER) MAT2016-76739-R MAT2016-76039-C4-3-R Basque Government Industry and Education Departments PIBA-2018-06 European Commission Research & Innovation H2020-MSCA-RISE-2017 INDESMOF project 778412