Chromium Speciation in Zirconium‐Based Metal–Organic Frameworks for Environmental Remediation

Abstract

Acute Cr VI water pollution duet oa nthropogenic activities is an increasing worldwide concern. The high toxicity and mobility of Cr VI makesi tn ecessary to develop dual adsorbent/ion-reductive materialst hat are able to capture Cr VI and transform it efficiently into the less hazardous Cr III. An accurated escription of chromium speciationa tt he adsorbent/ion-reductive matrix is key to assessing whether Cr VI is completely reduced to Cr III ,o ri fi ts 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 approachh as been applied to determine the chromium speciation within zirconium-basedm etal-organic frameworks (MOFs). Our findings point out that the generation of defects at Zr-MOFs boosts Cr VI adsorption, whilst the presence of reductiveg roups on the organic linkersp lay ak ey role in stabilizing it as isolated and/or clustered Cr III ions.

Modulation of the Bifunctional CrVI to CrIII Photoreduction and Adsorption Capacity in ZrIV and TiIV Benchmark Metal-Organic Frameworks

“…For hexavalent chromium, the equilibrium is reached within the first 15 min of the experiment. In agreement with previous works [37], linker defective UiO-66-NH 2 -def shows higher chromate adsorption capacity than the non-defective UiO-66-NH 2 (Figure 2a). It is well established that linker defective positions in Zr-based MOFs act as preferential adsorption points for anionic inorganic and organic species.…”

“…For instance, the chromium speciation within the Zr-MOF sorbents and photocatalysts has been successfully determined in our previous research by applying a multiple UV-Vis and electron paramagnetic resonance spectroscopy technique. Our findings confirmed that Cr VI to Cr III chemical and photoreduction processes are driven by the intermediate generation of pentavalent chromium transient species inside UiO-66-based materials [37] Nevertheless, this research does not unravel the fate of trivalent chromium phototransformed species in solution. This experimental gap-that is, the monitoring of both hexavalent and trivalent chromium in solution during working conditions-is common for most of the investigations carried out in Cr VI to Cr III photoreduction experiments.…”

Chitin/Metal‐Organic Framework Composites as Wide‐Range Adsorbent

“…The immobilization of hexavalent chromium anions in MOF-808, [47,64] CH/MOF-808 composites, and CH matrixes is governed by two factors: (i) adsorption at the CH/MOF-808 structure, [65][66][67] and (ii) reduction from Cr VI to Cr III due to the electron donor groups of CH matrix. [19,68] MOF-808 nanoparticles have a near 100 % capacity for the removal of Cr VI species from water; whilst CH and CH/MOF-808 show just a 40 % removal. Contrary to the expected tendency, the CH/MOF-808 composites do not show an increase of the chromate anions removal in comparison to CH matrix.…”

“…Therefore, in this work we have combined a macro‐ and mesoporous chitin (CH) [12–15] biopolymer with the MOF‐808 microporous metal‐organic framework (MOF) [16,25,17–24] sorbent to create a porous composite with multiple porosities and chemical functionalities [28–30] . CH is the second most abundant natural polymer [31,32] .…”

Processing Strategies to Obtain Highly Porous Silk Fibroin Structures with Tailored Microstructure and Molecular Characteristics and Their Applicability in Water Remediation

“…Indeed, arsenic and chromium exhibit acute toxicity in aqueous environments (e.g. genotoxic, mutagenic, teratogenic and carcinogenic), are non-biodegradable and longterm persistent, even when present at very low concentrations [2,33]. In addition, their varied chemistry and speciation, as well as their high solubility and mobility, makes current technologies inefficient to lower their concentration below the legal limits.…”