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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.

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To our knowledge this is the first manuscript describing a one step synthesis to produce an organic/inorganic hybrid material prepared by carbonization of municipal sewage sludge (AC RM ) that shows photoactivity for the photocatalytic degradation of methylene blue (MB). The hybrid material (AC RM ) exhibited a mesoporous texture while XRD and SEM-EDX showed Fe 2 O 3 and Fe 3 C crystallites. Photodegradation of MB was studied under two different lamps and results were compared against those obtained with a commercial TiO 2 . The photocatalytic tests showed that the hybrid material is photoactive and the binary composite TiO 2 -AC RM showed higher apparent first-order rate constants for the degradation of MB than those obtained on pure TiO 2 . A synergy effect between TiO 2 and AC RM was estimated at about 5 and 8 under lamps with UV-vis and almost pure visible light, respectively. It can be concluded that the photoactivity of TiO 2 -AC RM relative to neat TiO 2 was up to one order of magnitude higher, suggesting that iron phases in the hybrid material photo-assist the TiO 2 in the photodegradation of the methylene blue.

Metal chelators and porous sorbents are two of the forefront technologies applied for the recovery and separation of hazardous and/or valuable metal ions from aqueous solutions (i.e., polluted water sources, metal-rich mining wastewaters, acid leachates, and so forth). The transfer of the metal coordination functions of metal chelators to chemically stable host materials had only limited success so far. Here, we report the installation of natural acids (i.e., malic acid, mercaptosuccinic acid, succinic acid, fumaric acid, and citric acid) and amino acids (i.e., histidine, cysteine, and asparagine) within a porous zirconium-based trimesate metal−organic framework (MOF), namely, MOF-808. Applying this strategy, we were able to produce a pore environment spatially decorated with multiple functional groups usually found in commercial chelator molecules. The chemical stability of the amino acid molecules installed by the solvent-assisted ligand exchange has been studied to delimitate the applicability window of these materials. The adsorption affinity of MOF-808@(amino)acids in static and column-bed configurations can be finetuned as a function of the amino acid residues installed in the framework. MOF-808(amino)acid columns can be applied efficiently both for water remediation of heavy metals and for the separation of metal ions with different acidities. For instance, the initial trends for the dispersion of rare-earth elements have been identified. Electron paramagnetic resonance and inelastic neutron scattering spectroscopy reveal that MOF-808@(amino)acids stabilize metal centers as isolated and clustered species in a coordination fashion that involves both the amine and thiol functionals and that affects the vibrational freedom of some of the chemical groups of the amino acid molecules. The metal-ion stabilization within amino acid-decorated MOFs opens the avenue for application for pseudo biocatalysis purposes in the near future.

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