A significant synergic effect between a metal–organic framework (MOF) and Fe2SO4, the so‐called MOF+ technique, is exploited for the first time to remove toxic chromate from aqueous solutions. The results show that relative to the pristine MOF samples (no detectable chromate removal), the MOF+ method enables super performance, giving a 796 Cr mg g−1 adsorption capacity. The value is almost eight‐fold higher than the best value of established MOF adsorbents, and the highest value of all reported porous adsorbents for such use. The adsorption mechanism, unlike the anion‐exchange process that dominates chromate removal in all other MOF adsorbents, as unveiled by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), is due to the surface formation of Fe0.75Cr0.25(OH)3 nanospheres on the MOF samples.
Ferrihydrite commonly occurs in soils
and sediments, especially
in acid mine drainage (AMD). Solar irradiation may affect Fe(II)-catalyzed
transformation of metastable ferrihydrite to more stable iron oxides
on AMD surface. We investigated the Fe(II)-catalyzed transformation
process and mechanism of ferrihydrite under light irradiation. In
nitrogen atmosphere, Fe2+
aq could be oxidized
to goethite and lepidocrocite by hydroxyl radical (OH•), superoxide radical (O2
•–)
and hole (hvb
+) generated from ferrihydrite
under ultraviolet (UV) irradiation (300–400 nm) at pH 6.0,
and O2
•– and hvb
+ were mainly responsible for Fe2+
aq oxidation.
In addition, the ligand-to-metal charge-transfer (LMCT) process between
Fe(II) and ferrihydrite could be promoted by UV irradiation. Goethite
proportion increased with increasing Fe2+
aq concentration.
Both visible (vis) and solar irradiation could also lead to the oxidation
of Fe2+
aq to goethite and lepidocrocite, and
the proportion of lepidocrocite increased with increasing light intensity.
Fe2+
aq was photochemically oxidized to schwertmannite
at pH 3.0 and 4.5, and the oxidation rate was higher than that under
dark conditions in air. The photochemical oxidation rate of Fe2+
aq decreased in the presence of humic acid. This
study facilitates a better understanding of the formation and transformation
of iron oxides in natural environments and ancient Earth.
The aim of this work was to reduce/minimize Li in Li-LSX by replacing the 70% Li 1 cations in Li-LSX that are bonded to the interior or inaccessible sites which are not used for adsorption. Thus, mixed-cation LiCa-LSX containing minimum lithium were prepared by exchanging small fractions of Li 1 into Ca-LSX, followed by dehydration under mild conditions to avoid migration/equilibration of Li cations. Comparisons of adsorption isotherms of N 2 /O 2 and heats of adsorption for the LiCa-LSX samples with that for pure-cation Li-LSX and Ca-LSX provided strong evidence that significant amounts of these Li cations indeed remained on the exposed sites (SIII). The mixed-cation LiCa-LSX samples were compared against the pure-cation Ca-LSX and Li-LSX based on their performance for oxygen production by PSA, via model simulation. The results showed that the mixed-cation LiCa-LSX samples yielded significantly higher O 2 product productivities at the same product purity and recovery than their pure-cation precursor (Ca-LSX).
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