2 research outputs found
Chemical Insight into the Adsorption of Chromium(III) on Iron Oxide/Mesoporous Silica Nanocomposites
Magnetic
iron oxide/mesoporous silica nanocomposites consisting
of iron oxide nanoparticles embedded within mesoporous silica (MCM-41)
and modified with aminopropyl functional groups were prepared for
application to Cr(III) adsorption followed by magnetic recovery of
the nanocomposite materials from aqueous solution. The composite materials
were extensively characterized using physicochemical techniques, such
as powder X-ray diffraction, thermogravimetric and elemental analysis,
nitrogen adsorption, and zeta potential measurements. For aqueous
Cr(III) at pH 5.4, the iron oxide/mesoporous silica nanocomposite
exhibited a superior equilibrium adsorption capacity of 0.71 mmol/g,
relative to 0.17 mmol/g for unmodified mesoporous silica. The aminopropyl-functionalized
iron oxide/mesoporous silica nanocomposites displayed an equilibrium
adsorption capacity of 2.08 mmol/g, the highest adsorption capacity
for Cr(III) of all the materials evaluated in this study. Energy-dispersive
spectroscopy (EDS) with transmission electron microscopy (TEM) and
X-ray photoelectron spectroscopy (XPS) experiments provided insight
into the chemical nature of the adsorbed chromium species
Sequestration of U(VI) from Acidic, Alkaline, and High Ionic-Strength Aqueous Media by Functionalized Magnetic Mesoporous Silica Nanoparticles: Capacity and Binding Mechanisms
Uranium(VI) exhibits
little adsorption onto sediment minerals in
acidic, alkaline or high ionic-strength aqueous media that often occur
in U mining or contaminated sites, which makes U(VI) very mobile and
difficult to sequester. In this work, magnetic mesoporous silica nanoparticles
(MMSNs) were functionalized with several organic ligands. The functionalized
MMSNs were highly effective and had large binding capacity for U sequestration
from high salt water (HSW) simulant (54 mg U/g sorbent). The functionalized
MMSNs, after U exposure in HSW simulant, pH 3.5 and 9.6 artificial
groundwater (AGW), were characterized by a host of spectroscopic methods.
Among the key novel findings in this work was that in the HSW simulant
or high pH AGW, the dominant U species bound to the functionalized
MMSNs were uranyl or uranyl hydroxide, rather than uranyl carbonates
as expected. The surface functional groups appear to be out-competing
the carbonate ligands associated with the aqueous U species. The uranyl-like
species were bound with N ligand as η<sup>2</sup> bound motifs
or phosphonate ligand as a monodentate, as well as on tetrahedral
Si sites as an edge-sharing bidentate. The N and phosphonate ligand-functionalized
MMSNs hold promise as effective sorbents for sequestering U from acidic,
alkaline or high ionic-strength contaminated aqueous media