14 research outputs found
Screening of Zirconium-Based Metal–Organic Frameworks for Efficient Simultaneous Removal of Antimonite (Sb(III)) and Antimonate (Sb(V)) from Aqueous Solution
Seven kinds of zirconium-based metal–organic
frameworks (Zr-MOFs) with different aperture size and organic linkers
functionalized with different functional groups (−NH<sub>2</sub>, −OH, and −SO<sub>3</sub>H) were screened for their
ability to remove antimonite (SbÂ(III)) and antimonate (SbÂ(V)) anions
from water. Zr-bound hydroxides in Zr-MOFs can simultaneously remove
both SbÂ(III) and SbÂ(V) via a mechanism of anion exchange. For antimony
removal by UiO-66-NH<sub>2</sub>, the anion exchange seemed to be
strengthened due to the Lewis acid–base interactions between
the −NH<sub>2</sub> groups on the BDC ligand and the antimony
oxyanions. Among seven kinds of Zr-MOFs selected here, NU-1000 exhibited
fast adsorption kinetics and high removal capacity for both SbÂ(III)
(136.97 mg/g) and SbÂ(V) (287.88 mg/g), which was much higher than
many antimony adsorbents described to date. Uptake of antimony at
low concentrations of 100 μg/L (with a remaining antimony concentration
of only ∼2 μg/L in 10 min) disclosed that current U.S.
Environmental Protection Agency standards for antimony can be reached
by using NU-1000 as an adsorbent. Additionally, the effects of coexisting
anions such as AsÂ(III), AsÂ(V), PO<sub>4</sub><sup>3–</sup>,
SO<sub>4</sub><sup>2–</sup>, NO<sub>3</sub><sup>–</sup>, and F<sup>–</sup> on the antimony adsorption onto NU-1000
were also studied. Finally, the Sb adsorption mechanism of NU-1000
was studied via X-ray photon spectroscopy and attenuated total reflection
infrared spectroscopy techniques to explore the important characteristics
that make NU-1000 a compelling candidate for wastewater management
Highly Efficient Enrichment of Radionuclides on Graphene Oxide-Supported Polyaniline
Graphene
oxide-supported polyaniline (PANI@GO) composites were
synthesized by chemical oxidation and were characterized by SEM, Raman
and FT-IR spectroscopy, TGA, potentiometric titrations, and XPS. The
characterization indicated that PANI can be grafted onto the surface
of GO nanosheets successfully. The sorption of UÂ(VI), EuÂ(III), SrÂ(II),
and CsÂ(I) from aqueous solutions as a function of pH and initial concentration
on the PANI@GO composites was investigated. The maximum sorption capacities
of UÂ(VI), EuÂ(III), SrÂ(II), and CsÂ(I) on the PANI@GO composites at
pH 3.0 and <i>T</i> = 298 K calculated from the Langmuir
model were 1.03, 1.65, 1.68, and 1.39 mmol·g<sup>–1</sup>, respectively. According to the XPS analysis of the PANI@GO composites
before and after EuÂ(III) desorption, nitrogen- and oxygen-containing
functional groups on the surface of PANI@GO composites were responsible
for radionuclide sorption, and that radionuclides can hardly be extracted
from the nitrogen-containing functional groups. Therefore, the chemical
affinity of radionuclides for nitrogen-containing functional groups
is stronger than that for oxygen-containing functional groups. This
paper focused on the application of PANI@GO composites as suitable
materials for the preconcentration and removal of lanthanides and
actinides from aqueous solutions in environmental pollution management
in a wide range of acidic to alkaline conditions
Interaction between Eu(III) and Graphene Oxide Nanosheets Investigated by Batch and Extended X-ray Absorption Fine Structure Spectroscopy and by Modeling Techniques
The interaction mechanism between EuÂ(III) and graphene
oxide nanosheets
(GONS) was investigated by batch and extended X-ray absorption fine
structure (EXAFS) spectroscopy and by modeling techniques. The effects
of pH, ionic strength, and temperature on EuÂ(III) adsorption on GONS
were evaluated. The results indicated that ionic strength had no effect
on EuÂ(III) adsorption on GONS. The maximum adsorption capacity of
EuÂ(III) on GONS at pH 6.0 and <i>T</i> = 298 K was calculated
to be 175.44 mg·g<sup>–1</sup>, much higher than any currently
reported. The thermodynamic parameters calculated from temperature-dependent
adsorption isotherms suggested that EuÂ(III) adsorption on GONS was
an endothermic and spontaneous process. Results of EXAFS spectral
analysis indicated that EuÂ(III) was bound to ∼6–7 O
atoms at a bond distance of ∼2.44 Å in the first coordination
shell. The value of Eu–C bond distance confirmed the formation
of inner-sphere surface complexes on GONS. Surface complexation modeling
gave an excellent fit with the predominant mononuclear monodentate
>SOEu<sup>2+</sup> and binuclear bidentate (>SO)<sub>2</sub>Eu<sub>2</sub>(OH)<sub>2</sub><sup>2+</sup> complexes. This paper
highlights
the application of GONS as a suitable material for the preconcentration
and removal of trivalent lanthanides and actinides from aqueous solutions
in environmental pollution management
Cr(VI) Reduction and Immobilization by Core-Double-Shell Structured Magnetic Polydopamine@Zeolitic Idazolate Frameworks‑8 Microspheres
A well-defined
core-double-shell structured magnetic polydopamine@zeolitic
idazolate frameworks-8 (MP@ZIF-8) hydrid microsphere consisting of
the core of magnetic Fe<sub>3</sub>O<sub>4</sub> nanoparticles, the
inner shell of a polydopamine layer, and the outer shell of a porous
ZIF-8 nanocrystal was prepared through a facile and green approach
to achieve synergistic reduction and adsorptive removal of CrÂ(VI).
The microsphere property was characterized methodically. The batch
adsorption experiments showed that the MP@ZIF-8 exhibited high efficiency
in the CrÂ(VI) removal from aqueous solutions, affording CrÂ(VI) removal
capacity of 136.56 mg g<sup>–1</sup>, surpassing pristine MP
(92.27 mg g<sup>–1</sup>). The pseudo-second-order model fitted
the CrÂ(VI) removal kinetics well. CrÂ(VI) removal on the MP@ZIF-8 relied
highly on pH values. More significantly, with the reduction of nitrogen
atom group on ZIF-8 and PDA, CrÂ(VI) was easily converted into low
toxicity CrÂ(III) and then immobilized on the MP@ZIF-8. Thus, the hybrid
microspheres provided excellent adsorptive activity in treating Cr-contaminated
wastewater
Interaction Mechanism of Re(VII) with Zirconium Dioxide Nanoparticles Archored onto Reduced Graphene Oxides
Zirconium
oxide archored onto reduced graphene oxides (ZrO<sub>2</sub>@rGO)
was fabricated via a hydrothermal method and used for
ReÂ(VII) removal from aqueous solutions. Scanning electron microscopy,
Fourier transferred infrared spectroscopy, X-ray diffraction, thermogravimetric
analysis, and X-ray photoelectron spectroscopy were used to characterize
the as-prepared ZrO<sub>2</sub>@rGO. The results indicated that ZrO<sub>2</sub> was successfully decorated on rGO. The maximum sorption capacity
of ZrO<sub>2</sub>@rGO toward ReÂ(VII) was 43.55 mg/g. ZrO<sub>2</sub>@rGO exhibited enhanced sorption capacity for ReÂ(VII) in comparison
with bare ZrO<sub>2</sub> or rGO. The sorption kinetics could be described
by the pseudo-second-order equation. The sorption process of ReÂ(VII)
on ZrO<sub>2</sub>@rGO was endothermic and spontaneous. X-ray photoelectron
spectroscopy indicated the formation of an ionic bond of Zr–O
with ReÂ(VII). According to the density functional theory calculations,
O<sub>Re</sub>–Zr bonds on the surface of the monoclinic ZrO<sub>2</sub> plane (m-ZrO<sub>2</sub>) (111) plane and tetragonal ZrO<sub>2</sub> (t-ZrO<sub>2</sub>) (111) plane were formed when ReÂ(VII)
sorbs. The sorption energy of ReÂ(VII) onto the t-ZrO<sub>2</sub> (111)
plane was 3.87 eV, being higher than that of ReÂ(VII) onto m-ZrO<sub>2</sub> (1.26 eV)
Amino Siloxane Oligomer Modified Graphene Oxide Composite for the Efficient Capture of U(VI) and Eu(III) from Aqueous Solution
Poly 3-aminopropyltriethoxysilane
is a highly reactive high-molecular polymer because of the existence
of abundant amino groups, which presents a strong affinity toward
different metal cations. In view of this, the novel poly amino siloxane
oligomer modified graphene oxide composite (PAS–GO) was fabricated
by a facile cross-linking reaction and applied to capture UÂ(VI)/EuÂ(III)
ions from aqueous solution. The interaction mechanisms between the
PAS–GO and UÂ(VI)/EuÂ(III) were elaborated. The modification
by NH<sub>2</sub> increased the sorption sites and improved the sorption
capacities because of the synergistic effect of chelation with UÂ(VI)/EuÂ(III).
X-ray photoelectron spectroscopy revealed that nitrogen groups are
involved in the removal of UÂ(VI)/EuÂ(III) since nitrogen atoms of amine
groups provided the lone pair of electrons with UÂ(VI)/EuÂ(III) species.
The maximum sorption capacity of UÂ(VI) and EuÂ(III) on the PAS–GO
at 298 K calculated by the Langmuir isotherm model was 310.63 and
243.90 mg/g, respectively. The PAS–GO could be repeatedly used
for more than five cycles with slight degradation of sorption. High
sorption efficiency and excellent reusability make the PAS–GO
composite an ideal candidate for the capture of UÂ(VI)/EuÂ(III) from
aqueous solution
New Synthesis of nZVI/C Composites as an Efficient Adsorbent for the Uptake of U(VI) from Aqueous Solutions
New nanoscale zerovalent
iron/carbon (nZVI/C) composites were successfully
prepared via heating natural hematite and pine sawdust at 800 °C
under nitrogen conditions. Characterization by SEM, XRD, FTIR, and
XPS analyses indicated that the as-prepared nZVI/C composites contained
a large number of reactive sites. The lack of influence of the ionic
strength revealed inner-sphere complexation dominated UÂ(VI) uptake
by the nZVI/C composites. Simultaneous adsorption and reduction were
involved in the uptake process of UÂ(VI) according to the results of
XPS and XANES analyses. The presence of U–C/U-U shells demonstrated
that innersphere complexation and surface coprecipitation dominated
the UÂ(VI) uptake at low and high pH conditions, respectively. The
uptake behaviors of UÂ(VI) by the nZVI/C composites were fitted well
by surface complexation modeling with two weak and two strong sites.
The maximum uptake capacity of UÂ(VI) by the nZVI/C composites was
186.92 mg/g at pH 4.0 and 328 K. Additionally, the nZVI/C composites
presented good recyclability and recoverability for UÂ(VI) uptake in
regeneration experiments. These observations indicated that the nZVI/C
composites can be considered as potential adsorbents to remove radionuclides
for environmental remediation
Spectroscopic Investigation of Enhanced Adsorption of U(VI) and Eu(III) on Magnetic Attapulgite in Binary System
The
coadsorption of uranium and europium on magnetic attapulgite
(M-ATT) was explored through batch experiments and spectroscopic tests.
The adsorption processes of UÂ(VI) and EuÂ(III) onto M-ATT were highly
affected by the solution pH but not by the ionic strength, indicating
that the adsorption of the two metals was predominated through inner-sphere
surface complexation. Adsorption isotherms demonstrated that the maximum
adsorption capacities of UÂ(VI) on M-ATT in the single-solute system
(e.g., 60.48 mg g<sup>–1</sup> at pH 6.0) were lower than that
in the binary-solute system (e.g., 63.03 mg g<sup>–1</sup> at
pH 6.0), and the same trend was noticed for EuÂ(III) adsorption due
to their synergistic effect. The existence of UÂ(VI) and UÂ(IV) species
evidenced the partial reduction of adsorbed UÂ(VI) to UÂ(IV) by M-ATT
based on XPS tests. Hence, the enhanced adsorption of UÂ(VI) in the
existence of EuÂ(III) is ascribed to the primary coadsorption and then
the redox of adsorbed UÂ(VI) to UÂ(IV) by M-ATT, as well as the formation
of new sorbent active sites derived from reductive coprecipitation
(e.g., UO<sub>2+<i>x</i></sub>(s)), which also increased
the EuÂ(III) adsorption on M-ATT. The findings are significant for
coadsorption of radionuclides by magnetic adsorbents in environmental
pollution management
Direct Synthesis of Bacteria-Derived Carbonaceous Nanofibers as a Highly Efficient Material for Radionuclides Elimination
Bacteria-derived
carbonaceous nanofibers (CNFs) can be directly synthesized by the
pyrolysis of bacterial cellulose pellicles under N<sub>2</sub> atmosphere.
The batch adsorption experiments showed that the bacteria-derived
CNFs displayed the excellent adsorption performance for radionuclides.
The maximum adsorption capacities of the CNFs calculated from the
Langmuir model at pH 4.5 and 293 K were 67.11 mg/g for SrÂ(II) and
57.47 mg/g for CsÂ(I). The adsorption of CsÂ(I) and SrÂ(II) on the CNFs
decreased with increasing ionic strength at pH < 5.0, whereas no
effect of ionic strength was observed at pH > 6.0, indicating that
the outer-sphere surface complexation dominated the radionuclide adsorption
at pH < 5.0 whereas the adsorption was attributed to inner-sphere
surface complexation at pH > 6.0. The further evidence of surface
complexation modeling indicated that SrÂ(II) and CsÂ(I) adsorption on
the CNFs can be satisfactorily fitted by a double diffuse layer model
with an outer-sphere (SOHSr<sup>2+</sup>/SOHCs<sup>+</sup>) and an
inner-sphere complexes (SOSr<sup>+</sup>/SOCs). The X-ray photoelectron
spectroscopy analyses demonstrated that the adsorption of SrÂ(II) and
CsÂ(I) on the CNFs were ascribed to the combination of the oxygenated
functional groups of the CNFs. These observations indicated that the
CNFs, as inexpensive and available carbon-based nanomaterials, can
be regarded as a promising adsorbent for the removal of radionuclides
from aqueous solutions in environmental pollution cleanup
Biochar Derived from Sawdust Embedded with Molybdenum Disulfide for Highly Selective Removal of Pb<sup>2+</sup>
Surface
interactions between the adsorbents and heavy metal ions
play an important role in the adsorption process, and appropriately
decorating the material’s surface can significantly improve
the removal capacity of the adsorbents. So, the objective of this
study is to modify biochar by coating with molybdenum disulfide (MoS<sub>2</sub>) for enhancing the adsorption of Pb<sup>2+</sup>. The biochar
pyrolyzed at 600 °C was chosen as the base to combine the flowerlike
MoS<sub>2</sub> (MoS<sub>2</sub>@biochar) by solvothermal reaction,
in which the abundant S-containing functional groups may promote the
elimination of Pb<sup>2+</sup>. The prepared MoS<sub>2</sub>@biochar
exhibits excellent adsorption capacity (189 mg/g) to Pb<sup>2+</sup> in water solution. The adsorption of Pb<sup>2+</sup> maintains a
high level under the circumstance of coexisting ions (Mg<sup>2+</sup>, Ca<sup>2+</sup>, Co<sup>2+</sup>, and Cd<sup>2+</sup>), suggesting
the high selectivity for Pb<sup>2+</sup>. The adsorption mechanism
of Pb<sup>2+</sup> on MoS<sub>2</sub>@biochar is mainly ascribed to
the inner-sphere surface complexation, in particular, metal–sulfur
chemical complexation. The easily recycled MoS<sub>2</sub>@biochar
still has high adsorption capacity for Pb<sup>2+</sup>. This work
demonstrates that the MoS<sub>2</sub>@biochar is an excellent candidate
of adsorbent for Pb<sup>2+</sup> removal