6 research outputs found
Pyrite (FeS2)-supported ultrafiltration system for removal of mercury (II) from water
This study investigated the Hg(II) removal efficiencies of the reactive adsorbent membrane (RAM) hybrid filtration process, a removal process that produces stable final residuals. The reaction mechanism between Hg(II) and pyrite and the rejection of the solids over time were characterized with respect to flux decline, pH change, and Hg and Fe concentration in permeate water. Effects of the presence of anions (Clâ, SO42â, NO3â) or humic acid (HA) on the rejection of the Hg(II)-contacted pyrite were studied. The presence of both HA and Hg(II) increased the rate of flux decline due to the formation of irreversible gel-like compact cake layers as shown in the experimental data and modeling related to the flux decline and the SEM images. Stability experiments of the final residuals retained on the membrane using a thiosulfate solution (Na2S2O3) show that the Hg(II)-laden solids were very stable due to little or no detection of Hg(II) in the permeate water. Experiment on the possibility of continuously removing Hg(II) by reusing the Hg/pyrite-laden membrane shows that almost all Hg(II) was adsorbed onto the pyrite surface regardless of the presence of salts or HA, and the Hg(II)-contacted pyrite residuals were completely rejected by the DE/UF system. Therefore, a membrane filter containing pyrite-Hg(II) could provide another reactive cake layer capable of further removal of Hg(II) without post-chemical treatment for reuse.Other Information Published in: Emergent Materials License: https://creativecommons.org/licenses/by/4.0See article on publisher's website: http://dx.doi.org/10.1007/s42247-021-00282-7</p
Lithiated Polycalix[4]arenes for Efficient Adsorption of Iodine from Solution and Vapor Phases
Lithiated Polycalix[4]arenes for Efficient Adsorption
of Iodine from Solution and Vapor Phase
Shape-Dependent Charge Transfers in Crystalline ZnO Photocatalysts: Rods versus Plates
ZnO
particles with rod and plate configurations were synthesized
using a solvothermal method using zinc acetate and zinc chloride,
respectively. The surface of the as-synthesized ZnO rods and plates
were characterized using various analysis tools (XRD, XPS, photoluminescence,
FE-SEM, HR-TEM, BET, and UVâvis) and their photocatalytic activities
were examined for six different redox reactions. The surface areas
and bandgaps of the two ZnO samples were nearly identical; however,
XPS and photoluminescence (PL) studies showed that the rods and the
plates have relatively pronounced oxygen vacancy and oxygen interstitial
contributions, respectively. ZnO rods were found to be active for
the decomposition of methylene blue and phenol, the production of
OH radicals, and the generation of photocurrents, all of which are
associated with single-electron transfer reactions. On the other hand,
ZnO plates were more effective for the production of molecular hydrogen
and hydrogen peroxide, both of which are initiated by two-electron
transfer reactions. These single versus multiple charge transfers
are discussed with regard to the roles of oxygen vacancies and oxygen
interstitials, which are located near the conduction and the valence
bands, respectively
Redox-Responsive Viologen-Mediated Self-Assembly of CB[7]-Modified Patchy Particles
Sulfonated
surface patches of polyÂ(styrene)-based
colloidal particles (CPs) were functionalized
with cucurbit[7]Âuril (CB[7]). The macrocycles served as recognition
units for diphenyl viologen (DPV<sup>2+</sup>), a rigid bridging ligand.
The addition of DPV<sup>2+</sup> to aqueous suspensions of the particles
triggered the self-assembly of short linear and branched chainlike
structures. The self-assembly mechanism is based on hydrophobic/ion-charge
interactions that are established between DPV<sup>2+</sup> and surface-adsorbed
CB[7]. DPV<sup>2+</sup> guides the self-assembly of the CPs by forming
a ternary DPV<sup>2+</sup>â(CBÂ[7])<sub>2</sub> complex in which
the two CB[7] macrocycles are attached to two different particles.
Viologen-driven particle assembly was found to be both directional
and reversible. Whereas sodium chloride triggers irreversible particle
disassembly, the one-electron reduction of DPV<sup>2+</sup> with sodium
dithionite causes disassembly that can be reversed via air oxidation.
Thus, this bottom-up synthetic supramolecular approach allowed for
the reversible formation and directional alignment of a 2D colloidal
material
Redox-Responsive Viologen-Mediated Self-Assembly of CB[7]-Modified Patchy Particles
Sulfonated
surface patches of polyÂ(styrene)-based
colloidal particles (CPs) were functionalized
with cucurbit[7]Âuril (CB[7]). The macrocycles served as recognition
units for diphenyl viologen (DPV<sup>2+</sup>), a rigid bridging ligand.
The addition of DPV<sup>2+</sup> to aqueous suspensions of the particles
triggered the self-assembly of short linear and branched chainlike
structures. The self-assembly mechanism is based on hydrophobic/ion-charge
interactions that are established between DPV<sup>2+</sup> and surface-adsorbed
CB[7]. DPV<sup>2+</sup> guides the self-assembly of the CPs by forming
a ternary DPV<sup>2+</sup>â(CBÂ[7])<sub>2</sub> complex in which
the two CB[7] macrocycles are attached to two different particles.
Viologen-driven particle assembly was found to be both directional
and reversible. Whereas sodium chloride triggers irreversible particle
disassembly, the one-electron reduction of DPV<sup>2+</sup> with sodium
dithionite causes disassembly that can be reversed via air oxidation.
Thus, this bottom-up synthetic supramolecular approach allowed for
the reversible formation and directional alignment of a 2D colloidal
material
Viologen-Based Conjugated Covalent Organic Networks via Zincke Reaction
Morphology
influences the functionality of covalent organic networks and determines
potential applications. Here, we report for the first time the use
of Zincke reaction to fabricate, under either solvothermal or microwave
conditions, a viologen-linked covalent organic network in the form
of hollow particles or nanosheets. The synthesized materials are stable
in acidic, neutral, and basic aqueous solutions. Under basic conditions,
the neutral network assumes radical cationic character without decomposing
or changing structure. Solvent polarity and heating method determine
product morphology. Depending upon solvent polarity, the resulting
polymeric network forms either uniform self-templated hollow spheres
(<b>HS</b>) or hollow tubes (<b>HT</b>). The spheres develop
via an inside-out Ostwald ripening mechanism. Interestingly, microwave
conditions and certain solvent polarities result in the formation
of a robust covalent organic gel framework (<b>COGF</b>) that
is organized in nanosheets stacked several layers thick. In the gel
phase, the nanosheets are crystalline and form honeycomb lattices.
The use of the Zincke reaction has previously been limited to the
synthesis of small viologen molecules and conjugated viologen oligomers.
Its application here expands the repertoire of tools for the fabrication
of covalent organic networks (which are usually prepared by dynamic
covalent chemistry) and for the synthesis of viologen-based materials.
All three materialsî¸<b>HT</b>, <b>HS</b>, and <b>COGF</b>î¸serve as efficient adsorbents of iodine due to
the presence of the cationic viologen linker and, in the cases of <b>HT</b> and <b>HS</b>, permanent porosity