9 research outputs found
Hydrophobic Polydimethylsiloxane (PDMS) Coating of Mesoporous Silica and Its Use as a Preconcentrating Agent of Gas Analytes
Mesoporous silica with mean pore
size of ∼14 nm was coated
by polydimethylsiloxane (PDMS) using a thermal deposition method.
We showed that the inner walls of pores larger than ∼8 nm can
be coated by thin layers of PDMS, and the surfaces consisting of PDMS-coated
silica were superhydrophobic, with water contact angles close to 170°.
We used the PDMS-coated silica as adsorbents of various gas-phase
chemical warfare agent (CWA) simulants. PDMS-coated silica allowed
molecular desorption of various CWA simulants even after exposure
under highly humid conditions and, therefore, is applicable as an
agent for the preconcentration of gas-phase analytes to enhance the
sensitivities of various sensors
Unveiling the Complexity of the Degradation Mechanism of Semiconducting Organic Polymers: Visible-Light-Induced Oxidation of P3HT Films on ZnO/ITO under Atmospheric Conditions
The oxidation of
polyÂ(3-hexylthiophene) (P3HT) films deposited
on ZnO/indium tin oxide (ITO) under blue light irradiation in either
dry or humid atmospheres was studied using X-ray photoelectron spectroscopy
in combination with UV–vis absorption spectroscopy. From results
up to 12 h of reaction, ring-opening was hardly found, and it is suggested
that the water molecules chemisorbed competitively against O<sub>2</sub> (i.e., the major oxidizing agent), thereby decreasing the oxidation
of P3HT. Beyond 12 h, thiophene ring-opening took place at the topmost
surface layer of P3HT, and the humidity facilitated the ring-opening
of P3HT. Regarding the oxidation of the entire P3HT thin film, the
humidity did not have a large influence on the oxidation behavior
of P3HT. Here, the degree of oxidation of P3HT abruptly increased
when the reaction time exceeded 12 h. This suggests that the rate
of oxidation of the entire P3HT film is determined by the slow diffusion
of the activated oxygen species into the deeper layers of the P3HT
films. We also demonstrate that the photoinduced degradation of P3HT
can be retarded by turning off light between irradiation, which may
be due to the reversible desorption of activated oxygen species under
dark conditions
Initial Stage of Photoinduced Oxidation of Poly(3-hexylthiophene-2,5-diyl) Layers on ZnO under Dry and Humid Air
We studied the initial stage of the
oxidation behaviors of polyÂ(3-hexylthiophene-2,5-diyl) (P3HT) layers
on ZnO under visible light irradiation using in situ X-ray photoelectron
spectroscopy. In the S 2p core-level XPS spectra, partial oxidation
of S into sulfoxide was found with a sustained ring structure of P3HT
in both humid and dry atmospheric conditions. Much lower increases
in the XPS peak intensities were also found for sulfone and other
S species related to P3HT ring opening. However, the partial oxidation
of the P3HT layers resulted in significant changes in optical properties
by disturbing inter- and intra-Ï€-conjugation. P3HT oxidation
was more pronounced under humid air conditions. Incorporation of molecular
water into the P3HT lattice was also observed
Visible-Light-Induced Oxidation of Poly(3-hexylthiophene-2,5-diyl) Thin Films on ZnO Surfaces under Humid Conditions: Study of Light Wavelength Dependence
The
oxidation behaviors of polyÂ(3-hexylthiophene-2,5-diyl) (P3HT)
thin films (∼60 nm thickness)/ZnO irradiated with three different
wavelengths of visible light (blue, green, and red) in a humid atmosphere
were studied using X-ray photoelectron spectroscopy (XPS) and UV–vis
spectroscopy. The formation of sulfoxide states upon visible-light
irradiation was observed in the S 2p core-level XPS spectra, and more
importantly, this oxidation became pronounced with decreasing wavelength
of incident light. Photo-oxidation of P3HT films also resulted in
a reduction in optical absorption. In contrast to the XPS results,
changes in the UV–vis absorption spectrum were rather insensitive
to the wavelength of incident visible light. The wavelength dependency
of the photo-oxidation of P3HT films seen in the XPS spectra is attributed
to the more pronounced photoinduced oxidation of locally disordered
thiophene rings on the surfaces of P3HT films under irradiation with
shorter-wavelength visible light. The population of local-disordered
sites that increases the optical transition gap compared to that of
the well-ordered bulk P3HT film decreases from the top surface to
the interior of P3HT films due to stronger interchain interactions
in the interior portion of the films. Therefore, changes in the optical
absorbance seen in the UV–vis absorption spectra of the entire
P3HT film upon photoinduced oxidation are less sensitive to the wavelength
of incident light in the visible regime
Organic Solar Cells Fabricated by One-Step Deposition of a Bulk Heterojunction Mixture and TiO<sub>2</sub>/NiO Hole-Collecting Agents
Organic solar cells (OSCs) were fabricated using a one-step
deposition
of a mixture of NiO nanoparticles, region-regular polyÂ(3-hexylthiophene)
(P3HT), and [6,6]-phenyl-C<sub>61</sub>-butyric methyl ester (PCBM)
without polyÂ(3,4-ethylenedioxythiophene):polyÂ(styrenesulfonate) (PEDOT:PSS).
Although the intended NiO layer was successfully formed at the interface
between indium tin oxide (ITO) and the photoactive layer, only a marginal
increase in the power conversion efficiency (PCE) of the OSCs (from
0.773 to 1.171%) was found by addition of NiO nanoparticles to the
solution of the P3HT/PCBM mixture. Using X-ray photoelectron spectroscopy,
it was evidenced that P3HT was oxidized at interfaces of P3HT and
NiO, which can decrease the photovoltaic performance of an OSC. Ultrathin
TiO<sub>2</sub> wrapping layers (thickness ∼ 2 nm) on the surface
of NiO nanoparticles prepared by atomic layer deposition quenched
oxidation of P3HT resulted in a significant increase in PCE up to
2.684%. Our result shows that, in OSCs, oxidation of active polymers
at oxide/polymer interfaces should be of concern, and a strategy for
avoiding such degradation of polymers is required. Fabrication of
various core–shell nanostructures as oxide buffers can be useful
for quenching the oxidation of active polymers and increasing photovoltaic
performances
Structural Effect of Thioureas on the Detection of Chemical Warfare Agent Simulants
The ability to rapidly detect, identify,
and monitor chemical warfare
agents (CWAs) is imperative for both military and civilian defense.
Since most CWAs and their simulants have an organophosphonate group,
which is a hydrogen (H)-bond acceptor, many H-bond donors have been
developed to effectively bind to the organophosphonate group. Although
thioureas have been actively studied as an organocatalyst, they are
relatively less investigated in CWA detection. In addition, there
is a lack of studies on the structure–property relationship
for gas phase detection. In this study, we synthesized various thioureas
of different chemical structures, and tested them for sensing dimethylmethylphosphonate
(DMMP), a CWA simulant. Molecular interaction between DMMP and thiourea
was measured by <sup>1</sup>H NMR titration and supported by density
functional theory (DFT) calculations. Strong H-bond donor ability
of thiourea may cause self-aggregation, and CH−π interaction
can play an important role in the DMMP detection. Gas-phase adsorption
of DMMP was also measured using a quartz crystal microbalance (QCM)
and analyzed using the simple Langmuir isotherm, showing the importance
of structure-induced morphology of thioureas on the surface
Metal–Organic Framework@Microporous Organic Network: Hydrophobic Adsorbents with a Crystalline Inner Porosity
This
work reports the synthesis and application of metal–organic
framework (MOF)@microporous organic network (MON) hybrid materials.
Coating a MOF, UiO-66-NH<sub>2</sub>, with MONs forms hybrid microporous
materials with hydrophobic surfaces. The original UiO-66-NH<sub>2</sub> shows good wettability in water. In comparison, the MOF@MON hybrid
materials float on water and show excellent performance for adsorption
of a model organic compound, toluene, in water. Chemical etching of
the MOF results in the formation of hollow MON materials
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Peptide-Programmable Nanoparticle Superstructures with Tailored Electrocatalytic Activity
Biomaterials
derived <i>via</i> programmable supramolecular
protein assembly provide a viable means of constructing precisely
defined structures. Here, we present programmed superstructures of
AuPt nanoparticles (NPs) on carbon nanotubes (CNTs) that exhibit distinct
electrocatalytic activities with respect to the nanoparticle positions <i>via</i> rationally modulated peptide-mediated assembly. <i>De novo</i> designed peptides assemble into six-helix bundles
along the CNT axis to form a suprahelical structure. Surface cysteine
residues of the peptides create AuPt-specific nucleation site, which
allow for precise positioning of NPs onto helical geometries, as confirmed
by 3-D reconstruction using electron tomography. The electrocatalytic
model system, i.e., AuPt for oxygen reduction, yields electrochemical
response signals that reflect the controlled arrangement of NPs in
the intended assemblies. Our design approach can be expanded to versatile
fields to build sophisticated functional assemblies