9 research outputs found

    Hydrophobic Polydimethylsiloxane (PDMS) Coating of Mesoporous Silica and Its Use as a Preconcentrating Agent of Gas Analytes

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    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

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    The oxidation of poly­(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

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    We studied the initial stage of the oxidation behaviors of poly­(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-π-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

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    The oxidation behaviors of poly­(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

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    Organic solar cells (OSCs) were fabricated using a one-step deposition of a mixture of NiO nanoparticles, region-regular poly­(3-hexylthiophene) (P3HT), and [6,6]-phenyl-C<sub>61</sub>-butyric methyl ester (PCBM) without poly­(3,4-ethylenedioxythiophene):poly­(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

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    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

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    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

    Peptide-Programmable Nanoparticle Superstructures with Tailored Electrocatalytic Activity

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    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
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