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In this work, two-dimensional crystalline C3N4 (CCN) was obtained by promoting the self-condensation reaction of dicyandiamide in an air atmosphere via the molten salt method. Studies show that compared with polymer-C3N4 (PCN) ((9.8 m2/g)), CCN has a larger specific surface area (77.1 m2/g)) and better crystallinity. Additionally, the resistance of CCN in the air is 40 MΩ, 1250 times lower than that of polymer-C3N4 (PCN) (∼50000 MΩ). Secondly, when 50 ppm toluene gas analysis flows into the CCN based gas sensor at room temperature, the gas response value is 350. The CCN based gas sensor works for 60 days, or after 25 cycles continuously, the gas response value remains at about 350 (Rg/Ra), which is due to the excellent crystallinity, optimized π conjugate system, and enhanced interlayer van der Waals of CCN. Additionally, the critical effect of crystallinity on the gas sensitivity of carbon nitride is also discussed in detail.

For improving the sensor performance of molybdenum disulfide (MoS2), the modification of surface properties is essential. In this study, the surfaces of MoS2 nanoparticles with a mixture of 1T (metallic) and 2H (semiconductor) (1T/2H-MoS2) prepared solvothermally were modified by O2 plasma irradiation to enhance their humidity-sensing properties. The O2 plasma irradiation of MoS2 induced MoO3 formation on the surfaces. The amount of MoO3 increased with increasing O2 plasma irradiation time. The specific surface area, as well as total pore volume, increased after O2 plasma irradiation from 28 m2/g and 0.089 cm3/g to 185 m2/g and 0.279 cm3/g, respectively. The pore size distribution shifted to a lower value after O2 plasma irradiation. These results suggest that the O2 plasma irradiation can modify the surface nature of 1T/2H-MoS2 nanoparticles. The humidity-sensing properties of the obtained samples were evaluated with various relative humidity (RH) values. When the O2 plasma-irradiated MoS2 sensor was exposed to a higher RH, a higher response was obtained. The sensor response of the O2 plasma-irradiated MoS2 nanoparticles was significantly enhanced to around 100% at 95% RH compared with the sample before the O2 plasma irradiation. As a demonstration of a practical application, the materials were used for the sensing of human breath. The breath testing indicated a good response, and the sensor also distinguished wet and dry hands clearly. These results strongly suggested that the O2 plasma-irradiated MoS2 can be applied for breath testing as well as in skin monitoring devices.

In general, a rapid quenching is required to obtain an amorphous metal. It is known that an intensive ultrasonication generates a very high temperature within cavitation bubbles in a very short moment, which enables a rapid quenching process in a liquid phase synthesis. In this study, the sonochemically-derived "amorphous iron" from Fe(CO)5 was carefully examined by XRD, TEM, TG-DTA. The product was found to be an amorphous containing a certain amount (∼15%) of volatile component that can be removed by heating in a nitrogen flow. After annealed in the inert atmosphere at 600°C, cooled down to room temperature, and then exposed in air (oxygen), the sample showed a strong exotherm accompanied by a weight gain. This is due to oxidation of fine metallic iron. Experimental operations of such a reactive material were examined.

Adsorption and photocatalytic decomposition behaviors of gas-phase acetaldehyde (CH3CHO), together with carbon dioxide (CO2) formation have been measured for pure titania (TiO2) powders with three types of polymorphs (anatase, brookite, and rutile) under UV-light illumination, and assessed by a kinetic model that takes into account the immediate decomposition of CH3CHO attached on the surface, and the gradual decomposition of CH3CHO adsorbed on the surface. Experimental data are well reproduced by the present model, highlighting how adsorption-related pathways markedly contribute to overall CH3CHO removal kinetics even for pure titanias. Although the initial removal rate depends on the surface area, which affects the adsorption capacity, it is suggested that specific surface area-based adsorbability and decomposition reactivity are enhanced by heightened crystallinity. Our kinetic analysis demonstrates that anatase exhibits the highest photocatalytic activity as a result of superior adsorbability, as well as superior decomposition reactivity, compared to other polymorphs.

The structure, porosity, and adsorption properties of mixed metal oxides (MMO) were investigated according to the physical property of the starting materials. Layered double hydroxides (LDH), the pristine MMO, were prepared to have the same composition of Mg2Al(OH)6(CO3)0.5, but with different particle size. The prepared LDH were calcined at 400 °C to obtain MMO named CMO, HMO, and UMO corresponding to the pristine MMO synthesized by coprecipitation, hydrothermal treatment, and urea hydrolysis method, respectively. The particle sizes of CMO, HMO, and UMO were comparable to those of the pristine MMO in the order UMO > HMO > CMO; on the other hand, the crystallite sizes were almost the same as each other, regardless of the pristine MMO. According to the high-resolution transmission electron microscopy and X-ray diffraction, we could suggest that a single particle of MMO was composed of smaller domains of metal oxide crystallite. Consequently, small MMO particle tended to have interparticulate macropore, while large MMO particle had more possibility of containing intraparticulate mesopores, which was cross-confirmed by the N2 adsorption–desorption isotherms. Toluene and water vapor adsorption tests on three different MMO showed that the intraparticulate mesopores were advantageous to adsorb a variety of adsorbate. It was therefore concluded that MMO obtained by calcination of LDH would have high adsorption property when the pristine LDH has large particle dimension, thanks to the large portions of intraparticulate mesopores.

Herein, we report the self-assembly of a synthetic vanilloid receptor (VR) peptide that selectively binds capsaicin. We synthesized a 26-mer peptide-YSEILFFVQS-HHHHHH-LAMGWTNMLY (S3HS4)-comprising two chemoreceptor domains of transient receptor potential channel (TRPV1) linked by a hexahistidine sequence. High-speed atomic force microscopy (AFM) imaging in water revealed that the peptide structures alternated rapidly between wedge shape and linear forms. Circular dichroism spectroscopy showed that 65% of the amide units in the peptide chain adopted an α-helix structure, which was ascribed to the chemoreceptor domains. S3HS4 developed well-packed monolayers at the Ni-treated thiolated nitrilotriacetic acid self-assembled monolayers by chelation of the hexahistidine segment, as characterized by infrared spectroscopy and AFM, which exhibited statistically constant specific height. Therefore, S3HS4 was expected to fold spontaneously upon chelation, and the resulting helix-turn-helix conformers developed films while uniformly oriented: the tilt angle was 69° from the surface normal to the substrate. According to microgravimetric analysis using a quartz crystal microbalance (QCM), the adsorption was 84 ± 47 pmol cm