Recent Advances in Pristine Iron Triad Metal-Organic Framework Cathodes for Alkali Metal-Ion Batteries.

Pristine iron triad metal-organic frameworks (MOFs), i.e., Fe-MOFs, Co-MOFs, Ni-MOFs, and heterometallic iron triad MOFs, are utilized as versatile and promising cathodes for alkali metal-ion batteries, owing to their distinctive structure characteristics, including modifiable and designable composition, multi-electron redox-active sites, exceptional porosity, and stable construction facilitating rapid ion diffusion. Notably, pristine iron triad MOFs cathodes have recently achieved significant milestones in electrochemical energy storage due to their exceptional electrochemical properties. Here, the recent advances in pristine iron triad MOFs cathodes for alkali metal-ion batteries are summarized. The redox reaction mechanisms and essential strategies to boost the electrochemical behaviors in associated electrochemical energy storage devices are also explored. Furthermore, insights into the future prospects related to pristine iron triad MOFs cathodes for lithium-ion, sodium-ion, and potassium-ion batteries are also delivered.

CNT/VS2-MoS2 with multi-interface structure for improved hydrogen evolution reaction.

CNT/VS2-MoS2 with a multi-interface structure shows significantly enhanced catalytic activity compared with MoS2, CNT/MoS2, CNT/VS2 and VS2-MoS2, including a low overpotential of -215 mV at 10 mA cm-2 and a small Tafel slope of 64 mV dec-1. The enhanced catalytic activity could be ascribed to the multiple interfaces in CNT/VS2-MoS2, which can promote charge transfer and yield abundant active sites. This study provides a valuable route to improve the catalytic performance of two-dimensional electrocatalysts.

Improved surface-enhanced Raman scattering (SERS) sensitivity to molybdenum oxide nanosheets via the lightning rod effect with application in detecting methylene blue.

MoO2 nanomaterials show a superior surface-enhanced Raman scattering (SERS) property due to their high concentration of free electrons and low resistivity. However, the physical process of semiconductor-based SERS is still elusive because there are many factors that affect the local electromagnetic field intensity and the subsequent Raman intensity of the molecules in close proximity to the semiconductor nanomaterials. Herein, we investigate the important contribution of surface morphology to molybdenum oxide SERS. The MoO3/MoO2 nanosheets (NSs) are synthesized by oxidizing MoO2 NS, and the surface roughness of MoO3 can be controlled through adjusting the oxidization time. Compared with the MoO2 NS before oxidization, the MoO3/MoO2 NSs exhibit a much stronger SERS signal, which favors their application as a SERS substrate to detect trace amounts of methylene blue molecules. The minimum detectable concentration is up to 10-9 M and the maximum enhancement factor is about 1.4 × 105. Meanwhile, excellent signal reproducibility is also observed using the MoO3/MoO2 NSs as the SERS substrate. A simulated electric field distribution shows that a stronger electric field enhancement is formed due to the lightning rod effect in the gap of corrugated MoO3 NSs. These results demonstrate that the surface topography of molybdenum oxide may play a more important role than their oxidation state in SERS signal enhancement.

Ag Nanoparticle-Sensitized WO3 Hollow Nanosphere for Localized Surface Plasmon Enhanced Gas Sensors.

Ag nanoparticle (NP)-sensitized WO3 hollow nanospheres (Ag-WO3-HNSs) are fabricated via a simple sonochemical synthesis route. It is found that the Ag-WO3-HNS shows remarkable performance in gas sensors. Field-emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM) images reveal that the Agx-WO3 adopts the HNS structure in which WO3 forms the outer shell framework and the Ag NPs are grown on the inner wall of the WO3 hollow sphere. The size of the Ag NPs can be controlled by adjusting the addition amount of WCl6 during the reaction. The sensor Agx-WO3 exhibits extremely high sensitivity and selectivity toward alcohol vapor. In particular, the Ag(15nm)-WO3 sensor shows significantly lower operating temperature (230 °C), superior detection limits as low as 0.09 ppb, and faster response (7 s). Light illumination was found to boost the sensor performance effectively, especially at 405 and 900 nm, where the light wavelength resonates with the absorption of Ag NPs and the surface oxygen vacancies of WO3, respectively. The improved sensor performance is attributed to the localized surface plasmon resonance (LSPR) effect.

2D-MoO3 nanosheets for superior gas sensors.

By taking advantages of both grinding and sonication, an effective exfoliation process is developed to prepare two-dimensional (2D) molybdenum oxide (MoO3) nanosheets. The approach avoids high-boiling-point solvents that would leave a residue and cause aggregation. Gas sensors fabricated using the 2D-MoO3 nanosheets provide a significantly enhanced chemical sensor performance. Compared with the sensors using bulk MoO3, the response of the 2D-MoO3 sensor increases from 7 to 33; the sensor response time is reduced from 27 to 21 seconds, and the recovery time is shortened from 26 to 10 seconds. We attribute the superior performance to the 2D-structure with a much increased surface area and reactive sites.

A Se-doped MoS2 nanosheet for improved hydrogen evolution reaction.

Thanks to the increase in the number of active sites and enhanced conductivity, the Se-doped MoS2 shows excellent catalytic activity with a lower overpotential of -140 mV and a smaller Tafel slope of 55 mV dec(-1), exhibiting enhanced catalytic performance compared with that of pristine MoS2. This work offers an attractive strategy to improve the HER activity of MoS2-based catalysts.

[FTIR study on the leaf spots, near-spot and normal tobacco leaves].

Fourier transform infrared spectroscopy (FTIR) was used to study three group tobacco leaves of brown spot, angular spot and weather speck, with each group being composed of three samples, namely, leaf spots, near-spot and normal tobacco leaves. The results indicate that the absorption ratio A1631/A1025 of the three group tobacco leaves showed the same change tendency, with the normal tobacco leaves < the near-spot leaves < the leaf spots. For a more objective and comprehensive analysis, the original and second-derivative spectra were selected for distance analysis in the whole region. The results show that the Pearson correlation coefficient of the near-spot leaves and normal leaves is greater than the corresponding coefficient of leaf spots and normal leaves, which suggest that the near-spot leaves and normal leaves have a closer relationship compared with the leaf spots and normal leaves. The ratios of the A1631/A1025 and Pearson correlation coefficients show that the chemical composition of the near-spot leaves changed gradually, that is, the near-spot leaves were in a transient state between normal and disease leaves. In conclusion, FTIR spectroscopy is a promising technique for diagnosing tobacco disease in the incubation period.

[A study of Boletus bicolor from different areas using Fourier transform infrared spectrometry].

It is hard to differentiate the same species of wild growing mushrooms from different areas by macromorphological features. In this paper, Fourier transform infrared (FTIR) spectroscopy combined with principal component analysis was used to identify 58 samples of boletus bicolor from five different areas. Based on the fingerprint infrared spectrum of boletus bicolor samples, principal component analysis was conducted on 58 boletus bicolor spectra in the range of 1 350-750 cm(-1) using the statistical software SPSS 13.0. According to the result, the accumulated contributing ratio of the first three principal components accounts for 88.87%. They included almost all the information of samples. The two-dimensional projection plot using first and second principal component is a satisfactory clustering effect for the classification and discrimination of boletus bicolor. All boletus bicolor samples were divided into five groups with a classification accuracy of 98.3%. The study demonstrated that wild growing boletus bicolor at species level from different areas can be identified by FTIR spectra combined with principal components analysis.