Effect of laser power on force constant and phonon lifetime of stretching and bending vibration of Cu-doped WO3 nanostructures

Laser-power dependence effects on the structural stability of nanocomposite catalysts studied by Raman spectroscopy: On the structure-activity correlations in glycerol acetylation

Structural properties of binary CeAl, CeMn, NiAl, CeZr, SnTi and ZrMn nanocomposite oxide catalysts were monitored towards the Laser Raman spectroscopy investigations providing new insights to control catalytic applications upon temperature ranges at which the laser power was varied. The lattice vibrational properties were investigated by varying the incident laser power during Raman measurements from 0.017 mW to 4.0 mW. Structural changes in nanocomposites were achieved upon increasing laser power, which induced local heating disorder causing the sintering of CeMn, SnTi, and ZrMn nanocomposites. The laser-power dependence effects on the structural stability of CeAl, NiAl, and CeZr were observed with high amounts of oxygen vacancy defects over CeAl upon laser power heating. Both CeMn and ZrMn exhibited phase transitions from MnO₂ to α-Mn₂O₃ being the use of the latter nanocomposites limited to work at 1.1 mW. The structure-activity correlations for the nanocomposite oxide catalysts were evaluated through the acetylation of glycerol with acetic acid reaction to produce valuable acetins. Remarkable shifts in the Raman bands wavenumbers and other spectral changes in the lattice mode were caused by laser-induced phenomena accounting for the undesired phase formation and particle growths, as well. This resulted in a low catalytic performance of the NiAl, SnTi, CeMn and ZrMn owing to the thermal effects. Contrary, CeAl and CeZr were more active for acetins products avoiding the phase transformations due to their structural stability at high temperatures, which in turn avoided leaching of the active Ce sites during the reaction.

In-situ micro-Raman study of SnSe single crystals under atmosphere: Effect of laser power and temperature

Single crystal of tin selenide (SnSe) was studied by micro-Raman spectroscopy under atmosphere conditions. The effect of varying the incident laser power on the sample up to 2 mW was analyzed. The Raman spectra showed that the number of all vibrational modes have not decreased or increased, but all peaks red-shifted and softened obviously as the laser power increased to the threshold value. The temperature-dependent micro-Raman study of the single crystal was carried out for illustrating thermal effect due to the high incident laser power. A new SnSe₂ phase appeared at high temperature without vacuum and become the dominant phase at the surface of the crystal gradually because of oxidation. Detecting few amounts of SnSe₂ crystals on the surface of single crystal shows the high sensitivity of Raman spectroscopy. High resolution transmission electron microscopy (HRTEM) was also used to confirm that the newly generated SnSe₂ phase is precipitated by SnSe under high temperature oxidation conditions. To study the Raman spectra of low thermal conductivity materials under high temperature and non-vacuum conditions, lower incident laser power should be used to avoid the influence of additional thermal effects.

Kinetics and Adsorption Model of Methylene Blue on g-C3N4@WO3.H2O Nanoplate Composite

g-C3N4@WO3.H2O nanoplate composite adsorbents were prepared in a simple acid precipitation method at room temperature. The g-C3N4@WO3.H2O nanoplate composite adsorbents were characterized by X-ray powder diffraction, micro-Raman spectroscopy, Fourier transform infrared spectra, scanning electron microscopy and UV-vis diffuse reflectance spectroscopy. The results show that the orthorhombic-phase WO3.H2O nanoplates with dimensions of [Formula: see text][Formula: see text]nm3 were successfully composited with g-C3N4. The methylene blue dye generation activity of these adsorbents was evaluated. The kinetics and absorption model of g-C3N4@WO3.H2O nanoplate composite adsorbents were further studied.