Papers by Keyword: Raman Spectroscopy

Abstract: Carbon nanotubes (CNT) have been investigated for a wide range of applications. The combination of the CNT structure with semiconductors oxides opens up various application possibilities: water separation for hydrogen generation, degradation of pollutants in aqueous contamination and sewage treatment, photoreduction of CO₂ activity in self-cleaning air purification and dyes for solar cells. The junction multi-walled carbon nanotubes with dioxide titanium and zinc oxide (MWCNT-TiO₂-ZnO), when used as support, can facilitate a change in electron transfer, increasing the photocatalytic activity. MWCNTs/TiO₂/ZnO nanocomposites were prepared by the modified sol-gel method using MWCNTs, titanium (IV) propoxide, commercial TiO₂ (P25) as titanium sources, zinc oxide produced in the laboratory by thermal evaporation and commercial ZnO. The composites obtained from the titanium (IV) propoxide were prepared by solution processing followed by thermal treatment at 500° C. The results were associated with the characteristics of the nanocomposites using Raman spectroscopy. The photocatalytic activity on organic dye was associated to energy gap evaluated by diffuse reflectance spectroscopy.

Abstract: SOREME project (LIFE 11 ENV/IT/109) is aimed at synthesizing an innovative sorbent based on activated carbon obtained from the carbonization of waste tires. Microstructural characterization was mainly performed in order to define crystallinity, morphology and porosity of the activated carbon powders obtained in different conditions. In particular, XRD analysis always revealed a partially crystalline structure with different crystallite size of the nanographitic structure. The disorder of these structures was determined by Raman spectroscopy. This evaluation was made on the basis of the ratio of the integrated area of the D and G bands typical of the graphitic structure. Finally, SEM was used to put in evidence the mesopores and macropores.

Abstract: In this work, we focus on heavily aluminum (Al) doped 4H-SiC samples. We compare the effect of the Al concentration and Hall carrier concentration on the Raman spectra in a large frequency range. The Al concentration measured by Secondary Ion Mass Spectrometry ranged from 2×10¹⁶ to 8.4×10¹⁹ cm^-3 while the electrical measurement give a carrier concentration up to 5×10¹⁹ Al×cm^-3. On the Raman spectra, three different frequency domains have been analysed: i) at high frequency where we consider the change in longitudinal optical phonon-plasmon coupled mode; ii°) at low frequency where we consider the continuum of electronic transitions and iii°) finally, considering the Fano interference effect between the continuum of electronic transitions and the Folded Transverse Acoustic phonon modes. This analysis is applied to comment a Raman spectra mapping collected on a 4H-SiC 2 inch wafer.

Abstract: Diamond-like carbon (DLC) films were prepared on the Si (100) substrates by pulsed cathodic arc plasma. The influences of given pulse frequency on the microstructure, morphology, mechanical and optical properties of DLC films were investigated by Raman spectroscopy, atomic force microscopy, Knoop sclerometer, X-ray double-crystal surface profilometer. The results showed that the variation of pulse frequency could significantly change the microstructure of DLC films, including the size and ordering of sp² carbon clusters and movement or diffusion of carbon atoms. The increasing of pulse frequency led to the variation of the relative fraction of Csp³/Csp². The hardness and internal stress of the DLC films were affected accordingly. The results might contribute to the synthesis of DLC films with excellent structure and properties by cathodic arc evaporation.

Abstract: The MWCNTs was functionalized by refluxing commercial MWCNTs (a-MWCNTs) in concentrated HNO₃/H₂SO₄ (3:1 v/v) at 100°C for 6 hours. The dispersion of a-MWCNTs and functionalized MWCNTs (f-MWCNTs) were observed after 1 hour sonication in ethanol. Both samples were characterized by UV-vis spectroscopy for dispersion behavior. The dried f-MWCNTs and a-MWCNTs were characterized by Raman spectroscopy to estimate the defect level. The morphology of the samples were analyzed by Transmission Electron Microscopy (TEM). The f-MWCNTs was well dispersed in ethanol within 2 weeks of observations period. The colloidal stability of a-MWCNTs was low as it was easily sediment after 24 hours. The UV-vis spectra of f-MWCNTs show maximum absorbance at 250 nm meanwhile no absorbance was observed for a-MWCNTs. Analysis from Raman spectrum shows that the f-MWCNTs have relative intensity of 1.101 which is higher than a-MWCNTs that have relative intensity of 0.935. The image from TEM revealed that the f-MWCNTs have structural defects and the absence of amorphous carbon on sidewall meanwhile the a-MWCNTs indicate otherwise.

Abstract: To study the performance of chitosan nanoparticles systematically, we characterized MMA, chitosan and synthesized chitosan nanoparticles by Raman spectroscopy. Through analyzing the characteristic peaks of each substance, we found MMA grafted chitosan by opening its carbon-carbon double bond. So Raman spectroscopy is a very effective way in terms of the characterization of nanomaterials .

Abstract: The analytical method was established for identification of 100% cotton fabric by Raman spectroscopy. 100 samples were analyzed directly by Raman spectrometer with a 1064nm laser source. 1120-1180 cm^-1,1320-1400cm^-1 and 1560-1600cm^-1 were selected as important spectral regions by Random forest method. A Random forest model was established with 65 trees and 80 training samples. The result showed that different kind of textile can be identified by Raman spectroscopy coupled with random forest method.

Abstract: Carbon dioxide (CO₂) capturing has been an important issue for decades. Alkanoamines, such as diethanolamine (DEA) have been widely used for CO₂ separation by absorption process. During this process, CO₂ loading measurement is an imperative action for a proper process control. Currently used methods are titration based which requires a long processing time. In this work Raman spectroscopy is used to model and predict the CO₂ loading in wide range (0-0.97 CO₂ mole/amine mole). The models are developed by using Raman peak ratios to minimize the error due to peaks fluctuations. The Raman peak ratio of 1022 cm^-1/1461cm^-1 has been found as a good fit with the coefficient of determination (R²) of 0.92 and mean squared error (MSE) of 0.00656 CO₂ mole²/ amine mole² in prediction of CO₂ loading.

Abstract: Thermodynamic model is one of the important elements in designing and operating CO₂ removal systems, thus accurate determination of the thermodynamic properties of CO₂ in aqueous amine is of major interest for both technical and economical considerations. Quantitative Raman study of aqueous monoethanolamine (MEA) solutions of concentration ranging from 0 to 99 mass % in the spectral region between 300 and 3100 cm^{− 1} was performed. Band envelopes were resolved with Gaussian Lorentzian function. Progressive growth of area under these peaks with increasing concentration was used as the parameter to construct calibration curve. Area ratio of selected peaks was plotted against MEA concentration to depict the relationship between MEA concentration and each area ratio. Correlation for A₁₄₆₀/A₉₃₃ has coefficient of determination closest to unity and lowest mean squared area. MEA concentration can be calculated from the equation derived from correlation between A₁₄₆₀/A₉₃₃ and MEA mass %.

Abstract: Factor group analysis on the deformed pyrochlore-structure hydroxyl transition metal halides M₂(OH)₃X (M = Co, Fe and Mn; X = Cl, Br and I) with the crystal symmetry ≡ D_3d⁵ of space group No. 166 for their infrared (IR) and Raman spectroscopic studies are, for the fist time to the best of our knowledge, reported. Through a standard factor group analysis, we predict that there are 17 IR active normal modes (7A_2u+ 10E_u) and 12 Raman active modes (5A_1g + 7E_g), caused by five atomic site groups [HOM₃], [OM₃], [MO₄X₂], [ClM₃] and [MO₆], where the black body letters represent the site atoms. In addition we figure out all the atomic displacement patterns of 12 Raman active normal modes, and point out these results are completely same as those of the famous geometric frustration material Herbertsmithite ZnCu₃(OH)₆C_l2.