Journal of Raman Spectroscopy最新文献

Understanding the variation of proton concentration near the surface of the electrochemical interface is of great significance for understanding the mechanism of electrochemical reactions. In this work, 4-Mpy molecules that are protonated and deprotonated depending on the surrounding pH value adsorb on the Au nanoparticle film electrode with high SERS activity, and by virtue of the highly interfacial-sensitive EC-SERS technique, we systematically studied the effects of electrolyte pH value and external voltage on the protonation and deprotonation of 4-Mpy at the interface between Au-NP film electrode and phosphate buffer, to analyze the changes of near-surface proton concentration at the electrochemical interface. It is found that the pH value of the electrolyte plays a decisive role in the protonation process of 4-Mpy at the electrode interface at low reduction voltage (< −0.1 V). In acidic and neutral solution, 4-Mpy exists mainly in protonated form on the electrode surface. However, in alkaline solutions, 4-Mpy exists mainly on the electrode surface in the form of deprotonation. At high reduction voltage (≥ −0.1 V), the protonation and deprotonation of 4-Mpy on the electrode surface are mainly determined by the adsorption structure of 4-Mpy on the electrode surface. At the same time, we conducted a comparative study of 2-Mpy and 4-Mpy molecules and found that the adsorption modes were different depending on the position of the N atom. 2-Mpy is inclined adsorbed on the surface of the Au-NP film electrode, and 4-Mpy is vertically adsorbed on the surface of the Au-NP film electrode.

Raman spectra of KAl(SO₄)₂·12H₂O and KAl(SO₄)₂·12D₂O crystals in the range of 10–4000 cm⁻¹ were experimentally obtained and studied. An increase in the number of sulfate ions, oriented by oxygen atoms towards the K⁺ ion, was detected upon deuteration of the sample. Low-intensity Stokes components ν = 2485 cm⁻¹ (ν = 1820 cm⁻¹ for the deuterated crystal) were recorded, which indicates the formation of hydrogen bonds O–H•••SO₄²⁻ (O–D•••SO₄²⁻), where the donors are water molecules of the [Al(H₂O)₆]³⁺ complex and the oxygen atoms of the sulfate ion act as acceptors. The decrease in the wavenumbers of internal vibrations of the sulfate ion during deuteration was explained by an increase in the strength of hydrogen bonds. The results obtained indicate the direct influence of deuteration on the degree of initial disordering of sulfate ions and on the stability of the crystal structure of potassium alum.

To tackle the challenge of non-destructively analyzing complex oxide layers formed by atmospheric corrosion on active metals, we investigate the potential of inverse spatially offset Raman spectroscopy (inverse-SORS) to detect corrosion products and elucidate how the spectroscopic features of SORS vary. This study explores the utilization of inverse-SORS technology for longitudinal structural analysis of opaque CeO₂/La₂O₃ laminates, which serve as a proxy for corrosion products. Through a combination of experimental measurements and Monte Carlo simulation, it demonstrates the feasibility of inverse-SORS in non-destructively elucidating the layered structure of these laminates. With increasing the spatial offset of this technology, the Raman intensity ratio of La₂O₃-to-CeO₂ increases from 0.23 to 3.2 and then decreases to 0.27 for the CeO₂/La₂O₃ sample with a 34-μm-thick CeO₂ layer under 532-nm excitation, whereas the bottom La₂O₃ layer is hardly detected when the thickness of the upper La₂O₃ layer increases to 225 μm. The results reveal that a thinner CeO₂ layer facilitates the escape and detection of Raman signals originating from the bottom La₂O₃ layer, leading to an enhanced La₂O₃-to-CeO₂ signal ratio and a reduced offset at the characteristic peak. The research also sheds light on the intricate interplay among multiple variables, such as spatial offset, laser wavelength, the corresponding absorption factor, the thickness of the oxide layer, and the compactness. These insights suggest that SORS is a valuable and non-destructive approach for dissecting the structures of highly turbid composites of metallic compounds and semi-quantitatively deducing their thickness.

Microwave heating is an intriguing method for the synthesis of inorganic solids offering a variety of advantages over conventional furnace heating, such as fast heating and cooling rates as well as volumetric and selective heating of precursors. However, there are many open questions regarding this “black-box” process, and insights into the effect of microwave radiation on different types of solids are generally missing. In situ Raman spectroscopy is a powerful technique to unravel chemical transformations and identify intermediate species during microwave solid-state syntheses. A major challenge is the temperature measurement under microwave conditions because (metallic) thermocouples cannot be used and optical pyrometry has significant drawbacks. In contrast, Raman thermometry is a viable method that relies on the temperature-induced shift of Raman signals. Here, we use this method to estimate the temperature during microwave heating of a model system (titania) that undergoes a phase transition at temperatures >800°C. The estimation is derived from a flexible double exponential calibration function applied to Raman spectroscopic peak shifts in the temperature-resolved furnace heating data, which was found to describe two titania modes (one anatase and one rutile) extremely well. Based on a detailed error and uncertainty analysis, we suggest options to further optimize Raman thermometry for use in high-temperature microwave heating conditions.

The polarization-resolved Raman spectra of two-dimensional Cr₂Se₃ synthesized via chemical vapor deposition (CVD) and chemical vapor transport (CVT) techniques were investigated in detail. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). A distinct polarization dependence was observed in the Raman intensity of all the Cr-Cr, Cr-Se, and Se-Se modes in both samples. The observed angle-dependent Raman intensities of each peak could be related to the crystal structure-specific Raman tensor. XRD results of the bulk Cr₂Se₃ sample synthesized via CVT confirm its trigonal crystal structure, and the Raman peaks can be fitted using the Raman tensors for the 𝐴_𝑔 and 𝐸_𝑔 modes for both the parallel and crossed polarizations. However, for the Cr₂Se₃ samples directly grown on Si/SiO₂ substrates by CVD, it was necessary to assume the triclinic crystal structure in order to explain the polarized Raman dependence of all the peaks in both parallel and crossed polarization directions. This is the first experimental result suggesting the existence of triclinic Cr₂Se₃ crystal structure, which has been theoretically predicted in the Materials Project database.

Acetylacetone, double-deuterated acetylacetone and hexafluoroacetylacetone were isolated in inert matrices and investigated by means of Raman scattering and infrared absorption spectroscopic methods, combined with theoretical calculations. The ability of Raman spectroscopy to access low wavenumber modes enables the study of vibrational modes involved in internal hydrogen bonds that are challenging to observe with infrared absorption spectroscopy. An almost complete set of vibrational modes for the studied molecules was observed experimentally, facilitating a comprehensive assessment of different computational approaches. The large dataset obtained allowed for an improved assignment of vibrational bands and firmly confirmed the existence of only one chelated isomer of acetylacetone, double-deuterated acetylacetone and hexafluoroacetylacetone in matrices. The experimental data also highlighted the effects of deuteration and fluorination.

Nowadays, surface-enhanced Raman spectroscopy (SERS) has become a powerful tool for rapidly detecting and analyzing textile cultural relics due to its ability to provide chemical information with single-molecule sensitivity. However, preserving a high level of detection sensitivity while avoiding sample damage remains a persistent challenge. In this work, we developed a SERS approach with both microextraction and detection functions. The alcohol–water droplet with iodide-modified Au nanoparticles (AuIMNPs) is directly dropped on the textile, where dyes strongly bound on textiles can be extracted by ethanol (EtOH). As a result, the sample can be well preserved from being damaged. In particular, the volatility of EtOH allows the molecules to be captured in the hot spots through the capillary effect during droplet evaporation, resulting in a dramatic increase in Raman signal intensity. This highly sensitive strategy can be used to measure dyes in plant extracts and mock-up textiles. Furthermore, the capability of SERS to provide fingerprint information allows us to distinguish different dyes in overdyeing textiles. Eventually, this approach is successfully applied to identify dyes of authentic ancient Chinese textiles. This rapid, universal, and negligibly invasive approach provides a powerful way to study textile cultural relics.