Journal of Raman Spectroscopy最新文献

Lithium manganese oxide (LMO) is an effective absorbent for lithium recovery from brines, characterized by its high adsorption capacity, excellent regeneration performance, and selectivity. This study investigates the mechanisms of material degradation during lithium loading and unloading in LMO, employing a combination of time-resolved Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Key findings reveal that the A_1g vibrational mode wavenumber shifts from 635 cm⁻¹ at the onset of lithium ion exchange to 656 cm⁻¹ after 12 min, indicating local symmetry loss and manganese (Mn) loss during lithium intercalation. The proposed lithium exchange mechanism involves initial occupation of tetrahedral interstitial voids, followed by migration into interstitial sites between Mn octahedral sites. Computational modeling suggests that the loss of symmetry in MnO cubane-like groups occurs as lithium migrates, significantly affecting the Raman spectra. Importantly, the study demonstrates that after 100 cycles of lithium/hydrogen loading, a 24% loss in Mn is observed, which correlates with decreased structural stability; however, the structural integrity of LMO is enhanced when subjected to multiple cycles without complete loading. These insights contribute to the understanding of LMO's performance in lithium recovery applications and highlight potential strategies to optimize its use in future technologies.

Lapis lazuli is a semiprecious stone that falls under the category of blue-colored minerals that played a vital role in the cultural historic artwork throughout the world. Finding the provenance of lapis lazuli is a slightly challenging task. The sources of lapis lazuli pigments used at Ajanta Caves and its provenance have been a subject of interest and a research question. Six samples of lapis lazuli pigment of murals of 2nd century bce Ajanta Caves were examined using micro-Raman spectroscopy, Fourier transform infrared spectrophotometry (FTIR), X-ray fluorescence spectroscopy, spectrophotometry, X-ray diffractometry (XRD), and stereomicroscopy to find out the possible provenance raw materials through the mineralogical compositions. This study will be very helpful to tailor future conservation strategies. The results showed that these pigment samples are similar based on their composition, presenting diopside and specific trace element proportions as provenance markers. The results revealed that these raw materials for the lapis lazuli pigments used at Ajanta Caves may have been imported from lapis lazuli mines located at Badakhshan in Afghanistan, as the mines have been actively mined for over 6000 years, making them a significant source of lapis lazuli for ancient civilizations.

Graphite is a common mineral occurring in different metamorphic rocks, including high/ultrahigh-temperature and high/ultrahigh-pressure rocks. Raman spectroscopic studies combined with carbon isotope composition may highlight the carbon source (crustal or mantle) and PT conditions of graphite crystallization. In the present study, seven graphite-bearing samples of felsic granulite xenoliths from the “Eclogitovaya” pipe (the Eastern Pamir, Tajikistan) have been studied by Raman spectroscopy and analyzed its carbon isotope composition. Graphite crystals occur in the matrix as well as inclusions in rock-forming minerals (e.g., garnet and kyanite), indicating their simultaneous crystallization. The graphite formed as a result of the metamorphic transformation of carbonaceous material (δ¹³С ranges from −14.5‰ to −20.1‰) originally present in the rocks during subduction. Structural analysis of intact graphite inclusions in garnet revealed rims of disordered graphite surrounding well-ordered graphite cores. Composite inclusions consisting of disordered graphite, well-ordered graphite, and CO₂ were also observed. However, any evidence for precipitation of disordered graphite from fluid has not been found. It is likely that the origin of disordered graphite in the Eastern Pamir granulite xenoliths is attributed to the stress at the graphite–garnet interface during the rapid exhumation of the xenoliths.

Density functional theory (DFT) at the PBE0-D₃ hybrid functional and 6-311G + (d,p) basis set levels was employed to optimize the ground state of malachite green (MG). The optimized MG molecule has a nonplanar structure. The electrical properties and densities were calculated for MG by the natural population analysis (NPA) method at the same level. GaussView and Multiwfn software were used to draw a Fukui function electron density isosurface coloring map and an electrostatic potential coloring map of the MG molecular surface. We found that the region near the two N atoms in MG was most susceptible to an electrophilic reaction. Time-dependent density functional theory (TD-DFT) was used to calculate the electronic excitation data of MG and draw the UV–Vis spectrum of MG at the same level. By comparing the experimental UV–Vis spectrum with the calculated UV–Vis spectrum, it was found that the UV–Vis spectrum of MG has three peaks, of which the maximum peak is 616 nm (calculated as 586 nm). The structure of the MG-Ag₄ complex was optimized by using DFT. The resonance surface-enhanced Raman scattering (SERS) spectrum excited with 633-nm laser light was calculated and compared with the experimental results, and there was a high similarity in the characteristic peak positions between them. Further analysis showed that MG combined with the silver plane by the adsorption orientation of one of the N,N-dimethylaniline skeleton planes was almost perpendicular to the silver plane in SERS detection. One of the N atoms in N,N-dimethylaniline is combined with Ag and then adsorbed onto the silver substrate to form a special surface-bound compound.

Surface-enhanced Raman spectroscopy (SERS) is often considered as a versatile tool for high-sensitive detection of low concentrations of analytes. Typically, gold or silver patterned surfaces, namely the SERS substrates, are utilized to amplify Raman signal. However, most SERS substrates require microfabrication processes based on costly infrastructures. In this paper, we propose a simple yet effective scheme for fabricating SERS substrates on thermoplastics. The process involves ultrasonically stacking nanopowders on thermoplastic substrate via a stencil. We showed that gold surfaces on polymethly methacrylate (PMMA) substrates could be fabricated by ultrasonic means in less than 10 s by using a benchtop ultrasonic welder. We investigated the effect of process parameters, namely the pressure and the vibration time, on the surface topography and SERS performance. The results show that the process is mainly controlled by the vibration time, such that at moderate vibration times (~ 5 s), uniformly rough surfaces could be repeatably achieved. Fabricated samples were tested for SERS performance using 5,5′-ditiobis (2-nitrobenzoic acid) (DTNB) as the Raman reporter. We showed that the substrates fabricated under 2.7 MPa pressure and 5 s vibration time yielded comparatively low relative standard deviations (RSD) of SERS intensity—6.12% for point-to-point variation and 6.73% for batch-to-batch variation—along with an enhancement factor (EF) of 1.28 × 10⁵. The performance of the SERS substrates, considering RSD and EF, indicates that the proposed fabrication method could be a promising alternative for SERS based sensing applications.