Raman spectra of natural manganese oxides

Abstract

Manganese oxides occur typically as cryptocrystalline and fine-grained mixtures of different Mn-phases, carbonates, silicates, and Fe oxides/hydroxides; thus their characterization by standard methods, such as X-ray diffraction, is extremely challenging. These materials have been widely used in various applications over the millennia, for example, in art works as pigments for pottery, mural paintings, stained glass, and recently, as nanostructured materials with very attractive physicochemical properties. Furthermore, they are important geomaterials that could play a key role in environmental applications, by controlling the partitioning of arsenic and heavy metals between rocks, soils, and aqueous systems. Raman spectroscopy, which is a punctual and nondestructive technique, has been widely used to characterize these materials. However, literature data are often conflicting and contradictory, usually not allowing a proper identification of the Mn species. In this work, we characterize the most common natural manganese oxides by combining X-ray powder diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy. Our data show that some manganese oxides have characteristic Raman spectra and can be easily recognized by using Raman spectroscopy alone, whereas integration of Raman data with other techniques is mandatory to characterize minerals that have almost identical Raman spectra. With this respect, Raman spectroscopy is the only technique allowing an easy discrimination between hollandite [Ba(Mn 4+ 6 ,Mn 3+ 2 )O 16 ] and cryptomelane [K(Mn 4+ 7 ,Mn 3+ )O 16 ]. The final goal of this work is to provide reference Raman spectra, acquired on previously well-characterized Mn samples to facilitate the application of Raman spectroscopy in the study of these geomaterials.

Non-Invasive On-Site Raman Study of Pigments and Glassy Matrix of 17th–18th Century Painted Enamelled Chinese Metal Wares: Comparison with French Enamelling Technology

“…The presence of manganese oxide was only clearly detected for black and brown enamelled areas of F1429C tea pot which is a porcelain (not a metal ware) with the characteristic strong peak at 580-595 cm −1 [48,71] (Table 4, Figure 12D). On the other hand, hematite is found in red, yellow, orange and brown enamels of F1440C ( Figure 14C), F1467 ( Figure 7C) metal wares and F1429C ( Figure 12C) A more surprising feature is related to the detection of cassiterite which was found in the yellow and greenish yellow (light green) areas of the F1448C tripod with 631-780 cm −1 doublet ( Figure 5B-left bottom, spectrum C a,e).…”

Raman spectroscopy study of manganese oxides: Layer structures

“…DOI: https://doi.org/10.2138/am-2020-7666. http://www.minsocam.org/ 2015; Yang et al 2019;Boumaiza et al 2019;and Bernardini et al 2019) with various degrees of success. Such work has been invigorated in part by advancements in micro-Raman techniques that have resulted in greater availability of in-house Raman systems.…”

“…,Yang et al (2015),Boumaiza (2019), andBernardini (2019). These distinctly different spectra indicate that Raman spectroscopy, using the appropriate data collection conditions, is perhaps the most conclusive method for readily distinguishing triclinic from hexagonal birnessite.…”

Capturing Manganese Oxide Intermediates in Electrochemical Water Oxidation at Neutral pH by In Situ Raman Spectroscopy

“…Mn‐oxides exhibit extremely weak Raman bands owing to the relatively low Raman cross‐section. In addition, laser‐induced degradation of Mn‐oxide can occur which results in the shift or broadening of the Raman peak [45] …”