Bernardini Simone, Bellatreccia Fabio, Della Ventura Giancarlo, Ballirano Paolo, Sodo Armida
Dipartimento di Scienze, Università Roma Tre Viale G. Marconi 446 00146 Rome Italy
Dipartimento di Scienze della Terra, Sapienza Università di Roma P. le A. Moro 5 00185 Rome Italy.
RSC Adv. 2020 Jan 3;10(2):923-929. doi: 10.1039/c9ra08662e. eCollection 2020 Jan 2.
Manganese oxides are important geomaterials, used in a large number of applications. For instance, as pigments in art works or in the treatment and removal of heavy metals from drinking water. Particularly, ramsdellite [MnO] and groutellite [(Mn ,Mn )O(OH)], because of their 2 × 1 frameworks that enable proton diffusion, are very important cathode materials. Manganese oxides commonly occur as crypto-crystalline and very fine mixtures of different Mn-phases, iron oxides, silicates and carbonates. Thus, proper characterization can be a difficult task using XRPD. The lack of Raman data on groutellite and the little and conflicting data on ramsdellite do not allow their proper identification by Raman spectroscopy. In this work we characterize natural mixtures of ramsdellite and groutellite by combining SEM-EDS, XRPD, FT-IR and Raman spectroscopy, to provide reference Raman spectra. Our data show that they have a typical and unmistakable spectra, allowing clear recognition. Moreover, we have investigated their laser-induced degradation. Our data show that groutellite transforms into ramsdellite, by the loss of H and the oxidation of Mn to Mn, already at a very low laser power. Further increasing the laser power the formation of hausmannite [MnMn O] occurs the reduction of Mn cations. Our data can be used to study the discharge mechanism in cathodic battery materials, by monitoring the Mn reduction from ramsdellite to groutellite, and finally to groutite [α-MnOOH]. Moreover, Raman mapping allows the study of their distribution in all the investigated samples and, indirectly, those of H and Mn, which plays a key-role in electrochemical activity of these compounds.
氧化锰是重要的地质材料，有大量应用。例如，用作艺术品中的颜料或用于饮用水中重金属的处理和去除。特别是，兰姆多石[MnO]和水羟锰矿[(Mn,Mn)O(OH)]，因其能使质子扩散的2×1骨架，是非常重要的阴极材料。氧化锰通常以隐晶质形式存在，是不同锰相、氧化铁、硅酸盐和碳酸盐的非常精细的混合物。因此，使用X射线粉末衍射（XRPD）进行恰当表征可能是一项艰巨任务。水羟锰矿缺乏拉曼数据，而兰姆多石的相关数据很少且相互矛盾，这使得无法通过拉曼光谱对它们进行恰当识别。在这项工作中，我们通过结合扫描电子显微镜-能谱仪（SEM-EDS）、X射线粉末衍射（XRPD）、傅里叶变换红外光谱（FT-IR）和拉曼光谱对兰姆多石和水羟锰矿的天然混合物进行表征，以提供参考拉曼光谱。我们的数据表明它们具有典型且 unmistakable 的光谱，便于清晰识别。此外，我们研究了它们的激光诱导降解。我们的数据表明，在非常低的激光功率下，水羟锰矿通过失去H并将Mn氧化为Mn而转变为兰姆多石。进一步提高激光功率会形成黑锰矿[MnMn₂O₄]，即Mn阳离子的还原。我们的数据可用于通过监测从兰姆多石到水羟锰矿，最终到羟锰矿[α-MnOOH]的Mn还原过程来研究阴极电池材料中的放电机制。此外，拉曼映射允许研究它们在所有研究样品中的分布，以及间接研究H和Mn的分布，这在这些化合物的电化学活性中起关键作用。
