Barbera Vincenzina, Brambilla Luigi, Milani Alberto, Palazzolo Alberto, Castiglioni Chiara, Vitale Alessandra, Bongiovanni Roberta, Galimberti Maurizio
Politecnico di Milano, Department of Chemistry, Materials and Chemical Engineering "G. Natta", piazza Leonardo da Vinci, 32-via Mancinelli 7, 20131 Milano, Italy.
Politecnico di Torino, Department of Applied Science and Technology, Corso Duca degli Abruzzi 24, 10129 Torino, Italy.
Nanomaterials (Basel). 2018 Dec 30;9(1):44. doi: 10.3390/nano9010044.
The mechanism for the functionalization of graphene layers with pyrrole compounds was investigated. Liquid 1,2,5-trimethylpyrrole (TMP) was heated in air in the presence of a high surface area nanosized graphite (HSAG), at temperatures between 80 °C and 180 °C. After the thermal treatments solid and liquid samples, separated by centrifugation, were analysed by means of Raman, Fourier Transform Infrared (FT-IR) spectroscopy, X-Rays Photoelectron Spectroscopy (XPS) and ¹H-Nuclear Magnetic Resonance (¹H NMR) spectroscopy and High Resolution Transmission Electron Microscopy (HRTEM). FT-IR spectra were interpreted with the support of Density Functional Theory (DFT) quantum chemical modelling. Raman findings suggested that the bulk structure of HSAG remained substantially unaltered, without intercalation products. FT-IR and XPS spectra showed the presence of oxidized TMP derivatives on the solid adducts, in a much larger amount than in the liquid. For thermal treatments at T ≥ 150 °C, IR spectral features revealed not only the presence of oxidized products but also the reaction of intra-annular double bond of TMP with HSAG. XPS spectroscopy showed the increase of the ratio between C(sp²)N bonds involved in the aromatic system and C(sp³)N bonds, resulting from reaction of the pyrrole moiety, observed while increasing the temperature from 130 °C to 180 °C. All these findings, supported by modeling, led to hypothesize a cascade reaction involving a carbocatalyzed oxidation of the pyrrole compound followed by Diels-Alder cycloaddition. Graphene layers play a twofold role: at the early stages of the reaction, they behave as a catalyst for the oxidation of TMP and then they become the substrate for the cycloaddition reaction. Such sustainable functionalization, which does not produce by-products, allows us to use the pyrrole compounds for decorating sp² carbon allotropes without altering their bulk structure and smooths the path for their wider application.
研究了用吡咯化合物对石墨烯层进行功能化的机理。将液态1,2,5 - 三甲基吡咯（TMP）在高比表面积纳米石墨（HSAG）存在下于空气中加热，温度范围为80℃至180℃。热处理后，通过离心分离出固体和液体样品，然后借助拉曼光谱、傅里叶变换红外（FT - IR）光谱、X射线光电子能谱（XPS）、¹H - 核磁共振（¹H NMR）光谱以及高分辨率透射电子显微镜（HRTEM）进行分析。FT - IR光谱在密度泛函理论（DFT）量子化学建模的支持下进行解释。拉曼研究结果表明，HSAG的整体结构基本未改变，没有插层产物。FT - IR和XPS光谱显示在固体加合物上存在氧化的TMP衍生物，其含量比液体中的多得多。对于T≥150℃的热处理，红外光谱特征不仅揭示了氧化产物的存在，还表明了TMP的环内双键与HSAG的反应。XPS光谱显示，随着温度从130℃升高到180℃，观察到芳香体系中参与的C(sp²)N键与C(sp³)N键的比例增加，这是吡咯部分反应的结果。所有这些在建模支持下的发现，导致推测出一个级联反应，该反应涉及吡咯化合物的碳催化氧化，随后是狄尔斯 - 阿尔德环加成反应。石墨烯层起到双重作用：在反应的早期阶段，它们作为TMP氧化反应的催化剂，然后它们成为环加成反应的底物。这种不产生副产物的可持续功能化方法，使我们能够使用吡咯化合物修饰sp²碳同素异形体而不改变其整体结构，并为其更广泛的应用铺平了道路。
