Hao Si-Jia, Joly V L Joseph, Kaneko Satoshi, Takashiro Jun-ichi, Takai Kazuyuki, Hayashi Hitoshi, Enoki Toshiaki, Kiguchi Manabu
Department of Chemistry, Tokyo Institute of Technology, 2-12-1 Ookayama Meguro, Tokyo 152-8551, Japan.
Phys Chem Chem Phys. 2014 Apr 7;16(13):6273-82. doi: 10.1039/c4cp00199k.
We investigated the magnetic and electronic properties of nanographene and its charge transfer effect, using near edge X-ray absorption fine structure (NEXAFS), magnetic susceptibility and ESR measurements, and elemental analysis, with the employment of nanoporous carbon, which consists of a three dimensional disordered network of loosely stacked nanographene sheets, in relation to the host-guest interaction with HNO3 as the electron-accepting guest. The adsorption of electron acceptor HNO3 decreases the intensity of the edge state peak in NEXAFS as a result of the charge-transfer-induced Fermi energy downshift, in agreement with the decrease in the edge-state spin concentration, and it also induces the structural expansion, which makes the inter-nanographene sheet distance elongated, resulting in weakening of the inter-nanographene-sheet antiferromagnetic interaction as evidenced by the decrease in the Weiss temperature. In addition, the decomposition of HNO3, which takes place with the electron-rich edge state as an oxidation catalyst, results in the creation of oxygen/nitrogen-containing functional groups bonded to the periphery of the nanographene sheets. Heat-treatment of the HNO3-ACFs under evacuation desorbs the HNO3 molecules completely, though a part of the oxygen/nitrogen-containing species remains strongly bonded to the edge even at a high temperature of ∼800 °C, according to NEXAFS and elemental analysis results. These remaining species participate in the charge transfer, modifying the electronic structure as observed with the decrease in the orbital susceptibility and the strengthening of the inter-nanographene-sheet antiferromagnetic interaction.
我们利用近边X射线吸收精细结构（NEXAFS）、磁化率和电子自旋共振（ESR）测量以及元素分析，研究了纳米石墨烯的磁性和电子性质及其电荷转移效应。研究中使用了由松散堆叠的纳米石墨烯片组成的三维无序网络的纳米多孔碳，探讨其与作为电子接受客体的HNO₃的主客体相互作用。电子受体HNO₃的吸附由于电荷转移引起费米能下移，导致NEXAFS中边缘态峰强度降低，这与边缘态自旋浓度的降低一致，同时它还诱导结构膨胀，使纳米石墨烯片间距离拉长，导致纳米石墨烯片间反铁磁相互作用减弱，这由魏斯温度的降低得以证明。此外，以富电子边缘态作为氧化催化剂发生的HNO₃分解，导致在纳米石墨烯片边缘形成了与氧/氮相连的官能团。根据NEXAFS和元素分析结果，在抽真空条件下对HNO₃ - ACFs进行热处理能完全解吸HNO₃分子，不过即使在约800℃的高温下，仍有一部分含氧化合物/含氮化合物与边缘紧密相连。这些残留物质参与电荷转移，改变电子结构，如轨道磁化率降低和纳米石墨烯片间反铁磁相互作用增强所观察到的那样。
