Department of Chemistry, University of California , Berkeley, California 94720, United States.
Department of Chemistry, Tsinghua University , Beijing 100084, China.
J Am Chem Soc. 2017 Apr 26;139(16):5836-5841. doi: 10.1021/jacs.7b00474. Epub 2017 Apr 13.
The potential of rising two-dimensional materials, such as graphene, can be substantially expanded through chemistry. However, it has been a challenge to study how chemical reactions of two-dimensional materials progress. Existing techniques offer limited signal contrast and/or spatial-temporal resolution and are difficult to apply to in situ studies. Here we employ an optical approach, namely interference reflection microscopy, to quantitatively monitor the redox reaction dynamics of graphene and graphene oxide (GO) in situ with diffraction-limited (∼300 nm) spatial resolution and video-rate time resolution. Remarkably, we found that the oxidation kinetics of graphene is characterized by a seeded, autocatalytic process that gives rise to unique, wave-like propagation of reaction in two dimensions. The reaction is initially slow and confined to highly localized, nanoscale hot spots associated with structural defects, but then self-accelerates while propagating outward, hence flower-like, micrometer-sized reaction patterns over the entire sample. In contrast, the reduction of GO is spatially homogeneous and temporally pseudo-first-order, and through in situ data, we further identify pH as a key reaction parameter.
二维材料（如石墨烯）的潜力可以通过化学方法得到极大地扩展。然而，研究二维材料的化学反应如何进行一直是一个挑战。现有的技术提供的信号对比度和/或时空分辨率有限，并且难以应用于原位研究。在这里，我们采用光学方法，即干涉反射显微镜，以具有衍射极限（约 300nm）的空间分辨率和视频帧率的时间分辨率，原位定量监测石墨烯和氧化石墨烯（GO）的氧化还原反应动力学。值得注意的是，我们发现石墨烯的氧化动力学具有种子、自催化的特点，导致反应在二维空间中以独特的波浪状传播。该反应最初缓慢且局限于与结构缺陷相关的高度局部化的纳米级热点，然后在向外传播的过程中自加速，因此在整个样品上形成类似花朵的、微米级的反应图案。相比之下，GO 的还原在空间上是均匀的，时间上是准一级的，通过原位数据，我们进一步确定 pH 值是一个关键的反应参数。
