Synthesis of Monolayer-Patched Graphene from Glucose
Synthesis of Monolayer-Patched Graphene from Glucose
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DOI：
10.1002/anie.201203207
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Antonietti, Markus
中科院分区：
文献类型：
--
作者：
Li, Xin-Hao;Kurasch, Simon;Antonietti, Markus
石墨烯非凡的电子和机械性能[1,2]刺激了开发大规模合成石墨烯的简单方法的激烈研究。[1-9]通过化学气相沉积在任意基底上的各种含碳分子制备的高质量大面积石墨烯薄膜可以满足大面积电子应用的要求。[3 - 7]对于吨级导电石墨烯粉末的工业生产，[3,9,11 - 13]石墨矿物的化学剥落仍然是主要的制造途径。[3,8 - 10]另一方面，从简单单体中聚合出类石墨烯结构仍然是碳化学家面临的挑战。[14-19]通过掺杂进一步微调石墨烯的费米能级提供了一种控制碳质材料电子结构的方法[6,20 - 23]，并且对其在电子、电极和催化方面的应用具有重要意义。掺杂石墨烯的电子特性与掺杂浓度[24]密切相关，而目前的方法只能很差地控制掺杂浓度。因此，开发有效的方法以可控的方式制造廉价而高质量的石墨烯（例如高表面积，高导电性，掺杂水平和均匀形态）是非常具有挑战性的，但也是可取的。在这里，我们报告了一种简单而通用的方法，用于合成二维（2D）碳材料，从独立单层到低聚石墨烯，通过煅烧葡萄糖（一种最丰富、可持续的化合物）。在此合成中，只加入双氰胺（DCDA）作为牺牲模板，暂时原位形成层状图形氮化碳（gc3n4）。[25,26]这种方法还可以在不影响石墨烯形貌的情况下，在更大范围内逐渐调整氮掺杂的浓度。在典型的合成中，在氮气的保护流下对DCDA和葡萄糖的混合物进行两步加热，直接产生了28-60%的独立式石墨烯（基于葡萄糖添加的碳计算）。整个形成过程如图1所示：DCDA的热缩聚形成层状氮化碳模板（简化为gC 3N4，见支持信息中的图S1），通过供体-受体相互作用将形成的芳香碳中间体结合在其表面，最终在6008C时将其缩聚限制在gC 3N4的层间间隙内。两相的堆积高度由葡萄糖和双氰胺这两种单体的相对量控制。由于gC - 3N4模板在7508C时完全热裂解，在更高的温度下释放出最新的类石墨烯薄片（支持信息中的图S2）。在10008C下获得的样品含有微量的氮原子（4.3原子%），用gr表示。在增大放大倍率下，合成样品的代表性扫描电子显微镜（SEM）图像（支持信息中的图2a， b和图S3）显示出均匀的层状形貌。石墨样品是连续但纠缠的石墨烯薄片的整体，无需任何后纯化或分离过程。与通过加热氧化石墨烯或在高温下官能化石墨烯获得的化学还原石墨烯不同，氧化石墨烯通常会扩展聚集成厚片，而构成单体的初级纳米片薄且非常柔韧。典型的独立的皱纹…
The extraordinary electronic and mechanical properties [1, 2] of graphene have stimulated intense research on developing simple methods for the large-scale synthesis of graphene.[1–9] High-quality large-area graphene films prepared by the chemical vapor deposition of various carbon-containing molecules on arbitrary substrates could meet the requirements of large-area electronic applications.[3–7] For the industrial production of conductive graphene powder on the ton scale,[3, 9, 11–13] the chemical exfoliation of graphite minerals still remains the main manufacturing path.[3, 8–10] On the other hand, the exclusive two-dimensional polymerization of graphene-like structures from simple monomers still presents a challenge for carbon chemists.[14–19] Further fine-tuning of the Fermi level of graphene by doping offers a way to control the electronic structure of carbonaceous materials [6, 20–23] and is of major interest for their application in electronics, electrodes, and catalysis. The electronic properties of doped graphene are strongly linked to the dopant concentration,[24] which is only poorly controlled by current methods. It is therefore highly challenging but desirable to develop effective approaches for fabricating graphene that is cheap yet of high quality (eg high surface area, high conductivity, doping level, and uniform morphology) in a controlled manner. Herein we report a simple yet versatile approach for the synthesis of two-dimensional (2D) carbon materials ranging from free-standing monolayers to oligolayered graphene by the calcination of glucose, a most abundant, sustainable compound. In this synthesis only dicyandiamide (DCDA) was added for the temporary in situ formation of layered graphic carbon nitride (gC 3N4), which serves as a sacrificial template.[25, 26] This approach is also facile for gradually tuning the concentration of the nitrogen dopant in a broader range without disturbing the morphology of graphene. In a typical synthesis, the two-step heating of a mixture of DCDA and glucose under a protective flow of N2 directly resulted in freestanding graphene with a yield of 28–60%(calculated based on added carbon from glucose). The overall formation process is depicted in Figure1: Thermal condensation of DCDA creates a layered carbon nitride template (simplified as gC 3N4, see Figure S1 in the Supporting Information), which binds the as-formed aromatic carbon intermediates to its surface by means of donor–acceptor interactions and finally confines their condensation in a cooperative process to the interlayer gaps of gC 3N4 at 6008C. The stacking heights of the two phases are controlled by the relative amounts of the two monomers, glucose and dicyandiamide. Since the gC 3N4 template undergoes complete thermolysis at 7508C, the latest graphene-like sheets are liberated at higher temperatures (Figure S2 in the Supporting Information). Those obtained at 10008C contain minute amounts of nitrogen atoms (4.3 atom%) and are denoted as Gr.Representative scanning electron microscopy (SEM) images (Figure 2a, b and Figure S3 in the Supporting Information) of as-synthesized samples at increasing magnification reveal a uniform, layered morphology on a larger scale. The graphitic samples are obtained as monoliths of continuous but entangled thin graphene sheets without any post-purification or separation processes. Unlike chemically reduced graphene obtained by heating graphene oxides or functionalized graphene at high temperatures, which usually undergo extended aggregation into thick flakes,[27] the primary nanosheets constituting the monoliths are thin and very flexible. The typical wrinkles of free-standing …