Turbostratic carbon nitride prepared by pyrolysis of melamine
Turbostratic carbon nitride prepared by pyrolysis of melamine
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DOI：
10.1007/s10853-005-2096-3
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发表时间：
2005-05
影响因子：
4.5
通讯作者：
Yuanchun Zhao;D. Yu;H. W. Zhou;Yongjun Tian;Osamu Yanagisawa
中科院分区：
文献类型：
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作者：
Yuanchun Zhao;D. Yu;H. W. Zhou;Yongjun Tian;Osamu Yanagisawa
由于理论计算预测C3 N4共价化合物的硬度可能与金刚石相当甚至更高[1，2]，因此已经进行了许多尝试来合成这种新物质。然而，由于N2具有很大的热力学稳定性，从前驱体到结晶氮化碳的理想结构转变难以实现。在大多数情况下，仅获得具有低氮含量的无定形产物[3]。为了解决这一问题，首先制备石墨或乱层结构的氮化碳，然后以其为前驱体合成其他晶相的氮化碳是一种很好的方法。因此，石墨C3 N4最近引起了更多的关注。通过不同的路线，已经合成了石墨C3 N4 [4-6]。对于先前的工作，具有独特（002）衍射峰的所要求的类石墨C3 N4实际上具有乱层结构[7-10]，因为在其XRD图案中没有其他峰。同时，所获得的乱层碳氮化物的（002）间距在0.32- 0.33nm范围内。由Teter和Hemley [11]预测的石墨C3 N4可以被描述为三聚氰胺的完全脱氨缩聚物，因此，三聚氰胺通常被选择作为通过电沉积[6]和溶剂热法[7]合成石墨C3 N4的氮化碳前驱体。1988年研究了三聚氰胺的热解[12]，然而，作者只关注其热行为，他们没有考虑完全缩聚后作为碳氮化物的潜在候选者的可能性。最近，在高达700 ° C的温度下研究了三聚氰胺在高压下的热解[13]。明显的氮损失使尝试失败。在这封信中，我们报道了一种改进的热解路线，以三聚氰胺为原料制备乱层氮化碳。热解分两步进行：首先，温度保持在300 ℃，以实现尽可能完全的初级缩合（三聚氰胺→蜜白胺）;然后升至650 ℃，进行高级缩合。在实验中，三聚氰胺在直径为35 mm的石英管中热解，并使用外套筒形加热器。三聚氰胺被放置在石英管的中间。热解在300 ° C下进行1小时，然后在大气中在600 ° C下进行2小时;研磨后，将所得粉末在300 ° C下保持0.5小时，然后在真空中在650 ° C下保持1小时。最终得到一种棕色的氮化碳粉末。通过使用元素分析仪（LECO，CHN-1000）和EDX（EDAX INC.，Phoenix）。采用X射线衍射（XRD）和Cu-Kα射线对其进行了表征（JEOL，ROTEX JRX-12），傅立叶变换红外（FTIR）光谱（Bruker，EQUIN 0X 55），扫描电子显微镜（SEM）（TOPCON，SM-520）和透射电子显微镜（TEM）结合选区衍射（SAED）通过元素分析和EDX表征的产物的组成列于表I中。SEM观察发现，颗粒尺寸范围为5 μm至20 μm。大部分颗粒呈片状。图1显示了产物的典型XRD图谱。在27.62 nm处有一个单一的主峰，这表明产物是乱层的。其相应的d-间距为0.321 nm，类似于先前工作中获得的乱层/类石墨碳氮化物的（002）平面[9，14]。制备的乱层氮化碳和三聚氰胺的FTIR光谱如图2所示。红外光谱的…
Since the theoretical calculations predicted that the hardness of C3N4 covalent compound might be comparable to or even higher than that of diamond [1, 2], many attempts have been made to synthesis this novel substance. Due to the great thermodynamic stability of N2, however, the ideal structural transition from precursor to crystalline carbon nitride is difficult to realize. In most cases, only amorphous products with low nitrogen content were obtained [3]. To solve this problem, it is good to prepare carbon nitride in graphitic or turbostratic form firstly, and then using it as precursor to synthesize other carbon nitride crystalline phases. Therefore, graphitic C3N4 have recently attracted more attention. Through different routes, graphitic C3N4 has been synthesized [4–6]. For previous work, the claimed graphitic-like C3N4 with unique (002) diffraction peak has the turbostratic structure actually [7–10], for the lake of other peaks in their XRD patterns. Meanwhile, the (002) spacing of those obtained turbostratic carbon nitrides are in the range of 0.32–0.33 nm. The graphitic C3N4 predicted by Teter and Hemley [11] can be described as a perfect de-ammonation polycondensate of melamine, therefore, melamine was often chosen as the carbon nitride precursor to synthesize graphitic C3N4 by electrodeposition [6] and solvothermal method [7]. Pyrolysis of melamine was investigated [12] in 1988, however, the authors focused their attention only on its thermal behavior, and they didn’t consider the possibility as potential candidate for carbon nitrides after complete polycondensate. Recently, pyrolysis of melamine under high pressure was studied at the temperatures up to 700◦ C [13]. Obvious nitrogen loss made the attempt unsuccessful. In this letter, we report an improved pyrolysis route to prepare turbostratic carbon nitride from melamine. The pyrolysis was performed in two steps: first, the temperature was maintained at 300◦ C in order to realize the primary condensation (melamine→ melam) as complete as possible; and then it was risen to 650◦ C to perform the advanced condensation. In the experimental, melamine was pyrolyzed in a quartz tube with a diameter of 35 mm, and an outer-thimble-shape heater was used. Melamine was placed at the middle of the quartz tube. The pyrolysis was conducted at 300◦ C for 1 hr, then at 600◦ for 2 hr in atmosphere; after milling, the obtained powder was maintained at 300◦ C for 0.5 hr, then at 650◦ C for 1 hr in vacuum. Finally, a kind of brown carbon nitride powder was obtained. The chemical composition was analyzed by using elemental analyzer (LECO, CHN-1000) and EDX (EDAX INC., Phoenix). The product was characterized by X-ray diffraction (XRD) with Cu-Kα radiation (JEOL, ROTEX JRX-12), fourier transfer infrared (FTIR) spectroscopy (Bruker, EQUINOX55), scanning electron microscopy (SEM)(TOPCON, SM-520), and transmission electron microscopy (TEM) coupled with selected area diffraction (SAED)(JEOL, JEM-2010) and thermogravimetry (TG)(NETZSCH, STA449C/6/G).The composition of the product characterized by elemental analysis and EDX is listed in Table I. SEM observation found that the particles dimension ranged from 5 µm to 20 µm. Most of the particles show the flake-like morphology. Fig. 1 shows a typical XRD pattern of the product. There is a single main peak at the position of 27.62◦, which suggests that the product was turbostratic. Its corresponding d-spacing is 0.321 nm similar to the (002) plane of the turbostratic/graphitelike carbon nitrides obtained in previous work [9, 14]. The FTIR spectrum of the prepared turbostratic carbon nitride and melamine are shown in Fig. 2. The IR spectrum of …