每周分子 | Molecule of the Week

每周分子： 氮化碳

Molecule of the Week: Carbon nitride

氮化碳(C ₃ N ₄ )与元素碳一样，具有几种稳定的同素异形体。最常见的两种是类似于金刚石的β-C ₃ N ₄ (部分结构)和性质更像石墨的g-C ₃ N ₄ 。

在20世纪80年代后期，加州大学伯克利分校的理论物理学家Amy Y. Liu和劳伦斯伯克利实验室的Marvin L. Cohen预测β-C ₃ N ₄ 将具有短而强的键，并且可能比钻石更硬。事实证明，这种材料很难合成； 但在1993年，哈佛大学(美国马萨诸塞州剑桥)的Chunming Niu，Yuan Z. Lu和Charles M. Lieber*使用脉冲激光烧蚀石墨靶材，并结合强原子氮源制备了β-C ₃ N ₄ 薄膜。

同样在1993年，拜罗伊特大学(德国)的沃尔夫冈·施尼克(Wolfgang Schnick)回顾了β-C ₃ N ₄ 的理论和合成文献; 而且，像Liu和Cohen一样，他推测这种物质会比钻石更硬。但30年过去了，这一预测仍未得到证实。然而，已有研究表明，β-C ₃ N ₄ 的体积模量(抗压缩性)与金刚石相似。

正如预期的那样，g-C ₃ N ₄ 主要由平面分子单元组成，主要是庚嗪(缩合的s-三嗪)。通常在这些结构的外围含有少量的氢。2008年，Markus Antonietti和马克斯·普朗克胶体和界面研究所(德国戈尔姆)和马克斯·普朗克学会弗里茨·哈伯研究所(德国柏林)的合作者报道，g-C ₃ N ₄ 可以通过聚合C-N小分子(例如氰胺，双氰胺和三聚氰胺等)来合成。研究人员表示，这种石墨化合物的半导体特性使其对各种有机反应具有“意想不到”的催化活性。

随后，几个研究小组发现g-C ₃ N ₄ 是一种强大的光催化剂。这项工作的大部分内容总结在2021年出版的《光催化材料科学》( Materials Science in Photocatalysis )一书的摘录中。如果您想了解更多信息，请阅读高丽大学(韩国首尔)的Vincent Wing-hei Lau和马克斯普朗克固态研究所(德国斯图加特)的Bettina V. Lotsch合著的 “A Tour-Guide through Carbon Nitride-Land” ¹ (2021)。

1. https://onlinelibrary.wiley.com/doi/full/10.1002/aenm.202101078 

氮化碳信息速览

氮化碳危害信息

【 关于每周分子 】

Carbon nitride (C ₃ N ₄ ), like elemental carbon, has several stable allotropes. The two most common are β-C ₃ N ₄  (partial structure shown), which is analogous to diamond, and g-C ₃ N ₄ , whose properties are more like graphite.

In the late 1980s, theoretical physicists Amy Y. Liu at the University of California, Berkeley, and Marvin L. Cohen at Lawrence Berkeley Laboratory predicted that β-C ₃ N ₄  would have short, strong bonds and could be harder than diamond. The material proved to be difficult to synthesize; but in 1993, Chunming Niu, Yuan Z. Lu, and Charles M. Lieber at Harvard University (Cambridge, MA) created thin films of β-C ₃ N ₄  using pulsed laser ablation of graphite targets combined with an intense atomic nitrogen source.

Also in 1993, Wolfgang Schnick at the University of Bayreuth (Germany) reviewed the theoretical and synthetic literature on β-C ₃ N ₄ ; and, like Liu and Cohen, he surmised that the substance would be harder than diamond. But 30 years later, this prediction has not been demonstrated. It has been shown, however, that the bulk modulus (resistance to compression) of β-C ₃ N ₄  is similar to that of diamond.

g-C ₃ N ₄ , as might be expected, consists largely of planar molecular units, mostly heptazines (condensed s-triazines). It usually contains a small amount of hydrogen at the peripheries of these structures. In 2008, Markus Antonietti and coauthors at the Max Planck Institute of Colloids and Interfaces (Golm, Germany) and the Fritz Haber-Institute of the Max Planck-Society (Berlin) reported that g-C ₃ N ₄  can be made by polymerizing small C–N molecules such as cyanamide, dicyandiamide, and melamine. The researchers showed that the graphitic compound’s semiconductor properties give it “unexpected” catalytic activity for a variety of organic reactions.

Subsequently, several research teams found that g-C ₃ N ₄  is a powerful photocatalyst. Much of this work is summarized in excerpts from the 2021 book  Materials Science in Photocatalysis . If you want to learn even more, read “A Tour-Guide through Carbon Nitride-Land” (2021) ¹ by Vincent Wing-hei Lau at Korea University (Seoul) and Bettina V. Lotsch at the Max Planck Institute for Solid State Research (Stuttgart, Germany).

1. https://onlinelibrary.wiley.com/doi/full/10.1002/aenm.202101078

Graphitic carbon fast facts

Graphitic carbon hazard information

About Molecule of the Week

每周分子Molecule of the Week ：苯甲腈