Melissen Sigismund T A G, Le Bahers Tangui, Sautet Philippe, Steinmann Stephan N
Université de Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622 Lyon, France.
Université de Lyon, Université Claude Bernard Lyon 1, Ecole Normale Supérieure de Lyon, CNRS, 46 allée d'Italie, F-69007 Lyon Cedex, France.
Phys Chem Chem Phys. 2021 Feb 4;23(4):2853-2859. doi: 10.1039/d0cp06063a.
Graphitic carbon nitrides (g-CNs) have become popular light absorbers in photocatalytic water splitting cells. Early theoretical work on these structures focused on fully polymerized g-C3N4. Experimentally, it is known that the typically employed melamine polycondensation does not go toward completion, yielding structures with ∼15 at% hydrogen. Here, we study the conformational stability of "melon", with the [C6N9H3]n structural formula using DFT. Referencing to a 2D melon sheet, B3LYP-dDsC and PBE-MBD computations revealed the same qualitative trend in stability of the 3D structures, with several of them within 5 kJ mol-1 per tecton. Fina's orthorhombic melon is the most stable of the studied conformers, with Lotsch' monoclinic melon taking an intermediate value. Invoking a simple Wannier-Mott-type approach, Fina's and Lotsch' structures exhibited the lowest optical gaps (2.8 eV), within the error margin of the experimental value (2.7 eV). All conformers yielded gaps below that of the monolayer's (3.2 eV), suggesting Jelley-type ("J") aggregation effects.
石墨相氮化碳（g-CNs）已成为光催化水分解电池中受欢迎的光吸收剂。早期关于这些结构的理论研究集中在完全聚合的g-C3N4上。在实验中，已知通常采用的三聚氰胺缩聚反应不会完全进行，会生成含约15原子%氢的结构。在此，我们使用密度泛函理论（DFT）研究了具有[C6N9H3]n结构式的“蜜勒胺”的构象稳定性。以二维蜜勒胺片为参考，B3LYP-dDsC和PBE-MBD计算揭示了三维结构稳定性的相同定性趋势，其中一些结构每个结构单元的能量在5 kJ mol-1以内。菲纳的正交晶系蜜勒胺是所研究构象中最稳定的，洛奇的单斜晶系蜜勒胺处于中间值。采用一种简单的万尼尔-莫特型方法，菲纳和洛奇的结构表现出最低的光学带隙（2.8 eV），在实验值（2.7 eV）的误差范围内。所有构象的带隙均低于单层的带隙（3.2 eV），表明存在杰利型（“J”）聚集效应。
