Template free synthesis of lithium doped three-dimensional macroporous graphitic carbon nitride for photocatalytic N2 fixation: the effect of Li-N active sites

In this work, three-dimensional macroporous lithium doped graphitic carbon nitride was synthesized. XRD, N-2 adsorption, SEM, XPS, UV-Vis spectroscopy, N-2-TPD and photoluminescence were used to characterize the prepared catalysts. The result shows that lithium exists as a coordinative Li-N bond, which can chemisorb and activate N-2 molecules, and promote the electron transfer from the catalyst to the nitrogen molecules. The as-prepared lithium doped g-C3N4 shows a NH4+ production rate of 4.8 mg L-1 h(-1) g(cat)(-1), which is 20 times that of bulk g-C3N4. Density functional theory (DFT) simulations show that lithium doping can not only increase the N?N bond length, which activates N-2 molecules, but also promote the electron-hole separation efficiency of g-C3N4.

在这项工作中，合成了三维大孔锂掺杂石墨相氮化碳。利用X射线衍射（XRD）、N₂吸附、扫描电子显微镜（SEM）、X射线光电子能谱（XPS）、紫外 - 可见光谱、N₂ - 程序升温脱附（N₂ - TPD）和光致发光等方法对所制备的催化剂进行了表征。结果表明，锂以配位Li - N键的形式存在，它能够化学吸附并活化N₂分子，促进电子从催化剂向氮分子转移。所制备的锂掺杂g - C₃N₄的NH₄⁺生成速率为4.8 mg L⁻¹ h⁻¹ g(cat)⁻¹，是块状g - C₃N₄的20倍。密度泛函理论（DFT）模拟表明，锂掺杂不仅可以增加N≡N键长从而活化N₂分子，还能提高g - C₃N₄的电子 - 空穴分离效率。