Accurate K-edge X-ray photoelectron and absorption spectra of g-C3N4 nanosheets by first-principles simulations and reinterpretations
Accurate K-edge X-ray photoelectron and absorption spectra of g-C3N4 nanosheets by first-principles simulations and reinterpretations
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通过第一性原理模拟和重新解释获得 g-C3N4 纳米片的准确 K 边 X 射线光电子和吸收光谱
DOI：
10.1039/c9cp04573b
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发表时间：
2019-11-07
影响因子：
3.3
通讯作者：
Hua, Weijie
中科院分区：
文献类型：
--
作者：
Zhang, Jun-Rong;Ma, Yong;Hua, Weijie
我们进行了密度泛函理论（DFT）研究的X射线光电子（XPS）和吸收（XAS）光谱的石墨碳氮化物（g-C3 N4）纳米片在N和C K-边缘。采用组合的团簇-周期性方法来计算XPS谱，其中通过从气相IP（用大团簇模型获得）减去功函数（用周期性条件获得）来计算固体2D材料的芯离子势（IP）。用不同大小的氨基封端的超分子，我们得到了收敛的光谱，并提供了新的分配5氮[1 sp（2）; 4 sp（3）（桥接，叔，和伯/仲氨基氮）]和4碳（所有键合三个氮）的局部结构。获得了与实验良好的一致性，N1s（C1 s）主峰位置相差0.1-0.2 eV（0.5-0.8 eV）。我们的模拟结果表明，纯g-C3 N4的N1s XPS仅包含两个主要特征，分别来自sp（2）-N和sp（3）-N，在398.6和401.2 eV。所有sp（3）-N的化学位移非常接近（偏离0.3-0.6 eV），使得末端氨基-NHx（x = 1，2）只能在高分辨率测量中区分。在C1 s XPS中，所有碳显示出相似的（偏差< 0.2 eV）IP，如通过相同的最近邻测定的。我们进一步排除了震动卫星的影响，可能会改变我们的XPS解释等效核心孔时间相关DFT（ECH-TDDFT）模拟。振动耦合的影响是小的（再分配仅为0.1-0.3 eV的更高的能量区域），在N1s的边缘估计从不对称的主峰形状，和C1 s的边缘可以忽略不计。发现XAS比XPS具有更快的尺寸收敛。在N1s XAS，我们确定了一个弱的π * 光谱功能在400-401 eV的-NHX和叔氮。我们的研究为不同局部结构的X射线光谱指纹提供了明确的理论参考，这对于分析具有各种设计或不可避免的结构修饰的g-C3 N4基材料是有用的。我们还强调了我们的组合集群周期性的方法在计算K-边缘XPS光谱的一般二维材料，预测准确的绝对值。
We performed a density functional theory (DFT) study on X-ray photoelectron (XPS) and absorption (XAS) spectra of graphitic carbon nitride (g-C3N4) nanosheets at the N and C K-edges. A combined cluster-periodic approach was employed to calculate XPS spectra, in which the core ionic potential (IP) of the solid 2D material was computed by subtracting the work function (obtained with periodic conditions) from the gas phase IP (obtained with large cluster models). With amino-terminated supermolecules of different sizes, we obtained convergent spectra and provide new assignments for 5 nitrogen [1 sp(2); 4 sp(3) (bridging, tertiary, and primary/secondary amino nitrogens)] and 4 carbon (all bonded with three nitrogens) local structures. A good agreement with experiments was obtained, with the N1s (C1s) main peak position differing by 0.1-0.2 eV (0.5-0.8 eV). Our simulations show that N1s XPS of pure g-C3N4 contains only two major features at 398.6 and 401.2 eV, contributed from sp(2)-N and sp(3)-N, respectively. The chemical shifts of all sp(3)-N are so close (deviating by 0.3-0.6 eV) that terminal amino groups -NHx (x = 1, 2) will only be distinguished in high-resolution measurements. In C1s XPS, all carbons show similar (deviation < 0.2 eV) IPs, as determined by the same nearest neighbors. We further excluded the effect of shake-up satellites that may change our XPS interpretations by equivalent core hole time-dependent DFT (ECH-TDDFT) simulations. The effect of vibronic coupling is small (redistribution is only 0.1-0.3 eV to the higher-energy region) in the N1s edge as estimated from the asymmetric main peak shape, and negligible in the C1s edge. Quicker size convergence was found in XAS than XPS. In N1s XAS, we identified a weak pi* spectral feature at 400-401 eV for both -NHx and tertiary nitrogens. Our study provides a clear theoretical reference for X-ray spectral fingerprints of different local structures, which is useful for analysis of g-C3N4 based materials with various designed or unavoidable structural modifications. We also highlight our combined cluster-periodic approach in calculating the K-edge XPS spectra of general 2D materials which predicts accurate absolute values.