FT-IR、XPS和DFT研究水杨酸钠在针铁矿或赤铁矿上的吸附机理

采用傅里叶变换红外(FT-IR)光谱、X射线光电子能谱(XPS)以及基于周期平面波的密度泛函理论(DFT)分别研究了水杨酸钠在针铁矿或赤铁矿表面上的吸附结构，并将计算得到的光电子能谱移动(CLS)和电荷转移与实验得到的XPS结果进行对比。FT-IR结果表明，水杨酸钠可能以双齿双核(V)和双齿单核(IV)的形式分别吸附于针铁矿或赤铁矿表面。由DFT计算结果可知，水杨酸钠在针铁矿(101)晶面上形成双齿双核化合物(V)的吸附能为-5.46 eV。而水杨酸钠在针铁矿(101)晶面上形成双齿单核化合物(IV)的吸附能为3.80 eV，因此水杨酸钠在针铁矿上基本不以双齿单核化合物(IV)构型存在。水杨酸钠在赤铁矿(001)晶面上形成双齿单核化合物(IV)时吸附能为-4.07 eV，说明水杨酸钠在赤铁矿(001)晶面上形成了双齿单核化合物(IV)。另外，理论计算的针铁矿(101)晶面上吸附位点铁原子的Fe 2p的CLS值(-0.68 eV)与实验观察到的Fe 2p的CLS值(-0.5 eV)吻合。理论计算的赤铁矿(001)晶面上吸附位点铁原子的Fe 2p的CLS值(-0.80 eV)与实验观察到的Fe 2p的CLS值(-0.8 eV)吻合。因此，水杨酸钠吸附在针铁矿表面时能够通过羧酸基团上一个氧原子和酚羟基上的氧原子与针铁矿(101)表面上的两个铁原子形成双齿双核(V)结构，而在赤铁矿(001)表面上，水杨酸钠中羧酸基团上一个氧原子和酚羟基上的氧原子与赤铁矿(001)表面上的一个铁原子形成了双齿单核(IV)结构。

FT-IR,XPS and DFT Study of the Adsorption Mechanism of Sodium Salicylate onto Goethite or Hematite

The adsorption of sodium salicylate on goethite or hematite surfaces was investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoemission spectroscopy (XPS), and periodic plane-wave density functional theory (DFT) calculations. The core level shift (CLS) and charge transfer of the adsorbed surface iron sites calculated by DFT with periodic interfacial structures were compared with the X-ray photoemission experiments. The FT-IR results reveal that the interfacial structure of sodium salicylate adsorbed on goethite or hematite surfaces can be classified as bidentate binuclear (V) or bidentate mononuclear (IV), respectively. The DFT calculated results indicate that the bidentate binuclear (V) structure of sodium salicylate is favorable on the goethite (101) surface, with an adsorption energy of-5.46 eV, while the adsorption of sodium salicylate on the goethite (101) surface as a bidentate mononuclear (IV) structure is not predicted, as it has a positive adsorption energy of 3.80 eV. Conversely, on the hematite (001) surface, the bidentate mononuclear (IV) structure of the adsorbed sodium salicylate has anadsorption energy of-4.07 eV, confirming its favorability. Moreover, the calculated CLS of Fe 2p (-0.68 eV) for the adsorbed iron site on the goethite (101) surface is consistent with the experimentally observed CLS of Fe 2p (-0.5 eV) for SSa-treated goethite (goethite after the treatment of sodium salicylate). Our calculated CLS of Fe 2p (-0.80 eV) for the adsorbed iron site on the hematite (001) surface is likewise in good agreement with the experimentally observed CLS of Fe 2p (-0.8 eV) for SSa-treated hematite (hematite after the treatment of sodium salicylate). Thus, goethite is predicted to adsorb sodium salicylate as a bidentate binuclear (V) structure via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to two surface iron atoms of goethite (101). Meanwhile, on the hematite surface, the bidentate mononuclear (IV) complex formed via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to one surface iron atom of hematite (001) can be regarded as plausible.