Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA.
Langmuir. 2010 Nov 2;26(21):16246-53. doi: 10.1021/la101357y.
The photodissolution of the iron oxyhydroxide, ferrihydrite, in the presence of oxalic acid was investigated with vibrational spectroscopy, density functional theory (DFT) calculations, and batch geochemical techniques that determined the composition of the solution phase during the dissolution process. Specifically, in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR- FTIR) was used to determine the structure of the adsorbed layer during the dissolution process at a solution pH of 4.5. DFT based computations were used to interpret the vibrational data associated with the surface monolayer in order to help determine the structure of the adsorbed complexes. Results showed that at pH 4.5, oxalate adsorbed on ferrihydrite adopted a mononuclear bidentate (MNBD) binding geometry. Photodissolution at pH 4.5 exhibited an induction period where the rate of Fe(II) release was limited by a low concentration of adsorbed oxalate due to the site-blocking of carbonate that was intrinsic to the surface of the ferrihydrite starting material. Oxalate displaced this initial carbonate over time, and the dissolution rate showed a corresponding increase. Irradiation of oxalate/ferrihydrite at pH 4.5 also ultimately led to the appearance of carbonate reaction product (distinct from carbonate intrinsic to the starting material) on the surface.
在草酸存在的情况下，通过振动光谱、密度泛函理论（DFT）计算和批处理地球化学技术研究了氢氧化铁（FeOOH）的光溶解，这些技术确定了溶解过程中溶液相的组成。具体而言，在溶液 pH 值为 4.5 时，使用原位衰减全反射傅里叶变换红外光谱（ATR-FTIR）来确定溶解过程中吸附层的结构。基于 DFT 的计算用于解释与表面单层相关的振动数据，以帮助确定吸附配合物的结构。结果表明，在 pH 4.5 时，草酸在氢氧化铁上采用单核双齿（MNBD）结合几何形状。在 pH 4.5 下的光溶解表现出诱导期，Fe(II)释放的速率受到由于碳酸盐内在的位点阻塞而导致的吸附草酸浓度低的限制，而这种碳酸盐内在的位点阻塞是铁氢氧化物起始材料表面的固有特性。随着时间的推移，草酸取代了这种初始碳酸盐，溶解速率相应增加。在 pH 4.5 下辐照草酸/氢氧化铁最终也导致表面上出现碳酸盐反应产物（与起始材料中固有的碳酸盐不同）。
