Mendive Cecilia B, Bredow Thomas, Feldhoff Armin, Blesa Miguel A, Bahnemann Detlef
Institut für Technische Chemie, Leibniz Universität Hannover, Callinstr. 3-3A, D-30167, Hannover, Germany.
Phys Chem Chem Phys. 2009 Mar 21;11(11):1794-808. doi: 10.1039/b814608j. Epub 2009 Feb 2.
A combined experimental and theoretical study of the adsorption of oxalic acid from the aqueous phase at the surface of anatase nanoparticles has been performed. The interfaces were investigated by ATR-FTIR measurements and quantum-chemical calculations using the semiempirical method MSINDO. The vibration spectra of the most stable surface complexes have been calculated and used for the interpretation of experimental results. The theoretical studies have been done using the anatase (100) surface to model the adsorption of oxalic acid and water. The effect of interaction of water and oxalic acid on the adsorption mechanism and the vibration spectra was taken into account in the theoretical models. Inclusion of solvation effects was found crucial to determine the type of denticity and structure of adsorbed complexes. By comparison of experimental data and theoretical calculations the most likely surface species and the effects of hydration in their relative stabilities were determined. The present results are compared to previous studies preformed also by combination of experimental and theoretical calculations of analogous systems using nanoparticulate rutile [C. B. Mendive et al., Phys. Chem. Chem. Phys., 2008, 10, 1960, ref. 1]. Differences between surface complexes on anatase and rutile lie mainly on the denticity type. Whilst in the case of rutile the most stable species consist of two bidentate surface complexes followed in third place by a monodentated form, anatase allows the formation of four species in which the stability order is reversed with respect to the denticity type. In the case of anatase, the main contributors to the surface speciation are two monodentate species differing in the position of the H atom within the molecule (being more stable when it is placed in the O-C-O moiety not bound to the surface); and two bidentate species, one deprotonated and one monoprotonated, in which the C-C bond was parallel or perpendicular to the TiO2 surface, respectively.
对锐钛矿型纳米颗粒表面水相草酸吸附进行了实验与理论相结合的研究。通过衰减全反射傅里叶变换红外光谱（ATR-FTIR）测量和使用半经验方法MSINDO的量子化学计算对界面进行了研究。计算了最稳定表面络合物的振动光谱，并用于解释实验结果。理论研究使用锐钛矿（100）表面来模拟草酸和水的吸附。理论模型中考虑了水和草酸相互作用对吸附机理和振动光谱的影响。发现包含溶剂化效应对于确定吸附络合物的齿合度类型和结构至关重要。通过比较实验数据和理论计算，确定了最可能的表面物种及其相对稳定性中的水合作用影响。将本研究结果与之前同样通过实验和理论计算相结合对使用纳米颗粒金红石的类似体系进行的研究[C. B. 门迪夫等人，《物理化学化学物理》，2008年，10卷，1960页，参考文献1]进行了比较。锐钛矿和金红石表面络合物之间的差异主要在于齿合度类型。在金红石的情况下，最稳定的物种由两个双齿表面络合物组成，第三位是单齿形式，而锐钛矿则允许形成四种物种，其稳定性顺序相对于齿合度类型是相反的。在锐钛矿的情况下，表面物种形成的主要贡献者是两个单齿物种，它们在分子内H原子的位置不同（当它位于不与表面结合的O-C-O部分时更稳定）；以及两个双齿物种，一个去质子化，一个单质子化，其中C-C键分别与TiO2表面平行或垂直。
