Savić Tatjana D, Čomor Mirjana I, Nedeljković Jovan M, Veljković Dušan Ž, Zarić Snežana D, Rakić Vesna M, Janković Ivana A
Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia.
Phys Chem Chem Phys. 2014 Oct 14;16(38):20796-805. doi: 10.1039/c4cp02197e. Epub 2014 Aug 28.
The surface modification of nanocrystalline TiO2 particles (45 Å) with catecholate-type ligands having different electron donating/electron withdrawing substituent groups, specifically 3-methylcatechol, 4-methylcatechol, 3-methoxycatechol, 3,4-dihydroxybenzaldehyde and 4-nitrocatechol, was found to alter the optical properties of nanoparticles in a similar way to catechol. The formation of the inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and a reduction of the effective band gap, being slightly less pronounced in the case of electron withdrawing substituents. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of the catecholate type (binuclear bidentate binding-bridging) thus restoring six-coordinated octahedral geometry of surface Ti atoms. From the absorption measurements (Benesi-Hildebrand plot), the stability constants in methanol/water = 90/10 solutions at pH 2 in the order of 10(3) M(-1) have been determined. The binding structures were investigated by using FTIR spectroscopy. Thermal stability of CT-complexes was investigated by using TG/DSC/MS analysis. Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain the vibrational frequencies of charge transfer complexes, and the calculated values were compared with the experimental data.
用具有不同供电子/吸电子取代基的儿茶酚型配体，具体为3-甲基儿茶酚、4-甲基儿茶酚、3-甲氧基儿茶酚、3,4-二羟基苯甲醛和4-硝基儿茶酚，对纳米晶TiO₂颗粒（45 Å）进行表面改性，发现其改变纳米颗粒光学性质的方式与儿茶酚类似。与未改性的纳米微晶相比，内球电荷转移（CT）配合物的形成导致半导体吸收发生红移，有效带隙减小，在吸电子取代基的情况下这种现象稍不明显。所研究的配体具有与表面Ti原子结合的最佳几何结构，形成儿茶酚型的环配位配合物（双核双齿结合-桥联），从而恢复表面Ti原子的六配位八面体几何结构。通过吸收测量（贝内西-希尔德布兰德图），测定了在pH 2的甲醇/水= 90/10溶液中稳定性常数约为10³ M⁻¹。通过傅里叶变换红外光谱法研究了结合结构。通过热重/差示扫描量热/质谱分析研究了CT配合物的热稳定性。利用密度泛函理论（DFT）对模型体系进行量子化学计算，以获得电荷转移配合物的振动频率，并将计算值与实验数据进行比较。
