Among many transition-metal oxides, TiO₂ possesses high potential as an electrochemical sensing material because of its abundance, low cost and high stability. However, the wide-bandgap energy (3.2 eV) makes TiO₂ more appropriate for photocatalysis. Pure TiO₂ has rarely been used for electrochemical detection of heavy-metal ions due to its intrinsic low conductivity and poor reactivity, while modified materials, such as DNA/C/TiO₂ and Ti/TiO₂ nanotube/Au composites, show high electrochemical performance. However, it is still very challenging to directly apply a pure TiO₂-based electrode to electrochemical detection of heavy-metal ions.

Recently, a research group led by Prof. LIU Jinhuai and Prof. HUANG Xingjiu from Institute of Intelligent Machines, Hefei Institutes of Physical Science, Chinese Academy of Sciences, achieved an important progress in detecting Hg(II) through TiO₂-based electrode without other modification need. The study results were published in Anal. Chem. (Anal. Chem. 2017. DOI: 10.1021/acs.analchem.6b04023)

In the study, a sensitive electrochemical sensing performance of a defective single-crystalline (001) TiO₂-nanosheet toward heavy-metal ions (e.g., Hg(II)) is reported. By using the defective TiO₂ nanosheet-modified electrodes, the modification of TiO₂ with other materials for electrochemical detection is no longer necessary. The presence of surface Ti³⁺ ion and OVs is confirmed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, electron spin resonance (ESR), and Fourier-transform infrared (FTIR) spectroscopy. The effect of surface Ti³⁺ ion and OVs for enhancing the stripping signals is also investigated by adsorption experiments accompanying with the XPS and extended X-ray absorption fine structure (EXAFS) analysis.