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 to electrochemically detect 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.
In their work published in Anal. Chem, a research group led by Prof. LIU Jinhuai and Prof. HUANG Xingjiu at Institute of Intelligent Machines, Hefei Institutes of Physical Science reported their discovery in detecting Hg(II) through TiO2-based electrode without other modification need.
In the study, researchers reported a sensitive electrochemical sensing performance of a defective single-crystalline (001) TiO2-nanosheet toward heavy-metal ions (e.g., Hg(II)).
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 to enhance the stripping signals is also investigated by adsorption experiments accompanying with the XPS and extended X-ray absorption fine structure (EXAFS) analysis.
Particularly, the researchers not only expand the electrochemical sensing applications of pure semiconductors, but also open scientists up to new way of investigating atom-level electrochemical behaviors of semiconductors by surface electronic state modulation.
Figure: a) Overview high resolution transmission electron microscope (HRTEM) images; b) Compositional curves recorded according to the HRTEM images; c) Comparison of sensitivities toward Hg(II). Inset illustrates the role of the oxygen vacancy in catalysis. d) ESR spectra; e) Fourier transforms and their fits of EXAFS spectra with uncorrected phase shift. (Image by ZHOU Wenyi)
Institute of Intelligent Machines (http://english.iim.cas.cn/)
Hefei 230031, Anhui, China