Fig. a) Transmission electron microscope images of TiO2 samples with different surface defect states; b) Structural analysis based on high-resolution transmission electron microscopy shows the surface in the defect state; c) Oxygen vacancy participates in and catalyzes the electrochemical detection process; d) ESR spectrum verification The presence of Ti3+ and oxygen vacancies; e) EXAFS spectra of the Fourier transform of the Hg(II) adsorption-defective (T-1) and non-defective (T-3) sample surfaces.
Nanometer TiO2 is a typical n-type semiconductor material, and exhibits poor electrochemical activity because its eigenstate surface lacks active sites for interaction with target molecules and poor conductivity. Recently, based on the analysis of the electroanalytical chemistry of the preceding crystal face, the Huang Xingjiu Group of the Institute of Intelligent Machinery of the Chinese Academy of Sciences' Hefei Institute of Physical Science discovered that the 001 surface of the titania single crystal nanosheet was obtained by doping oxygen vacancies on the TiO2 surface. The electrochemical catalytic behavior of oxygen-hole-cavity synergy, and the titania single crystal nanosheet (001) exhibits a high electrochemical detection activity during the detection of heavy metal ions; at the same time, the research group uses XAFS (X-ray absorption fines) Structural) spectroscopy reveals its synergistic electrochemical catalytic behavior. Related results have been published in the American Chemical Society "Analytical Chemistry" (Anal. Chem. 2017. DOI: 10.1021/acs.analchem.6b04023).
The (001) crystal face of TiO2 crystal is generally considered to be a high-energy active crystal face due to its 100% unsaturated 5-coordinate Ti atom, and has been proved by theory and experiments. Based on this theory, the researchers prepared a high proportion of exposed TiO2 nanosheets with (001) crystal surface, and comprehensively proved the reductive nature through various means such as X-ray photoelectron spectroscopy, Raman and X-ray absorption near-side structure. Ti3+ and oxygen vacancies are successfully introduced into its surface atomic layer. In the analysis of the electrochemical behavior of heavy metal ions in water environment, it was found that heavy metal ions such as Hg(II) exhibited high sensitivity on the surface of TiO2 nanosheets, and their sensitivity changes were in accordance with the concentration of Ti3+ and oxygen vacancies on the surface of the material. . In addition, the researchers found that the surface Ti3+ and oxygen vacancies can modulate the electronic structure of the surface of the material and the Hg (II) adsorption performance, making it show good conductivity and strong adsorption performance. Through the Shanghai synchrotron radiation device (BL14W1 line station), the researchers used XAFS spectroscopy to prove that the oxygen hole on the surface of the material adsorbs O2 molecules, while the reducing Ti3+ transfers an electron to the adsorbed oxygen to form superoxide radicals, which can be used as The active site of Hg(II) adsorption and the active site of electron transport in the redox reaction serve to enhance the electrochemical detection signal.
This work not only confirms that the application of intrinsic semiconductor nanomaterials can be extended to electrochemical sensing analysis through the concept of surface electronic structure modulation, but also provides a new opportunity for future exploration of electrochemically sensitive behavioral mechanisms at the atomic scale. The research work was supported by the Innovation Crossing Team of the Chinese Academy of Sciences, the National Natural Science Foundation, and the Shanghai Synchrotron Radiation Facility (BL14W1 Line Station).
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