Latest researches suggest that tin dioxide (SnO₂), as a novel modified material, could dramatically increase the currents and sensitivities during the electrochemical detection of heavy metal ions (HMIs).

In fact, researchers always attribute the enhanced electrochemical performance to the relatively large adsorption capacity of enlarged microscopic surface area.

However, plenary theoretical investigations are expected to provide deeper insight into crystal facet effect, say, first-principles theoretical studies at atomic level.

Aiming at this, a study team led by Prof. HUANG Xingjiu from Institute of Intelligent Machines (IIM), Hefei Institutes of Physical Science of the Chinese Academy of Sciences gave the answer to question of why different exposed facets of SnO₂ nanomaterials exhibit different performances in electrochemical detection of HMIs.

In their work, electroanalysis studies from the three different shapes of octahedral, elongated dodecahedral and lance-shaped SnO₂ nanoparticles reported a novel exposed facet dependent electrochemical detection behavior.

The octahedral SnO₂ nanoparticles are mainly composed of {221} facets, while the exposed surfaces of lance-shaped SnO₂ nanoparticles are dominated with {110} facets.

The highest sensitivity toward Pb(II) and Cd(II) was obtained at lance-shaped SnO₂ nanoparticles modified electrode. Due to the lower diffusion energy and longer Pb-O bond length of SnO₂ {110} facet, the low-energy {110} facet showed excellent electrochemical performance in HMIs detection.

Detailed experimental and theoretical investigation reveals a reliable interpretation of the mechanism for electroanalysis of HMIs with nanomaterials exposed by different crystal facets.

Moreover, it provides a deep insight into the key factors to improve the electroanalysis performance in HMIs detection.

This work was detailed in Analytical Chemistry with the title of "Tin Oxide Crystals Exposed by Low-Energy {110} Facets for Enhanced Electrochemical Heavy Metal Ions Sensing: X-ray Absorption Fine Structure Experimental Combined with Density-Functional Theory Evidence."

This work was supported by the National Natural Science Foundation of China. The authors show their thanks to Shanghai Synchrotron Radiation Facility for providing measurement time. And Prof. HUANG acknowledges the Chinese Academy of Sciences Interdisciplinary Innovation Team of the Chinese Academy of Sciences, China, for financial support.

Schematics of how adsorptive SnO₂ nanomaterial exposed by different facets could be designed for an electrochemical sensing interface. (Image by YANG Meng) 

Figure 1. Electrochemical detection of HMIs and sensing mechanism studies. a), b) and c) Representative SEM images of the three different shapes of SnO₂ nanoparticles. d) and e) Calibration plots of bare GCE, octahedral, elongated dodecahedral, and lance-shaped SnO₂ nanoparticles modified GCE toward different concentrations of Pb(II) and Cd(II), respectively. f) and g) The transtion-state (TS) structure for Pb(II) on SnO₂ {110} and {221} surface, respectively. h) and i) Pb LIII-XAFS spectra of Pb(II)-adsorbed octahedral, elongated dodecahedral and lance-shaped SnO2 nanoparticles, respectively. (Imaged by YANG Meng)