Electrochemical analytical tools have been widely applied in toxic As(III) detection. However, the phenomenon that is the speciation of arsenic is different at different pH values, which would affect the accuracy of the arsenic detection, is usually ignored during the measurements of arsenic with electrochemical method.

In general, the environment of the groundwater is weakly alkaline, and both ionized As(III) species (H₂AsO₃) and nonionic arsenic (H₃AsO₃) are the dominant species. Therefore, developing a reliable method to detect As(III) in alkaline media might be more meaningful for practical applications.

Recently, a study team led by Prof. HUANG Xingjiu and Prof. LIU Jinhuai from Institute of Intelligent Machines (IIM), Hefei Institutes of Physical Science, explored the electrochemical detection of trace arsenic(III) by nanocomposite of nanorod-like αMnO₂ decorated with ～5 nm Au nanoparticles: considering the change of arsenic speciation.

In their study, a new nanocomposite of nanorod-like α-MnO₂ decorated with ～5 nm AuNPs (AuNPs/α-MnO₂), which overcomes the change of arsenic(III) speciation at different pH conditions, is found to be applicable in reliable detection of ultratrace original As(III) speciation in real water samples in alkaline media (pH 9.0).

Taking the different As(III) speciation at various pH media into account, the study team obtained As(III) adsorption isotherms data at different pH media, which are all better fitted by the Freundlich model, indicating a multilayer adsorption behavior of As(III) onto the AuNPs/α-MnO₂ nanocomposite.

Moreover, adsorption experiments and XPS results quantificationally reveal the largest amount of adsorbed As(III) on the AuNPs/α-MnO₂ nanocomposite at pH 9.0 Na₂CO₃-NaHCO₃ buffer solution.

Accordingly, such kind of nanocomposite operates based on a strategy combining excellent multilayer adsorption of nanorod-like α-MnO₂ with robust electrocatalytic ability of decorated ～5 nm AuNPs.

With the consideration of its improved sensitivity, limit of detection, ultrahigh anti-interference ability and the property that As(III) can maintain the original speciation in alkaline media, AuNPs/α-MnO₂ nanocomposite is expected to be more accurate and reliable to online monitorAs(III) in real water samples.

Their paper was published in Analytical Chemistry with title Electrochemical Detection of Trace Arsenic(III) by Nanocomposite of Nanorod-Like α-MnO₂ Decorated with ～5 nm Au Nanoparticles: Considering the Change of Arsenic Speciation. 

This work was supported by the National Natural Science Foundation of China.

Schematic of detection. a) Pathway of electron transfer through the interconnection of AuNPs and b) Schematic of in situ electrocatalysis for As(III) detection on AuNPs/α-MnO₂ nanocomposite modified GCE in alkaline media (pH 9.0) based on multilayer adsorption of nanorod-like α-MnO₂ and excellent electrocatalysis of ～5 nm AuNPs (Image by YANG Meng)

Sensitivity and mechanism studies. a) Typical SWASV responses of AuNPs/α-MnO₂/GCE for analysis of As(III) at pH 9.0 and pH 5.0 buffer solution, respectively. b) As(III) adsorption isotherms on AuNPs/α-MnO₂ at different pH media. c)high-resolution XPS spectra of As3d signature region for AuNPs/α-MnO₂ after As(III) absorption at different pH media. (Image by YANG Meng)