Electrochemical Detection Performance Of MnFe₂O₄ And Its Nanocomposites Toward Heavy Metal Ions

The pollution of toxic heavy metals caused serious threat to human health, therefore, it is significant to explore an effective method with rapid, sensitive and efficient to detect different species and contents of heavy metals. Electrochemical techniques is generally considered as an effective method to detect heavy metals due to its low cost, simple operation and high sensitivity. Metal oxides have a large specific surface area and abundant active sites, which can increase adsorption and the sensitivity of electrochemical detection of heavy metal ions, show a very broad application prospects in electrochemical detection of heavy metal ions. However, the role of a single metal oxide in detection of heavy metal ions play was still limited. To improve the sensitivity and selectivity of electrochemical detection of heavy metal ions, we had synthesized a double metal oxide and functionalized it, improving the sensitivity and selectivity of electrochemical detection of heavy metal ions effectively. This paper present the main research work as follow.（1） Double metal oxide MnFe₂O₄ NCs with mesoporous structure had been prepared successfully, which were used for selective detection of Pb（II） by anodic stripping voltammetry（SWASV）. The as-prepared Mn Fe₂O₄ NCs with diameter of 200 400 nm and mesoporous structure composed of nanocrystals with a size of about 8 12 nm. MnFe₂O₄ NCs modified electrode has a favorable sensitivity and LOD for Pb（II）. The sensitivity and LOD of MnFe₂O₄ NCs modified GCE toward Pb（II） are 19.9 μA μM-1 and 0.054 μM under the optimized conditions while the sensitivity of Cd（II）, Cu（II）, Hg（II） and Zn（II） is poor. No interference from Cd（II）, Zn（II） and Hg（II）, and favorable stability in the electrochemical determination of Pb（II）. The recovery of MnFe₂O₄ NCs modified electrode toward Pb（II） in practical sample is 92.1%.（2） MnFe₂O₄/Cys nanocomposite had been synthesized with L-Cysteine surface modification MnFe₂O₄ NCs and applied to electrochemical detection of heavy metal ions. MnFe₂O₄/Cys modified electrode had a higher detection sensitivity（57.0μA/μM） and selectivity towards Pb（II） were found by detecting inorganic heavy metal ions Pb（II）, Cd（II）, Hg（II） and Cu（II） separately and simultaneously. Meanwhile, taking an example of the best electrochemical response of Pb（II）, MnFe₂O₄/Cys modified electrodes showed favorable stability and reproducibility. The recovery of practical sample analysis toward Pb（II） is 93.5%, showed the actual value of MnFe₂O₄/Cys modified electrode, and provides a new research methods and ideas to develop new electrochemical sensors of heavy metal ions.（3） Due to special nature of trivalent arsenic detection, the MnFe₂O₄ NCs modified gold electrodes applied to the detection of trivalent arsenic in water. The sensitivity and LOD of MnFe₂O₄ NCs modified electrode toward As（III） were 0.295 μA / ppb and 1.95 ppb under optimal conditions. No significant inference from Cu（II） and Hg（II） in detection of As（III）. MnFe₂O₄ NCs modified electrode had a favorable stability to As（III）, and the recovery of actual samples toward As（III） was 95.6%, with a practical applications.（4） Core-shell structure MnFe₂O₄/Au nanocomposite had been synthesized and used for electrochemical detection of As（III）. By comparing the electrochemical characterization of MnFe₂O₄, MnFe₂O₄/Au and Au NPs modified electrodes and stripping voltammetry analysis of As（III）, MnFe₂O₄/Au nanocomposite had a higher detection sensitivity（0.315 μA/ppb） to As（III）. When the concentration of Cd（II）, Pb（II）, Cu（II） and Hg（II） was 10 times that of As（III）, the interference of Pb（II） was the maximum and others were relatively smaller. MnFe₂O₄/Au modified electrode good stability and the recovery of actual samples was 103%, is expected to be practical.