| For a long time, the pollution of heavy metal ions in groundwater has become a worldwide problem, which is seriously harmful to human health. Therefore, realizing the detection of heavy metal ions in rapidity, trace amount, high sensitivity and selectivity is significant to precisely evaluate the environmental pollution while it also receive great attention due to the difficulties.Due to the higher toxicity of Cr(Ⅵ) and As(Ⅲ) than other heavy metal ions, therefore, it is the most important for the detection of the two ions. However, previous reports always using stripping voltammetry, requiring the noble-metal electrodes or noble-metal nanoparticle-modified electrodes with homogeneous morphology; meanwhile the detection need to be carried out under harsh acid conditions due to the limitation of redox reaction. Our work focuses on how to avoid the defects, which the previously literature reported about the electrochemical detection of Cr(Ⅵ) and As(Ⅲ), but also for the sensitive and selective detection of them by electrochemical method. By constructing of two novel types of electrochemical sensors, which can be achieved the sensitive and selective detection of these two heavy metal ions.The signal layer materials are widely used in optical, electrical, photocatalytic degradation of wastewater, energy storage, photoelectric conversion and other fields, but relatively few reported in the field of electrochemical detection. According to the selective adsorption characteristics of signal layer of materials, they will be applied to the detection of heavy metal ions in water. This is another research carried out in this paper. The main parts of the results are summarized briefly as follows:(1) Utilizing the properties of the special interaction caused by the crown ethers and Cr(Ⅵ), resulted the inhibition of electron and mass transfer on the surface of the electrode, the researchers in the institute realize the detection of Cr(Ⅵ) with high sensitivity and selectivity by the method of the electrochemical impedance spectroscopy(EIS). In the pH range below5, Cr(Ⅵ) mainly presents in the form of HCrO4-ion, in the pH value5.0of the solution, one molecular azacrown could form a complexation with K+, according to host guest interaction principle. Thus, after introduction of Cr(Ⅵ), a sandwich complexes is formed via N…H-[HCrO4]-K+, through the effect of hydrogen bonding and electrostatic interaction, which is responsible for the inhibition of electron transfer, resulting in an increase impedance to achieve a sensitive and selective detection of Cr(Ⅵ). This method offers a detection limit of0.0014ppb Cr(Ⅵ) with a sensitivity of4575.28kΩ [log c (ppb)]-1over the linear range of1-100ppb (R2=0.994) at pH5.0.In addition, the azacrown self-assembled on Au electrode possesses a good selectivity toward Cr(Ⅵ) with a good stability and anti-interference. Finally, it is carried out as well as analysis of spiked Cr(Ⅵ) in real samples.(2) A super equivalent gold macrodisk electrode for ultrasensitive detection of As(Ⅲ) was designed and constructed. The electrode was constructed through abundantly dispersing Au nanoparticles (～5nm in diameter) on the surface of Fe3O4(～200-300nm in diameter), where Au/Fe3O4nanoparticles were covered by using the room temperature ionic liquid (RTIL). By combining the excellent catalytic properties of the gold, the good adsorption capacity of Fe3O4and good conductivity of RTIL for the first time, the Au/Fe3O4-RTIL composites modified screen-printed carbon electrode (SPCE) showed excellent performance on detection of arsenic under nearly neutral condition by square wave anodic stripping voltammetry while only using～1%by mass of the expensive gold material. The obtained sensitivity was458.66μA ppb-1cm-2in concentration range of0.1-1ppb, which was the highest as far as we know, and a low detection limit (3σ method) was0.0022ppb. Unlike previously developed electrodes, the electrode with well morphology after modification is available and repeatable. The reproducibility and reliability of the Au/Fe3O4-RTIL electrode were also evaluated with good results. Finally, this platform was successfully applied to analyze real sample.(3) Due to the poor conductivity of signal layer materials, which are not widely applied in the field of electrochemical detection. So far, applied the signal layer of TiP for the field of electrochemical detection has not been reported. After exfoliation, layered a TiP could expose the active groups adequately, enhancing the reaction activity of TiP, absorb more ions to the surface of the electrode. In this work, Based on the large and active surface, special adsorption of Pb2+, signal layer of TiP was used to modify the GCE, for the detection of Pb2+by SWASV. The obtained sensitivity was23.99μA μM-1(R2=0.992) in the lower concentration range, which was the highest as far as we know, and a low detection limit (3σ method) was0.5nM. Compared with the effect of layered TiP, the obtained sensitivity based on the signal layer of TiP has improved20.55times. Using the the signal layer of TiP modified electrode to detect other heavy metal ions(such as Cd2+, Cu2+, Hg2+and Zn2+), compared with the detection of Pb2+, the obtained sensitivity decreased nearly7-14times. |
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