# Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review
## 3 Application of Nanomaterials in HMIIECSs
### Carbon-Based Nanomaterials
#### 3.1.1 Carbon Nanotube Materials
In 2017, they prepared Zn\({}^{2+}\) IIPs by using AA as monomer and NNMBA as crosslink layered on vinyl functionalized MWCNTs and the designed electrochemical sensor (MWCNTs-Zn\({}^{2+}\)-IIP) showed great selectivity for Zn\({}^{2+}\) in the presence of other metal ions. [88]. The electrochemical properties of IIP modified electrodes were studied and optimized by CV. The LOD of Zn\({}^{2+}\) by DPV was 1.32 \(\times\) 10\({}^{-4}\) uM, and this system was suitable for the detection of Zn\({}^{2+}\) in paint industry wastewater. In 2018, they developed an electrochemical sensor for Cr\({}^{3+}\) detection based on MWCNT-IIP with high adsorption rate, selectivity and sensitivity [89]. The Cr\({}^{3+}\) IIP was synthesized by using MAA as the functional monomer, NNMBA as the crosslinking agent, potassium peroxo disulphate as the initiator and Cr (III) ion as the template ion. The sensor reacted quickly to Cr\({}^{3+}\) ions due to the presence of the MWCNTs nanolayer on IIP with specific binding sites. The preparation process of Pt-MWCNT-IIP was shown in Figure 5. DPV method was used to obtain the LOD of MWCNTs-Cr\({}^{3+}\)-IIP of 0.051 uM. The sensor also showed excellent selectivity, high sensitivity and good reproducibility. At the same time, it was confirmed that the adsorbent had significant selectivity for Cr\({}^{3+}\) in the presence of other competing metal ions, which had great relevance in the actual sample analysis without interference of other metal ions. The effect of adsorbent on Cr\({}^{3+}\) in wastewater of metal electroplating industry has been tested effectively. In the same year, they designed a highly selective Co\({}^{2+}\) electrochemical sensor based on vinyl-functionalized MWCNTs which was also prepared by IIT [90]. The Co\({}^{2+}\) binding site was formed by coating vinyl-functionalized MWCNTs using Co\({}^{2+}\) as a template and NNMBA crosslinked polyacrylic acid as solid polymer matrix. The developed system was successfully characterized by different analytical techniques. The selectivity of the system was checked with different metal ions, and the electrochemical response of the nanostructured modified platinum electrode was studied and optimized. The developed MWCNTs-IIP/Co/PE had fast sensing and high selectivity for Co\({}^{2+}\). The LOD of the sensor was investigated by using DPV and found to be 1.01 \(\times\) 10\({}^{-5}\) uM. The practicality of this sensor has been successfully applied for trace sensing and extraction of Co\({}^{2+}\) from practical samples such as fertilizers and batteries. In another report, they developed an IECS with good selectivity and high sensitivity for Ni\({}^{2+}\) using vinyl functionalized MWCNTs, taking into account the advantages of IIT and electrochemical methods [91]. This electrochemical sensor can easily identify Ni\({}^{2+}\) in the presence of other metal ions, with a LOD of 0.028 uM found by DPV. The practical applicability of the modified electrode was also investigated using real samples collected from lake, steel and electroplating industries. They constructed a Pb\({}^{2+}\) IIECS (MWCNTs-Pb(II)-IIP) with vinyl-functionalized MWCNTs as the backbone [92]. The characteristics of the developed Pb\({}^{2+}\) IIECS were investigated by CV and DPV. The study has shown that the developed sensor can detect Pb\({}^{2+}\) in the presence of other metal ions with a LOD of 2 \(\times\) 10\({}^{-2}\) uM. The sensing system was able to successfully identify Pb\({}^{2+}\) from a variety of actual samples, including lake water, mining wastewater, food samples and environmental samples such as cosmetics, with a recovery rate of 99%. They fabricated another Cd\({}^{2+}\)-templated sensor on vinyl-functionalized MWCNTs [93]. Compared with IIP, MWCNTs-IIP had a higher specific surface area, which was because the presence of MWCNTs can effectively enhance the adsorption of Cd\({}^{2+}\) on the adsorbent surface.