**4. Conclusions**

In this work, an electrochemical device with a three-electrode configuration covered by a layer of HAMA hydrogel was developed for in situ adsorption of Pb(II) ions in aqueous solutions. The devices were successfully fabricated using microfabrication technology along with a surface modification approach. The material properties of the synthesized HAMA hydrogels in the aspects of the swelling capacity, microscopic structure, as well as molecular composition, were systematically evaluated. Based on the analytical outcomes of the fabricated HAMA hydrogel-modified devices, an adsorption mechanism associated with a combined effect of molecular interaction and electrochemical accumulation, which could explain the observed experimental results, was proposed. By performing FTIR analysis on the Pb(II)-soaked HAMA hydrogel, the molecular interaction was corroborated to be the Pb(II)-amide complexation. We found that both nitrogen and the carbonyl oxygen of the amide group were responsible for the formation of the complex, though the carbonyl oxygen could play a dominant role in the course of intermolecular complexation. The contribution of electrochemical accumulation to the adsorption capability of the HAMA hydrogelmodified devices was also confirmed by activating/deactivating the deposition potential applied to the working electrode of the devices. The experimental investigation shows that 94.08% of Pb(II) ions present in the solution can be adsorbed by the device within 30 min. Application of the HAMA hydrogel-modified devices for removing Pb(II) ions in tap water reveals its potential for use for the rapid remediation of Pb(II) contamination. This study paves the way for the design of compact and portable electrochemical devices for in situ removal of Pb(II) ions. Future work will focus on exploring the HAMA hydrogel-modified devices for the simultaneous adsorption of multiple heavy metal ions and employing other validation methods to further investigate the molecular interaction between HAMA hydrogels and different kinds of heavy metal ions.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/bios12090714/s1, Figure S1: Schematic drawing to show detailed dimensions of the polycarbonate mold; Figure S2: The weight of the synthesized HAMA hydrogel samples measured before and after swelling in ultrapure water; Figure S3: Photograph of the synthesized HAMA hydrogel samples upon reaching the equilibrium state of swelling.

**Author Contributions:** Conceptualization, N.W.; formal analysis, N.W., M.B. and S.H.; investigation, N.W. and M.B.; writing—original draft preparation, N.W. and M.B.; writing—review and editing, S.H., K.T., J.W., L.H., J.L. and S.L.; supervision, M.S.T. and X.L.; project administration, N.W., M.S.T. and X.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Fundamental Research Funds for the Central Universities, grant numbers DUT21RC(3)054 and DUT21RC(3)020, and the National Key R&D Program of China, grant number 2021YFB3201302.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:**Data are availableupon reasonable request toNanWang (wang\_nan@dlut.edu.cn).

**Acknowledgments:** This research was supported by the Ministry of Education Singapore and the National Research Foundation of Singapore through the Singapore MIT Alliance for Research and Technology's Center for Environmental Sensing and Modeling interdisciplinary research program.

**Conflicts of Interest:** The authors declare no conflict of interest.
