*2.7. Investigation of Adsorption Efficiency of the Modified Device*

The adsorption rate of the HAMA hydrogel-modified electrochemical devices was determined by applying a deposition potential of −1.0 V (with respect to the Ag/AgCl reference electrode) for 5 min to the working electrode in a stirred (800 rpm) solution with 100 μg/L Pb(II). Thereafter, 5 mL of the test solution was transferred to a conical tube. The Pb(II) concentration in the solution was measured using an Agilent 7700 inductively coupled plasma mass spectrometry (ICP-MS) system (Agilent Technologies, Lexington, MA, USA). This series of experiments were repeated 8 times within 40 min, i.e., the Pb(II) concentration in each test solution was separately measured after a period of 5, 10, 15, 20, 25, 30, 35, and 40 min of adsorption. In order to further investigate the influence of electrochemical accumulation on the adsorption performance of the modified devices, another series of experiments were conducted with the same experimental procedure, except for applying the deposition potential, i.e., without the activation of electrochemical accumulation.

The applicability of the HAMA hydrogel-modified electrochemical devices was explored by testing the Pb(II) removal ability of the devices in tap water. Experiments were conducted by keeping the devices in tap water with 400 μg/L Pb(II) for 20 min with the activation of electrochemical accumulation. Thereafter, the Pb(II) concentration in the tap

water was measured using the ICP-MS system. The removal efficiency of each device was calculated based on the concentration difference before and after the adsorption.
