Trace Analysis of Heavy Metals (Cd, Pb, Hg) Using 3D Printed graphene/PLA Composite Electrodes

Here we investigate the use of 3D printed graphene/PLA electrodes for quantifying trace amounts of Hg, Pb, and Cd. We prepared cylindrical electrodes by sealing a 600 µm diameter graphene/PLA filament in a pipette tip filled with epoxy. We characterized the electrodes using scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry in ferrocene methanol. The physical characterization showed a significant amount of disorder in the carbon structure and the electrochemical characterization showed quasi-reversible behavior without any electrode pretreatment. We then used unmodified graphene/PLA electrode to quantify Hg, and Pb and Cd in 0.01 M HCl and 0.1 M acetate buffer using square wave anodic stripping voltammetry. We were able to quantify Hg with a limit of detection (LOD) of 6.1 nM (1.2 ppb), but Pb and Cd did not present measurable peaks at concentrations below ~400 nM. We improved the LODs for Pb and Cd by depositing Bi microparticles on the graphene/PLA and, after optimization, achieved clear stripping peaks at the 20 nM level for both ions (4.1 and 2.2 ppb for Pb2+ and Cd2+, respectively). The results obtained for all three metals allowed quantification below the EPA action limits in drinking water.