Cathodic stripping square-wave voltammetry for assessing As(III) removal with synthetic mixed oxides

In this work, the adsorption of As(III) species from aqueous solutions onto mixed oxides (MOs) synthesized from layered double hydroxides (LDHs) has been assessed by cathodic stripping square-wave voltammetry (CS-SWV). The optimized electrochemical protocol involves the accumulation of arsenic for 60 s at -0.4 V, in presence of 0.5 mM Cu(II), 0.3 mu M pyrrolidine dithiocarbamate (PDTC), and 0.9 M HCl, followed by a reductive scan to -1.0 V. A stable and well-defined peak was observed at -0.780 V, with a linear range that goes from 2 to 110 mu g L-1 of As(III). A value of limit of detection (LOD) = 4 mu g L-1 was calculated as three times the ratio between the standard deviation of the ordinate and slope of the linear regression curve. The presence of Cu(II) increases the signal of current and minimizes the effect of interfering species, while PDTC forms a complex that stabilizes the signal observed during the cathodic scan. Ternary LDHs and their MOs composed by MgAlFe were synthesized and characterized as potential filtering materials. X-ray photoelectron spectroscopy and UV-Vis diffuse reflectance analysis showed that the Fe(III) ions can be found in tetrahedral and octahedral coordination environments, while SEM micrographs evidenced the cluster formation and aggregates of particles when the Fe/(Fe+Al) molar ratio is increased. The capacity of MOs for removing As(III) has been studied at different contact times in a batch reactor, and in all cases, removals of As(III) above 75% were achieved.