Abstract
The formation of lead dioxide PbO(2), an important corrosion product in drinking water distribution systems with lead-bearing plumbing materials, has been hypothesized to involve Pb(III) intermediates, but their nature and formation mechanisms remain unexplored. This study employed the electrochemical (EC) method of rotating ring disk electrode (RRDE) and quantum chemical (QC) simulations to examine the generation of intermediates produced during the oxidation of Pb(II) to PbO(2). RRDE data demonstrate that PbO(2) deposition and reduction involves at least two intermediates. One of them is a soluble Pb(III) species that undergoes further transformations to yield immobilized PbO(2) nanoparticles. The formation of this intermediate in EC system is mediated by hydroxyl radicals (OH(•)), as was evidenced by the suppression of intermediates formation in the presence of the OH(•) scavenger para-chlorobenzoic acid. QC simulations confirmed that the oxidation of Pb(II) by OH(•) proceeds via Pb(III) species. These results show that Pb(III) intermediates play an important role in the reactions determining transitions between Pb(II) and Pb(IV) species and could impact lead release in drinking water.
Highlights
Lead dioxide PbO2 typically consisting of coalesced nanoparticles is commonly found on lead-containing plumbing materials exposed to drinking water containing chlorine.[1−3] Both scrutinyite α-PbO2 and plattnerite β-PbO2 form via the oxidation by chlorine of Pb(II) solids including hydrocerussite Pb3(CO3)2(OH)[2], cerussite PbCO3, and massicot PbO1,4−6 or via the oxidation of Pb(II) solutes.[6]
cyclic voltammetric (CV) scans obtained from the Pb(II)/ring disk electrode (RRDE) system had prominent features that depended on scan rate, rotation speed, solution pH, and evolution of the electrode surface
The fact that Peak 2 emerged at potentials higher than this threshold indicated that this peak was associated with the EC oxidation of Pb(II) to PbO2
Summary
Lead dioxide PbO2 typically consisting of coalesced nanoparticles is commonly found on lead-containing plumbing materials exposed to drinking water containing chlorine.[1−3] Both scrutinyite α-PbO2 and plattnerite β-PbO2 form via the oxidation by chlorine of Pb(II) solids including hydrocerussite Pb3(CO3)2(OH)[2], cerussite PbCO3, and massicot PbO1,4−6 or via the oxidation of Pb(II) solutes.[6]. The reduction of PbO2 to Pb(II) by bromide in acidic solution was hypothesized to proceed via two one-electron transfer steps with the formation of Pb(III) surface intermediates.[21] Examination of the oxidation of Pb(II) solids by chlorine 4,5,22 suggested the formation of transient species prior to the generation of PbO2 phase.
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