Oxidation of copper(I) in seawater at nanomolar levels

Abstract

The oxidation and reduction of nanomolar levels of copper in air-saturated seawater and NaCl solutions has been measured as a function of pH (7.17-8.49), temperature (5-35 °C) and ionic strength (0.1-0.7 M). The oxidation rates were fitted to an equation valid at different pH and ionic strength conditions in sodium chloride and seawater solutions:(log k(NaCl) = 5.221 + 0.609 pH - 1915 / T - 1.818 sqrt(I) + 0.408 I; log k(sw) = 5.036 + 0.514 pH - 1765 / T - 1.101 sqrt(I) + 0.233 I .). The reduction of Cu(II) was studied in both media for different initial concentrations of copper(II). When the initial Cu(II) concentration was 200 nM, the copper(I) productions were 20% and 9% for NaCl and seawater, respectively. The effect of speciation of copper(I) reduced from Cu(II) on the rates was studied. The Cu(I) speciation is dominated by the CuCl2- species. On the other hand, the neutral chloride CuCl species dominates the Cu(I) oxidation in the range of 0.1 M to 0.7 M chloride concentrations.