Visual detection of trace copper(ii) based on its catalytic action in the dissociation of thiosulfate

Abstract

In this study, we report a new method for the detection of Cu²⁺ based on triangular silver nanoplates (TAg-NPs), which could be corroded by sodium thiosulfate (Na₂S₂O₃). TAg-NPs with blue color can be changed to yellow color in the presence of a certain concentration of Na₂S₂O₃, however, its color change is unclear when Na₂S₂O₃ was heated in the presence of Cu²⁺. The reason may be that Na₂S₂O₃ dissociates on heating in the presence of Cu²⁺, which leads the concentration of Na₂S₂O₃ to be decreased. Furthermore, when the heating time is fixed, the decrease in the concentration of Na₂S₂O₃ is proportional to the concentration of Cu²⁺. As a result, the color of the mixture solution of TAg-NP/Cu²⁺/Na₂S₂O₃ and the absorbance at the position of the maximum absorption peak of TAg-NPs changed with the change in the concentration of Cu²⁺. The changes in the values of absorbance (ΔA, the absorbance of TAg-NP/Cu²⁺/Na₂S₂O₃ subtracted from that of TAg-NP/Na₂S₂O₃ at the position of the maximum absorption peak) were proportional to the concentrations of Cu²⁺. Thus, a new method was established by studying the UV-vis absorption spectrum or the naked eye observation, which is simple, fast and of low cost for copper ion detection. Using this method, the concentration of Cu²⁺ could be detected accurately in the range of 2.5 × 10⁻⁹ to 7.5 × 10⁻⁷ mol L⁻¹ with the correlation coefficient of r = 0.9983. Moreover, the color change of TAg-NPs could be observed in the Cu²⁺ concentration of 2.5 × 10⁻⁸ to 7.5 × 10⁻⁷ mol L⁻¹.