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