Colorimetric speciation analysis of chromium using 2-thiobarbituric acid capped silver nanoparticles

Abstract

In the present work, 2-thiobarbituric acid (TBA)-capped silver nanoparticles (AgNPs) have been introduced as a novel nanoprobe in the construction of a sensitive and selective colorimetric sensor for Cr(III) and Cr(VI) ions. Cr(III) can be linked to TBA on the AgNP surface via –N or –OH groups and form a bridge between two or more AgNPs causing their aggregation. This phenomenon leads to a dramatic color change in TBA-AgNPs from yellow to pinkish red. UV-Vis spectrophotometry, FT-IR and transmission electron microscopy (TEM) were utilized for quantitative analyses, characterization of modified AgNPs and determination of the interaction mechanism of TBA-AgNPs – Cr(III). The color change depended on the concentration of Cr(III) and the ratio of UV-Vis absorption intensity at 520 nm to that at 418 nm (A₅₂₀/A₄₁₈) was linearly proportional to the concentration of Cr(III) from 0.012 to 3.25 mg L⁻¹ (LOD = 8.4 µg L⁻¹). To eliminate or reduce the interference of other cations in Cr(III) determination, EDTA was used as a masking agent at pH 6.5. Moreover, the developed method was used for the determination of Cr(VI) in the presence of ascorbic acid (AA) (as a reducing agent) in the concentration range of 0.20 to 1.40 mg L⁻¹. The proposed probe was successfully applied for the determination of Cr(III) and Cr(VI) in cement factory wastewater.