Dual-modification strategy of Co(II) and g-C₃N₄ to CuS for efficient colorimetric determination of thioglycolic acid in daily cosmetics

A conventional colorimetric method based on CuS-catalyzed H₂O₂ is improved by a dual-modification strategy and employed for thioglycolic acid (TGA) determination. The doping of Co(II) can enhance ion exchange efficiency. Meanwhile, the modification of g-C₃N₄ can increase specific surface area and decrease unspecific aggregation. The constructed g-C₃N₄/Co-CuS nanocomposite exhibited a favorable catalytic feature. A Michaelis constant (K_m) value of 0.02 mM has been achieved, which is 1/160 of those of CuS and horseradish peroxidase (HRP). The g-C₃N₄/Co-CuS displays a rapid color response in 3 min and resulted in a stable measurable signal within 10 min. In the determination procedure, the sulfhydryl contained in TGA is capable of preventing TMB oxidation via competing the ·OH produced by catalysis and caused a color distinction that is related to the TGA amount. The distinctions of absorbance (λ_max = 652 nm) of different concentrations of TGA are recorded. Linearity is obtained in the ranges of 2.5 – 20 µM and 20 – 160 µM, and the LOD is 0.14 µM. In the real sample assays of perm agent and Qianhu lake water, the recoveries were 96.70 – 106.84% and 100.21 – 101.90%, respectively. This demonstrates that the proposed dual-modification strategy for CuS contributes to highly efficient and convenient determination of TGA in daily cosmetics and water analysis. Graphical