Colorimetric Response of Dithizone Product and Hexadecyl Trimethyl Ammonium Bromide Modified Gold Nanoparticle Dispersion to 10 Types of Heavy Metal Ions: Understanding the Involved Molecules from Experiment to Simulation
2013
Leng, Yumin | Li, Yonglong | Gong, An | Shen, Zheyu | Ma, Yukun | Wu, Aiguo
A new kind of analytical reagent, hexadecyl trimethyl ammonium bromide (CTAB), and dithizone product-modified gold nanoparticle dispersion, is developed for colorimetric response to 10 types of heavy metal ions (Mⁿ⁺), including Cr(VI), Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺. The color change of the modified gold nanoparticle dispersion is instantaneous and distinct for Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺. The color change results from the multiple reasons, such as electronic transitions, cation−π interactions, formation of coordination bonds, and Mⁿ⁺-induced aggregation of gold nanoparticles (AuNPs). The different combining capacity of heavy metal ions to modifiers results in the different broadening and red-shifting of the plasmon peak of modified AuNPs. In addition, Cr(VI), Cu²⁺, Co²⁺, Ni²⁺, and Mn²⁺ cause the new UV–vis absorption peaks in the region of 360–460 nm. The interactions between the modifiers and AuNPs, and between the modifiers and Mⁿ⁺, are investigated by using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results confirm that AuNPs are modified by CTAB and dithizone products through electrostatic interactions and Au–S bonds, respectively, and the Mⁿ⁺–N bonds form between Mⁿ⁺ and dithizone products. Furthermore, the experimental and density functional theory calculated IR spectra prove that dithizone reacts with NaOH to produce C₆H₅O– and [SCH₂N₄]²⁻. The validation of this method is carried out by analysis of heavy metal ions in tap water.
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