Tannic Acid for Simple and Highly Selective Visual Detection of Iron (II) and (III) Ions from Different Aqueous Environments
2021
Yıldız, Mustafa | Sahiner, Nurettin
Tannic acid (TA) was employed as a novel colorimetric iron ion sensor. TA showed highly selective recognition for only Fe²⁺ and Fe³⁺ among a range of tested metal ions such as Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Hg²⁺, and Pb²⁺. In the presence of these metal cation solutions, only Fe²⁺ and Fe³⁺ solutions underwent impressive color change detectable with the naked eye from colorless to purple and gray, respectively. Surprisingly, TA behaves as a highly selective sensor upon chemical oxidation of iron (Fe²⁺ and Fe³⁺) cations. In addition, various sensor applications of TA were performed. For this, TA-impregnated silica gel, alumina oxide sheet, and filter paper were used. Each test strip showed very high selectivity for iron ions. The detection limit of the sensor for Fe²⁺ and Fe³⁺ was found to be 1.0 × 10⁻⁶ M, and the association constant Kₐ was determined as 4.05 × 10⁴ M⁻¹ and 1.80 × 10⁷ M⁻¹. The order of ion binding power was determined to be Fe³⁺ > Fe²⁺ by UV-Vis spectroscopy. These discernable color changes due to the complexion of TA with Fe²⁺ and Fe³⁺ demonstrated the utilization of TA to selectively detect these metal cations. The use of tannic acid as a complexing agent that can detect Fe (II) and Fe (III) metal ions in environmental waters by colorimetry and spectrophotometry.
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