Dual sensing of copper ion and chromium (VI) oxyanions by benzotriazole functionalized UiO-66 metal-organic framework in aqueous media

A new dual chemosensor UiO-66-NH-BT (BT=1-methylenebenzotriazole) based on the UiO-66 (University of Oslo) framework, containing benzotriazole functionalized dicarboxylate struts was synthesized and characterized. This isoreticular Metal-Organic Framework (MOF) was found to be a very selective and ultrasensitive for copper ion and chromium oxyanions in aqueous media. It showed a detection limit of 16.9 ppb (0.266 μM) for Cu²⁺ ion, 280 ppb (1.3 μM) for Cr₂O₇ ²⁻ and 47.7 ppb (0.411 μM) for CrO₄ ²⁻ anions. The quenching constants (K_sv) for Cu²⁺, Cr₂O₇ ²⁻, CrO₄ ²⁻ was found to be 1.1x10⁵ M⁻¹, 3.9x10³ M⁻¹, and 6.7x10³ M⁻¹ respectively. The covalently bonded benzotriazole moiety with the UiO-66 framework not only produces an emission peak at 491 nm but also act as an intrinsic binding site for both cations and anions. The nature of the coordinative interaction between the analytes and the UiO-66-NH-BT has also been elaborated with the help of ICP and FTIR. This chemosensor also demonstrated a regenerative property without the loss in performance for five consecutive cycles.