Detection of Pesticides in Aqueous Medium and in Fruit Extracts Using a Three-Dimensional Metal-Organic Framework: Experimental and Computational Study.

A new, three-dimensional cadmium based metal-organic framework [Cd ₃ (PDA) ₁ (tz) ₃ Cl(H ₂ O) ₄ ]·3H ₂ O {PDA = 1,4-phenylenediacetate and tz = 1,2,4-triazolate}, 1, has been successfully synthesized using slow diffusion method at room temperature. The structure of compound 1 has been determined using single crystal X-ray diffraction. The triazolate ligands connect three different types of octahedral Cd ²⁺ ions to form a two-dimensional structure. The chloride ion and PDA ligands connect the two-dimensional layers to form a three-dimensional structure. The phase purity of 1 was confirmed by powder X-ray diffraction, thermogravimetric analysis, and IR spectroscopy. Aqueous dispersion of compound 1 gives intense luminescence emission at 290 nm upon excitation at 225 nm. This emission was used for the luminescence based detection of pesticides, especially azinphos-methyl, chlorpyrifos, and parathion in aqueous medium. The selectivity of pesticide detection remains unaltered even in the presence of surfactant molecules. The mechanisms of luminescence quenching were successfully explained by the combination of absorption of excitation light, resonance energy transfer, and the possibility of electron transfer. Experimental findings are also well supported by the density functional theory calculations. Selectivity of pesticides detection in real samples such as apple and tomato juice has also been observed.