Coordination polymer-derived nano-sized zinc ferrite with excellent performance in nitro-explosive detection

Abstract

Herein, a mixed metal coordination polymer, {(H₂pip)[Zn_1/3Fe_2/3(pydc-2,5)₂(H₂O)]·2H₂O} 1 {where H₂pip = piperazinediium and pydc-2,5 = pyridine-2,5-dicarboxylate}, was successfully synthesized using a hydrothermal technique. To confirm the structure and phase purity of 1, single crystals of an isomorphous pure Fe compound, {(H₂pip)[Fe(pydc-2,5)₂(H₂O)]·2H₂O} 1a, were synthesized based on similar synthetic conditions. Single crystal X-ray data of 1a confirmed the one-dimensional anionic metal–organic coordination polymer hydrogen bonded with protonated piprazine (piperazinediium) and lattice water molecules. The phase purity of 1 and 1a were confirmed via powder X-ray diffraction. Compound 1 was systematically characterized using IR, TGA, SEM, and EDX elemental mapping analysis. Compound 1 was used as a single source precursor for the preparation of nano-sized ZnFe₂O₄via thermal decomposition. The as-obtained ZnFe₂O₄ was fully characterized using PXRD, SEM, TEM, and EDX elemental mapping analysis. It was found that ZnFe₂O₄ was formed in its pure form with particle size in the nano-dimension. The aqueous dispersion of nano-sized ZnFe₂O₄ exhibits a strong emission at 402 nm upon excitation at 310 nm. This emissive property was employed for luminescence-based detection of nitroaromatic explosives in an aqueous medium through luminescence quenching for the first time. Importantly, selective detections have been observed for phenolic nitroaromatics based on differential luminescence quenching behaviour along with a detection limit of 57 ppb for 2,4,6-trinitrophenol (TNP) in water.