ZnO as an efficient nucleating agent and morphology template for rapid, facile and scalable synthesis of MOF-46 and ZnO@MOF-46 with selective sensing properties and enhanced photocatalytic ability

Abstract

MOF-46 and a novel core–shell heterostructure containing ZnO@MOF-46 rods have been successfully synthesized via a simple, versatile and economic method. The products have been characterized by X-ray diffraction (XRD), FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Time and solvent effects on the growth process of ZnO@MOF-46 were investigated. Luminescent properties of the activated sample showed distinct solvent-dependent photoluminescence emissions. The product also demonstrated unique sensing properties in the detection of aromatic compounds via a fluorescence quenching and enhancing mechanism. Aromatic compounds with electron-withdrawing substituents such as nitro act as fluorescence quenchers for ZnO@MOF-46 and aromatic compounds with electron-donating substituents such as CH₃ were found to enhance the ZnO@MOF-46 fluorescence. The ZnO@MOF-46 showed excellent photodegradation of methylene blue. The degradation rates in the presence of various scavengers including benzoquinone, isopropyl alcohol and ammonium oxalate (O₂˙⁻, OH˙ and h⁺ scavengers, respectively) were studied and the results showed that all of the species (O₂˙⁻, OH˙ and h⁺) contribute to degradation but OH˙ is the main active species which plays a major role in this system and hence photocatalyst degradation was supposed to have a radical mechanism. Band structure parameters of ZnO@MOF-46 were determined using cyclic voltammetry and DRUV/VIS spectroscopy and the mechanism of photodegradation was then discussed.