Optimizing ZIF-8 membrane growth on top of semiconductive Ga-doped ZnO sensitive layers†

Abstract

Functionalizing ZnO-based chemiresistive sensor surfaces with a ZIF-8 layer, which acts as a permselective membrane, is a well-established strategy to enhance sensor selectivity. This study examines the key factors influencing the conversion process, including the physicochemical properties of solvents or solvent mixtures and the thermal pretreatment, of Ga-doped ZnO (ZnO : Ga). We have evidenced that the polarity, viscosity, and interfacial tension of the solvent significantly affect the dissolution of ZnO : Ga and the crystallization of ZIF-8. Methanol–water mixtures were found to effectively control the conversion process, with a 3 : 1 MeOH/H₂O ratio being optimal for producing continuous ZIF-8 membranes. Additionally, it has been demonstrated that annealing can greatly enhance the reactivity of the oxide. However, while it enhances the dissolution of ZnO : Ga, excessively high temperatures can lead to over-dissolution, which hinders ZIF-8 formation. These insights are crucial for optimizing ZIF-8 layers on ZnO : Ga, paving the way for the development of highly selective chemiresistive sensors.