Nickel-Modified Fly-Ash Zeolite: Structural, Morphological, and Gas Sensing Properties

Abstract

This work reports the synthesis, structural characterization, and gas sensing properties of fly-ash-derived Ni-exchanged zeolite. Fly ash, a waste byproduct rich in silica and alumina, was converted into zeolite using an alkaline hydrothermal method and subsequently subjected to nickel ion exchange with Ni(NO₃)₂ solution. The resulting material was calcined to stabilize the Ni active sites. Structural confirmation was carried out using X-ray diffraction (XRD), which revealed well-defined crystalline reflections indicative of zeolite formation and successful Ni incorporation. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of characteristic T–O–T framework vibrations, hydroxyl groups, and sodalite cage linkages, with minor shifts attributed to Ni substitution. Scanning electron microscopy (SEM) revealed agglomerated nanocrystallites with porous morphology, beneficial for enhanced surface activity. Gas sensing studies demonstrated improved sensitivity, selectivity, and faster response–recovery behaviour of Ni-exchanged zeolite compared to the parent Na-zeolite, highlighting the role of nickel in promoting adsorption and charge transfer interactions. The study establishes a cost-effective and eco-friendly approach for converting fly ash into high-value functional materials with promising potential in environmental monitoring and industrial gas sensing.