Zn₂TiO₄–WO₃ nanocomposite thick-film sensors: Influence of WO₃ content on NH₃ gas sensing response and selectivity

Zn₂TiO₄–WO₃ nanocomposites with varying WO₃ contents (1, 3, 5, 7, 9, and 11 wt%) were synthesized via a hydrothermal route and explored for NH₃ gas sensing applications. The structural, morphological, compositional, and sensing properties were systematically investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), elemental mapping, Fourier transform infrared spectroscopy (FTIR), and electrical measurements. XRD analysis confirmed the coexistence of crystalline Zn₂TiO₄ and WO₃ phases without any detectable impurity phases, with crystallite size increasing from 29.4 nm to a maximum of 36.1 nm for the 9 wt% WO₃ composition FE-SEM results, supported by quantitative image analysis, revealed that WO₃ incorporation significantly influences surface morphology and particle distribution, with the 9 wt% composition exhibiting the highest surface porosity (∼40%) and grain density, leading to enhanced surface activity. EDS and elemental mapping confirmed uniform distribution of Zn, Ti, W, and O elements throughout the composite matrix. Gas sensing studies showed that the 9 wt% Zn₂TiO₄–WO₃ composition exhibits the best response toward NH₃, reaching a maximum response of ∼91% at 90 °C and at 400 ppm concentration. The sensor also demonstrates fast response and recovery times of ∼35 s and ∼30 s, respectively, indicating efficient surface adsorption and desorption processes. In addition, excellent selectivity toward NH₃ was observed, with a response of 91.2% compared to 23.7%, 17.3%, 13.7%, and 8.2% for NO₂, CO₂, LPG, and ethanol, respectively, together with good reproducibility and long-term stability retaining ∼98% of the initial response after 42 days. The enhanced sensing performance is attributed to optimized WO₃ loading, improved surface morphology, and synergistic interaction between Zn₂TiO₄ and WO₃ phases, which collectively facilitate effective gas adsorption and charge transport modulation. These results suggest that Zn₂TiO₄–WO₃ nanocomposites are promising candidates for low-temperature NH₃ sensing and environmental monitoring applications.