Defect-engineered Ti–Zn–Fe mixed metal oxide nanospheres for efficient NH₃ detection

Ti-based nanospheres (Ti#0Zn, Ti#2Zn, Ti#4Zn, Ti#2Zn4Fe, and Ti#4Zn4Fe) were synthesized via a facile sol–gel method with the aim of enhancing NH₃ gas sensing performance through defect engineering and co-doping strategy. Structural, morphological, and optical properties were examined using XRD, SEM, TEM, FTIR, UV–Vis, PL, Raman, XPS, and BET analyses. The results confirmed phase-pure anatase TiO₂ with reduced crystallite size, increased defect density, and enhanced surface area and porosity upon Zn and Fe incorporation. Gas sensing performance was assessed from 25 to 200 °C. The pristine Ti#0Zn exhibited the lowest response due to limited surface activity. Zn doping improved sensing behaviour by increasing oxygen vacancies and facilitating charge transport, while Fe functionalization further enhanced catalytic activity and surface reactivity. Among all samples, Ti#4Zn4Fe exhibited the highest response of 75.5% at 150 °C toward 100 ppm NH₃. The enhanced performance is attributed to synergistic effects of defect engineering, improved charge transport, and catalytic activation, promoting effective NH₃ chemisorption and interaction with reactive oxygen species. These findings establish 150 °C as the optimal operating temperature and demonstrate that Zn–Fe co-doping is an effective strategy for developing high-performance, low-temperature NH₃ gas sensors for environmental and industrial applications.