Defect engineered Co-doped SnO₂ thin films for highly sensitive NH₃ detection: a combined DFT and experimental study

This study presents an examination of the development of high-performance Co-doped SnO₂ nanocolloidal thin films, which are designed for the highly sensitive and selective detection of NH₃. By integrating precise sol-gel synthesis with first-principles Density Functional Theory (DFT), we elucidate the importance of defect engineering in modulating gas surface interactions. The XRD analysis confirmed the tetragonal rutile phase of SnO₂, revealing that the 2% Co-doped SnO₂ exhibits a significantly reduced crystallite size of 4.88 nm. Furthermore, XPS and PL characterization indicated an increase in surface Ov and O_C, while UV-vis results demonstrated band gap narrowing due to doping. The DFT calculations suggested that 2% Co-doping introduces mid-gap 3d states, which enhance electronic sensitization. In comparison to the relatively inert pristine SnO₂, the 2% Co-doped variant shows a remarkable 153.54% increase in conductivity upon NH₃ adsorption, achieving a selectivity ratio of 31.0 relative to H₂. Additionally, kinetic analysis revealed that the addition of Co improves sensor reversibility by lowering the NH₃ desorption barrier. The combination of reduced crystallite size, defect-rich surface chemistry, and optimized electronic pathways positions 2% Co-doped SnO₂ as an outstanding candidate for highly sensitive NH₃ detection.