Effect of CTAB on the Morphology of Sn-MOF and the Gas Sensing Performance of SnO₂ with Different Crystal Phases for H₂ Detection

Herein, a facile strategy was proposed to enhance the gas sensing performance of SnO₂ for H₂ by regulating its crystalline phase composition. Sn-based metal–organic framework (Sn-MOF) precursors with different morphologies were synthesized by introducing the surfactant cetyltrimethylammonium bromide (CTAB). Upon calcination, these precursors yielded either mixed-phase (orthorhombic and tetragonal, SnO₂-C) or single-phase (pure tetragonal, SnO₂-NC) SnO₂ nanoparticles. Structural characterization and gas sensing tests revealed that SnO₂-C exhibited a high response of 7.73 to 100 ppm H₂ at 280 °C, more than twice that of SnO₂-NC (3.75). Moreover, SnO₂-C demonstrated a faster response/recovery time (10/56 s), high selectivity, a ppb-level detection limit (~79 ppb), and excellent long-term stability. Notably, although the addition of CTAB reduced the specific surface area of SnO₂, the resulting lower surface area minimized oxygen exposure during calcination, facilitating the formation of a mixed-phase heterostructure. In addition, the calcination atmosphere of SnO₂-C (flowing air or Ar) was adjusted to further investigate the role of the crystal phase in gas sensing performance. The results clearly demonstrated that mixed-phase SnO₂ exhibited superior sensing performance, achieving a higher sensitivity and a faster response to H₂. These findings underscored the critical role of crystal phase engineering in the design of high-performance gas sensing materials.