Ga-Doped 3D Ordered Porous SnO2 for Enhanced Formaldehyde Sensing Performance

Pure and Ga-doped 3D ordered porous SnO2 (3DOPS) nanomaterials were synthesized by a simple template method, and SnO2 nanoparticles (NPs) were prepared by an annealing process. The presence of Ga in 3DOPS and the structure of 3DOPS were determined by X-ray powder diffraction (XRD), energy-dispersive spectroscopy (EDS), X-ray photoelectric spectroscopy (XPS), and scanning electron microscopy (SEM). The surface areas of the porous structure were measured by the BET method using a middle-high pressure physical gas adsorption instrument. Due to the porous structure and dopant effects on the SnO2 nanomaterials, 3 at % Ga-doped 3DOPS has the largest specific surface area (61.58 m2/g) compared with pure particle tin dioxide (38.60 m2/g). The 3 at % Ga-doped 3DOPS-based sensor exhibits a lower detection limit (2/0.1 ppm) and improved sensitivity (55/50 ppm) to formaldehyde (HCHO) at a low temperature (210 °C), and the response is 6.5 times higher than that of the pure SnO2 NP-based sensor (8.5/50 ppm). However, the response of pure 3DOPS (18/50 ppm) is only twice as high as that of the pure SnO2 NP-based sensor. In addition, the 3.0 at % Ga-doped level of the SnO2 sensor showed a fast response time (2 s) and excellent selectivity. The high sensitivity of SnO2 can be explained by the increase in the specific surface area and porosity brought by the 3D ordered porous structure, and the modified suface structure by precious metals.