Highly sensitive formaldehyde gas sensors based on SnO ₂-ZnO nanocomposites

A highly sensitive formaldehyde (HCHO) gas sensor was fabricated from SnO ₂-ZnO nanocomposite by sol-gel method on the microelectromechanical system (MEMS) gas sensor platform. SnO ₂-ZnO composites with different chemical compositions were synthesized and Pd nanoparticles were mixed with the nanocomposites as a catalytic material. The composites were characterized by structural analyses using X-ray diffraction, DSC-TGA, and SEM observation. The SnO ₂-ZnO nanocomposite system demonstrated high gas sensitivity to HCHO and the Pd nanoparticles served as an excellent support material that further enhanced the selective gas adsorption. In particular, the 1 wt% Pd-mixed SZ3 sensor displayed good HCHO sensitivity (R _S = R _g/R _a, R _S = 0.02 at 550 °C), response and recovery times (15 sec and 20 sec). Our synthesis method provided an inexpensive and flexible, wet-chemical route capable of tailoring semiconductor metal oxide nanocomposites for the selective and reproducible detection of HCHO gas at parts per billion levels.