Synergetic crystal phases of SnO₂/NiO heterostructure in an interconnected morphology for chemiresistive formaldehyde sensors

A SnO2/NiO heterostructure that is comprised of SnO2 and NiO nanoparticles was designed and demonstrated an extremely high sensing response toward formaldehyde detection. A facile one-step blending process with a low operating temperature of 80 degrees C enables an interconnected morphology for the SnO2/NiO heterostructure. Two particles were created in the morphology by encouraging the formation of crystal phases in each other, the synergetic crystal phases of the SnO2/NiO heterostructure were generated with excellent crystallinity and high crystallite size and chemically constructed. The synergetic crystalline morphology facilitates adsorbed oxygen species on the SnO2/NiO heterostructure to have effective chemical interaction with formaldehyde gas molecules in terms of not only surface and internal crystal structure but also electronic band structure. It thereby leads to an extremely high sensing response with a record value of 9121.74 in the detection of formaldehyde with a 10 ppm concentration. With the overwhelming response, the SnO2/NiO heterostructure-based sensor device showed a transient response time within 3 s, a significant stable result in repeatability including reproducibility with ca. 2% loss in the gas ON-OFF level in the 50 cycles, long-term stability for 12 days, and ultra-exclusive selectivity result. Our work suggests a realization method to develop SnO2/NiO heterostructure-based chemiresistive sensor with a superior sensing response, and thus it will be a leading research outcome in both communities of formaldehyde gas sensors and SnOx-based sensor devices.