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The development of NO 2 gas sensors with lower operating temperature and good thermal stability is always a challenge to solve. In this work, 2D loose porous ZnO/GaN heterogeneous nanosheets were synthesized by ultrasonic mixing, in which ZnO nanosheets and GaN nanoparticles were prepared by hydrothermal method and solid-state pyrolysis, respectively. BET characterization result showed that the specific surface area of loose porous ZnO nanosheets was 57.24 m2/g, and XPS tests proved that the formation of heterogeneous interface between ZnO and GaN can effectively increase the number of negative oxygen ion species on the surface. Noticeably, 15 mol % ZnO/GaN composites (Ga:Zn) exhibited the highest response of 134.5–2 ppm of NO 2 at 125 °C and lower limit of detection of 20 ppb. Furthermore, it showed outstanding selectivity, repeatability and long-term stability. The excellent gas-sensing properties can be attributed to the loose porous structure of ZnO and the formation of n-n heterojunction between ZnO and GaN. The gas-sensing mechanism of ZnO/GaN composites to NO 2 was also discussed in detail. • ZnO nanosheets and GaN nanoparticles were prepared by hydrothermal method and solid-state pyrolysis, respectively. • 2D loose porous ZnO/GaN heterogeneous nanosheets were synthesized by ultrasonic mixing. • The loose porous structure of ZnO and the formation of n-n heterojunction between ZnO and GaN improve the response. • The sensor operated at a lower temperature of 125 ℃ and the response to 20 ppb of NO 2 gas can reach 19.6. [ABSTRACT FROM AUTHOR]

The effective detection of ppb-level NO 2 is of great significance to the natural environment and human health. In this work, a series of In 2 O 3 nanoparticles modified peach kernel-like GaN for NO 2 detection was synthesized by a concise two-step method. The gas-sensing results showed that 10 mol% In 2 O 3 -decorated GaN (In: Ga) exhibited a response as high as 1070.9–1 ppm NO 2 at the working temperature of 100 ℃, as well as a low limit of detection (1 ppb). Furthermore, the sensor also possessed excellent selectivity, repeatability and fast response-recovery speed. The outstanding sensing performance was contributed to the rough and porous microstructure of GaN, abundant negative oxygen ion species originating from In 2 O 3 , and the heterojunction effect between GaN and In 2 O 3. The sensor proposed herein provide a useful reference for reliable detection of ppb-level NO 2 gas. • In 2 O 3 nanoparticles modified peach kernel-like GaN was synthesized by a concise two-step method. • In 2 O 3 nanoparticles greatly increased the adsorbed oxygen species on the surface of GaN. • The response of GaN/In 2 O 3 composites can reach 1070.9–1 ppm NO 2 , and the limit of detection is 1 ppb. [ABSTRACT FROM AUTHOR]