Hydrothermal Carbonaceous Nanospheres as Emerging Candidates for High-Performance Chemi-Resistive NO₂ Gas Sensing

Chemiresistive gas sensors have garnered increasing attention due to their critical role in environmental monitoring, industrial safety, and public health. Recently, metal-free carbon-based polymeric semiconductors have emerged as promising, offering advantages in processability, stability, and functional tunability. Building on this approach, hydrothermal carbonaceous nanospheres (HC-NSs) are designed as a new class of high-performance sensing materials for NO₂ detection. HC-NSs, synthesized via a one-step hydrothermal process, possess a conjugated sp²-hybridized carbon backbone decorated with oxygen-rich functional groups and exhibit a high specific surface area and mesoporous structure, offering abundant active sites and efficient gas diffusion pathways for enhanced sensing performance. These features endow the material with p-type semiconducting behavior and high surface reactivity, resulting in an impressive gas response of -74.4% toward 50 ppm NO₂ and a low detection limit of 80.6 ppb. Comparative analysis with benchmark tellurium nanowires highlights the superior sensitivity, selectivity, and environmental robustness of HC-NSs. The nanospheres maintain consistent sensing performance under wide-ranging humidity (20-80% RH) and elevated temperatures (up to 200 °C), demonstrating their resilience and reliability in diverse operating environments. The enhanced performance is attributed to the synergistic effects of oxygenated surface groups and sp² carbon network, which promote efficient NO₂ adsorption and charge transfer.