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

Abstract 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 NO 2 detection. HC‐NSs, synthesized via a one‐step hydrothermal process, possess a conjugated sp 2 ‐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 NO 2 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 sp 2 carbon network, which promote efficient NO 2 adsorption and charge transfer.