Efficient microwave synthesis of biochar from industrial hemp stalk for room-temperature ppb-level NO2 sensors

This study presents an energy-efficient microwave carbonization method to produce industrial hemp stalk biochar at 600 ℃ (IHSC-600) for ppb-level NO 2 detection at room temperature. Compared to conventional carbonization, microwave-assisted carbonization uses a unique inside-out heating mechanism which enables rapid synthesis of carbon materials. The resulting IHSC-600 exhibits abundant hierarchical porous structures and oxygen vacancies (O v ), a large specific surface area, trace K and Ca doping and defective carbon atoms. In addition, O 2 -TPD analysis confirms the presence of highly reactive oxygen species (O⁻, O 2 ⁻) on the surface, which facilitate gas adsorption and charge transfer. The sensor achieves an enhanced response to ppb levels of NO 2 in 60% Relative Humidity (RH) with a theoretical detection limit as low as 43 ppb. This work provides an efficient route to produce high-performance biomass-derived carbon materials for gas sensing applications.