Design of bifunctional nitrogen-doped biochar with adsorption and catalytic oxidation capabilities for enhanced toluene emission control

Volatile organic compounds (VOCs), such as toluene, are hazardous air pollutants that pose significant health and environmental risks. This study addresses remediation of toluene by developing a bifunctional nitrogen-doped biochar (NDB) activated with sodium hydroxide (NaOH), aimed at reducing toluene emissions through both adsorption and catalytic oxidation. A series of NDB samples were prepared via NaOH activation and pyrolysis at varying temperatures to optimize their adsorption capacity and catalytic performance. The results demonstrated that NaOH-activated NDB exhibits substantial mesopore volumes and excellent surface area, with adsorption performance highly dependent on surface area and catalytic performance strongly influenced by nitrogen species. The dynamic adsorption tests revealed that BUN-900 achieved an outstanding toluene adsorption capacity of 422.25 mg/g, attributed to its high specific surface area of 1321.72 m²/g. In contrast, BU-800 showed complete toluene conversion at 450 °C via catalytic oxidation, attributed to the presence of pyridinic-N species. Interestingly, while the sample with the best adsorption performance had the lowest catalytic oxidation performance, the sample with the best catalytic performance exhibited the lowest adsorption capacity. This study demonstrates that NaOH activation and nitrogen doping can significantly enhance the bifunctional properties of biochar, positioning it as a promising, sustainable material for VOC control through combined adsorption and catalytic oxidation.