Excellent adsorption and catalytic oxidation of toluene facilitated by metal-free nitrogen-doped mesoporous biochar

In this study, we synthesized a series of nitrogen-doped mesoporous biochar by a salt-templating method to assess the potential of our modified biochar for advanced remediation of toluene through either adsorption or catalytic oxidation. The principal findings indicated that the incorporation of nitrogen and the mesopore-forming agent significantly influenced the toluene removal performance by altering the physicochemical properties of the biochar. Notably, the sample synthesized at 900 °C (BUPZ-900) exhibited the exceptional toluene adsorption capacity, reaching 283.85 mg/g, due to its high surface area and mesopore volume. Advanced characterizations revealed that different nitrogen functionalities played distinct roles in the adsorption performance. The presence of graphitic nitrogen in BUPZ-900 enhanced toluene adsorption through π-π dispersion interactions. Conversely, BUPZ-600, boasting a high nitrogen content (8.66 at%) and a predominance of pyridinic-N (3.92 at%), exhibited the highest catalytic activity, despite its low adsorption capacity attributed to a smaller surface area. This heightened activity was attributed to the basicity of pyridinic-N, which acted as active sites, despite the material's lower surface area. Our study highlights the promise of nitrogen-doped mesoporous biochar as an effective adsorbent or catalyst for advanced remediation of volatile organic compounds (VOCs), even in the absence of metal catalysts. This work emphasizes the critical role of synthesis temperature and nitrogen functionalization in optimizing biochar properties for environmental applications.