Nitrogen-Doped Porous Biochar via Azotobacter chroococcum-Based Nitrogen Fixation for Improved Volatile Organic Compound Adsorption

Abstract

Nitrogen doping has been widely used to prepare porous carbon materials for the adsorption of volatile organic compounds (VOCs). However, in the current research, the nitrogen doping process is limited by the raw materials, and it is difficult to achieve simultaneous and precise synergistic regulation of the pore structure, doping quantity, and doping morphology. Inspired by the carbon–nitrogen cycle in nature, the symbiotic community of nitrogen-fixing microorganisms is an important functional group to regulate the elemental cycle. In this study, a novel biological nitrogen fixation incorporation doped method was proposed, i.e., Azotobacter chroococcum (A. chroococcum) is cultivated on the surface of the biochar and catalyzes the conversion of atmospheric nitrogen (N₂) to fixed nitrogen (NH⁴⁺) by nitrogen-fixing enzymes in the body of A. chroococcum, which leads to the formation of bionitrogen and thereby increases the total nitrogen content (0.99%) in the biochar material. The results showed that the content of pyrrole nitrogen in the material was 73.3% and that it possessed a larger specific surface area (1338.21 m²/g) and mesopore (0.499 cm³/g), which greatly improved its adsorption capacity (182.88 mg/g) for ethyl acetate. In addition, in order to elucidate the microscopic adsorption mechanism for enhanced adsorption performance, systematic theoretical calculations of adsorption amount, adsorption energy, and adsorption isotherm were carried out by molecular simulation. This study innovatively achieved green and safe regulation of biomass precursors by nitrogen-fixing bacteria without increasing the nitrogen source and provided a theoretical basis and technical methods to improve the quality and efficiency of the VOC adsorption materials.