Urea-Assisted One-Step Pyrolytic Synthesis of Macroporous Carbon Aerogel/MgO Composites for Rapid Phosphate Recovery

Addressing global phosphorus scarcity and eutrophication, MgO-based adsorbents face challenges of slow kinetics and low active-site utilization. In this study, a waste biomass-derived carbon aerogel (CA) was used as a support for a one-step pyrolysis method, simultaneously constructing a porous structure and achieving high-dispersion MgO loading. Results showed a maximum adsorption capacity of 399.8 mg P/g. Kinetic studies indicated 165.4 mg P/g adsorbed within 5 min, with 90% saturation achieved within 40 min. The Pseudo-second-order kinetic constants increased 11-fold compared to commercial MgO. By integrating experiments, machine learning (ML), and density functional theory (DFT), a multiscale investigation revealed the synergistic effect between MgO and the carbon aerogel support. It was demonstrated that the rapid adsorption kinetics originated from the macroporous structure of the support rather than a high specific surface area. Furthermore, urea participation during pyrolysis modulated the pyridinic-N content of the CA, thereby modifying the pH adaptability of the material. Collectively, this study provides a foundation for reusing waste biochar and designing high-performance phosphate adsorbents.