Single-step pyrolytic synthesis of ultra-microporous ammonialized biochar for carbon dioxide capture.

Carbon dioxide (CO2) is a significant greenhouse gas that plays a pivotal role in driving global warming and climate change. Its primary sources stem from human activities, notably transportation, power generation, and industrial processes. Directly capturing CO2 emissions at their origins is widely recognized as a potent and efficient approach to reducing emissions. Biochar has emerged as a promising material for capturing CO2 owing to its stability, hydrophobic nature, ease of preparation, and economic advantages. Nevertheless, its ability to adsorb CO2 is constrained in environments with relatively low pressure (<1 bar). Consequently, modifying and refining biochar is a strategy to enhance its affinity for CO2. In this work, Leucaena leucocephala, a major invasive species in Asia, was selected as the biomass precursor, and a single synthesis process combining pyrolysis and ammonialization was employed to produce the ammonialized biochar (ABC). Among the synthesized biochars, ABC800 (produced at 800 °C) exhibits desirable surface properties with high surface area (SBET = 836.5 m2/g), microporosity (Smicro = 753.3 m2/g), and ultra-microporosity (Sultra-micro = 376.9 m2/g). In addition, ABC800 demonstrates superior CO2 adsorption capacity (4.06 mmol/g at 0 °C). Isothermal and kinetic results show that ABC800's CO2 adsorption follows the Langmuir-Freundlich and pseudo-second-order (PSO) equations, indicating both physical and chemical interactions. The correlation between adsorption performance, pore structure, and nitrogen content highlights the potential of ABC800 for CO2 capture, particularly at elevated temperatures. Overall, this work offers new insights into a potentially sustainable approach for mitigating greenhouse gas emissions.