CO<sub>2</sub> capture performances of H<sub>3</sub>PO<sub>4</sub>/KOH activated microwave pyrolyzed porous biochar
Tianhao Qiu, Weitao Cao, Kaihan Xie, Faizan Ahmad, Wenke Zhao, Ehab M. Mostafa, Yaning Zhang
Abstract
As global climate change intensifies, carbon dioxide emissions have become a significant threat to ecological security and sustainable development. This study introduces a novel microwave-assisted two-step activation strategy (preliminary H<sub>3</sub>PO<sub>4</sub> activation and KOH etching), to prepare hierarchically porous biochar from corn straw with optimized CO<sub>2</sub> adsorption capacity. The investigation focused on the influence of the H<sub>3</sub>PO<sub>4</sub>-to-biomass impregnation ratio on the performance of the biochar. The results indicate that sample PKBC-3, synthesized at an impregnation ratio of 3:1, exhibits a specific surface area as high as 3,038.92 m<sup>2</sup>/g and a micropore volume of 1.089 cm<sup>3</sup>/g. Under conditions of 25 °C and 1 bar, PKBC-3 achieves a maximum CO<sub>2</sub> adsorption capacity of 3.434 mmol/g. Crucially, dynamic adsorption experiments (15% CO<sub>2</sub>, 100 mL/min) confirm that the 42.4% proportion of mesopore volume significantly enhances adsorption kinetics, resulting in a dynamic adsorption capacity of 3.02 mmol/g. Furthermore, the findings reveal that a low mesopore proportion (< 30%) can moderately retain adsorption capacity while restricting kinetics. Conversely, an excessive mesopore proportion (> 50%) may lead to micropore collapse, thereby reducing adsorption capacity. This research provides valuable insights for the design of biomass-derived adsorbents, aiming to achieve an optimal balance between high capacity and rapid kinetics through precise control of mesopore proportions.