Insect-derived biochar for CO₂ adsorption under humid conditions: Elucidating adsorption mechanisms and competitive...

The CO₂ adsorption capacity of biochar depends on the type of biomass used and its physicochemical properties; various sorption parameters including temperature, CO₂ concentration, and humidity affect the CO₂ adsorption capacity. Biochar derived from defatted black soldier fly larvae (BSFL) biomass was investigated for direct CO₂ capture and exhibited a hydrophilic/mesoporous structure that contained high concentrations of alkali and alkaline metals (>10 wt%), which contribute to CO₂ chemisorption. The CO₂ adsorption efficiency was higher at 25 °C compared with that at 30 °C and 35 °C, probably due to reduced Brownian motion of CO₂ molecules at lower temperatures. The adsorption process followed the Langmuir isotherm, suggesting monolayer adsorption. Kinetic modeling indicated that physical and chemical adsorption mechanisms were involved; physisorption predominated. The presence of water molecules resulted in competitive adsorption with CO₂, with 2.5 water molecules competing for adsorption sites at 70 % relative humidity and 1200 ppm CO₂. In the cyclic adsorption-desorption tests, the CO₂ adsorption capacity decreased by approximately 11 % after the first cycle, probably because a portion of the chemically adsorbed CO₂ did not fully desorb during regeneration. The findings of this study could aid in the development of more efficient biochar-based materials for CO₂ capture.