Direct air capture of CO₂ using biochar prepared from sewage sludge: Adsorption capacity and kinetics

As an emerging carbon-negative emission technology, carbon dioxide (CO₂) capture from the air is an essential safeguard for alleviating global warming. Sludge-activated carbon with excellent mesoporous structure is a potential material for CO₂ capture. In this paper, the amino modified sewage sludge materials were used to prepare the porous CO₂ adsorbent from air. The effect of preparation conditions on the microstructure of sewage sludge-based activated carbon materials was analyzed by microstructural characterization, and the impacts of activator, pyrolysis temperature, and the concentration of modifier on the CO₂ adsorption performance of sewage sludge-based activated carbon materials were also systematically investigated. The results show that the pyrolysis temperature, the type of activator and the modifier concentration significantly affect the adsorption performance of sewage sludge-based CO₂ adsorption materials. Among them, the sewage sludge-based CO₂ adsorption material prepared with solid NaOH as an activator, with an activation temperature of 600 °C and loading concentration of 20 %, exhibited the best performance, that is the CO₂ adsorption capacity reached 1.17 mmol/g, and the half time is about four min, which shows better performance, compared with other adsorbents for CO₂ capture from air. The research results can reduce CO₂ emissions on the one hand, and on the other hand, realize the resourceful utilization of sewage sludge, which sheds light on "treating the wastes with wastes".