Design and structuring of activated sludge-based adsorbents for the direct air capture of carbon dioxide

The preparation of activated carbon derived from municipal sludge and amino modification for CO₂ adsorption can not only achieve the resource utilization of sludge but also address the issue of CO₂ emission reduction. Municipal sludge was used in this study as a raw material to prepare CO₂ adsorbents via pyrolysis, activation, and amino modification. Microstructural characterization and CO₂ performance tests were conducted to analyze the influence of different activation agents, pyrolysis temperature, and pyrolysis time on the microstructural evolution and CO₂ adsorption performance of sludge-based activated carbon. The results indicate that the solid NaOH activator enabled the sludge to generate more pore structures. When the pyrolysis temperature was 600°C and the pyrolysis time was 60 min, an excellent pore structure was obtained. Nevertheless, an excessively high pyrolysis temperature and time would cause sintering of the samples, leading to pore collapse. Under the aforementioned preparation conditions, the sludge-activated carbon reached its maximum CO₂ adsorption capacity, with the maximum adsorption capacity of CO₂ being 1.369 mmol/g. The adsorption temperature had a significant influence on the final adsorption effect, and the optimal adsorption temperature is 25°C.