Insights into the microstructure evolution and CO2 adsorption of activated carbon derived from spent coffee grounds and sewage sludge

Based on the suitability of the raw materials and treatment processes as well as the structural differences and complementarities of activated carbon prepared from coffee grounds (CG) and sludge, this study proposed a strategy to blend various sludge with the higher (50.91%) and lower (34.19%) ash contents into CG to prepare porous activated carbon for CO2 adsorption. Compared with sludge with higher ash content (HS), the activated carbon prepared from sludge with lower ash content (LS) had superior defect degree and carbon skeleton stability. Moreover, the activated carbon (CLSAC-20) derived from LS blended into coffee grounds under a ratio of 20% continued to optimize the structure of that from coffee grounds (CAC), which is mainly microporous. This was attributed to the LS exhibiting the structure-oriented role, which increased the pore volume (from 0.664 to 0.766 cm(3)/g) and specific surface area (from 1217.84 to 1355.65 m(2)/g). Because of the structural improvement achieved by LS blending, the CLSAC-20 had a better CO2 adsorption capacity (3.75 mmol/g) than CAC (3.27 mmol/g). Both were superior to commercial activated carbon (2.6 mmol/g) and the adsorption efficiencies still maintained above 90% after 5 cycles of regeneration. In summary, this study developed a simple, efficient, and environmentally friendly strategy to convert organic solid waste into high-value-added CO2 adsorbent.