Waste-derived CaO from green mussel shells as a highly stabilized and superior sorbent for cyclic CO2 capture

A citric acid-assisted sol-gel method was applied to synthesize green calcium oxide (CaO) sorbents from diverse natural waste (eggshells, crab shells, and green mussel shells for effective CO₂ capture). Among them, CaO-gms derived from green mussel shells displayed the most advantageous porous morphological structure with a coral-like finger structure and the largest BET surface area and pore volume for textural properties. These properties play a crucial role in the diffusion of CO₂ through the pores and surface layer to enhance the interaction of CO₂ and interior CaO particles, promoting the highest CO₂ capture capacity. CaO-gms demonstrates a remarkable CO₂ uptake of 0.69 g -CO₂/g-sorbent (or 0.75 g -CO₂/g -CaO) at 700 °C, with 15 vol% inlet CO₂ concentration and a total gas flow rate of 100 mL/min. The sorbent was investigated for its sintering resistance, as it has been a major issue for large-scale deployment of cyclic CO₂ capture technology. CaO-gms exhibited robust cyclic performance in carbonation/calcination reactions with no sign of crystallite agglomeration (XRD analysis), maintaining a CO₂ uptake of approximately 0.65 g -CO₂/g -sorbent (or 0.71 g -CO₂/g -CaO) after 20 cycles. The results highlight the excellent resistance of the sorbent to crystallite sintering during the carbonation/calcination reaction sequence.