Synthesis and Formation Mechanism of Limestone-Derived Porous Rod Hierarchical Ca-based Metal-Organic Framework for Efficient CO₂ Capture

Limestone is a relatively abundant and low-cost material used for producing calcium oxide as a CO₂ adsorbent. However, the CO₂ capture capacity of limestone decreases rapidly after multiple carbonation/calcination cycles. To improve the CO₂ capture performance, we developed a process using limestone to transform the material into a rod Ca-based metal-organic framework (Ca-MOF) via a hydrothermal process with the assistance of acetic acid and terephthalic acid (H₂BDC). The structural formation of rod Ca-MOF may result from the (200) face-oriented attachment growth of Ca-MOF sheets. Upon heat treatment, a highly stable porous rod network with a calcined Ca-MOF-O structure was generated with a pore distribution of 50-100 nm, which allowed the rapid diffusion of CO₂ into the interior of the sorbent and enhanced the CO₂ capture capacity with high multiple carbonation-calcination cycle stability compared to limestone alone at the intermediate temperature of 450 °C. The CO₂ capture capacity of the calcined porous Ca-MOF-O network reached 52 wt% with a CO₂ capture stability of 80% after 10 cycles. The above results demonstrated that rod Ca-MOF can be synthesized from a limestone precursor to form a porous network structure as a CO₂ capture sorbent to improve CO₂ capture performance at an intermediate temperature, thus suggesting its potential in environmental applications.