T erminalia catappa shell-based activated carbon: N 2 activation strategically enhanced hierarchical porosity for CO 2 capture and dye removal applications

In the present work, we used an eco-friendly, simple, and selective nitrogen (N 2 ) activation strategy for the preparation of hierarchical porous activated carbon (HPAC) derived from abundant and low-cost Terminalia catappa shell (TCS) agro-waste. The effect of N 2 activation strategy compared to air activation is studied where the N 2 activated carbon (HPAC) showed enhancement in the specific surface area (SSA) (616.04 m 2 g −1 ) as compared to air activated carbon (HPC) which showed 243.97 m 2 g −1 . Both activated carbons were further explored for CO 2 capture studies and showed a relatively high capacity (2.73 mmol g −1 ) for HPAC than HPC (1.70 mmol g −1 ) at 288 K. The low N 2 capture capacity (0.22 mmol g −1 ) of HPAC suggests its selectivity toward CO 2 (41.80 at 288 K) is useful for gas separation. Obtained HPAC was successfully applied for adsorption removal of methyl orange (MO) dye with detailed kinetics studies resulting in 99.50% removal efficiency. The optimized adsorption conditions were further used for adsorption removal studies of methylene blue (MB), malachite green (MG), and bromophenol blue (BPB) with 75.30, 82.88, and 52.40% removal efficiency respectively. The superior CO 2 capture and potential dye removal property of obtained HPAC suggests its applicability in environmental remediation. Graphical abstract