Optimized H3PO4 activation of Nypa fruticans roots for high-performance activated carbon: Structural control and enhanced iodine adsorption

This study explores the sustainable transformation of Nypa fruticans roots (NFR) into high-performance activated carbon (AC) through optimized physical and chemical activation, addressing both biomass waste management and the demand for eco-friendly adsorbents. Collected from Bangladesh's Sundarbans mangrove forest, NFR was processed via pyrolysis (600 °C) and H 3 PO 4 activation (1.0–2.0 impregnation ratios) to produce four AC variants (N1–N4). Comprehensive characterization revealed N3 as the standout material, exhibiting exceptional microporosity (BET surface area: 680 m 2 /g), high fixed carbon (51.2 %), and superior iodine adsorption (1050 mg/g, Langmuir q max ). FTIR and XRD analyses correlated N3's performance with its graphitic C=C bonds (1600–1650 cm −1 ) and balanced oxygen groups, while FESEM confirmed a honeycomb pore structure. In contrast, N2's lower capacity (920 mg/g) was attributed to pore blockage from higher ash (12.5 %) and oxygen content (13 %). Iodine isotherm studies validated Langmuir monolayer dominance (R 2 > 0.98) and Freundlich heterogeneity (1/n = 0.58–0.65), with N3's optimal pore distribution making it ideal for gas purification, whereas N1/N4 (752–702 mg/g) suited water treatment. TGA highlighted N3's thermal stability, with lignin-derived carbonization above 400 °C yielding 19.8 % ash. Economically, NFR's abundance and the method's scalability underscore its potential for low-cost, renewable AC production. This work not only advances mangrove biomass valorization but also provides a blueprint for tailoring AC properties via activation protocols, bridging ecological conservation with material science innovation. Future research should explore pilot-scale production and application-specific modifications to optimize real-world performance.