Steam-activated carbon derived from nypa palm fronds (Nypa fruticans) for efficient adsorption of indigo carmine dye: Characterization, kinetics, isotherms, and thermodynamics

• Nypa palm fronds offer a low-cost and sustainable source for dye adsorbents • Steam activation yields micro–mesoporous carbon with iodine number 1063 mg/g • KAPN800 removes 99.75% of indigo carmine, outperforming commercial adsorbents Indonesia is a major textiles producer, generating substantial volumes of dye-contaminated wastewater, particularly indigo carmine (IC), a persistent anionic dye that poses significant risks to aquatic ecosystems and human health. The IC can be removed using the adsorption method with activated carbon. Activated carbon can be generated from sustainable material, namely nypa palm fronds ( Nypa fruticans ), an invasive plant species and abundant yet underutilized coastal biomass in estuarine ecosystems. The potential of nypa is significant and largely underexploited for carbon production. This research produced the activated carbon from nypa via steam activation at temperatures of 700 and 800°C and assessed it as a sustainable adsorbent for the adsorption process of indigo carmine dye. Several physicochemical analyses were conducted using the proximate analysis, TGA, FTIR, SEM, EDS, and BET. The activated carbon produced at 800°C (KAPN800) exhibits a high iodine adsorption of 1063.33 mg/g and a surface area of 203.303 m 2 /g, along with the formation of a well-defined micro-mesoporous structure. The effective conditions (0.1 g adsorbent, 120 minutes, 16 ppm IC, and 50°C) resulted in an efficiency removal of 99.752%. Kinetic analysis showed that the pseudo-second-order model best describes the adsorption process, while the equilibrium data align with the Langmuir isotherm, suggesting monolayer adsorption on a homogeneous surface. Thermodynamically, the adsorption reaction is spontaneous and exothermic. These findings demonstrate that nypa palm fronds are a potential, cost-effective, and renewable precursor for activated carbon with high-performance for IC removal, thereby contributing to the Sustainable Development Goals 3, 6, and 12.