Sustainable adsorption of methylene blue onto biochar-based adsorbents derived from oil palm empty fruit branch: Performance and reusability analysis

This study examines methylene blue (MeB) adsorption by biochar-based adsorbents made from oil palm empty fruit branches. Untreated biochar (BC) and treated activated carbons 1BT and 2BT for one- and two-step KOH treatments were analyzed using FTIR, XRD, SEM-EDX, and BET to determine their physical, chemical properties and adsorption reusability. Adsorption experiments fitted pseudo-second order kinetics which fit experimental data satisfactorily. Langmuir isotherm has the best fitting data, showing monolayer adsorption, moreover three-parameter models like Redlich-Peterson, Sips, and Toth also match well, confirming its trustworthiness. BC, 1BT, and 2BT have maximal adsorption capacities of 796.17–820.12 mg/g, 943.46–969.85 mg/g, and 1123.57–1153.72 mg/g, respectively. In addition, adsorbent reusability demonstrates gradual decreases in adsorption efficiency, and consistently remained high at 46.05 %, 48.99 %, and 48.15 % over five consecutive reuse cycles for BC, 1BT, and 2BT, respectively. These findings have significant implications for the practical application as additive materials in modern landfill liner.