Santosh Kokate

We present the synthesis of Activated Carbon (AC) by pyrolysis of Banana (Musa Acuminate) Stem Waste (BSW), and the ability of obtained AC for adsorptive removal of Pb(II) ions from water. Importantly, pyrolysis was performed at 750°C for 2.0 h in the presence of high surface area producing chemical activators such as NaOH, LiOH, H₃PO₄, ZnCl₂, and KOH. BET-surface areas of AC produced with activators NaOH, LiOH, H₃PO₄, ZnCl₂, and KOH were determined to be 908, 1531, 1670, 2245, and 2485 m² g⁻¹, respectively. Pore volume ascending order was determined as 0.59 (NaOH) < 0.68 (LiOH) < 0.86 (H₃PO₄) < 0.97 (ZnCl₂) 3 g⁻¹. SEM and TEM images revealed the porous nature of the ACs. ACs produced with H₃PO₄, ZnCl₂, and KOH exhibit type I adsorption isotherms, indicating their microporous nature. ACs prepared with NaOH and LiOH exhibit type II adsorption isotherms, indicating their macroporous nature. X-ray diffraction, X-Ray photoelectron, and Raman spectroscopy analysis revealed the graphitic structure of ACs. Pb(II) ion adsorption onto ACs surface obeyed the Langmuir model. It was found that the Pb(II) adsorption capacities of the ACs produced with NaOH, LiOH, H₃PO₄, ZnCl₂, and KOH as the chemical activators were 220, 283, 326, 329, and 435 mg g⁻¹, respectively, at the optimised conditions (pH = 6.6, contact time = 100 min, [ACs] = 0.125 g L⁻¹, at 30°C). The interaction between surface functional groups of ACs and Pb(II) ions was confirmed by X-Ray photoelectron and FT-Infrared spectroscopy. The negative values of ΔG^o and ΔH^o reveal that the Pb(II) ion adsorption onto the ACs surface is spontaneous and exothermic. The Pb(II) ion adsorption capacity increased with an increase in BET-SA and pore volume of ACs, with AC obtained from BSW with KOH exhibiting the highest adsorption capacity of 435 mg g⁻¹. Thus, the study highlights BSW, agricultural biomass waste is a low-cost and abundantly available carbon precursor to synthesise potential AC adsorbent for water treatment.