Phosphoric acid surface modified <i>Moringa oleifera</i> leaves biochar for the sequestration of methyl orange from aqueous solution: Characterizations, isotherm, and kinetics analysis
Md. Shahinoor Islam, Hridoy Roy, Sadiya Afrose
Abstract
Abstract Biochar is a promising engineering material to sequestrate organic pollutants from wastewater. In the current study, several surface‐modified Moringa (M.) oleifera leaf biochars were prepared and utilized for the sorption of methyl orange (MO) dye from an aqueous solution. Raw biochar was produced by the carbonization of M. oleifera leaves at 350°C in a muffle furnace for 2 h. The surface‐modified M. oleifera biochars were prepared at 400°C, 500°C, and 600°C using phosphoric acid (H 3 PO 4 ) at different combinations to improve the biochar pore structure, surface functional groups, and biochar stability. The highest surface area (267.15 ± 42.40 m 2 /g) of the modified biochar was achieved at 500°C with H 3 PO 4 to raw biochar ratio of 1.5. Surface morphological results revealed the formation of pores, troughs, and channels with the increasing activation temperature. The carbon (C) content (wt%) was maximum (79.61%) for activated biochar at 500°C. The presence of enhanced functional groups, e.g., hydroxyl, aliphatic carbon‐hydrogen, carbonyl, ester, and phenol structures in surface‐modified biochars was observed from FT‐IR results. The Langmuir isotherm model was fitted to better describe the adsorption phenomenon for both surface‐modified biochars and raw biochar compared to the Freundlich isotherm model. The highest adsorption capacity was 175 mg MO dye/g of activated biochar prepared at 500°C with an H 3 PO 4 impregnation ratio of 1.5. Pseudo‐1st order model fitted the best for raw biochars whereas pseudo‐2nd order and intraparticle diffusion models better describe the sorption of MO onto activated biochar. The results anticipated M. oleifera leaf‐activated biochar as an efficient tool for the treatment of MO contaminated wastewater.