Box‐Behnken Design Optimization of Methylene Blue Dye Adsorption Using Brinjal Stalk Activated Carbon: Kinetics, Isotherm, and Mechanism Studies

ABSTRACT An efficient activated carbon was prepared from brinjal ( Solanum melongena L.) stalk through a thermal process and used for methylene blue (MB) dye removal using the Box‐Behnken design (BBD) model. The brinjal stalk activated carbon (BSAC) was analyzed by several instrumental techniques. The BSAC has a BET surface area of 90.09 m 2 /g with a high disordered external surface. XRD and FESEM data revealed that the BSAC is an amorphous structure with regular active pores. FTIR studies indicated the existence of active binding sites (–OH and –COOH) on the BSAC surface. The process parameters for MB dye removal were optimized in the BBD model by varying adsorbent dosage (0.1–1.0 g/L), pH (4–10), and contact time (10–120 min). About 93% of MB dye was eliminated in the optimal conditions of a dose of 0.81 g, 8.34 pH, and contact time of 117.29 min. The adsorption kinetics of MB dye onto BSAC followed a pseudo‐second‐order model ( R 2 = 0.997), indicating a chemisorption‐controlled mechanism. The Langmuir isotherm best described the equilibrium data ( R 2 = 0.96), suggesting monolayer adsorption with a maximum adsorption capacity of 161.79 mg/g. The adsorption process was driven by electrostatic attraction, π–π interaction, hydrogen bonding, and the pore‐filling process.