Activated Carbon from Banana Pseudostem: Multivariate Optimization of Synthesis and Adsorption Study for Phosphorus Removal.

Abstract

This work aimed to develop a high-surface-area activated carbon using banana pseudostem as precursor and zinc chloride as a chemical activator, with synthesis conditions optimized via a central composite rotational design (CCRD) for phosphate adsorption. The resulting banana pseudostem activated carbon (BPAC) exhibited an exceptionally high specific surface area of 2415 m² g^-1, obtained at activation temperature (AT) of 400 °C, 2:1 impregnation ratio (IR), and pyrolysis time (PT) of 1 h in an air atmosphere muffle furnace. This result exceeds the CCRD-predicted value (1037 m² g^-1), highlighting the importance of post-pyrolysis factors, such as the duration of contact with the HCl soaking solution employed during the biochar cleaning stage. The pH at the point of zero charge (7.30) suggests that phosphate adsorption is favored below this value. X-ray diffraction analysis confirmed a primarily amorphous structure with a remaining lamellar zinc monohydrate peak. The CCRD demonstrated a significant effect of PT, IR, and AT. Batch adsorption assays showed that phosphate adsorption followed the pseudo-second-order kinetics, reaching equilibrium in approximately 7 h, and the Langmuir model fitted best, with a maximum adsorption capacity of 11.78 mg g^-1.