Preparation and characterization of banana trunk activated carbon using H₃PO₄ activation: A rotatable central composite design approach

Abstract

Banana trunk waste was utilized to produce activated carbons with improved surface area and phosphorous atom dispersed surface through the chemical activation method using phosphoric acid. Banana trunk activated carbon (BTAC) production was optimized through the rotatable central composite design (RCCD) approach of the response surface methodology (RSM). The independent variables selected for optimization were activation time (35.5–134.5 min), activation temperature (367–932 °C), and H3PO4 concentrations (0.36–8.14 mol/L). The optimized conditions of the independent variables obtained through RCCD were 50 min (activation time), 583 °C (activation temperature), and 6.60 mol/L (H3PO4 concentration) for a maximum Brunauer-Emmett-Teller (BET) surface area of 1290 m2/g. Banana trunk activated carbon samples were characterized for bulk and surface elemental composition, surface morphology, thermal stability, functional groups, pHzpc, and crystallinity behavior. The characterization results suggested that BTAC has a porous surface with carbon as the backbone element with the highest percentage of 78%. The oxygen atom occupies the surface with 12%, and the phosphorus atom is spread almost 6% over the carbon surface. The raw banana trunk was thermally decomposed at an onset temperature of 240 °C and above, whereas the banana trunk (BTAC) was thermally stable up to 700 °C. Phosphoric acid-activated banana trunk activated carbon composed of the following surface functional groups: –OH, –C = O, -P = O, -P-O-C, and multiple carbon-carbon bonds.