Multivariable optimization with desirability function for carbon porosity and methylene blue adsorption by watermelon rind activated carbon prepared by microwave assisted H 3 PO 4

In this study, the Box-Behnken design (BBD) with a desirability function was applied to optimize microwave activation conditions for conversion of watermelon rind (WMR) into mesoporous activated carbon (WMR-AC) using an acid (H 3 PO 4 ) activator. The desirability function results suggested the following optimum activation conditions: impregnation ratio (IR) (A; 1:2 MWR/H 3 PO 4 ), radiation power (RP) (B; 800 W), and radiation time (RT) (C;15 min). These optimum conditions were responsible for increasing the specific surface area (S BET = 4.85 m 2 /g) of WRM upon conversion into mesoporous activated carbon (WMR-AC), according to its greater S BET = (751.8 m 2 /g). The effectiveness of WMR-AC was evaluated by use of a dye removal method for methylene blue (MB) from aqueous media. Then, BBD with a desirability function was applied to optimize the adsorptive dye removal conditions for MB. The results for the desirability function suggested that the highest MB removal (95.8 ± 2%) can be achieved at the following operational conditions: WMR-AC dose (A, 0.1 g), solution pH (B, 7.8), and process temperature (C, 48 ºC). The kinetics of adsorption is well-described by the pseudo-second-order model, whereas the Freundlich model accounted for the isotherm profile results, with an estimate of the maximum adsorption capacity of MB (284 mg/g). This study introduces a fast conversion method of WMR into WMR-AC with improved adsorption properties for potential dye removal applications, as shown for MB.