Multivariable optimization with desirability function for carbon porosity and methylene blue adsorption by watermelon rind activated carbon prepared by microwave assisted H3PO4

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 (H3PO4) activator. The desirability function results suggested the following optimum activation conditions: impregnation ratio (IR) (A; 1:2 MWR/H3PO4), radiation power (RP) (B; 800 W), and radiation time (RT) (C;15 min). These optimum conditions were responsible for increasing the specific surface area (SBET = 4.85 m(2)/g) of WRM upon conversion into mesoporous activated carbon (WMR-AC), according to its greater SBET = (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 degrees C). 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.

Automated summary

The study optimized microwave activation conditions for conversion of watermelon rind into mesoporous activated carbon using a desirability function. The resulting product showed improved adsorption properties, with potential application for dye removal, particularly for methylene blue. The use of desirability function helped identify the optimal activation and dye removal conditions, indicating the method's potential for practical use.