Highly porous activated carbon derived from the papaya plant (stems and leaves) for superior adsorption of alizarin red s and methylene blue dyes from wastewater

Abstract

In this study, stems and leaves of the papaya plant were employed to prepare a high-quality porous adsorbent via carbonization and chemical activation using phosphoric acid. This adsorbent demonstrates superior adsorption capabilities for the efficient removal of hazardous alizarin red s (ARS) and methylene blue (MB) dyes. Thus, it contributes to waste reduction and promotes sustainable practices in environmental remediation, aligning with global efforts to develop sustainable materials that address water pollution while supporting circular economy principles. The structural properties of the activated carbon were characterized through various techniques, including BET surface area, FTIR, SEM, XPS, zeta potential measurements, and determination of the zero-point charge. The characterization results confirmed the preparation of highly porous activated carbon from papaya stems with a high surface area of 1053.52 m² g⁻¹. The batch experiments revealed that the maximum adsorption capacities for the stem-activated carbon (SAC) were 931 mg g⁻¹ for ARS and 990 mg g⁻¹ for MB. For the leave-activated carbon (LAC), the capacities were 410 mg g⁻¹ for ARS and 642 mg g⁻¹ for MB. SAC exhibited 100% removal of MB or ARS with concentrations lower than 150 ppm in 15 min. The data fitted well with the Langmuir model and pseudo-second-order model. Moreover, the reusability revealed that the SAC can be reused over 5 cycles without significant change in the removal efficiency. Overall, SAC and LAC derived from papaya plants exhibited excellent dye adsorption performance, suggesting potential for large-scale applications.