High surface area activated carbon from a pineapple (ananas comosus) crown via microwave-ZnCl2 activation for crystal violet and methylene blue dye removal: adsorption optimization and mechanism.

ABSTRACT

In this investigation, microwave irradiation assisted by ZnCl2 was used to transform pineapple crown (PN) waste into mesoporous activated carbon (PNAC). Complementary techniques were employed to examine the physicochemical characteristics of PNAC, including BET, FTIR, SEM-EDX, XRD, and pH at the point-of-zero-charge (pHpzc). PNAC is mesoporous adsorbent with a surface area of 1070 m2/g. The statistical optimization for the adsorption process of two model cationic dyes (methylene blue MB and, crystal violet CV) was conducted using the response surface methodology-Box-Behnken design (RSM-BBD). The parameters include solution pH (4-10), contact time (2-12) min, and PNAC dosage (0.02-0.1 g/100 mL). The Freundlich and Langmuir models adequately described the dye adsorption isotherm results for the MB and CV systems, whereas the pseudo-second order kinetic model accounted for the time dependent adsorption results. The maximum adsorption capacity (qmax) for PNAC with the two tested dyes are listed 263.9 mg/g for CV and 274.8 mg/g for MB. The unique adsorption mechanism of MB and CV dyes by PNAC implicates multiple contributions to the adsorption process such as pore filling, electrostatic forces, H-bonding, and π-π interactions. This study illustrates the possibility of transforming PN into activated carbon (PNAC) with the potential to remove two cationic dyes from aqueous media.

The novelty of this research work stems from the conversion of pineapple (Ananas comosus) crown wastes with no monetary value into an efficient activated carbon adsorbent with relatively high surface area. Furthermore, a fast and convenient microwave assisted ZnCl2 activation method was applied for producing the activated carbon (AC). The effectiveness of the produced AC was tested for the removal of two different cationic dyes crystal violet (CV) and methylene blue (MB). A statistical optimization that employs a response surface methodology with the Box-Behnken design was employed to optimize the adsorption variables for the optimal dye removal. Moreover, the dye adsorption kinetics and thermodynamics, equilibrium isotherms, and the details of the adsorption process were reported herein.