Adsorption of methylene blue dye onto phosphoric acid-treated pomegranate peel adsorbent: Kinetic and thermodynamic studies

Abstract

The orthophosphoric acid-treated pomegranate peels (POPAC) performance was investigated through batch mode for Methylene Blue dye (MB) adsorption from an aqueous solution. Although chemical activation using various chemical agents has been explored by other research work, but novelty application of H3PO4 in a 1:1 wt percentage for activation exhibits unprecedented performance in enhancing the efficiency of MB dye removal. Dependent parameters were optimized, with pH of the sample, contact interval, initial MB concentration, and dose of adsorbent. Excellent removal efficiency (above 92 %) was observed at pH 8 with a dose of 0.25 g/100 mL for 120 min of contact duration. At the qmax value of 14.03 mg/g, the Langmuir isotherm demonstrated the MB dye monolayer adsorption onto POPAC, elucidating the adsorption mechanism with R2 = 0.9883. The kinetics of MB adsorption fit excellently through the pseudo-second-order model with R2 = 0.9997, and the model's estimated adsorption capacity agreed well with the results obtained from the experimental investigation. Thermodynamic parameters, including ΔGᵒ, ΔH°, and ΔS°, additionally demonstrated the spontaneous as well as endothermic adsorption nature of MB on the POPAC’s surface. Furthermore, regeneration studies using 0.1 M NaOH and 0.1 M HCl solutions show adequate MB dye elimination after three cycles. According to the research findings, pomegranate peel may be an inexpensive, environmentally acceptable, and operative biosorbent to eliminate MB dye from polluted aqueous matrices.