Remediation of phenol and p-nitrophenol from contaminated water using raw and quaternized Annona muricata L. peels

Abstract

Phenol and p -nitrophenol (PNP) are toxic, widely occurring phenolic pollutants requiring cost-effective removal methods. This study evaluates raw Annona muricata L. peels (RGP) and peels chemically quaternized (QGP) as low-cost biosorbents for phenol and PNP remediation from aqueous media. Adsorbents were prepared, characterized, and tested in batch experiments to optimize pH, contact time, sorbent dose, initial concentration, and temperature. Optimal removal occurred at pH 4; QGP consistently outperformed RGP. Under optimized conditions (0.03 g, 30–45 min, 298 K), Langmuir isotherm described sorption better than Freundlich, yielding q max values of 54.945 mg/g (QGP–phenol), 8.787 mg/g (RGP–phenol), 17.490 mg/g (QGP–PNP) and 5.920 mg/g (RGP–PNP). Kinetic data fitted the pseudo-second-order model ( R 2 > 0.959), indicating physisorption dominance and good agreement between experimental and calculated q e . Thermodynamic parameters (ΔH° negative, ΔS° positive, ΔG° negative) suggest spontaneous, mainly exothermic physisorption with increased randomness at the solid–liquid interface. Regeneration with 0.5 M HCl showed limited desorption (31–41% first cycle) and declining efficiency over five cycles, indicating incomplete regeneration and need for improved desorption methods. Application to river water spiked with 5 mg/L phenols produced removal of 49–63%, lower than synthetic solutions due to competing constituents. Overall, quaternization markedly enhances A. muricata peel adsorption capacity, making QGP a promising, low-cost biosorbent for phenolic pollutant removal pending optimization of regeneration and scale-up studies.