CHEMICALLY ACTIVATED SUNFLOWER SEED SHELL BASED ACTIVATED CARBON FOR ALLOPURINOL REMOVAL: ISOTHERM, KINETICS AND REGENERATION STUDIES

Mohd Raziff  Mat Hasan; Azrina Aziz; Erniza Mohd Johan Jaya; Mohd Azmier Ahmad

Mohd Raziff Mat Hasan School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia.
Azrina Aziz School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia.
Erniza Mohd Johan Jaya School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia.
Mohd Azmier Ahmad School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia.

Keywords: Activated carbon, chemical activation, isotherm, kinetic, regeneration

Abstract

Allopurinol (ALP) is an emerging contaminant that enters aquatic environments due to incomplete removal in wastewater treatment plants. Its major metabolite, oxypurinol, can form riboside adducts through the purine metabolism pathway, potentially disrupting purine metabolism in aquatic organisms. This study aims to synthesize and evaluate sunflower seed shell-derived activated carbon (SSSAC) for the adsorption of ALP from aqueous solutions. The SSSAC was produced through chemical activation using potassium hydroxide (KOH). Scanning electron microscopy (SEM) revealed that the raw sunflower seed shells exhibited a dense and non-porous morphology, whereas the SSSAC displayed a well-developed porous texture. The zeta potential of the precursor was −33.00 mV, which decreased to −51.30 mV after KOH activation, indicating enhanced surface negativity. In batch adsorption studies, increasing the initial ALP concentration from 10 to 100 mg/L resulted in a rise in adsorption capacity from 9.11 to 74.37 mg/g, while the percentage removal declined from 91.10 % to 74.37 % at higher concentrations. The optimum pH for ALP adsorption was pH 5, achieving a maximum capacity of 87.54 mg/g. Isotherm study revealed that the Freundlich model best represented the adsorption behaviour, with the lowest root mean square error (RMSE) of 1.15 mg/g and an average error of 5.52 %, signifying a multilayer adsorption process. The Langmuir model predicted a maximum monolayer capacity (Qₘ) of 113.84 mg/g. Kinetic analysis confirmed that adsorption followed the pseudo-first-order (PFO) model. Regeneration studies showed that SSSAC remained reusable up to five cycles, after which the ALP uptake declined to 34.53 mg/g and the adsorbent yield decreased to 50.24 %. These findings demonstrate that SSSAC is a promising low-cost adsorbent for the effective removal of ALP from contaminated water systems.