Synthesis and characterization of pyrolyzed and H3PO4-activated maize cob for aspirin removal

The presence of pharmaceutical residues in the aquatic environment poses a serious threat to human health and ecosystems, and it is essential to develop efficient and sustainable treatment technologies. The aim of this work was to examine the adsorption of aspirin from aqueous solution using pyrolyzed maize cob (Pyr-MC) and H₃PO₄ - modified maize cob activated carbon (MCAC) as a low-cost adsorbent. The influences of initial concentration, pH, contact time and adsorbent dose on the performance of the adsorption method were investigated. Pyr-MC exhibited superior adsorption performance, achieving a maximum removal efficiency of 82.3% at pH 3 using 0.06 g adsorbent, whereas MCAC achieved 56% removal at pH 4 under the same conditions. The adsorption capacities of Pyr-MC and MCAC were 15.0 mg/g and 4.6 mg/g, respectively. The presence of well-developed pores and functional groups favourable for adsorption were confirmed by FESEM and FTIR analysis. Furthermore, BET results showed that Pyr-MC had a slightly higher surface area (111.36 m 2 /g) and pore volume (0.11 cm 3 /g) than MCAC (105.08 m 2 /g and 0.10 cm 3 /g), which suggested that a bigger pore diameter does not necessarily imply better adsorption performance. Adsorption equilibrium data were fitted to Freundlich isotherm equation with the best fit of R² = 0.96 for Pyr-MC and R² = 0.63 for MCAC. The results show that Pyr-MC is a promising, sustainable material for the removal of aspirin from wastewater.