Adsorption of acetaminophen from aqueous solution using rice straw activated carbon: Kinetic and isotherm studies

The increasing use of pharmaceuticals has heightened concerns about their potential effects on human health and water quality, as a significant fraction of these drugs is excreted as waste and ultimately enters water bodies. This study investigates the removal of acetaminophen (APAP) from aqueous solution using rice straw–activated carbon (RSAC) chemically modified with phosphoric acid as an adsorbent. Scanning electron microscopy revealed an irregular and heterogeneous RSAC surface with visible cavities and surface openings, while Fourier transform infrared spectroscopy indicated the presence of diverse surface functional groups potentially relevant to APAP adsorption. Optimization studies using Design-Expert 7.0 software determined the optimal conditions for APAP removal, resulting in an APAP removal efficiency of 88.98% ± 1.02% and an adsorption capacity of 238.10mg/g at an initial APAP concentration of 800 ppm, a 0.2 g RSAC adsorbent dose, and a contact time of 25 min. Isotherm analysis indicated heterogeneous adsorption, best described by the Freundlich model (R 2 = 0.9917). In contrast, kinetic analysis revealed an energetically heterogenous surface, with the Elovich kinetic model providing the best fit (R 2 = 0.9972). This study highlights the effectiveness of RSAC as an environmentally friendly adsorbent for removing APAP from water, providing valuable insights for advancing sustainable water treatment methods.