Optimized diclofenac sodium adsorption on Lecythis minor-derived activated carbon: Kinetics and isotherm analysis
Cindy J. Elles-Pérez, Amner Muñoz-Acevedo, Andrés Guzmán, Juan Carlos Moreno-Piraján, Jenny Paola Rodriguez Estupiñan
Abstract
Diclofenac sodium, an emerging pollutant, was studied for its adsorption on chemically modified activated carbons derived from Lecythis minor epicarp using nitric acid (NA) and ammonium persulfate (APS) as oxidizing agents. The activated carbons were characterized by BET surface area (1110–2334 m 2 /g), FTIR, and SEM analysis. The carbons developed predominantly micro-mesoporous surfaces with carboxylic, lactonic, and phosphate groups; nitric acid modification introduced nitrogenated functionalities, while ammonium persulfate treatment generated sulfonated groups. The adsorption kinetics revealed that the pseudo-second-order model best described the process, with rate constants (k2) ranging from 3.70 × 10 −5 to 6.83 × 10 −5 g/(mg·min). Equilibrium adsorption capacities were 211.2 mg/g for the unmodified carbon (CALM), 242.4 mg/g for CALM-NA, and 236.4 mg/g for CALM-APS, as determined by Langmuir isotherms. Temkin isotherms indicated an exothermic adsorption process, and the Freundlich heterogeneity factors confirmed the heterogeneous nature of the adsorbent surfaces. These results demonstrate the significant potential of chemically modified Lecythis minor activated carbons for removing diclofenac sodium, combining sustainability with high adsorption performance. • Chemically modified Lecythis minor activated carbon adsorbed 242 mg of diclofenac sodium/g. • Modification with nitric acid and ammonium persulfate enhanced adsorption by 15 %. • Isotherm models showed a favorable and exothermic adsorption process. • Adsorption kinetics followed the pseudo-second-order model (R 2 up to 0.99). • Agro-industrial waste was utilized to create sustainable adsorbents.