Development of eco-friendly activated carbon from olive pits for the adsorption of tartrazine with isotherm kinetic and thermodynamic studies

Synthetic dyes discharged into water bodies pose a persistent environmental threat owing to their resistance to natural degradation, toxicity, and long-term ecological impact. In this study, discarded olive pits were valorized as a lignocellulosic precursor for the production of activated carbon through phosphoric acid activation. Multiple analytical tools including pHpzc, FTIR, SEM, XPS, and XRD—were used to examine the structural, physicochemical, and morphological characteristics of the prepared material. The influence of key process variables on Tartrazine uptake was assessed through a series of batch-mode experiments, including pH, initial dye concentration, adsorbent dose, contact time, and temperature. Maximum adsorption was achieved in acidic medium (pH = 2) using an adsorbent dose of 40 mg, an initial Tartrazine concentration of 40 mg L −1 , a contact time of 24 h, and a temperature of 298 K. The maximum adsorption capacity reached 47.18 mg g −1 according to the BET model, while the pseudo-second-order kinetic model provided the best fit (R 2 = 0.9996) with an experimental Qe value of 31.39 mg g −1 . Thermodynamic parameters (ΔH° = − 10328 J mol −1 ; ΔG° = − 1409 to − 1794 J mol −1 ) confirmed that the process is exothermic and spontaneous. The results of the pseudo-second-order kinetic model and Thermodynamic analysis showed that the process is a mixed adsorption mechanism dominated by physisorption. These findings collectively establish H3PO4-activated olive pit carbon as a high-performance, cost-effective, and environmentally viable material for Tartrazine decontamination from water matrices.