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

Abstract

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 (R2 = 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.