Sustainable dye removal via Punica granatum waste-derived activated carbon: CCD-RSM optimization and adsorption insights

Byproducts from Punica granatum juice production, an agro-industrial waste, were valorized as a sustainable precursor for synthesizing mesoporous activated carbon (AC PG ) via phosphoric acid activation, yielding a high surface area of 1089 m²/g, as confirmed by N₂ adsorption–desorption isotherms. The performance of AC PG in removing Direct Blue 129 dye (DB129) from tannery effluent was evaluated through batch adsorption experiments. To optimize the adsorption process with respect to removal efficiency (R%), a central composite design-based Response Surface Methodology (CCD-RSM) was applied, considering pH, AC PG dosage, and dye concentration as independent variables. Twenty batch experiments revealed optimal conditions at pH 6, 0.55 g L −1 adsorbent dose, and 320 mg L −1 dye concentration, achieving a removal efficiency of 84 % with a desirability of 1.000. Under the optimized conditions established by response surface methodology (RSM) at 20 °C, AC PG exhibited a remarkable maximum adsorption capacity (q max ) of 528 mg g −1 , as determined from the Sips isotherm, with adsorption kinetics well described by the pseudo-second-order model. Thermodynamic evaluations indicated that the process is spontaneous and endothermic. Furthermore, regeneration studies confirmed the reusability of AC PG over five cycles, retaining more than 55 % of its initial performance, underscoring its potential as a sustainable adsorbent for the effective remediation of dye-polluted wastewater.