Coconut husk-derived extracted silica and activated carbon composite for removing carbamazepine: Batch and RSM optimization

The present study explored coconut husk as a fundamental ingredient for the synthesis of activated carbon (AcCH) and amorphous silica (SiO 2 ), and combined them as a composite (AcCH/SiO 2 ), for efficient removal of carbamazepine from the experimental solution. The physicochemical characterizations of the synthesized materials were performed. By the AcCH/SiO 2 composite, detailed batch adsorption studies were performed, where the maximum experimentally determined equilibrium adsorption capacity of 418.421 mg g −1 was found at pH 6 of the experimental solution, at 308 K and 130 rpm for 3 h, using an adsorbent dosage of 0.10 g L −1 , with carbamazepine initial concentration of 100 mg L −1 . Additionally, three important parameters, adsorbent dosage, initial concentration, and contact duration, were optimized by Box Behnken Design (BBD). The results demonstrated that the experimental data most closely fit the isotherm model of Langmuir (R 2 = 0.994), and the pseudo-second-order kinetics model. The adsorption experiment showed positive ΔH values (34855.61 J mol −1 ), indicating that the adsorption of carbamazepine on AcCH/SiO 2 composite is endothermic, while the negative ΔG value demonstrated that the process was spontaneous. The reusability study of the composite AcCH/SiO 2 demonstrated a removal efficiency of 69.298 % at the 5th cycle of regeneration, indicating the material's cost-effectiveness for wastewater treatment.