Characterization of activated carbon produced from the green algae Spirogyra used as a cost-effective adsorbent for enhanced removal of copper(ii): application in industrial wastewater treatment

Abstract

In this study, we prepared porous carbon (SPAC) derived from the green algae Spirogyra (SP), which was activated using natural lemon through pyrolysis at 600 °C for 3 h, and investigated its adsorption ability and performance towards copper ions in an aqueous solution. The physicochemical characteristics of SPAC were evaluated using FTIR, BET, SEM/EDS, XRD and pHPZC analyses and the results were compared with those of the raw algae (SP). The results indicated the presence of rich surface functional groups and that SPAC possessed a highly porous structure that increased the specific surface area by about 1.8 times compared to the SP surface (S_BET = 71.087 m² g⁻¹ and V_Total = 12.019 cm³ g⁻¹). XRD indicated that the main phase of the samples was CaCO₃. The pH_PZC value of activated carbon was 9.25. After optimizing the effects of operational parameters, the maximum adsorption efficiency of Cu²⁺ rapidly reached 95.09% after about 20 min of stirring time with an amount of 0.1 g adsorbent and an initial copper concentration of 200 mg L⁻¹ at an optimum pH of around 5.28 and ambient temperature of 25 °C. The pseudo-first-order (PFO) nonlinear model provided a good description of the adsorption kinetics of SPAC. The experimental equilibrium data fit the Sips and Liu models slightly better than other isotherm models. The calculated thermodynamic parameters ΔH°, ΔS°, and ΔG° revealed that the adsorption process of Cu²⁺ was spontaneous and exothermic. Physisorption was the dominant mechanism for Cu²⁺ adsorption onto SPAC; SPAC was also evaluated for the adsorption of copper ions present in wastewater from the cable industry. Overall, the findings suggest that the prepared activated carbon can be employed as a cost-effective and promising adsorbent for the removal of toxic Cu²⁺ from wastewater.