Simultaneous removal of methylene blue and Cd(II) by pecan shell-based activated carbon: adsorption kinetics,...

The coexistence of organic dyes and heavy metals in wastewater requires efficient and sustainable adsorbents capable of simultaneous contaminant removal. In this study, pecan shell-based activated carbons (PSC-0-PSC-3) were prepared by KOH activation using different impregnation ratios; their physicochemical properties and adsorption performance toward methylene blue (MB) and Cd(II) were systematically investigated under single- and binary-component systems. Among the prepared adsorbents, PSC-3 exhibited the highest BET specific surface area (2857 m² g^-1) and total pore volume (1.61 cm³ g^-1). MB adsorption was best described by the Freundlich isotherm model (R² = 0.998), indicating heterogeneous adsorption behavior. The Langmuir model estimated a maximum adsorption capacity of 529.5 mg g^-1. Under binary-component conditions, PSC-3 achieved nearly complete MB removal (≈ 100%), whereas Cd(II) removal was strongly dependent on solution pH and adsorbent dosage. The adsorption of Cd(II) was primarily governed by electrostatic attraction and surface complexation with oxygen-containing functional groups. Adsorption-desorption experiments demonstrated that PSC-3 retained approximately 85% and 80% of its initial adsorption efficiency for MB and Cd(II), respectively, after five regeneration cycles, indicating good reusability. These findings demonstrate that PSC-3 is a low-cost, sustainable, and highly efficient adsorbent with strong potential for the simultaneous removal of organic dyes and heavy metal ions from mixed wastewater.