ZnCl₂-activated laser-induced graphene from potato skins for Congo red dye adsorption

This study investigates the adsorption of Congo red (CR) dye onto laser-induced graphene derived from potato skins (LIGPS), a graphene-like material produced via rapid and cost-effective CO₂ direct laser writing. Raman spectroscopy and X-ray diffraction (XRD) confirmed the graphitic nature of LIGPS. Activation with ZnCl₂ (LIGPS50) altered the morphology of the material, as observed in SEM images. Additionally, ZnCl₂ activation significantly increased the surface area from 11.256 to 126.696 m² g⁻¹, total pore volume from 0.016 to 0.253 cm³ g⁻¹, and average pore diameter from 4.82 to 7.99 nm. The adsorption of CR was optimized at pH 9, where electrostatic and π-π interactions between CR and LIGPS were confirmed by FTIR spectra. Kinetic studies revealed first-order adsorption behavior, with equilibrium reached after 15 min. The maximum adsorption capacity of 278.65 mg g^-1 was determined from equilibrium studies, following the Freundlich model, indicating heterogeneous interactions. Thermodynamic analysis confirmed that the adsorption was spontaneous, exothermic, and predominantly physical, as indicated by the values of ∆G (- 4.185 to - 4.952 kJ mol⁻¹), ∆H (- 13.285 kJ mol⁻¹), and ∆S (- 27.927 kJ mol⁻¹). Also, the SEM-FEG images showed the CR particles attached to the LIGPS50 surface affirming the successful adsorption of the dye onto the material. These results demonstrate that LIGPS50 is a highly effective, low-cost, and sustainable alternative for CR dye removal, providing an eco-friendly alternative for both wastewater treatment and waste management.