Polyimide derived laser-induced graphene as adsorbent for cationic and anionic dyes

Laser-induced graphene (LIG) is fabricated on polyimide films directly by irradiation with a CO₂ laser. This reagent-free method to synthesize graphene in a single step is applicable for many uses including water treatment technology. Here we demonstrated that LIG is an effective adsorbent for water treatment and observed removal of methylene blue (MB) and methyl orange (MO) from aqueous solutions. LIG powder was obtained by sonication of LIG that was scraped from polyimide films. Raman and X-ray diffraction analysis confirmed the graphene component in the material, while high-resolution scanning electron microscopy and atomic-force microscopy analysis indicated the presence of multilayered graphene sheets. LIG powder showed significant removal of MB and MO dyes from the aqueous solutions where hydrophobicity played an important role, but especially a high adsorption of the MB dye was seen. Adsorption of MB and MO on LIG followed a pseudo-second-order kinetic model and the maximum adsorption capacity (Freundlich) was 926 mg g⁻¹ and 132 mg g⁻¹, respectively. The adsorption process was fast and exothermic, which involved both π-π interaction and electrostatic forces as observed using Raman spectroscopy. The expedient solvent-free fabrication of LIG that is generated on surfaces might be an advantageous graphene-based adsorbent for water remediation.