Novel nano-ferromagnetic activated graphene adsorbent extracted from waste for dye decolonization

Abstract

Polyethylene terephthalate (PET) waste was converted into graphene by pyrolysis, and the synthesized graphene (SG) was modified into activated graphene (AG) by potassium hydroxide (KOH) impregnation and nano-ferromagnetic activated graphene (NFMAG) by nanometric iron oxide coating via co-precipitation and external reduction method. The chemical, textural and structural properties of SG, AG and NFMAG were investigated using scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer Emmett Teller (BET) surface area analysis, energy dispersion X-rays spectroscopy (EDX), X-Ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. SG, AG and NFMAG exhibited microporous structures with high surface areas of 391.06, 460.01 and 319.62 m2 g−1 respectively. SG, AG and NFMAG were used in the removal of methylene blue (MB) dye from an aqueous solution. The effect of contact time, adsorbent dosage, initial solution pH, initial dye concentration and temperature were studied. The adsorption isotherms, kinetics and thermodynamics were investigated. A maximum monolayer adsorption capacity (qm) of 216.83, 348.30 and 291.78 mg g−1 were obtained for SG, AG and NFMAG respectively. AG and NFMAG showed superior adsorption capacity over their precursor SG due to the high surface area and surface chemistry. MB adsorption with all prepared adsorbents followed the pseudo-second-order kinetics model and Langmuir adsorption isotherm. The adsorption mechanisms were explained using FTIR, intraparticle diffusion and liquid-film diffusion. All MB-adsorbent systems were endothermic and spontaneous. The reusability of SG, AG and NFMAG was assessed for five adsorption cycles. NFMAG exhibited excellent stability and reusability due to its ease of magnetic separation.