Comparative Adsorption of Anionic Dyes (Eriochrome Black T and Congo Red) onto Jojoba Residues: Isotherm, Kinetics and Thermodynamic Studies

In this study, jojoba seeds residues are investigated for the removal of anionic dyes (Eriochrome black T and Congo red) from aqueous phase after extraction of oil and defatting (washing with n-hexane) from them. The fatted (F-JR) and defatted (DF-JR) jojoba residues were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron spectroscopy, thermogravimetric and BET analyzer. The results indicated that the surface of F-JR and DF-JR exhibited abundant oxygen functionalities (O–H, C–O, C=O, C–O–C) with highly porous surface morphology. The adsorption results showed that the removal of EBT and CR was significantly affected by solution pH and maximum removal of both dyes (EBT and CR) was obtained at pH 2 and 6, respectively, with equilibrium reached at 600 min. The kinetic results were best fitted with pseudo-second-order model. The Freundlich isotherm model well described the EBT adsorption, whereas CR adsorption better matches the Langmuir isotherm model for both F-JR and DF-JR. The maximum adsorption of EBT and CR was found to be 88.96 and 24.64 and 113.50 and 58.82 mg/g onto F-JR and DF-JR, respectively. The adsorption mechanism of EBT and CR mainly involved electrostatic attraction, chemical reactions, pi-pi interactions and development of hydrophobic forces. The adsorbent showed better removal performance of dyes, when compared to other agriculture residues, indicating potential and beneficial utilization of jojoba residues for effective decontamination of dye-contaminated wastewater.