Central composite methodology for methylene blue removal by Elaeagnus angustifolia as a novel biosorbent

In this research, the performance of Persian olive or Elaeagnus angustifolia (EA) as a potential biosorbent for the removal of methylene blue (MB) as a cationic dye from contaminated wastewaters was studied. In this regard, the response surface methodology (RSM) was used to investigate the effect of important parameters (time, pH, initial dye concentration and EA dosage) and their interaction on the removal efficiency, to optimize the process, and to model the experimental data. The Fourier transform infrared (FTIR) analysis, field emission electron microscope (FESEM) images, X-ray diffraction (XRD) pattern, Brunauer–Emmett–Teller (BET) surface area analysis, zeta potential and determination of isoelectric pH were employed to characterize the selected biosorbent. The dye removal efficiency of 95.66% was achieved at the predicted optimum conditions. The isotherm (Langmuir, Freundlich and Temkin), kinetic (pseudo-first-order, pseudo-second-order and intraparticle diffusion) and thermodynamic parameters were also investigated at equilibrium. High values of correlation coefficients indicated that experimental data are best fitted to Temkin isotherm and pseudo-second-order kinetic model. The thermodynamic parameters showed that the adsorption of MB onto the surface of EA was an exothermic and spontaneous process. This statistical survey illustrated that EA can be introduced as an effective biosorbent with high adsorption capacity of 185.185 (mg/g) for the removal of MB from colored industrial effluents.