Adsorption of acid red 18 from aqueous solutions by GO-COFe2O4: Adsorption kinetic and isotherms, adsorption mechanism and adsorbent regeneration

Abstract

In the present study, graphene oxide-cobalt ferrite (GO-CoFe2O4) was synthesized by sol-gel method as an adsorbent in the removal of acid red 18 (AR18) dye. The characteristics of the magnetic adsorbent were analyzed through SEM, TEM, XRD, FTIR, N2 adsorption-desorption, and VSM. The findings of the diagnostic analysis showed a surface area of 58.92 m2/g, a pore size of 2 nm, and a magnetic property of 3.82 emu/g for the GO-CoFe2O4 composite. The effect of the operational parameters determined the maximum removal efficiency (100%) at pH of 5, adsorbent dosage of 1 g/L, and AR18 concentration of 25 mg/L. The effect of anions on the removal rate of AR18 by GO-CoFe2O4 composite was evaluated, and the results were its negative effect in reducing the efficiency in the order of NaCl < NaNO3 < Na2SO4 < Na2CO3. Thermodynamic parameters including ΔG°, ΔH°, and ΔS° explained that the adsorption of AR18 on the synthesized composite is favorable, spontaneous, and endothermic. The experimental data was studied by four kinetic equations including pseudo-first-order, pseudo-second-order, Elovich and intraparticle-diffusion and the results based on R2 and qe were consistent with pseudo-second-order kinetics. Eleven isotherm models were selected for adsorption equilibrium data, and the data were fitted with all isotherm models with R2 > 0.95. The results of adsorbent regeneration by peroxymonosulfate (PMS) activation showed that with increasing treatment time and PMS amount (up to 10 mM), the regeneration efficiency increases significantly up to 73.72%.