Three novel biosorbents based on modified peanut shells for direct red 80 removal: parameter optimization, process kinetics and equilibrium

Abstract

In this study, we report three novel low-cost biosorbents based on modified peanut shells (TEPA-PS, TETA-PS and DETA-PS) prepared by epichlorohydrin and tetraethylenepentamine (TEPA), triethylenetetramine (TETA), or diethylenetriamine (DETA) as the etherifying and crosslinking agents, respectively. A single factor test was employed to optimize the corresponding preparation conditions and hence obtain a higher removal efficiency for direct red 80 (DR80) treatment. Consequently, a central composite design (CCD) was utilized to further analyze the individual and interactive effects of different process variables (such as initial concentration of the dye, temperature and adsorption time) of the adsorption capacity for dye removal onto the biosorbents. The corresponding experimental data could be simulated excellently using second order polynomial regression models due to high correlation coefficient values (R²) of 0.9973, 0.9944 and 0.9960, low p-value of 0.000, and their F values of 404, 196 and 274 for the TEPA-PS, TETA-PS and DETA-PS biosorbents, respectively. As a result, the optimum conditions were found to be C_DR80 = 145 or 143 mg L⁻¹, T = 75 °C and t = 161 min for DR80 adsorption by TEPA-PS and TETA-PS, or DETA-PS. The measured maximum experimental adsorption capacities for DR80 under the above optimum conditions were 690.18, 657.55 and 588.56 mg g⁻¹, which were in good agreement with their corresponding predicted values (679.96, 674.51 and 579.08 mg g⁻¹) owing to small relative errors of 1.48, −2.58 and 1.61%, respectively. In addition, many aspects of the kinetics and equilibrium isotherm of the dye adsorption onto modified PS were also investigated. The results indicate that pseudo-second-order and Langmuir models present the best fit to the kinetic and isotherm data. Finally, careful thermodynamic investigations demonstrate that the adsorption processes based on modified PS are spontaneous and endothermic.