Adsorption of metha-nitrophenol onto alumina and HDTMA modified alumina: Kinetic, isotherm and mechanism investigations

In this work, the removal of Metha-nitrophenol (MNP) from aqueous solutions onto γ-Al2O3 and hexadecyltrimethyl ammonium bromide modified alumina (HDTMA+/Al2O3) and its adsorption mechanism were investigated. Kinetics and isotherms experiments were made in batch experiments at pH = 6, versus time, initial concentrations of MNP and adsorption temperature. The results indicated that the MNP adsorption reached equilibrium within 1 h, and the removal efficiency of MNP was enhanced by HDTMA+/Al2O3 adsorbent, compared to alumina alone, and an increase in adsorption temperature, indicating the endothermic process. The experimental data were examined by using linear and nonlinear forms of the kinetics and the isotherms models. Based on the errors calculated values of R2 (Coefficient of determination), χ2 (Chi-square) and standard deviation (∆q (%)), it was found that the nonlinear forms of second order kinetic model and Freundlich isotherm model are best fit the experimental data for both adsorbents. FTIR analysis of both adsorbents, before and after adsorption of MNP, shows that the adsorption mechanism of MNP occurs on heterogeneous sites via the OH and NO2− functional groups of MNP, following two different mechanisms.