Ortho-Nitro-Phenol adsorption onto alumina and surfactant modified alumina: kinetic, isotherm and mechanism

Alumina (Al2O3) and its elaborated composite, Hexadecyl Tri Methyl Ammonium Bromide/Al2O3 (HDTMA/Al2O3), were used as adsorbents for removal of ortho-nitrophenol (ONP) from aqueous solution. The adsorbents were characterized by means of FTIR, B.E.T, XRD, and TEM analysis. Adsorption experiments were conducted in a batch system as a function of ONP concentration (4 × 10−4 M), contact time and temperature (25 to 45 °C). The experimental results indicate that, HDTMA/Al2O3 adsorbent possesses a greater affinity toward ONP than Al2O3 at pH = 6. Pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyze the kinetic data obtained at different concentrations. The pseudo-second-order kinetic model provided the best fit to the experimental data for the adsorption of ONP on both adsorbents, and the intra-particle diffusion was not only the rate controlling step. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Redlich-Peterson and Temkin isotherm models. The results indicate that the Langmuir model does not provide the best fit of the experimental data. A thermodynamic study indicates that the adsorption of ONP on both adsorbents has been found to be spontaneous and endothermic in nature.