Adsorption, equilibrium isotherm, and thermodynamic studies to the removal of acid orange 7

Abstract

Zero-valent FeNPs was prepared by using ascorbic acid and Fe(NO)3 redox system in presence of cetyltrimethylammonium bromide (CTAB). The morphology of the FeNPs was determined by SEM, TEM, EDX, FT-IR, XRD, and BET of FeNPs. The batch experiments were carried out to determine the effects of adsorbent dosage, contact time, pH, initial concentration of acid orange 7 and temperature. The mean of free energy pre molecule of adsorbent and heat adsorption showed that the physisorption and chemisorption both involved during the adsorption. Langmuir monolayer adsorption capacity Q0max(= 66.6 mg/g)is better than Dubinin-Radushkevich qDR (44.25 mg/g). The optimum pH for the adsorption was obtained at pH 4.0 for [acid orange 7]= 100 mg/L, amount of adsorbent = 0.05 g, and temperature = 298 K. Gibb's free energy (−0.72 to −3.8 kJ/mol), enthalpy (16.1 to 19.3 kJ/mol), and entropy changes (56.4 to 70.1 J/K/mol)on the chemisorption of orange 7, indicate endothermic, spontaneous, and feasibility nature of the adsorption process. The results showed that the Langmuir isotherm and pseudo-second-order kinetic models fitted the experimental data better than other isotherm and kinetic models. The kinetic studies suggest that the adsorption follow an involvement of film diffusion and intraparticle diffusion mechanism. The as prepared FeNPs can be an alternative for more costly nano-adsorbents used for toxic dye removal from aqueous solution.