Isotherm and Kinetic Studies of 4- nitrophenol Adsorption by NaOH-Modified Palm Oil Fuel Ash

The removal of 4-nitrophenol (4-NP) by NaOH-Modified Palm Oil Fuel Ash (POFA) from aqueous solutions was investigated. Experiments were carried out as function of contact time, initial concentrations (2500 mg/L – 4500 mg/L), pH (2 to 6), and temperature 30±1°C. The equilibrium adsorption data of 4-NP on activated palm ash were analyzed by Langmuir, Freundlich, and Temkin models. The results indicated that the Freundlich model provided the best correlation of the experimental data. The adsorption capacity of the activated POFA for the removal of 4-NP was determined with the Langmuir equation and found to be 500 mg/g. Adsorption data were modeled using Pseudo-First-Order, Pseudo-Second-Order, and Intra-Particle diffusion kinetics equations. It was shown that the Pseudo-second-order kinetic equation could be the best description of the adsorption kinetics. The particle diffusion mechanism is involved in the adsorption process, but it is not the rate controlling step. The results indicated that the activated POFA is suitable as adsorbent material for adsorption of 4-NP from aqueous solutions