Removal of diclofenac from wastewater by adsorption on a biosorbent from dragon fruit waste: equilibrium and kinetics.

This study aimed to investigate the equilibrium and kinetics of adsorption of diclofenac on non-activated and activated charcoal made from dragon fruit peel at a carbonization temperature of 500 °C. The experiments were carried out in agitated flasks containing the adsorbents and diclofenac solutions at initial adsorbate concentrations from ∼20 to 307 mg L-1 at ∼25 °C and pH 5.7. The highest adsorption capacity of the adsorbent was 64.54 mg g-1 by charcoal activation with inorganic acids. Using activated charcoal as adsorbent, the highest equilibrium yield of removal of diclofenac from the liquid was close to 91% in approximately 1 hr. At the examined pH, the deprotonation of activated charcoal and the almost complete dissociation of diclofenac indicate physical adsorption of the conjugate anion of diclofenac. These explanations are consistent with results of point of zero charge of activated charcoal, pKa of diclofenac, Brunauer-Emmett-Teller analysis, energy dispersive X-ray and Fourier transform infrared spectroscopy of the adsorbents. The equilibrium and kinetic results were described by the Langmuir and Freundlich isotherms and simplified kinetic models involving empirical pseudo first- and second-order adsorption rate expressions.