WITHDRAWN: Clean production of a new activated carbon/tungstate composite from olive mill wastewater for the removal of diclofenac and paracetamol: Adsorption mechanism and transition state

Abstract

A new carbon/tungstate composite based on liquid by-products, in particular olive mill wastewater (OMWW), was used to remove diclofenac and paracetamol, by adsorption. The composite was prepared using a clean method based on the addition of dissociated tungstate in hydrogen peroxide (H2O2), combined with single carbonization at 950 °C for 5 min. To study the effect of tungstate on composite properties, 4 carbon/tungstate combinations, varying as a function of the mass content of tungstate added, were studied: 0, 1, 2 and 3%wt. The optimum combination showed significant porosity, thermal stability and a wealth of sites suitable for adsorption. The adsorption tests showed that the Freundlich and double-layer adsorption models best described the equilibrium relationship, while the pseudo-second-order model best described the kinetics, regardless of adsorbate. Moreover, high saturation adsorption capacities, for diclofenac (712 mg g−1) and paracetamol (517 mg g−1), were obtained. Non-steric results showed a double-layer adsorption in a parallel orientation and an interaction ratio of 3 sites per molecule. The Activation parameters confirmed rapid adsorption kinetics, physical interactions and easy desorption from the surface. The chemical mechanism was governed by bi/tridentate interactions with a predominance of π-π interactions. The treatment of a real pharmaceutical wastewater with a chemical oxygen demand of 8.1 g(O2).L−1 resulted in 89% removal. Overall, this work presents a new clean solution for the capture of pharmaceutical molecules from water and a detailed presentation of adsorption mechanisms, in particular: chemical, physical, non-steric and at the transition state.