Feasibility and Mechanism of Desorption of Phenolic Compounds from Activated Carbons

The desorption efficiency (DE) of phenols, including p-nitrophenol, p-chlorophenol, p-hydroxybenzoic acid, phenol, and hydroquinone, from activated carbons (ACs), has been investigated with a variety of solvents to gain insight into the feasibility and mechanism of phenols desorption. Ultrasound (US), microwaves (MW), and flow mode have been used to facilitate phenols desorption. It was found that the basicity, polarity, and hydrogen bonds of solvents synergistically affected phenols desorption. The preferred solvents (Lewis basic solvents, acetic acid, and alcohols) gave highly efficient elution. Increasing the alkaline or/and hydrogen bonding interactions, by adding ammonia or urea, enhanced the desorption in most solvents. Moreover, although US and MW heating slightly improved desorption, complete desorption was easily achieved in flow mode. It is demonstrated herein that phenols adsorption on the ACs is a reversible physical process, thus proving the feasibility of phenols desorption with proper solvents. Comparison of DRIFT spectra and porosity properties measurements of pristine, loaded, and eluted ACs confirmed our results. It can therefore be stated that our procedure can be used to dispose of secondary pollution while cutting post-treatment costs thanks to the recovery of valuable compounds and ACs recycling.