Mechanism of irreversible adsorption of phenolic compounds by activated carbons

Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater

“…Highest affinity with sorbates is thus not always desirable because it may decrease their ability for regeneration. The surface groups of AC can enhance oxidative coupling of organic molecules (aromatic hydrocarbons) to form aromatic oligomers, which irreversibly adsorbed on the carbon surface [92][93][94][95]. Hence, the design of optimal AC adsorbents should provide suitable textural properties and surface groups.…”

“…The mechanism of oxidative phenol destruction is complex, but it is generally accepted that the liquid phase oxidation of phenols and substituted phenols by molecular oxygen is an electrophilic reaction that follows a heterogeneous-homogeneous free radical chain mechanism [65,[192][193][194]. According to the postulated mechanism, the easiness of the organic to form free radicals is a key parameter that can be inferred from critical oxidation [92] or halve-wave potentials [192]. Available literature values of the respective potentials are given in table 13.…”

“…The highest phenol feed concentration of 10 g/ L not only suppressed the carbon combustion providing short saturation time (2 h) and densely crowed phenol surface, but also produced a considerable irreversible weight gain as reported above. Activated carbon is well known to catalyse phenol coupling reactions [92][93][94][95] forming condensation products that can strongly adsorb onto the carbon. Not surprisingly, a batch study testing the CI carbon on phenol WAO [61] deduced from liquid and gas phase carbon balances the deposit of important amounts of carbonaceous matter on the carbon surface.…”

Kinetic and Isothermal Modelling of the Adsorption of Compounds from Olive Mill Wastewater onto Activated Carbon

“…This may be due to the increase in activity of phenolic compounds with decreasing pH and this infl uence on reversible uptake should be minimal at compound pH values well below the solute pK a . It can be concluded from the dependence of the irreversible adsorption that oxidative coupling of phenolic compounds is more facile in alkaline than in acidic media (21).…”

Desorption by ultrasound: Phenol on activated carbon and polymeric resin

“…Indeed, recently there has been an increasingly large amount of literature devoted to the study of adsorption for the removal of aqueous organic species such as phenols and substituted phenols using activated carbon (Grant and King, 1990;Stenzel, 1993;Karanfil et al, 1994;Leng and Pinto, 1996;Khan et al, 1997;Kilduff and King, 1997;Wang et al, 1997) and macrorecticular polymeric resins (Farrier et al, 1979;Goto et al, 1984;Furuya et al, 1Y89;Winkler et al, 1996;Lee and Ku, 1996). Although adsorption of phenolic compounds onto adsorbents such as granular activated carbon (GAC) and polymeric resins is relatively simple, the process of regenerating the adsorbent by desorption of the organic adsorbate still poses a major challenge to workers in this field, notably because of the high affinity of the compounds to the sorbent surface.…”