N-nitrosodimethylamine adsorption in aqueous phase by activated carbons with different porous and surface structures

N-nitrosodimethylamine (NDMA) is a member of the N-nitrosamines family, which are often found in foods, beers and cigarettes and considered to have carcinogenic, mutagenic and teratogenic properties. The adsorption of toxic NDMA from aqueous solution in activated carbons with different porous structures and surface properties was investigated. The activated carbons were modified by heating in nitrogen atmosphere. Nitrogen adsorption/desorption, infrared and thermogarvimetric techniques were utilized to characterize porous structures and surface properties. It was observed that equilibrium data followed the Freundlich isotherm, and most NDMA preferentially adsorbed in approximately 0.45-nm micropores by physisorption mechanism. The adsorption capacities of thermally treated samples were significantly higher, despite the decreases in micropore volume and surface area. Without thermal treatment, water molecules are preferentially adsorbed in micropores, resulting in lower NDMA adsorption capacity, whereas after treatment, improved hydrophobic pore properties increases NDMA adsorption because of reduced water competition in pores. Thermal treatments would significantly remove surface oxygen groups and carbon atoms, and change the morphology of pore walls, thus altering adsorption behavior. With enhanced surface properties, NDMA was possibly adsorbed with stronger dispersive interaction between the hydrophobic -CH ₃ and the aromatic rings of the carbon surface enabling higher adsorptive capacity.