Further insight into the adsorption mechanism of lead(ii) ion on anionic surfactant-modified activated carbon

In this paper, the detailed adsorption mechanism of lead ion (Pb(II)) solution in water on anionic surfactant-modified activated carbon (ASMAC) has been investigated. ASMAC were obtained from cigarette butt waste before being modified using anionic surfactant, i.e., disodium cocoyl glutamate solution in water with a concentration of 0.1 % (v/v). The synthesized ASMAC consists of aromatic rings functionalized by carboxyl and hydroxyl groups, which have an amorphous property and a slightly porous structure. The optimum adsorbent dosage and adsorption time were 10 mg of ASMAC and 35 min, respectively, producing the maximum adsorption capacity of 257.06 mg/g at the initial concentration of Pb(II) ion and temperature of 120 ppm and 303 K, respectively. The adsorption of Pb(II) ions on ASMAC obeys the Pseudo Second Order kinetic model and the Langmuir isotherm, suggesting that Pb(II) ions form a monolayer on the surface of ASMAC through chemisorption. The calculated thermodynamic parameters reveal that the adsorption process was endothermic and spontaneous. FTIR spectroscopy confirmed the changes of carbonyl group (C O) from ASMAC to the C-O group after Pb(II) ion adsorption. Hence, the proposed adsorption mechanism can be explained as follows: Initially, the film diffusion occurred due to the electrostatic interaction between Pb(II) ion and ASMAC, specifically on the deprotonated carboxyl moieties (-COO - ) of the ASMAC surface. This interaction formed a new chemical/covalent bonding between Pb(II) ion and oxygen atoms of carboxyl groups, forming a bidentate complex.