Adsorption process and mechanism of acetaminophen onto commercial activated carbon

The presence of acetaminophen (also known as paracetamol; PRC) micropollutant in water can cause some potential health risks for human. In this study, commercial activated carbon (CAC), which has been oxidized with HNO3 by supplier to increase the oxygen-functional groups, was applied to remove PRC from water. Results demonstrated that CAC is a dominantly mesoporous material (accounting for 76.3%) with large surface area (SBET = 1284 m2/g) and high total pore volume (VTotal = 0.680 cm3/g). CAC possessed abundantly oxygen-containing functionalities and low pHPZC (4.95). Raman spectrum of CAC indicated that CAC possessed a more disordered structure with a high intensity ratio of D band and G band (ID/IG = 2.011). Adsorption study showed that the adsorption capacity of CAC towards PRC was less affected by solution pH value (2.0-10), and ionic strength (0-1.0 M NaCl), and different water matrixes (distilled water, tap water, coastal water, wastewater from water treatment plant, groundwater, and wastewater from beauty salon). The adsorption process occurred rapidly, with around 52% of PRC in solution (∼517 mg/L) being removed within 5 min of contact. The Langmuir maximum adsorption capacity of CAC was 221 mg/g under 1.0 g/L of CAC, pH 7.0, 25 °C, and initial concentration of paracetamol (∼100-1200 mg/L). The pore-filling was the most important mechanism. The SBET and VTotal of CAC after adsorption decreased (by approximately 96% for both) to 45.6 m2/g and 0.039 cm3/g, respectively. The second important mechanism involved in n-πinteraction was established by a remarkably decrease in the band intensity (the FTIR spectrum after adsorption) at 1630 cm-1 (the C=O group). Weak π-πinteraction was confirmed a significant decrease in the ID/IG ratio from 2.011 to 1.947 after adsorption. Hydrogen bonding formations were recommended by decreasing band intensity in FTIR spectrum at 3448 cm-1 (O-H) and 1045 cm-1 (C-O). Weak van der Waals force was identified through the study of effect of solution temperature and desorption. Consequently, oxidized CAC can serve as a promising and potential material for efficiently eliminating PRC from water environments.