Role of the functional groups in the adsorption of bisphenol A onto activated carbon: thermal modification and mechanism

Surface properties of activated carbons play vital roles in adsorption of contaminants. Aiming to improve the adsorption of phenolic endocrine disrupting chemicals (EDCs), commercially activated carbon (W20) was modified via thermal treatment to obtain a carbon sample (W20N) with different characteristics. The content of acidic oxygen-containing groups of W20 was obviously reduced by the thermal modification. Bisphenol A (BPA) was chosen as the target compound. The adsorption results indicated that the acidic oxygen-containing groups (especially carboxyl groups) on the surface of activated carbons weakened the ability of carbon acting as pi-donors that lead to the reduction of BPA adsorption. Compared to W20, W20N with a greater number of phenyl groups exhibited higher adsorption capacity for BPA in a wide range of pH (4.0-10.0). Therefore, thermal modification improved BPA adsorption onto activated carbon. Furthermore, thermodynamic analysis and effect of solution pH revealed that BPA adsorption onto W20 and W20N probably followed face-to-face pi-pi dispersion interactions. Coexisting tannic acid (TA) formed BPA-TA complexes and played a negative role in BPA adsorption onto carbon based on the pi-pi dispersion interaction. This study should help broaden the scope of modification methods and the application of activated carbons to enhance the removal of phenolic EDCs.