Fast adsorption of BPA with high capacity based on Π-Π electron donor-acceptor and hydrophobicity mechanism using an in-situ sp² C dominant N-doped carbon

In this study, a high capacity (q_m = 1351 mg g⁻¹) with fast adsorption process (t < 5 min) towards bisphenol A (BPA) from water was achieved by an in-situ sp² C dominant N-doped carbon (polydopamine-carbon, PDA-C). The adsorption mechanism facilitating to the superior removal performance of PDA-C was systematically investigated by relationship study (adsorption capacity VS physiochemical property) and theoretical calculation. It could be concluded that the dominant sp² C (I_D/I_G = 0.92–1.02) and N-heteroatom (2.26–5.09 at. %) in PDA-C contributed to enhancing the adsorptive interactions of π-π electron donor-acceptor and hydrophobic effect between the PDA-C and BPA, thus realized a ~1.8 times enhancement of q_m in comparison with the conventional carbon (PRF-C). Calculated adsorption energy from the density functional theory (DFT) further demonstrated that the adsorption potential of N-doped carbon towards BPA increased linearly with increasing doping of N-heteroatom, especially for the pyridinic N which determined the hydrophobic effect of carbon. This finding firstly points out the dominant strengthening mechanism of N-heteroatom for carbonaceous adsorbent. The synthesized PDA-C showed a promising environmental application potential as revealed from the stable BPA adsorption efficiency in the interferences (H⁺/OH⁻, NaCl and HA), dynamic adsorption operation and multiple cycling test.