Facile nitrogen impregnation of granular activated carbon enhances organic micropollutant removal via electron donor-acceptor and electrostatic interactions

Organic micropollutants (OMPs) pose significant risks to aquatic ecosystems and drinking water safety. This study developed nitrogen–impregnated granular activated carbon (N-GAC) with ammonium chloride as a precursor to enhance OMP removal through surface functionalization. Optimal nitrogen loading (∼0.1 wt%) achieved minimal surface area loss (1.4%) while shifting the point of zero charge (pH pzc ) from pH ∼8 to 10. Four structurally diverse OMPs, including naproxen (NPX), bisphenol-A (BPA), diclofenac (DCF), and ibuprofen (IBP), were evaluated to establish structure-performance relationships. The most remarkable improvement was achieved in NPX removal, with pseudo first-order rate constants increasing by 67% at pH 6. The maximum adsorption capacity of IBP increased by 240%, compared to virgin GAC. Mechanistic investigations revealed that nitrogen impregnation could increase the abundance of pyridinic nitrogen and pH pzc , likely resulting in enhanced π-π electron donor-acceptor interactions, electrostatic attraction at environmentally relevant pH, and hydrogen bonding interactions between OMPs and GAC. Rapid small-scale column tests with settled water from a drinking water treatment plant validated practical applicability, achieving 86%, 70%, 33%, and 43% higher removal for NPX, BPA, DCF, and IBP respectively than virgin GAC over 30000 bed volumes treated. This study provides insights into a mechanism-driven strategy for enhancement in GAC performance targeting OMP removal.