Nitrogen-Doped Reduced Graphene Oxide as a Bifunctional Material for Removing Bisphenols: Synergistic Effect between Adsorption and Catalysis

Nitrogen modified reduced graphene oxide (N-RGO) was prepared by a hydrothermal method. The nitrogen modification enhanced its adsorption and catalysis ability. For an initial bisphenol concentration of 0.385 mmol L^–1, the adsorption capacity of N-RGO was evaluated as 1.56 and 1.43 mmol g^–1 for bisphenol A (BPA) and 1.43 mmol g^–1 for bisphenol F (BPF), respectively, both of which were about 1.75 times that (0.90 and 0.84 mmol g^–1) on N-free RGO. N-RGO could activate persulfate, producing strong oxidizing sulfate radicals. The apparent degradation rate constant of BPA on N-RGO was 0.71 min^–1, being about 700 times that (0.001 min^–1) on N-free RGO. In mixtures of various phenols, the degradation rate constant of each phenol was linearly increased with its adsorption capacity. A simultaneous use of N-RGO and persulfate yielded fast and efficient removal of bisphenols. The use of N-RGO (120 mg L^–1) and persulfate (0.6 mmol L^–1) almost completely removed the added bisphenols (0.385 mmol L^–1) at pH 6.6 within 17 min. A mechanism study indicated that the adsorption enriched the pollutant, and the catalytically generated sulfate radicals rapidly degrade the adsorbed pollutant, accelerating in turn the adsorption of residual pollutant