Fabrication of nitrogen-doped graphene nanosheets anchored with carbon nanotubes for the degradation of tetracycline in saline water.

The treatment of wastewater with high salinity is still a challenge because of the quenching effect of various anions on radical processes. The nonradical process may be a more promising pathway. Herein, a 3D structured nitrogen-doped graphene nanosheet anchored with carbon nanotubes (N-GS-CNTs) was prepared by direct pyrolysis of K3Fe(CN)6. The as-prepared catalyst can effectively activate peroxymonosulfate (PMS) for mineralization of tetracycline (TC) over a wide pH range (from 3 to 11) and even in high saline water (500 mM Cl-, HCO3-, etc.). The degradation mechanism was elucidated by both experimental characterizations and DFT calculations. The high catalytic efficiency was attributed to accelerated electron transfer from donor (TC) to acceptor (PMS) in the presence of the catalyst, which acts as electron shuttle mediators to promote a nonradical process. At the same time, the catalyst also enhances the production of singlet oxygen (1O2), hence further increasing the degradation rate. This study not only provides a simple method for synthesizing N-GS-CNT catalysts but also provides new insights into the electron transfer pathway for the removal of organic pollutants under high salinity conditions.