Facile assembly of novel g-CN@expanded graphite and surface loading of nano zero-valent iron for enhanced synergistic degradation of tetracycline.

The two-stage removal process of tetracycline (TC) in aqueous solutions using a novel photocatalyst based on nano-zero-valent iron (NZVI), g-CN and expanded graphite by carbon layer (EGC) is reported for the first time. The composite (NZVI/g-CN@EGC) exhibits remarkable adsorption, reduction ability and visible light activity over the reaction course. Compared with pristine g-CN (25.9%) and pure NZVI (45.9%), NZVI/g-CN@EGC achieves high degradation efficiency of TC (98.5%) due to the formation of a heterogeneous photo-Fenton system. This study shows that synergistic effects are achieved in the reaction system, including maintaining the reduction ability of NZVI and enhancing the photocatalytic activity of g-CN by facilitating the separation of photogenerated electrons (e) and holes (h). TC removal involved a two-stage process of adsorption-reduction and photo-degradation. The quencher experiments determined that holes (h) and superoxide radicals (˙O ) are the major reactive species in the degradation of TC. The degradation pathways of TC were proposed based on the analysis of the intermediates. In addition, NZVI/g-CN@EGC revealed a high stability in a five-cycle test and good magnetic properties for facile separation from aqueous solutions. From an application viewpoint, NZVI/g-CN@EGC has favorable prospects in the direction of the photocatalytic degradation of antibiotic wastewater.