The two-stage removal process of tetracycline (TC) in aqueous solutions using a novel photocatalyst based on nano-zero-valent iron (NZVI), g-C3N4 and expanded graphite by carbon layer (EGC) is reported for the first time. The composite (NZVI/g-C3N4@EGC) exhibits remarkable adsorption, reduction ability and visible light activity over the reaction course. Compared with pristine g-C3N4 (25.9%) and pure NZVI (45.9%), NZVI/g-C3N4@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-C3N4 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 (˙O2−) 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-C3N4@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-C3N4@EGC has favorable prospects in the direction of the photocatalytic degradation of antibiotic wastewater.
To solve severe photocorrosion of Ag 3 PO 4 , polyaniline for transporting holes and reduced graphene oxide (rGO) for transferring electrons were co-incorporated with Ag 3 PO 4 by an in-situ precipitation procedure and a following hydrothermal method , reaching the superior carrier separation efficiency via synergetic effect of PANI and rGO. Consequently, 5% rGO/Ag 3 PO 4 /PANI exhibited the excellent photocatalytic performance of 86.2% removal rate towards ciprofloxacin (CIP) within 15 min, which was much better than Ag 3 PO 4 , Ag 3 PO 4 /PANI and many reported photocatalysts . After four consecutive cycles, the composites performed better stability with 81.0% removal rate. Generally, photocatalytic activity depended on efficiencies of light absorption ( η abs ), charge separation ( η sep ) and charge injection ( η inj ). η sep of rGO/Ag 3 PO 4 /PANI was 11.5 and 8.70 folds higher than that of Ag 3 PO 4 and Ag 3 PO 4 /PANI, while η abs and η inj of rGO/Ag 3 PO 4 /PANI were not improved compared with Ag 3 PO 4 and Ag 3 PO 4 /PANI, strongly manifesting synergetic effect of PANI and rGO on Ag 3 PO 4 accelerated the charge separation and finally enhanced the photocatalytic activity . Besides, rGO greatly improved the adsorption efficiency for CIP and the maximum adsorption capacity was enhanced to be 19.4 mg/g which was 6.88 folds than that of Ag 3 PO 4 , being advantageous to enhancing the photocatalytic activity. The work offered an excellent reference for designing and constructing photocatalysts with superior charge separation showing excellent photocatalytic performance, which were potential candidates for degrading antibiotics in environmental treatment.
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