Flower-globular BiOI/BiVO4/g-C3N4 with a dual Z-scheme heterojunction for highly efficient degradation of antibiotics under visible light

A novel BiOI/BiVO4/g-C3N4 composite photocatalyst was successfully prepared via a simple ultrasonic-assisted hydrothermal method. The crystal structure, element composition, micro-morphology and optical performance of BiOI/BiVO4/g-C3N4 were analyzed. All composites showed better photocatalytic activity than pure BiVO4 in degrading levofloxacin hydrochloride (LEF). The kinetic constant of BiOI/BiVO4/g-C3N4 (0.0152 min−1) was 6.91, 3.10, 2.20 and 1.60 times that of g-C3N4 (0.0022 min−1), BiVO4 (0.0049 min−1), BiOI (0.0069 min−1) and BiVO4/g-C3N4 (0.0095 min−1), respectively. The degradation rate of LEF can reach 89.01% under optimal conditions. In addition, the influences of different pH values, inorganic salt ions and different kinds of antibiotics, binary and ternary compound antibiotics on photocatalytic activity were studied under visible-light driving. The photocatalyst showed excellent stability after being recycled three times. Three possible degradation pathways of LEF were analyzed by liquid chromatography-mass spectrometry (LC-MS). A possible mechanism of dual Z-scheme heterojunction electron transfer was put forward in this work. This transformation mode of electrons promotes the efficient separation of photo-excited carriers, which is also the reason why the photocatalytic activity is improved after constructing the heterostructure. The prepared composite exhibited eminent application prospects in the field of antibiotic wastewater treatment.