Highly efficient photodegradation of ciprofloxacin by dual Z-scheme Bi2MoO6/GQDs/TiO2 heterojunction photocatalysts: mechanism analysis and pathway exploration

Abstract

There is a high demand for photocatalysts that can efficiently degrade antibiotics; however, there are challenges in technological development related to charge transfer and light capture ability. In this study, ternary Bi2MoO6/GQDs/TiO2 (denoted as BGT; GQDs refer to graphene quantum dots) heterojunction photocatalysts with high ciprofloxacin (CIP) photodegradation efficiency were successfully prepared. BGT with a 0.20 mL GQD dispersion solution (BGT-2) exhibited the highest CIP photodegradation efficiency (90.21 %). The rate constant of BGT-2 was 15.49 × 10−3 min−1, which was 4.01, 4.16, and 9.22 times higher than those of Bi2MoO6/TiO2 (3.86 × 10−3 min−1), Bi2MoO6 (3.72 × 10−3 min−1), and TiO2 (1.68 ×10−3 min−1), respectively. The degradation efficiencies of amoxicillin and tetracycline hydrochloride were 78.98 % and 92.49 %, respectively. The effects of pH values, water sources, and inorganic anions on CIP degradation were systematically explored. In addition, three environmentally friendly degradation pathways were proposed based on liquid chromatography-mass spectrometry (LC-MS) results and the toxicity evaluation of the various intermediates. Testing the optical and electrochemical properties of the catalysts showed that the synthesized dual Z-scheme heterojunctions can significantly improve the light capture ability and reduce the photogenerated electron-hole recombination rate, effectively addressing the challenges encountered with the use of photocatalysts.