Improving photocatalytic activity by construction of immobilized Z-scheme CdS/Au/TiO2 nanobelt photocatalyst for eliminating norfloxacin from water.

To improve the photocatalytic activity of TiO2 NBs under irradiation of solar light, an immobilized Z-scheme composite photocatalyst CdS/Au/TiO2 NBs has been constructed. For the unique architectures, the TiO2 NBs provide more absorption and reaction sites, the CdS nanoparticles enhance overall light harvesting, and Au acts as the electron transfer mediator, promoting the interfacial charge transfer and efficient separation of electrons and holes. The morphology, elements, crystal structure, optical and photoelectrochemical properties, and photocatalytic activity of CdS/Au/TiO2 NBs were characterized. Results showed that CdS/Au/TiO2 NBs possesses higher photocatalytic activity toward the degradation of antibiotic norfloxacin under irradiation of simulated sunlight, which is attributed to the synergetic interaction of increased light absorption and separation of photogenerated electrons and holes. Besides, the degradation of norfloxacin was promoted by HCO3-, but inhibited by NO3- and Cl-. The radicals trapping experiments proved that superoxide radicals (O2-) was the dominating active species during the photocatalysis process. The photocatalytic degradation products of norfloxacin was analyzed, and nine intermediates were identified. Moreover, the photocatalytic degradation mechanism and photostability of CdS/Au/TiO2 NBs were analyzed in detail. The matched energy levels and unique ternary Z-scheme design are the key for improved photocatalytic activity. The deactivation of CdS/Au/TiO2 NBs after recycles mainly due to the release of CdS by photocorrosion and the loss of deposited Au.