3D Bombax-structured carbon nanotube sponge coupling with Ag3PO4 for tetracycline degradation under ultrasound and visible light irradiation.

A novel photocatalytic carbon nanotube sponge with three-dimensional Bombax-structure was fabricated by a facile chemical vapor deposition followed by in situ ion-exchange approach. The as-prepared sponge achieved both high-efficiency adsorption and photocatalysis towards antibiotics, which can remove up to 90% of tetracycline within an hour. The morphology and mechanism of the photocatalytic CNT sponge were explored by multiple measures. Results show the functional groups and high specific surface area of CNT sponge play vital roles in preparing this Bombax-structured Ag₃PO₄/CNT sponge, the band gap of which can be tuned by varying the ration between Ag₃PO₄ and CNT. The photodegradation experiments of tetracycline with the assistance of ultrasound irradiation were performed, Ag₃PO₄/CNT sponge exhibits preferable photocatalytic activity, which can be attributed to both the enhancement of specific surface area of Ag₃PO₄ and the cavitation effect on CNT surface. The efficiency contributed by ultrasound could account for more than half of the degradation efficiency when the ultrasound power was 100 W. The improvement in transfer efficiency and the delay in charge recombination of Ag₃PO₄/CNT sponge were further verified by Electrochemical impedance spectra (EIS) and Photoluminescence tests (PL). Reactive free-radical species were detected by the Electron Spin Resonance (ESR). The intermediates and possible pathway were analyzed by gas chromatography-mass spectrometer (GC-MS) technique.