Photocatalytic performance of multi-walled carbon nanotube/BiVO4 synthesized by electro-spinning process and its degradation mechanisms on oxytetracycline

Abstract

To enhance the photocatalytic performance of bismuth vanadate (BiVO4) and reveal its catalytic mechanism, a multi-walled carbon nanotube photocatalyst (MWCNT/BiVO4) was prepared by sol-gel preparation and an electro-spinning process. Oxytetracycline was used as the target trace persistent pollutant to research its potential degradation pathways catalyzed by MWCNT/BiVO4. X-ray powder diffraction spectroscopy (XRD), Raman spectra, field emission scanning electron microscopy (FE-SEM) and field emission transmission electron microscopy (FE-TEM) were used to observe the crystalline phase, morphological structure of MWCNT/BiVO4. The modification by MWCNTs caused changes of functional groups on the surface and a binding energy shift of Bi4f and V2p, as determined from X-ray photoelectron spectroscopy (XPS). Ultraviolet–visible diffuse reflectometry (UV–Vis DRS) revealed that the band gap became narrower and photoluminescence spectra suggested the recombination of photogenerated electron–hole pairs were inhibited after MWCNT modification. All of the characterizations showed enhancement of catalytic performance of MWCNT/BiVO4. The results from the high-performance liquid chromatography (HPLC) indicated that the degradation rate of oxytetracycline had increased by 42.2% and reached 88.7% within 60 min. Electron paramagnetic resonance (EPR) signals of ·OH and ·O2− were detected and potential photocatalytic mechanisms of the photocatalysts were put forward. Six reaction pathways were proposed based on ultra-performance liquid chromatography triple-quadrupole tandem mass spectrometry (UPLC–MS/MS) results: demethylation (−14 Da), secondary alcohol oxidation (−2 Da), dehydration (−18 Da), hydroxylation (+16 Da), decarbonylation (−28 Da) and deamination (−15 Da). The present study provides a reference for the application of photocatalytic degradation by MWCNT/BiVO4 on hard degradable substances in aquatic environment.