Synergistic Effects of Magnetic Z-Scheme g-C3N4/CoFe2O4 Nanofibres with Controllable Morphology on Photocatalytic Activity

Abstract

The rational design of interfacial contacts plays a decisive role in improving interfacial carrier transfer and separation in heterojunction photocatalysts. In Z-scheme photocatalysts, the recombination of photogenerated electron-hole pairs is prevented so that the redox capacity is maintained. Here, one-dimensional graphitic carbon nitride (g-C₃N₄)/CoFe₂O₄ fibres were synthesised as a new type of magnetic Z-scheme visible-light photocatalyst. Compared with pure g-C₃N₄ and CoFe₂O₄, the prepared composite photocatalysts showed considerably improved performance for the photooxidative degradation of tetracycline and methylene blue. In particular, the photodegradation efficiency of the g-C₃N₄/CoFe₂O₄ fibres for methylene blue was approximately two and seven times those of g-C₃N₄ and CoFe₂O₄, respectively. The formation mechanism of the Z-scheme heterojunctions in the g-C₃N₄/CoFe₂O₄ fibres was investigated using photocurrent spectroscopy and electrochemical impedance spectroscopy. We proposed that one of the reasons for the improved photodegradation performance is that the charge transport path in one-dimensional materials enables efficient photoelectron and hole transfer. Furthermore, the internal electric field of the prepared Z-scheme photocatalyst enhanced visible-light absorption, which provided a barrier for photoelectron-hole pair recombination.

Keywords: Z-scheme; magnetic; nanofibers; photocatalyst.

Scheme 1

Synthesis of the composite photocatalysts used in this study.

Figure 1

SEM images of CN/CFO-0.05 (a,b,e); TEM images of CN/CFO-0.05 (c,d); EDS elemental mapping images of CN/CFO-0.05 (f–j).

Figure 2

FT-IR patterns of pure CN, CFO and composite samples of different proportions (a); X-ray diffraction patterns of pure CN, CFO, and CN/CFO-0.05 (b); N₂ adsorption–desorption isotherms of pure CFO, CN/CFO-0.05, and CN/CFO-0.01 (c); pore size distribution of pure CFO, CN/CFO-0.05, and CN/CFO-0.01 (d).

Figure 3

Measured XPS spectrum of CN/CFO-0.05 (a); narrow-band Co 2p, Fe 2p, O 1s, C 1s, and N 1s spectra of CFO, CN, and the CN/CFO composites (b–f).

Figure 4

Photocatalytic degradation efficiency of CN/CFO for TC, first-order reaction kinetics, and degradation efficiency after three cycles (a–c); photocatalytic degradation efficiency of CN/CFO for MB, first-order reaction kinetics, and degradation efficiency after three cycles (d–f); EPR spectra of CN/CFO-0.05 and CN/CFO-0.01 in the presence of DMPO (g); radical capture experiment results (h); energy band structure of the catalysts (i).

Figure 5

UV–Vis absorption spectra (a), band gaps (b), and PL spectra (c) of CFO, CN, and CN/CFO-0.05; EIS impedance profiles of CFO, CN, and CN/CFO-0.05 (d); transient photocurrent responses of CFO, CN, and CN/CFO-0.05 (e).

Figure 6

Valence band positions of CN, CFO (a,b); transient fluorescence lifetime of CN/CFO-0.05 (c).

Figure 7

Electron-transfer pathways in the Z-scheme CN/CFO heterojunction composite photocatalysts.