Synthesis and Characterization of an α-Fe2O3-Decorated g-C3N4 Heterostructure for the Photocatalytic Removal of MO

Abstract

This study describes the preparation of graphitic carbon nitride (g-C₃N₄), hematite (α-Fe₂O₃), and their g-C₃N₄/α-Fe₂O₃ heterostructure for the photocatalytic removal of methyl orange (MO) under visible light illumination. The facile hydrothermal approach was utilized for the preparation of the nanomaterials. Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), and Brunauer-Emmett-Teller (BET) were carried out to study the physiochemical and optoelectronic properties of all the synthesized photocatalysts. Based on the X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance (DRS) results, an energy level diagram vs. SHE was established. The acquired results indicated that the nanocomposite exhibited a type-II heterojunction and degraded the MO dye by 97%. The degradation ability of the nanocomposite was higher than that of pristine g-C₃N₄ (41%) and α-Fe₂O₃ (30%) photocatalysts under 300 min of light irradiation. The formation of a type-II heterostructure with desirable band alignment and band edge positions for efficient interfacial charge carrier separation along with a larger specific surface area was collectively responsible for the higher photocatalytic efficiency of the g-C₃N₄/α-Fe₂O₃ nanocomposite. The mechanism of the nanocomposite was also studied through results obtained from UV-vis and XPS analyses. A reactive species trapping experiment confirmed the involvement of the superoxide radical anion (O₂^•-) as the key reactive oxygen species for MO removal. The degradation kinetics were also monitored, and the reaction was observed to be pseudo-first order. Moreover, the sustainability of the photocatalyst was also investigated.

Keywords: MO photodegradation; alignment of energy levels; g-C3N4; g-C3N4/α-Fe2O3 nanocomposite; heterostructure (type-II).

Figure 1

The XRD patterns.

Figure 2

SEM micrographs of (a) α-Fe₂O₃ agglomerated nanoparticles, (b) g-C₃N₄ crumpled nanosheet, and (c) g-C₃N₄/α-Fe₂O₃ nanosheet well decorated with nanoparticles.

Figure 3

EDS spectra of: (a) g-C₃N₄, (b) α-Fe₂O₃, and (c) g-C₃N₄/α-Fe₂O₃ with quantification of atomic percentages.

Figure 4

XPS spectra of g-C₃N₄/α-Fe₂O₃ nanocomposite: (a) C (1s), (b) N (1s), (c) Fe (2p), and (d) O (1s).

Figure 4

XPS spectra of g-C₃N₄/α-Fe₂O₃ nanocomposite: (a) C (1s), (b) N (1s), (c) Fe (2p), and (d) O (1s).

Figure 5

(a) N₂ adsorption–desorption isotherms and (b) pore size distributions of α-Fe₂O₃, g-C₃N₄, and α-Fe₂O₃/g-C₃N₄ samples.

Figure 5

(a) N₂ adsorption–desorption isotherms and (b) pore size distributions of α-Fe₂O₃, g-C₃N₄, and α-Fe₂O₃/g-C₃N₄ samples.

Figure 6

UV-vis absorption spectral changes of MO with time in (a) pure g-C₃N₄ and (b) g-C₃N₄/α Fe₂O₃ nanocomposite under light illumination.

Figure 7

(a) Plot of C/C_o vs. time. (b) The corresponding degradation efficiency of MO removal. (c) Plot of ln (C/C_o) vs. time.

Figure 7

(a) Plot of C/C_o vs. time. (b) The corresponding degradation efficiency of MO removal. (c) Plot of ln (C/C_o) vs. time.

Figure 8

XPS valence band spectra with insets representing magnified spectra of (a) g-C₃N₄ and (b) α-Fe₂O₃, and absorbance spectra with insets representing the Tauc plots for (c) g-C₃N₄ and (d) α-Fe₂O₃.

Figure 8

XPS valence band spectra with insets representing magnified spectra of (a) g-C₃N₄ and (b) α-Fe₂O₃, and absorbance spectra with insets representing the Tauc plots for (c) g-C₃N₄ and (d) α-Fe₂O₃.

Figure 9

(a) Alignment of energy levels in the g-C₃N₄/α-Fe₂O₃ nanocomposite. (b) Role of radical scavengers on MO photodegradation over g-C₃N₄/α-Fe₂O₃ nanocomposite.

Figure 10

g-C₃N₄/α-Fe₂O₃ nanocomposite stability.

Figure 11

Chemical structure of MO dye.