Development of Cuboidal KNbO3@α-Fe2O3 Hybrid Nanostructures for Improved Photocatalytic and Photoelectrocatalytic Applications

Abstract

Monophasic and hybrid nanostructures of KNbO₃ and α-Fe₂O₃ have been prepared using a hydrothermal process for photoelectrocatalytic and photocatalytic applications. Powder X-ray diffraction studies showed the formation of KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ with average grain sizes of 18.3, 11.5, and 26.1 nm and Brunauer-Emmett-Teller (BET) specific surface areas of 4, 100, and 20 m²/gm, respectively. Under simulated solar irradiation, the as-prepared heterostructure shows enhanced photoelectrocatalytic oxygen evolution reaction (OER) activity compared to pristine KNbO₃ and α-Fe₂O₃. Significant photocatalytic activity of as-synthesized KNbO₃/α-Fe₂O₃ heterostructure photocatalyst was obtained for removal of methylene blue organic dye under visible light, and the percentage activity was found to be 11, 49, and 89% for KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ photocatalysts, respectively. The dielectric constant was found to be 250.2, 65.2, and 251.5 for KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ heterostructure, respectively, at 50 °C and 500 kHz frequency.

Figure 1

XRD patterns of as-prepared KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃.

Figure 2

TEM micrographs of (a) KNbO₃, (b) α-Fe₂O₃, and (c) KNbO₃/α-Fe₂O₃.

Figure 3

FESEM micrographs of (a) KNbO₃, (b) α-Fe₂O₃, and (c) KNbO₃/α-Fe₂O₃; EDX spectra of (d) KNbO₃, (e) α-Fe₂O₃, and (f) KNbO₃/α-Fe₂O₃. The inset in (a) shows the particle size distribution histogram of KNbO₃.

Figure 4

Elemental mapping of KNbO₃/α-Fe₂O₃ heterostructure for (a) K, (b) Nb, (c) Fe, and (d) O.

Figure 5

(a) Full-range XPS spectra of KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ heterostructure, and high-resolution XPS spectra of (b) Nb, (c) K, (d) Fe, and (e) O in pure KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ heterostructure.

Figure 6

(a) BET surface area isotherm and (b) BJH pore size distribution plots of KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ heterostructure.

Figure 7

(a) LSV plots in dark (D) and light (L) and (b) Tafel slopes of PEC reaction in the presence of KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ catalysts.

Figure 8

(a) EIS Nyquist plots and (b) Mott–Schottky (MS) plots for bare core material KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ heterostructure in the presence of light.

Figure 9

(a) Percentage removal efficiency and (b) kinetics of photocatalytic reaction using bare KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ heterostructure.

Figure 10

Variation of dielectric constant and dielectric loss with frequency at 50 °C for (a) KNbO₃-, (b) α-Fe₂O₃-, and (c) α-Fe₂O₃-modified KNbO₃ heterostructure.

Figure 11

Variation of dielectric constant and dielectric loss with temperature at 500 kHz frequency for (a) KNbO₃-, (b) α-Fe₂O₃-, and (c) α-Fe₂O₃-modified KNbO₃ heterostructure.