Photoelectrocatalytic Degradation of Methylene Blue on Electrodeposited Bismuth Ferrite Perovskite Films

Abstract

Electrodeposited bismuth ferrite (BiFeO₃) thin films on fluorine-doped tin oxide (FTO) substrate were employed as photoanodes in the photoelectrocatalytic degradation of methylene blue. The BiFeO₃ thin films electrodeposited for 300 s, 600 s, 1200 s, 1800 s and 3600 s were characterised with XRD, field emission scanning electron microscopy (FESEM) and UV-vis diffuse reflectance spectroscopy. SEM images displayed different morphology at different electrodeposition times which affects the photoelectrocatalytic (PEC) performances. The FESEM cross-sectional area was used to measure the thickness of the film. The optical properties showed that the band gaps of the photoanodes were increasing as the electrodeposition time increased. The photocurrent response obtained showed that all thin film photoanodes responded to visible light and lower charge transfer resistance (from electrochemical impedance spectroscopy studies) was observed with photoanodes electrodeposited at a shorter time compared to those at a longer time. The PEC application of the photoanode for the removal of methylene blue (MB) dye in water showed that the percentage degradation decreased with an increase in electrodeposition time with removal rates of 97.6% and 70% observed in 300 s and 3600 s electrodeposition time, respectively. The extent of mineralisation was measured by total organic carbon and reusability studies were carried out. Control experiments such as adsorption, photolysis, photocatalysis and electrocatalysis processes were also investigated in comparison with PEC. The electrodeposition approach with citric acid exhibited improved electrode stability while mitigating the problem of catalyst leaching or peeling off during the PEC process.

Keywords: bismuth ferrite perovskite; citric acid; electrodeposition; film thickness; methylene blue; photoelectrocatalytic degradation.

Figure 1

(a) Schematic diagram for the preparation of BFO film using simple chemical bath electrodeposition method, (b) appearance of BFO films before and after annealing (c) XRD patterns of FTO and FTO/BFO at 300 s, 600 s, 1200 s, 1800 s, 3600 s, (d) XRD pattern of 300 s and enlarged image (inset) of 300 s photoanode.

Figure 1

(a) Schematic diagram for the preparation of BFO film using simple chemical bath electrodeposition method, (b) appearance of BFO films before and after annealing (c) XRD patterns of FTO and FTO/BFO at 300 s, 600 s, 1200 s, 1800 s, 3600 s, (d) XRD pattern of 300 s and enlarged image (inset) of 300 s photoanode.

Figure 1

(a) Schematic diagram for the preparation of BFO film using simple chemical bath electrodeposition method, (b) appearance of BFO films before and after annealing (c) XRD patterns of FTO and FTO/BFO at 300 s, 600 s, 1200 s, 1800 s, 3600 s, (d) XRD pattern of 300 s and enlarged image (inset) of 300 s photoanode.

Figure 2

(a(i–v)) SEM images, (b(i–v)) FESEM film thickness of (b(i)) = 300 s, (b(ii)) = 600 s, (b(iii)) = 1200 s, (b(iv)) = 1800 s and (b(v)) = 3600 photoanodes, (c) EDX line scan (20 KV beam voltage) of a cross-sectional area of 1200 s BFO photoanode, (d) EDX image showing the elemental composition.

Figure 2

(a(i–v)) SEM images, (b(i–v)) FESEM film thickness of (b(i)) = 300 s, (b(ii)) = 600 s, (b(iii)) = 1200 s, (b(iv)) = 1800 s and (b(v)) = 3600 photoanodes, (c) EDX line scan (20 KV beam voltage) of a cross-sectional area of 1200 s BFO photoanode, (d) EDX image showing the elemental composition.

Figure 2

(a(i–v)) SEM images, (b(i–v)) FESEM film thickness of (b(i)) = 300 s, (b(ii)) = 600 s, (b(iii)) = 1200 s, (b(iv)) = 1800 s and (b(v)) = 3600 photoanodes, (c) EDX line scan (20 KV beam voltage) of a cross-sectional area of 1200 s BFO photoanode, (d) EDX image showing the elemental composition.

Figure 2

(a(i–v)) SEM images, (b(i–v)) FESEM film thickness of (b(i)) = 300 s, (b(ii)) = 600 s, (b(iii)) = 1200 s, (b(iv)) = 1800 s and (b(v)) = 3600 photoanodes, (c) EDX line scan (20 KV beam voltage) of a cross-sectional area of 1200 s BFO photoanode, (d) EDX image showing the elemental composition.

Figure 2

(a(i–v)) SEM images, (b(i–v)) FESEM film thickness of (b(i)) = 300 s, (b(ii)) = 600 s, (b(iii)) = 1200 s, (b(iv)) = 1800 s and (b(v)) = 3600 photoanodes, (c) EDX line scan (20 KV beam voltage) of a cross-sectional area of 1200 s BFO photoanode, (d) EDX image showing the elemental composition.

Figure 3

(a) UV−visible diffuse reflectance spectra, (b) the band gap energies of 300 s, 600 s, 1200 s, 1800 s, 3600 s.

Figure 4

(a) Linear sweep voltammogram (LSV) under light with a scan rate of 0.1 V/s (inset: LSV plot under dark, (b) photocurrent response, (c) electrochemical impedance spectroscopy for 300 s, 600 s, 1200 s, 1800 s, 3600 s photoanodes.

Figure 5

(a) Photoelectrocatalytic degradation (b) kinetic plots for degradation of MB using 300 s, 600 s, 1200 s, 1800 s and 3600 s, (c) different processes of degradation, (d) kinetic plot for different processes of degradation of MB using 300 s photoanode, (e) TOC removal of methylene blue, (f) reusability study, (g) XRD patterns of BFO before and after 6 cycle degradation (5 ppm, 2 V, methylene blue, 3 h).

Figure 5

(a) Photoelectrocatalytic degradation (b) kinetic plots for degradation of MB using 300 s, 600 s, 1200 s, 1800 s and 3600 s, (c) different processes of degradation, (d) kinetic plot for different processes of degradation of MB using 300 s photoanode, (e) TOC removal of methylene blue, (f) reusability study, (g) XRD patterns of BFO before and after 6 cycle degradation (5 ppm, 2 V, methylene blue, 3 h).

Figure 5

(a) Photoelectrocatalytic degradation (b) kinetic plots for degradation of MB using 300 s, 600 s, 1200 s, 1800 s and 3600 s, (c) different processes of degradation, (d) kinetic plot for different processes of degradation of MB using 300 s photoanode, (e) TOC removal of methylene blue, (f) reusability study, (g) XRD patterns of BFO before and after 6 cycle degradation (5 ppm, 2 V, methylene blue, 3 h).