Hematite/Graphitic Carbon Nitride Nanofilm for Fenton and Photocatalytic Oxidation of Methylene Blue

Abstract

Hematite (α-Fe₂O₃)/graphitic carbon nitride (g-C₃N₄) nanofilm catalysts were synthesized on fluorine-doped tin oxide glass by hydrothermal and chemical vapor deposition. Scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses of the synthesized catalyst showed that the nanoparticles of g-C₃N₄ were successfully deposited on α-Fe₂O₃ nanofilm. The methylene blue degradation efficiency of the α-Fe₂O₃/g-C₃N₄ composite catalyst was 2.6 times greater than that of the α-Fe₂O₃ single catalyst under ultraviolet (UV) irradiation. The methylene blue degradation rate by the α-Fe₂O₃/g-C₃N₄ catalyst increased by 6.5 times after 1 mM of hydrogen peroxide (H₂O₂) was added. The photo-Fenton reaction of the catalyst, UV, and H₂O₂ greatly increased the methylene blue degradation. The results from the scavenger experiment indicated that the main reactants in the methylene blue decomposition reaction are superoxide radicals photocatalytically generated by g-C₃N₄ and hydroxyl radicals generated by the photo-Fenton reaction. The α-Fe₂O₃/g-C₃N₄ nanofilm showed excellent reaction rate constants at pH 3 (K_a = 6.13 × 10⁻² min⁻¹), and still better efficiency at pH 7 (K_a = 3.67 × 10⁻² min⁻¹), compared to other methylene blue degradation catalysts. As an immobilized photo-Fenton catalyst without iron sludge formation, nanostructured α-Fe₂O₃/g-C₃N₄ are advantageous for process design compared to particle-type catalysts.

1. Introduction

Advanced oxidation processes (AOPs) include various methods of decomposing organics through the generation of reactive oxygen species (ROS), such as hydroxyl radicals (•OH) or superoxide radicals (•O₂⁻) [1], which are intermediate reactants with strong oxidizing power. AOPs include the Fenton reaction, ozone (O₃)/hydrogen peroxide (H₂O₂), ultraviolet (UV)/H₂O₂, UV/O₃, and photocatalysis. Photocatalysis is promising because of its environmental stability, low processing costs, and wide applications [2]. Photocatalysts are semiconductors that can excite electrons with light energy and form hole–electron pairs. The excited electrons and generated holes are decomposed directly or indirectly by ROS generation through redox reactions. The energy levels in the valence and conduction bands where holes and electrons are present are important factors in photocatalytic activity. They determine the oxidizable organics and the ROS that can be produced depending on the redox potential. Another important factor in the development of photocatalytic processes is the bandgap energy, which is the difference between energy levels of the valence and conduction bands. Photocatalysts are activated by light with energy above the bandgap, and the energy of light is related to the wavelength of light available. Lower bandgaps have a wider spectrum of available light.

The Fenton process is a widely used AOP for water treatment, as it is inexpensive. It can be carried out at room temperature and low atmospheric pressure. In the Fenton reaction, ferric ions react with H₂O₂to form ROS species that oxidize organic matter as shown in Equation (1).

Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + •OH.

(1)

One disadvantage of the Fenton process is that H₂O₂ consumes radicals and wastes oxidizing agents, reducing oxidation efficiency. The other disadvantage is the loss of Fe ions and the formation of solid sludge. The photo-Fenton process, which combines UV with traditional Fenton reactions, is an alternative to the conventional Fenton process that increases oxidation efficiency and reduces sludge. The combination of UV with the Fenton process was reported to significantly reduce iron loss and sludge production [3]. The additional reaction by UV, as shown in Equations (2) and (3), allows the photo-Fenton process to generate more ROS than the simple Fenton process.

Fe(OH)₂⁺ + hv → Fe²⁺ + 2OH⁻,

(2)

H₂O₂ + hv → 2•OH.

(3)

Hematite (α-Fe₂O₃) can be used as a photocatalyst with a bandgap of 2.2 eV and also can be used as a catalyst for the Fenton reaction by the change of Fe ions on its surface. By combining α-Fe₂O₃ with H₂O₂ and UV, photocatalytic reactions can be carried out simultaneously. However, existing hematite-based photocatalysts exhibit high hole–electron recombination due to the narrow bandgap and limited ROS production. This is because of the low redox potential of the conduction band; as a result, it is not practical to apply to water treatment. To overcome these shortcomings, various modification studies have been carried out, testing non-metal doping [4,5], metal doping [6,7,8], shape control [9,10,11], and heterojunction [12,13,14]. A heterojunction with other catalysts accumulates charge and reduces hole–electron recombination by moving excited electrons to the energy levels of other catalysts through the interaction of two semiconductors with different band structures. Graphitic carbon nitride (g-C₃N₄) has a relatively low bandgap energy and enough conduction band potential for •O₂⁻ generation, making it suitable as a junction catalyst for α-Fe₂O₃ modification.

Nanostructured α-Fe₂O₃ has been studied to be used as a catalyst for the Fenton reaction. Guo et al. [15] confirmed that S-doped α-Fe₂O₃ exhibited excellent heterogeneous Fenton efficiency under UV/visible light, while little Fenton reactivity was observed in the dark. Liao et al. [16] reported that phenol and phenolic contaminants were decomposed using an α-Fe₂O₃ catalyst supported on multiwall carbon nanotubes, showing 20% higher degradation efficiency than bare α-Fe₂O₃. Chan et al. [17] reported that exposed surface facets play an important role in determining catalytic performance in methylene blue degradation with nanostructured α-Fe₂O₃. It was confirmed that the photocatalytic performance of three types of α-Fe₂O₃ nanoparticles was in the order of {113}> {104}> {001}. Liu et al. [18] reported that the increase in sintering temperature of α-Fe₂O₃ nanoparticles increased in methylene decomposition. They used α-Fe₂O₃ nanoparticles synthesized by a simple sodium dodecyl sulfate-assisted grinding reaction and subsequent heating treatment process. The α-Fe₂O₃ particles obtained at 500 °C showed the highest decomposition efficiency. Liu et al. [19] synthesized nanoring-type α-Fe₂O₃ by adding H₂PO₄, SO₄²⁻, and citric acid in a hydrothermal reaction and reported increased photo-Fenton decomposition of p-nitrophenol by activating photoabsorption and increasing surface-coupled Fe²⁺ content. Jiang et al. [20] reported that α-Fe₂O₃/BiOI catalysts showed 3 and 10 times higher decomposition efficiency than BiOI and α-Fe₂O₃ catalysts in methyl orange, phenol, and tetracycline hydrochloride decomposition. The interaction of the two catalysts increases the separation and transfer efficiency of photogenerated charges and results in an optimized Fenton reaction at the solid–liquid interface. Ren et al. [21] reported that Cu-doping interacted with α-Fe₂O₃ to have higher Fenton activity than undoped samples in methylene blue degradation. The previous studies show that nanostructured α-Fe₂O₃ can be used in the Fenton reaction and can increase the activity of the catalyst through shape control and doping. However, there are inherent limitations in the process design of nanoparticle-type catalysts. They require a separate catalyst recovery process after contaminant treatment. This may reduce the merits of decreased sludge generation by using α-Fe₂O₃, which is advantageous compared to the Fenton reaction using iron salt. The α-Fe₂O₃ catalyst with nanostructures in an immobilized form rather than in particle form can be easier to use and decrease the costs of process design and operation.

The α-Fe₂O₃ also is being actively studied as a photocatalyst. However, due to its low photoactivity when used alone, it is often used in heterojunction with other catalysts. The g-C₃N₄ is frequently used with α-Fe₂O₃ because of their band structures. It acts as a Z-scheme photocatalyst with the band of α-Fe₂O₃ and can produce •O₂⁻, that cannot be produced by α-Fe₂O₃. Bai et al. [22] reported that α-Fe₂O₃ and porous g-C₃N₄ composites (K_a = 1.28×10⁻¹ min⁻¹) showed 1.43 times better efficiency than pure g-C₃N₄ (ka = 5.64 × 10⁻² min⁻¹) in the degradation of Rhodamine B. Sun et al. [23] found that the α-Fe₂O₃/g-C₃N₄ heterojunction photocatalyst (K_a = 4.70 × 10⁻³ min⁻¹) showed increases of 11.8 and 5.9 times in arsenic removal efficiency relative to pure α-Fe₂O₃ and g-C₃N₄, respectively. Hao et al. [24] reported that 55% of methylene blue was removed in a 180 min reaction with g-C₃N₄ alone, while 75% of methylene blue was removed after 180 min with the α-Fe₂O₃/g-C₃N₄ complex photocatalyst. In the charge transfer characterization using electrochemical impedance spectroscopy and photocurrent, α-Fe₂O₃/g-C₃N₄ has a smaller charge transfer resistance and higher photocurrent response than g-C₃N₄. Zhou et al. [25] confirmed that the photo-Fenton reaction using the α-Fe₂O₃/g-C₃N₄ catalyst was 45.4 times and 8.4 times more efficient than those of pure α-Fe₂O₃ and g-C₃N₄, respectively. It also was 7.2 times more efficient than a mixture of the two catalysts. However, its potential as a Fenton catalyst was seldom utilized, as most studies focused on the use of α-Fe₂O₃ as a photocatalyst.

In this study, we synthesized a nanostructured α-Fe₂O₃/g-C₃N₄ catalyst on a fluorine-doped tin oxide (FTO) glass. The α-Fe₂O₃/g-C₃N₄ catalyst simultaneously acts as a photocatalyst and photo-Fenton catalyst. Catalysts immobilized on FTO glass have advantages in process design because they reduce the loss of iron ions and do not require a separate recovery process. A junction with g-C₃N₄ enables the use of more ROS species while improving the photoelectrochemical properties of the catalyst.

2. Experimental Section

2.1. Materials Synthesis

Nanostructured α-Fe₂O₃ films were synthesized on FTO glass simply by a modified hydrothermal method [26]. As a precursor for synthesizing α-Fe₂O₃ nanofilms, 10 mM FeCl₃•6H₂O and NaNO₃ were dissolved in 100 mL of 0.05 M HCl solution. The solution was put in a 150 mL Teflon liner. A piece of FTO glass ultrasonicated in acetone, ethanol, and distilled water was placed on the Teflon liner. Next, the Teflon liner was placed in a stainless-steel autoclave and heated at 95 °C for 4 h in an electric furnace. Akaganeite(β-FeOOH) films were successfully synthesized on the FTO glass. The obtained β-FeOOH films were washed with distilled water and sintered in an electric furnace at 520 °C for 2 h, resulting in the synthesis of red-colored α-Fe₂O₃ films.

The g-C₃N₄ was synthesized on α-Fe₂O₃ nanofilms by directly heating melamine [27]. First, 5 g of melamine was placed in a ceramic crucible with a cover. Then, the β-FeOOH films were placed on the melamine with β-FeOOH facing down. The crucible was partially covered and heated at 520 °C for 2 h in an electric furnace. The sample was then cooled to room temperature in the atmosphere. After the reaction, brick-colored α-Fe₂O₃/g-C₃N₄ films were obtained with yellow g-C₃N₄ powders on the bottom of the crucible. It was confirmed that 280 mg of catalyst was synthesized on one FTO substrate by comparing the weight before and after synthesis.

2.2. Materials Characterization

The morphology and nanostructures of the samples were analyzed by field-emission scanning electron microscopy (FE-SEM; JSM-6701F and FEI Nova NanoSEM 450, JEOL, Japan). Energy-dispersive spectroscopy (EDS) was used for surface elemental analysis using the FE-SEM. To analyze the crystal phase, X-ray diffraction (XRD; SmartLab, Rigaku, Japan) analysis was carried out with Cu kα radiation. XRD data were obtained at conditions of 45 kV, 200 mA, from 2θ = 20° to 80°, with a step size of 0.04° at 4°/min. X-ray photoelectron spectroscopy (XPS; K-alpha plus, Thermo Scientific, Massachusetts, US) was taken with Al kα (1486.6 eV).

2.3. Aqueous Organic Oxidation

The organic oxidation efficiency of the sample was confirmed by methylene blue decomposition. The sample was placed in a 250 mL quartz beaker and 200 mL of 10 mg/L methylene blue solution was added. The beaker was placed in a reactor with three UV lamps (254 nm, 6 W) and irradiated with light for the reaction for 90 min. The light intensity applied to the center of the catalyst was 2.88 mW/cm². It was measured using a lux meter (UVC-254SD, Lutron Electronics, Pennsylvania, US). During the reaction, the solution was stirred with an electric stirrer. Experiments were also carried out under the same conditions with addition of various concentrations of H₂O₂ (0.1, 0.2, 0.5, 1, and 2 mM) and pH (3, 5, 7, 9, and 11). Scavenger experiments were performed to measure the main reactants of the methylene blue degradation. The methylene blue degradations after addition of 1 mM benzoquinone (BQ) or tert-butyl alcohol (TBA) were compared after 90 min of reactions at the initial pH 7. A total of 4 mL of the solution was collected at regular intervals and filtered using a syringe filter (pore size: 0.45 µm, Whatman, UK). The filtered samples were analyzed by examining the absorbance of 665 nm light by a UV-vis spectrometer (DR 2800, HACH, Colorado, US) to determine the methylene blue degradation rate. All experimental data were duplicated and averaged.

3. Results and Discussion

3.1. Structural Analysis

Figure 1 shows the morphology and nanostructures of (a) β-FeOOH and (b) α-Fe₂O₃. The FeOOH has nanorods arranged like flowers. The nanorods are about 50 nm wide and angled. The nanostructure of α-Fe₂O₃ changed to a more rounded form after sintering, and both the width and length were smaller than those of the β-FeOOH nanorods. This change is due to the escape of H₂O when β-FeOOH is sintered and α-Fe₂O₃ is formed, as shown in Equation (4) [28].

2FeOOH → Fe₂O₃ + H₂O

(4)

Figure 2 shows the FE-SEM image and EDS analysis of the α-Fe₂O₃/g-C₃N₄ films. The particles of g-C₃N₄ were deposited on the α-Fe₂O₃ nanostructures. The g-C₃N₄ particles are less than 35 nm in size, and the shape of Fe₂O₃ is rounder due to further sintering. The C, N, Fe, and O peaks were identified in EDS analysis. The peaks of elements other than O were measured slightly lower because the analysis depth of EDS is greater than the thickness of α-Fe₂O₃/g-C₃N₄ films. As a result, the elements of the FTO under the catalyst are also measured. The peaks between 3 and 4 keV correspond to Sn, which is a component of FTO.

Figure 3 shows the XRD patterns of β-FeOOH, α-Fe₂O₃, and α-Fe₂O₃/g-C₃N₄ samples and bare FTO. The peak of FeOOH was observed on the FTO substrate after the hydrothermal synthesis. After sintering, FeOOH was successfully converted to α-Fe₂O₃, and the eight characteristic peaks of α-Fe₂O₃ ({012}, {104}, {110}, {113}, {024}, {116}, {214}, and {300}) were observed [29]. The peaks of the FTO glass were also observed in the samples due to the thinness of the α-Fe₂O₃ film layer. No characteristic peaks of g-C₃N₄ were observed in the α-Fe₂O₃/g-C₃N₄ samples, and only the peaks of α-Fe₂O₃ and FTO were identified. This may be because the amount of g-C₃N₄ deposited on the surface is relatively small, and it is dispersed well on the surface without affecting the structure of α-Fe₂O₃.

XPS analysis was performed to confirm the synthesis of g-C₃N₄. Figure 4 shows (a) the XPS spectrum of α-Fe₂O₃/g-C₃N₄ and the (b) C 1s and (c) N 1s regions. Four elements (Fe, O, C, and N) were detected in the XPS spectra. The most prominent peak in the C 1s region is attributed to the carbon–nitrogen bond structure (N-C = N) of the aromatic systems. The peak at 398.3 eV seen in the N 1s region is the peak attributed to graphene N and generally indicates the case where the nitrogen atom is incorporated into the graphene layer to replace the carbon atom. The peak at 401.0 eV is attributed to nitrogen spiked with three sp² carbon atoms [30,31]. The peaks in the C 1s and N 1s regions show that the melamine produced g-C₃N₄ with a graphitic structure through heating and was successfully deposited on the α-Fe₂O₃ surface.

3.2. Methylene Blue Degradation

Methylene blue degradation results are shown in Figure 5. No significant changes were observed when the experiment was performed using bare FTO glass. Only 12% of methylene blue was degraded with pure α-Fe₂O₃ after the 90 min reaction even under UV irradiation, whereas 31% of methylene blue was degraded with the α-Fe₂O₃/g-C₃N₄ heterojunction catalyst. This is because the band structure of α-Fe₂O₃, which cannot generate •O₂⁻, is not suitable for methylene blue decomposition, whereas the conduction band of g-C₃N₄ has enough redox potential for •O₂⁻ production. In the decomposition of photocatalytic organic matter of α-Fe₂O₃/g-C₃N₄, g-C₃N₄ can be said to be the main catalyst, as opposed to α-Fe₂O₃.

After addition of 1 mM H₂O₂, the methylene blue degradation rate increased significantly in all samples. The increase in methylene blue degradation rate in bare FTO samples was due to the UV/H₂O₂ reaction, and the increases in degradation efficiency due to H₂O₂ addition in α-Fe₂O₃ and α-Fe₂O₃/g-C₃N₄ samples were greater than that by the UV/H₂O₂ reaction. This means that there is an interaction between the α-Fe₂O₃ and α-Fe₂O₃/g-C₃N₄ catalyst and H₂O₂ in addition to the UV/H₂O₂ reaction. The methylene blue degradation rate of the α-Fe₂O₃ catalyst under UV irradiation increased from 12% to 77% with H₂O₂ addition after 90 min of reaction. Methylene blue degradation of α-Fe₂O₃/g-C₃N₄ showed 31% degradation efficiency after 90 min of reaction under UV irradiation, but after H₂O₂ addition, the complete decomposition of methylene blue was achieved in only 75 min of reaction. This is due to the Fenton reaction, in which the Fe³⁺ on the surface of α-Fe₂O₃ becomes Fe²⁺ due to the excited α-Fe₂O₃ electrons under UV light. They, in turn, reacted with H₂O₂ to form •OH [17,32].

The change of methylene blue decomposition efficiency caused by the concentration of H₂O₂ added is shown in Figure 6. For H₂O₂ concentrations of up to 1 mM, the higher the concentration of the H₂O₂ added, the higher the decomposition efficiency will be. However, no noticeable change in efficiency was seen at 1 and 2 mM. This may be due to the saturation of the number of surface Fe ions reacting with H₂O₂ at 1 mM H₂O₂. The effect of the initial pH is presented in Figure 7. At low initial pH concentrations, the methylene blue decomposition efficiency was increased. This optimal pH is similar to those of the Fenton process. This shows that the α-Fe₂O₃/g-C₃N₄ catalyst performs both Fenton and photocatalytic oxidation simultaneously.

3.3. Detection of Reactive Species

ROS scavengers were added to the methylene blue oxidation to identify the main reactants. BQ was introduced as an •O₂⁻ scavenger, and TBA was used as an •OH scavenger [33]. As shown in Figure 8, the effect of the •OH scavenger was low without H₂O₂ addition. On the other hand, when the •O₂⁻ scavenger was added, the reaction was significantly inhibited. This means that, in the absence of H₂O₂, the main reactant of methylene blue oxidation is the •O₂⁻ produced in the conduction band of g-C₃N₄. However, when H₂O₂ assists in oxidation, the degradation rate was significantly lowered when •OH scavenger was added. This shows that the •OH generated by the Fenton reaction is one of the major reactants in the methylene blue decomposition reaction.

3.4. Degradation Kinetics

The methylene blue degradation during the first 45 min of this study can be explained by the pseudo-first-order reaction kinetics of Equation (5).

ln (C₀/C) = K_a × t + constant,

(5)

where C₀ is the initial concentration of methylene blue, C is the methylene blue concentration at time t, and K_app is the first-order reaction constant. K_a was chosen as a kinetic parameter to compare the catalytic activity of different systems independently of concentration. Kinetic parameters for each methylene blue degradation process are listed in

Table 1. Kinetic parameters of different methylene blue decomposition systems in this study.

Type of Oxidation Process	Ka (min−1)	R2
FTO + UV	1.40 × 10−4	0.99
α-Fe2O3 + UV	1.80 × 10−3	0.99
α-Fe2O3/g-C3N4 + UV	5.65 × 10−3	0.99
FTO + UV + H2O2	4.11 × 10−3	0.99
α-Fe2O3 + UV + H2O2	1.52 × 10−2	0.99
α-Fe2O3/g-C3N4 + UV + H2O2	3.67 × 10−2	0.99

and

Table 2. Kinetic parameters of the methylene blue degradation of α-Fe₂O₃/g-C₃N₄ nanofilm according to concentration of added H₂O₂ and initial pH.

H2O2 (mM)	pH	Ka (min−1)	R2
0.1	7	1.10 × 10−2	0.99
0.2	7	1.50 × 10−2	0.99
0.5	7	2.73 × 10−2	0.99
1	7	3.67 × 10−2	0.99
2	7	3.72 × 10−2	0.99
1	3	6.13 × 10−2	0.99
1	5	5.15 × 10−2	0.99
1	9	1.07 × 10−2	0.99
1	11	4.70 × 10−3	0.99

. All results followed a linear regression and K_a effectively expressed the methylene blue decomposition efficiency. The reaction rate of α-Fe₂O₃/g-C₃N₄ nanofilm was 2.4 times higher than that of theα-Fe₂O₃ film under conditions of pH 7 and 1 mM H₂O₂ concentration, and the methylene blue decomposition rate of α-Fe₂O₃/g-C₃N₄ nanofilms at the initial pH 3 increased by 67% over that at pH 7. Previous studies on methylene blue degradation are listed in

Table 3. Comparison of K_app values of previous studies of methylene blue degradation.

Catalyst	Ka (/min)	Light Source	Reference
TiO2–curcumin	3.05 × 10−2	UV	[34]
Cu doped ZnS	1.45 × 10−2	UV	[35]
ZIF-8	1.70 × 10−2	UV	[36]
TiO2/rGO nanocomposites	1.12 × 10−2	UV	[37]
CA/TPNC	1.26 × 10−2	Solar	[38]
TiO2/graphene	2.08 × 10−2	Solar	[39]
TiO2 NRAs/graphene/ZnO NPs	1.65 × 10−2	Visible	[40]
(Mo,C)-TiO2/FTO	2.95 × 10−2	Visible	[41]
g-C3N4-10RGO-TiO2	1.47 × 10−2	Visible	[42]
This study (1mM H2O2, pH 7)	3.67 × 10−2	UV	-
This study (1mM H2O2, pH 3)	6.13 × 10−2	UV	-

, demonstrating that α-Fe₂O₃/g-C₃N₄ nanofilms are excellent even in neutral conditions.

3.5. Methylene Blue Degradation Mechanism

The degradation mechanism of the catalyst based on these results is shown in Figure 9. Traditional dual-carrier delivery systems, shown in Figure 9a, cannot account for the high activity of •O₂⁻ in reactions without H₂O₂. When the redox potential for generating the •O₂⁻ is −0.046 (eV vs. normal hydrogen electrode) and the electrons move to the conduction band of α-Fe₂O₃, the photocatalytic activity is somewhat lower [43]. The holes and electrons accumulated due to the Z-scheme process of α-Fe₂O₃/g-C₃N₄ can be used for photocatalytic oxidation, as shown in Figure 9b. The Z-scheme action of the α-Fe₂O₃/g-C₃N₄ heterojunction catalyst in the field of electrolysis and CO₂ reduction has been reported [44,45,46]. However, the activity of low •OH in the absence of H₂O₂ cannot be explained with the Z-scheme system. If the •OH is produced in the valence band of α-Fe₂O₃, there should be enough •OH activity even without H₂O₂. Thus, the combination of photocatalytic and Fenton processes is presented in Figure 9c. The high activity of •OH in the presence of H₂O₂ means that •OH involved in photodegradation is generated in H₂O₂. The electrons excited by UV can change Fe³⁺ to Fe²⁺ on the α-Fe₂O₃ surface, and Fe²⁺ reacts with H₂O₂ to generate •OH [32,47]. The difference in the energy levels of g-C₃N₄ and α-Fe₂O₃ induces charge transfer. The junctions of two semiconductors with different band structures can accumulate charge by shifting the photoexcited electrons to the energy levels of the other catalysts. The coupled g-C₃N₄ valence band acts as an electron trap for electrons excited by the conduction band of α-Fe₂O₃. Catalysts composed of highly efficient nanostructures have low electron resistance, and the heterojunction structures of both catalysts make charge separation more efficient and reduce hole–electron recombination caused by instability of excited electrons.

4. Conclusions

Nano-structured α-Fe₂O₃ was successfully synthesized on FTO glass. Nanoparticles of g-C₃N₄ were successfully deposited on the synthesized α-Fe₂O₃ films. In the methylene blue oxidation using α-Fe₂O₃/g-C₃N₄ nanofilm, the activity of •OH under UV irradiation was low when H₂O₂ was not present. XPS analysis showed changes in Fe ions on the α-Fe₂O₃ surface by H₂O₂, which is similar to the change in iron ions in the Fenton reaction. The Fenton reaction of iron ions on the surface of α-Fe₂O₃ activated by H₂O₂ and the photocatalytic activity of g-C₃N₄ nitride enhanced through heterojunction with α-Fe₂O₃ are suggested as the main mechanisms of α-Fe₂O₃/g-C₃N₄ nanofilms. The α-Fe₂O₃/g-C₃N₄ nanofilms as immobilized Fenton-photocatalytic composite catalysts are advantageous for reactor design as an alternative to conventional treatment with iron salts.