Photocatalyst comprising magnetized semiconductor

Abstract

The present invention relates to a magnetized semiconductor photocatalyst characterized by improved activity and reaction rate of the photocatalyst by synthesizing a magnetized semiconductor into a ferromagnetic material by doping iron (Fe) into TiO2, a three-dimensional semiconductor material.

Description

Technology Field

[0001] The present invention relates to a magnetizing semiconductor photocatalyst, and more specifically, to a magnetizing semiconductor characterized by improved activity and reaction rate of the photocatalyst by synthesizing a three-dimensional semiconductor material into a ferromagnetic material through doping to produce the magnetizing semiconductor.

[0002] In addition, the present invention was developed as a result of the research on "Photocatalysts for the application of magnetized semiconductor materials" of the industry-academia joint research project, supported by JC Inc. Background Technology

[0003] 1. Introduction

[0004] Two-dimensional materials exhibit properties different from three-dimensional materials due to the restricted electron motion in two dimensions. This means that even identical materials can display different properties. A representative example is graphene, the first two-dimensional material composed of carbon. Unlike conventional carbon-based three-dimensional materials such as diamond and graphite, graphene displays unique properties, including strength 200 times greater than steel, electrical conductivity 100 times higher than copper, and thermal conductivity twice as high as diamond. These changes in properties are caused by an increase in surface energy.

[0005] Due to the groundbreaking properties of graphene, interest in two-dimensional materials has surged, leading to numerous commercialization efforts. However, one drawback is that it is difficult to maintain its shape due to its two-dimensional nature.

[0007] 2. Literature Review

[0008] 2.1. Magnetized semiconductor

[0009] 2D materials have the advantage of being able to improve various properties, but there are several limitations in synthesizing such materials. Magnetic semiconductors aim to achieve property changes similar to those of 2D materials in 3D materials through ferromagnetic magnetization.

[0010] Magnetization refers to the alignment of magnetic moments within a material by an external magnetic field, and ferromagnets maintain their magnetization even after the external magnetic field is removed. The magnetization of ferromagnets can restrict the direction of electron movement through local internal magnetic forces (Hall effect). Magnetized semiconductors utilize this phenomenon to induce electron movement similar to that of 2D materials, thereby effectively converting 3D materials into a structure similar to 2D.

[0011] 2D materials have surfaces composed of atomic layers, which increase carrier mobility and reduce recombination in photocatalytic reactions. This effect can also be obtained in magnetized semiconductors. Therefore, this study aims to induce ferromagnetism in a 3D material (TiO2) and observe changes in efficiency according to the direction of magnetization.

[0012] As shown in Fig. 1, there are two methods for the ferromagnetic conversion of photocatalysts. The first method is to induce ferromagnetic conversion by directly immersing the photocatalyst in ferromagnetic particles. The second method is to induce ferromagnetic conversion through structural changes by doping existing materials with other substances.

[0013] In this study, photocatalysts were synthesized using two methods, and changes in photocatalytic efficiency were observed by magnetizing them in the top, bottom, and lateral directions using doping.

[0015] 2.2. Two-dimensional materials

[0016] Materials can be classified according to the size of each dimension, and there are a total of four classifications ranging from 0 to 3 dimensions. Depending on the dimension, the relationship between atomic bonding forces and van der Waals forces varies, which in turn affects the electrical, magnetic, optical, and mechanical properties of the materials.

[0017] Zero-dimensional materials refer to materials in which all three dimensions (x, y, z) are within the nanometer range (< 10 nm), one-dimensional materials refer to materials in which two dimensions (x and y) are within the nanometer range (< 10 nm) and the other dimension (z) is outside the nanometer range, and two-dimensional materials refer to materials in which one dimension (x) is within the nanometer range (1 nm < x < 100 nm) and forms a sheet-like structure. Three-dimensional materials refer to bulk materials in which none of the dimensions are within the nanometer range (< 100 nm).

[0018] Currently, 2D materials being actively researched include h-BN, black phosphorus, and phosphorene. These 2D materials are heterostructures that combine the desired properties of different materials to create new properties and functionalities. However, 2D materials composed of atomic layers have a disadvantage in that they have high surface reactivity, making it difficult to maintain their shape and leading to aggregation.

[0020] 2.3. Theory of Ferromagnetic Materials

[0021] 2.3.1. Magnetic Materials

[0022] Within magnetic materials, there are regions called magnetic domains in which magnetic dipole moments are aligned in the same direction. Each domain contains approximately 1,015 to 1,016 atoms and varies in size from micrometers to millimeters. Magnetization refers to the alignment of the orientation of these magnetic domains by an external magnetic field. Magnetic materials are classified according to the way these magnetic domains align during magnetization.

[0023] Factors representing magnetic properties include relative magnetic permeability (μ r ) and self-susceptibility (X m Relative magnetic permeability is the magnitude of magnetization exhibited by a magnetic material, and when this value approaches 1, the material is considered non-magnetic. Magnetic susceptibility indicates the degree of magnetization under the same magnetic field.

[0025] 2.3.2 Types of Magnetic Materials

[0026] Magnetic materials refer to substances that can be magnetized in a magnetic field. Depending on the direction of magnetization, magnetic materials are broadly classified into ferromagnets, paramagnets, and diamagnets. Ferromagnets are materials that maintain their magnetization even when affected by a magnetic field due to their high magnetic susceptibility. Paramagnets are materials that are affected by a magnetic field but fail to maintain their magnetization due to their low magnetic susceptibility. Diamagnets, on the other hand, exhibit no magnetism because their magnetic susceptibility is close to 1.

[0028] 2.3.3. Types of Ferromagnetic Materials

[0029] Generally, as mentioned above, ferromagnets refer to materials that retain magnetization. Ferromagnets are further classified into ferromagnets, antiferromagnets, and ferrimagnets based on the magnetization direction of their magnetic domains. Ferromagnets are materials in which spin moments are aligned in one direction. Antiferromagnets are materials in which neighboring magnetic atoms spontaneously interact to align in opposite directions in a 1:1 ratio; spin moments of equal magnitude repeatedly align in parallel and in opposite parallel, and there is no externally exposed magnetism. Ferrimagnets, which are similar to antiferromagnets, are materials in which neighboring magnetic atoms spontaneously interact to align in opposite directions, but are partially aligned in opposite directions due to crystal structural factors.

[0031] 2.3.4. Curie Temperature, Neel Temperature

[0032] Ferromagnets and antiferromagnets exhibit changes in magnetization with temperature. Below a certain temperature, magnetization increases as the temperature rises, and below that temperature, magnetization decreases. In the case of ferromagnets, this specific temperature is the Curie temperature (T c It is called the ) and in the case of antiferromagnets, the Nel temperature (T nThis is referred to as ) and can be represented as shown in Fig. 2. In the case of ferromagnets, an increase in initial temperature improves the movement of magnetic spin moments, thereby increasing magnetism. However, if heat above the Curie temperature is supplied, the thermodynamic disorder of the material increases, causing alignment to break and magnetism to decrease. In the case of antiferromagnets, an increase in initial temperature breaks the antiparallel alignment of spin moments through thermal motion, thereby increasing magnetism. However, similar to ferromagnets, if the temperature exceeds the Neel temperature, thermal disorder within the material increases, causing magnetism to decrease. This unique characteristic of antiferromagnets results in the highest magnetic susceptibility at the Neel temperature, which then decreases as the temperature increases further. This phenomenon observed in antiferromagnets exhibits a unique characteristic where magnetic susceptibility peaks at the Neel temperature and then decreases.

[0034] 2.3.5. Hysteresis Loop

[0035] The hysteresis loop is a characteristic exhibited by ferromagnets; it is a curve representing magnetism based on the direction and strength of an external magnetic field and can be represented as shown in Fig. 3. Ferromagnets acquire a magnetic flux density B depending on the external magnetic field H. At this point, Br is called the remanent magnetism, which is the residual magnetization remaining in the material when the external magnetic field is removed. Hc is called the coercivity, which is the magnitude of the external magnetic field that returns a magnetized magnetic material to an unmagnetized state. If the remanent magnetism is high, the material can retain more magnetic force, but if the coercivity is low, it is prone to losing its magnetic force.

[0037] 2.3.6. Hall Effect

[0038] The Hall effect occurs due to the influence of the Lorentz force. The Lorentz force is expressed as F = q(E + v × B), where E represents the electric field, B represents the magnetic field, v represents the velocity of the particle, and X represents the cross-product. Therefore, when a charged particle is accelerated in an electric field (E) and passes through a magnetic field (B), Fleming's right-hand rule applies.

[0039] When a magnetic field perpendicular to the current is present, the Lorentz force generates an electric field that moves the flow of electric charge in a direction perpendicular to both the current and the magnetic field. This phenomenon is known as the Hall effect, and the resulting potential difference is called the Hall voltage. The Hall effect also occurs in magnetized ferromagnetic materials and exhibits a greater effect than the general Hall effect. This is called the anomalous Hall effect (AHE). In addition to the Hall voltage generated by the influence of electrons, there is a phenomenon called the Phonon Hall effect (PHE), where phonons are affected, causing a difference in heat transfer.

[0041] 2.4. Ferromagnetic material Fe2O3

[0042] The most commonly found natural forms of iron oxide are magnetite, maghemite, and hematite. Magnetite exhibits strong ferromagnetism at room temperature and, unlike other iron oxides, has a structure containing both Fe2+ and Fe3+ ions. Fe(III) ions randomly occupy octahedral and tetrahedral sites, whereas Fe(II) ions occupy only octahedral sites. Hematite exhibits weak ferromagnetism or antiferromagnetism at room temperature. 2- While the ion has a close-packed hexagonal crystal structure, Fe 3+ Ions occupy two-thirds of the octahedral sites within the cavity, producing hematite with corundum and rhombohedral structures. Maghemite exhibits ferromagnetism and converts into hematite above 673 K due to thermal instability. It has a spinel crystal structure similar to magnetite but contains cation lattice defects. Fe(III) ions occupy two-thirds of the lattice sites, while the remaining one-third is empty.

[0044] 2.5. Semiconductors

[0045] 2.5.1 Energy Bands

[0046] An energy band is a collection of energy levels, which are generated by wave interference between individual atoms. Within this range, only electrons can exist, and the region between energy bands where electrons cannot exist is called the band gap.

[0048] 2.5.2. Classification of Semiconductors

[0049] Generally, the energy band above the band gap is classified as the conduction band, and the energy band below it is classified as the valence band gap. Based on this, materials are classified as conductors, semiconductors, and insulators. If the valence band gap and the conduction band overlap (e.g., < 0 eV), it is classified as a conductor; if they are far apart (e.g., > 4 eV), it is classified as an insulator; and if they are moderately separated (0 eV < Eg < 4 eV), it is classified as a semiconductor.

[0051] 2.5.3. Direct Bandgap and Indirect Bandgap

[0052] Semiconductor band gaps are classified into two categories: direct band gaps and indirect band gaps. A direct band gap occurs when the minimum energy point of the conduction band (CBM) and the maximum energy point of the atomic band (VBM) coincide in momentum space. In this case, electrons can transition directly between bands without additional movement. On the other hand, an indirect band gap occurs when the momentum of the CBM and VBM do not coincide. In the case of an indirect band gap, phonon-assisted transitions are required for electron movement between bands. Consequently, once separated, hole-electron pairs tend to remain in the conduction band longer compared to direct band gap materials.

[0054] 2.6. Photocatalyst

[0055] 2.6.1. Photocatalytic Reaction

[0056] TiO2 absorbs light in the ultraviolet region, and electrons are excited from the valence band to the conduction band.

[0057] This process generates hole-electron pairs that induce redox reactions in the surrounding environment. When TiO2 is exposed to light, it becomes activated to generate holes (h+) and electrons (e-) (Reaction (I)). The generated holes and electrons produce highly reactive substances through the following reactions. Holes react with water and OH- ions to generate OH radicals (Reactions (II) and (III)). Electrons react with oxygen to produce reactive oxygen species (Reaction (IV)).

[0058] However, the generated hole-electron pairs can recombine. Generally, this recombination reaction occurs faster than the redox reaction, resulting in lower efficiency.

[0060] 2.6.2. Photocatalytic Activity and Reaction Rate

[0061] In chemical reactions, the reaction rate generally depends on the concentration of the reactants. For this reason, expressing the reaction rate as a function of the substances involved in the chemical reaction is called a rate law or rate equation.

[0062] In this study, the reaction rate of the catalyst for dye degradation follows a pseudo-first-order reaction rate according to the Langmuir-Hinshelwood mechanism. This mechanism explains the catalytic reaction rate particularly when reactants are adsorbed onto the catalyst surface. This means that the reaction rate depends on the adsorption of reactants onto the catalyst surface and the subsequent reaction. In the case of dye degradation using a photocatalyst with a significantly low concentration of reactants, the rate law can be simplified.

[0064] 2.7. Photocatalyst TiO2

[0065] 2.7.1. Characteristics of Photocatalytic TiO2

[0066] Photocatalytic titanium dioxide (TiO2) possesses the characteristic of becoming activated when exposed to light, as electrons move from the valence band to the conduction band. This TiO2 is doped with various materials and utilized in diverse fields such as air purification, wastewater treatment, and water splitting.

[0067] The structures of photocatalytic TiO2 are generally classified into anatase, brookite, and rutile; while anatase and rutile both possess a tetragonal structure, they differ in the connection angles of the octahedra composed of Ti and O, whereas brookite has an orthorhombic structure.

[0068] Among the three crystal structures, rutile is the thermodynamically most stable phase. Therefore, anatase and brookite transform into rutile when heated. Ananatase transforms into rutile between 600 and 700°C, and brookite transforms between 500 and 600°C.

[0069] Furthermore, although the bandgap energies of anatase and rutile are 3.2 eV and 3.0 eV, respectively, anatase generally exhibits better photocatalytic performance than structurally stable rutile. This is because rutile is a direct bandgap semiconductor, whereas anatase is an indirect bandgap semiconductor. As an indirect bandgap semiconductor, anatase has relatively less hole-electron recombination compared to rutile, resulting in better photocatalytic activity.

[0071] 2.7.2. Visible Light Photocatalyst TiO2

[0072] Meanwhile, since the bandgap energy of pure TiO2 is activated in the ultraviolet region, leading to hole-electron recombination issues, extensive research is being conducted to lower the bandgap energy for activation in the visible light region. This is achieved through additions classified into metal doping and non-metal doping.

[0073] The above additions include two types: doping, which replaces existing elements in the molecular structure; and impregnation, which adds new compounds to existing materials; and the synthesis method and resulting outcome vary depending on the chosen approach.

[0075] 2.7.3. Fe-added TiO2

[0076] There are various methods for adding Fe to lower the bandgap energy of TiO2, and there are also various synthesis methods. The characteristics of the resulting catalyst vary depending on the synthesis method. Prior art literature

[0077] S. Ahmed, A. (2017). Ferromagnetis m in Cr-, Fe-, and Ni doped TiO2 samples. Journal of Magnetism and Magnetic Materials. 442 , 1 52 - 1 57.R. Zahid et al. (2018). Influence of Iron Doping on Structure, Optical and Magnetic Properties of TiO2 Nanoparticles. 14. 587- 593.S. Balaji Prasath et al. (2024). Ferromagnetic ordering in Fe: TiO2 solid solutions: A vis ual electron density mapping by maximum entropy method us ing powder X-ray data. 683.41 5955Pedro M. lvarez. et al. (2010). Preparation and characterization of magnetic TiO 2 nanoparticles and their utilization for the degradation of emerging pollutants in water. 1 00( 1 - 2 ) . 338- 345Xiao-Quan Chen et al. (2018). Preparation and characterization of the magnetic Fe3O4@TiO2 nanocomposite with the in-s itu synthesis coating method. Materials Chemistry and Physics. 216. 496-501 The problem to be solved

[0078] This study aims to develop a ferromagnetic photocatalyst doping technology capable of applying ferromagnetic magnetization technology. means of solving the problem

[0079] According to the present invention, a magnetized semiconductor was manufactured by doping Fe into TiO2, a three-dimensional semiconductor material, to synthesize it into a ferromagnetic material and performing magnetization. Subsequently, to confirm the influence of the magnetized semiconductor on the photocatalyst, the change in photodecomposition efficiency according to the magnetization direction was confirmed. Effects of the invention

[0080] It was confirmed that the anatase was synthesized as a single phase through XRD, Raman shift, and FE-SEM, and the structural, optical, and magnetic properties were confirmed by additionally analyzing BET, DRS, PL, and VSM.

[0081] As a result of analyzing the photocatalytic activity and reaction rate through dye decomposition to evaluate photocatalytic activity according to the presence and direction of magnetization, it was confirmed that the dye decomposition efficiency and reaction rate of Fe-doped TiO2 improved depending on the direction of magnetization. This is believed to be due to the Hall effect through magnetization maximizing electron transport control, and it indicates that magnetization enables electron transport control of photocatalytic materials, thereby making it possible to convert three-dimensional materials into two-dimensional ones. Brief explanation of the drawing

[0082] Figure 1 is a diagram briefly illustrating an example of a ferromagnetic change and magnetization method of a photocatalyst. Figure 2 is a graph illustrating the Curie temperature and the Nel temperature. Figure 3 is a graph illustrating a hysteresis loop. Figure 4 shows the process of preparing an α-Fe2O3 / TiO2 impregnated sample by impregnation method 1. Figure 5 is the XRD pattern of Fe-impregnated TiO2 by impregnation method 1 at 500 ℃. Figure 6 is the XRD pattern of Fe-impregnated TiO2 by impregnation method 1 at 600 ℃. Figure 7 is an SEM image of (a) pure TiO2 at 500 ℃, (b) Fe-impregnated TiO2 by impregnation method 1 at 500 ℃, (c) pure TiO2 at 600 ℃, and (d) Fe-impregnated TiO2 samples by impregnation method 1 at 600 ℃. Figure 8 shows the process of preparing an α-Fe2O3 / TiO2 impregnated sample by impregnation method 2. Figure 9 is the XRD pattern of Fe-impregnated TiO2 by impregnation method 2. Figure 10 shows the Raman spectra of pure TiO2 and Fe-impregnated TiO2 samples by impregnation method 2. Figure 11 shows the results of the methylene blue (MB) photocatalytic decomposition experiment on a pure TiO2 sample. Figure 12 shows the results of a methylene blue photocatalytic decomposition experiment on a 5% Fe-impregnated TiO2 sample by impregnation method 2. Figure 13 shows the photocatalytic decomposition rate over time of pure TiO2 and Fe-impregnated TiO2 samples by impregnation method 2. Figure 14 is a flowchart briefly illustrating the process of manufacturing a ferromagnetic Fe-TiO2 catalyst through doping. Figure 15 shows the XRD patterns of pure TiO2 and Fe-doped TiO2. Figure 16 shows the results of observing pure TiO2 (a) and 0.5% (b), 5% (c), and 10% (d) Fe-doped TiO2 samples through FE-SEM analysis. Figure 17 is an FE-SEM image for confirming the particle size of a 5% Fe-doped TiO2 sample. Figure 18 shows the Raman spectra of pure TiO2 and Fe-doped TiO2 samples. Figure 19 is a graph showing the nitrogen adsorption-desorption isotherm and pore size distribution of the catalyst sample. Figure 20 shows the DRS spectra of pure TiO2 and Fe-doped TiO2 samples. Figure 21 is a graph showing the calculated band gap energy of pure TiO2. Figure 22 is a graph showing the calculated band gap energy of 0.5% Fe-doped TiO2. Figure 23 is a graph showing the calculated band gap energy of 5% Fe-doped TiO2. Figure 24 is a graph showing the calculated band gap energy of 10% Fe-doped TiO2. Figure 25 shows the PL spectra of pure TiO2 and Fe-doped TiO2 samples. Figure 26 is a graph showing the magnetic hysteresis loop (10 kOe) of pure TiO2 and 5% Fe-doped TiO2 samples. Figure 27 is a graph showing the coercivity (10 kOe) in the magnetic hysteresis loop of pure TiO2 and 5% Fe-doped TiO2 samples. FIG. 28 is a diagram showing a magnetization method according to a magnetizer (a) and magnetization directions ((b): SM (side magnetization), (c): DM (downward magnetization), (d): UM (upward magnetization)). Figure 29 is a graph showing the methylene blue (MB) decomposition curves of pure TiO2 and Fe-doped TiO2 samples. Figure 30 is a graph showing the photocatalytic reaction rates of pure TiO₂ and Fe-doped TiO₂ calculated using MB decomposition. Figure 31 is a graph showing the methylene blue (MB) decomposition curve of a 0.5% Fe-doped TiO2 sample. Figure 32 is a graph showing the photocatalytic reaction rate of 0.5% Fe-doped TiO₂ calculated using MB decomposition. Figure 33 is a graph showing the methylene blue (MB) decomposition curve of a 5% Fe-doped TiO2 sample. Figure 34 is a graph showing the photocatalytic reaction rate of 5% Fe-doped TiO₂ calculated using MB decomposition. Figure 35 is a graph showing the methylene blue (MB) decomposition curve of a 10% Fe-doped TiO2 sample. Figure 36 is a graph showing the photocatalytic reaction rate of 10% Fe-doped TiO₂ calculated using MB decomposition. Specific details for implementing the invention

[0083] 3. Research Results and Discussion

[0084] 3.1 Ferromagnetic α-Fe2O3 / TiO2 catalyst by impregnation

[0085] 3.1.1. Method for preparing ferromagnetic α-Fe2O3 / TiO2 catalyst by impregnation

[0086] In this experiment, P25 (TiO2, Sigma Aldrich, > 99.5%) and ferrous sulfate heptahydrate (FeSO4·7H2O, Sigma Aldrich, > 99%) were used. Ferrous sulfate heptahydrate was added to 1.5 mL of deionized water to achieve Fe ratios of 0 and 1.0 mol%. The mixture was then dried in an oven at 100°C for 1 hour to remove the solvent. After drying, the samples were calcined at 500°C and 600°C for 6 hours at a heating rate of 5°C / min. Each prepared sample was analyzed using X-ray diffraction (XRD), with conditions set to an angular range of 20°–80° and a scan rate of 4° / min. The detailed procedure of this experiment is described in Fig. 4.

[0087] 3.1.1.1. XRD Analysis

[0088] To investigate the crystal structure of the samples, XRD patterns of pure TiO2 and Fe-impregnated TiO2 are shown in Figures 5 and 6. The peaks of the synthesized particles partially coincided with the peaks of anatase (JCPDS Card: 84-1286), rutile (JCPDS Card: 89-555), and hematite (JCPDS Card: 73-2234).

[0089] As shown in Table 1 below, it was observed that the crystal size and the ratio of the rutile phase decreased as the impregnation concentration increased, regardless of the calcination temperature. Calculations for the phase composition were performed using Equation 1 below. Here, X A represents the Anathas composition, and X B represents the rutile composition, and I 27.3(rutile) represents the rutile main peak intensity, and I 25.3(anatase) It represents the main peak intensity of Anathas.

[0090] In Table 1 below, it can be seen that the crystal size of both the pure sample and the impregnated sample at 500°C is smaller than the crystal size at 600°C. In addition, it was confirmed that the anatase ratio at 500°C is higher than the anatase ratio at 600°C, and that the anatase ratio increases upon iron impregnation.

[0091] (Equation 1)

[0092]

[0093] [Table 1] α-Fe2O3 / TiO2 Crystal Size and Phase Composition According to Calcination Temperature and Impregnation Concentration

[0094]

[0095] 3.1.1.2. SEM Analysis

[0096] The SEM image according to Fig. 7 confirms that the crystal size at 500°C is smaller than at 600°C and that the crystal size decreases with iron impregnation. This supports the XRD results. However, blocked pores were observed in all Fe-impregnated samples, which appears to be a result of iron impregnation.

[0098] 3.1.1.3. Results and Discussion

[0099] In this experiment, Fe-impregnated TiO2 was prepared using P25 at calcination temperatures of 500°C and 600°C for 0% and 10% samples.

[0100] In Figures 5 and 6, it can be seen that anatase, rutile, and hematite coexist. Additionally, Table 1 shows the change in the ratio of anatase to rutile. Furthermore, the SEM image in Figure 7 shows a sample with clogged pores due to high temperature and rapid heating rate.

[0101] Such pore clogging can affect the photocatalytic reaction of the catalyst. To address this problem, Anathas was used instead of P25 in the following experiment, the calcination temperature was 500°C, and the heating rate was lower. Iron impregnation ratios of 5%, 10%, and 20% were prepared to observe the changes.

[0103] 3.1.2. Preparation of Ferromagnetic α-Fe2O3 / TiO2 Catalyst by Impregnation Method 2

[0104] In this experiment, Anathas (TiO2, Sigma Aldrich, > 99%), ferrous nitrate nonahydrate (Fe(NO3)3·9H2O, Sigma Aldrich, > 98%), and ethanol (C2H5OH, Daejung, > 99.5%) were used. Ferrous nitrate was dissolved in 50 mL of ethanol at Fe ratios of 0, 5, 10, and 20 mol%, and 2 g of Anathas was added. The mixture was stirred using a magnetic stirrer for 24 hours. Then, the ethanol was evaporated at room temperature for 30 minutes, followed by drying in an 85°C oven for 15 hours. Finally, the sample was ground and calcined at 500°C for 3 hours (at a rate of 2°C / min). The prepared powder was processed into a non-magnetic powder that does not react to magnets and a ferromagnetic powder that acquires magnetization through a magnetizer. The detailed procedure of this experiment is illustrated in Fig. 8. Each prepared sample was analyzed using an XRD device under conditions of an angle range of 20° to 80° and a scan speed of 1° / min.

[0106] 3.1.2.1. XRD Analysis

[0107] XRD patterns of pure TiO2 and Fe-impregnated TiO2 are shown in Fig. 9 to investigate the crystal structure of the samples. The peaks of the synthesized particles partially matched the peaks of anatase (JCPDS Card: 84-1286) and hematite (JCPDS Card: 73-2234), but rutile was not observed.

[0108] In addition, as shown in Table 2, the crystal size remained constant regardless of the impregnation amount. This indicates that the crystal structure of anatase did not change, and hematite was synthesized separately without altering the crystal structure of anatase regardless of the impregnation amount.

[0109] [Table 2] α-Fe2O3 / TiO2 Impregnation Concentration and Crystal Size

[0110]

[0112] 3.1.2.2. Raman Spectroscopic Analysis

[0113] Raman spectroscopy was performed to further analyze the structural phases of pure TiO2 and Fe-impregnated TiO2, as shown in Fig. 10. All samples exhibited five major bands corresponding to six Raman modes: 1-E g (145 cm -1 ), 2-E g (197 cm -1 ), B1 g (397 cm -1 ), B1 g + A 1g (516 cm -1 ), 3-E g (640 cm -1 ). These characteristics indicate anatase TiO2. However, the hematite observed in XRD was not detected even in the 20% Fe-impregnated sample. Hematite is at 226 cm⁻¹ -1 , 245 cm -1 , 293 cm -1 , 298 cm -1 , 412 cm -1 , 497 cm -1 , 613 cm-1 It has 7 Raman modes. In addition, the peak observed for Fe-impregnated TiO2 was weaker compared to pure TiO2.

[0115] 3.1.2.3. Evaluation of Photocatalytic Activity

[0116] To evaluate photocatalytic activity, methylene blue (MB) was selected, and dye degradation experiments were performed using pure TiO2 and Fe-impregnated TiO2. The degradation experiments were conducted using a solar simulator (xenon lamp, 500W) as the light source. The initial concentration was 10 ppm, and the volume of the reaction solution was 30 mL. 0.2 g of photocatalyst was added to a 40 mL crystallization dish (Φ50 x h30 mm). MB measurements were taken at light exposure intervals of 30, 60, 120, and 180 minutes. The degree of degradation was measured using a UV-Vis spectrometer at 1 nm intervals within the wavelength range of 500–750 nm, and the results are shown in Figures 11 and 12. The degradation efficiency of MB was calculated based on changes in concentration using Equation 2.

[0117] (Equation 2)

[0118]

[0120] As shown in Figure 13, the decomposition efficiency of pure TiO2 after 30 minutes was approximately 82%. On the other hand, 5% Fe-impregnated TiO2 showed a decomposition efficiency of approximately 39%, 10% Fe-impregnated TiO2 showed approximately 32%, and 20% Fe-impregnated TiO2 showed approximately 15% after 30 minutes, indicating a significant difference in efficiency.

[0122] 3.1.2.4. Results and Discussion

[0123] In the above experiment, iron-impregnated TiO2 samples were prepared using Anathalase and fired at 500°C with compositions of 0%, 5%, 10%, and 20%.

[0124] In Figure 9, it can be seen that anatase and hematite coexist. Table 3 indicates that the crystal size remained constant regardless of the iron impregnation ratio. However, in Figure 10, anatase was identified via the Raman spectrum, but hematite was not detected. Additionally, the peaks in the data for iron-impregnated TiO2 are slightly weaker compared to pure TiO2, which may affect the efficiency of the photocatalyst. This was further confirmed by the fact that the decomposition efficiency of the impregnated sample was lower than that of the pure sample, as shown in Figure 13.

[0125] Therefore, in subsequent experiments, Fe-doped TiO2 was synthesized at 0%, 0.5%, 5%, and 10% by weight and the changes were observed.

[0127] 3.2.1. Preparation of Ferromagnetic Fe-TiO2 Catalyst via Doping

[0128] In this experiment, titanium tetrachloride (TiCl4, Sigma Aldrich, > 99.9%), ferric chloride hexahydrate (FeCl3·6H2O, Sigma Aldrich, > 99.0%), sodium hydroxide solution (NaOH, Samchun, 30%), and ethanol (C2H5OH, Daejung, > 99.5%) were used. Titanium tetrachloride and ferric chloride hexahydrate were dissolved in 40 mL of ice-distilled water at ratios of 0, 1, 5, and 10 wt%, and then cooled to obtain a clear solution. Then, the pH was adjusted to 7-8 using a 30% NaOH solution via an OH substitution reaction, and the mixture was hydrothermally treated in an autoclave at 160°C for 12 hours. The resulting slurry was separated using a centrifuge and then washed three times each with water and ethanol. The washed material was evaporated at 45°C for 2 hours and dried overnight in an oven at 80°C. Then, the sample was ground and calcined at 500°C for 10 hours (at a rate of 2°C / min). The detailed procedure for this experiment is shown in Fig. 14.

[0130] 3.2.1.1. XRD Analysis

[0131] To investigate the crystal structure of the samples, XRD patterns of pure TiO2 and Fe-doped TiO2 are presented in Fig. 15. Each prepared sample was analyzed using an XRD device under conditions of an angle range of 20°–80° and a scan rate of 1° / min. The peaks of the synthesized particles were identified, matching the peaks of Ananatas (JCPDS Card: 84-1 286), indicating successful doping. No evidence of phase transformation to rutile or the presence of iron oxide was observed.

[0132] This means that iron oxide was not formed on the TiO2 surface, but Fe 3+ This suggests that it was successfully incorporated into the TiO2 lattice structure in ionic form. Therefore, it was observed that the size of the main peak (101) of Anathas decreased as the doping concentration increased, indicating that the overall size of the synthesized crystals decreased. This phenomenon is due to Fe 3+ It occurs because particle growth in the TiO2 photocatalyst is inhibited due to doping.

[0133] [Table 3] Fe-TiO2 Doping Concentration and Crystal Size

[0134]

[0136] 3.2.1.2. FE-SEM Analysis

[0137] Pure TiO2 and 0.5%, 5%, and 10% Fe-doped TiO2 samples were observed via FE-SEM analysis and are presented in Fig. 16. All samples exhibited a spherical shape, and no pore collapse was observed. Additionally, Fig. 17 confirmed that the particle size of the samples was approximately 20-30 nm, which is consistent with the grain size calculated from the XRD data shown in Table 3.

[0139] 3.2.1.3. Raman Spectroscopic Analysis

[0140] Raman spectroscopy was performed to further analyze the structural phases of pure TiO2 and Fe-doped TiO2 as shown in Fig. 18. All samples exhibited five major bands corresponding to six Raman active modes. 1-E g (145 cm -1 ), 2-E g (197 cm -1 ), B 1g (397 cm -1 ), B 1g + A 1g (516 cm -1 ), 3-E g (640 cm -1 ). These characteristics indicate anatase TiO2. Iron was not detected, which indicates that the analyzed material consists of a pure anatase phase. This finding supports the XRD results. However, 1-E g ( 145 cm -1 A slight shift in the high-frequency direction was observed at the Raman peak position. Similar behavior in Raman mode signals after Fe doping has been reported elsewhere and is considered a signal of structural defects. This difference leads to changes in force constants and vibrational dynamics due to volumetric shrinkage effects. This is Fe 3+ and Ti 4+ This is attributed to the difference in ionic radii between ions. Additionally, XRD analysis showed that the particle size of Fe-doped TiO2 decreases as the Fe concentration increases.

[0142] 3.2.1.4. Texture Analysis

[0143] The surface of the sample was measured using the Brunauer-Emmett-Teller (BET) method with N2 at 77.3 K to obtain adsorption-desorption isotherms. Additionally, the pore size distribution was measured using the Barrett-Joyner-Halenda (BJH) method. These results are shown in Fig. 19. According to the IUPAC classification, the N2 adsorption-desorption isotherm of the sample is classified as Type IV with an H3 hysteresis loop, indicating the presence of a mesoporous structure in the sample. As can be seen in Fig. 19, the pore size distribution is 0–50 nm. It was observed that the SBET, pore volume, and pore size of the sample increased with increasing Fe concentration. However, the pore size was observed to decrease by only 10%, which may be due to pore blockage caused by metal oxide species resulting from excessive doping of Fe ions.

[0144] [Table 4] Texture characteristics of pure TiO2 and Fe-doped TiO2 samples

[0145]

[0147] 3.2.1.5. DRS Analysis

[0148] The DRS spectra of pure and Fe-doped TiO2 were measured in the range of 300–11,000 nm as shown in Fig. 20. As the Fe doping concentration increased, the reflectance in the visible light region (380–780 nm) decreased, indicating that absorption increased in this region. Additionally, for 5% and 10% Fe-doped TiO2, it was observed that absorption also increased in the IR region (above 780 nm).

[0149] The bandgap energy was 3.60 eV for pure TiO2, 3.59 eV for 0.5% Fe-doped TiO2, 3.63 eV for 5% Fe-doped TiO2, and 3.57 eV for 1.0% Fe-doped TiO2, showing no significant change at 3.60 eV.

[0150] [Table 5] Bandgap energies of pure TiO2 and Fe-doped TiO2 samples by DRS spectrum

[0151]

[0152] 3.2.1.6. PL Analysis

[0153] The PL spectra of pure and Fe-doped TiO2 were recorded in the wavelength range of 400–700 nm after excitation at 310 nm, as shown in Fig. 25. PL spectra are generated by the recombination of electrons and holes at specific wavelengths. The recombination rate is related to the electronic and structural properties of the material. The wavelength and intensity of the PL spectrum depend directly on the doping ions. The peak intensity of Fe-doped TiO2 is lower than that of pure TiO2, indicating that the electron-hole recombination rate of Fe-doped TiO2 is significantly lower than that of pure TiO2.

[0155] 3.2.1.7. VSM Analysis

[0156] Vhe measurements were performed using VSM with a field increase of 125 Oersted from 1 Tesla (10,000 Oersted) as shown in Fig. 26. The saturation magnetization and coercivity determined by VSM were found to be 1.774 emu / g and 22.845 G, respectively, for pure TiO2, and 1.835 emu / g and 35.371 G, respectively, for 5% Fe-doped TiO2. This confirms that Fe doping enhances both saturation magnetization and coercivity.

[0157] [Table 6] Saturated Magnetization and Coercivity of Pure TiO2 and 5% Fe-Doped TiO2 Samples

[0158]

[0160] 3.2.1.8. Evaluation of Photocatalytic Activity and Kinetics

[0161] The evaluation of photocatalytic activity was performed using the same method described in Section 3.2.2.3 above, with the only change being the use of a different catalyst. Additionally, 0.5%, 5%, and 10% Fe-doped TiO2 samples were tested with different magnetization orientations. The magnetization orientations were classified as follows: NM (non-magnetization), SM (lateral magnetization), DM (downward magnetization), and UM (upward magnetization).

[0162] Using the dye degradation data obtained from these experiments, the reaction rate constant was calculated using the equation (Equation 2) derived from Section 2.6.2, Photocatalytic Activity and Kinetics.

[0163] (Equation 2)

[0164]

[0165] The results of decomposition using a photocatalyst for 180 minutes showed that pure TiO2 was 41.6%, 0.5% Fe-TiO2 was 32.9%, 5% Fe-TiO2 was 31.8%, and 10% Fe-TiO2 was 22.3%. In relation to decomposition experiments performed according to magnetization direction, it was observed that the activity and kinetics of all samples improved under DM conditions, whereas they decreased under SM conditions. This is shown in Table 7. Specifically, for 10% Fe-TiO2 under DM conditions, the decomposition rate and rate constant increased by 13.9% and 16.3%, respectively.

[0166] [Table 7] Photocatalytic Performance Analysis

[0167]

[0169] 3.2.1.9. Results and Discussion

[0170] In the above experiments, Fe-doped TiO2 samples were prepared using TiCl4 precursors and calcined at 500 °C for compositions of 0, 0.5, 5, and 10 wt%. According to the XRD analysis shown in Fig. 15, only the Anathalus peak was observed. Furthermore, Table 3 indicates that the grain size decreased from 30 nm to 20 nm as the doping amount increased. This decrease in grain size was further confirmed by FE-SEM images, which showed spherical particles with no other impurities detected in any of the samples. As shown in Fig. 18, Raman analysis similarly displayed only the Raman active mode of Anathalus, and 1-E g (1 45 cm -1 The ) mode showed a shift due to Fe doping.

[0171] BET analysis was performed to investigate texture characteristics, revealing that the pore size in all samples was consistently mesoporous (0–50 nm). Additionally, both SBET and pore volume increased with doping amount, but at 10% doping, the pore volume decreased, suggesting that Fe metal oxides were formed due to excessive Fe ion doping.

[0172] In DRS analysis, as Fe doping increased, absorption in the visible light range increased, and in the IR range, it increased further at 5% and 10% doping levels. However, there was minimal change in the band gap energy, which remained at approximately 3.60 eV.

[0173] PL analysis of optical properties indicates that the peak intensity of Fe-doped TiO2 is reduced compared to pure TiO2, suggesting that hole-electron recombination is reduced.

[0174] VSM analysis confirmed that saturation magnetization and coercivity increase as the iron doping level increases.

[0175] As a result of dye degradation experiments investigating photocatalytic activity and reaction rate according to magnetization direction, pure TiO2 showed the highest degradation rate of 41.6% under NM conditions. However, the degradation rates of 0.5% and 5% Fe-doped TiO2 were 32.9% and 31.8%, respectively, showing no significant difference between the two materials. Additionally, in experiments related to magnetization, 10% Fe-doped TiO2 showed the largest changes in activity and reaction rate, with increases of 13.9% and 16.3%, respectively. This is due to the presence of undoped Fe metal oxide.

[0177] 4. Conclusion

[0178] In this study, ferromagnetism was induced in TiO2 by adding Fe, and changes in photocatalytic activity and kinetics were investigated through dye degradation according to the magnetization direction. This study was designed to control electron transport via the Hall effect by inducing ferromagnetism in TiO2, thereby enabling it to operate similarly to 2D materials. The analysis of these experimental results is as follows.

[0179] 1. Fe was impregnated and added to TiO2 to enable performance according to the magnetization direction, and XRD, SEM, and Raman analysis were performed. Through these analyses, Fe-doped TiO2 was synthesized in a single-phase anatase form.

[0180] 2. To observe changes in photocatalytic activity and kinetics according to magnetization direction, dye degradation experiments were conducted using a solar simulator and UV-Vis using synthesized Fe-doped TiO2. The magnetization methods used were NM (None Magnetization), DM (Down Magnetization), UM (Up Magnetization), and SM (Side Magnetization).

[0181] 3. It was confirmed that the efficiency of magnetized Fe-doped TiO2 increased in DM and decreased slightly in SM. Magnetized Fe-doped TiO2 showed a maximum efficiency increase of 13.9% after 180 minutes. These results are believed to be due to the maximum control of electron transport through the Hall effect depending on the magnetization direction.

[0182] By choosing to dope TiO2 with Fe, Fe-doped TiO2 was produced in a single-phase anatase form. It was confirmed that photocatalytic activity and kinetics can be positively influenced by the magnetization direction. Additionally, 10% Fe-doped TiO2 showed a maximum efficiency increase of 13.9% under DM conditions after 180 minutes. This phenomenon is believed to be due to the maximal control of electron transport through the Hall effect depending on the magnetization direction.

Claims

Claim 1 A magnetized semiconductor photocatalyst comprising titanium dioxide (TiO2); iron (Fe) doped into the titanium dioxide, wherein the iron-doped titanium dioxide has an anatase single phase and has different photocatalytic activity depending on the magnetization direction. Claim 2 A magnetized semiconductor photocatalyst according to claim 1, characterized in that the iron content is 0.5 wt% to 10%. Claim 3 A magnetized semiconductor photocatalyst according to claim 1, characterized in that the pore size distribution of the magnetized semiconductor photocatalyst is 50 nm or less. Claim 4 A magnetized semiconductor photocatalyst according to claim 1, characterized in that the crystal grains of the magnetized semiconductor photocatalyst have a size of 20 to 30 nm. Claim 5 A method for manufacturing a magnetized semiconductor photocatalyst, characterized by comprising: (a) a step of preparing a mixed solution of a titanium precursor and an iron precursor; (b) a step of forming iron-doped titanium dioxide by hydrothermal treatment after adjusting the pH of the mixed solution of step (a); (c) a step of separating and drying the slurry produced in step (b); and (d) a step of grinding and calcining the sample produced in step (c). Claim 6 A method for manufacturing a magnetized semiconductor photocatalyst, characterized in that, in claim 5, the titanium precursor and the iron precursor are each chlorides. Claim 7 A method for decomposing a dye, characterized by including the step of contacting a magnetizing semiconductor photocatalyst according to any one of claims 1 to 4 or a magnetizing semiconductor photocatalyst manufactured according to any one of claims 5 and 6 with a dye in the presence of light. Claim 8 A method for decomposing dyes according to claim 7, characterized in that the magnetized semiconductor photocatalyst is magnetized in a predetermined direction. Claim 9 A method for decomposing a dye, characterized in that, in claim 8, the direction of the magnetization is downward magnetization (DM).

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