Preparation method and application of Fe / Cu / BiOCl composite photocatalyst

Abstract

The invention discloses a preparation method and application of a Fe / Cu / BiOCl composite photocatalyst, a Fe < 3 + > and Cu < 2 + > co-doped BiOCl composite photocatalyst is synthesized based on a simple one-step hydrothermal method, and the energy band structure of BiOCl can be effectively regulated and controlled by adjusting the doping proportion of Fe and Cu ions. Compared with undoped BiOCl and Fe / Cu single metal ion doped BiOCl, a Fe and Cu co-doped sample shows higher visible light absorption capacity and lower electron-hole recombination efficiency. When the doping molar ratio of Fe < 3 + > to Cu < 2 + > is 9: 1, the photocatalytic performance of the composite photocatalyst is optimal, and the removal rate of Cr (VI) reaches 91.3% after the composite photocatalyst is irradiated by visible light for 120 min and is remarkably higher than that of pure BiOCl (64.4%). In addition, the composite photocatalyst also shows good stability and recycling performance, and has potential application value in the field of water treatment.

Description

Technical Field

[0001] This invention belongs to the field of inorganic environmentally friendly composite photocatalytic materials technology, specifically relating to a preparation method and application of a Fe / Cu / BiOCl composite photocatalyst. Background Technology

[0002] With the rapid development of industries such as decorative chromium plating, corrosion-resistant chromium plating, and papermaking, the industrial consumption of chromium has continued to increase, leading to the discharge of large amounts of wastewater containing hexavalent chromium (Cr(VI)) into water bodies, posing a potential threat to human health. Cr(VI) is approximately 100 times more toxic than trivalent chromium (Cr(III)), possessing not only extremely high water solubility and carcinogenicity but also causing severe damage to the human enzyme system through various exposure pathways. To address the environmental and health risks posed by Cr(VI), researchers have developed various treatment technologies such as bioremediation, chemical reduction, and reverse osmosis. However, these methods often suffer from high operating costs and insufficient environmental friendliness, limiting their large-scale application. Photocatalysis technology, due to its high efficiency, greenness, and sustainability, has attracted much attention in the removal and reduction of Cr(VI). This technology can directly convert highly toxic Cr(VI) into less toxic Cr(III) using light energy, making it a promising water treatment method.

[0003] BiOCl is a typical layered ternary oxide semiconductor material with a PbFCl-like layered structure. Its crystals consist of alternating layers of [Bi₂O₂]. 2+ Layer and double Cl - BiOCl is composed of layers with tightly bonded atoms both within and between layers. This unique layered configuration allows for the formation of an internal electric field, which helps suppress the recombination of photogenerated carriers. Furthermore, BiOCl is an important photocatalytic material due to its abundant raw material sources, simple preparation process, and environmental friendliness. However, its wide band gap (3.0–3.6 eV) means it primarily absorbs ultraviolet light, limiting its utilization efficiency for visible light. Despite the presence of an internal electric field, the rapid recombination of photogenerated carriers still restricts the improvement of its photocatalytic performance. To address this, researchers have proposed various modification strategies. For example, increasing the specific surface area and improving light absorption efficiency can be achieved by controlling the material morphology (e.g., preparing nanorods or nanosheets); heterojunctions can be constructed to promote the separation of photogenerated carriers; or elemental doping can adjust the band structure and expand the spectral response range. Among these, doping with specific metals or non-metals can effectively adjust the band gap and introduce a local electric field or defect states within the crystal, which helps separate photogenerated electrons and holes, thereby reducing their recombination rate.

[0004] Ion co-doping, as a highly efficient material modification strategy, exhibits significant advantages in the field of photocatalytic materials by simultaneously introducing two or more different ions. This method can produce a synergistic effect, allowing different ions to complement each other in performance, thereby improving the overall performance of photocatalytic materials. Simultaneously, ion co-doping can effectively optimize the electronic structure of photocatalytic materials, improve conductivity, and promote carrier migration. In recent years, transition metal ion doping has received widespread attention in the preparation of BiOCl-based photocatalysts. Among them, Fe... 3+ With Cu 2+ The introduction of Fe can create new energy levels in the material's band gap, effectively reducing the band gap width and promoting the excitation and migration of photogenerated electrons. Furthermore, Fe... 3+ and Cu 2+ ionic radii (respectively) and All are less than Bi 3 + This makes it easier for the material to enter the BiOCl lattice, thus achieving effective doping.

[0005] Patent document CN201610834591.1 discloses a method for preparing the composite photocatalyst Fe-BiOCl. The specific synthesis steps are as follows: bismuth nitrate is dissolved in ethylene glycol to prepare solution 1; ferric chloride is dissolved in ethylene glycol to prepare solution 2; and hexadecyltrimethylammonium chloride is dissolved in ethylene glycol to prepare solution 3. Solution 2 is slowly added dropwise to solution 1, and after stirring, solution 3 is added dropwise to solution 1. After continuous stirring, the mixture is placed in a microwave reactor for 10 minutes at a power of 200W. The resulting precipitate is centrifuged, washed sequentially with distilled water and anhydrous ethanol, and then vacuum dried at 60°C to obtain the corresponding Fe-BiOCl photocatalytic material. This patent document describes the preparation of Fe-BiOCl photocatalytic material for the degradation of Rhodamine B solution by light radiation using a microwave method, but it does not involve the preparation of Fe / Cu / BiOCl composite photocatalysts or the photocatalytic removal of Cr(VI) pollutants in water. Patent document CN202010581799.3 discloses a method for preparing and applying a two-dimensional layered bismuth oxychloride-Fe-doped modified photocatalytic material. A novel molten salt (NaNO3 and KNO3) method was used to prepare pure BiOCl and Fe-doped modified BiOCl. NaNO3 and KNO3 were weighed and ground together. Bi(NO3)3·5H2O, KCl, and Fe(NO3)3·9(H2O) were added to the mixed salt and ground until homogeneous. The mixed powder was then placed in an alumina crucible for heat treatment to obtain Fe-doped modified BiOCl. This material exhibits a typical layer-to-layer structure with numerous surface active regions, visible light response, and stable photocatalytic performance. This patent document uses the molten salt method to prepare Fe-doped modified BiOCl for degrading RhB solutions, but does not involve the preparation of Fe / Cu / BiOCl composite photocatalysts or the photocatalytic removal of Cr(VI) pollutants from water. Patent document CN201810139088.3 discloses a method for preparing Cu(II)-modified BiOCl and its application. It describes a simple one-step hydrothermal method for preparing helical BiOCl nanosheets, followed by in-situ photoreduction modification of Cu(II) without reducing or protecting agents to obtain a Cu(II)-modified BiOCl catalyst. This catalyst effectively reduces the recombination rate of electron-hole pairs and exhibits good visible-light photocatalytic performance for the degradation of Rhodamine B. However, this patent document, based on the hydrothermal method for preparing a Cu(II)-modified BiOCl catalyst for Rhodamine B degradation, does not involve the preparation of Fe / Cu / BiOCl composite photocatalysts or the photocatalytic removal of Cr(VI) pollutants from water.

[0006] This invention successfully prepared Fe using a one-step hydrothermal method. 3+ and Cu 2+Co-doped BiOCl composite photocatalysts exhibit optimized band structures by adjusting the Fe / Cu doping ratio. Compared to undoped BiOCl and Fe / Cu single-metal-ion-doped BiOCl, the multi-metal-ion co-doped photocatalyst shows significantly enhanced absorption in the visible light region and a markedly reduced electron-hole recombination rate. These properties suggest that this composite photocatalytic material shows promising application prospects in the photocatalytic reduction of hexavalent chromium. Currently, there are no related reports in this area. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a simple and mild method for preparing a Fe / Cu / BiOCl composite photocatalyst. The composite photocatalyst prepared by this method exhibits a broad spectral response and high quantum efficiency, enabling efficient and rapid removal of Cr(VI) pollutants from water under illumination. Simultaneously, this composite photocatalyst possesses good structural stability and recyclability, making it an ideal photocatalytic material for purifying Cr(VI)-containing wastewater and suitable for the photocatalytic removal of Cr(VI) from Cr(VI)-polluted water.

[0008] To address the aforementioned technical problems, this invention employs the following technical solution: a method for preparing a Fe / Cu / BiOCl composite photocatalyst. By optimizing the doping ratio of Fe and Cu ions, the band structure of BiOCl can be effectively controlled. Compared to undoped BiOCl and Fe / Cu single-metal ion-doped BiOCl, the Fe / Cu co-doped sample exhibits significantly enhanced visible light absorption performance and lower electron-hole recombination efficiency. These characteristics make this material show promising application prospects in the photocatalytic reduction of hexavalent chromium.

[0009] A method for preparing a Fe / Cu / BiOCl composite photocatalyst is disclosed. Using Bi(NO3)3·5H2O, Fe(NO3)3·9H2O, and Cu(NO3)2·3H2O as raw materials, the Fe / Cu / BiOCl composite photocatalyst is prepared by a hydrothermal method at 150–170 °C. By optimizing the Fe / Cu ion doping ratio to 9:1, the band structure of BiOCl can be effectively controlled, exhibiting significantly enhanced visible light absorption performance and lower electrostatic discharge (ESD). The electron-hole recombination efficiency was improved, enabling photocatalytic degradation of Cr(VI). The prepared Fe / Cu / BiOCl composite photocatalyst exhibited a flower-like spherical morphology. The XPS spectrum of the Fe / Cu / BiOCl composite photocatalyst showed binding energies at 159.4 eV, 164.8 eV, 530.6 eV, 531.6 eV, 198.2 eV, 199.8 eV, 710.5 eV, 722.9 eV, and 940.9 eV. Bi... In the 4f spectrum, 159.4 eV and 164.8 eV correspond to Bi 4f7 / 2 and Bi 4f5 / 2, respectively. In the O 1s spectrum, 530.6 eV and 531.6 eV correspond to lattice oxygen and surface adsorbed oxygen, respectively. In the Cl 2p spectrum, 198.2 eV and 199.8 eV are assigned to Cl 2p3 / 2 and Cl 2p1 / 2, respectively. In the Fe 2p spectrum, 710.5 eV and 722.9 eV correspond to Fe 2p3 / 2 and Fe 2p1 / 2, respectively. In the Cu 2p spectrum, 940.9 eV corresponds to Cu 2p3 / 2. The co-doping of Fe / Cu significantly increases the specific surface area of ​​the Fe / Cu / BiOCl composite photocatalyst, which is beneficial for providing more reactive sites.

[0010] The preparation method of the Fe / Cu / BiOCl composite photocatalyst of the present invention includes the following steps: Bi(NO3)3·5H2O, Fe(NO3)3·9H2O and Cu(NO3)2·3H2O are added to an ethylene glycol solution and stirred until a clear and transparent solution is formed; then NaCl is added and stirred until the mixture is homogeneous; the mixture is transferred to a polytetrafluoroethylene-lined reactor and reacted at 150-170℃ for 2-4 hours; after the reaction is completed, the mixture is cooled to room temperature, the precipitate is separated by centrifugation, and the precipitate is washed several times with deionized water and ethanol alternately and then dried to obtain the Fe / Cu / BiOCl composite photocatalyst.

[0011] The application of the Fe / Cu / BiOCl composite photocatalyst described in this invention in photocatalytic reduction reactions.

[0012] The application of the Fe / Cu / BiOCl composite photocatalyst described in this invention in the photocatalytic reduction of Cr(VI).

[0013] The application of the Fe / Cu / BiOCl composite photocatalyst described in this invention in the photocatalytic removal of Cr(VI) from Cr(VI) polluted water.

[0014] Compared with existing technologies, this invention has the following advantages and beneficial effects: By optimizing the doping ratio of Fe and Cu, this invention can effectively control the band structure of BiOCl. Compared with undoped BiOCl and Fe / Cu single-metal ion doped BiOCl, the Fe and Cu co-doped sample exhibits significantly enhanced visible light absorption performance and lower electron-hole recombination efficiency. These characteristics make this composite photocatalytic material show promising application prospects in the photocatalytic reduction of hexavalent chromium. Performance test results show that when Fe... 3+ With Cu 2+ The sample prepared at a molar ratio of 9:1 exhibited the best catalytic activity. After 120 min of illumination, the removal efficiency of Cr(VI) reached 91.3%, significantly higher than the 64.4% of BiOCl alone. Free radical capture results showed that photogenerated electrons (e... - Fe is the main active species in photocatalytic reactions. The increased catalytic activity can be attributed to Fe. 3+ and Cu 2+ The impurity energy levels formed by doping not only effectively narrow the band gap of the composite photocatalytic material and improve its visible light absorption capacity, but also act as electron trapping centers, effectively promoting the separation of photogenerated carriers and thus enhancing the photocatalytic activity of BiOCl photocatalysts. These studies provide important theoretical and technical support for the practical application of Fe / Cu / BiOCl composite photocatalysts in water pollution control. Attached Figure Description

[0015] Figure 1 (a) XRD patterns of BiOCl, Fe / BiOCl, Cu / BiOCl and Fe / Cu / BiOCl, and (b) FT-IR patterns of the sample.

[0016] Figure 2 SEM images of different samples: (a)~(b) BiOCl; (c) Cu / BiOCl; (d) Fe / BiOCl; (e)~(f) Fe / Cu / BiOCl.

[0017] Figure 3 XPS spectra of Fe / Cu / BiOCl: (a) full spectrum; (b) Bi 4f; (c) O 1s; (d) Cl 2p; (e) Fe 2p; (f) Cu 2p.

[0018] Figure 4The N2 adsorption-desorption isotherms and their pore size distribution curves are shown for BiOCl, Fe / BiOCl, Cu / BiOCl and Fe / Cu / BiOCl (the inset shows the pore size distribution).

[0019] Figure 5 The photocatalytic reduction performance of BiOCl, Fe / BiOCl, Cu / BiOCl and Fe / Cu / BiOCl on Cr(VI) is evaluated.

[0020] Figure 6 The effects of photocatalytic reaction conditions: (a) catalyst concentration; (b) initial pollutant concentration; (c) different initial pH values; (d) the effect of coexisting anions.

[0021] Figure 7 (a) Recycling performance of Fe / Cu / BiOCl; (b) Comparison of XRD spectra before and after use; (c) Comparison of SEM images before and after use.

[0022] Figure 8 (a) PL spectrum; (b) electrochemical impedance spectroscopy; (c) photocurrent response curve.

[0023] Figure 9 (a) UV-Vis DRS spectrum; (b) (αhν) calculated based on the Tauc formula. 1 / 2 (c) Mott-Schottky curve of BiOCl; (d) Mott-Schottky curve of Fe / Cu / BiOCl.

[0024] Figure 10 The effect of different trapping agents on the photocatalytic reduction of Cr(VI) by Fe / Cu / BiOCl.

[0025] Figure 11 This is a schematic diagram of the mechanism of photocatalytic reduction of Cr(VI) by Fe / Cu / BiOCl. Detailed Implementation

[0026] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0027] Example

[0028] Preparation of Fe / Cu / BiOCl composite photocatalyst: 2 mmol Bi(NO3)3·5H2O (0.9701 g), 0.09 mmol Fe(NO3)3·9H2O (0.0363 g), and 0.01 mmol Cu(NO3)2·3H2O (0.0024 g) were weighed and dissolved in 60 mL ethylene glycol. After stirring until the solution was clear, 2 mmol NaCl (0.1170 g) was added and stirring was continued for 30 min. The mixed solution was transferred to a 100 mL polytetrafluoroethylene reaction vessel and reacted at 160 °C for 3 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was separated by centrifugation. After washing with deionized water and ethanol alternately, the precipitate was dried under vacuum at 80 °C for 12 h to finally obtain the Fe / Cu / BiOCl material. For comparison, undoped BiOCl, Fe-doped Fe / BiOCl, and Cu-doped Cu / BiOCl samples were prepared under the same conditions.

[0029] The crystal structure and phase composition of the photocatalyst were analyzed by XRD. Figure 1 (a) shows the XRD patterns of BiOCl, Fe / BiOCl, Cu / BiOCl and Fe / Cu / BiOCl. As can be seen from the figure, the characteristic peaks of all materials are consistent with the (001), (101), (110), (102), (200) and (211) crystal planes. They are in perfect agreement with the tetragonal phase of BiOCl (JCPDS No. 06-0249) standard card. No diffraction peaks of other impurities were observed, indicating that the samples have high crystallinity and purity. Figure 1 The FT-IR spectra in (b) show that all samples are within 3340 cm⁻¹. -1 and 1620cm -1 Absorption peaks for OH stretching and bending vibrations are present at 1379 cm⁻¹. -1 and 1052cm -1 Corresponding to the asymmetric and symmetric stretching vibrations of the Bi–Cl bond, 517 cm -1 The result is attributed to the Bi-O bond symmetric stretching vibration, further confirming that Fe / Cu doping did not significantly alter the BiOCl molecular structure.

[0030] SEM characterization ( Figure 2 The results showed that pure BiOCl exhibited a flower-like spherical morphology, and samples doped with Fe and Cu, as well as those co-doped, maintained a similar structure, indicating that doping did not cause significant morphological changes. XPS testing confirmed the presence of five elements in the material: Bi, O, Cl, Fe, and Cu. Figure 3 As shown in (a), the 159.4 eV and 164.8 eV values ​​in the Bi 4f spectrum correspond to Bi 4f7 / 2 and Bi 4f5 / 2, respectively. Figure 3As shown in (b), Bi exists in the +3 valence state. The O 1s spectra at 530.6 eV and 531.6 eV correspond to lattice oxygen and surface adsorbed oxygen, respectively, as shown in Figure 1. Figure 3 As shown in (c), the 198.2 eV and 199.8 eV values ​​in the Cl 2p spectrum are assigned to Cl 2p3 / 2 and Cl 2p1 / 2, respectively. Figure 3 As shown in (d), 710.5 eV and 722.9 eV in the Fe 2p spectrum correspond to Fe 2p3 / 2 and Fe 2p1 / 2, respectively. Figure 3 As shown in (e), it is confirmed that Fe exists in the +3 oxidation state; 940.9 eV in the Cu 2p spectrum corresponds to Cu 2p3 / 2, as shown in (e). Figure 3 As shown in (f), Cu exists in the +2 oxidation state. N2 adsorption-desorption test ( Figure 4 The data showed that all samples exhibited a type IV isotherm, with specific surface areas of, in descending order: BiOCl 9.47 m². 2 / g, Cu / BiOCl 12.07m 2 / g, Fe / BiOCl 13.80m 2 / g, Fe / Cu / BiOCl 17.76m 2 / g. Doping significantly increases the specific surface area, which is beneficial for providing more reactive sites.

[0031] To systematically evaluate the degradation performance of photocatalytic materials and screen for optimized materials, this study investigated the removal performance of BiOCl, Fe / BiOCl, Cu / BiOCl, and Fe / Cu / BiOCl for Cr(VI) under simulated sunlight irradiation, using potassium dichromate as the target pollutant. The experimental conditions were a catalyst dosage of 0.5 g / L and a target pollutant concentration of 10 mg / L. The results showed that... Figure 5 After 120 minutes of illumination, the removal rate of Cr(VI) by undoped BiOCl was only 64.4%. Metal doping significantly improved the catalytic performance: single Cu doping increased the removal rate to 66.7%, single Fe doping to 80.4%, and the Fe / Cu co-doped sample achieved the highest removal rate of 91.3%. This performance improvement is mainly attributed to Fe. 3+ and Cu 2+ The doping effect in the BiOCl lattice: On the one hand, the doping elements introduce impurity energy levels in the band gap, effectively narrowing the band gap of BiOCl, significantly broadening its absorption range for visible light, and improving the light energy utilization rate; on the other hand, an appropriate amount of doped ions, as "electron traps", promote the separation and transfer of photogenerated carriers, providing more active species for the reaction, thereby greatly improving the photocatalytic efficiency.

[0032] Furthermore, the conditions for photocatalytic removal of Cr(VI) by the material were optimized. First, the effect of the initial Cr(VI) concentration on the removal efficiency was investigated. For example... Figure 6 As shown in Figure (a), when the initial Cr(VI) concentrations were 2.5 mg / L and 5 mg / L, the pollutant could be completely reduced within 60 minutes. The removal efficiency decreased accordingly with increasing initial concentration. Based on actual wastewater treatment requirements, this study selected 10 mg / L as the Cr(VI) concentration for subsequent experiments. Secondly, the effect of photocatalyst dosage on Cr(VI) removal efficiency was systematically studied. Figure 6 As shown in (b), Cr(VI) was hardly reduced in the absence of a catalyst. With increasing catalyst dosage, both the adsorption and photocatalytic reduction efficiencies of Cr(VI) gradually improved. However, when the dosage increased to 1.0 g / L, although the adsorption amount increased significantly, the degradation efficiency did not further improve. This is mainly due to two reasons: firstly, the mutual obstruction between excess catalyst particles severely reduced the light energy utilization efficiency; secondly, nanoparticles are prone to aggregation, leading to the coating of active sites, reducing the effective reaction interface, and hindering the contact between reactants and active sites, thereby inhibiting the improvement of catalytic activity. Therefore, an appropriate catalyst dosage is beneficial for providing sufficient adsorption and active sites in the system to achieve higher photocatalytic efficiency.

[0033] To evaluate the stability and reusability of Fe / Cu / BiOCl, four consecutive cyclic degradation experiments were conducted. Figure 7 As shown in Figure (a), Fe / Cu / BiOCl exhibits good stability, maintaining a reduction efficiency of 58% for Cr(VI) after four cycles. The decrease in activity may be related to the adsorption of impurities or product accumulation on the catalyst surface during the reaction, leading to a reduction in active sites. Further structural characterization of the samples before and after cycling was performed using XRD and SEM, with results as shown in Figure (b). Figure 7 (b) and Figure 7 As shown in (c), the XRD pattern of the sample after cycling showed no new diffraction peaks, only a slight decrease in peak intensity, indicating that its crystal structure remained largely intact. SEM images showed no significant change in the microstructure of the material before and after cycling. These results demonstrate that Fe / Cu / BiOCl possesses good structural stability and recyclability, exhibiting potential for practical applications.

[0034] To further explore the mechanism of enhanced photocatalytic performance of Fe / Cu / BiOCl, its photoelectrochemical properties were characterized by photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), and photocurrent measurement. Figure 8 As shown in (a), the PL emission intensity of Fe / Cu / BiOCl is significantly reduced compared to pure BiOCl, indicating that Fe... 3+ Cu2+ Co-doping effectively suppressed photogenerated carrier recombination. EIS results showed that the Nyquist radius of Fe / Cu / BiOCl was smaller than that of the undoped sample, indicating a decrease in charge transfer resistance and an increase in carrier migration efficiency. Figure 8 As shown in (b), photocurrent response testing further confirmed that the photocurrent density of Fe / Cu / BiOCl was significantly higher than that of pure BiOCl, as shown in (b). Figure 8 As shown in (c). The above results indicate that Fe 3+ and Cu 2+ Doping can effectively promote the separation and transport of photogenerated carriers, thereby improving the photocatalytic performance of the material.

[0035] Ultraviolet-visible diffuse reflectance spectroscopy was used to test BiOCl, Fe / BiOCl, Cu / BiOCl, and Fe / Cu / BiOCl to determine their optical absorption properties and band gap structure. Figure 9 As shown in (a), the absorption edge of pure BiOCl is located at 372 nm, while the visible light absorption range of the doped sample is significantly broadened. Analysis of UV-vis DRS data based on the Tauc equation is shown below. Figure 9 As shown in (b), the calculated band gap of BiOCl is 3.16 eV, while the band gap of Fe / Cu / BiOCl decreases to 1.93 eV. This indicates that Fe and Cu co-doping effectively reduces the band gap of the material and significantly enhances its absorption capacity in the visible light region.

[0036] To further elucidate the band structure characteristics of BiOCl, Mott-Schottky tests were performed. Figure 9 As shown in (c), the flat-band potential (E) of BiOCl is... fb The conduction band potential is -0.31V (vs. Ag / AgCl). Based on the characteristics of n-type semiconductors, its conduction band potential (E...) is... CB Typically, it is about 0.2V negatively shifted from the flat-band potential. Therefore, the E of BiOCl is... CB The voltage is -0.51V (vs. Ag / AgCl). This is determined using the standard hydrogen electrode conversion formula: in The value is 0.197V (pH = 7.0, vs. Ag / AgCl). The calculated E of BiOCl is... CB It is 0.1 eV. Then, according to the equation: E VB =E CB +E g The valence band potential (E) of BiOCl can be calculated. VB The value is 3.26 eV. Similarly, the E value for Fe / Cu / BiOCl can be calculated. CB It is 0.1 eV, E VB It is 2.03 eV.

[0037] Free radical capture experiments were conducted on the Fe / Cu / BiOCl photocatalytic process. Potassium iodide (KI) was added to the reaction system to capture h. + Isopropanol (IPA, capture ·OH), p-benzoquinone (BQ, capture ·O2) - ) and potassium persulfate (K2S2O8, which captures e) - The study aimed to examine the contribution of each species to Cr(VI) reduction. The results are as follows: Figure 10 As shown, the addition of IPA had the least effect on the reduction efficiency of Cr(VI), while BQ and KI had more significant effects. The reduction process was significantly inhibited after the addition of K₂S₂O₈. This indicates that in the photocatalytic reduction of Cr(VI) by Fe / Cu / BiOCl, photogenerated electrons (e) play a crucial role. - ) is the dominant active species.

[0038] Based on the above experimental results and characterization analysis, the mechanism of Fe / Cu / BiOCl photocatalytic reduction of Cr(VI) is proposed, such as... Figure 11 As shown. Fe 3+ and Cu 2+ Doping in the BiOCl lattice introduces impurity energy levels, narrowing the band gap. Under illumination, electrons in the BiOCl valence band (VB) are excited to the impurity energy levels and further transition to the conduction band (CB). The impurity energy levels formed by Fe and Cu doping act as "bridges" in the electron transition process, not only promoting electron transfer but also broadening the material's response range to visible light. Ultimately, electrons in the conduction band (e... - The photogenerated electrons undergo a reduction reaction with Cr(VI) to convert it into Cr(III). This mechanism is consistent with the results of free radical capture experiments, further confirming that photogenerated electrons are the main active species in the reduction process.

[0039] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A method for preparing a Fe / Cu / BiOCl composite photocatalyst, characterized in that: A Fe / Cu / BiOCl composite photocatalyst was prepared by hydrothermal method at 150–170 °C using Bi(NO3)3·5H2O, Fe(NO3)3·9H2O, and Cu(NO3)2·3H2O as raw materials. By optimizing the Fe / Cu ion doping ratio to 9:1, the band structure of BiOCl could be effectively controlled, exhibiting significantly enhanced visible light absorption performance and lower electron-hole recombination efficiency, enabling photocatalytic degradation of Cr(VI). The prepared Fe / Cu / BiOCl composite photocatalyst exhibited a flower-like spherical morphology. The XPS spectrum of the Fe / Cu / BiOCl composite photocatalyst showed binding energies at 159.4 eV, 164.8 eV, 530.6 eV, 531.6 eV, 198.2 eV, 199.8 eV, 710.5 eV, 722.9 eV, and 940.9 eV. In the 4f spectrum, 159.4 eV and 164.8 eV correspond to Bi 4f7 / 2 and Bi 4f5 / 2, respectively. In the O 1s spectrum, 530.6 eV and 531.6 eV correspond to lattice oxygen and surface adsorbed oxygen, respectively. In the Cl 2p spectrum, 198.2 eV and 199.8 eV are assigned to Cl 2p3 / 2 and Cl 2p1 / 2, respectively. In the Fe 2p spectrum, 710.5 eV and 722.9 eV correspond to Fe 2p3 / 2 and Fe 2p1 / 2, respectively. In the Cu 2p spectrum, 940.9 eV corresponds to Cu 2p3 / 2. The co-doping of Fe / Cu significantly increases the specific surface area of ​​the Fe / Cu / BiOCl composite photocatalyst, which is beneficial for providing more reactive sites.

2. The preparation method of the Fe / Cu / BiOCl composite photocatalyst according to claim 1, characterized in that... The specific preparation steps are as follows: Bi(NO3)3·5H2O, Fe(NO3)3·9H2O and Cu(NO3)2·3H2O are added to an ethylene glycol solution and stirred until a clear and transparent solution is formed; then NaCl is added and stirred until the mixture is homogeneous. The mixture is then transferred to a polytetrafluoroethylene-lined reactor and reacted at 150-170℃ for 2-4 hours. After the reaction is completed, the mixture is cooled to room temperature, centrifuged to separate the precipitate, and washed several times with deionized water and ethanol alternately before drying to obtain the Fe / Cu / BiOCl composite photocatalyst.

3. The application of the Fe / Cu / BiOCl composite photocatalyst prepared according to claim 1 or 2 in photocatalytic reduction reactions.

4. The application of the Fe / Cu / BiOCl composite photocatalyst prepared according to claim 1 or 2 in the photocatalytic reduction of Cr(VI).

5. The application of the Fe / Cu / BiOCl composite photocatalyst prepared according to claim 1 or 2 in the photocatalytic removal of Cr(VI) from Cr(VI) polluted water.

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