Method for constructing composite material MIL-101 (Fe) / KBiO3 by solvothermal in-situ doping method and application of composite material MIL-101 (Fe) / KBiO3

Abstract

The invention provides a method for constructing a composite material MIL-101 (Fe) / KBiO3 by a solvothermal in-situ doping method, which comprises the following steps: adding FeCl3. 6H2O into N, N-dimethylformamide to obtain a liquid A; terephthalic acid and KBiO3 are added into N, N-dimethylformamide, and liquid B is obtained; and carrying out ultrasonic dispersion on the liquid A and the liquid B, carrying out heat treatment washing with a solvent at 110 DEG C, and drying to obtain the composite material MIL-101 (Fe) / KBiO3. The invention also provides application of the composite material MIL-101 (Fe) / KBiO3, and the composite material MIL-101 (Fe) / KBiO3 is used for photocatalytic degradation of Cr (VI). The composite material KBiO3 / MIL-101 (Fe) is prepared by adopting a solvothermal in-situ doping method, and the photocatalytic performance of the MIL-101 (Fe) on Cr (VI) is remarkably improved. The prepared composite material MIL-101 (Fe) / KBiO3 has a remarkable improvement effect in the field of degradation of heavy metal Cr (VI, and a new material choice is provided for heavy metal pollution treatment.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic degradation technology, specifically relating to a method and application of constructing composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping. Background Technology

[0002] Traditional methods for treating chromium-containing wastewater include physical adsorption, chemical flocculation and oxidation, and biodegradation, but these methods have limitations. Physical adsorption is simple to operate and inexpensive, but adsorbent regeneration is difficult and can easily generate secondary pollution; chemical oxidation is fast, but reagent costs are high and it may produce harmful intermediate products; biodegradation is environmentally friendly, but its efficiency is low and its ability to degrade complex dyes is limited. In contrast, photocatalysis technology has become a research hotspot in wastewater treatment due to its advantages such as being green, efficient, and having mild reaction conditions. Developing a novel material that simultaneously possesses high adsorption capacity and rapid photocatalytic reduction performance is crucial for improving wastewater treatment efficiency. This study designed and prepared a composite photocatalytic material. By optimizing the charge transport path through a heterojunction structure, the synergistic effect of chromium ion adsorption and photocatalytic reduction is enhanced, thereby achieving efficient purification of chromium-containing wastewater. Summary of the Invention

[0003] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method and application for constructing the composite material MIL-101(Fe) / KBiO3 using a solvothermal in-situ doping method. This method prepares the composite material KBiO3 / MIL-101(Fe) using a solvothermal in-situ doping method, significantly improving the photocatalytic performance of MIL-101(Fe) for Cr(VI). This composite material exhibits a significant improvement in the degradation of the heavy metal Cr(VI), providing a new material option for the remediation of heavy metal pollution.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping, the method being as follows: S1. Add FeCl3·6H2O to N,N-dimethylformamide and stir magnetically until homogeneous to obtain liquid A; S2. After mixing and grinding NaBiO3·2H2O and KOH, the temperature was raised to 224℃, kept at a constant temperature, and then naturally cooled to room temperature. The mixture was washed with deionized water until the pH value of the system was 7. After vacuum filtration and drying, KBiO3 was obtained. S3. Add terephthalic acid and the KBiO3 obtained in S2 to N,N-dimethylformamide, stir magnetically until homogeneous, and obtain liquid B; S4. After mixing and ultrasonically dispersing the liquid A obtained in S1 and the liquid B obtained in S3, the mixture is subjected to solvothermal treatment at a temperature of 110℃. Then, the product after the reaction is washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and dried to obtain the composite material MIL-101(Fe) / KBiO3.

[0005] Under visible light irradiation, both KBiO3 and MIL-101(Fe) are simultaneously excited, generating photogenerated electrons (e electrons). - ) and holes (h + Under the drive of the built-in electric field, electrons with weak reducing power in the conduction band of MIL-101(Fe) recombine with holes with weak oxidizing power in the valence band of KBiO3 through the interface. This pathway allows for the effective spatial separation and retention of electrons with strong reducing power in the conduction band of KBiO3 and holes with strong oxidizing power in the valence band of MIL-101(Fe). The MIL-101(Fe) / KBiO3 direct Z-type heterojunction constructed in this invention, through a unique interfacial charge transfer path, efficiently separates photogenerated carriers while retaining the strong reducing electrons of KBiO3 and the strong oxidizing holes of MIL-101(Fe). On the one hand, the porous structure of MIL-101(Fe) is used to rapidly enrich Cr(VI); on the other hand, the adsorbed Cr(VI) is efficiently and completely reduced to the low-toxicity Cr(III) by means of the in-situ constructed strong reducing interface. For a Cr(VI) solution with an initial concentration of 30 mg / L, under the condition of a dosage of 0.15 g / L, MIL-101(Fe) / KBiO3 achieved a 100% removal rate of Cr(VI) within 60 minutes under visible light, and exhibited good cycle stability.

[0006] Preferably, the ratio of FeCl3·6H2O to N,N-dimethylformamide in S1 is 0.96 g: 30 mL.

[0007] Preferably, the molar ratio of NaBiO3·2H2O and KOH in S2 is 1:2; the heating rate in S2 is 5℃ / min; the holding time in S2 is 2h; and the drying temperature in S2 is 60℃.

[0008] Preferably, the ratio of terephthalic acid, KBiO3 and N,N-dimethylformamide in S3 is 0.3g:0.27g:30mL.

[0009] Preferably, the magnetic stirring conditions in S1 are: 500 rpm for 30 min; the magnetic stirring conditions in S3 are: 500 rpm for 15 min; and the ultrasonic dispersion conditions in S4 are: 400 W for 20 min.

[0010] Preferably, the solvent heat treatment time in S4 is 20h; the drying conditions in S4 are: 60℃, 20h.

[0011] Preferably, the mass fraction of KBiO3 in the composite material MIL-101(Fe) / KBiO3 in S4 is 20% to 50%.

[0012] Preferably, the mass fraction of KBiO3 in the composite material MIL-101(Fe) / KBiO3 is 30%.

[0013] The present invention also provides the application of the composite material MIL-101(Fe) / KBiO3 constructed by the above method, wherein the composite material MIL-101(Fe) / KBiO3 is used for photocatalytic degradation of Cr(VI).

[0014] Compared with the prior art, the present invention has the following advantages: This invention employs a solvothermal in-situ doping method to prepare the composite material KBiO3 / MIL-101(Fe), which significantly enhances the photocatalytic performance of MIL-101(Fe) for Cr(VI). The KBiO3 / MIL-101(Fe) composite material prepared in this invention exhibits a significant improvement in the degradation of the heavy metal Cr(VI), providing a new material option for the remediation of heavy metal pollution.

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 These are SEM images of MIL-101(Fe) / KBiO3 with different doping ratios of KBiO3 in Example 1 of this invention. (a) is a scanning electron microscope image of KBiO3, (b) is a scanning electron microscope image of MIL-101(Fe), and (cf) is a scanning electron microscope image of MIL / KBO-X% (X=20, 30, 40, 50).

[0017] Figure 2 These are the EDS elemental scan (a) and elemental spectrum (b) of MIL / KBO-30% in Embodiment 1 of the present invention.

[0018] Figure 3 These are the low-resolution transmission electron microscope (a) and high-resolution transmission electron microscope (b) images of MIL / KBO-30% in Example 1 of this invention.

[0019] Figure 4 These are the X-ray diffraction patterns of KBiO3, MIL-101(Fe), and MIL / KBO-X% (X=20, 30, 40, 50) in Example 1 of this invention.

[0020] Figure 5 These are the infrared FT-IR spectra of KBiO3, MIL-101(Fe), and MIL / KBO-30% in Example 1 of this invention.

[0021] Figure 6 This is the overall spectrum of the X-ray photoelectron spectroscopy (XPS) of KBiO3, MIL-101(Fe), and MIL / KBO-30% in Example 1 of this invention.

[0022] Figure 7 This is the Bi4f spectrum of the X-ray photoelectron spectroscopy (XPS) of KBiO3, MIL / KBO-30% in Example 1 of this invention.

[0023] Figure 8 This is the Fe 2p spectrum of the X-ray photoelectron spectroscopy (XPS) of MIL-101(Fe) and MIL / KBO-30% in Example 1 of this invention.

[0024] Figure 9 This is the C 1s spectrum of the X-ray photoelectron spectroscopy (XPS) of MIL-101(Fe) and MIL / KBO-30% in Example 1 of this invention.

[0025] Figure 10 This is the O 1s spectrum of the X-ray photoelectron spectroscopy (XPS) of KBiO3, MIL-101(Fe), and MIL / KBO-30% in Example 1 of this invention.

[0026] Figure 11 The UV-Vis diffuse reflectance spectra (a) of KBiO3, MIL-101(Fe), and MIL / KBO-X% (X=20, 30, 40, 50) in Example 1 of this invention and the band gaps (b) of KBiO3 and MIL-101(Fe) are shown.

[0027] Figure 12 This is the standard curve of Cr(VI) in Embodiment 1 of the present invention.

[0028] Figure 13 This is a graph showing the photocatalytic degradation performance of Cr(VI) by KBiO3, MIL-101(Fe), and MIL / KBO-X% (X=20, 30, 40, 50) in Example 1 of this invention. (a) shows the pH curve of Cr(VI) photocatalytic degradation, (b) shows the curve of Cr(VI) photocatalytic degradation, (c) shows the degradation rate of Cr(VI) photocatalytic degradation, (d) shows the kinetic curve of Cr(VI) photocatalytic degradation, (e) shows the apparent rate constant of Cr(VI) photocatalytic degradation, (f) shows the cycle experiment graph of Cr(VI) photocatalytic degradation, and (g) shows the XRD pattern after four cycles of Cr(VI) photocatalytic degradation.

[0029] Figure 14 The effects of different capture agents on the photocatalytic degradation of Cr(VI) by MIL / KBO-30% in Example 1 of this invention (a), ·O2 - EPR spectrum of ·OH (b) and EPR spectrum of ·OH (c).

[0030] Figure 15 This is a schematic diagram of the mechanism of Cr(VI) degradation by the Z-type heterojunction of the MIL / KBO-30% composite material in Example 1 of the present invention.

[0031] Figure 16 These are the photoelectrochemical performance characterization diagrams of KBiO3, MIL-101(Fe), and MIL / KBO-30% in Example 1 of this invention. (a) Transient photocurrent response spectrum, (b) Electrochemical impedance spectroscopy (EIS), (c) Photoluminescence spectrum, (d) XPS-VB diagram of MIL-101(Fe), and (e) XPS-VB diagram of KBiO3. Detailed Implementation

[0032] Example 1 The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping in this embodiment is as follows: S1. Add FeCl3·6H2O to N,N-dimethylformamide and stir magnetically for 30 minutes at 500 rpm until homogeneous to obtain liquid A; the ratio of FeCl3·6H2O to N,N-dimethylformamide is 0.96 g: 30 mL. S2. Mix and grind 3.16 g (0.01 mol) NaBiO3·2H2O and 1.12 g (0.02 mol) KOH, then heat the mixture from room temperature to 224℃ at a heating rate of 5℃ / min, keep it at this temperature for 2 hours, cool it naturally to room temperature, let it cool completely overnight, wash it with deionized water until the pH of the system is 7, filter it under vacuum pump, and dry it at 60℃ for 12 hours to obtain brick-red KBiO3. S3. Add terephthalic acid and the KBiO3 obtained in S2 to N,N-dimethylformamide, and stir magnetically for 15 minutes at a speed of 500 rpm until homogeneous to obtain liquid B; the ratio of terephthalic acid, KBiO3 and N,N-dimethylformamide is 0.3 g: 0.27 g: 30 mL. S4. Liquid A obtained in S1 and liquid B obtained in S3 are mixed and ultrasonically dispersed for 20 min under a power of 400 W. Then, the mixture is subjected to solvothermal treatment at a temperature of 110 °C for 20 h. The product after reaction is washed sequentially with N,N-dimethylformamide and anhydrous ethanol and dried at a temperature of 60 °C for 20 h to obtain the composite material MIL-101(Fe) / KBiO3. The mass ratio of KBiO3 to MIL-101(Fe) in the composite material MIL-101(Fe) / KBiO3, i.e., the doping ratio of KBiO3, is 30%, denoted as MIL / KBO-30%.

[0033] Under high temperature and high pressure solvothermal conditions, KBiO3 particles directly participate in the crystallization and growth process of MIL-101(Fe). This ensures that KBiO3 is uniformly and firmly anchored in the MOF framework, forming an atomically compact heterogeneous interface. This highly integrated interface maximizes electronic coupling and directional transport between the two materials, thereby constructing an efficient and stable direct Z-type charge transfer channel.

[0034] The constructed MIL-101(Fe) / KBiO3 direct Z-type heterojunction, through a unique interfacial charge transfer path, efficiently separates photogenerated carriers while retaining the strong reducing electrons of KBiO3 and the strong oxidation holes of MIL-101(Fe). The unique carrier transport path of the Z-type heterojunction not only enhances the redox capability but also strengthens the interfacial charge separation efficiency through a built-in electric field.

[0035] In addition, this embodiment also prepared MIL-101(Fe) / KBiO3 composite materials with different doping ratios of KBiO3 for performance testing, namely MIL / KBO-X% (X=20,30,40,50), where X=30 is the MIL / KBO-30 prepared in this embodiment.

[0036] This embodiment also prepared MIL-101(Fe) using a solvothermal method. 0.96 g of FeCl3·6H2O was added to 30 mL of N,N-dimethylformamide solution and stirred magnetically for 30 min. Similarly, 0.3 g of terephthalic acid was added to a fresh 30 mL N,N-dimethylformamide solution and stirred magnetically for 30 min. This ensured that FeCl3·6H2O and terephthalic acid were fully dissolved in the N,N-dimethylformamide solution. The mixture was then sonicated for 15 min, poured into an autoclave, and subjected to solvothermal treatment at 110 °C for 20 h. Finally, the sample was thoroughly washed with DMF and anhydrous ethanol, centrifuged, and dried in a vacuum oven at 60 °C for 20 h. The final result was an octahedral MIL-101(Fe) sample.

[0037] (I) Structural characterization of MIL-101(Fe) / KBiO3 1) SEM morphological characterization: Figure 1 SEM images of MIL-101(Fe) / KBiO3 composites with different doping ratios of KBiO3. Figure 1 (a) It can be seen that KBiO3 has an irregular blocky morphology with a diameter of about 2 μm. Figure 1 (b) MIL-101(Fe) has a complete, smooth, and flat octahedral morphology with a diameter of approximately 500 nm. This is consistent with the description in the literature, indicating that the ideal MIL-101(Fe) was successfully prepared. Figure 1 (cf) shows the morphology of MIL / KBO at different doping ratios (X=20, 30, 40, 50). It can be seen that the catalyst morphology changed significantly after the formation of the composite material. When the doping ratio was 20%, a small amount of KBiO3 particles were loaded onto a smooth, flat octahedral morphology. When the doping ratio was 30%, the octahedral morphology changed to a spindle-shaped structure with KBiO3 particles loaded on the surface. The spindle-shaped structure increased the contact area between the surface and the KBiO3 active sites. With the increase of the doping ratio, the density of KBiO3 particles loaded on the spindle-shaped structure gradually increased, and the interaction between KBiO3 and MIL-101(Fe) was enhanced, resulting in a more compact packing of particles on the spindle-shaped structure, further masking the surface of MIL-101(Fe). Figure 1 (f). Therefore, electron microscopy reveals that MIL-101(Fe) and KBiO3 form a tight interface, providing a theoretical basis for the formation of heterojunctions.

[0038] 2) EDS elemental scanning Electron microscopy revealed that MIL / KBO-30% consists of KBiO3 particles loaded onto the spindle-shaped structure of MIL-101(Fe). Figure 2 (a) is the elemental distribution diagram of MIL / KBO-30%. It can be seen that the synthesized MIL / KBO-30% is mainly composed of four elements: C, Fe, Bi, and O, and their distribution is uniform on the surface. Bi and O are provided by KBiO3, and the distribution ranges of Bi and O elements are consistent in the diagram. C and Fe are mainly provided by MIL-101(Fe), and the distribution ranges of C and Fe elements are consistent in the diagram. Comparing the distribution ranges of Fe and Bi elements, Fe is more concentrated within the spindle-shaped structure of MIL-101(Fe), while Bi is more uniformly distributed around the spindle-shaped structure of MIL-101(Fe). This further verifies the spatial positions of Bi and Fe elements loaded on the spindle-shaped structure, which is consistent with the surface of the electron micrograph. Furthermore, in... Figure 2 (b) As shown in the elemental spectrum, this preparation method can make the elemental distribution of MIL-101(Fe) and KBiO3 uniform.

[0039] 3) TEM analysis Figure 3 (a) is a low-resolution transmission electron microscope image of MIL / KBO-30%. It can be observed that the KBiO3 particles are anchored to the spindle shape of MIL-101(Fe) in the composite material. Figure 3 (b) is a high-resolution transmission electron microscope (TEM) image of MIL / KBO-30%. The fringe spacings of 0.316 nm, 0.196 nm, and 0.267 nm correspond to the (310), (510), and (321) crystal planes of KBiO3. The fringe spacings of 0.192 nm and 0.351 nm correspond to the (119) and (112) planes of MIL-101(Fe), respectively. This indicates that MIL-101(Fe) and KBiO3 have a tightly connected layered structure, forming a good heterojunction.

[0040] 4) X-ray diffraction analysis Figure 4X-ray diffraction patterns of KBiO3, MIL-101(Fe), and MIL / KBO-X% (X=20, 30, 40, 50) composite materials are shown. The characteristic diffraction peaks of MIL-101(Fe) are similar to its simulated X-ray diffraction pattern (CCDC card number 605510), consistent with relevant literature reports. Characteristic diffraction peaks of pure potassium bismuthate are observed at diffraction angles 2θ of 12.5°, 17.7°, 28.2°, 33.5°, and 46.3°. These peaks are strong and sharp, corresponding to the (110), (200), (310), (321), and (510) crystal planes, respectively. The characteristic diffraction peaks of the sample completely correspond to the standard card PDF:00-047-0879 for KBiO3, and no other diffraction peaks are observed, indicating that the KBiO3 generated at this time has excellent crystallinity. After loading KBiO3 onto MIL-101(Fe), the constructed MIL / KBO-X% (X=20, 30, 40, 50) composites exhibited the typical peaks of MIL-101(Fe). The intensity of the typical peak of MIL-101(Fe) gradually decreased with increasing doping ratio, possibly because the incorporation of more KBiO3 particles hindered the synthesis of MIL-101(Fe). The composite material MIL / KBO-30% effectively demonstrated the characteristic peaks of both MIL-101(Fe) and KBiO3.

[0041] 5) Infrared FT-IR spectroscopy like Figure 5 The infrared FT-IR spectra of KBiO3, MIL-101(Fe), and MIL / KBO-30% are shown. (At 546 cm⁻¹) -1 The spectral peak of KBiO3 observed at 547.78 cm⁻¹ is due to the absorption peak caused by the stretching mode vibration of the Bi-O bond. This peak was also observed in MIL-101(Fe). -1 The vibrational peak corresponding to the Fe-O bond originates from the coordination of the metal node (Fe3O cluster) with the carboxyl oxygen. 748.38 cm⁻¹ -1 The vibrational peak corresponding to the CH bond likely originates from the out-of-plane bending vibration of the benzene ring in terephthalic acid. (1396 cm⁻¹) -1 and 1595 cm -1 These correspond to the coordinating carboxyl groups (-COO) - Asymmetric and symmetric stretching vibrations, 1655cm -1 This corresponds to the C=O stretching vibration of the uncoordinated carboxyl group (-COOH). All characteristic peaks of KBiO3 and MIL-101(Fe) were identified in MIL / KBO-30%. We found that the CH bond in MIL-101(Fe) starts from 748.38 cm⁻¹. -1 It was moved to 799 cm -1The carboxyl group (-COO) of MIL-101(Fe) - The asymmetric and symmetric stretching vibrations of 1396 cm -1 and 1595 cm -1 Moved to 1392 cm -1 and 1618 cm -1 The MIL-101(Fe) corresponds to the C=O stretching vibration of the uncoordinated carboxyl group (-COOH). From 1655 cm⁻¹ -1 Transferred to 1618cm -1 This indicates the existence of heterojunction interfacial interactions between MIL-101(Fe) and KBiO3. This also marks the successful synthesis of the MIL / KBO-X% composite material.

[0042] 6) XPS Surface Elemental Composition and Chemical State Analysis XPS analysis was performed on KBiO3, MIL-101(Fe), and MIL / KBO-30% to further obtain elemental information and analyze the chemical state of the surface. Figure 6 The full spectrum analysis confirmed the presence of K, Bi, and O elements in KBiO3, and Fe, O, and C elements in MIL-101(Fe). This is consistent with previous literature reports. The XPS of the MIL / KBO-30% composite material contains both KBiO3 and MIL-101(Fe), thus laying a theoretical foundation for constructing a heterostructure using the MIL / KBO-30% composite material. Figure 7 High-resolution HR-XPS spectra of Bi4f for KBiO3 and MIL / KBO-30% are shown, with peaks at binding energies of 163.9 eV and 158.6 eV corresponding to Bi4f, respectively. 5+ Bi4f 5 / 2 and Bi 4f 7 / 2 This is consistent with previous literature reports. Figure 10 The O1s core energy spectrum of KBiO3 was shown, where the binding energy of 529.88 eV corresponds to lattice oxygen (Bi-O), and the deconvolution peak with a binding energy of 532 eV usually corresponds to chemisorbed oxygen (OH-), which is consistent with previous literature reports. Figure 8 The Fe2p spectrum of MIL-101(Fe) shows that Fe... 3+ The hallmark signals of the ions are Fe2p. 3 / 2 (711.6 eV), Fe2p 1 / 2The C 1s core spectrum of MIL-101(Fe) shows a binding energy of 725.2 eV and satellite peaks (717.8 eV and 731.4 eV). The binding energy of 284.7 eV primarily originates from the benzene ring carbon (CC) in the terephthalic acid ligand, indicating the integrity of the carbon skeleton in the organic ligand. The binding energy of 288.5 eV originates from the carboxyl carbon (C=O) in the terephthalic acid ligand, representing the coordination bond between the organic ligand and the metal cluster (Fe-O cluster). The O 1s core spectrum of MIL-101(Fe) shows a binding energy of 531.5 eV, representing the terephthalic acid ester linker oxygen. Figure 7 Bi 4f spectral region of MIL / KBO-30% composite material is shown 5+ Bi4f 5 / 2 and Bi4f 7 / 2 The binding energy shifts positively, while the Fe2p spectrum shows Fe... 3+ Fe2p 3 / 2 and Fe2p 1 / 2 The satellite peak binding energy is negatively shifted, while that of Bi4f indicates a greater positive shift in the binding energy. Doping with KBiO3 strengthens the interfacial interactions of the composite material and enhances interfacial electron exchange. Figure 9 The C 1s spectral region of the MIL / KBO-30% composite material shows a lower C=O binding energy compared to the MIL-101(Fe) C 1s spectral region. This may be due to the transfer of carboxyl carbon electrons from the terephthalic acid ligand in aromatic compounds, indicating that charge transfer occurs at the heterojunction interface of the MIL / KBO-30% composite material, shifting from the valence band of KBiO3 to the conduction band of MIL-101(Fe). Figure 10 In the O 1s spectral region of MIL / KBO-30%, lattice oxygen (Bi-O) and defect oxygen (OH-) belonging to KBiO3, and terephthalic acid ester joint oxygen belonging to MIL-101(Fe) were observed. The lattice oxygen (Bi-O) and defect oxygen (OH-) belonging to KBiO3, and the terephthalic acid ester joint oxygen belonging to MIL-101(Fe) all shift towards directions with higher binding energies, indicating the formation of new chemical bonds at the interface, which is consistent with the conclusions of infrared analysis. This further demonstrates that the composite material improves the material's electrical conductivity and ion transport properties.

[0043] (II) Photocatalytic performance of MIL-101(Fe) / KBiO3 like Figure 11(a) Solid-state UV-Vis diffuse reflectance spectroscopy was used to investigate the light absorption capabilities of MIL-101(Fe) and MIL / KBO-X% (X=20, 30, 40, 50) composites. The results show that absorption edges of KBiO3 and MIL-101(Fe) were observed near 700 nm and 640 nm. With the introduction of KBiO3 to a proportion of 30% (MIL / KBO), the absorption edge of the MIL-101(Fe) composite exhibited a red shift. Conversely, with further increases in the KBiO3 content, the absorption edge of the MIL-101(Fe) composite exhibited a blue shift. The maximum absorption edge of the composite reached 750 nm with 30 wt% (MIL / KBO). (αhv) is based on the UV-Vis DRS results of the samples. 2 The relationship with hv is as follows Figure 11 As shown in (b), the estimated band gap values ​​of KBiO3 and MIL-101(Fe) are 1.74 eV and 2.18 eV, respectively. The results indicate that both the pure sample and the composite catalyst possess visible light photocatalytic activity. After the combination of KBiO3 and MIL-101(Fe), a certain degree of red shift occurs with increasing KBiO3 content, and the band gap width also narrows accordingly. This is one of the reasons why the catalyst exhibits significant photocatalytic activity.

[0044] (III) Photocatalytic degradation performance of MIL-101(Fe) / KBiO3 composite material for Cr(VI) 1) Plotting the standard curve The photocatalytic activity of the obtained composite material was evaluated by the photocatalytic reduction of Cr(VI) under visible light. For example... Figure 12 A standard curve for Cr(VI) was prepared. Potassium dichromate was added to a volumetric flask and deionized water to prepare a 300 mg / L standard stock solution. A series of solutions with varying concentrations were prepared from the standard stock solution. The Abs values ​​of Cr(VI) were measured using a UV-Vis spectrophotometer to plot the standard curve. The maximum absorption wavelength λmax of Cr(VI) was 350 nm. The results are shown below. Figure 12 The standard curve shown is: A = 0.01068X - 0.00841, R 2 =0.9995. The goodness of fit of the standard curve for this solution exceeds 0.999, indicating a strong linear relationship.

[0045] 2) The photocatalytic performance of the composite material MIL-101(Fe) / KBiO3 was evaluated by adsorption-coupled photodegradation of Cr(VI) under visible light, demonstrating that the composite material exhibits superior performance in reducing Cr(VI) compared to either KBiO3 or MIL-101(Fe) alone. 3 mg of photocatalyst MIL / KBO-X% (X=20, 30, 40, 50), KBiO3, and MIL-101(Fe) were added to 20 mL of potassium dichromate solution (CO=30 mg / L). While stirring in the dark, 3.0 mL of the suspension was collected every 5 min in a 5 mL centrifuge tube, centrifuged at 11000 r / min for 10 min, and the supernatant was collected. After reaching dark adsorption-desorption equilibrium, the photoreaction was initiated under light irradiation. A 500 W xenon lamp equipped with a filter (λ > 420 nm) was used as the light source. The pH was adjusted to 3. Every 30 minutes, 3.0 mL of the suspension was taken out and placed into a 5 mL centrifuge tube to obtain the supernatant.

[0046] The performance of photocatalytic Cr(VI) degradation at different time points was analyzed, and the obtained experimental data provided an experimental basis for establishing photocatalytic kinetics. The degradation rate (η) of photocatalytic Cr(VI) was calculated using formula (1).

[0047] Where C0 is the initial concentration of the pollutant, and C is the residual concentration of the pollutant at time t.

[0048] The photocatalytic performance of KBiO3, MIL-101(Fe), and MIL / KBO-30% was investigated by degrading hexavalent Cr(VI). Photocatalytic experiments were conducted under the conditions of Cr(VI) concentration of 30 mg / L, solution volume of 20 mL, dosage of 0.15 g / L, and pH=3. Figure 13 From (a~b), it can be seen that after 40 min of dark adsorption, the adsorption rates of KBiO3, MIL-101(Fe), and MIL / KBO-30% were 8.8%, 4.14%, and 32.9%, respectively. Figure 13 (c) After 60 min of illumination, the degradation rates of KBiO3, MIL-101(Fe), and MIL / KBO-30% were 77%, 82%, and 100%, respectively. The blank sample maintained stable solution concentrations under the same dark and light conditions. Figure 13 (d) shows the first-order kinetic curves of photocatalytic degradation of Cr(VI), and the R values ​​for KBiO3, MIL-101(Fe), and MIL / KBO-30%. 2 The values ​​of 0.940, 0.987, and 0.990, respectively, indicate that the photocatalytic degradation of Cr(VI) follows a first-order kinetic curve. Figure 13(e) Reflects its apparent rate constant (K) app The concentrations of KBiO3, MIL-101(Fe), and MIL / KBO-30% were 0.036 min. -1 0.037 min -1 0.041 min -1 The apparent rate constants of MIL / KBO-30% were significantly improved compared to both MIL-101(Fe) and KBiO3. Therefore, the successful preparation of this composite material significantly enhanced the photocatalytic degradation performance of Cr(VI) by MIL-101(Fe). Figure 13 (f) After four cycles of experimentation, MIL / KBO-30% still achieved a 100% degradation rate of Cr(VI) after 60 minutes of illumination, demonstrating excellent photocatalytic activity. Figure 13 (g) shows the XRD pattern after four cycles of photocatalytic degradation of Cr(VI) by MIL / KBO-30% . The main characteristic peaks of the XRD pattern remain consistent, indicating that the structure of the MIL / KBO-30% composite material remains stable after four cycles. This demonstrates that the construction of the heterojunction not only enhances the photocatalytic performance of MIL / KBO-30% , but also improves its stability energy.

[0049] (iv) Free radical analysis To investigate the mechanism of photocatalytic degradation, a free radical capture experiment was employed. In this experiment, methanol, p-benzoquinone (BQ), isopropanol (IPA), and silver nitrate (AgNO3) were used as holes (h0, h ... + ), superoxide radicals (·O2) - ), hydroxyl radicals (·OH) and electrons (e - To determine the active species in the MIL / KBO-X% (X=20, 30, 40, 50) photocatalytic process, a sample aqueous solution with a concentration of 1 mg / mL was prepared and ultrasonically dispersed. 100 μL of this solution was then added to 100 μL of a 100 mM DMPO solution, mixed thoroughly, and sealed using a capillary tube. Electron spin resonance (ESR) testing was performed, and the sample was then placed in the sample tube and tested in the instrument to collect data, obtaining the amount of hydroxyl radicals (·OH) generated during the photocatalytic process. Similarly, data were collected to obtain the amount of superoxide radicals (·O2) generated during the photocatalytic process. - The amount of ) generated.

[0050] To investigate the mechanism of action of MIL / KBO-30% in degrading dye molecules, benzoquinone (BQ,·O2) was used. - (Scavenger), isopropanol (IPA, ·OH scavenger), methanol (MeOH, h) +(capture agent) and silver nitrate (AgNO3, e) - The removal test was conducted using the trapping agent. Figure 14 As shown in (a), the photocatalytic reduction efficiency of Cr(VI) by MIL / KBO-30% was basically consistent with that of the blank group after the addition of methanol (MeOH). However, the photocatalytic degradation efficiency of Cr(VI) by MIL / KBO-30% was significantly inhibited after the addition of benzoquinone (BQ) and silver nitrate (AgNO3). Furthermore, the addition of isopropanol (IPA) also inhibited the photocatalytic degradation efficiency of Cr(VI), decreasing it from 100% to 79.9%. Therefore, this indicates that... - and e - Hydroxyl radicals (·OH) play a decisive role in the degradation process, while superoxide radicals (·O2) play an auxiliary role. Electron paramagnetic resonance (EPR) can be used to analyze hydroxyl radicals (·OH) and superoxide radicals (·O2) in the photocatalytic system. - The generation of ). For example Figure 14 As shown in (b) and (c), no ·OH and ·O2 were produced in the EPR spectrum under dark conditions. - The signal was observed. After 5 minutes of illumination, the EPR spectrum began to show ·OH and ·O2. - The signals, ·OH and ·O2, increased with illumination time up to 10 min. - The signal also strengthens accordingly. This indicates that hydroxyl radicals (·OH) and superoxide radicals (·O2) can be generated in both photocatalytic systems. - ).like Figure 15 The mechanism diagram of the Z-type heterojunction of MIL / KBO-30% composite material for Cr(VI) degradation is shown. The MIL / KBO-30% composite material exhibits highly efficient and stable performance in the photocatalytic reduction of Cr(VI) by constructing a Z-type heterojunction. The mechanism can be summarized as a multi-level synergistic process: Under visible light excitation, conduction band (CB) electrons of MIL-101(Fe) and valence band (VB) holes of KBiO3 undergo directional migration through the heterojunction interface, forming a Z-type carrier transport path. This mechanism effectively suppresses the recombination of photogenerated electron-hole pairs while retaining the highly reducing electrons (ep, ep, ep) of the KBiO3 conduction band. - Strong oxidizing holes (h) in the valence band of MIL-101(Fe) + Among them, the electrons enriched in the conduction band of KBiO3 can directly bind highly toxic Cr(VI) (such as Cr2O7). 2-The Cr(VI) / Cr(III) is reduced to the less toxic Cr(III), while the valence band holes of MIL-101(Fe) generate hydroxyl radicals (·OH) by oxidizing adsorbed H2O or surface hydroxyl groups (-OH), further mineralizing coexisting organic pollutants or intermediates. Furthermore, the built-in electric field at the interface accelerates charge separation efficiency and optimizes the redox potential through band matching: the negative potential of the KBiO3 conduction band (approximately -0.36 eV vs. NHE) is sufficient to drive the reduction reaction of Cr(VI) / Cr(III) (E... 0 =+1.33 eV), while the positive potential of the MIL-101(Fe) valence band (approximately +2.01 eV) ensures the ·OH(E 0 The efficient generation of superoxide radicals (+1.99 eV) was further confirmed by experimental characterization (such as EPR and radical quenching experiments). - ) is generated by the reaction of residual electrons with O2, which helps to destroy the molecular structure of pollutants; while the porous framework of MIL-101(Fe) not only enhances the adsorption and enrichment of Cr(VI), but also through Fe 3+ / Fe 2+ Cyclic processes promote interfacial electron transfer. This Z-shaped heterojunction system achieves integrated optimization of light absorption, carrier separation, and surface reactions through space charge layer regulation and synergy with multiple active species, providing a new strategy for the treatment of heavy metal-organic compound pollution.

[0051] (V) Analysis of photocatalytic optical properties The photoelectrochemical properties of KBiO3, MIL-101(Fe), and MIL / KBO-30% composite materials were characterized. Figure 16 (a) shows the transient photocurrent response spectra of KBiO3, MIL-101(Fe), and MIL / KBO-30% photocatalysts. The photocurrent density intensity of all samples remained stable within 9 on / off cycles, indicating that all three photocatalysts possess high photoresponse stability. Among them, the MIL / KBO-30% composite material exhibited the strongest photocurrent response intensity, suggesting that the MIL / KBO-30% composite material can generate more photogenerated carriers, which is beneficial for the photocatalytic degradation of dyeing and printing wastewater. The photocurrent density intensities of KBiO3, MIL-101(Fe), and MIL / KBO-30% were 0.11 µA / cm², respectively. 2 0.26 µA / cm 2 0.36 µA / cm 2 The MIL / KBO-30% concentration is three times that of KBiO3 and 1.4 times that of MIL-101(Fe). This indicates that the introduction of KBiO3 successfully formed a heterojunction with MIL-101(Fe), significantly improving its carrier separation efficiency. Figure 16(b) shows the electrochemical impedance spectroscopy (EIS) spectra of KBiO3, MIL-101(Fe), and MIL / KBO-30% photocatalysts. It can be observed that the composite material MIL / KBO-30% has the smallest spectral radius, indicating that the composite material has lower resistance to the migration of photogenerated carriers and the fastest interfacial charge transfer. Figure 16 (c) shows the photoluminescence spectra of KBiO3, MIL-101(Fe), and MIL / KBO-30%. The emission peak intensity of the composite material MIL / KBO-30% at 430 nm is lower than that of KBiO3 and MIL-101(Fe), indicating that MIL / KBO-30% has high carrier separation efficiency in the process of photocatalytic degradation of dyeing and printing wastewater and effectively suppresses carrier recombination. Figure 16 (d~e) are the valence band XPS spectra (VB-XPS) of KBiO3 and MIL-101(Fe), with the VB positions of the valence bands of KBiO3 and MIL-101(Fe) being 2.01 V and 1.36 V, respectively.

[0052] This invention employs a solvothermal method to prepare the composite material MIL-101(Fe) / KBiO3, significantly enhancing the photocatalytic performance of MIL-101(Fe) for Cr(VI). Experiments show that under visible light irradiation, the degradation performance of MIL / KBO-30% for Cr(VI) is significantly superior to that of KBiO3 and MIL-101(Fe) alone. For a Cr(VI) solution with an initial concentration of 30 mg / L, at a dosage of 0.15 g / L, MIL / KBO-30% achieved a 100% removal rate within 60 minutes, far exceeding the 77% of KBiO3 and the 82% of MIL-101(Fe). This indicates that MIL / KBO-30% has a significant enhancing effect in the degradation of the heavy metal Cr(VI), providing a new material option for the remediation of heavy metal pollution.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for constructing the composite material MIL-101(Fe) / KBiO3 using a solvothermal in-situ doping method, characterized in that, The method is as follows: S1. Add FeCl3·6H2O to N,N-dimethylformamide and stir magnetically until homogeneous to obtain liquid A; S2. After mixing and grinding NaBiO3·2H2O and KOH, the temperature was raised to 224℃, kept at a constant temperature, and then naturally cooled to room temperature. The mixture was washed with deionized water until the pH value of the system was 7. After vacuum filtration and drying, KBiO3 was obtained. S3. Add terephthalic acid and the KBiO3 obtained in S2 to N,N-dimethylformamide, stir magnetically until homogeneous, and obtain liquid B; S4. After mixing and ultrasonically dispersing the liquid A obtained in S1 and the liquid B obtained in S3, the mixture is subjected to solvothermal treatment at a temperature of 110℃. Then, the product after the reaction is washed sequentially with N,N-dimethylformamide and anhydrous ethanol, and dried to obtain the composite material MIL-101(Fe) / KBiO3.

2. The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping according to claim 1, characterized in that, The ratio of FeCl3·6H2O to N,N-dimethylformamide in S1 is 0.96 g: 30 mL.

3. The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping according to claim 1, characterized in that, The molar ratio of NaBiO3·2H2O and KOH in S2 is 1:2; the heating rate in S2 is 5℃ / min; the holding time in S2 is 2h; and the drying temperature in S2 is 60℃.

4. The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping according to claim 1, characterized in that, The ratio of terephthalic acid, KBiO3, and N,N-dimethylformamide in S3 is 0.3g:0.27g:30mL.

5. The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping according to claim 1, characterized in that, The magnetic stirring conditions in S1 were: 500 rpm for 30 min; the magnetic stirring conditions in S3 were: 500 rpm for 15 min; and the ultrasonic dispersion conditions in S4 were: 400 W for 20 min.

6. The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping according to claim 1, characterized in that, The solvent heat treatment time in S4 is 20h; the drying conditions in S4 are: 60℃, 20h.

7. The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping according to claim 1, characterized in that, The mass fraction of KBiO3 in the composite material MIL-101(Fe) / KBiO3 described in S4 is 20% to 50%.

8. The method for constructing the composite material MIL-101(Fe) / KBiO3 by solvothermal in-situ doping according to claim 7, characterized in that, The mass fraction of KBiO3 in the composite material MIL-101(Fe) / KBiO3 is 30%.

9. An application of the composite material MIL-101(Fe) / KBiO3 constructed by the method according to any one of claims 1-8, characterized in that, The composite material MIL-101(Fe) / KBiO3 is used for photocatalytic degradation of Cr(VI).

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