Synthesis methods and applications of crystalline BI4O5I2 / amorphous Fe2O3 heterojunctions

Abstract

The application discloses a synthesis method and application of a crystalline BI4O5I2 / amorphous Fe2O3 heterojunction, and belongs to the technical field of catalysts. The synthesis method comprises the following steps: step one, dissolving ferric nitrate and trisodium citrate in deionized water, stirring until completely dissolved, transferring the obtained solution into a reaction kettle to perform a hydrothermal reaction, washing and drying the product after the reaction is completed, and obtaining amorphous Fe2O3; step two, dissolving bismuth nitrate in ethylene glycol, stirring, adding the amorphous Fe2O3 prepared in step one and mixing uniformly, dropwise adding a potassium iodide solution into the mixture, transferring the obtained mixture into a reaction kettle to perform a hydrothermal reaction, washing and drying the product after the reaction is completed, and obtaining the crystalline Bi4O5I2 / amorphous Fe2O3. By adjusting the amount of trisodium citrate and key parameters such as bismuth nitrate in the hydrothermal synthesis process, the heterojunction material is successfully constructed, and the material can be used for photocatalytic removal of Cr(VI) at a concentration of 100mg·L ‑1 Cr(VI).

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to the synthesis method and application of crystalline BI4O5I2 / amorphous Fe2O3 heterojunctions. Background Technology

[0002] Photocatalysis technology has attracted much attention in the treatment of heavy metal ions, and the core of its catalyst design is to improve the separation efficiency of bulk carriers. However, in traditional catalysts (such as bismuth-rich Bi4O5I2), after photogenerated electrons are excited, they undergo multiple decays, and only a small number can migrate to the surface to participate in the reaction. Furthermore, they have obvious drawbacks such as severe exciton recombination and a narrow visible light response range.

[0003] Constructing heterojunctions is an effective improvement strategy. Heterojunctions utilize a built-in electric field to spatially separate electrons and holes, increasing their distance and reducing Coulomb attraction. Replacing one component in a traditional crystalline heterojunction with an amorphous material can form a unique amorphous / crystalline heterojunction interface. This interface effectively reduces the charge migration barrier, provides a directional, high-speed separation path, and significantly suppresses bulk recombination. Simultaneously, the work function difference between the amorphous and crystalline components is usually more significant than in crystalline heterojunctions, resulting in more intense band bending at the interface, thus forming a stronger built-in electric field that drives the reverse migration of photogenerated electrons and holes, achieving efficient spatial separation. Furthermore, the difference in their band structures also helps accelerate the separation and transport of bulk carriers.

[0004] Despite the excellent photocatalytic potential of crystalline / amorphous heterojunctions, research on the synthesis methods of heterojunctions constructed from crystalline Bi4O5I2 and amorphous Fe2O3, as well as their application in the treatment of high-concentration chromium-containing wastewater, remains very limited. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for synthesizing crystalline BI4O5I2 / amorphous Fe2O3 heterojunctions and their applications.

[0006] The objective of this invention can be achieved through the following technical solutions: A first aspect of the present invention relates to a method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, comprising the following steps: Step 1: Dissolve ferric nitrate and trisodium citrate in deionized water and stir until completely dissolved. Transfer the resulting solution to a reaction vessel for hydrothermal reaction. After the reaction is complete, wash and dry the product to obtain amorphous Fe2O3. Step 2: Dissolve bismuth nitrate in ethylene glycol, stir, add the amorphous Fe2O3 prepared in Step 1 and mix evenly, then add potassium iodide solution dropwise, transfer the resulting mixture to a reaction vessel for hydrothermal reaction, wash and dry the product after the reaction to obtain crystalline Bi4O5I2 / amorphous Fe2O3.

[0007] Optionally, in step one, the concentration of ferric nitrate is 0.014~0.107 mol·L⁻¹. -1 The molar ratio of ferric nitrate to trisodium citrate is 1:1 to 1:1.5.

[0008] Optionally, in step one, the temperature of the hydrothermal reaction is 120~200℃, and the reaction time is 4~18h.

[0009] Optionally, in step two, the molar ratio of amorphous Fe2O3 to bismuth nitrate is 0.15:1 to 2.19:1, and the mass of amorphous Fe2O3 is 0.05 to 0.7 g.

[0010] Optionally, in step two, the temperature of the hydrothermal reaction is 140~170℃, and the reaction time is 8~16h.

[0011] A second aspect of the present invention relates to a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, wherein the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction is prepared by the above-described synthesis method.

[0012] Optionally, the optical absorption wavelength range of the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction is 667~870nm, and the photocurrent signal is 2.02~3.01µA·cm. -2 The interface resistance is 278~1578Ω.

[0013] Optionally, the crystalline Bi4O5I2 is a monoclinic crystal system, and its X-ray diffraction pattern is consistent with the standard card JCPDS no. 71-3448.

[0014] A third aspect of the present invention relates to the application of the above-described crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction in the visible light catalytic reduction of Cr(VI).

[0015] Optionally, the concentration of Cr(VI) is 100 mg·L⁻¹. -1 .

[0016] The beneficial effects of this invention are: This invention provides a method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction and its application in the efficient catalysis of high-concentration Cr(VI) under visible light. Fe2O3, as a visible-light-responsive catalyst, provides photogenerated electrons for Cr(VI) catalysis due to its conduction band potential. The amorphous structure facilitates carrier separation. Crystalline Bi4O5I2 not only acts as a center for electron generation and transfer but also forms a heterojunction with Fe2O3 through interfacial coupling. A simple hydrothermal process is used, and by controlling parameters such as the trisodium citrate content, an amorphous phase can be introduced into Fe2O3. Simultaneously, an alkaline environment promotes the transformation of BiOI into the crystalline Bi4O5I2 phase. This amorphous-crystalline heterojunction structure effectively suppresses the recombination of photogenerated carriers. Experimental results show that under visible light irradiation, this system effectively catalyzes high-concentration Cr(VI) catalysis at concentrations of 100 mg·L⁻¹. -1 The photocatalytic degradation kinetic constant of Cr(VI) was increased by 7.44~29.89 times and 2.03~8.15 times compared with pure crystalline Bi4O5I2 and pure amorphous Fe2O3, respectively, achieving efficient photocatalysis of high concentration of Cr(VI). Attached Figure Description

[0017] The invention will now be further described with reference to the accompanying drawings.

[0018] Figure 1 A scanning electron microscope (SEM) image of the product obtained in an embodiment of the present invention; Figure 2 This is a transmission electron microscope (TEM) image of the product obtained in an embodiment of the present invention; Figure 3 The X-ray diffraction (XRD) pattern of the product obtained in an embodiment of the present invention; Figure 4 The image shows the photocatalytic performance of the product obtained in the embodiments of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: This embodiment of the invention discloses a method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, comprising the following steps: A method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction includes the following steps: Step 1: Dissolve ferric nitrate in a beaker containing deionized water, add trisodium citrate, and stir until completely dissolved. Transfer the resulting solution to a polytetrafluoroethylene-lined reactor for reaction. After the reaction is complete, wash and dry the product to obtain pure amorphous Fe₂O₃.

[0021] Step 2: Add 25 mmol·L -1 Bismuth nitrate was dissolved in 80 mL of ethylene glycol and stirred until a clear, transparent solution was formed. Amorphous Fe₂O₃ prepared in step one was added and mixed thoroughly. Then, 2 mmol of potassium iodide solid was added dropwise. The mixture was transferred to a reaction vessel for reaction. After the reaction was complete, the product was washed and dried to obtain a crystalline Bi₄O₅I₂ / amorphous Fe₂O₃ heterojunction.

[0022] In step one: the concentration of ferric nitrate is 0.107 mol·L⁻¹. -1 The molar ratio of ferric nitrate to trisodium citrate was 1:1; the reaction temperature was 160℃; and the reaction time was 12h.

[0023] After trisodium citrate dissolves in deionized water, it coordinates with the iron ions in ferric nitrate, and the mixture is then transferred to a reactor to react and generate Fe₂O₃. During this process, the strong coordination effect of the citrate ions favors the formation of the amorphous phase. When the concentration of trisodium citrate is low (ferric nitrate:trisodium citrate = 1:0–1:0.1), the complexation effect is too weak to significantly maintain the amorphous component state, resulting in a very low amorphous content. Within a suitable concentration range (ferric nitrate:trisodium citrate = 1:0.1–1:1.5), the amorphous component content increases with the increase of the trisodium citrate ratio, thereby promoting charge separation and enhancing photocatalytic activity. However, when the concentration exceeds the optimal threshold (ferric nitrate:trisodium citrate > 1:1.5), excessive trisodium citrate leads to an overly strong coordination effect, making it difficult for the hydrolysis reaction to break this coordination, ultimately reducing the product yield, although the amorphous component is still maintained.

[0024] In step two: the molar ratio of amorphous Fe2O3 to bismuth nitrate is 0.15:1; the mass of amorphous Fe2O3 is 0.05; the reaction temperature is 140℃; and the reaction time is 8h.

[0025] In step one, the amorphous Fe₂O₃ particles synthesized interact with water molecules to form a surface hydroxyl layer (≡Fe-OH). Under alkaline conditions, protons are released from the surface, giving it an anionic property that is conducive to the adsorption of cationic precursors. After mixing with bismuth nitrate, Bi… 3+ Ions and I - Ions are adsorbed onto amorphous Fe₂O₃ particles. Through a low-temperature reaction, BiOI is successfully coupled in situ. During the coupling process, some iodide ions in the BiOI react with OH⁻. -The material dissolves in the presence of iodine, while the remaining iodine leads to the formation of Bi4O5I2. It is important to note that excessive Bi4O5I2 content can increase agglomeration between components, thereby increasing carrier recombination and ultimately causing a decline in the material's structure and photocatalytic performance.

[0026] Example 2: A crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction was prepared according to the synthesis method of the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction described in Example 1. It possesses the following physicochemical properties: light absorption wavelength range of 701 nm, and photocurrent signal of 2.13 µA·cm⁻¹. -2 The interface resistance is 1321Ω.

[0027] Example 3: This example discloses the application of the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction prepared in Example 1. The crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction is directly applied to high-concentration Cr(VI) photocatalysis. Specifically, the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction exhibits high Cr(VI) photocatalysis performance under visible light at 100 mg·L⁻¹. -1 The photocatalytic degradation kinetic constant of Cr(VI) is increased by 8.14 times and 2.35 times compared with crystalline Bi4O5I2 and amorphous Fe2O3, respectively.

[0028] Currently, most photocatalysts can effectively treat concentrations of 20–50 mg·L⁻¹. -1 In Cr(VI) solutions, a few materials can photocatalyze 100 mg·L⁻¹ -1 The Cr(VI) solution. Unlike existing materials, the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction prepared in this invention has not been reported. Under visible light irradiation, this heterojunction can efficiently process concentrations up to 100 mg·L⁻¹. -1 The simulated Cr(VI) wastewater demonstrated the material's great potential for treating high-concentration industrial-grade pollutants. Especially under these concentration conditions, the photocatalytic degradation kinetic constant of Cr(VI) by the material was increased by 7.44–29.89 times compared to crystalline Bi4O5I2 and by 2.03–8.15 times compared to amorphous Fe2O3, significantly enhancing the separation and migration efficiency of photogenerated carriers and fully demonstrating the crucial promoting role of the amorphous-crystalline heterojunction in photocatalytic performance.

[0029] Example 4: A method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, comprising the following steps: the preparation method is the same as in Example 1, except that the concentration of ferric nitrate in step one is 0.107 mol·L⁻¹. -1 The molar ratio of ferric nitrate to trisodium citrate was 1:1.5; the reaction temperature was 200℃; and the reaction time was 18h.

[0030] The prepared crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction exhibits the following physicochemical properties: the optical absorption edge is located at 681 nm, and the photocurrent density is 2.31 µA·cm. -2 The interfacial charge transfer resistance is 880 Ω. Under visible light, the resistance at 100 mg·L⁻¹ is... - 1 In the photocatalytic degradation reaction of Cr(VI) solution, the kinetic constants of this heterojunction are 7.44 times and 2.03 times that of pure crystalline Bi4O5I2 and amorphous Fe2O3, respectively.

[0031] Example 5: A method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, comprising the following steps: the preparation method is the same as in Example 1, except that in step one, the concentration of ferric nitrate is 0.014 mol·L⁻¹. -1 The molar ratio of ferric nitrate to trisodium citrate was 1:1; the reaction temperature was 120℃; and the reaction time was 4 hours.

[0032] The prepared crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction exhibits the following physicochemical properties: the optical absorption edge is located at 667 nm, and the photocurrent density is 2.02 µA·cm. -2 The interfacial charge transfer resistance is 1578 Ω. Under visible light, the resistance at 100 mg·L⁻¹ is... - 1 In the photocatalytic degradation reaction of Cr(VI) solution, the kinetic constants of this heterojunction are 7.55 times and 2.06 times that of pure crystalline Bi4O5I2 and amorphous Fe2O3, respectively.

[0033] Example 6: A method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, comprising the following steps: the preparation method is the same as in Example 1, except that in step two, the molar ratio of amorphous Fe2O3 to bismuth nitrate is 2.19:1; the mass of amorphous Fe2O3 is 0.7g; the reaction temperature is 170℃ and the reaction time is 16h.

[0034] The prepared crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction exhibits the following physicochemical properties: the optical absorption edge is located at 720 nm, and the photocurrent density is 2.52 µA·cm. -2 The interfacial charge transfer resistance is 550 Ω. Under visible light, the resistance of 100 mg·L⁻¹ is... - 1 In the photocatalytic degradation reaction of Cr(VI) solution, the kinetic constants of this heterojunction are 11.55 times and 3.15 times that of pure crystalline Bi4O5I2 and amorphous Fe2O3, respectively.

[0035] Example 7: A method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, comprising the following steps: the preparation method is the same as in Example 1, except that in step two, the molar ratio of amorphous Fe2O3 to bismuth nitrate is 0.94:1; the mass of amorphous Fe2O3 is 0.3g; the reaction temperature is 150℃ and the reaction time is 10h.

[0036] For the pure components, the synthesis conditions of amorphous Fe2O3 are the same as in step one of Example 1, but step two is not required. The synthesis conditions of crystalline Bi4O5I2 are the same as in step two of Example 1, but step one is not required. The difference is that the amorphous Fe2O3 prepared in step one is not required in step two. The reaction temperature and time in the reactor are 150℃ and 10h, respectively.

[0037] The prepared crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction exhibits the following physicochemical properties: the optical absorption edge is located at 870 nm, and the photocurrent density is 3.01 µA·cm. -2 The interfacial charge transfer resistance is 278 Ω. Under visible light, the resistance at 100 mg·L⁻¹ is... - 1 In the photocatalytic degradation reaction of Cr(VI) solution, the kinetic constants of this heterojunction are 29.89 times and 8.15 times that of pure crystalline Bi4O5I2 and amorphous Fe2O3, respectively.

[0038] The light absorption edge, photocurrent density, and interfacial charge transfer resistance of crystalline Bi4O5I2 are 704 nm, 0.62 µA·cm, and respectively. -2 The optical absorption edge, photocurrent density, and interfacial charge transfer resistance of amorphous Fe₂O₃ are 2172 Ω. These values ​​are 639 nm, 0.62 µA·cm⁻¹, and 2172 Ω⁻¹, respectively. -2 ,2023Ω.

[0039] In implementation cases 1-7, the parameters involved in the photocatalytic performance test are as follows: measured pH 2.01, catalyst dosage 1.0 g·L⁻¹. -1 The dark adsorption time was 40 minutes, and the light source was a 300W xenon lamp (illuminance 200mW·cm). -2 ).

[0040] The products of the comparative example and Example 7 were analyzed and described using scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), and photocatalytic performance diagrams.

[0041] 1. Analysis of Scanning Electron Microscopy (SEM) Images Figure 1These are the results of scanning electron microscopy (SEM) of the product. The images show that the nanosheets are crystalline Bi4O5I2 with a diameter of approximately 1 μm. The surface-bonded particles are amorphous Fe2O3, exhibiting a micron-sized particle structure. After hydrothermal treatment, these two different morphologies coexist in the images, indicating the successful preparation of a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction.

[0042] 2. Analysis of Transmission Electron Microscopy (TEM) Images Figure 2 This is a transmission electron microscope (TEM) image of the product. The results show that the coexistence of micron-sized particles and sheet-like structures further confirms the formation of heterostructures. Figure 2 a). High-resolution transmission electron microscopy (HR-TEM) images ( Figure 2 b) shows that the lattice fringe spacing is 0.31 nm, corresponding to the (411) crystal plane of crystalline Bi4O5I2; at the same time, typical amorphous regions are visible, forming a characteristic amorphous / crystalline interface with the lattice fringes. The presence of this heterogeneous interface is beneficial to the separation and transport of photogenerated carriers.

[0043] 3. X-ray diffraction (XRD) spectrum analysis Figure 3 The X-ray diffraction (XRD) spectra of the products are shown. The results show that the diffraction peaks of crystalline Bi4O5I2 are highly consistent with the monoclinic crystal system standard card (JCPDS no. 71-3448), while amorphous Fe2O3 does not exhibit characteristic diffraction peaks, showing a typical amorphous structure. In the XRD spectrum of the crystalline Bi4O5I2 / amorphous Fe2O3 composite material, the main diffraction peak of Bi4O5I2 shifts to higher angles, and the peak intensity is significantly reduced, indicating a strong interfacial interaction between the two phases, providing direct evidence of close contact between the components.

[0044] 4. Photocatalytic performance analysis Figure 4 The image shows the photocatalytic performance of the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction for Cr(VI) under visible light irradiation. After 120 min of visible light irradiation, the removal capacity of pure crystalline Bi4O5I2 for Cr(VI) was 22.21 mg·L⁻¹. -1 The removal amount of pure amorphous Fe2O3 was 38.29 mg·L⁻¹. -1 This indicates that recombination of the photogenerated carrier phase is significant in the single component. When the two recombine to form a heterojunction, the removal concentration of Cr(VI) increases to 97.17 mg·L⁻¹. -1 This confirms that the strong interface effect formed between amorphous and crystalline states significantly accelerates the photocatalytic reaction.

[0045] In summary, in this invention, crystalline Bi₄O₅I₂ serves as a narrow-light-response visible-light photocatalyst, its unique band structure generating photogenerated electrons required for Cr(VI) catalysis. Amorphous Fe₂O₃ not only acts as a center for electron generation and transfer but also forms a heterojunction through interfacial coupling. A simple hydrothermal process is employed, and the formation of amorphous Fe₂O₃ is induced by adjusting parameters such as the trisodium citrate content. System optimization promotes the formation of an amorphous / crystalline interface in the heterojunction, effectively suppressing the recombination of photogenerated carriers, ultimately enabling the system to achieve a visible light response of 100 mg·L⁻¹. -1 The removal rate of Cr(VI) reached 29.89 times that of pure crystalline Bi4O5I2, achieving a highly efficient photocatalytic effect of Cr(VI).

[0046] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] The foregoing has shown and described 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 merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for synthesizing a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, characterized in that, Includes the following steps: Step 1: Dissolve ferric nitrate and trisodium citrate in deionized water and stir until completely dissolved. Transfer the resulting solution to a reaction vessel for hydrothermal reaction. After the reaction is complete, wash and dry the product to obtain amorphous Fe2O3. Step 2: Dissolve bismuth nitrate in ethylene glycol, stir, add the amorphous Fe2O3 prepared in Step 1 and mix evenly, then add potassium iodide solution dropwise, transfer the resulting mixture to a reaction vessel for hydrothermal reaction, wash and dry the product after the reaction to obtain crystalline Bi4O5I2 / amorphous Fe2O3.

2. The method for synthesizing crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction according to claim 1, characterized in that, In step one, the concentration of ferric nitrate is 0.014~0.107 mol·L⁻¹. -1 The molar ratio of ferric nitrate to trisodium citrate is 1:1 to 1:1.

5.

3. The method for synthesizing crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction according to claim 1, characterized in that, In step one, the temperature of the hydrothermal reaction is 120~200℃, and the reaction time is 4~18h.

4. The method for synthesizing crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction according to claim 1, characterized in that, In step two, the molar ratio of amorphous Fe2O3 to bismuth nitrate is 0.15:1 to 2.19:1, and the mass of amorphous Fe2O3 is 0.05 to 0.7 g.

5. The method for synthesizing crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction according to claim 1, characterized in that, In step two, the temperature of the hydrothermal reaction is 140~170℃, and the reaction time is 8~16h.

6. A crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction, characterized in that, The crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction is prepared by the synthesis method according to any one of claims 1 to 5.

7. The crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction according to claim 6, characterized in that, The optical absorption wavelength range of the crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction is 667~870nm, and the photocurrent signal is 2.02~3.01µA·cm. -2 The interface resistance is 278~1578Ω.

8. The crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction according to claim 6, characterized in that, The crystalline Bi4O5I2 is a monoclinic crystal system, and its X-ray diffraction pattern is consistent with the standard card JCPDS no. 71-3448.

9. The application of a crystalline Bi4O5I2 / amorphous Fe2O3 heterojunction as described in any one of claims 6 to 8 in the visible light catalytic reduction of Cr(VI).

10. The application according to claim 9, characterized in that, The concentration of Cr(VI) is 100 mg·L⁻¹. -1 .

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