An afe2o3 / bi2o3 amorphous / crystalline heterojunction material and its application in visible light catalytic reduction of hexavalent cr

Abstract

The application relates to the technical field of wastewater treatment, in particular to an aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material and application thereof in visible light catalytic reduction of hexavalent Cr. Amorphous iron oxide and bismuth oxide are compounded by using a one-step hydrothermal method; the introduction of amorphous iron oxide can solve the rapid recombination between photo-generated carriers of single-component Bi2O3; the amorphous / crystalline structure provides more abundant active sites, expands the light response range, and significantly improves the catalytic reaction rate. It can be observed from a scanning electron microscope that the introduction of aFe2O3 is beneficial to the size control of the composite components in the hydrothermal process. The application has the advantages of simple synthesis, low raw materials, and sufficient reaction; under the optimal conditions, the Cr(VI) reduction rate reaches 98%, and the application has practical industrial application prospects.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental water treatment, and in particular to an aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material and its application in visible light catalytic reduction of Cr(VI). BACKGROUND

[0002] Cr(VI) is inevitably discharged from various light industries, such as electroplating, wood processing, and chromite processing. This has brought serious harm to human health and the ecological system, so it is necessary to find an effective method to remove Cr(VI) from wastewater. At present, there are many technologies that can solve the pollution of Cr(VI) in water, such as electrochemical reduction, coprecipitation, adsorption and photocatalysis. Photocatalysis has some unique advantages in terms of energy and efficiency, and the photocatalytic process does not cause secondary pollution, and can utilize solar energy to achieve the removal of Cr(VI).

[0003] Iron oxide is a n-type semiconductor photocatalyst with a characteristic red color, with an indirect band gap of 2.1 eV. Because of its special stability in air, easy recovery and abundant elements on earth, it has become a promising material. As a photocatalyst, Fe2O3-based photocatalysts exhibit excellent activity. However, when Fe2O3 is used as an independent semiconductor photocatalyst, it is mainly due to its highly positive CB potential, resulting in weak thermodynamic energy and low utilization of photoelectrons. Among the various techniques reported, the construction of heterojunctions and the improvement of crystalline structure to achieve rapid separation of charge carriers in photocatalysts have attracted attention.

[0004] Chinese invention patent CN202011108636.X discloses a preparation method of a nitrogen defect structure Z-type g-C3N X / Fe2O3 catalyst. The method disperses the carbon nitride precursor in lye, stirs and then dries to collect for standby use. Continue to mix and grind the iron source with the obtained powder, then add it to a crucible for calcination to prepare the nitrogen defect structure Z-type g-C3N X / Fe2O3 catalyst. However, the above method for preparing photocatalysts requires high-temperature calcination, the reaction conditions are severe, the equipment requirements are high, which increases the cost pressure, and the sulfur contained in the raw materials will cause secondary pollution and harm to the environment.

[0005] In fact, it has been reported that amorphous metal oxides can be obtained by using the adsorption of organic molecules trisodium citrate to improve the thermodynamic stability of amorphous state, thereby reducing the driving force of the material. The article "Synergistic effect of amorphous ZnO / crystalline N-TiO2 interface for photoreduction of high concentration Cr(VI)" (Optical Materials, Vol. 143, 114176, 2023) studies the effect of trisodium citrate as an amorphous stabilizer on the crystallization of the material, and it is pointed out in the article that trisodium citrate as a reaction solvent effectively affects the crystallization of the material, thereby generating amorphous zinc-based materials. Further improve the separation efficiency of photo-generated electrons and holes, so that the material has higher photocatalytic capacity. However, the process for synthesizing the above catalyst is complex and is not suitable for industrial production.

[0006] In view of the above defects, the inventor of the present application has finally obtained the present application after a long period of research and practice. SUMMARY

[0007] The purpose of the present application is to solve the problem that photocatalytic water treatment has been limited by poor charge carrier separation and transfer in photocatalysts, and to provide a aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material and its application in visible light catalytic reduction of hexavalent Cr.

[0008] In order to achieve the above purpose, the present application discloses a preparation method of a aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material, comprising the following steps:

[0009] S1, after ultrasonic dissolution of trisodium citrate, trisodium citrate solution is obtained, then bismuth oxide is added to the trisodium citrate solution and stirred to obtain a mixed solution A;

[0010] S2, after ultrasonic dissolution of the nine water iron nitrate and trisodium citrate, they are added to the mixed solution A, and after stirring, a mixed solution B is obtained;

[0011] S3, the mixed solution B is transferred to a sealed reaction kettle for reaction, after the reaction is completed, it is washed and dried to obtain a aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material.

[0012] In step S1, the stirring time is 30 min.

[0013] In step S2, the amount of nine water iron nitrate added is 0.505 g, and the amount of trisodium citrate added is 0.161 g, and the nine water iron nitrate and trisodium citrate are ultrasonically dissolved in 55.0 mL of deionized water.

[0014] The stirring time in the step S2 is 30 min.

[0015] The reaction temperature in the step S3 is 160-200 DEG C, and the reaction time is 12 h.

[0016] The application further discloses the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material prepared by the preparation method.

[0017] The application further discloses application of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in visible light catalytic treatment of Cr(Ⅵ) wastewater, and the specific method is as follows: the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material is added into water containing Cr(Ⅵ) ions, the reaction pH is controlled to be 1-7, the reaction is carried out at normal temperature, dark adsorption is carried out for 1 h, and photocatalytic reaction is carried out for 2 h.

[0018] The concentration ratio of Cr(Ⅵ) ions in the water containing Cr(Ⅵ) ions to the concentration of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material is 1:10-1:50.

[0019] The photocatalytic reduction principle is as follows:

[0020] Since the Fermi level of the n-type semiconductor is close to the position of the conduction band, it means that the Fermi level of the aFe2O3 is higher than that of the Bi2O3. Under the excitation of visible light, the electron transfer in the aFe2O3 moves to the Bi2O3, so that the aFe2O3 loses electrons and has positive electricity, and the Bi2O3 obtains electrons and has negative electricity. The continuous process of the above process improves the separation of the electron / hole pairs of the material. From the perspective of thermodynamics, the conduction band (-0.64ev) of the aFe2O3 is lower than the standard reduction potential of ·O2 - / O2 potential (-0.33eV vs NHE), and the generated electrons of the material are part of the ·O2 - , which is also far lower than the standard reduction potential of Cr(Ⅲ) / Cr(Ⅵ) (1.23eV vs NHE). The result shows that the photocatalytic reduction of Cr(Ⅵ) is achievable.

[0021] Compared with the prior art, the beneficial effects of the present application are that: the present application obtains amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) by compounding aFe2O3 and Bi2O3, the introduction of aFe2O3 can reduce the size of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material and improve the adsorption capacity of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material; the adsorption of organic molecules trisodium citrate on metal ions improves the thermodynamic stability of the amorphous state, and the unique amorphous / crystalline heterojunction interface can significantly shorten the electron diffusion path and improve the actual catalytic activity of the material. The difference in band structure in the amorphous / crystalline heterojunction material also helps to accelerate the separation and transport of body carriers. The introduction of amorphous iron oxide is beneficial to the size control of the composite components in the hydrothermal process, the specific surface area is expanded, the light response region of the composite bismuth oxide is expanded, and the number of photocatalytic reaction active sites is increased. The present application has the advantages of simple synthesis, low raw materials, and full reaction; under the optimal conditions, the Cr(VI) reduction rate reaches 98%, and has practical industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM spectrum of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material obtained in Example 1;

[0023] Figure 2 XRD graph of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material obtained in Example 1;

[0024] Figure 3 Cr(VI) concentration detection results of the effluent after the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 2 was subjected to photocatalysis;

[0025] Figure 4 Cr(VI) concentration detection results of the effluent after the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 6 was subjected to photocatalysis;

[0026] Figure 5 Cr(VI) concentration detection results of the effluent after the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 11 was subjected to photocatalysis;

[0027] Figure 6 Cr(VI) concentration detection results of the effluent after the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 12 was subjected to photocatalysis;

[0028] Figure 7 Cr(VI) concentration detection results of the effluent after the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 13 was subjected to photocatalysis. DETAILED DESCRIPTION

[0029] The above and other technical features and advantages of the present invention are described in more detail below with reference to the accompanying drawings.

[0030] Example 1

[0031] (1) Accurately weigh trisodium citrate in 55 mL of deionized water and dissolve it using an ultrasonic reactor.

[0032] (2) Accurately weigh bismuth oxide and add it to the solution obtained in (1) and stir evenly for 30 minutes to obtain a mixed solution A;

[0033] (3) Accurately weigh ferric nitrate nonahydrate and trisodium citrate in 55 mL of deionized water and dissolve them using ultrasound to obtain a mixed solution B;

[0034] (4) Add mixed solution B dropwise to mixed solution A and stir for 30 min to obtain mixed solution C;

[0035] (5) The mixed solution C obtained in step (4) was transferred to a sealed reactor (polytetrafluoroethylene lined) and maintained at 180°C for 12 h;

[0036] (6) After the reaction is completed, the product is washed with deionized water and ethanol and dried.

[0037] The above products were scanned by electron microscope to observe the microstructure of the materials and analyze them. Figure 1 As shown in the SEM images, Figure a shows pure iron oxide, while Figures bf show composite materials of amorphous iron oxide / bismuth oxide (aFe2O3 / Bi2O3) in varying proportions. Bismuth oxide and iron oxide are used for composite modification to form a heterojunction where iron oxide adheres to the surface of bulk bismuth oxide, achieving a high electron-hole separation rate and improving the chromium ion reduction efficiency. However, as the proportion of iron oxide increases, the iron oxide aggregates on the bismuth oxide surface. This hinders the formation of the composite material, hinders the contact of photogenerated carriers, and leads to a decrease in catalytic performance.

[0038] Example 2

[0039] (1) Seven groups of 40 mL solutions containing 50 mg / L Cr(VI) were prepared and HCl was added to control the pH of the solutions. The pH values ​​of the solutions in each group were 1.01, 2.02, 2.99, 4.02, 4.98, 6.02, and 7.02, respectively.

[0040] (2) Adding amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) to the solution after adjusting the pH value in step (1) at a concentration of 1.0 g / L. The reaction was carried out at room temperature, with dark adsorption for 1 hour and photocatalytic reaction for 2 hours;

[0041] (3) The reaction solution of (2) is subjected to a centrifugal device to separate the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) from the solution;

[0042] (4) The concentration of Cr(VI) in the effluent after photocatalysis is detected by the diphenyl carbazide spectrophotometric method.

[0043] By controlling the pH value of the solution in (1), the detection results of Cr(VI) are as shown in the following table: Figure 3 When the pH value is equal to 2.01, the reduction efficiency is as high as 98.5%, and when the pH value is equal to 4.02 or above, the reduction efficiency is reduced to less than 50%, so we select the pH value of the Cr(VI) medium to be equal to 2.

[0044] Example 3

[0045] The difference between this example and Example 1 is that in step (3), the molar amount of trisodium citrate added is 0 mmol, and the other process conditions are the same as in Example 1.

[0046] Example 4

[0047] The difference between this example and Example 1 is that in step (3), the molar amount of trisodium citrate added is 0.25 mmol, and the other process conditions are the same as in Example 1.

[0048] Example 5

[0049] The difference between this example and Example 1 is that in step (3), the molar amount of trisodium citrate added is 0.85 mmol, and the other process conditions are the same as in Example 1.

[0050] Example 6

[0051] (1) 40 mL of a solution containing 50 mg / L of Cr(VI) is taken in six groups, and HCl is added to control the pH value of the solution, and the pH value of each group of solutions is 2;

[0052] (2) Amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) containing different amounts of aFe2O3, Bi2O3 and trisodium citrate (prepared in Examples 1 and 3-5) are added to the solution with adjusted pH value in step (1), and the concentration is 1.0 g / L, and the reaction is carried out at room temperature, dark adsorption for 1 h, and photocatalytic reaction for 2 h;

[0053] (3) The reaction solution of (2) is subjected to a centrifugal device to separate the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) from the solution;

[0054] (4) The concentration of Cr(VI) in the effluent after photocatalysis was detected by the diphenyl carbazide spectrophotometric method.

[0055] By controlling the content of trisodium citrate in (2), the detection results of Cr(VI) are shown in the following table. Figure 4 The amorphous metal oxide was obtained by using the strong adsorption of trisodium citrate. The catalytic effect of trisodium citrate with different proportions was different. When the molar amount of trisodium citrate was 0.55 mmol, the catalytic effect was optimal.

[0056] Example 7

[0057] The difference between this example and Example 1 is that the reaction temperature in step (5) is 160℃, and the other process conditions are the same as in Example 1.

[0058] Example 8

[0059] The difference between this example and Example 1 is that the reaction temperature in step (5) is 170℃, and the other process conditions are the same as in Example 1.

[0060] Example 9

[0061] The difference between this example and Example 1 is that the reaction temperature in step (5) is 190℃, and the other process conditions are the same as in Example 1.

[0062] Example 10

[0063] The difference between this example and Example 1 is that the reaction temperature in step (5) is 200℃, and the other process conditions are the same as in Example 1.

[0064] Example 11

[0065] (1) Take 5 groups of 40mL solution containing 50mg / L Cr(VI), add HCl to control the pH value of each group of solution to be 2;

[0066] (2) Add the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) obtained in Examples 1 and 7-10 to the solution with adjusted pH value in (1) respectively, with a concentration of 1.0g / L. React at room temperature, dark adsorption for 1h, and photocatalytic reaction for 2h;

[0067] (3) The reaction complete solution in (2) is subjected to centrifugal device for solid-liquid separation of the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3);

[0068] (4) The concentration of Cr(VI) in the effluent after photocatalysis was detected by the diphenyl carbazide spectrophotometric method.

[0069] The Cr(VI) detection results of the amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) synthesized at different temperatures in (2) are shown in FIG. 2. The reduction efficiency of aFe2O3 / Bi2O3 is as high as 98% when the temperature is 180°C, while the reduction rate is only 82% at a temperature of 160°C. Figure 5

[0070] Example 12

[0071] (1) 5 groups of 40 mL solutions each containing 50 mg / L Cr(VI) were taken, and HCl was added to control the pH value of each group of solutions to be 2;

[0072] (2) The amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) prepared in Example 1 were added to the solutions after pH adjustment in (1) to prepare a group of solutions each containing 1.0 g / L of the amorphous iron oxide / bismuth oxide materials. The reaction was carried out at room temperature, and the dark adsorption was 1 h, and the photocatalytic reaction was 2 h;

[0073] (3) The amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) were separated by a centrifugal device after the reaction in (2);

[0074] (4) The concentration of Cr(VI) in the water after photocatalysis was detected by the diphenyl carbonyl hydrazine spectrophotometric method.

[0075] The Cr(VI) detection results of the amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) synthesized at different temperatures in (2) are shown in FIG. 2. The reduction efficiency of aFe2O3 / Bi2O3 is as high as 98% when the temperature is 180°C, while the reduction rate is only 82% at a temperature of 160°C. Figure 6

[0076] Example 13

[0077] (1) 5 groups of 40 mL solutions each containing different concentrations of Cr(VI) were taken, and HCl was added to control the pH value of each group of solutions to be 2, and the concentration of Cr(VI) in each group of solutions was 25 mg / L, 50 mg / L, 75 mg / L, 100 mg / L, and 125 mg / L, respectively.

[0078] (2) The amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) prepared in Example 1 were added to the solutions after pH adjustment in (1) to prepare a group of solutions each containing 1.0 g / L of the amorphous iron oxide / bismuth oxide materials. The reaction was carried out at room temperature, and the dark adsorption was 1 h, and the photocatalytic reaction was 2 h;

[0079] ​​(3) The reaction solution of (2) is subjected to a centrifugal device to separate the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) from the solution;

[0080] (4) The concentration of Cr(VI) in the effluent after photocatalysis is detected by the diphenyl carbonyl hydrazine spectrophotometry.

[0081] By controlling the solution of different concentrations of Cr(VI) in (1), the detection results of Cr(VI) are shown in the following table. Figure 7 As can be seen, when the initial concentrations of Cr(VI) are 25 mg / L, 50 mg / L, 75 mg / L, 100 mg / L and 125 mg / L, the degradation efficiencies within 80 min are 99%, 88%, 69%, 50% and 47%, respectively. It is speculated that the reduction in catalytic efficiency may be that the reduction products compete with the remaining Cr(VI) ions for the active sites on the material surface.

[0082] The above description is merely preferred embodiments of the present application, which are illustrative only, not restrictive. Those skilled in the art will understand that many changes, modifications, even equivalents, can be made to the present application within the spirit and scope of the claims defined by the present application.

Claims

1. A method for preparing aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material, characterized in that: The following steps are involved: S1, dissolving trisodium citrate by ultrasonication to obtain a trisodium citrate solution, then adding bismuth oxide to the trisodium lemonade solution and stirring to obtain a mixed solution A; S2, dissolving ferric nitrate nonahydrate and trisodium citrate by ultrasonication, adding the mixture to the mixed solution A, and stirring to obtain a mixed solution B; S3, transferring the mixed solution B to a sealed reactor for reaction, and after the reaction is complete, washing and drying to obtain aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material; In step S2, the molar amount of trisodium citrate added is 0.25-0.85 mmol; In step S3, the reaction temperature is 160-190° C., and the reaction time is 12 h.

2. The method for preparing aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material according to claim 1, characterized in that: In step S1, the stirring time is 30 minutes.

3. The method for preparing aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material according to claim 1, characterized in that: In step S2, the amount of ferric nitrate nonahydrate added is 0.505 g, the amount of trisodium citrate added is 0.161 g, and the ferric nitrate nonahydrate and trisodium citrate are ultrasonically dissolved in 55.0 mL of deionized water.

4. The method for preparing aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material according to claim 1, characterized in that: In step S2, the stirring time is 30 minutes.

5. An aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material as claimed in claim 5 in visible light photocatalytic treatment of hexavalent Cr wastewater.

7. The use of an aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in visible light photocatalytic treatment of hexavalent Cr wastewater according to claim 6, characterized in that: The specific method is as follows: add aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material to water containing hexavalent chromium ions, control the reaction pH to 2, react at room temperature, dark adsorption for 1 hour, and photocatalytic reaction for 2 hours.

8. The use of an aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in visible light photocatalytic treatment of hexavalent Cr wastewater according to claim 7, characterized in that: The ratio of the concentration of hexavalent chromium ions in the water containing hexavalent chromium ions to the concentration of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material is 1:10 to 1:50.

Images