AFe2O3 / Bi2O3 amorphous / crystal heterojunction material and application thereof in visible light catalytic reduction of hexavalent Cr

Abstract

The invention relates to the technical field of wastewater treatment, in particular to an aFe2O3 / Bi2O3 amorphous / crystal heterojunction material and application of the aFe2O3 / Bi2O3 amorphous / crystal heterojunction material in visible light catalytic reduction of hexavalent Cr. Amorphous iron oxide and bismuth oxide are compounded by utilizing a one-step hydrothermal method, and rapid compounding between photon-generated carriers of single-component Bi2O3 can be solved by introducing the amorphous iron oxide; the amorphous / crystalline structure provides richer active sites, enlarges the photoresponse range, and significantly improves the catalytic reaction rate. It can be observed through a scanning electron microscope that introduction of aFe2O3 is beneficial to size control of the composite component in the hydrothermal process. The method has the advantages of simple synthesis, cheap raw materials and sufficient reaction; the Cr (VI) reduction rate reaches 98% under the optimal condition, and the method has the actual industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental water treatment, and in particular to an aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material and application thereof in visible light catalytic reduction of hexavalent Cr. Background Art

[0002] Cr(VI) is inevitably discharged from various light industries, such as electroplating, wood processing, and chromite processing. This has caused serious harm to human health and the ecosystem, so there is a need to find effective methods to remove Cr(VI) from wastewater. Currently, there are many technologies that can solve Cr(VI) pollution in water, such as electrochemical reduction, coprecipitation, adsorption and photocatalysis. Photocatalysis has some unique advantages in terms of energy and efficiency. The photocatalytic process does not cause secondary pollution, and solar energy can be used to achieve the removal of hexavalent chromium.

[0003] Iron oxide is an n-type semiconductor photocatalyst with a characteristic red color and an indirect band gap of 2.1 eV. It has become a promising material because of its exceptional stability in air, easy recycling, and abundance of elements on earth. As a photocatalyst, Fe2O3-based photocatalysts exhibit excellent activity. However, when Fe2O3 is used as a stand-alone semiconductor photocatalyst, it suffers from weak thermodynamic energy and low utilization of photoelectrons, mainly due to its highly positive CB potential. Among the various techniques that have been reported, constructing heterostructures and improving crystalline structures to achieve rapid separation of charge carriers in photocatalysts have received attention.

[0004] Chinese invention patent CN202011108636.X discloses a nitrogen-containing defect structure Z-type g-C3N X / Fe2O3 catalyst preparation method. The method comprises dispersing a carbon nitride precursor in an alkaline solution, stirring, drying and collecting for later use. The iron source is then mixed with the obtained powder and ground, and then added to a crucible for calcination to obtain a nitrogen-containing defect structure Z-type g-C3N X / Fe2O3 catalyst. However, the above method for preparing photocatalysts requires high-temperature calcination, severe reaction conditions, high requirements for equipment, increased cost pressure, and the sulfur contained in the raw materials will cause secondary pollution and harm the environment.

[0005] In fact, it has been reported that the use of the organic molecule trisodium citrate adsorption to improve the thermodynamic stability of the amorphous state, thereby reducing the driving force of the material to obtain amorphous metal oxides, has been reported. "Synergistic effect of amorphousZnO / crystalline N-TiO2 interface for photoreduction of high concentration Cr(VI)" (Optical Materials, 2023, Vol. 143, 114176) studied the effect of trisodium citrate as an amorphous stabilizer on the crystallization of the material. The article pointed out that trisodium citrate, as a reaction solvent, effectively affected the crystallization of the material, thereby generating an amorphous zinc-based material. This in turn improves the separation efficiency of photogenerated electrons and holes, giving the material a higher photocatalytic ability. However, the process for synthesizing the above-mentioned catalyst is complicated and not suitable for industrial production.

[0006] In view of the above-mentioned defects, the inventors of the present invention finally obtained the present invention after a long period of research and practice. Summary of the invention

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

[0008] In order to achieve the above object, the present invention discloses a method for preparing aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material, comprising the following steps:

[0009] S1, dissolving trisodium citrate by ultrasonication to obtain a trisodium citrate solution, and then adding bismuth oxide to the trisodium lemonade solution and stirring to obtain a mixed solution A;

[0010] 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;

[0011] S3, transferring the mixed solution B to a sealed reactor for reaction, and after the reaction is completed, washing and drying to obtain aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material.

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

[0013] In the 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.

[0014] In step S2, the stirring time is 30 minutes.

[0015] In step S3, the reaction temperature is 160-200° C. and the reaction time is 12 h.

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

[0017] The present invention also discloses the application of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in the visible light catalytic treatment of hexavalent Cr wastewater. The specific method is as follows: adding the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material to water containing hexavalent chromium ions, controlling the reaction pH to 1-7, reacting at room temperature, dark adsorption for 1 hour, and photocatalytic reaction for 2 hours.

[0018] The ratio of the concentration of hexavalent chromium ions in the water containing hexavalent chromium ions to the concentration of aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material is 1:10 to 1:50.

[0019] The principle of photocatalytic reduction is as follows:

[0020] Since the Fermi level of n-type semiconductors is close to the position of the conduction band, this means that the Fermi level of aFe2O3 is higher than that of Bi2O3. Under the excitation of visible light, the electrons in aFe2O3 are transferred to Bi2O3, so aFe2O3 loses electrons and becomes positively charged, while Bi2O3 gains electrons and becomes negatively charged. The continuation of the above process improves the separation of electron / hole pairs in the material. From a thermodynamic point of view, the conduction band of aFe2O3 (-0.64ev) is lower than that of Bi2O3. - / O2 potential (-0.33eVvsNHE) standard reduction potential, part of the electrons generated by the material will produce ·O2 - , which is also much lower than the standard reduction potential of Cr(Ⅲ) / Cr(Ⅵ) (1.23 eV vs NHE). The results show that photocatalytic reduction of Cr(Ⅵ) is achievable.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention composites aFe2O3 with Bi2O3 to obtain an amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3), and the introduction of aFe2O3 can reduce the size of the amorphous / crystalline heterojunction material of aFe2O3 / Bi2O3 and improve the adsorption capacity of the amorphous / crystalline heterojunction material of aFe2O3 / Bi2O3; the adsorption of metal ions by organic molecule trisodium citrate is used to improve 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 the energy band structure in the amorphous / crystalline heterojunction material also helps to accelerate the separation and transmission of body carriers. It can be observed through a scanning electron microscope that the introduction of amorphous iron oxide is conducive to the size control of the composite component in the hydrothermal process, the specific surface area is enlarged, the light response area of ​​bismuth oxide is enlarged after the composite, and the number of active sites of the photocatalytic reaction is increased. The present invention has the advantages of simple synthesis, low raw materials, and sufficient reaction; under the optimal conditions, the Cr(VI) reduction rate reaches 98%, and has practical industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0024] Figure 3 The results of the Cr(VI) concentration test in the effluent water after the photocatalysis of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 2;

[0025] Figure 4 The results of the Cr(VI) concentration test in the effluent water after the photocatalysis of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 6;

[0026] Figure 5 The results of the Cr(VI) concentration test in the effluent water after the photocatalysis of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 11;

[0027] Figure 6 The results of the Cr(VI) concentration test in the effluent water after the photocatalysis of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 12;

[0028] Figure 7 This is the result of detecting the Cr(VI) concentration in the effluent water after photocatalysis of the aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material in Example 13. DETAILED DESCRIPTION

[0029] The above and other technical features and advantages of the present invention are described in more detail below in conjunction with 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 weighing bismuth oxide and adding it to the solution obtained in (1) and stirring for 30 minutes to obtain a mixed solution A;

[0033] (3) accurately weighing ferric nitrate nonahydrate and trisodium citrate into 55 mL of deionized water, and dissolving them with the aid of 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) transferring the mixed solution C obtained in step (4) to a sealed reactor (polytetrafluoroethylene lined) and maintaining it at 180° C. for 12 h;

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

[0037] The above products were scanned by electron microscope to observe the microscopic morphology of the materials and analyze them. Figure 1 As shown. In the SEM spectrum, Figure a is pure iron oxide, and Figures bf are composite materials of amorphous iron oxide / bismuth oxide (aFe2O3 / Bi2O3) in different proportions. Bismuth oxide and iron oxide are used for composite modification to form a heterojunction in which iron oxide is attached to the surface of bulk bismuth oxide, achieving a higher electron-hole separation rate and improving the reduction efficiency of chromium ions. However, as the proportion of iron oxide increases, iron oxide agglomerates on the surface of bismuth oxide. This is not conducive to the formation of composite materials, hindering the contact of photogenerated carriers, and resulting in a decrease in catalytic performance.

[0038] Example 2

[0039] (1) Take 7 groups of 40 mL solutions containing 50 mg / L Cr(VI) and add HCl to control the pH of the solutions. The pH of the solutions in each group is 1.01, 2.02, 2.99, 4.02, 4.98, 6.02, and 7.02, respectively;

[0040] (2) Add 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. React at room temperature, dark adsorption for 1 hour, and photocatalytic reaction for 2 hours;

[0041] (3) passing the reaction solution of (2) through a centrifugal device to separate the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) into solid and liquid;

[0042] (4) The concentration of Cr(VI) in the effluent after photocatalysis was detected using diphenylcarbazide spectrophotometry.

[0043] By controlling the pH value of the solution in (1), the Cr(VI) test results are shown in the attached figure. Figure 3 At pH 2.01, the reduction efficiency reached a maximum of 98.5%, while at pH 4.02 and above, the reduction efficiency dropped to less than 50%, so we chose the pH of the Cr(VI) medium to be 2.

[0044] Example 3

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

[0046] Example 4

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

[0048] Example 5

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

[0050] Example 6

[0051] (1) Take 6 groups of 40 mL solutions containing 50 mg / L Cr(VI) and add HCl to control the pH of the solutions. The pH of each solution is 2.

[0052] (2) adding aFe2O3, Bi2O3 and amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) with different contents of trisodium citrate (prepared in Example 1 and Examples 3-5) to the solution after adjusting the pH value in step (1) at a concentration of 1.0 g / L, reacting at room temperature, dark adsorption for 1 h, and photocatalytic reaction for 2 h;

[0053] (3) passing the reaction solution of (2) through a centrifugal device to separate the aFe2O3, Bi2O3 and amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) with different contents of trisodium citrate into solid and liquid;

[0054] (4) The concentration of Cr(VI) in the effluent after photocatalysis was detected using diphenylcarbazide spectrophotometry.

[0055] By controlling the content of trisodium citrate in (2), the Cr(VI) test results are shown in the attached figure. Figure 4 As shown. Amorphous metal oxides are obtained by using the strong adsorption of trisodium citrate. The catalytic effects of trisodium citrate with different ratios are different. When the molar amount of trisodium citrate is 0.55mmol, the catalytic effect is optimal.

[0056] Example 7

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

[0058] Example 8

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

[0060] Example 9

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

[0062] Example 10

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

[0064] Embodiment 11

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

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

[0067] (3) passing the reaction solution of (2) through a centrifugal device to separate the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) into solid and liquid;

[0068] (4) The concentration of Cr(VI) in the effluent after photocatalysis was detected using diphenylcarbazide spectrophotometry.

[0069] By controlling the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) synthesized at different temperatures in (2), the Cr(VI) detection results are shown in the attached figure. Figure 5 As shown in Figure 2, the reduction efficiency of aFe2O3 / Bi2O3 is as high as 98% at 180°C, while the reduction rate is only 82% at 160°C.

[0070] Example 12

[0071] (1) Take 5 groups of 40 mL solutions containing 50 mg / L Cr(VI) and add HCl to them to control the pH value of each solution to be 2;

[0072] (2) Add different concentrations of amorphous iron oxide / bismuth oxide materials (aFe2O3 / Bi2O3) to the clear solution after adjusting the pH value in (1). The amorphous iron oxide / bismuth oxide materials prepared in Example 1 were added to each group of solutions at concentrations of 0.5 g / L, 1.0 g / L, 1.5 g / L, 2.0 g / L, and 2.5 g / L, respectively. The reaction was carried out at room temperature, dark adsorption for 1 h, and photocatalytic reaction for 2 h;

[0073] (3) passing the reaction solution of (2) through a centrifugal device to separate the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) into solid and liquid;

[0074] (4) The concentration of Cr(VI) in the effluent after photocatalysis was detected using diphenylcarbazide spectrophotometry.

[0075] By controlling the concentration of amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) in (2), the Cr(VI) test results are shown in the attached figure. Figure 6 The content of the catalyst is positively correlated with the photocatalytic degradation of Cr(VI). When the catalyst concentration is 2.5 g / L, 95% of the Cr(VI) solution (50 mg / L) can be catalyzed in 40 minutes.

[0076] Example 13

[0077] (1) Take 5 groups of 40 mL solutions containing different concentrations of Cr(VI), add HCl, and control the pH value of each solution to 2. The concentrations of Cr(VI) in each solution are 25 mg / L, 50 mg / L, 75 mg / L, 100 mg / L, and 125 mg / L, respectively.

[0078] (2) Add the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) prepared in Example 1 to the solution after adjusting the pH value in (1) at a concentration of 1.0 g / L. React at room temperature, dark adsorption for 1 h, and photocatalytic reaction for 2 h;

[0079] (3) passing the reaction solution of (2) through a centrifugal device to separate the amorphous iron oxide / bismuth oxide material (aFe2O3 / Bi2O3) into solid and liquid;

[0080] (4) The concentration of Cr(VI) in the effluent after photocatalysis was detected using diphenylcarbazide spectrophotometry.

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

[0082] The above description is only a preferred embodiment of the present invention, which is only illustrative and not restrictive of the present invention. Those skilled in the art understand that many changes, modifications, and even equivalences may be made to the present invention within the spirit and scope defined by the claims of the present invention, but all of them will fall within the scope of protection of the present invention.

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, and 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 completed, washing and drying to obtain aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material.

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 the 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. The method for preparing aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material according to claim 1, characterized in that: In the step S2, the molar amount of trisodium citrate added is 0-0.85 mmol.

6. The method for preparing aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material according to claim 1, characterized in that: In step S3, the reaction temperature is 160-200° C. and the reaction time is 12 h.

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

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

9. The use of a Fe2O3 / Bi2O3 amorphous / crystalline heterojunction material in visible light photocatalytic treatment of hexavalent Cr wastewater as claimed in claim 8, characterized in that: The specific method is as follows: add aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material into water containing hexavalent chromium ions, control the reaction pH to 2, react at room temperature, dark adsorb for 1 hour, and photocatalytically react for 2 hours.

10. The use of a Fe2O3 / Bi2O3 amorphous / crystalline heterojunction material in visible light photocatalytic treatment of hexavalent Cr wastewater as claimed in claim 9, characterized in that: The ratio of the concentration of hexavalent chromium ions in the water containing hexavalent chromium ions to the concentration of aFe2O3 / Bi2O3 amorphous / crystalline heterojunction material is 1:10 to 1:50.

Images