Bio-fe2o3 / fewo4 heterojunction material, preparation and application thereof in photocatalysis

Abstract

The application belongs to the field of wastewater treatment, and specifically discloses a Bio-Fe2O3 / FeWO4 heterojunction material, which is a material with a waxberry-shaped morphology assembled by Fe2O3 / FeWO4 heterojunctions and comprises a core and fiber-shaped protrusions uniformly dispersed on the surface of the core. In addition, preparation of the material and application of the material as a photocatalyst for treatment of Cr wastewater are also disclosed. The photocatalyst has excellent catalytic activity and stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of heavy metal wastewater treatment, and particularly relates to the field of photocatalysts. BACKGROUND

[0002] The rapid industrialization has increased the discharge of heavy metal-containing wastewater, causing serious environmental problems. Hexavalent chromium (Cr(VI)) has strong toxicity in mutagenesis and carcinogenesis, and its high mobility enables it to migrate to the biological chain and accumulate in the organism. It is often used in electroplating, leather tanning, paint production and textile industry, and the wastewater generated by these industries inevitably leads to its serious over-standard. The Environmental Protection Bureau of China stipulates that the Cr(VI) emission limits of agricultural water, drinking water and industrial wastewater in China are 0.1, 0.05 and 0.5 mg / L, respectively. The conversion of Cr(VI) to Cr(III) is one of the key steps in the process of industrial wastewater treatment, because Cr(VI) has lower toxicity than Cr(III), including biological reduction, chemical precipitation and adsorption. But these methods have long processing time, high cost consumption and limited practical application for many chromium-containing industrial wastewater. For example, for chromium-containing acid mine wastewater, due to the large volume of water body, multiple pollution sources and dispersion, it is difficult to use the treatment methods for conventional industrial chromium-containing wastewater. Photocatalytic technology has the advantages of high efficiency, low energy consumption and mild reaction conditions in the removal of toxic heavy metal ions, because it utilizes renewable solar energy to realize the redox process of the system through light-responsive materials. However, light is basically simulated sunlight, visible light or ultraviolet light by photocatalytic equipment, which is not conducive to the removal of multi-source dispersed wastewater. Therefore, it is necessary to prepare photocatalysts with high photochemical response, and to use natural solar energy to drive the redox process to realize the reduction removal of Cr(VI).

[0003] In the process of treating industrial Cr(VI)-containing wastewater, inexpensive reagent materials and simple process operation are needed in the actual industrial water treatment. For example, the preparation method of the living bacteria composite biomaterial for repairing Cr(VI)-contaminated water body disclosed in Chinese patent application CN202211138658.X, the method for rapidly reducing hexavalent chromium ions based on oxalic acid strengthening disclosed in CN202010583807.8 and the method for removing hexavalent chromium and dye pollutants by in-situ synthesis of iron-based materials using plant polyphenols disclosed in CN201710104040.4 have high cost, slow reduction rate of Cr(VI) in chromium-containing industrial wastewater, long period and difficulty in realizing the application of large-scale industrial wastewater. Oxalic acid serves as an industrial cleaner, soil leaching agent, mordant and tanning agent in various processes due to its low cost and easy degradation of molecules. Importantly, the reduction of Cr(VI) by oxalic acid is thermodynamically feasible, but the reaction is very slow. SUMMARY

[0004] In view of the complexity of Cr(IV) wastewater and the high cost of treatment process, the first object of the present application is to provide a Bio-Fe2O3 / FeWO4 heterojunction material, which aims to provide a new material with special physicochemical structural characteristics and excellent Cr(IV) photocatalytic reduction activity and cycle stability.

[0005] The second object of the present application is to provide a preparation method of the Bio-Fe2O3 / FeWO4 heterojunction material, which aims to prepare a new material with special physicochemical structural characteristics and excellent photocatalytic activity.

[0006] The third object of the present application is to provide the application of the Bio-Fe2O3 / FeWO4 heterojunction material as a photocatalyst.

[0007] A Bio-Fe2O3 / FeWO4 heterojunction material is a material with a waxberry-like morphology assembled by Fe2O3 / FeWO4 heterojunction, which includes a core and fiber-like protrusions uniformly dispersed on the surface of the core.

[0008] The present application provides a new Fe2O3 / FeWO4 heterojunction material with a waxberry-like morphology, and it is found that the material with the above-mentioned physicochemical characteristics unexpectedly has excellent photocatalytic activity and photocatalytic stability.

[0009] The present application also provides a preparation method of the Bio-Fe2O3 / FeWO4 heterojunction material, which obtains a bacteria solution capable of oxidizing ferrous iron, then adds ferrous iron source and tungstate source components, performs biological oxidation treatment, then performs solid-liquid separation to obtain a tungstate-doped scheelite mineral; and then calcines the tungstate-doped scheelite mineral to obtain the Bio-Fe2O3 / FeWO4 heterojunction material.

[0010] In order to successfully prepare the Bio-Fe2O3 / FeWO4 heterojunction material with special physicochemical characteristics, the present application innovatively prepares a tungstate-hybridized scheelite mineral based on a biological oxidation method, and further calcines it, so as to obtain the Bio-Fe2O3 / FeWO4 heterojunction material with special waxberry-like structure and unexpectedly excellent photocatalytic activity and stability.

[0011] In the present application, the bacteria liquid contains at least one of the acidophilic iron-oxidizing bacteria and the acidophilic iron-sulfur-oxidizing bacteria; the bacteria can be conventional bacteria capable of oxidizing ferrous iron, for example, can include at least one of Leptospirillum ferrooxidans, Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans.

[0012] In the present application, the method for obtaining the bacteria liquid can be conventional.

[0013] For example, the bacteria is inoculated in a culture medium, and cultured with iron source as a substrate to obtain the bacteria liquid.

[0014] In the present application, the culture medium can be 9K culture medium.

[0015] In the present application, the iron source includes at least one of ferrous salt and iron powder; preferably, the ferrous salt is at least one of ferrous sulfate heptahydrate and ammonium ferrous sulfate.

[0016] In the present application, the pH of the bacteria liquid is 1.5-2.8.

[0017] In the present application, the concentration of the bacteria in the bacteria liquid is 1x10 7 -1x10 8 cell / mL.

[0018] In the present application, ferrous source and tungstic acid source are added to the bacteria liquid, and then cultured to realize biological oxidation.

[0019] In the present application, the ferrous source can be any water-soluble ferrous component, for example, can be at least one of ferrous sulfate heptahydrate and ammonium ferrous sulfate.

[0020] In the present application, the concentration of the ferrous source in the starting solution of biological oxidation is 4-15 g / 100 ml.

[0021] In the present application, the tungstic acid source is at least one of tungstic acid and water-soluble tungstate.

[0022] Preferably, the W / Fe molar ratio of the tungstic acid source and the ferrous source is 0.005-0.05:1, preferably 0.03-0.035:1.

[0023] In the present application, the temperature of the biological oxidation stage is 10-45℃, and can be further 25-45℃; the time is more than 60 hours, and can be further 70-96 h.

[0024] After the biological oxidation is completed, the tungstate-doped scheelite mineral can be separated based on a known process and is subjected to calcination treatment, so that the shape-preserving calcination can be realized and the heterojunction structure can be successfully constructed.

[0025] In the present application, the atmosphere for calcination is not particularly required, and air can be directly used in consideration of the convenience of treatment.

[0026] Preferably, the temperature for calcination is 250-750 DEG C, and further 300-700 DEG C.

[0027] Preferably, the holding time at the temperature for calcination is 1-3 hours.

[0028] The present application further provides an application of the Bio-Fe2O3 / FeWO4 heterojunction material as a photocatalyst.

[0029] The application of the present application is used as a photocatalyst for photocatalysis of Cr(VI) containing pollutants.

[0030] In the present application, the amount of the Bio-Fe2O3 / FeWO4 heterojunction material can be reasonably controlled according to the pollution condition.

[0031] In the present application, the Cr(VI) containing pollutants can be at least one of acid mine wastewater, industrial wastewater and surface water containing Cr(VI), and in particular, a plurality of pollutants difficult to be treated in the prior art can be treated.

[0032] Preferably, an organic acid additive is further added in the photocatalysis process.

[0033] Preferably, the organic acid additive includes at least one of oxalic acid, citric acid, tartaric acid and malic acid.

[0034] In the present application, the amount of the organic acid additive can be reasonably controlled according to the pollution condition.

[0035] In the present application, the Bio-Fe2O3 / FeWO4 heterojunction material can be used as a photocatalyst for photocatalytic detoxification treatment of Cr(VI) based on known principles and methods.

[0036] Advantages

[0037] 1. The present application provides a novel Fe2O3 / FeWO4 heterojunction material with a Yangmei-shaped morphology, and further finds that it has excellent photocatalytic activity and photocatalytic stability.

[0038] 2. The present invention innovatively prepares tungstate-hybridized Schmidt mineral based on a bio-oxidation method and further calcines it, thereby obtaining the Bio-Fe2O3 / FeWO4 heterojunction material with the special bayberry-like structure and unexpectedly excellent photocatalytic activity and stability.

[0039] 3. The photocatalyst described in the present invention can treat large-volume, multi-source Cr(VI)-containing acidic mine wastewater, and can effectively mediate the reduction of heavy metal Cr(VI) by organic acid under natural or simulated sunlight conditions.

[0040] The method of the present invention has a green and environmentally friendly preparation process with simple technology and easy industrial-scale production. In terms of application, the bio-source Bio-Fe2O3 / FeWO4 photocatalytic heterojunction has many advantages in the reductive removal of Cr(VI) in wastewater, such as low cost, high efficiency and wide application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The scanning electron microscope and transmission electron microscope characterization images of the bio-Fe2O3 / FeWO4 and Bio-Fe2O3 in Example 1 and Comparative Example 1 are shown. Figure 1 -a is a scanning electron microscope image of bio-Fe2O3 / FeWO4, with a scale of 1 μm. Figure 1 -b is a transmission electron microscope image of bio-Fe2O3 / FeWO4, with a scale of 200 nm. Figure 1 -c is a scanning electron microscope image of bio-Fe2O3, the scale is 1μm, Figure 1 -d is the transmission electron microscope image of biogenic Bio-Fe2O3, the scale bar is 200nm.

[0042] Figure 2 The X-ray crystal diffraction patterns of the bio-source Bio-Fe2O3 / FeWO4 prepared in Example 1 and the Bio-Fe2O3 prepared in Comparative Example 1 are ( Figure 2 -a) and Fourier infrared spectrum ( Figure 2 -b).

[0043] Figure 3 These are the electrochemical impedance spectroscopy images of the biogenic Bio-Fe2O3 / FeWO4 and Bio-Fe2O3 in Example 1 and Comparative Example 1.

[0044] Figure 4 It is a comparison chart of the Cr(VI) reduction effects of various biosources Bio-Fe2O3 / FeWO4 and Bio-Fe2O3 under various conditions in Application Example 1, as well as a performance chart of the preferred Bio-Fe2O3 / FeWO4 photocatalytic heterojunction. Figure 4-a is a comparison chart of Cr(VI) reduction effect of different materials, whether containing oxalic acid and light conditions, Figure 4 -b is the efficiency comparison of Bio-Fe2O3 / FeWO4 of various biological sources in mediating oxalic acid reduction of Cr(VI) and the effect optimization of photocatalytic materials.

[0045] Figure 5 is the application example 2 for evaluating the recycling and anti-interference performance of Bio-Fe2O3 / FeWO4 of biological sources, Figure 5 -a is the evaluation of Bio-Fe2O3 / FeWO4 of biological sources for Cr(VI) reduction and removal under five cycles, Figure 5 -b is the evaluation of Bio-Fe2O3 / FeWO4 of biological sources for Cr(VI) reduction and removal in different water qualities, Figure 5 -c is the evaluation of Bio-Fe2O3 / FeWO4 of biological sources for Cr(VI) reduction and removal under the condition of interference of various cations, Figure 5 -d is the evaluation of Bio-Fe2O3 / FeWO4 of biological sources for Cr(VI) reduction and removal under the condition of interference of various anions.

[0046] Figure 6 is the application example 3 for comparing the effect of Bio-Fe2O3 / FeWO4 of biological sources and Bio-Fe2O3 in mediating oxalic acid reduction of Cr(VI) under natural sunlight and dark conditions.

[0047] Figure 7 is the SEM chart of the material finally prepared in example 2;

[0048] Figure 8 is the XRD chart of the material finally prepared in example 2;

[0049] Figure 9 is the photocatalytic effect chart of the material finally prepared in example 2;

[0050] Figure 10 is the photocatalytic effect chart of the material prepared in example 4;

[0051] Figure 11 is the photocatalytic effect chart of comparative example 2;

[0052] Figure 12 is the photocatalytic effect chart of comparative example 3; DETAILED DESCRIPTION

[0053] The embodiments of the present application are described in detail below, which are implemented on the premise of the technical scheme of the present application, but the protection scope of the present application is not limited to the following embodiments.

[0054] The application provides a brand-new Bio-Fe2O3 / FeWO4 heterojunction material, and a preparation method by preparing tungstate-doped schroeckingerite in advance and then calcining.

[0055] The application provides a method for preparing a Bio-Fe2O3 / FeWO4 photocatalytic heterojunction, which comprises the following steps:

[0056] (1) inoculating acidophilic iron or iron-sulfur oxidizing bacteria strains into a 9K culture medium, taking ferrous sulfate or sulfur powder as energy, and enriching and culturing in a shaking bed for 3-7 days, so as to obtain a bacterial suspension by filtering, centrifuging and washing;

[0057] (2) dispersing the bacterial suspension obtained in step (1) in an acidic aqueous solution, adding a certain proportion of ferrous sulfate and sodium tungstate, and obtaining tungstate-doped schroeckingerite by filtering, washing and drying after 3-4 days of bio-oxidation of the acidophilic bacteria;

[0058] (3) placing the dried precursor in step (2) in a corundum magnetic boat and calcining in a muffle furnace at high temperature, so as to obtain a Bio-Fe2O3 / FeWO4 photocatalytic heterojunction;

[0059] Further, the acidophilic iron or iron-sulfur oxidizing bacteria in step (1) are one or more mixed strains selected from the group consisting of Leptospirillum ferrooxidans, Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans.

[0060] Further, the ferrous sulfate, sulfur powder, sodium tungstate and reagents used in the 9K salt ion culture medium in steps (1) and (2) are all analytically pure reagents.

[0061] Further, the bacterial suspension in step (2) is a liquid in which bacteria are dispersed in a dilute sulfuric acid solution, and the bacterial concentration is ensured to be 1x10 7 -1x10 8 cell / mL when the bacterial suspension is added to the synthesis system of schroeckingerite.

[0062] Further, the pH value of the acidic aqueous solution in step (2) is an acidic environment suitable for the survival of acidophilic iron and iron-sulfur oxidizing bacteria, and the pH value is between 1.5 and 2.8.

[0063] Further, the proportion of ferrous sulfate and sodium tungstate in step (2) can be adjusted as needed, for example, 7.5 g of ferrous sulfate heptahydrate and 0.25 g of sodium tungstate can be added to 100 mL of the acidic aqueous solution.

[0064] Further, the high-temperature calcination condition in step (3) is that the holding temperature is 250-750 DEG C, further 300-700 DEG C, the temperature rising speed is 1-10 DEG C / min, and the calcination time is maintained at 1-3 hours.

[0065] An alternative method for photocatalysis of Cr(VI) by oxalic acid using the biological source Bio-Fe2O3 / FeWO4 photocatalytic heterojunction, comprising the following steps: adding the obtained biological source Bio-Fe2O3 / FeWO4 photocatalytic heterojunction and oxalic acid into wastewater containing Cr(VI) according to a certain dosage, and reducing and removing Cr(VI) under sunlight irradiation.

[0066] The dosage of the photocatalyst is 0.1 g / L or more, and the dosage of oxalic acid is 0.6-1.0 mM / L per 10 mg / L of the initial concentration of Cr(VI) in the wastewater.

[0067] The sunlight used for the reduction and removal of Cr(VI) is natural sunlight or simulated sunlight of a xenon lamp in a photocatalytic instrument.

[0068] In the present application, the heavy metal wastewater treatment method for reducing Cr(VI) under the condition of natural sunlight by using biological source Bio-Fe2O3 / FeWO4 photocatalytic heterojunction mediated by oxalic acid takes the process of synthesizing schultenite by acidophilic iron and iron-sulfur-oxidizing bacteria as a template, introduces tungstic acid source into the system, prepares tungstate-doped schultenite precursor, and obtains biological source Bio-Fe2O3 / FeWO4 photocatalytic heterojunction by high-temperature calcination in a muffle furnace. A certain amount of biological source Bio-Fe2O3 / FeWO4 and oxalic acid are added into wastewater containing Cr(IV), and the process of reducing and removing Cr(VI) is realized under the condition of natural or simulated sunlight.

[0069] The following is a more specific scheme:

[0070] Example 1

[0071] The biogenic Bio-Fe2O3 / FeWO4 photocatalytic heterojunction used in this embodiment is prepared by enriching and culturing Acidithiobacillus ferrooxidans in 9K medium with ferrous sulfate heptahydrate as metabolic energy in a constant temperature shaker at 30°C and 180 rap for five days, filtering the slag with qualitative filter paper to obtain a bacterial solution, and obtaining a bacterial suspension using a high-speed centrifuge. The bacterial suspension is then washed and suspended with a sulfuric acid aqueous solution having a pH of 2. 15 g of ferrous sulfate heptahydrate and 0.1 g (Group A), 0.25 g (Group B), 0.5 g (Group C), and 0.75 g (Group D) of sodium tungstate are added to 200 mL of sulfuric acid solution having a pH of 2, and 5 x 10 7 cell / mL of Acidithiobacillus ferrooxidans bacterial liquid was used to synthesize tungstate-doped Schrödinger mineral in a constant temperature shaker at 30℃ and 180rap for 4 days, and then simply filtered, deionized and dried in vacuum; the tungstate-doped Schrödinger mineral was placed in a corundum magnetic boat and calcined at 600℃ (calcination temperature) for 2 hours in a muffle furnace at a heating rate of 5℃ / min. After cooling to room temperature, biogenic Bio-Fe2O3 / FeWO4-0.1 (group A), Bio-Fe2O3 / FeWO4-0.25 (group B), Bio-Fe2O3 / FeWO4 (group C) and Bio-Fe2O3 / FeWO4-0.75 (group D) were obtained respectively.

[0072] Comparative Example 1

[0073] Compared with Example 1, the only difference is that no sodium tungstate is added during the preparation process, and the material finally obtained by sintering is bio-source Bio-Fe2O3.

[0074] SEM and TEM testing:

[0075] The SEM and TEM images of the materials obtained in Example 1 and Comparative Example 1 are shown in Figure 1 Figure a is a scanning electron microscopy image of supplemented Schroeder mineral, with a scale of 2 μm; Figure d is a scanning electron microscopy image of supplemented tungstate-doped Schroeder mineral, with a scale of 2 μm. Figure b is a scanning electron microscopy image of biogenic Bio-Fe2O3 / FeWO4, with a scale of 1 μm; Figure c is a transmission electron microscopy image of biogenic Bio-Fe2O3 / FeWO4, with a scale of 200 nm; Figure e is a scanning electron microscopy image of biogenic Bio-Fe2O3, with a scale of 1 μm; and Figure f is a transmission electron microscopy image of biogenic Bio-Fe2O3, with a scale of 200 nm.

[0076] from Figure 1It can be seen that the biological source Bio-Fe2O3 / FeWO4 presents a ball structure with thorns; the particle size is 500-700 nm, the particle thickness is thin, and different species are dispersed in disorder. The biological source Bio-Fe2O3 presents an irregular half-sphere structure with thorns; the transmission electron microscopy shows that the particle size of the biological source Bio-Fe2O3 is obviously larger than that of the biological source Bio-Fe2O3 / FeWO4 photocatalytic heterojunction, and the particle size is thicker.

[0077] XRD / FTIR test:

[0078] In this embodiment, the biological source Bio-Fe2O3 / FeWO4 and Bio-Fe2O3 obtained in Example 1 and Comparative Example 1 are subjected to X-ray crystal diffraction and Fourier infrared spectrum analysis, and the results are shown in Figure 2 The X-ray crystal diffraction results show that the biological source Bio-Fe2O3 / FeWO4 exists hematite and iron tungstate; and the biological source Bio-Fe2O3 only exists hematite. The Fourier infrared spectrum results show that the biological source Bio-Fe2O3 / FeWO4 exists symmetric and asymmetric vibration peaks of FeO6 central iron at 468 and 536 cm -1 , respectively; and the symmetric vibration peak of oxygen in Fe-O-W at 930 and 1120 cm -1 ; and the vibration peaks of oxygen in SO4 -1 at 620 and 1050 cm 2- . The biological source Bio-Fe2O3 only exists the symmetric and asymmetric vibration peaks of FeO6 central iron and the vibration peaks of oxygen in SO4 2- . The biological source Bio-Fe2O3 / FeWO4 exists two kinds of hematite and iron tungstate, and the phase presents a heterojunction structure.

[0079] Electrochemical impedance test:

[0080] In this embodiment, the biological source Bio-Fe2O3 / FeWO4 and Bio-Fe2O3 obtained in Example 1 and Comparative Example 1 are subjected to electrochemical impedance analysis, and the results are shown in Figure 3 The slope of the line in the electrochemical impedance diagram can represent the resistance of the electronic transfer in the material, and the results show that the internal resistance of the biological source Bio-Fe2O3 / FeWO4 is obviously lower than that of Bio-Fe2O3.

[0081] Application Example 1

[0082] In this embodiment, the biological source Bio-Fe2O3 / FeWO4 and Bio-Fe2O3 obtained in Example 1 and Comparative Example 1 are used to mediate the photocatalytic reduction of Cr(VI) in wastewater. Figure 4-a shows different conditions, including: Group A: oxalic acid + natural light; Group B: Bio-Fe2O3 / FeWO4 + natural light; Group C: Bio-Fe2O3 / FeWO4 + oxalic acid; Group D: Bio-Fe2O3 / FeWO4 + oxalic acid + natural light; Group E: Bio-Fe2O3 + oxalic acid + natural light system. The system conditions are 20 mg / L Cr(VI), 0.3 g / L photocatalyst, 2.0 mM / L oxalic acid, pH = 3.9, reaction time is 60 minutes, and xenon lamp irradiation is 600 W / m 2 Light radiation intensity. Figure 4 -b shows the comparison of the reduction efficiency of Cr(VI) in wastewater by photocatalytic oxalic acid reduction mediated by various biogenic Bio-Fe2O3 / FeWO4. The system conditions are 20 mg / L Cr(VI), 0.3 g / L photocatalyst, 2.0 mM / L oxalic acid, pH=3.9, reaction time 60 minutes, and xenon lamp irradiation at 600 W / m 2 The results showed that the efficiency of the biogenic Bio-Fe2O3 / FeWO4 photocatalytic heterojunction in catalyzing the oxalic acid reduction of Cr(VI) was significantly higher than that of Bio-Fe2O3. Moreover, among the Bio-Fe2O3 / FeWO4 with different proportions of iron tungstate, the Bio-Fe2O3 / FeWO4 prepared by calcining the precursor with 0.5g of sodium tungstate had the highest efficiency in the photocatalytic reduction of Cr(VI).

[0083] Application Example 2

[0084] This example is a test of the cycling performance of the bio-Fe2O3 / FeWO4 photocatalytic heterojunction obtained in Example 1, a test of the influence of various water qualities and a test of the interference performance of typical anions and cations in the environment. The results are as follows: Figure 5 As shown. Figure 5 -a shows the reductive removal effect of Cr(VI) in wastewater by bio-Fe2O3 / FeWO4 under five cycles. The system conditions are 20 mg / L Cr(VI), 0.3 g / L photocatalyst, 2.0 mM / L oxalic acid, pH = 3.9, each reaction time is 60 minutes, and the xenon lamp is irradiated at 600 W / m 2 The light irradiation intensity can effectively and thoroughly remove Cr(VI) under multiple cycle conditions; Figure 5 -b shows the Cr(VI) reduction effect of bio-Fe2O3 / FeWO4 in deionized water, ultrapure water, tap water, lake water and river water. The system conditions are 20 mg / L Cr(VI), 0.3 g / L photocatalyst, 2.0 mM / L oxalic acid, pH = 3.9, reaction time 60 minutes, xenon lamp irradiation 600 W / m 2The light irradiation intensity and water quality system conditions have interference on the reduction efficiency of chromium, especially the Xiangjiang River water containing more organic matter and the tap water containing high salt, but the reduction efficiency of Cr(VI) can be improved after the treatment time is prolonged; Figure 5 - c shows the reduction effect evaluation of Bio-Fe2O3 / FeWO4 of biological origin on Cr(VI) under the interference of various cations at 2 and 10 mM / L, including Mn 2+ , Fe 3+ , Ni 2+ , Cu 2+ , Zn 2+ , Co 2+ and NH4 + , the system conditions are 20 mg / L Cr(VI), 0.3 g / L photocatalyst, 2.0 mM / L oxalic acid, pH = 3.9, the reaction time is 60 minutes, and the xenon lamp irradiation intensity is 600 W / m 2 The results show that the various cations have little interference on the reduction efficiency of chromium at low concentration, and Cu ions have obvious inhibitory effect at high concentration; Figure 5 - d shows the reduction effect evaluation of Bio-Fe2O3 / FeWO4 of biological origin on Cr(VI) under the interference of various anions at 2 and 10 mM / L, including HCO3 - , NO3 - , H2PO4 - , SO4 2- and Cl - , the system conditions are 20 mg / L Cr(VI), 0.3 g / L photocatalyst, 2.0 mM / L oxalic acid, pH = 3.9, the reaction time is 60 minutes, and the xenon lamp irradiation intensity is 600 W / m 2 The results show that NO3 - , SO4 2- and Cl - have no interference on the reduction of Cr(VI), H2PO4 - has little interference, and with the increase of the concentration, the influence on the reduction of Cr(IV) is greater, and HCO3 - has great influence on the reduction of Cr(VI), because it affects the pH of the system solution and inhibits the reduction process of Cr(IV).

[0085] Application Example 3

[0086] This example is to evaluate the performance of bio-source Bio-Fe2O3 / FeWO4 and Bio-Fe2O3 obtained in Example 1 and Comparative Example 1 in reducing Cr(VI) mediated by bio-source Bio-Fe2O3 / FeWO4 and Bio-Fe2O3 under natural sunlight intensity conditions, including Bio-Fe2O3 / FeWO4+ oxalic acid+ sunlight, Bio-Fe2O3+ oxalic acid+ sunlight, Bio-Fe2O3 / FeWO4+ oxalic acid+ darkness and Bio-Fe2O3+ oxalic acid+ darkness systems, with the conditions of 20 mg / L Cr(VI), 0.3 g / L photocatalyst, 2.0 mM / L oxalic acid, pH = 3.9, and reaction time of 60 minutes. As shown in Figure 6 , when oxalic acid is photocatalyzed, the light condition is necessary, and the result of the reduction of Cr(VI) shows that bio-source Bio-Fe2O3 / FeWO4 has stronger reaction efficiency under natural light conditions, and the reduction efficiency is significantly stronger than Bio-Fe2O3.

[0087] Example 2

[0088] Compared with Group C of Example 1, the only difference is that the strain type is changed, respectively, Acidithiobacillus ferrooxidans (abbreviated as A.f, Example 1 scheme), Leptospirillum ferrooxidans (abbreviated as L.f), and Sulfobacillus thermosulfidooxidans (abbreviated as S.t). Other operations and parameters are the same as Example 1. The SEM of W-doped schreyerite obtained by different strains is shown in Figure 7 , and the XRD is shown in Figure 8 , which shows that different strains can generate schreyerite through biological oxidation process (as shown in the following SEM and XRD), and there is no obvious difference in the photocatalytic performance of Bio-Fe2O3 / FeWO4 obtained by pyrolysis calcination.

[0089] In addition, according to the method of Group D of Application Example 1, each component of this example is used as a photocatalyst to test Cr(VI), and the result is shown in Figure 9 , which shows that good catalytic effect can also be obtained.

[0090] Example 3

[0091] Compared with Example 2, the only difference is that the culture conditions of the bacterial solution are changed, and the experimental groups are:

[0092] Group A: Leptospirillum ferrooxidans (L.f) culture conditions are 40℃; other conditions are the same as in Example 2.

[0093] Group B: Sulfobacillus thermosulfidooxidans (S.t, culture temperature is 45℃; other conditions are the same as in Example 2.

[0094] It is found that the material of the application can be obtained under the different culture conditions, and similar photocatalytic effects can be obtained.

[0095] Example 4

[0096] Compared with Example 1, the only difference is that the calcination temperature is changed, which is 300, 400, 500, 600, 700℃, respectively, and the materials prepared are named as Bio-Fe2O3 / FeWO4-300, Bio-Fe2O3 / FeWO4-400, Bio-Fe2O3 / FeWO4-500, Bio-Fe2O3 / FeWO4 (i.e. Example 1), Bio-Fe2O3 / FeWO4-700, respectively.

[0097] According to the method of Group D of Application Example 1, each component of the present example is used as a photocatalyst to test Cr(VI), and the results are shown in Table 1. Figure 10 ; it shows that similar photocatalytic effects can be obtained.

[0098] Comparative Example 2

[0099] Compared with Group C of Example 1, the only difference is that the same weight of PVA is used to replace sodium tungstate in it, and other operations and parameters are the same as in Example 1. The difference in the preparation process of PVA-doped schiillerite is that 15g of ferrous sulfate heptahydrate and 2g of PVA powder are added to 200ml of pH=2 sulfuric acid aqueous solution, and the solution is cultured at 1.0*10 7 cell / ml of Af bacteria for 3 days, and then the material is calcined at 700℃ in an inert gas for 2 hours to obtain the material, which is marked as C-Sch-PVA.

[0100] According to the method of Group D of Application Example 1, each component of the present example is used as a photocatalyst to test Cr(VI), and the results are shown in Table 1. Figure 11 It can be seen from the comparison of the cycle performance that C-Sch-PVA shows poor Cr(VI) reduction effect after the second cycle.

[0101] Comparative Example 3

[0102] The difference from Example 1 is that the W-doped scheelite obtained in Group C is not calcined, but directly used as a photocatalyst, and each component of this example is used as a photocatalyst according to the method of Group D of Application Example 1, and a Cr(VI) test is performed, and the results are shown in Table 1. Figure 12 As such, it can be seen that the non-calcined Cr treatment capacity is not ideal.

Claims

1. A method for preparing a photocatalytic heterojunction material, characterized in that: A bacterial liquid capable of oxidizing ferrous iron is obtained, and then a ferrous source and a tungstate source are added to perform biological oxidation treatment, followed by solid-liquid separation to obtain tungstate-doped Schrödinger mineral; and the tungstate-doped Schrödinger mineral is then calcined to obtain the photocatalytic heterojunction material.

2. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The bacterial solution contains at least one of acidophilic iron-oxidizing bacteria and acidophilic iron-sulfur-oxidizing bacteria.

3. The method for preparing a photocatalytic heterojunction material according to claim 2, wherein: The bacterial solution comprises at least one bacterium selected from the group consisting of Leptospirillum ferrooxidans, Acidithiobacillus ferrooxidans and Thiobacillus thermooxidans.

4. The method for preparing a photocatalytic heterojunction material according to claim 3, wherein: The bacteria are inoculated into a culture medium and cultured with an iron source as a substrate to obtain the bacterial solution.

5. The method for preparing a photocatalytic heterojunction material according to claim 4, wherein: The culture medium is 9K culture medium.

6. The method for preparing a photocatalytic heterojunction material according to claim 4, wherein: The iron source includes at least one of ferrous salt and iron powder; wherein the ferrous salt is at least one of ferrous sulfate heptahydrate and ammonium ferrous sulfate.

7. The method for preparing a photocatalytic heterojunction material according to claim 4, wherein: The pH of the bacterial solution is 1.5~2.

8.

8. The method for preparing a photocatalytic heterojunction material according to claim 4, wherein: In the bacterial solution, the bacterial concentration is 1×10 7 ~1×10 8 cell / mL.

9. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The ferrous source is at least one of ferrous sulfate heptahydrate and ferrous ammonium sulfate.

10. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The concentration of the ferrous source in the starting solution of biological oxidation is 4~15 g / 100ml.

11. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The tungstic acid source is at least one of tungstic acid or water-soluble tungstate.

12. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The W / Fe molar ratio of the tungstate source to the ferrous source is 0.005-0.05:

1.

13. The method for preparing a photocatalytic heterojunction material according to claim 12, wherein: The W / Fe molar ratio of the tungstate source to the ferrous source is 0.03-0.035:

1.

14. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The temperature of the biological oxidation stage is 10~45℃.

15. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The biological oxidation time is more than 60 hours.

16. The method for preparing a photocatalytic heterojunction material according to claim 15, wherein: The biological oxidation time is 70~96h.

17. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The calcination temperature is 250~750℃.

18. The method for preparing a photocatalytic heterojunction material according to claim 17, wherein: The calcination temperature is 300~700℃.

19. The method for preparing a photocatalytic heterojunction material according to claim 1, wherein: The holding time at the calcination temperature is 1 to 3 hours.

20. Use of a photocatalytic heterojunction material prepared by the preparation method according to any one of claims 1 to 19, characterized in that: Use it as a photocatalyst.

21. The use according to claim 20, characterized in that It is used as a photocatalyst for the photocatalysis of Cr(VI)-containing pollutants.

22. The use according to claim 21, characterized in that The Cr(VI)-containing pollutant is at least one of Cr(VI)-containing acidic mine wastewater, industrial wastewater and surface water.

23. The use according to any one of claims 20 to 22, wherein: Organic acid additives are also added during the photocatalytic process.

24. The use according to claim 23, characterized in that The organic acid adjuvant includes at least one of oxalic acid, citric acid, tartaric acid and malic acid.

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