Ultrafine nano alpha-Fe2O3 photocatalytic material prepared on basis of rolled steel mud and application of ultrafine nano alpha-Fe2O3 photocatalytic material

Abstract

The invention discloses a preparation method for preparing a superfine nano alpha-Fe2O3 photocatalytic material based on rolled steel iron mud, which comprises the following steps: heating and modifying the rolled steel iron mud, adding free acid, and reacting to obtain a clear solution; heating the clarified solution in a water bath, recovering vapor volatilized by heating through a condensation pipe, stopping heating when a layer of crystal film is generated on the surface of the solution, and then cooling and crystallizing the solution to obtain a crystal water-containing ferric salt; and adding an alkaline precipitator into the ferric salt, mixing and grinding to obtain a reddish brown mixture, and finally carrying out solvent-free reaction. The invention also discloses the superfine nano alpha-Fe2O3 material prepared by the method and application of the material in wastewater containing heavy metals or organic matters. The prepared nano alpha-Fe2O3 has high porosity and photocatalytic activity, and can be used as a photocatalyst to treat wastewater containing heavy metals. The green development goal of treating waste with waste is achieved, and the method has high economic value and social value.

Description

[0001] This application is a divisional application of the invention patent with the application number CN202211738520.3 and the invention name "Preparation method and application of an ultrafine nano-α-Fe2O3 photocatalytic material based on steel rolling iron mud". The original application date was December 30, 2022. Technical Field

[0002] The present invention belongs to the fields of nanomaterial preparation, resource conservation and environmental governance, and relates to a preparation method of an ultrafine nano-α-Fe2O3 photocatalytic material based on steel rolling iron mud, and the application of this α-Fe2O3 photocatalytic material in the treatment of wastewater containing heavy metals such as Cr(VI) and organic matter. Background Art

[0003] A large amount of steel rolling iron mud is generated during the heat treatment processes such as hot rolling and forging of steel, accounting for about 3%-5% of the mass of the processed steel. In 2020, the steel rolling iron mud generated by national steel enterprises was approximately 40 million tons. The steel rolling iron mud has a relatively high iron content and is a valuable secondary metallurgical resource. The resource utilization of these waste residues is extremely urgent, which is a common concern of researchers.

[0004] At present, the reuse of steel rolling iron mud at home and abroad mainly focuses on aspects such as remelting and reuse, pelletizing in blast furnaces, and preparation of reduced iron powder. Most of the research focuses on aspects such as remelting and primary processing of low-value-added products. Given the huge environmental, economic, social benefits and application technologies of steel rolling iron mud, it is possible to research and utilize steel rolling iron mud to produce high-value-added industrial products. Steel rolling iron mud mainly consists of iron oxides, so it can be used as a raw material for producing nano-α-Fe2O3.

[0005] Nano-α-Fe2O3 is an n-type semiconductor with a band gap of 1.9 - 2.5 eV. It has a stable structure and excellent photocatalytic and adsorption properties. Nano-α-Fe2O3 has been widely used in many fields such as photocatalysis, environmental protection, magnetic materials, decorative materials, biomedicine, gas-sensitive materials, and lithium-ion batteries. Currently, the main methods for preparing nano-α-Fe2O3 are hydrothermal method, precipitation method, sol-gel method, solid-phase method, and template method. The products prepared by the hydrothermal method have high purity and good dispersibility, and the morphology of the products can be regulated by adding different additives. However, its disadvantages are the generation of a large amount of secondary wastewater and the high requirements for reaction equipment. The precipitation method has the advantages of uniform product particles, low equipment investment, and low cost. The disadvantages are that the precipitate is prone to agglomeration during drying and calcination, resulting in poor dispersibility, and impurities are easily introduced during the precipitation process, resulting in low product purity. The sol-gel method has a relatively simple preparation process, and the prepared nano-α-Fe2O3 has a small particle size and a relatively uniform crystal morphology. However, the preparation cost is high, which is not conducive to industrial production. The nano-α-Fe2O3 particles prepared by the solid-phase method are not easy to agglomerate, and the preparation process is simple. However, the disadvantages are the high requirements for equipment, and irritating gases may be released during the grinding process.

[0006] The currently commonly used methods for preparing nano-α-Fe2O3 generally have problems such as high cost, complex operation, and secondary pollution. This not only restricts the large-scale industrial production of nano-α-Fe2O3, but also causes great pressure on the environment.

[0007] In view of this, the present invention is specifically proposed. Summary of the Invention

[0008] To solve the problems existing in the preparation of the existing α-Fe2O3, the main objectives of the present invention are threefold: (1) to provide a new idea for the high-value reuse of steel rolling sludge; (2) to provide a new process route for the preparation of nano-α-Fe2O3, with no secondary pollution and being green and environmentally friendly during the synthesis process; (3) compared with the existing technologies, the nano-α-Fe2O3 prepared by this method has extremely fine particle size; (4) the prepared nano-α-Fe2O3 material is applied to the treatment of heavy metal-containing wastewater and organic matter, expanding its practical application value.

[0009] The present invention uses steel rolling sludge as a raw material to prepare nano-α-Fe2O3 by a solvent-free method and uses it to treat Cr(VI)-containing wastewater, which can realize the high-value reuse of steel rolling sludge. Moreover, the preparation method and equipment of nano-α-Fe2O3 are simple, the process parameters are controllable, the repeatability is high, and there is no secondary pollution during the synthesis process.

[0010] To solve the above technical problems, the present invention provides the following technical solutions:

[0011] A preparation method of an ultrafine nano-α-Fe2O3 photocatalytic material based on steel rolling iron sludge, the method comprising the following steps:

[0012] (1) Heating and modifying the steel rolling iron sludge in a muffle furnace to obtain the pretreated steel rolling iron sludge;

[0013] (2) Adding free acid to the pretreated steel rolling iron sludge obtained in step (1) and reacting to obtain a clear solution;

[0014] (3) Subjecting the clear solution obtained in step (2) to water bath heating, recovering the steam volatilized by heating through a condenser, stopping heating when a crystal film forms on the surface of the solution, and then cooling and crystallizing the solution to obtain an iron salt containing crystal water;

[0015] (4) Mixing and grinding the iron salt prepared in step (3) with a basic precipitant to obtain a reddish-brown mixture;

[0016] (5) Transferring the reddish-brown mixture obtained in step (4) to a high-pressure reactor for hydrothermal reaction, washing and drying the product to obtain the ultrafine nano-α-Fe2O3 material.

[0017] Preferably, in step (1), the particle size of the steel rolling iron sludge is 100-300 mesh, the roasting temperature is 500-600 °C, and the treatment time is 1-2 h, and the function is to convert FeO and Fe3O4 in the steel rolling iron sludge into Fe2O3.

[0018] Preferably, in step (2), the addition amount of the steel rolling iron sludge to the free acid is 1 g:(2-3) ml, and the reaction time is 1-2 h. Since HNO3 has oxidizing property and can convert FeO and Fe3O4 in step (1) into Fe2O3, the free acid is preferably a nitric acid solution with a concentration of 65%, and this nitric acid solution can be directly purchased.

[0019] Preferably, in step (3), the temperature of the water bath heating is 50-70 °C, the heating time is 1 h, and the water bath heating method is used to make the solution heat more evenly. Stop heating when a crystal film forms on the surface of the solution, and this is the most favorable for the crystallization of the iron salt. The temperature of the cooling crystallization is 3-5 °C, and the cooling time is 4 h. The iron salt containing crystal water obtained by this method is Fe(NO3)3·9H2O.

[0020] Preferably, in step (4), to make the reaction proceed rapidly, a basic precipitant needs to be added. Since NaOH has too strong alkalinity and will cause the reaction to be completed before the crystals are fully nucleated, and nano-α-Fe2O3 cannot be obtained. Therefore, the basic precipitant is anhydrous Na2CO3, and the molar ratio of the iron source to anhydrous Na2CO3 is 1:(2.5-4.5).

[0021] Preferably, in step (5), the temperature of the solvent-free reaction is 130-160 °C, and the reaction time is 12-48 h.

[0022] The present invention also provides an ultrafine nano-α-Fe2O3 material prepared by the above method. The microscopic morphology of this material is a nanosphere formed by the accumulation of fine nanoparticles, which has a relatively high porosity, specific surface area and photocatalytic active sites, and is beneficial to improving the photocatalytic performance of the material.

[0023] The present invention also provides the application of the ultrafine nano-α-Fe2O3 material as a photocatalytic material in wastewater containing heavy metals or organic substances.

[0024] Preferably, the wastewater is Cr(VI)-containing wastewater.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a method for preparing an extremely fine nano-α-Fe2O3 photocatalytic material based on steel rolling sludge. First, the steel rolling sludge is pretreated, and the pretreated steel rolling sludge is used as a raw material to prepare an iron salt with crystal water. Then, the obtained iron salt with crystal water is fully mixed with an alkali source and reacted at a high temperature to obtain a nano-α-Fe2O3 material. Specifically:

[0027] (1) The steel rolling sludge mainly consists of iron oxides, so it can be used as a raw material for producing nano-α-Fe2O3. The present invention realizes the high-value utilization of steel rolling sludge;

[0028] (2) Compared with the existing preparation technologies, the solvent-free method has simple operation, controllable process parameters, high repeatability, and no secondary pollution is generated during the preparation process;

[0029] (3) Compared with the existing technologies, the samples prepared by this method have smaller particle sizes, thereby increasing the specific surface area, porosity and active sites of the material, and improving its application performance.

[0030] (4) The preparation raw materials are rich, the cost is low, and it is convenient for large-scale production.

[0031] (5) The nano-α-Fe2O3 prepared by the present invention has a relatively high porosity and photocatalytic activity, and can be used as a photocatalyst to treat heavy metal-containing wastewater. It realizes the green development goal of "treating waste with waste" and has high economic value and social value. Description of the Drawings

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0033] Figure 1 XRD picture of the nano-α-Fe2O3 material in Embodiment 1 of the present invention;

[0034] Figure 2 A and Figure 2 B are SEM pictures of the nano-α-Fe2O3 material in Embodiment 1 of the present invention, where Figure 2 B is Figure 2 the enlarged view of A;

[0035] Figure 3 BET and BJH pictures of the nano-α-Fe2O3 material in Embodiment 1 of the present invention;

[0036] Figure 4 Removal rate effect diagram of photocatalytic degradation of Cr(VI) by the nano-α-Fe2O3 material in Embodiment 1 of the present invention at different pH values. Specific embodiments

[0037] The following will combine the embodiments of the present invention to elaborate on the technical solutions and the technical problems to be solved in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention patent, rather than all embodiments.

[0038] Embodiment 1

[0039] (1) Take a certain amount of 200-mesh rolled steel sludge and calcine it in a muffle furnace at 600 °C for 2 h to completely convert FeO and Fe3O4 into Fe2O3.

[0040] (2) Take 5 g of the calcined raw material, add 15 mL of concentrated nitric acid with a mass concentration of 65%, and react for 1.5 h to obtain an iron-containing solution;

[0041] (3) Heat the iron-containing solution in a water bath at 60 °C, collect the nitric acid volatilized by heating through a condenser, stop heating when a crystal film appears on the surface of the solution, transfer the solution to an environment at about 4 °C and cool it for crystallization for 4 h to obtain Fe(NO3)3·9H2O.

[0042] (4) According to n(Fe(NO3)3·9H2O) / n(Na2CO3) = 1:3, add the above iron salt and anhydrous sodium carbonate to a mortar and grind and mix them in the mortar for 5 min to obtain a reddish-brown mixture.

[0043] (5) Add the reddish-brown mixture into a high-pressure reactor, keep it at a constant temperature of 150 °C and stand for crystallization for 36 h. Then take out the reactor, quickly cool it with water and take out the reaction product. Wash the nano α-Fe2O3 with deionized water and absolute ethanol repeatedly for three times, and dry the washed nano α-Fe2O3 in a constant-temperature drying oven at 80 °C for 2 h to obtain nano α-Fe2O3.

[0044] Test Example

[0045] Perform X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area and pore size distribution (BET, BJH) tests on the nano α-Fe2O3 prepared in Example 1.

[0046] Figure 1 As shown in the XRD pattern of this material, it can be seen that the diffraction peaks correspond to nano α-Fe2O3, which proves that the synthesized product is nano α-Fe2O3.

[0047] Figure 2 A and Figure 2 B is the SEM image of this material. Figure 2 B is Figure 2 The enlarged image of A. It can be seen that the microscopic morphology of this nano α-Fe2O3 is a spherical structure, with an average diameter of about 80 - 90 nm. The high-magnification image clearly shows the microscopic structure of the sample, which is composed of many small nanoparticles with a size of about 12.58 nm.

[0048] Figure 3 As shown in the BET diagram of this material, it can be seen that nano α-Fe2O3 has a type IV isotherm and an H3-type hysteresis loop in the region of p / p0 = 0.8 - 1, indicating that there are a large number of mesopores in the adsorbent.

[0049] Add 50 mL / 25 mg / L Cr(VI) solution into a conical flask, then adjust the pH of the reaction system with 0.1 M sodium hydroxide solution and sulfuric acid solution. Add 0.1 g nano α-Fe2O3 as a photocatalyst into this conical flask, shake well, and first place it in a constant-temperature shaking incubator with a shaking rate of 180 r / min and a constant temperature of 25 °C for a 30-min dark adsorption experiment. Then carry out a photocatalytic reaction on this system under a 300 W xenon lamp, and detect the Cr(VI) concentration every 30 min. The results of the photocatalytic experiment are as Figure 4 shown. The results show that when pH = 2, the maximum removal rate can reach 98.03%, indicating that this material has good photocatalytic activity for Cr(VI).

[0050] Comparative Example 1

[0051] The free acid used in step (2) is hydrochloric acid with a concentration of 20%, and other parameters are the same as those in the embodiment. The experimental results show that the desired nano-α-Fe2O3 is not obtained. This is because when the free acid is a non-oxidizing acid such as hydrochloric acid, Fe(II) in the raw materials cannot be oxidized to Fe(III), so it is difficult to obtain nano-α-Fe2O3.

[0052] Comparative Example 2

[0053] In step (3), the iron-containing solution is heated in a water bath at 60°C, and the nitric acid volatilized by heating is collected through a condenser. Heating is stopped before a crystal film is formed on the surface of the solution, and other parameters are the same as those in the embodiment. The experimental results show that the desired iron salt containing crystal water (Fe(NO3)3·9H2O) cannot be obtained at this time because when the crystal film has not yet formed on the surface of the solution, the supersaturation of the solution is too low to meet the crystallization conditions of Fe(NO3)3·9H2O, so the desired nano-α-Fe2O3 cannot be obtained at this time.

[0054] Comparative Example 3

[0055] In step (4), the basic precipitant is replaced with sodium hydroxide, and other parameters are the same as those in the embodiment. Since the alkalinity of sodium hydroxide is too strong, the reaction is completed before the crystals are fully nucleated and grown, so the desired nano-α-Fe2O3 cannot be obtained at this time.

[0056] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An ultrafine nano α-Fe2O3 photocatalytic material, characterized in that, Prepared by the following method: (1) Heat and modify the steel rolling sludge in a muffle furnace to obtain the pretreated steel rolling sludge; (2) Add free acid to the pretreated steel rolling sludge obtained in step (1), and react to obtain a clear solution; (3) Perform water bath heating on the clear solution obtained in step (2), recover the volatilized steam through a condenser, stop heating when a crystal film appears on the surface of the solution, and then cool and crystallize the solution to obtain hydrated iron salt; (4) Mix and grind the iron salt prepared in step (3) with a basic precipitant to obtain a reddish-brown mixture; (5) Transfer the reddish-brown mixture obtained in step (4) to a high-pressure reaction kettle for solvent-free reaction, wash and dry the product to obtain the ultrafine nano-α-Fe2O3 material.

2. The photocatalytic material according to claim 1, characterized in that, The particle size of the steel rolling sludge is 100-300 mesh, the roasting temperature is 500-600 °C, and the treatment time is 1-2 h.

3. The photocatalytic material according to claim 1, characterized in that, In step (2), the addition amount of the steel rolling sludge and the free acid is 1 g:(2-3) ml, the reaction time is 1-2 h, and the preferred free acid is a nitric acid solution with a concentration of 65%.

4. The photocatalytic material according to claim 1, characterized in that, In step (3), the temperature of the water bath heating is 50-70 °C, and the heating time is 1 h; the temperature of the cooling crystallization is 3-5 °C, and the cooling time is 4 h.

5. The photocatalytic material according to claim 1, characterized in that, In step (4), the basic precipitant is anhydrous Na2CO3, and the molar ratio of the iron source to anhydrous Na2CO3 is 1:(2.5-4.5).

6. The photocatalytic material according to claim 1, wherein In step (5), the temperature of the hydrothermal reaction is 130-160 °C, and the reaction time is 12-48 h.

7. Use of the photocatalytic material as claimed in claim 1 as a photocatalytic material in the treatment of wastewater containing heavy metals or organic substances.

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