A composite material for assisting degradation of dye wastewater and a preparation method and application thereof

Abstract

The present application relates to the field of catalytic composite material, and specifically discloses a composite material for assisting degradation of dye wastewater, and a preparation method and application thereof.The present application takes hydrotalcite and lanthanum salt as the main body, and utilizes the composite of hydrotalcite and lanthanum salt with p-n heterojunction structure prepared by the coprecipitation method.The composite material can assist peroxymonosulfate to oxidatively degrade harmful substances in azo dye wastewater, improve the degradation efficiency of peroxymonosulfate, and the composite material has stable catalytic performance, is simple to use, and can be reused, thereby greatly saving the cost of degrading dye wastewater.The present application effectively solves the problems of unstable catalyst performance, greatly reduced catalytic activity after 2-3 times of use, and increased cost of degrading dye wastewater and complicated operation in the prior art of using photocatalysts to assist peroxymonosulfate to degrade dye wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalytic composite materials, and particularly discloses a composite material for assisting degradation of dye wastewater, and a preparation method and application thereof. BACKGROUND

[0002] With the continuous improvement of social industrialization level, various enterprises are developing, and the wastewater produced by various industries has become a major hidden danger to the environment and human health. According to reports, more than 100,000 dyes have been artificially synthesized in the world for industrial and textile industries, and nearly 700,000 tons of dye wastewater are generated every year. Among them, azo dyes are the most common dyes, which are easy to decompose carcinogenic aromatic amines during production and use, and with the rapid development of the dye industry, a large amount of dyes are directly discharged into water bodies to form dye wastewater, causing serious harm to the water environment.

[0003] For the treatment and degradation of dye wastewater, scientists have made various attempts in the past few decades. Among them, the advanced oxidation process based on persulfate has the advantages of strong oxidative degradation of organic matter, wide pH value range, and little influence of other inorganic ions in sewage, thereby attracting widespread attention. However, in the prior art, persulfate is generated by activation through ultraviolet, ultrasonic, and transition metal methods, but there are problems such as high operation cost and poor activation efficiency. Some people combine photocatalysts and persulfate for degradation of dye wastewater, but the photocatalysts used are unstable, and the activity greatly decreases after 2-3 times of use, which cannot be used for a long time, resulting in high degradation cost and complex operation. Therefore, it is of great significance to develop a material for assisting the degradation of azo dye wastewater by persulfate in the field of catalytic materials and environmental governance. SUMMARY

[0004] In view of the problems in the prior art that the photocatalyst-assisted persulfate degradation of dye wastewater has unstable catalyst performance, the catalytic activity greatly decreases after 2-3 times of use, and the degradation cost of dye wastewater is high and the operation is complex, the present application provides a composite material for assisting degradation of dye wastewater, and a preparation method and application thereof. The present application uses hydrotalcite and lanthanum salt as the main body of the composite material, and uses the coprecipitation method to prepare a composite material for assisting degradation of dye wastewater with a p-n heterojunction structure. The composite material can greatly improve the catalytic efficiency of persulfate for degrading azo dye wastewater, and the composite material has stable performance and can be repeatedly used, thereby saving the cost of degrading dye wastewater.

[0005] To achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The first aspect of the present application provides a composite material for assisting degradation of dye wastewater, wherein the composite material comprises a lanthanum salt and hydrotalcite loaded on the surface of the lanthanum salt, and the lanthanum salt and the hydrotalcite form a p-n heterojunction structure.

[0007] Compared with the prior art, the present application provides a composite material for assisting degradation of dye wastewater, wherein the composite material is a p-n heterojunction structure, the p-n heterojunction is a structure composed of a p-type semiconductor and an n-type semiconductor, and due to the difference in electron concentration between the p-type semiconductor and the n-type semiconductor, an electric potential barrier is formed, and the flow and control of electrons can be achieved. In the present application, the composite material comprises a lanthanum salt and hydrotalcite loaded on the surface of the lanthanum salt, the lanthanum salt has a narrow band gap value (2.0-2.7 eV) and a unique electronic and crystal structure, and is a p-type semiconductor, which has a certain response ability to ultraviolet light and visible light, and can form a heterojunction with the hydrotalcite. The hydrotalcite has the advantages of adjustable layered structure, high anion exchange capacity and rich surface hydroxyl groups, and can reduce the recombination of photo-generated electron-hole pairs. The p-n heterojunction structure formed by the hydrotalcite and the lanthanum salt in the present application can accelerate the migration of electron-hole pairs, and the lanthanum salt can further improve the degradation effect of persulfate by using visible light energy, and the hydrotalcite can improve the ability of persulfate to produce active oxygen, and the p-n junction structure effectively combines visible light energy and persulfate oxidation technology, thereby achieving the purpose of improving the efficient degradation of dye wastewater by persulfate.

[0008] Preferably, the hydrotalcite is cobalt-iron hydrotalcite.

[0009] The cobalt-iron hydrotalcite has the advantages of adjustable layered structure, high anion exchange capacity and rich surface hydroxyl groups, and can reduce the recombination of photo-generated electron-hole pairs and improve the ability of persulfate to produce active oxygen.

[0010] Preferably, the lanthanum salt is nano lanthanum ferrite.

[0011] The nano lanthanum ferrite has a narrow band gap and excellent visible light response ability, but the ordinary lanthanum ferrite particles have a large particle size and a small specific surface area, resulting in limited oxidation ability. The nano lanthanum ferrite has a larger specific surface area, and the metal active sites on the surface are more likely to activate peroxymonosulfate to produce strong oxidizing power of sulfate radicals and hydroxyl radicals.

[0012] The second aspect of the present application provides a preparation method of the composite material for assisting degradation of dye wastewater, comprising the following steps:

[0013] Step one, dissolving a soluble lanthanum salt and a soluble iron salt in deionized water, adding an organic acid, and mixing uniformly to obtain a metal salt mixed solution;

[0014] Step two, the metal salt mixed solution is subjected to hydrothermal reaction under 0.6-0.8 MPa, cooled, centrifuged, washed, dried, and the metal salt precipitate is obtained;

[0015] Step three, the metal salt precipitate is subjected to primary calcination at 480-520 DEG C for 2.5-3.5 h, and then subjected to secondary calcination by increasing the temperature to 650-750 DEG C, and cooled, and the lanthanum ferrite powder is obtained;

[0016] Step four, a soluble iron salt and a soluble cobalt salt are dissolved in deionized water to obtain solution A;

[0017] The lanthanum ferrite powder is dispersed in deionized water to obtain a suspension;

[0018] Step five, the solution A and the suspension are mixed uniformly, the pH is adjusted to 9.2-9.5, aged, centrifuged, washed, dried, and the composite material for assisting degradation of dye wastewater is obtained.

[0019] The present application uses soluble lanthanum salt and soluble iron salt as raw materials, and the lanthanum ferrite powder is obtained through hydrothermal reaction and high-temperature calcination, and then the composite material for assisting degradation of dye wastewater is obtained through co-precipitation.

[0020] Preferably, in step one, the soluble lanthanum salt is lanthanum nitrate.

[0021] Preferably, in step one, the soluble iron salt is any one of ferric nitrate or ferric chloride.

[0022] Preferably, in step one, the organic acid is a citric acid aqueous solution, and the concentration is 0.25-0.5 mol / L.

[0023] Preferably, in step one, the molar ratio of La 3+ , Fe 3+ and citric acid in the metal salt mixed solution is 0.9-1.1:1:2.

[0024] Preferably, in step one, the frequency of the ultrasonic is 30-40 kHz, and the ultrasonic time is 30-50 min.

[0025] Preferably, in step two, the temperature of the hydrothermal reaction is 160-180 DEG C, and the reaction time is 12-14 h.

[0026] The present application carries out hydrothermal reaction under high temperature and high pressure, which avoids large crystal grains, defect formation and impurity introduction.

[0027] Preferably, in step two, the rotation speed of the centrifugation is 400-600 rpm, and the centrifugation time is 8-12 min.

[0028] Preferably, in step two, the washing is alternating washing with 30 mL-50 mL of deionized water and anhydrous ethanol, and the washing is performed 3-5 times.

[0029] Preferably, in step two, the drying temperature is 60℃-80℃, and the drying time is 3h-5h.

[0030] Preferably, in step three, the second calcination is performed for 2h-4h.

[0031] Preferably, in step three, the first calcination and the second calcination are both performed by temperature programming, wherein the first calcination is performed at a rate of 2℃ / min-4℃ / min, and the second calcination is performed at a rate of 1℃ / min-3℃ / min.

[0032] High-temperature calcination can further remove residual organic acids and crystal water, and construct good crystal form and crystal size

[0033] Preferably, in step four, the molar ratio of Fe 3+ and Co 2+ in the A solution is 0.5-0.6:1.5-1.8.

[0034] Preferably, in step four, the mass concentration of lanthanum ferrite powder in the suspension is 3g / L-4g / L.

[0035] Preferably, in step five, the solution used for adjusting pH is an alkali solution.

[0036] Further preferably, the alkali solution is a sodium hydroxide solution with a concentration of 0.7mol / L-1.0mol / L.

[0037] Preferably, in step five, the mass ratio of the A solution to the suspension is 1:1-1:1.2.

[0038] Preferably, in step five, the aging temperature is 65℃-80℃, and the aging time is 18h-24h.

[0039] Preferably, in step five, the centrifugation time is 3min-6min.

[0040] Preferably, in step five, the drying temperature is 65℃-80℃, and the drying time is 10h-14h.

[0041] The third aspect of the present application provides an application of the composite material for assisting degradation of dye wastewater in catalytic persulfate degradation of dye wastewater, comprising the following steps:

[0042] S1, uniformly mixing the composite material with the dye wastewater in a dark environment to obtain a mixed wastewater solution;

[0043] S2, placing the mixed wastewater solution under visible light, adding persulfate, and performing photocatalytic degradation.

[0044] Preferably, in S1, the mass-volume ratio of the composite material to the dye wastewater is 1 mg:(1.9-2.1) mL.

[0045] Preferably, in S1, the mass concentration of the dye in the dye wastewater is ≥100 mg / L.

[0046] Preferably, in S2, the mass ratio of the persulfate to the composite material is 4:1-4:1.1.

[0047] Preferably, in S2, the persulfate is peroxymonosulfate.

[0048] Preferably, in S2, the light source of the visible light is a xenon lamp, the wavelength of the xenon lamp is ≥420 nm, and the output light intensity of the xenon lamp is ≥302.6 mW / cm 2 .

[0049] Preferably, the specific operation of the photocatalytic degradation is: taking 1.5 mL-2 mL of the reaction sample, quenching with alcohol, filtering, analyzing the dye concentration by ultraviolet-visible absorption spectroscopy, and evaluating the photocatalytic efficiency.

[0050] Further preferably, the alcohol is anhydrous methanol.

[0051] Further preferably, the volume ratio of the reaction sample to the alcohol is 1:2-3.

[0052] Further preferably, the filtering uses a 0.45 μm-0.5 μm syringe filter.

[0053] Further preferably, the analysis wavelength is 521.4 nm.

[0054] In summary, the present application provides a composite material for assisting in the degradation of dye wastewater, taking cobalt-iron hydrotalcite and nano lanthanum ferrite as the main body of the composite material, and preparing a composite material for assisting in the degradation of dye wastewater with a p-n heterojunction structure. The composite material not only greatly improves the catalytic efficiency of persulfate in degrading azo dye wastewater, which can be as high as 90% or more, but also has stable performance and can be repeatedly used, thereby saving the cost of degrading dye wastewater. The problem of high cost and complex operation caused by the instability of the catalytic performance of the photocatalyst in assisting the persulfate in degrading dye wastewater after 2-3 uses is effectively solved. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1XRD patterns of the composite materials obtained in Examples 1-3 and Comparative Examples 1-2;

[0056] Figure 2 The electron microscope photos of the composite material obtained in Example 2; wherein (A) is a scanning electron microscope photo; (B) is a high-magnification transmission electron microscope photo;

[0057] Figure 3 The results of the diffuse reflectance absorption test and fluorescence test of the composite materials obtained in Examples 1-3 and Comparative Examples 1-2, wherein (A) is the ultraviolet diffuse reflectance spectrum of the composite materials obtained in Examples 1-3 and Comparative Examples 1-2; (B) is the photoluminescence spectrum of the composite materials obtained in Example 2 and Comparative Example 1;

[0058] Figure 4 The structural characterization test of the composite materials obtained in Example 2 and Comparative Examples 1-2, wherein (A) is the Mott-Schottky curve of the composite material obtained in Comparative Example 2; (B) is the Mott-Schottky curve of the composite material obtained in Comparative Example 1; (C) is the band gap alignment diagram calculated from the composite materials obtained in Comparative Examples 1 and 2; (D) is the transient photocurrent curve of the composite materials obtained in Example 2 and Comparative Example 1;

[0059] Figure 5 The effect comparison diagram of the composite materials obtained in Examples 1-3 in assisting the degradation of different azo dyes (acid red, methylene blue and crystal violet) by persulfate; wherein (a) is the effect comparison diagram of the composite materials in assisting the degradation of acid red by persulfate; (b) is the effect comparison diagram of the composite materials in assisting the degradation of methylene blue by persulfate; (c) is the effect comparison diagram of the composite materials in assisting the degradation of crystal violet by persulfate;

[0060] Figure 6 The effect comparison diagram of the composite material obtained in Example 2 and the composite materials obtained in Comparative Examples 1-2 in assisting the degradation of acid red by persulfate under darkness and visible light;

[0061] Figure 7 The efficiency comparison diagram of the composite material obtained in Example 2 in assisting the degradation of acid red 4 times by persulfate. DETAILED DESCRIPTION

[0062] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0063] Example 1

[0064] The present embodiment provides a composite material for assisting the degradation of dye wastewater, which specifically comprises the following steps:

[0065] Step one, 0.01 mol of lanthanum nitrate and 0.01 mol of iron nitrate were dissolved in 40 mL of deionized water, mixed uniformly, 40 mL of citric acid with a concentration of 0.5 mol / L was added, and ultrasonic was performed at a frequency of 35 kHz for 40 min to obtain a metal salt mixed solution;

[0066] Step two, the metal salt mixed solution was transferred to a polytetrafluoroethylene lined stainless steel autoclave, and hydrothermal reaction was performed at 0.65 MPa and 170℃ for 13 h, cooled to room temperature, centrifuged at a speed of 500 rpm for 10 min, the supernatant was discarded, the obtained solid material was washed with 30 mL of deionized water and anhydrous ethanol alternately for 4 times, and dried at 70℃ for 4 h to obtain a metal salt precipitate;

[0067] Step three, the metal salt precipitate was once calcined at 500℃ for 3 h at a heating rate of 3℃ / min, and then twice calcined at 700℃ for 3 h at a heating rate of 2℃ / min, cooled to room temperature, ground, and lanthanum ferrite powder was obtained;

[0068] Step four, 0.05 mol of iron chloride and 0.15 mol of cobalt chloride were mixed and dissolved in 50 mL of deionized water to obtain solution A; 0.1 g of the lanthanum ferrite powder was dispersed in 50 mL of deionized water to obtain a suspension;

[0069] Step five, the solution A, the suspension and 0.8 mol / L of sodium hydroxide solution were mixed uniformly at a mass ratio of 1:1:0.9, the pH of the mixed solution was controlled at 9.3, and the mixed solution was continuously stirred at room temperature for 1 h, and then aged at 70℃ for 20 h. The obtained solid material was washed with anhydrous ethanol and deionized water alternately for 5 times, and dried at 70℃ for 12 h to obtain the composite material LDH for assisting degradation of dye wastewater. 0.1 LFO.

[0070] Example 2

[0071] The embodiment provides a composite material for assisting degradation of dye wastewater, and specifically comprises the following steps:

[0072] Step one, 0.008 mol of lanthanum nitrate and 0.009 mol of iron nitrate were dissolved in 40 mL of deionized water, mixed uniformly, 36 mL of citric acid with a concentration of 0.5 mol / L was added, and ultrasonic was performed at a frequency of 35 kHz for 30 min to obtain a metal salt mixed solution;

[0073] Step two, transfer the metal salt mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave, and perform hydrothermal reaction at 0.7 MPa and 160°C for 13 h, cool to room temperature, centrifuge at a speed of 500 rpm for 10 min, discard the supernatant, and wash the obtained solid material with 35 mL of deionized water and anhydrous ethanol alternately for 4 times, and dry at 70°C for 5 h to obtain a metal salt precipitate;

[0074] Step three, increase the temperature of the metal salt precipitate to 480°C at a rate of 2°C / min, and perform first calcination for 3.5 h, then increase the temperature to 650°C at a rate of 3°C / min, and perform second calcination for 4 h, cool to room temperature, and grind to obtain lanthanum ferrite powder;

[0075] Step four, mix 0.06 mol of iron chloride and 0.18 mol of cobalt chloride, and dissolve in 50 mL of deionized water to obtain solution A; and disperse 0.2 g of the lanthanum ferrite powder in 50 mL of deionized water to obtain a suspension;

[0076] Step five, mix the solution A, the suspension, and a 0.8 mol / L sodium hydroxide solution in a mass ratio of 1:1:1, control the pH of the mixed solution to be 9.4, continuously stir at room temperature for 1 h, then age at 65°C for 24 h, centrifuge at a speed of 7000 rpm for 6 min, discard the supernatant, wash the obtained solid material with anhydrous ethanol and deionized water alternately for 5 times, and dry at 75°C for 10 h to obtain the composite material LDH for assisting degradation of dye wastewater 0.2 LFO.

[0077] Example 3

[0078] The embodiment provides a composite material for assisting degradation of dye wastewater, and specifically comprises the following steps:

[0079] Step one, dissolve 0.01 mol of lanthanum nitrate and 0.01 mol of iron nitrate in 40 mL of deionized water, mix uniformly, add 20 mL of citric acid with a concentration of 0.5 mol / L, and ultrasonic at a frequency of 35 kHz for 40 min to obtain a metal salt mixed solution;

[0080] Step two, transfer the metal salt mixed solution to a polytetrafluoroethylene-lined stainless steel autoclave, and perform hydrothermal reaction at 0.8 MPa and 170°C for 13 h, cool to room temperature, centrifuge at a speed of 500 rpm for 10 min, discard the supernatant, and wash the obtained solid material with 30 mL of deionized water and anhydrous ethanol alternately for 4 times, and dry at 70°C for 4 h to obtain a metal salt precipitate;

[0081] Step three, the metal salt precipitate is calcined at 520℃ for 2.5h at a temperature increasing rate of 3℃ / min, then is calcined at 750℃ for 2h at a temperature increasing rate of 3℃ / min, is cooled to room temperature, is ground, and lanthanum ferrite powder is obtained;

[0082] Step four, 0.05mol of iron chloride and 0.15mol of cobalt chloride are mixed and dissolved in 50mL of deionized water to obtain solution A; 0.3g of the lanthanum ferrite powder is dispersed in 50mL of deionized water to obtain a suspension;

[0083] Step five, the solution A, the suspension and 0.8mol / L of sodium hydroxide solution are uniformly mixed at a mass ratio of 1:1:1.2, the pH of the mixed solution is controlled to be 9.2, stirring is continuously performed at room temperature for 1h, aging is performed at 80℃ for 18h, centrifugation is performed at a rotating speed of 8000rpm for 4min, the supernatant is discarded, the obtained solid substance is washed with anhydrous ethanol and deionized water alternately for 5 times, and drying is performed at 70℃ for 12h, and the composite material LDH for assisting degradation of dye wastewater is obtained 0.3 LFO.

[0084] Comparative example 1

[0085] The present comparative example provides a composite material for assisting degradation of dye wastewater, which is different from example 2 in that the composite material is lanthanum ferrite, and specifically comprises the following steps:

[0086] Step one, 0.008mol of lanthanum nitrate and 0.009mol of iron nitrate are dissolved in 40mL of deionized water, are uniformly mixed, 36mL of citric acid with a concentration of 0.5mol / L is added, and ultrasonic treatment is performed at a frequency of 35kHz for 30min, and a metal salt mixed solution is obtained;

[0087] Step two, the metal salt mixed solution is transferred to a polytetrafluoroethylene-lined stainless steel autoclave, a hydrothermal reaction is performed at 0.7MPa and 160℃ for 13h, is cooled to room temperature, centrifugation is performed at a rotating speed of 500rpm for 10min, the supernatant is discarded, the obtained solid substance is washed with 35mL of deionized water and anhydrous ethanol alternately, and washing is performed 4 times, and drying is performed at 70℃ for 5h, and a metal salt precipitate is obtained;

[0088] Step three, the metal salt precipitate is calcined at 520℃ for 2.5h at a temperature increasing rate of 3℃ / min, then is calcined at 750℃ for 2h at a temperature increasing rate of 3℃ / min, is cooled to room temperature, is ground, and lanthanum ferrite powder is obtained;

[0089] Step four, 0.2g of the lanthanum ferrite powder is dispersed in 50mL of deionized water to obtain a suspension;

[0090] Step five, the suspension and 0.8 mol / L sodium hydroxide solution are mixed uniformly at a mass ratio of 1:1, the pH of the mixed solution is controlled at 9.4, stirring is continued at room temperature for 1 h, aging is carried out at 65℃ for 24 h, centrifugation is carried out at a speed of 7000 rpm for 6 min, the supernatant is discarded, the obtained solid material is washed with anhydrous ethanol and deionized water alternately for 5 times, and drying is carried out at 75℃ for 10 h, to obtain the composite material LFO for assisting degradation of dye wastewater.

[0091] Comparative example 2

[0092] The present comparative example provides a composite material for assisting degradation of dye wastewater, which is different from example 2 in that the composite material is a layered iron-cobalt hydrotalcite material, and specifically comprises the following steps:

[0093] Step one, 0.06 mol of iron chloride and 0.18 mol of cobalt chloride are mixed and dissolved in 50 mL of deionized water to obtain an A solution;

[0094] Step two, the A solution and 0.8 mol / L sodium hydroxide solution are mixed uniformly at a mass ratio of 1:1, the pH of the mixed solution is controlled at 9.4, stirring is continued at room temperature for 1 h, aging is carried out at 65℃ for 24 h, centrifugation is carried out at a speed of 7000 rpm for 6 min, the supernatant is discarded, the obtained solid material is washed with anhydrous ethanol and deionized water alternately for 5 times, and drying is carried out at 75℃ for 10 h, to obtain the composite material LDH for assisting degradation of dye wastewater.

[0095] In order to further embody the technical effect of the present application, the composite materials obtained in examples and comparative examples 1-2 are tested for degradation of azo dye wastewater, the specific test steps are as described in the test example, the test instrument is a UV-2700 ultraviolet spectrophotometer of Shimadzu Enterprise Management (China) Co., Ltd., and the test results are shown in Table 1.

[0096] Test example

[0097] S1, 50 mg of the composite material is added into 100 mL of 200 mg / L azo dye aqueous solution, stirring is carried out in the dark for 30 min, so that the composite material and the pollutants in the azo dye reach adsorption-desorption equilibrium, to obtain a mixed wastewater solution;

[0098] S2, the mixed wastewater solution is placed under visible light, 200 mg of persulfate is added, a xenon lamp (λ≥420 nm, output light intensity 302.6 mW / cm 2 ) is started, and a degradation reaction is carried out, during the reaction process, 2 mL of reaction sample is taken every 5 min, quenched with 5 mL of methanol, filtered with a 0.45 μm syringe, the concentration of azo dye is analyzed at 521.4 nm by ultraviolet-visible absorption spectrum, and the photocatalytic efficiency is evaluated;

[0099] The azo dye may be any one of Acid Red (AR27), Methylene Blue (MB), or Crystal Violet (CV).

[0100] Table 1. Test results of wastewater from the degradation of azo dyes in each example and comparative example.

[0101]

[0102]

[0103] As can be seen from Table 1, the LDH@ provided in Embodiments 1-3 of this invention 0.1 LFO, LDH@ 0.2 LFO and LDH@ 0.3 LFO has a significant catalytic effect on assisting the degradation of dye wastewater by persulfate, especially the LDH@ obtained in Example 2. 0.2 LFO can degrade Acid Red to a residual rate of only 0.111, Methylene Blue to a residual rate of only 0.051, and Crystal Violet to a residual rate of only 0.071 within 30 minutes.

[0104] The present invention also conducted XRD tests and analyses on the composite materials obtained in Examples 1-3 and Comparative Examples 1-2, and the results are as follows: Figure 1 As shown. According to Figure 1 It can be seen that LDH@ with different lanthanum ferrite doping levels 0.1 LFO, LDH@ 0.2 LFO and LDH@ 0.3 The XRD curve of LFO shows characteristic peaks of both LDH and LFO, indicating that the two materials have been successfully combined.

[0105] according to Figure 2 It can be seen that the composite material LDH@ obtained in Example 2 0.2 LFO exhibits a structural morphology characterized by an interweaving of spherical and lamellar particles, representing a composite state of lanthanum ferrite and hydrotalcite. The lattice spacing revealed by high-magnification transmission electron microscopy (TEM) images shows that LDH@ 0.2 The LFO has a spacing of 0.24 nm between the hydrotalcite (012) crystal planes and 0.28 nm between the lanthanum ferrite (121) crystal planes, which also indicates the successful composite of hydrotalcite and lanthanum ferrite materials.

[0106] To further confirm that the composite material provided by this invention is a pn heterojunction structure of hydrotalcite and lanthanum ferrite, the photoelectric properties of the obtained composite material were tested, and the results are as follows: Figure 3 and Figure 4 As shown. According to Figure 3 and Figure 4It can be seen that the photoelectric performance of the composite material provided by the embodiment of the present application is better than that of single hydrotalcite and lanthanum ferrite material, and it is proved that the hydrotalcite is an n-type semiconductor, and the lanthanum ferrite is a p-type semiconductor, and the energy band structures of the two materials have the condition of forming a p-n heterojunction.

[0107] The present application further studies and compares the effects of the composite materials obtained in Examples 1-3 on the degradation of different azo dyes (acid red, methylene blue and crystal violet) assisted by persulfate photocatalysis, as shown in Table 1. Figure 4 As shown in Table 2. Figure 4 It is not difficult to see that the composite material provided by the embodiment of the present application can basically reach the degradation end point within 15 minutes, and the degradation effect is greater than 80%.

[0108] The present application also tests the LDH 0.2 The LFO provided by Example 2, the LFO provided by Comparative Example 1 and the LDH provided by Comparative Example 2 are tested for the degradation of acid red dye assisted by persulfate in the dark and under visible light, and the residual rate of the obtained acid red dye is shown in Table 2 and Figure 3 .

[0109] Table 2 Test results of the composite materials obtained in Examples 2 and Comparative Examples 1-2 under the assistance of dark and visible light

[0110]

[0111]

[0112] According to Table 2 and Figure 5 It can be seen that the composite material LDH 0.2 LFO provided by Example 2 has better performance than the composite material LFO obtained in Comparative Example 1 and the composite material LDH obtained in Comparative Example 2 in the degradation of acid red dye assisted by persulfate in the dark or under visible light. According to Table 2, when the composite material LFO obtained in Comparative Example 1 is added in the dark, the degradation rate of acid red assisted by persulfate is less than 5%, and after lightening, it increases to 29.9%, which shows that LFO is a visible light catalyst, and the activation of persulfate under light can produce reactive oxygen to degrade acid red. The composite material LDH obtained in Comparative Example 2 has little difference in the assisted degradation effect in the dark and under visible light, and both can assist persulfate to degrade about 90% of acid red in 25 minutes. While the composite material LDH 0.2 LFO obtained in Example 2 has a removal rate of 92.3% for AR27 in 30 minutes, which shows that the existence of metal active sites can promote the degradation of LDH 0.2 LFO to activate persulfate, thereby promoting the degradation of dye wastewater.

[0113] For the practical application of the multi-phase photocatalyst, durability and stability are key factors. The improvement of the recycling performance is also one of the key research directions of catalyst modification. In order to explore the reuse performance of the composite material obtained in the application, the composite material obtained in example 2 is assisted by persulfate to degrade acid red to carry out a cycle experiment, the reusability of LDH@LFO is studied, and the results are shown in Figure 6 As can be seen from Figure 6 It is not difficult to see that after each operation of the composite material obtained in example 2 of the application, the used photocatalyst is recovered by centrifugal filtration and distilled water washing, and has good performance. After 4 cycles, the photocatalyst can still assist persulfate to completely oxidize and degrade acid red dye wastewater within 30 min.

[0114] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement or improvement made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A composite material for assisting degradation of dye wastewater, characterized by: The composite material comprises nano lanthanum ferrite and cobalt-iron hydrotalcite loaded on the surface of the nano lanthanum ferrite, and the nano lanthanum ferrite and the cobalt-iron hydrotalcite form a p-n heterojunction structure. The preparation method of the composite material for assisting degradation of dye wastewater comprises the following steps: Step one, dissolving a soluble lanthanum salt and a soluble iron salt in deionized water, adding an organic acid, and mixing uniformly to obtain a metal salt mixed solution; Step two, performing hydrothermal reaction on the metal salt mixed solution at 0.6-0.8 MPa, cooling, centrifuging, washing, and drying to obtain a metal salt precipitate; Step three, once calcining the metal salt precipitate at 480-520 DEG C for 2.5-3.5 h, then performing secondary calcination by increasing the temperature to 650-750 DEG C, and cooling to obtain lanthanum ferrite powder; Step four, dissolving a soluble iron salt and a soluble cobalt salt in deionized water to obtain an A solution; Dispersing the lanthanum ferrite powder in deionized water to obtain a suspension; Step five, mixing the A solution and the suspension uniformly, adjusting the pH value to 9.2-9.5, aging, centrifuging, washing, and drying to obtain the composite material for assisting degradation of dye wastewater.

2. A process for the preparation of a composite material for the assisted degradation of dye effluents as claimed in claim 1, characterized in that: Comprise the following steps: Step one, dissolving a soluble lanthanum salt and a soluble iron salt in deionized water, adding an organic acid, and mixing uniformly to obtain a metal salt mixed solution; Step two, performing hydrothermal reaction on the metal salt mixed solution at 0.6-0.8 MPa, cooling, centrifuging, washing, and drying to obtain a metal salt precipitate; Step three, once calcining the metal salt precipitate at 480-520 DEG C for 2.5-3.5 h, then performing secondary calcination by increasing the temperature to 650-750 DEG C, and cooling to obtain lanthanum ferrite powder; Step four, dissolving a soluble iron salt and a soluble cobalt salt in deionized water to obtain an A solution; Dispersing the lanthanum ferrite powder in deionized water to obtain a suspension; Step five, mixing the A solution and the suspension uniformly, adjusting the pH value to 9.2-9.5, aging, centrifuging, washing, and drying to obtain the composite material for assisting degradation of dye wastewater.

3. The method for preparing the composite material for assisting in the degradation of dye wastewater as described in claim 2, characterized in that: In step one, the soluble lanthanum salt is lanthanum nitrate; and / or In step one, the soluble iron salt is any one of ferric nitrate or ferric chloride; and / or In step one, the organic acid is a citric acid aqueous solution with a concentration of 0.25 mol / L-0.5 mol / L, and the molar ratio of La 3+ , Fe 3+ and citric acid in the mixed solution of metal salts is 0.9-1.1:1:

2.

4. The method for preparing the composite material for assisting in the degradation of dye wastewater as described in claim 2, characterized in that: In step two, the temperature of the hydrothermal reaction is 160-180 DEG C, and the reaction time is 12-14 h; and / or In step three, the secondary calcination time is 2-4 h.

5. The method for preparing the composite material for assisting in the degradation of dye wastewater as described in claim 2, characterized in that: In step three, the first calcination and the second calcination are both performed by increasing the temperature in a programmed manner, wherein the first calcination is increased at a rate of 2-4 DEG C / min, and the second calcination is increased at a rate of 1-3 DEG C / min.

6. The method for preparing the composite material for assisting in the degradation of dye wastewater as described in claim 2, characterized in that: In step four, the molar ratio of Fe 3+ and Co 2+ in the A solution is 0.5-0.6:1.5-1.8; and / or In step four, the mass concentration of the lanthanum ferrite powder in the suspension is 3-4 g / L; and / or In step five, the mass ratio of the A solution to the suspension is 1:1-1:1.

2.

7. Use of the composite material for the degradation of dye wastewater as claimed in claim 1 in catalytic persulfate degradation of dye wastewater, characterized in that: Comprise the following steps: S1, mixing the composite material and dye wastewater uniformly in a dark environment to obtain a mixed wastewater solution; S2, placing the mixed wastewater solution under visible light, adding persulfate, and performing photocatalytic degradation.

8. Use of the composite material according to claim 7 for catalytic persulfate degradation of dye wastewater, characterized by: In S1, the mass-volume ratio of the composite material to the dye wastewater is 1 mg:(1.9-2.1) mL; and / or In S1, the mass concentration of the dye in the dye wastewater is ≥100 mg / L.

9. Use of the composite material according to claim 7 for catalytic persulfate degradation of dye wastewater, characterized by: In S2, the mass ratio of the persulfate salt to the composite material is 4:1-4:1.1; and / or In S2, the light source of the visible light is a xenon lamp, the wavelength of the xenon lamp is ≥420nm, and the output light intensity of the xenon lamp is ≥302.6mW / cm 2 .

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