Preparation method of biomass cellulose carbon aerogel loaded iron-copper bimetallic catalyst

Abstract

The invention discloses a preparation method of a biomass cellulose carbon aerogel loaded iron-copper bimetallic catalyst. The method comprises the following steps: (1) cleaning, drying, crushing and sieving a biomass raw material to obtain biomass powder, carrying out alkali washing with a NaOH solution, bleaching with sodium chlorite and acetic acid, washing with a hydrochloric acid solution, washing with water, and drying to obtain cellulose powder; (2) dispersing the cellulose powder in a low-temperature mixed solution of sodium hydroxide and urea, stirring and cooling for multiple times to obtain a clear and transparent suspension, and adjusting the suspension to be neutral with hydrochloric acid; and (3) pouring the mixture into a forming mold for suction filtration forming, and freeze-drying for a period of time to obtain the cellulose aerogel. (4) dipping a certain amount of cellulose aerogel in an ethanol solution of ferric nitrate and copper nitrate in a certain mixing ratio, carrying out ultrasonic treatment for a certain time, and drying in a vacuum drying oven; and calcining at high temperature in N2 to obtain the cellulose carbon aerogel loaded iron-copper bimetallic catalyst. (6) the catalyst has excellent Fenton-like catalytic degradation performance on high-concentration rhodamine B (200-1000ppm), and the required catalyst and hydrogen peroxide are low in concentration; the degradation rate of the rhodamine B solution with the concentration of 600ppm in 30 minutes is 90% or above, and the degradation effect on methylene blue, tetracycline hydrochloride, methyl orange, Congo red, coomassie brilliant blue and the like is good.

Description

Technical Field

[0001] The present invention relates to a preparation method of a biomass cellulose carbon aerogel supported iron-copper bimetallic heterogeneous Fenton catalyst, belonging to the technical field of catalyst design and preparation. Background Art

[0002] Printing and dyeing wastewater has complex components and a large discharge volume, and is one of the main water pollution sources. High-concentration printing and dyeing wastewater has the characteristics of high concentration, high toxicity, and difficult biodegradation. At present, the treatment of high-concentration printing and dyeing wastewater faces the problems of low efficiency and high cost. If only the treatment process for medium- and low-concentration wastewater is used, it will lead to problems such as a significant decrease in treatment efficiency and a significant increase in treatment cost.

[0003] Fenton catalysts utilize Fe(II) ions to catalyze the decomposition of H2O2 to generate extremely oxidizing hydroxyl radicals (·OH, oxidation potential up to 2.8 eV) and oxygen anion radicals (·O2 - , oxidation potential of 1.73 eV), and have good catalytic oxidation ability for various organic substances, so they are widely used in the treatment of refractory wastewater. Heterogeneous Fenton-like catalysts overcome the deficiencies of homogeneous Fenton catalysts such as difficult separation, large amounts of newly generated iron mud, and narrow applicable pH range. Some of the supported multi-metal Fenton-like catalysts even exhibit better catalytic activity and stability than single-metal iron-based Fenton-like catalysts. Agricultural and forestry waste such as corn cobs is mainly composed of biological macromolecules such as cellulose, hemicellulose, pectin (galacturonic acid), and lignin. Among them, cellulose has a high content and stable properties, and cellulose contains abundant hydroxyl groups, which can be used as anchoring groups for loading iron and copper metals and their oxides, greatly reducing the surface energy of its nanocrystalline particles and effectively inhibiting nanoparticle aggregation. As an excellent biomass cellulose carrier, it can be used to load multi-metals to prepare highly efficient heterogeneous Fenton catalysts.

[0004] The present invention prepares a carbon aerogel carrier using corn cobs as raw materials, and successfully synthesizes a heterogeneous Fenton-like catalyst Fe / Cu@CA by impregnation and calcination to load iron and copper bimetals. Physical property characterizations of the catalyst and its related control samples are carried out in detail by analytical methods such as SEM, TEM, ICP-AES, and XRD. The experimental results show that Fe / Cu@CA with a low catalyst concentration (0.1 g / L) can efficiently catalyze the Fenton-like oxidation degradation of high-concentration (1000 ppm) rhodamine B (RhB), and the degradation rate is as high as 93.7% after 1 h of reaction. The purpose of the present invention is to develop a low-cost biomass cellulose carbon supported iron-copper bimetallic heterogeneous Fenton catalyst, which has the advantages of simple process, high catalytic activity, large treatment capacity, and low cost, and can be used to effectively degrade high-concentration printing and dyeing wastewater and achieve multiple recycling. Summary of the Invention

[0005] The present invention uses corn cob as a biomass raw material to prepare a cellulose aerogel carrier, and loads iron and copper bimetals by the impregnation-calcination method to synthesize a heterogeneous Fenton-like catalyst, which has excellent catalytic degradation effect on organic matters such as rhodamine B. The catalyst of the present invention is prepared by the following steps:

[0006] (1) First, clean, dry, crush, and sieve the biomass raw material to obtain biomass cellulose powder, denoted as CC.

[0007] (2) Place the above CC and NaOH solution in a three-necked flask, heat it to a constant temperature using an oil bath and maintain magnetic stirring; let it stand and discard the supernatant, and repeatedly wash the product with deionized water until the supernatant is neutral. Put the obtained product, NaClO2, acetic acid, and deionized water into the three-necked flask, heat it to a constant temperature again and maintain stirring, let it stand and separate to obtain a solid, and wash it with deionized water until it is neutral. The product is dispersed in a hydrochloric acid solution, and the inorganic salts and other impurities in the cellulose are removed by stirring. Then wash it to neutral and dry to obtain cellulose powder.

[0008] (3) Weigh NaOH and urea and dissolve them in deionized water, and cool the solution in a freezer for a certain time; dissolve the cellulose powder in the alkaline solution and stir, and then cool it again. Repeat the process of "stirring and cooling" until the solution is slightly viscous and clear and transparent. Pour the cellulose solution into deionized water and stir slowly. Let it stand and discard the supernatant, and adjust the pH value of the remaining solution to neutral with hydrochloric acid to obtain a well-dispersed cellulose suspension.

[0009] (4) Pour the cellulose suspension into a forming mold for suction filtration to form, place it in liquid nitrogen for freezing, and then put it into a vacuum freeze dryer for freeze drying for a period of time to obtain a cellulose aerogel.

[0010] (5) Weigh a certain mixing ratio of iron nitrate and copper nitrate and dissolve them in an ethanol solution, immerse a certain amount of cellulose aerogel in the salt solution for ultrasonic treatment, and put the impregnated aerogel into a vacuum drying oven for drying treatment.

[0011] (6) Put the dried aerogel into a tube furnace and calcine it in an N2 atmosphere. After the tube furnace cools to room temperature, grind the calcined aerogel into powder, denoted as Fe / Cu@CA.

[0012] Preferably, in step (1), the biomass raw material is one of corn cob, pomelo peel or coconut shell, the drying condition is to keep it in an oven at 50-70 °C for 12-48 h, and the mesh number of the sieve used is 60-100.

[0013] Preferably, in step (2), the mass fraction of the NaOH solution used is 5%-10%, the heating method is to keep the oil bath at a constant temperature of 80-90 °C, and the duration of maintaining magnetic stirring is 3-6 h.

[0014] Preferably, in step (3), the mass of NaOH is 7 - 10 g, the mass of urea is 10 - 15 g, the deionized water is 60 - 100 mL, the cooling time is 5 - 10 min, and the concentration of hydrochloric acid is 3 - 7 mol / L. The deionized water used to dilute the cellulose solution is 1000 - 2000 mL.

[0015] Preferably, in step (4), the liquid nitrogen freezing duration is 3 - 10 min, and the freeze-drying duration is 24 - 72 h.

[0016] Preferably, in step (5), the mass ratio of iron nitrate to copper nitrate is 0.5 - 1.5, the volume of ethanol used to dissolve iron nitrate and copper nitrate is 50 - 100 mL, the mass of the cellulose aerogel is 0.5 - 1.0 g, the ultrasonic duration is 10 - 30 min, the drying temperature under vacuum conditions is 40 - 60 °C, and the duration is 10 - 30 min.

[0017] Preferably, in step (6), the heating rate of the tubular furnace is 2 - 10 °C / min, the high-temperature range is 600 - 800 °C, and the calcination time is 1 - 3 h.

[0018] Compared with the prior art, the main innovation points of the present invention are as follows: Utilizing the characteristic that agricultural and forestry waste is rich in cellulose, a biomass cellulose aerogel carrier is developed. After impregnating with an iron and copper metal salt solution and calcining at high temperature, a biomass cellulose carbon-supported iron and copper bimetallic catalyst is obtained. Compared with traditional carbon-based supported single-metal heterogeneous Fenton catalysts, this catalyst has higher catalytic activity and cyclic stability, is applicable to the degradation of high-concentration (1000 ppm) rhodamine B, and has good effects on the catalytic degradation of up to 8 kinds of organic pollutants. The catalytic oxidation reaction conforms to the first-order kinetic model, and a catalytic mechanism of Cu(0) substitution accelerating Fe(II) regeneration is proposed, which greatly improves the generation rate of oxidative active species (mainly ·OH). This method involves inexpensive and easily available raw materials, can greatly reduce the production cost of the catalyst, and the preparation method meets the development concept of green environmental protection, laying a foundation for large-scale industrial application. Description of the Drawings

[0019] Figure 1 a is the scanning electron microscope photograph of the catalyst Cu@CA prepared in Comparative Example 1, Figure 1 b is the scanning electron microscope photograph of the catalyst Fe@CA prepared in Comparative Example 2; Figure 1 c is the scanning electron microscope photograph of the catalyst Fe / Cu@CA prepared in Example 1.

[0020] Figure 2a is the TEM image of Fe / Cu@CA-600; Figure 2b and 2cHRTEM image of local nanoparticles of Fe / Cu@CA-600 Figure 2d -g is the elemental surface scan image of Fe / Cu@CA-600

[0021] Figure 3 is the X-ray diffraction pattern of the catalyst

[0022] Figure 4 is the comparison of catalytic performance of different catalysts

[0023] Figure 5 is the cyclic performance test of Fe / Cu@CA-600

[0024] Figure 6 is the degradation effect of Fe / Cu@CA-600 on tetracycline hydrochloride (TCH), oxytetracycline hydrochloride (OCH), coomassie brilliant blue (CBB), basic fuchsin (BF), congo red (CR), methyl orange (MO), methylene blue (MB), rhodamine B Detailed implementation manners

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention

[0026] Comparative Example 1: Copper loaded on biomass cellulose carbon aerogel Cu@CA

[0027] (1) The corn cob is washed, dried, crushed, and sieved to obtain biomass cellulose powder, denoted as CC

[0028] (2) Extract cellulose: A certain mass of CC and NaOH solution are placed in a three-necked flask for alkali washing, heated to a constant temperature with an oil bath and magnetically stirred; after standing, the supernatant is discarded, and the product is repeatedly washed with deionized water until the supernatant is neutral. The obtained product, NaClO2, acetic acid, and deionized water are put into a three-necked flask for acid washing, heated to a constant temperature and kept stirring, and after standing and separating, the solid is obtained and washed with deionized water until neutral. The product is dispersed in hydrochloric acid solution to remove inorganic salts and other impurities in the cellulose. The obtained cellulose is washed to neutral and then dried

[0029] (3) Dispersed cellulose: Weigh NaOH and urea and dissolve them in deionized water. Place the solution in a freezer to cool for a certain period of time. Dissolve the cellulose powder in the alkaline solution and keep stirring. Then cool it again. Repeat the process of "stirring and cooling" until the solution is slightly viscous, clear and transparent. Pour the cellulose solution into deionized water and keep stirring slowly. Let it stand and discard the supernatant. Adjust the pH value of the remaining solution to neutral with hydrochloric acid to obtain a well-dispersed cellulose suspension.

[0030] (4) Freeze-dried cellulose: Pour the cellulose suspension into a forming mold for suction filtration to form a shape. Place it in liquid nitrogen for freezing, and then put it into a vacuum freeze dryer for freeze-drying for a period of time to obtain a cellulose aerogel.

[0031] (5) Weigh 1.66 g of copper nitrate trihydrate and dissolve it in 50 mL of ethanol solution. Immerse about 0.6 g of cellulose aerogel in the solution and sonicate for 20 min. The impregnated aerogel is placed in a vacuum drying oven at 50 °C for drying for 20 min.

[0032] (6) Put the dried aerogel into a tube furnace. Heat it up to 600 °C at a heating rate of 5 °C / min in an N2 atmosphere and keep the carbonization temperature for 2 h. After the tube furnace cools down to room temperature, grind the calcined aerogel into powder, denoted as Cu@CA.

[0033] Comparative Example 2: Biomass cellulose carbon aerogel supported iron Fe@CA

[0034] (1) Wash the corn cob, dry it, crush it, and sieve it to obtain biomass cellulose powder, denoted as CC.

[0035] (2) Extract cellulose: Place a certain mass of CC and NaOH solution in a three-necked flask for alkali washing. Use an oil bath to heat to a constant temperature and keep magnetic stirring. Let it stand and discard the supernatant. Wash the product repeatedly with deionized water until the supernatant is neutral. Put the obtained product, NaClO2, acetic acid and deionized water into the three-necked flask for acid washing. Heat to a constant temperature and keep stirring. Let it stand and separate to obtain a solid, and wash it with deionized water until neutral. The product is dispersed in hydrochloric acid solution to remove inorganic salts and other impurities in the cellulose. Wash the obtained cellulose until neutral and then dry it.

[0036] (3) Dispersed cellulose: Weigh NaOH and urea and dissolve them in deionized water. Place the solution in a freezer to cool for a certain period of time. Dissolve the cellulose powder in the alkaline solution and keep stirring. Then cool it again. Repeat the process of "stirring and cooling" until the solution is slightly viscous, clear and transparent. Pour the cellulose solution into deionized water and keep stirring slowly. Let it stand and discard the supernatant. Adjust the pH value of the remaining solution to neutral with hydrochloric acid to obtain a well-dispersed cellulose suspension.

[0037] (4) Freeze-dried cellulose: Pour the cellulose suspension into a forming mold for suction filtration to form a shape, place it in liquid nitrogen for freezing, and then put it into a vacuum freeze dryer for freeze-drying for a period of time to obtain cellulose aerogel.

[0038] (5) Weigh 2 g of ferric nitrate nonahydrate and dissolve it in 50 mL of ethanol solution. Immerse about 0.6 g of cellulose aerogel into the solution and ultrasonicate for 20 min. The impregnated aerogel is placed in a vacuum drying oven at 50 °C and dried for 20 min.

[0039] (6) Put the dried aerogel into a tube furnace, heat it to 600 °C at a heating rate of 5 °C / min in an N2 atmosphere, and maintain the carbonization temperature for 2 h. After the tube furnace cools to room temperature, grind the calcined aerogel into powder, denoted as Fe@CA.

[0040] Example 1: Heterogeneous Fenton catalyst Fe / Cu@CA-600 with corn cob cellulose carbon aerogel supported iron and copper

[0041] (1) Crush the dry corn cob with a pulverizer, sieve the powder and place it in a wide-mouth reagent bottle for later use, hereinafter referred to as CC.

[0042] (2) Place 20 g of CC and 1000 mL of 5% NaOH solution by mass in a three-necked flask, and magnetically stir at a constant temperature in an 80 °C oil bath for 3 h; let it stand and discard the supernatant, and repeatedly wash the product with deionized water until the supernatant is neutral.

[0043] (3) Put the obtained product, 15 g of NaClO2, 5000 μL of acetic acid and 1000 mL of deionized water into a three-necked flask, magnetically stir at a constant temperature in an 80 °C oil bath for 3 h, let it stand for separation and wash the product with deionized water until neutral.

[0044] (4) Disperse the product in 2% hydrochloric acid solution and magnetically stir for 6 h to remove inorganic salts and other impurities in the cellulose. Wash the obtained cellulose to neutral and then dry it to obtain cellulose powder.

[0045] (5) Weigh 7 g of NaOH and 12 g of urea and dissolve them in 81 mL of deionized water. Put the solution in the refrigerator to cool for 5 min; dissolve 5 g of cellulose powder in the alkali solution and continuously stir, and then cool for 5 min again. Repeat the process of "stirring, cooling" until the solution is slightly viscous and clear and transparent.

[0046] (6) Pour the cellulose solution into 1500 mL of deionized water and keep stirring slowly. Let it stand and discard the supernatant, and adjust the pH value of the remaining solution to neutral with 6 mol / L hydrochloric acid to obtain a well-dispersed cellulose suspension.

[0047] (7) Pour the cellulose suspension into a mold, filter it to form a shape, place it in liquid nitrogen for freezing for 5 min, and then put it into a vacuum freeze dryer for freeze drying for 72 h to obtain a cellulose aerogel.

[0048] (8) Weigh 2.0173 g of ferric nitrate nonahydrate and 1.6643 g of copper nitrate trihydrate and dissolve them in 50 mL of an ethanol solution. Immerse about 0.6 g of the cellulose aerogel into the solution and ultrasonicate for 20 min. The impregnated aerogel is placed in a vacuum drying oven at 50 °C and dried for 20 min.

[0049] (9) Put the dried aerogel into a tube furnace, heat it up to 600 °C at a heating rate of 5 °C / min in an N2 atmosphere, and hold for 2 h. After the tube furnace cools down to room temperature, grind the calcined aerogel into a powder and denote it as Fe / Cu@CA-600.

[0050] Example 2: Heterogeneous Fenton catalyst Fe / Cu@CA-800 with corn cob cellulose carbon aerogel loaded with iron and copper

[0051] (1) Crush the dry corn cob with a pulverizer, sieve the powder and place it in a wide-mouth reagent bottle for later use, hereinafter referred to as CC.

[0052] (2) Place 20 g of CC and 1000 mL of a 5% NaOH solution by mass in a three-necked flask, and magnetically stir at a constant temperature in an 80 °C oil bath for 3 h; let it stand and discard the supernatant, and repeatedly wash the product with deionized water until the supernatant is neutral.

[0053] (3) Put the obtained product, 15 g of NaClO2, 5000 μL of acetic acid and 1000 mL of deionized water into a three-necked flask, magnetically stir at a constant temperature in an 80 °C oil bath for 3 h, let it stand for separation and wash the product with deionized water until neutral.

[0054] (4) Disperse the product into a 1 mol / L hydrochloric acid solution and magnetically stir for 6 h to remove inorganic salts and other impurities in the cellulose. After washing the obtained cellulose to neutral and drying it, cellulose powder is obtained.

[0055] (5) Weigh 7 g of NaOH and 12 g of urea and dissolve them in 81 mL of deionized water. Place the solution in a refrigerator to cool down for 5 min; dissolve 5 g of cellulose powder into the alkaline solution and continuously stir, and then cool down again for 5 min. Repeat the process of "stirring and cooling" until the solution is slightly viscous and clear and transparent.

[0056] (6) Pour the cellulose solution into 1500 mL of deionized water and keep stirring slowly. Let it stand and discard the supernatant, and adjust the pH value of the remaining solution to neutral with 6 mol / L hydrochloric acid, thus obtaining a well-dispersed cellulose suspension.

[0057] (7) Pour the cellulose suspension into a mold, filter it to form a shape, place it in liquid nitrogen for freezing for 5 min, and then put it into a vacuum freeze dryer for freeze drying for 24 h to obtain the cellulose aerogel.

[0058] (8) Weigh 2.0173 g of ferric nitrate nonahydrate and 1.6643 g of copper nitrate trihydrate and dissolve them in 50 mL of ethanol solution. Immerse about 0.6 g of the cellulose aerogel into the solution and ultrasonicate for 20 min. The impregnated aerogel is placed in a vacuum drying oven at 50 °C for drying for 20 min.

[0059] (9) Put the dried aerogel into a tube furnace, heat it up to 800 °C at a heating rate of 5 °C / min in an N2 atmosphere, and maintain the carbonization temperature for 2 h. After the tube furnace cools down to room temperature, grind the calcined aerogel into powder, denoted as Fe / Cu@CA-800.

[0060] Performance characterization of the material

[0061] (1) Morphology characterization (SEM and TEM)

[0062] Figure 1 The SEM photos shown respectively correspond to Comparative Example 1 ( Figure 1 a), Comparative Example 2 ( Figure 1 b), Example 1 ( Figure 1 c) scanning electron microscope photos. The structure of the catalyst Fe / Cu@CA-600 was characterized by transmission electron microscopy as shown in Figure 2a shown. The matrix has a layered structure, and a large number of nanoparticles are relatively evenly distributed on its rough surface, with a particle size of about 20 - 30 nm. The final existence forms of Fe and Cu were observed by HRTEM, as shown in Figure 2b and 2c shown. The lattice fringes of 0.602 nm and 0.210 nm correspond to the (110) plane of Fe3O4 and the (111) plane of Cu respectively, indicating that iron mainly exists in the form of Fe3O4 nanocrystals and copper mainly exists in the form of Cu elemental crystals. Figure 2d -g indicates that the catalyst contains elements such as carbon, iron, and copper.

[0063] Dissolve the catalyst in aqua regia, filter to remove the undissolved carbon, dilute with water, and make up the volume in a volumetric flask. Use inductively coupled plasma - atomic emission spectrometry ICP - AES to determine the contents of iron and copper in the sample to be 12.34 wt% and 16.51 wt% respectively.

[0064] (2) X - ray diffraction analysis (XRD)

[0065] The obtained catalyst samples were characterized by XRD. Scanning was performed from 5° to 80° at a rate of 5° / min, and the obtained diffraction peak data were input into the jade software to analyze its composition and crystal structure. The results are as Figure 3 shown. The XRD diffraction peaks are consistent with the characteristic diffraction peaks of Fe3O4 (PDF 19-0629) and Cu (PDF 04-0836) on the standard cards.

[0066] According to the XRD pattern, the (111), (220), (311), (422), (511), (440), (553) crystal planes of cubic Fe3O4 correspond to the diffraction peaks at 2θ = 18.23°, 30.03°, 35.39°, 53.40°, 56.93°, 62.52°, 74.03° respectively; the (111), (200) planes of cubic Cu correspond to the diffraction peaks at 2θ = 43.28°, 50.37° respectively.

[0067] (3) RhB dye degradation experiment

[0068] Into a RhB solution at 40 °C, 100 mL, 600 ppm, and pH = 2.5, 1 mL of 30% H2O2 and 10 mg of the catalyst were added. The results are as Figure 4 shown. Through the control experiment, the catalytic degradation performance of Fe / Cu@CA-600 and Fe / Cu@CA-800 is significantly better than that of Fe@CA and Cu@CA.

[0069] (4) Catalyst cycle stability experiment

[0070] In a RhB solution at 40 °C, 20 mL, 100 ppm, and pH = 2.5, 15 mg of Fe / Cu@CA-600 and 200 μL of H2O2 were added to the solution for the cycle performance test. To reduce the influence brought by the change of solution volume and catalyst mass, only 3 sampling points were set for each cycle. After the cycle ended, the catalyst samples were recovered by suction filtration. The results are as Figure 5 shown. The degradation rates and the degradation rates at 30 min in the first two cycles are basically the same. The reaction has basically completed the complete degradation of RhB at 5 min, and the degradation rates at 30 min are all above 99%. As the number of cycles increases, the degradation rate at 30 min gradually decreases. The reason may be the loss of active metals in Fe / Cu@CA-600 during the cycle. When the number of cycles reaches the ninth time, Fe / Cu@CA-600 can still degrade more than 75% of RhB within 30 min, indicating its good cycle stability.

[0071] (5) Degradation of other dyes

[0072] Respectively take 20 mL of rhodamine B, methylene blue, methyl orange, congo red, basic fuchsin, coomassie brilliant blue, tetracycline hydrochloride, and oxytetracycline hydrochloride solutions with a concentration of 100 ppm. Under the condition of a constant temperature water bath at 40 °C, add 5 mg of Fe / Cu@CA-600, 2 drops of 0.6 mol / L hydrochloric acid, and 200 μL of H2O2 to the solution for catalytic degradation. The reaction results after 1 h are as Figure 6 shown, indicating that Fe / Cu@CA-600 has good catalytic effects on the oxidation degradation systems of various organic compounds.

Claims

1. A method for preparing a biomass cellulose carbon aerogel-supported iron-copper bimetallic catalyst, comprising the following steps: (1) First, the biomass raw material is washed, dried, crushed, and sieved to obtain biomass cellulose powder, which is recorded as CC. (2) Extraction of cellulose: Place a certain amount of CC and NaOH solution in a three-necked flask for alkaline washing, heat to a constant temperature in an oil bath and maintain magnetic stirring; let stand and discard the supernatant, and repeatedly wash the product with deionized water until the supernatant is neutral. Place the obtained product, NaClO2, acetic acid and deionized water in a three-necked flask for acid washing, heat to a constant temperature and maintain stirring, let stand to separate the solid and wash it with deionized water until neutral. The product is dispersed in a hydrochloric acid solution to remove impurities such as inorganic salts in the cellulose. The obtained cellulose is washed to neutrality and then dried. (3) Dispersing cellulose: Weigh NaOH and urea and dissolve them in deionized water. Place the solution in a freezer and cool it down for a certain period of time. Dissolve the cellulose powder in the alkali solution and continue stirring. Then cool it down again. Repeat the "stirring and cooling" process until the solution is slightly viscous and clear. Pour the cellulose solution into deionized water and stir slowly. Let it stand and discard the supernatant. Use hydrochloric acid to adjust the pH value of the remaining solution to neutral to obtain a well-dispersed cellulose suspension. (4) Freeze-dried cellulose: The cellulose suspension is poured into a molding mold and filtered to form the suspension, frozen in liquid nitrogen, and then placed in a vacuum freeze dryer for freeze drying to obtain a cellulose aerogel. (5) Preparation of catalyst by loading metal: Weigh a certain ratio of iron nitrate and copper nitrate and dissolve them in an ethanol solution. Immerse a certain amount of cellulose aerogel in the solution and perform ultrasonic treatment. The impregnated aerogel is placed in a vacuum drying oven for drying. The catalyst is obtained by high-temperature calcination in N2. It is denoted as Fe / Cu@CA.

2. The preparation method according to claim 1, characterized in that: The biomass raw material is one of corn cobs, grapefruit peels or coconut shells. The drying condition is to keep it in an oven at 50-70° C. for 12-48 hours, and the mesh number of the screen used is 60-100.

3. The preparation method according to claim 1, characterized in that: The mass of biomass added during cellulose extraction is 10-30g; the mass fraction of NaOH solution used for alkali washing is 5%-10%; the mass of NaClO2 used for bleaching is 10-20g, and the volume of acetic acid is 3-10mL; the heating temperature for alkali washing and bleaching is 80-90℃ oil bath reflux, and magnetic stirring is 2-6h. The concentration of hydrochloric acid used for washing is 2-5wt%.

4. The preparation method according to claim 1, characterized in that: The mass of NaOH used to disperse cellulose is 7-10g, the mass of urea is 10-15g, the mass of deionized water is 60-100mL, the cooling time is 5-10min, the concentration of hydrochloric acid is 3-7mol / L, and the mass of deionized water used to dilute the cellulose solution is 1000-2000mL.

5. The preparation method according to claim 1, characterized in that: The liquid nitrogen freezing time used for freeze-dried cellulose is 3-10 minutes, and the freeze-drying time is 24-72 hours.

6. The preparation method according to claim 1, characterized in that: The mass ratio of ferric nitrate nonahydrate to copper nitrate trihydrate used for impregnation of metal salts is 0.5-1.5, the volume of ethanol is 50-100 mL, the mass of cellulose aerogel is 0.5-1.0 g, the ultrasonic duration is 10-30 min, the drying temperature under vacuum conditions is 40-60° C., the duration is 20-60 min. The heating rate of the tubular furnace is 2-10° C. / min, the calcination temperature is 600-800° C., and the calcination time is 1-3 h.

7. The preparation method according to claim 1, characterized in that: The size of the iron-copper bimetallic nanoparticles is 20-30 nm, and the content of iron and copper is 12-18 wt %.

8. The catalytic degradation reaction according to claim 1, characterized in that: The reaction temperature is 30-50° C., the concentration of rhodamine B is 200-1000 ppm, the pH is 2-3, and the molar concentration of hydrogen peroxide is 0.05-0.2 mol / L.

9. The catalytic degradation reaction according to claim 1, characterized in that: Fe / Cu@CA catalyzes the Fenton-like reaction, and the degradation rate of 600ppm rhodamine B solution is above 90% in 30min. It also has good degradation rates for methylene blue, methyl orange, Congo red, Coomassie brilliant blue, tetracycline hydrochloride, oxytetracycline hydrochloride, etc.

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