Method for preparing porous biochar through high-temperature carbonization of molten salt and application of porous biochar

Abstract

The invention discloses a preparation method for preparing a biomass porous carbon material through high-temperature carbonization of molten salt and application of the biomass porous carbon material, and belongs to the technical field of synthesis of inorganic functional materials. According to the technical scheme, the method is characterized in that sodium chloride and potassium chloride are mixed into mixed salt according to different proportions, then the mixed salt is mixed with enteromorpha biomass according to a certain proportion, the mixture is placed in a porcelain crucible, the mixed salt is added for covering, the porcelain crucible is placed in a muffle furnace to be heated and carbonized, and the porous biomass carbon material is obtained after water washing and drying. The enteromorpha biomass is selected as the raw material, the operation is simple and controllable, the cost is low, batch production can be realized, and the prepared novel porous biomass carbon material has a complex porous structure, a large specific surface area, a very good catalytic effect, strong adsorption capacity and good conductivity, and shows excellent performance when being applied to the field of advanced oxidation.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthesis of advanced oxidation catalytic materials, and specifically relates to a method for preparing porous biochar by high-temperature carbonization of molten salt and application thereof. Background Art

[0002] With the development of society, the application scope of antibiotics in human medicine and animal and plant medicine is becoming more and more extensive, resulting in the gradual aggravation of water pollution. Therefore, how to remove antibiotics efficiently and greenly is the focus of current research. At present, the main technologies for removing antibiotics are biological methods, photodegradation methods, physical methods, and chemical methods. Compared with several other removal methods, advanced oxidation technology has attracted the attention of scientists with its degradation rate and harmless products. In advanced oxidation technology, strong oxidizing substances are usually required, such as hydrogen peroxide (H2O2), persulfate (Na2S2O8), etc., but the (OH·) produced by H2O2 is easily quenched by inorganic ions, has a short survival time, and is also subject to the influence of pH, resulting in limitations in its application. In recent years, the free radicals (SO4·) produced by persulfate (Na2S2O8) - ) has attracted widespread attention, SO4· - Higher sensitivity to electron transfer oxidation reactions expands the range of pollutant conversion pathways. Current persulfate activation methods primarily utilize heat, ultraviolet light, ultrasound, transition metal ions, and alkali. However, heat and ultraviolet activation consume high energy, ultrasound activation is ineffective, and alkali activation requires altering the reaction pH to a strong alkaline state. Strong alkalis can corrode and damage equipment. Therefore, the development of green and efficient catalysts for persulfate activation is crucial.

[0003] Biochar (BC) is a carbonaceous material that is mostly made from agricultural and forestry waste. High-temperature pyrolysis decomposes large wood fiber molecules into small solid carbon molecules. The main component is carbon molecules, which are stable, porous, and high in organic matter. The material is widely available and inexpensive. It is mainly used for physical adsorption of heavy metals in soil and water. Furthermore, studies have shown that the oxygen-containing functional groups ·COOH and ·OH on the surface of biochar can effectively activate persulfate and produce a large amount of SO4· ... - , achieving the purpose of degrading organic pollutants. Currently, many biomass materials, such as crop waste (tobacco petioles, rice straw), seaweed waste (seaweed), and food waste (shells, banana peels), are used to prepare biochar materials. Biochar materials have also attracted widespread attention from scientists due to their simple preparation process and wide application. Therefore, it is necessary to develop more biomass materials that can be used to prepare biochar.

[0004] Enteromorpha is a genus of green algae, about 40 species, although no toxic but also can harm the ecosystem of large-scale breeding. As a biomass, biomass charcoal material has rich surface active groups and high specific surface area, has wide application value, the patent with publication number CN110255526A will fresh enteromorpha after cleaning, preforming, drying, carbonization to prepare a kind of biomass charcoal solar water evaporation material, it has long-range through hole, can strongly absorb sunlight and convert into heat energy, realize high efficiency solar water evaporation. Wei Du et al. pointed out that enteromorpha biomass charcoal can be used as high-efficiency supercapacitor electrode material; Mingbo Wu et al. used the enteromorpha in the South China Sea as raw material, and prepared an intestinal crystal supercapacitor with ZNO as activator. It was found through test that it had excellent electrochemical performance. Cheng Chen et al. prepared a Fe / N co-doped enteromorpha biomass charcoal, which was applied to the activation of peroxymonosulfate and the degradation of organic pollutants. Yanqing Wang et al. pointed out that enteromorpha biomass charcoal can be used as electrode material of lithium battery, which has excellent performance. As a biomass charcoal material, enteromorpha is widely studied by scholars, but the preparation method of biochar often needs inert gas protection, corrosive activator and high temperature treatment, which has the disadvantages of high production cost and complex production process. Therefore, it is of great significance to find a better preparation process of biomass activated carbon.

[0005] Molten salt method is a green preparation method without inert gas protection and corrosive activator. It mainly uses the template etching effect of molten salt to make pores in biomass, and prepare biomass charcoal material containing high specific surface area and rich oxygen-containing functional groups. The patent with publication number CN105314622A uses LiCl and KCl with a mass ratio of 59 / 41 to prepare biomass charcoal material. The patent with publication number CN108622895A prepares mixed salt with sodium alginate:KCl:ZnCl2=1:1.6~4.6:4.4~8.4, and then mixes it with biomass to prepare biomass charcoal material. In summary, molten salt method has great potential in preparing biomass charcoal material. SUMMARY

[0006] The present application provides a kind of cost low preparation process simple molten salt high temperature carbonization preparation porous biochar method. Raw material selects easy biomass, simple and controllable operation, low cost, can batch production, the new porous biomass charcoal material prepared, with complex porous structure, specific surface area, can be applied in many fields.

[0007] The present application provides a kind of cost low preparation process simple molten salt high temperature carbonization preparation porous biochar method. Raw material selects easy biomass, simple and controllable operation, low cost, can batch production, the new porous biomass charcoal material prepared, with complex porous structure, specific surface area, can be applied in many fields.

[0008] Step 1: The aquatic algae biomass is washed with tap water to remove the silt on the surface of the biomass, and then washed with secondary water for 3-4 times. After drying in a constant temperature drying oven at 50℃ for 24 hours, the biomass is crushed to obtain a biomass powder.

[0009] Step 2: The sodium chloride and potassium chloride are mixed in a ratio of 1:1-3:1 to form a low-melting-point mixed salt. The biomass powder and the low-melting-point mixed salt are mixed uniformly in a mass ratio of 1:2-1:4, and then the mixture is placed in a porcelain boat and covered with a 1cm layer of the low-melting-point mixed salt to obtain an intermediate product.

[0010] Step 3: The porcelain boat in Step 2 is placed in a muffle furnace and heated to 400-800℃ at a heating rate of 5-10℃ / min for 1-3 hours.

[0011] Step 4: The carbon material obtained by calcination is ultrasonically treated in 2M hydrochloric acid for 10 minutes, soaked overnight, washed with secondary water until neutral, and then dried in a drying oven to obtain a porous biomass carbon material.

[0012] Preferably, the aquatic algae biomass in Step 1 is Enteromorpha.

[0013] Preferably, the low-melting-point mixed salt in Step 2 is a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1.

[0014] Preferably, the mass ratio of the Enteromorpha biomass powder to the mixed salt in Step 2 is 7:15.

[0015] Preferably, the carbonization method in Step 3 is to heat to 700℃ at a heating rate of 10℃ / min for 1 hour.

[0016] The preparation method of the present application is simple and the reaction cost is low. The biomass carbon material prepared has a high specific surface area, abundant oxygen-containing functional groups, and provides good electron transport channels, thus showing good adsorption and catalytic performance, and has a wide application prospect in adsorption and advanced oxidation degradation of organic pollutants. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 SEM image of the biomass carbon material prepared by the molten salt method of Example 1.

[0018] Figure 2 TEM image of the biomass carbon material prepared by the molten salt method of Example 1. DETAILED DESCRIPTION

[0019] The above content of the present application is further described in detail through the following examples, but this should not be understood as limiting the scope of the above subject matter of the present application to only the following examples. Any technology realized based on the above content of the present application falls within the scope of the present application.

[0020] Example 1

[0021] Step 1: First, wash the surface of Enteromorpha with tap water to remove the mud and sand, then rinse with secondary water for 3 times, dry in a constant temperature drying oven at a temperature of 50℃ for 24h, then crush the biomass to obtain biomass powder.

[0022] Step 2: Mix sodium chloride and potassium chloride in a ratio of 1:1 to form a low-melting-point mixed salt, then mix the biomass powder and the low-melting-point mixed salt uniformly in a mass ratio of 7:15, and then place the mixture in a porcelain boat, cover it with 1cm of low-melting-point mixed salt to obtain an intermediate product.

[0023] Step 3: Place the porcelain boat in the muffle furnace and heat it to 700℃ at a heating rate of 10℃ / min for 1 hour.

[0024] Step 4: Ultrasonic the carbon material prepared in step 3 in 2M hydrochloric acid for 10 minutes, then soak it overnight, wash it with secondary water until it is neutral, and then dry it in a drying oven to obtain a porous biomass carbon material. Figure 1 The SEM image of the biomass carbon material prepared by the molten salt method in Example 1, as can be seen from the figure, the material contains multi-level pore structure (macropore, mesopore). Figure 2 The TEM image of the biomass carbon material prepared by the molten salt method in Example 1, as can be seen from the figure, the material not only has macropore and mesopore but also has micropore, this structure has large specific surface area, which is beneficial to expose more active sites, and can effectively activate persulfate.

[0025] Example 2

[0026] Step 1: First, wash the surface of Enteromorpha with tap water to remove the mud and sand, then rinse with secondary water for 3 times, dry in a constant temperature drying oven at a temperature of 50℃ for 24h, then crush the biomass to obtain biomass powder.

[0027] Step 2: Mix sodium chloride and potassium chloride in a ratio of 2:1 to form a low-melting-point mixed salt, then mix the biomass powder and the low-melting-point mixed salt uniformly in a mass ratio of 1:2, and then place the mixture in a porcelain boat, cover it with 1cm of low-melting-point mixed salt to obtain an intermediate product.

[0028] Step 3: Place the porcelain boat in the muffle furnace and heat it to 700℃ at a heating rate of 10℃ / min for 1 hour.

[0029] Step 4: Ultrasonic the carbon material prepared in step 3 in 2M hydrochloric acid for 10 minutes, then soak it overnight, wash it with secondary water until it is neutral, and then dry it in a drying oven to obtain a porous biomass carbon material.

[0030] Example 3

[0031] Step 1: First, wash away the mud and sand on the surface of the Enteromorpha with tap water, then rinse with secondary water three times, dry in a constant temperature drying oven at 50°C for 24 hours, and then crush the biomass to obtain biomass powder.

[0032] Step 2: Sodium chloride and potassium chloride are mixed in a ratio of 1:1 to form a low-melting-point mixed salt. Then, the biomass powder and the low-melting-point mixed salt are evenly mixed in a mass ratio of 7:15. The mixture is placed in a porcelain boat and covered with 1 cm of low-melting-point mixed salt to obtain an intermediate product.

[0033] Step 3: Place the porcelain boat prepared in step 2 in a muffle furnace and heat it to 600°C at a heating rate of 10°C / min for carbonization for 3 hours.

[0034] Step 4: Ultrasonicate the fired carbon material in 2M hydrochloric acid for ten minutes, soak it overnight, then wash it with water twice until it is neutral, and dry it in a drying oven to obtain a porous biomass carbon material.

[0035] Comparative Example

[0036] Step 1: First, wash away the mud and sand on the surface of the Enteromorpha with tap water, then rinse with secondary water three times, dry in a constant temperature drying oven at 50°C for 24 hours, and then crush the biomass to obtain biomass powder.

[0037] Step 2: Sodium chloride and potassium chloride are mixed in a ratio of 1:1 to form a low-melting-point mixed salt, the pure biomass powder is covered with 1 cm of the low-melting-point mixed salt, and then the mixture is placed in a porcelain boat to obtain an intermediate product.

[0038] Step 3: Place the porcelain boat prepared in step 2 in a muffle furnace and heat it to 700°C at a heating rate of 10°C / min for carbonization for 1 hour.

[0039] Step 4: Ultrasonicate the fired carbon material in 2M hydrochloric acid for ten minutes, soak it overnight, then wash it with water twice until it is neutral, and dry it in a drying oven to obtain a porous biomass carbon material.

[0040] The biochar produced in this example was used for the degradation of bisphenol A (20 mg / L) in water using a persulfate (potassium peroxydisulfate, 2 mmol / L) advanced oxidation method. With a carbon addition of 0.1 g / L and a reaction time of 1 hour, the bisphenol A degradation efficiency reached ~92%, significantly higher than that of the biochar produced in Example 1 (~78%), Example 3 (~67%), and the comparative example (~42%). This indicates that the biochar produced in Example 1, due to its high specific surface area, abundant active groups, and good electron transport channels, facilitates rapid electron transport, thereby exhibiting good catalytic activity.

[0041] The above examples describe the basic principles, main features and advantages of the present application, and those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made without departing from the principles of the present application, and such changes and improvements fall within the scope of the present application.

Claims

1. A method for preparing porous biochar by high-temperature carbonization of molten salt, characterized in that The specific steps are: Step 1: First, wash away the mud and sand on the surface of the aquatic algae biomass with tap water, then rinse with secondary water 3-4 times, dry in a constant temperature drying oven at 50°C for 24 hours, and then crush the biomass to obtain biomass powder. Step 2: Sodium chloride and potassium chloride are mixed in a ratio of 1:1-3:1 to form a low-melting-point mixed salt, and then the biomass powder and the low-melting-point mixed salt are evenly mixed in a mass ratio of 1:2 to 1:

4. The mixture is placed in a porcelain boat and covered with 1 cm of low-melting-point mixed salt to obtain an intermediate product. Step 3: Place the porcelain boat prepared in step 2 in a muffle furnace, heat the temperature to 400-800°C at a heating rate of 5-10°C / min, and carbonize for 1-3 hours. Step 4: Ultrasonicate the fired carbon material in 2M hydrochloric acid for ten minutes, soak it overnight, then wash it with water twice until it is neutral, and dry it in a drying oven to obtain a porous biomass carbon material.

2. The method for preparing porous biochar by high-temperature carbonization of molten salt according to claim 1, characterized in that: The aquatic algae biomass in step 1 is Enteromorpha.

3. The method for preparing porous biochar by high-temperature carbonization of molten salt according to claim 1, characterized in that: The low melting point mixed salt in step 2 is a mixture of sodium chloride and potassium chloride in a mass ratio of 1:

1.

4. The method for preparing porous biochar by high-temperature carbonization of molten salt according to claim 1, characterized in that: The mass ratio of the Enteromorpha biomass powder to the mixed salt described in step 2 is 7:

15.

5. The method for preparing porous biochar by high-temperature carbonization of molten salt according to claim 1, characterized in that: The carbonization method in step 3 is to heat the temperature to 700° C. at a heating rate of 10° C. / min and carbonize for 1 hour.

Images