Modified bamboo reed biochar as well as preparation method and application thereof

Abstract

The invention relates to modified bamboo reed biochar and a preparation method thereof, the specific surface area is greater than 250m < 2 > / g, and the strength of persistent free radicals (PFRs) is greater than 0.5 a.u. The preparation method of the biochar comprises the following steps: (1) crushing bamboo reed into powder, mixing the powder with alkali according to a mass ratio of (0.5-1.5): 1, adding water, stirring for 3-6 hours, uniformly mixing, and drying to obtain modified bamboo reed powder; (2) carbonizing the modified bamboo reed powder for 1-3 hours at 500-700 DEG C under the protection of nitrogen, and naturally cooling to room temperature to obtain charcoal; and (3) performing acid pickling on the biochar, performing suction filtration, washing the obtained filter cake with water, drying, and grinding to obtain the biochar. According to the method, the reed leaves are modified to obtain the biochar which is larger in specific surface area, higher in persistent free radical strength and richer in pore structure, and complexed nickel and TOC in water can be efficiently removed.

Description

Technical Field

[0001] The invention relates to the field of environmental protection, and in particular to a modified Phragmites australis biochar, a preparation method thereof and an application thereof. Background Art

[0002] Heavy metal ions in industrial wastewater usually form complex heavy metals with coexisting matrices such as citric acid and EDTA. They are highly stable and complex in form, making them difficult to remove efficiently through conventional techniques such as adsorption and ion exchange. They are more concealed and mobile in the environment. Taking heavy metal nickel as an example, long-term exposure to nickel can lead to diseases such as asthma and cancer. High concentrations of nickel are also highly toxic. The complex nickel formed after chelation with organic chelating agents (such as citric acid, humic acid, etc.) has stronger chemical stability. At present, the main method for removing complex heavy metals in wastewater is advanced oxidation technology, which first oxidizes the ligand to decomplex it, releases the free metal ions, and then combines them with conventional means for removal. This type of method has relatively cumbersome steps, and the added persulfate, hydrogen peroxide, etc. also have certain environmental risks and increased costs.

[0003] Biochar is a new type of biomaterial. Thanks to its porosity and surface functional groups with various chemical properties, it can adsorb heavy metals through complexation with functional groups, cation-π bonds, ion exchange, and electrostatic adsorption. In addition, biochar is also a potential catalytic material. The persistent free radicals (PFRs) of biochar and the lone pair electrons of Lewis base sites (such as oxygen atoms in C=O) can provide electrons to generate active oxygen free radicals to participate in redox reactions.

[0004] Phragmites australis is a herbaceous plant that grows widely along riverbanks in South China and East China. It has strong reproductive capacity, making it a good raw material for preparing biochar. However, the relatively poor adsorption capacity and oxidation performance of Phragmites australis biochar limit its large-scale application to a certain extent. Summary of the invention

[0005] The present invention aims to provide a modified Phragmites australis biochar having a specific surface area greater than 250 m 2 / g, preferably greater than 350m 2 / g, more preferably greater than 550m 2 / g.

[0006] In a preferred technical solution of the present invention, the intensity of the persistent free radicals (PFRs) of the biochar is greater than 0.5 au, preferably greater than 1 a.u., and more preferably greater than 1.5 au.

[0007] In the preferred technical solution of the present invention, the pore volume of the biochar is 0.1-1cm 3 / g, preferably 0.2-0.6cm 3 / g.

[0008] In a preferred technical solution of the present invention, the average pore size of the biochar is 1-10 mm, preferably 2-6 nm.

[0009] In the preferred technical solution of the present invention, the method for preparing the modified Phragmites australis biochar comprises the following steps:

[0010] (1) crushing the reed into powder, mixing it with alkali in a mass ratio of 0.5-1.5:1, adding water and stirring for 3-6 hours to mix evenly, and drying to obtain modified reed powder;

[0011] (2) carbonizing the modified Phragmites australis powder obtained in step (1) at 500-700° C. for 1-3 h under nitrogen protection, and then naturally cooling to room temperature to obtain biochar;

[0012] (3) The biochar obtained in step (2) is acid-washed, filtered, and the filter cake is washed with water, dried, and ground to obtain the product.

[0013] In a preferred technical solution of the present invention, in step (1), the Phragmites australis is any one of Phragmites australis leaves and Phragmites australis stems, or a combination thereof.

[0014] In a preferred technical solution of the present invention, in step (1), the stirring rate is 300-800 rpm, preferably 400-500 rpm, and the stirring time is 2-6 h, preferably 3-4 h.

[0015] In the preferred technical solution of the present invention, in step (1), the drying temperature is 60-80°C, preferably 65-70°C.

[0016] In the preferred technical solution of the present invention, in step (2), the carbonization conditions are: heating at a rate of 5 to 10°C to 500-700°C and maintaining for 1-3h.

[0017] In the preferred technical solution of the present invention, in step (3), the grinding is followed by passing through a 60-100 mesh sieve.

[0018] In the preferred technical solution of the present invention, in step (3), the drying condition is 70-90°C.

[0019] Another object of the present invention is to provide a method for preparing modified Phragmites australis biochar, comprising the following steps:

[0020] (1) crushing the reed into powder, mixing it with alkali in a mass ratio of 0.5-1.5:1, adding water and stirring for 3-6 hours to mix evenly, and drying to obtain modified reed powder;

[0021] (2) carbonizing the modified Phragmites australis powder obtained in step (1) at 500-700° C. for 1-3 h under nitrogen protection, and then naturally cooling to room temperature to obtain biochar;

[0022] (3) The biochar obtained in step (2) is acid-washed, filtered, and the filter cake is washed with water, dried, and ground to obtain the product.

[0023] In a preferred technical solution of the present invention, in step (1), the Phragmites australis is any one of Phragmites australis leaves and Phragmites australis stems, or a combination thereof.

[0024] In a preferred technical solution of the present invention, in step (1), the stirring rate is 300-800 rpm, preferably 400-500 rpm, and the stirring time is 2-6 h, preferably 3-4 h.

[0025] In the preferred technical solution of the present invention, in step (1), the drying temperature is 60-80°C, preferably 65-70°C.

[0026] In the preferred technical solution of the present invention, in step (2), the carbonization conditions are: heating at a rate of 5 to 10°C to 500-700°C and maintaining for 1-3h.

[0027] In the preferred technical solution of the present invention, in step (3), the grinding is followed by passing through a 60-100 mesh sieve.

[0028] In the preferred technical solution of the present invention, in step (3), the drying condition is 70-90°C.

[0029] Another object of the present invention is to provide an application of the modified Phragmites australis biochar of the present invention for removing pollutants in water.

[0030] In a preferred technical solution of the present invention, the pollutant is any one of complexed nickel and TOC or a combination thereof.

[0031] In a preferred technical solution of the present invention, the complexed nickel is any one of nickel citrate, nickel humate, nickel tartrate, EDTA-nickel, nickel malate, and nickel gluconate, or a combination thereof.

[0032] In a preferred technical solution of the present invention, the concentration of complexed nickel in the water is 1-100 mg / L.

[0033] In a preferred technical solution of the present invention, the biochar can be recycled and reused 1-5 times.

[0034] In the preferred technical solution of the present invention, the reused biochar can be regenerated after eluting the adsorbed nickel.

[0035] In a preferred technical solution of the present invention, the eluent is an aqueous solution containing 0.1M hydrochloric acid and 5% NaCl.

[0036] The present invention adopts the following detection method:

[0037] 1. Use the fully automatic specific surface and porosity analyzer (Micromeritics TriStar IIPlus) to test the specific surface area, pore volume and pore diameter;

[0038] 2. Use TESCAN CLARA scanning electron microscope to detect SEM; use the desktop electron paramagnetic resonance spectrometer (EPR200M) produced by Guoyi Quantum to detect EPR;

[0039] 3. An atomic absorption spectrometer (PerkinElmer PinAAcle 900) was used to detect the nickel content in nickel citrate and nickel humate solutions; a total organic carbon analyzer (TOC-V CPH) produced by Shimadzu Corporation was used to detect the TOC concentration.

[0040] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0041] (1) The present invention modifies reed leaves to obtain biochar with a larger specific surface area, stronger persistent free radical strength, and richer pore structure, which can efficiently remove complex nickel in water (the removal rate can reach more than 98% within 4 hours) and can also effectively remove TOC in water at the same time.

[0042] (2) The preparation method of the present invention is safe and non-toxic, does not produce by-products, has a simple process, and can realize waste resource treatment at a low cost and can be used for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 SEM graph of the surface microstructure of the modified Phragmites australis biochar of the present invention.

[0044] Figure 2 The EPR test spectrum of the modified Phragmites australis biochar of the present invention;

[0045] Figure 3 Study on the effect of modified Phragmites australis biochar on removing nickel citrate;

[0046] Figure 4 Study on the effect of modified Phragmites australis biochar on TOC removal;

[0047] Figure 5 The effect of the modified Phragmites australis leaf biochar on removing humic acid nickel was studied. DETAILED DESCRIPTION

[0048] The following is a detailed description of the embodiments of the present invention in conjunction with examples, but these examples are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0049] After the collected Phragmites australis was dried in the sun, it was crushed into powder using a crusher, washed three times in tap water, and then washed three times with deionized water. The washed Phragmites australis powder was collected and dried in a forced air drying oven at 60° C. for 48 hours and used in the following examples.

[0050] Example 1 Preparation of modified Phragmites australis biochar of the present invention

[0051] The preparation of modified Phragmites australis biochar of the present invention comprises the following steps:

[0052] (1) 10 g of Phragmites australis powder was placed in 150 mL of deionized water, 5 g of potassium hydroxide was added under stirring, and the mixture was stirred at 450 rpm for 4 h on a magnetic stirrer, and then placed in a forced air drying oven and dried at 80° C. for 8 h to obtain modified Phragmites australis powder;

[0053] (2) placing the modified Phragmites australis powder obtained in step (1) in a tube furnace, introducing nitrogen at a flow rate of 50 mL / L, heating the temperature to 600° C. at a heating rate of 5° C. / min and then maintaining the temperature for 2 h, and then naturally cooling the temperature to room temperature to obtain biochar;

[0054] (3) The biochar from step (2) was slowly poured into 100 mL of 0.1 M dilute hydrochloric acid and stirred for 10 min to remove ash and impurities. The biochar was filtered using a 0.45 μm filter membrane and a circulating water vacuum pump. The filter cake was repeatedly rinsed with deionized water for 5 times, dried in an oven at 70 ° C, ground with an agate mortar, and passed through an 80-mesh sieve.

[0055] Example 2 Preparation of modified Phragmites australis biochar of the present invention

[0056] The preparation of modified Phragmites australis biochar of the present invention comprises the following steps:

[0057] (1) 10 g of Phragmites australis powder was placed in 150 mL of deionized water, 10 g of potassium hydroxide was added under stirring, and the mixture was stirred at 450 rpm for 4 h on a magnetic stirrer, and then placed in a forced air drying oven and dried at 80° C. for 8 h to obtain modified Phragmites australis powder;

[0058] (2) placing the modified Phragmites australis powder obtained in step (1) in a tube furnace, introducing nitrogen at a flow rate of 50 mL / L, heating the temperature to 600° C. at a heating rate of 5° C. / min and then maintaining the temperature for 2 h, and then naturally cooling the temperature to room temperature to obtain biochar;

[0059] (3) The biochar from step (2) was slowly poured into 100 mL of 0.1 M dilute hydrochloric acid and stirred for 10 min to remove ash and impurities. The biochar was filtered using a 0.45 μm filter membrane and a circulating water vacuum pump. The filter cake was repeatedly rinsed with deionized water for 5 times, dried in an oven at 70 ° C, ground with an agate mortar, and passed through an 80-mesh sieve.

[0060] Example 3 Preparation of modified Phragmites australis biochar of the present invention

[0061] The preparation of modified Phragmites australis biochar of the present invention comprises the following steps:

[0062] (1) 10 g of Phragmites australis powder was placed in 150 mL of deionized water, 15 g of potassium hydroxide was added under stirring, and the mixture was stirred at 450 rpm for 4 h on a magnetic stirrer, and then placed in a forced air drying oven and dried at 80° C. for 8 h to obtain modified Phragmites australis powder;

[0063] (2) placing the modified Phragmites australis powder obtained in step (1) in a tube furnace, introducing nitrogen at a flow rate of 50 mL / L, heating the temperature to 600° C. at a heating rate of 5° C. / min and then maintaining the temperature for 2 h, and then naturally cooling the temperature to room temperature to obtain biochar;

[0064] (3) The biochar from step (2) was slowly poured into 100 mL of 0.1 M dilute hydrochloric acid and stirred for 10 min to remove ash and impurities. The biochar was filtered using a 0.45 μm filter membrane and a circulating water vacuum pump. The filter cake was repeatedly rinsed with deionized water for 5 times, dried in an oven at 70 ° C, ground with an agate mortar, and passed through an 80-mesh sieve.

[0065] Example 4 Preparation of modified Phragmites australis biochar of the present invention

[0066] The preparation of modified Phragmites australis biochar of the present invention comprises the following steps:

[0067] (1) 10 g of Phragmites australis powder was placed in 150 mL of deionized water, 10 g of sodium hydroxide was added under stirring, and the mixture was stirred at 450 rpm for 4 h on a magnetic stirrer, and then placed in a forced air drying oven and dried at 80° C. for 8 h to obtain modified Phragmites australis powder;

[0068] (2) placing the modified Phragmites australis powder obtained in step (1) in a tube furnace, introducing nitrogen at a flow rate of 50 mL / L, heating the temperature to 600° C. at a heating rate of 5° C. / min and then maintaining the temperature for 2 h, and then naturally cooling the temperature to room temperature to obtain biochar;

[0069] (3) The biochar from step (2) was slowly poured into 100 mL of 0.1 M dilute hydrochloric acid and stirred for 10 min to remove ash and impurities. The biochar was filtered using a 0.45 μm filter membrane and a circulating water vacuum pump. The filter cake was repeatedly rinsed with deionized water for 5 times, dried in an oven at 70 ° C, ground with an agate mortar, and passed through an 80-mesh sieve.

[0070] Example 5 Preparation of modified Phragmites australis biochar of the present invention

[0071] The preparation of modified Phragmites australis biochar of the present invention comprises the following steps:

[0072] (1) 10 g of Phragmites australis powder was placed in 150 mL of deionized water, 10 g of calcium hydroxide was added under stirring, the mixture was stirred at 450 rpm for 4 h on a magnetic stirrer, and then placed in a forced air drying oven and dried at 80° C. for 8 h to obtain modified Phragmites australis powder;

[0073] (2) placing the modified Phragmites australis powder obtained in step (1) in a tube furnace, introducing nitrogen at a flow rate of 50 mL / L, heating the temperature to 600° C. at a heating rate of 5° C. / min and then maintaining the temperature for 2 h, and then naturally cooling the temperature to room temperature to obtain biochar;

[0074] (3) The biochar from step (2) was slowly poured into 100 mL of 0.1 M dilute hydrochloric acid and stirred for 10 min to remove ash and impurities. The biochar was filtered using a 0.45 μm filter membrane and a circulating water vacuum pump. The filter cake was repeatedly rinsed with deionized water for 5 times, dried in an oven at 70 ° C, ground with an agate mortar, and passed through an 80-mesh sieve.

[0075] Comparative Example 1

[0076] The preparation method of Phragmites australis biochar comprises the following steps:

[0077] (1) 10 g of Phyllostachys reed powder was placed in a tube furnace, nitrogen was introduced at a flow rate of 50 mL / L, the temperature was increased to 600 °C at a heating rate of 5 °C / min, and then the temperature was maintained for 2 h, and the temperature was naturally cooled to room temperature to obtain biochar;

[0078] (2) The biochar prepared in step (1) was slowly poured into 100 mL of 0.1 M dilute hydrochloric acid and stirred for 10 min to remove ash and impurities. The biochar was filtered using a 0.45 μm filter membrane and a circulating water vacuum pump. The filter cake was repeatedly rinsed with deionized water for 5 times, dried in an oven at 70° C., ground with an agate mortar, and passed through an 80-mesh sieve.

[0079] Experimental Example 1 Performance Characterization of Modified Phragmites australis Biochar of the Present Invention

[0080] The specific surface area and pore size of the Phragmites australis biochars prepared in Examples 1-3 and Comparative Example 1 were tested, as shown in Table 1.

[0081] Table 1

[0082]

[0083] The morphology of the reed biochars of Example 2 and Comparative Example 1 was analyzed, and the SEM images with the surface magnified 50,000 times were as follows: Figure 1 As shown. The biochar of Comparative Example 1 ( Figure 1 a) shows a disordered, pore-deficient morphology, and the biochar of Example 2 ( Figure 1b) It exhibits a regular honeycomb structure. The free space formed by this ordered, loose and porous structure gives it a strong potential for the adsorption of organic matter and heavy metals.

[0084] The biochars of Example 2 and Comparative Example 1 were subjected to EPR testing, and the intensity of the persistent free radicals detected was as follows: Figure 2 The biochar of Example 2 has a stronger persistent free radical strength, and can achieve the removal of complexed nickel.

[0085] Experimental Example 2 Study on the removal effect of nickel citrate by modified Phragmites australis biochar of the present invention

[0086] Take two conical flasks containing 50mL of 15mg / L nickel citrate solution (in terms of nickel concentration), add 0.05g of Example 2 and 0.05g of Comparative Example 1, respectively, and place them in a constant temperature shaker at 25°C and 160rpm for removal experiments. Take 2mL of the solution before addition and 10min, 30min, 60min, 90min, 120min, 180min, and 240min after addition to detect the nickel concentration and TOC concentration therein.

[0087] The removal curve of nickel ions is as follows Figure 3 As shown, within 4 hours, the removal rate of nickel citrate by the reed bamboo biochar of Example 2 was higher than 98%, which was much higher than the removal rate of nickel citrate by the reed bamboo biochar of Comparative Example 1 (30%).

[0088] The change curve of TOC is as follows Figure 4 As shown, the removal rate of TOC by the reed bamboo biochar in Example 2 is 30.9%, which is higher than the removal rate of TOC by the reed bamboo biochar in Comparative Example 1 (6.5%). This indicates that the reed bamboo biochar of the present invention can achieve the simultaneous removal of nickel citrate and TOC by rapidly decomposing the nickel citrate complex.

[0089] In addition, the biochar in the solution can be separated and cleaned and reused for the removal of nickel citrate, or it can be immersed in an aqueous solution containing 0.1M hydrochloric acid and 5% NaCl for 1 hour to desorb the adsorbed nickel and then reused for the removal of nickel citrate.

[0090] Experimental Example 3 Study on the removal effect of modified Phragmites australis biochar on humic acid nickel

[0091] Take two conical flasks containing 50mL of 15mg / L nickel citrate solution (in terms of nickel concentration), add 0.05g of Phragmites australis biochar of Example 2, put them in a constant temperature shaker at 25℃, and perform the removal experiment at 160rpm. Take 2mL of the solution before addition and at 10min, 30min, 60min, 90min, 120min, 180min, and 240min after addition to test the nickel concentration. Figure 5As shown, the removal rate of humic acid nickel by the biochar of the present invention is as high as 99% within 4 hours.

[0092] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A modified Phragmites australis biochar with a specific surface area greater than 250m 2 / g, preferably greater than 350m 2 / g, more preferably greater than 550m 2 / g.

2. The biochar according to claim 1, wherein the intensity of persistent free radicals (PFRs) of the biochar is greater than 0.5 au, preferably greater than 1 a.u., and more preferably greater than 1.5 au.

3. The biochar according to any one of claims 1 to 2, wherein the pore volume of the biochar is 0.1-1 cm 3 / g, preferably 0.2-0.6cm 3 / g.

4. The biochar according to any one of claims 1 to 3, wherein the average pore size of the biochar is 1-10 mm, preferably 2-6 nm.

5. The biochar according to any one of claims 1 to 4, wherein the method for preparing the modified Phragmites australis biochar comprises the following steps: (1) crushing the reed into powder, mixing it with alkali in a mass ratio of 0.5-1.5:1, adding water and stirring for 3-6 hours to mix evenly, and drying to obtain modified reed powder; (2) carbonizing the modified Phragmites australis powder obtained in step (1) at 500-700° C. for 1-3 h under nitrogen protection, and then naturally cooling to room temperature to obtain biochar; (3) The biochar obtained in step (2) is acid-washed, filtered, and the filter cake is washed with water, dried, and ground to obtain the product.

6. The method for preparing the modified Phragmites australis biochar according to any one of claims 1 to 5, comprising the following steps: (1) crushing the reed into powder, mixing it with alkali in a mass ratio of 0.5-1.5:1, adding water and stirring for 3-6 hours to mix evenly, and drying to obtain modified reed powder; (2) carbonizing the modified Phragmites australis powder obtained in step (1) at 500-700° C. for 1-3 h under nitrogen protection, and then naturally cooling to room temperature to obtain biochar; (3) The biochar obtained in step (2) is acid-washed, filtered, and the filter cake is washed with water, dried, and ground to obtain the product.

7. The method according to claim 6, wherein in step (1), the stirring rate is 300-800 rpm, preferably 400-500 rpm, and the stirring time is 2-6 h, preferably 3-4 h.

8. The method according to any one of claims 6 to 7, wherein in step (1), the drying temperature is 60-80°C, preferably 65-70°C.

9. The method according to any one of claims 6 to 8, wherein in step (2), the carbonization conditions are: heating to 500-700°C at a rate of 5-10°C and maintaining for 1-3h.

10. Use of the modified Phragmites australis biochar according to any one of claims 1 to 5 for removing pollutants in water, preferably, the pollutants are any one of complexed nickel and TOC or a combination thereof.

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