Preparation method of bismuth oxide modified straw biochar and application of bismuth oxide modified straw biochar in estrogen contaminated soil remediation

Abstract

The invention provides a preparation method of bismuth oxide modified straw biochar and application of the bismuth oxide modified straw biochar in estrogen contaminated soil remediation. The preparation method comprises the following steps: SS1, pretreatment of biochar; step SS2, preparation of biochar; and step SS3, grinding, screening, cleaning and drying the prepared biochar to obtain the bismuth oxide modified straw biochar. Straw particles and a bismuthic acid solution are mixed, surface modification and ultrasonic activation are carried out, then anaerobic pyrolysis of the biochar is carried out, the prepared bismuth oxide-biochar has the advantages that the infiltration capacity of bismuth oxide is larger, the loading capacity is higher, the combination of the bismuth oxide and the biochar is firmer, and the use durability is better.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation materials, and in particular to a method for preparing bismuth oxide-modified straw biochar and application of the biochar in remediation of estrogen-contaminated soil. Background Art

[0002] In recent years, large-scale agricultural breeding and livestock manure applied to farmland, coupled with sewage irrigation, industrial emissions through atmospheric deposition, water circulation and other channels, a large amount of estrogen enters farmland, causing serious soil pollution, which not only increases the production cost of agricultural cash crops such as grain, but also leads to problems such as excessive residues in agricultural products, seriously affecting food safety. Therefore, the problem of soil estrogen pollution needs to be solved urgently. Compared with heavy metal pollution, soil estrogen pollution is more difficult to control.

[0003] At present, the research on the degradation of organic pollutants in water and soil mainly reports on two substances, bismuth tungstate and bismuth ferrite, especially bismuth tungstate (Bi2WO6). Bismuth tungstate is a new type of semiconductor photocatalytic material with a narrow band gap of ternary metal oxide n-type. It has visible light activity at around 470nm. It is a photocatalyst with excellent visible light catalytic performance and good application prospects and has gradually attracted attention. Studies have shown that bismuth tungstate-based biochar photocatalyst is a biochar-based composite or doped modification, which can effectively prepare a biochar-based bismuth tungstate catalyst with photocatalytic activity, which can effectively degrade organic pollutants in water. For example, the invention patents with publication numbers CN111036273A "A method for preparing corn straw biochar and Bi2WO6 photocatalyst for efficient degradation of organic pollutants" and CN111530487A "A method for preparing bismuth tungstate nitrogen-sulfur co-modified biochar" both report the synthesis of this photocatalyst and its degradation of organic pollutants in water, such as rhodamine dye, tetracycline hydrochloride and ciprofloxacin, all of which have a certain degradation effect.

[0004] Patent CN115634702A "A bismuth oxycarbonate / biochar composite photocatalyst and its preparation method and application" discloses a method for synthesizing bismuth-modified biochar, which is to first prepare biochar by pyrolysis and then use a bismuth compound to modify its surface through the liquid phase, that is, the bismuth compound is purely combined with the biochar by physical and chemical action. In this patent, the synthesis of bismuth oxycarbonate is to use a soluble salt of bismuth, bismuth chloride or bismuth nitrate, to react with a soluble carbonate to precipitate bismuth carbonate, which is used to modify the surface of the fired biochar, and then dried to obtain a bismuth oxycarbonate-biochar composite photocatalyst. Through this chemical reaction, bismuth carbonate is obtained (bismuth oxide will not be obtained if it is not sintered at high temperature. Bismuth oxycarbonate and bismuth oxide are completely two substances, each with its own characteristics) which is deposited on the surface of the biochar and will not be loaded into the interior of the biochar, and the degradation of organic matter is limited. There are even fewer reports on the remediation of soil organic pollutants by bismuth-modified biochar, such as the authorization announcement number CN115368911B "A method for remediating soil contaminated by fluoroquinolone antibiotics", which reports that the matrix biochar, TiO2 and bismuth tungstate are closely combined with chitosan, which can significantly improve the photocatalytic activity, light absorption efficiency and redox capacity of the composite photocatalyst, and apply it to the photocatalytic degradation of fluoroquinolone antibiotics in soil, achieving certain results. However, the degradation of organic pollutants by bismuth tungstate composite biochar is mainly based on its photocatalytic properties, and for the polluted medium of soil, its light transmittance is very poor, so this technology can only degrade organic pollutants on the surface of the soil, and the degradation of organic pollutants inside the soil is negligible, so there are obvious technical deficiencies.

[0005] Based on this, developing a technology that can effectively degrade organic pollutants on the soil surface and inside the soil, and in which the process of degrading organic pollutants is not restricted by light conditions, is a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing bismuth oxide modified biochar which can effectively degrade organic pollutants on the soil surface and inside the soil, and the process of degrading organic pollutants is not limited by light conditions.

[0007] Remediation using modified biochar and its composite materials is a feasible technical path. Bismuth is a green metal. The bismuth oxide modified straw biochar prepared from its compounds has good adsorption capacity and a certain oxidation capacity for organic matter. It is a remediation material with excellent adsorption-oxidation capacity and can be used for the remediation of organic pollution in water and soil. At the same time, green metal bismuth and its oxides are not easily absorbed by plants. Applying them to soil remediation can not only achieve good remediation effects, but also ensure the safety of growing crops, killing two birds with one stone.

[0008] The bismuth oxide modified biochar prepared by the present invention has more surface positive charges, a multi-level pore structure, and abundant surface functional groups, that is, a larger comparative area and more active sites, and thus has a stronger adsorption capacity, which can more effectively fix organic pollutants in the soil such as estrogen on the biochar.

[0009] Bismuth oxide modification makes the biochar surface have stronger electron transfer ability and more phenolic and quinone groups, which can transfer electrons with transition metal elements (such as iron, manganese, etc.) in the soil to form persistent free radicals and stimulate activated oxygen to generate reactive oxygen free radicals. At the same time, bismuth modification increases the concentration of persistent free radicals on the biochar surface. The oxidation-reduction alternating process caused by changes in water activates oxygen to generate hydroxyl free radicals, thereby achieving effective oxidative degradation of estrogen adsorbed on the biochar surface, effectively overcoming the technical shortcoming of being limited by light conditions when using bismuth tungstate modified biochar. Therefore, it has more practical application value for the remediation of soil organic pollutants.

[0010] Specifically, the method for preparing bismuth oxide-modified straw biochar provided by the present invention comprises the following steps:

[0011] Step SS1: pre-treatment of biochar;

[0012] Step SS2: preparation of biochar;

[0013] Step SS3: The prepared biochar is ground, screened, cleaned and dried to obtain bismuth oxide-modified straw biochar.

[0014] Furthermore, in step SS1, the biochar raw material is selected from one of wheat, rice, and corn straw.

[0015] Furthermore, the specific steps of the pretreatment of biochar in step SS1 are: removing impurities from the crop straw, washing it with deionized water for the first time, drying it for the first time, crushing and sieving it to 1 mm, adding 0.1-0.15 mol / L bismuth oxide acid solution thereto, heating and stirring it in a 60-80°C hot water bath for 1-2 hours, and then ultrasonically activating it at an intensity of 10 kHz for 0.5-1 hour, filtering it, washing it for the second time, and drying it for the second time at 100-120°C for 2-4 hours.

[0016] Furthermore, the specific steps for preparing the biochar in step SS2 are: placing the dried product obtained in step SS1 in a muffle furnace, performing anaerobic pyrolysis at 400-600°C under nitrogen protection, with a temperature increase gradient of 5-10°C / min, a holding time of 1-2 hours, and naturally cooling to room temperature after the holding period.

[0017] Furthermore, in step SS3, the biochar ground with a mortar is sieved with a 10-mesh sieve, the sieve is washed three times with deionized water, and dried at 100-120° C. for 4-6 hours.

[0018] Furthermore, in step SS1, the first drying is performed at 90-120° C. for 2-4 hours, and the stirring speed is 100-200 rpm.

[0019] Furthermore, after the acid solution of bismuth oxide is added in step SS1, the weight volume ratio of the straw and the bismuth solution is maintained at 1:10-15, w / V.

[0020] Furthermore, in step SS1, the first cleaning and the second cleaning are performed three times with excess deionized water.

[0021] The present invention also provides an application of the bismuth oxide-modified straw biochar prepared as described above in the remediation of estrogen-contaminated soil.

[0022] Furthermore, estrogen-contaminated soil refers to soil contaminated by estrone E1.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are:

[0024] 1. The present invention first mixes straw particles with bismuth oxide acid solution, first performs surface modification and ultrasonic activation, and then performs anaerobic pyrolysis to prepare composite modified biochar. This high-temperature anaerobic pyrolysis plays a sintering role. Sintering causes a large number of vacancies to be formed inside the biochar. During the mixing process with the bismuth oxide acid solution, the functional material penetrates into the biochar to form a sintered body, forming more adsorption sites, that is, preparing a bismuth oxide-biochar composite material, wherein the penetration of bismuth oxide is larger, so its load capacity is also greater, and this process of first modifying and then firing, the combination of bismuth oxide and biochar is more firmly, and its durability is also better, that is, the process of first modifying and then firing the biochar can make the load capacity of the composite functional material larger, the combination is more firmly, and the cycle of recycling is longer.

[0025] 2. The present invention uses cheap crop straw as raw material to prepare a bismuth oxide-modified biochar remediation material with both adsorption and oxidation properties, which has a good remediation effect on soil organic pollution, thereby providing an effective remediation means for organically contaminated soil, and realizing the efficient resource recovery and utilization of agricultural waste straw, achieving the purpose of treating waste with waste, and has good application prospects and practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The SEM and FTIR images of the bismuth oxide modified rice straw biochar prepared in Example 1;

[0027] Figure 2The SEM and FTIR images of the bismuth oxide-modified wheat straw biochar prepared in Example 2;

[0028] Figure 3 This is a diagram showing the effect of bismuth oxide-modified wheat straw biochar on the restoration of estrogen-contaminated soil in Example 3;

[0029] Figure 4 This is a diagram showing the remediation effect of bismuth oxide-modified rice straw biochar on estrogen-contaminated soil in Example 3. DETAILED DESCRIPTION

[0030] The present invention can be better understood according to the following examples. However, it is easy for those skilled in the art to understand that the contents described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims.

[0031] The technical solution of the present invention is further described below in conjunction with implementation cases.

[0032] Example 1

[0033] This embodiment provides a method for preparing bismuth oxide-modified rice straw biochar, and the specific steps are as follows:

[0034] Step SS1: pre-treatment of biochar;

[0035] The rice straw was removed from impurities in sequence, washed with excess deionized water for 3 times, and then placed in an electric furnace for drying at 105° C. for 2 hours, crushed and sieved to a particle size of 1 mm, and then a 0.1 mol / L acid solution of bismuth oxide was added thereto so that the straw concentration reached 100 g / L, and heated in a 70° C. hot water bath for 1 hour with a stirring speed of 100 rpm, and then ultrasonically activated for 0.5 hour at an intensity of 10 kHz, filtered, and the filtrate was washed with excess deionized water for 3 times, placed in a crucible for drying at 105° C. for 2 hours, and then compacted for use;

[0036] Step SS2: preparation of biochar;

[0037] The compact obtained in step SS1 is placed in a muffle furnace, nitrogen is used as a protective gas, the heating rate is controlled at 5°C / min, and when the temperature reaches 450°C, it is kept warm for 2 hours, and then naturally cooled at room temperature to obtain bismuth oxide-modified rice straw biochar;

[0038] Step SS3: The prepared rice straw biochar was ground in a mortar and passed through a 10-mesh sieve to a particle size of less than 0.25 mm, and washed with excess deionized water for 3 times. After drying at 105° C. for 4 hours, the final product of bismuth oxide-modified rice straw biochar was obtained.

[0039] Example 2

[0040] This embodiment provides a method for preparing bismuth oxide-modified wheat straw biochar. For specific steps, refer to Example 1. The difference between this embodiment and Example 1 is that the raw material of this embodiment is wheat straw.

[0041] Example 3

[0042] This embodiment provides an application of bismuth oxide-modified straw biochar in estrogen-contaminated soil.

[0043] The test soil was collected from the surface soil (0-20cm) of farmland that was contaminated by estrogen for a long time around the breeding farm in the eastern suburbs of Nanjing. After the soil was collected, the plant roots, gravel and other debris were removed first, and then air-dried and passed through a 2mm sieve. The basic physical and chemical properties of the sieve were tested as follows: pH 6.56, sand (28.48%), powder (39.02%) and clay (22.50%), total organic carbon (7.35g / kg), total nitrogen (1.4g / kg), total phosphorus (0.89g / kg), total potassium (16.9g / kg), and the content of estrogen-estrone E1 in the test soil was tested to be 417±25μg / kg dry soil.

[0044] Soil culture experiment: After the test soil is fully mixed, it is added into a cylindrical polyethylene container (20 cm in height and 20 cm in diameter), and the bismuth oxide modified straw biochar prepared in Example 1 and Example 2 is added into the container at 0.0% (control group), 0.2%, 0.5%, 1% and 2% (mass percentage) respectively, and fully mixed with the soil, and then deionized water is added to 60% of the field water holding capacity, and water is replenished regularly every week. Three sets of parallel samples are set for each condition experiment of bismuth oxide modified rice straw biochar and bismuth oxide modified wheat straw biochar to repair estrogen-estrone E1 contaminated soil, and cultured at a temperature close to the natural environment for four months, and 10g of soil samples are taken every 30 days, and after accelerated solvent extraction and solid phase extraction purification, the estrone E1 content in the sample is analyzed by liquid chromatography-mass spectrometry.

[0045] After 120 days of indoor testing, the repair results are as follows: Figure 3 and Figure 4 shown.

[0046] Results from the examples Figure 3 and Figure 4It can be seen that the two bismuth oxide modified straw biochars of the present invention were added to the soil contaminated by estrogen-oestrone E1. After 120 days of restoration, both had obvious removal effects on estrone E1 in the soil, and the experimental results were basically the same. When the biochar addition amount reached 2%, the restoration effect was the best. After 120 days of restoration, the maximum removal rate of estrone E1 by the two biochars exceeded 80%. Compared with the blank group, the maximum removal rate of estrone E1 by the rice straw biochar and wheat straw biochar addition groups modified by bismuth oxide was increased by more than 40% compared with the blank group.

[0047] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing bismuth oxide modified straw biochar, characterized in that: The following steps are involved: step SS1: pretreatment of biochar; Step SS2: preparation of biochar; Step SS3: The prepared biochar is ground, screened, cleaned and dried to obtain bismuth oxide-modified straw biochar.

2. The method for preparing bismuth oxide modified straw biochar according to claim 1, characterized in that: In step SS1, the biochar raw material is selected from one of wheat, rice and corn straw.

3. The method for preparing bismuth oxide modified straw biochar according to claim 1, characterized in that: The specific steps of the pretreatment of biochar in step SS1 are: removing impurities from the crop straw, washing it with deionized water for the first time, drying it for the first time, crushing and sieving it to 1 mm, adding 0.1-0.15 mol / L bismuth oxide acid solution thereto, heating and stirring it in a hot water bath at 60-80°C for 1-2 hours, and then ultrasonically activating it at an intensity of 10kHz for 0.5-1 hour, filtering it, washing it for the second time, and drying it for the second time at 100-120°C for 2-4 hours.

4. The method for preparing bismuth oxide modified straw biochar according to claim 1, characterized in that: The specific steps for preparing biochar in step SS2 are as follows: placing the dried product obtained in step SS1 in a muffle furnace, performing anaerobic pyrolysis at 400-600°C under nitrogen protection, with a temperature increase gradient of 5-10°C / min, a heat preservation time of 1-2 hours, and naturally cooling to room temperature after the heat preservation is completed.

5. The method for preparing bismuth oxide modified straw biochar according to claim 3, characterized in that: In step SS3, the biochar ground with a mortar is sieved with a 10-mesh sieve, the sieve is washed three times with deionized water, and dried at 100-120° C. for 4-6 hours.

6. The method for preparing bismuth oxide modified straw biochar according to claim 3, characterized in that: In step SS1, the first drying is carried out at 90-120° C. for 2-4 hours, and the stirring speed is 100-200 rpm.

7. The method for preparing bismuth oxide modified straw biochar according to claim 3, characterized in that: After the acid solution of bismuth oxide is added in step SS1, the weight volume ratio of straw to bismuth solution is maintained at 1:10-15, w / V.

8. The method for preparing bismuth oxide modified straw biochar according to claim 3, characterized in that: In step SS1, the first and second washings are washed three times with excess deionized water.

9. Use of the bismuth oxide-modified straw biochar prepared according to any one of claims 1 to 8 in the remediation of estrogen-contaminated soil.

10. The use according to claim 9, characterized in that: Estrogen-contaminated soil refers to soil contaminated by estrone E1.

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