A kind of magnetic modified biochar, preparation method and application thereof

Abstract

The present invention belongs to the field of pesticide detection, and specifically relates to a magnetically modified biochar, a preparation method and application thereof. The preparation method is as follows: carbonizing waste biomass under heating and oxygen-free conditions to obtain biochar; mixing the biochar with an acidic solution and letting it stand, and then washing and drying it in sequence to obtain acid-modified biochar; mixing the acid-modified biochar, ferric chloride hexahydrate and ferrous chloride tetrahydrate and dissolving them in water, then adding ammonia water and stirring the reaction, and then washing and drying them in sequence. The separation of the magnetically modified biochar from the water sample and the eluent is simpler, and does not require the aid of external force. The separation can be completed under the action of only one magnet, which can save time and efficiently complete the extraction and desorption process.

Description

Technical Field

[0001] The present invention belongs to the field of pesticide detection, and in particular relates to magnetically modified biochar, a preparation method and application thereof. Background Art

[0002] Triazine herbicides are a traditional herbicide class, invented and used as early as the 1950s. They are used in large quantities and can accumulate in surface and groundwater upon discharge. To date, 36 triazine herbicides have been developed, including atrazine, terbuthylazine, ametryn, simazine, and prometryn. Atrazine is the most widely used of these, accounting for approximately one-third of this class of herbicides.

[0003] At present, the adsorption performance of triazine herbicide adsorbents still needs to be improved, and the desorption efficiency is lacking. It is based on this that the technical solution of the present invention is proposed. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for preparing magnetically modified biochar, which comprises the following steps:

[0005] (1) Carbonizing waste biomass under heating and oxygen-free conditions to obtain biochar;

[0006] (2) mixing the biochar with an acidic solution and allowing the mixture to stand, and then washing and drying the mixture in sequence to obtain acid-modified biochar;

[0007] (3) The acid-modified biochar, ferric chloride hexahydrate and ferrous chloride tetrahydrate are mixed and dissolved in water, and then ammonia water is added to stir and react, and then washed and dried in sequence to obtain magnetically modified biochar.

[0008] Preferably, in step (1), the waste biomass is one of corn cobs, corn stalks or reed stalks.

[0009] Preferably, in step (1), the waste biomass is heated to 500-520° C. at a rate of 10-12° C. / min under a nitrogen atmosphere, and carbonized for 2-2.5 hours, and then cooled to obtain biochar.

[0010] Preferably, in step (2), the acidic solution is a 20-25 wt.% nitric acid solution;

[0011] and / or, the mass volume ratio of the biochar to the acidic solution is 1:40 / g:mL;

[0012] And / or, the standing time is 3 to 5 hours;

[0013] And / or, the drying temperature is 80-85° C., and the drying time is 12-14 hours.

[0014] Preferably, in step (3), the mass ratio of the acid-modified biochar, ferric chloride hexahydrate and ferrous chloride tetrahydrate is 1:2.35:0.86.

[0015] Preferably, in step (3), after adding ammonia water, the pH of the solution is greater than 9;

[0016] And / or, the reaction temperature is 80-85° C., and the reaction time is 30-40 min;

[0017] And / or, the drying temperature is 80-85° C., and the drying time is 12-14 hours.

[0018] Based on the same technical concept, another solution of the present invention is to provide a magnetically modified biochar obtained by the above preparation method.

[0019] Similarly, the present invention provides a method for using magnetically modified biochar as an adsorbent for triazine herbicides. Using magnetically modified biochar as a dispersed solid-phase extractor in water samples containing triazine herbicides not only allows for rapid adsorption and efficient enrichment, but also facilitates subsequent detection, facilitating species identification and concentration detection, and providing rational interpretation of toxicological effects and environmental contamination.

[0020] To facilitate understanding of the present invention, the principle of adsorption and detection of triazine herbicides by magnetically modified biochar is described below:

[0021] 1. Adsorption Process: Under high-temperature, oxygen-deficient conditions, heteroatoms and oxygen atoms are removed from biomass, leaving mostly carbon and hydrogen. The carbon content far outweighs the oxygen content, increasing unsaturation and the degree of aromatization. Acid modification enriches the biomass's pore structure and surface area, while also introducing a large number of oxygen-containing functional groups, such as -COOH and -OH, onto the benzene rings. Triazines are six-membered heterocycles containing three nitrogen atoms. The structural similarity, hydrogen bonding forces, and the porous structure of the adsorbent surface make it easier for triazines in water to escape from the water and be adsorbed onto the biochar.

[0022] 2. Desorption process: Ethyl acetate is used in the desorption process. Its polarity is similar to that of triazine compounds, which can easily elute the triazine compounds adsorbed on the biochar. And because it is insoluble in water, it reduces the desorption of impurities and provides convenience for the subsequent instrument detection.

[0023] The method for using the magnetically modified biochar to adsorb triazine herbicides is as follows: the magnetically modified biochar is passed through a 100-mesh sieve, 150 mg is taken and placed in a centrifuge tube containing 5 mL of a triazine-tested water sample, vortexed for 4 minutes, and a magnet is placed at the bottom of the centrifuge tube. After the magnetic biochar settles to the bottom, the centrifuge tube is tilted and the resulting supernatant is discarded (under the condition of an external magnetic source, the magnetic biochar will quickly settle to the bottom of the centrifuge tube and be adsorbed by the external magnetic source, and will not flow out with the supernatant). Subsequently, 1 mL of ethyl acetate is added and the target is completely eluted under vortex oscillation for 4 minutes. The magnetic biochar is then sedimented using the same method, and the supernatant is collected for testing.

[0024] The beneficial effects of the present invention are:

[0025] The preparation method described in the present invention first pyrolyzes the waste biomass under anaerobic conditions to obtain a larger total pore volume and specific surface area, while also having a higher yield; then acid-modifies the biochar to increase the number of its oxygen-containing functional groups, thereby improving the pore structure and specific surface area of ​​the biochar, thereby enabling rapid and effective adsorption between the acid-modified biochar and triazine herbicides, significantly improving the adsorption efficiency compared to the original biochar; finally, magnetic modification simplifies the separation of the biochar from water samples and eluents, without the need for external force, and the separation can be completed using only a magnet, saving time and efficiently completing the extraction and desorption processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is the infrared spectrum of the magnetically modified biochar obtained in Example 1 of the present invention.

[0028] Figure 2 This is a transmission electron microscope image of the magnetically modified biochar obtained in Example 1 of the present invention (scale 100 nm).

[0029] Figure 3 This is a transmission electron microscope image of the magnetically modified biochar obtained in Example 1 of the present invention (scale 50 nm).

[0030] Figure 4 This is a scanning electron microscope image of the acid-modified biochar obtained in Example 1 of the present invention.

[0031] Figure 5 This is a scanning electron microscope image of the magnetically modified biochar obtained in Example 1 of the present invention.

[0032] Figure 6 This is a hysteresis loop data diagram of the magnetically modified biochar obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a method for preparing magnetically modified biochar, which comprises the following steps:

[0036] (1) Place the discarded corn cobs in a carbonization furnace, heat them to 500°C at a rate of 10°C / min under a nitrogen atmosphere (to ensure the absence of oxygen), and maintain them for 2 hours to carbonize them. After cooling, biochar is obtained.

[0037] (2) The biochar was crushed using a grinder and passed through a 100-mesh sieve. 15 g of the biochar was placed in 600 mL of a 20% nitric acid solution and allowed to stand for 3 h. The biochar was then rinsed with deionized water until the pH was constant and dried in an oven at 80°C for 12 h to obtain acid-modified biochar.

[0038] (3) 2.35 g of ferric chloride hexahydrate and 0.86 g of ferrous chloride tetrahydrate were added to 140 mL of deionized water and stirred to dissolve, and then 1 g of acid-modified biochar was added. After ultrasonic treatment for 10 min, ammonia water was added to adjust the pH to 9.1, and then stirred and reacted at 80 ° C for 30 min. Finally, it was rinsed with deionized water until the pH was constant, and then placed in an 80 ° C oven for drying for 12 h to obtain magnetically modified biochar.

[0039] Example 2

[0040] This embodiment provides a method for preparing magnetically modified biochar, which comprises the following steps:

[0041] (1) Waste corn straw was placed in a carbonization furnace, heated to 520°C at a rate of 12°C / min under a nitrogen atmosphere (to ensure the absence of oxygen), and maintained for 2.5 hours to carbonize, and biochar was obtained after cooling;

[0042] (2) The biochar was crushed using a grinder and passed through a 100-mesh sieve. 15 g of the biochar was placed in 600 mL of a 25% nitric acid solution and allowed to stand for 5 h. The biochar was then rinsed with deionized water until the pH was constant and dried in an oven at 85°C for 14 h to obtain acid-modified biochar.

[0043] (3) 2.35 g of ferric chloride hexahydrate and 0.86 g of ferrous chloride tetrahydrate were added to 140 mL of deionized water and stirred to dissolve. Then 1 g of acid-modified biochar was added. After ultrasonic treatment for 10 min, ammonia water was added to adjust the pH to 11. Then, the mixture was stirred and reacted at 85 °C for 40 min. Finally, the mixture was rinsed with deionized water until the pH was constant. The mixture was then placed in an oven at 85 °C and dried for 14 h to obtain magnetically modified biochar.

[0044] Example 3

[0045] This embodiment provides a method for preparing magnetically modified biochar, which comprises the following steps:

[0046] (1) The discarded reed straw was placed in a carbonization furnace, heated to 510°C at a rate of 11°C / min under a nitrogen atmosphere (to ensure the absence of oxygen), and maintained for 2 h to carbonize, and biochar was obtained after cooling;

[0047] (2) The biochar was crushed using a grinder and passed through a 100-mesh sieve. 15 g of the biochar was placed in 600 mL of a 22% nitric acid solution and allowed to stand for 4 h. The biochar was then rinsed with deionized water until the pH was constant and dried in an oven at 82°C for 13 h to obtain acid-modified biochar.

[0048] (3) 2.35 g of ferric chloride hexahydrate and 0.86 g of ferrous chloride tetrahydrate were added to 140 mL of deionized water and stirred to dissolve. Then 1 g of acid-modified biochar was added. After ultrasonic treatment for 10 min, ammonia water was added to adjust the pH to 10. Then, the mixture was stirred and reacted at 82 °C for 35 min. Finally, the mixture was rinsed with deionized water until the pH was constant. The mixture was then placed in an oven at 82 °C and dried for 13 h to obtain magnetically modified biochar.

[0049] Comparative Examples 1 to 7

[0050] Comparative Example 1: A method for preparing biochar is provided (ie, step 1), which differs from Example 1 in that the discarded corn cobs in Example 1 are replaced with discarded bamboo, and the other operations remain unchanged.

[0051] Comparative Example 2: A method for preparing biochar (i.e., step 1) is provided. The difference from Example 1 is that the discarded corn cobs in Example 1 are replaced with discarded coconut shells, and the other operations remain unchanged.

[0052] Comparative Example 3: A method for preparing biochar (i.e., step 1) is provided, which differs from Example 1 in that the discarded corn cobs in Example 1 are replaced with discarded walnut shells, and the other operations remain unchanged.

[0053] Comparative Example 4: A method for preparing biochar (ie, step 1) is provided, which differs from Example 1 in that the discarded corn cobs in Example 1 are replaced with discarded rice husks, and the other operations remain unchanged.

[0054] Comparative Example 5: A method for preparing biochar is provided (i.e., step 1). The difference from Example 1 is that the discarded corn cobs in Example 1 are replaced with coal, and the other operations remain unchanged.

[0055] Comparative Example 6: A method for preparing biochar is provided (ie, step 1), which differs from Example 1 in that the discarded corn cobs in Example 1 are replaced with birch, and the other operations remain unchanged.

[0056] Comparative Example 7: A method for preparing biochar is provided (i.e., step 1). The difference from Example 1 is that the discarded corn cobs in Example 1 are replaced with poplar wood, and the other operations remain unchanged.

[0057] Comparative Examples 8 to 9

[0058] Comparative Example 8: A method for preparing acid-modified biochar (i.e., step 2) is provided. The difference from Example 1 is that the "standing for 3 hours" in step (2) of Example 1 is changed to "magnetic stirring for 3 hours", and the other operations remain unchanged.

[0059] Comparative Example 9: A method for preparing acid-modified biochar (i.e., step 2) is provided. The difference from Example 1 is that the "standing for 3 hours" in step (2) of Example 1 is changed to "constant temperature oscillation for 3 hours", and the other operations remain unchanged.

[0060] Comparative Example 10

[0061] A method for preparing acid-modified biochar (i.e., step 2) is provided. The difference from Example 1 is that the "nitric acid solution with a mass fraction of 20%" in step (2) of Example 1 is replaced with "phosphoric acid solution with a mass fraction of 80%", and the other operations remain unchanged.

[0062] Analysis example

[0063] (1) Infrared spectroscopy analysis

[0064] The magnetic modified biochar obtained in Example 1 was analyzed by infrared spectroscopy. Figure 1 As shown by Figure 1It can be seen that the absorption peak near 582.24 corresponds to the Fe-O-Fe vibration of Fe3O4, the absorption peak near 1380.93 corresponds to the CO stretching on the carboxylic acid, the absorption peak near 1613.95 corresponds to the CO stretching on the carboxylic acid, and the absorption peak near 3386.38 corresponds to the in-plane bending of the OH on the carboxylic acid, which means that the magnetic modified biochar was successfully prepared.

[0065] (2) Transmission electron microscopy analysis

[0066] The magnetic modified biochar obtained in Example 1 was characterized using transmission electron microscopy. Figure 2 、 Figure 3 As shown in the figure, it can be seen that iron nanoparticles are evenly distributed on the surface of magnetically modified biochar, and the diameter of iron nanoparticles is about 20nm.

[0067] (3) Scanning electron microscopy analysis

[0068] The acid-modified biochar obtained in Example 1 (product of step 2) was characterized using scanning electron microscopy. Figure 4 As shown by Figure 4 It can be seen that acid-modified biochar has a rich pore structure.

[0069] Scanning electron microscopy was used to characterize the magnetic modified biochar obtained in Example 1. Figure 5 As shown by Figure 5 It can be seen that after magnetic modification, iron nanoparticles are evenly distributed on the surface of the material without obvious agglomeration.

[0070] (4) Magnetic properties analysis

[0071] The magnetic properties of the magnetic modified biochar obtained in Example 1 were analyzed, and the obtained hysteresis loop was as follows: Figure 6 As shown by Figure 6 It can be seen that this magnetic material has strong magnetism and exhibits almost zero coercive force and remanence at room temperature.

[0072] (V) Effect analysis of different raw materials

[0073] Ten types of biochar obtained in Examples 1 to 3 and Comparative Examples 1 to 7 were selected, and 150 mg of each of the ten biochars was weighed and placed in 5 ml of a 0.5 μg / mL atrazine (a triazine herbicide) aqueous solution. After vortexing for 4 minutes, the mixture was centrifuged for 3 minutes, and the supernatant was discarded. At this time, almost all of the atrazine was transferred to the biochar. 2 mL of ethyl acetate was added, vortexed for 4 minutes, and centrifuged again for 3 minutes. At this time, the atrazine was transferred from the biochar to the desorbent ethyl acetate. At this time, the ethyl acetate was introduced into a gas chromatograph-mass spectrometer through an automatic sampler for analysis. The peak areas of atrazine in the ten samples were compared to compare the adsorption capacities of the ten biochars. The peak areas are shown in Table 1:

[0074] Table 1

[0075]

[0076]

[0077] As can be seen from Table 1, the peak areas of Examples 1 to 3 are all greater than 2000, and the adsorption effects are significantly better than those of Comparative Examples 1 to 7, which are more conducive to the subsequent preparation of magnetically modified biochar with excellent adsorption performance.

[0078] (6) Analysis of the effects of different processes

[0079] After being treated in three different ways, namely, standing (Example 1), magnetic stirring (Comparative Example 8), and constant temperature oscillator (Comparative Example 9), the obtained materials were rinsed with deionized water and dried in an oven to obtain three acid-modified biochars. 150 mg of each of the three acid-modified biochars were weighed and placed in 5 mL of a 0.5 μg / mL atrazine aqueous solution. After vortexing for 4 minutes, the samples were centrifuged for 3 minutes. The supernatant was discarded. At this time, almost all of the atrazine was transferred to the acid-modified biochar adsorbent. 1 mL of ethyl acetate was added, vortexed for 4 minutes, and centrifuged again for 3 minutes. At this time, the atrazine was transferred from the adsorbent to the desorbent ethyl acetate. The ethyl acetate was then introduced into a gas chromatograph-mass spectrometer via an automatic sampler for analysis. The adsorption capacity of the three acid-modified biochars was compared. The peak area is shown in Table 2:

[0080] Table 2

[0081] Group Peak area Standing (Example 1) 6773 Magnetic stirring (Comparative Example 8) 6403 Constant temperature oscillation (Comparative Example 9) 4122

[0082] As shown in Table 2, the acid-modified biochar obtained by the process of Example 1 has the best effect, which is better than Comparative Examples 8 and 9, and is more conducive to the subsequent preparation of magnetically modified biochar with excellent adsorption performance.

[0083] (VII) Analysis of the effects of different acid solutions

[0084] Corn cobs were soaked in 20 wt.% nitric acid (Example 1) or 80 wt.% phosphoric acid (Comparative Example 10) for 3 hours to obtain acid-modified biochars. Their adsorption capacity for atrazine was compared by peak area. 150 mg of each of the two acid-modified biochars were weighed and placed in 5 ml of a 0.5 μg / mL atrazine aqueous solution. After vortexing for 4 minutes, the samples were centrifuged for 3 minutes. The supernatant was discarded. At this time, almost all of the atrazine was transferred to the acid-modified biochar adsorbent. 1 mL of ethyl acetate was added, vortexed for 4 minutes, and centrifuged again for 3 minutes. At this time, the atrazine was transferred from the adsorbent to the desorbent ethyl acetate. At this time, the ethyl acetate was introduced into a gas chromatograph-mass spectrometer through an automatic sampler for analysis. The adsorption capacity of the two acid-modified biochars was compared. The peak area values ​​are shown in Table 3:

[0085] Table 3

[0086] Group Peak area 20 wt.% nitric acid (Example 1) 3646 80 wt.% phosphoric acid (Comparative Example 10) 3134

[0087] As shown in Table 3, the acid-modified biochar obtained in Example 1 has the best effect, which is better than that in Comparative Example 10, and is more conducive to the subsequent preparation of magnetically modified biochar with excellent adsorption performance.

[0088] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. Application of magnetically modified biochar as an adsorbent for triazine herbicides, characterized in that: The preparation method of magnetic modified biochar is as follows: (1) Carbonizing waste biomass under heating and oxygen-free conditions to obtain biochar; wherein: The waste biomass is one of corn cobs, corn stalks or reed stalks; (2) mixing the biochar with an acidic solution and allowing the mixture to stand, and then washing and drying the mixture in sequence to obtain acid-modified biochar; wherein: The standing time is 3 to 5 hours; the acidic solution is a 20 to 25 wt.% nitric acid solution; (3) The acid-modified biochar, ferric chloride hexahydrate and ferrous chloride tetrahydrate are mixed and dissolved in water, and then ammonia water is added to stir and react, and then washed and dried in sequence to obtain magnetically modified biochar.

2. The use of the magnetically modified biochar as a triazine herbicide adsorbent according to claim 1, characterized in that: In step (1), the waste biomass is heated to 500-520°C at a rate of 10-12°C / min under a nitrogen atmosphere, and carbonized for 2-2.5 hours, and then cooled to obtain biochar.

3. The use of the magnetically modified biochar as a triazine herbicide adsorbent according to claim 1, characterized in that: In step (2), the mass volume ratio of the biochar to the acidic solution is 1:40 / g:mL; the drying temperature is 80-85°C, and the drying time is 12-14 hours.

4. The use of the magnetically modified biochar as a triazine herbicide adsorbent according to claim 1, characterized in that: In step (3), the mass ratio of the acid-modified biochar, ferric chloride hexahydrate and ferrous chloride tetrahydrate is 1:2.35:0.

86.

5. The use of the magnetically modified biochar as a triazine herbicide adsorbent according to claim 1, characterized in that: In step (3), after adding ammonia water, the pH value of the solution is greater than 9; the reaction temperature is 80-85°C, and the reaction time is 30-40 minutes; the drying temperature is 80-85°C, and the drying time is 12-14 hours.

Images