Preparation method and application of super-hydrophobic modified nitrogen and phosphorus co-doped sedimental biochar

Abstract

This invention discloses a method for preparing superhydrophobically modified nitrogen-phosphorus co-doped sediment biochar, comprising: drying and pulverizing river and lake sediment; mixing the pulverized river and lake sediment with a nitrogen-phosphorus modifier and adding ethanol; and preparing nitrogen-phosphorus co-doped sediment biochar by pyrolysis; and then modifying the sediment biochar prepared in the first step with a hydrophobic modifier. This invention uses ammonium dihydrogen phosphate as the nitrogen-phosphorus modifier and stearic acid and its derivatives as the hydrophobic modifier, resulting in the formation of carbon atom defect structures and electron-rich regions on the surface of the superhydrophobically modified nitrogen-phosphorus co-doped sediment biochar. This significantly enhances both adsorption capacity and catalytic activity, making it suitable not only as an adsorbent for the treatment of heavy metal ion pollution but also for the catalytic degradation of organic matter, while exhibiting good stability.

Description

Technical Field

[0001] This invention relates to new materials in environmental pollution treatment technology, and in particular to a method for preparing and applying superhydrophobic modified nitrogen and phosphorus co-doped bottom sediment biochar. Background Technology

[0002] In river and lake pollution control, once external pollution sources are effectively controlled, sediment pollution becomes a key factor affecting water quality. In recent years, the resource utilization of river and lake sediments has become a hot research topic in addressing sediment accumulation during dredging. However, due to the inherent physicochemical properties of the sediments themselves, commonly prepared sediment biochar suffers from problems such as limited surface functional groups, strong hydrophilicity, and small specific surface area, resulting in limited adsorption and catalytic capabilities, particularly poor adsorption of hydrophobic pollutants. Furthermore, recovery is difficult after water remediation, thus limiting the application of sediment biochar. Therefore, existing technologies utilize modification techniques such as chemical and physical modifications to alter biochar.

[0003] CN116116382A discloses a method for preparing nitrogen-phosphorus modified rice husk biochar. The method involves pyrolyzing rice husk and ammonium dihydrogen phosphate in a muffle furnace at 250-350℃ for 4.5-5.5 hours to prepare nitrogen-phosphorus modified biochar, which is mainly used for adsorbing and removing cadmium ions. The preparation process of this invention is simple, but the function is relatively limited and recycling is difficult.

[0004] CN119303548A discloses a method for preparing micro / narrow mesoporous highly hydrophobic biochar. The method involves pyrolyzing phosphoric acid and coconut coir in a tube furnace at 800℃ for 2 hours to prepare biochar, followed by hydrophobic modification using methyltrimethoxysilane under vacuum drying at 120℃ to obtain micro / narrow mesoporous highly hydrophobic biochar. This invention uses waste coconut coir as raw material and has high recycling efficiency; however, the silane coupling agent is costly and may impact water quality.

[0005] However, existing biochar modification methods often only increase the specific surface area of ​​biochar, adjust its pore structure, and enhance its physical adsorption capacity. Furthermore, conventionally prepared powdered biochar, after being used for water remediation, is uniformly dispersed in the water, making it difficult to recycle and resulting in material waste. Moreover, while some modified sediment biochars possess high hydrophobicity, they are costly and prone to introducing new pollution. Summary of the Invention

[0006] In view of this, the present invention proposes a method for preparing superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar, and the present invention also provides the application of superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The method for preparing superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar according to the present invention includes: The first step involves drying and crushing the river and lake bottom sediment, mixing the crushed river and lake bottom sediment with a nitrogen and phosphorus modifier, adding ethanol, and preparing nitrogen and phosphorus co-doped bottom sediment biochar using a pyrolysis method; wherein the nitrogen and phosphorus modifier is any one or any combination of two or more of urea phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate. The second step involves using a hydrophobic modifier to modify the sediment biochar prepared in the first step, so that the contact angle of the modified sediment biochar is greater than or equal to 145°. In the first step, the carbon content in the sediment is greater than or equal to 20%, and in the second step, the hydrophobic modifier is any one or any combination of two or more of stearic acid, stearate, and isostearic acid.

[0008] The beneficial effects are as follows: This invention uses ammonium dihydrogen phosphate as a nitrogen and phosphorus modifier, which not only provides nitrogen and nitrogen and phosphorus doping for the modification of bottom sediment biochar, but also increases the specific surface area and number of pores of biochar by decomposing it during pyrolysis, thus ensuring its adsorption performance. Specifically, the doped nitrogen mainly exists in the form of graphitic nitrogen, enhancing the electrocatalytic ability of biochar; the doped phosphorus mainly exists in the form of phosphate esters, enhancing the coordination ability and synergistic catalytic ability of biochar to metals.

[0009] In this invention, nitrogen and phosphorus doping and hydrophobic modification create carbon atom defect structures and electron-rich regions on the surface of biochar, significantly enhancing both adsorption capacity and catalytic activity, thus facilitating the adsorption and catalytic degradation of organic matter. Furthermore, the hydrophobically modified nitrogen and phosphorus co-doped sediment biochar in this invention exhibits a contact angle SA = 150.8°, demonstrating exceptionally high hydrophobicity, which aids in the degradation of organic matter in water and facilitates separation.

[0010] Preferably, in the first step, after the river and lake bottom sediment is crushed, it is sieved with a sieve aperture of 75 μm; the nitrogen and phosphorus modifier is ammonium dihydrogen phosphate, and its mass ratio with the river and lake bottom sediment is 1:2.

[0011] Preferably, in the first step, after mixing river and lake sediment and ammonium dihydrogen phosphate and adding ethanol, the mixture is first subjected to ultrasonic treatment to make the ammonium dihydrogen phosphate and river and lake sediment evenly mixed. After ultrasonic treatment, the mixture is stirred and heated to make the ethanol evaporate. After the ethanol evaporates, a pyrolysis reaction is carried out in a nitrogen atmosphere, and the pyrolysis temperature is controlled at 600-700℃.

[0012] Preferably, in the second step, the amount of the hydrophobic modifying agent is 0.5%-2.5% of the mass of the sediment biochar; the mass ratio of stearic acid and stearic acid derivative in the hydrophobic modifying agent is 1:(0-1).

[0013] Preferably, in the second step, when hydrophobically modifying the sediment biochar, the hydrophobic modifier is dissolved in ethanol, then added to the sediment biochar, ultrasonically mixed, and shaken at room temperature for 60-120 minutes. After filtration or centrifugation, it is finally vacuum dried at 35-40°C to obtain superhydrophobically modified nitrogen-phosphorus co-doped sediment biochar.

[0014] This invention also provides the application of superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar as an adsorbent in the remediation of heavy metal pollution, wherein the heavy metal ions include Cd. 2+ Pb 2+ Cu 2+ and Zn 2+ The nitrogen and phosphorus modifier of this invention generates gas through decomposition during pyrolysis, increasing the specific surface area and number of pores in the biochar, thereby enhancing its adsorption capacity and promoting the physical adsorption of metal ions by the biochar. Furthermore, the phosphorus doped in this invention mainly exists in the form of phosphate esters, enhancing the coordination ability of the biochar to metals and further promoting the adsorption performance of the biochar for metal ions. Moreover, the superhydrophobic properties of this invention facilitate the separation of the biochar, preventing dissolution during use.

[0015] This invention also provides the application of superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar as a degradation material in the degradation of sulfonamide antibacterial drugs in water. Specifically, an oxidant is added during the degradation of sulfonamide antibacterial drugs; the oxidant is any one or a combination of two or more of hydrogen peroxide, persulfate, and perdisulfate. In this invention, sulfonamide antibacterial drugs such as sulfadiazine are hydrophobic pollutants. This invention significantly enhances the physical adsorption of sulfonamide antibacterial drugs by hydrophobically modifying the nitrogen-phosphorus co-doped sediment biochar. Furthermore, this invention can also promote the oxidative degradation of sulfonamide antibacterial drugs, and the degradation pathway includes... • OH radical pathway and 1 O2 is a non-radical pathway, and 1 O2 is the main reactive oxygen species in the system, while the graphitic nitrogen and COP bonds in biochar participate in the catalytic production of hydrogen peroxide. 1 The O2 process further promotes the degradation of sulfonamide antibacterial drugs.

[0016] Compared with the prior art, the advantages of the present invention are as follows: The present invention uses ammonium dihydrogen phosphate as a nitrogen and phosphorus modifier, which can not only provide nitrogen and nitrogen and phosphorus elements for the modification of bottom sediment biochar, but also increase the specific surface area and number of pores of biochar by generating gas during pyrolysis, thereby improving the adsorption performance.

[0017] In this invention, the doped nitrogen element mainly exists in the form of graphitic nitrogen, enhancing the electrocatalytic ability of biochar; the doped phosphorus element mainly exists in the form of phosphate esters, enhancing the coordination ability and synergistic catalytic ability of biochar to metals. Furthermore, the modified biochar surface forms carbon atom defect structures and electron-rich regions, significantly enhancing both adsorption capacity and catalytic activity. Experiments show that the hydrophobically modified nitrogen-phosphorus co-doped sediment biochar of this invention has a contact angle SA = 150.8°, exhibiting extremely high hydrophobicity and facilitating separation. Attached Figure Description

[0018] Figure 1 These are SEM-EDS characterization images of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention. The left image is the SEM image, and the right image is the EDS image.

[0019] Figure 2 This is the XRD pattern of the superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar of this invention.

[0020] Figure 3 This is the water contact angle diagram of superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar (CA=150.7°).

[0021] Figure 4 This is a high-resolution XPS image of N and P elements in superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar.

[0022] Figure 5 This invention describes the adsorption effect of superhydrophobic modified nitrogen-phosphorus co-doped bottom mud biochar with different ammonium dihydrogen phosphate doping ratios on heavy metal ions in Example 1 of this invention.

[0023] Figure 6 This refers to the effect of different pyrolysis temperatures on the Cd content of superhydrophobic modified nitrogen-phosphorus co-doped bottom mud biochar in Example 2 of the present invention. 2+ The effect of adsorption.

[0024] Figure 7 This is a graph showing the degradation effect of superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar on sulfadiazine in Example 4 of the present invention (in the vertical axis C / C0, C is the concentration of sulfadiazine at time t, and C0 is the initial concentration of sulfadiazine).

[0025] Figure 8 This describes the precipitation of the superhydrophobic modified nitrogen and phosphorus co-doped bottom mud biochar during the first cycle degradation reaction of this invention.

[0026] Figure 9 In Figure a, the precipitation of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention during the second cycle degradation reaction is shown, and in Figure b, the precipitation during the third cycle degradation is shown.

[0027] Figure 10In Figure a, the precipitation of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention during the fourth cycle degradation reaction is shown, and in Figure b, the precipitation during the fourth cycle degradation is shown.

[0028] Figure 11 This is a diagram showing the degradation effect of superhydrophobic modified nitrogen and phosphorus co-doped bottom mud biochar on sulfadiazine during recycling in Example 5.

[0029] Figure 12 This is a high-resolution XPS image of N and P elements after the superhydrophobic modified nitrogen and phosphorus co-doped bottom sediment biochar catalytic reaction of the present invention (after one use). Detailed Implementation

[0030] It should be noted that all chemical reagents used in this invention are commercially available conventional reagents.

[0031] This invention proposes a method for preparing superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar, comprising: The first step is the preparation of nitrogen and phosphorus co-doped sediment biochar. Dry the river and lake bottom sediment (preferably oven drying), crush it, and pass it through a 200-mesh sieve to obtain river and lake bottom sediment (in powder form) with a particle size ≤75 μm. If it cannot be used in time, seal the bottom sediment and place it in a dry container. Mix river and lake bottom sediment with ammonium dihydrogen phosphate at a certain mass ratio, add ethanol, and sonicate for 30 minutes. After sonication, the mixture was stirred in a constant temperature water bath at 35℃ to allow the ethanol to evaporate. After the ethanol evaporated, a pyrolysis reaction was carried out in a nitrogen atmosphere. The pyrolysis temperature was controlled at 600-700℃ and the pyrolysis time was controlled within 6 hours. After the pyrolysis was completed, the mixture was washed with deionized water and dried at 100℃ under normal pressure to constant weight to obtain nitrogen and phosphorus co-doped bottom mud biochar. The second step involves superhydrophobic modification of nitrogen and phosphorus co-doped sediment biochar. Dissolve the hydrophobic modifier in ethanol, then add nitrogen and phosphorus co-doped bottom sediment biochar, stir at room temperature for 5 min, sonicate for 20-30 min, and then shake for 60-120 min; After oscillation, filter (or centrifuge), and vacuum dry the filter material at 35-40℃ for 3 hours to obtain superhydrophobic modified nitrogen and phosphorus co-doped bottom mud biochar.

[0032] In the above preparation method, the sediment used in the first step of the present invention must meet the following requirements: the carbon content (mass fraction, dry weight content) of the sediment must be ≥20%; the ammonium dihydrogen phosphate in the first step can also be replaced with diammonium hydrogen phosphate or urea phosphate, which has pyrolytic volatility; in the second step, the amount of hydrophobic modifying agent used is 0.5%-2.5% of the mass of the sediment biochar; the mass ratio of stearic acid and stearic acid derivative in the hydrophobic modifying agent is 1:(0-1), and the stearic acid derivative is preferably stearate.

[0033] The first step of this invention uses ethanol as a solvent and ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and / or urea phosphate as nitrogen and phosphorus modifying agents. Pyrolysis is used to ensure that nitrogen exists primarily in the form of graphite nitrogen, enhancing the electrocatalytic ability of biochar, while phosphorus exists primarily in the form of phosphate esters, enhancing the coordination and synergistic catalytic ability of biochar to metals. Furthermore, the gas generated during the pyrolysis of the phosphoric acid modifier helps to increase the specific surface area and pore number of the modified biochar, thereby improving its adsorption performance. In this first step, the ratio of river / lake sediment to ethanol is 100 g: 1 L.

[0034] The second step of this invention uses ethanol as a solvent. Leveraging ethanol's low surface energy and high permeability, stearic acid and its derivatives undergo hydrolysis, condensation, polar adsorption, and other chemical reactions, as well as physical adsorption, with the polar head groups in their molecular structure on the surface and within the pores of the nitrogen-phosphorus co-doped biochar. This further allows stearic acid and its derivatives to be tightly modified and grafted onto the biochar surface, with the hydrophobic tail chains of stearic acid and its derivatives facing the air, ensuring the hydrophobic properties of the biochar and reducing its recovery difficulty. In this second step, the ratio of nitrogen-phosphorus co-doped bottom sediment biochar to ethanol is 100g:1L.

[0035] The present invention will now be described in more detail with reference to the accompanying drawings. It should be noted that the sediment in the present invention is derived from the surface sediment (30 cm thick) of Wuliangsuhai Lake, and the carbon content of the sediment is 20.2% (dry weight).

[0036] Example 1: Effect of nitrogen and phosphorus modifier dosage on the biochar of the present invention This embodiment uses ammonium dihydrogen phosphate as a nitrogen-phosphorus modifier to investigate the effect of ammonium dihydrogen phosphate dosage on the performance of superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar, specifically including the following: The first step is the preparation of nitrogen and phosphorus co-doped sediment biochar. Dry the river and lake bottom sediment (preferably oven drying), pulverize it, and pass it through a 200-mesh sieve to obtain river and lake bottom sediment (in powder form) with a particle size ≤75 μm. Mix 20g of ammonium dihydrogen phosphate and river and lake bottom sediment in a certain mass ratio, add 500ml of ethanol, and sonicate for 30min. After sonication, stir at a constant temperature of 35℃ to allow the ethanol to evaporate. After the ethanol evaporates, a pyrolysis reaction is carried out in a nitrogen atmosphere. The pyrolysis temperature is controlled at 700℃ and the pyrolysis time is controlled within 3 hours. After the pyrolysis is completed, the mixture is washed with deionized water and dried at 100℃ to constant weight to obtain nitrogen and phosphorus co-doped bottom mud biochar with different doping amounts. The mass ratios of ammonium dihydrogen phosphate and sediment were 3:1, 2:1, 1:1, 1:2, and 1:3, respectively, and nitrogen-phosphorus co-doped sediment biochar with different nitrogen and phosphorus doping amounts was prepared based on the different raw material ratios. The second step involves superhydrophobic modification of nitrogen and phosphorus co-doped sediment biochar. Dissolve 2g of stearic acid in 500ml of ethanol, then add nitrogen and phosphorus co-doped sediment biochar (the amount of stearic acid is 2.5% of the amount of nitrogen and phosphorus co-doped sediment biochar), stir at room temperature for 5min, sonicate for 20-30min, and then shake for 60-120min; after shaking, filter, and vacuum dry the filter at 35-40℃ for 3h to obtain superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar (hereinafter referred to as "NPSBC"). The third step is to use Pb 2+ Cu 2+ Cd 2+ and Zn 2+ To investigate the adsorption performance of bottom sediment biochar prepared at different mass ratios for metal ions (all four metal ions at a concentration of 100 mg / L), the following was observed: (Specifically, using Pb...) 2+ Taking adsorption as an example, take multiple equal volumes (100 ml each) of Pb 2+ The solution was divided into five groups, and Pb was added. 2+ NPSBC was added to the solution (the same mass ratio of NPSBC was added to each group), with an addition amount of 1.0 g / L; similarly, Cu was obtained. 2+ Cd 2+ and Zn 2+ The corresponding NPSBC processing group; Each treatment group was shaken for 180 minutes, and samples were taken periodically to detect the concentration of metal ions in the samples. Based on the initial concentration and the concentration at reaction time t, the removal rate of metal ions by the modified co-doped adsorbent of this invention was calculated (removal rate = (C0 - C)). t ()×100% / C0), see details Figure 5 .

[0037] Depend on Figure 5 It can be seen that modified co-doped biochar with different mass ratios all showed good removal capacity for lead ions. When the mass ratio of ammonium dihydrogen phosphate to river and lake sediment was 1:2, adsorption equilibrium was quickly reached, and Pb... 2+ The removal rate is as high as 99% or more; for Cd 2+ and Zn 2+ Generally speaking, the removal effect is best when the mass ratio of ammonium dihydrogen phosphate to river and lake sediment is 1:2; for Cu 2+ In general, except for the mass ratio of 1:3, the modified co-doped biochar corresponding to the other mass ratios affects Cu. 2+ Their removal capabilities are basically the same.

[0038] Experimental results show that adding excessive amounts of ammonium dihydrogen phosphate to the sediment can lead to more N / P heteroatoms entering the biochar lattice, thereby relatively reducing the number of C atoms per unit volume and decreasing the degree of biochar carbonization. Furthermore, considering that polluted water bodies typically contain various heavy metal ions, the mass ratio of ammonium dihydrogen phosphate to river and lake sediment is preferably controlled at 1:2 in this invention.

[0039] Example 2 I. This embodiment investigates the effect of pyrolysis temperature as a variable and a mass ratio of ammonium dihydrogen phosphate to river and lake sediment of 1:2 on the performance of superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar: In this embodiment, the pyrolysis temperatures of the sediment and ammonium dihydrogen phosphate are 300℃, 500℃, 600℃, 700℃, and 800℃, respectively; the second step is the same as in Example 1, to obtain hydrophobically modified nitrogen-phosphorus co-doped biochar. For easy distinction, they are respectively designated as NPSBC300, NPSBC500, NPSBC600, NPSBC700, and NPSBC800.

[0040] This embodiment uses Cd at a concentration of 100 mg / L. 2+ To process the object, take multiple equal volumes (100 ml each) of Cd. 2 + The solution was divided into five groups (three in each group), and then applied to Cd. 2+ Modified co-doped biochar (each group corresponds to a pyrolysis temperature) was added to the solution at a rate of 1.0 g / L. Each group was shaken for 180 minutes, and samples were taken periodically to detect the concentration of metal ions in the samples. Based on the initial concentration and the concentration at reaction time t, the removal rate of metal ions by the modified co-doped adsorbent of this invention was calculated (removal rate = (C0 - C)). t ()×100% / C0), see details Figure 6 .

[0041] Depend on Figure 6 It can be seen that as the pyrolysis temperature of biochar increases, the effect of modified co-doped biochar on Cd... 2+ The removal rate gradually increased, and the modified co-doped biochar at a pyrolysis temperature of 700℃ showed the best performance in removing Cd. 2+ The removal rate was highest at 800℃, while the removal rate of Cd was highest at 800℃. 2+ The removal rate actually decreased.

[0042] The results show that, within a certain range, increasing the pyrolysis temperature helps to improve the carbonization degree of the bottom sediment biochar and increase its specific surface area; however, if the temperature is too high, the carbon matrix of the biochar decomposes again due to heat, leading to a decrease in the carbonization degree of the biochar. Therefore, this invention uses 700℃ as the optimal pyrolysis temperature.

[0043] Example 3 This invention characterizes superhydrophobically modified nitrogen-phosphorus co-doped sediment biochar (i.e., NPSBC700 in Example 2) with an ammonium dihydrogen phosphate to sediment mass ratio of 1:2 and a pyrolysis temperature of 700℃, based on Examples 1-2: 1. The SEM-EDS characterization results of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention are as follows: Figure 1 As shown. By Figure 1 As shown in the left figure, the hydrophobically modified nitrogen-phosphorus co-doped sediment biochar of this invention has a rough and porous surface, indicating that the biochar has good adsorption potential. Figure 1 As shown in the right figure, in addition to C, the biochar of this invention contains Fe, which helps to improve the catalytic performance of the biochar.

[0044] 2. The XRD results of the superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar of this invention are as follows: Figure 2 As shown in the figure. The results show that the modified biochar of the present invention contains a large amount of SiO2 crystal structure, which is consistent with the main components of river and lake sediments; typical carbon nitride structure (C3N4) was also detected on the surface of the modified biochar, indicating that the modified biochar of the present invention has good electron transfer performance and active catalytic performance; various metal minerals (such as Ca and Fe) were also detected in the modified biochar, which helps to improve the catalytic ability of the biochar.

[0045] 3. The hydrophobicity results of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention are as follows: Figure 3 As shown, its water contact angle SA = 150.8°, exhibiting superhydrophobicity, facilitates separation and recycling.

[0046] 4. The high-resolution energy dispersive spectroscopy (EDS) spectrum of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention is shown in Figure 4. Combined with... Figure 4 It can be seen that the doped N in the modified biochar mainly exists in three forms: pyridine N (18.3%), pyrrole N (22.1%), and graphitic nitrogen (59.6%), proving that N has been successfully doped into the C lattice framework; the doped P in the modified biochar mainly exists in the forms of CPO (approximately 50.3%) and COP (approximately 49.7%), proving that P has been successfully doped into the C lattice framework.

[0047] 5. Adsorption-desorption test results of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention show that the specific surface area of ​​the modified biochar of this invention is 263 m². 2 / g, far exceeding that of conventional biochar (80 m 2 / g).

[0048] In summary, the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention not only exhibits superhydrophobicity, preventing dissolution in aqueous reaction systems and facilitating recovery, but also possesses a large specific surface area and a rough, porous surface, demonstrating excellent adsorption performance for heavy metals. Therefore, it can be used for the remediation of heavy metal pollution in soil / water bodies. Furthermore, the superhydrophobicity of this invention, combined with the C3N4 on the biochar surface and the metal minerals within the biochar, significantly enhances the biochar's catalytic activity, providing a foundation for the adsorption and catalytic degradation of organic matter in water.

[0049] Example 4: Application of the bottom sediment biochar of the present invention in the catalytic degradation of sulfonamide antibacterial drugs This invention uses sulfadiazine as the degradation target, NPSBC700 from Example 2 as the adsorbent and catalyst, and hydrogen peroxide as the oxidant to catalyze the degradation of sulfadiazine in an aqueous system, specifically including: Add 0.2 ml of H2O2 (concentration 20 mM) to 100 ml of sulfadiazine solution (dissolved by heating and stirring with deionized water, concentration 20 mg / L). The total volume of the reaction system is close to 100 ml. Add NPSBC700 to the reaction system at a dosage of 1.0 g / L. The pH is at its natural value. The reaction system was shaken at room temperature for 2 hours. During the shaking reaction, samples were taken at 0, 15, 30, 60, 90, and 120 min, with a sample volume of 500 μL. After sampling, 500 μL of methanol was added to the sample to terminate the degradation reaction of sulfadiazine. The samples were then filtered through a 0.22 μm organic filter, and the concentration of sulfadiazine in each sample was measured. The results are shown in [Figure number missing]. Figure 7 .

[0050] The superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar of this invention catalyzes the production of H2O2 during degradation. 1 O2 (non-free radical) then decomposes sulfadiazine through reactive oxygen species oxidation. On the other hand, the biochar of this invention generates a large number of surface carbon free radicals during pyrolysis, which promote the formation of [something] on the surface of the biochar in the aqueous system. • OH radicals can further promote the oxidative degradation of sulfadiazine, increasing the degradation rate of the target compound. Results show (see...) Figure 7 As time progressed, the concentration of the target substance in the reaction system gradually decreased. After 2 hours of degradation, the removal rate of sulfadiazine reached 97.6%, indicating that the biochar of this invention has a good degradation ability for sulfadiazine and has practical application value.

[0051] Example 5: Stability and recyclability of bottom sediment biochar of the present invention in the catalytic degradation of sulfonamide antibacterial drugs I. This invention examines the stability of bottom sediment biochar in the catalytic degradation of sulfonamide antibacterial drugs by considering the heavy metal ion precipitation in the reaction system. Specifically, this includes the following: 1. The first round of degradation reaction was carried out according to the reaction system and reaction conditions in Example 4 (reaction time: 240 min). Samples were taken every 30 min during the reaction, with a sample volume of 500 μL. After sampling, 500 μL of methanol was added to the sample to terminate the degradation reaction of sulfadiazine. The sample was then filtered through a 0.22 μm organic filter. After treatment, the heavy metal ions in each sample were detected and analyzed, as detailed in [link to details]. Figure 8 Combining Figure 8 It can be seen that no heavy metal ions were detected during the first round of degradation. A small amount of silicate on the surface of NPSBC700 was dissolved and released into the solution, indicating that it exhibited good stability in the first round of degradation.

[0052] 2. After the first round of degradation reaction is completed, centrifuge to obtain the single-use NPSBC700, wash it three times with ultrapure water, dry it, and add the single-use NPSBC700 to the reaction system of Example 4 to carry out the second round of degradation reaction. Samples are taken every 30 minutes during the reaction, and the sample processing is the same as in the first round of degradation reaction. The precipitation of heavy metal ions in the sample is measured, as detailed in [link to example]. Figure 9 Figure a in the middle.

[0053] The results showed that, in addition to a small amount of silicon precipitating in the reaction system, Cu also precipitated. 2+ Mn 2+ Zn 2+ A small amount of As (total arsenic, the same below) precipitates out, including Cu. 2+ With As (total arsenic) close to 0, Zn 2+ The maximum leaching amount is close to 1 mg / L, and the concentration of the leached metal is within the industry requirements.

[0054] 3. After the second round of degradation reaction is completed, recover NPSBC700 as described in step 2, and use the used NPSBC700 for the third round of degradation reaction. Take samples every 30 minutes during the reaction, processing them as in the first round of degradation reaction, and determine the precipitation of heavy metal ions from the samples. See details below. Figure 9 Image C in the middle.

[0055] Depend on Figure 9 As can be seen from b, during the degradation process, the bottom sediment biochar of this invention contains only Cu, in addition to a small amount of silicon precipitating out. 2+ Mn 2+ Zn 2+ A small amount of As (total arsenic) and Cu precipitate out. 2+ Trace amounts of As (total arsenic) and Zn are released. 2+The maximum precipitation amount is approximately 0.5 mg / L, and precipitation equilibrium is reached. The precipitation concentration of metal ions is within the range required by national standards.

[0056] 4. Similarly, after the third round of degradation reaction is completed, the fourth and fifth rounds of degradation reaction are carried out sequentially. The precipitation of heavy metals in NPSBC700 is as follows: Figure 10 As shown.

[0057] Depend on Figure 8-10 It can be seen that during the degradation process, the superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar of this invention only precipitates silicon and a small amount of Cu. 2+ Mn 2+ Zn 2+ The presence of As and the leaching of heavy metals are all within the range required by national standards, indicating that the superhydrophobic modified nitrogen and phosphorus co-doped sediment biochar of this invention exhibits good stability when used for the degradation of sulfonamide antibacterial drugs, thereby avoiding secondary pollution to the environment.

[0058] II. Cyclic Degradation Performance of Bottom Sediment Biochar of the Present Invention in Catalytic Degradation of Sulfonamide Antibacterial Drugs In the first to fifth rounds of degradation reactions described above, sulfadiazine was detected in each sample, and the results are shown below. Figure 11 Combining Figure 11 It can be seen that the superhydrophobic modified nitrogen and phosphorus co-doped bottom mud biochar of the present invention still has a removal rate of sulfadiazine of more than 80% when used for the third time, indicating that the present invention has a certain degree of recyclability in the degradation of sulfadiazine.

[0059] III. High-resolution characterization of the superhydrophobically modified nitrogen-phosphorus co-doped sediment biochar used once was shown in the figure. Figure 12 To combine with Figure 4 In comparison, the proportions of graphite nitrogen and COP on the surface of the biochar of this invention are significantly reduced, indicating that graphite N and COP bonds play a key role in the catalytic process.

[0060] Example 6: Stability of the bottom sediment biochar of the present invention during storage This invention uses TCLP, HJ557-2010, and HJ / T299-2007 to extract heavy metal ions from the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention, specifically including the following: When extracting heavy metal ions from superhydrophobic modified nitrogen-phosphorus co-doped bottom sludge biochar using the TCLP method, glacial acetic acid with a pH of 2.88±0.05 was used as the extractant to simulate the leaching properties of heavy metal elements in a landfill and leachate environment. The liquid-to-solid ratio was 20L:1kg (i.e., 2000mL of extractant was added to 100g of superhydrophobic modified nitrogen-phosphorus co-doped bottom sludge biochar). The leaching of metal elements in the extract is shown in Table 1.

[0061] When extracting heavy metal ions from superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar using the HJ557-2010 method, ultrapure water or distilled water was used as the extractant to simulate the leaching characteristics of toxic substances in the groundwater environment. The liquid-to-solid ratio was 10L:1kg (i.e., 1000mL of extractant was added to 100g of superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar), and the mixture was horizontally shaken for 8 hours. The leaching of metal elements in the extract is shown in Table 1.

[0062] When extracting heavy metal ions from superhydrophobic modified nitrogen-phosphorus co-doped bottom mud biochar according to HJ / T299-2007, a mixed acid solution with pH=3.20±0.05 was prepared using concentrated sulfuric acid (analytical grade, AR) and concentrated nitric acid (analytical grade, AR) at a mass ratio of 2:1 as the extractant. The liquid-solid ratio was 10L:1kg (i.e., 1000mL of extractant was added to 100g of superhydrophobic modified nitrogen-phosphorus co-doped bottom mud biochar). The solution was inverted and shaken. The leaching of metal elements in the extract after shaking is shown in Table 1.

[0063] Table 1. Leaching of heavy metals from bottom sediment biochar according to TCLP, HJ557-2010 and HJ / T299-2007 Table 1 shows that no significant metal leaching occurred in any of the three simulated scenarios, and the leaching amounts of the few leached metals were extremely low, all falling below the thresholds specified in the toxic substance leaching standards. The results indicate that the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar of this invention exhibits good stability in all three simulated scenarios. This is attributed to the presence of numerous basic functional groups (such as ketones, quinones, pyridine nitrogen, pyrrole nitrogen, etc.) on the surface of the co-doped sediment biochar. These basic functional groups facilitate the immobilization of heavy metals, resulting in good stability and safety of this invention.

[0064] In summary, the superhydrophobic nitrogen-phosphorus co-doped sediment biochar obtained by using ammonium dihydrogen phosphate as a nitrogen-phosphorus modifier and modifying it with stearic acid and its derivatives not only has excellent adsorption performance for the treatment of heavy metal pollution, but can also be used to degrade organic pollutants. It also has good stability and is worthy of promotion.

Claims

1. A method for preparing superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar, characterized in that: The preparation method includes the following: The first step involves drying and crushing the river and lake bottom sediment, mixing the crushed river and lake bottom sediment with a nitrogen and phosphorus modifier, adding ethanol, and preparing nitrogen and phosphorus co-doped bottom sediment biochar using a pyrolysis method; wherein the nitrogen and phosphorus modifier is any one or any combination of two or more of urea phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate. The second step involves using a hydrophobic modifier to modify the sediment biochar prepared in the first step, so that the contact angle of the modified sediment biochar is greater than or equal to 145°. In the first step, the carbon content in the sediment is greater than or equal to 20%, and in the second step, the hydrophobic modifier is any one or any combination of two or more of stearic acid, stearate, and isostearic acid.

2. The method for preparing superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar according to claim 1, characterized in that: In the first step, after the river and lake bottom sediment is crushed, it is sieved with a sieve aperture of 75 μm; the nitrogen and phosphorus modifier is ammonium dihydrogen phosphate, and its mass ratio with the river and lake bottom sediment is 1:

2.

3. The method for preparing superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar according to claim 1, characterized in that: In the first step, the river and lake bottom sediment and ammonium dihydrogen phosphate are mixed and ethanol is added. The mixture is then ultrasonically treated to ensure that the ammonium dihydrogen phosphate and the river and lake bottom sediment are mixed evenly. After ultrasonic treatment, the mixture is stirred and heated to allow the ethanol to evaporate. After the ethanol has evaporated, a pyrolysis reaction is carried out in a nitrogen atmosphere, with the pyrolysis temperature controlled at 600-700℃.

4. The method for preparing superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar according to claim 1, characterized in that: In the second step, the amount of the hydrophobic modifying agent is 0.5%-2.5% of the mass of the bottom sediment biochar; the mass ratio of stearic acid and stearic acid derivative in the hydrophobic modifying agent is 1:(0-1).

5. The method for preparing superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar according to claim 1, characterized in that: In the second step, when hydrophobically modifying the sediment biochar, the hydrophobic modifier is dissolved in ethanol, then added to the sediment biochar, ultrasonically mixed, and shaken at room temperature for 60-120 minutes. After filtration or centrifugation, it is finally vacuum dried at 35-40℃ to obtain superhydrophobically modified nitrogen and phosphorus co-doped sediment biochar.

6. The application of the superhydrophobically modified nitrogen-phosphorus co-doped sediment biochar prepared according to any one of claims 1-5 as an adsorbent in the remediation of heavy metal pollution, wherein, Heavy metals include Cd 2+ Pb 2+ Cu 2+ and Zn 2+ .

7. The application of the superhydrophobic modified nitrogen-phosphorus co-doped sediment biochar prepared according to any one of claims 1-5 as a degradation material in the degradation of sulfonamide antibacterial drugs in water, wherein, An oxidizing agent is added during the degradation of sulfonamide antibacterial drugs. The oxidizing agent is any one or a combination of two or more of hydrogen peroxide, persulfate, and perdisulfate.

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