N and P co-doped charcoal-silicon dioxide composite material and application thereof in adsorbing phenols in oilfield wastewater

Abstract

The invention discloses an N and P co-doped charcoal-silicon dioxide composite material and application thereof in adsorbing phenols in oilfield wastewater, and belongs to the technical field of environmental functional materials. The composite material comprises a biochar matrix, silicon dioxide, and an N element and a P element which are co-doped on the surface of the material and in a skeleton. Silicon dioxide serves as a framework, the high-porosity structure of the material is supported and maintained, the thermal stability of the material is improved, rich surface active sites are introduced through co-doping of N and P, and the adsorption capacity of the material to phenolic pollutants is remarkably improved through the synergistic effect of the silicon dioxide and the N and P. The adsorption capacity of the material to typical oilfield phenols such as phenol, cresol, chlorophenol, nitrophenol and the like is 150-200 mg / g, the adsorption efficiency can reach 96% or above, and the recycling performance can be good through acid and alkali heat treatment. The invention effectively solves the problems of poor adsorption effect, high material cost, insufficient stability, secondary pollution and the like in oilfield wastewater phenol treatment.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials, specifically to an N,P co-doped biochar-silica composite material and its application in adsorbing phenols from oilfield wastewater. Background Technology

[0002] Oilfield wastewater is complex in composition, and phenolic compounds (such as phenol, cresol, chlorophenol, and nitrophenol) have become significant pollutants threatening the ecological environment and human health due to their high toxicity, reluctance to degrade, and tendency to accumulate. Currently, common methods for treating phenols include biodegradation, chemical oxidation, and physical adsorption, with adsorption being particularly popular due to its simplicity and relatively low cost. However, traditional adsorption materials such as activated carbon and resins still face challenges in practical applications, including limited adsorption capacity, poor selectivity, and regeneration difficulties. This is especially true in oilfield wastewater systems containing high levels of salt and organic matter, where their adsorption performance often declines significantly, failing to meet the requirements for efficient purification.

[0003] Existing adsorbent materials still have significant shortcomings in terms of structural and functional design. For example, although ordinary biochar is widely available and inexpensive, its pore structure is prone to collapse during preparation, resulting in a limited specific surface area and a single surface functional group, leading to weak affinity for phenolic pollutants and thus low adsorption capacity. Furthermore, while some modified materials have improved surface activity by introducing single heteroatoms, they have not effectively solved the problems of poor structural stability and poor recyclability. Especially in the high-temperature, high-acid-base-fluctuation environments of oilfield wastewater treatment, materials are prone to structural damage or loss of active sites, severely impacting their long-term economic viability and reliability.

[0004] Meanwhile, high material costs, complex preparation processes, and the potential for secondary pollution also hinder their large-scale application. Many high-performance adsorbents rely on expensive precursors or complex synthesis steps, making industrial production difficult; some materials are difficult to regenerate after use, and their disposal may pose new environmental risks. Therefore, developing a novel composite material that combines high adsorption performance, good stability, low cost, and environmental friendliness has become a key direction for solving the problem of phenolic pollution control in oilfield wastewater, and is also a current research hotspot and challenge in the field of environmental functional materials. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide an N,P co-doped biochar-silica composite material and its application in adsorbing phenols in oilfield wastewater, which solves multiple industry pain points such as poor effect, high cost, material insufficiency, and secondary pollution in the treatment of phenols in oilfield wastewater.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A N,P co-doped biochar-silica composite material specifically includes a biochar matrix, silica, and N and P elements co-doped in the surface and framework of the composite material.

[0008] Preferably, the biochar is derived from biomass materials, and more preferably from corn stalks.

[0009] Preferably, the nitrogen content is 3.5 at% to 5.0 at%.

[0010] Preferably, the P element content is 3.0 at%-4.5 at%.

[0011] Preferably, the specific surface area of ​​the composite material is 500-700. .

[0012] Preferably, the silica is uniformly distributed in the biochar matrix in the form of nano- or submicron-sized particles.

[0013] Preferably, the N and P elements are obtained by impregnating biochar with ammonium dihydrogen phosphate using ultrasound assistance, followed by calcination at a temperature of 600-800°C, which allows the N and P elements to chemically bond with the surface of the biochar and silica.

[0014] Preferably, the composite material has an adsorption capacity of 150-200 mg / g for phenolic pollutants.

[0015] An application of an N,P co-doped biochar-silica composite material for adsorbing phenols in oilfield wastewater: The N,P co-doped biochar-silica composite material is brought into contact with oilfield wastewater containing phenols to achieve adsorption and removal of phenolic pollutants.

[0016] Preferably, the phenols include phenol, cresol, chlorophenol, and nitrophenol.

[0017] The technical effects and advantages of this invention, which describes an N,P co-doped biochar-silica composite material and its application in adsorbing phenols from oilfield wastewater, are as follows:

[0018] 1. This invention, by constructing a biochar-silica composite framework and achieving co-doping of N and P elements, produces a significant synergistic enhancement effect. Silica, acting as a rigid framework support, effectively prevents the structural shrinkage and collapse of biochar during high-temperature carbonization, thereby maintaining a high strength of up to 620. The specific surface area is 0.65 The total pore volume provides abundant physical adsorption space. At the same time, N and P elements are successfully doped and anchored to the material surface in the form of chemical bonds, introducing a large number of nitrogen- and phosphorus-containing polar functional groups as chemical active sites. The synergistic effect of these two mechanisms enables it to achieve an adsorption capacity of 185 mg / g for phenols in oilfield wastewater, with an adsorption efficiency of up to 96%, which significantly surpasses materials with single structures or no doping.

[0019] 2. This invention achieves precise control over the pore structure and surface chemical properties of materials, thereby optimizing the adsorption process. The uniform dispersion of silica nano / submicron particles constructs a well-developed mesoporous and macroporous network, which greatly promotes the diffusion and mass transfer of phenolic pollutant molecules into the material interior. Furthermore, the N and P co-doping not only increases the surface's hydrophilicity and electronegativity, which is beneficial for adsorbing phenolic molecules through electrostatic interactions, hydrogen bonds, and π-π interactions, but also enhances the chemical affinity of the material surface.

[0020] 3. The composite material prepared by this invention is rich in N and P active sites on its surface, which significantly enhances its specific adsorption capacity and binding strength for phenolic pollutants. Through ultrasonic loading and calcination of ammonium dihydrogen phosphate, N and P elements are firmly bound into the carbon-silicon framework, forming a stable surface chemical environment. These active sites interact strongly with the benzene ring and hydroxyl functional groups of phenolic pollutants, and may even form surface complexes, thereby greatly improving the adsorption capacity and saturated adsorption amount.

[0021] 4. This invention provides materials and application methods that offer comprehensive advantages of high efficiency, environmental friendliness, economy, and easy regeneration. The materials utilize biomass waste such as corn stalks as raw materials, achieving resource utilization and reducing costs. Its preparation process is clear and controllable. In terms of application, this material exhibits excellent adsorption performance for common pollutants in oilfield wastewater, such as phenol, cresol, chlorophenol, and nitrophenol, demonstrating strong adaptability. Attached Figure Description

[0022] Figure 1 The FT-IR spectrum of an N,P co-doped biochar-silica composite material proposed in this invention and its application in adsorbing phenols in oilfield wastewater;

[0023] Figure 2 This is a 1000x scanning electron microscope image of an N,P co-doped biochar-silica composite material proposed in this invention and its application in adsorbing phenols from oilfield wastewater.

[0024] Figure 3 This is a scanning electron microscope image (8000x magnification) of an N,P co-doped biochar-silica composite material proposed in this invention and its application in adsorbing phenols from oilfield wastewater. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0027] Example 1

[0028] This embodiment provides an application of N,P co-doped biochar-silica composite material for adsorbing phenols in oilfield wastewater. Specific implementation steps include:

[0029] Experimental materials:

[0030] Corn stalks, 1 mol / L hydrochloric acid, 0.1 mol / L hydrochloric acid, 1 mol / L sodium hydroxide, 0.5 mol / L ammonium dihydrogen phosphate, deionized water.

[0031] Experimental objective:

[0032] N,P co-doped biochar-silica composite material was prepared using corn stalks.

[0033] Experimental steps:

[0034] S1: Place the corn stalks in a pulverizer at 2000 rpm and crush for 1 hour. Then, wash the powder in deionized water for 30 minutes. Finally, dry the washed powder in a vacuum drying oven at 70°C for 2 hours.

[0035] S2: Add 1 mol / L hydrochloric acid to the corn stalk powder prepared in S1 at a solid-liquid ratio of 1:10, and then place the mixture under reflux at 90°C for 2 hours.

[0036] S3: The corn stalks that have undergone heat reflux treatment in S2 are filtered through 0.22-micron filter paper to obtain the filtrate;

[0037] S4: The filtrate obtained in S3 is dispersed in a 1 mol / L sodium hydroxide solution at a solid-liquid ratio of 1:10, and then the liquid is heated to 80°C and refluxed for 1.5 hours.

[0038] S5: The corn straw filtrate after the sodium hydroxide thermal reflux treatment in S4 is placed in a muffle furnace and heated to 600℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and held for 2 hours.

[0039] S6: Add the calcined powder obtained in S5 to 1 mol / L hydrochloric acid at a solid-liquid ratio of 1:10, then heat the liquid to 80°C, and finally reflux for 1 hour.

[0040] S7: The powder obtained from the acid reflux treatment in S6 is placed in 0.5 mol / L ammonium dihydrogen phosphate at a solid-liquid ratio of 1:10, and then subjected to ultrasonic treatment at 40 kHz and 200 W for 30 minutes.

[0041] S8: The biochar-silica material modified with ammonium dihydrogen phosphate obtained in S7 was calcined at 700°C under a nitrogen atmosphere for 1 hour, then acidified with 0.1 mol / L hydrochloric acid, and finally the powder was dried in a vacuum drying oven at 80°C for 2 hours.

[0042] Experimental results: See Table 1 for details.

[0043] Table 1: Test Results of Example 1

[0044] Specific surface area Total capacity N content P content Phenolic adsorption capacity Adsorption efficiency Example 1 620 0.65 4.2at% 3.8at% 185mg / g 96%

[0045] Example 1 successfully prepared an N,P co-doped biochar-silica composite material through a process involving impurity removal with hydrochloric acid and sodium hydroxide, high-temperature carbonization, ultrasonic loading with ammonium dihydrogen phosphate, and secondary calcination doping. The material possesses both a high specific surface area and abundant pore structure, with a surface rich in N and P active sites. It exhibits an adsorption capacity of 185 mg / g for phenols from oilfield wastewater, with an adsorption efficiency of 96%, demonstrating the synergistic effect of silica framework support and N and P surface modification, while also improving the material's thermal stability.

[0046] Example 2

[0047] This embodiment provides an application of N,P co-doped biochar-silica composite material for adsorbing phenols in oilfield wastewater. Specific implementation steps include:

[0048] Experimental materials:

[0049] Corn stalks, 1 mol / L hydrochloric acid, 0.1 mol / L hydrochloric acid, 1 mol / L sodium hydroxide, 0.5 mol / L ammonium dihydrogen phosphate, deionized water.

[0050] Experimental objective:

[0051] Preparation was carried out without sodium hydroxide thermal reflux treatment to illustrate the key role of purification in adsorption performance.

[0052] Experimental steps:

[0053] S1: Place the corn stalks in a pulverizer at 2000 rpm and crush for 1 hour. Then, wash the powder in deionized water for 30 minutes. Finally, dry the washed powder in a vacuum drying oven at 70°C for 2 hours.

[0054] S2: Add 1 mol / L hydrochloric acid to the corn stalk powder prepared in S1 at a solid-liquid ratio of 1:10, and then place the mixture under reflux at 90°C for 2 hours.

[0055] S3: The corn stalks treated by heat reflux in S2 are filtered through 0.22-micron filter paper to obtain filtrate, the solid filter residue is retained and the filtrate is discarded;

[0056] S4: The corn straw filtrate after the S3 filtration process is placed in a muffle furnace and heated to 600℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and held for 2 hours.

[0057] S5: Add the calcined powder obtained in S4 to 1 mol / L hydrochloric acid at a solid-liquid ratio of 1:10, then heat the liquid to 80°C, and finally reflux for 1 hour.

[0058] S6: The powder obtained from the acid reflux treatment in S5 is placed in 0.5 mol / L ammonium dihydrogen phosphate at a solid-liquid ratio of 1:10, and then subjected to ultrasonic treatment at 40 kHz and 200 W for 30 minutes.

[0059] S7: The biochar-silica material modified with ammonium dihydrogen phosphate obtained in S6 was calcined at 700°C under a nitrogen atmosphere for 1 hour, then acidified with 0.1 mol / L hydrochloric acid, and finally the powder was dried in a vacuum drying oven at 80°C for 2 hours.

[0060] Experimental results: See Table 2 for details.

[0061] Table 2: Test Results of Example 2

[0062] Specific surface area Total capacity N content P content Phenolic adsorption capacity Adsorption efficiency Example 2 280 0.32 4.0at% 3.5at% 85mg / g 78%

[0063] Example 2 was prepared by omitting the sodium hydroxide reflux step, resulting in incomplete removal of impurities from the cellulose. The results showed that the incomplete removal severely limited the physical adsorption space, and even surface chemical modification could not compensate for the structural defects.

[0064] Example 3

[0065] This embodiment provides an application of N,P co-doped biochar-silica composite material for adsorbing phenols in oilfield wastewater. Specific implementation steps include:

[0066] Experimental materials:

[0067] Corn stalks, 1 mol / L hydrochloric acid, 0.1 mol / L hydrochloric acid, 1 mol / L sodium hydroxide, 0.5 mol / L ammonium dihydrogen phosphate, deionized water.

[0068] Experimental objective:

[0069] Biochar-silica composite materials were prepared without ultrasonic treatment for N and P doping.

[0070] Experimental steps:

[0071] S1: Place the corn stalks in a pulverizer at 2000 rpm and crush for 1 hour. Then, wash the powder in deionized water for 30 minutes. Finally, dry the washed powder in a vacuum drying oven at 70°C for 2 hours.

[0072] S2: Add 1 mol / L hydrochloric acid to the corn stalk powder prepared in S1 at a solid-liquid ratio of 1:10, and then place the mixture under reflux at 90°C for 2 hours.

[0073] S3: The corn stalks that have undergone heat reflux treatment in S2 are filtered through 0.22-micron filter paper to obtain the filtrate;

[0074] S4: The filtrate obtained in S3 is dispersed in a 1 mol / L sodium hydroxide solution at a solid-liquid ratio of 1:10, and then the liquid is heated to 80°C and refluxed for 1.5 hours.

[0075] S5: The corn straw filtrate after the sodium hydroxide thermal reflux treatment in S4 is placed in a muffle furnace and heated to 600℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and held for 2 hours.

[0076] S6: Add the calcined powder obtained in S5 to 1 mol / L hydrochloric acid at a solid-liquid ratio of 1:10, then heat the liquid to 80°C, and finally reflux for 1 hour.

[0077] S7: The acid-refluxed powder obtained in S6 is placed in 0.5 mol / L ammonium dihydrogen phosphate at a solid-liquid ratio of 1:10 and mechanically stirred for 30 minutes.

[0078] S8: The biochar-silica material modified with ammonium dihydrogen phosphate obtained in S7 was calcined at 700°C under a nitrogen atmosphere for 1 hour, then acidified with 0.1 mol / L hydrochloric acid, and finally the powder was dried in a vacuum drying oven at 80°C for 2 hours.

[0079] Experimental results: See Table 3 for details.

[0080] Table 3: Test Results of Example 3

[0081] Specific surface area Total capacity N content P content Phenolic adsorption capacity Adsorption efficiency Example 3 520 0.58 0at% 0at% 40mg / g 88%

[0082] This embodiment describes the preparation of ammonium dihydrogen phosphate under mechanical stirring. Its adsorption capacity for phenols was 40 mg / g, indicating low adsorption efficiency. This suggests that the lack of ultrasonic treatment for N and P doping leads to insufficient surface chemical activity, and the adsorption process mainly relies on physical processes, limiting further improvement in adsorption capacity.

[0083] Example 4

[0084] This embodiment provides an application of N,P co-doped biochar-silica composite material for adsorbing phenols in oilfield wastewater. Specific implementation steps include:

[0085] Experimental materials:

[0086] Corn stalks, 1 mol / L hydrochloric acid, 0.1 mol / L hydrochloric acid, 1 mol / L sodium hydroxide, 0.5 mol / L ammonium dihydrogen phosphate, deionized water.

[0087] Experimental objective:

[0088] To investigate the effect of low calcination temperature on material properties.

[0089] Experimental steps:

[0090] S1: Place the corn stalks in a pulverizer at 2000 rpm and crush for 1 hour. Then, wash the powder in deionized water for 30 minutes. Finally, dry the washed powder in a vacuum drying oven at 70°C for 2 hours.

[0091] S2: Add 1 mol / L hydrochloric acid to the corn stalk powder prepared in S1 at a solid-liquid ratio of 1:10, and then place the mixture under reflux at 90°C for 2 hours.

[0092] S3: The corn stalks that have undergone heat reflux treatment in S2 are filtered through 0.22-micron filter paper to obtain the filtrate;

[0093] S4: The filtrate obtained in S3 is dispersed in a 1 mol / L sodium hydroxide solution at a solid-liquid ratio of 1:10, and then the liquid is heated to 80°C and refluxed for 1.5 hours.

[0094] S5: The corn straw filtrate after the sodium hydroxide thermal reflux treatment in S4 is placed in a muffle furnace and heated to 600℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and held for 2 hours.

[0095] S6: Add the calcined powder obtained in S5 to 1 mol / L hydrochloric acid at a solid-liquid ratio of 1:10, then heat the liquid to 80°C, and finally reflux for 1 hour.

[0096] S7: The powder obtained from the acid reflux treatment in S6 is placed in 0.5 mol / L ammonium dihydrogen phosphate at a solid-liquid ratio of 1:10, and then subjected to ultrasonic treatment at 40 kHz and 200 W for 30 minutes.

[0097] S8: The biochar-silica material modified with ammonium dihydrogen phosphate obtained in S7 was calcined at 600°C under a nitrogen atmosphere for 1 hour, then acidified with 0.1 mol / L hydrochloric acid, and finally the powder was dried in a vacuum drying oven at 80°C for 2 hours.

[0098] Experimental results: See Table 4 for details.

[0099] Table 4: Test Results of Example 4

[0100] Specific surface area Total capacity N content P content Phenolic adsorption capacity Adsorption efficiency Example 4 520 0.55 3.6at% 3.2at% 150mg / g 92%

[0101] Example 4 investigated the effect of temperature on N and P doping efficiency and material structural stability by lowering the calcination temperature of the biochar-silica material under a nitrogen atmosphere from 700℃ to 600℃. The experimental results showed that although the specific surface area and pore volume remained high, the N and P content and phenol adsorption capacity were lower than in Example 1. This indicates that while the lower calcination temperature can partially maintain the pore structure, it is insufficient to achieve sufficient chemical bonding between N and P elements and the carbon-silicon framework, thus affecting the adsorption performance. This result further confirms that high-temperature calcination is a key step in ensuring stable N and P doping and forming highly efficient chemisorption sites.

[0102] Example 5

[0103] This embodiment provides an application of N,P co-doped biochar-silica composite material for adsorbing phenols in oilfield wastewater. Specific implementation steps include:

[0104] Experimental materials:

[0105] Wheat straw, 1 mol / L hydrochloric acid, 0.1 mol / L hydrochloric acid, 1 mol / L sodium hydroxide, 0.5 mol / L ammonium dihydrogen phosphate, deionized water.

[0106] Experimental objective:

[0107] To investigate the effect of wheat bio-based N,P co-doped biochar-silica composite material on its performance.

[0108] Experimental steps:

[0109] S1: Place wheat straw in a pulverizer at 2000 rpm and crush for 1 hour. Then, wash the powder in deionized water for 30 minutes. Finally, dry the washed powder in a vacuum drying oven at 70°C for 2 hours.

[0110] S2: Add 1 mol / L hydrochloric acid to the wheat straw powder prepared in S1 at a solid-liquid ratio of 1:10, and then place the mixture under reflux at 90°C for 2 hours.

[0111] S3: The wheat straw that underwent heat reflux treatment in S2 was filtered through 0.22-micron filter paper to obtain the filtrate;

[0112] S4: The filtrate obtained in S3 is dispersed in a 1 mol / L sodium hydroxide solution at a solid-liquid ratio of 1:10, and then the liquid is heated to 80°C and refluxed for 1.5 hours.

[0113] S5: Place the wheat straw filtrate after the sodium hydroxide thermal reflux treatment in S4 into a muffle furnace, heat it to 600℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and hold it at that temperature for 2 hours.

[0114] S6: Add the calcined powder obtained in S5 to 1 mol / L hydrochloric acid at a solid-liquid ratio of 1:10, then heat the liquid to 80°C, and finally reflux for 1 hour.

[0115] S7: The powder obtained from the acid reflux treatment in S6 is placed in 0.5 mol / L ammonium dihydrogen phosphate at a solid-liquid ratio of 1:10, and then subjected to ultrasonic treatment at 40 kHz and 200 W for 30 minutes.

[0116] S8: The biochar-silica material modified with ammonium dihydrogen phosphate obtained in S7 was calcined at 700°C under a nitrogen atmosphere for 1 hour, then acidified with 0.1 mol / L hydrochloric acid, and finally the powder was dried in a vacuum drying oven at 80°C for 2 hours.

[0117] Experimental results: See Table 5 for details.

[0118] Table 5: Test Results of Example 5

[0119] Specific surface area Total capacity N content P content Phenolic adsorption capacity Adsorption efficiency Example 5 580 0.60 4.0at% 3.5at% 170mg / g 94%

[0120] Example 5 describes the preparation of N,P co-doped biochar-silica composite materials using wheat bio-based materials. The N,P co-doped biochar-silica composite materials were prepared under the same process conditions. The specific surface area, pore volume, N and P content, and adsorption capacity of the obtained material were slightly lower than those of the material prepared from corn straw in Example 1, but still significantly better than the undoped or structurally incomplete control material. This indicates that the composition and structure differences of different biomass affect the final pore development and surface chemical properties of the composite material. However, the process route of this invention still has good universality for different biomass and can prepare high-performance adsorbent materials, further demonstrating the raw material adaptability and scalability of this method.

[0121] Comparative Example 1

[0122] This embodiment provides a traditional method for preparing biochar and its application in adsorbing phenols in oilfield wastewater. The specific implementation steps include:

[0123] Experimental materials:

[0124] Corn stalks, deionized water.

[0125] Experimental objective:

[0126] Traditional biochar was prepared by directly carbonizing corn stalks without any chemical treatment, in order to illustrate the limitations of raw biochar in terms of adsorption performance without structural regulation and surface modification.

[0127] Experimental steps:

[0128] S1: Place the corn stalks in a pulverizer at 2000 rpm and crush for 1 hour. Then, wash the powder in deionized water for 30 minutes. Finally, dry the washed powder in a vacuum drying oven at 70°C for 2 hours.

[0129] S2: Place the dried corn stalk powder from S1 directly into a muffle furnace, heat it to 600°C at a rate of 5°C / min under a nitrogen atmosphere, and hold it at that temperature for 2 hours.

[0130] S3: Wash the calcined powder from S2 with deionized water until neutral, and then dry it in a vacuum drying oven at 80°C for 2 hours to obtain ordinary biochar.

[0131] Experimental results: See Table 4 for details.

[0132] Table 4: Test Results of Comparative Example 1

[0133] Specific surface area Total capacity N content P content Phenolic adsorption capacity Adsorption efficiency Comparative Example 1 150 0.18 0.5at% 0.5at% 45mg / g 52%

[0134] This comparative example employs a simple direct carbonization process, and the prepared traditional biochar has not undergone any chemical activation or doping treatment. It has a low specific surface area and pore volume, with almost no N or P active sites on its surface, resulting in an adsorption capacity of only 45 mg / g for phenols and an adsorption efficiency of 52%. This indicates that the adsorption performance of the raw biochar without structural regulation and surface modification is far lower than that of the embodiments of this invention, highlighting the limitations of traditional methods in material functionalization.

[0135] Example 1 employed a complete acid-base-calcination-doping multi-step process to obtain a specific surface area of ​​620. 0.65 pores A composite material with N content of 4.2 at% and P content of 3.8 at% exhibited an adsorption capacity of 185 mg / g for phenols and an adsorption efficiency of 96%. The results indicate that the synergistic effect of silica framework support and N and P surface-active modification optimizes the physical adsorption space, chemical adsorption activity, and thermal stability of the material, thereby achieving excellent adsorption performance.

[0136] Example 2 was prepared without sodium hydroxide treatment, which resulted in insufficient treatment of impurities such as cellulose, making physical adsorption capacity the main limiting factor.

[0137] Example 3 uses materials without N and P ultrasonic doping. The physical structure of the material is not sufficiently doped, and almost no N and P are detected on the surface. This indicates that the material's adsorption potential is not fully realized because it relies solely on physical adsorption and lacks surface chemical active sites.

[0138] Example 4 investigated the effect of calcination temperature on N and P doping efficiency and material adsorption performance by using a process condition with a calcination temperature reduced to 600°C. The specific surface area and pore volume of the material remained at a high level, but the N and P doping content and adsorption capacity were lower than those in Example 1. This indicates that although the lower calcination temperature can partially maintain the pore structure, it is insufficient to achieve sufficient chemical bonding between N and P elements and the carbon-silicon framework, thereby affecting the stability of surface active sites and adsorption performance.

[0139] Example 5 uses wheat straw as a biomass raw material to prepare N,P co-doped biochar-silica composite material under the same process conditions. The results show that the specific surface area, pore volume, N and P content and adsorption capacity of the obtained material are slightly lower than those of Example 1 prepared from corn straw, but are still significantly better than the undoped or structurally incomplete comparative material. This indicates that the composition and structure of different biomass will affect the final performance of the composite material. However, the preparation process of the present invention still has good universality and scalability for different biomass raw materials.

[0140] Comparative Example 1, using the traditional method of direct carbonization, yielded biochar with a specific surface area of ​​only 150. Kong Rong 0.18 With extremely low N and P content, the adsorption capacity is only 45 mg / g and the adsorption efficiency is 52%. This highlights the severe limitation of the adsorption performance of raw biochar without any structural regulation or surface modification, and the obvious inadequacy of traditional methods in terms of functionalization.

[0141] Example 1 employs a complete process of "hydrochloric acid impurity removal—sodium hydroxide silicon extraction—high-temperature carbonization—ammonium dihydrogen phosphate ultrasonic loading—secondary calcination doping," achieving an optimal balance between specific surface area, pore structure, and surface chemical modification. It cleverly enhances the material's adsorption performance for phenolic pollutants through a silica framework support and synergistic N and P co-doping, making it suitable for efficient treatment of oilfield wastewater. Example 2, although involving N and P doping, skipped the sodium hydroxide impurity removal step, resulting in a denser material structure, a significant decrease in specific surface area, and a marked deterioration in adsorption performance. Example 3, without ultrasonic introduction of N and P active sites, resulted in a homogeneous surface chemical composition. Example 4, by lowering the secondary calcination temperature, further verified the crucial role of 700℃ heat treatment in stabilizing N and P doping and forming surface active sites. Although its adsorption performance decreased slightly, it still exhibited good structural retention and considerable adsorption capacity. Example 5, using wheat straw as raw material, confirmed the applicability and scalability of this preparation process to different biomass sources, providing practical evidence for developing high-efficiency adsorption materials based on diverse biomass waste. Comparative Example 1, using the traditional direct carbonization method, yielded biochar with a simple structure and inert surface, exhibiting the worst adsorption performance, highlighting the functional limitations of traditional biochar in adsorbing phenols from oilfield wastewater. Therefore, this invention, through multi-step chemical treatment and doping processes, successfully constructed an N,P co-doped biochar-silica composite material with both high porosity and abundant surface functional groups, significantly improving its adsorption capacity for phenols in oilfield wastewater and possessing significant practical application value.

[0142] refer to Figure 1 , Figure 2 and Figure 3 The successful preparation and structural advantages of N,P co-doped biochar-silica composite materials were verified from both chemical structure and microstructure perspectives. Figure 1 The FT-IR spectrum clearly shows the characteristic absorption peaks of nitrogen- and phosphorus-containing functional groups on the material surface, confirming that N and P elements were successfully doped and anchored on the surface of the composite material in the form of chemical bonds, introducing abundant chemical adsorption active sites.

[0143] Figure 2 and Figure 3Scanning electron microscope images visually demonstrate that the material has a well-developed hierarchical porous structure. Silica is uniformly dispersed in the biochar matrix in the form of nano or submicron particles, forming a stable composite framework. This effectively maintains a high specific surface area and interconnected channels, providing ample diffusion paths and physical adsorption space for pollutant molecules. The combination of these three factors indicates that the material described in this invention possesses both ideal surface chemical activity and optimized physical structure, providing sufficient structural and performance basis for its efficient adsorption of phenols from oilfield wastewater.

[0144] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims.

[0145] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An N, P co-doped biochar-silica composite material and its application in adsorbing phenols in oilfield wastewater, characterized in that, The composite material comprises a biochar matrix, silicon dioxide, and N and P elements co-doped in the surface and skeleton of the composite material.

2. The N, P co-doped biochar-silica composite material of claim 1, wherein, The biochar is derived from corn stalks.

3. The N, P co-doped biochar-silica composite material of claim 1, wherein, The N element content is 3.5 at%-5.0 at%.

4. The N, P co-doped biochar-silica composite material of claim 1, wherein, The P element content is 3.0 at%-4.5 at%.

5. The N, P co-doped biochar-silica composite material of claim 1, wherein, The specific surface area of the composite material is 500-700 .

6. The N, P co-doped biochar-silica composite material of claim 1, wherein, The silicon dioxide is uniformly distributed in the biochar matrix in the form of nano or sub-micron particles.

7. The N, P co-doped biochar-silica composite material of claim 1, wherein, The N and P elements are introduced into the biochar by ultrasonic-assisted ammonium dihydrogen phosphate impregnation, and then the N and P elements are combined with the surface of the biochar and silicon dioxide in the form of chemical bonds by calcination at a temperature of 600-800 DEG C.

8. The N, P co-doped biochar-silica composite material of claim 1, wherein, The adsorption capacity of the composite material for phenolic pollutants is 150-200 mg / g.

9. The use of N, P co-doped biochar-silica composite material for adsorbing phenols from oilfield wastewater, characterized in that, The N, P co-doped biochar-silicon dioxide composite material is contacted with oilfield wastewater containing phenols to achieve adsorption and removal of phenolic pollutants.

10. Use of the N, P co-doped biochar-silica composite material of claim 9 for adsorbing phenols from oilfield wastewater, wherein, The phenols include phenol, cresol, chlorophenol, nitrophenol.

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