Magnesium-based glucose carbon composite adsorbent as well as preparation method and application thereof

Abstract

The invention provides a magnesium-based glucose carbon composite adsorbent and a preparation method and application thereof, and belongs to the technical field of environmental functional materials, the composite adsorbent is composed of glucose-based carbon spheres and magnesium oxide particles, the glucose-based carbon spheres serve as a carrier framework, the magnesium oxide particles are loaded on the surfaces of the glucose-based carbon spheres, and the magnesium oxide particles are loaded on the surfaces of the glucose-based carbon spheres. The composite adsorbent is prepared by preparing glucose-based carbon spheres through a hydrothermal method and then loading magnesium oxide particles through a co-impregnation-pyrolysis method. Glucose and magnesium chloride are used as cheap and non-toxic raw materials, the preparation process is simple, the phosphate adsorption capacity is high, the selectivity is high, the ammonium and phosphorus synergistic adsorption characteristic is achieved, regeneration and reuse can be achieved eight or more times, the integrated function of removing phosphorus in water, fixing phosphorus in soil, increasing available phosphorus and recycling agricultural fertilizer can be achieved, secondary pollution is avoided, and the method is suitable for industrial production. The method is suitable for agricultural and industrial multi-scene application.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials technology, and in particular to a magnesium-based glucose-carbon composite adsorbent, its preparation method, and its application. Background Technology

[0002] With the rapid development of industry and agriculture, the treatment of eutrophication in water bodies, the efficient utilization of soil phosphorus resources, and the coordinated development of agricultural circular economy have become important directions for technological research. On the one hand, adsorption methods, which are simple to operate and produce low secondary pollution, are gradually becoming a research hotspot for phosphorus removal from water bodies, addressing the ecological problems caused by excessive nitrogen and phosphorus in water bodies. On the other hand, magnesium is a medium-quantity element that is abundant on Earth and essential for plants. Magnesium-modified carbon-based materials have strong adsorption activity for phosphates and good biocompatibility, making the use of magnesium-modified carbon materials a key direction for improving adsorption performance. At the same time, using glucose, which is non-toxic, inexpensive, and has a single composition, as a carbon source to prepare carriers, combined with a circular model of "pollution control - resource recycling - agricultural utilization," meets the needs of green and sustainable development and has become a major research and development trend combining environmental functional materials with agricultural applications.

[0003] Current methods for phosphorus removal from water bodies mainly include flocculation and sedimentation, bioremediation, and adsorption. Researchers often use unmodified biochar and sludge carbon as traditional adsorbent materials. To improve adsorption performance, they further modify the carbon materials with metal oxides (such as Fe2O3, Al2O3, and MgO). However, these traditional adsorbent materials themselves have problems such as low adsorption capacity and poor selectivity. Some materials are also prone to introducing heavy metals. Even after modification, they do not effectively connect with the subsequent phosphorus resource recycling and soil phosphorus regulation needs. At the same time, there is excessive application of phosphate fertilizers in agricultural production, which leads to serious phosphorus leaching losses in the soil. This not only reduces the efficiency of phosphorus resource utilization but also exacerbates the risk of water pollution. When the phosphorus concentration in water exceeds 0.02 mg / L, it will accelerate algae reproduction, destroy aquatic ecosystems, deteriorate water quality, and endanger human health.

[0004] However, existing technologies have three main drawbacks: First, traditional adsorption materials are inadequate in performance. Unmodified biochar, sludge carbon, and other materials have low adsorption capacity and poor selectivity, and are prone to introducing heavy metals, posing a risk of secondary pollution. Second, there is a lack of technology for phosphorus resource recycling and soil phosphorus regulation, which cannot achieve the synergistic effect of "water phosphorus removal - soil phosphorus fixation - effective phosphorus enhancement - adsorption phosphorus fertilizerization". The problem of phosphorus leaching loss in the soil has not been effectively solved, resulting in low phosphorus resource utilization efficiency. Third, adsorption materials have limited functions and low recycling rates. Most materials can only be used for phosphorus removal in water, lacking adaptability to multiple scenarios. Furthermore, the recycling performance of existing adsorption materials is poor, making it difficult to meet the needs of cost control and green recycling in large-scale applications. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a magnesium-based glucose-carbon composite adsorbent, its preparation method, and its application. Using glucose and magnesium chloride as inexpensive and non-toxic raw materials, the preparation process is simple. It has high phosphate adsorption capacity, strong selectivity, and ammonium-phosphorus synergistic adsorption characteristics. It can be regenerated and reused more than 8 times. It can achieve integrated functions of phosphorus removal from water, phosphorus fixation and effective phosphorus enhancement in soil, and agricultural fertilizer recycling, without secondary pollution. It is suitable for multiple applications in agriculture and industry.

[0006] To achieve the above objectives, the present invention provides the following solution: One objective of this invention is to provide a magnesium-based glucose-carbon composite adsorbent, which is composed of glucose-based carbon spheres and magnesium oxide particles. The glucose-based carbon spheres serve as the carrier framework, and the magnesium oxide particles are loaded on the surface of the glucose-based carbon spheres. The composite adsorbent is prepared by preparing glucose-based carbon spheres by a hydrothermal method, and then loading magnesium oxide particles by a co-impregnation-pyrolysis method.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned magnesium-based glucose carbon composite adsorbent, comprising the following steps: Glucose-based carbon spheres were prepared by hydrothermal method: glucose, sodium dodecyl sulfonate and deionized water were mixed and added to a reaction vessel, stirred until uniformly dissolved, and reacted at a preset reaction temperature for a preset time; after the reaction was completed, the reaction product was filtered, washed with anhydrous ethanol and deionized water in sequence until neutral, and dried to obtain glucose-based carbon spheres. Magnesium oxide particles were loaded by co-impregnation-pyrolysis: the glucose-based carbon spheres were impregnated in a solution containing magnesium chloride hexahydrate, stirred for a preset time, and then dried to constant weight to obtain the dried product; Preparation of magnesium-based glucose carbon composite adsorbent: The dried product was placed in an atmosphere furnace and heated to the calcination temperature at a preset heating rate under argon protection and held at the temperature for a preset time; after cooling, it was washed until pH=7 and dried again to obtain the magnesium-based glucose carbon composite adsorbent.

[0008] A third objective of this invention is to provide an application of the aforementioned magnesium-based glucose-carbon composite adsorbent for removing phosphate from aqueous solutions. The procedure includes: adding the composite adsorbent to an aqueous solution containing phosphate, controlling the solid-liquid ratio at 0.4 g / L; adsorbing at a temperature of 298-318 K with shaking at a rate of 160-260 r / min for 4.5-72 h until equilibrium is reached; the initial concentration of phosphate in the aqueous solution containing phosphate is 1-200 mg(P)·L. -1 Furthermore, the pH of the aqueous solution is adjusted to 2.0-11.0.

[0009] The fourth objective of this invention is to provide an application of the above-mentioned magnesium-based glucose carbon composite adsorbent for soil phosphorus fixation and available phosphorus enhancement. The operation includes: uniformly mixing the composite adsorbent with soil, controlling the amount of composite adsorbent added to be 0.5%-2% of the soil mass; after the soil and composite adsorbent are mixed, the cumulative leaching amount of soil phosphate is reduced by not less than 85%, and the available phosphorus content of the soil is increased to 1.94-2.15 times that of soil without the addition of the composite adsorbent.

[0010] The fifth objective of this invention is to provide a regeneration method for the above-mentioned magnesium-based glucose carbon composite adsorbent, the operation of which includes: soaking the adsorbent saturated with adsorption in a 1 mol / L sodium hydroxide solution and stirring for 24 h for desorption, then washing with deionized water until neutral, drying at 80°C for 4 h, and then repeating the adsorption for phosphate; after 8 adsorption-desorption cycles, the phosphate removal rate is not less than 67%.

[0011] The sixth objective of this invention is to provide an application of the above-mentioned magnesium-based glucose carbon composite adsorbent, including the following two categories: Agricultural fertilizer recycling uses: The composite adsorbent after adsorbing phosphate is directly applied to farmland soil; in the composite adsorbent after adsorbing phosphate, the phosphate exists in the form of magnesium hydrogen phosphate and magnesium phosphate, which provides phosphorus nutrition to crops as a slow-release phosphate fertilizer; Practical applications of phosphorus-containing wastewater treatment: The actual phosphorus-containing wastewater includes aquaculture wastewater, agricultural non-point source pollution wastewater, or industrial phosphorus-containing wastewater; when the initial concentration of phosphate in the wastewater is 2.37 mg(P)·L... -1 When the composite adsorbent is added at a concentration of 1.0-1.2 g / L to the wastewater, the phosphate removal rate is not less than 99.82%, and the phosphate concentration in the treated wastewater is less than 50 μg(P)·L. -1 .

[0012] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: (1) The magnesium-based glucose carbon composite adsorbent provided by the present invention has excellent adsorption performance and strong environmental adaptability. Under the condition of 318K, the maximum adsorption capacity for phosphate can reach 240.23 mg(P)·g. -1 It is far higher than that of traditional unmodified biochar (usually less than 100 mg(P)·g). -1 The adsorption process conforms to both the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model, and adsorption equilibrium is reached in 4.5 hours in low-concentration phosphorus-containing aqueous solutions; simultaneously, in solutions containing 1-10 mmol / L LF... - Cl - SO4 2- NO3 - HCO3 - SiO32- In water bodies where anions coexist, the adsorption rate of phosphate remains above 50%. This is especially true if the water contains 100 mg (N)·L⁻¹. -1 The ammonium ions can also promote the adsorption of phosphates, increasing the adsorption capacity by 10%-15%, which can effectively meet the treatment needs of complex nitrogen and phosphorus mixed wastewater.

[0013] (2) The present invention has significant effects on soil phosphorus regulation and agricultural safety application. When the composite adsorbent is mixed with soil with pH 8.1 and texture of loam at a ratio of 0.5%-2% of soil mass, the cumulative leaching amount of soil phosphate can be reduced by more than 85%, and the effective phosphorus content of the soil can be increased to 1.94-2.15 times that of soil without adsorbent. This not only reduces the leaching loss of agricultural phosphate fertilizer, but also improves the utilization rate of soil phosphorus resources. At the same time, the adsorbent is made from glucose and magnesium chloride, and the preparation process does not introduce heavy metals. The MgHPO4 and Mg3(PO4)2 formed after adsorbing phosphate can be directly applied to farmland as slow-release phosphate fertilizer. Mg is an essential medium element for plants, has no environmental risk, and is fully compatible with the safety requirements of agricultural ecosystems.

[0014] (3) This invention has good circular economy and practical application value. The raw materials glucose and magnesium chloride are cheap and readily available. The preparation process only requires hydrothermal method (preparation of glucose-based carbon balls at 180℃) and co-impregnation-pyrolysis method (calcination at 600℃), and the process is simple and easy to operate. After the adsorbent is saturated, it can be desorbed and regenerated by soaking and stirring with 1mol / L sodium hydroxide solution for 24h. After 8 adsorption-desorption cycles, the phosphate removal rate still remains above 67%, which greatly reduces the operating cost. In actual phosphorus-containing wastewater treatment, for an initial phosphate concentration of 2.37mg(P)·L -1 Adding 1.0-1.2 g / L of adsorbent to aquaculture wastewater, agricultural non-point source pollution wastewater, or industrial phosphorus-containing wastewater can achieve a phosphate removal rate of over 99.82%, with the treated concentration below 50 μg(P)·L⁻¹. -1 It meets EPA emission standards and can effectively help manage eutrophication of water bodies. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A flowchart of the preparation method of magnesium-based glucose carbon composite adsorbent provided by the present invention; Figure 2The graph shows the effect of magnesium content on adsorption performance in the magnesium-based glucose-carbon composite adsorbent provided by this invention; wherein, Figure 2 (a) in the figure is a comparison of the adsorption capacity of phosphate after glucose-based carbon spheres are combined with magnesium chloride hexahydrate in different mass ratios. Figure 2 (b) in the figure is the thermogravimetric analysis (TGA) curve of the magnesium-based glucose carbon composite adsorbent during the calcination process; Figure 3 Scanning electron microscope (SEM) images and elemental distribution mapping diagrams of the magnesium-based glucose carbon composite adsorbent provided by this invention; wherein, Figure 3 (a) is a SEM image at a magnification of 10 μm. Figure 3 (b) is a SEM image at a magnification of 3μm. Figure 3 (c), (d), and (e) in the diagram are mapping diagrams of different element distributions (C, O, Mg); Figure 4 The material characterization spectrum of the magnesium-based glucose carbon composite adsorbent provided by this invention; wherein... Figure 4 (a) in the image shows the X-ray diffraction (XRD) pattern of the MgO-GCM composite material. Figure 4 (b) in the figure is the Fourier transform infrared (FTIR) spectrum of the MgO-GCM composite material; Figure 5 The images show the microstructure of the magnesium-based glucose-carbon composite adsorbent provided by this invention before and after phosphate adsorption; wherein, Figure 5 Image (a) is a scanning electron microscope (SEM) image of the composite adsorbent after adsorbing phosphate. Figure 5 (b) in the image is the SEM image of the corresponding region with element labels. Figure 5 (c), (d), (e), and (f) in the figure are mapping diagrams of the distribution of C, O, Mg, and P elements, respectively. Figure 6 A diagram showing the chemical state changes of the magnesium-based glucose-carbon composite adsorbent before and after adsorbing phosphate, provided by this invention. Figure 6 (a) in the figure is a comparison of the FTIR spectra before and after adsorption. Figure 6 (b) in the figure is a comparison of the XRD patterns before and after adsorption. Figure 6 (c) in the image is the full XPS spectrum after adsorption; Figure 7 The XPS fine peak diagrams of different elements after adsorption by the magnesium-based glucose carbon composite adsorbent provided by this invention are shown below; Figure 7 (a) in the figure is the fine XPS peak diagram of C after adsorption. Figure 7 (b) in the figure is the fine XPS peak diagram of O element after adsorption. Figure 7(c) in the figure is the XPS fine peak diagram of Mg after adsorption. Figure 7 (d) in the figure is the XPS fine peak diagram of P element after adsorption; Figure 8 This is a correlation diagram showing the influence and mechanism of the MgO-GCM composite material's phosphate adsorption performance provided by the present invention; wherein, Figure 8 (a) shows the adsorption performance of MgO-GCM composite material for phosphate under different initial pH conditions. Figure 8 (b) shows the Zeta potential curve of the MgO-GCM composite material and the pH change of the solution after adsorption. Figure 8 (c) in the figure shows the effect of different concentrations of coexisting anions on the phosphate adsorption performance; Figure 9 Kinetic curves and model fitting diagrams of phosphate adsorption by MgO-GCM composite material under different initial phosphorus concentrations provided by the present invention; Figure 10 Isotherms and Langmuir and Freundlich model fitting diagrams of phosphate adsorption by MgO-GCM composite material at different temperatures provided by the present invention; Figure 11 The graph shows the changes in the equilibrium adsorption capacity and removal rate of ammonia nitrogen and phosphate by the MgO-GCM composite material in different pH ranges provided by this invention. Figure 12 The graph shows the changes in phosphorus leaching characteristics and available phosphorus content in soil under different treatment groups; among them, Figure 12 In the figure, (a) represents the cumulative phosphate leaching amount in each treatment group. Figure 12 (b) in the figure shows the curves of phosphate concentration changes in the leachate at different leaching times. Figure 12 (c) in the figure is a bar chart of available phosphorus content in the soil; Figure 13 The graph shows the adsorption-desorption cycle regeneration removal rate of the composite adsorbent and the actual treatment effect on aquaculture wastewater; among them, Figure 13 (a) in the figure is a bar chart showing the phosphate removal rate of the adsorbent after different adsorption-desorption cycles. Figure 13 (b) in the figure shows the relationship between the amount of adsorbent added and the phosphate concentration and removal rate in the actual treatment of aquaculture wastewater. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1 like Figure 1 As shown, this embodiment provides a method for preparing a magnesium-based glucose-carbon composite adsorbent, including the following steps: Step 100: Preparation of glucose-based carbon spheres by hydrothermal method: Glucose, sodium dodecyl sulfonate and deionized water are mixed and added to a reaction vessel, stirred until uniformly dissolved, and reacted at a preset reaction temperature for a preset time; after the reaction is completed, the reaction product is filtered, washed successively with anhydrous ethanol and deionized water until neutral, and dried to obtain glucose-based carbon spheres.

[0020] Step 100 specifically includes: weighing 15g of glucose and 0.375g of sodium dodecyl sulfonate (SDS), adding them to a 250mL polytetrafluoroethylene reactor, adding 150mL of deionized water at a glucose + SDS to deionized water solid-liquid ratio of 1:10, and magnetically stirring for 30min until the raw materials are completely dissolved to ensure the formation of a homogeneous precursor solution; sealing the reactor and placing it in an oven, maintaining the temperature at 180℃ for 4h, as a reaction temperature below 180℃ will not form a stable six-membered carbon ring structure, and exceeding 4h will cause excessive carbonization of the carbon spheres, clogging the pores; after the reaction is completed, cooling to room temperature and filtering through a 0.22μm filter membrane. It can accurately separate carbon spheres from unreacted small molecule impurities, avoiding carbon sphere loss or impurity residue. First, it is washed three times with anhydrous ethanol, 50 mL each time, to remove uncarbonized organic matter remaining on the surface of the carbon spheres. Then, it is repeatedly washed with deionized water until the pH of the filtrate is 7 to ensure no SDS residue, so as to avoid affecting the magnesium oxide loading in the future. The washed product is placed in an 80℃ forced-air drying oven and dried for 12 h. The drying temperature of 80℃ can avoid high-temperature oxidation of carbon spheres, and 12 h is the preferred value in the range of 4-12 h to ensure complete removal of water. Finally, spherical glucose-based carbon spheres (GCM) are obtained, whose aggregated and interwoven structure provides sufficient loading sites for MgO.

[0021] Step 200: Loading magnesium oxide particles by co-impregnation-pyrolysis method: Impregnate the glucose-based carbon spheres in a solution containing magnesium chloride hexahydrate, stir for a preset time, and then dry to constant weight to obtain the dried product.

[0022] Step 200 specifically includes: weighing 5g of the glucose-based carbon spheres obtained in step 100, adding 100mL of an aqueous solution containing 20g of magnesium chloride hexahydrate (MgCl2·6H2O), ensuring that the mass ratio of glucose-based carbon spheres to MgCl2·6H2O is 1:4. As the amount of magnesium chloride hexahydrate added increases, the mass ratio of GCM to MgCl2·6H2O becomes 1:0, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, etc. Figure 2 As shown in (a), the composite adsorbents are labeled MC0, MC1, MC2, MC3, MC4, MC5, and MC6, respectively. The equilibrium adsorption capacity (q) of the composite adsorbent for phosphate is... e The mixture exhibits a rapid initial increase followed by a gradual plateau, reaching its maximum at MC4 (i.e., a mass ratio of 1:4 between glucose-based carbon spheres and MgCl2·6H2O). At this ratio, MgO can be fully loaded onto the GCM surface, and the composite material achieves maximum phosphate adsorption, exceeding 390% compared to GCM without MgO loading. A ratio lower than 1:4 leads to insufficient magnesium oxide loading, while a ratio higher than 1:4 easily causes magnesium oxide particle agglomeration. The mixture is placed in a magnetic stirrer and stirred continuously at room temperature for 24 hours. Stirring for less than 24 hours will prevent MgCl2·6H2O from fully penetrating into the pores of the carbon spheres, while stirring for more than 24 hours will not provide additional benefits. After stirring, the mixture is transferred to an oven and dried at 80°C to constant weight. This avoids premature decomposition of MgCl2·6H2O, and constant weight ensures stable magnesium chloride content during subsequent calcination, resulting in a dried product.

[0023] Step 300: Preparation of magnesium-based glucose carbon composite adsorbent: The dried product is placed in an atmosphere furnace and heated to the calcination temperature at a preset heating rate under argon protection and held at the temperature for a preset time; after cooling, it is washed until pH=7, and dried again to obtain magnesium-based glucose carbon composite adsorbent.

[0024] The above step 300 specifically includes: loading the obtained dried product into a ceramic crucible and placing it in an atmosphere furnace; introducing argon gas and controlling the flow rate to 80 mL / min; setting the atmosphere furnace heating program: heating to 600℃ at a heating rate of 10℃ / min, turning off the heating after holding at that temperature, and allowing the atmosphere furnace to cool naturally to room temperature; taking out the product and washing it repeatedly with deionized water until the washing solution pH=7 to remove residual HCl and unreacted MgCl2; placing the washed product in an 80℃ forced-air drying oven and drying for 6 hours to obtain a magnesium-based glucose carbon composite adsorbent. Based on the ratio of GCM to MgCl2·6H2O=1:4, the obtained magnesium-based glucose carbon composite adsorbent is named MgO-GCM composite material.

[0025] In this embodiment, thermogravimetric analysis (TGA) was used to analyze the formation process of MgO-GCM. For example... Figure 2As shown in (b), the TGA curves of the MgO-GCM composite material exhibit different changes in four temperature ranges: 25-105℃, 105-300℃, 300-450℃, and 450-650℃. The first stage of weight loss originates from the dehydration reaction; the second stage of weight loss occurs when MgCl2·4H2O loses two molecules of water of crystallization and decomposes into MgCl2·2H2O; the third stage involves the further decomposition of MgCl2·2H2O to generate MgOHCl; the fourth stage shows the largest weight loss, which can be attributed to the decomposition of MgOHCl to generate magnesium oxide (MgO), as shown in the following reaction: MgCl2·6H2O→MgCl2·4H2O+2H2O (25-105℃); MgCl2·4H2O→MgCl2·2H2O+2H2O (105-300℃); MgCl2·2H2O→MgOHCl+HCl+H2O (300-450℃); MgOHCl→MgO+HCl (>450℃); Argon protection can remove HCl byproducts.

[0026] Furthermore, the MgO-GCM composite material was characterized: Scanning electron microscopy (SEM) of MgO-GCM, such as... Figure 3 As shown in (a) and (b), the composite material exhibits an agglomerated and interwoven state, with MgO particles deposited on the GCM surface. Figure 3 As shown in (c), (d), and (e), the color distribution from the SEM-mapping indicates that oxygen (O) and magnesium (Mg) are both uniformly distributed, reflecting a close correlation between their distributions in the composite material. Figure 4 As shown in (a), the crystallinity of the MgO-GCM composite material was characterized using X-ray diffraction (XRD) patterns in the range of 10°–90°. Comparison with data from the Joint Committee on Powder Diffraction Standards (JCPDS) shows that the characteristic peaks at 37°, 43°, 62°, 75°, and 79° correspond to periclase-type MgO (PDF#45-0946). Furthermore, as... Figure 4 As shown in (b) of the figure, the 485 cm⁻¹ Fourier transform infrared spectrum (FTIR) shows... -1 The appearance of a new characteristic peak confirms the presence of Mg-O bonds.

[0027] This embodiment also explores in depth the adsorption mechanism of phosphate by the magnesium-based glucose-carbon composite adsorbent by analyzing the changes in the microstructure and chemical state of the material before and after adsorption. Figure 5 As shown in (a) to (f), the elemental distribution mapping diagrams clearly demonstrate that the adsorbed P element is uniformly distributed across the entire material surface. Figure 6As shown in (a), the comparison of FTIR spectra before and after adsorption shows that the FTIR spectrum after adsorption is at 1052 cm⁻¹. -1 A distinct P=O characteristic stretching vibration peak appears at 985 cm⁻¹. -1 and 875cm -1 The characteristic absorption peak of PO appears at 560 cm⁻¹, and at the same time at 560 cm⁻¹. -1 The appearance of characteristic absorption peaks for Mg-OP bonds confirms the formation of stable chemical bonds between phosphate and magnesium oxide. Figure 6 As shown in (b), the comparative analysis of XRD patterns before and after adsorption shows that new diffraction peaks appeared after adsorption, corresponding to the characteristic peaks of Mg2PO4OH, MgHPO4·3H2O, Mg3(PO4)2·8H2O, and Mg3(PO4)2·22H2O, respectively. This proves that a stable magnesium phosphate crystalline compound was generated during adsorption, which is an important reason for the high adsorption capacity of the adsorbent. Figure 6 As shown in (c), the XPS full spectrum after adsorption clearly shows the appearance of P 2p and P 2s characteristic peaks, further confirming that phosphate was successfully adsorbed on the material surface.

[0028] In addition, fine-grained spectral peak analysis was performed on each element, such as... Figure 7 As shown in (a), (b), (c), and (d) in the image: the characteristic peaks of the C 1s spectrum at 284.8 eV, 286.2 eV, and 288.5 eV correspond to C / C=C, CO, and OC=O bonds, respectively; the characteristic peaks of the O 1s spectrum at 531.2 eV and 532.6 eV correspond to Mg-O and P=O / PO bonds, respectively; the characteristic peak of the Mg 1s spectrum at 1304.5 eV indicates that Mg exists in the Mg-O form; and the characteristic peak of the P 2p spectrum at 133.6 eV further confirms that P exists in the form of PO4. 3- It exists in a stable Mg-OP chemical bond with Mg. The above characterization results collectively demonstrate that the magnesium-based glucose carbon composite adsorbent achieves efficient adsorption of phosphate through the synergistic effect of multiple mechanisms such as surface deposition, ligand exchange, and chemical precipitation, among which the formation of Mg-OP chemical bonds is the key guarantee for adsorption stability.

[0029] Example 2 This embodiment aims to test the adsorption performance of MgO-GCM composite material on aqueous phosphate. First, the effect of solution pH on adsorption performance was investigated. The MgO-GCM composite material prepared in Example 1 (0.4 g·L⁻¹) was used. -1 ) was added to a solution of 50 mg (P)·L prepared with KH2PO4. -1Phosphate solution was used to investigate the influence of MgO-GCM composite materials on the phosphate adsorption effect at different initial pH values (2.0 - 11.0). Hydrochloric acid (HCl) and sodium hydroxide (NaOH) with a concentration of 0.1 - 1.0 mol·L -1 were used to adjust the solution pH. Figure 8 In (a) of -1 , the phosphate adsorption performance of MgO-GCM composite materials under different initial pH conditions is as follows: when pH = 2.0, the phosphorus adsorption amount of the composite material is only 1.05 mg(P)·g -1 ; when pH = 3.0, the adsorption amount sharply rises to 89.37 mg(P)·g

[0030] As Figure 8 shown in (b) of - , the isoelectric point (pH when Zeta potential = 0) of MgO-GCM composite materials is 3.2. When pH < 3.2, the surface of the composite material is positively charged; when pH > 3.2, the surface is negatively charged. Phosphate has three dissociation constants, which are 2.15, 7.19, and 12.35 respectively; when pH < 2.15, phosphate mainly exists in the form of H3PO4; when 2.15 < pH < 7.19, phosphate in the solution is mainly in the form of H2PO4

[0031] When 2.15 < pH < 3.2, on the one hand, there is a strong electrostatic attraction between MgO-GCM composite materials and negatively charged H2PO4 - ; on the other hand, MgO in the composite material dissolves in water to form Mg(OH)2, and Mg(OH)2 reacts with H2PO4 - in the solution, displacing OH - and releasing it into the solution, resulting in an increase in the solution pH after adsorption. Referring to Figure 8 the upward trend of the solution pH after adsorption in (b) confirms this reaction mechanism. As the pH further increases, OH - in the solution competes with H2PO4 - for the active adsorption sites on the surface of MgO-GCM composite materials, inhibiting the ligand exchange reaction, and thus leading to a decrease in the adsorption amount. This result indicates that ligand exchange plays a key role in the phosphate adsorption process.

[0032] In addition, this example also verified the influence of coexisting anions on the adsorption performance. The experiment on the influence of competitive anions on phosphate adsorption was carried out in a 100 mL centrifuge tube, and the system contained 50 mg(P)·L -1Phosphate solution and 1mM / 10mM coexisting anions (F - Cl - SO4 2- NO3 - HCO3 - SiO3 2- The addition amount of MgO-GCM composite material is 0.4 g·L⁻¹. -1 .

[0033] Depend on Figure 8 As shown in (c), when the concentration of coexisting anions is 1 mmol·L⁻¹ -1 At the initial concentration, all ions had no significant effect on phosphate adsorption; however, when the concentration increased to 10 mmol·L⁻¹, the effect was less pronounced. -1 At that time, SiO3 2- With HCO3 - The presence of HCO3- leads to a decrease in phosphate adsorption, among which... - The composite material reduced the phosphate removal rate by 32%, while the phosphate removal rate remained above 50% in the presence of other anions.

[0034] The above results indicate that the MgO-GCM composite material exhibits high adsorption selectivity for phosphates and is essentially unaffected by Cl-. - SO4 2- NO3 - Interference from competing ions. Its high selectivity mainly stems from the adsorption and binding of the adsorbent and phosphate through an inner-layer complexation mechanism, forming a stable chemical bond that is not easily affected by coexisting ions. NO3... - Cl - Other anions can only undergo non-specific outer layer complexation with metal oxides, and the inner layer complexation force is much stronger than the outer layer complexation force.

[0035] SiO3 2- With HCO3 - The competitive adsorption of phosphates occurs for the following reasons: First, the introduction of weak acid anions increases the pH of the system; second, these two ions have similar properties to phosphates and can react with metal oxides or hydroxides on the adsorbent surface through ligand exchange to form inner-layer complexes. Furthermore, the solubility products (Ksp) of magnesium carbonate and magnesium silicate are both lower than those of magnesium phosphate, therefore SiO3... 2- With HCO3 - They preferentially occupy the active adsorption sites of the MgO-GCM composite material. The differences in the influence of different coexisting ions further confirm that the MgO-GCM composite material mainly adsorbs phosphate by forming inner-layer complexes through ligand exchange.

[0036] In addition, this embodiment also provides a kinetic simulation and fitting analysis of the adsorption process, specifically including: preparing an initial concentration of 50 mg (P)·L. -1 100mg(P)·L -1 The pH of the KH2PO4 solution was adjusted to 5.0. 50 mL of the above solution was placed in a centrifuge tube, and 0.02 g of MgO-GCM composite material was added. The mixture was then shaken at 160 r / min at 298 K for adsorption. Samples were taken at 0.5, 1, 2, 4.5, 8, 12, 24, and 72 h. After filtration through a 0.22 μm filter membrane, the phosphate concentration was determined by colorimetry. The adsorption capacity and removal rate were calculated, and the adsorption kinetic model was obtained by fitting pseudo-first-order and pseudo-second-order kinetic equations.

[0037] according to Figure 9 The results showed that the initial phosphorus concentration was 50 mg(P)·L. -1 At that time, the MgO-GCM composite material reached adsorption equilibrium in 5.48 h; the initial concentration was 100 mg(P)·L⁻¹. -1 When the equilibrium time was extended to 19.55 h, the phosphorus adsorption rates at the two concentrations reached 98.27% and 92.22% at 60 h, respectively. Under the above two initial concentration conditions, both the pseudo-first-order kinetic model and the pseudo-second-order kinetic model showed high coefficients of determination (R²). 2 (See Table 1 for specific results) This indicates that the adsorption process involves both physical and chemical adsorption. The adsorption rate constants k1 (pseudo-first-order) and k2 (pseudo-second-order) both decrease with increasing initial phosphorus concentration, indicating that chemical adsorption dominates at higher solution concentrations.

[0038] Table 1 Kinetic model parameters for phosphate adsorption of MgO-GCM composite material

[0039] To this end, this embodiment also verifies adsorption using an adsorption isotherm model, specifically including: preparing an initial concentration of 1-200 mg(P)·L. -1 The pH of the KH₂PO₄ solution was adjusted to 5.0; adsorption was performed at 298 K, 308 K, and 318 K using the method described above, and the equilibrium concentration was determined and the adsorption capacity was calculated. The analytical data were fitted using the Langmuir and Freundlich models to obtain an isothermal adsorption model, as shown below. Figure 10 As shown in Table 2, the adsorption capacity of the MgO-GCM composite material gradually increases with the initial concentration of phosphate in the solution. When the adsorption reaches dynamic equilibrium, the adsorption capacity no longer changes with the initial concentration.

[0040] Table 2. Isothermal model parameters for phosphate adsorption by MgO-GCM composite material

[0041] It can be observed that the equilibrium adsorption capacity of the composite material for phosphorus is 211.36 mg·g⁻¹ under the conditions of 298 K, 308 K, and 318 K. -1 227.38 mg·g -1 240.23 mg·g -1 The Langmuir model fitting results show that the maximum adsorption capacity reaches 244.37 mg(P)·g at 318 K. -1 , R 2 >0.98 indicates that adsorption is mainly monolayer adsorption.

[0042] Furthermore, this embodiment also verified the synergistic adsorption of ammonium and phosphate. Ammonia nitrogen is a common cation in wastewater. To evaluate the impact of ammonia nitrogen on phosphate removal, the study simulated the presence of ammonia nitrogen in wastewater. When the pH was between 3 and 9, the proportions of both ammonia nitrogen and phosphate exceeded 90%, and the adsorption capacity of the composite material for ammonia nitrogen was 95–106 mg(N)·g. -1 Experimental results show that ammonia nitrogen can promote the adsorption of phosphate, and phosphate can also promote the adsorption of ammonia nitrogen; the synergistic effect of the two is significant. (Refer to...) Figure 11 It is speculated that during the adsorption process, the MgO on the surface of the MgO-GCM composite material reacts with phosphate and ammonia nitrogen in the solution as follows: MgO + H₂O → Mg(OH)₂ → Mg 2+ +2OH - ; Mg 2+ +NH 4+ +HnPO4 (3-n)- +6H₂O→MgNH₄PO₄·6H₂O+nH + ; In the formula, n ranges from 0 to 3, determined by the pH of the solution. When pH < 3 and n = 3, the main form of phosphate ions in the solution is H3PO4; when pH is 3-12, the main form is H2PO4. - HPO4 2- PO4 3- They coexist and interconvert. H₂ in the solution... + It reduces electrostatic repulsion, resulting in a higher phosphate removal rate in the pH range of 3-9.

[0043] Example 3 This embodiment provides the application of magnesium-based glucose-carbon composite adsorbent in soil phosphorus regulation. Through soil column experiments, the actual effect of composite adsorbent in soil phosphorus fixation and available phosphorus enhancement is verified, focusing on solving the problems of severe phosphorus leaching loss and low phosphorus resource utilization in agricultural production.

[0044] Soil samples were collected from farmland in a certain area. The soil had a pH of 8.1 and a loam texture. The soil was sieved through a 2mm sieve and dried at 105℃ for later use. Five treatment groups were set up: CK group (soil only), T0 group (soil + 200mg / kg KH2PO4), T1 group (soil + 200mg / kg KH2PO4 + 0.5% composite adsorbent), T2 group (soil + 200mg / kg KH2PO4 + 1% composite adsorbent), and T3 group (soil + 200mg / kg KH2PO4 + 2% composite adsorbent), with three replicates for each group. 500g of soil was thoroughly mixed with the corresponding reagents and placed into an acrylic column (20cm long, 2.5cm inner diameter). A 2cm thick layer of quartz sand was placed on top of the soil column to prevent surface erosion during leachate application. The bottom layer was then filled with a 2cm thick layer of quartz sand followed by nylon cloth to prevent soil particles from being lost with the leachate. Water was added to the soil column to bring the soil moisture content to 70% of field capacity. Then, on days 1, 2, 3, 4, 5, 7, 11, 15, and 25, 100 mL of deionized water was poured into the upper layer of the soil column each time. The leachate was collected, and the phosphate concentration in the leachate was determined using a colorimetric method. The cumulative phosphate content in the leachate was calculated using the following formula: ; ; In the formula, It represents the accumulation of phosphates, measured in mg. This is the phosphate concentration, expressed in mg / L. It is the volume of liquid leached out, in mL; It is the cumulative phosphate in the leachate, measured in mg.

[0045] After the experiment, the available phosphorus content of the soil in each group was determined by sodium bicarbonate extraction-molybdenum antimony spectrophotometry.

[0046] like Figure 12As shown in (a) and (b), on day 2 of leaching, the phosphate concentrations in the leaching solutions of treatments T0, T1, T2, and T3 were 2.78, 0.78, 0.62, and 0.41 mg (P) / L, respectively. These phosphate concentrations were 28.1%, 22.3%, and 14.7% of those in treatment T0, respectively. The cumulative phosphate leaching amounts in treatments T1, T2, and T3 with the addition of the composite adsorbent remained consistently low. The cumulative phosphate leaching amount in treatment T0 was 1.54 mg, while that in treatment T3 was only 0.23 mg, a decrease of 85.1% compared to group T0. This indicates that the composite adsorbent effectively inhibited the leaching loss of phosphorus. This effect stems from the dual function of the composite adsorbent: on the one hand, the magnesium oxide in the adsorbent reacts with free phosphorus in the soil to form stable crystals such as magnesium hydrogen phosphate and magnesium phosphate. These crystals are difficult to infiltrate with leachate water, thereby reducing phosphorus leaching loss; on the other hand, glucose-based carbon spheres can physically adsorb some of the more mobile phosphorus in the soil, further preventing phosphorus loss.

[0047] In addition, according to the results of soil available phosphorus testing, as shown... Figure 12 In (c), the available phosphorus content in the soil of groups CK, T0, T1, T2, and T3 were 16.91 mg / kg, 96.21 mg / kg, 186.34 mg / kg, 191.35 mg / kg, and 206.67 mg / kg, respectively. The available phosphorus content in groups T1, T2, and T3 was 1.94–2.15 times that of group T0. This is because the phosphorus fixed by the composite adsorbent exists in a slow-release form. Under the influence of soil moisture, the magnesium hydrogen phosphate and magnesium phosphate fixed in the adsorbent slowly release H2PO4 that can be absorbed by crops. - and HPO4 2- This not only avoids the problem of easy loss after rapid release of traditional phosphate fertilizers, but also continuously replenishes the soil with available phosphorus, improving the utilization efficiency of phosphorus resources.

[0048] Example 4 This embodiment provides the regeneration performance and actual wastewater treatment test of magnesium-based glucose carbon composite adsorbent. From the two dimensions of material recycling and practical application, the regeneration performance and actual phosphorus-containing wastewater treatment effect of composite adsorbent are tested to verify its industrial application potential.

[0049] In the regeneration performance test, the composite adsorbent that was saturated with adsorption (adsorbing 50 mg (P)·L) was first used to regenerate the adsorbent. -1The adsorbent (after solution removal) was soaked in a 1 mol / L sodium hydroxide solution and stirred for 24 hours for desorption. After desorption, the adsorbent was separated by filtration and repeatedly washed with deionized water until the washing solution was neutral. The adsorbent was then dried at 80℃ for 4 hours to complete one regeneration. The regenerated adsorbent was reused in the phosphate adsorption experiment for 8 cycles, and the phosphate removal rate was recorded for each cycle. Figure 13 Results (a) show that the adsorption rate was 94.26% in the first cycle, 88.5% in the second, 81.3% in the third, 73.5% in the fourth, 67.1% in the fifth, 65.2% in the sixth, 63.8% in the seventh, and 62.5% in the eighth. Even after eight adsorption-desorption cycles, the removal rate of phosphate by the adsorbent remained above 62%. This regeneration effect is achieved because a 1 mol / L sodium hydroxide solution can break the Mg-OP bond formed between magnesium oxide and phosphate on the surface of the composite adsorbent, allowing the phosphate to be converted to PO42-. 3- The adsorbent desorbs from the surface of the adsorbent into the solution in the form of MgO. At the same time, the sodium hydroxide solution does not destroy the framework structure of the glucose-based carbon spheres, nor does it affect the loading state of magnesium oxide on the surface of the carbon spheres. Therefore, the adsorbent can repeatedly maintain its adsorption activity.

[0050] In the actual wastewater treatment test, aquaculture wastewater from an agricultural experimental station was selected as the treatment target. The initial phosphate concentration of this wastewater was 2.37 mg(P)·L⁻¹. -1 Composite adsorbent at concentrations of 0.8 g / L, 1.0 g / L, and 1.2 g / L were added to the wastewater, respectively. Adsorption was carried out at 308 K with shaking for 24 h. After adsorption, the wastewater was filtered through a 0.22 μm filter membrane, and the phosphate concentration in the treated wastewater was measured. Figure 13 Results (b) show that when the adsorbent dosage was 1.0 g / L, the phosphate removal rate reached 99.82%, and the phosphate concentration in the treated wastewater decreased to 1.90 μg(P)·L. -1 When the adsorbent dosage was 1.2 g / L, the phosphate removal rate was further improved, and the phosphate concentration in the treated wastewater was even lower. The phosphate concentration in the wastewater treated by both dosages was significantly lower than 50 μg(P)·L. -1 The US EPA emission standards indicate that the composite adsorbent can maintain a high phosphate removal efficiency even in the complex environment of actual wastewater (containing suspended particles, organic matter and various coexisting ions), and is applicable to the treatment of various actual phosphorus-containing wastewaters such as aquaculture wastewater, agricultural non-point source pollution wastewater and industrial phosphorus-containing wastewater.

[0051] Therefore, the above-mentioned magnesium-based glucose-carbon composite adsorbent and its preparation method and application use glucose and magnesium chloride as inexpensive and non-toxic raw materials. The preparation process is simple, and it has high phosphate adsorption capacity, strong selectivity and ammonium-phosphorus synergistic adsorption characteristics. It can be regenerated and reused more than 8 times. It can realize the integrated functions of phosphorus removal in water, phosphorus fixation and effective phosphorus enhancement in soil, and agricultural fertilizer recycling, without secondary pollution, and is suitable for multiple applications in agriculture and industry.

[0052] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0053] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A magnesium-based glucose-carbon composite adsorbent, characterized in that, The composite adsorbent is composed of glucose-based carbon spheres and magnesium oxide particles. The glucose-based carbon spheres serve as the carrier framework, and the magnesium oxide particles are loaded on the surface of the glucose-based carbon spheres. The composite adsorbent is prepared by preparing glucose-based carbon spheres by a hydrothermal method, and then loading magnesium oxide particles by a co-impregnation-pyrolysis method.

2. A method for preparing the magnesium-based glucose-carbon composite adsorbent according to claim 1, characterized in that, Includes the following steps: Glucose-based carbon spheres were prepared by hydrothermal method: glucose, sodium dodecyl sulfonate and deionized water were mixed and added to a reaction vessel, stirred until uniformly dissolved, and reacted at a preset reaction temperature for a preset time; after the reaction was completed, the reaction product was filtered, washed with anhydrous ethanol and deionized water in sequence until neutral, and dried to obtain glucose-based carbon spheres. Magnesium oxide particles were loaded by co-impregnation-pyrolysis: the glucose-based carbon spheres were impregnated in a solution containing magnesium chloride hexahydrate, stirred for a preset time, and then dried to constant weight to obtain the dried product; Preparation of magnesium-based glucose carbon composite adsorbent: The dried product was placed in an atmosphere furnace and heated to the calcination temperature at a preset heating rate under argon protection and held at the temperature for a preset time; after cooling, it was washed until pH=7 and dried again to obtain the magnesium-based glucose carbon composite adsorbent.

3. The preparation method of a magnesium-based glucose-carbon composite adsorbent according to claim 2, characterized in that, In the process of preparing glucose-based carbon spheres by hydrothermal method, the solid-liquid ratio of glucose and sodium dodecyl sulfonate to deionized water is 1:8-1:10, the reaction temperature is 180℃, the preset time is 4h, the filtration uses a 0.22μm microporous membrane, the drying temperature is 80℃, and the drying time is 4-12h.

4. The preparation method of a magnesium-based glucose-carbon composite adsorbent according to claim 2, characterized in that, In the process of loading magnesium oxide particles by co-impregnation-pyrolysis, the mass ratio of the glucose-based carbon spheres to magnesium chloride hexahydrate is 1:4, the stirring time is preset to 24 hours, and the drying temperature is 80°C.

5. The preparation method of a magnesium-based glucose-carbon composite adsorbent according to claim 2, characterized in that, In the preparation of the magnesium-based glucose carbon composite adsorbent, the argon flow rate is 50-100 mL / min, the heating rate is 5-10 °C / min, the calcination temperature is 600 °C, the holding time is 2 h, the drying temperature is 80 °C, and the drying time is 4-6 h.

6. The use of the magnesium-based glucose-carbon composite adsorbent according to claim 1 for removing phosphate from aqueous solution, characterized in that, The operation comprises: adding the composite adsorbent into a phosphatase-containing aqueous solution, controlling the solid-liquid ratio to be 0.4 g / L; oscillating adsorption at a temperature of 298-318 K and a speed of 160-260 r / min for 4.5-72 h to reach equilibrium; the initial concentration of the phosphatase in the phosphatase-containing aqueous solution is 1-200 mg(P)·L -1 , and the pH of the aqueous solution is adjusted to 2.0-11.

0.

7. The use of the magnesium-based glucose-carbon composite adsorbent according to claim 6 for removing phosphate from aqueous solutions, characterized in that, When the phosphate-containing aqueous solution contains 1-10 mmol / L of fluoride, chloride, sulfate, nitrate, bicarbonate, or silicate ions, the adsorption rate of the composite adsorbent for phosphate is not less than 50%; when the phosphate-containing aqueous solution simultaneously contains 100 mg (N)·L... -1 When ammonium ions are present, the adsorption capacity of ammonium ions and phosphates mutually increases by 10%-15%.

8. The use of the magnesium-based glucose-carbon composite adsorbent according to claim 1 for soil phosphorus fixation and available phosphorus enhancement, characterized in that, The operation includes: uniformly mixing the composite adsorbent with the soil, controlling the amount of composite adsorbent added to be 0.5%-2% of the soil mass; after the soil and composite adsorbent are mixed, the cumulative leaching amount of soil phosphate is reduced by no less than 85%, and the available phosphorus content of the soil is increased to 1.94-2.15 times that of the soil without the addition of the composite adsorbent.

9. A method for regenerating the magnesium-based glucose-carbon composite adsorbent according to claim 1, characterized in that, The operation includes: soaking the adsorbed composite adsorbent in 1 mol / L sodium hydroxide solution and stirring for 24 h for desorption, then washing it with deionized water until neutral, drying it at 80 °C for 4 h, and then repeating it for phosphate adsorption; after 8 adsorption-desorption cycles, the phosphate removal rate is not less than 67%.

10. The use of the magnesium-based glucose carbon composite adsorbent according to claim 1, characterized in that, Includes the following two categories: Agricultural fertilizer recycling uses: The composite adsorbent after adsorbing phosphate is directly applied to farmland soil; in the composite adsorbent after adsorbing phosphate, the phosphate exists in the form of magnesium hydrogen phosphate and magnesium phosphate, which provides phosphorus nutrition to crops as a slow-release phosphate fertilizer; Practical applications of phosphorus-containing wastewater treatment: The actual phosphorus-containing wastewater includes aquaculture wastewater, agricultural non-point source pollution wastewater, or industrial phosphorus-containing wastewater; when the initial concentration of phosphate in the wastewater is 2.37 mg(P)·L... -1 When the composite adsorbent is added at a concentration of 1.0-1.2 g / L to the wastewater, the phosphate removal rate is not less than 99.82%, and the phosphate concentration in the treated wastewater is less than 50 μg(P)·L. -1 .

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