Calcium carbonate coated calcium peroxide slow-release nano material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of environmental restoration, and discloses a calcium carbonate coated calcium peroxide slow-release nano material as well as a preparation method and application thereof. The slow-release nano material comprises calcium peroxide and calcium carbonate and is of a core-shell structure, an inner core layer is calcium peroxide, and a shell is calcium carbonate; the preparation method comprises the following steps: continuously stirring a calcium peroxide suspension for 5-60 minutes in a normal-temperature normal-pressure and open system to spontaneously finish calcium carbonate coating without using other materials or chemical reagents. The calcium carbonate shell in the slow-release nano material provided by the invention not only enables calcium peroxide to realize H2O2 slow release, but also widens the pH application range of the material to 3.0-11.0. Compared with the prior art, the method is extremely simple in preparation process, low in cost, green, environmentally friendly and suitable for in-situ chemical oxidation repair of organic matter polluted sites.

Description

Technical Field

[0001] A calcium carbonate-coated calcium peroxide slow-release nanomaterial, its preparation method, and its application. Background Technology

[0002] With the rapid pace of industrialization, groundwater pollution is becoming increasingly severe. Studies have shown that extractable shallow groundwater is already contaminated. Among the pollutants, persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs), chlorinated hydrocarbons, and petroleum hydrocarbons, which degrade slowly under natural conditions, pose a significant challenge to groundwater remediation.

[0003] Currently, groundwater remediation technologies are mainly divided into in-situ and ex-situ remediation technologies. Compared with traditional ex-situ remediation technologies, in-situ remediation technologies treat the contaminated area directly, avoiding secondary transfer and diffusion of pollutants and reducing remediation costs. However, in-situ remediation technologies still face problems such as rapid depletion of active substances and short remediation effectiveness, which makes it easy for pollutant concentrations to rebound several hours after the injection of remediation agents is stopped. In recent years, the development of slow-release materials has provided an effective solution to address these challenges. Slow-release materials extend the effective remediation duration by continuously releasing active substances such as H2O2 and persulfate, thereby ensuring the long-term effectiveness of the remediation.

[0004] Calcium peroxide (CaO2) has become a focus of attention in the field of environmental remediation due to its continuous release of H2O2 in water and its non-toxic and harmless nature. Compared with other slow-release materials, its environmental friendliness is prominent, showing good application prospects. However, CaO2 particles often have high reactivity and violent reactions, making it difficult to ensure that the active substances in the reaction system maintain a stable and effective concentration over a period of time. To address this issue, researchers have proposed reducing the reactivity of CaO2 through coating methods, thereby achieving long-term release of active substances. Currently, large molecular organic compounds such as sodium alginate, stearic acid, polyethylene glycol, and its monomethyl ether are commonly used as coating agents to prepare coated calcium peroxide slow-release materials. However, the organic matter in these slow-release materials is easily released into the environment during practical use, posing a risk of secondary pollution, and it will compete with organic pollutants for reactive oxygen species in the reaction system, reducing the removal efficiency of the target pollutants. In addition, existing coated calcium peroxide slow-release materials are generally limited by a narrow pH range; under neutral or alkaline conditions, the release of active substances (H2O2) is often significantly inhibited.

[0005] Therefore, there is an urgent need to find a green, long-lasting, and environmentally adaptable calcium peroxide-based slow-release material and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to overcome the technical problems of secondary pollution and narrow pH range in the remediation process of existing technologies, and to provide a calcium carbonate-coated calcium peroxide slow-release nanomaterial. This slow-release nanomaterial has advantages such as slow H2O2 release rate, non-toxicity and harmlessness, and wide pH range, and can effectively remediate organic polluted groundwater.

[0007] To achieve the above objectives, the first aspect of the present invention provides a calcium carbonate-coated calcium peroxide slow-release nanomaterial, characterized in that it is composed of the following components in mass percentage: 60.6% to 76.5% calcium peroxide and 23.5% to 39.4% calcium carbonate; and the material has a core-shell structure, with the core being calcium peroxide and the outer shell being calcium carbonate.

[0008] A second aspect of this invention provides a method for preparing calcium carbonate-coated calcium peroxide slow-release nanomaterials, the method comprising the following steps: (1) Dissolve 5.0 g of anhydrous calcium chloride in 50 mL of deionized water and add 30 mL of ammonia water (25%~28%). Slowly add 30 mL of hydrogen peroxide (15%) at room temperature and continue stirring. After the addition is complete, filter and dry the solid component at 80℃ for 4 h to obtain solid calcium peroxide. (2) Add calcium peroxide to deionized water to form a suspension; (3) The above suspension is continuously stirred in an open system to allow calcium peroxide to react fully with water and carbon dioxide in the air to generate calcium carbonate, which is then deposited on the surface of calcium peroxide to form a coating layer. (4) After the reaction is complete, filter to separate the solid components, and then dry with a forced air to obtain calcium carbonate coated calcium peroxide slow-release nanomaterials.

[0009] In one embodiment of the present invention, the concentration of calcium peroxide in the suspension is 3.0 to 7.5 g / L.

[0010] In one embodiment of the present invention, the stirring speed is 500-700 rpm, and the reaction time of calcium peroxide with water and carbon dioxide in the air is 5-60 min.

[0011] In one embodiment of the present invention, the blowing drying temperature is 80-100 °C and the drying time is 4-6 h.

[0012] This invention provides a calcium carbonate-coated calcium peroxide slow-release nanomaterial prepared by the above method.

[0013] This invention provides an application of the above-mentioned calcium carbonate-coated calcium peroxide slow-release nanomaterial in the field of environmental remediation.

[0014] In one embodiment of the present invention, the application in the field of environmental remediation includes the remediation of soil and water pollution.

[0015] In one embodiment of the present invention, the application involves using the above-mentioned calcium carbonate-coated calcium peroxide slow-release nanomaterial and ferrous salt to form a Fenton-like system, which generates free radicals through reaction to oxidize and degrade organic pollutants in water.

[0016] In one embodiment of the present invention, the application in the field of environmental remediation includes the remediation of soil and water pollution. In one embodiment of the invention, the molar ratio of calcium peroxide to ferrous salt in the calcium carbonate-coated calcium peroxide slow-release nanomaterial is 3:1 to 4.

[0017] In one embodiment of the present invention, the divalent ferric salt used is ferrous sulfate or ferrous chloride.

[0018] In one embodiment of the present invention, the free radicals used are hydroxyl radicals and carbonate radicals.

[0019] In one embodiment of the present invention, the organic pollutant used is naphthalene.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] This invention utilizes only water and carbon dioxide from the air to spontaneously coat calcium peroxide with calcium carbonate, eliminating the need for other materials or chemical reagents, resulting in low cost and environmental friendliness. The calcium carbonate shell in the calcium carbonate-coated calcium peroxide slow-release nanomaterial provided by this invention not only enables the slow release of H2O2 from calcium peroxide but also broadens the material's pH range to 3.0–11.0. The coating mechanism lies in the fact that calcium hydroxide, present in calcium peroxide itself or generated from its reaction with water, reacts with dissolved CO2 in the air to form insoluble calcium carbonate, which deposits as a shell on the surface of the calcium peroxide. The CaCO3 shell significantly reduces the probability of contact between calcium peroxide and water, thus achieving the slow release of H2O2. Simultaneously, the continuously dissolved CO3 from the CaCO3 shell... 2- It has the ability to buffer pH fluctuations, enabling the material to maintain stable performance over a wider pH range. Compared with existing technologies, the preparation process of this invention is extremely simple, easy to scale up for industrial production, and has better application prospects, providing a new material for in-situ chemical oxidation remediation of organic contaminated sites. Attached Figure Description

[0022] Figure 1 The X-ray diffraction pattern of CaO2@CaCO3NPs in Example 1 of this invention is shown.

[0023] Figure 2This is a thermogravimetric analysis diagram of CaO2@CaCO3NPs in Example 1 of the present invention.

[0024] Figure 3 This is a compositional diagram of CaO2@CaCO3NPs in Example 1 of the present invention.

[0025] Figure 4 This is a scanning electron microscope image of CaO2@CaCO3NPs from Example 1 of the present invention.

[0026] Figure 5 This is a projection electron microscope image of CaO2@CaCO3NPs from Example 1 of the present invention.

[0027] Figure 6 This is a comparison diagram of the H2O2 sustained-release effect of the material prepared in Example 1 of the present invention.

[0028] Figure 7 This is a comparison chart of the H2O2 conversion efficiency of the materials prepared in Example 1 of the present invention.

[0029] Figure 8 The H2O2 conversion efficiency of the material prepared in Example 1 of this invention at different initial pH values ​​is shown.

[0030] Figure 9 The degradation effects of different systems on naphthalene.

[0031] Figure 10 The initial pH value for CaO2@CaCO3NPs / Fe 2+ The effect of system degradation of naphthalene.

[0032] Figure 11 EPR test patterns for different systems.

[0033] Figure 12 For Fe 2+ Concentration of CaO2@CaCO3NPs / Fe 2+ The effect of system degradation of naphthalene.

[0034] Figure 13 The percentage of each component in CaO2@CaCO3NPs prepared under different calcium peroxide dosages is shown in the figure.

[0035] Figure 14 H2O2 release curves of CaO2@CaCO3NPs prepared under different calcium peroxide dosages.

[0036] Figure 15 H2O2 release curves of CaO2@CaCO3NPs prepared under different calcium peroxide dosages. Detailed Implementation

[0037] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0038] In the following examples, all raw materials used were obtained through commercial purchase;

[0039] The composition and structure of the core and shell were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

[0040] The calcium peroxide content in calcium carbonate-coated calcium peroxide slow-release nanomaterials was determined by potassium permanganate titration: 0.05 g of the test sample was accurately weighed and placed in a 250 mL Erlenmeyer flask, and 10 mL of phosphoric acid (4 mol / L) and 10 mL of sulfuric acid (4 mol / L) were added successively. After dissolution, the solution was titrated with 0.02 mol / L potassium permanganate until the solution turned red.

[0041] The calcium carbonate content in calcium carbonate-coated calcium peroxide slow-release nanomaterials was determined by an elemental analyzer: the carbon content in the sample was determined by an elemental analyzer and then converted into the calcium carbonate content.

[0042] The concentration of H2O2 in the solution was determined by potassium titanium oxalate spectrophotometry: 1.0 mL of sample was placed in a 25 mL colorimetric tube, and 1.0 mL of potassium titanium oxalate solution (0.08 mol / L) and 1.0 mL of sulfuric acid solution (4 mol / L) were added respectively. After color development for 10 min, the absorbance was measured at a wavelength of 358 nm using a UV spectrophotometer, and the corresponding concentration was calculated according to the calibration curve.

[0043] Fe in solution 2+ The concentration was determined by the o-phenanthroline spectrophotometric method: 1.0 mL of sample was placed in a 25 mL colorimetric tube, and 1.0 mL (0.5%) and 1.0 mL o-phenanthroline solution (4 mol / L) were added respectively. After color development for 10 min, the absorbance was measured at a wavelength of 510 nm using a UV spectrophotometer, and the corresponding concentration was calculated according to the mark.

[0044] The concentration of naphthalene in the solution was determined by high performance liquid chromatography: 1.0 mL of sample was taken, 0.1 mL of methanol was added to quench the reaction, a 0.22 μm polytetrafluoroethylene filter membrane was used, and then the concentration of naphthalene in the filtrate was determined by high performance liquid chromatography.

[0045] The type of free radicals in the reaction system was determined by electron paramagnetic resonance (EPR): 1.0 mL of sample was taken into a 3.0 mL sample tube, followed by the addition of 20 μL of 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO). The mixture was shaken to allow the free radicals and DMPO to react fully. The sample was taken with a glass capillary tube and loaded into an NMR tube. Finally, the sample was tested using an electron paramagnetic resonance spectrometer.

[0046] The H2O2 conversion rate of the material obtained in the example was calculated according to the following formula:

[0047] W = (5CVM / 2mω) × 100%

[0048] In the formula, C: concentration of H2O2 in the solution, mol / L; V: volume of the solution, L; M: relative molecular weight of calcium peroxide, g / mol; m: mass of calcium peroxide weighed, g; ω: calcium peroxide content in the material, %.

[0049] Example 1:

[0050] The preparation method of calcium carbonate-coated calcium peroxide slow-release nanomaterials in this embodiment includes the following steps:

[0051] (1) Dissolve 5.0 g of anhydrous calcium chloride in 50 mL of deionized water and add 30 mL of ammonia water (25%~28%). Slowly add 30 mL of hydrogen peroxide (15%) at room temperature and stir continuously. After the addition is complete, filter and dry the solid component at 80℃ for 4 h to obtain solid calcium peroxide (CaO2).

[0052] (2) Take 1.0 g of calcium peroxide and add it to 200 mL of deionized water to form a suspension. Stir the suspension continuously in an open system for 60 min to allow the calcium peroxide to react fully with water and carbon dioxide in the air to generate calcium carbonate, which is then deposited on the surface of the calcium peroxide to form a coating layer.

[0053] (3) After the reaction is complete, filter to separate the solid components, and then dry them at 80°C to obtain calcium carbonate coated calcium peroxide slow-release nanomaterials, abbreviated as CaO2@CaCO3NPs.

[0054] like Figure 1 As shown, the main components of the CaO2@CaCO3NPs prepared in this embodiment are calcium carbonate and calcium peroxide; compared with CaO2, the content of calcium carbonate in CaO2@CaCO3NPs increases, while the content of calcium peroxide decreases.

[0055] like Figure 2As shown, the weight loss peaks on the DTG curves of CaO2@CaCO3NPs prepared in this embodiment are attributed to calcium peroxide and calcium carbonate, respectively, while the weight loss peaks on the DTG curve of CaO2 are attributed to calcium peroxide and calcium hydroxide, respectively. This indicates that calcium hydroxide will be converted into calcium carbonate during the coating reaction.

[0056] like Figure 3 As shown, the mass percentages of calcium carbonate and calcium peroxide in the CaO2@CaCO3NPs prepared in this embodiment are 68.2% and 31.8%, respectively; while the contents of calcium peroxide, calcium hydroxide and calcium carbonate in CaO2 are 79.4%, 9.4% and 11.2%, respectively, indicating that calcium hydroxide in CaO2 will be converted into calcium carbonate during the coating reaction.

[0057] like Figure 4 As shown, by comparing the scanning electron microscope images of CaO2@CaCO3NPs and CaO2 prepared in this embodiment, it can be seen that the particle morphology did not change significantly, and the particles were still spherical with obvious agglomeration and a particle size distribution of 50-100 nm.

[0058] like Figure 5 As shown, by comparing the transmission electron microscope images of CaO2@CaCO3NPs and CaO2 prepared in this embodiment, it can be seen that the surface of CaO2 particles shows uniform (112) crystal plane characteristic stripes; while the surface of CaO2@CaCO3NPs particles mainly shows (112) crystal plane and (110) crystal plane characteristic stripes, indicating that calcium carbonate is coated on the surface of calcium peroxide.

[0059] Example 2:

[0060] This embodiment studies the H2O2 slow-release performance and conversion efficiency of calcium carbonate-coated calcium peroxide slow-release nanomaterials.

[0061] The calcium peroxide and calcium carbonate-coated calcium peroxide slow-release nanomaterials prepared in Example 1 were used as the control and experimental groups, respectively. The static slow-release experiments of H2O2 were conducted in 250 mL capped glass bottles at a temperature controlled at (25 ± 0.5)℃. 0.02 g of material was added to a capped glass bottle containing 200 mL of water. To ensure uniform dispersion, a magnetic stirrer was added to the bottle, and the bottle was placed on a magnetic stirrer and stirred uniformly at 500 r / min. Subsequent sample analysis was performed using a time-lapse sampling method, with 1.0 mL samples taken each time. After filtration through a 0.22 μm filter membrane, the concentration of H2O2 in the sample was determined using potassium titanate oxalate spectrophotometry.

[0062] like Figure 6As shown, by comparing the H2O2 release kinetics of CaO2@CaCO3NPs and CaO2 prepared in Example 1, it can be seen that, compared with CaO2, the H2O2 release process of CaO2@CaCO3NPs is slower, the time to reach the maximum concentration (0.89 mmol / L) is extended by 60 min, and the initial release rate is reduced by 36.7%.

[0063] like Figure 7 As shown, by comparing the H2O2 conversion efficiency of CaO2@CaCO3NPs and CaO2 prepared in Example 1, it can be seen that the H2O2 conversion efficiency of CaO2 is only 81%, while the H2O2 conversion efficiency of CaO2@CaCO3NPs reaches 96%, indicating that calcium carbonate coating significantly improves the conversion efficiency of calcium peroxide to H2O2.

[0064] Example 3:

[0065] This embodiment investigates the effect of initial pH value on the H2O2 release process of calcium carbonate-coated calcium peroxide slow-release nanomaterials.

[0066] The calcium peroxide and calcium carbonate-coated calcium peroxide slow-release nanomaterials prepared in Example 1 were used as the control and experimental groups, respectively, to conduct static slow-release experiments of H2O2 at different initial pH values ​​(3.0, 5.0, 7.0, 9.0, 11.0). All H2O2 static slow-release experiments were conducted in 250 mL capped glass bottles at a temperature controlled at (25 ± 0.5)℃. 0.02 g of material was added to a capped glass bottle containing 200 mL of water (previously adjusted to pH with 1.0 mol / L sulfuric acid or sodium hydroxide). To ensure uniform dispersion, a magnetic stirrer was added to the glass bottle, and the bottle was placed on a magnetic stirrer and stirred uniformly at 500 r / min. Subsequent sample analysis was performed using a time-lapse sampling method, with 1.0 mL samples taken each time. After filtration through a 0.22 μm filter membrane, the concentration of H2O2 in the sample was determined using potassium titanate oxalate spectrophotometry.

[0067] like Figure 8 As shown, the CaO2@CaCO3NPs prepared in Example 1 exhibited good H2O2 slow-release effects over a wide pH range (3.0-11.0), and the H2O2 conversion efficiency of CaO2@CaCO3NPs did not decrease significantly under alkaline conditions. Compared with the control group CaO2, CaO2@CaCO3NPs showed better H2O2 slow-release effects under strongly acidic conditions (pH = 3.0). Figure 8It can be seen that the H2O2 conversion efficiency of CaO2 decreases significantly under strong alkaline conditions (pH = 11.0), from 81% to 66%, while the H2O2 conversion efficiency of CaO2@CaCO3NPs remains as high as 89% under the same pH conditions. The above experimental results indicate that CaO2@CaCO3NPs has a wide applicable pH range.

[0068] Example 4:

[0069] This embodiment uses naphthalene as the target pollutant to study the degradation effect of a Fenton-like system based on calcium carbonate-coated calcium peroxide slow-release nanomaterials on organic pollutants.

[0070] The calcium peroxide and calcium carbonate-coated calcium peroxide slow-release nanomaterials prepared in Example 1 were used as the control and experimental groups, respectively. All experiments were conducted in 250 mL capped glass bottles at (25 ± 0.5) °C. A magnetic rotor was added to the glass bottle, and the bottle was placed on a magnetic stirrer and stirred uniformly at 500 r / min. 200 mL of 0.05 mmol / L naphthalene solution was added to the glass bottle, followed by the addition of ferrous sulfate to initially adjust the Fe content in the solution. 2+ The concentration was 0.5 mmol / L. Finally, 0.03 g of nano-calcium peroxide or calcium carbonate-coated calcium peroxide slow-release nanomaterials were added to start the reaction. After a certain time interval, a sample was taken and an excess of methanol quencher was added to terminate the reaction. The sample was then filtered through a 0.22 μm filter membrane and the concentration of naphthalene in the sample was determined by high performance liquid chromatography (HPLC).

[0071] like Figure 9 As shown, by comparing the degradation effects of CaO2@CaCO3NPs and the Fenton-like system of CaO2 prepared in Example 1 on naphthalene, it can be seen that the CaO2 / Fe 2+ Compared to the system, CaO2@CaCO3NPs / Fe 2+ The system showed better degradation of naphthalene, increasing the degradation rate by 11.4%.

[0072] Example 5:

[0073] This embodiment uses naphthalene as the target pollutant to study the effect of initial pH value on the degradation of organic pollutants by a Fenton-like system based on calcium carbonate-coated calcium peroxide slow-release nanomaterials.

[0074] The calcium carbonate-coated calcium peroxide slow-release nanomaterials prepared in Example 1 were used as the research object to conduct naphthalene degradation experiments at different initial pH values ​​(3.0, 5.0, 7.0, 9.0, 11.0). All experiments were conducted in 250 mL capped glass bottles, with the temperature controlled at (25 ± 0.5)℃. A magnetic rotor was added to the glass bottle, and the bottle was placed on a magnetic stirrer and stirred uniformly at 500 r / min. 200 mL of a 0.05 mmol / L naphthalene solution (previously adjusted to pH with 1.0 mol / L sulfuric acid or sodium hydroxide) was added to the glass bottle, followed by the addition of ferrous sulfate to initially adjust the Fe content in the solution. 2+ The concentration was 1.0 mmol / L. Finally, 0.03 g of calcium carbonate-coated calcium peroxide slow-release nanomaterial was added to start the reaction. After a certain time interval, a sample was taken and an excess of methanol quencher was added to terminate the reaction. The sample was then filtered through a 0.22 μm filter membrane and the concentration of naphthalene in the sample was determined by high performance liquid chromatography (HPLC).

[0075] like Figure 10 As shown, when the initial pH increases from 3.0 to 9.0, the CaO2@CaCO3NPs / Fe 2+ The degradation effect of the system on naphthalene did not change significantly, with degradation rates all above 90%. Only when the pH continued to increase to 11.0 did the degradation effect of naphthalene decrease significantly, with the removal rate dropping to 53%. This indicates that the degradation effect of CaO2@CaCO3NPs / Fe 2+ The system has a wide applicable pH range.

[0076] Example 6:

[0077] In this embodiment, the type of free radical in a Fenton-like system based on calcium carbonate-coated calcium peroxide slow-release nanomaterials was identified by electromagnetic paramagnetic resonance (EPR).

[0078] The calcium peroxide and calcium carbonate-coated calcium peroxide slow-release nanomaterials prepared in Example 1 were used as the control and experimental groups, respectively. All experiments were conducted in 250 mL capped glass bottles at (25 ± 0.5) °C. A magnetic rotor was added to the glass bottle, and the bottle was placed on a magnetic stirrer and stirred uniformly at 500 r / min. 200 mL of 0.05 mmol / L naphthalene solution was added to the glass bottle, followed by the addition of ferrous sulfate to initially adjust the Fe content in the solution. 2+ The concentration was 1.0 mmol / L. Finally, 0.03 g of nano-calcium peroxide or calcium carbonate-coated calcium peroxide slow-release nanomaterials were added to start the reaction. After 2 min of reaction, 1.0 mL of sample was taken and 20 μL of DMPO was added to capture free radicals. After filtration through a 0.22 μm filter membrane, the free radicals present in the sample were measured using an EPR instrument.

[0079] like Figure 11 As shown, CaO2 / Fe 2+ The system mainly contains hydroxyl radicals ( • OH), while CaO2@CaCO3NPs / Fe 2+ The system contains hydroxyl radicals ( • OH) and carbonate radicals (CO3) •－ Compared to • OH, CO3 •－ It has the characteristics of long lifespan, high reaction selectivity, and strong anti-interference ability, therefore CaO2@CaCO3NPs / Fe 2+ CO3 produced in the system •－ It can further promote the degradation of target pollutants.

[0080] Example 7:

[0081] This embodiment uses naphthalene as the target pollutant to study Fe. 2+ The effect of concentration on the degradation of organic pollutants by a Fenton-like system based on calcium carbonate-coated calcium peroxide slow-release nanomaterials.

[0082] The calcium peroxide and calcium carbonate-coated calcium peroxide slow-release nanomaterials prepared in Example 1 were used as the control and experimental groups, respectively. All experiments were conducted in 250 mL capped glass bottles at (25 ± 0.5) °C. A magnetic rotor was added to the glass bottle, and the bottle was placed on a magnetic stirrer and stirred uniformly at 500 r / min. 200 mL of 0.05 mmol / L naphthalene solution was added to the glass bottle, followed by the addition of ferrous sulfate to initially adjust the Fe content in the solution. 2+ The concentrations were set at (0.5, 1.0, 1.5, 2.0 mmol / L). Finally, 0.03 g of nano-calcium peroxide or calcium carbonate-coated calcium peroxide slow-release nanomaterials (calcium peroxide dosage was 1.5 mmol / L) were added to start the reaction. After a certain time interval, samples were taken and excess methanol quencher was added to terminate the reaction. The samples were then filtered through a 0.22 μm filter membrane and the concentration of naphthalene in the samples was determined by high performance liquid chromatography (HPLC).

[0083] like Figure 12 As shown, in CaO2 / Fe 2+ In the system, the degradation rate of naphthalene increases with the amount of Fe. 2+ Increased concentration leads to higher Fe 2+ The optimal concentration was 1.5 mmol / L, with a naphthalene degradation rate of 94%; while in CaO2@CaCO3NPs / Fe 2+ In the system, the degradation rate of naphthalene also increases with the amount of Fe. 2+ Increased concentration leads to higher Fe 2+The optimal concentration is 1.0 mmol / L, with a naphthalene degradation rate of 98%. Therefore, compared to CaO2 / Fe... 2+ System, CaO2@CaCO3NPs / Fe 2+ Fe in the system 2+ The dosage can be reduced by 33%. Furthermore, in CaO2 / Fe... 2+ In the system, the degradation of naphthalene was basically completed within 2 minutes, while the degradation of CaO2@CaCO3NPs / Fe... 2+ The degradation time of naphthalene by the system can reach 20 min, which is 9 times longer, indicating that CaO2@CaCO3NPs / Fe 2+ The reaction in the system is slower, which increases the contact efficiency between pollutants and active substances, improves the degradation efficiency of pollutants, and can form a stable and long-lasting in-situ remediation zone during the in-situ chemical oxidation remediation process.

[0084] Example 8:

[0085] This embodiment investigates the effects of different calcium peroxide dosages on the phase composition and H2O2 release of the prepared calcium carbonate-coated calcium peroxide slow-release nanomaterials.

[0086] (1) Dissolve 5.0 g of anhydrous calcium chloride in 50 mL of deionized water and add 30 mL of ammonia water (25%~28%). Slowly add 30 mL of hydrogen peroxide (15%) at room temperature and stir continuously. After the addition is complete, filter and dry the solid component at 80℃ for 4 h to obtain solid calcium peroxide (CaO2).

[0087] (2) Weigh 0.6 g, 1.0 g, and 1.5 g of calcium peroxide respectively and add them to 200 mL of deionized water to form a suspension. Stir the suspension continuously in an open system for 60 min to allow the calcium peroxide to fully react with water and carbon dioxide in the air to generate calcium carbonate, which is then deposited on the surface of the calcium peroxide to form a coating layer.

[0088] (3) After the reaction is complete, the solid components are separated by filtration and then dried at 80°C. The calcium carbonate coated calcium peroxide slow-release nanomaterials are referred to as CaO2@CaCO3NPs-3.0, CaO2@CaCO3NPs-5.0 and CaO2@CaCO3NPs-7.5, respectively.

[0089] The contents of calcium peroxide and calcium carbonate in the above-prepared material were determined by potassium permanganate method and elemental analysis.

[0090] The calcium carbonate-coated calcium peroxide slow-release nanomaterials prepared in the above examples were used as experimental subjects. Static H2O2 slow-release experiments were conducted in 250 mL capped glass bottles at a temperature controlled at (25 ± 0.5)℃. 0.02 g of CaO2@CaCO3NPs-3.0, CaO2@CaCO3NPs-5.0, and CaO2@CaCO3NPs-7.5 were added to capped glass bottles containing 200 mL of water, respectively. To ensure uniform material dispersion, a magnetic stirrer was added to the glass bottles, and the bottles were placed on a magnetic stirrer and stirred uniformly at 500 r / min. Subsequent sample analysis was performed using a time-lapse sampling method, with 1.0 mL samples taken each time. After filtration through a 0.22 μm filter membrane, the concentration of H2O2 in the samples was determined using potassium titanate spectrophotometry.

[0091] like Figure 13 As shown, when the calcium peroxide dosage is 3.0 g / L, 5.0 g / L, and 7.5 g / L, the calcium carbonate content in the prepared CaO2@CaCO3NPs is 23.5%, 31.8%, and 39.4%, respectively, while the calcium peroxide content is 76.5%, 68.2%, and 60.6%, respectively. This indicates that the calcium carbonate content in CaO2@CaCO3NPs increases with the increase of calcium peroxide dosage.

[0092] like Figure 14 As shown, the maximum H2O2 release concentrations of CaO2, CaO2@CaCO3NPs-3.0, CaO2@CaCO3NPs-5.0, and CaO2@CaCO3NPs-7.5 were 0.89 mmol / L, 0.91 mmol / L, 0.89 mmol / L, and 0.75 mmol / L, respectively. This indicates that excessively high calcium peroxide dosage will decrease the H2O2 release from the prepared CaO2@CaCO3NPs. Considering both the yield per preparation and water consumption, the optimal calcium peroxide dosage is 5.0 g / L.

[0093] Example 9:

[0094] This embodiment investigates the effect of different reaction times on the phase composition of the prepared calcium carbonate-coated calcium peroxide slow-release nanomaterials.

[0095] (1) Dissolve 5.0 g of anhydrous calcium chloride in 50 mL of deionized water and add 30 mL of ammonia water (25%~28%). Slowly add 30 mL of hydrogen peroxide (15%) at room temperature and stir continuously. After the addition is complete, filter and dry the solid component at 80℃ for 4 h to obtain solid calcium peroxide (CaO2).

[0096] (2) Weigh 1.0 g of calcium peroxide and add it to 200 mL of deionized water to form a suspension. Stir the suspension continuously in an open system for a certain period of time (5 min, 15 min, 30 min, 60 min) so that the calcium peroxide reacts with water and carbon dioxide in the air to form calcium carbonate and deposits on the surface of the calcium peroxide to form a coating layer.

[0097] (3) After the set reaction time is reached, the solid components are filtered and separated, and then dried at 80°C to obtain calcium carbonate coated calcium peroxide slow-release nanomaterials at different reaction times.

[0098] like Figure 15 As shown in the figure, when the reaction time was 5 min, 15 min, 30 min, and 60 min, the calcium carbonate content in the prepared CaO2@CaCO3NPs was 32.1%, 33.3%, 32.0%, and 31.8%, respectively, while the calcium peroxide content was 67.9%, 66.7%, 68.0%, and 68.2%, respectively. This indicates that the calcium carbonate coating reaction of calcium peroxide in this reaction system was basically completed within 5 minutes and then tended to stabilize. In addition, the prepared CaO2@CaCO3NPs all contained only calcium carbonate and calcium peroxide components, and had a core-shell structure, with the core being calcium peroxide and the outer shell being calcium carbonate.

Claims

1. A calcium carbonate-coated calcium peroxide slow-release nanomaterial, characterized in that, It is composed of the following components by mass percentage: calcium peroxide 60.6%–76.5% and calcium carbonate 23.5%–39.4%; and the material has a core-shell structure, with the core being calcium peroxide and the outer shell being calcium carbonate.

2. A method for preparing calcium carbonate-coated calcium peroxide slow-release nanomaterials, characterized in that, The method includes the following steps: (1) Dissolve anhydrous calcium chloride in deionized water. After it is completely dissolved, add ammonia and stir until it is fully mixed. Slowly add hydrogen peroxide at room temperature while stirring continuously. After the addition is complete, filter and dry to obtain solid calcium peroxide. (2) Add calcium peroxide to deionized water to form a suspension; (3) The above suspension is continuously stirred in an open system to allow calcium peroxide to react fully with water and carbon dioxide in the air to generate calcium carbonate, which is then deposited on the surface of calcium peroxide to form a coating layer. (4) After the reaction is complete, filter to separate the solid components, and then dry with a forced air to obtain calcium carbonate coated calcium peroxide slow-release nanomaterials; In step (2), the concentration of calcium peroxide in the suspension is 3.0–7.5 g / L; In step (3), the stirring speed is 500-700 rpm, and the reaction time of calcium peroxide with water and carbon dioxide in the air is 5-60 min; In step (4), the blowing drying temperature is 80-100℃ and the drying time is 4-6 h.

3. The application of the calcium carbonate-coated calcium peroxide slow-release nanomaterial as described in claim 1 in the field of environmental remediation.

4. The application according to claim 3, characterized in that, The application uses the calcium carbonate-coated calcium peroxide slow-release nanomaterial described in claim 1 and a ferrous salt to form a Fenton-like system, which generates free radicals through reaction to oxidize and degrade organic pollutants in water.

5. The application according to claim 3, characterized in that, In the application, the molar ratio of calcium peroxide to ferrous salt in the calcium carbonate-coated calcium peroxide slow-release nanomaterial is 3:1 to 4.

6. The application according to claim 3, characterized in that, The divalent ferric salt used in this application is ferrous sulfate or ferrous chloride.

7. The application according to claim 3, characterized in that, The free radicals used in this application are hydroxyl radicals and carbonate radicals.

8. The application according to claim 3, characterized in that, The organic pollutant used in this application is naphthalene.

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