Preparation method of a sustained-release / temperature-controlled ferrate-silicon dioxide core-shell material and its application in removing antibiotics

Abstract

The present invention belongs to the field of water environment restoration materials, and discloses a method for preparing a slow-release / temperature-controlled ferrate-silicon dioxide core-shell material and its effect of removing antibiotics. The method mainly includes: using an in-situ growth coating synthesis method, based on a silica material with excellent biocompatibility, large specific surface area and pore volume and easy surface modification, combined with potassium ferrate with strong oxidizing properties, to prepare a slow-release ferrate-silicon dioxide core-shell material; further, by loading a phase change material on a slow-release ferrate iron-silicon dioxide core-shell material, a slow-release and temperature-controlled composite material is prepared, and efficient utilization and precise release of oxidative active substances are achieved. The present invention realizes the slow-release efficient utilization and temperature-controlled precise release of oxidative active substances, and improves the oxidation utilization efficiency and removal capacity of oxidants for target pollutants.

Description

Technical Field

[0001] The invention relates to the field of water environment restoration materials, and in particular to a preparation method of a slow-release / temperature-controlled ferrate-silicon dioxide core-shell material and an application thereof in removing antibiotics. Background Art

[0002] Pollutants such as antibiotics have extremely strong persistent emissions, stability and biological effects, causing continuous damage to the ecosystem. Antibiotics in water bodies can induce the production and growth of drug-resistant bacteria or drug-resistant genes, which will not only reduce the effectiveness of multiple antibiotics in disease prevention and treatment, but also have a potential huge impact on human health. Therefore, it is of great significance to develop new materials and methods for efficiently removing antibiotics from water. The iron element in potassium ferrate is the highest valence state of +6, and the ferrate ion has a spatial tetrahedral molecular structure. Its redox potential in aqueous solution under acidic and alkaline conditions is +2.20V and +0.72V, respectively. As an important strong oxidant in the chemical oxidation process of water treatment, its green, environmentally friendly, highly selective and highly active characteristics play an important role in the removal of water pollutants. However, potassium ferrate is prone to rapid self-decomposition and is affected by the competitive consumption of coexisting reducing substances in water, which restricts its large-scale application in sewage, river water and groundwater. Therefore, developing effective sustained-release and precise controlled-release materials of potassium ferrate and exploring its application effect in removing antibiotics in water are of great significance for promoting the widespread application of potassium ferrate in the field of water body remediation. Summary of the invention

[0003] The purpose of the present invention is to propose a method for preparing a sustained-release / temperature-controlled ferrate-silica core-shell material and its application in the removal of antibiotics. The method can use the ferrate-silica core-shell material to remove norfloxacin in water, achieve efficient utilization and precise release of oxidative active substances, and improve the oxidative utilization efficiency and removal ability of oxidants for target pollutants.

[0004] The technical solution of the present invention is: a method for preparing a sustained-release / temperature-controlled ferrate-silicon dioxide core-shell material, comprising the following steps:

[0005] (1) 1 mL of ultrapure water and 1.7 mL of aqueous ammonia were added to 50 mL of anhydrous ethanol. Anhydrous ethanol was used as a solvent for TEOS. Ammonia catalyzed the hydrolysis of TEOS to generate silicon dioxide. After magnetic stirring and mixing, a certain amount of tetraethyl silicate (TEOS) was quickly added. After mixing, solid potassium ferrate was added.

[0006] (2) After adding the solid, the mixture was placed in a constant temperature water bath and magnetic stirring was continued at a speed of 300 r / min. After stirring for a period of time, 1 mL of TEOS was added again, and the reaction was continued at a constant temperature and speed for a period of time to obtain a solution of potassium ferrate solid wrapped in a white colloid.

[0007] (3) The sample solution was centrifuged and washed three times with anhydrous ethanol. The sample was vacuum dried at 60° C. for 24 h and ground.

[0008] (4) The obtained sustained-release ferrate-silicon dioxide core-shell material is stored in a sealed dry environment for later use.

[0009] (5) The optimal synthesis conditions were determined with the mass ratio of potassium ferrate to TEOS being 0.2:1, 0.4:1, 0.6:1, 0.8:1 and 1:1 and the synthesis time being 60, 180 and 360 min as the influencing factors and the removal efficiency of the synthetic material for norfloxacin as the evaluation index.

[0010] The mass ratio of K2FeO4 and TEOS during the synthesis process has a significant impact on the oxidation capacity of the slow-release material. When the mass ratio of K2FeO4 and TEOS is 0.2:1, the removal rate of the target pollutant NOR by the slow-release material is only 24.1%. When the amount of K2FeO4 added in the slow-release material increases the mass ratio to 0.4:1, the removal rate of NOR is significantly improved to 48.2%. At a low mass ratio, that is, when there is an excess of TEOS in the synthesis system, the SiO2 generated by hydrolysis will form an overly thick coating layer on the surface of K2FeO4, thereby hindering the effective release of K2FeO4 and its full contact with pollutants. In addition, when the mass of the synthetic materials added to the reaction system remains consistent, the content of K2FeO4 in the material synthesized with a low mass ratio is relatively low, while the content of the oxidant in the material synthesized with a high mass ratio is higher. Therefore, materials with a higher mass ratio can provide more oxidants when removing pollutants, thereby achieving a more efficient removal effect.

[0011] When the ratio of K2FeO4 to TEOS is further increased, the removal rate of NOR by the synthesized material shows a decreasing trend. Since there is a threshold for the coating ability of the SiO2 shell to K2FeO4, when this threshold is exceeded, the coating effect of the shell no longer increases. At this time, the uncoated K2FeO4 will be exposed to the outside of the SiO2 shell and react preferentially with air or aqueous solution. The Fe(OH)3 precipitates generated by these reactions will further flocculate and deposit on the SiO2 shell, which not only hinders the contact and reaction of the active ingredients of K2FeO4 with pollutants, but also promotes the self-decomposition reaction of K2FeO4. Therefore, the optimal mass ratio of K2FeO4 to TEOS in the synthesis process is selected as 0.4:1.

[0012] The optimal synthesis time of SiO2 coated K2FeO4 was further explored. The silica synthesis method used in this study is the sol seed method. First, TEOS and ammonia water are added to initiate the hydrolysis reaction to start generating SiO2, followed by adding K2FeO4 solid to use the K2FeO4 particles as seeds. The generated SiO2 grows on the surface of K2FeO4. After stirring and growing for a period of time, a certain amount of TEOS is added to continue the reaction, allowing SiO2 to continue to grow, strengthen the coating of K2FeO4 and generate a synthetic product with uniform particle size. The synthesis time discussed, that is, the total time required for the synthesis process, has a significant effect on the performance of the materials synthesized under different mass ratio conditions. Figure 2 As shown, as the synthesis time increases, the removal effect of the slow-release material on pollutants gradually increases. This is mainly because the growth of SiO2 requires a long slow stirring process, and the length of the synthesis time directly affects the encapsulation effect of SiO2 on the active ingredient K2FeO4. Based on the above experimental results and analysis, the present invention determines that the synthesis time of 360 minutes is used as the optimal process parameter of the slow-release material in order to obtain the best pollutant removal performance.

[0013] (6) Weigh a certain amount of phase change material, add it to 50 mL of anhydrous ethanol, and add the prepared sustained-release ferrate-silica core-shell material after it dissolves. Place the material in a constant temperature water bath and stir it magnetically at a speed of 300 r / min.

[0014] The present invention selects three representative phase change materials, namely, n-tridecyl alcohol, n-heneicosane and lauric acid, to load and modify the potassium ferrate sustained-release material. Comparing the removal rates of NOR by the three temperature control materials at 30°C and 50°C, the temperature control material loaded with n-tridecyl alcohol has a NOR removal rate of 27.0% and 33.7% at 30°C, which may be due to the melting point of n-tridecyl alcohol being between 32 and 33°C, and being unable to maintain a solid form under relatively low temperature conditions, thereby releasing the oxidative active components to degrade NOR; the temperature control material loaded with n-heneicosane also has a certain removal effect on NOR at 30°C, which may be due to the fact that the loading amount of n-heneicosane on the SiO2 layer is too small, so that a part of the potassium ferrate active components can still react with pollutants in water at room temperature; the temperature control material loaded with lauric acid can effectively wrap the potassium ferrate sustained-release material at 30°C, and the NOR removal rate is only 3.2% and 7.8%, and the oxidative components can be accurately released at 50°C, with the NOR removal rate as high as 36.1% and 40.1%. Therefore, lauric acid was selected as the phase change material to prepare potassium ferrate temperature control material.

[0015] Weigh a certain amount of lauric acid, add it to 50 mL of anhydrous ethanol, dissolve it, add the sustained-release ferrate iron-silica core-shell material, put it in a constant temperature water bath and stir it magnetically at a speed of 300 r / min;

[0016] The sample solution was washed with anhydrous ethanol three times after centrifugation and vacuum dried at 50°C for 24h. The synthesis time was 1, 2, 4, 6 and 8h, the synthesis temperature was 30, 40, 50, 60 and 70°C, and the mass ratio of lauric acid to potassium ferrate sustained-release material was 5:1, 5:2, 5:3, 5:4 and 5:5 as influencing factors. The removal efficiency of the synthetic material for norfloxacin was used as the evaluation index to determine the optimal synthesis conditions.

[0017] Under the conditions of fixed synthesis temperature of 30°C and synthesis time of 4h, the mass ratio of lauric acid to potassium ferrate sustained-release material was set to 5:1, 5:2, 5:3, 5:4 and 5:5 respectively to synthesize a series of temperature control materials. The present invention uses NOR removal rate as the main evaluation index to evaluate the performance of temperature control materials and screen the optimal synthetic material ratio.

[0018] Under the same reaction material dosage (1 g / L) and pollutant concentration (40 μM) conditions, the results of NOR removal by temperature-controlled materials prepared with different synthetic material ratios are shown in Figure 2. Figure 3 As shown. With the gradual decrease in the proportion of phase change materials in the temperature control material and the corresponding increase in the proportion of potassium ferrate slow-release materials, the removal rate of pollutants by the temperature control material at 70°C showed a steady upward trend. When the synthetic material ratio was 5:1 and 5:2, the final removal rates of NOR at 70°C were 26.3% and 26.5%, respectively, and the removal effect was relatively limited. However, when the synthetic material ratio increased to 5:3, 5:4 and 5:5, the removal rate of NOR was significantly increased to 32.9%, 35.7% and finally 40.7%, indicating that the increase in the proportion of potassium ferrate slow-release materials has a positive effect on improving the NOR removal performance of the temperature control material.

[0019] Based on the above experimental results and analysis, the present invention adopts a phase change material and potassium ferrate sustained-release material with a mass ratio of 5:5, and synthesizes at a temperature of 30°C for 4 hours to prepare a temperature control material. By optimizing the synthesis conditions, the performance stability and NOR removal efficiency of the temperature control material are further improved.

[0020] (7) After centrifugation, the sample solution was washed three times with anhydrous ethanol and dried under vacuum at 50°C for 24 h to obtain a sustained-release / temperature-controlled ferrate-silica core-shell material.

[0021] (8) The optimal synthesis conditions were determined with synthesis time of 1, 2, 4, 6 and 8 h, synthesis temperature of 30, 40, 50, 60 and 70 °C, and the mass ratio of lauric acid to potassium ferrate sustained-release material of 5:1, 5:2, 5:3, 5:4 and 5:5 as influencing factors, and the removal efficiency of the synthetic material for norfloxacin as the evaluation index.

[0022] (9) Characterization of the physical and chemical properties of the prepared core-shell materials: Pure potassium ferrate, slow-release ferrate-silicon dioxide core-shell materials, and slow-release / temperature-controlled ferrate-silicon dioxide core-shell materials were taken and their phase compositions were analyzed by XRD. Figure 4 The specific surface area, average pore size and pore volume of the prepared core-shell materials were measured by multi-point BET nitrogen adsorption method.

[0023] X-ray diffraction (XRD) analysis was performed on pure potassium ferrate and its sustained-release core-shell material, where pure potassium ferrate had characteristic diffraction peaks of potassium ferrate at 2θ of 21.167°, 23.151°, 25.927°, 31.978° and 57.069°. Compared with pure potassium ferrate, the sustained-release core-shell material also showed characteristic diffraction peaks of potassium ferrate at 28.903° and 30.391°, indicating that the active ingredient of potassium ferrate exists in the sustained-release material. Since the preparation process will cause the crystal form of potassium ferrate to change, the characteristic peak has a small offset. The prepared sustained-release / temperature-controlled core-shell material showed a characteristic diffraction peak at 29.3°, which is similar to the characteristic peak position of pure potassium ferrate, but the peak intensity is significantly weakened and the peak shape is relatively wide. This indicates that potassium ferrate active ingredients still exist in the sustained-release / temperature-controlled core-shell material, and the loading process of the phase change material affects the crystal structure of potassium ferrate, making it present a diffraction feature different from that of pure potassium ferrate. The specific surface area, average pore size and pore volume of the prepared core-shell material were measured by multi-point BET nitrogen adsorption method. The specific surface area of ​​the sustained-release material is 13.73 m 2 / g, the average pore diameter is 15.84nm, and the total pore volume is 0.054cm 3 / g. Larger specific surface area and pore volume are conducive to the full contact between the oxidative active components in the slow-release material and the pollutants, thus achieving better removal effect. The specific surface area of ​​the temperature control material is 18.08m 2 / g, the average pore diameter is 13.83nm, and the total pore volume is 0.063cm 3 / g. Compared with the sustained-release material, its specific surface area is increased, the average pore size is reduced, and the total pore volume is increased.

[0024] (10) Determination of sustained release performance of the prepared core-shell material in aqueous solution: Weigh the sustained release material, add 50 mL of ultrapure aqueous solution with pH values ​​of 5, 7 and 9, respectively, and place the conical flask in an oscillator at 30°C and 200 r / min for reaction. At 0, 5, 10, 15, 20, 30, 45, 60, 90, 120, 360, 720, 1080 and 1440 min after addition, measure the content of potassium ferrate, and calculate the release rate (%) of the sustained release material according to the following formula:

[0025]

[0026] Where: Ct is the potassium ferrate content of the sample released into the solution at time t (mol / L); C a is the total amount of potassium ferrate in the prepared material (mol / L).

[0027] Under the condition that the dosage of the prepared ferrate-silicon dioxide core-shell material was 1g / L, the release curve of the potassium ferrate sustained-release material was measured. Figure 5 As shown. In the initial stage, the prepared ferrate-silica core-shell material showed rapid release characteristics in aqueous solutions with different pH values. In the first 5 minutes, the release rate was particularly significant, which was mainly attributed to the fact that part of the potassium ferrate was located in a shallow position of the SiO2 shell, so it was easy to dissolve and release in the aqueous solution. In the following 60 minutes, the release rate R gradually increased with time, but the growth rate slowed down after 60 minutes until a stable system was formed in the solution. This phenomenon is due to the fact that the potassium ferrate coated by SiO2 needs to diffuse and release through the pores of the SiO2 shell or the pores formed by the dissolution of potassium ferrate, and the diffusion rate of deep potassium ferrate is correspondingly reduced due to greater resistance.

[0028] Different pH values ​​have a certain effect on the release of the prepared ferrate-silica core-shell materials. Within 120 minutes, with the increase of pH value, the sustained release rate and release rate of the prepared ferrate-silica core-shell materials increased. Under the conditions of pH 5, 7 and 9, the release rates of the sustained release materials at 120 minutes were 56.4%, 59.8% and 70.8%, respectively. During the reaction time of up to 1440 minutes, the sustained release materials in different pH systems can effectively maintain the stable level of potassium ferrate active ingredient. After 1440 minutes of reaction, the release rates of the sustained release materials at pH 5, 7 and 9 were 60.9%, 65.0% and 73.5%, respectively. The release rate in the system was the highest at pH 9, while the release rate at pH 7 was slightly higher than that of the system at pH 5. This phenomenon can be attributed to the better stability of potassium ferrate in an alkaline environment, which effectively inhibits its self-decomposition process, making the sustained release effect more prominent, so the active ingredient of potassium ferrate in the alkaline system can be maintained at a high level.

[0029] The sustained release of the prepared ferrate-silica core-shell material in aqueous solution and its own self-decomposition together promote the active ingredient of potassium ferrate in the aqueous solution to reach a state of equilibrium, which fully demonstrates that the core-shell structure formed by SiO2 and potassium ferrate has excellent stable sustained-release performance.

[0030] Among them, potassium permanganate concentration determination:

[0031] The method for determining potassium ferrate concentration in this study is direct spectrophotometry. Weigh a certain amount of potassium ferrate solid, prepare potassium ferrate solution with boric acid / phosphate buffer solution at pH 9.0, and measure the absorbance at a wavelength of 510nm. Calculate the potassium ferrate concentration in the solution according to Lambert-Beer's law:

[0032] Abs=ε×b×C Fe (2)

[0033] Where Abs is the absorbance of potassium ferrate solution; ε is the molar absorption coefficient, and the molar absorption coefficient of potassium ferrate is ε = 1150M -1 cm -1 ; b is the optical path, i.e. the thickness of the cuvette; C Fe is the concentration of potassium ferrate in the solution (mol / L).

[0034] The second technical solution of the present invention is to use a sustained-release / temperature-controlled ferrate-silicon dioxide core-shell material prepared by the above method for the oxidation removal of antibiotics.

[0035] Temperature regulation of core-shell materials and analysis of antibiotic oxidation removal performance:

[0036] This experiment used a 100mL brown conical flask for the reaction. During the reaction, 50mL of norfloxacin working solution and a certain amount of potassium ferrate were added to prepare the core-shell material. Under the conditions of 2g / L of temperature-controlled material, 800μM of potassium ferrate initial concentration, and 40μM of norfloxacin concentration, the effect of the prepared core-shell material on the removal efficiency of norfloxacin in water was investigated under two temperatures (30℃ and 50℃) and five pH conditions (3, 5, 7, 9 and 11). The conical flask was placed in a constant temperature oscillator at 200r / min for reaction. At a specific time point, 2mL of liquid sample was taken in a 5mL centrifuge tube, and 100μL of 1.0mol / L sodium thiosulfate solution was added as a quencher to terminate the reaction. The sample was drawn with a syringe and filtered through a 0.22μm organic filter membrane and injected into a brown liquid injection bottle. The concentration of norfloxacin was determined by high performance liquid chromatography.

[0037] Among them, the antibiotic concentration was determined as follows:

[0038] In the experiment, the concentration of norfloxacin was quantitatively analyzed using a high performance liquid chromatograph equipped with a C18 column (250 mm × 4.6 mm, 5 μm) at a wavelength of 278 nm. The mobile phase used for norfloxacin was 100% methanol (phase A) and 0.1% formic acid aqueous solution (phase B). The injection volume was 10 μL, the column temperature was 40°C, and the flow rate was 1.0 mL / min.

[0039] Among them, the removal rate of norfloxacin is calculated as:

[0040]

[0041] In the formula, C k is the concentration of norfloxacin in the blank control (μM), C t is the concentration of norfloxacin in the sample at time t (μM).

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention adopts an in-situ growth coating synthesis method, based on a silica material with excellent biocompatibility, large specific surface area and pore volume, and easy surface modification, combined with potassium ferrate with strong oxidizing properties, to prepare a sustained-release ferrate-silicon dioxide core-shell material; further, by loading a phase change material on the sustained-release ferrate iron-silicon dioxide core-shell material, a sustained-release and temperature-controlled composite material is prepared to achieve efficient utilization and precise release of oxidative active substances; the structural characteristics of the sustained-release material and the temperature-controlled sustained-release material are characterized, and their sustained-release performance and stability are systematically evaluated; norfloxacin in quinolone antibiotics is selected as the target pollutant, and the removal efficiency of the sustained-release / temperature-controlled ferrate-silicon dioxide core-shell material for norfloxacin in water under different pH conditions is explored. The present invention realizes the sustained-release efficient utilization and temperature-controlled precise release of oxidative active substances, and improves the oxidation utilization efficiency and removal capacity of the oxidant for the target pollutant. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention, the drawings of the embodiments are introduced below.

[0045] Figure 1 The effect of the mass ratio of potassium ferrate and tetraethyl silicate on the degradation of NOR in sustained-release materials;

[0046] Figure 2 The effect of different synthesis time on the degradation of NOR by potassium ferrate sustained-release material;

[0047] Figure 3 NOR removal rate of temperature-controlled materials with different material ratios at low and high temperatures at 120 min;

[0048] Figure 4 XRD diffraction spectra of pure potassium ferrate (K2FeO4), prepared slow-release core-shell material (K2FeO4@SiO2), and prepared slow-release / temperature-controlled core-shell material (K2FeO4@SiO2-LA);

[0049] Figure 5 Release curves of the prepared sustained-release core-shell materials in different pH solutions: (a) 0-1600 min and (b) 0-120 min release curves;

[0050] Figure 6 The removal rate of norfloxacin by the core-shell materials prepared at different temperatures and pH values;

[0051] Figure 7 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0052] In order to more clearly understand the above-mentioned purposes, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that the embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0053] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0054] Figure 7 The flowchart of the method of the present invention. The present invention aims to achieve long-term sustained release and release the active components of potassium ferrate through precise temperature control to prolong the contact time with pollutants, thereby improving the utilization efficiency of potassium ferrate. Therefore, the sustained release technology is introduced into the potassium ferrate system, and the potassium ferrate is coated with SiO2 to achieve the effects of sustained release, long-term and sustained oxidation. The in-situ coating synthesis method can effectively preserve and release the active components of potassium ferrate, thereby showing a significant effect in the process of removing pollutants in water.

[0055] In summary, the present invention is based on silica materials with excellent biocompatibility, large specific surface area and pore volume, and easy surface modification, combined with potassium ferrate with strong oxidizing properties, and uses an in-situ coating synthesis method to prepare a sustained-release ferrate-silicon dioxide core-shell material; further, by loading a phase change material on the sustained-release ferrate iron-silicon dioxide core-shell material, a sustained-release and temperature-controlled composite material is prepared to achieve efficient utilization and precise release of oxidative active substances; the structural characteristics of the sustained-release material and the temperature-controlled sustained-release material are characterized, and their sustained-release performance and stability are systematically evaluated; norfloxacin in quinolone antibiotics is selected as the target pollutant, and the removal efficiency of sustained-release / temperature-controlled ferrate-silicon dioxide core-shell materials for norfloxacin in water under different pH conditions is explored. The present invention realizes the sustained-release efficient utilization and temperature-controlled precise release of oxidative active substances, and improves the oxidative utilization efficiency and removal capacity of oxidants for target pollutants.

[0056] (1) Add 1 mL of ultrapure water and 1.7 mL of aqueous ammonia to 50 mL of anhydrous ethanol, stir the mixture with a magnetic stirrer until it is evenly mixed, then quickly add a certain amount of tetraethyl silicate (TEOS), mix the mixture evenly, and then add potassium ferrate solid.

[0057] (2) After adding the solid, the mixture was placed in a constant temperature water bath and magnetic stirring was continued at a speed of 300 r / min. After stirring for a period of time, 1 mL of TEOS was added again, and the reaction was continued at a constant temperature and speed for a period of time to obtain a solution of potassium ferrate solid wrapped in a white colloid.

[0058] (3) The sample solution was centrifuged and washed three times with anhydrous ethanol. The sample was vacuum dried at 60° C. for 24 h and ground.

[0059] (4) The obtained sustained-release ferrate-silicon dioxide core-shell material is stored in a sealed dry environment for later use.

[0060] (5) The optimal synthesis conditions were determined with the mass ratio of potassium ferrate to TEOS being 0.2:1, 0.4:1, 0.6:1, 0.8:1 and 1:1 and the synthesis time being 60, 180 and 360 min as the influencing factors and the removal efficiency of the synthetic material for norfloxacin as the evaluation index.

[0061] (6) Weigh a certain amount of lauric acid, add it to 50 mL of anhydrous ethanol, and add the prepared sustained-release ferrate-silica core-shell material after it is dissolved. Place the material in a constant temperature water bath and stir it magnetically at a speed of 300 r / min.

[0062] (7) After centrifugation, the sample solution was washed three times with anhydrous ethanol and dried under vacuum at 50°C for 24 h to obtain a sustained-release / temperature-controlled ferrate-silica core-shell material.

[0063] (8) The optimal synthesis conditions were determined with synthesis time of 1, 2, 4, 6 and 8 h, synthesis temperature of 30, 40, 50, 60 and 70 °C, and the mass ratio of lauric acid to potassium ferrate sustained-release material of 5:1, 5:2, 5:3, 5:4 and 5:5 as influencing factors, and the removal efficiency of the synthetic material for norfloxacin as the evaluation index.

[0064] (9) Characterization of the physical and chemical properties of the prepared core-shell materials: Pure potassium ferrate, slow-release ferrate-silicon dioxide core-shell materials, and slow-release / temperature-controlled ferrate-silicon dioxide core-shell materials were taken and their phase compositions were analyzed by XRD. Figure 4. X-ray diffraction (XRD) analysis was performed on pure potassium ferrate and its sustained-release core-shell materials, where pure potassium ferrate had characteristic diffraction peaks of potassium ferrate at 2θ of 21.167°, 23.151°, 25.927°, 31.978° and 57.069°. Compared with pure potassium ferrate, the sustained-release core-shell material also showed characteristic diffraction peaks of potassium ferrate at 28.903° and 30.391°, indicating that the active ingredient of potassium ferrate exists in the sustained-release material. Since the preparation process will cause the crystal form of potassium ferrate to change, the characteristic peak has a small offset. The prepared sustained-release / temperature-controlled core-shell material showed a characteristic diffraction peak at 29.3°, which is similar to the characteristic peak position of pure potassium ferrate, but the peak intensity is significantly weakened and the peak shape is relatively wide. This indicates that potassium ferrate active ingredients still exist in the sustained-release / temperature-controlled core-shell material, and the loading process of the phase change material affects the crystal structure of potassium ferrate, making it present a diffraction feature different from that of pure potassium ferrate. The specific surface area, average pore size and pore volume of the prepared core-shell material were measured by multi-point BET nitrogen adsorption method. The specific surface area of ​​the sustained-release material is 13.73 m 2 / g, the average pore diameter is 15.84nm, and the total pore volume is 0.054cm 3 / g. Larger specific surface area and pore volume are conducive to the full contact between the oxidative active components in the slow-release material and the pollutants, thus achieving better removal effect. The specific surface area of ​​the temperature control material is 18.08m 2 / g, the average pore diameter is 13.83nm, and the total pore volume is 0.063cm 3 / g. Compared with the sustained-release material, its specific surface area is increased, the average pore size is reduced, and the total pore volume is increased.

[0065] (10) Determination of sustained release performance of the prepared core-shell material in aqueous solution: Weigh the sustained release material, add 50 mL of ultrapure aqueous solution with pH values ​​of 5, 7 and 9, respectively, and place the conical flask in an oscillator at 30°C and 200 r / min for reaction. At 0, 5, 10, 15, 20, 30, 45, 60, 90, 120, 360, 720, 1080 and 1440 min after addition, measure the content of potassium ferrate, and calculate the release rate (%) of the sustained release material according to the following formula:

[0066]

[0067] Where: C t is the potassium ferrate content of the sample released into the solution at time t (mol / L); C a is the total amount of potassium ferrate in the prepared material (mol / L).

[0068] Under the condition that the dosage of the prepared ferrate-silicon dioxide core-shell material was 1g / L, the release curve of the potassium ferrate sustained-release material was measured. Figure 5 As shown. In the initial stage, the prepared ferrate-silica core-shell material showed rapid release characteristics in aqueous solutions with different pH values. In the first 5 minutes, the release rate was particularly significant, which was mainly attributed to the fact that part of the potassium ferrate was located in a shallow position of the SiO2 shell, so it was easy to dissolve and release in the aqueous solution. In the following 60 minutes, the release rate R gradually increased with time, but the growth rate slowed down after 60 minutes until a stable system was formed in the solution. This phenomenon is due to the fact that the potassium ferrate coated by SiO2 needs to diffuse and release through the pores of the SiO2 shell or the pores formed by the dissolution of potassium ferrate, and the diffusion rate of deep potassium ferrate is correspondingly reduced due to greater resistance.

[0069] Different pH values ​​have a certain effect on the release of the prepared ferrate-silica core-shell materials. Within 120 minutes, with the increase of pH value, the sustained release rate and release rate of the prepared ferrate-silica core-shell materials increased. Under the conditions of pH 5, 7 and 9, the release rates of the sustained release materials at 120 minutes were 56.4%, 59.8% and 70.8%, respectively. During the reaction time of up to 1440 minutes, the sustained release materials in different pH systems can effectively maintain the stable level of potassium ferrate active ingredient. After 1440 minutes of reaction, the release rates of the sustained release materials at pH 5, 7 and 9 were 60.9%, 65.0% and 73.5%, respectively. The release rate in the system was the highest at pH 9, while the release rate at pH 7 was slightly higher than that of the system at pH 5. This phenomenon can be attributed to the better stability of potassium ferrate in an alkaline environment, which effectively inhibits its self-decomposition process, making the sustained release effect more prominent, so the active ingredient of potassium ferrate in the alkaline system can be maintained at a high level.

[0070] The sustained release of the prepared ferrate-silica core-shell material in aqueous solution and its own self-decomposition together promote the active ingredient of potassium ferrate in the aqueous solution to reach a state of equilibrium, which fully demonstrates that the core-shell structure formed by SiO2 and potassium ferrate has excellent stable sustained-release performance.

[0071] Among them, potassium permanganate concentration determination:

[0072] The method for determining potassium ferrate concentration in this study is direct spectrophotometry. Weigh a certain amount of potassium ferrate solid, prepare potassium ferrate solution with boric acid / phosphate buffer solution at pH 9.0, and measure the absorbance at a wavelength of 510nm. Calculate the potassium ferrate concentration in the solution according to Lambert-Beer's law:

[0073] Abs=ε×b×CFe (2)

[0074] Where Abs is the absorbance of potassium ferrate solution; ε is the molar absorption coefficient, and the molar absorption coefficient of potassium ferrate is ε = 1150M -1 cm -1 ; b is the optical path, i.e. the thickness of the cuvette; C Fe is the concentration of potassium ferrate in the solution (mol / L).

[0075] (11) Temperature control and antibiotic oxidation removal performance analysis of the prepared core-shell materials:

[0076] In this experiment, a 100mL brown conical flask was used for the reaction. During the reaction, 50mL of norfloxacin working solution and a certain amount of potassium ferrate were added to prepare the core-shell material. Under the conditions of 2g / L of temperature-controlled material, 800μM of potassium ferrate initial concentration and 40μM of norfloxacin concentration, the effect of the prepared core-shell material on the removal efficiency of norfloxacin in water was investigated under two temperatures (30℃ and 50℃) and five pH conditions (3, 5, 7, 9 and 11). The conical flask was placed in a constant temperature oscillator at 200r / min for reaction. At a specific time point, 2mL of liquid sample was taken in a 5mL centrifuge tube, and 100μL of 1.0mol / L sodium thiosulfate solution was added as a quencher to terminate the reaction. The sample was drawn with a syringe and filtered through a 0.22μm organic filter membrane and injected into a brown liquid injection bottle. The concentration of norfloxacin was determined by high performance liquid chromatography.

[0077] Among them, the antibiotic concentration was determined as follows:

[0078] In the experiment, the concentration of norfloxacin was quantitatively analyzed using a high performance liquid chromatograph equipped with a C18 column (250 mm × 4.6 mm, 5 μm) at a wavelength of 278 nm. The mobile phase used for norfloxacin was 100% methanol (phase A) and 0.1% formic acid aqueous solution (phase B). The injection volume was 10 μL, the column temperature was 40°C, and the flow rate was 1.0 mL / min.

[0079] Experimental study on the effect of the prepared ferrate-silica core-shell material on removing antibiotics from water:

[0080] The effect of slow-release temperature-controlled materials on the removal of antibiotics in water was tested at temperatures of 30 and 50 °C and under five pH conditions (3, 5, 7, 9 and 11). The results are as follows: Figure 6As shown. Under the condition of pH 3, the removal rate of norfloxacin of the prepared sustained-release / temperature-controlled core-shell material at 30°C and 50°C was about 54%, showing similar degradation efficiency. When the pH value was 5-11, the removal rate of norfloxacin of the prepared sustained-release / temperature-controlled core-shell material at 30°C was significantly reduced to about 8.8%-19.5%, and the removal rate of norfloxacin at 50°C was slightly reduced to about 50%-54%. The good temperature control effect of the prepared sustained-release / temperature-controlled core-shell material is fully demonstrated.

[0081] Among them, the removal rate of norfloxacin is calculated as:

[0082]

[0083] In the formula, C k is the concentration of norfloxacin in the blank control (μM), C t is the concentration of norfloxacin in the sample at time t (μM).

[0084] In summary, the present invention is based on silica materials with excellent biocompatibility, large specific surface area and pore volume, and easy surface modification, combined with potassium ferrate with strong oxidizing properties, and uses an in-situ coating synthesis method to prepare a sustained-release ferrate-silicon dioxide core-shell material; further, by loading a phase change material on a sustained-release ferrate iron-silicon dioxide core-shell material, a sustained-release and temperature-controlled composite material is prepared to achieve efficient utilization and precise release of oxidative active substances; the structural characteristics of the sustained-release material and the temperature-controlled sustained-release material are characterized, and their sustained-release performance and stability are systematically evaluated; norfloxacin in quinolone antibiotics is selected as the target pollutant, and the removal efficiency of the sustained-release / temperature-controlled ferrate-silicon dioxide core-shell material for norfloxacin in water under different pH conditions is explored. The present invention realizes the sustained-release efficient utilization and temperature-controlled precise release of oxidative active substances, and improves the oxidative utilization efficiency and removal capacity of the oxidant for the target pollutant.

[0085] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope provided by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a sustained-release / temperature-controlled ferrate-silicon dioxide core-shell material, characterized in that: The following steps are involved: 1) Using the in-situ growth coating synthesis method, SiO2 was synthesized in situ on the surface of potassium ferrate by the solution seed method to prepare a slow-release ferrate-silica core-shell material; Ultrapure water and ammonia water were added to anhydrous ethanol, and tetraethyl silicate was quickly added after being evenly mixed by magnetic stirring, and potassium ferrate solid was added after being evenly mixed; After adding potassium ferrate, the mixture was placed in a constant temperature water bath and magnetic stirring was continued. After stirring and reacting, TEOS was added again, and the reaction was continued at a constant temperature and speed to obtain a solution in which a white colloid encapsulated potassium ferrate solid; The sample solution was centrifuged and washed three times with anhydrous ethanol, and the sample was vacuum dried and ground; The obtained sustained-release ferrate-silicon dioxide core-shell material is placed in a sealed dry environment for storage; The mass ratio of potassium ferrate to tetraethyl silicate is 0.2:1-1:1, and the synthesis time is 60-360 min; 2) Select phase change materials to load and modify potassium ferrate sustained-release materials; Weigh the phase change material, add it to anhydrous ethanol, add the sustained-release ferrate-silicon dioxide core-shell material after dissolving, and place it in a constant temperature water bath for magnetic stirring; The sample solution was washed with anhydrous ethanol after centrifugation and vacuum dried after centrifugation; The synthesis temperature is 30-70°C, and the mass ratio of the phase change material to the sustained-release ferrate-silicon dioxide core-shell material is 5:1-5:5; The phase change material is selected from any one of n-tridecanol, n-heneicosane and lauric acid.

2. The method for preparing a sustained-release / temperature-controlled ferrate-silicon dioxide core-shell material according to claim 1, characterized in that: Weigh the sustained-release material, add 50 mL of ultrapure aqueous solution with pH values ​​of 5, 7 and 9, respectively, and place the conical flask in an oscillator at 30 °C and 200 r / min for reaction; at 0, 5, 10, 15, 20, 30, 45, 60, 90, 120, 360, 720, 1080 and 1440 min after addition, measure the content of potassium ferrate, and calculate the release rate of the sustained-release material according to the following formula: （1） Where: C t is the potassium ferrate content of the sample released into the solution at time t, mol / L; C a is the total amount of potassium ferrate in the prepared material, mol / L; Among them, potassium permanganate concentration determination: The method for determining the concentration of potassium ferrate is direct spectrophotometry.

3. Use of a sustained-release / temperature-controlled ferrate-silica core-shell material obtained by the preparation method according to claim 1 or 2 for the oxidative removal of antibiotics.

4. The use according to claim 3, characterized in that The removal rates of NOR by three temperature-controlled materials at 30°C and 50°C were compared, and the removal efficiency of the synthetic materials for norfloxacin was used as an evaluation index to determine the optimal synthesis conditions.

5. The use according to claim 3, characterized in that: The temperature control and antibiotic oxidation removal performance analysis are as follows: A brown conical flask was used for the reaction, and a core-shell material prepared by adding a norfloxacin working solution and a certain amount of potassium ferrate was added during the reaction; Under the conditions of an initial potassium ferrate concentration of 800 μM and a norfloxacin concentration of 40 μM, the effects of the prepared core-shell materials on the removal efficiency of norfloxacin in water were investigated at temperatures of 30°C and 50°C and pH values ​​of 3, 5, 7, 9 and 11. The conical flask was placed in a constant temperature oscillator at 200 r / min for reaction. At a specific time point, 2 mL of liquid sample was taken into a 5 mL centrifuge tube, and 100 μL of 1.0 mol / L sodium thiosulfate solution was added as a quencher to terminate the reaction. The sample was aspirated with a syringe and filtered through a 0.22 μm organic filter membrane before being injected into a brown liquid injection bottle. The concentration of norfloxacin was determined by HPLC.

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