A core-shell-shell three-level structure composite material and a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic functional materials, and specifically provides a core-shell-shell three-level structure composite material and a preparation method and application thereof, and belongs to the technical field of photocatalytic functional materials. The core-shell-shell three-level structure composite material takes an up-conversion micron particle as a core, graphite phase carbon nitride as an intermediate shell layer, and magnetic sepiolite as an outer shell layer. The core-shell combination of the UCMPs and g-C3N4 is realized through a one-step calcination method, the sepiolite is magnetically modified through a coprecipitation method, and finally, the core-shell-shell structure is formed through interface self-assembly. The obtained material has both photocatalytic activity and magnetic separation performance, the degradation efficiency of organic pollutants under simulated sunlight is increased by more than 257% compared with a single component, and the material can be quickly recycled and reused through an external magnetic field. The application has simple process and low cost, and is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic functional materials, and particularly relates to a core-shell-shell three-level structure composite material and a preparation method and application thereof. BACKGROUND

[0002] Photocatalytic technology uses solar energy as driving force, realizes pollutant degradation and CO2 resource conversion through nanomaterial-mediated redox reaction, and provides a sustainable path for the conversion of ecological value to economic value. Compared with the high-temperature energy consumption of incineration treatment and the saturation failure defect of adsorption technology, photocatalytic nanoparticles can realize the targeted activation of pollutant molecules at room temperature and normal pressure, avoid the generation of by-products and additional energy input, due to their high specific surface area, adjustable electronic structure and multi-phase interface activity. The existing single nanomaterial has problems of narrow spectral response range and low photocatalytic efficiency. SUMMARY

[0003] In order to solve the above technical problems, the application provides a core-shell-shell three-level structure composite material and a preparation method and application thereof. The core-shell-shell three-level structure composite material has ternary synergy of upconversion microparticles, graphite phase carbon nitride and magnetic sepiolite, which significantly improves the photocatalytic efficiency and cycle stability.

[0004] To achieve the above purpose, the application first provides a core-shell-shell three-level structure composite material, which comprises upconversion microparticles, graphite phase carbon nitride and magnetic sepiolite; the upconversion microparticles are the core, the graphite phase carbon nitride is the intermediate shell layer, and the magnetic sepiolite is the outer shell layer; the upconversion microparticles comprise Yb and Tm doped β-NaYF4.

[0005] In some embodiments, the molar ratio of β-NaYF4, Yb and Tm in the upconversion microparticles is (0.79-0.8):(0.2-0.21):(0.01-0.02); further, the molar ratio of β-NaYF4, Yb and Tm is 0.79:0.2:0.01.

[0006] In some embodiments, the upconversion microparticles are β-NaYF4, 20% Yb and 1% Tm. Among them, β-NaYF4, 20% Yb and 1% Tm mean that in β-NaYF4, 20% Yb and 1% Tm, the molar ratio of β-NaYF4 is 79%, the molar ratio of Yb is 20%, and the molar ratio of Tm is 1%.

[0007] In some embodiments, the particle size of the composite material is 3-5 μm.

[0008] In some embodiments, the mass ratio of the upconversion microparticles, graphite phase carbon nitride and magnetic sepiolite of the composite material is 1:1:0.5.

[0009] Based on a total inventive concept, the application also provides a preparation method of a core-shell-shell three-level structure composite material, comprising the following steps:

[0010] Step 1, mix sodium citrate solution, yttrium nitrate solution, ytterbium nitrate solution and thulium nitrate solution, stir at 500 rpm~600 rpm for 20 min~25 min, drop sodium fluoride solution, then stir for 30 min~35 min, then transfer the mixed solution to a polytetrafluoroethylene lined autoclave, and perform hydrothermal reaction at 200℃~205℃ for 24 h~25 h; the obtained precipitate is washed, dried, and annealed at 500℃~510℃ for 2 h~2.5 h in a nitrogen atmosphere to obtain upconversion microparticles;

[0011] Step 2, mix and grind the upconversion microparticles with urea, then calcine, cool, and obtain the upconversion microparticle@g-C3N4 core-shell structure material.

[0012] Step 3: prepare a mixed solution by adding FeCl3·6H2O and FeSO4·7H2O in deionized water, stir to dissolve, then add sepiolite, heat to 60℃~65℃ at a rate of 5℃ / min~6℃ / min under argon protection, add concentrated ammonia water dropwise to adjust the pH to 9.5~10.5 after magnetic stirring for 10 min~20 min, continue to react for 1 h~1.5 h; then age in a vacuum environment at 35℃~40℃ for 1.5 h~2.5 h; after aging, wash with deionized water and ethanol alternately for 3~4 times, and vacuum dry to obtain magnetic sepiolite;

[0013] Step 4: disperse the magnetic sepiolite and the upconversion microparticle@g-C3N4 core-shell structure material obtained in step 2 in deionized water respectively, heat the dispersion liquid of the magnetic sepiolite to 55℃~65℃, add the dispersion liquid of the upconversion microparticle@g-C3N4 core-shell structure material drop by drop under stirring, continue stirring for 2 h~3 h after the addition is completed, take the precipitate by centrifugation and dry to obtain the core-shell-shell three-level structure composite material.

[0014] In some embodiments, in step 1, the molar ratio of sodium citrate, yttrium nitrate, ytterbium nitrate, thulium nitrate and sodium fluoride is 1:(0.79~0.8):(0.2~0.21):(0.01~0.02):(12~12.1).

[0015] In some embodiments, in step 1, the dropwise addition rate of the sodium fluoride solution is 0.03 ml / s~0.05 ml / s. By controlling the dropwise addition rate of the sodium fluoride solution, the morphology of the upconversion microparticles can be controlled to be more uniform.

[0016] In some embodiments, in step 1, the concentration of the sodium citrate solution is 0.3 mol / L, the concentration of the Y(NO3)3 solution is 0.208 mol / L, the concentration of the Yb(NO3)3 solution is 0.24 mol / L, the concentration of the Tm(NO3)3 solution is 0.048 mol / L, and the concentration of the NaF solution is 0.5 mol / L.

[0017] In some embodiments, in step 2, the mass ratio of the upconversion microparticles to urea is 1:(1-10); preferably, the mass ratio of the upconversion microparticles to urea is 1:(5-7); further preferably, the mass ratio of the upconversion microparticles to urea is 1:(6.6-6.62).

[0018] In some embodiments, in step 2, the calcination step comprises heating at a rate of 4℃ / min-6℃ / min to 500℃-600℃ for 4h-5h. Preferably, heating at a rate of 5℃ / min to 550℃ for 4h.

[0019] In some embodiments, in step 3, the total molar concentration of FeCl3·6H2O and FeSO4·7H2O in the mixed solution prepared from FeCl3·6H2O and FeSO4·7H2O is 0.3 mol / L.

[0020] In some embodiments, the molar ratio of FeCl3·6H2O to FeSO4·7H2O is (1-3):1; preferably, the molar ratio of FeCl3·6H2O to FeSO4·7H2O is (1.74-1.76):1. By controlling the ratio of Fe 3+ to Fe 2+ , the magnetic properties and stability of the product are improved.

[0021] In some embodiments, the ratio of the total mass of FeCl3·6H2O and FeSO4·7H2O to the mass of sepiolite is (0.8-0.9):1. Preferably, the ratio of the total mass of FeCl3·6H2O and FeSO4·7H2O to the mass of sepiolite is (0.81-0.82):1.

[0022] In some embodiments, in step 4, the mass ratio of the magnetic sepiolite to the upconversion microparticle@g-C3N4 core-shell structure material is 1:(1-10). Preferably, the mass ratio of the magnetic sepiolite to the upconversion microparticle@g-C3N4 core-shell structure material is 1:(1-5); further preferably, the mass ratio of the magnetic sepiolite to the upconversion microparticle@g-C3N4 core-shell structure material is 1:4.

[0023] In some embodiments, in step 4, the dropwise adding speed of the dispersion liquid of the upconversion microparticle @-g-C3N4 core-shell structure material is 0.03 ml / s~0.05 ml / s.

[0024] Based on the overall inventive concept, the application further provides an application of the core-shell-shell ternary structure composite material in photocatalytic degradation and removal of organic pollutants in water.

[0025] In some embodiments, the application of the core-shell-shell ternary structure composite material in photocatalytic degradation and removal of organic pollutants in water comprises the following steps:

[0026] Mixing the core-shell-shell ternary structure composite material and the solution to be degraded, and placing in dark conditions for 30 min~40 min; then performing degradation under light irradiation conditions.

[0027] In some embodiments, the light irradiation conditions are 980 nm near-infrared light irradiation or irradiation under simulated sunlight conditions.

[0028] In some embodiments, the organic pollutants are ofloxacin.

[0029] In some embodiments, the concentration of the organic pollutants in the solution to be degraded is ≤500 μmol / L.

[0030] In some embodiments, the pH value of the solution to be degraded is 6.5~10.

[0031] The photocatalytic degradation mechanism of the core-shell-shell ternary structure nanocomposite material prepared by the application for pollutants is as follows:

[0032] The above conversion microparticles (UCMPs) are used as the core, graphite phase carbon nitride g-C3N4 is used as the intermediate shell layer, and magnetic sepiolite (MSEP) is used as the outer shell layer. The UCMPs and the g-C3N4 are combined into a core-shell structure through a one-step calcination method, the sepiolite is magnetically modified through a coprecipitation method, and finally, a core-shell-shell three-level structure is formed through interface self-assembly. The core and the intermediate shell layer form a heterojunction structure, the driving force brought by the built-in electric field is used to realize the separation of electrons and holes in the spatial scale, the lifetime of the photo-generated carriers is effectively prolonged, more effective charges are provided for the photocatalytic reaction, and the photocatalytic performance is improved. Further, in the UCMPs@g-C3N4@MSEP material, the UCMPs can absorb near-infrared light to convert into visible light and be absorbed by the g-C3N4, the g-C3N4 can absorb light less than 500 nm in the simulated sunlight to generate reactive oxygen species for degrading antibiotics. The MSEP is the outermost layer, on the one hand, the sepiolite can improve the hydrophilicity of the material and actively adsorb pollutants in wastewater, so that the pollutants can be effectively degraded, and on the other hand, the magnetism can improve the recycling efficiency. Finally, the core-shell-shell structure design can inhibit the recombination of excitons and improve the photocatalytic efficiency.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] (1) The present application realizes the core-shell combination of the UCMPs and the g-C3N4 through a one-step calcination method, magnetically modifies the sepiolite through a coprecipitation method, and finally forms a core-shell-shell structure through interface self-assembly. The UCMPs are used as the core, the graphite phase carbon nitride g-C3N4 is used as the intermediate shell layer, and the magnetic sepiolite (MSEP) is used as the outer shell layer. The process is simple, the cost is low, and it is suitable for large-scale production.

[0035] (2) The material prepared in the present application has both photocatalytic activity and magnetic separation performance. The degradation efficiency of organic pollutants under simulated sunlight is improved by more than 257% compared with a single component, and it can be quickly recycled and reused through an external magnetic field. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0037] Figure 1 The X-ray powder diffraction (XRD) test result graph of the UCMPs@g-C3N4@MSEP prepared in Example 1, the UCMPs, the MSEP, and the g-C3N4 prepared in Comparative Example 1.

[0038] Figure 2 SEM images and mapping energy spectrum of UCMPs, UCMPs@g-C3N4 and UCMPs@g-C3N4@MSEP prepared in Example 1; wherein (a) is the SEM image of UCMPs, (b) is the SEM image of UCMPs@g-C3N4, (c) is the SEM image of UCMPs@g-C3N4@MSEP, (d) is the mapping image of Y element in UCMPs, (e) is the mapping image of N element in UCMPs@g-C3N4, (f) is the mapping image of Si element in UCMPs@g-C3N4@MSEP.

[0039] Figure 3 Water contact angle test results of UCMPs, UCMPs@g-C3N4 and UCMPs@g-C3N4@MSEP prepared in Example 1; wherein (a) is the water contact angle test image of UCMPs, (b) is the water contact angle test image of UCMPs@g-C3N4, (c) is the contact angle test image of UCMPs@g-C3N4@MSEP.

[0040] Figure 4 Magnetic performance test results of UCMPs@g-C3N4 and UCMPs@g-C3N4@MSEP prepared in Example 1.

[0041] Figure 5 Scanning Kelvin probe force microscopy (KPFM) test results of UCMPs@g-C3N4@MSEP, UCMPs@g-C3N4 prepared in Example 1 and g-C3N4 prepared in Comparative Example 1, wherein Figure 5 (a) is the surface potential two-dimensional mapping image of g-C3N4 under dark (Dark) condition, (b) is the surface potential two-dimensional mapping image of g-C3N4 under light (Light) condition, (c) is the local area potential line distribution curve of g-C3N4, (d) is the surface potential two-dimensional mapping image of UCMPs@g-C3N4 under dark (Dark) condition, (e) is the surface potential two-dimensional mapping image of UCMPs@g-C3N4 under light (Light) condition, (f) is the local area potential line distribution curve of UCMPs@g-C3N4, (g) is the surface potential two-dimensional mapping image of UCMPs@g-C3N4 under dark (Dark) condition, (h) is the surface potential two-dimensional mapping image of UCMPs@g-C3N4 under light (Light) condition, (i) is the local area potential line distribution curve of UCMPs@g-C3N4.

[0042] Figure 6 The photocurrent response test results of UCMPs@g-C3N4@MSEP and UCMPs@g-C3N4 prepared in Example 1 are shown in the following figures.

[0043] Figure 7 The photocatalytic degradation effect of g-C3N4 and UCMPs@g-C3N4 on 400 μmol / L ofloxacin under near-infrared light is shown in the following figure.

[0044] Figure 8 The photocatalytic degradation effect of each component material on 400 μmol / L ofloxacin under simulated sunlight and the fitting kinetic curve are shown in the following figures, wherein (a) is the photocatalytic degradation effect of each component material on 400 μmol / L ofloxacin under simulated sunlight; (b) is the fitting kinetic curve.

[0045] Figure 9 The degradation effect of UCMPs@g-C3N4@MSEP on different concentrations of ofloxacin is shown in the following figure.

[0046] Figure 10 The degradation effect of UCMPs@g-C3N4@MSEP on ofloxacin under different pH conditions is shown in the following figure.

[0047] Figure 11 The cycle stability test results of UCMPs@g-C3N4@MSEP are shown in the following figure. DETAILED DESCRIPTION

[0048] In order to make the technical problems, technical solutions and advantages of the present application clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0049] The following examples are used to illustrate the present application, but are not used to limit the scope of the present application. Modifications or replacements of the methods, steps or conditions of the present application, without departing from the spirit and essence of the present application, all belong to the scope of the present application.

[0050] If not specifically indicated, the technical means used in the examples is the conventional means known to those skilled in the art; if not specifically indicated, the reagents used in the examples are commercially available.

[0051] Example 1: Preparation of nanocomposite UCMPs@g-C3N4@MSEP with core-shell-shell tertiary structure.

[0052] Step 1, hydrothermal synthesis of β-NaYF4:20%Yb, 1%Tm upconversion microparticles (UCMPs): in a 50 mL beaker, 4 mL of 0.3 mol / L sodium citrate solution was mixed with 4.6 mL of 0.208 mol / L Y(NO3)3, 1.0 mL of 0.24 mol / L Yb(NO3)3 and 0.25 mL of 0.048 mol / L Tm(NO3)3 aqueous solution, and the mixture was continuously stirred at a rate of 500 rpm for 20 minutes. Then 29 mL of 0.5 mol / L NaF solution was added dropwise, and the stirring was continued for 30 minutes before being transferred to a polytetrafluoroethylene-lined autoclave for hydrothermal reaction at 200 ℃ for 24 hours. The obtained precipitate was washed and dried, and then annealed at 500 ℃ for 2 hours under nitrogen atmosphere to obtain UCMPs.

[0053] Step 2, preparation of UCMPs@g-C3N4 core-shell structure composite: 300 mg of UCMPs was mixed with 1.985 g of urea in a agate mortar and ground for 5 minutes, then transferred to a ceramic crucible and covered with a lid, and then placed in a muffle furnace and heated to 550 ℃ at a rate of 5 ℃ / min for calcination for 4 hours, and then naturally cooled to obtain UCMPs@g-C3N4 particles; in the UCMPs@g-C3N4 particles, the mass ratio of UCMPs to g-C3N4 was 1:1.

[0054] Step 3, preparation of magnetic sepiolite MSEP: 1.0328 g of FeCl3·6H2O and 0.6066 g of FeSO4·7H2O were added to 25 ml of deionized water, and after stirring and dissolving, the mixture was transferred to a 250 ml three-necked round-bottom flask and 2 g of sepiolite was added. After rapid heating to 60 ℃ under argon protection and magnetic stirring for 15 minutes, concentrated ammonia water was added dropwise to adjust the pH to 10, and the reaction was continued for 1 hour. After the reaction was completed, the product was placed in a vacuum drying oven and aged at 35 ℃ for 2 hours under vacuum. After aging, the product was washed with deionized water and ethanol alternately for 3 times, and then placed in a vacuum drying oven and heated to 60 ℃ for vacuum drying. After the product was completely dried, it was ground into powder for use, and MSEP was obtained.

[0055] Step 4, preparation of UCMPs@g-C3N4@MSEP composite photocatalyst: 25 mg of MSEP was dispersed in deionized water and ultrasonicated for 30 minutes, and 100 mg of UCMPs@g-C3N4 was dispersed in deionized water and ultrasonicated for 30 minutes. After the dispersion was completed, the MSEP dispersion was heated to 60 ℃ and stirred using a mechanical stirring device. After the stirring started, the UCMPs@g-C3N4 dispersion was added dropwise to the MSEP dispersion, and the stirring was continued for 2 hours. The precipitate was collected by centrifugation and dried at 60 ℃ to obtain the UCMPs@g-C3N4@MSEP composite material.

[0056] Comparative Example 1

[0057] Preparation of g-C3N4 particles: 1.985 g of urea was mixed and ground in a marble mortar for 5 minutes, then transferred to a ceramic crucible and covered with a lid, and then placed in a muffle furnace to be calcined at 5 ℃ / min to 550 ℃ for 4 hours, and then naturally cooled to obtain g-C3N4 particles.

[0058] Performance test and analysis:

[0059] XRD test: UCMPs@g-C3N4@MSEP, UCMPs, g-C3N4 and MSEP were respectively subjected to XRD test analysis, and the results are shown in Figure 1 From Figure 1 it can be seen that the characteristic absorption peaks of UCMPs, g-C3N4 and MSEP correspond to the characteristic absorption peaks of UCMPs@g-C3N4@MSEP.

[0060] SEM and mapping spectrum test: UCMPs, UCMPs@g-C3N4 and UCMPs@g-C3N4@MSEP prepared in Example 1 were respectively subjected to SEM test and mapping spectrum analysis; the specific results are shown in Figure 2 , wherein Figure 2 (a) of is the SEM image of UCMPs, (b) is the SEM image of UCMPs@g-C3N4, (c) is the SEM image of UCMPs@g-C3N4@MSEP, (d) is the mapping image of Y element in UCMPs, (e) is the mapping image of N element in UCMPs@g-C3N4, and (f) is the mapping image of Si element in UCMPs@g-C3N4@MSEP. From the figure, it can be seen that Y, N and Si elements are uniformly distributed, Y is the main component element of UCMPs, N is the main element of g-C3N4, and Si is the main element of MSEP, so the uniform and same area distribution of the three elements also indicates the construction of the core-shell-shell structure.

[0061] Water contact angle test: UCMPs, UCMPs@g-C3N4 and UCMPs@g-C3N4@MSEP prepared in Example 1 were respectively subjected to water contact angle test, and the results are shown in Figure 3The water contact angle of UCMPs is 134.5°, the water contact angle of UCMPs@g-C3N4 is 43.5°, and the contact angle of UCMPs@g-C3N4@MSEP is 18.1°, as can be seen from the figure, and UCMPs@g-C3N4@MSEP has good hydrophilicity.

[0062] Magnetic performance test: the magnetic performance of UCMPs@g-C3N4 and UCMPs@g-C3N4@MSEP prepared in Example 1 was tested respectively, the relationship between the magnetization of the material and the magnetic field strength in the periodically changing external magnetic field was observed, and the hysteresis loop curve was drawn, and the results are shown in Figure 4 The test results of the hysteresis loop show that the ordinate of the hysteresis loop curve of UCMPs@g-C3N4@MSEP is higher than that of UCMPs@g-C3N4, indicating that after the surface of UCMPs@g-C3N4 is wrapped with a MSEP shell, the magnetic property of the composite material is improved. The improvement of the magnetic property can enhance the recovery efficiency of the composite material during photocatalytic degradation.

[0063] Kelvin voltage test: UCMPs@g-C3N4@MSEP, UCMPs@g-C3N4 prepared in Example 1 and g-C3N4 prepared in Comparative Example 1 were respectively subjected to scanning Kelvin probe force microscope (KPFM) test, the surface potential distribution and the performance of photo-induced charge separation of the materials were observed under dark (Dark) and light (Light) conditions, and the two-dimensional mapping of surface potential and the local area potential line distribution curve were collected. The results are shown in Figure 5 , wherein Figure 5(a) is a two-dimensional mapping diagram of the surface potential of g-C3N4 in the dark state, (b) is a two-dimensional mapping diagram of the surface potential of g-C3N4 under light, (c) is a local region potential line distribution curve of g-C3N4, (d) is a two-dimensional mapping diagram of the surface potential of UCMPs@g-C3N4 in the dark state, (e) is a two-dimensional mapping diagram of the surface potential of UCMPs@g-C3N4 under light, (f) is a local region potential line distribution curve of UCMPs@g-C3N4, (g) is a two-dimensional mapping diagram of the surface potential of UCMPs@g-C3N4@MSEP in the dark state, (h) is a two-dimensional mapping diagram of the surface potential of UCMPs@g-C3N4@MSEP under light, and (i) is a local region potential line distribution curve of UCMPs@g-C3N4@MSEP. From Figure 5 It can be seen that the g-C3N4 sample exhibits a negative surface photovoltage (SPV = -25.35 mV), which confirms its typical n-type semiconductor characteristics, i.e., photo-excited electrons migrate to the bulk phase, while holes accumulate on the surface. Although this charge separation mode is beneficial to surface oxidation reactions, the relatively low absolute SPV value indicates that there is a considerable degree of charge recombination, which limits the photocatalytic efficiency. In contrast, the UCMPs@g-C3N4 composite material exhibits a positive SPV response under light (+40.84 mV), indicating that the direction of electron transfer is reversed, which is likely due to the interface built-in electric field formed by the incorporation of UCMPs, which promotes the migration of electrons to the surface while inhibiting charge recombination. Further modification with MSEP (i.e., UCMPs@g-C3N4@MSEP) increases the SPV to +42.36 mV, indicating that charge recombination is further reduced. The above KPFM analysis shows that the core-shell-shell structure design significantly improves the exciton separation efficiency.

[0064] Photoelectric current response test: The UCMPs@g-C3N4@MSEP and UCMPs@g-C3N4 prepared in Example 1 were subjected to a photoelectric current response test, and periodic "light-dark" cycle conditions were set to observe the photoelectric conversion and photogenerated carrier separation / recombination kinetics performance of the materials under alternating light and dark conditions. The periodic change of current density with time was used to analyze the photocurrent intensity, response speed, and cycle stability. The results are shown in Figure 6 Figure 6 ​It can be seen that although both UCMPs@g-C3N4 and UCMPs@g-C3N4@MSEP exhibit fast photocurrent switching response, the photocurrent density of UCMPs@g-C3N4@MSEP composite is increased by 43%, which directly proves the improvement of charge separation efficiency, because the size of photocurrent is directly related to the number of photo-generated carriers successfully migrated to the electrode surface without recombination. This improvement is due to the hierarchical interface effect in the core-shell-shell structure, which helps to separate electrons and holes. The test results of the photocurrent response test are consistent with the conclusion in the KPFM analysis that the core-shell-shell structure design significantly improves the exciton separation efficiency.

[0065] Application Example 1

[0066] 30 mg of UCMPs@g-C3N4 prepared in Example 1 and 30 mg of g-C3N4 prepared in Comparative Example 1 were respectively mixed with 40 mL of an aqueous solution of ofloxacin with a concentration of 400 μmol / L (pH = 7) uniformly, and left to stand in the dark for 30 min. Then, under the irradiation of 980 nm 1.5 W / cm 2 Under the irradiation of near-infrared laser, the photodegradation experiment was carried out, and the concentration of ofloxacin in the two groups of mixed solutions was recorded every 10 min, and the results are shown in Figure 7

[0067] Application Example 2

[0068] 30 mg of UCMPs@g-C3N4@MSEP, UCMPs, MSEP, UCMPs@g-C3N4 prepared in Example 1 and g-C3N4 prepared in Comparative Example 1 were respectively mixed with 40 mL of an aqueous solution of ofloxacin with a concentration of 400 μmol / L (pH = 7) uniformly, and left to stand in the dark for 30 min. Then, under the irradiation of simulated sunlight (100 mW / cm 2 ), the photodegradation experiment was carried out, and the concentration of ofloxacin in each group of mixed solutions was recorded every 10 min, and the results are shown in Figure 8 (a).

[0069] Then the degradation kinetics of each component was calculated according to Figure 8 (a), and the results are shown in Figure 8 (b).

[0070] Application Example 3

[0071] ​30 mg of UCMPs@g-C3N4@MSEP prepared in Example 1 was mixed with 40 mL of ofloxacin aqueous solutions at concentrations of 200 μmol / L, 300 μmol / L, 400 μmol / L, and 500 μmol / L (pH=7), respectively. After standing in the dark for 30 min, a photodegradation experiment was conducted under simulated sunlight. The concentration of ofloxacin in each mixed solution was recorded every 10 min. The results are as follows: Figure 9 As shown.

[0072] Application Example 4

[0073] 30 mg of UCMPs@g-C3N4@MSEP prepared in Example 1 was mixed with 40 mL of ofloxacin aqueous solutions with pH values ​​of 3, 5, 7, and 9 and a concentration of 400 μmol / L, respectively. After standing in the dark for 30 min, photodegradation experiments were conducted under simulated sunlight. The concentration of ofloxacin in each mixed solution was recorded every 10 min. The results are as follows: Figure 10 As shown.

[0074] Application Example 5

[0075] 30 mg of UCMPs@g-C3N4@MSEP was mixed with 40 mL of ofloxacin solution at a concentration of 400 mol / L (pH=7). After standing in the dark for 30 min, a photodegradation experiment was conducted under simulated sunlight, and the concentration was recorded every 10 min. This cyclic experiment was repeated 5 times. After each reaction, the catalyst was recovered, dried, and replenished to the initial mass to evaluate its degradation stability. The results are as follows: Figure 11 As shown.

[0076] Combination Figures 7-8 To conduct analysis, from Figure 7 As can be seen, when combined with UCMPs, the UCMPs in UCMPs@g-C3N4 can convert 980nm near-infrared light into visible light. The visible light is then absorbed by g-C3N4, generating reactive oxygen species, thus producing the ability to photocatalytically degrade ofloxacin. However, g-C3N4 alone cannot absorb 980nm light, so it has no degradation effect in this case. Figure 8 Figure (a) shows the degradation results of various materials for ofloxacin under simulated sunlight, with UCMPs@g-C3N4@MSEP showing the best degradation effect. Figure (b) is the first-order kinetic curve corresponding to Figure (a). As can be seen from Figure (b), UCMPs@g-C3N4@MSEP has the fastest degradation rate. Figure 9 The graph shows the degradation effect of UCMPs@g-C3N4@MSEP on different concentrations of ofloxacin. Figure 9 It can be seen that the lower the concentration, the better the degradation effect; when the concentration exceeds 500 μM, the degradation effect decreases.Figure 10 The figure shows the degradation effect of UCMPs@g-C3N4@MSEP on ofloxacin under different pH conditions. The degradation effect is good under acidic and neutral conditions, but decreases under alkaline conditions. Figure 11 The figure shows the results of the cyclic stability test of UCMPs@g-C3N4@MSEP. The degradation effect of UCMPs@g-C3N4@MSEP on ofloxacin remains above 97% after 5 cycles, indicating good stability and high recovery rate.

[0077] Example 2

[0078] The preparation method of this example is basically the same as that of Example 1, except that the mass ratio of magnetic sepiolite and upconversion microparticle@g-C3N4 core-shell structure material is different. In this example, the dosage ratio of MSEP to UCMPs@g-C3N4 is 1:2.

[0079] Example 3

[0080] The preparation method of this example is basically the same as that of Example 1, except that the mass ratio of magnetic sepiolite and upconversion microparticle@g-C3N4 core-shell structure material is different. In this example, the dosage ratio of MSEP to UCMPs@g-C3N4 is 1:10.

[0081] Example 4

[0082] The preparation method of this example is basically the same as that of Example 1, except that the mass ratio of UCMPs to urea in step 2 is different. In this example, the mass ratio of UCMPs to urea in step 2 is 1:1.

[0083] Example 5

[0084] The preparation method of this example is basically the same as that of Example 1, except that the mass ratio of UCMPs to urea in step 2 is different. In this example, the mass ratio of UCMPs to urea in step 2 is 1:10.

[0085] 0.01 g of UCMPs@g-C3N4@MSEP prepared in Examples 1-4 was mixed with 20 mL of ofloxacin aqueous solution with a concentration of 200 μmoL / L (pH=7), placed in the dark for 30 min, and then subjected to photocatalytic degradation under simulated sunlight (100 mW / cm 2 ) for 40 min. The degradation rate of ofloxacin by UCMPs@g-C3N4@MSEP prepared in each example was recorded. The degradation rate = (ofloxacin concentration initial concentration C0- ofloxacin concentration after degradation C) / ofloxacin initial concentration C0*100%. The results are shown in Table 1:

[0086]

[0087] As can be seen from Table 1, the UCMPs@g-C3N4@MSEP prepared in Examples 1-5 all have a certain degradation effect on ofloxacin. Compared with Example 1, the proportion of UCMPs@g-C3N4 in Example 2 is reduced, and the degradation rate is reduced due to the significant reduction of g-C3N4 which produces active oxygen species. Compared with Example 1, the proportion of UCMPs@g-C3N4 in Example 3 is increased, and the degradation rate is reduced because the amount of MSEP is not enough to cover all UCMPs@g-C3N4, resulting in an increase in material charge recombination speed and a decrease in exciton separation efficiency; in addition, the decrease in the amount of MSEP reduces the hydrophilicity of the material, which affects the dispersion effect of the material in water. In Example 4, the mass ratio of UCMPs to urea is reduced, resulting in a decrease in the proportion of g-C3N4 in UCMPs@g-C3N4@MSEP, and the degradation rate is reduced because the decrease in the mass ratio of urea reduces the generation of g-C3N4. The g-C3N4 content in the UCMPs@g-C3N4@MSEP prepared in Example 5 is higher, resulting in a decrease in the uniformity of the core-shell UCMPs@g-C3N4 structure, and then when coated with MSEP, the three-level structure of core-shell-shell is not as good as that of Example 1, and the inhibition effect of charge recombination is reduced, so the degradation rate is reduced compared with Example 1.

[0088] The preferred embodiments of the present application are described above, but the protection scope of the present application is not limited to the above examples. Improvements and changes made by those skilled in the art without departing from the technical concept of the present application should also be considered as the protection scope of the present application.

Claims

1. A core-shell-shell three-level composite material, characterized in that, It includes upconversion micron particles, graphitic carbon nitride, and magnetic sepiolite; the upconversion micron particles are the core, the graphitic carbon nitride is the intermediate shell, and the magnetic sepiolite is the outer shell; the upconversion micron particles include Yb and Tm-doped β-NaYF4.

2. The composite material according to claim 1, characterized in that, In the upconversion micron particles, the molar ratio of β-NaYF4, Yb and Tm is (0.79~0.8):(0.2~0.21):(0.01~0.02).

3. The composite material according to claim 1, characterized in that, The particle size of the composite material is 3μm~5μm; the mass ratio of the upconversion micron particles to the graphite phase carbon nitride and the magnetic sepiolite is 1:1:0.

5.

4. A method for preparing the composite material according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1: Mix sodium citrate solution, yttrium nitrate solution, ytterbium nitrate solution, and thulium nitrate solution, and stir at 500-600 rpm for 20-25 minutes. Add sodium fluoride solution dropwise, and stir for another 30-35 minutes. Then transfer the mixed solution to a polytetrafluoroethylene-lined autoclave and carry out a hydrothermal reaction at 200-205℃ for 24-25 hours. The resulting precipitate is washed, dried, and annealed at 500-510℃ for 2-2.5 hours in a nitrogen atmosphere to obtain upconversion micron particles. Step 2: The upconversion micron particles are mixed and ground with urea and then calcined. After cooling, the upconversion micron particles@g-C3N4 core-shell structure material is obtained. Step 3: Prepare a mixed solution by adding FeCl3·6H2O and FeSO4·7H2O to deionized water, stir to dissolve, then add sepiolite. Under argon protection, heat to 60℃~65℃ at a rate of 5℃ / min~6℃ / min and stir magnetically for 10min~20min. Then, add concentrated ammonia dropwise to adjust the pH to 9.5~10.5 and continue the reaction for 1h~1.5h. Then, age in a vacuum environment at 35℃~40℃ for 1.5h~2.5h. After aging, wash with deionized water and ethanol alternately by filtration 3~4 times, and dry under vacuum to obtain magnetic sepiolite. Step 4: Disperse the magnetic sepiolite and the upconversion micron particles @g-C3N4 core-shell structure material obtained in Step 2 in deionized water respectively. Heat the dispersion of the magnetic sepiolite to 55℃~65℃, and add the dispersion of the upconversion micron particles @g-C3N4 core-shell structure material dropwise under stirring. After the addition is completed, continue stirring for 2h~3h. Centrifuge, collect the precipitate and dry it to obtain the core-shell-shell three-level structure composite material.

5. The preparation method according to claim 4, characterized in that, In step 1, the molar ratio of sodium citrate, yttrium nitrate, ytterbium nitrate, thulium nitrate, and sodium fluoride is 1:(0.79~0.8):(0.2~0.21):(0.01~0.02):(12~12.1).

6. The preparation method according to claim 4, characterized in that, The mass ratio of the upconversion micron particles to the urea is 1:(1~10).

7. The preparation method according to claim 4, characterized in that, The calcination step in step 2 includes heating at 4℃ / min to 6℃ / min to 500℃ to 600℃ for 4h to 5h.

8. The preparation method according to claim 4, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The total molar concentration of FeCl3·6H2O and FeSO4·7H2O in the mixed solution prepared by FeCl3·6H2O is 0.3 mol / L; (2) The molar ratio of FeCl3·6H2O and FeSO4·7H2O is (1~3):1; (3) The ratio of the total mass of FeCl3·6H2O and FeSO4·7H2O to the mass of sepiolite is (0.8~0.9):

1.

9. The preparation method according to claim 4, characterized in that, In step 4, the mass ratio of the magnetic sepiolite to the upconversion micron particles @g-C3N4 core-shell structure material is 1:(1~10).

10. The application of the core-shell-shell tertiary structure composite material according to any one of claims 1 to 3 or the core-shell-shell tertiary structure composite material obtained by the preparation method according to any one of claims 4 to 9 in the photocatalytic degradation and removal of organic pollutants in water.

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