Preparation method of magneto-photonic crystal thin film and its visual detection of heavy metal Ni 2+ Use

Abstract

The present invention discloses a preparation method of a magneto-optical photonic crystal thin film and its use for visual detection of heavy metal Ni<supgt;2+< / supgt;, belonging to the fields of thin film preparation technology and analytical detection based on nanomaterials. This method uses silica core-shell structured magnetic nanoparticles as the building materials for photonic crystals, combines with polymer P(AM-ATU) nanoparticles, and by introducing a magnetic field, realizes a magneto-optical photonic crystal thin film with the ordered arrangement of magnetic nanoparticles driven by the magnetic field through spin coating. On the one hand, the ordered and disordered arrangements of the silica core-shell structured magnetic nanoparticles will cause obvious color changes; on the other hand, the polymer P(AM-ATU) nanoparticles have a strong adsorption effect on heavy metal ions, and at the same time, the distance is likely to change in an aqueous solution, thus causing a change in the color of the emitted light. The two are superimposed on each other to construct a new method for rapid visual detection of heavy metal Ni<supgt;2+< / supgt>.

Description

Technical Field

[0001] The present invention belongs to the fields of magnetically assembled nanomaterial photonic crystal thin films and heavy metal ion detection, and particularly relates to a preparation method of a magneto-optical photonic crystal thin film and its use for visual detection of heavy metal Ni 2+ and its use. Background Art

[0002] Heavy metal ion Ni 2+ pollution can seriously harm the environment. The accumulation of Ni 2+ in the environment exceeding the standard can cause contact dermatitis, damage the digestive system, irritate the respiratory system, lead to neurasthenia and even cause cancer. By detecting the concentration of heavy metal ion Ni 2+ the degree of environmental pollution can be determined, the human health risk can be evaluated, the environmental pollution sources and treatment effects can be monitored, and a scientific basis can be provided for formulating environmental protection policies and regulations.

[0003] At present, the detection of heavy metal ion Ni 2+ mainly relies on large-scale precision instruments. These instruments have extremely high accuracy and sensitivity (i.e., very low detection limits), but the precision instruments are expensive, require skilled operators to operate the instruments, and complex samples need to be prepared during the detection process. This results in poor universality of Ni 2+ detection. Currently, there is an urgent need for a Ni 2+ detection method that is low-cost, convenient, visually readable, and does not require large-scale equipment.

[0004] Magneto-optical photonic crystals are composed of two or more different refractive index materials arranged periodically, and have a wavelength selection function. They can selectively allow light of a certain wavelength band to pass through while blocking light of other wavelengths, and the non-passing light is reflected. When the lattice spacing and refractive index of the material are within a certain range, light in the visible light region can be reflected, thus showing a structural color. Thiosemicarbazide-functionalized copolymers can adsorb Ni 2+ and, with the change of the copolymer chemical structure, the functional copolymer layer in the photonic material expands sharply in water, and the penetrated Ni 2+ chelates with the copolymer ligands on the polymer layer, triggering a large-volume shrinkage of the polymer layer, ultimately resulting in a blue shift of the diffraction wavelength of the photonic structure and automatically converting it into a visually perceivable color change. By combining the advantages of both, the advantages of magneto-photonic crystals and copolymer-conjugated heavy metal ions are utilized to achieve highly sensitive and visual selective detection of Ni 2+ and its use for visual detection of heavy metal Ni Summary of the Invention

[0005] The present invention provides a preparation method of a magneto-optical photonic crystal thin film and its use for visual detection of heavy metal Ni 2+ and its use, aiming to detect Ni 2+, to reduce the problem that the existing Ni 2+ The detection relies on large equipment.

[0006] For this reason, the present invention adopts the following technical solutions:

[0007] A preparation method of a magneto-optical photonic crystal thin film, comprising the following steps:

[0008] 1) Obtain or prepare Fe 3 O 4 Magnetic nanoparticles are prepared by using the solvothermal method;

[0009] 2) Preparation of silica core-shell structured magnetic nanoparticles: Mix the Fe 3 O 4 Magnetic nanoparticles in step 1) with tetraethyl orthosilicate (TEOS), liquid alcohol and concentrated ammonia water in proportion, and react under ultrasonic conditions to prepare silica core-shell structured magnetic nanoparticles; on the one hand, silica coating can play a stabilizing role in the solution dispersion, and on the other hand, as a magneto-optical photonic crystal material, it has good light reflection effect after being orderly arranged under the action of a magnetic field;

[0010] 3) Preparation of polymer P(AM-ATU) nanoparticles: Mix AM (acrylamide), ATU (N-allylthiourea), surfactant AOT (sodium dioctyl sulfosuccinate), toluene, and AIBN (azobisisobutyronitrile) successively, condense and reflux the hot reaction solution with stirring, and precipitate with ethanol after the reaction to obtain polymer P(AM-ATU) nanoparticles; the copolymer has high swelling property in water, so as to provide enough space for the shrinkage of the polymer layer during Ni 2+ treatment;

[0011] 4) Preparation of magneto-optical photonic crystal thin film: Take the polymer P(AM-ATU) nanoparticle dispersion prepared in step 3) and prepare the first layer of thin film by spin coating;

[0012] Take the silica core-shell structured magnetic nanoparticle dispersion prepared in step 2) and prepare the second layer of thin film by spin coating above the first layer of thin film; immediately apply a magnetic field after spin coating, and make the silica core-shell structured magnetic nanoparticles be orderly arranged under the action of the magnetic field; repeat this step to prepare 2-5 layers of thin films in total, so as to prepare the magneto-optical photonic crystal thin film.

[0013] Furthermore, the PDI (aggregation degree index) of the silica core-shell structured magnetic nanoparticles prepared in step 2) is <0.1, showing a monodisperse state;

[0014] Furthermore, the mixing reaction steps in step 3) are as follows:

[0015] 1) Prepare the reaction solution

[0016] Dissolve AM (acrylamide) and ATU (N-allylthiourea) with a mass ratio of 1:1 - 5:1 in 1 ml - 5 ml of deionized water to form monomer solution A;

[0017] Dissolve 5 mg - 15 mg of AIBN (azobisisobutyronitrile) in 1 ml - 5 ml of toluene to form solution B;

[0018] Dissolve 1 g - 5 g of AOT (sodium docusate) in 50 ml of toluene solution to form solution C;

[0019] 2) Reaction process

[0020] Under the conditions of nitrogen protection and condensation reflux, heat solution C to a temperature of 50 °C - 90 °C to form a thermal reaction solution; then add solution B to this thermal reaction solution; finally, inject solution A into the above thermal reaction solution at a rate of 0.5 ml·min -1 - 2 ml·min -1 and react for 0.5 h - 2 h.

[0021] Furthermore, the mass concentration of the polymer P(AM-ATU) nanoparticles prepared in step 3) dispersed in water is 2% - 10%.

[0022] Furthermore, the substrate for preparing the magnetophotonic crystal film in step 4) is a silicon wafer (<111>, <100>) with a silicon oxide layer with crystal plane orientation on its surface.

[0023] Furthermore, the magnetophotonic crystal film prepared in step 4) is 2 - 5 layers, where the first layer is a dispersion of polymer P(AM-ATU) nanoparticles, which is used to improve the binding property of the magnetophotonic crystal film; the second layer is a dispersion of silica core-shell structured magnetic nanoparticles; the third to fifth layers are in turn.

[0024] Furthermore, in the preparation of the first layer, the rotation speed of the spin coater is 2000 rpm - 5000 rpm, the time is 20 s - 80 s, and it is dried at 100 °C - 200 °C for 1 min - 5 min; for the second layer, its dispersion is water, ethanol, ethylene glycol, and a dispersion of polymer P(AM-ATU) nanoparticles, the rotation speed of the spin coater is 1000 rpm - 4000 rpm, the time is 20 s - 80 s, it is cured at a magnetic field strength of 20 mT - 60 mT for 3 min - 10 min, and dried at 100 °C - 200 °C for 1 min - 5 min; the preparation conditions for the third to fifth layers are in turn.

[0025] A method for visual and rapid detection of heavy metal Ni 2+ by a magnetophotonic crystal film, comprising the following steps:

[0026] 1) Prepare aqueous solutions of Ni with different concentrations, drop the aqueous solutions of Ni with different concentrations onto the magneto - photonic crystal film, with the reaction time being 1 min - 20 min, observe the color change. As the concentration increases, the color change trend is a gradual blue shift; 2+ of the aqueous solution, 2+ aqueous solution is dropped onto the magneto - photonic crystal film, with the reaction time being 1 min - 20 min, observe the color change. As the concentration increases, the color change trend is a gradual blue shift;

[0027] 2) Use a Hailight optical spectrometer to measure the reflection spectrum and establish a standard curve. Its detection linear range of Ni 2+ is 1×10 -7 mol / L - 2×10 -1 mol / L.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. The present invention selects monodisperse (PDI < 0.1) silica core - shell magnetic nanoparticles as the magnetic - response photonic crystal material, which has the characteristics of fast response rate, high sensitivity, rapid migration along the magnetic field direction and self - assembly arrangement to form a stable chain - like structure under the action of an external magnetic field. Its magnetic - response bandgap can cover the entire visible spectrum and has fast, bright and reversible diffraction changes.

[0030] 2. A thiourea - functional polymer P(AM - ATU) is prepared as a high - cost - performance material for indicating Ni in an aqueous solution. As the chemical structure of the copolymer changes, the functional copolymer layer in the photonic material in water expands sharply, triggering a large - volume shrinkage of the polymer layer, ultimately resulting in a blue shift of the diffraction wavelength of the photonic structure and automatically converting it into a visually perceivable color change. At the same time, the combination of Ni 2+ and the polymer shrinkage - induced water exclusion change the refractive index, which also contributes to the optical sensing signal. 2+ Combined with the polymer shrinkage - induced water exclusion change the refractive index, which also contributes to the optical sensing signal.

[0031] 3. The transition of the magnetic nanoparticles from an ordered arrangement to a disordered arrangement at a certain concentration will also cause a change in the diffraction wavelength of the photonic structure. Therefore, the gradual disordering of the ordered magnetic nanoparticles in the magneto - photonic crystal film in the solution will cause a color change. Combining the functional polymer and the magnetic nanoparticles makes the reflection color change more significantly.

[0032] 4. The present invention indicates different concentrations of Ni 2+ through the different reaction colors of the magneto - photonic crystal film. It can be judged by the naked eye whether it exceeds the standard without the aid of any instrument. Therefore, the detection cost is low, the operation is simple, and a method for highly sensitive, low - cost and simple detection of Ni 2+ is established. Description of the Drawings

[0033] Figure 1 is the schematic diagram of the preparation of the magneto - photonic crystal film and its visualization detection;

[0034] Figure 2 TEM image and particle size distribution diagram of monodisperse silica core-shell structured nanoparticles;

[0035] Figure 3 SEM image of spin-coated magnetic nanoparticles solidified under a magnetic field;

[0036] Figure 4 Photos of spin-coated magnetic photonic crystal films with different numbers of layers;

[0037] Figure 5 Reflectance spectra of the reaction between a 3-layer magnetic photonic crystal film and Ni with different concentrations 2+ Specific implementation mode

[0038] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0039] The preparation steps of the magnetic photonic crystal film are as follows:

[0040] 1) Obtain Fe 3 O 4 nanomagnetic particles

[0041] Dissolve 1.7 g of FeCl 3 ·6H 2 O and 4.5 g of NaAc·3H 2 O in 300 ml of ethylene glycol, add 1 ml of deionized water, transfer the brown solution to a 500 ml high-temperature and high-pressure reaction kettle after complete dissolution, control the rotation speed at 300 r / min, and heat in two stages; heat at 160 °C for 3 h in the first stage and at 200 °C for 5 h in the second stage. After natural cooling, wash with absolute ethanol 3 - 5 times, and finally disperse in absolute ethanol.

[0042] 2) Preparation of silica core-shell structured nanomagnetic particles

[0043] Disperse the Fe 3 O 4 nanomagnetic particles prepared in 3 times in step 1) in 2 L of an alcohol solution, which includes 750 ml of deionized water and 1250 ml of absolute ethanol; ultrasonically disperse for 20 min, add 125 ml of ammonia water, and then dropwise add 6.25 ml of tetraethyl orthosilicate (TEOS), and ultrasonically react for 40 min; after the reaction, perform magnetic separation and wash with absolute ethanol 3 - 5 times to obtain silica core-shell structured magnetic nanoparticles; then prepare magnetic nanoparticle dispersions with three concentration levels of 10 mg / ml, 20 mg / ml, and 30 mg / ml; it can be seen from Figure 2 that the silica core-shell magnetic nanoparticles have good dispersibility, and their PDI index is less than 0.1.​

[0044] 3) Preparation of Polymer P(AM-ATU) Nanoparticles

[0045] Dissolve AM (acrylamide) and ATU (N-allylthiourea) in 1 ml of deionized water at a mass ratio of 1:1 to form solution A; simultaneously, dissolve 5 mg of AIBN (azobisisobutyronitrile) in 1 ml of toluene to form solution B; dissolve 1 g of AOT (sodium dioctyl sulfosuccinate) in 50 ml of toluene solution to form solution C. Under the conditions of nitrogen protection and reflux condensation, heat solution C to 50 °C and then add solution B to the hot reaction solution; finally, inject solution A into the reaction solution at a rate of 0.1 ml·min -1 and react for 0.5 h. After the reaction, cool naturally, add anhydrous ethanol with a volume twice that of the mixed solution for precipitation, remove the supernatant, and prepare a 2% mass concentration dispersion of polymer P(AM-ATU).

[0046] 4) Preparation of Magneto-Photonic Crystal Film

[0047] Using a silicon wafer with an oriented <111> silica layer as the substrate, spin-coat the polymer P prepared in step 3) at a speed of 2000 rpm for 20 s and then dry it at 100 °C for 1 min.

[0048] Example 2

[0049] The preparation steps of the magneto-photonic crystal film are as follows:

[0050] 1) Obtain Fe 3 O 4 nanomagnetic particles

[0051] Dissolve 1.7 g of FeCl 3 ·6H 2 O and 4.5 g of NaAc·3H 2 O in 300 ml of ethylene glycol, add 1 ml of deionized water, and after complete dissolution, transfer the brown solution to a 500 ml high-temperature and high-pressure reaction kettle, rotate at 300 r / min, and heat in two stages. Heat at 160 °C for 3 h in the first stage and at 200 °C for 5 h in the second stage. After natural cooling, wash with anhydrous ethanol 3 - 5 times, and finally disperse in anhydrous ethanol.

[0052] 2) Preparation of Silica Core-Shell Structure Nanomagnetic Particles

[0053] The Fe 3 O 4The nano magnetic particles are dispersed in 2 L of an alcohol solution, which includes 750 ml of deionized water and 1250 ml of absolute ethanol; ultrasonically disperse for 20 min, add 125 m ammonia water and then dropwise add 6.25 ml of tetraethyl orthosilicate (TEOS), ultrasonically react for 40 min. After the reaction ends, perform magnetic separation and wash with absolute ethanol 3 - 5 times to obtain magnetic nanoparticles with a silica core - shell structure, and prepare magnetic nanoparticle dispersions with three concentrations of 10 mg / ml, 20 mg / ml, and 30 mg / ml;

[0054] 3) Preparation of polymer P(AM - ATU) nanoparticles

[0055] Dissolve AM (acrylamide) and ATU (N - allylthiourea) in a mass ratio of 1:1 in 1 ml of deionized water to form solution A; simultaneously dissolve 5 mg of AIBN (azobisisobutyronitrile) in 1 ml of toluene to form solution B; dissolve 1 g of AOT (sodium dioctyl sulfosuccinate) in 50 ml of toluene solution to form solution C. Under the conditions of nitrogen protection and reflux condensation, heat solution C to 50 °C, then add solution B to the hot reaction solution. Finally, inject solution A into the reaction solution at a rate of 0.1 ml·min -1 and react for 0.5 h. After the reaction ends, cool naturally, add anhydrous ethanol twice the volume of the solution for precipitation, remove the supernatant, and prepare a polymer P(AM - ATU) dispersion with a mass concentration of 2%.

[0056] 4) Preparation of magneto - photonic crystal thin films

[0057] Using a silicon wafer with an oriented <111> silica layer as the substrate, spin - coat the polymer P prepared in step 3) at a speed of 2000 rpm for 20 s and then dry at 100 °C for 1 min to obtain the first layer of film; spin - coat the magnetic nanoparticle dispersion of the silica core - shell structure prepared in step 2) at a speed of 2000 rpm above the first layer of film for 20 s, then stand still for 1 min under a magnetic field of 20 mT, and then dry at 100 °C for 1 min. It can be seen that after applying the magnetic field, the magnetic nanoparticles are arranged orderly in the film. Figure 3 It can be seen that after applying the magnetic field, the magnetic nanoparticles are arranged orderly in the film.

[0058] In Examples 3 - 7, the preparation conditions of the magnetic nanoparticles with a silica core - shell structure are the same as those in steps 1) and 2) of Example 1, and the steps of steps 3) and 4) are the same. The specific material usage and reaction conditions of the raw materials are shown in Tables 1 and 2 as follows:

[0059] Table 1

[0060]

[0061] Table 2

[0062]

[0063] After consulting the literature, it is found that most of the preparation methods of conventional magnetophotonic crystal thin films choose the mold method, that is, a fixture with a certain thickness is processed, and magnetic nanoparticles with photonic effects and organic substances are mixed in proportion and then injected into the fixture and a fixed magnetic field is applied. The magnetophotonic crystal thin films prepared by such methods are relatively thick, remaining at the millimeter level and cannot achieve the composite superposition of multilayer films, and the preparation conditions are relatively complex. Compared with the traditional preparation methods, the thin films prepared by the spin-coating method are thin, and after detection, they belong to the micron level. After applying a magnetic field, the magnetic nanoparticles can quickly achieve an ordered arrangement, the curing rate is fast, and there are outstanding advantages such as fast, convenient and simple in realizing the preparation of multilayer films. At the same time, due to the thin thickness of the thin film, the time for the color to change during detection in the solution is short, which can greatly improve the detection efficiency and provide a solution for the composite processing of subsequent multifunctional layers.

[0064] Figure 1 It is the schematic diagram of the color change of the magnetophotonic crystal thin film. Figure 4 It is the color of the thin film after multilayer spin-coating. The ligand on the thin film layer spin-coated with polymer P(AM-ATU) nanoparticles can chelate with metal Ni 2+ to cause a large-volume shrinkage of the polymer layer, ultimately resulting in a blue shift of the diffraction wavelength of the photonic structure and automatically converting it into a visually perceivable color change; at the same time, by adding magnetophotonic crystals, the magnetophotonic crystal thin films that are spin-coated in multiple layers and ordered under a magnetic field gradually become disordered in an aqueous solution, which will also cause a change in the reflected light. Combining the two, the color change before and after detection will be greatly enhanced compared with the single-layer film, which can improve the detection line and specificity of Ni 2+ in the aqueous solution. As Figure 5 shown, the color change span before and after the reaction is large and it is very easy to distinguish.

[0065] Taking Example 5 as an example, reacting with Ni 2+ solutions with concentrations of 0 µm, 200 µm, 400 µm, 600 µm, and 800 µm for 1 min, there are obvious color changes in the reaction system. The reflection spectra are measured by a portable spectrometer. As Figure 5 shown, as the concentration of Ni 2+ increases, the color of the reflection peak position undergoes an obvious blue shift.

Claims

1. A magneto-photonic crystal film for rapid visualization of heavy metal Ni 2+ The method is characterized in that The following steps are involved: Preparation of different concentrations of Ni 2+ The aqueous solution of different concentrations of Ni 2+ The aqueous solution was dripped onto the magneto-photonic crystal film, and the reaction time was 1min-20min. The color change was observed. With the increase of concentration, the color change trend was gradually blue shift. The reflectance spectrum was measured by Haiyang optical spectrometer, and a standard curve was established to detect Ni 2+ The linear range is 1×10 -7 mol / L—2×10 -1 mol / L; The method for preparing a magneto-photonic crystal film comprises the following steps: 1) Obtaining or preparing Fe3O4 magnetic nanoparticles; 2) Preparation of silicon oxide core-shell structured magnetic nanoparticles: The Fe3O4 magnetic nanoparticles prepared in step 1) are mixed with tetraethyl orthosilicate TEOS, liquid alcohol and concentrated ammonia water in proportion, and reacted under ultrasonic conditions to prepare silicon oxide core-shell structured magnetic nanoparticles; the prepared silicon oxide core-shell structured magnetic nanoparticles have an aggregation index PDI < 0.1, and are monodispersed; 3) Preparation of polymer P AM-ATU nanoparticles: acrylamide, N-allylthiourea, sodium docusate, toluene, and azobisisobutyronitrile are mixed successively, the hot reaction liquid is condensed, refluxed, and stirred, and after the reaction is completed, ethanol is used for precipitation to obtain polymer P AM-ATU nanoparticles; the mixing reaction steps are as follows: a. Prepare the reaction solution Dissolve acrylamide and N-allylthiourea in a mass ratio of 1:1-5:1 in 1 ml-5 ml of deionized water to form a monomer solution A; Dissolve 5 mg to 15 mg of azobisisobutyronitrile in 1 ml to 5 ml of toluene to form solution B; Dissolve 1 g to 5 g of docusate sodium in 50 ml of toluene solution to form solution C; b. Reaction process Solution C is heated to a temperature of 50°C to 90°C under nitrogen protection and condensation reflux conditions to form a hot reaction liquid; Then add solution B to the hot reaction solution; finally, add solution A at 0.5 ml min -1 —2ml·min -1 Inject into the hot reaction liquid at a rate of and react for 0.5h-2h; 4) Preparation of magneto-photonic crystal film: Take the polymer P AM-ATU nanoparticle dispersion prepared in step 3) and prepare the first film by spin coating; Take the silicon oxide core-shell structure magnetic nanoparticle dispersion prepared in step 2) and prepare a second film layer on top of the first film layer by spin coating; immediately apply a magnetic field after the spin coating is completed, so that the silicon oxide core-shell structure magnetic nanoparticles are orderly arranged under the action of the magnetic field; repeat this step to prepare a total of 2 to 5 layers of film, thereby preparing a magneto-photonic crystal film.

2. The magneto-photonic crystal film according to claim 1 can be used to rapidly detect heavy metal Ni 2+ The method is characterized in that The mass concentration of the polymer P AM-ATU nanoparticles prepared in step 3) dispersed in water is 2%-10%.

3. The magneto-photonic crystal film according to claim 1 can be used to rapidly detect heavy metal Ni 2+ The method is characterized in that The substrate for preparing the magneto-photonic crystal film in step 4) is a silicon wafer having a crystal plane-oriented silicon oxide layer on the surface, and the crystal plane orientation is <111> , <100> .

4. The magneto-photonic crystal film according to claim 1 can be used to rapidly detect the heavy metal Ni 2+ The method is characterized in that The magneto-photonic crystal film prepared in step 4) has 2 to 5 layers, wherein the first layer is a dispersion of polymer P AM-ATU nanoparticles, which is used to improve the bonding of the magneto-photonic crystal film; the second layer is a dispersion of silicon oxide core-shell structure magnetic nanoparticles; and the third to fifth layers are analogous.

5. The magneto-photonic crystal film according to claim 4 is used for rapid visualization of heavy metal Ni 2+ The method is characterized in that In the preparation of the first layer, the speed of the spin coater is 2000rpm-5000rpm, the time is 20s-80s, and it is dried at 100℃-200℃ for 1min-5min; in the preparation of the second layer, the speed of the spin coater is 1000rpm-4000rpm, the time is 20s-80s, and it is cured for 3min-10min at a magnetic field strength of 20mT-60mT, and dried at 100℃-200℃ for 1min-5min; the preparation conditions of the third to fifth layers are similar.

Images