CN109499615B

CN109499615B - Polyoxometallate-doped solid-state luminescent nano material and preparation method and application thereof

Info

Publication number: CN109499615B
Application number: CN201811524340.9A
Authority: CN
Inventors: 王冠; 赵媛; 孟茹茹
Original assignee: Henan University
Current assignee: Henan University
Priority date: 2018-12-13
Filing date: 2018-12-13
Publication date: 2021-04-27
Anticipated expiration: 2038-12-13
Also published as: CN109499615A

Abstract

The invention belongs to the technical field of solid luminescent nano material preparation, and particularly relates to a polyoxometallate doped solid luminescent nano material, and a preparation method and application thereof. In the invention, different types of POMs are adopted as dopants, and CeF is discussed₃The invention adopts PVP as a reaction medium and synthesizes CeF with higher crystallinity at low temperature₃And POMs/CeF₃The catalytic degradation rate of the nano material serving as a catalyst to rhodamine B is 98% at most after the nano material is irradiated by light for 6 hours, and the method shows that the prepared nano material serving as the photocatalyst has a good application prospect in the aspect of degrading pollutants in waste water.

Description

Polyoxometallate-doped solid-state luminescent nano material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of solid luminescent nano material preparation, and particularly relates to a polyoxometallate doped solid luminescent nano material, and preparation and application thereof.

Background

As an important inorganic compound, POMs (polyoxometallates) have wide application prospects in the fields of catalysis, pharmacology, electronics, magnetic materials, photoluminescence and the like.

Polyoxometallate-based nanomaterials (PNMs) are a branch of POMs, and as their morphology, composition or size can be adjusted by modern synthesis techniques, they have practical application values, and PNMs have attracted considerable attention for their excellent properties compared to other conventional single crystal POMs compounds. In 2002, Zhang et al used the reverse microemulsion method (Zhang X H, Xie S Y, Jiang Z Y, et al Starlike nanostructures of polyoxometalates K₃ [PMo₁₂O₄₀]· nH₂O synthesized and assembled by an inverse microemulsion method[J]Chemical Communications, 2002 (18): 2032-₃[PMo₁₂O₄₀]·nH₂An O star nanostructure. In 2003, Liu et al performed extensive systematic studies on PNMs (Liu T, Diemann E, Li H, et al. Self-assembly in aqueous solution of reel-shaped Mo₁₅₄ oxide clusters into vesicles[J]Nature, 2003, 426(6962): 59.) they found Mo having a wheel shape₁₅₄The nano-sized metal oxide aggregate can be self-assembled into small bubbles with the average radius of about 45 nm in aqueous solution, and the nano-sized metal oxide aggregate presents a hollow spherical structure, and meanwhile, a series of nano-vesicles with a blackberry type structure are obtained, and the properties of the nano-vesicles are studied in detail in solution. Recently, the Cronin group of subjects discovered the growth phenomenon of inorganic hollow tubular structures (Cooper G J T, Boulay A G, Kitson P J, et al, Osmologically drive crystalline morphology: a general approach to the architecture of micro-meter-scale tubular structures on polyoxometalates [ J]Journal of the American Chemical Society, 2011, 133(15): 5947- > 5954.), which may be of great significance to the interpretation of structures found in bioprocess fossil records. Reports of different morphologies of PNMs show their diversity in chemical self-assembly.

Photoluminescence (PL) properties have received increasing attention in recent years as an important property of PNMs, but photoluminescence properties are relatively less studied than other properties of PNMs. Research shows that during the self-assembly process of the nano material, POMs as dopants can influence the appearance of the nano material, thereby generating products with different shapes. Furthermore, POMs are efficient electron acceptors and carriers, and this electron transfer mediating action also causes POMs to alter the properties of PL materials.

The photocatalyst is commonly called photocatalyst, and refers to a chemical substance capable of playing a catalytic role under the excitation of photons. It plays an important role in the photocatalytic decomposition of organic substances harmful to human bodies and the environment, and in the processes of saving resources and avoiding environmental pollution. Nano-scale composite photocatalyst POM/CeF₃Due to the characteristic of high specific area, more active sites can be provided for adsorbing pollutants, and photocatalysis is facilitated. Therefore, a POM/CeF with different luminescent properties and different morphologies is researched₃The photocatalytic functional nano material has important significance.

Disclosure of Invention

The invention aims to solve the technical problem of preparing the POM/CeF with different morphologies and luminescent property₃A photocatalytic functional nano material.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of polyoxometallate doped solid-state luminescent nano material comprises the following steps:

1) collecting soluble cerium salt, polyvinylpyrrolidone (PVP) and KBF₄Putting the POMs and the POMs into a reaction kettle with the volume of 25 ml, adding distilled water to dissolve a sample, and stirring at normal temperature for 20-40 min to obtain a mixed solution;

2) transferring the reaction kettle into an oven, raising the temperature to 40-180 ℃ at the rate of 0.1-2 ℃/min, raising the pressure in the reaction kettle to 110-170 KPa at the rate of 3-40 KPa/h, keeping the constant temperature and the constant pressure for 6-24 h, cooling to room temperature, carrying out solid-liquid separation, washing the solid for 2-5 times by using a mixed solution (1-5 mL) of deionized water and ethanol, wherein the volume ratio of the deionized water to the ethanol in the mixed solution is (1-3): 1, and then drying at 50-70 ℃ overnight to obtain the solid luminescent nano material POM/CeF₃。

The soluble cerium salt is cerium nitrate, cerium sulfate or cerium chloride.

Wherein the POMs are Na₃PMo₁₂O₄₀、K₄SiW₁₂O₄₀、Na₃PW₁₂O₄₀One or more of them, Na for convenience of explanation₃PMo₁₂O₄₀、K₄SiW₁₂O₄₀、Na₃PW₁₂O₄₀Are respectively abbreviated as alpha-PMo₁₂、α-SiW₁₂、α-PW₁₂The synthesis method thereof is referred to as: Masteri-Farahani M, Ghorbani M, Ezabadi A, et al Star-shaped Keggin-type heteropolytungstate nanostructure as a new catalyst for the preparation of quinoxaline derivatives[J]. Comptes Rendus Chimie, 2014, 17(11): 1136-1143。

Specifically, the soluble cerium salt and KBF in the step 1)₄The mass ratio of (1): (1-3) specifically, soluble cerium salt and KBF₄In a mass ratio of 1:1, 1:2 or 1:3, or a soluble cerium salt and KBF₄In a molar ratio of 1: (4-5).

Specifically, the mass ratio of the soluble cerium salt to the POMs in the step 1) is (1-9): specifically, the mass ratio of the soluble cerium salt to the POMs is (13: 1.5), (13: 5) or (13: 10), or the molar ratio of the soluble cerium salt to the POMs is (60-5): specifically, the molar ratio of the soluble cerium salt to the POMs is (299: 5), (299: 8), (299: 14), (299: 26), or (299: 53).

Further, in step 1), the amount of PVP is 0.02-0.08 g per 0.130 g of soluble cerium salt, preferably 0.05 g per 0.130 g of soluble cerium salt.

Polyoxometallate-doped solid-state luminescent nano material POM/CeF prepared by adopting method₃。

The polyoxometallate-doped solid luminescent nano material POM/CeF₃The application of the composite material in degrading pollutants in wastewater is specifically that the pollutants are dye or formaldehyde, the dye can be rhodamine B, methylene blue, alizarin red S, gardenia yellow G or Congo red, and when the composite material is applied, 0.06-0.12G of nano material POM/CeF is added₃Adding the mixture into a solution with the volume of 40-45 mL and containing the pollutants, wherein the concentration of the pollutants is 10-20 mg/L.

The preparation process of the invention can be seen as follows: in CeF₃In the nanocrystals, these crystals are aggregated together to form a disc-shaped nanosheet, which is loosely aggregated together, so that there are very small micropores, and in the absence of POMs, these disc-shaped nanosheets gradually grow into a regular hexagonal structure through the neck.

In POMs/CeF₃In the sample, when a small amount of POMs is introduced, the dopant will occupyIntermediate holes and micropores, a compact aggregation state can not be formed, and the disc-shaped nanosheet is formed. As the number of POMs increases, the growth mechanism may change. It can be concluded that supersaturation of the reaction system has a critical effect on crystal growth. With increasing POMs content, the total concentration of starting material increases, on the one hand the dislocation-driven growth will cause the nanocrystals to aggregate into spheres, and on the other hand the rapid nucleation and high supersaturation promote the formation of many active centers in the system, so that the nuclei cannot grow all the way along certain crystallographic directions, thus leading to dendritic growth and finally to flower morphology.

In CeF₃The doping of POMs in the nano-crystal can cause the change of the crystal appearance, meanwhile, the PL performance of the doped nano-composite materials is different, and different types of POM/CeF are doped₃With different emission peaks. By adjusting the doping amount, POMs/CeF can be doped₃The shape of the nanocrystals is controlled and, in addition, their PL properties can be tailored.

The invention has the following beneficial effects:

1) inorganic fluorescent fluoride CeF₃The crystal has very low vibration energy, the invention adopts POMs with photocatalysis function as dopant, discusses the CeF₃Influence of nanocrystal morphology and PL properties. Furthermore, the method has potential application value for solving the problems that the morphology and FL performance of the nano material cannot be effectively adjusted in simple biological imaging, wastewater organic matter degradation and fluorescence chemical sensors.

2) Three kinds of alpha-PMo₁₂，α-SiW₁₂And alpha-PW₁₂Polyoxometallates (POMs) are doped into CeF respectively₃In the solid luminescent nano material, flower shape, sheet shape and spherical shape are respectively obtained. Because the POMs have the characteristic of efficiently accepting electrons and carriers, the POMs are used as a dopant to influence CeF₃The self-assembly morphology also has an influence on the FL properties of the host. The invention dopes POMs in CeF₃In (1) causing CeF₃Lattice defects are generated, the photocatalytic performance of the material is enhanced, and the CeF is realized₃Nano meterThe controllability adjustment of the fluorescence property (FL) of the crystal generates blue shift and red shift, and the dual controllability adjustment of the morphology and the performance of the crystal is completed in the nanometer material. The preparation method has wide application prospect in the aspect of morphological performance control in material science, and the prepared nano material has potential application value in simple biological imaging, wastewater organic matter degradation and fluorescence chemical sensors.

3) The invention adopts PVP as a reaction medium and synthesizes POMs/CeF with higher crystallinity at low temperature₃A nanomaterial powder. The preparation method has the advantages of simple operation, easy repetition, cheap and easily obtained raw materials, low sintering temperature and the like. The material has high catalytic efficiency and repeated utilization rate in photocatalytic degradation, and has less resource waste and additional pollution.

Drawings

FIG. 1 is a PMo prepared in example 1₁₂/CeF₃SiW prepared in example 2₁₂/CeF₃PW prepared in example 3₁₂/CeF₃And CeF₃A performance test chart;

FIG. 2 is a PMo prepared in example 1₁₂/CeF₃SEM and EDX images of the nanoflower crystals;

FIG. 3 is SiW prepared in example 2₁₂/CeF₃Nanoplates and PW prepared in example 3₁₂/CeF₃SEM image of nanospheres;

FIG. 4 is a PMo graph using different doping levels in examples 5 and 7₁₂ / CeF₃SEM picture of (1);

FIG. 5 is a graph of different reaction temperature vs. PMo for examples 6, 4, 1 and 16₁₂/CeF₃The effect of formation;

FIG. 6 is the reaction time vs. PMo for examples 1, 8-15₁₂/CeF₃The effect of formation;

FIG. 7 is PMo in example 1₁₂/CeF₃SEM images of nanocrystal stability in water studies;

FIG. 8 is PMo in example 1₁₂/CeF₃"ShiSiW in example 2₁₂/CeF₃And PW in example 3₁₂/CeF₃An emission spectrum of the nanocrystal;

FIG. 9 is a PMo prepared in examples 1-3₁₂/CeF₃、SiW₁₂/CeF₃And PW₁₂/CeF₃As a relational graph of degradation time-degradation efficiency of the photocatalyst on rhodamine B;

FIG. 10 is a PMo prepared in examples 1-3₁₂/CeF₃、SiW₁₂/CeF₃And PW₁₂/CeF₃And (3) a test result chart of the cyclic utilization times of the photocatalyst cyclic reaction.

Detailed Description

The following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation processes are given, but the scope of the invention is not limited by the following examples.

A hydrothermal reaction kettle with the volume of 25 ml is adopted, the material of the hydrothermal reaction kettle is 316 type stainless steel, and the wall thickness is 7 mm; the inside lining is polytetrafluoroethylene, and inside lining thickness is 5 mm.

Example 1

Polyoxometallate-doped solid luminescent nano material PMo₁₂ / CeF₃The preparation method comprises the following steps:

1) 0.130 g of Ce (NO)₃)₃·6H₂O (0.299 mmol), PVP (polyvinylpyrrolidone) 0.050 g, and KBF 0.151 g₄(1.199 mmoL) and 0.050 g α -PMo₁₂(0.026 mmoL) is placed in a 25 mL reaction kettle, 18.5 mL distilled water is added, and after vigorous stirring is carried out for 30 min at normal temperature, a mixed solution is obtained;

2) transferring the reaction kettle into an oven, increasing the temperature to 140 ℃ at the rate of 1.2 ℃ per minute, increasing the pressure in the reaction kettle to 149 KPa at the rate of 26 KPa/h, keeping the temperature and the pressure at constant pressure for 12 h, naturally and slowly cooling the high-pressure reaction kettle to room temperature to obtain yellow precipitate, centrifugally separating the precipitate at the rate of 2500 r/pm for 10 min, and then using 2 mL of mixed solution (V) of deionized water and ethanol_H2O:V_CH3CH2OH= 1: 1) washed three times and then dried at 60 ℃ overnightFinally obtaining PMo₁₂ / CeF₃Flower-like nanoparticles.

Example 2

Polyoxometallate-doped solid luminescent nano material SiW₁₂ / CeF₃The preparation method comprises the following steps:

1) 0.130 g of Ce (NO)₃)₃·6H₂O (0.299 mmol), PVP 0.050 g, KBF 0.151 g₄(1.199 mmoL) and 0.015 g of alpha-SiW₁₂(0.005 mmoL) is placed in a 25 mL reaction kettle, 19 mL distilled water is added, and after vigorous stirring is carried out for 35 min at normal temperature, a mixed solution is obtained;

2) transferring the reaction kettle into an oven, increasing the temperature to 180 ℃ at the rate of 1.6 ℃ per minute, increasing the pressure in the reaction kettle to 163 KPa at the rate of 35 KPa/h, keeping the temperature and the pressure at constant pressure for 12 h, naturally and slowly cooling the high-pressure reaction kettle to room temperature to obtain yellow precipitate, centrifugally separating the precipitate at the rate of 2500 r/pm for 5 min to obtain precipitate, and then using 3 mL of mixed solution (V) of deionized water and ethanol_H2O:V_CH3CH2OH= 2: 1) washed three times and then dried at 70 ℃ overnight to obtain SiW₁₂ / CeF₃Nanosheets.

Example 3

Polyoxometallate-doped solid-state luminescent nano material PW₁₂ / CeF₃The preparation method comprises the following steps:

1) 0.130 g of Ce (NO)₃)₃·6H₂O (0.299 mmol), PVP 0.050 g, KBF 0.151 g₄(1.199 mmoL) and 0.040 g of alpha-PW₁₂(0.014 mmoL) is placed in a 25 mL reaction kettle, 20 mL distilled water is added, and after vigorous stirring is carried out for 25 min at normal temperature, a mixed solution is obtained;

2) transferring the reaction kettle into an oven, increasing the temperature to 120 ℃ at the rate of 1 ℃ per minute, increasing the pressure in the reaction kettle to 141 KPa at the rate of 21 KPa/h, keeping the temperature and the pressure at constant pressure for 12 h, naturally and slowly cooling the high-pressure reaction kettle to room temperature to obtain yellow precipitate, centrifugally separating the precipitate at the rate of 2500 r/pm for 10 min to obtain precipitate, and then adding 5 mL of mixed solution (V) of deionized water and ethanol_H2O:V_CH3CH2OH= 3: 1) washed three times and then dried at 50 ℃ overnight to finally obtain PW₁₂ / CeF₃Nanospheres.

Example 4

1) 0.130 g of Ce (NO)₃)₃·6H₂O (0.299 mmol), PVP 0.050 g, KBF 0.151 g₄(1.199 mmoL) and 0.050 g α -PMo₁₂(0.026 mmoL) is placed in a 50 mL reaction kettle, 17 mL distilled water is added, and after vigorous stirring is carried out for 40 min at normal temperature, a mixed solution is obtained;

2) transferring the reaction kettle into an oven, increasing the temperature to 80 ℃ at the rate of 0.6 ℃ per minute, increasing the pressure in the reaction kettle to 127 KPa at the rate of 13 KPa/h, keeping the temperature and the pressure at constant pressure for 12 h, naturally and slowly cooling the high-pressure reaction kettle to room temperature to obtain yellow precipitate, centrifugally separating the precipitate at the rate of 2500 r/pm for 5 min to obtain precipitate, and then using 2 mL of mixed solution (V) of deionized water and ethanol_H2O:V_CH3CH2OH= 1: 1) washed three times and then dried at 55 ℃ overnight to give PMo₁₂ / CeF₃Flower-like nanoparticles.

Example 5

1) 0.130 g of Ce (NO)₃)₃·6H₂O (0.299 mmol), PVP 0.050 g, KBF 0.151 g₄(1.199 mmoL) and 0.050 g α -PMo₁₂(0.026 mmoL) is placed in a 50 mL reaction kettle, 17.5 mL distilled water is added, and after 20 min of vigorous stirring is carried out at normal temperature, a mixed solution is obtained;

2) transferring the reaction kettle into an oven, increasing the temperature to 40 ℃ at a rate of 0.15 ℃ per minute, increasing the pressure in the reaction kettle to 113 KPa at a rate of 3.6 KPa/h, keeping the constant temperature and the constant pressure for 12 h, naturally and slowly cooling the high-pressure reaction kettle to room temperature to obtain yellow precipitate, and adding 2500 r/p of the precipitate to obtain a solutionCentrifuging at m speed for 5 min to obtain precipitate, and adding 4 mL of mixed solution of deionized water and ethanol (V)_H2O:V_CH3CH2OH= 3: 1) washed three times and then dried at 65 ℃ overnight to give PMo₁₂ / CeF₃Flower-like nanoparticles.

Example 6

This example differs from example 1 in that the temperature in step 2) was raised to 40 ℃.

Example 7

This example differs from example 1 in that the α -PMo in step 1)₁₂The dosage of the medicine is 0.016 g (0.008 mmoL); in step 2), the temperature is raised to 40 ℃.

Example 8

The difference between this example and example 1 is that the heating time in step 2) is 0.5 h.

Example 9

The difference between this example and example 1 is that the heating time in step 2) is 1 h.

Example 10

The difference between this example and example 1 is that the heating time in step 2) is 2 h.

Example 11

The difference between this example and example 1 is that the heating time in step 2) is 4 h.

Example 12

The difference between this example and example 1 is that the heating time in step 2) is 6 h.

Example 13

The difference between this example and example 1 is that the heating time in step 2) is 8 h.

Example 14

The difference between this example and example 1 is that the heating time in step 2) is 14 h.

Example 15

The difference between this example and example 1 is that the heating time in step 2) is 24 h.

Example 16

This example differs from example 1 in that the temperature in step 2) is raised to 180 ℃.

The following samples prepared in examples 1-16 and CeF₃Detection and analysis were performed:

composition and phase purity of the sample

FIG. 1a is CeF₃PMo in example 1₁₂/CeF₃SiW in example 2₁₂/CeF₃PW in example 3₁₂/CeF₃The XRD pattern of (1) shows that there is almost no hetero-peak in XRD of the obtained sample, and it can be seen from the pattern that CeF is₃A hexagonal phase (pdf No. 891933) and good crystallinity, 2 θ appearing at 26 °, 27 °, 30 °, 47 °, 55 ° correspond to the (512), (611), (612), (611) and (550) crystal planes, respectively. It should be noted that the POMs were not detectable in this test, probably because the content of POMs in each sample was lower than that of CeF₃Thus, the diffraction peaks of POMs are relatively weak in intensity and can be overlapped and covered.

FIG. 1b shows PMo in example 1₁₂/CeF₃SiW in example 2₁₂/CeF₃PW in example 3₁₂/CeF₃Characteristic vibration peak of infrared at PMo₁₂/CeF₃In the sample, 1061 cm appeared^‒1 (P‒O)，957 cm^‒1(Mo ‒ O) and 876 cm^‒1(Mo ‒ O ‒ Mo) characteristic peak, proving alpha-PMo₁₂Presence of (a); in addition, in SiW₁₂/CeF₃In the spectrum, absorption peaks appear at 972, 924 and 885 cm^‒1Respectively belong to v (W ‒ O)_d)，ν(Si‒O_a) And v (W ‒ O)_b) Characteristic peak, proving alpha-SiW₁₂Are present. Finally, the peaks appear at 1081, 980 and 897 cm^‒1Proves alpha-PW₁₂Is also successfully doped with CeF₃In (1). FIGS. 1c and 1d show PMo in example 1₁₂/CeF₃The XPS spectrum of the nano flower-shaped crystal proves that the valence states of Mo and Ce are +6 and +3 respectively.

FIG. 2 is PMo in example 1₁₂/CeF₃SEM and EDX images of the nanoflower crystals. FIG. 2(a, b, c) isFlower-like PMo₁₂/CeF₃Nanocrystalline SEM images. The sample is uniformly monodisperse, and the yield is greater than or equal to 99.8% from the morphology. From the statistical 50 particles, flower-like PMo₁₂/CeF₃The average diameter of the nanocrystals is about 630 nm, and the distribution is narrow. Flower-shaped PMo in the figure₁₂/CeF₃The size of the nanocrystals is 645 nm and, under high resolution observation, it is constituted by thin platelets with a thickness of about 22 nm (see fig. 2 c), flower-like morphology being a common structure in nanomaterials, in particular in the field of the study of transition metal oxides, however, with rare earth fluorides (in particular CeF @)₃) The underlying flower-like structures have so far been rarely reported, especially in the presence of POMs. FIG. 2d is PMo of example 1₁₂/CeF₃EDX map of flower-like nanocrystals, including mapping map of corresponding elements. The sample is characterized by using a silicon wafer as a substrate, and the analysis result proves that the components P, Mo, O, Ce and F exist, and meanwhile, the elements of Mo and Ce are mapped and uniformly distributed in the nano composite material.

FIG. 3 is SiW in example 2₁₂/CeF₃Nanosheets (as in figures 3a, 3 b) and PW in example 3₁₂/CeF₃SEM images of nanospheres (see fig. 3c, 3 d). SiW in example 2₁₂/CeF₃Nanosheets and CeF₃The nanostructure is similar, except that the structure is composed of disk-shaped particles, similar to a regular hexagonal CeF₃There are great differences in nanostructures. SiW₁₂/CeF₃The size of the nanosheets was about 446 nm and the thickness was about 177 nm (as in fig. 3 b). FIGS. 3c and 3d are PW₁₂/CeF₃SEM image of nanocrystal, PW₁₂/CeF₃Spherical, with a size of about 568 nm (FIG. 3 d).

FIG. 4 is a PMo graph using different doping levels in examples 5 and 7₁₂ / CeF₃SEM image of (d). When alpha-PMo was added as shown in example 7₁₂When the amount is 0.016 g (0.008 mmoL) to the mixture, PMo in the form of tablet is obtained₁₂ / CeF₃Nanoplatelets (fig. 4a, 4 b). However, with regular hexagonal CeF₃In contrast, its edges and cornersBecome less apparent, it is known that alpha-PMo₁₂For CeF₃The polymerization of the nanocrystals has a significant impact. When alpha-PMo is used as in example 5₁₂When the amount reached 0.100 g (0.053 mmol), no separation of crystals was obtained in this reaction system (as shown in FIG. 4c, FIG. 4 d).

FIG. 5 is a graph of different reaction temperature vs. PMo for examples 6, 4, 1 and 16₁₂/CeF₃Influence of formation, resulting PMo₁₂/CeF₃SEM image of (d). As shown in example 6, at 40 ℃, a smaller amount of flower-like particles were obtained, and amorphous lumps were observed, with the rest of the particles being irregularly shaped (fig. 5 a). With increasing temperature to 80 ℃ as in example 4, flower-like PMo₁₂/CeF₃The size distribution of the nanocrystals was broad and the number was gradually increased (fig. 5 b). When the temperature was further raised to 140 ℃ as in example 1, flower-like PMo₁₂/CeF₃The shape of the nanocrystals became uniform, and most flower-like PMo₁₂/CeF₃The structure of the nanocrystals was not sufficiently complete (fig. 5 c). When the temperature reached 180 ℃, as in example 16, a large amount of debris appeared, indicating that the high temperature broke the uniform structure (fig. 5 d).

FIG. 6 is the reaction time vs. PMo for examples 1, 8-15₁₂/CeF₃The impact of the formation. Flower-like PMo with different reaction times₁₂/CeF₃The nanocrystal growth was studied. At a reaction time of 0.5 h in example 8 and 1h in example 9, PMo was formed₁₂/CeF₃The particles are shown in fig. 6a and 6b, respectively, and they have almost no flower shape, but it can be clearly observed that the particles are composed of nanosheets. As can be seen from FIGS. 6c to 6i, the SEM images show PMo₁₂/CeF₃The reaction time of the nanocrystals was 2 h, 4 h, 6 h, 8 h, 12 h, 14 h and 24 h (corresponding to examples 10-13, 1 and 14-15). It can be seen that PMo increases with reaction time₁₂/CeF₃The granules take on a flower shape.

And (3) sample stability research: PMo prepared in example 1₁₂/CeF₃After 12 h, 24 h, 36 h and 48 h (corresponding to fig. 7a, 7b, 7c and 7d, respectively) in water, as shown in fig. 7. FIG. 7 is a study of flower-like PMo₁₂/CeF₃SEM images of nanocrystals stability in water were explored. As can be seen, this flower-like PMo₁₂/CeF₃The stability of the nano crystal in the water solution is better. The uniformly monodisperse flower shape remained essentially unchanged within 48 h. Thus, this stability imparts flower-like PMo₁₂/CeF₃The practical application value of the nano crystal in a solution system.

(II) photoluminescence property

FIG. 8 is PMo in example 1₁₂/CeF₃SiW in example 2₁₂/CeF₃And PW in example 3₁₂/CeF₃Emission spectrum of the nanocrystals. CeF at 324 nm under 250 nm excitation light₃Show strong emission peaks, which are comparable to the previous literature Liu Y, ZHao Y, Luo H, et al₃nanocrystals and characterization[J]Journal of Nanoparticle Research, 2011, 13(5): 2041-. Under the same conditions, PMo₁₂/CeF₃、SiW₁₂/CeF₃And PW₁₂/CeF₃Nanocrystals also showed significant emission bands at 305 nm, 333 nm and 338 nm, respectively. And CeF₃Peak emission ratio, PMo₁₂/CeF₃Blue-shifted by 19 nm. In contrast, SiW₁₂/CeF₃And PW₁₂/CeF₃Red-shifted by 9 nm and 14 nm, respectively.

(III) photocatalytic Properties

PMo from example 1₁₂/CeF₃SiW in example 2₁₂/CeF₃And PW in example 3₁₂/CeF₃Experiment as photocatalyst for catalytic degradation of rhodamine B:

0.12 g of photocatalyst (PMo) is added under the irradiation of a 500W mercury lamp with an ultraviolet invisible light source₁₂/CeF₃，SiW₁₂/CeF₃Or PW₁₂/CeF₃) To 40 mL of rhodamine B solution (wherein the concentration of the rhodamine B is 10 mg/L), obtainingAnd (5) timing the final solution, sampling every 1h after the illumination time, and performing ultraviolet test analysis. FIG. 9 is PMo in example 1₁₂/CeF₃SiW in example 2₁₂/CeF₃And PW in example 3₁₂/CeF₃And (3) respectively degrading the dye (rhodamine B). The results show that the three catalysts PMo after 6 h of light irradiation₁₂/CeF₃，SiW₁₂/CeF₃And PW₁₂/CeF₃The degradation rates of (A) were 87%, 98% and 58.5%, respectively. The three photocatalysts have good application prospects in degrading rhodamine B in industrial wastewater treatment. FIG. 10 is a graph showing the results of the test of the number of catalyst cycles, in which the degradation rate is plotted on the Y-axis and the number of catalyst cycles is plotted on the X-axis. As can be seen, the catalyst (PMo) used in four cycles₁₂/CeF₃、SiW₁₂/CeF₃And PW₁₂/CeF₃) Still maintaining the catalytic activity. This shows that the three composite catalysts prepared in examples 1 to 3 have high activity. Meanwhile, the prepared catalyst with high catalytic efficiency can have good recycling value in the field of industrial wastewater treatment.

In conclusion, the solid luminescent nano material PMo prepared by the invention₁₂/CeF₃、SiW₁₂/CeF₃Or PW₁₂/CeF₃Three nano-crystals PMo with luminescent property and controllable appearance₁₂/CeF₃、SiW₁₂/CeF₃Or PW₁₂/CeF₃Respectively has structures in the shapes of nanometer flowers, nanometer sheets and nanometer spheres. In addition, the PL properties of these nanocomposites are also very different. Doping different types of POM, POM/CeF₃The composite material has different emission peaks, and the method disclosed by the invention can be used for adjusting the performance of PL by doping different types of POMs, and meanwhile, the composite nano material has very high photocatalytic performance due to very high specific surface area, so that the degradation rate of rhodamine B can be improved. Therefore, the nano material of the invention can degrade pollutants in waste water, and can be used as a fluorescence chemical sensor and a photoelectric sensor in the aspects of morphology and performance control of material scienceThe device and other fields have wide application prospects.

The foregoing examples are illustrative of embodiments of the present invention, and although the present invention has been illustrated and described with reference to specific examples, it should be appreciated that embodiments of the present invention are not limited by the examples, and that various changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims

1. A preparation method of polyoxometallate doped solid-state luminescent nano material is characterized by comprising the following steps:

1) collecting soluble cerium salt, polyvinylpyrrolidone, and KBF₄And POMs are uniformly dissolved in water to obtain a mixed solution;

2) reacting the mixed solution obtained in the step 1) at the temperature of 40-180 ℃ and the pressure of 110-170 KPa for 6-24 h at constant temperature and constant pressure, cooling to room temperature, carrying out solid-liquid separation, washing and drying to obtain the solid luminescent nano material POM/CeF₃；

The mass ratio of the soluble cerium salt to the POMs in the step 1) is (1-9): 1;

the soluble cerium salt is cerium nitrate, cerium sulfate or cerium chloride;

the POMs are Na₃PMo₁₂O₄₀、K₄SiW₁₂O₄₀、Na₃PW₁₂O₄₀One or more of them.

2. The method of claim 1, wherein the soluble cerium salt and KBF in step 1) are mixed₄The mass ratio of (1): (1-3).

3. The preparation method as claimed in claim 1, wherein, during the reaction in step 2), the temperature of the mixed solution is raised to 40-180 ℃ at a rate of 0.1-2 ℃/min, the pressure is raised to 110-170 KPa at a rate of 3-40 KPa/h, and the reaction is carried out at constant temperature and pressure for 6-24 h.

4. The preparation method of claim 1, wherein in the step 2), the mixture of deionized water and ethanol is used for washing for 2-5 times, the volume of the mixture is 1-5 mL, and the volume ratio of the deionized water to the ethanol in the mixture is (1-3): 1.

5. polyoxometallate doped solid state luminescent nanomaterial prepared by the method according to any one of claims 1 to 4.

6. Use of a polyoxometalate-doped solid state luminescent nanomaterial in degrading pollutants in wastewater as claimed in claim 5 wherein the pollutant is a dye or formaldehyde.

7. The use of claim 6, wherein the dye is rhodamine B, methylene blue, alizarin Red S, gardenia yellow G, or Congo Red.