A fluorescent composite nanomaterial for detecting formaldehyde and a preparation method and application thereof

Abstract

The application discloses a fluorescent composite nanometer material for detecting formaldehyde and a preparation method and application thereof, and belongs to the technical field of formaldehyde detection. The fluorescent composite nanometer material is Cs2NaYF6@CDs@SiO2@MIP, has a multilayer core-shell structure, and comprises, from inside to outside, a core layer, an up-conversion luminescent nanoparticle Cs2NaYF6:Yb 3+ ,Tm 3+ , a middle modification layer, CDs loaded on the surface of the core layer, a protection and function interval layer, a SiO2 shell layer, and a specific recognition layer, an aldehyde molecular imprinting polymer shell layer, wherein the MIP layer has imprinting cavities complementary to formaldehyde molecules and can realize specific recognition and capture of formaldehyde. The fluorescent composite luminescent nanometer material prepared by the application can realize specific detection of formaldehyde, has high measurement stability, and has a short response time.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde detection technology, specifically relating to a fluorescent composite nanomaterial for formaldehyde detection, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Formaldehyde is a colorless gas with a strong, pungent odor. It is highly volatile at room temperature and pressure, readily soluble in water, alcohols, and ethers. Its aqueous solution is commonly known as formalin, and in industrial production, it can be formulated into liquid products of varying concentrations as needed. As an important organic chemical raw material, formaldehyde is widely used in building materials, furniture manufacturing, textile printing and dyeing, and pharmaceuticals. Formaldehyde can enter the human body through indoor air volatilization, industrial wastewater discharge, illegal food additives, and release from building materials. Long-term exposure or ingestion can seriously harm the respiratory, nervous, and immune systems, and may even induce cancer. Therefore, developing simple, rapid, and sensitive detection methods to strengthen the monitoring of formaldehyde is essential.

[0004] Currently, methods for formaldehyde detection mainly include high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and spectrophotometry. While these methods can achieve accurate formaldehyde detection, they generally rely on expensive, sophisticated instruments, have complex operating procedures, and long analysis cycles. For example, HPLC requires multiple pretreatment steps such as derivatization and hexane extraction before detection; the phenol reagent method requires sampling and subsequent laboratory testing for color development and absorbance measurement, neither of which meets the needs of rapid on-site detection. Electrochemical detection methods have also been reported, which involve an electrochemical reaction between formaldehyde and a sensitive material modified on the electrode surface, establishing a concentration standard curve based on changes in redox current for quantitative detection. However, electrochemical detection methods have significant limitations: although the response speed is fast, the sensor stability is extremely poor, and the electrode catalyst is prone to aging, requiring frequent calibration and maintenance. Fluorescence detection, with its advantages of fast response, strong environmental tolerance, and portable equipment, has become an ideal choice for on-site detection. However, there is a significant technological gap in this field: most of the reported fluorescent materials are based on a single matrix, which is susceptible to interference from other volatile organic compounds in complex environments, and their long-term storage stability is insufficient. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a fluorescent composite nanomaterial for formaldehyde detection, its preparation method, and its application. The fluorescent composite nanomaterial for formaldehyde detection provided by the present invention has the advantage of strong fluorescence emission, enabling accurate measurement of formaldehyde in the range of 0~15 mg / L, with high measurement accuracy and strong specificity.

[0006] This invention discloses a fluorescent composite nanomaterial for formaldehyde detection and its preparation method. The preparation method provided by this invention is as follows: preparing Yb-doped nanomaterials. 3+ and Tm 3+ Cs2NaYF6 nanoparticles (Cs2NaYF6:Yb 3+ ,Tm 3+ ); doping Yb 3+ and Tm 3+ Cs₂NaYF₆ nanoparticles, CDs (carbon dots), surfactant (hexadecyltrimethylammonium bromide), formaldehyde solution, alkali (sodium hydroxide), silane coupling agent (3-aminopropyltriethoxysilane), silicate ester (tetraethyl silicate), and ethyl acetate were mixed in a solvent, stirred, and heated to react. The resulting solution was then added to a methanol / acetic acid mixture, stirred for a set time, centrifuged, and washed to obtain the final product. The fluorescent composite luminescent nanomaterial prepared by this invention can achieve specific detection of formaldehyde in the range of 0-15 mg / L, exhibiting high measurement stability, short response time, and the ability to perform on-site detection using a 365 nm excitation light source. This method is convenient, fast, and cost-effective. Furthermore, the synergistic effect of the formaldehyde molecularly imprinted polymer (MIP) shell and the SiO₂ shell significantly improves detection sensitivity and anti-interference ability.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a fluorescent composite nanomaterial for detecting formaldehyde. The fluorescent composite nanomaterial is Cs2NaYF6@CDs@SiO2@MIP, and has a multi-layered core-shell structure, comprising, from the inside out:

[0009] Core layer: Upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ ;

[0010] Intermediate modification layer: CDs loaded on the surface of the core layer;

[0011] Protective and functional spacer layer: an outer silica shell;

[0012] Specific recognition layer: The outermost formaldehyde molecularly imprinted polymer (MIP) shell has imprinted holes that are complementary to formaldehyde molecules, enabling specific recognition and capture of formaldehyde.

[0013] The surface of the fluorescent composite nanomaterial has a porous structure of specific shape and size.

[0014] Secondly, the present invention provides a method for preparing the above-mentioned fluorescent composite nanomaterial for formaldehyde detection, comprising the following steps:

[0015] S1. Preparation of upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ ;

[0016] S2. Upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ CDs, surfactants, formaldehyde solution, alkali, silane coupling agent, silicon source, and ethyl acetate are mixed in a solvent, stirred and heated to react, and then the reacted solution is added to a methanol / acetic acid mixture, stirred, centrifuged, and washed to obtain the final product.

[0017] Thirdly, the present invention provides the application of the above-mentioned fluorescent composite nanomaterials for formaldehyde detection in formaldehyde detection.

[0018] Fourthly, the present invention provides a method for formaldehyde detection, which uses the above-mentioned fluorescent composite nanomaterial for formaldehyde detection. The specific steps are as follows: the fluorescent composite nanomaterial for formaldehyde detection is placed in a formaldehyde-containing environment, and an excitation light source with a wavelength of 360~370nm is used as the excitation light to detect the emission spectrum.

[0019] One or more of the above technical solutions have the following advantages or beneficial effects:

[0020] This invention first utilizes a solvothermal method to prepare doped Yb 3+ and Tm 3+ Cs2NaYF6 nanoparticles (Cs2NaYF6:Yb 3+ ,Tm 3+ The core consists of CDs loaded onto its surface, and SiO2 is then coated onto its outer layer as a shell, forming the core-shell structure intermediate material Cs2NaYF6@CDs@SiO2. Finally, using molecular imprinting technology with formaldehyde as a template molecule, a MIP layer is synthesized on the surface of this intermediate material, thus forming the final target fluorescent composite nanomaterial Cs2NaYF6@CDs@SiO2@MIP.

[0021] The method of this invention provides a fluorescent composite nanomaterial for detecting formaldehyde. This material is highly stable and its properties and functions do not change during long-term storage.

[0022] The fluorescent composite luminescent nanomaterials prepared using this method, when mixed with formaldehyde at a certain concentration gradient, exhibit a linear change in the peak value of the emitted spectrum as the formaldehyde concentration increases. This method demonstrates high measurement accuracy and a wide measurement range, capable of accurate measurement within the range of 20–600 μmol / L. Furthermore, it exhibits good selectivity, enabling specific detection of formaldehyde. This invention utilizes a fluorescence method for determination, resulting in high measurement stability, short response time, and the ability to perform on-site detection, offering convenience, speed, and low cost. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] Figure 1 Cs2NaYF6:Yb in Embodiment 1 of the present invention 3+ / Tm 3+ Transmission electron microscope (TEM) image of nanoparticles, scale bar 100 nm;

[0025] Figure 2 It is the Cs2NaYF6:Yb prepared in Example 1 of this invention. 3+ / Tm 3+ X-ray diffraction (XRD) pattern of nanoparticles;

[0026] Figure 3 It is Cs2NaYF6 and Cs2NaYF6:Yb 3+ / Tm 3+ The emission spectrum;

[0027] Figure 4 These are TEM images of the CDs prepared in Example 2 of this invention;

[0028] Figure 5 This is the emission spectrum of the CDs prepared in Example 2 of this invention;

[0029] Figure 6 This is a scanning electron microscope (SEM) image of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial prepared in Example 3 of this invention;

[0030] Figure 7 The image shows a transmission electron microscope (TEM) image of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial in Example 3 of this invention, with a scale bar of 100 nm.

[0031] Figure 8This is the Fourier transform infrared (FTIR) spectrum of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial prepared in Example 3 of this invention;

[0032] Figure 9 This is the emission spectrum of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial prepared in Example 3 of this invention;

[0033] Figure 10 This is the Fourier transform infrared (FTIR) spectrum of the Cs2NaYF6@CDs@SiO2@NIP composite nanomaterial prepared in Comparative Example 4 of this invention;

[0034] Figure 11 This is a graph showing the relationship between the emission intensity of the fluorescent composite nanomaterial Cs2NaYF6@CDs@SiO2@MIP prepared in Example 3 of this invention at 422 nm and the formaldehyde concentration.

[0035] Figure 12 This is a graph showing the relationship between the emission intensity of the fluorescent composite nanomaterial Cs2NaYF6@CDs@SiO2@NIP prepared in Comparative Example 4 of this invention at 422 nm and the formaldehyde concentration.

[0036] Figure 13 This is a graph showing the specificity test results of the fluorescent composite nanomaterial prepared in Example 3 of this invention for formaldehyde. Detailed Implementation

[0037] In one embodiment, the present invention provides a fluorescent composite nanomaterial for detecting formaldehyde, wherein the fluorescent composite nanomaterial is Cs2NaYF6@CDs@SiO2@MIP, having a multi-layer core-shell structure, comprising, from the inside out: a core layer: upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ Intermediate modification layer: CDs loaded on the surface of the core layer; Protective and functional spacer layer: The outermost silica shell; Specific recognition layer: The outermost formaldehyde molecularly imprinted polymer (MIP) shell.

[0038] It should be noted that in this invention, formaldehyde solution is added during the preparation process to achieve the preparation of the outermost formaldehyde molecularly imprinted polymer (MIP) shell. If the addition of formaldehyde solution is omitted, a NIP shell is formed. NIP is an abbreviation for Non-Imprinted Polymer, and it is a contrasting concept with MIP (Molecularly Imprinted Polymer).

[0039] Upconversion luminescent nanoparticles Cs2NaYF6:Yb3+ ,Tm 3+ The Y, Yb, and Tm elements are all selected from acetates. The molar ratio of the acetate containing Y, the acetate containing Yb, and the acetate containing Tm is (54~65):(34~45):1, preferably (58~60):(39~41):1. Specifically, the molar ratio of Y(Ac)3·6H2O, Yb(Ac)3·6H2O, and Tm(Ac)3·6H2O is (58~60):(39~41):1, preferably 59:40:1.

[0040] Upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ The mass ratio of CDs to CDs is (34~68):1, preferably (40~53):1, and more preferably (43~50):1.

[0041] The fluorescent composite nanomaterial has a porous structure of specific shape and size on its surface. These pores are left after the template formaldehyde molecules are eluted, and are cavities that are complementary to the shape, size, and functional groups of the formaldehyde molecules.

[0042] The CDs loading and SiO2 shell thickness are not specifically limited. The adjustability of the composite structure provided by this invention (such as CDs loading and SiO2 shell thickness) enables it to adapt to the formaldehyde detection needs in different complex environments, thus broadening the practical application scenarios.

[0043] In another embodiment, the present invention provides a method for preparing the above-mentioned fluorescent composite nanomaterial for formaldehyde detection, comprising the following steps:

[0044] S1. Preparation of upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ ;

[0045] S2. Upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ CDs, surfactant, formaldehyde solution, alkali, silane coupling agent, silicon source, and ethyl acetate are mixed in a solvent, stirred and heated to react. Then, the reacted solution is added to a methanol / acetic acid mixture, stirred, centrifuged, and washed to obtain Cs2NaYF6@CDs@SiO2@MIP.

[0046] Surfactants include hexadecyltrimethylammonium bromide (CTAB).

[0047] Bases include sodium hydroxide. The concentration of bases is 1~3 mol / L.

[0048] Silane coupling agents include 3-aminopropyltriethoxysilane (APTES).

[0049] The silicon source includes silicate esters, including tetraethyl silicate (TEOS).

[0050] Ethyl acetate is a moderately polar organic solvent, slightly soluble in water. The addition of ethyl acetate disrupts the micellar equilibrium and emulsion stability of CTAB (i.e., demulsification). It alters the polar environment of the solvent, causing changes in the solubility of CTAB in water or its critical micelle concentration, leading to decreased colloidal stability. Finally, the nanoparticles flocculate, transforming the homogeneous, translucent solution into a turbid suspension, allowing for easy collection of the product with only very low centrifugation speeds.

[0051] In this invention, the thickness of SiO2 can be controlled by adjusting the amounts of APTES and TEOS, while keeping the amounts of other components constant.

[0052] In this invention, preferably, the doped Yb 3+ and Tm 3+ Cs2NaYF6 nanoparticles (i.e., upconversion luminescent nanoparticles Cs2NaYF6:Yb) 3+ ,Tm 3+ The proportions of the following components are as follows: CDs, hexadecyltrimethylammonium bromide, formaldehyde solution, sodium hydroxide, 3-aminopropyltriethoxysilane, tetraethyl silicate, and ethyl acetate are (115~116mg):(2~3mg):50mg:20mg:12mg:(18~20mg):(138~140mg):(445~455mg). Water is chosen as the solvent. Water acts as a good solvent to fully dissolve and uniformly mix the reactants, thus promoting the reaction. Formaldehyde is a water-soluble organic compound, and water acts as a good organic solvent to ensure uniform dispersion, allowing for better contact and interaction with other substances.

[0053] In step S2, the specific preparation method includes the following steps:

[0054] (1) Yb doping 3+ and Tm 3+ Cs2NaYF6 nanoparticles were dissolved in chloroform solution to obtain Cs2NaYF6:Yb 3+ / Tm 3+ A chloroform dispersion was mixed with a surfactant and a CDs solution, ultrasonicated, and heated to remove the chloroform, yielding a clear and transparent aqueous solution of UCNPs, which was then stabilized at a set temperature.

[0055] (2) Add formaldehyde solution, alkali, silane coupling agent, silicon source and ethyl acetate to the stabilized UCNPs aqueous solution, and heat to react;

[0056] (3) Add methanol / acetic acid mixed solution to the solution after reaction in step (2), stir, centrifuge and wash to obtain Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterial.

[0057] The Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterials have spherical nanoparticles with a size of approximately 30~100 nm, preferably 45~50 nm.

[0058] Cs2NaYF6:Yb 3+ / Tm 3+ The ratio of chloroform dispersion, CDs solution, surfactant, formaldehyde solution, alkali, silane coupling agent, silicon source, and ethyl acetate is (5~10mL):(0.5~2mL):(40~60mg):(40~60μL):(100~200μL):(10~30μL):(100~200μL):(0.1~1mL), preferably (5~7mL):(0.8~1.2mL):(45~55mg):(45~65μL):(140~160μL):(15~25μL):(140~160μL):(0.4~0.6mL).

[0059] The CDs solution is a mixture of CDs and water, wherein the volume ratio of the two is 1:(60~65), preferably 1:64.

[0060] Cs2NaYF6:Yb 3+ / Tm 3+ The concentration of the chloroform dispersion is 0.01~0.1 mmol / mL, preferably 0.03~0.04 mmol / mL, and most preferably 0.033 mmol / mL.

[0061] The concentration of the formaldehyde solution is 37% to 40% of the commercially available formaldehyde concentration.

[0062] The volume ratio of ethyl acetate and methanol / acetic acid mixed solution is (0.1~1mL):(10~30mL), preferably (0.4~0.6mL):(15~25mL).

[0063] Furthermore, in step (1), the ultrasonic treatment is performed for 10-60 min, preferably 20-40 min. The UCNPs aqueous solution is stabilized at 60-80℃ for 5-15 min, in order to allow the nanoparticle system encapsulated by CTAB micelles to reach equilibrium and stability at the reaction temperature, thereby providing a uniform reaction interface for the subsequent formation of a uniform and complete SiO2 shell.

[0064] Furthermore, in step (2), an oil bath heating method is adopted, with an oil bath at 50~80℃ for 1~5 hours, preferably at 60~75℃ for 3~5 hours.

[0065] Furthermore, in step (3), the volume ratio of methanol to acetic acid is (5~10):1, preferably 9:1. The centrifugation conditions are: centrifugation at 10000~15000 r / min for 10~30 min, preferably 10~20 min. The mixed solution of methanol and acetic acid is a template eluent, and its core function is to completely elute the formaldehyde molecules, which serve as the "mold," from the newly formed molecularly imprinted polymer, thereby leaving cavities in the MIP layer that can specifically recognize formaldehyde.

[0066] Furthermore, the Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterials were washed and dispersed in water to obtain an aqueous solution of Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterials.

[0067] In the preparation method provided by this invention, 3-aminopropyltriethoxysilane serves as a silane coupling agent. The amino groups in its molecule can interact with carboxyl groups, hydroxyl groups, and other groups that may be present on the surface of carbon dots (CDs) (such as hydrogen bonding and condensation reactions), thereby anchoring the carbon dots to the doped Yb. 3+ and Tm 3+ The surface of Cs2NaYF6 nanoparticles; simultaneously, under the alkaline environment provided by sodium hydroxide, tetraethyl silicate undergoes a hydrolysis-condensation reaction to generate SiO2, and hexadecyltrimethylammonium bromide acts as a surfactant to regulate the growth morphology of SiO2, ultimately forming Cs2NaYF6:Yb 3+ ,Tm 3+ Fluorescent composite nanomaterials with a core-shell structure of @CDs@SiO2@MIP.

[0068] Yb doping 3+ and Tm 3+ Cs2NaYF6 nanoparticles, serving as an upconversion luminescent matrix, can absorb long-wavelength excitation light and convert it into short-wavelength fluorescence, effectively avoiding interference from background fluorescence in the detection system and providing stable excitation energy for carbon dots. As the main fluorescence response unit, carbon dots have abundant functional groups (such as hydroxyl and amino groups) on their surface, which can specifically react with formaldehyde, leading to regular changes in the fluorescence signal. The outer SiO2 shell not only enhances the chemical stability and dispersibility of the material but also reduces interference from other impurities in the environment on the fluorescence signal.

[0069] When these three components are combined, a synergistic enhancement effect is achieved through energy transfer from upconversion nanoparticles, the specific fluorescence response of carbon dots, and the protective effect of the SiO2 shell. This not only improves the intensity and stability of the fluorescence signal but also enhances the ability to recognize formaldehyde through specific reactions, significantly improving detection sensitivity and selectivity. Furthermore, the tunability of this composite structure (such as carbon dot loading and SiO2 shell thickness) allows it to adapt to the formaldehyde detection needs in various complex environments, broadening its practical application scenarios.

[0070] In the preparation process of the fluorescent composite nanomaterial of the present invention, the addition of formaldehyde enables the fluorescent composite nanomaterial to generate coordination with formaldehyde (equivalent to "pores"). Subsequently, formaldehyde is removed by washing with methanol and acetic acid, thereby forming a pore structure with a specific shape and size on the surface of the fluorescent composite nanomaterial, so as to facilitate subsequent applications such as adsorption, separation or detection of specific substances (formaldehyde). The pores are located on the shell surface.

[0071] Yb doping 3+ and Tm 3+ The Cs2NaYF6 nanoparticles are dot-shaped with a size of 5~50nm, preferably 10~20nm.

[0072] CDs are dot-shaped nanoparticles with a size of 1~10nm, preferably 2~3nm.

[0073] The preparation method of CDs nanoparticles includes the following steps: mixing citric acid and water, then adding ethanolamine and stirring to obtain a homogeneous and clear mixed solution; subjecting the mixed solution to a solvothermal or hydrothermal reaction to obtain the final product. Further, the molar ratio of citric acid, water, and ethanolamine is (0.05~0.5mol):(10~30mL):(0.1~0.5mol), preferably (0.1~0.2mol):(15~25mL):(0.15~0.25mol), and most preferably 0.1mol:20mL:0.2mol. The solvothermal or hydrothermal reaction conditions are: holding at 150~200℃ for 2~10h, preferably at 170~190℃ for 5~7h. During the preparation of carbon dots, the stirring speed is controlled as follows: 300~400 rpm during the citric acid dissolution stage, and adjusted to 600~800 rpm after the addition of ethanolamine, with a stirring time of 15~20 min; the heating rate of the autoclave is 5~8℃ / min to ensure that the system temperature rises uniformly to 180℃.

[0074] In this invention, the doped Yb 3+ and Tm 3+ Cs2NaYF6 nanoparticles (Cs2NaYF6:Yb 3+ ,Tm 3+ The preparation method of ) is as follows:

[0075] (1) Mix yttrium salt, ytterbium salt, thulium salt, oleic acid, octadecene and oleylamine, heat under a protective gas and stir to form a light yellow transparent lanthanide-oleic acid precursor solution, and then let the solution cool naturally to room temperature;

[0076] (2) Dissolve the sodium salt and cesium salt together in an alcohol solvent, sonicate until clear, add it to the above precursor solution while stirring, heat to the set temperature and keep warm to obtain a mixed solution;

[0077] (3) In a sealed environment, the mixed solution is evacuated and kept under a vacuum for a set time, then heated and kept warm under a protective gas, and then the solution is naturally cooled to room temperature to obtain the crude product solution;

[0078] (4) The crude product solution is then post-treated to obtain the final product.

[0079] In one or more embodiments, step (4) includes the following post-processing: adding excess alcohol solvent, centrifuging, and washing repeatedly for purification. Specifically, the alcohol includes anhydrous ethanol. The centrifugation conditions are centrifugation at 8000~150000 r / min for 5~15 min. The white precipitate at the bottom (i.e., Cs2NaYF6:Yb) is collected by centrifugation. 3+ / Tm 3+ The nanoparticles were repeatedly washed with cyclohexane to remove the precipitate. Finally, the purified nanoparticles were dispersed in cyclohexane and stored in a sealed, light-protected container for later use. Nitrogen protection throughout the process prevented lanthanide ion oxidation, and the purification method of ethanol precipitation followed by cyclohexane dispersion ensured product purity. Furthermore, Yb... 3+ Tm 3+ The doping ratio meets the requirements for fluorescence properties.

[0080] In one or more embodiments, in step (1), the ratio of yttrium salt, ytterbium salt, thulium salt, oleic acid, octadecene, and oleylamine is (0.4~0.7mmol):(0.2~0.6mmol):(0.005~0.02mmol):(12~20mL):(12~20mL):(5~10mL), preferably (0.54~0.65mmol):(0.34~0.45mmol):0.01mmol:(15~17mL):(15~17mL):(7~9mL), and most preferably 0.59 mmol:0.4mmol:0.01 mmol:16mL:16mL:8mL.

[0081] The ratio of yttrium salt, cesium salt, and sodium salt is (0.4~0.7mmol):(8~12mmol):(8~12mmol), preferably (0.5~0.65mmol):(9~11mmol):(9~11mmol), more preferably (0.55~0.6mmol):(9.5~10.5mmol):(9.5~10.5mmol), and most preferably 0.59mmol:10mmol:10mmol.

[0082] Oleylamine, as an auxiliary solvent, is a crucial surfactant, morphology modifier, and reaction activator.

[0083] Yttrium salts include Y(Ac)3·4H2O. Ytterbium salts include Yb(Ac)3·4H2O. Thulium salts include Tm(Ac)3·4H2O. Sodium salts include Na(Ac)3·3H2O. Cesium salts include CsF.

[0084] The protective gas includes, but is not limited to, nitrogen. The flow rate of the protective gas is 50-100 mL / min. The heating temperature is 100-150℃, preferably 120-140℃. The stirring time is 20-60 min, preferably 30-40 min.

[0085] In one or more embodiments, in step (2), the alcohol solvent includes methanol. The ratio of sodium salt, cesium salt, and alcohol solvent is (9~11 mmol):(9~11 mmol):(5~10 mL). The dropping rate is 1~2 mL / min to avoid excessively high local concentrations. The temperature is raised to 50~100℃, preferably 60~80℃, and held for 20~60 min, preferably 20~40 min.

[0086] In one or more embodiments, in step (3), a vacuum is maintained for 10-30 minutes. The protective gas includes, but is not limited to, nitrogen. The heating temperature is 300-310°C and maintained for 1-2 hours. During heating, the stirring speed is 300-400 rpm to ensure uniform crystal growth.

[0087] In one or more embodiments, in step (4), the post-processing includes: adding excess alcohol solvent, centrifuging, and washing repeatedly for purification. Specifically, the alcohol includes ethanol. The centrifugation conditions are centrifugation at 8000~150000 r / min for 5~15 min. The white precipitate at the bottom (i.e., Cs2NaYF6:Yb) is collected by centrifugation. 3+ / Tm 3+ The nanoparticles were washed with cyclohexane (each time, the nanoparticles were ultrasonically dispersed in 15 mL of cyclohexane and then centrifuged). Finally, the purified nanoparticles were dispersed in cyclohexane, sealed and protected from light for later use.

[0088] Preferably, the doped Yb 3+ and Tm 3+ The preparation method of Cs2NaYF6 nanoparticles is as follows: First, prepare the core raw materials according to a specific ratio, wherein the molar ratio of Y(Ac)3·4H2O, Yb(Ac)3·4H2O, and Tm(Ac)3·4H2O is (58~60):(39~41):1, and CsF and Y 3+ The molar ratio of Na(Ac)·3H2O to Y is approximately 16.9:1. 3+ The molar ratio is 16.9:1, the volume ratio of oleic acid to octadecene is 1:1, and each 1 mmol of lanthanide salt corresponds to 16 mL of oleic acid, 16 mL of octadecene, and 8 mL of oleylamine.

[0089] Add a high-temperature magnetic stir bar to a three-necked flask, then add Y(Ac)3·4H2O, Yb(Ac)3·4H2O, and Tm(Ac)3·4H2O in the above-mentioned proportions, along with the corresponding amounts of oleic acid and octadecene. Purge the air with high-purity nitrogen at a flow rate of 50–100 mL / min, heat to 130°C, and stir for 30–40 min to form a light yellow, transparent lanthanide-oleic acid precursor solution. Allow the solution to cool naturally to room temperature. Weigh out the corresponding amounts of CsF and Na(Ac)3H2O. The precursor solution was dissolved in methanol and sonicated until clear. The solution was then added dropwise at a rate of 1–2 mL / min with stirring. The mixture was heated to 70 °C and held for 30 min before removing the methanol. A three-necked flask was evacuated and held for 15 min. Nitrogen gas was then introduced for protection, and the temperature was raised to 310–320 °C. The mixture was stirred and held at this temperature for 1–1.5 h. Afterward, the mixture was allowed to cool naturally to room temperature under nitrogen purging to obtain the crude product solution. Anhydrous ethanol was added to the crude product solution, and the mixture was stirred for 10 min. The white precipitate was collected by centrifugation, dispersed in cyclohexane using sonication, and washed by centrifugation. Finally, the precipitate was dispersed in cyclohexane to obtain clear and transparent Cs2NaYF6:Yb. 3+ ,Tm 3+ The nanoparticle dispersion was sealed and stored in a light-proof environment. Nitrogen protection throughout the process prevented lanthanide ion oxidation. CsF provided the fluorine source, and the purification methods of ethanol precipitation and cyclohexane dispersion ensured product purity. Furthermore, Yb... 3+ Tm 3+ The doping ratio meets the requirements for upconversion fluorescence characteristics, and the prepared nanoparticles have uniform particle size and crystal structure consistent with the standard card (PDF#20-1214).

[0090] In another specific embodiment, the present invention also provides the application of the above-mentioned fluorescent composite nanomaterials for formaldehyde detection in formaldehyde detection.

[0091] In another specific embodiment, the present invention provides a method for formaldehyde detection using the above-mentioned fluorescent composite nanomaterial for formaldehyde detection, the method being as follows: the fluorescent composite nanomaterial for formaldehyde detection is mixed with formaldehyde solutions of different concentrations, an excitation light source with a wavelength of 365nm is used as the excitation light, the emission spectrum is detected, and a standard curve is established based on the relationship between the fluorescence intensity at 422nm of the emission spectrum and the concentration.

[0092] The formaldehyde solution to be tested is then mixed with a fluorescent composite nanomaterial for formaldehyde detection. A 365nm wavelength excitation source is used as the excitation light, and the emission spectrum is detected. The concentration of the formaldehyde solution to be tested is determined based on a standard curve. The detection range of the formaldehyde solution is 0.75~15mg / L, and the power of the excitation source is 5~10W, preferably 8W.

[0093] In this invention, unless otherwise specified, all other experimental materials and instruments are conventional experimental materials in the art and can be purchased through commercial channels. This invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well-known to those skilled in the art can be used. Room temperature in the following embodiments refers to 25±3℃.

[0094] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0095] Example 1

[0096] This embodiment provides a visualization of upconversion composite nanomaterials (upconversion luminescent nanoparticles Cs2NaYF6:Yb). 3+ / Tm 3+ The preparation method of nanoparticles specifically includes the following steps:

[0097] (1) Add a high-temperature magnetic rod to a three-necked flask, add Y(Ac)3·4H2O (0.59 mmol, 59%), Yb(Ac)3·4H2O (0.4 mmol, 40%), Tm(Ac)3·4H2O (0.01 mmol, 1%), then add 16 mL of oleic acid, 16 mL of octadecene, and 8 mL of oleylamine. Then heat the solution to 120°C under nitrogen protection and stir continuously for 30-40 min until a light yellow transparent solution is formed. Then the solution is allowed to cool naturally to room temperature.

[0098] (2) Dissolve 10 mmol Na(Ac)·3H2O and 10 mmol CsF in 10 mL of methanol solution, add this solution to the above cooled solution, heat the mixed solution to 70 °C and keep it for 30 min, and completely remove methanol under magnetic stirring (to prevent residual methanol from affecting the subsequent solvothermal reaction).

[0099] (3) In a sealed three-necked flask, the above mixed solution was evacuated and kept for 20 minutes. Then, it was heated to 320°C under nitrogen protection and kept for 1 hour. During this period, the stirring rate was maintained at 300~400 rpm to ensure uniform crystal growth. The solution was then allowed to cool naturally to room temperature.

[0100] (4) Add excess ethanol (40 mL) to the solution after the reaction, centrifuge at 10000 r / min for 10 min, and collect the white precipitate at the bottom (i.e., Cs2NaYF6:Yb). 3+ / Tm 3+ (Nano particles), then add cyclohexane and ultrasonically disperse, centrifuge at 4500 r / min for 5 min, retain the precipitate and supernatant, and finally disperse the precipitate in 10 mL of cyclohexane, seal and store in the dark for later use.

[0101] Figure 1 For step (4) of this embodiment, Cs2NaYF6:Yb 3+ / Tm 3+ TEM image of nanoparticles, scale bar 100nm. The image shows that the nanoparticles are dot-shaped and 12nm in size.

[0102] Figure 2 For step (4) of this embodiment, Cs2NaYF6:Yb 3+ / Tm 3+ The X-ray diffraction (XRD) pattern of the nanomaterial is used to characterize the crystal structure and phase purity of the material, and is consistent with the standard card (PDF#20-1214).

[0103] Figure 3 For step (4) of this embodiment, Cs2NaYF6:Yb 3+ / Tm 3+ Emission spectra of nanoparticles used to characterize Yb doping. 3+ and Tm 3+ Fluorescence emission properties of post-upconversion nanoparticles. The excitation source used was 980 nm with a power of 8 W. As can be seen from the figure, Cs₂NaYF₆:Yb 3+ / Tm 3+ The emission peak of the nanoparticles is 477 nm.

[0104] Example 2

[0105] This embodiment provides a method for preparing CDs nanoparticles, specifically including the following steps:

[0106] (1) Add 0.1 mol of citric acid and 20 mL of deionized water to a beaker, turn on the magnetic stirrer (300-400 rpm), and stir until the citric acid is completely dissolved to form a transparent solution;

[0107] (2) Add 0.2 mol of ethanolamine to the above solution, adjust the stirring speed to 600~800 rpm, stir vigorously for 15~20 min, and obtain a homogeneous and clear mixed solution;

[0108] (3) Transfer the mixed solution to a 50 mL polytetrafluoroethylene-lined autoclave and seal the autoclave.

[0109] (4) Place the pressure vessel lined with the pressure vessel into an oven, set the temperature to 180℃, and keep the reaction at this temperature for 6 hours.

[0110] (5) After the reaction is complete, close the oven and let the autoclave cool naturally to room temperature. Remove the inner liner of the autoclave to obtain a reddish-brown CDs colloidal solution.

[0111] Figure 4 The image shows a TEM image of the carbon dots (CDs) in step (5) of this embodiment, used to observe the morphology and particle size of the carbon dots. The image shows that the nanoparticles are dot-shaped with a size of 2-3 nm.

[0112] Figure 5 The figure shows the emission spectrum of carbon dots (CDs) in step (5) of this embodiment, used to characterize the fluorescence emission characteristics and wavelength range of pure carbon dots. The excitation source used is 365 nm with a power of 8 W. As can be seen from the figure, the emission peak of the carbon dot particles is 474 nm.

[0113] Example 3

[0114] This embodiment provides a method for preparing the fluorescent composite nanomaterial Cs2NaYF6@CDs@SiO2@MIP for formaldehyde detection, specifically including the following steps:

[0115] (1) Take 2 ml of Cs2NaYF6:Yb from Example 1 3+ / Tm 3+ Cyclohexane solution, after precipitation and centrifugation with ethanol, was dispersed in 6 mL of chloroform to obtain 0.033 mmol / mL Cs₂NaYF₆:Yb 3+ / Tm 3+ Chloroform dispersion.

[0116] (2) Take 6 mL of Cs2NaYF6:Yb from step (1). 3+ / Tm 3+The chloroform dispersion was added to 25 ml of an aqueous solution containing 50 mg of cetyltrimethylammonium bromide (CTAB), and then 1 ml of a 1:64 CDs solution (CDs to water volume ratio) prepared in Example 2 was added. The mixture was sonicated for 30 min, and the chloroform was evaporated in an oil bath at 60 °C to obtain a clear and transparent UCNPs aqueous solution, which was stabilized at 70 °C for 10 min.

[0117] (3) Add 50 μL of formaldehyde solution, 150 μL of 2 mol / L NaOH, 20 μL of a mixture of 3-aminopropyltriethoxysilane (APTES) and 150 μL of tetraethyl silicate (TEOS) (dropped in), and 0.5 ml of ethyl acetate to the UCNPs aqueous solution, and incubate in an oil bath at 70°C for 3 h.

[0118] (4) Add 20 mL of methanol and acetic acid at a volume ratio of 9:1 and stir for 24 hours. Then centrifuge at 12000 r / min for 15 minutes, wash twice with water and disperse in 10 mL of water to obtain an aqueous solution of Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterials.

[0119] Figure 6 The scanning electron microscope (SEM) image of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial prepared in this embodiment clearly shows the overall morphology, dispersion state, and surface structure characteristics of the material. It can be seen that the nanoparticles are spherical with a size of approximately 45-50 nm.

[0120] Figure 7 The image shows a transmission electron microscope (TEM) image of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial in Example 3 of this invention. The scale bar is 100 nm, and a clear core-shell structure can be seen.

[0121] Figure 8 The Fourier transform infrared (FTIR) spectrum of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial prepared in this embodiment is used to characterize the types of functional groups and chemical bonding on the material surface. 3430 cm⁻¹ -1 1646cm -1 The absorption peak at 1080 cm⁻¹ is a typical stretching vibration peak of an amide bond, indicating that an amide bond is formed through dehydration condensation between the amino and carboxyl groups; -1 The absorption peak at this point is a typical stretching vibration peak of silicon-oxygen bonds, indicating that the SiO2 shell has been successfully coated on the Cs2NaYF6@CDs surface; and Figure 9 The absence of aldehyde bonds indicates that the formaldehyde has been washed away, successfully forming a porous structure with a specific shape and size, which facilitates subsequent applications such as adsorption, separation, or detection of specific substances (formaldehyde).

[0122] Figure 9 The emission spectrum of the Cs2NaYF6@CDs@SiO2@MIP composite nanomaterial prepared in this embodiment is shown to characterize its fluorescence emission properties. The excitation source used was 365 nm with a power of 8 W. The results show that the emission peak of this fluorescent composite nanomaterial is at 441 nm.

[0123] Comparative Example 1

[0124] The difference between this comparative example and Example 1 is that in Cs2NaYF6:Yb 3+ / Tm 3+ In the preparation of nanoparticles, this comparative example did not dope Cs2NaYF6 with rare earth ions, that is, in step (1), Tm(Ac)3·4H2O and Yb(Ac)3·4H2O were not added, only Y(Ac)3·4H2O was added, and the content of other components and operations were the same as in step (1) of Example 1; the component content and preparation method of steps (2) to (4) were the same as in steps (2) to (4) of Example 1, and finally undoped Yb was obtained. 3+ / Tm 3+ Cs2NaYF6 nanoparticles.

[0125] The undoped Yb prepared in this comparative example 3+ / Tm 3+ The Cs2NaYF6 nanoparticles have a crystal structure consistent with the standard card (PDF#20-1214), and their particle size and dispersibility are similar to those of Example 1. The product purity meets the requirements. However, due to the lack of Yb... 3+ (Sensitized ions) and Tm 3+ The synergistic effect of (activating ions) results in no upconversion fluorescence emission signal under a 980nm excitation light source, making it impossible to achieve fluorescence visualization. Therefore, it cannot be used for the fluorescence detection of formaldehyde and can only be used as a basic fluoride nanoparticle.

[0126] Comparative Example 2

[0127] This comparative example provides a visualized upconversion composite nanomaterial and its preparation method. The difference between this example and Example 1 is that the prepared material is Cs2NaGdF6:Yb. 3+ / Tm 3+ Nanoparticles were prepared by replacing Y element with Gd element and adding Gd(Ac)3·4H2O (0.59 mmol, 59%), Yb(Ac)3·4H2O (0.4 mmol, 40%), and Tm(Ac)3·4H2O (0.01 mmol, 1%). The content of other components and the operation were the same as in step (1) of Example 1. The content of components and the preparation method of steps (2) to (4) were the same as in steps (2) to (4) of Example 1.

[0128] The Cs2NaGdF6:Yb prepared in this comparative example 3+ / Tm 3+ Nanoparticles, although capable of forming stable fluoride crystal structures, but Gd 3+ electronic configuration (4f) 7 ) and Y 3+ (4f) 0 The difference exists and will disrupt Yb 3+ To Tm 3+ The energy transfer efficiency was significantly reduced. Under 980 nm excitation, the fluorescence emission intensity at 477 nm was only 20%~30% of that in Example 1, indicating a significant decrease in fluorescence quantum yield; and Gd 3+ The introduction of [a substance] alters the surface charge distribution of nanoparticles, leading to decreased stability in subsequent composites with CDs, SiO2, and MIPs, ultimately reducing the sensitivity of the composite material for formaldehyde detection.

[0129] Comparative Example 3

[0130] This comparative example provides a visualized upconversion composite nanomaterial and its preparation method. The difference between this example and Example 1 is that the prepared material is Cs2NaLaF6:Yb. 3+ / Tm 3+ The nanoparticles, with Y element replaced by La element, specifically include the following steps: adding La(Ac)3·4H2O (0.59 mmol, 59%), Yb(Ac)3·4H2O (0.4 mmol, 40%), Tm(Ac)3·4H2O (0.01 mmol, 1%), and the content and operation of the remaining components are the same as step (1) in Example 1; the component content and preparation method of steps (2) to (4) are the same as steps (2) to (4) in Example 1.

[0131] The Cs2NaLaF6:Yb prepared in this comparative example 3+ / Tm 3+ Nanoparticles, due to La 3+ Ionic radius greater than Y 3+ This leads to lattice distortion in fluoride crystals, resulting in decreased crystal purity. Lattice distortion further hinders the growth of Yb. 3+ With Tm 3+ Energy transfer between them is almost non-exhibitory under 980nm excitation; at the same time, lattice defects make the nanoparticles less dispersed and prone to agglomeration, making it difficult to form a uniform core-shell structure in subsequent composite processes. Ultimately, it is impossible to prepare a stable fluorescent composite detection material and completely lose the ability to detect formaldehyde.

[0132] Comparative Example 4

[0133] The difference between this comparative example and Example 3 is that, in the preparation of a fluorescent composite nanomaterial for formaldehyde detection, no formaldehyde solution was added in this comparative example, resulting in a fluorescent composite nanomaterial Cs2NaYF6@CDs@SiO2@NIP without formaldehyde recognition sites. Specifically, the following steps are included:

[0134] (1) Take Cs2NaYF6:Yb from Example 1 3+ / Tm 3+ Cyclohexane solution, after precipitation and centrifugation with added ethanol, was dispersed in 6 mL of chloroform to obtain Cs2NaYF6:Yb 3+ / Tm 3+ Chloroform dispersion.

[0135] (2) Take 6 mL of Cs2NaYF6:Yb from step (1). 3+ / Tm 3+ The chloroform dispersion was added to 25 ml of an aqueous solution containing 50 mg of cetyltrimethylammonium bromide (CTAB), and then 1 ml of the 1:64 CDs solution prepared in Example 2 was added. The mixture was sonicated for 30 min, and the chloroform was evaporated in an oil bath at 60 °C to obtain a clear and transparent UCNPs aqueous solution, which was stabilized at 70 °C for 10 min.

[0136] (3) Add 150 μL of 2 mol / L NaOH, 20 μL of a mixture of 3-aminopropyltriethoxysilane (APTES) and 150 μL of tetraethyl silicate (TEOS) (dropped in), and 0.5 ml of ethyl acetate to the UCNPs aqueous solution, and incubate in an oil bath at 70°C for 3 h.

[0137] (4) Centrifuge at 12000 r / min for 15 minutes, wash twice with ethanol, wash once with water, and finally disperse in 10 ml of water to obtain an aqueous solution of Cs2NaYF6@CDs@SiO2@NIP fluorescent composite nanomaterials.

[0138] Figure 10 The Fourier transform infrared (FTIR) spectrum of the Cs2NaYF6@CDs@SiO2@NIP composite nanomaterial prepared in this comparative example is used to characterize the types of functional groups and chemical bonding on the material surface, and is compared with that of Example 3. Figure 8 To create a contrast. 3419cm -1 1633cm -1 The absorption peak at 1095 cm⁻¹ is a typical stretching vibration peak of an amide bond, indicating that an amide bond is formed through dehydration condensation between the amino and carboxyl groups; -1 The absorption peak at this point is a typical stretching vibration peak of silicon-oxygen bonds, indicating that the SiO2 shell has been successfully coated on the Cs2NaYF6@CDs surface.

[0139] Comparative Example 5

[0140] This comparative example provides a visualized upconversion composite nanomaterial and its preparation method. The difference between this example and Example 1 is that the prepared material is Cs2NaYCl6:Yb. 3+ / Tm 3+ Nanoparticles, with F element replaced by Cl element, and CsCl (10 mmol) added, the content of other components and operation are the same as step (2) in Example 1; the content of components and preparation methods of steps (1), (3) to (4) are the same as steps (1), (3) to (4) in Example 1.

[0141] Chloride lattices exhibit poor stability in aqueous solutions, leading to easy aggregation of nanoparticles and an increased particle size distribution. Furthermore, the lack of highly electronegative fluoride sites on the chloride surface makes it difficult for the silane coupling agent (APTES) to anchor during subsequent composite processes with CDs and SiO2, resulting in incomplete shell coating and exposing the particle surface, which triggers fluorescence quenching. Consequently, the subsequently prepared composite nanomaterials show almost no response to formaldehyde, rendering their detection performance completely ineffective.

[0142] Comparative Example 6

[0143] This comparative example provides a visualized upconversion composite nanomaterial and its preparation method. The difference between this example and Example 1 is that the prepared material is Cs2NaYF6:Yb. 3+ / Er 3+ Nanoparticles, Tm 3+ Replace element with Er 3+ The elements were added as follows: Y(Ac)3·4H2O (0.59 mmol, 59%), Yb(Ac)3·4H2O (0.4 mmol, 40%), and Er(Ac)3·4H2O (0.01 mmol, 1%). The content of the remaining components and the operation were the same as in step (1) of Example 1. The component content and preparation method of steps (2) to (4) were the same as in steps (2) to (4) of Example 1.

[0144] The Cs2NaYF6:Yb prepared in this comparative example 3+ / Er 3+ The nanoparticles have a crystal structure consistent with the standard card (PDF#20-1214) and uniform particle size, but the fluorescence properties of the doped ion combination differ significantly from those of Example 1. Yb 3+ / Er 3+ As a typical red-green upconversion luminescent system, under 980 nm excitation, its characteristic emission peaks are 540 nm (green light) and 654 nm (red light), which do not overlap with the 474 nm emission peak of CDs in Example 2, thus failing to achieve fluorescence resonance energy transfer between UCNPs and CDs. The subsequently prepared composite nanomaterials exhibit fluorescence signals with Er... 3+It exhibits predominantly red and green fluorescence, lacks synergistic response with CDs, lacks a specific fluorescence quenching mechanism for formaldehyde detection, and has weak resistance to interference from other ions in the environment.

[0145] Comparative Example 7

[0146] The difference between this comparative example and Example 3 is that the preparation of the shell layer is omitted, that is, APTES and TEOS are not added in step (3), while the content of other components and the operation are the same as in Example 3.

[0147] The composite nanomaterial prepared in this comparative example lacks the "isolation-bridging" effect of a shell, with molecularly imprinted polymers (MIPs) directly coated on the surface. Simultaneously, without the protection of a shell, the UCNPs@CDs cores easily aggregate in the aqueous phase reaction, and the MIP recognition sites are randomly distributed, failing to form a pore structure that matches formaldehyde molecules. The adsorption of formaldehyde by this composite material is non-specific, and the detection repeatability is extremely poor. After multiple cycles of detection, the fluorescence response signal fluctuates, making it unsuitable for the quantitative detection of formaldehyde.

[0148] Experimental Example 1

[0149] Formaldehyde concentration was detected using the Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterial from Example 3:

[0150] (1) Prepare formaldehyde aqueous solutions of different concentrations of 0.75~15 mg / L. Take 250 μL of each concentration and add it to a 1.5 mL centrifuge tube. Add 250 μL of the Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterial aqueous solution of Example 3 to each centrifuge tube.

[0151] (2) Under laser excitation at 365 nm and 8 W, the emission intensity of the solution in all centrifuge tubes (385-700 nm) was tested, and the linear relationship between formaldehyde concentration and emission intensity of fluorescent composite nanomaterial at 422 nm was obtained.

[0152] Figure 11 This is a graph showing the relationship between the emission intensity of the fluorescent composite nanomaterial Cs2NaYF6@CDs@SiO2@MIP prepared in Example 3 of this invention at 422 nm and the formaldehyde concentration. The excitation light source wavelength was 365 nm and the power was 8 W during the test, used to establish a quantitative detection standard curve for formaldehyde. The fitted linear equation is y = 0.07579x + 3.0062, and the goodness of fit R0 is [value missing]. 2 =0.99064, indicating that the regression line fits the detection value well.

[0153] Experimental Example 2

[0154] The concentration of formaldehyde was detected using the Cs2NaYF6@CDs@SiO2@NIP fluorescent composite nanomaterials of Comparative Example 4:

[0155] (1) Prepare formaldehyde aqueous solutions of different concentrations of 0.75~15mg / L. Take 250μL of each concentration and add it to a 1.5mL centrifuge tube. Add 250μL of the Cs2NaYF6@CDs@SiO2@NIP fluorescent composite nanomaterial aqueous solution of Example 3 to each centrifuge tube.

[0156] (2) Under laser excitation at 365 nm and 8 W, the emission intensity (385-700 nm) of the solution in all centrifuge tubes was tested, and the relationship between formaldehyde concentration and emission intensity at 422 nm of fluorescent composite nanomaterial was obtained.

[0157] Figure 12 This figure shows the relationship between the emission intensity of the fluorescent composite nanomaterial Cs2NaYF6@CDs@SiO2@NIP prepared in Comparative Example 4 of this invention at 422 nm and the formaldehyde concentration. The excitation light source wavelength was 365 nm and the power was 8 W during the test to compare the response performance of the composite nanomaterial without a molecularly imprinted layer to formaldehyde. As shown in the figure, the emission intensity does not follow a clear pattern with increasing formaldehyde concentration, exhibiting a chaotic fluctuating pattern.

[0158] Experimental Example 3

[0159] Specificity test of formaldehyde for the Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterial in Example 3:

[0160] (1) Prepare solutions of 2-bromo-4-nitrophenol, 4-hydroxybenzoic acid, acetone, bisphenol A, anhydrous ethanol, n-propanol and formaldehyde of the same concentration (100 μmol / L). Take 250 μL of each solution and add it to a 1.5 ml centrifuge tube. Add 250 μL of the Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterial aqueous solution from Example 3 to each centrifuge tube.

[0161] (2) Under laser excitation at 365 nm and 8 W, the emission intensity of 250 μL of fluorescent composite nanomaterial at 422 nm was tested.

[0162] (3) Under laser excitation at 365 nm and 8 W, the emission peak intensity of the solution in all centrifuge tubes at 422 nm was measured, and the difference between the emission intensity of the solution and that of the fluorescent composite nanomaterial was recorded, i.e., the emission intensity of the solution minus the emission intensity of the fluorescent composite nanomaterial. The test results are as follows: Figure 13 As shown, the fluorescent composite nanomaterials prepared in this invention have good detection specificity for formaldehyde.

[0163] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fluorescent composite nanomaterial for detecting formaldehyde, characterized in that, The fluorescent composite nanomaterial is Cs2NaYF6@CDs@SiO2@MIP, which has a multi-layered core-shell structure, comprising, from the inside out: Core layer: Upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ ; Intermediate modification layer: CDs loaded on the surface of the core layer; Protective and functional spacer layer: an outer SiO2 shell; Specific recognition layer: Formaldehyde molecular imprinted polymer shell, the MIP layer has imprinted holes that are complementary to formaldehyde molecules; The preparation method of CDs includes the following steps: mixing citric acid, water and ethanolamine, and then subjecting them to a solvothermal or hydrothermal reaction to obtain the product; The ratio of citric acid, water, and ethanolamine used is (0.05~0.3mol):(10~30mL):(0.1~0.5mol); The conditions for solvothermal or hydrothermal reactions are to maintain the temperature at 150~200℃ for 4~10 hours; Upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ The Y, Yb and Tm elements in the mixture are all selected from acetates. The molar ratio of the acetate containing Y, the acetate containing Yb and the acetate containing Tm is (58~60):(39~41):

1. The morphology of Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterials is spherical nanoparticles with a size of 30~100nm; CDs are dot-shaped nanoparticles with a size of 1~10nm; Preparation methods include: S1. Preparation of upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ ; S2, (1) Cs2NaYF6:Yb 3+ / Tm 3+ A UCNPs aqueous solution was prepared by mixing chloroform dispersion, surfactant, and CDs solution, and then stabilized at a set temperature. (2) Add formaldehyde solution, alkali, silane coupling agent, silicon source and ethyl acetate to the stabilized UCNPs aqueous solution, and heat to react; (3) Add methanol / acetic acid mixed solution to the solution after the reaction in step (2) to obtain Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterial.

2. The fluorescent composite nanomaterial for formaldehyde detection according to claim 1, characterized in that, Upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ The mass ratio of CDs to CDs is (43~50):

1.

3. A method for preparing a fluorescent composite nanomaterial for formaldehyde detection as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Preparation of upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ ; S2, (1) Cs2NaYF6:Yb 3+ / Tm 3+ A UCNPs aqueous solution was prepared by mixing chloroform dispersion, surfactant, and CDs solution, and then stabilized at a set temperature. (2) Add formaldehyde solution, alkali, silane coupling agent, silicon source and ethyl acetate to the stabilized UCNPs aqueous solution, and heat to react; (3) Add methanol / acetic acid mixed solution to the solution after the reaction in step (2) to obtain Cs2NaYF6@CDs@SiO2@MIP fluorescent composite nanomaterial.

4. The preparation method according to claim 3, characterized in that, Surfactants include hexadecyltrimethylammonium bromide; Silane coupling agents include 3-aminopropyltriethoxysilane; Silicon sources include silicates; Cs2NaYF6:Yb 3+ / Tm 3+ The volume ratio of chloroform dispersion, CDs solution, surfactant, formaldehyde solution, alkali, silane coupling agent, silicon source, and ethyl acetate is (5~10mL):(0.5~2mL):(40~60mg):(40~60μL):(100~200μL):(10~30μL):(100~200μL):(0.1~1mL); Cs2NaYF6:Yb 3+ / Tm 3+ The concentration of the chloroform dispersion was 0.01~0.1 mmol / mL; The volume ratio of ethyl acetate to methanol / acetic acid mixed solution is (0.1~1mL):(10~30mL); The concentration of the alkali is 1~3 mol / L.

5. The preparation method according to claim 3, characterized in that, In step (1), the UCNPs aqueous solution is stable at 60~80℃ for 5~15 min; In step (2), an oil bath heating method is used, with an oil bath temperature of 50~80℃ for 1~5 hours; In step (3), the volume ratio of methanol to acetic acid is (8~10):1; the centrifugation conditions are: centrifugation at 10000~15000r / min for 10~30min.

6. The preparation method according to claim 3, characterized in that, The upconversion luminescent nanoparticles Cs2NaYF6:Yb 3+ ,Tm 3+ The preparation method is as follows: (1) Mix yttrium salt, ytterbium salt, thulium salt, oleic acid, octadecene and oleylamine, heat under a protective gas and stir to form a precursor solution; (2) Dissolve the sodium salt and cesium salt in an alcohol solvent, add them to the precursor solution, heat to the set temperature and keep warm to obtain a mixed solution; (3) In a sealed environment, the mixed solution is evacuated and kept under a vacuum for a set time, and then heated and kept warm under a protective gas to obtain a crude product solution; (4) The crude product solution is purified by centrifugation and washing; The ratio of yttrium salt, ytterbium salt, thulium salt, oleic acid, octadecene, and oleylamine is (0.4~0.7mmol):(0.2~0.6mmol):(0.005~0.02mmol):(12~20mL):(12~20mL). 0 mL): (5~10 mL); the ratio of yttrium salt, cesium salt, and sodium salt is (0.4~0.7 mmol): (8~12 mmol): (8~12 mmol); yttrium salt includes Y(Ac)3·4H2O; ytterbium salt includes Yb(Ac)3·4H2O; thulium salt includes Tm(Ac)3·4H2O; the sodium salt includes Na(Ac)3·3H2O; the cesium salt includes CsF; In step (1), the protective gas includes nitrogen; the heating temperature is 100~150℃; and the stirring time is 20~60min. In step (2), the alcohol solvent includes methanol; the ratio of sodium salt, cesium salt and alcohol solvent is (8~12 mmol):(8~12 mmol):(5~10 mL); the temperature is raised to 50~100℃ and held for 60~80 min; In step (3), the vacuum is maintained for 10~30 minutes; the heating temperature is 310~330℃ and maintained for 1~2 hours.

7. The application of a fluorescent composite nanomaterial for formaldehyde detection as described in claim 1 or 2, or a fluorescent composite nanomaterial for formaldehyde detection prepared by the preparation method described in any one of claims 3 to 6, characterized in that, The application is for detecting formaldehyde.

8. A method for formaldehyde detection, characterized in that, The fluorescent composite nanomaterial for formaldehyde detection, prepared using the fluorescent composite nanomaterial for formaldehyde detection as described in claim 1 or 2, or the preparation method described in any one of claims 3 to 6, is as follows: The fluorescent composite nanomaterial for formaldehyde detection was placed in a formaldehyde-containing environment, and an excitation light source with a wavelength of 360~370nm was used as the excitation light to detect the emission spectrum.

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