A fluorescent composite material, a preparation method thereof and application thereof in detecting formaldehyde

Abstract

The application discloses a fluorescent composite material, a preparation method thereof and application thereof in detecting formaldehyde, and belongs to the technical field of formaldehyde detection. The fluorescent composite material is of a NaYF4@CDs@SiO2@MIP structure and is in a multilayer core-shell configuration, and its components are sequentially arranged from inside to outside as follows: an up-conversion energy core layer: NaYF4:Yb 3+ / Er 3+ nanoparticles; a fluorescent response intermediate layer: carbon quantum dots loaded on the surface of the core layer; a protection and function interval layer: a mesoporous SiO2 shell layer coated on the outer layer of the CDs; and a specific recognition outer layer: a formaldehyde molecular imprinting polymer shell layer with imprinting cavities complementary to the spatial structure and functional groups of formaldehyde molecules. The material can realize accurate quantitative detection of formaldehyde in the range of 0.003-12.1 mg / L, has a response time of less than 5 min under a 980 nm excitation light source, has excellent fluorescence stability and strong anti-interference capability, and can be directly applied to on-site detection of complex substrates.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde detection technology, specifically relating to a fluorescent composite material, its preparation method, and its application in formaldehyde detection. 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, a typical highly toxic volatile organic pollutant, is a potent carcinogen and biotoxic agent. It originates widely from building materials, industrial emissions, and food preservatives. It enters the human body through inhalation and skin contact, causing irreversible damage to the respiratory, nervous, and immune systems. With increasingly stringent environmental protection requirements, accurate detection and real-time monitoring of formaldehyde have become crucial issues in environmental governance and public health.

[0004] Currently available formaldehyde detection technologies are mainly divided into two categories: laboratory testing and on-site testing. Laboratory testing technologies (such as high-performance liquid chromatography and gas chromatography-mass spectrometry) have high detection accuracy, but they suffer from drawbacks such as expensive instruments, complex sample pretreatment, and long detection cycles, making it difficult to meet the rapid response requirements of sudden pollution events. On-site testing technologies (such as electrochemical sensor methods and portable spectrophotometry) are easy to operate, but they suffer from problems such as weak anti-interference ability, low detection sensitivity, and poor stability. Electrochemical sensors are easily affected by coexisting ions and organic matter, requiring frequent calibration. Traditional spectrophotometry is affected by the stability of chromogenic agents, resulting in poor reproducibility of detection results.

[0005] Fluorescence sensing technology has become an ideal choice for rapid on-site detection due to its advantages such as fast response speed, high detection sensitivity, and portable equipment. However, existing fluorescence detection materials still face key technical bottlenecks: most fluorescent materials rely on a single fluorescent matrix, and the excitation wavelength is mostly in the ultraviolet-visible region, which easily causes matrix background fluorescence interference in the detection system, resulting in a decrease in the detection signal-to-noise ratio; at the same time, the material surface lacks specific recognition sites, and is easily interfered with by other volatile organic compounds, metal ions, etc. in complex environments, resulting in insufficient detection specificity; in addition, some fluorescent materials have poor chemical stability and are prone to aggregation and fluorescence quenching during long-term storage, which limits their practical application life.

[0006] Existing technologies include formaldehyde detection materials based on the NaYF4@CDs binary structure. However, these materials lack effective protective and specific recognition enhancement structures, exhibit weak anti-interference capabilities, and are difficult to adapt to complex matrix detection. Other fluorescent probes are based on the NaYF4@SiO2@MIP structure, but these materials lack a carbon dot fluorescence response layer and are designed for targets such as PFOS. The size of the imprinted holes and the arrangement of functional groups do not match the spatial structure and chemical properties of formaldehyde molecules. Directly applying this structure cannot achieve efficient and specific recognition of formaldehyde. Furthermore, the SiO2 shell has a random pore structure, failing to achieve precise mass transfer matching with the target molecule, thus failing to meet the sensitivity and specificity requirements for formaldehyde detection. In addition, even existing multilayer fluorescent materials often involve simple stacking of functional layers without synergistic effects between layers. This leads to a trade-off between mass transfer efficiency and recognition efficiency, making it difficult to simultaneously achieve high sensitivity and strong anti-interference capabilities. Therefore, developing novel fluorescent detection materials with high sensitivity, high specificity, and high stability is of significant practical importance for the precise control of formaldehyde. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a fluorescent composite material, its preparation method, and its application in formaldehyde detection. Specifically, this invention provides a multi-layer core-shell fluorescent composite material with NaYF4 as the upconversion core, its efficient preparation method, and its application in accurate formaldehyde detection.

[0008] In this invention, the fluorescent composite material is a fluorescent composite nanomaterial, specifically a multilayer core-shell structure fluorescent composite nanomaterial based on the NaYF4 upconversion system. The invention employs the following technical solution: First, Yb is prepared via high-temperature pyrolysis. 3+ and Er 3+ Co-doped NaYF4 upconversion nanoparticles (UCNPs) serve as the energy core for near-infrared excitation-visible light emission. Subsequently, fluorescently responsive carbon dots (CDs) are grafted onto the surface of the UCNPs via covalent bonding to construct an efficient energy transfer channel. Then, a mesoporous SiO2 shell is coated on the outer layer of the CDs using a sol-gel method to form a physical protection and functional spacer structure. Its 2-3 nm pore size is precisely matched with the molecular dynamics diameter of formaldehyde, enabling rapid mass transfer of formaldehyde. Finally, using formaldehyde as a template molecule, a specific recognition shell (MIP) is constructed on the SiO2 surface through molecular imprinting polymerization. After stepwise elution, imprinted holes that are complementary to the spatial structure of formaldehyde molecules are formed, ultimately yielding NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterials.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] In a first aspect, the present invention provides a fluorescent composite material, which is NaYF4@CDs@SiO2@MIP, exhibiting a multi-layered core-shell structure, consisting of four layers from the inside out:

[0011] The first layer is an upconversion energy core layer, using NaYF4:Yb 3+ / Er 3+ Upconversion luminescent nanoparticles can convert long-wavelength excitation light into short-wavelength fluorescence, effectively avoiding background fluorescence interference in the detection system and providing stable excitation energy for carbon dots;

[0012] The second layer is a fluorescence-responsive intermediate layer, consisting of carbon quantum dots (CDs, also known as carbon dots) loaded on the surface of the core layer. Anchored to the core layer surface by the SiO2 shell framework, the absorption peaks of the CDs are similar to those of the NaYF4:Yb core layer. 3+ / Er 3+ The 545nm emission peak overlaps with the core, allowing for efficient capture of energy transferred from the core layer via resonance energy transfer (FRET), achieving a signal conversion from near-infrared excitation to red light response and avoiding background fluorescence interference. CDs, as the core fluorescence response unit, are rich in functional groups such as hydroxyl and amino groups on their surface, enabling them to react specifically with formaldehyde and promote regular changes in the fluorescence signal.

[0013] The third layer is a protective and functional spacer layer, a mesoporous SiO2 shell covering the fluorescent response intermediate layer. With a pore size of 2-3 nm and controllable thickness, it enhances the material's chemical stability and dispersibility, while simultaneously enabling precise mass transfer of formaldehyde molecules and impurity shielding. This pore size precisely matches the dynamic diameter of formaldehyde molecules (approximately 0.45 nm), ensuring rapid diffusion of formaldehyde molecules to the CDs response layer while shielding against large molecular impurities and coexisting organic matter.

[0014] The fourth layer is the specific recognition outer layer, which is the formaldehyde molecular imprinted polymer layer (MIP). Through template elution, imprinted holes that are complementary to the spatial structure and functional groups of formaldehyde molecules are formed, which can achieve targeted recognition and specific binding of formaldehyde molecules.

[0015] The fluorescent composite nanomaterial is uniformly spherical with regularly distributed imprinted holes on its surface. The pore size matches the size of formaldehyde molecules, and the imprinted hole density of the MIP layer is 1.0 × 10⁻⁶. 18 ~1.3×10 18 pcs / cm 3 The density was determined by nitrogen adsorption-desorption method; the material had a detection recovery rate of 90-110% in complex matrices containing methanol and ethanol (both concentrations ≤100μM), and the relative standard deviation (RSD) was ≤3%.

[0016] Secondly, the present invention provides a method for preparing the above-mentioned fluorescent composite material, comprising the following steps:

[0017] S1. Preparation of NaYF4:Yb 3+ / Er 3+ Upconversion luminescent nanoparticles;

[0018] S2, NaYF4:Yb 3+ / Er 3+ A chloroform dispersion of upconversion luminescent nanoparticles and a surfactant solution were mixed, heated, and then the mixture was kept at a constant temperature to obtain an aqueous solution of UCNPs.

[0019] S3. After the UCNPs aqueous solution, CDs dispersion, formaldehyde solution, alkaline solution, silane coupling agent, silicon source and ethyl acetate have been stabilized at constant temperature, they are mixed and reacted at constant temperature.

[0020] S4. Add the product after the reaction to a methanol / acetic acid mixture, centrifuge, and wash to obtain the final product.

[0021] Thirdly, the present invention provides an application of the above-mentioned fluorescent composite material, wherein the application is in the detection of formaldehyde.

[0022] Fourthly, the present invention provides a method for detecting formaldehyde, which uses the above-mentioned fluorescent composite material. The specific steps are as follows: the fluorescent composite material is placed in a formaldehyde-containing environment, an excitation light source with a wavelength of 970~990nm is used as the excitation light, and the emission spectrum at 600~610nm is detected.

[0023] One or more of the above technical solutions have the following advantages or beneficial effects:

[0024] 1. The fluorescent composite material provided in this invention is a multilayer core-shell structure fluorescent composite nanomaterial based on the NaYF4 upconversion system. Through the synergistic design of "upconversion energy supply - carbon dot fluorescence response - mesoporous silica shell mass transfer protection - molecular imprint recognition", it breaks through the technical bias of mutual restriction between mass transfer and recognition in existing multilayer structures, and achieves high specificity and high sensitivity detection of formaldehyde. At the same time, it provides a simple and scalable synthesis method to solve the problems of poor anti-interference, insufficient stability and low detection accuracy of traditional fluorescent materials.

[0025] 2. The fluorescent composite material provided in this invention can achieve accurate quantitative detection of low concentrations of formaldehyde in the range of 0.003~12.1 mg / L. The response time is less than 5 min under an excitation light source of 970~990 nm (preferably 980 nm). It has excellent fluorescence stability and strong anti-interference ability. It can be directly applied to the on-site detection of complex matrices. The detection cost is low and the operation is simple.

[0026] 3. Significant synergistic effect: The SiO2 shell (pore size 2~3nm) and the MIP imprinted holes form a "dual screening", which not only ensures the rapid diffusion of formaldehyde molecules to the CDs response layer (mass transfer rate increased by 40%), but also shields against interference from macromolecular impurities and coexisting organic matter, thereby improving the specific recognition efficiency by more than 50%. The core layer, CDs, and SiO2 shell form an integrated system of "energy transfer-signal response-environmental protection". This "mass transfer-recognition-energy transfer synergy" is not disclosed in existing technologies and breaks through the technical bias of mutual constraint between mass transfer and recognition in existing multilayer structures.

[0027] 4. Optimized and efficient process: The stepwise elution process increases the template molecule elution rate from 75% to 98% and the imprinted hole utilization rate by 40%. The optimal ratio of 3-aminopropyltriethoxysilane (APTES) to tetraethyl silicate (TEOS) ensures the stability of the MIP layer structure and the detection repeatability (RSD) is ≤3%. The heating rate, raw material ratio and other parameters of CDs preparation have been optimized to ensure the stability of CDs fluorescence performance.

[0028] 5. Excellent overall performance: wide detection range, high sensitivity, strong specificity, recovery rate of 90-110% in complex matrices, fluorescence stability (fluorescence intensity retention rate of 92.5% after 72 hours of continuous detection) is far superior to existing technologies, and the preparation process is simple, low cost, and easy to scale up production.

[0029] 6. Unique application scenarios: It is specifically adapted to the detection of complex matrices containing high concentrations of alcohols and volatile organic compounds, solving the pain points of poor anti-interference and low recovery rate of existing technologies in such scenarios. Attached Figure Description

[0030] 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.

[0031] Figure 1 It is the NaYF4:Yb prepared in Example 1 of this invention. 3+ / Er 3+ Scanning electron microscope (SEM) image;

[0032] Figure 2 It is the NaYF4:Yb prepared in Example 1 of this invention. 3+ / Er 3+ X-ray diffraction (XRD) patterns of nanomaterials;

[0033] Figure 3 It is the NaYF4:Yb prepared in Example 1 of this invention. 3+ / Er 3+ Emission spectrum under 980 nm excitation;

[0034] Figure 4 This is a transmission electron microscope (TEM) image of the CDs prepared in Example 2 of the present invention;

[0035] Figure 5 This is the emission spectrum of CDs dispersions prepared in Example 2 of this invention with different volume ratios of CDs and water under 545 nm excitation;

[0036] Figure 6 This is the absorption spectrum of CDs dispersions obtained by different volume ratios of CDs and water prepared in Example 2 of the present invention;

[0037] Figure 7 These are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the NaYF4@CDs@SiO2@MIP composite nanomaterials prepared in Example 3 of this invention; wherein, A is a scanning electron microscope image and B is a transmission electron microscope image.

[0038] Figure 8 The emission spectrum of the NaYF4@CDs@SiO2@MIP composite nanomaterial in Example 3 of this invention under 980 nm excitation;

[0039] Figure 9 The emission spectrum of the NaYF4@CDs@SiO2@MIP composite nanomaterial in Example 3 of this invention under 545 nm excitation;

[0040] Figure 10 This is a graph showing the relationship between the emission intensity of the fluorescent composite nanomaterial NaYF4@CDs@SiO2@MIP prepared in Example 3 of this invention at 602 nm and the formaldehyde concentration.

[0041] Figure 11 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

[0042] This invention provides a fluorescent composite material, which is NaYF4@CDs@SiO2@MIP, and has a multi-layered core-shell structure consisting of four layers from the inside out: the first layer is an upconversion energy core layer, using NaYF4:Yb 3+ / Er 3+The novel fluorescent composite nanomaterial comprises four layers: an upconversion luminescent nanoparticle layer; a second fluorescent responsive intermediate layer consisting of CDs loaded on the surface of the core layer; a third protective and functional spacer layer, a mesoporous SiO2 shell covering the intermediate modification layer; and a fourth specific recognition outer layer, a formaldehyde molecularly imprinted polymer layer (MIP). This invention enables the specific detection of formaldehyde within a concentration range of 0.003–12.1 mg / L, exhibiting excellent detection stability, short response time, and the ability to perform rapid on-site detection using only a 980 nm excitation source. The method is simple to operate and has low detection costs.

[0043] In a typical embodiment, the present invention provides a fluorescent composite material for formaldehyde detection. This material has a NaYF4@CDs@SiO2@MIP structure and exhibits a multi-layered core-shell configuration. Its composition, from the inside out, is as follows:

[0044] Upconversion energy core layer: Yb 3+ and Er 3+ Co-doped NaYF4 nanoparticles (i.e., NaYF4:Yb) 3+ / Er 3+ Upconversion luminescent nanoparticles);

[0045] Intermediate modification layer (or fluorescence-responsive intermediate layer): Carbon dots (CDs) anchored to the surface of the core layer through the SiO2 shell framework, and are spherical in shape;

[0046] Protective and functional spacer layer: a mesoporous SiO2 shell covering the outer layer of CDs, with a pore size of 2~3 nm and a thickness of 5~15 nm, which can enhance the chemical stability and dispersibility of the material, while realizing the precise mass transfer of formaldehyde molecules and impurity shielding.

[0047] Specific recognition outer layer: Formaldehyde molecularly imprinted polymer (MIP) shell, which forms imprinted holes that are complementary to the spatial structure and functional groups of formaldehyde molecules through template elution, enabling targeted recognition and specific binding of formaldehyde molecules.

[0048] It should be noted that, in the preparation process of this material, the MIP shell can be constructed by adding formaldehyde solution as a template molecule to the system; where MIP is the abbreviation for Molecularly Imprinted Polymer.

[0049] The hole density of the MIP layer imprint is 1.0 × 10⁻⁶. 18 ~1.3×10 18 pcs / cm 3 The density was determined by nitrogen adsorption-desorption method. The material had a detection recovery rate of 90-110% in complex matrices containing methanol and ethanol (both concentrations ≤100μM) and a relative standard deviation (RSD) ≤3%.

[0050] In the preparation method of this invention, 3-aminopropyltriethoxysilane acts as a silane coupling agent, playing a dual bridging role. The amino groups on its molecule can interact with the active groups such as carboxyl and hydroxyl groups on the surface of CDs through hydrogen bonding, condensation reactions, etc., to stably anchor the CDs to NaYF4:Yb. 3+ / Er 3+ On the surface of upconversion luminescent nanoparticles, tetraethyl silicate undergoes hydrolysis and condensation reaction to generate SiO2 in an alkaline system constructed with sodium hydroxide. Hexadecyltrimethylammonium bromide acts as a morphology regulator to control the growth process and microstructure of SiO2, ultimately achieving the controllable synthesis of NaYF4@CDs@SiO2@MIP core-shell structured fluorescent composite nanomaterials.

[0051] NaYF4:Yb 3+ / Er 3+ Upconversion luminescent nanoparticles, as the upconversion luminescent matrix, can realize the conversion of long-wavelength excitation light to short-wavelength fluorescence, effectively avoiding background fluorescence interference in the detection system and providing stable excitation energy for carbon dots. As the core fluorescence response unit, carbon dots are rich in functional groups such as hydroxyl and amino groups on their surface, which can react specifically with formaldehyde, causing the fluorescence signal to show regular changes. The outer SiO2 shell can not only improve the chemical stability and dispersibility of the material, but also achieve rapid mass transfer of formaldehyde molecules and impurity shielding through precise pore size design.

[0052] The three components work synergistically: the core layer provides the energy source for near-infrared excitation and visible light emission, with its 545 nm emission peak matching the CDs absorption peak for efficient energy transfer; the carbon dots, as the core fluorescence response unit, exhibit a 602 nm fluorescence intensity change regulated by formaldehyde; and the SiO2 shell shields against impurity interference. Together, they form an integrated system of 'energy transfer-signal response-environmental protection,' significantly improving detection performance. Furthermore, this composite structure possesses excellent tunability; by adjusting parameters such as the carbon dot loading and SiO2 shell thickness, it can adapt to formaldehyde detection requirements under various complex environments, effectively expanding the material's practical application scenarios.

[0053] In the preparation of this fluorescent composite nanomaterial, the introduction of formaldehyde enables the material to form a coordination structure (i.e., imprinted cavities) that matches the formaldehyde molecules. After the formaldehyde template molecules are removed by elution with a methanol / acetic acid mixed solution, a pore structure with a specific morphology and pore size can be formed on the shell surface of the material, thus providing a structural basis for the specific adsorption, separation and detection of formaldehyde molecules.

[0054] The Y element in the core layer is derived from yttrium salt (including YCl3·6H2O), the Yb element is derived from ytterbium salt (including YbCl3·6H2O), and the Er element is derived from erbium salt (including ErCl3·6H2O). The ratio of yttrium salt, ytterbium salt, and erbium salt is (38~42 mmol):(8.8~9.2 mmol):1 mmol.

[0055] The mass ratio of the core layer to CDs is (22~55):1, preferably (30~45):1, and more preferably (35~42):1.

[0056] CDs are spherical in shape, with a size of 2-10 nm, preferably 3-6 nm. CDs are red light-emitting quantum dots with an emission peak of 615-615 nm, preferably 610 nm.

[0057] The SiO2 shell thickness is 5~15 nm.

[0058] The fluorescent composite material is spherical with a size of 80~150 nm.

[0059] NaYF4:Yb 3+ / Er 3+ The nanoparticles are spherical with a size of 20-30 nm, preferably around 25 nm.

[0060] The pore size of the mesoporous SiO2 shell is 1~10 nm, preferably 2~3 nm. The 2~3 nm pore size of the mesoporous SiO2 shell is precisely matched with the molecular dynamics diameter of formaldehyde (approximately 0.45 nm), enabling rapid mass transfer of formaldehyde molecules and shielding against large molecular impurities.

[0061] In this invention, the different pore sizes of mesoporous SiO2 are not achieved by changing the amount of tetraethyl orthosilicate. Under the preparation conditions described in this invention, by controlling the type and amount of organic components (such as hexadecyltrimethylammonium bromide) added to the reaction system and the hydrolysis reaction conditions, the system can form ordered assembly structures of different sizes. Based on this structure, tetraethyl orthosilicate hydrolyzes and condenses to form a SiO2 framework. After removing the organic components, mesoporous SiO2 with the corresponding pore size is obtained.

[0062] Tetraethyl orthosilicate is used only as a precursor for silicon dioxide. Its dosage mainly affects the amount of SiO2 generated and the thickness of the coating layer, but does not determine the pore size.

[0063] The NaYF4@CDs@SiO2@MIP fluorescent composite material has the morphology of spherical nanoparticles with a size of approximately 80~150 nm, preferably 90~120 nm.

[0064] The fluorescent composite nanomaterial has a porous structure of specific shape and size on its surface. These pores are imprinted holes formed by template elution, which are complementary to the spatial structure and functional groups of formaldehyde molecules, enabling targeted recognition and specific binding of formaldehyde molecules. The SiO2 shell has a pore size of 2-3 nm, which is precisely matched with the size of formaldehyde molecules, forming a "mass transfer-recognition synergy" system.

[0065] In this invention, the loading amount of CDs and the thickness of the SiO2 shell are not specifically limited. The composite nanomaterial has tunable structural features and can be adapted to formaldehyde detection requirements under different complex environments by adjusting the loading amount of CDs and the thickness of the SiO2 shell, effectively broadening the practical application scenarios of the material.

[0066] In another typical embodiment, the present invention provides a method for preparing the above-mentioned fluorescent composite material, comprising the following steps:

[0067] S1. Preparation of NaYF4:Yb 3+ / Er 3+ Upconversion luminescent nanoparticles;

[0068] S2, NaYF4:Yb 3+ / Er 3+ A chloroform dispersion of upconversion luminescent nanoparticles and a surfactant solution were mixed, heated, and then the mixture was kept at a constant temperature to obtain an aqueous solution of UCNPs.

[0069] S3. After the UCNPs aqueous solution, CDs dispersion, formaldehyde solution (template molecule), alkaline solution, silane coupling agent, silicon source and ethyl acetate have been stabilized at constant temperature, they are mixed and reacted at constant temperature.

[0070] S4. Add the product after the reaction to a methanol / acetic acid mixture, centrifuge, and wash to obtain the final product.

[0071] Ethyl acetate is a moderately polar organic solvent, only slightly soluble in water. Its addition to the reaction system demulsifies the emulsion, disrupting the micellar equilibrium established by CTAB and destabilizing the emulsion system. The introduction of this reagent alters the overall solvent polarity of the system, thereby changing the solubility of CTAB in the aqueous phase and the critical micelle formation concentration, leading to a significant decrease in the stability of the colloidal system and inducing flocculation of nanoparticles. The system also transforms from a homogeneous, semi-transparent state into a turbid suspension. Ultimately, the target product can be conveniently and efficiently separated and collected using only low-speed centrifugation, eliminating the need for high-speed centrifugation.

[0072] 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.

[0073] In this embodiment, in step S1, NaYF4:Yb 3+ / Er 3+ Upconversion luminescent nanoparticles, i.e., Yb-doped nanoparticles 3+ and Er 3+ The preparation method of NaYF4 nanoparticles is as follows:

[0074] (1) Under a protective gas atmosphere, a solution of yttrium salt, ytterbium salt, erbium salt, oleic acid and 1-octadecene was heated until a light yellow transparent solution was formed, and then cooled to room temperature;

[0075] (2) The alkali and NH4F are dissolved in the alcohol solvent, and then the cooled solution is added. The alcohol solvent is removed by heating and keeping warm.

[0076] (3) Under a protective gas atmosphere, heat the solution obtained in step (2), cool it and then centrifuge it to obtain the final product.

[0077] Further, in step (1), the ratio of yttrium salt, ytterbium salt, erbium salt, oleic acid, and 1-octadecene is (38~42 mmol):(8.8~9.2 mmol):1 mmol:(0.89~1.02 mol):(2.26~2.34 mol). Alternatively, the ratio of yttrium salt, ytterbium salt, erbium salt, oleic acid, and 1-octadecene is (38~42 mmol):(8.8~9.2 mmol):1 mmol:(5~10 mL):(8~17 mol). The protective gas includes, but is not limited to, nitrogen, and the flow rate of the protective gas is 50~100 mL / min, and the heating temperature is 140~160℃. In step (1), after heating to this temperature, it needs to be maintained until a light yellow transparent solution is formed. There is no fixed holding time; the endpoint is when the solution reaches the specified state.

[0078] Further, in step (2), the molar ratio of alkali to NH4F is (2~3):(3~5), preferably (2~3):(3.5~4.5). The alcohol solvent includes methanol. The ratio of alkali to alcohol solvent is (2~3 mmol):(5~10 mL). The temperature is raised to 60~80℃ and held for 20~40 min to remove the alcohol solvent.

[0079] Further, in step (3), the heating temperature is 290~320℃, preferably 300℃, and the time is 0.5~2 h, preferably 1 h. Add excess alcohol solvent and centrifuge. Centrifuge at 8000~12000 r / min for 5~15 min. Collect the bottom precipitate (i.e., NaYF4:Yb) after centrifugation. 3+ / Er 3+ The nanoparticles were washed with cyclohexane (15 mL of cyclohexane was used for ultrasonic dispersion followed by centrifugation each time), and finally the purified nanoparticles were dispersed in cyclohexane, sealed and protected from light for later use.

[0080] In this embodiment, step S2 specifically includes: preparing NaYF4:Yb 3+ / Er 3+ The upconversion luminescent nanoparticles were mixed with a chloroform dispersion and a surfactant solution, sonicated for 20-40 min, heated to remove chloroform, sonicated for 1-10 min, and stabilized at a set temperature (60-80℃ for 8-10 min).

[0081] Furthermore, when removing chloroform by heating, the mixture is stirred at 60-80°C for 1-5 hours, preferably at 65-70°C for 2-3 hours.

[0082] Furthermore, the UCNPs aqueous solution was kept at a constant temperature of 60-80℃ for 8-10 minutes.

[0083] In this embodiment, in step S3, NaYF4:Yb 3+ / Er 3+ The ratio of chloroform dispersion, surfactant (hexadecyltrimethylammonium bromide), CDs solution (CDs dispersion), formaldehyde, alkaline solution, silane coupling agent (3-aminopropyltriethoxysilane), and ethyl acetate is (2~6mL):(40~60mg):(0.5~2mL):(0.1~0.5mL):(100~200μL):(15~25μL):(0.2~1mL), preferably 2.5mL:50mg:0.5mL:0.2mL:150μL:20μL:0.5mL.

[0084] The mass ratio of silane coupling agent (3-aminopropyltriethoxysilane, APTES) to silicon source (tetraethyl silicate, TEOS) is 1:(5~10). In order to obtain a larger imprinted hole density, a lower detection limit, and better detection repeatability, the mass ratio is preferably 1:(7~8).

[0085] Furthermore, the reaction is carried out under constant temperature conditions in an oil bath, specifically at 60~80℃ for 3~5 hours, preferably at 65~70℃ for 3~4 hours.

[0086] Water is used as the solvent in the preparation process. Water has excellent solubility, which allows the reactants to be fully dissolved and form a homogeneous system, effectively promoting the efficient reaction. Formaldehyde itself has good water solubility. Using water as the reaction medium allows formaldehyde molecules to be uniformly dispersed in the system, thereby greatly increasing its contact area with other reactants and ensuring that the interaction between the substances occurs fully and efficiently.

[0087] The surfactant includes cetyltrimethylammonium bromide (CTAB), and the mass-volume ratio of surfactant to water is (40~60 mg):(20~30 mL), preferably (45~55 mg):(20~30 mL).

[0088] Silane coupling agents include 3-aminopropyltriethoxysilane. Silicon sources include tetraethyl silicate. The alkaline solution is a 1-3 mol / L sodium hydroxide solution.

[0089] The CDs solution is a mixture of CDs and water with a volume ratio of 1:(8~8192), preferably 1:(32~512), and more preferably 1:(128~512).

[0090] The formaldehyde used was a commercially available 37%~40% formaldehyde solution, diluted tenfold with deionized water before use. In the examples, a commercially available formaldehyde solution diluted 8~10 times was used.

[0091] Step S2 includes nanoparticle purification and hydrophobic dispersion, as well as surfactant assembly and chloroform removal. Specifically, nanoparticle purification and hydrophobic dispersion includes: preparing Yb... 3+ and Er 3+ Co-doped NaYF4 nanoparticles were dispersed in cyclohexane. Excess anhydrous ethanol was added to the dispersion system to remove residual impurities and unreacted materials from the nanoparticle surface through sedimentation. The precipitate was then collected by centrifugation and redispersed in chloroform, followed by ultrasonic dispersion to obtain a uniformly concentrated and stably dispersed NaYF4:Yb nanoparticle. 3+ / Er 3+ Chloroform dispersion of upconversion luminescent nanoparticles. The surfactant assembly and chloroform removal process specifically includes: mixing the surfactant (CTAB) with water, stirring and heating until the solution is completely transparent, ensuring full dissolution of CTAB; and adding NaYF4:Yb to the CTAB aqueous solution. 3+ / Er 3+ The upconversion luminescent nanoparticles in chloroform were ultrasonically dispersed to form a stable mixed system. The mixed system was then heated and stirred at a constant temperature to completely remove the chloroform. The system was then ultrasonically dispersed again to effectively prevent the nanoparticles from agglomerating, resulting in a uniformly dispersed precursor system.

[0092] In one embodiment of this method, step S3 involves the following steps: dissolving formamide and citric acid in an organic solvent to obtain a mixed solution, subjecting it to a hydrothermal reaction, and then washing and centrifuging to obtain the final product. The organic solvent includes ethanol. The excitation wavelength of the CDs is 540-560 nm.

[0093] Furthermore, the specific preparation method of CDs includes: dissolving citric acid in ethanol, adding formamide and stirring vigorously until clear, and carrying out hydrothermal reaction of the mixture; after the reaction, washing with anhydrous ethanol and deionized water alternately, taking the sample and mixing it with ethanol and alkaline solution, centrifuging to remove impurities, and taking the lower layer to obtain the red light CDs solution.

[0094] Furthermore, the ratio of citric acid, organic solvent, and formamide is (2~4 g):(10~20 mL):(10~20 mL), preferably (2.5~3.5 g):(14~16 mL):(14~16 mL). Alternatively, the ratio of citric acid, organic solvent, and formamide is (0.014~0.016 mol):(0.24~0.26 mol):(0.365~0.370 mol).

[0095] Furthermore, the hydrothermal reaction conditions are 150-180 °C for 6-10 h, preferably 155-160 °C for 7-8 h. During the carbon point preparation process, the stirring time is 15-20 min, and the heating rate of the autoclave reaction is 5-8 °C / min to ensure that the system temperature rises uniformly to 160 °C.

[0096] Furthermore, ethanol and an alkaline solution are added to the product after the hydrothermal reaction, and then the mixture is centrifuged. The volume ratio of the product, ethanol, and alkaline solution after the hydrothermal reaction is (0.5~2):(3~5):(0.5~1.5). The concentration of the alkaline solution is 8~12 mol / L. The reason for using concentrated alkali (10 mol / L sodium hydroxide solution) is: to adjust the pH of the system, which on the one hand promotes the dissociation of functional groups on the surface of red carbon quantum dots (CDs) and improves their dispersion stability; on the other hand, it neutralizes the acidic substances remaining from the reaction, removes impurities, and improves the purity and fluorescence properties of the product.

[0097] Step S3 involves core-shell assembly and cross-linking polymerization. Specifically, in a temperature-stable system, CDs solution, formaldehyde solution (template molecule), and alkaline solution are added sequentially to adjust the reaction environment. Then, a pre-mixed solution of 3-aminopropyltriethoxysilane (APTES) and tetraethyl silicate (TEOS) (APTES to TEOS mass ratio of 1:7~8) is added. Finally, ethyl acetate is added as a co-solvent, and the reaction is carried out under constant temperature stirring in an oil bath. Through the sol-gel reaction, CDs composite, SiO2 shell coating, and cross-linking polymerization of molecularly imprinted polymer (MIP) are simultaneously achieved to form a NaYF4@CDs@SiO2@MIP core-shell composite structure.

[0098] In the embodiment of this implementation, in step S4, the centrifugation conditions are: centrifugation at 11000~12000 r / min for 10~15 min, template molecule elution rate ≥98%, and the elution rate is determined by high performance liquid chromatography.

[0099] Step S4 involves template elution and product purification. Specifically: after the reaction, the system is cooled to room temperature, and the solid precipitate is collected by centrifugation. A stepwise elution process is used to remove the formaldehyde template molecule from the precipitate. The precipitate is then collected by centrifugation and repeatedly washed with deionized water. After washing, the precipitate is redispersed in deionized water to obtain the NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterial. This stepwise elution process achieves a template molecule elution rate of ≥98%, significantly higher than the approximately 75% of existing technologies.

[0100] A mixed solution of methanol and acetic acid is used as a template eluent. Its key role is to completely remove the formaldehyde template molecules from the newly generated molecularly imprinted polymer, thereby constructing imprinted holes in the MIP layer that can specifically recognize formaldehyde.

[0101] The template molecules are removed using a stepwise elution process. Specifically, the template molecules are first eluted with a methanol / acetic acid mixed solution at a volume ratio of (8~10):1 (preferably 9:1) at room temperature with stirring for 1~3 h. Then, the template molecules are eluted with a methanol / acetic acid mixed solution at a volume ratio of (3~5):1 (preferably 8:2) at 50~70 ℃ (preferably 60 ℃) for 0.5~2 h (preferably 1 h). After multiple centrifugation and washing, the NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterial is obtained.

[0102] In a preferred embodiment, the preparation method of the above-mentioned fluorescent composite material specifically includes the following steps:

[0103] (1) Preparation of Yb 3+ and Er 3+ Co-doped NaYF4 nanoparticles;

[0104] (2) Yb 3+ and Er 3+ Co-doped NaYF4 nanoparticles were dispersed in cyclohexane, purified by precipitation with excess ethanol, and the precipitate was collected by centrifugation and redispersed in chloroform to obtain a chloroform dispersion of nanoparticles.

[0105] (3) Weigh the surfactant and add it to water, stir and heat until completely transparent, add the nanoparticle chloroform dispersion obtained in step (2), ultrasonically disperse to form a stable mixed system, heat and stir at 60°C to remove chloroform, ultrasonically disperse to avoid particle agglomeration;

[0106] (4) Heat the above system to 70°C and keep it stable at a constant temperature. Add CDs dispersion, formaldehyde (molar ratio of template molecule to APTES is 1:(6~8)), alkaline solution, and a mixed solution of 3-aminopropyltriethoxysilane (APTES) and tetraethyl silicate (TEOS) (mass ratio of APTES to TEOS is 1:(7~8)) in sequence. Finally, add ethyl acetate and react at a constant temperature under oil bath conditions.

[0107] (5) After the reaction was completed, the precipitate was collected by centrifugation and the template molecules were removed by stepwise elution process: first, the precipitate was eluted by stirring at room temperature with a methanol / acetic acid mixed solution with a volume ratio of 9:1 for 2 h, and then eluted by heating at 60°C with a methanol / acetic acid mixed solution with a volume ratio of 8:2 for 1 h. After multiple centrifugation and washing, NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterials were obtained.

[0108] In one typical embodiment, the present invention provides an application of the above-mentioned fluorescent composite material, wherein the application is the detection of formaldehyde, preferably the detection of formaldehyde in a complex matrix, wherein the complex matrix is ​​industrial wastewater containing methanol and ethanol (both concentrations ≤100 μM) or food packaging leachate containing acetaldehyde and acetone (both concentrations ≤50 μM).

[0109] This material can be used as a highly specific fluorescent probe for the quantitative detection of formaldehyde in complex scenarios such as industrial wastewater containing methanol and ethanol (concentration ≤100 μM) and food packaging leachate containing acetaldehyde and acetone (concentration ≤50 μM). It is especially suitable for rapid on-site screening of low-concentration formaldehyde (0.003~12.1 mg / L), and the detection results are accurate, reliable and have strong anti-interference ability.

[0110] In a typical embodiment, the present invention provides a formaldehyde detection method, which uses the above-mentioned fluorescent composite material as a detection reagent, mixes it with the sample to be tested, excites it with an excitation light source of 970~990 nm (preferably 975~985 nm, most preferably 980 nm), detects the emission spectrum at 600~610 nm (preferably 600~605 nm, most preferably 602 nm), and determines the formaldehyde concentration according to the standard curve.

[0111] The method is as follows: the fluorescent composite nanomaterial for detecting formaldehyde is mixed with formaldehyde solutions of different concentrations, a 980 nm excitation light source 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 602 nm of the emission spectrum and the concentration.

[0112] The formaldehyde solution to be tested was then mixed with a fluorescent composite nanomaterial for formaldehyde detection. An excitation light source with a wavelength of 980 nm was used as the excitation light, and the emission spectrum was detected. The concentration of the formaldehyde solution to be tested was determined according to a standard curve. The detection range of the formaldehyde solution was 0.003–12.1 mg / L.

[0113] The formaldehyde detection range is 0.003~12.1 mg / L, the relative standard deviation (RSD) is ≤3%, the response time is ≤5 min, and no complex pretreatment is required.

[0114] Unless otherwise explicitly stated, all experimental materials and instruments used in this invention are conventional items in the relevant technical field and can be obtained through commercial channels. For the various reagents used in the following embodiments, this invention does not have any special source restrictions and commercially available products known to those skilled in the art can be used.

[0115] 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.

[0116] Example 1

[0117] This embodiment provides a visualization of upconversion composite nanomaterials (NaYF4:Yb). 3+ / Er 3+ The preparation method of nanoparticles specifically includes the following steps:

[0118] (1) Press Y 3+ 80%, Yb 3+ 18%, Er 3+ Weigh out the corresponding amounts of YCl3·6H2O, YbCl3·6H2O, and ErCl3·6H2O with a molar percentage of 2% and place them in a three-necked flask. Add 6 mL of oleic acid and 15 mL of 1-octadecene. Heat to 150°C under nitrogen protection until a light yellow transparent solution is formed. Cool to room temperature.

[0119] (2) Dissolve 2.5 mmol NaOH and 4 mmol NH4F in 8 mL methanol, pour the solution into the above solution, heat to 70℃ and keep warm for 30 min to remove methanol;

[0120] (3) The solution obtained in step (2) was heated to 300°C under nitrogen protection in a closed environment and held for 1 h. The solution was then allowed to cool naturally to room temperature.

[0121] (4) Add excess ethanol (40 mL) to the reaction solution (i.e., the solution obtained in step (3)), centrifuge at 10000 r / min for 10 min, and collect NaYF4:Yb 3+ / Er 3+Upconversion nanoparticles were dispersed in 10 mL of cyclohexane for later use.

[0122] Figure 1 NaYF4:Yb in Embodiment 1 of the present invention 3+ / Er 3+ Scanning electron microscope (SEM) images of nanoparticles show that the nanoparticles are spherical with a size of 20-40 nm.

[0123] Figure 2 It is the NaYF4:Yb prepared in Example 1 of this invention. 3+ / Er 3+ X-ray diffraction (XRD) pattern of nanomaterials.

[0124] Figure 3 It is the NaYF4:Yb prepared in Example 1 of this invention. 3+ / Er 3+ The emission spectrum is used to characterize the Yb doping. 3+ and Er 3+ Fluorescence emission properties of post-upconversion nanoparticles.

[0125] Example 2

[0126] This embodiment provides a method for preparing CDs nanoparticles, specifically including the following steps:

[0127] (1) Add 15 mL of formamide to 15 mL of ethanol solution containing 3 g of citric acid and stir vigorously until a clear solution is obtained;

[0128] (2) Then the mixed solution was sealed in a 50 mL polytetrafluoroethylene high-pressure reactor and placed in an oven at 160 °C for 8 h. After the reaction was completed, it was washed alternately with anhydrous ethanol and deionized water.

[0129] (3) Take 1 mL of sample, mix 4 mL of ethanol solution and 1 mL of concentrated sodium hydroxide solution (10 mol / L), centrifuge at 10000 r / min for 10 min to remove unreacted precursors and byproducts, and take the lower layer to obtain red light CDs solution.

[0130] Figure 4 This is a transmission electron microscope (TEM) image of the CDs prepared in Example 2 of this invention.

[0131] Figure 5 The emission spectra of CDs dispersions prepared in Example 2 of this invention with different volume ratios of CDs and water are used to characterize the fluorescence emission characteristics and wavelength range of pure carbon dots. Figure 5The ratios indicated by the curves (e.g., 1:8, 1:16, 1:32, etc.) refer to the dilution ratio of the CDs solution in Example 2, that is, the volume ratio of the CDs stock solution to deionized water. For example, 1:8 means that the CDs stock solution and deionized water are mixed and diluted at a volume ratio of 1:8, and so on.

[0132] Figure 6 This is the absorption spectrum of CDs dispersions obtained by different volume ratios of CDs and water prepared in Example 2 of the present invention. Figure 6 The ratios indicated by the curves (e.g., 1:512, 1:1024, 1:2048, etc.) refer to the dilution ratio of the CDs solution prepared in Example 2, that is, the volume ratio of the CDs stock solution to deionized water. For example, 1:512 means that the CDs stock solution and deionized water are mixed and diluted at a volume ratio of 1:512, and so on.

[0133] Combining fluorescence emission and absorption properties, Figure 5 The optimal ratio is 1:256. Figure 6 The optimal ratio is 1:512.

[0134] Figure 5 (Emission spectrum of CDs dispersion) Explanation: This graph characterizes the fluorescence emission properties and wavelength range of CDs at different dilution ratios (1:8 to 1:2048). The 1:256 ratio corresponds to the highest fluorescence intensity peak, proving that CDs have the best dispersibility and the most stable fluorescence emission performance at this dilution ratio, making it the optimal ratio to ensure the fluorescence signal intensity for formaldehyde detection.

[0135] Figure 6 (Absorption spectrum of CDs dispersion) Explanation: This figure characterizes the light absorption properties of CDs at high dilution ratios (1:512 to 1:8192). The 1:512 ratio corresponds to the highest absorption peak and the most complete characteristic absorption peak morphology, proving that the light absorption efficiency of CDs is optimal at this dilution ratio, which can maximize the utilization of excitation light energy and provide a basis for fluorescence response.

[0136] Example 3

[0137] This embodiment provides a method for preparing the fluorescent composite nanomaterial NaYF4@CDs@SiO2@MIP for formaldehyde detection, specifically including the following steps:

[0138] (1) Take 2 mL of NaYF4:Yb dispersed in cyclohexane from Example 1. 3+ / Er 3+ Add excess ethanol to precipitate, centrifuge, and disperse in 6 mL chloroform to obtain NaYF4:Yb 3+ / Er 3+ Chloroform dispersion;

[0139] (2) Weigh 50 mg of surfactant, add 25 mL of water, stir and heat until completely transparent, then add NaYF4:Yb dispersed in chloroform. 3+ / Er 3+ Sonicate for 30 min, heat and stir at 60℃ for 2-3 h, evaporate chloroform, sonicate for 5 min, stabilize at 70℃ for 10 min;

[0140] (3) Add 0.5 mL of CDs dispersion (the volume ratio of red light CDs solution to water in Example 2 is 1:256), 0.1 mL of formaldehyde (37% formaldehyde solution diluted ten times with deionized water), 150 μL of NaOH solution (2 mol / L), and a mixed solution of (20 μL) 3-aminopropyltriethoxysilane (APTES) and (150 μL) tetraethyl silicate (TEOS) to the system obtained in step (2) in sequence. Finally, add 0.5 mL of ethyl acetate and react at a constant temperature under oil bath conditions (70℃, 3h).

[0141] (4) After the reaction was completed, the precipitate was collected by centrifugation and eluted with a methanol / acetic acid mixture with a volume ratio of 9:1 at room temperature for 2 h, followed by elution with a methanol / acetic acid mixture with a volume ratio of 8:2 at 60°C with heating and stirring for 1 h. After centrifugation and washing, NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterials were obtained. The material was spherical with a size of about 100 nm, a mesoporous SiO2 shell thickness of about 10 nm, a SiO2 layer pore size of 2~3 nm, and an imprinted hole density of 1.25×10⁻⁶ in the MIP layer. 18 pcs / cm 3 .

[0142] Figure 7 In Figure A, the image shows a scanning electron microscope (SEM) image of the NaYF4@CDs@SiO2@MIP composite nanomaterial prepared in Example 3 of this invention, clearly displaying 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 100 nm.

[0143] Figure 7 B in the figure is a transmission electron microscope (TEM) image of the NaYF4@CDs@SiO2@MIP composite nanomaterial prepared in Example 3 of this invention. As can be seen from the figure, the material has a core-shell structure.

[0144] Figure 8 This is the emission spectrum of the NaYF4@CDs@SiO2@MIP composite nanomaterial prepared in Example 3 of this invention under 980 nm excitation.

[0145] Figure 9This is the emission spectrum of the NaYF4@CDs@SiO2@MIP composite nanomaterial prepared in Example 3 of this invention under 545 nm excitation.

[0146] Example 4

[0147] Unlike Example 3, the ratio of APTES to TEOS is different, with a mass ratio of 1:5, that is, a volume ratio of 20 μL:100 μL.

[0148] Example 5

[0149] Unlike Example 3, the ratio of APTES to TEOS is different, with a mass ratio of 1:10, which is a volume ratio of 20 μL:200 μL.

[0150] Comparative Example 1

[0151] Unlike Example 3, the addition of tetraethyl silicate was omitted, and NaYF4@CDs@MIP material was prepared.

[0152] Comparative Example 2

[0153] The preparation of NaYF4@CDs includes the following steps:

[0154] (1) NaYF4:Yb 3+ / Er 3+ Preparation of nanoparticles: The preparation method is the same as in Example 1;

[0155] (2) Preparation of NaYF4@CDs composite material:

[0156] The above NaYF4:Yb 3+ / Er 3+ Nanoparticles were dispersed in cyclohexane and sonicated for 30 min. 0.5 mL of red light CDs dispersion (CDs stock solution to deionized water volume ratio of 1:256) was added to the system and stirred at room temperature for 1 h. The mixture was then reacted at 60 °C for 2 h. After the reaction was completed, the mixture was centrifuged, washed several times with ethanol, and dried under vacuum to obtain NaYF4@CDs composite material.

[0157] Comparative Example 3

[0158] Unlike Example 3, NaYF4@CDs, mesoporous SiO2 particles and MIP particles were prepared separately and mixed in the same mass ratio.

[0159] The specific preparation process of mesoporous SiO2 particles is as follows: Tetraethyl orthosilicate (TEOS) is mixed with ethanol and deionized water at a volume ratio of 1:4:2. The mixture is stirred and hydrolyzed at 30 °C for 2 h under the catalysis of ammonia water (2 mL). The product is centrifuged, washed with ethanol three times, vacuum dried at 60 °C, and then calcined at 550 °C for 3 h to remove the template agent, thus obtaining mesoporous SiO2 particles.

[0160] The specific preparation process of MIP particles is as follows: using formaldehyde (37% aqueous solution, 0.5 mL) as template molecule, methacrylic acid (2 mL) as functional monomer, ethylene glycol dimethacrylate (8.0 mL) as crosslinking agent, and azobisisobutyronitrile (0.1 g) as initiator, bulk polymerization is carried out in acetonitrile (30 mL) at 60 °C for 12 h; after the reaction, the template molecule is removed by Soxhlet extraction with methanol / acetic acid (volume ratio 9:1) for 24 h, and MIP particles are obtained after vacuum drying at 60 °C.

[0161] Comparative Example 4

[0162] Unlike Example 3, a traditional one-step elution process was used: only a methanol / acetic acid mixed solution with a volume ratio of 9:1 was used, and the mixture was stirred and eluted at room temperature for 3 hours. The remaining preparation steps were exactly the same as in Example 3.

[0163] In Comparative Example 4, the template molecule elution rate was 75% and the imprinted hole utilization rate was 60%; in Example 3, a stepwise elution process was used, and the template molecule elution rate was 98% and the imprinted hole utilization rate was 84%.

[0164] Compared with the comparative example, the stepwise elution process described in Example 3 can increase the template molecule elution rate by about 30.7% and the imprinted hole utilization rate by 40%.

[0165] Experimental Example 1

[0166] This invention conducted comparative experiments to investigate different structural materials.

[0167] (1) Experimental samples: ① Four-layer material of Example 3 (NaYF4@CDs@SiO2@MIP); ② Three-layer material prepared in Comparative Example 1 (lacking SiO2, NaYF4@CDs@MIP); ③ Two-layer material prepared in Comparative Example 3 (NaYF4@CDs);

[0168] (2) Experimental conditions: The detection system was a formaldehyde standard solution (concentration 0.08~400 μM), and the complex matrix was simulated industrial wastewater containing 100 μM methanol and 50 μM acetone; the excitation conditions were a 980 nm excitation light source with a power of 8 W.

[0169] (3) Detection indicators: limit of detection (LOD, S / N=3), response time, recovery rate of complex matrix, fluorescence stability (fluorescence intensity retention rate after continuous detection for 72 h);

[0170] (4) The experimental results are shown in Table 1. Compared with the materials prepared in Comparative Examples 1 and 2, the NaYF4@CDs@SiO2@MIP provided by this invention has a lower detection limit, shorter response time, and significantly improved recovery rate and fluorescence stability in complex matrices. For example, compared with the NaYF4@CDs prepared in Comparative Example 2, the detection limit of this invention is reduced by 90.8%, the response time is shortened by 54.8%, the recovery rate in complex matrices is increased by more than 30%, and the fluorescence stability is improved by 34.65%. Therefore, this indicates that the SiO2 layer and the MIP layer have a certain synergistic effect in the NaYF4 upconversion system of this invention.

[0171] Table 1. Comparison of the effectiveness of different structural materials in formaldehyde detection.

[0172]

[0173] Experimental Example 2

[0174] The present invention also conducted a screening experiment for MIP layer parameters. By setting different mass ratios of APTES to TEOS (1:5 in Example 4, 1:7.5 in Example 3, and 1:10 in Example 5), the imprinted hole density (nitrogen adsorption-desorption method), detection limit, and detection repeatability (RSD) were detected. It should be noted that when calculating the mass ratio of the two, the density was calculated in 1 g / mL.

[0175] The experimental results are shown in Table 2. The optimal mass ratio of APTES to TEOS defined in this invention is 1:(7~8), which results in the highest imprinted hole density, lower detection limit, and better detection repeatability.

[0176] Table 2. Effect of different mass ratios (APTES and TEOS) on the results.

[0177]

[0178] Experimental Example 3

[0179] Anti-interference experiment of complex matrix

[0180] (1) Experimental design: simulated industrial wastewater containing 100 μM methanol and 50 μM acetone was prepared, and formaldehyde standard solutions of different concentrations (0.1 μM, 10 μM, 300 μM) were added. The four-layer material (NaYF4@CDs@SiO2@MIP) of Example 3 and the two-layer material (NaYF4@CDs) of Comparative Example 2 were compared and tested.

[0181] (2) Detection indicator: Spike recovery rate;

[0182] (3) The experimental results are shown in Table 3. The NaYF4@CDs@SiO2@MIP material prepared in this invention maintained a recovery rate of 95.2-102.4% during spiked testing, while the recovery rate of NaYF4@CDs in Comparative Example 2 was only 68.7-76.5%. Obviously, this invention significantly improves the anti-interference ability in complex matrices through the synergistic design of "SiO2 layer optimization and MIP layer specific recognition".

[0183] Table 3 Results of materials at different formaldehyde spiking concentrations

[0184]

[0185] Test Example 4

[0186] Performance Comparison Experiment of Core-Shell Integrated Structure and Physical Hybrid Structure

[0187] (1) Experimental samples: ① Core-shell integrated material (NaYF4@CDs@SiO2@MIP) of Example 3; ② Physically mixed material (NaYF4@CDs, mesoporous SiO2 particles and MIP particles mixed in the same mass ratio) of Comparative Example 3;

[0188] (2) Experimental conditions: Formaldehyde standard solution concentration 0.003 mg / L, complex matrix is ​​simulated industrial wastewater containing 100 μM methanol and 50 μM acetone; excitation conditions 980 nm excitation light source, power 8 W;

[0189] (3) Detection indicators: detection limit, recovery rate, fluorescence intensity retention rate;

[0190] (4) The experimental results are shown in Table 4. As can be seen from Table 4, when the core-shell integrated structure material provided by the present invention is used to detect formaldehyde, its detection limit is much lower than that of the physically mixed structure, and its recovery rate and fluorescence stability are also better than those of the physically mixed structure. This proves that the "upconversion energy supply-carbon dot fluorescence response-mesoporous silica shell mass transfer protection-molecular imprint recognition" synthesized by the direct one-step method of the present invention has a certain synergistic effect.

[0191] Table 4. Performance of the materials prepared in Example 3 and Comparative Example 3 in formaldehyde detection.

[0192]

[0193] Experimental Example 5

[0194] Experiment on the effect of different SiO2 pore sizes on mass transfer efficiency

[0195] (1) Experimental design: Materials with different SiO2 pore sizes (1 nm, 2~3 nm, 5 nm, 8 nm) were prepared. Other preparation conditions were the same as in Example 3. The formaldehyde concentration was 0.003 mg / L. The mass transfer rate was tested.

[0196] (2) Detection index: the time it takes for formaldehyde molecules to reach the CDs response layer;

[0197] (3) The experimental results are shown in Table 5. When the SiO2 pore size is 2~3 nm, the mass transfer time is the shortest (3.8 min), which is precisely matched with the molecular dynamic diameter of formaldehyde (about 0.45 nm), proving that this pore size design is the key to achieving rapid mass transfer.

[0198] Table 5. Effect of different aperture sizes on the results

[0199]

[0200] Experimental Example 6

[0201] Formaldehyde concentration was detected using the NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterial from Example 3:

[0202] (1) Prepare formaldehyde aqueous solutions of different concentrations from 0 to 450 μmol / L. Take 250 μL of each concentration and add it to a 1.5 mL centrifuge tube. Add 250 μL of the NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterial aqueous solution from Example 3 to each centrifuge tube.

[0203] (2) Under laser excitation at 980 nm and 8 W, the core layer NaYF4:Yb 3+ / Er 3+ By exciting CDs with resonant energy transfer, the emission intensity of the solutions in all centrifuge tubes at 602 nm was tested, and the linear relationship between formaldehyde concentration and emission intensity of fluorescent composite nanomaterials was obtained.

[0204] Figure 10 This is a graph showing the relationship between the emission intensity of the fluorescent composite nanomaterial NaYF4@CDs@SiO2@MIP prepared in Example 3 of this invention at 602 nm and the formaldehyde concentration. The excitation light source wavelength was 980 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 = 1.387x + 2522, and the goodness of fit R0 is [value missing]. 2 =0.998, indicating that the regression line fits the detection value well.

[0205] Experimental Example 7

[0206] Specificity test of formaldehyde for the NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterial in Example 3:

[0207] (1) Prepare solutions of acetone, 2-bromo-4-nitrophenol, anhydrous ethanol, methanol, 4-hydroxybenzoic acid, ascorbic acid, formaldehyde, n-propionaldehyde, and ammonia at the same concentration (1 mol / L). Take 0.25 mL of each solution and add it to a 1.5 mL centrifuge tube. Add 0.25 mL of the NaYF4@CDs@SiO2@MIP fluorescent composite nanomaterial aqueous solution prepared in Example 3 to each centrifuge tube.

[0208] (2) The emission intensity of 250 μL of fluorescent composite nanomaterial at 602 nm was measured under laser excitation at 980 nm and 8 W;

[0209] (3) Under laser excitation at 980 nm and 8 W, the emission peak intensity of the solution in all centrifuge tubes at 602 nm was measured, and the difference between this intensity and the emission intensity 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 11 As shown, the fluorescent composite nanomaterials prepared in this invention have good detection specificity for formaldehyde.

[0210] 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 material, characterized in that, The fluorescent composite material has a NaYF4@CDs@SiO2@MIP structure, exhibiting a multi-layered core-shell configuration. Its composition, from the inside out, is as follows: The first layer is the upconversion energy core layer: NaYF4:Yb 3+ / Er 3+ Upconversion luminescent nanoparticles; The second layer is a fluorescence-responsive intermediate layer: CDs loaded on the surface of the upconversion energy core layer; The third layer is a protective and functional spacer layer: a mesoporous SiO2 shell covering the outer layer of CDs, with a pore size of 1~10nm; The fourth layer is the specific recognition outer layer: the formaldehyde molecule imprinted polymer shell, which has imprinted holes that are complementary to the spatial structure and functional groups of the formaldehyde molecule, enabling targeted recognition and specific binding of the formaldehyde molecule. NaYF4:Yb 3+ / Er 3+ In upconversion luminescent nanoparticles, Y 3+ Yb 3+ and Er 3+ The molar ratio is (78~82):(16~20):(1~3); The morphology of the NaYF4@CDs@SiO2@MIP fluorescent composite material is spherical nanoparticles; The preparation method of CDs includes the following steps: formamide and citric acid are dissolved in an organic solvent to obtain a mixed solution, which is then subjected to a hydrothermal reaction, washed, and centrifuged to obtain the final product; The preparation method of the fluorescent composite material includes the following steps: S1. Preparation of NaYF4:Yb 3+ / Er 3+ Upconversion luminescent nanoparticles; S2, NaYF4:Yb 3+ / Er 3+ A chloroform dispersion of upconversion luminescent nanoparticles and a surfactant solution were mixed, heated, and then the mixture was kept at a constant temperature to obtain an aqueous solution of UCNPs. S3. After the UCNPs aqueous solution, CDs dispersion, formaldehyde solution, alkaline solution, silane coupling agent, silicon source and ethyl acetate have been stabilized at constant temperature, they are mixed and reacted at constant temperature. S4. Add the product after reaction to a methanol / acetic acid mixture, centrifuge, and wash to obtain the final product.

2. The fluorescent composite material according to claim 1, characterized in that, The pore size of the mesoporous SiO2 shell is 2~3 nm, and the thickness is 5~20 nm; The imprinted hole density of the formaldehyde molecularly imprinted polymer shell is 1.0 × 10⁻⁶. 18 ~2×10 18 pcs / cm 3 ; The mass ratio of upconversion energy core layer to CDs is (22~55):1; NaYF4:Yb 3+ / Er 3+ The upconversion luminescent nanoparticles are spherical in shape and have a size of 20~30nm; The size of the NaYF4@CDs@SiO2@MIP fluorescent composite material is 80~150nm.

3. The fluorescent composite material according to claim 1, characterized in that, In step S2, the specific preparation method includes: mixing NaYF4:Yb 3+ / Er 3+ The upconversion luminescent nanoparticles were mixed with a chloroform dispersion and a surfactant solution, sonicated for 20-40 min, heated to remove chloroform, sonicated for 1-10 min, and stabilized at 60-80℃ for 8-10 min.

4. The fluorescent composite material according to claim 1, characterized in that, NaYF4:Yb 3+ / Er 3+ The ratio of chloroform dispersion, surfactant, CDs dispersion, formaldehyde solution, alkaline solution, silane coupling agent, and ethyl acetate for upconversion luminescent nanoparticles is (2~6mL):(40~60mg):(0.5~2mL):(0.1~0.5mL):(100~200μL):(15~25μL):(0.2~1mL); The mass ratio of silane coupling agent to silicon source is 1:(5~10); the temperature is kept constant in an oil bath at 60~80℃ for 3~5h; the surfactant includes hexadecyltrimethylammonium bromide; the silane coupling agent includes 3-aminopropyltriethoxysilane; the silicon source includes tetraethyl silicate; In the CDs dispersion, the volume ratio of CDs to water is 1:(8~8192).

5. The fluorescent composite material according to claim 1, characterized in that, In step S4, formaldehyde is the template molecule, with an elution rate ≥98%, and a stepwise elution process is used to remove the template molecule.

6. The fluorescent composite material according to claim 5, characterized in that, In step S4, the stepwise elution process specifically includes: first, eluting with a methanol / acetic acid mixed solution of volume ratio (8~10):1 at room temperature for 1~3 h by stirring, and then eluting with a methanol / acetic acid mixed solution of volume ratio (3~5):1 at 50~70℃ for 0.5~2 h by heating.

7. The application of the fluorescent composite material according to any one of claims 1 to 6, characterized in that, The application is for the detection of formaldehyde.

8. A method for formaldehyde detection, characterized in that, The fluorescent composite material described in any one of claims 1 to 6 was used. It was placed in a formaldehyde-containing environment and excited by an excitation light source of 970 to 990 nm. The emission spectrum at 600 to 610 nm was detected.

9. The formaldehyde detection method according to claim 8, characterized in that, The detection range of the formaldehyde solution is 0.003~12.5 mg / L; the relative standard deviation of the detection is ≤3%, and the response time is ≤5 min.

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