Porous metal organic hybrid glass for detecting moisture content in industrial oil

Abstract

The invention discloses porous metal organic hybrid glass for detecting the moisture content in industrial oil as well as a preparation method and application of the porous metal organic hybrid glass. The structural general formula of the hybrid glass is RExM (1-x) (NO3) y (C5H2N4) z, RE is at least one light-emitting rare earth ion of Tb < 3 + >, Eu < 3 + >, Sm < 3 + > and Dy < 3 + >, M is at least one non-light-emitting or weak-light-emitting low-cost cation of Zn < 2 + >, Mg < 2 + >, Ca < 2 + > and Al < 3 + >, and x is the mole fraction of RE in total cations and meets the condition that xlt is larger than or equal to 0.1; and in the formula, C5H2N4 is a 4, 5-dicyanoimidazole ligand. According to the material, a precursor solution is heated and evaporated, and micron-sized porous structures which are communicated with one another are formed in situ in the curing process. The porous structure greatly increases the specific surface area, so that the material has rapid and sensitive fluorescence response to water in oil. When the material is in contact with water-containing industrial oil, an energy transfer path from a ligand to rare earth ions in the material is damaged by water molecules, so that the rare earth characteristic fluorescence intensity is linearly quenched along with the increase of the water content. The material has the advantages of simplicity and convenience in preparation, controllable cost, quick response, high sensitivity, good selectivity, easiness in integration and the like, and is suitable for quick and online detection of trace moisture in industrial oil such as cutting oil, lubricating oil, hydraulic oil and the like.

Description

Technical Field

[0001] This invention belongs to the field of functional materials and sensing technology, specifically relating to a porous metal-organic hybrid glass material, its preparation method, and the application of this material as a sensing element in the rapid and sensitive detection of moisture content in industrial oils (such as cutting oil, lubricating oil, hydraulic oil, etc.). Background Technology

[0002] In high-precision manufacturing and mechanical equipment operation, industrial oils play crucial roles in lubrication, cooling, rust prevention, and cleaning. Even trace amounts of water in oils can severely affect their chemical stability and performance, such as accelerating oxidation and deterioration, causing additive failure, reducing lubricity, and triggering cavitation under high temperature and pressure conditions, thus exacerbating equipment wear and impairing processing accuracy and equipment lifespan. Therefore, accurate and rapid monitoring of trace amounts of water in industrial oils is of great significance for ensuring production safety, improving product quality, and implementing predictive maintenance.

[0003] Currently, methods for detecting moisture in oils mainly include Karl Fischer titration, gas chromatography, and oven drying. While these methods are accurate, they typically require complex sample pretreatment, specialized operators, and demanding laboratory environments, making them unsuitable for rapid, in-situ, and online monitoring in industrial settings. In recent years, optical sensing methods, particularly fluorescence sensing, have attracted widespread attention due to their rapid response, high sensitivity, and ease of device implementation. The core of these methods lies in developing fluorescently sensitive materials that specifically respond to moisture.

[0004] Rare earth ions (such as Tb) 3+ Eu 3+ Rare earth ions (REEs, etc.) are often used as luminescent centers for fluorescent probes due to their excellent optical properties, such as narrow emission peaks, long lifetimes, and large Stokes shifts. However, REEs themselves have weak light absorption (ff transition forbidden), resulting in low direct excitation efficiency and weak luminescence signals. Sensitization via an "antenna effect" using organic ligands is usually required; that is, the ligand absorbs light energy and excites the REE ions to emit light through energy transfer. This process is highly susceptible to interference from the surrounding environment (especially water molecules), because high-energy vibrational groups (OH) in water molecules can quench the triplet excitons of the ligands or coordinate with the REE ions, blocking the energy transfer path and causing quenching of the characteristic fluorescence of REEs. Utilizing this phenomenon holds promise for achieving specific sensing of water.

[0005] However, existing rare-earth fluorescent sensing materials mostly exist in the form of powders, nanocrystals, or coordination polymers. When used directly in oil systems, they suffer from problems such as easy agglomeration, difficulty in dispersion, difficulty in separation from the oil, and potential introduction of impurities that affect oil performance. Furthermore, designing material structures to achieve rapid response and high-sensitivity detection of moisture in oil remains a challenge.

[0006] Metal-organic hybrid glasses, as an emerging amorphous material, combine the stability of inorganic glasses with the functional tunability of organic components, and are easy to process and shape. Therefore, developing a novel rare-earth hybrid glass material that can be stably immersed in oil, is sensitive to moisture, and is easily integrated into sensing devices is of significant application value. Furthermore, partially replacing expensive rare-earth ions with low-cost metal ions reduces manufacturing costs. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a novel porous metal-organic hybrid glass material. This material not only possesses stable luminescent properties, but more importantly, its photoluminescence intensity is extremely sensitive to changes in the moisture content of industrial oils, enabling rapid and highly selective detection of trace amounts of moisture. This invention allows for controllable rare earth element usage, reducing manufacturing costs. This invention also provides a simple preparation method for this material and its application in industrial oil moisture content detection sensors.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a porous metal-organic hybrid glass for detecting the water content in industrial oil.

[0010] The general structural formula of the hybrid glass is: RE x M 1-x (NO3) γ (C5H2N4)2, where:

[0011] ·RE is selected from Tb 3+ Eu 3+ 、Sm 3+ Dy 3+ At least one luminescent rare earth ion in it;

[0012] M is selected from Zn 2+ Mg 2+ Ca 2+ Al 3+ At least one non-luminescent or weakly luminescent low-valence cation;

[0013] ·x is the mole fraction of RE in the total cations (RE+M), and satisfies 0.1≤x<1.0;

[0014] • C5H2N4 is a 4,5-dicyanimidazolium ligand (DCI);

[0015] The hybrid glass has a porous structure;

[0016] The photoluminescence intensity of the hybrid glass decreases linearly with increasing moisture content in the industrial oil environment it contacts. Preferably, the porous structure originates from bubbles generated and retained within the precursor solution during heating and evaporation. This loose, porous structure significantly increases the specific surface area of ​​the material, providing channels for the rapid adsorption and diffusion of water molecules, thereby significantly shortening the sensor's response time.

[0017] Preferably, the mole fraction x of RE in the total cations satisfies 0.1 ≤ x ≤ 0.5. Within this range, the material can maintain sufficient luminescence signal intensity while exhibiting good structural stability and glass-forming properties.

[0018] Preferably, the excitation light source wavelength of the hybrid glass is 250 nm to 400 nm. When RE is Tb 3+ At that time, its characteristic emission peak at 545nm (5D4→ 7 The F5 transition intensity shows a strong linear negative correlation with moisture content, making it ideal for quantitative moisture analysis.

[0019] This invention provides the application of the aforementioned porous metal-organic hybrid glass in the detection of water content in industrial oils. By placing the hybrid glass in the oil to be tested and monitoring the attenuation of its photoluminescence intensity, quantitative or qualitative detection of the water content in the oil can be achieved. Experiments show that this material has a wide linear detection range for water (0% to 5%, v / v), a low detection limit (not higher than 0.11%), and high selectivity for common oily components and ionic interference.

[0020] This invention provides a method for preparing the above-mentioned porous metal-organic hybrid glass, comprising the following steps:

[0021] (1) Dissolve rare earth nitrate, substituted cation salt and 4,5-dicyanimidazol together in deionized water and stir to form a uniform and clear precursor solution; wherein the molar percentage of rare earth ions in the total cations is not less than 10%.

[0022] (2) The precursor solution is heated and evaporated at 130-180°C to remove the solvent. During the evaporation process, a large number of bubbles are generated inside the solution due to boiling. As the solvent is continuously removed, the morphology of these bubbles is "frozen" and retained in the gradually solidifying glass, thereby forming a unique, interconnected micron-sized porous structure in situ, ultimately resulting in a transparent or translucent glass. The heating and evaporation time is 1 to 3 hours, preferably 1 to 2 hours.

[0023] Preferably, the alternative cationic salt is zinc nitrate. 2+ The introduction of [the material] helps stabilize the glass network structure and has little interference with light emission.

[0024] This invention provides an industrial oil and moisture content detection sensor, comprising:

[0025] The porous metal-organic hybrid glass described above is used as a sensing element;

[0026] A light source (such as an LED or laser diode with a wavelength of 250-400 nm) is used to excite the hybrid glass;

[0027] Detectors (such as photodiodes or CCDs) used to detect the intensity of their photoluminescence signals;

[0028] And a signal processing unit, which is configured to convert the real-time detected photoluminescence signal intensity value (or its attenuation value) into the corresponding moisture content value and output it for display, according to a pre-calibrated light intensity-moisture content relationship curve. Attached Figure Description

[0029] Figure 1 The photographs of the Tb-based porous metal-organic hybrid glass (P-Tb-glass) prepared in Example 1 of this invention under fluorescent and 365nm ultraviolet light show its rich internal porous / bubble structure.

[0030] Figure 2 Scanning electron microscope (SEM) image of P-Tb-glass (left) and bubble micrograph, showing the porous / bubble structure at the micrometer scale.

[0031] Figure 3 The X-ray diffraction (XRD) pattern shows the amorphous structure of the material.

[0032] Figure 4 The Fourier transform infrared (FTIR) spectrum of P-Tb-glass shows its abundant hydrophilic groups.

[0033] Figure 5 The UV-Vis absorption spectra of P-Tb-glass and P-Tb-glass in water-containing cutting oil are shown.

[0034] Figure 6 The sensing performance of P-Tb-glass for water content in cutting oil: fluorescence intensity decay curve over time in oil with 5% water content (response kinetics).

[0035] Figure 7 P-Tb-glass sensing performance of water content in cutting oil: P-Tb spectra in oils with different water contents (0-5%)

[0036] Figure 8The sensing performance of P-Tb-glass for moisture content in cutting oil: a linear calibration curve of the logarithm of fluorescence intensity at 545 nm versus moisture content.

[0037] Figure 9 This is a selective evaluation chart of P-Tb-glass for moisture detection in cutting oil systems. The effects of various potential interfering substances (polar solvents, metal ions, etc.) on fluorescence intensity were compared when present alone and coexisting with 3% water. (1. Ethanol; 2. Ethyl acetate; 3. Oleic acid; 4. Dimethyl silicone oil; 5. Octadecylene; 6. Cyclohexane; 7. NaCl; 8. AlCl3; 9. FeCl3; 10. CuCl2)

[0038] Figure 10 Comparison of P-Tb-glass photographs under sunlight (top row) and ultraviolet light (365nm, bottom row), showing the glass body, immersed in dry cutting oil, and immersed in water-containing cutting oil, respectively.

[0039] Figure 11 The changes in fluorescence intensity of P-Tb-glass in cyclohexane, octadecene, ethyl acetate, ethanol, and water after reaction times of 1 and 2 h are shown. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0041] Example 1: Preparation of porous Tb / Zn hybrid glass (P-Tb-glass), x = 0.5

[0042] Weigh out 0.6795 g (1.5 mmol) of Tb(NO3)3·6H2O, 0.4455 g (1.5 mmol) of Zn(NO3)2·6H2O, and 0.7086 g (6.0 mmol) of 4,5-dicyanimidazole (DCI). Add 2 mL of deionized water. Place the vial on a heating plate at 140 °C and stir to obtain a clear precursor solution. Then, transfer the solution to a preheated silica gel mold (2 cm × 2 cm × 2 cm) and place the mold in an oven at 140 °C for 1 hour to evaporate. During this process, bubbles are continuously generated and released inside the solution. After the water has completely evaporated and the material has solidified, allow it to cool naturally to room temperature and demold to obtain a transparent, pale green glass containing numerous micropores, denoted as P-Tb-glass. Its structure corresponds to the case where x = 0.5 in the general formula.

[0043] Example 2: Preparation of porous Tb / Zn hybrid glass, x = 0.33

[0044] Weigh out 0.2265 g (0.5 mmol) of Tb(NO3)3·6H2O, 0.2975 g (1.0 mmol) of Zn(NO3)3·6H2O, and 0.3543 g (3.0 mmol) of DCI, and prepare glass according to the same procedure as in Example 1 (evaporation at 140 °C for 1 hour). The total molar fraction of Tb and Zn cations in the resulting glass, x(Tb) = 0.33. This glass also exhibits a porous structure, with a slightly lower luminescence intensity than that of Example 1, but better structural stability and lower cost.

[0045] Example 3: Characterization of Material Structure and Morphology

[0046] The P-Tb-glass prepared in Example 1 was characterized as follows:

[0047] Morphological observation: Actual photos of fluorescent lamps and ultraviolet lamps ( Figure 1 Scanning electron microscope (SEM) images Figure 2 (left) and photomicrograph ( Figure 2 The right image clearly shows that there are a large number of closed or semi-closed pores / bubbles of varying sizes inside the material, confirming the effectiveness of the method of inducing bubble formation and retention through heating and evaporation to construct a porous structure.

[0048] Structural analysis: X-ray diffraction (XRD) patterns Figure 3 The product is shown to be amorphous, lacking sharp crystalline diffraction peaks, indicating its glassy nature. Fourier transform infrared (FTIR) spectroscopy... Figure 4 The characteristic cyano (C≡N) stretching vibration peak of DCI (~2245 cm⁻¹) can be seen in the image. -1 ) and nitrate characteristic peak (1385 cm⁻¹) -1 This confirmed the integrity of the organic ligands and their binding with metal ions.

[0049] Example 4: Study on optical properties and sensing mechanism

[0050] Absorption and luminescence properties: such as Figure 5 As shown, the UV-Vis absorption peak of P-Tb-glass in water-containing cutting oil red-shifts from 376 nm to 388 nm, indicating that the electronic structure of the glass changes after contact with water.

[0051] Moisture sensing response performance: When the P-Tb-glass was immersed in cutting oil with a water content of 5% (v / v), its fluorescence intensity at 545 nm decreased rapidly and reached equilibrium within 30 minutes. Figure 6 This indicates a rapid response. The material was placed in a series of cutting oils with different water contents (0–5%), and after equilibration, the PL spectrum was measured. Figure 7 As water content increases, Tb 3+The intensities of each characteristic peak (at 490, 545, 585, and 622 nm) decrease systematically. The logarithm (lgI) of the intensity of the 545 nm peak decreases. 545 A graph showing the moisture content exhibits a good linear relationship within the range of 0–5%. Figure 8 ):lgI 545 =6.736–0.056C, R 2 =0.996. Based on the 3.3σ / k rule, the limit of detection (LOD) is 0.108%.

[0052] Selective assessment: such as Figure 9 As shown, the response of P-Tb-glass to common potential interfering substances in cutting oils was tested. These included polar solvents such as ethanol and ethyl acetate, as well as Na... + Cl - Plasma has a negligible effect on fluorescence signals. Al 3+ Fe 3+ Cu 2+ Metal ions cause a decrease in fluorescence due to their self-quenching effect, but when they coexist with 3% water, the decrease in fluorescence intensity is mainly contributed by water, indicating that P-Tb-glass has a dominant response to moisture. Oily substances such as oleic acid, silicone oil, and alkanes have virtually no interference.

[0053] Visual demonstration: Figure 10 The photographs compared the appearance and luminescence of P-Tb-glass in three states: the glass body, immersed in dry cutting oil, and immersed in water-containing cutting oil. Under a 365nm ultraviolet lamp, the first two emitted bright green fluorescence, while the latter's fluorescence dimmed significantly or even disappeared, which was visible to the naked eye, directly demonstrating the material's sensitive response to moisture. Figure 11 The results show that when P-Tb-glass is immersed in a series of solvents of different polarities, bright green fluorescence is observed in cyclohexane, octadecene, ethyl acetate, and ethanol, while the green fluorescence disappears in aqueous solution. This represents the quenching effect of aqueous solution on the luminescence of P-Tb-glass.

[0054] Example 5: Sensor Device Construction and Application Demonstration

[0055] A simple detection unit was constructed: a P-Tb-glass (approximately 5mm × 5mm × 1mm) prepared in Example 1 was fixed in the sample cell as a sensing probe. A 365nm UV-LED was placed above it as an excitation source, and connected to a miniature spectrometer (detector) via optical fiber on the side. The sample cell was immersed in the cutting oil to be tested.

[0056] Before use, the system was calibrated using a series of standard oil samples with known water content to establish a calibration curve of 545nm fluorescence intensity versus water content.

[0057] In actual testing, the oil sample to be tested is injected into the sample cell, the system automatically collects the fluorescence spectrum, extracts the 545nm intensity value, and compares it with the calibration curve through the built-in signal processing unit, so that the water content (%) of the oil sample can be read directly on the display screen.

[0058] Spiked recovery experiments were conducted on actual cutting oil samples (Table 1). The recovery rates ranged from 97.6% to 101.3%, and the relative standard deviation (RSD) was less than 7%, demonstrating the accuracy and reliability of this method in practical applications.

[0059] Table 1. Results of water spike recovery experiments in actual cutting oil samples (n=3)

[0060]

[0061] In summary, the porous metal-organic hybrid glass provided by this invention forms a porous structure through a unique "evaporation-induced foaming" process. It achieves strong luminescence through efficient energy transfer from DCI to rare-earth ions and utilizes an energy transfer quenching effect highly sensitive to water molecules, enabling highly sensitive, selective, and rapid detection of trace amounts of moisture (0-5%) in industrial oils. This material is morphologically stable and easy to integrate, providing an ideal sensitive material for developing novel online oil moisture monitoring sensors.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A porous metal-organic hybrid glass for detecting the water content in industrial oil, characterized in that: The general structural formula of the hybrid glass is RE x M (1-x) (NO3) y (C5H2N4) z ,in: ·RE is selected from Tb 3+ Eu 3+ 、Sm 3+ Dy 3+ At least one luminescent rare earth ion in it; M is selected from Zn 2+ Mg 2+ Ca 2+ Al 3+ At least one non-luminescent or weakly luminescent low-valence cation; ·x is the mole fraction of RE in the total cations (RE+M), and satisfies 0.1≤x<1.0; • C5H2N4 is a 4,5-dicyanimidazolium ligand; The hybrid glass has a porous structure; Furthermore, the photoluminescence intensity of the hybrid glass decreases linearly with the increase of moisture content in the industrial oil environment it contacts, thus serving as an optical sensor for moisture content.

2. The porous metal-organic hybrid glass according to claim 1, characterized in that: The porous structure originates from the bubbles generated and retained inside the precursor solution during the heating and evaporation process.

3. The porous metal-organic hybrid glass according to claim 1 or 2, characterized in that: The mole fraction x of RE in the total cations satisfies 0.1 ≤ x ≤ 0.

5.

4. The porous metal-organic hybrid glass according to claim 1 or 2, characterized in that: The excitation light source wavelength of the hybrid glass is 250 nm to 400 nm, and its Tb 3+ The intensity of the characteristic emission peak at 545 nm of the doped sample was used for moisture quantification, and the intensity variation of the strongest emission peak among other rare earth ions was used for moisture quantification.

5. An application of a porous metal-organic hybrid glass as described in any one of claims 1-4 in the detection of moisture content in industrial oil, characterized in that: The hybrid glass is placed in the oil to be tested, and the water content in the oil is quantitatively or qualitatively detected by monitoring the attenuation of its photoluminescence intensity; wherein the detected water content range is 0% to 5% (v / v); preferably, the detection limit for water is not higher than 0.11%.

6. A method for preparing the porous metal-organic hybrid glass as described in claim 1, characterized in that, Includes the following steps: (1) Rare earth nitrate, substituted cation salt and 4,5-dicyanimidazolium are dissolved together in deionized water to form a homogeneous precursor solution; wherein the molar percentage of rare earth ions in the total cations is not less than 10%. (2) The precursor solution is heated and evaporated at 130-180°C to remove the solvent. During the evaporation process, a large number of bubbles are generated inside the solution. As the solvent is removed, the bubble morphology is retained in the solid glass, thereby forming a porous structure in situ, and finally obtaining a transparent or translucent glass. The heating and evaporation time is 1 to 3 hours.

7. The method according to claim 6, characterized in that: The alternative cationic salt is zinc nitrate.

8. An industrial oil and water content detection sensor, characterized in that, include: The porous metal-organic hybrid glass as described in any one of claims 1-4 is used as the sensing element; A light source used to excite the hybrid glass; A detector used to detect the intensity of its photoluminescence signal; And a signal processing unit, which is configured to convert the attenuation value of the detected photoluminescence signal intensity into the corresponding moisture content value and output it according to a pre-calibrated light intensity-moisture content relationship curve.

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