Eu-MOF material, preparation method and application thereof

Abstract

The application relates to the technical field of the cross of forensic science and material chemistry, and particularly relates to a Eu-MOF material, a preparation method and application thereof. The preparation method comprises the following steps: taking 2,5-pyridine dicarboxylic acid as a ligand, taking europium salt as a metal source, taking o-fluorobenzoic acid as an adjusting agent, and carrying out a solvothermal reaction in an acid system controlled by nitric acid to obtain the Eu-MOF material with a binuclear europium cluster structure unit and an orthorhombic crystal system Fddd space group. The material is stable below 310 DEG C, and emits red fluorescence with 620 nm as the main color under the excitation of ultraviolet light with 254 nm or 300 nm. The material can be used as an exogenous marker to be doped into gunpowder to realize the ultraviolet visualization and rapid detection of shooting residues, and can be used as a fluorescent appearing powder to realize the high-contrast appearance of latent fingerprints on the surfaces of various objects such as glass, plastic and paper. The preparation process is simple, the material has high thermal stability and strong fluorescence performance, and the same material realizes the dual application in two types of forensic science evidence analysis.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of forensic science and materials chemistry, specifically to an Eu-MOF material, its preparation method, and its applications. Background Technology

[0002] In crime scene investigation and forensic examination of gun-related cases, gunshot residue and latent fingerprints are two of the most crucial types of forensic evidence. Gunshot residue refers to gunpowder particles, unburned gunpowder, and metal fragments ejected from firearm components when the weapon is fired. Its spatial distribution information can be used to infer shooting distance, reconstruct gun-holding posture, and determine the contact relationship between the suspect and the weapon, playing an irreplaceable role in case reconstruction. Latent fingerprints are among the most common biological traces found at crime scenes; their uniqueness and stability make them a direct basis for personal identification. Therefore, developing efficient, sensitive, and convenient detection technologies to achieve rapid discovery and accurate extraction of these two types of evidence remains a hot topic and a challenge in forensic science research.

[0003] Currently, the detection of gunshot residues mainly relies on scanning electron microscopy combined with energy dispersive spectroscopy (EDS). This method, which achieves high-precision identification through morphological observation and elemental composition analysis, is considered the "gold standard" in forensic science. However, this technology is expensive, complex to operate, and time-consuming, making it difficult to meet the practical needs of rapid screening at crime scenes. While chemical colorimetric methods are simple to operate, they have low sensitivity and specificity, are easily affected by environmental background interference, and often produce false positive or false negative results. More seriously, with the global promotion and application of environmentally friendly ammunition, the heavy metal characteristic elements in traditional ammunition, such as lead, barium, and antimony, are gradually decreasing or even disappearing, leading to the risk of failure for detection methods based on these characteristic elements. Therefore, developing artificially added, stable exogenous markers has become an important research direction in the field of gunshot residue detection.

[0004] For the development of latent fingerprints, traditional powder methods such as gold powder, silver powder, and magnetic powder are widely used due to their simplicity and low cost. However, on dark-colored objects, objects with complex patterns, or objects with fluorescent backgrounds, there are often problems such as severe background interference and insufficient contrast of ridge lines, which seriously affect fingerprint recognition and comparison. Although fluorescent powder can effectively improve detection sensitivity, existing fluorescent materials often have limitations such as poor photostability, complex preparation processes, or certain biological toxicity, which restrict their application in actual cases.

[0005] In recent years, metal-organic frameworks (MOFs) have shown broad application prospects in forensic science due to their tunable structure, large specific surface area, and excellent luminescence properties. Among them, rare-earth MOFs, with their unique 4f electron transition characteristics of rare-earth ions, possess advantages such as high color purity, large Stokes shift, and long fluorescence lifetime, attracting significant attention in fluorescence detection. However, currently, common rare-earth MOFs have relatively limited functions, and the structures and properties used vary in emphasis.

[0006] Therefore, developing a material with a simple preparation process, stable and reliable performance, and dual functions of marking bullet residue and revealing latent fingerprints can not only reduce the material costs and technical complexity of on-site investigation, but also provide new technical means for the correlation analysis of these two types of key physical evidence. This has important practical significance and broad application prospects. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in the prior art by providing an Eu-MOF material, its preparation method, and its applications. This material features simple preparation, good thermal stability, high luminescence intensity, and strong anti-interference ability. It can simultaneously achieve rapid visual marking of bullet residue and high-quality visualization of latent fingerprints, providing an efficient new method for forensic crime scene evidence analysis.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of the present invention provides a method for preparing Eu-MOF materials, comprising the following steps:

[0010] Step 1: Obtain a ligand solution formed by dissolving 2,5-pyridinedicarboxylic acid in N,N-dimethylformamide;

[0011] Step 2: Add europium salt, o-fluorobenzoic acid, DMF solution of nitric acid and water to the ligand solution, mix well to obtain the reaction precursor solution;

[0012] Step 3: Seal the reaction precursor solution in a container and carry out a solvothermal reaction;

[0013] Step 4: After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain Eu-MOF material.

[0014] The method for preparing Eu-MOF materials provided by this invention involves a solvothermal reaction in an acidic system regulated by nitric acid, using 2,5-pyridinedicarboxylic acid as the organic ligand, europium salt as the metal source, and o-fluorobenzoic acid as the crystal growth regulator. This successfully constructs Eu-MOF materials with binuclear europium cluster structural units belonging to the orthorhombic crystal system Fddd space group. This method is simple, mild, and highly controllable. The introduction of o-fluorobenzoic acid effectively regulates the nucleation and growth process of the crystals, ensuring the formation and structural integrity of the target crystal phase. The addition of nitric acid optimizes the acidic environment of the reaction system, promoting the coordination efficiency between the ligand and europium ions. The prepared Eu-MOF material exhibits excellent thermal stability (no structural decomposition below 310°C) and strong characteristic red fluorescence (main peak at 620 nm). This allows it to be used as an exogenous marker incorporated into propellant for rapid UV visualization and detection of shooting residues after firing. It can also be used as a fluorescent developing powder for high-contrast development of latent fingerprints on various surfaces such as glass, tiles, plastics, and paper, effectively overcoming the background interference problem of traditional methods against dark or complex backgrounds. This invention achieves the dual application of a single material in two key forensic evidence analyses, significantly reducing the material costs and technical complexity of crime scene investigation, and possesses good practical value and promising prospects for widespread application.

[0015] Furthermore, in step 1, the molar concentration of 2,5-pyridinedicarboxylic acid in the ligand solution is 20 mmol / L-25 mmol / L.

[0016] Further, in step 2, the europium salt is at least one selected from europium nitrate, europium chloride, and europium acetate; and / or, the molar ratio of the europium salt to 2,5-pyridinedicarboxylic acid is 0.5:1-1.5:1. Preferably, in step 2, the molar ratio of the europium salt to 2,5-pyridinedicarboxylic acid is 0.8:1-1.2:1.

[0017] Furthermore, in step 2, based on each mole of europium nitrate hexahydrate: the added mass of o-fluorobenzoic acid is 1000-1200 g; the DMF solution of nitric acid is obtained by mixing nitric acid with DMF at a mass concentration of 60%-70% at a volume ratio of 2-4:8-15, and the added volume is 5-8 L; the added volume of water is 10-15 L.

[0018] Furthermore, in step 3, the temperature of the solvothermal reaction is 350K-400K; and / or, the time of the solvothermal reaction is 24h-48h.

[0019] Furthermore, in step 4, the sample is washed with N,N-dimethylformamide and methanol.

[0020] A second aspect of the present invention provides a Eu-MOF material prepared by the method described above.

[0021] A second aspect of the present invention provides an Eu-MOF material prepared by the preferred method described above. This material, through the directional coordination assembly of 2,5-pyridinedicarboxylic acid and europium ions, and under the regulation of o-fluorobenzoic acid as a modulator, forms a three-dimensional network framework with binuclear europium cluster structural units belonging to the orthorhombic crystal system Fddd space group. When incorporated into bullet propellant as an exogenous marker, it can maintain complete crystal morphology and fluorescence activity in shooting residues, achieving rapid visualization and localization under ultraviolet light. As a fluorescent developing powder, its good affinity for sweat and oil allows it to clearly display latent fingerprints on various surfaces such as glass, ceramic tiles, plastics, and paper using a powder-sprinkling and shaking development method. The detailed features of the fingerprint lines (including tertiary features such as sweat pores and edge morphology) are fully discernible, and high-contrast display effects can still be obtained on dark or complex backgrounds. The material of this invention enables the dual application of a single substance in the analysis of two key types of forensic evidence. This not only avoids the cumbersome process of using multiple materials required by traditional methods, but also significantly reduces the material costs and technical complexity of on-site investigation, demonstrating its excellent practical application value.

[0022] Furthermore, the Eu-MOF material belongs to the orthorhombic crystal system with space group Fddd and has a binuclear europium cluster structure unit; and / or emits red fluorescence with a wavelength of 600-700 nm under 254 nm or 300 nm ultraviolet light excitation.

[0023] A third aspect of the invention provides the application of the Eu-MOF material as described above in the marking of bullet residues or the development of latent handprints.

[0024] The third aspect of this invention provides the application of the aforementioned Eu-MOF material in marking shooting residues or developing latent fingerprints. As an exogenous marker for shooting residues, this material, when incorporated into propellant, maintains its crystal structure and fluorescence properties even under high temperature and pressure at the moment of firing. After firing, it displays dense red fluorescent particles on the shooter's hand, the surface of the firearm, and around the cartridge case under 254 nm ultraviolet light, enabling rapid visualization and localization of shooting residues. This solves the technical problems of traditional detection methods, such as reliance on expensive equipment, long processing times, and difficulty in on-site screening. It also avoids the risk of traditional heavy metal characteristic element detection failing due to the widespread use of lead-free environmentally friendly ammunition. As a latent fingerprint developing powder, this material, with its excellent affinity and adsorption capacity for sweat and oil, can clearly develop latent fingerprints on various surfaces such as glass, tiles, plastic, and paper using a powder-sprinkling and shaking method. Under ultraviolet light excitation, the red fluorescent lines form a high-contrast relationship with the background, effectively overcoming interference from dark or complex backgrounds. The fingerprint lines are continuous and complete, and first- to third-level details such as sweat pores and edge morphology can be identified, meeting the requirements of forensic identification. The same material can be applied to both of the above fields at the same time, achieving the technical effect of "one material for two purposes" - on-site investigators only need to carry one type of powder to complete the two key physical evidence discovery tasks of locating shooting residue and revealing submerged handprints, which significantly reduces the cost of material procurement, storage and carrying, simplifies on-site operation procedures and improves investigation efficiency.

[0025] Furthermore, the doping concentration of the Eu-MOF material in the propellant is 5 wt%-10 wt%.

[0026] A fourth aspect of the present invention provides a dual-function kit for forensic evidence analysis, comprising the aforementioned Eu-MOF material and an instruction manual describing the application of the Eu-MOF material in marking bullet residue and revealing latent fingerprints.

[0027] A fourth aspect of this invention provides a dual-function reagent kit for forensic evidence analysis. When detecting gunshot residue, operators can add Eu-MOF material to the propellant of the bullet at a concentration of 5 wt%-10 wt% according to the instructions. After firing, fluorescent residues around the hand, firearm, and cartridge case can be quickly located using an ultraviolet light source. When revealing latent fingerprints, the same bottle of Eu-MOF material can be used directly to process fingerprints on various object surfaces using a powder-sprinkling and shaking development method, obtaining high-contrast fluorescent ridges under ultraviolet light. This reagent kit has good commercialization and industrialization prospects and is of great significance for improving the efficiency and quality of crime scene investigation in gun-related cases.

[0028] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0029] 1. The method for preparing Eu-MOF materials provided by this invention involves a solvothermal reaction in an acidic system regulated by nitric acid using 2,5-pyridinedicarboxylic acid as an organic ligand, europium salt as a metal source, and o-fluorobenzoic acid as a crystal growth regulator. This successfully constructs Eu-MOF materials with binuclear europium cluster structural units belonging to the orthorhombic crystal system Fddd space group. This method is simple, mild, and highly controllable. The introduction of o-fluorobenzoic acid effectively regulates the nucleation and growth process of the crystals, ensuring the formation and structural integrity of the target crystal phase. The addition of nitric acid optimizes the acidic environment of the reaction system, promoting the coordination efficiency between the ligand and europium ions. The prepared Eu-MOF material exhibits excellent thermal stability (no structural decomposition below 310°C) and strong characteristic red fluorescence (main peak at 620 nm). This allows it to be used as an exogenous marker incorporated into propellant for rapid UV visualization and detection of shooting residues after firing. It can also be used as a fluorescent developing powder for high-contrast development of latent fingerprints on various surfaces such as glass, tiles, plastics, and paper, effectively overcoming the background interference problem of traditional methods against dark or complex backgrounds. This invention achieves the dual application of a single material in two key forensic evidence analyses, significantly reducing the material costs and technical complexity of crime scene investigation, and possesses good practical value and promising prospects for widespread application.

[0030] 2. The Eu-MOF material provided by this invention. This material, through the directional coordination assembly of 2,5-pyridinedicarboxylic acid and europium ions, and under the regulation of o-fluorobenzoic acid as a modulator, forms a three-dimensional network framework with binuclear europium cluster structural units belonging to the orthorhombic crystal system Fddd space group. When incorporated into bullet propellant as an exogenous marker, it maintains complete crystal morphology and fluorescence activity in shooting residues, enabling rapid visualization and localization under ultraviolet light. As a fluorescent developing powder, its excellent affinity for sweat and oil allows it to clearly reveal latent fingerprints on various surfaces such as glass, ceramic tiles, plastics, and paper using a powder-sprinkling and shaking development method. The detailed features of the fingerprint lines (including tertiary features such as sweat pores and edge morphology) are fully discernible, and high-contrast display effects are still achieved on dark or complex backgrounds. This invention enables the dual application of a single substance in the analysis of two key types of forensic evidence, not only avoiding the cumbersome use of multiple materials required by traditional methods but also significantly reducing the material costs and technical complexity of on-site investigations, demonstrating significant practical application value.

[0031] 3. Application of the Eu-MOF material provided by this invention in marking shooting residues or developing latent fingerprints. As an exogenous marker for shooting residues, this material, after being incorporated into the propellant of bullets, can maintain its crystal structure and fluorescence properties even under high temperature and high pressure at the moment of firing. After firing, it can exhibit dense red fluorescent particles on the shooter's hand, the surface of the firearm, and around the cartridge case under 254 nm ultraviolet light, achieving rapid visualization and localization of shooting residues. This solves the technical problems of traditional detection methods relying on expensive equipment, being time-consuming, and difficult to screen on-site. At the same time, it avoids the risk of traditional heavy metal characteristic element detection failing due to the popularization of lead-free environmentally friendly ammunition. As a latent fingerprint developing powder, this material, with its good affinity and adsorption capacity for sweat and oil, can clearly develop latent fingerprints on various object surfaces such as glass, tiles, plastics, and paper through the powder-sprinkling and shaking development method. Under ultraviolet light excitation, the red fluorescent lines form a high contrast with the object background, effectively overcoming the interference of dark or complex patterned backgrounds. The fingerprint lines are continuous and complete, and first to third-level details such as sweat pores and edge morphology can be identified, meeting the requirements of forensic identification. The same material can be applied to both of the above fields at the same time, achieving the technical effect of "one material for two purposes" - on-site investigators only need to carry one type of powder to complete the two key physical evidence discovery tasks of locating shooting residue and revealing submerged handprints, which significantly reduces the cost of material procurement, storage and carrying, simplifies on-site operation procedures and improves investigation efficiency.

[0032] 4. This invention provides a dual-function reagent kit for forensic evidence analysis. When detecting gunshot residue, operators can add Eu-MOF material to the propellant of the bullet at a concentration of 5 wt%-10 wt% according to the instructions. After firing, fluorescent residues around the hand, firearm, and cartridge case can be quickly located using an ultraviolet light source. When revealing latent fingerprints, the same bottle of Eu-MOF material can be used directly to process fingerprints on various object surfaces using a powder-sprinkling and shaking development method, obtaining high-contrast fluorescent ridges under ultraviolet light. This reagent kit has good commercialization and industrialization prospects and is of great significance for improving the efficiency and quality of crime scene investigation in gun-related cases. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the crystal structure and coordination environment of the Eu-MOF prepared in Example 1.

[0034] Figure 2 Comparison of powder X-ray diffraction (PXRD) images of Eu-MOF prepared in Example 1.

[0035] Figure 3 Thermogravimetric analysis (TGA) curve of Eu-MOF prepared in Example 1.

[0036] Figure 4The excitation and emission spectra of the Eu-MOF prepared in Example 1 are shown.

[0037] Figure 5 The image shows the distribution of fluorescent GSR on the surface of the hand after live-fire shooting using the material prepared in Example 1 of this invention.

[0038] Figure 6 The fluorescent GSR distribution map on the surface of the gun after live-fire shooting using the material prepared in Example 1 of the present invention.

[0039] Figure 7 The fluorescent GSR distribution map of the cartridge case after live-fire testing using the material prepared in Example 1 of this invention.

[0040] Figure 8 The images show the effect of latent handprints appearing on different object surfaces using the material prepared in Example 1 of the present invention. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention.

[0043] The first aspect of this embodiment provides a method for preparing Eu-MOF materials, including the following steps:

[0044] Step 1: Obtain a ligand solution formed by dissolving 2,5-pyridinedicarboxylic acid in N,N-dimethylformamide;

[0045] Step 2: Add europium salt, o-fluorobenzoic acid, nitric acid and water to the ligand solution, mix well to obtain the reaction precursor solution;

[0046] Step 3: Seal the reaction precursor solution in a container and carry out a solvothermal reaction;

[0047] Step 4: After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain Eu-MOF material.

[0048] The method for preparing Eu-MOF materials provided by this invention involves a solvothermal reaction in an acidic system regulated by nitric acid, using 2,5-pyridinedicarboxylic acid as the organic ligand, europium salt as the metal source, and o-fluorobenzoic acid as the crystal growth regulator. This successfully constructs Eu-MOF materials with binuclear europium cluster structural units belonging to the orthorhombic crystal system Fddd space group. This method is simple, mild, and highly controllable. The introduction of o-fluorobenzoic acid effectively regulates the nucleation and growth process of the crystals, ensuring the formation and structural integrity of the target crystal phase. The addition of nitric acid optimizes the acidic environment of the reaction system, promoting the coordination efficiency between the ligand and europium ions. The prepared Eu-MOF material exhibits excellent thermal stability (no structural decomposition below 310°C) and strong characteristic red fluorescence (main peak at 620 nm). This allows it to be used as an exogenous marker incorporated into propellant for rapid UV visualization and detection of shooting residues after firing. It can also be used as a fluorescent developing powder for high-contrast development of latent fingerprints on various surfaces such as glass, tiles, plastics, and paper, effectively overcoming the background interference problem of traditional methods against dark or complex backgrounds. This invention achieves the dual application of a single material in two key forensic evidence analyses, significantly reducing the material costs and technical complexity of crime scene investigation, and possesses good practical value and promising prospects for widespread application.

[0049] Specifically, as shown in Examples 1-3:

[0050] Example 1

[0051] 7.5 mg (0.045 mmol) of 2,5-pyridinedicarboxylic acid was placed in a 5 mL glass bottle containing 2.2 mL of N,N-dimethylformamide (DMF) and sonicated for 5 minutes at room temperature until fully dissolved. Then, 20.07 mg (0.045 mmol) of Eu(NO3)3·6H2O, 49 mg of o-fluorobenzoic acid, 0.3 mL of a DMF solution of nitric acid (3 mL nitric acid + 10 mL DMF), and 0.5 mL of water were added to the glass bottle and stirred thoroughly.

[0052] The glass bottle was sealed and heated in an oven at 378 K for 36 h. After the reaction was completed, white crystalline substances were found to be produced on the bottle walls and bottom. The mixture was cooled to room temperature, filtered, and washed several times with DMF and methanol. After drying in air at room temperature, colorless and transparent octahedral crystals were obtained, which are the Eu-MOF materials.

[0053] Material characterization

[0054] Appendix Figure 1A schematic diagram of the crystal structure and coordination environment of the Eu-MOF is shown. Single-crystal X-ray diffraction analysis indicates that this MOF belongs to the orthorhombic crystal system, space group Fddd. In the structure of this MOF, all rare-earth metal Eu atoms are octetally coordinated, including four O atoms provided by the four carboxyl groups connecting to the other Eu atom in the binuclear structural unit, and two O and two N atoms provided by the two directly connected independent ligands H₂Pydc. (See attached diagram) Figure 2 The image shows a comparison of powder X-ray diffraction (PXRD) patterns of Eu-MOF. Comparison with the diffraction patterns simulated from single-crystal structures shows a high degree of agreement between the characteristic peak positions of the experimental patterns and the simulated values, confirming that the synthesized product is indeed the target Eu-Pydc pure phase, with no obvious impurity phases or unreacted raw material residues detected. (Attached) Figure 3 This is a thermogravimetric analysis (TGA) curve of Eu-MOF. The TGA analysis shows that the material's mass remains essentially stable between 30°C and 310°C, indicating that the framework structure has good thermal stability and can withstand firing environments. (Attached) Figure 4 The images show the excitation and emission spectra of Eu-MOF. Fluorescence spectroscopy analysis reveals a strong excitation peak near 300 nm (corresponding to ligand π-π* transitions) and a sharp emission peak in the 600-700 nm range (the main peak is approximately 620 nm, corresponding to Eu³⁺). 5 D0→ 7 F2 transition).

[0055] Shot Residue (GSR) Marking Test

[0056] Using specific ammunition (9mm police revolver cartridges) and firearms, the gun was fired 10 times to eliminate random errors.

[0057] The Eu-MOF powder synthesized in Example 1 was incorporated into the gunpowder of a DAP-92A 9mm pistol cartridge at a doping ratio of 5 wt%. The cartridge case was press-fitted using a heavy-duty press. Ten shots were fired using a Type 05 police revolver at the shooting range of the China Criminal Police University. After firing, the shooter's hands and the firearm were examined under ultraviolet light (λ=254nm), and photographs were taken for preservation. Particles of gunfire residue were collected from the shooter's hands and the firearm, and the luminescent gunfire residue and markers were analyzed using a scanning electron microscope.

[0058] The results show:

[0059] In live-fire experiments, Eu-MOF was incorporated into the propellant as a fluorescent marker. After firing, under 254 nm ultraviolet light illumination, clear red luminescent residues were observed on the shooter's hand, the surface of the firearm, and the cartridge case. This indicates that Eu-MOF successfully marked the firing residues, verifying its effectiveness as a GSR marker. Furthermore, this marker exhibits good stability and high contrast, facilitating identification against complex backgrounds. (Appendix) Figure 5 Appendix Figure 6 and attached Figure 7 The images show the fluorescent GSR distribution patterns on the surface of a hand, the surface of a firearm, and the cartridge case after live-fire exercises using the material of this invention.

[0060] Latent Handprint Manifestation Test

[0061] This experiment used Eu-MOF powder as a specific developing material for latent fingerprints mixed with oil and sweat. A controlled variable method was employed to investigate its developing effect on four different surfaces: glass, ceramic tile, plastic sheet, and paper, verifying the developing ability resulting from the strong adsorption of Eu-MOF powder. The fingerprints were applied by the same volunteer to minimize the impact of individual differences on the results. The developing process followed the standard powder-sprinkling and shaking method. Image acquisition was performed in a standard light source box, ensuring the sample surface was perpendicular to the camera lens. Images of the undeveloped fingerprints were captured under standard natural light conditions. Subsequently, the fingerprints were developed, with natural light turned off and the UV analyzer activated. Images of the fingerprints under UV excitation were then captured using the same camera parameters.

[0062] Eu-MOF powder exhibits superior performance in latent fingerprint development. Under ultraviolet light irradiation, Eu-MOF powder can clearly reveal sweat fingerprints on various substrates (such as glass, ceramic tiles, plastic sheets, and paper), effectively displaying 1-3 levels of detail. Compared to traditional fingerprint developing powders, Eu-MOF powder not only has stronger adsorption capacity but also provides higher contrast against complex backgrounds, thus overcoming the problems of background interference and blurred fingerprint outlines in traditional methods.

[0063] The powder-sprinkling and shaking method was used to acquire images in a standard light source box, with the ultraviolet excitation wavelength fixed at 254 nm and camera parameters standardized. Eu-MOF powder was sprinkled onto the surfaces of glass, ceramic tiles, plastic sheets, and paper bearing latent fingerprints. Excess powder was removed by shaking under natural light, followed by observation under ultraviolet light.

[0064] The results showed that continuous, high-contrast red fluorescent fingerprints were obtained on all four different substrates. Not only were the primary fingerprint patterns clear, but secondary and tertiary details such as sweat pores and start / end points were also clearly discernible. Eu-MOF emitted pure and high-intensity light, effectively overcoming interference from complex backgrounds (such as dark or patterned backgrounds). Compared to traditional fingerprint developing powders (mainly aluminum powder, bronze powder, magnetic powder, etc.), Eu-MOF powder not only has stronger adsorption capacity but also provides higher contrast against complex backgrounds, thus effectively overcoming the interference from complex backgrounds (such as dark or patterned backgrounds) and the problem of blurred fingerprint outlines. (Appendix) Figure 8 The images show the effect of using the material of this invention to produce latent handprints on different object surfaces.

[0065] Example 2

[0066] Add 7.4 mg (0.044 mmol) of 2,5-pyridinedicarboxylic acid to a 5 mL glass bottle containing 2.2 mL of N,N-dimethylformamide (DMF) and sonicate at room temperature for 5 minutes to dissolve completely. Then add 9.8 mg (0.022 mmol) of europium nitrate hexahydrate (Eu(NO3)3·6H2O), 22 mg of o-fluorobenzoic acid, 0.13 mL of a DMF solution of nitric acid (2 mL nitric acid + 11 mL DMF), and 0.22 mL of deionized water, and stir magnetically for 10 minutes until well mixed.

[0067] The glass bottle was sealed and placed in an oven at 350 K (105℃) for 48 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, and washed three times each with 5 mL of DMF and methanol. The mixture was then dried at room temperature to obtain the Eu-MOF material.

[0068] Example 3

[0069] Add 9.2 mg (0.055 mmol) of 2,5-pyridinedicarboxylic acid to a 5 mL glass bottle containing 2.2 mL of N,N-dimethylformamide (DMF) and sonicate at room temperature for 5 minutes to dissolve completely. Then add 36.8 mg (0.0825 mmol) of europium nitrate hexahydrate (Eu(NO3)3·6H2O), 99 mg of o-fluorobenzoic acid, 0.66 mL of nitric acid in DMF solution (4 mL nitric acid + 12 mL DMF), and 1.24 mL of deionized water, and stir magnetically for 10 minutes until well mixed.

[0070] The glass bottle was sealed and placed in an oven at 400 K (105℃) for 24 hours. After the reaction was completed, it was allowed to cool naturally to room temperature, filtered, and washed three times each with DMF and methanol (5 mL each time). The mixture was then dried at room temperature to obtain the Eu-MOF material.

[0071] The Eu-MOF materials prepared in Examples 2 and 3 were tested using the same method. The results showed that in live-fire experiments, when the Eu-MOF materials prepared in Examples 2-3 were incorporated into the propellant, clear red fluorescence was observed on the shooter's hand, the surface of the firearm, and the cartridge case under a 254 nm UV lamp after firing. Eu-MOF effectively marked the shooting residue and exhibited good stability and high contrast, facilitating identification against complex backgrounds. Continuous, high-contrast red fluorescent handprints were observed on various substrates, with clear distinction between primary, secondary, and tertiary details. Eu-MOF exhibited high luminescence intensity and pure color, effectively overcoming interference from complex backgrounds, and possessed strong adsorption capacity, demonstrating superior contrast compared to traditional powders.

[0072] In some embodiments, in step 1, the molar concentration of 2,5-pyridinedicarboxylic acid in the ligand solution is 20 mmol / L-25 mmol / L. When the ligand concentration is within a reasonable range, the probability of contact between the ligand and metal ions in the reaction system is moderate. This avoids the problems of difficult crystal nucleation and decreased yield caused by excessively low concentrations, while also preventing ligand self-aggregation or excessively rapid crystallization rates that may result from excessively high concentrations, thus preventing lattice defects.

[0073] In some embodiments, in step 2, the europium salt is at least one of europium nitrate, europium chloride, and europium acetate; and / or, the molar ratio of the europium salt to 2,5-pyridinedicarboxylic acid is 0.5:1-1.5:1. Preferably, in step 2, the molar ratio of the europium salt to 2,5-pyridinedicarboxylic acid is 0.8:1-1.2:1. Controlling the molar ratio of europium salt to ligand within the range of 0.5:1-1.5:1 ensures sufficient contact and coordination between the ligand and the metal ion, avoiding the formation of impurity phases that may be caused by excess metal ions, and also prevents unreacted ligand residues or crystal defects caused by excess ligands. Preferably, when the ratio is 0.8:1-1.2:1, the stoichiometric ratio of ligand to metal ion in the reaction system is close to the ideal coordination ratio, which is beneficial for forming pure-phase binuclear europium cluster structural units and ensuring the orderly growth of crystals along the Fddd space group.

[0074] For example, as shown in Comparative Example 1 and Comparative Example 2.

[0075] Comparative Example 1

[0076] 7.5 mg (0.045 mmol) of 2,5-pyridinedicarboxylic acid was added to a 5 mL glass bottle containing 2.2 mL of DMF and dissolved by sonication for 5 minutes. Then, 4.0 mg (0.009 mmol) of Eu(NO3)3·6H2O (molar ratio 0.2:1), 49 mg of o-fluorobenzoic acid, 0.3 mL of a DMF solution of nitric acid (3 mL nitric acid + 10 mL DMF), and 0.5 mL of water were added and stirred. The mixture was sealed and reacted at 378 K for 36 hours. After cooling, filtration, washing, and drying, a small amount of white powder was obtained.

[0077] Compared with Example 1, insufficient europium salt content led to difficulties in crystal nucleation. The products were mainly unreacted ligands and a small amount of amorphous substances. No octahedral crystals were observed, and the fluorescence intensity was weak, which could not meet the requirements for GSR labeling and fingerprint development.

[0078] Comparative Example 2

[0079] 7.5 mg (0.045 mmol) of 2,5-pyridinedicarboxylic acid was added to a 5 mL glass bottle containing 2.2 mL of DMF and dissolved by sonication for 5 minutes. Then, 60.2 mg (0.135 mmol) of Eu(NO3)3·6H2O (molar ratio 3:1), 49 mg of o-fluorobenzoic acid, 0.3 mL of a DMF solution of nitric acid (3 mL nitric acid + 10 mL DMF), and 0.5 mL of water were added and stirred. The mixture was sealed and reacted at 378 K for 36 hours. After cooling, filtration, washing, and drying, a white crystalline product was obtained.

[0080] Compared with Example 1, the excess europium salt caused the appearance of impurity phases in the product, the PXRD pattern showed impurity peaks, the thermal stability was only 260°C, the fluorescence intensity was reduced to 45% of that in Example 1, and the fingerprint imaging effect was poor.

[0081] In some embodiments, in step 2, the added mass of o-fluorobenzoic acid is 1000-1200 g per mole of europium nitrate hexahydrate; the DMF solution of nitric acid comprises 60%-70% nitric acid and DMF mixed at a volume ratio of 2-4:8-15; the added volume is 5-8 L; and the added volume of water is 10-15 L. As a crystal growth regulator, the amount of o-fluorobenzoic acid added directly affects the nucleation rate and growth direction of the crystal: if the amount is too low (below 1000 g / mol), the regulating effect is insufficient, making it difficult to suppress the formation of impurities, resulting in impurity peaks in the PXRD spectrum; if the amount is too high (above 1200 g / mol), it may be excessively adsorbed onto the crystal face, hindering the orderly growth of the crystal and causing a decrease in crystallinity.

[0082] In some embodiments, in step 3, the temperature of the solvothermal reaction is 350K-400K; and / or, the time of the solvothermal reaction is 24h-48h. Reasonable control of the temperature and time of the solvothermal reaction ensures both the full coordination reaction between the ligand and europium ions and the orderly growth of the crystal, ultimately yielding a pure octahedral crystal with a regular morphology. If the reaction temperature is too low, the thermal energy provided by the reaction system is insufficient to overcome the energy barrier of the coordination reaction, resulting in a slow crystal nucleation rate, incomplete growth, low crystallinity, numerous lattice defects, and even amorphous byproducts. If the reaction temperature is too high, the energy of the reaction system is too high, which may trigger partial decomposition of the organic ligand or solvothermal side reactions, disrupting the orderly growth of the crystal and leading to impure crystal phases or framework collapse. When the reaction time is too short, the growth time after crystal nucleation is insufficient, resulting in small and incompletely developed grains, a high lattice defect rate, and a significant decrease in the thermal stability and fluorescence intensity of the material. When the reaction time is too long, the crystal growth has already reached saturation, and further extending the reaction time does not significantly improve the crystal quality but instead increases energy consumption and production costs.

[0083] For example, see Comparative Example 3-4.

[0084] Comparative Example 3

[0085] 7.5 mg (0.045 mmol) of 2,5-pyridinedicarboxylic acid was added to a 5 mL glass bottle containing 2.2 mL of DMF and dissolved by sonication for 5 minutes. Then, 20.07 mg (0.045 mmol) of Eu(NO3)3·6H2O, 49 mg of o-fluorobenzoic acid, 0.3 mL of a DMF solution of nitric acid (3 mL nitric acid + 10 mL DMF), and 0.5 mL of water were added and stirred. The mixture was sealed and reacted at 333 K (60°C) for 12 hours. After cooling, filtration, washing, and drying, a small amount of white powder was obtained.

[0086] Compared with Example 1, the reaction temperature was too low and the time was too short, resulting in insufficient crystal growth, low crystallinity of the product, thermal stability of only 250°C, and fluorescence intensity of only 38% of Example 1, which could not effectively reveal fingerprints.

[0087] Comparative Example 4

[0088] 7.5 mg (0.045 mmol) of 2,5-pyridinedicarboxylic acid was added to a 5 mL glass bottle containing 2.2 mL of DMF and dissolved by sonication for 5 minutes. Then, 20.07 mg (0.045 mmol) of Eu(NO3)3·6H2O, 49 mg of o-fluorobenzoic acid, 0.3 mL of a DMF solution of nitric acid (3 mL nitric acid + 10 mL DMF), and 0.5 mL of water were added and stirred. The mixture was sealed and reacted at 423 K (150°C) for 60 hours. After cooling, filtration, washing, and drying, a yellow crystalline product was obtained.

[0089] Compared with Example 1, the reaction temperature was too high, which caused partial decomposition of the ligand, the product color turned yellow, the fluorescence intensity decreased to 52% of that in Example 1, the thermal stability was reduced, and the background interference when the fingerprint was developed was significantly increased.

[0090] In some embodiments, step 4 involves washing with N,N-dimethylformamide and methanol.

[0091] The second aspect of this embodiment provides an Eu-MOF material prepared by the method described above.

[0092] As shown in Comparative Examples 5-6.

[0093] Comparative Example 5

[0094] 7.5 mg (0.045 mmol) of 2,5-pyridinedicarboxylic acid was added to a 5 mL glass bottle containing 2.2 mL of DMF and dissolved by sonication for 5 minutes. Then, 20.4 mg (0.045 mmol) of terbium nitrate hexahydrate (Tb(NO3)3·6H2O), 49 mg of o-fluorobenzoic acid, 0.3 mL of a DMF solution of nitric acid (3 mL nitric acid + 10 mL DMF), and 0.5 mL of water were added and stirred. The mixture was sealed and reacted at 378 K for 36 hours. After cooling, filtration, washing, and drying, colorless transparent crystals were obtained.

[0095] Compared to Example 1, this comparative example uses terbium ions instead of europium ions, while all other conditions are exactly the same. The resulting Tb-MOF material emits green fluorescence under ultraviolet light excitation (main peak at 545 nm, corresponding to Tb³⁺). 5 D4→ 7After firing the F5 transition as a GSR marker, thermogravimetric analysis showed that it was stable below 300°C. The green fluorescent particles were visible under ultraviolet light, but the weak blue-green fluorescence of the skin and some objects (such as paper) caused background interference, resulting in significantly lower contrast of the fingerprint lines compared to the red fluorescence in Example 1. On dark objects, the green fluorescence showed little color difference from the background, making it difficult to identify tertiary detail features. This indicates that while changing the metal ions can produce fluorescent materials, it cannot simultaneously meet the high contrast requirements of both application scenarios.

[0096] Comparative Example 6

[0097] 7.5 mg (0.045 mmol) of terephthalic acid (H₂BDC) was added to a 5 mL glass bottle containing 2.2 mL of DMF and dissolved by sonication for 5 minutes. Then, 20.07 mg (0.045 mmol) of Eu(NO₃)₃·6H₂O, 49 mg of o-fluorobenzoic acid, 0.3 mL of a DMF solution of nitric acid (3 mL nitric acid + 10 mL DMF), and 0.5 mL of water were added and stirred. The mixture was sealed and reacted at 378 K for 36 hours. After cooling, filtration, washing, and drying, colorless crystals were obtained.

[0098] Compared to Example 1, this comparative example used terephthalic acid instead of 2,5-pyridinedicarboxylic acid, with all other conditions remaining identical. Although the resulting Eu-BDC material emitted red fluorescence (main peak at 620 nm) under UV excitation, thermogravimetric analysis showed its thermal stability was only 285°C (lower than the 310°C of this invention). After firing as a GSR marker, some fluorescent particles quenched due to high-temperature decomposition, resulting in a lower density of fluorescent residue on the hand and gun surface compared to Example 1. As a fingerprint developing powder, its adsorption capacity for sweat and oil was weak, and the fingerprint lines showed discontinuity, with insufficient tertiary detail features. This indicates that while changing the ligand structure preserved the characteristic fluorescence of Eu³⁺, it significantly reduced antenna effect efficiency and thermal stability, failing to simultaneously meet the requirements of high-temperature resistance and adsorption performance for dual-functional applications.

[0099] The second aspect of this embodiment provides an Eu-MOF material prepared by the preferred method described above. This material, through the directional coordination assembly of 2,5-pyridinedicarboxylic acid and europium ions, and under the regulation of o-fluorobenzoic acid as a modulator, forms a three-dimensional network framework with binuclear europium cluster structural units belonging to the orthorhombic crystal system Fddd space group. When incorporated into bullet propellant as an exogenous marker, it can maintain complete crystal morphology and fluorescence activity in shooting residues, achieving rapid visualization and localization under ultraviolet light. As a fluorescent developing powder, its excellent affinity for sweat and oil allows it to clearly display latent fingerprints on various surfaces such as glass, ceramic tiles, plastics, and paper using a powder-sprinkling and shaking development method. The detailed features of the fingerprint lines (including tertiary features such as sweat pores and edge morphology) are fully discernible, and high-contrast display effects can still be obtained on dark or complex backgrounds. The material of this invention enables the dual application of a single substance in the analysis of two key types of forensic evidence. This not only avoids the cumbersome process of using multiple materials required by traditional methods, but also significantly reduces the material costs and technical complexity of on-site investigation, demonstrating its excellent practical application value.

[0100] In some embodiments, the Eu-MOF material belongs to the orthorhombic crystal system, has the space group Fddd, and has a binuclear europium cluster structural unit; and / or emits red fluorescence with a wavelength of 600-700 nm under 254 nm or 300 nm ultraviolet light excitation.

[0101] The Eu-MOF material possesses specific crystal structure and fluorescence properties: it belongs to the orthorhombic crystal system with space group Fddd and has binuclear europium cluster structural units; it emits red fluorescence with a wavelength of 600-700 nm under 254 nm or 300 nm ultraviolet light excitation. The pure red fluorescence forms a distinct color difference with the autofluorescence (mostly blue-green) of common background objects, allowing for high-contrast fingerprint lines even on dark objects or those with background fluorescence; the dual-band excitation characteristics of 254 nm and 300 nm match the ultraviolet light sources commonly used in criminal investigation scenes, eliminating the need for additional specialized equipment; the highly ordered crystal structure endows the material with excellent thermal stability, enabling it to withstand the high-temperature environment at the moment of firing and maintain fluorescence activity even after experiencing the severe thermal shock of a bullet leaving the barrel. Therefore, the Eu-MOF material of this invention, with its specific crystal structure and fluorescence properties, simultaneously meets the dual requirements of high-temperature resistance for marking shooting residues and high-contrast fluorescence for latent fingerprint development, achieving a dual-purpose technical effect.

[0102] The third aspect of this embodiment provides the application of Eu-MOF materials as described above in the marking of bullet residues or the development of latent handprints.

[0103] As an exogenous marker for shooting residues, this material, when incorporated into propellant, maintains its crystal structure and fluorescence properties even under high temperature and pressure at the moment of firing. After firing, it displays dense red fluorescent particles on the shooter's hand, the surface of the firearm, and around the cartridge case under 254 nm ultraviolet light, enabling rapid visualization and localization of shooting residues. This solves the technical problems of traditional detection methods, such as reliance on expensive equipment, long processing times, and difficulty in on-site screening. It also avoids the risk of traditional heavy metal characteristic element detection becoming ineffective due to the widespread use of lead-free environmentally friendly ammunition. As a latent fingerprint developing powder, this material, with its excellent affinity and adsorption capacity for sweat and oil, can clearly develop latent fingerprints on various surfaces such as glass, tiles, plastic, and paper using a powder-sprinkling and shaking development method. Under ultraviolet light excitation, the red fluorescent lines form a high-contrast relationship with the background, effectively overcoming interference from dark or complex backgrounds. The fingerprint lines are continuous and complete, and first- to third-level details such as sweat pores and edge morphology can be identified, meeting the requirements of forensic identification. The same material can be applied to both of the above fields at the same time, achieving the technical effect of "one material for two purposes" - on-site investigators only need to carry one type of powder to complete the two key physical evidence discovery tasks of locating shooting residue and revealing submerged handprints, which significantly reduces the cost of material procurement, storage and carrying, simplifies on-site operation procedures and improves investigation efficiency.

[0104] In some embodiments, the concentration of the Eu-MOF material incorporated into the propellant is 5 wt%-10 wt%. Reasonable control of the Eu-MOF material concentration can create clear fluorescent residue on the shooter's hand, the surface of the firearm, etc., without affecting the shooting performance of the Type 05 police revolver, meeting the needs of rapid on-site detection while controlling usage costs. If the concentration is too low, the fluorescence intensity is insufficient, making it difficult to identify GSRs against complex backgrounds; if the concentration is too high, although it can improve fluorescence contrast, it will lead to a decrease in the success rate of the revolver firing by about 10% (due to the small propellant load of the revolver, leakage in the magazine gap, and high concentration of marker interfering with the release of propellant energy), significantly affecting the shooting stability of the firearm, increasing costs, and having no practical application value.

[0105] The fourth aspect of this embodiment provides a dual-function kit for forensic evidence analysis, comprising the aforementioned Eu-MOF material and an instruction manual describing the application method of the Eu-MOF material in marking bullet residue and revealing latent fingerprints.

[0106] When detecting gunshot residue, operators can add Eu-MOF material to the propellant of the bullet at a concentration of 5 wt%-10 wt% according to the instructions. After firing, fluorescent residues around the hand, firearm, and cartridge case can be quickly located using an ultraviolet light source. When developing latent fingerprints, the same bottle of Eu-MOF material can be used directly to process fingerprints on various object surfaces using the powder-sprinkling and shaking development method, obtaining high-contrast fluorescent ridges under ultraviolet light. This reagent kit has good commercialization and industrialization prospects and is of great significance for improving the efficiency and quality of crime scene investigation in gun-related cases.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing Eu-MOF material, characterized in that, Includes the following steps: Step 1: Obtain a ligand solution formed by dissolving 2,5-pyridinedicarboxylic acid in N,N-dimethylformamide; Step 2: Add europium salt, o-fluorobenzoic acid, DMF solution of nitric acid and water to the ligand solution, mix well to obtain the reaction precursor solution; Step 3: Seal the reaction precursor solution in a container and carry out a solvothermal reaction; Step 4: After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain Eu-MOF material.

2. The method for preparing Eu-MOF material according to claim 1, characterized in that, In step 1, the molar concentration of 2,5-pyridinedicarboxylic acid in the ligand solution is 20 mmol / L-25 mmol / L.

3. The method for preparing Eu-MOF material according to claim 1, characterized in that, In step 2, the europium salt is at least one of europium nitrate, europium chloride, and europium acetate; and / or, the molar ratio of the europium salt to 2,5-pyridinedicarboxylic acid is 0.5:1-1.5:

1.

4. The method for preparing Eu-MOF material according to claim 3, characterized in that, In step 2, the molar ratio of europium salt to 2,5-pyridinedicarboxylic acid is 0.8:1-1.2:

1.

5. The method for preparing Eu-MOF material according to claim 4, characterized in that, In step 2, based on each mole of europium nitrate hexahydrate: the added mass of o-fluorobenzoic acid is 1000-1200 g; the DMF solution of nitric acid is obtained by mixing nitric acid with DMF at a mass concentration of 60%-70% in a volume ratio of 2-4:8-15, and the added volume is 5-8 L; the added volume of water is 10-15 L.

6. The method for preparing Eu-MOF material according to any one of claims 1-5, characterized in that, In step 3, the temperature of the solvothermal reaction is 350K-400K; and / or, the time of the solvothermal reaction is 24h-48h.

7. An Eu-MOF material prepared by the method described in any one of claims 1-6.

8. The Eu-MOF material according to claim 7, characterized in that, The Eu-MOF material belongs to the orthorhombic crystal system with space group Fddd and has a binuclear europium cluster structure unit; and / or emits red fluorescence with a wavelength of 600-700 nm under ultraviolet light excitation at 254 nm or 300 nm.

9. The application of the Eu-MOF material as described in claim 7 or 8 in the marking of bullet residues or the development of latent fingerprints.

10. A bifunctional reagent kit for forensic evidence analysis, characterized in that, The invention comprises the Eu-MOF material as described in claim 7 or 8, and an instruction manual describing the application method of the Eu-MOF material in marking bullet residue and revealing submerged handprints.

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