A dual-emission fluorescent sensor for malachite green detection and removal, and a preparation method and application thereof

Abstract

The application belongs to the field of fluorescent sensors, and discloses a dual-emission fluorescent sensor for malachite green detection and removal, and a preparation method and application thereof. 3+ By introducing 2-quinoxaline carboxylic acid into UiO-66-(COOH)2, and then modifying and doping Eu 0000001 , the Eu-MOF luminescent material EuUQCA is constructed. The material can be used as a fluorescent sensor to quickly and sensitively detect MG, and can realize quantitative detection of MG in complex fishpond water and fish samples, and good recovery is obtained. More importantly, the EuUQCA powder can effectively adsorb and remove MG from fishpond water. The material can realize recycling as a fluorescent sensor and an adsorbent, and provides an effective method for constructing a sensing and adsorbing material which can sensitively detect MG and effectively remove MG residues.

Description

Technical Field

[0001] This invention belongs to the field of fluorescence sensors, specifically relating to a dual-emission fluorescence sensor for the detection and removal of malachite green, its preparation method, and its application. Background Technology

[0002] Aquatic products are a major source of highly nutritious protein and trace elements, and aquaculture is one of the fastest-growing and most developed sectors in aquatic product production. To prevent fish diseases and increase yields, farmers overuse veterinary drugs, sometimes even illegally using banned ones, leading to excessive drug residues in aquatic products and threatening human health. Malachite green (MG) is a triphenylmethane compound, both an organic dye and a veterinary drug used to treat fungi, bacteria, and parasites. Due to its low price and high efficacy, it has gradually become the most frequently used veterinary drug in aquaculture. MG can protect various aquatic animals from fungal attacks, protozoan infections, and other diseases caused by worms in the aquaculture food industry, such as houttuynia cordata disease, bronchitis, and leptospirosis. However, MG is highly toxic, teratogenic, carcinogenic, and mutagenic. In 2002, China's Ministry of Agriculture and Rural Affairs included MG in the "List of Prohibited Drugs and Compounds in Food and Animals," classifying it as a Group 2 carcinogen. MG is toxic and acts as an oxidizing agent. If untreated MG is present in the environment, aquatic life and human health will suffer enormous damage and harm. Although some countries have explicitly banned the use of MG in aquaculture and aquatic food production, its low cost and high efficacy mean that illegal use of MG still exists, which often poses a challenge to supervision.

[0003] To date, numerous analytical methods exist for detecting MG residues, including electrochemical methods, high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and colorimetric methods. However, these methods typically require complex pretreatment procedures, expensive equipment, and skilled operators. Similarly, in the adsorption removal of MG, adsorbents such as organically modified hydroxyapatite, modified nano-gamma-alumina, composite nanofibers, and carbon-shell biochar can effectively remove MG. However, due to the limitations of analytical methods and the instability of adsorbents, developing efficient, stable, and recyclable fluorescent sensor materials for the simultaneous detection and adsorption removal of MG has become a critical issue. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a dual-emission fluorescence sensor for the detection and removal of malachite green, its preparation method, and its application. Specifically, the following technical solution is adopted:

[0005] According to a first aspect of the present invention, a dual-emission fluorescence sensor for the detection and removal of malachite green is provided, wherein 2-quinoxalocarboxylic acid is introduced into UiO-66-(COOH)2, and then modified with Eu dopant. 3+ It was obtained.

[0006] The dual-emission fluorescent material EuUQCA synthesized in this invention has two emission centers at 435 nm and 613 nm, respectively, and both emission intensities are quite stable in aqueous media with pH values ​​of 4–10. Furthermore, EuUQCA exhibits a specific fluorescence quenching response to MG as a sensor, with a calculated detection limit as low as 16.83 nM. This sensor is also suitable for detecting MG in fishpond water and fish meat, with recoveries of 90.17–105.57%. EuUQCA can also effectively remove MG from fishpond water as an adsorbent. The MG removal process follows a pseudo-second-order kinetic model and a Freundlich isotherm model. EuUQCA can be recycled as either a sensor or an adsorbent.

[0007] According to a second aspect of the present invention, a method for fabricating the above-described dual-emission fluorescence sensor is also provided, the method comprising the following steps:

[0008] (1) Preparation of UiO-66-(COOH)2 / 2-QCA: ZrCl4, 1,2,4,5-benzenetetracarboxylic acid and 2-quinoxaloline carboxylic acid were dispersed in 50 mL of N,N-dimethylformamide. The mixture was then refluxed at 100 °C for 24 hours, centrifuged for 8 minutes, and the white solid was collected, washed and dried to obtain UiO-66-(COOH)2 / 2-QCA.

[0009] (2) Preparation of EuUQCA: The UiO-66-(COOH)2 / 2-QCA obtained in step (1) was added to the aqueous solution of Eu(NO3)3·6H2O, stirred at 80 °C for 36 hours, the white solid was collected, washed and dried to obtain EuUQCA.

[0010] This invention utilizes 2-quinoxaloline carboxylic acid and Eu 3+ By introducing Eu into UiO-66-(COOH)2 material, post-synthetic modified doped Eu was prepared. 3+ The invention relates to a metal-organic framework material (EuUQCA). The preparation method employed in this invention is simple, safe, and convenient, requiring no high-risk equipment or raw materials. The recyclable dual-emission fluorescent material shows great promise for the detection and removal of veterinary drug residues.

[0011] Preferably, the concentration ratio of ZrCl4, 1,2,4,5-benzenetetracarboxylic acid, and 2-quinoxalocarboxylic acid in step (1) is 2.0 mmol:2.8 mmol:1.2 mmol, which is considered the optimal addition ratio. This is because excessive amounts of 2-quinoxalocarboxylic acid can lead to an unstable or even collapsed synthetic material skeleton.

[0012] Preferably, in step (2), the mass ratio of UiO-66-(COOH)2 / 2-QCA to Eu(NO3)3·6H2O is 0.50 g:0.45 g. The concentration of Eu(NO3)3·6H2O is 1.0 mmol. Excess Eu(NO3)3·6H2O ensures that all free carboxyl groups are associated with Eu. 3+ Coordination.

[0013] Preferably, in step (1), the white solid is washed three times each with N,N-dimethylformamide and ethanol.

[0014] Preferably, in step (2), the white solid is washed three times with H2O and ethanol respectively.

[0015] According to a third aspect of the present invention, an application of the above-described dual-emission fluorescence sensor in the field of malachite green detection is also provided.

[0016] Preferably, the dual-emission fluorescence sensor is used to detect malachite green in fishpond water and fish meat samples.

[0017] According to a fourth aspect of the present invention, an application of the above-described dual-emission fluorescence sensor in the field of malachite green removal is also provided.

[0018] The beneficial effects of this invention are as follows: This invention introduces 2-quinoxaloline carboxylic acid (2-QCA) into UiO-66-(COOH)2 and then modifies it by doping with Eu. 3+ A Eu-MOF luminescent material, EuUQCA, was constructed. This material can be used as a fluorescence sensor for rapid and sensitive detection of MG, achieving quantitative detection of MG in complex fishpond water and fish meat samples with good recovery rates. More importantly, EuUQCA powder can effectively adsorb and remove MG from fishpond water. This material can be recycled as both a fluorescence sensor and an adsorbent, providing an effective method for constructing highly sensitive MG detection and simultaneously effectively removing MG residues. Attached Figure Description

[0019] Figure 1 The synthesis route of the fluorescent sensor EuUQCA is shown.

[0020] Figure 2The figure shown is a material characterization diagram of UiO-66-(COOH)2 / 2-QCA and EuUQCA.

[0021] Among them, (a) powder X-ray diffraction patterns of UiO-66-(COOH)2 / 2-QCA and EuUQCA; (b) Fourier transform infrared spectra of UiO-66-(COOH)2 / 2-QCA and EuUQCA; (c) X-ray photoelectron spectra of UiO-66-(COOH)2 / 2-QCA and EuUQCA (changes in oxygen binding energy); (d) changes in nitrogen binding energy;

[0022] Figure 3 The figures show the N2 adsorption-desorption isotherms and pore size distribution for the specific surface areas of UiO-66-(COOH)2 / 2-QCA and EuUQCA; where (a) is the N2 adsorption-desorption isotherm and (b) is the pore size distribution.

[0023] Figure 4 The figure shows the thermal stability performance of UiO-66-(COOH)2 / 2-QCA and EuUQCA.

[0024] Figure 5 The fluorescence spectra of UiO-66-(COOH)2 / 2-QCA and EuUQCA are shown below.

[0025] Figure 6 The following figures are shown: (a) the fluorescence emission spectrum of EuUQCA suspension after continuous immersion in water for 7 days; (b) the fluorescence intensity change of EuUQCA suspension under different pH conditions.

[0026] Figure 7 The fluorescence intensity of EuUQCA under different veterinary drug conditions is shown; (a) at 435 nm; (b) at 613 nm; (c) at 435 nm after adding MG; (d) at 613 nm after adding MG.

[0027] Figure 8 The figure shows the fluorescence response of EuUQCA to different concentrations of MG; where (a) is the fluorescence spectrum of the EuUQCA solution after the addition of MG; (b) is the fluorescence image of the EuUQCA solution after the addition of MG; (c) is the fluorescence spectrum of the EuUQCA solution after the addition of MG. F 0 / F ) 435nm Linear relationship with MG concentration; (d) F 0 / F ) 613nm Linear relationship with MG concentration;

[0028] Figure 9 The figure shows the time response of MG added to EuUQCA suspension;

[0029] Figure 10 The diagram shows the mechanism of MG quenching EuUQCA fluorescence; (a) PXRD of EuUQCA after MG reaction; (b) excitation and emission spectra of EuUQCA and UV absorption spectrum of MG.

[0030] Figure 11 The following are fluorescence spectra of EuUQCA added to fishpond water and fish meat processing solution, respectively;

[0031] Figure 12 The diagram shows the kinetic model of EuUQCA adsorption; where (a) is the experimental kinetic model of EuUQCA adsorption of MG; (b) is the pseudo-first-order kinetic model; and (c) is the pseudo-second-order kinetic model.

[0032] Figure 13 The figure shows the EuUQCA isothermal adsorption model diagram; where (a) isotherm fitting of EuUQCA adsorbing MG; (b) Langmuir model; (c) Freundlich model;

[0033] Figure 14 The figure shown is a diagram of the three adsorption steps of MG adsorption by EuUQCA simulated by the Weber-Morris model.

[0034] Figure 15 The experiment shows the recycling of EuUQCA; (a) EuUQCA fluorescence sensor is used to detect MG in a cycle; (b) EuUQCA is used to adsorb MG in a cycle.

[0035] Figure 16 The figure shows the material characterization diagram after EuUQCA adsorbs MG; (a) isotherms of N2 adsorption and desorption before and after EuUQCA adsorbs MG; (b) pore size distribution before and after MG adsorption. Detailed Implementation

[0036] The following will provide a clear and complete description of the concept and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully understand the purpose, solution and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0037] Example 1

[0038] A method for preparing a dual-emission fluorescence sensor for the detection and removal of malachite green specifically includes the following steps (synthetic route as follows). Figure 1 (as shown)

[0039] (1) Synthesis of UiO-66-(COOH)2 / 2-QCA: ZrCl4 (466 mg, 2.00 mmol), 1,2,4,5-benzenetetracarboxylic acid (H4betc) (710 mg, 2.8 mmol), and 2-quinoxalocarboxylic acid (2-QCA) (205 mg, 1.2 mmol) were mixed in DMF (50 mL) and refluxed at 100 °C for 24 hours. A white precipitate was obtained by centrifugation at 10,000 rpm for 8 minutes. The white precipitate was washed several times with DMF and ethanol and then dried at 80 °C for 12 hours to obtain a white powder.

[0040] (2) Synthesis of EuUQCA: UiO-66-(COOH)2 / 2-QCA (0.50 g) was added to 40 mL of Eu(NO3)3·6H2O (0.45 g, 1.00 mmol) aqueous solution, and the mixture was stirred at 80 °C for 36 hours. The white product was obtained by centrifugation, washed carefully several times with H2O and ethanol, and finally dried under vacuum at 80 °C for 10 hours.

[0041] Example 2

[0042] This embodiment characterizes the structures of UiO-66-(COOH)2 / 2-QCA and EuUQCA prepared in Example 1 by powder X-ray diffraction (PXRD) patterns.

[0043] like Figure 2 As shown in (a), the PXRD patterns of UiO-66-(COOH)2 / 2-QCA and EuUQCA are consistent with the diffraction peaks of the simulated UiO-66, indicating that UiO-66-(COOH)2 / 2-QCA and UiO-66 are isomorphic, and that the later-synthesized Eu-doped... 3+ The original crystal structure was not affected. Furthermore, the PXRD pattern of EuUQCA after immersion in the solvent for 7 days showed no significant change, indicating that the EuUQCA structure is very stable in DMF.

[0044] The FT-IR spectrum of UiO-66-(COOH)2 / 2-QCA is similar to that of EuUQCA. ​​For example... Figure 2 As shown in (b), 1712 cm -1 The peak at 1712 cm⁻¹ is attributed to uncoordinated -COOH, in EuUQCA. -1 The peak at that location is weaker than that of UiO-66-(COOH)2 / 2-QCA, indicating that UiO-66-(COOH)2 / 2-QCA interacts with Eu through the carboxyl group. 3+ Coordination.

[0045] X-ray photoelectron spectroscopy (XPS) further confirmed -COO- With Eu 3+ Coordination. For example... Figure 2 As shown in (c), UiO-66-(COOH)2 / 2-QCA contains four elements: C, O, N, and Zr, while EuUQCA contains five elements: C, O, N, Zr, and Eu. The photoelectron spectral line at 1134.74 eV belongs to the Eu 3d spectrum, confirming that Eu... 3+ It has been successfully doped into UiO-66-(COOH)2 / 2-QCA. For example... Figure 2 (c) As shown in the inset, compared to UiO-66-(COOH)2 / 2-QCA, the binding energy of O 1s in EuUQCA shifts from 531.47 eV to 531.52 eV, indicating that the carboxyl O atom binds to Eu. 3+ Coordination between them. It can be seen that the binding energy of N 1s in EuUQCA has also changed compared with the binding energy in UiO-66-(COOH)2 / 2-QCA. Figure 2 (d) indicates that the N element in UiO-66-(COOH)2 / 2-QCA is related to Eu 3+ There is also a coordination relationship between them. Ultraviolet light and ICP-MS also verified the presence of Eu in EuUQCA. 3+ The presence of Zr was determined by quantitative analysis using ICP-MS. 4+ With Eu 3+ The molar ratio is 5.22:1.

[0046] Example 3

[0047] This embodiment measures the specific surface area and pore size of UiO-66-(COOH)2 / 2-QCA and EuUQCA prepared in Example 1.

[0048] The specific surface area and pore size of UiO-66-(COOH)2 / 2-QCA and EuUQCA were measured using N2 adsorption-desorption isotherms. Figure 3 As shown, the isotherms of the synthetic materials all belong to type II isotherms, and their BET specific surface areas are 318.07 m². 2 / g and 171.45 m 2 / g, with average pore sizes of 2.65 nm and 2.49 nm, respectively, doped with Eu 3+ The change in aperture distribution afterward is very small.

[0049] Example 4

[0050] In this embodiment, the thermal stability of UiO-66-(COOH)2 / 2-QCA and EuUQCA prepared in Example 1 was studied using thermogravimetric analysis (TGA).

[0051] like Figure 4 As shown, the weight losses of UiO-66-(COOH)2 / 2-QCA and EuUQCA were 10.58% and 11.02% respectively at 90-110 °C, which are attributed to the loss of solvent molecules in the pores of the MOF materials. The structures of UiO-66-(COOH)2 / 2-QCA and EuUQCA were relatively stable before 500 °C. After 500 °C, the weight decreased sharply, indicating that the framework structure began to collapse and decompose. TGA results analysis showed that UiO-66-(COOH)2 / 2-QCA and EuUQCA have good thermal stability.

[0052] Example 5

[0053] This embodiment presents a fluorescence performance experiment on the EuUQCA prepared in Example 1.

[0054] The powder fluorescence emission spectrum of UiO-66-(COOH)2 / 2-QCA is shown in 5(a). Its solid-state spectrum exhibits three emission peaks at 496, 594, and 635 nm, which is attributed to charge transfer from the ligand to the metal. However, the solid-state powder fluorescence spectrum of EuUQCA is completely different from that of UiO-66-(COOH)2 / 2-QCA. Figure 5 (b)). EuUQCA shows Eu 3+ Characteristic emission peaks are observed at 592 nm and 613 nm. Therefore, the red fluorescence of EuUQCA powder can be clearly observed under ultraviolet light irradiation. As shown in Figure 5(c), the optimal excitation wavelength for the EuUQCA suspension was determined to be 305 nm using three-dimensional fluorescence spectroscopy. At the optimal excitation wavelength, the EuUQCA suspension has two emission centers at 435 nm and 613 nm. Figure 5 (d) A broad, weak emission band was observed at 435 nm, attributed to the fluorescence of the organic ligand 2-QCA. In addition to the characteristic emission band of 2-QCA, Eu 3+ The characteristic emission values ​​are located at 578, 592, 613, 638, and 698 nm, respectively. EuUQCA dispersed in DMF solvent also exhibits bright red fluorescence under ultraviolet light.

[0055] Example 6

[0056] This embodiment measures the luminescence stability of EuUQCA prepared in Example 1 in DMF.

[0057] like Figure 6As shown in (a), the fluorescence intensity of EuUQCA remained almost unchanged after immersion in DMF for 7 days, indicating that the synthesized fluorescence sensor is highly stable in the solvent. Furthermore, the fluorescence of EuUQCA at 435 nm and 613 nm was also stable within a pH range of 4–10. Figure 6 (b)). The excellent structural and fluorescence stability of EuUQCA demonstrates its potential application value as a fluorescence sensor.

[0058] Example 7

[0059] This embodiment compares the fluorescence sensing of EuUQCA prepared in Example 1 with other veterinary drugs.

[0060] The preparation method is as follows: MG solutions of different standard concentrations are added to 3 mL of EuUQCA (1.5 mg) DMF suspension, and then the fluorescence emission spectra are recorded respectively.

[0061] To verify the specificity of EuUQCA in detecting MG, 21 commonly used veterinary drugs were selected, including albendazole, avermectin, enrofloxacin, nitrofurazone, furazolidone, florfenicol, erythromycin, ciprofloxacin, sulfadiazine, sulfaguanidine, sulfadiazine, thiamphenicol, quinethol, kanamycin sulfate, streptomycin sulfate, doxycycline hydrochloride, furazolidone hydrochloride, ivermectin, diethylstilbestrol, leucovorin, and leucomalle green. Each veterinary drug (10 mM, 9 μL) was added dropwise to a suspension of EuUQCA (0.5 mg / mL, 3 mL) (10 mM, 6 μL). Simultaneously, an interference resistance experiment was conducted on the sensor by dispersing EuUQCA in mixed solutions containing MG (10 mM, 6 μL) and other veterinary drugs (10 mM, 6 μL), and recording fluorescence data.

[0062] like Figure 7 As shown, only MG significantly quenched the fluorescence of EuUQCA at 435 nm and 613 nm, while other veterinary drugs had a weak effect on the sensor's fluorescence. These results indicate the high selectivity of EuUQCA for detecting MG. When MG was added to a suspension containing other veterinary drugs, the fluorescence at 435 nm and 613 nm was also effectively quenched, indicating that EuUQCA has good anti-interference properties for detecting MG. The fluorescence intensity of EuUQCA gradually decreased with increasing MG concentration. Figure 8 (a)), and the red fluorescence is significantly quenched under UV light ( Figure 8 (b)). Interestingly, the quenching efficiency of the sensor at 435 nm and 613 nm ( F 0 / F ) 435 and(F 0 / F ) 613 All showed a good linear relationship with the concentration of MG (1–15 µM). Figure 8 (c), (d)). Sensitivity is quantitatively determined by the Stern–Volmer equation:

[0063] F 0 / F = 1 + K sv [MG]

[0064] in F 0 and F These are the initial fluorescence intensity of EuUQCA and the fluorescence intensity in the presence of MG, respectively. K sv is the quenching constant in the Stern–Volmer equation, and [MG] is the concentration of MG. Based on 3σ / slope, calculations show that MG at 435 nm and 613 nm... K sv are 169300 M -1 and 108400 M -1 The limits of detection (LODs) were 16.83 μM and 24.55 μM, respectively. Figure 9 As shown, after adding MG, the fluorescence intensity at both emission centers (435 nm and 613 nm) of EuUQCA was effectively quenched within one minute, indicating that the fluorescence sensor has a very fast time response to MG. These results demonstrate that EuUQCA possesses characteristics such as good selectivity for MG, strong anti-interference ability, and fast response speed, showcasing its significant potential application value.

[0065] Example 8

[0066] This embodiment describes the fluorescence quenching mechanism of the EuUQCA sensor prepared in Example 1.

[0067] To gain a more comprehensive understanding of the reasons why MG causes fluorescence quenching in EuUQCA, we analyzed the data from UV-vis absorption spectroscopy, excitation spectroscopy, emission spectroscopy, and PXRD. Figure 10 As shown in (a), the PXRD spectra of MG and EuUQCA after the reaction correspond one-to-one with their original PXRD peaks, indicating that the reaction with MG did not change its original structure, and the fluorescence quenching was not caused by the collapse of the material framework. Furthermore, the UV-vis absorption spectrum of MG and the excitation and emission spectra of EuUQCA were recorded respectively. Figure 10(b) The excitation spectrum of the fluorescence sensor almost completely overlaps with the absorption peak of MG at 300-320 nm, suggesting an internal filtering effect (IFE) during fluorescence quenching, which effectively prevents EuUQCA from being excited and thus affects its emission. Furthermore, the UV absorption peak of MG at 600-620 nm highly overlaps with the emission spectrum of the sensor (λem, max = 613 nm), indicating that the fluorescence of EuUQCA at 613 nm is effectively quenched due to the FRET effect. Therefore, the quenching of EuUQCA fluorescence by MG is likely due to a combination of the internal filtering effect (IFE) and the FRET effect.

[0068] Example 9

[0069] This embodiment involves pretreatment of pond water and fish meat samples and experiments on the recovery rate of MG spikes.

[0070] The preparation method was as follows: Fishpond water was centrifuged at 10,000 rpm for 5 minutes, and the supernatant was filtered through a 0.22 μm microporous membrane. The filtered supernatant was then added to MG standard solutions of different concentrations. Next, 30 μL of the pretreated water sample was added to 3.0 mL of 0.50 mg / mL EuUQCA suspension to achieve MG concentrations of 0.3, 0.7, and 1.0 μM, respectively. Finally, the fluorescence emission spectra of the mixed solutions were recorded.

[0071] The QuEChERS method was used for the pretreatment of fish meat samples, which significantly shortens the sample pretreatment time. First, 5.0 g of homogenized fish meat sample was vigorously mixed with 2.0 g MgSO4, 0.5 g NaCl, and 5 mL acetonitrile for 1 minute, followed by centrifugation at 8000 rpm for 5 minutes. Next, to remove impurities such as sugars, fatty acids, and lipids, 0.2 g PSA, 0.2 g C18, and 0.6 g MgSO4 were added to 3 mL of supernatant, shaken for 1 minute, and then centrifuged at 8000 rpm for 5 minutes. MG standard solutions of different concentrations were prepared by filtering 2 mL of the supernatant through a 0.22 μm organic membrane, and then spiked for recovery and quantitative analysis using the same method as for fishpond water. EuUQCA was used to detect MG in both fishpond water and fish meat. The actual sample recovery rate was calculated using the standard addition method and a linear equation at 613 nm.

[0072] like Figure 11As shown in Table 1, the fishpond water and fish meat pretreatment solution had almost no effect on the fluorescence of the sensor. The recoveries of MG in the fishpond water and fish meat were 93.19–105.57% and 90.17–100.13%, respectively, with RSD values ​​less than 4%. These results demonstrate the reliability of the EuUQCA fluorescence sensor for the quantitative detection of MG in fishpond water and fish meat, showing great promise for practical applications.

[0073] Table 1. Quantification of mg in pond water and fish samples using EuUQCA

[0074]

[0075] Example 10

[0076] This embodiment measures the adsorption and removal of MG by EuUQCA prepared in Example 1 in fishpond water.

[0077] The preparation method is as follows: Before the adsorption experiment, EuUQCA needs to be dried overnight under vacuum at 100 °C to remove free solvent molecules. Adsorption kinetics experiments were conducted on a vibrating shaker at 180 rpm and 25 °C. 4 mg of EuUQCA was added to 8 mL of the target pollutant (MG) solution (50 mg / L), and the mixture was continuously shaken at 25 °C for a period of time (5 min–24 h). Simultaneously, adsorption isotherms of EuUQCA and MG at different initial concentrations (C0 from 1–60 mg / L) were tested at 25 °C. After the final adsorption experiment, the supernatant was filtered through a 0.22 μm membrane. All test data were used to calculate the MG concentration in the resulting solution by recording the absorbance at 614 nm using UV-vis absorption spectroscopy. All experiments were performed in triplicate.

[0078] The concentration of the supernatant after MG adsorption was calculated according to Beer-Lambert's law:

[0079]

[0080] Where A0 is the absorbance of the target pollutant solution (1-60 mg / L), A t Ct represents the absorbance of the filtrate, C0 represents the concentration of the target pollutant in the solution (1-60 mg / L), and Ct represents the concentration of the target pollutant in the solution. t The concentration of MG in the supernatant at time t (mg / L) is given.

[0081] Adsorption capacity Q of MG t (mg / g) and removal efficiency R (%) are calculated using the following formulas (2) and (3):

[0082]

[0083] Where C0 and Ct V represents the initial time and the MG concentration (mg / L) after adsorption time t, respectively. V is the total volume of the MG solution (L), and M represents the amount of adsorbent.

[0084] The corresponding formulas for the pseudo-first-order and pseudo-second-order dynamic models are shown in formulas (4) and (5):

[0085]

[0086] Q t and Q e t represents the amount of MG adsorbed (mg / g) at adsorption time t and equilibrium, respectively. k1 represents the equilibrium rate constant of the pseudo-first-order kinetic model, and k2 represents the equilibrium rate constant of the pseudo-second-order kinetic model.

[0087] Equations (6) and (7) of the Langmuir and Freundlich model are shown:

[0088]

[0089] Where C e Q represents the MG concentration (mg / L) at adsorption equilibrium. e Q is the amount of MG adsorbed at adsorption equilibrium (mg / g). max K represents the theoretical maximum adsorption capacity (mg / g). L The constant representing the Langmuir model (L / mg), k F And n represents the Freundlich constant.

[0090] In addition to being used as a fluorescent sensor to detect residual MG, this work also attempts to use EuUQCA powder as an adsorbent to remove MG. Pseudo-first-order and pseudo-second-order kinetic models were used to determine the diffusion during the adsorption process. Figure 12 As shown in (a), the adsorption of MG increased significantly in the first 200 minutes, then increased slowly and tended to reach equilibrium at 400 minutes. The fitting results are as follows... Figure 12 As shown in (b) and (c), the R values ​​of the two dynamic models are... 2 The values ​​are 0.9204 and 0.9995, respectively. Due to the R-values ​​of the quasi-second-order kinetic model... 2 The value is higher than that of the pseudo-first-order kinetic model, so the pseudo-second-order kinetic model describes the adsorption process of MG by EuUQCA very well.

[0091] Adsorption isotherms help to understand the distribution of MG on EuUQCA at adsorption equilibrium. A series of MG standard solutions (1, 5, 10, 20, 30, 40, 50, 60 mg / L) were prepared for isotherm testing. Two classic isotherm models, Langmuir and Freundlich, were used to fit the adsorption results; the fitting plots and relevant parameters are listed below. Figure 13 In the middle. Compared with the Langmuir model (R 2 Compared to (= 0.9388), the adsorption process is closer to the Freundlich model (R² = 0.9388). 2 = 0.9987). The maximum adsorption capacity of EuUQCA for MG (Q) was calculated. max The adsorption concentration (1 / n) was 9.48 mg / g. Furthermore, the value of 1 / n is generally considered to correspond to the difficulty of adsorption, such as favorable adsorption (0 < 1 / n < 1), irreversible adsorption (1 / n = 0), and difficult adsorption (1 / n > 1). The 1 / n for EuUQCA adsorption of MG was 0.3455, which means the adsorption process was spontaneous.

[0092] Furthermore, the Weber-Morris model was used to infer the rate-controlling step and diffusion mechanism of the adsorption process. Three separate steps occurred during adsorption: first, MG diffused from the solution to the outer surface of the EuUQCA adsorbent; then, MG migrated from the adsorbent surface to the pores or cavities; and finally, the adsorption dynamic equilibrium process controlled the final stage. The fact that the curve did not pass through the origin indicates that intraparticle diffusion is not only a rate-controlling step but also a multiphase adsorption process. Figure 14 ).

[0093] Example 11

[0094] This embodiment is an experiment on the recyclability of EuUQCA prepared in Example 1.

[0095] The recyclability of materials is of great practical significance for both fluorescence sensors and adsorbents. For example... Figure 15 As shown in (a), after adding sufficient MG to quench the fluorescence of EuUQCA, the fluorescence intensity could be restored to the original value after centrifugation and washing with DMF. After five recycling cycles, the fluorescence of EuUQCA could still be restored. The PXRD spectrum showed that the structure of EuUQCA did not change after five cycles. Figure 10 (a)). Furthermore, such as Figure 15 As shown in (b), EuUQCA powder, as an adsorbent, after several washes and drying with DMF, still achieved a removal efficiency of over 90% of the initial removal efficiency for MG. Figure 16As shown in the N2 adsorption-desorption isotherm results, it can be seen that after washing to remove the adsorbed MG, the specific surface area of ​​EuUQCA recovers to 159.88 m². 2 The pore size distribution and pore volume were restored to some extent. Therefore, we believe that the pore structure of EuUQCA can be restored after removing MG by washing with DMF and drying to remove solvent molecules from the pores. EuUQCA has good recycling performance, whether used as a fluorescence sensor or an adsorbent.

[0096] In summary, the UiO-66 Eu-MOF dual-emission fluorescent sensor (EuUQCA) prepared by the solvothermal method in this invention exhibits good structural stability and fluorescence performance, and is quite stable in solvents with pH values ​​of 4-10. EuUQCA can rapidly and sensitively identify MG, a commonly used antibacterial drug in aquaculture, with a detection limit of 16.83 nM, which is superior to most reported fluorescent sensors. Furthermore, this fluorescent sensor has been validated for the quantitative detection of MG in fishpond water and fish meat samples, achieving satisfactory recovery results. The adsorption and removal of MG in water by EuUQCA powder as an adsorbent were also investigated. Fitting of experimental data showed that the MG adsorption process follows a pseudo-second-order kinetic model and a Freundlich isotherm model. More importantly, EuUQCA, as a promising Eu-MOF material, exhibits good recyclability and has excellent application prospects, whether used as a fluorescent sensor or an adsorbent.

[0097] Although the description of the invention has been quite detailed and particularly of several described embodiments, it is not intended to limit it to any of these details or embodiments or any particular embodiment, but should be considered as providing a broad possible interpretation of the claims by referring to the appended claims and taking into account the prior art, thereby effectively covering the intended scope of the invention. Furthermore, the invention has been described above with respect to embodiments foreseeable by the inventors in order to provide a useful description, and non-substantial modifications to the invention that have not yet been foreseen may still represent equivalent modifications.

Claims

1. A dual-emission fluorescence sensor for the detection and removal of malachite green, characterized in that, 2-Quinoxalocarboxylic acid was introduced into UiO-66-(COOH)2, and then modified with Eu dopant. 3+ Prepared; The dual-emission fluorescence sensor was obtained by the following preparation method, which includes the following steps: (1) Preparation of UiO-66-(COOH)2 / 2-QCA: ZrCl4, 1,2,4,5-benzenetetracarboxylic acid and 2-quinoxaloline carboxylic acid were dispersed in 50 mL of N,N-dimethylformamide. The mixture was then refluxed at 100 °C for 24 hours, centrifuged for 8 minutes, and the white solid was collected, washed and dried to obtain UiO-66-(COOH)2 / 2-QCA. (2) Preparation of EuUQCA: The UiO-66-(COOH)2 / 2-QCA obtained in step (1) was added to the aqueous solution of Eu(NO3)3·6H2O, stirred at 80℃ for 36 hours, the white solid was collected, washed and dried to obtain EuUQCA.

2. A method for preparing a dual-emission fluorescence sensor for the detection and removal of malachite green, characterized in that, 2-Quinoxalocarboxylic acid was introduced into UiO-66-(COOH)2, and then modified with Eu dopant. 3+ Prepared; The preparation method includes the following steps: (1) Preparation of UiO-66-(COOH)2 / 2-QCA: ZrCl4, 1,2,4,5-benzenetetracarboxylic acid and 2-quinoxaloline carboxylic acid were dispersed in 50 mL of N,N-dimethylformamide. The mixture was then refluxed at 100 °C for 24 hours, centrifuged for 8 minutes, and the white solid was collected, washed and dried to obtain UiO-66-(COOH)2 / 2-QCA. (2) Preparation of EuUQCA: The UiO-66-(COOH)2 / 2-QCA obtained in step (1) was added to the aqueous solution of Eu(NO3)3·6H2O, stirred at 80℃ for 36 hours, the white solid was collected, washed and dried to obtain EuUQCA; The concentration ratio of ZrCl4, 1,2,4,5-benzenetetracarboxylic acid and 2-quinoxaloline carboxylic acid in step (1) is 2.0 mmol: 2.8 mmol: 1.2 mmol.

3. The preparation method according to claim 2, characterized in that, The mass ratio of UiO-66-(COOH)2 / 2-QCA and Eu(NO3)3·6H2O in step (2) is 0.50 g: 0.45 g.

4. The preparation method according to claim 2, characterized in that, In step (2), the concentration of Eu(NO3)3·6H2O is 1.0 mmol.

5. The preparation method according to claim 2, characterized in that, The white solid described in step (1) was washed three times each with N,N-dimethylformamide and ethanol.

6. The preparation method according to claim 2, characterized in that, The white solid described in step (2) was washed three times with H2O and ethanol respectively.

7. The application of the dual-emission fluorescence sensor as described in claim 1 in the field of malachite green detection.

8. The application according to claim 7, characterized in that, The dual-emission fluorescence sensor is used to detect malachite green in fishpond water and fish meat samples.

9. The application of a dual-emission fluorescence sensor as described in claim 1 in the field of malachite green removal.

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