CN110128673A - A cerium-based metal-organic framework for Cr(VI) detection, preparation method and application - Google Patents

Abstract

The invention relates to the technical field of optical sensing, and specifically discloses a cerium-based metal-organic framework for Cr(VI) detection, a preparation method and an application. The cerium-based metal-organic framework uses cerium oxide nanorods with simulated enzyme activity as a template, provides cerium ions as ion centers, and adds terephthalic acid to nucleate and grow into a cerium-based metal-organic framework. The cerium dioxide nanorods are obtained by mixing cerium nitrate hexahydrate and sodium hydroxide, centrifuging, washing, and vacuum drying. The cerium-based metal-organic framework is used to detect Cr(VI). The present invention uses the sacrificial template method to synthesize the cerium-based metal-organic framework for the first time, which has stronger oxidase activity and selectivity _than CeO2 nanomaterials, realizes sensitive detection of Cr(VI), and has high sensitivity, good selectivity, The advantages of simplicity and speed have good application prospects.

Description

A cerium-based metal-organic framework for Cr(VI) detection, preparation method and application

technical field

The invention belongs to the technical field of optical sensing, and in particular relates to a cerium-based metal-organic framework for Cr(VI) detection, a preparation method and an application.

Background technique

Chromium is the 21st most abundant element in the earth's crust, and there are mainly two oxidation states of Cr(III) and Cr(VI) in the environment. Metal plating and processing, leather tanning, industrial cooling water preservatives, and wood preservative treatments can all lead to increased chromium concentrations in the environment. The two oxidation states of Cr have distinctly different chemical properties and human toxicity. Cr(III) is a trace element required by the human body and is less toxic. It can form trivalent cations (or hydrolysis products), which strongly bind to mineral surfaces and form metal hydroxides with limited solubility. Cr(VI) is usually used as a chromate oxyanion and is a known human respiratory carcinogen. In addition to carcinogenicity, some compounds containing Cr(VI) have also been found to be powerful epithelial irritants and nerve tissue degradation factors. It also tends to move around in the environment, endangering water quality. The World Health Organization clearly stipulates in the "Guidelines for Drinking Water Quality (Fourth Edition)" that the maximum pollution level of total chromium in water is 50 μg/L. Therefore, the monitoring, accurate identification and quantitative detection of Cr(VI) are very important. So far, there are few methods for the direct detection of Cr(VI) in aqueous environments except traditional analytical methods such as mass spectrometry, electrochemistry, chromatography, and fluorescence spectroscopy. Moreover, these methods usually require a long time and complicated operations, and are not suitable for rapid and effective determination of Cr(VI). In recent years, emerging colorimetric strategies based on nanozyme materials have been widely used in water pollutant detection due to their detection stability and ability to resist interference from complex media.

Cerium oxide nanomaterials have excellent physical and chemical properties such as high oxygen vacancies, defects, and the presence of double oxidation states, which can effectively adsorb and remove Cr(VI) (Mishra, PK; Kumar, R.; Rai, PK Surfactant-free one-pot synthesis of CeO ₂ , TiO ₂ and Ti@Ce oxide nanoparticles for the ultrafast removal of Cr(VI) from aqueous media. Nanoscale, 2018, 10(15), 7257-7269). Furthermore, the low solubility and low toxicity of ceria nanomaterials in acidic media make them more attractive than other metal oxides for water remediation. As one of the emerging nanomaterials, nanozymes have higher stability and lower cost than natural enzymes, and are widely used in biosensors and nanomedicine. Cerium oxide has two oxidation valence states and a large number of oxygen vacancies and has excellent nanoenzyme activity (Cao, F.; Zhang, Y.; Sun, Y.; Wang, Z.; Zhang, L.; Huang, Y. ; Liu C.; Liu, Z.; Ren, J.; Qu, X. Ultrasmall nanoparticles isolated within porous carbonaceous frameworks for synergistic cancer therapy: enhanced oxidative damage and reduced energy supply. Chemistry of Materials, 2018, 30(21), 7831- 7839).

Metal-organic framework (MOF) materials are a current research hotspot, and the development of new types of platforms based on MOF for loading functional materials has attracted attention. Compared with MOFs, heterostructures combining MOFs with other functional materials have shown great advantages due to the synergistic effect. The sacrificial template method was first proposed by the Kitagawa research group in 2012. Pseudomorphicmineral replacement (that is, the transformation of an unbalanced mineral phase into a thermodynamically more stable phase involves dissolution and reprecipitation, dissolution kinetics, and nucleation and crystallization kinetics of new phases. Combining the natural phenomenon of retaining the shape and size of the substituted parent phase) to construct a porous coordination polymer with alumina as a template, the organic matter is combined with the pre-formed metal oxide matrix, and the porous coordination is made through Pseudomorphic mineral replacement Aggregation occurs at the molecular scale simultaneously with retention of the parent (Reboul, J.; Furukawa, S.; Horike, N.; Tsotsalas, M.; Hirai, K.; Uehara, H.; Kondo, M.; Louvain, N.; Sakata, O.; Kitagawa, S. Mesoscopic architectures of porous coordination polymers fabricated by pseudomorphic replication. Nature materials, 2012, 11(8), 717). In 2017, Lu's group used the sacrificial template method to synthesize a variety of metal-organic frameworks with metal oxides as templates, and adjusted the spatial distribution of metal-composite metal nanoparticles in MOFs by changing the concentration of organic ligands to improve catalytic efficiency (Yang, Q.; Liu, W.; Wang, B.; Zhang, W.; Zeng, X.; F.; Lu, J. Regulating the spatial distribution of metal nanoparticles within metal-organic frameworks to enhance catalytic efficiency. Nature communications, 2017, 8, 14429). In the sacrificial template method, metal oxide templates can sacrifice themselves to provide metal ions, and then initiate the growth of MOFs without any surface modification.

Using the sacrificial template method to synthesize cerium-based metal-organic frameworks, and combining the oxidase activity of cerium-based metal-organic frameworks with the new Cr(VI)-TMB system to construct a new colorimetric method for Cr(VI) detection, has not yet been seen. to related reports.

Contents of the invention

The technical problem to be solved by the present invention is to provide a cerium-based metal-organic framework for Cr(VI) detection, a preparation method and an application for the defects and deficiencies of existing Cr(VI) detection methods. The present invention uses the sacrificial template method to synthesize the cerium-based metal-organic framework for the first time, which has stronger oxidase activity and selectivity _than CeO2 nanomaterials, realizes sensitive detection of Cr(VI), and has high sensitivity, good selectivity, The advantages of simplicity and speed have good application prospects.

Principle of the present invention is:

Using cerium oxide nanorods (CeO ₂ NRs) with mimic enzyme activity as a template to provide cerium ions as ion centers, the addition of terephthalic acid triggers the nucleation and growth of cerium-based metal-organic frameworks (CeO ₂ NRs-MOF), and also The morphology and properties of CeO ₂ NRs are preserved. The CeO ₂ NRs-MOF formed based on the sacrificial template method has stronger oxidase activity and selectivity than CeO ₂ nanomaterials, and Cr(VI _{) can replace H 2 O 2 and combine with} TMB constitutes a new Cr(VI)-TMB system, and oxidizes TMB to develop color. The ultraviolet absorption peak of TMB at 650 nm increases with the increase of Cr(VI) concentration. A simple and sensitive colorimetric method of enzymatic activity for the quantitative analysis and adsorption studies of Cr(VI) in environmental samples.

The present invention adopts the following technical solutions to achieve the purpose of the invention.

First, the present invention provides a cerium-based metal-organic framework for Cr(VI) detection.

The cerium-based metal-organic framework uses cerium oxide nanorods (CeO ₂ NRs) with mimic enzyme activity as a template, provides cerium ions as ion centers, and adds terephthalic acid to nucleate and grow into a cerium-based metal-organic framework (CeO ₂ NRs-MOF).

Further, the cerium oxide nanorods (CeO ₂ NRs) are obtained by mixing and reacting cerium nitrate hexahydrate and sodium hydroxide, centrifuging, washing and vacuum drying.

Further, the cerium-based metal-organic framework (CeO ₂ NRs-MOF) was diluted and dispersed with ultrapure water to form a suspension with a concentration of 1 mg/mL.

Secondly, the present invention provides a method for preparing a cerium-based metal-organic framework for Cr(VI) detection.

The preparation method comprises the following steps: (1) preparation of ceria nanorods (CeO ₂ NRs); (2) nucleation of cerium-based metal organic framework (CeO ₂ NRs-MOF); (3) ultrapure water dilution Dispersion: A cerium-based metal-organic framework (CeO ₂ NRs-MOF) suspension with a concentration of 1 mg/mL was obtained.

Further, the preparation of the cerium oxide nanorods (CeO ₂ NRs) described in the step (1) is specifically as follows: in parts by mass, 1 part of cerous nitrate hexahydrate and 10-12 parts of sodium hydroxide are dissolved Stir and mix in ultrapure water for 20-40 minutes, react at 95-105°C for 20-30 hours, cool to room temperature, wash the product successively with ultrapure water and ethanol for 2-4 times, and vacuum dry at 50-70°C For 12-24 hours, CeO2 nanorods _were prepared.

Further, the nucleation of the cerium-based metal-organic framework (CeO ₂ NRs-MOF) described in step (2) is specifically as follows: in parts by mass, 1 part of CeO ₂ nanorods and terephthalic acid containing Mix 70-80 parts of DMF (N,N-dimethylformamide) solution, react at 65-75°C for 10-15 hours, after cooling to room temperature, wash the product successively with DMF and ethanol for 2-4 times, 50 Vacuum drying at -70°C for 12-24 hours to obtain a cerium-based metal-organic framework.

Finally, the present invention provides an application of a cerium-based metal-organic framework.

The cerium-based metal-organic framework was applied to detect Cr(VI).

The detection of Cr(VI) is specifically: in parts by volume, 1 part of the suspension of cerium-based metal organic framework (CeO ₂ NRs-MOF), TMB(3,3',5,5'- 0.1 part of tetramethylbenzidine) solution, 0.5 part of Cr(VI) solution with different concentrations in the range of 0-5 μM and 0.5 part of HEPES (4-hydroxyethylpiperazineethanesulfonic acid) buffer solution were mixed, and diluted with ultrapure water to 5 parts of solution total volume, carry out mixing reaction, adopt the absorption spectrum of mixed reaction solution in 330nm-800nm wavelength range to measure immediately by ultraviolet-visible spectrophotometer, according to the linear relationship between TMB ultraviolet absorption spectrum intensity and Cr(VI) concentration, Sensitive detection of Cr(VI) is achieved.

Further, the concentration of the cerium-based metal organic framework suspension is 1 mg/mL; the concentration of the TMB solution is 20 mM.

Further, the HEPES buffer solution has a pH of 4 and a concentration of 100 mM.

Beneficial effect:

(1) The cerium-based metal-organic framework synthesized by the sacrificial template method in the present invention has stronger oxidase activity _than CeO2 nanomaterials.

( ₂ ) The cerium _- based metal-organic framework synthesized in the present invention can oxidize TMB to show blue color, and at the same time, it can also selectively adsorb highly toxic Cr(VI) and reduce it to Cr(III), without the presence of H2O2, Cr(VI) can replace H ₂ O ₂ and TMB to form a new redox cycle system.

(3) The present invention combines the oxidase activity of the cerium-based metal-organic framework with the new Cr(VI)-TMB system, constructs a new colorimetric method for detecting Cr(VI), and realizes the detection of Cr(VI) in environmental water bodies The detection has the advantages of high sensitivity, good selectivity, simplicity and speed, and has a good application prospect.

Description of drawings

Figure 1: TEM images of cerium-based metal-organic frameworks. A is the TEM image of CeO ₂ NRs, B is the TEM image of CeO ₂ NRs-MOF;

Figure 2: UV-Vis absorption spectra of CeO ₂ NRs and CeO ₂ NRs-MOF in response to Cr(VI).

Fig. 3: Schematic diagram of the principle of detection of Cr(VI) by oxidase activity based on CeO ₂ NRs-MOF.

Figure 4: UV-Vis spectrum for colorimetric detection of Cr(VI).

Figure 5A: UV-Vis absorption spectrum of colorimetric method in response to different concentrations of Cr(VI);

Figure 5B: Calibration curve between the concentration of Cr(VI) and the intensity of the characteristic absorption peak of TMB.

Figure 6: Selectivity plot for Cr(VI) detection by colorimetric method.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods are conventional methods unless otherwise specified. The raw materials can be obtained from open commercial channels unless otherwise specified.

Example 1: Preparation of cerium-based metal-organic framework

Dissolve 0.434g of cerous nitrate hexahydrate and 4.8g of sodium hydroxide in 20mL of ultrapure water, stir and mix for 30 minutes, place the mixed solution in an autoclave at 100°C for 24 hours, and after cooling to room temperature, the product Centrifuge and wash with ultrapure water and ethanol three times in turn, and then place in a vacuum oven at 60°C overnight to prepare CeO ₂ nanorods; mix 20 mg of CeO ₂ nanorods with 30 mL of DMF solution containing 1.4952 g of terephthalic acid, and place Reaction in a high-pressure reactor at 70°C for 12 hours, after cooling to room temperature, the product was washed with DMF and ethanol three times, and then placed in a vacuum oven at 60°C overnight to obtain a cerium-based metal-organic framework (CeO ₂ NRs- MOF).

Example 2: Preparation of cerium-based metal-organic framework

Dissolve 0.434g of cerous nitrate hexahydrate and 4.34g of sodium hydroxide in 20mL of ultrapure water, stir and mix for 20 minutes, place the mixed solution in an autoclave at 95°C for 20 hours, and after cooling to room temperature, the product Centrifuge and wash twice with ultrapure water and ethanol in turn, and place in a vacuum oven at 50°C for 12 hours to prepare CeO ₂ nanorods; mix 20 mg CeO ₂ nanorods with 30 mL DMF solution containing 1.4 g terephthalic acid Mix, place in a high-pressure reactor at 65°C for 10 hours, cool to room temperature, wash the product twice with DMF and ethanol, and place it in a vacuum oven at 60°C for 12 hours to obtain a cerium-based metal-organic framework (CeO ₂ NRs-MOF).

Example 3: Preparation of cerium-based metal-organic framework

Dissolve 0.434g of cerous nitrate hexahydrate and 5.208g of sodium hydroxide in 20mL of ultrapure water, stir and mix for 40 minutes, place the mixed solution in an autoclave at 105°C for 30 hours, cool to room temperature, and prepare the product Centrifugal washing with ultrapure water and ethanol four times in sequence, and then placed in a vacuum oven at 70 °C for 24 hours to prepare CeO2 nanorods; mix _{20 mg} of CeO2 nanorods with 30 mL of DMF solution containing 1.6 g of terephthalic acid , placed in a high-pressure reactor at 75 ° C for 15 hours, after cooling to room temperature, the product was sequentially washed with DMF and ethanol four times, and then placed in a vacuum oven at 70 ° C for 24 hours to obtain a cerium-based metal organic framework ( CeO ₂ NRs-MOF).

Example 4: Characterization of cerium-based metal-organic frameworks

The morphology of the CeO ₂ NRs-MOF obtained in Example 1 was characterized by a transmission electron microscope (TEM), and the results are shown in FIG. 1 . A is the TEM image of CeO ₂ NRs, B is the TEM image of CeO ₂ NRs-MOF. From the TEM images of CeO ₂ NRs and CeO ₂ NRs-MOF, it can be seen that both CeO ₂ NRs and CeO ₂ NRs-MOF have a rod _- like structure, the width of CeO ₂ NRs is about 5-10nm, and the length is about 120nm. ₂ The periphery of NRs is wrapped with a thin layer with a thickness of about 2-5nm.

The elements and valence states of CeO ₂ NRs-MOF were characterized by X-ray photoelectron spectroscopy (XPS). The O 1s XPS spectra of CeO ₂ NRs and CeO ₂ NRs-MOF showed that the characteristic peaks of Ce(III)-O and Ce(IV)-O appeared in CeO ₂ NRs at 528.7eV and 530.4eV, respectively, and CeO ₂ NRs - The characteristic peaks of MOF at 528.9eV and 530.7eV correspond to Ce(III)-O and Ce(IV)-O, respectively, indicating that both CeO ₂ NRs and CeO ₂ NRs-MOF have mixed valences of trivalent and tetravalent cerium state, so that both have oxidase activity; further peak-integrated calculation of XPS, Ce(III)-O/Ce(IV)-O ratio is 0.3874, which is higher than 0.2641 of CeO ₂ NRs, indicating that CeO ₂ NRs- The content of trivalent cerium in MOF is more than that of CeO ₂ NRs, indicating that CeO ₂ NRs-MOF has stronger oxidase activity than CeO ₂ NRs, which is consistent with the report in the literature that the activity of cerium oxide nanoenzyme increases with the content of trivalent cerium Consistent with (Heckert, EG; Karakoti, AS; Seal, S.; Self, WT The role of ceriumredox state in the SOD mimetic activity of nanoceria.Biomaterials, 2008,29 (18), 2705-2709), show that the present invention successfully prepared CeO ₂ NRs-MOF with strong oxidase activity was obtained.

The oxidase activity of CeO ₂ NRs and CeO ₂ NRs _- MOF was characterized by ultraviolet-visible absorption (UV-Vis) spectroscopy. Figure ₂ shows the UV- Vis Spectrogram. Mix 100 μL of 1 mg/mL cerium-based MOF, 10 μL of 20 mM TMB solution, 50 μL of 10 μM Cr(VI) solution and 50 μL of 100 mM pH 4 HEPES buffer solution, add ultrapure water until the total volume of the solution is 500 μL, mix well and immediately The absorption spectrum of the mixed reaction solution in the wavelength range of 330nm-800nm was measured by a UV-2450 ultraviolet-visible spectrophotometer. CeO ₂ NRs cannot oxidize TMB in a short time, so the absorption peaks at 370nm and 650nm are very weak, while CeO ₂ NRs-MOF has stronger oxidase activity, which can quickly oxidize TMB to develop color, so it appears at 370nm and 650nm The strong absorption peak of oxidized TMB was observed.

Example 5: Principle and feasibility analysis of Cr(VI) detection based on CeO ₂ NRs-MOF oxidase activity

The procedure for constructing a colorimetric method to detect Cr(VI) based on CeO ₂ NRs-MOF prepared by the sacrificial template method is simple, and it only needs to measure the characteristic changes of the ultraviolet spectrum of the mixed solution of CeO ₂ NRs-MOF, TMB and Cr(VI) Target detection. Compared with CeO ₂ nanomaterials, CeO _{2 NRs -} MOF has stronger oxidase activity and selectivity, and can directly oxidize TMB for color development and selectively adsorb Cr(VI) and reduce Cr(III), Cr(VI) can replace conventionally used H ₂ O ₂ to form a new redox cycle system with TMB, and realize rapid colorimetric detection of Cr(VI). The detection principle is shown in Figure 3.

Utilize UV-Vis spectrometry to verify the feasibility of the colorimetric method constructed by the present invention, and Fig. 4 is the UV-Vis spectrogram of Cr(VI) detected by the colorimetric method constructed by the present invention under different experimental conditions. It can be seen from Figure 4 that in the aqueous solution of HEPES containing 10mM pH 4, CeO ₂ NRs-MOF (marked as CeO ₂ -MOF in the figure), TMB and Cr(VI) have no characteristic absorption peaks in the wavelength range of 330nm-800nm, There is no obvious characteristic absorption peak when the above three are mixed in pairs. Only when CeO ₂ NRs-MOF, TMB and Cr(VI) exist at the same time, there will be obvious characteristic absorption of oxidized TMB at 370nm and 650nm. peak. The above results show that the CeO ₂ NRs-MOF prepared by the method of the present invention has good oxidase activity, combined with the new Cr(VI)-TMB redox system, a new colorimetric method has been successfully constructed and can be used to detect Cr(VI).

Example 6: Analysis of the detection performance of Cr(VI) by a colorimetric method based on CeO ₂ NRs-MOF

Dilute and disperse the cerium-based metal-organic framework obtained in Example 1 with ultrapure water into 100 μL of a suspension with a concentration of 1 mg/mL, 10 μL of a 20 mM TMB solution, Cr(VI) solutions with different concentrations in the range of 0-5 μM and 100 mM Mix 50 μL of HEPES buffer solution with pH 4, add ultrapure water until the total volume of the solution is 500 μL, and immediately measure the absorption spectrum of the mixed reaction solution in the wavelength range of 330nm-800nm with a UV-2450 ultraviolet-visible spectrophotometer after mixing evenly. The ultraviolet-visible absorption spectrum diagram of the colorimetric method constructed by the invention in response to different concentrations of Cr(VI) is shown in Figure 5A; the calibration curve between the concentration of Cr(VI) and the intensity of the characteristic absorption peak of TMB is shown in Figure 5B.

It can be seen from Figure 5A that with the increase of Cr(VI) concentration (0, 0.03, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2, 3, 4 and 5 μM), the blue color of the solution gradually becomes darker , the intensity of the absorption peak at 650nm is gradually enhanced; as can be seen from Figure 5B, the difference between the absorbance at 650nm and the absorbance of the baseline at 750nm (ΔA=A _650nm -A _750nm ) and the concentration of Cr(VI) show a good relationship in the range of 30nM-5μM The linear relationship, the detection limit is 20nM. Colorimetric detection of Cr(VI) based on gold nanoparticle coordination (linear range 0.5-2.5 μM, detection limit 0.07 μM) (Du, J.; Ge, H.; Gu, Q.; Du, H.; Fan, J.; Peng, X. Goldnanoparticle-based nano-probe for the colorimetric sensing of Cr ³⁺ and Cr ₂ O ₇ ^2- by the coordination strategy. Nanoscale, 2017, 9(48), 19139-19144), using Zr ⁴⁺ MOF Specific Adsorption and Detection of Cr(VI) (Detection Range 0.5-96μM, Detection Limit 77nM) (Rapti, S.; Sarma, D.; Diamantis, SA; Skliri, E.; Armatas, GS; Tsipis, AC ; Hassan, YS; Alkordi, M.; ^Malliakas , CD; Kanatzidis, MG; Lazarides T.; Journal of Materials Chemistry A, 2017, 5(28), 14707-14719), chitosan and glutaraldehyde were cross-linked by Schiff base reaction to synthesize non-conjugated polymer fluorophores for selective detection of Cr(VI)( Detection range 0-50 μM, detection limit 0.22 μM) (Song, J.; Zhou, H.; Gao, R.; Zhang, Y.; Zhang, H.; Zhang, Y.; Wang, G.; Wong, PK ; Zhao, H. Selective determination of Cr(VI) by glutaraldehyde cross-linked chitosan polymer fluorophores. ACS sensors, 2018, 3(4), 792-798) have good effect. It can be seen that the cerium-based metal-organic framework prepared by the method of the present invention has good sensitivity and reliability for detecting Cr(VI).

Example 7: Selectivity of Cr(VI) detection by colorimetric method based on CeO ₂ NRs-MOF

The selectivity of the colorimetric method based on CeO ₂ NRs-MOF for Cr(VI) detection was investigated, as shown in Figure 6. It can be seen from Figure 6 that even if the concentration of 17 kinds of cations and anions that may exist in water is ten times that of Cr(VI), for example, when Cr(VI) is 1 μM and other ions are 10 μM, there is almost no response. This is due to the dual effect of the size selection effect of the MOF on the outer layer of CeO ₂ NRs-MOF and the absence of H ₂ O ₂ in the chromogenic system to avoid the interference of ions (such as iron ions, copper ions) that have peroxidase activity themselves . In summary, the method of the present invention has good selectivity for the detection of Cr(VI).

Similarly, the cerium-based metal-organic framework prepared in Example 2 and the cerium-based metal-organic framework prepared in Example 3 were repeatedly tested and tested according to the methods described in Examples 4-7, and the obtained The detection and experimental results are basically the same as the results of Examples 4-7 of the cerium-based metal-organic framework prepared in Example 1.

The specific embodiments of the present invention have been described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, equivalent changes and modifications made without departing from the spirit and scope of the present invention fall within the scope of the present invention.

Claims (10)

1. A cerium-based metal-organic framework for Cr(VI) detection, characterized in that: with cerium dioxide nanorods (CeO ₂ NRs) with simulated enzyme activity as a template, cerium ions are provided as ion centers, and the pair Phthalic acid, nucleated and grown into cerium-based metal-organic frameworks (CeO ₂ NRs-MOF). 2. A kind of cerium-based metal organic framework for Cr (VI) detection according to claim ₁ , is characterized in that: described ceria nanorod (CeO NRs) is made of cerous nitrate hexahydrate and Sodium hydroxide mixed reaction, obtained by centrifugation, washing and vacuum drying. 3. A cerium-based metal-organic framework for Cr(VI) detection according to claim 1, characterized in that: the cerium-based metal-organic framework (CeO NRs _- MOF) is diluted with ultrapure water Disperse into a suspension with a concentration of 1mg/mL. 4. A method for preparing a cerium-based metal-organic framework for Cr(VI) detection, characterized in that: comprising the following steps: (1) preparation of ceria nanorods (CeO ₂ NRs); (2) cerium-based Nucleation of metal-organic framework (CeO ₂ NRs-MOF); (3) Ultrapure water dilution and dispersion: a cerium-based metal-organic framework (CeO ₂ NRs-MOF) suspension with a concentration of 1 mg/mL was obtained. 5. A method for preparing a cerium-based metal-organic framework for Cr(VI) detection according to claim 4, characterized in that the preparation of the cerium oxide nanorods (CeO NRs) described in step ( ₁ ) , specifically: in parts by mass, 1 part of cerous nitrate hexahydrate and 10-12 parts of sodium hydroxide are dissolved in ultrapure water, stirred and mixed for 20-40 minutes, and reacted at 95-105 ° C for 20-30 hours, after cooling to room temperature, the product was centrifuged and washed with ultrapure water and ethanol for _2-4 times, and vacuum-dried at 50-70°C for 12-24 hours to obtain CeO2 nanorods. 6. A method for preparing a cerium-based metal-organic framework for Cr(VI) detection according to claim 4, characterized in that the cerium-based metal-organic framework (CeO ₂ NRs-MOF) described in step (2) ) nucleation generation, specifically: in parts by mass, ₁ part of CeO2 nanorods are mixed with a DMF solution containing 70-80 parts of terephthalic acid, reacted at 65-75 °C for 10-15 hours, and cooled to After room temperature, the product was centrifuged and washed with DMF and ethanol for 2-4 times, and vacuum-dried at 50-70° C. for 12-24 hours to obtain a cerium-based metal-organic framework. 7. An application of a cerium-based metal-organic framework, characterized in that it is applied to the detection of Cr(VI). 8. The application of a cerium-based metal-organic framework according to claim 7, characterized in that the detection of Cr(VI) is specifically: the cerium-based metal-organic framework (CeO ₂ 1 part of NRs-MOF) suspension, 0.1 part of TMB solution, Cr(VI) solution with different concentrations in the range of 0-5 μM and 0.5 part of HEPES buffer solution were mixed, and diluted with ultrapure water to 5 parts of the total solution volume, Carry out the mixed reaction, immediately measure the absorption spectrum of the mixed reaction solution in the wavelength range of 330nm-800nm, and realize the sensitive detection of Cr(VI) according to the linear relationship between the intensity of TMB ultraviolet absorption spectrum and the concentration of Cr(VI). 9. The application of a cerium-based metal-organic framework according to claim 8, characterized in that: the cerium-based metal-organic framework suspension has a concentration of 1 mg/mL; the TMB solution has a concentration of 20 mM . 10. The application of a cerium-based metal-organic framework according to claim 8, wherein the HEPES buffer solution has a pH of 4 and a concentration of 100 mM.