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Article

Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72−

by
Jie Yin
,
Hongtao Chu
*,
Shili Qin
,
Haiyan Qi
and
Minggang Hu
College of Chemistry and Chemical Engineering, Qiqihaer University, Qiqihaer 161006, China
*
Author to whom correspondence should be addressed.
Sensors 2021, 21(21), 7355; https://doi.org/10.3390/s21217355
Submission received: 29 September 2021 / Revised: 27 October 2021 / Accepted: 3 November 2021 / Published: 5 November 2021
(This article belongs to the Section Optical Sensors)
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Abstract

:
Luminescent Ln-MOFs (Eu0.075Tb0.925-MOF) were successfully synthesised through the solvothermal reaction of Tb(NO3)3·6H2O, Eu(NO3)3·6H2O, and the ligand pyromellitic acid. The product was characterised by X-ray diffraction (XRD), TG analysis, EM, X-ray photoelectron spectroscopy (XPS), and luminescence properties, and results show that the synthesised material Eu0.075Tb0.925-MOF has a selective ratio-based fluorescence response to Fe3+ or Cr2O72−. On the basis of the internal filtering effect, the fluorescence detection experiment shows that as the concentration of Fe3+ or Cr2O72− increases, the intensity of the characteristic emission peak at 544 nm of Tb3+ decreases, and the intensity of the characteristic emission peak at 653 nm of Eu3+ increases in Eu0.075Tb0.925-MOF. The fluorescence intensity ratio (I653/I544) has a good linear relationship with the target concentration. The detection linear range for Fe3+ or Cr2O72− is 10–100 μM/L, and the detection limits are 2.71 × 10−7 and 8.72 × 10−7 M, respectively. Compared with the sensor material with a single fluorescence emission, the synthesised material has a higher anti-interference ability. The synthesised Eu0.075Tb0.925-MOF can be used as a highly selective and recyclable sensing material for Fe3+ or Cr2O72−. This material should be an excellent candidate for multifunctional sensors.

1. Introduction

Heavy metals and inorganic anion pollutants in water pose hidden dangers to human health [1]. The United Nations Sustainable Development Goals set in September 2015 indicated that countries are expected to greatly improve human water quality by 2030. Thus, the detection of pollutants in water has become increasingly important. Fe3+ is one of the basic trace elements in humans. The lack or excess of this element can cause many physiological disorders, such as nausea, abdominal pain, anaemia, liver cirrhosis, and organ failure [2,3,4]. Salonen et al. [2] confirmed that elevated iron content is an important risk factor for acute myocardial infarction, Bijeh et al. [3] confirmed that the increased risk of cardiovascular disease is related to elevated iron content, and Jehn et al. [4] confirmed that elevated iron could lead to abnormal baseline metabolism. In addition, Cr2O72− is an important oxidant in laboratories and industry [5], and it is highly carcinogenic in the environment and harmful to the ecology, environment, and biological system [6,7,8,9]. Mansi et al. [6] confirmed that it is the second most abundant inorganic groundwater pollutant due to its wide application in many industrial fields, such as electroplating chrome, dyes, and leather tanning. Costa [7] confirmed that it is mutagenic and carcinogenic to organisms’ sexual function. Therefore, the selective sensing of Fe3+ and Cr2O72− in water quality has attracted growing attention from scholars. Many methods are used for the determination of Fe3+ and Cr2O72−, such as atomic emission spectrometry, atomic absorption spectrometry, inductively coupled plasma mass spectrometry, electrochemical methods, and ion chromatography. However, these methods are complicated to operate, costly, and have a long detection time. Therefore, developing a simple and efficient method to determine Fe3+ and Cr2O72− is of practical significance. Fluorescence sensing technology can meet the requirements of new analysis and detection technology due to its high sensitivity, fast analysis speed, strong selectivity, simple operation, and low experimental cost. In recent years, it has received extensive attention [10].
Ln-MOFs materials refer to the self-assembly connection of metal ions and organic ligands by coordination bonds to form network complexes. Ln-MOFs materials have outstanding luminescence characteristics; that is, they have the advantages of large Stokes shift, high quantum yield and luminescence intensity, narrow emission spectrum range, flexible coordination mode, and long luminescence life. MOFs fluorescent probes are commonly used as sensors [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]. Hna et al. [26] synthesised Ce-MOF to detect Fe3+, and Gai et al. [27] synthesised dual-sensor Eu-MOF to detect Fe3+ and Cr2O72−. The ratio fluorescent probe is based on measuring the ratio of the fluorescence intensity of two independent fluorescence emission peaks for quantitative analysis, which can effectively reduce the influence of excitation light, environment, and probe concentration changes, and greatly improve the accuracy of the method. At present, the usual design method of the Ln-MOFs ratio probe is to select two kinds of Ln3+ to synthesise by different molar ratios [28,29,30] or to combine Ln-MOFs with one or two substances with different fluorescence emission wavelengths, including carbon dots (CDs), quantum dots, and fluorescent dyes [31,32,33,34,35]. Zhang et al. [30] used two different molar ratios of Tb and Eu as the metal centre. 2,2′-bipyridine-6,6′-dicarboxylate acid (H2bpdc) is a ligand to synthesise Eu0.6059Tb0.3941-ZMOF, which can realise the selective detection of haemolysed phosphate (lysophosphatidic acid or LPA) in human plasma. Xu et al. [31] reported that CDs with strong fluorescence activity and Eu3+ were encapsulated in MOF-253, and the dual-emission ratio probe Eu3+/CDs@MOF-253 was synthesised to detect Hg2+. Therefore, the development of ratio fluorescent probe Ln-MOFs to detect Fe3+ and Cr2O72− has great application prospects.
The selective fluorescence detection of Fe3+ and Cr2O72− using ratio fluorescent probe Ln-MOFs is rarely reported in the literature. In this paper, luminescent Eu0.075Tb0.925-MOF was successfully synthesised by the solvothermal reaction of Tb(NO3)3·6H2O, Eu(NO3)3·6H2O, and ligand pyromellitic acid. Eu0.075Tb0.925-MOF was comprehensively characterised by XRD, thermogravimetric analysis (TG), elemental analysis, Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and XPS. Eu0.075Tb0.925-MOF has excellent stability in aqueous solution, and it can detect Fe3+ and Cr2O72− in aqueous solution by dual-emission ratio fluorescence sensing, which provides a new idea for the fluorescence detection of Fe3+ and Cr2O72−.

2. Materials and Methods

Commercially available reagents and solvents were used. XRD characterisation was performed to determine the regular arrangement of atoms or ions in the Eu0.075Tb0.925-MOF, which is one of the commonly used methods to explore the structure of matter. An elemental analyser was used for elemental analysis. FTIR was used to scan and analyse the range of 4000–400 cm−1 to determine the functional groups and chemical bonds of Eu0.075Tb0.925-MOF. The thermal stability of Eu0.075Tb0.925-MOF was analysed by TG, which was performed under N2 protection. TEM and SEM were used to observe the specific morphology of Eu0.075Tb0.925-MOF. The FL/FS900 fluorescence spectrometer was used to record the steady-state luminescence performance of Eu0.075Tb0.925-MOF. XPS and UV spectrophotometers were used to investigate the reaction mechanism.
Synthesis of Eu0.075Tb0.925-MOF: Product preparation was the first step. Eu0.075Tb0.925-MOF with Tb and Eu were prepared as the metal centre, and pyromellitic acid was prepared as the organic ligand as follows: Dissolved Tb(NO3)3·6H2O + Eu(NO3)3·6H2O (0.2 mmol), pyromellitic acid (0.2 mmol), DMF (8 mL), distilled water (4 mL), and CH3CH2OH (4 mL) were transferred to an autoclave (volume: 25 mL). The product was then sealed and heated in a 120 °C vacuum drying oven for 48 h and gradually cooled to ambient temperature. After the autoclave was opened, the product was collected after centrifugation, washed thoroughly with DMF and ethanol, paralleled three times, and dried. Thus, the target product Eu0.075Tb0.925-MOF was obtained.

3. Results and Discussion

3.1. XRD Characterisation

Eu-MOF, Tb-MOF, and Eu0.075Tb0.925-MOF combined with lanthanide nitrate and pyromellitic acid were prepared by the solvothermal method. Figure 1 shows the XRD patterns of Ln-MOFs. As shown in the figure, the 2θ diffraction angle peak positions of the simulated XRD pattern and the synthesised samples Eu-MOF, Tb-MOF, and Eu0.075Tb0.925-MOF are the same, and there are sharp peaks at the diffraction angles from 9 to 10. At the same time, the diffraction peaks 9 to 10 of the crystal synthesised by Silva et al. [36] are basically the same, indicating that the synthesised Eu0.075Tb0.925-MOF has high purity and good crystallinity [36,37,38,39].

3.2. TG Analysis

Figure 2 shows the TG analysis results of Ln-MOFs. The weight loss of Ln-MOFs is mainly divided into two stages. Before 340 °C, Eu0.075Tb0.925-MOF has good thermal stability.

3.3. FTIR Analysis

Figure 3 shows the FTIR spectrum of Ln-MOFs. Compared with the FTIR spectrum of pyromellitic acid, the main characteristic peaks in the FTIR spectrum of Eu0.075Tb0.925-MOF are similar to those of pyromellitic acid, but the C=O stretching vibration peak disappeared at 1720 cm−1 in the original pyromellitic acid spectrum (significantly weakened), thereby indicating that the carboxyl oxygen is coordinated with Tb and Eu atoms in the ligand.

3.4. Elemental Analysis and XPS

A comparison of elemental (Table 1) and XPS (Figure 4) analyses shows that, corresponding to the content of the element, the distribution ratio of Eu to Tb in Eu0.075Tb0.925-MOF is 0.075:0.925. The specific loadings of Tb(NO3)3 and Eu(NO3)3 are 42.74% and 3.46% respectively, and the cooling rate is 0.017 K/s.

3.5. EM Characterisation

Figure 5 shows the TEM and SEM images of Eu0.075Tb0.925-MOF, which indicate that the prepared Eu0.075Tb0.925-MOF has a regular external morphology, a nanocolumn shape, and a diameter of about 500 nm.

3.6. Adsorption Characteristics of Eu0.075Tb0.925-MOF

Figure 6 shows the N2 adsorption desorption isotherms of Eu0.075Tb0.925-MOF. The adsorption capacity increases slowly with the increase of pressure at the middle–high-pressure stage, indicating that Eu0.075Tb0.925-MOF is a porous material with an average pore size of 3.38 nm, a BJH average pore diameter of 20.99 nm, and a BET specific surface area of 12.9542 m2/g.

3.7. Photoluminescence Characteristics

Figure 7a shows the fluorescence emission spectrum of Eu0.075Tb0.925-MOF measured at ambient temperature. The figure shows that Eu0.075Tb0.925-MOF exhibits characteristic transitions of Tb3+ and Eu3+ under the excitation of 310 nm light, located at 544 and 653 nm respectively, showing the same intensity of fluorescence emission. This finding indicates that the ligand can effectively transfer energy to Tb3+ and Eu3+ at the same time [40,41,42,43,44].
As shown in the CIE diagram in Figure 7c,d, Eu-MOF shows red fluorescence, and Tb-MOF shows green fluorescence. When Eu3+ and Tb3+ synthesise Eu0.075Tb0.925-MOF at a ratio of 0.075:0.925, Eu0.075Tb0.925-MOF shows the intermediate colour of the two, which is a yellow-green fluorescence sensitive to the human eye. This material has potential application as a luminescent material and a light-sensitive material for naked-eye detection [45].

3.8. Fluorescence Sensing of Fe3+

Gao and Ma [46,47] prepared Tb-MOF and used it for sensitive fluorescence sensing of Fe3+ and Cr2O72−. On this basis, this paper designs a ratio fluorescent probe, Eu0.075Tb0.925-MOF, for the fluorescence sensing of Fe3+ and Cr2O72− to improve the measurement accuracy and expand the linear range of the test. To determine the fluorescence performance of Eu0.075Tb0.925-MOF to Fe3+, the fluorescence response of Eu0.075Tb0.925-MOF to Fe3+ was investigated, and the results are shown in Figure 8.
Figure 8a shows that with the increase of the Fe3+ concentration, the characteristic emission peak intensity of Tb3+ decreases at 544 nm, and the characteristic emission peak intensity of Eu3+ increases at 653 nm. The intensity at IEu = 653 nm and ITb = 544 nm is used to calculate the intensity change I0/I, where I0 (IEu0/ITb0) is the initial fluorescence intensity before fluorescence, and I (IEu/ITb) is the fluorescence intensity in the presence of Fe3+. Figure 8b shows that I0/I and Fe3+ present a linear relationship in the concentration range of 10–100 μM/L, and the linear regression equation is:
I0/I = 0.71 − 7948.64x.
The limit of detection (LOD) of Fe3+ is evaluated by the equation 3Sb/S, where Sb is the standard deviation of repeated detection of the original solution, and S is the slope of the linear fit. The LOD is calculated as 2.71 × 10−7 M. Figure 8c shows that the colour change trend of Eu0.075Tb0.925-MOF is yellow green–yellow–orange–red with the increase in Fe3+ concentration. This material is expected to achieve naked-eye detection of Fe3+.
The prepared Eu0.075Tb0.925-MOF was subjected to a cyclic application experiment, and KNO3 solution was used to wash the used materials. Figure 8d,e shows that the ratio of the luminous intensity of the material and the XRD did not change considerably, even after five cycles. Eu0.075Tb0.925-MOF is very stable in the sensing experiment.
The fluorescence sensing selectivity of Eu0.075Tb0.925-MOF to Fe3+ was investigated through the anti-interference experiment. The Eu0.075Tb0.925-MOF sample was immersed in NaX solution (Mg2+, K+, Pb2+, Al3+, Na+, Cd2+, Mn2+, Zn2+, Ni2+, Fe2+, Cu2+, Hg2+) at a concentration of 1 × 10−4 M. The results are shown in Figure 8f. Except for Fe3+, the luminous intensity ratio of Eu0.075Tb0.925-MOF exhibits almost no change after the addition of metal ions. However, when the same amount of Fe3+ was added to the Mg2+, K+, Pb2+, Al3+, Na+, Cd2+, Mn2+, Zn2+, Ni2+, Fe2+, Cu2+, and Hg2+ solution containing Eu0.075Tb0.925-MOF, the luminous intensity ratio of IEu/ITb was significantly higher. This result shows that the sensing ability of Eu0.075Tb0.925-MOF on Fe3+ will not be interfered with by the presence of other metal ions. Therefore, Eu0.075Tb0.925-MOF has a high selectivity for Fe3+ in an aqueous solution.

3.9. Fluorescence Sensing of Cr2O72−

To determine the fluorescence performance of Eu0.075Tb0.925-MOF to Cr2O72−, the fluorescence response of Eu0.075Tb0.925-MOF to Cr2O72− was investigated, and the results are shown in Figure 9.
Figure 9a shows that with the increase in Cr2O72− concentration, the characteristic emission peak intensity of Tb3+ decreases at 544 nm, and the characteristic emission peak intensity of Eu3+ increases at 653 nm. At the same time, I0/I and Cr2O72− showed a linear correlation in the concentration range of 10–100 μM/L, the linear regression equation is:
I0/I = 0.81 − 9660.83x,
and the LOD was 8.72 × 10−7 M. The CIE diagram in Figure 9c shows that with the increase in Cr2O72− concentration, the colour change trend of Eu0.075Tb0.925-MOF is yellow green–yellow–orange–red, which is expected to realise the naked-eye detection of Cr2O72−.
A cyclic application experiment was performed on Eu0.075Tb0.925-MOF. Figure 9d shows that the luminous intensity ratio of Eu0.075Tb0.925-MOF does not change much after five cycles. Eu0.075Tb0.925-MOF was very stable in the sensing experiment.
Similarly, the fluorescence sensing selectivity of Eu0.075Tb0.925-MOF to Cr2O72− was investigated through the anti-interference experiment. Eu0.075Tb0.925-MOF was dispersed into a solution containing F−, Cl−, I−, Br−, NO3−, CrO42−, SCN−, IO3−, CO32−, and Cr2O72− with the same concentration. The results are shown in Figure 9e. Except for Cr2O72−, the luminous intensity ratio of Eu0.075Tb0.925-MOF is almost unchanged after the addition of anions. However, when the same amount of Cr2O72− was added to the F−, Cl−, I−, Br−, NO3−, CrO42−, SCN−, IO3−, and CO32− solution containing Eu0.075Tb0.925-MOF, the luminous intensity ratio of IEu/ITb was significantly higher. This result shows that the sensing ability of Eu0.075Tb0.925-MOF on Cr2O72− will not be interfered with by the presence of other anions. Therefore, Eu0.075Tb0.925-MOF has a high selectivity for Cr2O72− in an aqueous solution.

3.10. Comparison with Other Sensors That Detect Fe3+ and Cr2O72− Ions

Compared with the Fe3+ and Cr2O72− detection methods used in other studies, as shown in Table 2, the prepared Eu0.075Tb0.925-MOF can reduce the effects of interference caused by excitation light, the environment, and probe concentration changes, and it has improved the detection accuracy relative to other methods.

3.11. Mechanism Study

The mechanism of Fe3+ and Cr2O72− on Eu0.075Tb0.925-MOF fluorescence sensing is examined. Figure 10a shows that the UV absorption spectrum of Fe3+ overlaps with the excitation spectrum of Eu0.075Tb0.925-MOF, which indicates that Fe3+ and Eu0.075Tb0.925-MOF are competitively adsorbed. At the same time, Figure 4 shows that Fe3+ is attached to the surface of Eu0.075Tb0.925-MOF and that the interaction between Fe3+ and the uncoordinated O atom in the ligand is weak. Eu0.075Tb0.925-MOF reduces the energy transfer from the ligand to Tb3+, and Tb3+ is quenched. As a result, the energy transfer from the ligand to Eu3+ is increased, and the characteristic red fluorescence of Eu3+ is displayed. Figure 10b shows that the UV absorption spectrum of Cr2O72− overlaps with the excitation spectrum of Eu0.075Tb0.925-MOF, which indicates that Cr2O72− and Eu0.075Tb0.925-MOF are competitively adsorbed. It will also cause the energy transfer from the ligand to Eu3+ to increase and show the characteristic red fluorescence of Eu3+.

3.12. Application in Actual Water Sample Analysis

The ratio fluorescent probe Eu0.075Tb0.925-MOF was used for Fe3+ and Cr2O72− in tap water. The results are shown in Table 3. The sample recovery rate is 101–114%, thereby showing that the established method has high accuracy and precision for the determination of Fe3+ and Cr2O72− content in actual samples.

4. Conclusions

The ratio fluorescent probe Eu0.075Tb0.925-MOF was synthesised in this experiment by using the solvothermal method and was used for Fe3+ and Cr2O72− determination. Mainly on the basis of the internal filtering effect, the characteristic fluorescence emission peak intensity of Tb3+ decreased, and the characteristic emission peak intensity of Eu3+ increased on Eu0.075Tb0.925-MOF as the concentration of Fe3+ and Cr2O72− increased. The ratio of the emission fluorescence intensity at the two wavelengths has a linear relationship with the target concentration, which realises the selective detection of Fe3+ and Cr2O72−. The linear detection range was 10–100 μM, and the LOD was 2.71 × 10−7 and 8.72 × 10−7 M, respectively. The synthesised material was used as a ratio fluorescent probe, which can effectively eliminate background fluorescence interference in the detection process and improve the detection accuracy. The trend of the fluorescence colour change of the synthesised material during the detection process indicates that the material is expected to realise naked-eye detection of Fe3+ and Cr2O72−.

Author Contributions

Conceptualisation, H.C.; methodology, J.Y.; investigation, J.Y. and H.C.; resources, H.C.; validation, J.Y., H.C. and S.Q.; formal analysis, J.Y. and H.C.; data curation, J.Y.; writing—original draft preparation, J.Y.; writing—review and editing, J.Y. and H.C.; supervision, H.C., S.Q., H.Q. and M.H.; project administration, H.C.; funding acquisition, H.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Research and Innovation Platform Project of Fundamental Scientific Research Business Expenses for Undergraduate Universities in Heilongjiang Province, grant number [135509304].

Acknowledgments

We are very grateful for the financial support provided by Research and Innovation Platform Project of Fundamental Scientific Research Business Expenses for Undergraduate Universities in Heilongjiang Province (135509304) for this research.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) XRD patterns of Ln-MOFs. (b) Enlarged version.
Figure 1. (a) XRD patterns of Ln-MOFs. (b) Enlarged version.
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Figure 2. TG of Ln-MOFs.
Figure 2. TG of Ln-MOFs.
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Figure 3. FTIR spectra of Benzene-1,2,4,5-tetracarboxylic acid and Ln-MOFs.
Figure 3. FTIR spectra of Benzene-1,2,4,5-tetracarboxylic acid and Ln-MOFs.
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Figure 4. XPS of Eu0.075Tb0.925-MOF before and after Fe3+ addition: (a) Tb 3d, (b) Eu 3d, and (c) O 1s.
Figure 4. XPS of Eu0.075Tb0.925-MOF before and after Fe3+ addition: (a) Tb 3d, (b) Eu 3d, and (c) O 1s.
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Figure 5. (a) TEM and (b) SEM of Eu0.075Tb0.925-MOF.
Figure 5. (a) TEM and (b) SEM of Eu0.075Tb0.925-MOF.
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Figure 6. The N2 adsorption desorption isotherms of Eu0.075Tb0.925-MOF.
Figure 6. The N2 adsorption desorption isotherms of Eu0.075Tb0.925-MOF.
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Figure 7. (a) Emission spectra of Eu0.075Tb0.925-MOF, (b) CIE of Eu0.075Tb0.925-MOF, (c) CIE of Eu-MOF, and (d) CIE of Tb-MOF.
Figure 7. (a) Emission spectra of Eu0.075Tb0.925-MOF, (b) CIE of Eu0.075Tb0.925-MOF, (c) CIE of Eu-MOF, and (d) CIE of Tb-MOF.
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Figure 8. (a) The emission spectra of Eu0.075Tb0.925-MOF dispersions with different Fe3+ concentrations under 310 nm excitation light. (b) Calibration line with Fe3+(in the range of 10–100 μM/L), (c) CIE, (d) cycles of Eu0.075Tb0.925-MOF, (e) XRD pattern of Eu0.075Tb0.925-MOF after five cycles, and (f) IEu/ITb histogram of Eu0.075Tb0.925-MOF dispersion containing metallic cations.
Figure 8. (a) The emission spectra of Eu0.075Tb0.925-MOF dispersions with different Fe3+ concentrations under 310 nm excitation light. (b) Calibration line with Fe3+(in the range of 10–100 μM/L), (c) CIE, (d) cycles of Eu0.075Tb0.925-MOF, (e) XRD pattern of Eu0.075Tb0.925-MOF after five cycles, and (f) IEu/ITb histogram of Eu0.075Tb0.925-MOF dispersion containing metallic cations.
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Figure 9. (a) The emission spectra of Eu0.075Tb0.925-MOF dispersions with different Cr2O72− concentrations under 310 nm excitation light. (b) Calibration line with Cr2O72−(in the range of 10–100 μM/L), (c) CIE, (d) cycles of Eu0.075Tb0.925-MOF, and (e) IEu/ITb histogram of Eu0.075Tb0.925-MOF dispersion containing anions.
Figure 9. (a) The emission spectra of Eu0.075Tb0.925-MOF dispersions with different Cr2O72− concentrations under 310 nm excitation light. (b) Calibration line with Cr2O72−(in the range of 10–100 μM/L), (c) CIE, (d) cycles of Eu0.075Tb0.925-MOF, and (e) IEu/ITb histogram of Eu0.075Tb0.925-MOF dispersion containing anions.
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Figure 10. (a) Fluorescence excitation spectra of Eu0.075Tb0.925-MOF and UV-Vis absorption spectra of Fe3+. (b) Fluorescence excitation spectra of Eu0.075Tb0.925-MOF and UV-Vis absorption spectra of Cr2O72−. (c) The mechanism of Fe3+ and Cr2O72− on Eu0.075Tb0.925-MOF fluorescence sensing.
Figure 10. (a) Fluorescence excitation spectra of Eu0.075Tb0.925-MOF and UV-Vis absorption spectra of Fe3+. (b) Fluorescence excitation spectra of Eu0.075Tb0.925-MOF and UV-Vis absorption spectra of Cr2O72−. (c) The mechanism of Fe3+ and Cr2O72− on Eu0.075Tb0.925-MOF fluorescence sensing.
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Table
Table 1. Element analysis table.
Table 1. Element analysis table.
Ln-MOFsCHNOEu/Tb
Eu-MOF30.37%1.87%1.87%26.64%39.25%
Tb-MOF22.01%1.84%1.13%26.11%48.91%
Eu0.075Tb0.925-MOF23.53%1.85%1.56%26.85%46.21%
Table
Table 2. Comparison of the reported methods for Fe3+ and Cr2O72− using Ln-MOFs.
Table 2. Comparison of the reported methods for Fe3+ and Cr2O72− using Ln-MOFs.
Ln-MOFsDetect IonLOD (M)Ratio Fluorescent ProbeLinear RangeReferences
Eu0.075Tb0.925-MOFFe3+2.71 × 10−7Dual emission10–100 μM
(R2 = 0.99919, R2 = 0.99937)		This work
Cr2O72−8.72 × 10−7
Eu-MOF; Tb-MOF
[Eu/Tb, 4,4′-(((5-
carboxy-1,3-phenylene)bis(azanediyl))bis(carbonyl)) dibenzoic acid]		Fe3+1 × 10−5Single emission0–1.0 mM
(R2 = 0.9021, R2 = 0.9752)		[47]
Cr2O72−8.94 × 10−5
Eu-MOF
[Eu, 5-(2′,5′-dicarboxylphenyl) picolinic acid ligand]		Fe3+5.7 × 10−7Single emission0–50 μM
(R2 = 0.9948, R2 = 0.9979)		[48]
Cr2O72−4.2 × 10−7
Tb-MOF [Tb,H3BTB]Fe3+1 × 10−5Single emission-[49]
Eu-MOF [Eu, 2-aminoterephthalic acid 1,10-phenanthroline]Fe3+4.5 × 10−5Single emission0–0.25 mM
(R2 = 0.992)		[50]
Tb-MOF [Tb, 2-(2-carboxyphenoxy)terephthalic acid]Fe3+2.0 × 10−4Single emission10−4–10−3 M
(R2 = 0.978)		[51]
Eu-MOF [Eu, 2-(3′,4′-dicarboxylphenoxy)isophthalic acid, 4,4′-bis(imidazolyl) biphenylFe3+1.32 × 10−5Single emission0–10−5 M
(R2 = 0.9885, R2 = 0.9927)		[52]
Cr2O72−1.01 × 10−5
Table
Table 3. Determination of Fe3+ and Cr2O72− in real samples (n = 3).
Table 3. Determination of Fe3+ and Cr2O72− in real samples (n = 3).
SampleSpiked (nM)Found (nM)Recovery (%)
Tap water (Fe3+)20.022.1110.5
40.045.7114.3
60.061.6102.7
80088.7110.9
Tap water (Cr2O72−)20.020.9104.5
40.041.3103.3
60.060.9101.5
80.080.8101.0
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Yin, J.; Chu, H.; Qin, S.; Qi, H.; Hu, M. Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72−. Sensors 2021, 21, 7355. https://doi.org/10.3390/s21217355

AMA Style

Yin J, Chu H, Qin S, Qi H, Hu M. Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72−. Sensors. 2021; 21(21):7355. https://doi.org/10.3390/s21217355

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Yin, Jie, Hongtao Chu, Shili Qin, Haiyan Qi, and Minggang Hu. 2021. "Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72−" Sensors 21, no. 21: 7355. https://doi.org/10.3390/s21217355

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