Elsevier

Analytica Chimica Acta

Volume 1221, 15 August 2022, 340115
Analytica Chimica Acta

A highly water-stable dual-emission fluorescent probe based on Eu3+-loaded MOF for the simultaneous detection and quantification of Fe3+ and Al3+ in swine wastewater

https://doi.org/10.1016/j.aca.2022.340115Get rights and content

Highlights

  • A highly water-stable dual-emission Eu3+-loaded MOF (EuUCH) has been successfully fabricated.

  • EuUCH specifically recognizes Fe3+ and Al3+ with two different response signals.

  • The simultaneous quantification of Fe3+ and Al3+ in their mixture is achieved.

  • The probe could be practically applied for simultaneous quantification of Fe3+ and Al3+ in environmental wastewater.

Abstract

A novel dual-emissive Eu3+-loaded metal–organic framework (MOF) is designed and successfully fabricated by introducing 2-hydroxyterephthalic acid (H2BDC-OH) and Eu3+ ions into an UiO-66-type MOF material. The obtained MOF, here referred to as EuUCH, exhibits dual emission at 450 and 614 nm, and both emissions are quite stable in aqueous media in the pH range of 4–11. EuUCH is characterized by a high selectivity and sensitivity toward Fe3+ and Al3+, which yield different responsive modes. The two emissions of EuUCH are quenched by Fe3+; by contrast, only the emission at 450 nm is quenched by Al3+ showing a ratiometric fluorescence signal. More importantly, as there is no clear interference between the signals of Fe3+ and Al3+, EuUCH is successfully utilized for the simultaneous detection of Fe3+ and Al3+ in their mixtures. In addition, the simultaneous quantification of Fe3+ and Al3+ is achieved in more complicated swine wastewater with good recoveries. This work provides a water-stable dual-emissive probe and the possibility to achieve the simultaneous quantification of Fe3+ and Al3+ in complicated environment wastewater.

Introduction

In recent years, the luminescent detection method has drawn considerable attention owing to its high sensitivity, good selectivity, convenient detection capability, and rapid response [[1], [2], [3]]. Numerous luminescent chemical probes have been developed and proved to be highly effective tools for sensing biological and chemical species in the healthcare [4,5], environmental protection [6], industrial and agricultural production [7,8], safety, and defense sectors [9]. With the rapid development of the modern sensor technology, luminescent sensors exhibiting a differential response toward multiple analytes are highly desirable for sensing applications. Many multi-responsive probes have been investigated; however, most of these show the same fluorescent signals to different analytes, namely, either an intensity variation or a wavelength shift of a single emission band [[10], [11], [12]]. As a consequence, it is difficult to avoid the cross interference among different analytes. Therefore, it is important to be able to achieve the simultaneous detection of multiple analytes in their mixtures exploiting different responsive modes to each analyte.

Multi-emissive sensors could meet this requirement because they are well known for their environment-free disturbance and visible detection with the color change. Some multi-emissive organic sensors have been reported; however, the design and synthesis of organic compounds is complex [13,14]. On the other hand, it is easier to prepare metal–organic frameworks (MOFs), exhibiting multi-emission properties because their chromophores can be ligands, metal ions, and guest molecules. There are generally six types of multi-emission MOFs under single-wavelength excitation. The simultaneous use of luminescent metal ions and luminescent ligands in a single MOF is a promising strategy to obtain MOFs with multiple luminescent emission [15,16]. Herein, in order to fabricate a novel dual-emission MOF material, 2-hydroxyterephthalic acid (H2BDC-OH) was incorporated into UiO-66-(COOH)2 to obtain a blue emission, and post-modification with Eu3+ ions was then conducted to obtain a red emission.

Metal ions play a vital role in our daily life and environment; however, an excessive use of metal ions causes serious environmental pollution and is a threat to human health [17]. Therefore, it is important to detect biologically and environmentally important metal ions in aqueous media. Compared with traditional analysis techniques, fluorescence spectroscopy is characterized by numerous advantages, such as a high specificity, sensitivity, rapidity, simplicity, and the possibility to achieve real-time monitoring [18,19]. However, most of the reported fluorescent probes for detecting metal ions have been used in organic media or mixed-solvent media. In particular, the simultaneous detection and quantification of multiple ions in aqueous solutions with a single sensor has been rarely achieved due to the limited availability of multi-emissive materials and the easy interference between the metal ions [20,21].

Fe3+ ions play an important role in many biological processes, such as cellular metabolism [22], oxygen carrying [23], enigmatic reactions [24], and several biosynthesis processes [25]. However, the excess and deficiency of Fe3+ ions in an organism can lead to abnormal physiological functions, which may cause liver damage [26], anemia [27], heart disease [28], and cancer [[29], [30], [31]]. Thus, it is very important for human health to efficiently detect Fe3+ ions [32].

Aluminum is the most abundant metal element in the Earth's crust [33]. Al and its compounds are extensively employed in our daily life, such as for cooking utensils [34], water treatment [35], food additives [36], and pharmaceuticals [37]. However, free Al3+ ions are highly toxic to plant growth because they affect the uptake of Ca2+ ions by plants [38,39]. Moreover, free Al3+ ions are toxic to biological species and can cause several diseases, such as breast cancer, Parkinson's disease, and Alzheimer's disease [[40], [41], [42]]. Therefore, the detection of trace concentrations of Al3+ ions in aqueous solutions is urgently required. It is extremely challenging to prepare Al3+-based chemical sensors as Al3+ ions have a weak coordination ability and a strong hydration ability [43]. In particular, they lack spectroscopic characteristics and they can be easily mistaken for other metal ions, such as Cr3+ and Fe3+ ions. Many Al3+-based responsive sensors have been reported; however, they are affected by several drawbacks, such as complex synthetic procedures and a poor solubility in aqueous solutions, which limit their further application to real sample analysis [44].

In this work, a dual-emissive MOF, here referred to as EuUCH, was constructed by incorporating 2-hydxoxyterephthalic acid (H2BDC-OH) into UiO-66-(COOH)2 and through subsequent post-modification with Eu3+ ions (Scheme 1). The dual-emissive EuUCH probe was employed as a heterogeneous sensing material to detect Fe3+ and Al3+ ions in aqueous media, from which two different response signals could be clearly observed by naked eyes. More importantly, the proposed EuUCH probe was successfully used for the simultaneous quantification of Fe3+ and Al3+ ions, which is practically applied in complicated swine wastewater.

Section snippets

General information

All solvents and chemicals were purchased from commercial suppliers and were used without further purification. Aqueous solutions of the metal ions were prepared from their chlorates or nitrates. Powder X-ray diffraction patterns (PXRD) were recorded on a Bruker D8 advance diffractometer with CuKα radiation. N2 adsorption–desorption isotherms were measured at 77 K using a Micrometrics TriStar II Plus surface analyzer (Micromeritics, U.S.A). Fourier-transform infrared (FT-IR) spectra were

Characterization

The as-synthesized MOFs, UiO-66-(COOH)2/OH, and EuUCH were characterized via PXRD. Fig. 1(a) indicates that the PXRD patterns are in good agreement with the simulated pattern of the UiO-66 single-crystal structure. This signifies that the MOFs were successfully synthesized, and the post-modification did not influence the topological structure. Notably, the PXRD pattern of EuUCH was retained well after it was immersed in H2O for 7 days, suggesting that EuUCH was very stable in aqueous media (

Conclusion

In summary, a dual-emission fluorescent probe, EuUCH, was rationally designed and successfully fabricated based on the introduction of two different luminescent components, namely H2BDC-OH and Eu3+ ions, into an UiO-66-type MOF to achieve different responsive modes for multiple analytes. The EuUCH probe was explored as a fluorescence sensor for the selective detection of Fe3+ and Al3+ with different responsive modes. The detection of both Fe3+ and Al3+ exhibits a high sensitivity, a low

CRediT authorship contribution statement

Yi-Fan Xia: Investigation, Writing – original draft. Guang-Ming Bao: Funding acquisition, Writing – review & editing. Xiong-Xin Peng: Formal analysis. Xin-Yu Wu: Investigation. Hui-Fang Lu: Investigation. Yu-Fei Zhong: Investigation, Validation. Wei Li: Validation. Jia-Xin He: Investigation. Si-Yi Liu: Investigation. Qing Fan: Investigation. Si-Han Li: Validation. Wei Xiao: Formal analysis. Hou-Qun Yuan: Supervision, Funding acquisition, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (Nos. 22165012, 31960720, 22166018), Natural Science Foundation of Jiangxi Province (No. 20192ACBL21018), and Education Department of Jiangxi Province (No. GJJ190215).

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