A research team has successfully synthesized 3D copper-based complexes by introducing H4SiW12O40 and rare earth metals into a 2D structure. This innovative method led to the creation of three isostructural 3d−4f metal-incorporated POMs, showcasing significant promise for environmental monitoring.
These complexes were then explored for their applications in fluorescence and electrochemistry. Surprisingly, the expanded structure proved effective as a fluorescence sensor, capable of detecting nickel cations (Ni2+), chromium (Cr3+), and nitrite (NO2-). Additionally, it served as an electrochemical sensor for nitrite, a toxic substance with serious health implications.
This groundbreaking work has been documented in the Polyoxometalates journal. Polyoxometalates (POMs) are versatile inorganic molecular materials, boasting diverse structures and functions. They find utility in numerous fields, such as materials science, catalysis, medicine, environmental protection, and hydrogen production.
However, the inherent solubility of POMs in acidic or neutral solutions has limited their applications. One potential solution is to create metal complexes by combining POMs with metal ions.
To achieve this, the research team transformed 2D copper-based complexes into 3D structures by introducing silicotungstic acid (H4SiW12O40) and rare earth metals using a hydrothermal method. A nitrogen and carboxylic acid-containing ligand acted as a binder, extending the complex into the 3D realm.
The researchers successfully produced three 3d-4f bimetallic POMs complexes, a category encompassing coordination compounds featuring transition metal ions and rare earth metals known as lanthanides.
Subsequently, they scrutinized the purity, thermal stability, optical properties, and electrochemical behavior of these complexes. Techniques like X-ray diffraction, infrared spectrum analysis, thermogravimetric analysis, and ultraviolet-visible absorption spectra analysis were employed for characterization.
One of these compounds, Cu-Sm-CP, was chosen for detailed sensor studies. It functioned as a fluorescence probe, demonstrating remarkable prowess in identifying metal cations, with a particular focus on 13 different metal ions in water. Moreover, it exhibited excellent electrochemical sensing capabilities for nitrite, a highly toxic substance.
Wei Yao, affiliated with the University of Science and Technology Liaoning, explained, “We synthesized three isostructural 3d-4f POMs and selected Cu-Sm-CP among them as fluorescence and electrochemical dual-function sensors to detect Cr3+ and Ni2+ using fluorescence sensing, as well as nitrite through electrochemical sensing.” This is especially relevant as the detection of trace metal ions has gained increasing attention due to their potential toxicity and acute poisoning risks.
The research highlighted Cu-Sm-CP's outstanding fluorescence sensing abilities for Cr3+ and Ni2+ in aqueous solutions, demonstrating exceptional recognition and interference resistance. Yao also noted, “Finally, Cu-Sm-CP, as an electrochemical sensor, demonstrates excellent electrocatalytic performance for nitrite oxidation.”
This work not only presents a straightforward method for crafting 3d−4f metal-incorporated POMs complexes but also delivers effective materials for fluorescence and electrochemical sensing applications.
In terms of future research, the team aspires to expand their investigations into real-world environmental conditions, aiming to detect harmful ions in natural waters. This endeavor holds significant promise for environmental monitoring.