Lanthanide Coordination Polymer-Based Composite Films for Selective and Highly Sensitive Detection of Cr₂O₇^2– in Aqueous Media

Abstract

Due to the high carcinogenicity and bioaccumulation effects of dichromate ions in the human body, sensitive and rapid detection of Cr 2 O 7 2− ions is necessary. Herein, two lanthanide coordination polymers based on a linear dicarboxylic acid ligand, named {Ln(cpon)(Hcpon)(H 2 O) 3 } n [Ln = Tb, Tbcpon; Eu, Eucpon; H 2 cpon = 5-(4-carboxy-phenoxy)-nicotinic acid], have been successfully synthesized. These two isostructural compounds contain one-dimensional zigzag chains that consist of uncoordinated carboxyl groups and pyridine groups in the framework, and the onedimensional chains can further form a three-dimensional supramolecular stacking structure by intermolecular interaction. Both Tbcpon and Eucpon show good luminescence performance and high stability. Tbcpon exhibits a good ability to sense Cr 2 O 7 2− ions in aqueous solution. Moreover, the composite film material composed of Tbcpon and poly(methyl methacrylate) (PMMA) exhibits superior luminescence properties compared to those of pure Tbcpon. The Tbcpon-PMMA film exhibits an excellent ability to recognize Cr 2 O 7 2− ions with high selectivity and a low detection limit of 5.6 ppb, which is much lower than the maximum contamination standard of 100 ppb in drinking water specified by the U.S. Environmental Protection Agency. Furthermore, the Tbcpon-PMMA film shows good recyclability for more than five cycles and anti-interference ability. After the introduction of the slightly soluble polymer poly(vinyl alcohol) (PVA), the Tbcpon-PVA composite film can effectively detect Cr 2 O 7 2− ions in as little as 1 min. These composite films could be potentially used as test strips for trace detection and rapid detection of Cr 2 O 7 2− ions in aqueous solution.

Luminescent Hydrogel Based on Silver Nanocluster/Malic Acid and Its Composite Film for Highly Sensitive Detection of Fe3+

“…The composite material obtained by doping the xerogel into the polymer matrix has the advantages of easy processing and good flexibility and can enhance the practical application of the gel [ 32 , 33 ]. PMMA has good UV resistance, chemical durability, and good mechanical properties.…”

“…With the gradual increase of c Fe3+ , the luminescence intensities at 628 nm are significantly weakened. In order to investigate the luminescence quenching efficiency, the Stern–Volmer (S-V) equation was used to quantitatively analyze the quenching curve [ 32 ]: where I 0 and I are the luminescence intensity at 640 nm when c = 0 and c = M , respectively, K SV is the quenching coefficient of Fe 3+ ions, and [ M ] is the molar concentration of Fe 3+ ions. The quenching curve shows a well-fitted linear relationship at low c Fe3+ (1–100 μM).…”

“…Fluorescent film sensors are widely considered, due to their advantages, such as convenient portability, real-time detection, and no pollution to the system, for testing [ 32 , 33 , 34 , 35 , 36 , 37 ]. Compared with the solution and powder detection forms, the adjustable shape, size, and flexibility of the fluorescent film makes it have wider application prospects.…”

Metal–organic framework thin films as versatile chemical sensing materials

“…These films are typically fabricated by deposition on substrates such as glass, 128,129,144 metal oxides, 102 and paper, 148,167 or through dispersion in glues 113 and transparent polymers 131 such as poly(methyl methacrylate). 127 Additionally, it is often straightforward to reuse immobilized MOF thin films across multiple sensing cycles, whereas MOFs dispersed in solution are typically more difficult to recover and regenerate (Table 4). For example, MOF thin film ion sensors are often regenerated by exposing the film to a chelating agent (e.g.…”

“…As shown in Table 3, luminescence-based MOF thin film sensors have been designed to detect a range of analytes, included gases, 146 organic vapors, 96 ions, 112 explosives, 122 pharmaceuticals, 123 and even temperature. 149 Ion Sensors: The rapid, sensitive, and selective detection of ions has utility in a wide range of areas, including prospecting for high-value elements, 90 identifying heavy metal contaminants in water sources, 127,131 and medical diagnostics. 103,132 Please do not adjust margins Please do not adjust margins through binding sites within the MOF, 103,131 or through electrostatic interactions 101 (e.g.…”