Dual sensing of copper ion and chromium (VI) oxyanions by benzotriazole functionalized UiO-66 metal-organic framework in aqueous media

Strategies for preparation of chitosan based water-soluble fluorescent probes to detect Cr3+ and Cu2+ ions

The low solubility of chitosan (CS) imposes adverse effects on its application. In this work, one of the aims is to improve the water solubility of CS. By introducing water-soluble side chains to CS, this aim was achieved. Besides, fluorescent moieties were incorporated into the side chains, the fluorescent copolymers were endowed with Cr3+ and Cu2+ ions recognition ability. Firstly, a reversible addition-fragmentation chain transfer polymerization (RAFT) reagent with naphthalimide units and CC groups was prepared. Water-soluble monomer methyl acrylic acid (MAA) was employed in the RAFT polymerization. Thus, water-soluble polymer with fluorescent unit and -C ≡ C on both ends of the polymer was obtained. They were introduced into CS, and the CS-based fluorescent copolymers were obtained eventually. The amount of MAA introduced could be tuned to obtain three side chains of different lengths. It was found that the more MAA was introduced, the better the solubility of CS-TP was. The detection limits (LOD) of Cr3+ and Cu2+ were 44.6 nM and 54.5 nM, respectively. The detection of Cr3+ and Cu2+ ions is further combined with a mobile APP to realize real-time, portable, and visual detection. And the application in the logic gate, a new detection platform, is prepared.

Reticular Chemistry for Optical Sensing of Anions

In the last few decades, reticular chemistry has grown significantly as a field of porous crystalline molecular materials. Scientists have attempted to create the ideal platform for analyzing distinct anions based on optical sensing techniques (chromogenic and fluorogenic) by assembling different metal-containing units with suitable organic linking molecules and different organic molecules to produce crystalline porous materials. This study presents novel platforms for anion recognition based on reticular chemistry with high selectivity, sensitivity, electronic tunability, structural recognition, strong emission, and thermal and chemical stability. The key materials for reticular chemistry, Metal-Organic Frameworks (MOFs), Zeolitic Imidazolate Frameworks (ZIFs), and Covalent-Organic Frameworks (COFs), and the pre- and post-synthetic modification of the linkers and the metal oxide clusters for the selective detection of the anions, have been discussed. The mechanisms involved in sensing are also discussed.

Multifunctional luminescent Zr(IV)-MOF for rapid and efficient detection of vanillin, CrO42- and Cr2O72- ions

Fast and efficient detection of pollutants in the food or wastewater is an urgent need for protecting human health and ecological environment. Herein, a luminescent Zr(IV)-MOF (HBU-20) has been conveniently synthesized. It could be used as a fluorescent probe for detection of vanillin, CrO₄^2-, and Cr₂O₇^2- in aqueous medium. All the fluorescence response time is less than 10 s and the detection limits of vanillin, CrO₄^2- and Cr₂O₇^2- achieve 0.38 μM, 0.065 μM and 0.0089 μM, respectively. Interestingly, common anions, cations and amino acids in the solution can not affect the fluorescence detection. Meanwhile, the fluorescence detection process can be successfully implemented even under strong acid or strong alkaline conditions. Further research shows that the inner filter effect (IFE) plays a major role in the sensing process. The rapid and sensitive fluorescence responses indicate that the compound is a promising multifunctional probe for sensing toxic substance. The results can provide an important reference for the design of new fluorescent probes.

An ultra-sensitive selective fluorescent sensor based on a 3D zinc-tetracarboxylic framework for the detection and enrichment of trace Cu2+ in aqueous media

Herein, a novel and fluorescent zinc-organic framework sensor [Zn₃(μ₃-Hbptc)₂(μ₂-4,4'-bpy)₂(H₂O)₄]_n·2nH₂O (1) (H₄bptc = 2,3,3',4'-biphenyl tetracarboxylic acid, 4,4'-bpy = 4,4'-bipyridine) is synthesized and characterized, demonstrating its excellent fluorescence performance for Cu²⁺ detection and the enrichment of Cu²⁺ in aqueous media. The fluorescence intensity of 1 can be selectively quenched by Cu²⁺ in a linear range of Cu²⁺ concentrations of 0-0.7 μM. The limit of detection (LOD) value is as low as 32.4 nM, which is superior to those of most of the fluorescent sensors based on metal-organic frameworks (MOFs). It is also far below the maximum allowable concentration of Cu²⁺ in drinking water as defined by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO), so it is employed for the detection of Cu²⁺ in actual water samples. More importantly, the nature of the interaction between the active coordination site (COO^-) of 1 and Cu²⁺ determines the quenching mechanism, that is Cu²⁺ in the analyte is captured by MOF 1, which has been investigated by ICP, luminescence, UV-vis, XPS, and lifetime studies. Besides, the chemosensor shows regeneration performance without the loss of performance in five consecutive cycles. So MOF 1 is a simple and convenient probe used not only for the rapid detection but also for the enrichment of trace amounts of Cu²⁺ in aqueous media, and the application can be further extended to a variety of environmental and biological analysis processes.

Pyridinyl Conjugate of UiO-66-NH2 as Chemosensor for the Sequential Detection of Iron and Pyrophosphate Ion in Aqueous Media

A new chemosensor UiO-66-N-Py (Py = 2-methinepyridine, N = imine nitrogen) based on isoreticular UiO-66 (University of Oslo) Metal–Organic Framework (MOF) containing 2-methinepyridine functionalized organic linker was solvothermally synthesized and characterized. This UiO-66-N-Py was very selective and sensitive for detecting the Fe3+ ion and sequential detection of the pyrophosphate (PPi) anion. The limits of detection for the Fe3+ ion and PPi were calculated to be 10 ppb (0.19 μM) and 50 ppb (0.3 μM), respectively. The quenching constant Ksv for Fe3+ and the binding constant for PPi were 1.4 × 105 M−1 and 1.7 × 105 M−1, respectively. The functionalization of UiO-66-NH2 with 2-methinepyridine enhanced its fluorescence emission properties and introduced more binding sites for the analytes. We additionally studied the interaction of the sensor and the analytes with Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This chemosensor also demonstrated a regenerative emission property without loss in the detection ability for six consecutive cycles.

From lamellar net to bilayered-lamella and to porous pillared-bilayer: reversible crystal-to-crystal transformation, CO2 adsorption, and fluorescence detection of Fe3+, Al3+, Cr3+, MnO4−, and Cr2O72− in water

Layered coordination polymers of different network topologies have showed reversible structural transformations and fluorescence detection toward Fe³⁺, Al³⁺, Cr³⁺, MnO₄^–, and Cr₂O₇^2– in water.