Colorimetric and visual determination of ultratrace uranium concentrations based on the aggregation of amidoxime functionalized gold nanoparticles

Advanced "turn-on" colorimetric uranium platform based on the enhanced nanozyme activity of a donor-acceptor structured covalent organic framework

BACKGROUND

The increasing uranium containing wastes generated during uranium mining and finishing pose a huge threat to the environment and human health, and thus robust strategies for on-site monitoring of uranium pollutant are of great significance for environmental protection around uranium tailings.

RESULTS

Herein, a facile "turn-on" colorimetric platform that can achieve uranium detection by spectrometry and naked eyes was developed based on the uranium-enhanced nanozyme activity of covalent organic framework (JUC-505). Thanks to the extended π-conjugated skeleton and donor-acceptor (D-A) structure, JUC-505 exhibited superior photo-activated nanozyme activity, which would be prohibited when the cyano group in JUC-505 skeleton was transformed to the amidoxime group. Further results elucidated that the coordination of uranium with amidoxime groups led to the electron transfer between uranium and the JUC-505-AO skeleton, and thus significantly restored the nanozymatic activity of JUC-505-AO with the subsequent remarkable color changes. Moreover, the uranium concentrations in uranium tailing wastewater detected by the present "turn-on" colorimetric method were well agreed with those by ICP-MS, demonstrating a high accuracy of the present method in real samples.

SIGNIFICANCE

The D-A structured JUC-505 with superior photocatalytic property and nanozymatic activity was applied to facilitate colorimetric detection of uranium, which displays the advantages of low detection limit, excellent selectivity, fast response and simple operation for uranium detection in real samples, and shows a great potential in on-site monitoring of uranium pollutant around uranium tailings as well as nuclear power plant.

A Novel Eco-Friendly and Highly Sensitive Solid Lead-Tin Microelectrode for Trace U(VI) Determination in Natural Water Samples

For the first time a solid state lead-tin microelectrode (diameter ϕ 25 µm) was utilized for U(VI) ion determination by adsorptive stripping voltammetry. The described sensor is characterized by high durability, reusability and eco-friendly features, as the need for using lead and tin ions for metal film preplating has been eliminated, and consequently, the amount of toxic waste has been limited. The advantages of the developed procedure resulted also from the utilization of a microelectrode as a working electrode, because a restricted amount of metals is needed for its construction. Moreover, field analysis is possible to perform thanks to the fact that measurements can be carried out from unmixed solutions. The analytical procedure was optimized. The proposed procedure is characterized by two orders of magnitude linear dynamic range of U(VI) determination from 1 × 10^-9 to 1 × 10^-7 mol L^-1 (120 s of accumulation). The detection limit was calculated to be 3.9 × 10^-10 mol L^-1 (accumulation time of 120 s). RSD% calculated from seven subsequent U(VI) determinations at a concentration of 2 × 10^-8 mol L^-1 was 3.5%. The correctness of the analytical procedure was confirmed by analyzing a natural certified reference material.

A novel CPE procedure by oil-in-water microemulsion for preconcentrating and analyzing thorium and uranium

A novel cloud point extraction (CPE) procedure was developed to preenrich Th4+ and UO2 2+ by oil-in-water (O/W) microemulsion. Coupling CPE to ICP-MS, the separation and analysis were achieved at a trace level, in which the low detection limits were 0.019 and 0.042 ng mL−1 for Th(IV) and U(VI), respectively. N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), as an extremely hydrophobic extractant, was failed to dissolve in single or mixed micelles, but was successfully solubilized to CPE system owing to O/W microemulsion. The extraction efficiency and selectivity for Th4+ and UO2 2+ were excellent under acidic condition of 1.0 mol L−1 HNO3, and the recovery of ultra-trace Th4+ and UO2 2+ was almost 100% even at the presence of large amounts of lanthanides, exhibiting high tolerance limits for lanthanides. The solubilization, extraction and coordination behaviours were studied systematically via DLS, UV–vis, 1H NMR and FT-IR. Moreover, the solubilization of N,N′-dioctyl-N,N′-dioctyl-2,9-diamide-1,10-phenanthroline (Oct-Oct-DAPhen) and efficient extraction for UO2 2+ were also realized by O/W microemulsion, which further proved the feasibility of the method.

Colorimetric detection for uranyl ions in water using vinylphosphonic acid functionalized gold nanoparticles based on smartphone

A simple and portable colorimetric sensor for colorimetric detection of UO₂²⁺ in aqueous solution based on vinylphosphonic acid functionalized gold nanoparticles (VPA-AuNPs) has been developed. The VPA-AuNPs solution was prepared by sodium borohydride reduction in the presence of vinylphosphonic acid. The addition of UO₂²⁺ would induce aggregation of VPA-AuNPs, resulting in the color change from wine-red to blue, and red-shift of the ultraviolet-visible (UV-vis) spectra. The UO₂²⁺ assay based on VPA-AuNPs showed good selectivity and sensitivity, with a limit of detection to be approximately 2.0 μM by naked eyes and 1.07 μM by UV-vis (S/N = 3) respectively. Additionally, a smartphone with a free application named "PhotoMetrix" was employed to estimate the color intensities (red, green, blue value) of VPA-AuNPs in the presence of UO₂²⁺ with different concentrations, and the concentration of UO₂²⁺ samples could be conveniently exported by the calculated univariate calibration curves. This method shows good feasibility for on-site UO₂²⁺ detection in an aqueous solution.

Selective separation of uranyl ions from some lanthanide elements using a promising β-enaminoester ligand by cloud point extraction

For uranyl extraction, a distinctive chelating ligand, namely ethyl 2-amino-6-hydroxy-5-(4-methoxyphenyldiazenyl)-4-phenyl-4H-benzo[f]chromene-3-carboxylate, has been synthesized and characterized using FT-IR, NMR, and ESI-MS.

Rapid and selective magnetic separation of uranium in seawater and groundwater using novel phosphoramidate functionalized citrate-Fe3O4@Ag nanoparticles

One-pot magnetic separation of uranium (U) in seawater and groundwater samples has been made possible by synthesizing phosphoramidate functionalized Ag coated citrate-Fe₃O₄ nanoparticles (NPs). The magnetic saturation value of these functionalized NPs is 27.1 emu g^-1. The synergistic extraction mechanism of U(VI) ion by the surface-modified phosphoramidate and citrate molecules make these NPs highly selective towards U(VI). The adsorption kinetics follows a pseudo-second-order model and the adsorption isotherm fits successfully to the Langmuir adsorption model. The functionalized NPs show quantitative extraction efficiency in the pH range of 6.5-8 with a maximum loading capacity (Q_m) of 108.7 mg g^-1. The equilibration time required by these functionalized NPs to attain the Q_m value is 120 s. The recycling of these NPs can be done up to 5-6 times with 1.0 mol L^-1 of Na₂CO₃ or NH₄OH for quantitative extraction of U(VI). These functionalized NPs show high resilience towards large number of naturally abundant metal ions.

Amplified electrochemical determination of UO22+ based on the cleavage of the DNAzyme and DNA-modified gold nanoparticle network structure

A superior electrochemical biosensor was designed for the determination of UO₂²⁺ in aqueous solution by integration of DNAzyme and DNA-modified gold nanoparticle (DNA-AuNP) network structure. Key features of this method include UO₂²⁺ inducing the cleavage of the DNAzyme and signal amplification of DNA-AuNP network structure. In this electrochemical method, the DNA-AuNP network structure can be effectively modified on the surface of gold electrode and then employed as an ideal signal amplification unit to generate amplified electrochemical response by inserting a large amount of electrochemically active indicator methylene blue (MB). In the presence of UO₂²⁺, the specific sites on DNA-AuNP network structure can be cleaved by UO₂²⁺, releasing the DNA-AuNP network structure with detectable reduction of electrochemical response intensity. The electrochemical response intensity is related to the concentration of UO₂²⁺. The logarithm of electrochemical response intensity and UO₂²⁺ concentration showed a wide linear range of 10~100 pM, and the detection limit reached 8.1 pM (S/N = 3). This method is successfully used for determination of UO₂²⁺ in water samples. Graphical abstract Fabricated DNAzyme network structure for enhanced electrical signal. Numerical experiments show that the current signal decreases as the concentration of UO₂²⁺ increases. It can be seen that the biosensors could be used to detect UO₂²⁺ in aqueous solution effectively.