ADVERTISEMENT

Spectroscopic And Theoretical Study Of The Microstructures Of Radionuclides

With the development of nuclear power plant and industry, “radionuclide contamination” has increasingly seen worldwide attention. The study on the properties of radionuclides, especially in the natural environment can reveal more about the toxicity of radionuclides in the environment, thereby allowing people to deal with them more effectively.

The chemical species and microstructures of radionuclides at solid particle surfaces are closely associated with its transport, hazardous and bioavailability in the environment. Recently, professor Xiangke Wang from North China Electric Power University (China) reported a series of works on the interaction mechanism of radionuclides with different clay materials at a molecular level by the advanced synchrotron radiation technique and computational theoretical calculations.

ADVERTISEMENT

Wang’s group applied X-ray absorption fine structure (XAFS) spectroscopy including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to provide the structure information (e.g., the bond distances and coordination numbers of neighbors) of radionuclides at a molecular level. They also applied plasma- and chemical-grafted amidoxime/carbon nanofiber hybrids (p-AO/CNFs and c-AO/CNFs) to remove 238U(VI) from wastewater. The chemical species and microstructures of U(VI) at the two kinds of nanomaterials are investigated by EXAFS (Environmental Science & Technology, 2017, 51, 12274-12282). Figure 1A and 1B showed the spectroscopy information of U(VI) on the nanomaterials, these characterizations suggested that U(VI) formed strong inner-sphere surface complexes even at low pH, which is very important for the application of such nanomaterials in the removal of U(VI) from wastewater.

The removal of U(VI) onto sericite in the presence of Bacillus subtilis (B. subtilis) is also studied using EXAFS techniques (Geochimica et Cosmochimica Acta, 2016, 180: 51-65). Figure 1C and 1D also show that inner-sphere surface complexation between U(VI) and sericite + B. subtilis at pH 7.0 and pH 4.0 are ascribed to the U-Al/Si or U-C shell and U-P shell, respectively.

Figure 1. The k2-weighted U LIII-edge EXAFS spectra (A) and corresponding Fourier Transmission (FT) (B) of references and U(VI) sorption samples, CU(VI) = 10 mg/L, m/v = 0.6 g/L, I = 0.01 mol/L NaCl, T = 293 K. Uranium LIII-edge EXAFS spectra (C) and corresponding Fourier transform (D) for U(VI)-reacted sericite, B. subtilis and sericite + B. subtilis at pH 4.0 and 7.0 under atmospheric conditions, CU(VI) = 6.3 Οmol/L, Csericite = 2.0 g/L, CB. subtilis = 0.5 g/L, I = 0.01 mol/L NaClO4, T = 293 K. Reproduced with permission from the publisher.

Due to the limited sensitivity of the XAFS technique, it is still challenging to use it on radionuclide analysis at environmental concentrations. Furthermore, for some actinides (e.g., Am, Np, Cm, Pu), the radionuclide operation license makes it difficult to carry out the XAFS measurements. Density functional theory (DFT), one of the most powerful theoretical tools, is applied efficiently to calculate correlation energy and electronic structures. For instance, the theoretical calculation provides the differences in the interactions between CNTs with Eu(III) and 243Am(III) ions (Environmental Science & Technology, 2015, 49, 11721-11728). Figure 2 shows that the charge transfer interaction between CNTs and Eu(III) are much stronger than that of 243Am(III). This can help us to understand the difference between lanthanides and actinides on nanomaterials.

Figure 2. The difference density between the oxidized CNTs_M(III)8W and its two fragments (oxidized CNTs and M(III)8W). The violet color and yellow color represent the increase and decrease of electron density, respectively. Both of the two colors indicated that the charge transfer interaction exists. The significant increase electron density indicates the strong charge transfer interaction. Reproduced with permission from the publisher.

In order to more fully understand the transport of radionuclides in the natural environment, the combination of batch technique, theoretical calculation, and spectroscopy analysis are helpful to understand the interaction mechanisms and to safely predict the disposal of long-lived radionuclides.

ADVERTISEMENT

The interaction between U(VI) and graphene oxides (GOs) with different surface properties are studied by the combination of EXAFS technique and DFT calculations (Environmental Science & Technology, 2015, 49, 4255-4262). Based on the EXAFS analysis (Figure 3A), the sorption of U(VI) on GOs with different surface functional groups are different, which is also evidenced by the theoretical calculations (Figure 3B).

Figure 3. (A) The k2-weighted U LIII-edge EXAFS spectra (left) and the corresponding Fourier Transforms (right) of the reference and samples before and after desorption, m/V = 0.25 g/L, C U(VI) = 60.0 mg/L, I = 0.01 mol/L NaClO4, T = 293 K. (B) The DFT-optimized geometries of the rGOs_uranyl complexes and GOs_uranyl complexes. Reproduced with permission from the publisher.

The microstructures and speciation of radionuclides studied by advanced spectroscopy and theoretical calculation are crucial to understanding the physicochemical properties of radionuclides in the natural environment.

These findings are described in the article entitled Microstructures and speciation of radionuclides in natural environment studied by advanced spectroscopy and theoretical calculation, published in the journal Science China Chemistry. This work was led by Xiangke Wang from North China Electric Power University.

Comments

READ THIS NEXT

My Science Life: Dr. Stephen Johnston – University Of Alberta Earth & Atmospheric Sciences

Welcome to the My Science Life feature of Dr. Stephen Johnston, Chair / Professor in Tectonics at the Earth & […]

Monitoring Water Quality From Space: Investigating The Sediment Concentration In Green Bay, WI

The Great Lakes are an important resource to the population living in the US and Canada. They provide drinking water […]

Reasoning Comes In Degrees, Not Different Kinds

That the mind is comprised of distinct systems is one of the earliest and most recurring ideas in psychology. Plato […]

Designing A Nuclear Reactor Core Using Genetic Algorithms 

During the normal operation of a nuclear reactor, the nuclear fuel in the reactor’s core is continuously being “burned”, i.e., […]

Creating Stretchable, Flexible Electronics With MINE Structures

The future of electronics will include soft, stretchable devices that can conform to the human body for an entirely new […]

Exactly How Much A Gallon Of Water Weighs

Exactly how much does a gallon of water weigh? A gallon of water in the US weighs approximately 8.34 lbs […]

The Nitrogen Ice Activity On Pluto Explored With Numerical Modeling  

Numerical modeling of the nitrogen cycle on Pluto explains the distribution, color, geology, and morphology of the different nitrogen ice […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?