Exploring Optical and Vibrational Properties of the Uranium Carbonate

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C: Plasmonics, Optical Materials, and Hard Matter

Exploring Optical and Vibrational Properties of the Uranium Carbonate Andersonite with Spectroscopy and First-Principles Calculations Nataliya Kalashnyk, Dale L. Perry, Florian Massuyeau, and Eric Faulques J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b00871 • Publication Date (Web): 13 Mar 2018 Downloaded from http://pubs.acs.org on March 14, 2018

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The Journal of Physical Chemistry

Exploring Optical and Vibrational Properties of the Uranium Carbonate Andersonite with Spectroscopy and First-Principles Calculations

Nataliya Kalashnyk,†,§ Dale L. Perry,‡ Florian Massuyeau,† and Eric Faulques*,†

†

Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3, France

‡

Lawrence Berkeley National Laboratory, University of California, Mail Stop 70A1150, Berkeley, CA 94720, USA

*

Author

to

whom

correspondence

should

be

addressed. Email: [email protected] Phone: +33 (0) 240373977 Fax: +33 (0) 240373995 ACS Paragon Plus Environment

1

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT

Original periodic first-principles calculations based on the generalized gradient approximation combined with several analyses in microspectroscopy are presented for a hydrated uranium carbonate crystal, andersonite, possessing a unique, channeled structure. Infrared and ultraviolet-visible

absorption,

Raman

scattering,

steady-state

and

time-resolved

photoluminescence spectroscopy are used to address the atomic vibrations of water, uranyl, and carbonate ions, to determine the fluorescence decay time (around 220 µs), and to estimate the amplitude of the optical gap (close to 3 eV). The role of structural water for andersonite stability is discussed by performing also calculations on a dehydrated model structure. Experiments and calculations address both the intra-channel and extra channel possibilities for the water molecules. The current research is a detailed study of a water-containing channel uranium system using a combined infrared/Raman treatment coupled with a DFT calculation, providing new physical insight into the spectroscopic understanding of these channels.

INTRODUCTION Andersonite, Na2Ca[UO2(CO3)3]·xH2O (x = 5.3-5.6), is a relatively rare compound of uranium which is comprised of discrete uranyl cations bonded to different arms of the carbonate anion as well as water molecules.1,2 This species belongs to a class of materials particularly important for environmental impact of nuclear power and renewable energy sources. The X-ray crystallographically documented structure of andersonite exhibits features that are common to many uranium(VI) chelating molecules, including a central U(VI) ion bonded to two oxygen atoms that are in close proximity, with the rest of the positions of the central hexagonal bipyramidal coordination being occupied with six oxygen atoms donated by their surrounding bidentate groups. The slightly linear uranyl ion is surrounded by the three bidentate carbonate ions, yielding the well-documented ACS Paragon Plus Environment

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carbonato-uranyl polyhedral cluster. Each of the polyhedra is bonded to two symmetrically related calcium atoms and two symmetrically distinct sodium atoms. The two sodium atoms and one calcium atom have coordination numbers of six and seven, respectively. Interestingly, as detailed in the experimental section, the andersonite structure possesses large channels running parallel to the c-axis where the presence of water was speculated.2 This nanostructure is seen especially clearly in the center of Figure 1(b), and in Figure S1 (a). The binary linkage species U(VI), oxygen atoms, and water play an important role in many uranyl minerals that occur in nature and thus act as true, legitimate, experimental model for uranium in the environment. A molecularly similar complex, CaUO2(CO3)3, has been shown to be a major constituent of seawater;3 and as a result uranium carbonates have been used both in models and experimental approaches for the extraction of uranium from seawater.4 Uranium carbonates are also a focal point for topical areas of study such as uranium-series age screening of carbonates by various types of instrumental analysis.5 Furthermore, their environmental role becomes crucial after the discovery that they appear as alteration products of the Chernobyl lava and thus are relevant to hazardous consequences of nuclear accidents.6 The present work discusses infrared, reflectance, microprobe Raman, and multi-emission photoluminescence data generated from natural andersonite. The spectra are correlated with the known, molecular structure of the synthetic compound that has been earlier obtained by X-ray crystallography.1 A detailed analysis related to the molecular water in the structure is given, with the water-related vibration bands being consistent with another metal ion-aqueous uranyl carbonate system.7 As discussed below, only a few spectroscopy works were already published specifically on andersonite. DFT simulations on water-free and on synthetic hydrated andersonite structures have been conducted here at the PBE level of theory to complement analysis of the spectra acquired during the

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present study, with theoretical values obtained being in good agreement with experimental results. Calculated vibrational frequencies at the Brillouin zone center have been determined and several features in the phonon density of states coincide satisfactorily with experimental vibrational group frequencies found in IR and Raman spectra. More specifically, a discussion is given about the possible location of water molecules in the channels by examining the OH frequencies and their associated vibrational eigenvectors, compared to vibrational experiments. Finally, electronic band structures and gaps have been predicted for the dehydrated and hydrated investigated systems and reveal values close to those obtained from experimental diffuse reflectance.

EXPERIMENTAL Sample. The geographical origin of the sample investigated in this study is the Atomic King #2 Mine, San Juan County, Utah, USA. The sample of 4.0 × 2.5 cm in size consists of rich veinlets and coatings of yellow andersonite in and on matrix. Under 365 nm UV lamp andersonite fluoresces strongly with green color. Microcrystals were gently removed from the matrix and studied under several microscope objectives for different spectroscopic studies. Spectroscopy. Fourier-transform Infrared (FTIR) attenuated total reflectance (ATR) spectra were obtained on a Bruker Vertex instrument using an ATR Specac apparatus between 400 and 4000 cm-1 with a resolution of 4 cm-1. Raman experiments were performed with a Renishaw inVia™ microscope at laser excitation λ0 = 785 nm provided by a diode laser source, and with a diffraction grating of 1200 grooves per mm. The choice of the deep red excitation was justified by the need to limit any luminescence superimposed to the Raman spectrum. Spectra were collected in the ranges from 100 cm-1 and up to 4000 cm-1 to seek for possible water signals. The diameter of the laser spot on the sample surface was about 2 µm for the fully focused


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laser beam with a 50× (0.35) long working distance objective (18 mm). The laser power onto the sample was kept below 0.5 mW to avoid degradation due to overheating. Steady-state photoluminescence (PL) spectra were obtained between 350 and 700 nm using a Horiba Jobin-Yvon LabRam spectrometer operated in PL configuration with a 40× NUV objective of working distance 1 mm and excited with a CdHe UV laser source (λ0 = 325 nm). A diffraction grating of 600 grooves per mm was used and the spot size on the crystals was ∼2 µm. These two Raman instruments were calibrated against the Stokes Raman signal of pure Si at 520.5 cm-1 using a silicon wafer. The spectral resolution was ∼2 cm-1. The time-resolved photoluminescence (TRPL) setup is described in SI and in a previous paper.8 UV-visible reflectance experiments were performed using a Lambda 1050 Perkin Elmer spectrometer equipped with a beam condenser, a 150 mm Spectralon® integrating sphere, and PMT – InGaAs detectors. Total reflectance spectra were acquired on andersonite microcrystals deposited on silica glass.

COMPUTATIONAL METHODOLOGY Choice of the method. The periodic DFT study of properties of andersonite crystals was undertaken in this study with the academic CASTEP code 16.3 implemented as a module of Materials Studio 6.0 software.9 The strong on-site Coulomb interaction of localized f electrons of uranium is not correctly described in DFT by the local density approximation (LDA) or by the generalized gradient approximation (GGA), but can be implemented with an additional Hubbard-like term U. This DFT+U method has been applied to actinides and UO2.10-12 However, proper choices of U energy should be made for f orbitals. Calculations can be also computationally prohibitive for large systems and may converge to metastable states.12 Therefore, it was decided here to use GGA and the



Perdew-Burke-Ernzherhof (PBE) functional without U terms because it is simpler and cost-effective for large-scale DFT calculations.13,14 GGA-PBE is recommended for Hbonded systems and this functional was widely employed for uranyl carbonates, other oxides, or complexes, allowing direct comparison with previous works.15-21 In CASTEP a FFT method is used to speed up the calculations with the GGA-PBE functional which usually overestimates the cell parameters14 and underestimates the band gap as observed below. Application of GGA-PBE functional for modeling andersonite crystals. The Broyden–Fletcher–Goldfarb–Shanno (BFGS) optimization scheme22-25 was used with a convergence threshold for the maximum Hellmann-Feynman force of 0.01 eV A-1. The outer shell electrons for uranium 5f36s26p66d17s2, calcium 3s23p64s2, sodium 2s22p63s1, oxygen 2s22p4, and carbon 2s22p2, were treated as valence electrons. All calculations were performed on primitive cells to reduce computational time. In the CASTEP code used here, a norm-conserving pseudopotential (NCPP) was not available for uranium preventing Raman intensity calculations. Therefore, all atomic wave functions were described in the present work with ultrasoft pseudo potentials (USPP). As a result, the plane-wave cut-off energy was fixed here at a relatively low value of 410 eV (30.13 Ry) comparable to that used by Lan et al.21 in their PBE treatment of U(VI)/calcite interaction in aqueous solution. A 1 × 1 × 1 Monkhorst–Pack k-point mesh was used for the Brillouin zone sampling of the large primitive cell. The total energy of the crystals was relaxed until the difference value was smaller than 5×10-6 eV/atom. The synthetic andersonite structure experimentally determined with X-rays by Coda et al.1 was introduced as initial geometry in the calculation. This compound belongs to hexagonal m (R3 2/m) with parameters a = 17.902(4), c = 23.734(4) Å, Z = 18 space group # 166 R3 and x = 5.6. The primitive cell contains 198 atoms. This initial structure was chosen because the crystallographic file lists the positions of the water molecules.


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The same calculations on a test structure were also performed with the same conditions by removing all water molecules from the andersonite unit cell, resulting in a dehydrated andersonite crystal framework containing 108 atoms per primitive cell with the same initial lattice parameters and space group as pristine andersonite (see Table S1). Note that the structure of natural andersonite found by Plasil and Cejka2 also belongs to m, with parameters a = 17.8589(6), c = 23.6935(8) Å, and Z =18. There is space group R3 another synthetic phase of composition between liebigite and andersonite which belongs to space group Pnnm, sharing many structural features of pure natural or synthetic andersonite.26 However, those latter two structures were not used for the current DFT study. Optimization of the primitive cell of andersonite was achieved by attaching hydrogen atoms to the water oxygen atoms anchored at the water positions compiled by Coda et al.1 from X-ray analysis, and leaving the structure relaxing very slowly. Initial and final parameters as well as main bond lengths and angles are listed in Table S1. Phonon states were calculated at phonon wave vector q = 0 (Γ-point) with the finite-displacement supercell method.

RESULTS AND DISCUSSION Experimental structure. The crystalline architecture of both natural and synthetic andersonite shows nanostructured morphology visible in the xy plane (Figures 1 and S1) with hexagonal channels running parallel to c-axis.1,2 The channels of about 5 Å diameter are formed by (UO8) units linked to CO32- units assembled in six [(UO2)(CO3)3]4- uranyl tricarbonate clusters (UTC), six Na and six Ca clusters. These voids form paddle wheel structures with UTC arranged in an array of regular triangles similar to other uranyl carbonate structures.27 Smaller channels of about 2 Å diameter are formed by remaining CO32- units, and are located in the centers of triangles made by the UTC. The larger



channels have a size comparable to those found in some metal-organic frameworks (MOF) and beryl (5.1 Å).28,29 In the description of natural andersonite structure obtained by X-rays, Plasil and Cejka2 concluded that most water molecules are coordinated to the Na and Ca sites while one third of them should be localized within the large channels.

Figure 1. Unit cell (a) and rhombohedral representation (b) of synthetic andersonite in the xy plane, projected along [001], from Coda et al.1 The channel nanostructure is visible in panel a. Light blue: water molecules. Green, red, violet, blue, and grey balls (with linkages) represent calcium, oxygen, sodium, uranium, and carbon atoms respectively. Water molecules are located outside and around the channels (30 in panel b, of which 3 are hidden). Recent X-ray data of Plasil and Cejka2 on natural andersonite suggests the presence of water molecules centered in the channels with a maximum water content x = 5.333.

Raman spectroscopy. In order to analyze the vibrational spectra the calculation of vibrational frequencies has be made for phonon wave vector q = 0. Table 1 summarizes the positions of experimental vibrational bands found in IR and Raman spectroscopy for andersonite and their tentative assignment from eigenvector analysis of the present DFT calculations.


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The Raman spectrum of andersonite is composed of very intense lines (Figure 2(a)). The most intense vibration located at 833 cm-1 is related to the vibrational frequency of the UO22+ cation ascribed to the ν1 symmetric stretching as described by Hoekstra and Siegel30,31, Bullock,32 Faulques et al.,33,34 Frost et al.35, Driscoll et al.36 Other strong Raman modes appear at 1080, 1091, 1361 cm-1 which can be ascribed to CO32vibrations35 and their origin is confirmed by the present DFT calculations as well as by the experimental and theoretical work of Bonales et al.17 on UO2CO3. The frequencies of these lines are in the range expected for bidentate carbonate ions. A weak bump around 1609-1625 cm-1 may stem from the H2O wagging and/or bending mode ν2. A distinct water signal occurs at 3306 cm-1, with weaker shoulder components around 3350 and 3425 cm-1 (inset in Figure 2), all due either to H2O symmetric or asymmetric stretching vibrations ν1, ν3. As discussed below, the sharp band at 3306 cm-1 might be attributed to less vibrating-free H2O molecules external to channels. The weaker Raman band between 180 and 300 cm-1 (see SI for magnification) corresponds well with the features found in H2O-containing beryl and ascribed to vibrations of water molecules in the 5Å-beryl channels.37,38 The presence of such low-frequency vibrations for water is also confirmed here with the calculations.

Figure 2. Infrared and Raman spectra of natural andersonite. Inset: Raman signal of structural water. Laser excitation 785 nm. The IR spectrum is obtained with attenuated total reflectance. ACS Paragon Plus Environment


Infrared spectroscopy. As clearly evidenced by the comprehensive study of Beiswenger et al.,39 infrared reflectance spectroscopy is a powerful technique to discriminate uranium minerals in natural and anthropogenic materials. Figure 2(b) displays the ATR spectrum recorded on andersonite crystallites of this work. The shape, intensity, and frequency maxima of IR-ATR peaks coincide well with those of Frost et al.35 Energy transfers below 400 cm-1 are not accessible with the setup employed. The medium to strong lines between 695 and 847 cm-1, and at 1082, 1348, 1370, 1524, 1556 cm-1 can be ascribed to deformations, bending and stretching vibrations of the CO32- units.35 The intense peak at 898 cm-1 could originate either from the carbonate group or more likely from the ν3 asymmetric O-U-O stretching35. The low value of ν3(O-U-O) with respect to other uranyl salts studied for instance by Hoekstra31, Bullock32, Johnson et al,40 and other,41-44 could be explained here by the fact that in hydrated uranyl compounds hydrogen bonding between equatorial ligand and uranyl oxygen can occur. This results in a weakening of the U-O bond which increases its length, and then in a lowering of the O-U-O stretching frequency. The ATR technique is usually insensitive to atmospheric water. The water signal recorded for andersonite is therefore intrinsic to water molecules of the structure. This rich water region is characterized by well-resolved components at 1656, 3053, 3200, 3391, 3495, 3542, 3607 cm-1. From DFT calculation the shoulder peak at ν2 ~ 1656 cm-1 can be ascribed to the H2O bending mode. Since water molecules have an approximate van der Waals size of ~2.8 Å the ~5Å andersonite cavity is therefore large enough to accommodate one single free water molecule, its cross-section in the xy plane leaving likely not enough space for another free water molecule, like in beryl which has similar channel diameter.37,38 DFT calculations show that OH bond lengths range from 0.981 to 0.987 Å, and 1.05 to 1.017 Å for the shortest and the longest ones, respectively, while the H-O-H angles are found between 101.87° and 106.91° (Table S1). These values can be


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compared with intra-channel water in beryl having shortest OH bonds (0.941 Å), but similar angle (106.9°).29 Besides, the highest experimental IR frequencies of the water band in andersonite, located at 3495, 3542 and 3607 cm-1, correspond well with DFTcalculated frequencies assigned mainly to strong stretching motions of OH fragments of water surrounding the channel cavities (“near-channel” water, see Figures 1 and S1). The 3607 cm-1 IR line match also the sharp IR OH-stretching ν1 lines of water in beryl channels resolved at 5K at 3593 and 3607 cm-1 by Kolesov and Geiger (see Figure S2(b) in SI).37 However, Zhukova et al.38 later re-assigned experimentally the symmetric ν1 and antisymmetric ν3 H2O stretching bands in beryl at higher frequency (3657 and 3756 cm1

), while they found the ν2 bending mode at 1595 cm-1. Therefore, the IR peaks found

here at ν1 ~3607 cm-1 and ν2 ~ 1656 cm-1 arise perhaps from weakly or non-bonded molecular water occupying the channels, as also suggested by Plasil and Cejka.2 IR frequencies below ~3400 cm-1 might stem from less free vibrating water molecules sitting outside the channel structures, complexed for instance through Na···O-H contacts or through short-range water-water interactions.45 Whether intra-channel water molecules, if they exist, form H-bonds or not with the andersonite channel cavity walls is unclear in absence of more experimental evidence by other tools. It might be possible, however, that water molecules in channels are mutually hydrogen-bonded along the zdirection.

Table 1 Experimental and calculated vibrational frequencies of andersonite, in cm-1 (tentative matches). Frequency maxima are listed. w: weak, m: medium, (v)s: (very)strong, def: deformation, sh: shoulder. Assignment is made from eigenvector analysis. “Near-channel water” is coined for water surrounding the 5Å-channel cavities forming H2O-“rings” in the optimized structure (see Figures 1(a) and S1). Complexed water sits outside the large channels, for instance near 2Å-small channels.

Raman

Calculation

Proposed assignment

IR

Calculation


Proposed assignment


135 m 166 m 184 w

134 165 184

225 m

225

285 m

283

297 w

294

352 w

350

484 w 564 w 696 w

480 561 695

742 m 833 vs

739 818-822

931 w

921

1080 s 1091 s 1261 m 1363 s

1078 1088 1354

1501 m 16091625 broad, m 1742 m 3306s

1505 1607-1625

3308

3350w

3352

3425w

3410

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Na,Ca,water motions Na,Ca,water motions Na,Ca,C,water motions UO2 bend, Ca, water motions UO2 bend + CO3 libration, CO3 libration + Ca…O elongation CO3 libration + nearchannel water def. Water twist Water rock Water twist

421 m 463 m 520 m

416 461 522

Water libration (rock.) Water twist Water libration

677 m

675

Water libration

695 m

688-693

724 m

728

Water twist + CO3 bend Water wag+ CO3 bend

778 m

772

Water wag+CO3 def

797 m 847 m 898 s

796 845 894

Water twist s UO2 sym. stretch, s + CO3 def + water wag UO2 asym. stretch + water twist CO3 breath CO3 breath

1006 m 1082 m

1009 1066-1078

Water wag+ CO3 def. Water wag+CO3 def. UO2 antisym. stretch+ water twist Water def. CO3 breath s

1348 s

1347

CO3 stretch + def.

1370 s 1524 s 1556 s 1656 w

1369 1520 1453 1605-16251645-1650

2613 w 2650 w

-

CO3 stretch + def. CO3 stretch CO3 stretch H2O ν2 bending + wag near-channel + H2Oring breathing vs N/A N/A

2852 w 2925 w

-

N/A N/A

3200 m

3214

3391 s

3380

3495 s

3460

3542 s

3525-3576

3607 m, sh

3584

Sym. H2O ν1 stretch near-channel—m Antisym. H2O ν3 stretch near-channel - s Sym. H2O ν1 stretch near-channel - vs Sym. H2O ν1 stretch near-channel - vs Antisym. H2O ν3 stretch near-channel w

CO3 stretch

CO3 stretch H2O ν2 bending + wag near-channel + H2Oring breathing vs H2O sym. ν1 stretch of complexed water - w H2O sym. ν1 stretch of complexed water - s Antisym. H2O ν3 stretch near-channel - s

Zone center phonons and intra-channel water. To compare the vibrational responses of hydrated and dehydrated structures it is worth to examine the phonon density of states (pDOS) defined by

= ∑ − ACS Paragon Plus Environment

(1)

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where ωi(q) is the i-th phonon frequency for vector q. This quantity is the number of phonon modes per unit frequency interval per unit of q. Figure 3 displays vibrational frequency histograms corresponding to the pDOS calculated at q = 0 for optimized dry and hydrated andersonite structures. There is good correspondence between these two pDOS. The effect of structural water on crystal vibrations is particularly visible on the intense clump of frequencies centered at 200 cm-1, supporting our assumption that water contributes to the Raman spectrum in this low-frequency region, in agreement with the comparison made with the beryl system. Other aftermath of water presence occur between 400 and 900 cm-1, and also in the 1400-1700 cm-1 range. Above 400 cm-1, the most intense pDOS contributions appear around 810 and 1062/1645 cm-1 frequencies corresponding to vibrations of uranyl and carbonates ions in the structures, respectively. The water contribution in hydrated crystal to the calculated pDOS is shown in the inset between 3000 and 3740 cm-1. As already mentioned, the eigenvector analysis of the phonons for the optimized structure suggests that H2O frequencies above 3400 cm-1 might stem from water molecules near or inside the large channels with strong OH stretching, while the frequencies between 2900 and 3400 cm-1 might characterize mainly inter-channel water molecules in the lattice with moderate OH stretching.



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Figure 3. Phonon density of states of andersonite and its dehydrated framework obtained for wave vector q =0 (Γ-point) with a frequency interval of 10 cm-1 in the histograms.

Hydrogen bonds from structural water molecules inside or outside the channels. The distribution of experimental frequencies between 3053 cm-1 to 3620 cm-1 should be related to stiffening or softening of O-H bonds within H2O in the andersonite structure due to the different lattice sites for H2O inside or outside the channels and the distinct geometries adopted by the water molecules. In the optimized structure O-H bond lengths vary between 0.981 Å and 1.015 Å. Furthermore, DFT calculations show that relatively short hydrogen bonds linkages can occur between CO32- units and H2O molecules. After structural optimization, the OH…O=C or OH…OH distances between water and carbonyl or water molecules alone range from 1.894 Å to 2.966 Å. Interestingly, the experimentally observed O-H stretching frequencies ν(OH) of water (ν1, ν3) can be deduced from the hydrogen bond distances d(O···H) measured directly on the initial and optimized structures as shown by Libowitzky for many minerals.46,47 This author assumed that the correlation between d and ν(OH) can be described by an exponential growth law:

= − ∙

(2)

With d, C in Å and A, B in cm-1. Conversely, the d(O···H) distances can be obtained from experimental ν(OH) frequencies using an empirical logarithmic function

= − ∙

(3)

Parameters A = 3642 cm-1, B = 1.38·106 cm-1, C = 0.2227 Å have been chosen among those given by Libowitzky to estimate d(O···H).47 From the above correlation, the strong OH Raman line at 3306 cm-1 may correspond to a short OH···O distance of 1.853 Å, while the strong IR line centered at 3391 cm-1 would be characteristic of an OH···O distance of 1.918 Å. These distances should involve water


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molecules interacting with CO32- outside the channels. They are close to the distances between carbonyl oxygen and hydrogen of water calculated for aqueous carbonates by Kumar et al.48 Other observed ν(OH) lines between 3420 and 3500 cm-1 in IR could correspond to intermediate H bonds between 1.95 and 2.04 Å. The occurrence of such relatively strong H-bond linkages derived from this empirical analysis indicates that andersonite should be stable in natural environments and in humidity.49 As discussed above, free or weakly bonded water molecules in the lattice should have characteristic frequencies above 3600 cm-1. It is likely that the only place where they can be free to move or form weaker hydrogen bonds would be to sit at the center of the channels.2,29 From Eq. 3, hydrogen bonds distances would be in that case between 2.9 and 3.15 Å. It is, however difficult, to tell whether this relationship applied to andersonite reflects the real hydrogen bonding distances in the real structure, or if another correlation should be taken. Band structure calculations. Figure 4 presents the band structure and density of electronic states (DOS) obtained after optimization of the dehydrated framework and of andersonite with a smearing of 0.2 eV. The DOS is defined as g(E)dE which is the number of one-electron levels between energy E and E + dE with g(E) is computed as: #

!" = ∑)

∑( %" − " &' $

(4)

where k is the wave vector in reciprocal space, N is the total number of electronic bands, and

V is the volume of the primitive cell over the first Brillouin zone. The very small nonzero DOS contribution above EF (right panels of Figure 5(a) and 5(b)) could indicate that andersonite might be a metal. In fact, such a prediction is a known DFT failure not related to the smearing value or to precision of the calculation.50 For example small nonzero DOS or nonzero partial DOS above EF has been also computed in semiconducting perovskites or oxides with GGA-PBE.51,52 In fact, a well-defined semiconducting gap opens up by computing with CASTEP the electronic band structure of the present compounds (left panel of ACS Paragon Plus Environment


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Figure 5(a) and 5(b)), in agreement with optical experiments described hereafter. The calculated direct gap is 2.566 eV in water-rich andersonite and 2.570 eV in the dry framework structure, indicating that water molecules in the crystal have no effect on the gap opening at the PBE level of theory. For both crystals the electronic band structure is monotonously flat along the Brillouin zone (BZ) due to the very large unit cells of the compounds. Close examination of the valence band maximum (VBM) region shows that the topmost band has a small parabolic curvature extending over 0.01 eV. The effective mass me* of an electron travelling in the band is inversely proportional to the band curvature according to

*+∗ =

/

-.

0. 1 3 02.

(5)

Figure 4. Band structure and full electronic density of states of andersonite (b) and its dehydrated framework (a) after optimization at PBE level of theory.

It can be therefore assumed that me* is large in andersonite, making it a semi-conductor with low carrier mobility. The same flat band effect is predicted from DFT calculations of UO2CO3 uranium carbonate, rutherfordine, and other minerals.15-17


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The partial (or projected) DOS, gµ(E)dE, is the number of one-electron levels with weight on orbital µ between energy E and E + dE, where gµ(E) is related to g(E) by !" = ∑4 !4 " and writes as #

:

!4 " = ∑)

∑(567 &584 95 %" − " &' $

(6)

The wave functions 7 are linear combinations of the atomic bases 84 with eigenvalues Ei(k).

7 ( = ∑= < = &8=

(7)

And the overlap matrices elements of the atomic bases are

68= 584 9 = >4=

(8)

Therefore, the following quantity is computed in CASTEP for each orbital µ #

∗ ∗ !4 " = ∑)

∑( ∑= ∑=? 4=? %" − " &' $

(9)

Figure 5. Calculated partial electronic density of states of andersonite (b) and its dehydrated framework (a) for U, O, C, H, Ca, Na orbitals after optimization with PBE functional.



Irrespective of the very small DOS contribution of O2p orbitals occurring above EF (Figure 6), the partial DOS for each element of the dehydrated and water-rich andersonite crystals can be very useful for identifying the bonding character between atoms and the influence of water molecules in the bonding scheme. In both structures, uranium and carbon levels show O-U-O and C-O covalency due to the overlaps of energy regions as exemplified by rectangles in Figure 6(a). In hydrated andersonite, the proton gives also peaks at -4.8 and -6.5 eV intermixed with oxygen orbitals near the VBM highlighted by rectangles in Figure 6(b). Finally, Na and Ca atoms have nonbonding orbitals and present rather deep levels weakly interacting with O orbitals in the bottom of the valence band. Steady-state photoluminescence. When irradiated at 325 nm excitation wavelength, andersonite luminesces green. The steady-state PL spectrum of the studied sample has very sharp and intense vibronic features, appearing between 425 and 700 nm with excellent spectral resolution at room temperature (Figure 7(a)). Peaks wavelengths are compiled in Table 2. This PL spectrum agrees well with those of synthetic andersonite recorded by Vochten et al.7 and with that of natural andersonite illustrated in a database of luminescent minerals (±1 nm shift) for a laser excitation at 405 nm.53 The very weak A-band at 453 nm (see inset Figure 7(a)) is the highest energetic feature that can be discerned in the spectrum. It is anticipated that this feature is a hot PL line. The energy interval with the following B-band is ~686 cm-1 and should correspond to the symmetric O-U-O stretching vibration in the excited state, as found in rutherfordine and uranyl phosphates. 41,43


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Figure 6. (a) Steady-state photoluminescence of natural andersonite for laser excitation 325 nm. The arrow denotes a possible hot band magnified in the inset. The intensity is proportional to photons per nm. (b) Tauc plot of diffuse reflectance after Kubelka-Munk transformation and gap estimate by linear fitting of absorption edge.

The intervals between the most intense bands (CD, DE, EF, FG) are 814, 828, 805, 824 cm-1, respectively, matching the 833 cm-1 frequency of the symmetric O-U-O stretching determined by Raman spectroscopy in the ground state. Other vibronic separations (BC, GH, HI) observed are 778, 860, 957 cm-1. Agreement between Raman frequencies and vibronic separations confirms that the steady-state PL spectrum originates from the andersonite crystal.

Table 2. Main electronic transitions observed for andersonite from steady-state PL, TRPL and diffuse reflectance experiments.



Page 20 of 38

Steady-state PL (nm)a Time-resolved PL (nm)a 53 This study Natural This study Natural49 Synthetic49 (452.5)h (452) 447.5 467 (467)sh 464.2 468.4 470.6 472sh 469.1sh 484.6 483 482.5 485.2 486.1 504.5 504 502.5/509.5sh 504.8 505 .4 526.5 526 519.2sh/523/(527.3) 526.2 526.7 549.8 550 545.1 549.6 549.6 575.9 577 570.5 575.4 573.9 (605.9) 607 600.7 (643.2) 640 (676) (711) a h: hot band; sh: shoulder; parenthesis: weak peak. b italics: very weak peaks may stem from PL excited by white light. UV-visible reflectance spectra.

Reflectance (nm)b This study 378sh 372 362 353 348sh 428/442/457 473 484 504 527 551 586

In the present work reflectance spectra reveal a fine

vibronic structure between 300 nm (33333 cm-1) and 500 nm (20000 cm-1) (See Figure S2). The optical bandgap Eg of andersonite can be obtained experimentally by using a Tauc equation involving the Kubelka-Munk (KM) transformation54 @AB :

CD. @AB FG⁄H = J%D − DK '

(10) LM G⁄L

where the reflectance can be approximated to AB = G − N

(K and S are the

absorption and scattering coefficients, respectively), Ε = hν is the energy of light at frequency ν and A a constant. The value of the exponent n depends on the nature of the sample transition. Here, n = 1/2 because a direct transition is allowed. The Tauc plot of the andersonite reflectance for the direct-allowed transition yields enhanced vibronic features and an experimental optical bandgap estimate of about 3.05 eV (Figure 7(b)). Hence, the gap value found above by DFT is underestimated as expected by using the GGA-PBE level of theory.55 The peak positions of the vibronic progression in the absorption spectrum are listed in Table 2. Small peaks appearing between 450 and 500 nm correspond likely to weak emissions and may not be characteristic of the excited state. The most intensive peaks have consecutive separations AB = 426, BC =743, CD = 704, and DE = 407 cm-1. The largest vibronic gaps BC and


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CD should reflect the symmetric stretching vibration of O-U-O bonds in the excited state.56,57 Multi-emission time-resolved photoluminescence. Figure 8(a) displays the time-resolved PL images obtained during this investigation, recorded with the 400 nm femtosecond laser excitation. The transient spectra match very well the steady-state PL spectra for peak positions and separations (Table 2), except for relative intensities of the vibronic progression. In particular, the presence of a hot band is ascertained as shown in the inset of Figure 8(b). Moreover additional bands were possible to distinguish in these TRPL spectra with respect to those reported previously with a different TRPL setup.49 Here, it is found that the fluorescence of andersonite decays with perfect mono-exponential depopulation rates at the emissive energies of the uranyl vibronic components (Figure 8(c)).

Figure 7. Multi-channel time-resolved photoluminescence of natural andersonite with intensity proportional to photons per nm. (a) Streak image acquired between 327 nm and 688 nm on the time window extending vertically from 0 to 1.02248 ms, rectangles show thin vertical and horizontal regions of interest (ROI) used for instance in (c); (b) spectrum integrated on the whole image with a possible hot band denoted by an arrow in inset, (c) Multi-emission PL decays extracted from vertical ROIs at the energy of the ACS Paragon Plus Environment


Page 22 of 38

different vibronic components and PL decay integrated on the whole spectrum (bottom). Solid lines are fits using Eq. (12). Femtosecond laser excitation 400 nm.

The PL kinetics was modelled including the temporal dependence of the Gaussian laser pulse with σ width in a two-level approach comprising the electronic ground state and one excited state OH OP

= QP − RH

(11)

where G(t) is the Gaussian exciton generation function, n is the total population of photogenerated moieties in the excited energy state with initial condition n(-∞) = 0, and k = τ-1 is the inverse of decay lifetime (i.e. the rate constant) from excited state. The solution of Eq. (11) is given by #

S = T :

/

UV ((W . X:Y:YZ 3 .

[\

√:Y(W . YZ :W

+ 1

(12)

where I is related to the Gaussian pulse intensity, σ to the temporal pulse width, and t0 is the time offset. The dynamic properties of the sample studied were confirmed by repeating TRPL experiments on different crystallites. Following Eq. (11), the most important difference from literature concerns the luminescence lifetime. An averaged decay time of 218 µs was obtained on the spectrally integrated PL decay. All vibronic PL components decay almost at the same rate. In particular, the most intense emissions at 465 nm, 482 nm, 502 nm and 523 nm, decay respectively in 224 µs, 227 µs, 210 µs, and 221 µs, respectively. The mean value of these different lifetimes is 220.5 µs, comparable to that obtained for the full spectrum (Figure 8(c)). This lifetime is longer than those already reported in the literature (33 and 65 µs),49 perhaps due to the use of a different setup or variation in mineral composition but it is in the range given in a database of luminescent minerals (150 µs at 500 nm excitation).53 Wang et al. reported a faster lifetime for rutherfordine


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(UO2CO3, 16.8 µs,) and a slightly longer one for liebigite (Ca2(UO2)(CO3)3·11H2O, 349 µs).58 In the present study, the same linear slope in the TRPL decay of vibronic components is a signature that only one kind of population decays on a single lattice site of U(VI).59 It was also found by Maloubier et al.3 that metal uranyl carbonate ions (Ca, Mg, Sr) in solution give lifetimes between 0.013 and 0.04 µs, while the uranyl ion alone, or uranyl complexes with hydroxide species (OH-, (OH)22-, (OH)33-) could yield longer fluorescence with lifetimes in the range 0.8 - 80 µs. Therefore, one can assume that the water molecules present in large amount in andersonite structure (~5.6 H2O per formula) may contribute to the relatively long fluorescence observed in this system.

CONCLUSIONS In this study, a detailed investigation of the electronic, optical and vibrational properties of andersonite has been presented, combined with periodic first-principles calculations carried out at the PBE level of theory. The results obtained on a dehydrated fictitious model framework and on synthetic hydrated andersonite were compared with a broad range of datasets obtained with different techniques. Optical absorption gives an estimate of the gap around 3 eV that agrees with the calculated value of 2.57 eV. A long fluorescence lifetime of about 220 µs is found with green emission around 500 nm. Vibrational analysis and the DFT model indicate that the symmetric and asymmetric ν1 and ν3 O-U-O stretching frequencies occur at 833 and 898 cm-1, respectively. CO32- vibrations have been also well characterized. The location of structural water in the mineral and how water affects the vibrational spectra or participates to the crystal stability have been discussed. The Raman spectrum and the



broad experimental water band observed in the infrared with well-resolved peaks reveal that different water molecules occupy different sites in the crystal. Analysis of OH vibrations above 3400 cm-1 suggests that water molecules may occupy channel cavities in the real structure. While these investigations have given additional insights on the water species in this mineral, there are still difficult issues to be solved regarding the nature and the orientation of water in the andersonite channels. Inelastic neutron-scattering experiments and DFT calculations with H2O siting in channels would be necessary to explore more deeply the precise vibrational and optical states of the water molecules in the crystal.2,29 Finally, the present spectroscopic results can be used for identification of uranyl carbonate species in nuclear forensic analysis and in various environmental settings.60

ASSOCIATED CONTENT Supporting information Further details on structure of andersonite, vibrational spectra, absorption spectrum and timeresolved fluorescence setup are included in the Supporting Information document. This material is available free of charge via the Internet at http://pubs.acs.org/. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] §

N. K. is also at Institut Parisien de Chimie Moléculaire (IPCM) UMR 8232 CNRS - Université

Pierre et Marie Curie 4 Place Jussieu, 75252 Paris Cedex 05, France, and Service de Physique de l’Etat Condensé (SPEC) UMR 3680 CNRS CEA - Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France. Email: [email protected]


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ORCID Nataliya Kalashnyk: 0000-0003-0314-6091 Eric Faulques: 0000-0002-7761-8509 Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was supported by Centre National de la Recherche Scientifique. This research used resources of CCIPL (Centre de Calcul Intensif des Pays de Loire), Nantes, France. N. K. thanks hospitality of IMN where she performed this study. REFERENCES

(1)

Coda, A.; Giusta, A. D.; Tazzoli, V. The Structure of Synthetic Andersonite,

Na2Ca[UO2(CO3)3]·xH20 (x ~ 5.6). Acta Cryst. 1981, B37, 1496–1500. (2)

Plasil, J.; Cejka, J. A note on the Molecular Water Content in Uranyl Carbonate

Mineral Andersonite. J. Geosci. 2015, 60, 181–187. (3)

Maloubier, M; Solari, P. L.; Moisy, P.; Monfort, M.; Auwer C. D.; Moulin, C. XAS

and TRLIF Spectroscopy of Uranium and Neptunium in Seawater. Dalton Trans. 2015, 44, 5417–5427. (4)

Lu, Y. Uranium Extraction: Coordination Chemistry in the Ocean. Nat. Chem. 2014,

6, 175–177. (5)

Spooner, P. T.; Chen, T.; Robinson, L. F.; Coath, C. D. Rapid Uranium-Series Age

Screening of Carbonates by Laser Ablation Mass Spectrometry. Quat. Geochronol. 2016, 31, 28–39. (6)

Burakov, B. E.; Strykanova, E. E.; Anderson, E. B. Secondary Uranium Minerals on

the Surface of Chernobyl "Lava". Mat. Res. Soc. Symp. Proc. 1997, 465, 1309–1311. (7)

Vochten, R.; Van Haverbeke, L.; Van Springel, K. Synthesis of Liebigite and

Andersonite and Study of their Thermal Behavior and Luminescence. Can. Mineral. 1993, 31, 167–171. (8)

Massuyeau, F.; Perry, D. L.; Kalashnyk, N.; Faulques, E. Spectroscopic Markers for

Uranium(VI) Phosphates. Part II: the Use of Time-Resolved Photoluminescence. RSC Adv. 2017, 7, 919-926. (9)

Clark, S. J.;Segall, M. D.; Pickard, C. J.; Hasnip, P.J.; Probert, M. J.; Refson, K.;

Payne, M. C. First Principles Methods Using CASTEP. Z. Kristallogr. 2005, 220, 567–570. ACS Paragon Plus Environment


(10)

Page 26 of 38

Zhang, J.; Zhou, Z.-J.; Lan, J.-H.; Bo, T.; Ge, C.-C.; Chai, Z.-F.; Shi, W.-Q.

Theoretical Investigation on Electronic and Mechanical Properties of Ternary Actinide (U, Np, Pu) Nitrides. J. of Appl. Phys. 2017, 122, 115109-7. (11)

Pegg, J.T.; Apparicio-Anglès, X.; Storr, M.; de Leeuw, N.

DFT+U Study of the

Structures and Properties of the Actinide Dioxides. J. Nucl. Mater. 2017, 492, 269-278 (12)

Thompson, A.L.; Meredig, B.; Stan, M.; Wolverton, C. Interatomic Potential for

Accurate Phonons and Defects in UO2. J. Nucl. Mater. 2014, 446, 155-162. (13)

Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made

Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (14)

Xu, X.; Goddard III, W.A. The Extended Perdew-Burke-Ernzerhof Functional with

Improved Accuracy for Thermodynamic and Electronic Properties of Molecular Systems. J. Chem. Phys. 2004, 121, 4069-4082. (15)

Matar, S. F. Lattice Anisotropy, Electronic and Chemical Structures of Uranyl

Carbonate, UO2CO3, from First Principles. Chem. Phys. 2010, 372, 46–50. (16)

Zhao, Z.; Li, Z.; Zou, Z. Electronic Structure and Optical Properties of Monoclinic

Clinobisvanite BiVO4. Phys. Chem. Chem. Phys. 2011, 13, 4746–4753. (17)

Bonales, L. J.; Colmenero, F.; Cobos, J.; Timon, V. Spectroscopic Raman

Characterization of Rutherfordine: a Combined DFT and Experimental Study. Phys. Chem. Chem. Phys. 2016, 18, 16575–16584. (18)

Colmenero, F.; Bonales, L. J. ; Cobos, J. ; Timón, V. Thermodynamic and

Mechanical Properties of the Rutherfordine Mineral Based on Density Functional Theory. J. Phys. Chem. C 2017, 121, 5994–6000. (19)

Molinari, M.; Brincat, N. A.; Allen, G. C.; Parker, S. C. Structure and Properties of

Some Layered U2O5 Phases: A Density Functional Theory Study. Inorg. Chem. 2017, 56, 4468−4473. (20)

Anderson, N.H.; Xie, J.; Ray, D.; Zeller, M.; Gagliardi, L.; Bart, S. C. Elucidating

Bonding Preferences in Tetrakis(imido)uranate(VI) Dianions. Nat. Chem. 2017, 9, 850– 855. (21)

Lan, J.-H.; Chai, Z.-F. ; Shi, W.-Q. A Combined DFT and Molecular Dynamics

Study of U(VI)/Calcite Interaction in Aqueous Solution. Sci. Bull. 2017, 62, 1064-1073. (22)

Broyden, C.G. The Convergence of a Class of Double Rank Minimization

Algorithms, 2, The New Algorithm, J. Inst. Math. Applic, 1970, 6, 222–231. (23)

Fletcher, R. A New Approach to Variable Metric Algorithms. Computer J. 1970 13,

317-322.


Page 27 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24)

Goldfarb, D. A Family of Variable-Metric Methods Derived by Variational Means.

Math. Comput. 1970, 24, 23-26. (25)

Shanno, D.F. Conditioning of Quasi-Newton Methods for Function Minimization.

Math. Comput. 1970, 24, 647-656. (26)

Vochten, R.; Van Haverbeke, L.; Van Springel, K.; Blaton, R.; Peeters, O. M. The

Structure and Physicochemical Characteristics of a Synthetic Phase Compositionally Intermediate between Liebigite and Andersonite. Can. Mineral. 1994, 32, 553–561. (27)

Y. Li, Y.; Krivovichev, S. V.; Burns,P. C. The Crystal Structure of Na4(UO2)(CO3)3

and its Relationship to Schröckingerite. Mineral. Mag. 2001, 65, 297–304. (28)

Shang, C.; Gautier, R.; Jiang, T.; Faulques, E.; Latouche, C.; Paris, M.; Cario, L.;

Bujoli-Doeuff, M.; Jobic, S. A p Type Zinc-Based Metal-Organic Framework. Inorg. Chem. 2017, 56, 6208-6213. (29)

Kolesnikov, A. I.; Reiter, G. F.; Choudhury, N.;

Prisk, T. R.; Mamonto, E.;

Podlesnyak, A.; Ehlers, G.; Seel, A. G.; Wesolowski, D.J.; Anovitz, L. M. Quantum Tunneling of Water in Beryl: A New State of the Water Molecule. Phys. Rev. Lett. 2016, 116, 167802-6. (30)

Hoekstra, H. R.; Siegel, S. The Uranium-Oxygen System: U3O8-UO3. J. Inorg. Nucl.

Chem. 1961, 18, 154-165. (31)

Hoekstra, H. R. Uranium-Oxygen Bond Lengths in Uranyl Salts: Uranyl Fluoride

and Uranyl Carbonate. Inorg. Chem. 1963, 2.3, 492-495. (32)

Bullock, J. I. Raman and Infrared Spectroscopic Studies of the Uranyl Ion: the

Symmetric Stretching Frequency, Force Constants, and Bond Lengths. J. Chem. Soc. A: Inorg, Phys. Theor. 1969,781-784. (33)

Faulques, E.; Russo, R.; Perry, D.L. Raman Spectral Studies of Uranyl Sulphate and

its Urea Complex Structural Isomers. Spectrochim. Acta, Part A 1993, 49, 975–983. (34)

Faulques, E.; Russo, R.; Perry, D.L. Raman studies of Uranyl Nitrate and its

Hydroxy Bridged Dimer. Spectrochim. Acta, Part A 1994, 50, 757–763. (35)

Frost, R. L.; Carmody, O.; Erickson, K. L.; Weier, M. L.; Cejka, J. Molecular

Structure of the Uranyl Mineral Andersonite – a Raman Spectroscopic Study. J. Mol. Struct. 2004, 703, 47–54. (36)

Driscoll, R. P. J.; Wolverson, D.; Mitchels, J. M.; Skelton, J. M.; Parker, S. C.;

Molinari, M.; Khan, I.; Geeson, D.; Allen, G. C. A Raman Spectroscopic Study of Uranyl Minerals from Cornwall, UK. RSC Adv. 2014, 4, 59137-59149. (37)

Kolesov, B. A; Geiger, C. A.

The Orientation and Vibrational States of H2O in

Synthetic Alkali-Free Beryl. Phys. Chem. Minerals 2000, 27, 557-564. ACS Paragon Plus Environment


(38)

Zhukova, E. S.; Torgashev, V. I.; Gorshunov, B. P.; Lebedev,V. V.; Shakurov, G. S.;

Kremer, R. K.; Pestrjakov, E. V.; Thomas, V.G.; Fursenko, D. A.; Prokhorov, A. S.; Dressel, M. Vibrational States of a Water Molecule in a Nano-Cavity of Beryl Crystal Lattice. J. Chem. Phys. 2014, 140, 224317-11. (39)

Beiswenger, T. N.; Gallagher, N. B.; Myers, T. L.; Szecsody, J. E.; Tonkyn, R. G.;

Su, Y-F.; Sweet, L. E.; Lewallen, T.A.; Johnson, T. J. Identification of Uranium Minerals in Natural U-Bearing Rocks via Infrared Reflectance Spectroscopy. Appl. Spectrosc. 2017, doi: 10.1177/0003702817743265 (40)

Johnson, T.J.; Sweet, L.E.; Meier, D.E.; Mausolf, E.J; Kim, E.; Weck, P.F.; Buck,

E.C.; McNamara, B.K. Time-Resolved Infrared Reflectance Studies of the DehydrationInduced Transformation of Uranyl Nitrate Hexahydrate to the Trihydrate Form. J. Phys. Chem. A 2015, 115, 9996−10006. (41)

Kalashnyk, N.; Perry, D. L.; Massuyeau, F.; Faulques, E. Spectroscopy and DFT

Studies of Uranyl Carbonate, Rutherfordine, UO2CO3: a Model for Uranium Transport, Carbon Dioxide Sequestration, and Seawater Species. J. Phys. D Appl. Phys. 2017, 50, 505501-9. (42)

Frost, R. L.; Cejka, J. A Raman Spectroscopic Study of the Uranyl Mineral

Rutherfordine – Revisited. J. Raman Spectrosc. 2009, 40, 1096–1103. (43)

Faulques, E.; Massuyeau, F.; Kalashnyk, N.; Perry, D. L. Spectroscopic Markers for

Uranium(VI) Phosphates: a Vibronic Study. RSC Adv. 2015, 5, 71219–71227. (44)

Wu, Q.-Y.; Lan, J.-H.; Wang C.-Z.; Xiao, C.-L.; Zhao, Y.-L.; Wei, Y.-Z.; Chai, Z.-

F.; Shi, W.-Q. Understanding the Bonding Nature of Uranyl Ion and Functionalized Graphene: A Theoretical Study. J. Phys. Chem. A 2014, 118, 2149−2158. (45)

Aines, R. D.; Rossman, G. R. Water in Minerals? A Peak in the Infrared. J.

Geophys. Res. 1984, 89, 4059–4071. (46)

Libowitzky, E.; Rossman, G. R. An IR Absorption Calibration for Water in

Minerals. Am. Mineral. 1997, 82, 1111–1115. (47)

Libowitzky, E. Correlation of O-H Stretching Frequencies and O-H···O Hydrogen

Bond Lengths in Minerals. Monatsh. Chem. 1999, 130, 1047–1059. (48)

Kumar, P. P.; Kalinichev, A.G.; Kirkpatrick, R. J. Hydrogen-Bonding Structure and

Dynamics of Aqueous Carbonate Species from Car-Parrinello Molecular Dynamics Simulations. J. Phys. Chem. B 2009, 113, 794–802. (49)

Amayri, S.; Arnold, T.; Reich, T.; Foerstendorf, H; Geipel, G.; Bernhard, G.;

Massanek, A. Spectroscopic Characterization of the Uranium Carbonate Andersonite Na2Ca[UO2(CO3)3]·6H2O. Environ. Sci. Technol. 2004, 38, 6032–6036. ACS Paragon Plus Environment

Page 28 of 38

Page 29 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(50)

Sholl, D.S.; Steckel, J. A. Density functional theory. A practical introduction. John

Wiley & Sons, Inc., Hoboken, New Jersey, 2009. (51)

Liao W-Q.; Zhang, Y.; Hu, C-L.; Mao, J-G.; Ye, H-Y.; Li, P-F.; Huang, S.D.;

Xiong, R-G. A Lead-Halide Perovskite Molecular Ferroelectric Semiconductor. Nat. Commun. 2015, 6, 7338. (52)

Bian, Q.; Yang, Z.; Wang, Y.; Cao, C.; Pan, S. Predicting Global Minimum in

Complex Beryllium Borate System for Deep-Ultraviolet Functional Optical Applications. Sci. Rep. 2016, 6, 34839-9. (53)

Barmarin,

G.

Online

Database

of

Luminescent

Minerals

at

https://www.fluomin.org/uk/fiche.php?id=75. (54)

Kubelka, P.; Munk, F. Ein Beitrag zur Optik der Farbanstriche. Z. Techn. Physik

1931, 12, 593–601. (55)

Clark, S. J.; Robertson, J. Screened Exchange Density Functional Applied to Solids.

Phys. Rev. B 2010, 82, 085208-11. (56)

Jørgensen, C. K.; Reisfeld, R. The Uranyl Ion, Fluorescent and Fluorine-Like: A

Review. J. Electrochem. Soc. 1983, 681–684. (57)

Denning, R. G.; Electronic Structure and Bonding in Actinyl Ions and their

Analogs. J. Phys. Chem. A 2007, 111, 4125–4143. (58)

Wang, Z.; Zachara, J. M.; Liu, C.; Gassman, P. L.; Felmy, A. R.; Clark, S. B. A

Cryogenic Fluorescence Spectroscopic Study of Uranyl Carbonate, Phosphate and Oxyhydroxide Minerals. Radiochim. Acta 2008, 96, 591–598. (59)

Baumann, N.; Arnold, T.; Foerstendorf, H.; Read, D. Spectroscopic Verification of

the Mineralogy of an Ultrathin Mineral Film on Depleted Uranium. Environ. Sci. Technol. 2008, 42, 8266–8269. (60)

Baker, R. J. Uranium Minerals and Their Relevance to Long Term Storage of

Nuclear Fuels. Coordin. Chem. Rev. 2014, 266-267, 123–136. .



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Ca

Na EF -25 -20 -15 -10 -5

Energy (eV)


0

5

10

a

b

Wavenumber (cm-1) 22100 20800 19500 D

PL intensity (arb. unit)

16900

160

Wavenumber (cm-1) 21000

24000

27000

Page 36 of 38 30000

33000

B C D

40

120

E

C

E

A

32

80 40

F B

0

441 450 459

G

A 450

18000

15600

(KME)2

12500

1 2 3 10000 4 5 7500 6 7 5000 8 9 2500 10 11 0 12 13 14

18200


24 16 8

H

I

0 ACS Paragon Plus Environment 480

510

540

570

Wavelength (nm)

600

630

2.4

2.7

3.0

3.3

3.6

Energy (eV)

3.9

4.2

a

c

1

Page 37 ofThe 38 Journal of Physical0.1 Chemistry 0.01

465 nm

Normalized intensity

TRPL intensity (arb. unit)

1 1 0.1 2 482 nm 3 0.01 4 1 5 0.1 Wavenumber (cm-1) b6 502 nm 0.01 7 22100 20800 19500 18200 16900 15600 1 C D 90 8750 0.1 9600 60 523 nm E 10 0.01 450 30 B 11 1 300 441 450 459 F 12 0.1 150 G H Plus Environment ACS Paragon 13 A Full 0.01 0 14 450 480 510 540 570 600 630 0.0 0.2 0.4 0.6 15 Wavelength (nm) Time (ms)

0.8

1.0

The Journal of Physical Chemistry Page 38 of 38 1 2 3 4 5


Exploring Optical and Vibrational Properties of the Uranium Carbonate

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