Time-resolved Laser Fluorescence Spectroscopy Research Articles

The use of Raman and TRLF spectroscopy for differentiating early stage alteration products of spent nuclear fuel

Non-invasive techniques capable of distinguishing the alteration products of spent nuclear fuel during prolonged storage would be of great benefit when assessing the potential mobility of uranium from the fuel matrix. Two potential alteration products, becquerelite (Ca(UO2)6O4(OH)6·8(H2O)) and vandendriesscheite (Pb1.5(UO2)10O6(OH)11·11(H2O)), were characterised by multiple laser-wavelength Raman and time-resolved laser fluorescence spectroscopy (TRLFS). Chemical composition was confirmed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Well-defined Raman features were obtained, particularly with a 785 nm laser, allowing subtle differences between the two minerals to be observed. Differences were also found in the Raman spectra using lasers at 457, 532 and 633 nm, with the degree of luminescence depending on the metal cation present. Chemical quenching of luminescence in Raman data correlated with luminescence excitation and emission spectra results. Five and seven luminescence emission peaks were resolved for becquerelite and vandendriesscheite, respectively. The first reported luminescence excitation spectra were collected for each mineral but not all of the spectral ranges could be resolved into individual peaks. A luminescence decay lifetime of 5.5 ± 0.9 μs was obtained for vandendriesscheite. This study demonstrates that Raman spectroscopy and TRLFS are potentially valuable techniques for characterising uranyl oxy-hydroxides and could be used in conjunction with other methods, such as laser induced breakdown spectroscopy (LIBS), as part of a remote analysis package in nuclear waste management.

Excitation and Emission Properties of Adsorbed U(VI) on Amorphous Silica Surface

In the geochemical field, the chemical speciation of hexavalent uranium (U(VI)) has been widely investigated by performing measurements to determine its luminescence properties, namely the excitation, emission, and lifetime. Of these properties, the excitation has been relatively overlooked in most time-resolved laser fluorescence spectroscopy (TRLFS) studies. In this study, TRLFS and continuous-wave excitation–emission matrix spectroscopy are adopted to characterize the excitation properties of U(VI) surface species that interact with amorphous silica. The luminescence spectra of U(VI) measured from a silica suspension and silica sediment showed very similar spectral shapes with similar lifetime values. In contrast, the excitation spectra of U(VI) measured from these samples were significantly different. The results show that distinctive excitation maxima appeared at approximately 220 and 280 nm for the silica suspension and silica sediment, respectively.

Complexation of Nd(III)/Cm(III) with gluconate in alkaline NaCl and CaCl2 solutions: Solubility, TRLFS and DFT studies

The effect of gluconate on the solubility and aqueous speciation of An(III) and Ln(III) was studied using a combination of Nd(III) solubility experiments, Cm(III) time-resolved laser fluorescence spectroscopy (TRLFS) and density functional theory (DFT) calculations.Solubility experiments were performed under an Ar-atmosphere using a well-defined Nd(OH)3(s) solid phase equilibrated in NaCl (0.1–5.0 M) and CaCl2 (0.1–3.5 M) solutions with 9 ≤ pHc ≤ 13 and 10−6 M ≤ [GLU]tot ≤ 10−2 M. The solubility of Nd(OH)3(s) remains mostly unaffected in NaCl solutions with [GLU]tot = 10−3 M, whereas a clear increase in solubility is observed in dilute CaCl2 solutions with the same [GLU]tot and pHc ≥ 11. In concentrated CaCl2 solutions, gluconate does not affect the solubility of Nd(III) due to the competition with Ca–GLU complexes.Cm(III) TRLFS spectra collected in NaCl solutions with pHc ≈ 12 confirm the formation of weak Cm(III)–GLU complexes. The very strong red shift observed in dilute CaCl2 solutions in connection with high fluorescence intensities supports the formation of ternary Ca–Cm(III)–GLU complexes. The speciation of Cm(III) in 3.5 M CaCl2 solutions is mostly dominated by the complex Ca3[Cm(OH)6]3+, although the formation of ternary Ca–Cm(III)–GLU species is hinted at high gluconate concentrations. DFT calculations provide additional support to the formation of stable ternary Ca–Nd(III)–GLU aqueous complexes.This work provides key information to understand the chemical speciation and relevant equilibrium processes of An(III) and Ln(III) in the presence of gluconate under conditions relevant for nuclear waste disposal.

Characterisation of meta-autunite: Towards identifying potential alteration products of spent nuclear fuel

Laser-based spectroscopic techniques offer potential for characterising the alteration products of spent nuclear fuel in settings where the use of more traditional analytical methods is impracticable. Among these alteration products, uranyl phosphate phases have long attracted interest owing to their potential to form passivating surfaces on primary uranium phases inhibiting further uranium dissolution. Two strontium-rich meta-autunite ((Ca,Sr)(UO2)2(PO4)2·2–8(H2O)) samples from the Mount Spokane uranium deposit, Washington, USA were characterised by multiple laser wavelength Raman and time-resolved laser fluorescence spectroscopy. Well-defined Raman features were obtained, particularly at a laser wavelength of 785 nm, but partially hydrated meta-autunite phases could not be differentiated by Raman alone. However, subtle differences in three key modes were observed between meta-autunite and published data for fully hydrated autunite specimens enabling these minerals to be distinguished. Seven luminescence emission and several excitation features were resolved for the two samples, with the latter being the first reported excitation data for meta-autunite. The luminescence decay lifetime was found to be significantly longer than previously reported and sensitive to the meta-autunite dehydration phase.

Electrochemical and Spectroscopic Study of EuIII and EuII Coordination in the 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid.

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and EuIII /EuII electrochemical behavior as a function of water content in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf2 ]) was investigated using UV-visible spectrophotometry, time-resolved laser fluorescence spectroscopy, electrochemistry, and X-ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, EuIII and EuII were complexed by NTf2 , forming Eu-O and Eu-(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of EuII , and in quasi-reversible oxidation-reduction with an E0 ' potential of 0.18 V versus the ferrocenium/ferrocene (Fc+ /Fc) couple. Upon increasing water content, progressive incorporation of water in the EuIII coordination sphere occurred. This led to reversible oxidation-reduction reactions, but also to a decrease in stability of the +II oxidation state (E0 '=-0.45 V vs. Fc+ /Fc in RTIL containing 1300 mm water).

Study of Aqueous Am(III)-Aliphatic Dicarboxylate Complexes: Coordination Mode-Dependent Optical Property and Stability Changes.

The thermodynamics of Am(III) complex formation in natural groundwater systems is one of the major topics of research in the field of high-level radioactive waste management. In this study, we investigate the absorption and luminescence properties of aqueous Am(III) complexes with a series of aliphatic dicarboxylates in order to learn the thermodynamic complexation behaviors in relation to binding geometries. The formation of Am(III) complexes with these carboxylate ligands induced distinct red shifts in the absorption spectra, which enabled chemical speciation. The formation constants determined by deconvolution of the absorption spectra showed a linear decrease for the three ligands (oxalate (Ox), malonate (Mal), and succinate (Suc)) and a mild decrease for the remaining ligands (glutarate (Glu) and adipate (Adi)). Time-resolved laser fluorescence spectroscopy (TRLFS) was used to obtain information about the aqua ligand, which indirectly indicated the bidentate bindings of these dicarboxylate ligands. A complementary attenuated total reflectance Fourier transform infrared (ATR-FTIR) study on Eu(III), which is a nonradioactive analogue of Am(III) ion, showed that the coordination modes differ depending on the alkyl chain length. Ox and Mal bind to Am(III) via side-on bidentate bindings with two carboxylate groups, resulting in the formation of stable 5- and 6-membered ring structures, respectively. On the other hand, Suc, Glu, and Adi form end-on bidentate bindings with a single carboxylate group, resulting in a 4-membered ring structure. Density functional theory calculations provided details about the bonding properties and supported the experimentally proposed coordination geometries. This study demonstrates that coordination mode-dependent changes in optical properties occur along with thermodynamic stability changes in Am(III)-dicarboxylate complexes.

Trivalent Actinide Ions Showing Tenfold Coordination in Solution.

Trivalent actinides generally exhibit ninefold coordination in solution. 2,6-Bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (nPr-BTP), a tridentate nitrogen donor ligand, is known to form ninefold coordinated 1:3 complexes, [An(nPr-BTP)3]3+ (An = U, Pu, Am, Cm) in solution. We report a Cm(III) complex with tenfold coordination in solution, [Cm(nPr-BTP)3(NO3)]2+. This species was identified using time-resolved laser fluorescence spectroscopy (TRLFS), vibronic side band spectroscopy (VSBS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). Adding nitrate to a solution of the [Cm(nPr-BTP)3]3+ complex in 2-propanol shifts the Cm(III) emission band from 613.1 to 617.3 nm. This bathochromic shift is due to a higher coordination number of the Cm(III) ion in solution, in agreement with the formation of the [Cm(nPr-BTP)3(NO3)]2+ complex. The formation of this complex exhibits slow kinetics in the range of 5 to 12 days, depending on the water content of the solvent. Formation of a complex [Cm(nPr-BTP)3(X)]2+ was not observed for anions other than nitrate (X- = NO2-, CN-, or OTf-). The formation of the [Cm(nPr-BTP)3(NO3)]2+ complex was studied as a function of NO3- and nPr-BTP concentrations, and slope analyses confirmed the addition of one nitrate anion to the [Cm(nPr-BTP)3]3+ complex. Experiments with varied nPr-BTP concentration show that [Cm(nPr-BTP)3(NO3)]2+ only forms at nPr-BTP concentrations below 10-4 mol/L whereas for concentrations greater than 10-4 mol/L the formation of the tenfold species is suppressed and [Cm(nPr-BTP)3]3+ is the only species present. The presence of the tenfold coordinated complex is supported by VSBS, XPS, and DFT calculations. The vibronic side band of the [Cm(nPr-BTP)3(NO3)]2+ complex exhibits a nitrate stretching mode not observed in the [Cm(nPr-BTP)3]3+ complex. Moreover, XPS on [M(nPr-BTP)3(NO3)](NO3)2 (M = Eu, Am) yields signals from both non-coordinated and coordinated nitrate. Finally, DFT calculations reveal that the energetically most favored structure is obtained if the nitrate is positioned on the C2 axis of the D3 symmetrical [Cm(nPr-BTP)3]3+ complex with a bond distance of 413 pm. Combining results from TRLFS, VSBS, XPS, and DFT provides sound evidence for a unique tenfold coordinated Cm(III) complex in solution-a novelty in An(III) solution chemistry.

Investigating the Sulfur "Twist" on the Photophysics of DBD Dyes.

The so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes are a new class of fluorescent dyes, with tunable photophysical properties like absorption, fluorescence lifetime, and Stokes shift. With the development of sulfur based DBDs, this dye class is extended even further for possible applications in spectroscopy and microscopy. In this paper we are investigating the basic photophysical properties and their implications for future applications for S4-DBD as well as O4-DBD. On the basis of time-resolved laser fluorescence spectroscopy, transient absorption spectroscopy, and UV/vis-spectroscopy, we determined the rate constants of the radiative and nonradiative deactivation processes as well as the energy of respective electronic states involved in the electronic deactivation of S4-DBD and of O4-DBD. For S4-DBD we unraveled the triplet formation with intersystem crossing quantum yields of up to 80%. By TD-DFT calculations we estimated a triplet energy of around 13500-14700 cm-1 depending on the DBD dye and solvent. Through solvent dependent measurements, we found quadrupole moments in the range of 2 B.

Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems.

The hydration process of Portland cement in a cementitious system is crucial for development of the high‐quality cement‐based construction material. Complementary experiments of X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time‐resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time‐dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium−silicate−hydrates (C−S−H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C−S−H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.

Evaluation of the Hydrophilic Complexant N,N,N’,N’-tetraethyldiglycolamide (TEDGA) and its Methyl-substituted Analogues in the Selective Am(III) Separation

ABSTRACTN,N,N’,N’-tetraethyldiglycolamide (TEDGA) is used in the French EXAm (extraction of americium) process to separate Am(III) from Cm(III) and Ln(III). In this study, the complexation behavior of TEDGA towards actinides(III) and lanthanides(III) was compared to its methyl-substituted derivatives Me-TEDGA and Me2-TEDGA under experimental conditions applying to the EXAm process. Using the EXAm solvent, 0.6 mol/L N,N’-dimethyl-N,N’-dioctyl-hexylethoxymalonamide (DMDOHEMA) and 0.45 mol/L bis(2-ethylhexyl)-phosphoric acid (HDEHP), An(III) and Ln(III) distribution ratios increase in the order TEDGA < Me-TEDGA < Me2-TEDGA. This is explained by differences in the strength of complexation in the aqueous phase: Conditional stability constants for the formation of [Cm(DGA)x]3+ complexes decrease in the order TEDGA > Me-TEDGA > Me2-TEDGA, as shown by time-resolved laser fluorescence spectroscopy (TRLFS). TRLFS measurements verified the exclusive existence of [Cm(DGA)3]3+ complexes in the aqueous phase. Both the homoleptic [Cm(DMDOHEMA)n]3+ and the heteroleptic [Cm(DGA)x(DMDOHEMA)y]3+ complexes were detected in the organic phase, as postulated in the literature.[14]

Erratum on “Complexation of radionuclide 152+154Eu(III) with alumina-bound fulvic acid studied by batch and time-resolved laser fluorescence spectroscopy”

In the above referenced publication [1], the Figure 5 and data in Table 1 are correct, but we ignored to present the final pH values of the system, which is very important to understand the properties.

The complexation of Eu(III) and Cm(III) with polyacrylate as a model compound for complex polycarboxylates studied by laser fluorescence spectroscopy

The complexation of the trivalent heavy metals Eu(III) and Cm(III) with polyacrylate as a model ligand is investigated by time-resolved laser fluorescence spectroscopy (TRLFS) and subsequent thermodynamic modelling (charge neutralization model). The aqueous speciation of both metals is investigated as a function of temperature (20–60 °C) and ligand concentration (0–0.4 g/kg) in 0.1 mol/kg NaCl solution ([H+]total ≈ 10−4 mol/kg). Only one complex species is observed at all experimental conditions. With increasing temperature the aqueous Eu(III) and Cm(III) speciation is slightly shifted towards the complexes species. This effect is attributed to the stronger deprotonation of the polymer, which is also reflected by an increase of its loading capacity. The complex stability constants, however, show no visible temperature dependency. Log β’(T) ranges between 5.8 and 5.9 for both Eu(III) and Cm(III) over the whole range of experimental conditions.

Flow-Electrode CDI Removes the Uncharged Ca-UO2-CO3 Ternary Complex from Brackish Potable Groundwater: Complex Dissociation, Transport, and Sorption.

Unacceptably high uranium concentrations in decentralized and remote potable groundwater resources, especially those of high hardness (e.g ., high Ca2+, Mg2+, and CO32- concentrations), are a common worldwide problem. The complexation of alkali earth metals, carbonate, and uranium(VI) results in the formation of thermodynamically stable ternary aqueous species that are predominantly neutrally charged (e.g ., Ca2(UO2)(CO3)30). The removal of the uncharged (nonadsorbing) complexes is a problematic issue for many water treatment technologies. As such, we have evaluated the efficacy of a recently developed electrochemical technology, termed flow-electrode capacitive deionization (FCDI), to treat a synthetic groundwater, the composition of which is comparable to groundwater resources in the Northern Territory, Australia (and elsewhere worldwide). Theoretical calculations and time-resolved laser fluorescence spectroscopy analyses confirmed that Ca2(UO2)(CO3)30 was the primary aqueous species followed by Ca(UO2)(CO3)32- (at circumneutral pH values). Results under different operating conditions demonstrated that FCDI is versatile in reducing uranium concentrations to <10 μg L-1 with low electrical consumption (e.g ., ∼0.1 kWh m-3). It is concluded that the capability of FCDI to remove uranium under these common conditions depends on the dissociation kinetics of the Ca2(UO2)(CO3)30 complex in the electrical field. The subsequent formation of the negatively charged Ca(UO2)(CO3)32- species results in the efficient transport of uranium across the anion exchange membrane followed by immobilization on the positively charged flow (anode) electrode.

Spectroscopic speciation of aqueous Am(iii)-oxalate complexes.

Transportation of actinides through the geosphere is facilitated by complexation with organic ligands dissolved in groundwater. Carboxylic groups can interact directly with actinide ions and are found among the most abundant organic ligands in alkaline aquatic systems like underground water. In this study, the complexation of organic carboxylic groups with Am(iii) was investigated by monitoring the interactions of Am(iii) with oxalate (Ox), the simplest dicarboxylate ligand, in solution. UV-Vis spectrophotometry coupled with a liquid waveguide capillary cell (100 cm optical path-length) and time-resolved laser fluorescence spectroscopy were employed for quantitative detection of the respective Am(iii)-Ox species. Increasing the Ox concentration caused significant spectral changes, i.e., red-shifts in both the absorption and luminescence maxima with increased molar absorption coefficients, enhanced luminescence intensities, and prolonged luminescence lifetimes. Individual spectra of AmOx+(aq), Am(Ox)2-(aq), and Am(Ox)33-(aq) were resolved by deconvolution of the absorption spectra, with apparent formation constants of log β1,1 = 5.34 ± 0.05, log β1,2 = 9.14 ± 0.18, and log β1,3 = 11.49 ± 0.30, respectively, in I = 0.1 M NaClO4 and 0-30 mM Na2Ox. The absorption and luminescence spectral changes suggest bidentate complexation of Ox with Am(iii) via inner-sphere interactions. The geometry of the Am(iii)-Ox complexes was optimized by density functional theory, where the bonding characteristics were in good agreement with the experimental results. Thorough spectroscopic characterization enabled speciation of the Am(iii)-Ox complexes and determination of their formation constants. This spectroscopic approach is generally applicable in the investigation of molecular interactions between Am(iii) and various ligands in aqueous solution.

Formation of CaUO2(CO3)32- and Ca2UO2(CO3)3(aq) complexes at variable temperatures (10-70 °C).

The ternary complexation of calcium uranyl tricarbonate species, CaUO2(CO3)32- and Ca2UO2(CO3)3(aq), which are the predominant U(vi) complexes in groundwater and seawater, was investigated at variable temperatures from 10 to 70 °C. Time-resolved laser fluorescence spectroscopy (TRLFS), calcium ion-selective electrode potentiometry, and ultraviolet/visible (UV/Vis) absorption spectroscopy were complementarily employed to determine the formation constants (log Kx13, x = 1 and 2 for mono- and dicalcium complexes, respectively). at infinite dilution (zero ionic strength) was determined by correction using specific ion interaction theory (SIT), and an increasing tendency of with temperature was observed. In addition, the molar enthalpy of complexation (ΔrHm) was measured by calorimetry at 25 °C. Based on thermodynamic data obtained in this work, the approximation models were examined for the prediction of the temperature effect on the complexation, and the constant enthalpy approximation with the chemical complexation reaction modified to an isoelectric reaction showed a satisfactory prediction of in the temperature range of 10-70 °C. Finally, the results of U(vi) speciation in groundwater indicated that the dominance of calcium uranyl tricarbonate complexes would be weakened at elevated temperatures by the strongly enhanced hydrolysis of U(vi).

Interaction of Cm(III) with human serum albumin studied by time-resolved laser fluorescence spectroscopy and NMR

The complexation of Cm(III) with human serum albumin (HSA) was investigated using time-resolved laser fluorescence spectroscopy (TRLFS). The Cm(III) HSA species is dominating the speciation between pH 7.0 and 9.3. The first coordination sphere is composed by three to four H2O molecules and five to six coordinating ligands from the protein. For the complex formation at pH 8.0 a conditional stability constant of logK = 6.16 ± 0.50 was determined. Furthermore, information on the Cm(III) HSA binding site were obtained. With increasing Cu(II) concentration the Cm(III) HSA complexation is suppressed whereas the addition of Zn(II) has no effect. This points to the complexation of Cm(III) at the N-terminal binding site (NTS) which is the primary Cu(II) binding site. NMR experiments with Cu(II), Eu(III) and Am(III) HSA show a decrease of the peak assigned to the His C2 proton of His 3, which is part of the NTS, with increasing metal ion concentration. This confirms the complexation of Eu(III) and Am(III) at the Cu(II) binding site NTS. The results presented in this study contribute to a better understanding of relevant biochemical reactions of incorporated actinides.

Thermodynamics of the complexation of curium(III) with chloride in alkali and alkali earth metal solutions at elevated temperatures

The complexation of trivalent curium (Cm(III)) with chloride up to its respective saturation concentration is studied in dependency of the chloride-bearing electrolyte (LiCl, NaCl, MgCl2, CaCl2) in the temperature range of 25–200 °C by time-resolved laser fluorescence spectroscopy (TRLFS). At low chloride concentrations and temperatures the Cm(III) aquo ion dominates the species distribution. However, at both elevated chloride concentrations and temperatures speciation is dominated by CmCl2+(aq) and CmCl2+(aq), and significant molar fractions are even contributed by CmCl3 (aq) and CmCl4-(aq). Conditional stability constants log β′n(t) are determined and extrapolated to the thermodynamic reference state using the specific ion-interaction theory (SIT). Modeling results in standard stability constants log β°2(t) with slight deviation with respect to the valency of the electrolyte. As a result, an average value of log β°2(25 °C) = (−1.16 ± 0.10) is derived for the formation of CmCl2+. The complexation is found to be both endothermic as well as entropy driven with ΔrH° = (60.5 ± 1.5) kJ mol−1, and ΔrS° = (180.7 ± 3.9) J mol−1 K−1.

A spectroscopic study of the complexation reaction of trivalent lanthanides with a synthetic acrylate based PCE-superplasticizer.

The interaction between different trivalent lanthanides and a synthetic acrylate based PCE-superplasticizer (52IPEG4.5) is investigated by using a combination of laser- and synchrotron based spectroscopic techniques. Time-resolved laser fluorescence spectroscopy (TRLFS) is used to obtain thermodynamic data (stability constants (log β'(T)), reaction enthalpy (ΔrH) and entropy(ΔrS)) of the complexation reaction of Eu(III) and 52IPEG4.5 as a function of the temperature (20-80 °C) and ligand concentration (<2 g/kg) in 0.1 mol/kg NaCl solution. Under the chosen experimental conditions, the increase in temperature mainly affects the complexation properties (loading capacity) of the macromolecule itself rather than the stability constant of the formed complex (log β'(T) ranging between 6.5 and 5.9). The thermodynamic results are complemented by extended X-ray absorption fine structure (EXAFS) spectroscopic measurements to resolve the molecular structure of 52IPEG4.5 complexes with Eu(III), Gd(III), and Tb(III). The results show, that each metal ion is coordinated by three carboxylic groups within the 52IPEG4.5 complexes. Furthermore, the determined interatomic distances exhibit that the functional groups are attached in a bidentate end-on fashion.

Hydrophobic Properties of Calcium-Silicate Hydrates Doped with Rare-Earth Elements

In this study, the apparent relationship between the transport process and the surface chemistry of the Calcium-Silicate Hydrate (CSH) phases was investigated. For this purpose, a method was developed to synthesize ultrathin CSH phases to be used as a model substrate with the specific modification of their structure by introducing europium (Eu(III)). The structural and chemical changes during this Eu(III)-doping were observed by means of infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and time-resolved laser fluorescence spectroscopy (TRLFS). These alterations of the CSH phases led to significant changes in the surface chemistry and consequently to considerable variations in the interaction with water, as evidenced by measurements of the contact angles on the modified model substrates. Our results provide the basis for a more profound molecular understanding of reactive transport processes in cement-based systems. Furthermore, these results broaden the perspective of improving the stab...

TRLFS study of hydrolyzed Eu(III) species

The hydrolysis of Eu(III) and Am(III) begins near neutral pH conditions, above which precipitation occurs due to low solubility. Careful sample characterization steps are a prerequisite for the speciation study of hydrolyzed Eu(III) complexes without the interference of colloidal particles or precipitation. Herein, the hydrolysis reaction of Eu(III) was studied using time-resolved laser fluorescence spectroscopy (TRLFS). Laser-induced breakdown detection was employed to monitor the presence of colloidal particles. The luminescence properties of Eu(III) and precipitated Eu(OH)3(s) were investigated and comparisons were made to those of aqua Eu3+. Parallel factor analysis was applied for the deconvolution of the TRLFS results. Both primary hydrolyzed Eu(III), EuOH2+ and precipitated Eu(OH)3(s) showed distinct luminescence spectral properties, including an enhanced hypersensitive luminescence peak (J = 2). An increased luminescence lifetime was observed for both EuOH2+ (τ = 130 ± 1 μs) and precipitated Eu(OH)3(s) (τ = 158 ± 7 μs) compared to that of aqua Eu3+ (τ = 112 ± 1 μs). A formation constant log*β1,1 of EuOH2+ at I = 0.1 M NaClO4 and 25 °C was measured to be –8.28 ± 0.22, which was converted to log*β°1,1 = –7.87 ± 0.22 at an infinitely diluted condition of I = 0 based on the specific ion interaction theory.