Surface speciation of Eu3+ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)

Adsorption behaviour of pollutants: Heavy metals, radionuclides, organic pollutants, on clays and their minerals (raw, modified and treated): A review

The increasing anthropogenic pressure results in environmental pollution and thus adversely affects the integrity of ecosystems. Consequently, various methods of removing pollutants from effluents have been developed and used to minimise this negative impact, with adsorption on clay minerals identified as the most promising approach. This review examines the adsorption of heavy metals, radionuclides, and organic pollutants on clays/clay minerals and their composites under diverse conditions and deals with the applications of these materials in the construction of engineering barriers for waste management. Additionally, we discuss the efficiency and mechanisms of pollutant adsorption on clays subjected to various treatments and modifications while describing the beneficial effects of such modification/treatment on adsorption performance, reusability, and in vivo/in vitro toxicity.

UV Time-Resolved Laser-Induced Fluorescence Spectroscopy of Amino Acids Found in Meteorites: Implications for Space Science and Exploration

Laser-induced fluorescence spectroscopy is a useful laboratory and in situ technique for planetary exploration, with applications in biosignature detection and the search for life on Mars. However, little work has been completed on the utility of fluorescence spectroscopy techniques on asteroid relevant material. In preparation for asteroid sample return missions such as NASA's OSIRIS-REx and JAXA's Hayabusa2, we conducted UV time resolved laser-induced fluorescence spectroscopy (TR-LIF) analysis of 10 amino acids, all of which have been found in the carbonaceous meteorites Murchison and Allende. We present the calculation of decay rates of each amino acid (1.55-3.56 ns) and compare with those of relevant homogeneous minerals (15-70 ns). Moreover, we demonstrate a linear relationship between calculated lifetimes and elemental abundance of nitrogen and carbon (p < 0.025). The quantitative and qualitative fluorescence analyses presented in this work will lead to more reliable identification of organic material within meteorites and asteroids in a time-efficient, minimally destructive way.

Luminescence spectroscopic investigations of europium complexes formed in the kaolinite-humic acid/citric acid systems

In the present study, the nature of Eu(III) complexes (Eu(III) was used as a surrogate for Am(III)) formed in kaolinite–humic acid (HA)/citric acid (CA) system was investigated by luminescence spectroscopy. In addition to the ternary system (kaolinite + Eu + L(CA/HA)), the binary system (Eu-L) was also looked at for a better understanding of the complexes formed at the kaolinite surface. The lifetime and emission spectra of Eu-L complexes on the kaolinite surface differ considerably as compared to the same in the aqueous phase. The Eu-HA aqueous complexation shows differences in the excitation spectra with similar decay lifetimes with increasing aqueous HA concentrations. The ligand-to-metal charger transfer (LMCT) in the Eu-HA excitation spectra suggests the complexation of Eu(III) with HA at pH ∼ 4. Although the mode of Eu(III) binding to the kaolinite surface in the presence of CA/HA was the same i.e. metal-bridged ternary complex formation, the local surroundings around the sorbed Eu(III) differ in the two cases. The loading of HA in the Eu-HA-kaolinite system does not have a large effect on the local structure around the sorbed Eu(III) ion, but enhances the percentage of Eu(III) uptake onto the kaolinite surface. The number of H2O molecules in the primary hydration sphere of sorbed Eu(III) differs in the Eu-HA-kaolinite and Eu-CA-kaolinite systems. In addition, Eu(III) assisted precipitation of HA was also seen using a radiometric method.

Adsorption of natural annatto dye by kaolin: kinetic and equilibrium

The adsorption of annatto dye was analysed using kaolin clay as the adsorbent. In this work, the influence of the adsorbent particle size, agitation (0 and 100 rpm), temperature (25, 40, and 60°C), and salt presence (sodium chloride and sodium sulphate at 1, 2 and 3 wt%) on the adsorption process was studied. The adsorption increased 14.21% for particles smaller than 45 µm and the agitation (100 rpm) led to an increase of 22.41% compared to the system without agitation. The ΔG° (237.711 kJmol^-1) indicated that the adsorption process was spontaneous. The negative value of ΔS° (-408.999 Jmol^-1K^-1) and ΔH° (-115.829 kJmol^-1) showed an exothermic physisorption process. The adsorption kinetics follows the pseudo-second-order model. In the adsorption equilibrium, the tested models provided good correlation coefficients ranging from 0.744 to 0.999 with the best fit observed for the Langmuir model. The maximum adsorption capacity of the kaolin clay for the annatto dye was obtained at 25°C with 1% of sodium sulphate (q _max = 59.88 mgg^-1).

Spectroscopic Studies of Mössbauer, Infrared, and Laser-Induced Luminescence for Classifying Rare-Earth Minerals Enriched in Iron-Rich Deposits

Rare-earth (RE) phosphates often appear as an accessory phase in igneous or metamorphic rocks; however, these rocks are composed of myriad chemical elements and nuclides that interfere with the qualitative or quantitative analyses of the RE phosphates over a range of concentrations in the absence of a pretreatment. In addition, the limit of each analytical methodology constrains the approach as well as the usefulness of the results in geoscience applications. Here, we report the specific mineral characterization of RE-containing ores from Yen Phu mine, Vietnam, using a range of state-of-the-art spectroscopic techniques in conjunction with microscopy: Mössbauer spectroscopy, infrared microspectroscopy, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Because the distribution of each element in the deposit differs, such combinatorial works are necessary and could lead to more plausible answers to questions surrounding the point of origin of RE elements. The results of our Mössbauer spectroscopic analysis indicate that the three ores sampled at different locations all contain magnetite-like, hematite-like, and iron(III) salts other than hematite. In addition, we confirmed the presence of phosphate around the grain boundary in the magnetite-like mineral phase by infrared microspectroscopic analysis. The present analytical findings of trace amounts of europium(III) using TRLFS suggest that the europium ions generate identical luminescence spectra despite being embedded in three different matrices of iron minerals. This demonstration highlights the benefits of combinatorial spectroscopic analyses to gain insights into the effects of the environment of REs on their solid-state chemistry and shows the potential utility of TRLFS as a resource mining tool. Further applications of this approach in the analytical screening of rocks and minerals are feasible.

Chemisorption of lanthanide ions on succinate-functionalized mesoporous silica: An in situ characterization by fluorescence

Chemisorption of Eu³⁺ and Tb³⁺ on SBA-15 functionalized with succinic groups has been studied by in situ steady-state fluorescence measurements. The enhancement of the emission sensitive bands indicates that both ions adsorb forming inner-sphere surface complexes. Adsorption is a fast process that attains equilibrium in about 5min. The variation of the peaks maxima (I₅₉₂ and I₆₁₆, for europium, and I₄₉₀ and I₅₄₅, for terbium) with the total ion concentration is accounted for by the sum of the contributions due to the adsorbed and free ions. The former contribution is langmuirian. At pH 4.5, the respective adsorption constants are 5×10⁵ and 3×10⁵M^-1, and the maximum adsorption capacities are 5.10×10^-4 and 5.23×10^-4molg^-1. The mismatch between the latter values and the number of attached carboxylic groups is discussed. Comparison with other functionalized mesoporous silicas indicates that the anchored succinic groups are very efficient for removing lanthanide ions from aqueous solutions.

Effect of different complexing ligands on europium uptake from aqueous phase by kaolinite: batch sorption and fluorescence studies

The fluorescence studies suggested that the Eu(iii) sorbs as Eu(iii)–oxalate complex (binary system) onto kaolinite surface in the ternary system of Eu(iii), oxalic acid and kaolinite at circumneutral pH conditions.

Different Interaction Mechanisms of Eu(III) and (243)Am(III) with Carbon Nanotubes Studied by Batch, Spectroscopy Technique and Theoretical Calculation

Herein the sorption of Eu(III) and (243)Am(III) on multiwalled carbon nanotubes (CNTs) are studied, and the results show that Eu(III) and (243)Am(III) could form strong inner-sphere surface complexes on CNT surfaces. However, the sorption of Eu(III) on CNTs is stronger than that of (243)Am(III) on CNTs, suggesting the difference in the interaction mechanisms or properties of Eu(III) and (243)Am(III) with CNTs, which is quite different from the results of Eu(III) and (243)Am(III) interaction on natural clay minerals and oxides. On the basis of the results of density functional theory calculations, the binding energies of Eu(III) on CNTs are much higher than those of (243)Am(III) on CNTs, indicating that Eu(III) could form stronger complexes with the oxygen-containing functional groups of CNTs than (243)Am(III), which is in good agreement with the experimental results of higher sorption capacity of CNTs for Eu(III). The oxygen-containing functional groups contribute significantly to the uptake of Eu(III) and (243)Am(III), and the binding affinity increases in the order of ≡S-OH < ≡S-COOH < ≡S-COO(-). This paper highlights the interaction mechanism of Eu(III) and (243)Am(III) with different oxygen-containing functional groups of CNTs, which plays an important role for the potential application of CNTs in the preconcentration, removal, and separation of trivalent lanthanides and actinides in environmental pollution cleanup.

The interaction of Eu(iii) with organoborates – a further approach to understand the complexation in the An/Ln(iii)–borate system

A combination of different spectroscopy techniques, DFT calculations and advanced data analysis explained the Eu(iii)–organoborate complexation.

Formation of a Eu(iii) borate solid species from a weak Eu(iii) borate complex in aqueous solution

Using time-resolved laser-induced fluorescence spectroscopy (TRLFS) the transformation of a dissolved Eu(iii) borate species into a solid Eu(iii) borate was observed.