Heavy Alkali Metals Research Articles

Variations in local heavy metal concentrations over the last 16,000 years in the central Atacama Desert (22°S) measured in rodent middens

Mining is a major industry in the Atacama Desert, one of the world's leading regions for copper and other minerals. Intense industrialization of copper mining in the mid-twentieth century has likely led to significant environmental pollution through the deposition of heavy metals in the hyperarid Atacama, but how heavy metal pollution has changed over time in arid regions have rarely been assessed. Here, we analyzed both modern and ancient fecal pellets from paleomiddens collected in the central Atacama for heavy metals and by comparing current heavy metal concentrations with pre-industrial ones, we establish ecological baselines for such pollution. Sixteen paleomiddens spanning the last 1000 years from multiple localities in the eastern Calama Basin (22°S) show elevated concentrations of Cu and As in modern compared to older middens, and that heavy metal, alkali metals and alkaline earth metals show positive correlations with each other. Heavy metals also tend to be higher in paleomiddens collected along perennial rivers in comparison to those collected from surrounding ranges, irrespective of sample age. Twenty paleomiddens spanning the last c. 16,000 years from a single locality (El Hotel) between the Calama and San Pedro de Atacama basins were used to establish long term variations in plant communities and associated heavy metals since the last glacial termination. Results show that heavy metal concentrations including Cr, Mo and B vary over time and tend to be higher in paleomiddens for which Cactaceae are more abundant whereas those dominated by annuals show less of an effect from trace metals. Our results imply that climate change-driven plant community composition plays a key role in explaining how contamination varies in these desert ecosystems and show that paleomiddens are a unique and unexplored source for understanding how heavy metals vary over time. Given their ubiquity in many of the world's arid regions, they can be used to establish long-term ecological baselines to compare against human alterations.

Experimental and Computational Approaches for the Structural Study of Novel Ca-Rich Zeolites from Incense Stick Ash and Their Application for Wastewater Treatment

At present, chemical Si/Al sources are mainly used as precursor materials for the manufacturing of zeolites. Such precursor materials are quite expensive for commercial synthesis. Here, we have reported the synthesis of Ca-based zeolite from incense stick ash waste by the alkali-treatment method for the first time. Incense stick ash (ISA) was used as a precursor material for the synthesis of low Si zeolites by the alkali-treatment method. The as-synthesized zeolites were characterized by various instruments like particle size analyzer (PSA), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), electron diffraction spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray fluorescence (XRF). FTIR and XRD helped in the identification of the microstructure and crystalline nature of the zeolites and also confirmed the synthesis of Ca-based zeolite with two thetas at 25.7°. The microscopic analysis by FESEM and TEM exhibited that the size of synthesized Ca-rich zeolites varies from 200 to 700 nm and they are aggregated and cuboidal in shape. Additionally, structural, electronic, and density of states’ characteristics of gismondine (Ca2Al4Si4O16·9H2O) structures were evaluated by computational simulations (first principle, density functional theorem). The structural optimization of structures was carried out in the first stage under the lowest condition of total energy and forces acting on atoms for the lattice constant, as well as the available experimental and theoretical findings. The present research approach predicted the transformation of ISA waste into a value-added mineral, i.e., zeolite, which was further used for the removal of both heavy metals and alkali metals from fly ash-based wastewater using inductively coupled plasma-optical emission spectroscopy (ICP-OES).

Structural Similarity in a Series of Alkali Metal Aluminates with Heteroleptic tert‐Butoxide–Isobutyl Ligand Sets

With the aim of increasing the number of well‐defined alkali metal aluminates, six new crystalline examples containing heteroleptic tert‐butoxide – isobutyl ligand sets are reported. NMR spectroscopic studies in C6D6 solution have determined their common general formula [(iBu)2Al(OtBu)2AM·(D)], where AM = Li, D = 2 THF, TMEDA or PMDETA; AM = Na, D = TMEDA or PMDETA; and AM = K, D = PMDETA. X‐ray crystallographic studies show that despite the different sized alkali metals involved all six complexes adopt a common dinuclear motif with [AlO(AM)O] ring cores. Though Al–OtBu–Li linkages are common, the heavier alkali metal examples reported here are exceptionally rare. These structures could be interpreted as co‐complexes between monomeric forms of tBuO(AM) and (iBu)2Al(OtBu).

Intercalation of sodium and heavy alkali metals into graphenic foams

Abstract Most of alkali metals are well-known to easily intercalate into graphite to form stage-1 graphite intercalation compounds (GIC) whose structure and physical properties have been extensively studied. This work is focused on the intercalation of potassium, sodium and cesium into graphenic foams prepared by a solvothermal-based process. The as-obtained samples are analyzed by means of X-ray diffraction and Raman spectroscopy, and reveal a double phenomenon: the intercalation of alkali metals between the interplanar spaces of the multi-layer graphene stackings, and their sorption into the porosity of the host sample. This kind of behavior has already been reported when studying the reactivity of alkali metals with disordered carbon. Interestingly, our study shows a low stage intercalation in the case of sodium. Moreover, the dispersion of the potassium-intercalated samples into a polar solvent leads to a few-layer graphene dispersion stable for months.

Lithium-Doping Effects in Cu(In,Ga)Se2 Thin-Film and Photovoltaic Properties.

The beneficial effects of heavy alkali metals such as K, Rb, and Cs in enhancing Cu(In,Ga)Se2 (CIGS) photovoltaic efficiencies are widely known, though the detailed mechanism is still open for discussion. In the present work, the effects of the lightest alkali metal, Li, on CIGS thin-film and device properties are focused upon and compared to the effects of heavy alkali metals. Till date, the beneficial effects of elemental Li on Cu2ZnSnS4 photovoltaic devices in enhancing efficiencies have been reported. On the other hand, it is shown in the present work that the beneficial effects of Li on CIGS are not so significant. In contrast to the effects of Na or Rb in enhancing CIGS(112) growth orientation, Li was revealed not to affect CIGS growth orientation. The most distinctive feature observed between Li and other alkali metals was the elemental depth profile in CIGS films. Namely, Na and heavier alkali metals show a concentration peak near the surface (relatively Cu-poor) region of CIGS films, whereas elemental Li showed no such trend, suggesting that Li has no significant effect on CIGS surface modification. Nonetheless, Li was found to have some effect in enhancing the PL peak intensity and photovoltaic performance of CIGS, though the effect is relatively small in comparison to that obtained with other alkali metals.

Investigation of heavy metals in agricultural soils and vegetables irrigated with river water exposed to industrial effluent in Mojo, Ethiopia

The objective of this study was to examine the level of heavy metals and alkali metals in soil, cabbage and water samples collected from Qoka Negewo, where Mojo River is used for irrigation. Mixture of nitric acid, perchloric acid, and hydrogen peroxide was used for optimizing the wet digestion method for soil and cabbage samples. One way anova test result revealed that there were significant difference (p < 0.05) at 95 percent confidence level in concentration of metals among soil, cabbage and water in all samples. The heavy metal concentration of soil samples was found to be relatively a little higher than the corresponding concentration in cabbage samples. The concentration of the metals was compared with internationally recommended permissible limits, and most of them were found below the permissible limits, indicating insignificant health risk by consuming the cabbage, and using the water for irrigation purpose. The hazard risk index calculated for cabbage was found to be <1, which also indicates the predicted exposure is unlikely to pose potential health risks.

Revealing the origin of the beneficial effect of cesium in highly efficient Cu(In,Ga)Se2 solar cells

The record conversion efficiency of thin-film solar cells based on Cu(In,Ga)Se2 (CIGS) absorbers has exceeded 23%. Such a high performance is currently only attainable by the incorporation of heavy alkali metals like Cs into the absorber through an alkali fluoride post-deposition treatment (PDT). As the effect of the incorporated heavy alkali metals is under discussion, we investigated the local composition and microstructure of high efficiency CIGS solar cells via various high-resolution techniques in a combinatory approach. An accumulation of Cs is clearly detected at the p-n junction along with variations in the local CIGS composition, showing the formation of a beneficial secondary phase with a laterally inhomogeneous distribution. Additionally, Cs accumulations were detected at grain boundaries with a random misorientation of the adjacent grains where a reduced Cu concentration and increased In and Se concentrations are detected. No accumulation was found at Σ3 twin boundaries as well as the grain interior. These experimental findings are in excellent agreement with complementary ab-initio calculations, demonstrating that the grain boundaries are passivated by the presence of Cs. Further, it is unlikely that Cs with its large ionic radius is incorporated into the CIGS grains where it would cause detrimental defects.

Unveiling the potential of superalkali cation Li3+ for capturing nitrogen.

The potential of the superalkali cation Li3+ for capturing N2 and its behavior in gaseous nitrogen have been theoretically studied at the MP2/6-311+G(d) level. The evolution of structures and stability of the Li3+(N2)n (n = 1-7) complexes shows that the N2 molecules tend to bind to different vertices of the Li3+ core, and that Li3+ might have the capacity to capture up to twelve nitrogen molecules in the first coordination shell. Based on natural population and molecular orbital analyses, Li3+ keeps its superatom identity in the lowest-lying Li3+(N2)n (n = 1-4) complexes. The change in the Gibbs free energies of possible fragmentation channels also indicates the thermodynamic stability of Li3+ in the (N2)n clusters when n ≤ 4. Different from the case of Li3+(H2O)n, where the electrostatic interaction is dominant, the electrostatic and polarization components are found to make nearly equal contributions to Li3+(N2)n complex formation. In addition, it can be concluded that the superalkali cation Li3+ surpasses heavy alkali metal cations in capturing N2 molecules, since it has a larger binding energy with N2 than Na+ and K+ ions.

Alkali-induced grain boundary reconstruction on Cu(In,Ga)Se2 thin film solar cells using cesium fluoride post deposition treatment

Heavy alkali metal treatment is a key factor to approach high efficiency in Cu(In, Ga)Se2 (CIGS) solar cells. Here, we show that the Cs-induced surface modification on CIGS thin-film solar cells, especially on grain boundary reconstruction generated from cesium fluoride post-deposition treatment (CsF-PDT). The CsInSe2 phase can be synthesized by CsF-PDT process without extra assistant species, and specifically favors grain boundaries (GBs), which was further characterized by FE-EPMA, TEM, and SIMS analysis. The Cs-contained GBs may both create the valence-band downshift and conduction-band upward. By controlling the Cs-contained layer thickness and modifying absorber, the spike at conduction-band can be overcome by tunneling while remaining high valence-band downshift to suppress the GBs recombination. The efficiency was improved from 15.1 to 18.3% after CsF-PDT; the voltage loss of Eg/q–Voc was down below 0.4 V. Those improvements are mainly contributed from the grain boundary reconstruction at the junction area using CsF-PDT to reduce the recombination.

Anionic Polymerization of Butadiene Using Lithium/Potassium Multi-metallic Systems: Influence on Polymerization Control and Polybutadiene Microstructure

Thermal, mechanical, and viscoelastic properties of polybutadiene-based rubber materials are highly dependent on polybutadiene microstructure. The use of polar modifier in association with alkyllithium is a well-known method to obtain polybutadiene with a high vinyl content. Another approach is to use bimetallic initiating species such as alkyllithium combined to heavier alkali metal alkoxide (RONa, ROK…). The polymerization control is nevertheless not achieved and several parameters were found to influence it. Using bimetallic initiating systems based on alkyllithium and a potassium alkoxide, alkyllithium structure, initiator preformation time, and initiator composition were identified as parameters influencing the anionic polymerization process of butadiene and/or polybutadiene microstructure. In addition, the use of trimetallic systems based on alkyllithium, potassium alkoxide, and alkylaluminum was investigated in order to prevent side reactions regardless of the [K]/[Li] ratio and of the initiator preformation time.

Covalently decorated crown ethers on magnetic graphene oxides as bi-functional adsorbents with tailorable ion recognition properties for selective metal ion capture in water

Metal ions (Mn+) in water are considered as environmental pollutants, as industrial impurities or as potential secondary sources for valuable metals. Increasing generation of complex feed streams has raised the need for more specialized adsorbents that could preferentially capture the target Mn+. While graphene oxide (GO) is an effective adsorbent, its indiscriminate sequestration negatively affects its selectivity. To meet the growing demand for more Mn+-selective materials, GO adsorbents with dual features of ion recognition and magnetic responsiveness were developed. The bi-functional GOs were fabricated by in-situ nucleation of Fe3O4 nanoclusters on GO oxygenous groups and by direct grafting of ethynylbenzene linkers on its backbone, which served as tethering sites for the macrocyclic crown ether (CEs) ligands with tunable Mn+ affinities (i.e. CE@Fe3O4-rGO). As proof-of-concept, 12CE4@Fe3O4-rGO was proven highly selective for Li+ capture, achieving α = 367–14,513 against Na+, K+, Mg2+, Ca2+ in seawater. Its Langmuir-type Li+ adsorption achieved nearly ~100% 12CE4 utilization (1.03 mmol g−1 CE loading). Its pseudo-second uptake rate demonstrated its rapid Li+ capture. 12CE4@Fe3O4-rGO is water-dispersible, magnetically retrievable, and recyclable with consistent Li+ uptake performance. By replacing the CEs with aza15CE5, aza18CE6 and dibenzo-24CE8, three more types of CE@Fe3O4-rGOs (1.24–1.71 mmol CE g−1) were successfully synthesized with varying affinities towards heavy metals, radionuclides and alkali metal ions. These findings highlight the versatility of the proposed technique in producing a wide selection of CE@Fe3O4-rGOs which can be used for selective Mn+ capture in various application for water decontamination, salts removal, and resource recovery.

Mutual diffusion in liquid alloys of heavy alkali metals with bismuth

Interdiffusion coefficients for liquid cesium–bismuth alloys containing from 20 to 40 at. % Bi are measured using a gamma-ray attenuation technique. The obtained results are compared with the data on mutual diffusion in the rubidium–bismuth melts studied earlier. The comparison shows that the concentration dependences of the interdiffusion coefficient for Rb–Bi and Cs–Bi liquid systems demonstrate common features, namely, pronounced maxima at certain compositions. The origin of these features is briefly discussed.

Efficient Non‐dissociative Activation of Dinitrogen to Ammonia over Lithium‐Promoted Ruthenium Nanoparticles at Low Pressure

AbstractThere is an exciting possibility to decentralize ammonia synthesis for fertilizer production or energy storage without carbon emission from H2 obtained from renewables at small units operated at lower pressure. However, no suitable catalyst has yet been developed. Ru catalysts are known to be promoted by heavier alkali dopants. Instead of using heavy alkali metals, Li is herein shown to give the highest rate through surface polarisation despite its poorest electron donating ability. This exceptional promotion rate makes Ru–Li catalysts suitable for ammonia synthesis, which outclasses industrial Fe counterparts by at least 195 fold. Akin to enzyme catalysis, it is for the first time shown that Ru–Li catalysts hydrogenate end‐on adsorbed N2 stabilized by Li+ on Ru terrace sites to ammonia in a stepwise manner, in contrast to typical N2 dissociation on stepped sites adopted by Ru–Cs counterparts, giving new insights in activating N2 by metallic catalysts.

Efficient Non-dissociative Activation of Dinitrogen to Ammonia over Lithium-Promoted Ruthenium Nanoparticles at Low Pressure.

There is an exciting possibility to decentralize ammonia synthesis for fertilizer production or energy storage without carbon emission from H2 obtained from renewables at small units operated at lower pressure. However, no suitable catalyst has yet been developed. Ru catalysts are known to be promoted by heavier alkali dopants. Instead of using heavy alkali metals, Li is herein shown to give the highest rate through surface polarisation despite its poorest electron donating ability. This exceptional promotion rate makes Ru-Li catalysts suitable for ammonia synthesis, which outclasses industrial Fe counterparts by at least 195 fold. Akin to enzyme catalysis, it is for the first time shown that Ru-Li catalysts hydrogenate end-on adsorbed N2 stabilized by Li+ on Ru terrace sites to ammonia in a stepwise manner, in contrast to typical N2 dissociation on stepped sites adopted by Ru-Cs counterparts, giving new insights in activating N2 by metallic catalysts.

Evidence for superconductivity in Rb metal above 55 GPa pressure

The only alkali metal known to be superconducting at ambient pressure is Li at 0.4 mK. Under 30 GPa pressure \textit{T}$_{c}$ for Li rises to 14 K. In addition, nearly 50 years ago the heavy alkali metal Cs was reported to become superconducting near 1.3 K at 12 GPa. In the present experiment the superconductivity of Cs under pressure is confirmed. In addition, strong evidence is presented in electrical resistivity measurements that neighboring Rb also becomes superconducting near 2 K at 55 GPa as it enters the \textit{oC}16 phase, as for Cs, where \textit{T}$_{c}$ decreases under the application of pressure. It would seem likely that under the right temperature/pressure conditions all alkali metals, including metallic hydrogen, will join the ranks of the superconducting elements. With the addition of Rb, 55 of the 92 naturally occurring elements are superconducting at ambient or high pressure.

Photoemission spectroscopy of rubrene thin films doped with heavy alkali metal: A first-principles investigation

In this work, the photoemission spectroscopy (PES) of rubrene thin films deposited with heavy alkali metal (cesium, rubidium, and potassium) at the alkali/rubrene stoichiometric ratio of 1:1 are studied with density functional theory (DFT) and compared with experiments available in the literature. The common characteristics of PES observed in the rubrene thin films doped with heavy alkali metal are explicable with the DFT simulations. Detailed analysis on the geometric and electronic structures of cesium-, rubidium-, and potassium-rubrene complexes reveals two fundamental reasons for the commonness of their photoemission spectra. First, the electronic structures demonstrated with the energy density-of-states analysis are not much affected by the different adsorption sites of the alkali atom on the tetracene-like backbone of rubrene. Second, the minimum-energy structures of the three (heavy-alkali)-rubrene complexes are similar. The (heavy-alkali)-rubrene complexes differ from the (light-alkali)-rubrene complexes (lithium- and sodium-rubrene) in minimum-energy geometries and the orbital constituents of the highest occupied molecular orbital (HOMO) level.

Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB3 H8 (M=K, Rb, and Cs), Mechanisms of Formation, and the Crystal Structure of KB3 H8.

A facile synthesis of heavy alkali metal octahydrotriborates (MB3 H8 ; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH3 , does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH4 /NaBH4 with THF⋅BH3 have to be carried out under reflux. The high stability and solubility of KB3 H8 were examined, and a crystal structure thereof was obtained for the first time.

Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB3H8 (M=K, Rb, and Cs), Mechanisms of Formation, and the Crystal Structure of KB3H8

AbstractA facile synthesis of heavy alkali metal octahydrotriborates (MB3H8; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF⋅BH3, does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH4/NaBH4 with THF⋅BH3 have to be carried out under reflux. The high stability and solubility of KB3H8 were examined, and a crystal structure thereof was obtained for the first time.

Alkali Metals Doping for High‐Performance Planar Heterojunction Sb2S3 Solar Cells

Sb2S3 as a stable light harvesting material has received increasing attention for solar cell applications. To improve the device efficiency, much effort has been put into the materials synthesis, interfacial engineering, and device structure design. Here, it is demonstrated that doping of alkali metal (Li, Na, K, Rb, Cs) ions essentially affects the morphological, crystal, optical and electrical properties of Sb2S3 films. The structural and compositional analysis shows that the doping is in form of alkali metal‐sulfur chemical bond at both surface and grain boundaries of Sb2S3 films. Compared with the pristine Sb2S3, we observe that Li and Na doping are not able to improve the device efficiency, while K, Rb, and Cs notably increase energy conversion efficiency. The most effective enhancement is found in Cs‐doped Sb2S3, where the carrier concentration, crystallinity, and film formability show remarkable improvement. The device based on the Cs‐Sb2S3 film delivers a power conversion efficiency of 6.56%, which is the highest efficiency in planar heterojunction Sb2S3 solar cells, regardless of whether the films are fabricated by a solution process or thermal deposition. This research identifies that doping of heavy alkali metals is an effective approach to improve the performance of Sb2S3 solar cells.

High-pressure vibrational properties of dense rubidium

At ambient conditions, alkali metals adopt the body centered cubic structure, while if compressed up to tens of GPa and above, they exhibit complex low-symmetry modifications, due to the density-driven transition of the valence electrons from the $s$ state to states of higher angular momentum. These high-pressure, low-symmetry phases, whose unit cells may include up to tens of atoms, allow rich Raman activity, which was previously observed only in lighter alkalis Na and Li. Here we report an extensive study of the optical phonons of highly dense Rb up to 100 GPa in diamond anvil cells, conducted by challenging experimental Raman spectroscopy measurements and ab initio computer simulations. The relative (relative to the normal condition value) density behavior of Raman frequencies of Rb is compared to that of Na and Li, once the frequencies of the two light alkali elements have been rescaled by $\sqrt{{M}_{\mathrm{Na}}/{M}_{\mathrm{Rb}}}$ and $\sqrt{{M}_{\mathrm{Li}}/{M}_{\mathrm{Rb}}}$, respectively, where ${M}_{\mathrm{Na}}$, ${M}_{\mathrm{Li}}$, and ${M}_{\mathrm{Rb}}$ are the atomic masses of the here considered alkali elements. Importantly, while the rescaled density behaviors of Na and Li agree with each other, Rb significantly differs, which highlights the different nature of the valence electron transition being of the $s\text{\ensuremath{-}}d$ and of the $s\text{\ensuremath{-}}p$ type in heavy and light alkali metals, respectively, a result that calls for further similar investigations of K and Cs.