Metals Sr Research Articles

Development of highly oriented crystals in the magnetoplumbite structure of metal (Sr, Cr, Sc) doped M-type BaFe12O19 hexaferrite films with improved optical and magnetic properties

We have deposited magnetoplumbite (P63/mmc) structured Ba-hexaferrite (BaFe12O19) and its metal (T: Sc and Cr) doped (Ba0.7Sr0.3Fe12O19 and BaFe11.5T0.5O19) films on Si substrate using the Pulsed Laser Deposition technique. The as-grown films showed preferential orientation of the crystals along (2 0 3), (2 0 7), (1 1 14), and (4 0 5) directions. The post-heat treatment oriented the crystals only along (2 0 7) direction. The Fe ions varied it charge state from +3 at the surface of the films to a mixed charge state in the interior, which promoted a local clustering of Fe3O4-like phase. Ferrimagnetic properties of the hexaferrite films have been modified due to metal doping. The bi-phased magnetic structure, arising from clustering of the soft ferrimagnetic Fe3O4 phase in the matrix of hard ferrimagnetic hexaferrite films, is suitable for tuning the magnetic coercivity and moment over a wide range of temperatures. The optical band gap in the range of 3.40–3.50 eV and a strong magneto-optical Kerr signal are promising for potential applications of the films in magneto-optical devices working in UV regime of radiation.

EDTA-Assisted MPT-MS for Trace Analysis of Heavy Metals in Fireworks.

A novel method was developed for the rapid detection of heavy metals in firework solutions with high sensitivity and minimal pretreatment by enriching them with ethylenediaminetetraacetic acid (EDTA) reagent and analyzing them using microwave plasma torch mass spectrometry (MPT-MS). Quantitative results showed that the limits of detection and quantification for heavy metals (Pb, Ba, Sr, and Ag) ranged from 0.05 to 0.25 and 0.38 to 0.71 μg·L-1, respectively. The linear dynamic ranges covered at least two orders of magnitude, with correlation coefficients exceeding 0.99. Fireworks from five regions in China were also analyzed quantitatively, detecting heavy metals including Pb, Ba, Sr, and Ag, with recovery rates ranging from 87.9% to 107.5%. Good separation between the firework samples from different regions was achieved by using element ratios and principal component analysis (PCA). These results from the preliminary study showed that the EDTA-assisted MPT-MS combined with PCA is a powerful tool for characterizing firework samples and tracing them back to their sources, which is valuable to effectively regulate and manage banned fireworks.

Assessment of seasonal variations in soil heavy metal concentrations and potential health risks in Gujarat, India.

This study investigates the prevalence, distribution, and ecological consequences of 21 heavy metals (Ag, Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Li, Mg, Mn, Na, Ni, Pb, Sr, and Zn) in the soils between the Mahi and Dhadhar rivers in Gujarat, India. It aims to assess the seasonal variations in soil contamination and the potential human health risk associated with the heavy metal exposure through ingestion, inhalation, and dermal contact pathways. Soil samples were collected from 57 sites across three distinct seasons and analyzed using indices such as the geo-accumulation index, contamination factor, pollution load index, ecological risk factor, and global potential ecological risk. Human health risks were also evaluated for carcinogenic and non-carcinogenic effects. The findings reveal significant soil contamination, especially during the Monsoon and Post-Monsoon seasons, with heavy metals like Ag, Cd, Cr, Cu, Co, Ni, and Pb posing considerable ecological threats. Cr and Ni were identified as presenting the highest carcinogenic risks, while Fe and Cr posed major non-carcinogenic challenges. Seasonal variations significantly influenced heavy metal concentrations and distribution patterns. The study highlights the urgent need for comprehensive policies and sustainable practices to mitigate soil contamination and protect environmental health. It emphasizes the critical role of human activities, such as industrial, agricultural, and mining operations, in soil degradation and calls for increased community awareness and action to address these challenges.

Exploring enhanced syngas production via the catalytic performance of metal‐doped X‐Ni/CeO2 (X = Zr, La, Sr) in the dry reforming of methane

AbstractBackgroundThe quest to manufacture large amounts of syngas to bridge fossil fuels and the renewable energy ecosystem stimulates the creation of efficient and stable heterogeneous catalysts. The NiCeO2 catalysts, synthesized via ultrasonic‐assisted citric acid complexation, are highly efficient for the dry reforming of methane (DRM) reaction. Different promoter metals (Zr, La and Sr) were tested for catalytic performance and syngas production. A range of analyses, including X‐ray diffraction (XRD), N2 physisorption, H2 temperature‐programmed reduction, CO2 temperature‐programmed desorption, field emission scanning electron microscopy (FESEM), transmission electron microscopy and X‐ray photoelectron spectroscopy, were employed to characterize the physicochemical properties of the catalysts.ResultsXRD results indicated the formation of NiO, CeO2, solid solution ceria–zirconia, perovskite LaNiO3 and SrNiO3 crystalline phases. FESEM results showed the promoted catalysts (Zr, La, Sr) produce large pores to facilitate reactant diffusion, with zirconia specifically creating a spiderweb morphology. At 800 °C, the CH4 and CO2 conversions follow the sequence of NiCeO2 catalyst (CH4 = 54%, CO2 = 45%) < Sr/NiCeO2 (CH4 = 60%, CO2 = 67%) < La/NiCeO2 (CH4 = 85%, CO2 = 84%) < Zr/NiCeO2 (CH4 = 95%, CO2 = 87%). The integration of promoters in DRM catalysts has notably improved carbon formation resistance, as evidenced by the following ranking: Zr/NiCeO2 (5.1 wt%) < commercial catalyst (6.0 wt%) < La/NiCeO2 (7.85 wt%) < Sr/NiCeO2 (10.9 wt%) < NiCeO2 (11.3 wt%).ConclusionThis study demonstrates that incorporating promoters, particularly Zr, in NiCeO2 significantly enhances resistance to carbon formation. It offers valuable insights into selecting metal catalyst promoters for excellent catalytic performance in DRM. © 2024 Society of Chemical Industry (SCI).

Twin Peaks: Interrogating Otolith Pairs to See Whether They Keep Their Stories Straight

To tackle the question of the reliability of otoliths as recorders of individual life events, we compared the information enclosed in otolith pairs: the sagittae pair and the sagitta/lapillus pair. We used the synchrotron XRF scanning imaging method, which enabled the comparison of this information at both global and hyperfine scales. Using otoliths of diadromous pipefish, we compared element incorporation in each pair with a focus on (i) environment and transition between water bodies with strontium (Sr) and heavy metals, (ii) temporal information and age estimation based on sulphur (S) incorporation, and (iii) otolith growth and biomineralization processes with zinc (Zn). Results show that the global information in terms of Sr and heavy metals given by both otoliths of a pair is the same and that any otolith may be used to retrieve such global data. In terms of S-based growth increment counts, the numbers are the same between two otoliths of the same kind, but the sagitta/lapillus pairs show a significant difference. Hyperfine-scale analysis of element distribution reveals that a given otolith is under the control of specific growth mechanisms, which can lead to heterogeneous elemental incorporation. The present results lead us to consider otolith growth dynamics and biomineralization processes in the context of a fluid mosaic perspective.

Spatial variations and health risk assessment of heavy metal levels in groundwater of Qatar

The present work’s objective is to give a comprehensive overview of the quality of groundwater in Qatar in terms of heavy metals content as well as investigating the cause and effect of the elevation in their levels above the WHO/US-EPA standards. The scope of the study included (1) physical and chemical analysis of 82 groundwater samples collected from various locations around Qatar, (2) development of ArcGIS maps depicting the variations in the levels, (3) assessment of the human health risks associated with the existing levels using three of the most used models which are: Hazard index (HI), Nemerow comprehensive pollution index (NCPI) and Incremental Lifetime Cancer Risk (ILCR). There is no extensive study ever reported to assess the health risks linked with the consumption of groundwater characterized with such heavy metals levels in Qatar. The chronic daily intake (CDI) of the investigated heavy metals (Ag, Mn, Cr, V, Mo and Sr) through ingestion and dermal pathways had a range of 1.4 × 10–5–6.7 × 10–1 mg/kg/day while the NCPI’s range was reported at 0–4.39. Moreover, the HI and ILCR were found to have a range of 0–3.2 and 5.6 × 10–4–5.5 × 10–2, respectively. The assessment of health risks, conducted in the present work, could be beneficial in building the baseline of heavy metals levels in groundwater in Qatar. This will also help in the determination of any future contamination of groundwater.

Physical properties and power conversion efficiency of SrZrX3 (X=S and Se) chalcogenide perovskite solar cell

The search for efficient substances in energy conversion devices, which are low-cost, highly stable, and not hazardous to humanity has intensified among material scientists. Here, we have investigated the chalcogenide-based metal (Sr — strontium) perovskites in the context of developing materials. We have identified the electrical and optical features of these materials using the modified Becke–Johnson potential, revealing information about their nature. With computed values of 2.009[Formula: see text]eV for SrZrS3 and 1.096[Formula: see text]eV for SrZrSe3, respectively, they have shown to be direct bandgap semiconductors. We have also found that both materials exhibit transparency to the striking photon at low energy and demonstrate absorption and optical conduction in the UV region. These materials will be useful in thermoelectric devices because the transport property calculation shows that their figure of merit is unity at both low and high temperatures. In regard to applications, we determined the spectroscopic limited maximum efficiency (SLME) of SrZrS3 (SrZrSe3) and discovered that the efficiency increases from 6.3% to 22.3% (7.9% to 32%) when the film thickness is increased from 100[Formula: see text]nm to 1[Formula: see text][Formula: see text]m at 300[Formula: see text]K, after that it stabilizes. This research shows that these materials ought to be utilized as an alert substance in the design of energy conversion products, and the proposed results are supported by experimental and other theoretical data. We suggest that these substances are strong contenders for use in power conversion equipment depending upon their optical and transport characteristics.

Characterising the decay of organic metal complexes in speleothem-forming cave waters

Organic metal complexes (OMCs) transport trace metals (e.g., Co, Ni, Cu) from surface soils, via the unsaturated zone, to sites of cave carbonate (speleothem) formation. OMCs clearly imprint on speleothem trace element chemistry, but the role of kinetic factors in the signal transfer process has yet to be elucidated. We investigated whether OMCs may viably link metal concentrations in stalagmites and local hydrology (i.e., drip rate), via their time-sensitive dissociation (or ‘decay’) in the speleothem water thin-film. We performed competitive ligand exchange experiments using water and soil samples from eight geographically diverse Aotearoa New Zealand caves, providing a first comparative characterisation of speleothem-specific OMC kinetics. Critically, this approach corroborated that NOM ligands limit transition metal availability at the dripwater-speleothem interface, exhibiting stabilities on the order Cu ≈ Co > Ni, whereas organic complexation of the alkaline earth metals Mg and Sr was virtually absent. Systematic variations of OMC stability with natural organic matter characteristics were not observed amongst water samples, whilst enhanced complexation was clearly evident in the comparably organic-rich soil extracts. Our results imply that the supply of transition metals to speleothems is inversely related to drip rate, increasing with drip interval via the decay of OMCs. This process appears most sensitive on time-scales relevant to typical speleothem-forming settings (<0 to ca. 40 drips min−1, corresponding to ca. <5.6 mL min−1), and therefore provides a general, mechanistic link to a quantitative proxy of palaeoclimatic cave drip rates.

Alkaline earth metal modified La-Fe based perovskite enhances hydroxyl radicals for efficient coke cleaning

The low conversion rate of coke during online coke cleaning is due to the stable structure of graphite carbon, which makes it difficult to react with steam. Therefore, there is an urgent need to design a catalyst for catalytic graphite carbon conversion to achieve efficient in situ coke cleaning. Alkaline earth metal Sr modified La-Fe based perovskite LSF-x (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were prepared by hydrothermal method. DFT and experimental results indicate that doping Sr at the A-site reduces the adsorption energy barrier of water molecules, promotes the decomposition of water molecules to produce absorbed and free hydroxyl radicals, and thereby enhances the conversion of graphite carbon. At 900 °C, a catalytic coke conversion of 97.32% in the presence of La0.2Sr0.8FeO3 was achieved, which was 2.09 times the value without a catalyst. The research results provide a certain theoretical basis for catalytic heterogeneous reactions.

Exposure to Environmental Pollution in Schools of Puchuncaví, Chile: Characterization of Heavy Metals, Health Risk Assessment, and Effects on Children’s Academic Performance

In Chile, Puchuncaví and Quintero face substantial environmental pollution challenges. Industrial and vehicular emissions expose schoolchildren to elevated levels of pollutants, decreasing sustainability and posing risks to both their health and educational advancement. The aim of this study is to determine the distribution of heavy metals (Li, Be, V, Cr, Mn, Co, Ni, Zn, As, Se, Sr, Mo, Cd, Sb, Tl, Pb, and Cu) in the dust in and around the schools in these cities. We also evaluate the associated carcinogenic and non-carcinogenic risks, as well as whether their concentrations affect the academic performance (AP) of the students. The chemical composition of the collected dust samples is analyzed using positive matrix factorization, and two interpretable factors related to two sources of contamination (industrial and traffic + crustal) are determined. The health risk is assessed using a model including inhalation, dermal contact, and ingestion, and the influence of metal concentration on the AP of students is determined using an econometric model. The metal concentration is found to be related to the distance to the pollution source, and differences are observed between indoor and outdoor samples. The carcinogenic risk is low, while the non-carcinogenic risk is high in Greda School. The levels of heavy metals inside and outside the schools are found to influence AP. In these cities, children are exposed to high levels of environmental pollution, which may pose a risk to their health and impact their AP.

Modeling Hexaazacylcododeca Metal Complexes as a Radical Trapping Antioxidant: Prospects as a Potential Drug

AbstractFree radicals produced due to the disturbance in homeostasis bring about oxidative stress causing various diseases. This oxidative stress can be prevented by using antioxidants. In this article, a hexaazacylcododeca copper complex is reported as a radical‐trapping antioxidant (RTA). A detailed mechanistic study suggests that the designed complex is capable of trapping six radicals. The study confirms Path 6 as the most probable pathway, which is the radical addition to the ethene moiety of the complex. Moreover, it has a lower N−H bond dissociation enthalpy (BDE) than the recently reported bis(thiosemicarbazone) copper complex suggesting it could be a better antioxidant. In addition, the effect of different metals (Co, Fe, Pt, Ca, Ba, Sr, Au, Ag, Ni, and Zn) in their antiradical activity has been studied which suggests that among the studied metal complexes the Cu metal complex is the best metal complex for radical trapping. Further, the drug‐likeness is tested with the Lipinski filter along with the absorption, distribution, metabolism, and excretion (ADME) properties. Lastly, docking analysis tested against proteins responsible for ferroptosis shows that the modeled RTA can inhibit such diseases. Thus, it can be proposed that the designed RTA is a potential drug candidate.

Spin-Orbit Excitons in a Correlated Metal: Raman Scattering Study of Sr_{2}RhO_{4}.

Using Raman spectroscopy to study the correlated 4d-electron metal Sr_{2}RhO_{4}, we observe pronounced excitations at 220meV and 240meV with A_{1g} and B_{1g} symmetries, respectively. We identify them as transitions between the spin-orbit multiplets of the Rh ions, in close analogy to the spin-orbit excitons in the Mott insulators Sr_{2}IrO_{4} and α-RuCl_{3}. This observation provides direct evidence for the unquenched spin-orbit coupling in Sr_{2}RhO_{4}. A quantitative analysis of the data reveals that the tetragonal crystal field Δ in Sr_{2}RhO_{4} has a sign opposite to that in insulating Sr_{2}IrO_{4}, which enhances the planar xy orbital character of the effective J=1/2 wave function. This supports a metallic ground state, and suggests that c-axis compression of Sr_{2}RhO_{4} may transform it into a quasi-two-dimensional antiferromagnetic insulator.

Catalytic bi-reforming of methane as a potential source of hydrogen rich syngas: Promotional effect of strontium on the catalytic performance of Ni/MgO-ZrO2

Bi-reforming of methane (BRM) has gained significant attention due to escalating environmental concerns. This study investigates the performance of a monometallic Ni/MgO-ZrO2 catalyst with varying strontium (Sr) content ranging from 0 to 10 wt% added to the 10 wt% nickel, utilized in BRM. The synthesis of the MgO-ZrO2 support employed the co-precipitation method, while both Ni and Sr metals were added via impregnation route. The physiochemical properties of the prepared catalysts were analyzed using various characterization techniques such as X-Ray Diffraction (XRD), N2-Physisorption Analysis, Temperature-Programmed Reduction (TPR), Temperature-Programmed Desorption (TPD), X-ray Photoelectron Spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM). To assess catalytic performance, the catalyst was tested in a fixed-bed continuous reactor using a reactant mixture of CH4, H2O, and CO2 in a 3:2:1 ratio, respectively, at a temperature of 800 °C. The Ni-6%Sr/ZrO2-MgO catalyst provided optimal conversion rates for both CH4 and CO2 at 95.2% and 85.7% respectively, without significant deactivation observed even after 36 h of reaction. This excellent catalytic performance was attributed to several factors, including smaller metal particle size, improved metal dispersion, stabilization of the t-phase in zirconia and synergistic effects between the Ni and Sr particles. The spent catalyst characterization including XRD, FESEM and HRTEM revealed that the addition of Sr significantly reduced carbon deposition. It also demonstrated that stable and best performance of the Ni-Sr/MgO-ZrO2 catalyst is ascribed to the production of filamentous carbon with a crystalline nanotubular structure. Conversely, the rapid deactivation of the Ni/MgO-ZrO2 monometallic catalyst may be attributed to amorphous carbon.

Alkali metal and alkali earth metal-modified La-Fe-based perovskite catalyzed coke combustion

Coke catalytic gasification is an efficient method of burning coke. The core of this technology is the preparation of efficient and stable catalysts. A series of different type La-Fe-based perovskite catalysts, including ABO3 (La1-xSrxFeO3, LaK0.04Sr0.25FeO3), R-P (LaK1.7Sr0.2Fe1.7O6) and A2B2O6 (LaKSr0.17Fe1.5O6, LaKSr0.2Fe1.8O6) were prepared by sol-gel method and calcination of metal-organic framework (MOF) precursor method. The activity of perovskite catalytic coke was tested by thermogravimetric analysis and tubular reactor. Among them, LaKSr0.17Fe1.5O6−MOF has the best catalytic activity, with T10, T50, and T90 values of 610.65 °C, 666.86 °C, and 705.84 °C, respectively. LaKSr0.17Fe1.5O6−MOF not only improves coke conversion but also reduces reaction temperature. DFT and experimental results show that doped K and Sr metals promote the formation of many active sites (oxygen vacancies) on the surface of LaKSr0.17Fe1.5O6−MOF, which reduces the adsorption energy of O2 molecules, realizes the oxygen exchange kinetics. The oxygen release regeneration process is achieved between perovskite lattice oxygen and O2 molecules. These processes synergistically promote coke conversion. In addition, it also has strong stable regeneration performance. These results provide a promising strategy for designing and preparing efficient and low-cost catalysts for the practical application of coke removal.

Spatial and seasonal variability of dissolved metals in a monsoonal estuarine environment

Distribution of metals in estuarine surface water reflects their respective sources and abundances in the fresh- and marine- water end-members, mixing processes and ability to take part in various geochemical reactions prevailing in the transitional zone. However, these elements tend to show complex geochemical behaviour, which varies both within and among different estuaries. This makes it difficult to delineate a universal distribution pattern. In this study, the behaviour of multiple dissolved metals (Sr, Ba, Fe, Mn, Mo, V, Co, Cr, Cu, Ni, Zn, U and Pb) have been evaluated in a tropical monsoonal estuary located on the east coast of India during summer (May, 2018), monsoon (September, 2018) and winter (February, 2019) season. Concentration of Sr, Mo, V, Cu and U increases towards the mouth of the estuary, whereas, Ba, Fe, Mn, Pb and Cr concentration shows a declining trend along increasing salinity gradient. All the elements show non-conservative behaviour in the estuary during at least one season within the studied period. Rapid removal of Fe and Mn takes place in the low salinity region, whereas, Mo, V, Pb and U get removed in the low- to mid- salinity zone of the estuary as a result of salinity-induced flocculation. A pronounced mid-estuarine maxima is exhibited by Ni and Zn. Barium shows peak concentrations in the low salinity region. Spatial variation in the occurrence of Ba maxima along the salinity gradient exists between the low and high discharge periods. Seasonally, highest concentration of Sr, Mo, V and U are found in the summer, followed by winter and monsoon. On the other hand, Ba, Fe, Mn, Co, Cr, Cu, Ni and Zn exhibit the highest concentrations during the monsoon period as a result of increased inputs from fluvial sources. The intrusion of seawater during the dry seasons and dilution during monsoon, which shows the highest freshwater discharge, are responsible for the seasonal variations. Thus, this study highlights the variability in distribution of elements as well as the differences in the behaviour of individual elements under contrasting environmental conditions within an estuary.

Dynamics of pollutants accumulation in the snow of an urban agglomeration

Snowpack properties allow using snow as a convenient indicator of atmospheric air pollution, precipitation, and eventually soil pollution. There is a high probability of trace elements and organic pollutants accumulation on the snow cover acting as the deposit matrix. In this study, we analyzed the dynamics of the content of metals (Ca, Mn, Fe, Zn, Sr, Pb and Ba) in filtered and unfiltered samples and the content of polyaromatic hydrocarbons (18 basic PAHs) in weekly snow sampling in the city and nearby. The obtained results were collated with the content of the same contaminants in the snow sampled layer by layer at the end of the season (layer thickness was 0.1 m). In result of the study, we concluded that the sampling should be carried out right after the precipitation for the purpose of atmospheric pollution estimation, because most of heavy metals migrate through the snow layers into soil cover and get lost by the end of the season. The organic pollutants, such as PAHs, are also lost. The sampling of snow during the whole season allows identifying the global and local sources of contaminants released into the atmosphere.

An electrolysis–displacement–distillation approach for the production of Li, Mg, Ca, Sr, and Ba metals

This paper describes a new advancement in the field of green energetic metal production, a finding that unlocks access to extracting Li, Mg, Ca, Sr, and Ba metals that are hitherto produced with the generation of Cl2 and heavy CO2.

Emergence of superconductivity by intercalation of alkali metals and alkaline earth metals in Janus transition-metal dichalcogenide heterostructures.

Superconductivity in two-dimensional materials has attracted considerable attention. A new material belonging to the family of Janus transition metal dichalcogenides with out-of-plane structural asymmetry has been recently found to show interesting physical and chemical properties. Using density functional theory and density functional perturbation theory, within the generalized gradient approximation with van der Waals correction, we performed a detailed investigation of the electronic structure, phonon dispersion, Eliashberg spectral function, and electron-phonon coupling of Janus MSSe bilayers (M = Mo or W) and the Janus MoSSe/WSSe heterostructure intercalated with alkali metals (Li, Na, and K) or alkaline earth metals (Mg, Ca, and Sr). We found that the Janus MoSSe bilayer, Janus WSSe bilayer, and Janus MoSSe/WSSe heterostructure transform from a direct band gap semiconductor to a metal or semimetal due to charge transfer from intercalated atoms to the Se and S planes. We showed that all compounds are dynamically stable conventional superconductors. In addition, the Janus heterostructure MoSSe/WSSe intercalated with K exhibits the highest electron-phonon coupling of about 2.12 and the highest superconducting transition temperature of about 14.77 K. Our results indicate the potential application of the Janus materials we investigated in superconductivity.

Investigation of the antibacterial activity of synthesized hydroxyapatite Sr-doped nanocomposite

Hydroxyapatite is a mineral compound with a composition resembling the components found in human teeth and bones. Hydroxyapatite possesses osteoconductive, bioactive, and biocompatible characteristics. Nevertheless, hydroxyapatite has limitations, particularly its limited antibacterial activity. Therefore, this research uses the sol-gel method to synthesize and characterize strontium hydroxyapatite doped composites (HAp-Sr doped composites). The calcium precursor used in this research comes from the green mussel shells (Perna viridis); the main component is CaCO3, which will later be converted into CaO compounds. HAp Sr-doped composites were synthesized by varying the concentration of Sr metal (5%, 10%, and 20% w/w), which aimed to determine its good antibacterial ability. The X-ray fluorescence analysis reveals that green mussel shells contain 97.261% calcium oxide (CaO). The X-ray diffraction analysis reveals that the pattern observed at an angle of 2θ corresponds to the hydroxyapatite standard from ICDD (No.96-101-1243), which possesses a hexagonal structure. The Fourier transform infrared spectroscopy spectra reveal the presence of PO43− groups in the sample at wave numbers 528 cm−1, 604 cm−1, 945 cm−1, and 1,018 cm−1. The antibacterial activity of the HAp-Sr doped composite was evaluated against Staphylococcus aureus and Escherichia coli bacteria. The results indicated that the 5% HAp-Sr doped composite exhibited antibacterial activity. Therefore, it can potentially be utilized in bone grafts and implants.

Transition Metal Behavior of Heavier Alkaline Earth Elements in Doped Monocyclic and Tubular Boron Clusters.

Quantum chemical calculations are carried out to design highly symmetric-doped boron clusters by employing the transition metal behavior of heavier alkaline earth (Ae = Ca, Sr, and Ba) metals. Following an electron counting rule, a set of monocyclic and tubular boron clusters capped by two heavier Ae metals were tested, which leads to the highly symmetric Ae2B8, Ae2B18, and Ae2B30 clusters as true minima on the potential energy surface having a monocyclic ring, two-ring tubular, and three-ring tubular boron motifs, respectively. Then, a thorough global minimum (GM) structural search reveals that a monocyclic B8 ring capped with two Ae atoms is indeed a GM for Ca2B8 and Ba2B8, while for Sr2B8 it is a low-lying isomer. Similarly, the present search also unambiguously shows the most stable isomers of Ae2B18 and Ae2B30 to be highly symmetric two- and three-ring tubular boron motifs, respectively, capped with two Ae atoms on each side of the tube. In these Ae-doped boron clusters, in addition to the electrostatic interactions, a substantial covalent interaction, specifically the bonding occurring between (n - 1)d orbitals of Ae and delocalized orbitals of boron motifs, provides the essential driving force behind their highly symmetrical structures and overall stability.