Substitution Of Divalent Cations Research Articles

Effect of divalent cations (Co2+ and Ni2+) on microstructure, physical properties and application of Nd

The nanocrystalline samples Nd1–xMxFeO3 (x = 0.0 and 0.1; M: Co2+ and Ni2+) were prepared using the citrate combustion method. The X-ray diffraction (XRD) pattern confirmed that the nanoparticles were synthesized in an orthorhombic structure. The particle size of Nd1–xMxFeO3 is in the range of 29–59 nm. The selected area electron diffraction (SAED) indicates the samples were prepared in a polycrystalline nature. The samples Nd1–xMxFeO3 (x = 0.0 and 0.1; M: Co2+ and Ni2+) have antiferromagnetic behavior. The Fe3+ spins are aligned antiparallel, forming the antiferromagnetic (AFM) properties, which are affected by many factors such as the bond angle between the Fe3+ (Fe3+–O2––Fe3+) and the Dzyaloshinskii-Moriya (D-M) interaction. The doping of Co2+ and Ni2+ ions in NdFeO3 enhances the magnetic properties of the NdFeO3. The saturation magnetization (Ms) of Nd0.90Co0.10FeO3 increases 1.8 times more than that of NdFeO3. The exchange bias field (HEX) of the Co-doped sample is two times greater than that of NdFeO3. The magnetic anisotropy constant (K) of the 10 % Co-doped sample increases by 11 factors compared to that of NdFeO3. The Tauc plot illustrates that the samples have a direct optical transition. The divalent cation substitution (Co2+ and Ni2+) decreases the optical band gap of NdFeO3, leading to the recommendation of using the samples Nd0.90Co0.10FeO3 and Nd0.90Ni0.10FeO3 in photocatalysis of dye degradation from water. The removal efficiencies of Cr6+ at pH = 6 are 88.06 %, 85.54 %, and 85.52 % for the samples NdFeO3, Nd0.90Co0.10FeO3, and Nd0.90Ni0.10FeO3, respectively. The Freundlich isotherm mode is the best-fit model for NdFeO3 to adsorb Cr6+ ions from aqueous solutions.

Discerning the crystal structure and engineering the optoelectronic properties through substitution of divalent cations (M= Zn, N = Ge) in C3H3MxN1-xI3 for solar cell applications

Herein, we identified the ground state crystal structures of C3H3ZnxGe1-xI3 hybrid perovskite materials and investigated their optoelectronic properties for the first time using van der Waals correction, included ab initio calculations with hybrid functionals. The energy difference and formation energy calculations are done to perceive the information related to their structural phase transition and stability. Chemical bonding between the atomic constituents are found from charge density distribution, projected crystal orbital Hamiltonian population (pCOHP) and its integration (IpCOHP) results. Our electronic structure calculations predict the compositions with x = 0, 0.25, 0.5, 0.833 as indirect band gap materials and x = 0.667 and 1 as direct band gap materials. Our results also predict that the composition with x = 0.833 value belongs to the classification of intermediate band gap semiconductor. The effective mass of holes and electrons are calculated at valence and conduction band edges, respectively, to realize the transport property of carriers. The absorption coefficient calculations infer that composition with x = 0.667 shows better optical absorption property in the visible region compared to other compositions. The applicability of these materials towards solar cell device performance is explored by calculations of cell parameters and it is found that the power conversion efficiency is higher for the composition with higher Ge concentration than Zn. Specifically, low PCE values in the range of 8.66–17.32% corresponds to C3H3Zn0.833Ge0.167I3 and high PCE values in the range of 16.52–33.04% corresponds to C3H3Zn0.5Ge0.5I3.

A high-pressure structural transition of norsethite-type BaFe(CO3)2: Comparison with BaMg(CO3)2 and BaMn(CO3)2

Abstract Investigations on the phase stability of the norsethite-type family [BaMg(CO3)2, BaMn(CO3)2, BaFe(CO3)2] under high-pressure conditions are of great significance for understanding the structure and metal cationic (Mg2+, Fe2+, Mn2+) substitution mechanism in double divalent metal carbonates. The structural evolution and equation of state of BaFe(CO3)2 were studied at high pressure up to ~7.3 GPa by synchrotron X-ray diffraction (XRD) in diamond-anvil cell (DAC) in this study. BaFe(CO3)2 undergoes a reversible phase transition from R3m (α-phase) to C2/c (γ-phase) space groups at ~3.0 GPa. The fitted elastic parameters are V0 = 377.79(2) Å3 and K0 = 40.3(7) GPa for α-BaFe(CO3)2, V0 = 483.24(5) Å3 and K0 = 91.2(24) GPa for γ-BaFe(CO3)2 using second-order Birch-Murnaghan equation of state (BM2-EoS). Besides, the vibrational properties and structural stability of complete norsethite-type minerals were also investigated first by Raman spectroscopy combined with DAC up to 11.1 GPa. Similar structural phase transitions occur in BaMg(CO3)2, BaFe(CO3)2, BaMn(CO3)2 at 2.2–2.6, 2.6–3.7, and 3.7–4.1 GPa, respectively. The onset phase transition pressures of the norsethite-type family are much lower than that of dolomite-type Ca(Mg,Fe,Mn)(CO3)2 and calcite-type (Mg,Fe,Mn)CO3 carbonates. These results provide new insights into the divalent cation substitution effects on the stability and structural evolution of carbonates under high-pressure conditions.

Optical, Structural, Morphological, Antibacterial, and Photodegradation Characteristics of BaxMg0.8−xFe2O4(x = 0.2, 0.4, and 0.6) Nanocrystalline Powders Synthesized by Combustion Method

Herein, a series of barium‐doped magnesium ferrites [BaxMg0.8−xFe2O4(x = 0.2, 0.4, and 0.6)] with metal nitrates and egg white solution are prepared to show how simultaneous substitution of divalent cations affects the structural, morphological, antibacterial, and photocatalytic capabilities of ferrites. A cubic spinel and hexagonal structures are discovered through a wide particle size dispersion in the sample. The infrared (IR) spectra of the octahedral and tetrahedral sites exhibit two prominent absorption bands about 576 and 450 cm−1. With increasing Ba2+doping, the optical band gaps decreased from 6 to 5.6 eV. The elemental analysis of Ba, Mg, Fe, and O is confirmed using energy dispersive X‐ray spectroscopy (EDX) analysis. High‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies reveal the formation of spherical nanoparticles along with some hexagonal structures. For antibacterial studies, BaxMg0.8−xFe2O4nanoparticles are tested against Gram‐positive and Gram‐negative bacteria. The photodegradation test of the produced nanoparticles for the degradation of Congo red and methylene blue dyes is examined under ultraviolet (UV) light irradiation.

Enhanced removal performance and mechanistic study of Cu2+, Cd2+, and Pb2+ by magnetic layered double hydroxide nanosheets assembled on graphene oxide

Devising effective measures for removing heavy metals from water has become a serious concern. In this study, MgAl-layered double hydroxide nanosheets were assembled on graphene oxide (GL) and its magnetic product (Fe3O4@GL) as excellent adsorbents for Cu2+, Cd2+, and Pb2+ and were synthesized by a simple hydrothermal method. The morphology and surface chemical properties were observed to establish the construct-activity relationships. The characterization results showed that the adsorbents combined rich functional groups with large specific surface areas. The effective removal of heavy metals by GL and Fe3O4@GL was achieved under neutral and weakly alkaline conditions. The pseudo-second-order kinetic equation described the experimental results well, and the equilibrium data were in good agreement with the Freundlich model for Cu2+ and Cd2+ and the Langmuir model for Pb2+. The maximum adsorption capacity of GL (Cu2+: 89.26 mg/g, Cd2+: 76.67 mg/g, Pb2+: 226.98 mg/g) was slightly larger than that of Fe3O4@GL (Cu2+: 80.72 mg/g, Cd2+: 70.26 mg/g, Pb2+: 213.96 mg/g). The main mechanisms include the surface complexation of hydroxyl groups, precipitation reactions of metal hydroxides and metal carbonates, and isomorphic substitution of divalent metal cations. Thus, the enhanced adsorption capacity and mechanistic study provide new insights into the environmental remediation of heavy metals.

Sol–Gel Auto-combustion Preparation of M2+ = Mg2+, Mn2+, Cd2+ Substituted M0.25Ni0.15Cu0.25Co0.35Fe2O4 Ferrites and Their Characterizations

Cost-effective and controllable synthesis of M0.25Ni0.15Cu0.25Co0.35Fe2O4 (M2+ = Mg2+, Mn2+, and Cd2+) ferrites via the sol–gel auto-combustion technique. The impact of divalent cations on the structural, dielectric, and optoelectrical properties of ferrites was examined by XRD, FTIR, Raman, LCR, UV–Vis, and two probe I-V measurement techniques. The crystallite size was 52.66 nm, and the minimum specific surface area was observed 5.1507 m2/g for Mg2+ doped NCCF ferrite. The FTIR and Raman analysis also confirmed the substitution of divalent cations (M2+ = Mg2+, Mn2+, and Cd2+) at their respective lattice sites. The maximum energy bandgap was 1.67 eV Mg2+-doped NCCF ferrite as compared to other divalent ion-doped ferrites. The dielectric loss decreased while the ac conductivity increased with increasing frequency, and the minimum values were observed for Mg2+-doped NCCF ferrite. The activation energy was observed maximum for Mg2+-doped NCCF ferrite (0.2234 eV). Due to incredible properties including small specific surface area, large energy band gap, high resistivity, and loss dielectric loss of Mg2+-doped NCCF ferrite have potential applications in different fields.

Influence of ternary divalent cations (Mg2+, Co2+, Sr2+) substitution on the physicochemical, mechanical and biological properties of carbonated hydroxyapatite scaffolds

Substitution of ionic either anion or cation in a controlled amount into carbonated hydroxyapatite (CHA) structure is one of the efficient and safest ways in enhancing the properties of the materials. However, most of the works studied only focused on the physical and mechanical properties of single ionic substitution. For the first time, the influence of simultaneous ternary substitutions of divalent cations into porous CHA scaffolds on the physicochemical, mechanical, degradative, and in vitro biological properties is investigated in the present study. Three different compositions of porous scaffolds with binary and ternary divalent cations, namely, pure CHA (S11), CoSr CHA (S21), and MgCoSr CHA (S31) were fabricated using a polyurethane (PU) foam replication technique. Despite a small amount of Mg2+, Co2+, and Sr2+ being added, these divalent cations had successfully substituted into the Ca2+ site and remained as single-phase B-type CHA. The produced scaffolds demonstrated open, interconnected, and uniform pores. Interestingly, simultaneous ternary divalent cation substitution into CHA structure had successfully enhanced the compressive strength of the sintered scaffolds and also promoted better cell attachment and activities than the binary doped- and pure CHA scaffolds. It is important to note that choosing the right divalent cation can be the determining factor in tuning the physicochemical, mechanical, and biological properties of CHA scaffolds.

Preparation and characterisation of green nano-sized ceramic pigments with the spinel structure AB2O4 (A = Co, Ni and B = Cr, Al)

Inorganic pigments based on AB2O4 (A = Co, Ni; B = Cr, Al) spinel structures with green colour were successfully synthesised by the polymeric route. The effect of the substitution of trivalent and divalent cations on the structural, optical and morphological properties of the pigments was investigated. The synthesised nanopowders were examined using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller analysis (BET), UV–vis diffuse reflectance measurements, and CIEL*a*b* colorimetric analyses. The results show that the CoCr2O4 spinel and the spinels substituted by nickel and aluminium cations were obtained with a single phase after heat treatment at 900 °C. The produced powders present shades of the green colour with improvement in morphology for the substituted samples. The Ni0·5Co0·5CrAlO4 nanoparticles consisted of grains of quasi-spherical shape with sizes between 50 and 75 nm. This powder was used in small quantities with glazes for colouring tests on the surfaces of ceramic substrates.

Insight into effects of divalent cation substitution stabilizing P2-Type layered cathode materials for sodium-ion batteries

Manganese-based P2-type cathodes appear to be promising candidates in practical applications of sodium-ion batteries owing to their low cost, exciting electrochemical performance, and feasibility for commercial production. However, the P2-type cathode usually suffers from undesired P2-O2 phase transition at high voltage during Na+ extraction which leads to a poor cycle life. Although their stability is greatly improved with elements substitution, the rationale behind still needs to be understood. Divalent cation substituted P2-type Na0.67Ni0.23Mn0.67M0.1O2 materials were explored considering the similar ionic radii and same valence state. The substitution of divalent cations in P2-type cathodes enlarges the lattice parameters. Both Mg2+ and Cu2+ substitutions effectively improve cycling performances and suppress the P2-O2 phase transition. A combination of electrochemical profiles and in-situ X-ray diffraction analysis reveals the solid-solution reactions during Na+ extraction and insertion. Besides, fast Na-ion diffusion in the Mg-substituted P2-NaNM material leads to its high rate capability. Therefore, this study may give a new insight into the rational design of cathode materials with stable structure and high capacity for sodium-ion batteries.

Water versus Asphaltenes; Liquid\u2013Liquid and Solid\u2013Liquid Molecular Interactions Unravel the Mechanisms behind an Improved Oil Recovery Methodology

Understanding of possible molecular interactions at liquid-liquid and solid-liquid interfaces can shed lights onto the nature’s design and authorise fine manipulation aptitude in biological, manufacturing, microfluidic and oil recovery applications. Of particular interest is the capability to control the aggregation of organic and biological macromolecules, which typically poses significant challenges for oil industry and human life, respectively. Following asphaltene aggregation phenomenon through π-stacking and hydrogen bonding interactions, asphaltene aggregates can form a thin layer at the crude oil-brine interface through noncovalent interactions such as -O-H···O hydrogen bonds and/or alter the wettability state of the solid surface from initially water-wet into mixed-oil wetting. Here, we probe the impact of water with variety of salinities and ion types on formation of water in oil micro-emulsions, asphaltene deposition, and induced water wettability transition at micro scale. For the first time we investigate the influence of water in oil micro-emulsions on asphaltene aggregation and deposition phenomena at elevated pressure and temperature conditions. We also monitor the micro-wettability alterations of gold surface of the QCM owing to ion valency/concentration changes using state of the art ESEM imaging facility. Our results depict that owing to the substitution of divalent cations with monovalent ones, asphaltene deposition is repelled and the solid surface becomes more hydrophilic, proposing a generalizable strategy to control wettability and an elucidation for the profitability of so-called low salinity water flooding, an enhanced oil recovery methodology. For the biological applications, this study provides insights into the potential roles of ions and hydrogen bonds in the protein deposition in tissues and self-assembly interactions and efficiency of drugs against protein aggregation drivers.

Ionic Liquid-Assisted Hydrothermal Synthesis of a Biocompatible Filler for Photo-Curable Dental Composite: From Theory to Experiment.

Nanostructured hydroxyapatite (HA) is a new class of biocompatible fillers which has been recently utilized in bio hybrid materials by virtue of its excellent tissue bioactivity and biocompatibility. However, the need for higher thermal stability, solubility, surface bioactivity, radiopacity, and remineralization ability suggests a divalent cation substitution of HA for use in light curable dental restorative composites. In this work, structural and optical properties of Sr-doped hydroxyapatite were studied using first-principle calculations based on density functional theory (DFT). Next, Sr-doped hydroxyapatite (HA) was prepared via a new ionic liquid-assisted hydrothermal (ILH) route. Samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET) surface area analysis, and cell viability. The obtained experimental data showed that the nucleation and crystal growth process controlled by [BMIM]Br molecules results in uniform products with small and regular particles and high specific surface areas. Finally, cytotoxicity tests showed that the as-prepared Sr-doped HA nanoparticles have good biocompatibility (≥91%), confirming their potential for use in photo-curable dental restorative composites.

The influence of simultaneous divalent cations (Mg2+, Co2+ and Sr2+) substitution on the physico-chemical properties of carbonated hydroxyapatite

Bone is generally known as calcium-apatite which contains considerable amounts of various trace elements, mainly carbonate. Thus, bone is usually referred as carbonated hydroxyapatite (CHA). The incorporation of dopants into calcium-apatite has been proposed. This approach provides a safer and efficient platform for enhancing bone remodelling. However, reports that emphasize on the influence of multi-dopant substitutions into the CHA structure particularly in the form of as-synthesized powders are limitedly available. The present study investigates the influence of simultaneous substitution of divalent cations, Mg2+, Co2+ and Sr2+ into CHA structure by a nanoemulsion method. Several combinations of ions were doped into the CHA structure. The XRD and FTIR results confirmed that the phase purity and crystallinity were not affected by the simultaneous incorporation of multi-doped ions; all powders remained as amorphous B-type CHA. Despite the small amount of dopants used, all the three cations were successfully substituted into the Ca2+ site of CHA structure. The crystallite size of the as-synthesized powder decreased as the amount of incorporated dopants increased. Interestingly, the particle shape showed the transformation from near spherical structures into needle-like structures with increasing amount of dopants. Our finding highlights that the incorporation of these cations into the CHA structure results in crystal imperfections, which cause a substantial dislocation of the crystal lattice, as seen by the alteration of the lattice parameters, crystallite and particle sizes of the as-synthesized powders.

Multiscale structural modulation of layered double hydroxide nanosheets and their application in solar-driven catalysis

Due to the high photocatalytic efficiency in activating chemical bonding under mild reaction conditions, photocatalysis has been acted as a green and promising technology. However, how to improve the quantum efficiency and solar energy utilization to further enhance the photocatalytic performance remains a challenge, and it is highly desirable to rational synthesize photocatalyst with suitable energy band structure, and efficient active sites. Layered double hydroxides (LDHs) is a kind of two-dimensional materials, with molecular formula [M12-+ x M x 3+(OH)2] x + [A x / n ] n -·mH2O. The layered structure of LDHs is similar to brucite Mg(OH)2, which is connected by the octahedral MO6 sites. The substitution of divalent metal cations (M2+) with trivalent metal cations (M3+) makes the layers positively charged, in which M2+, M3+ can be as one or more of the elements such as Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, In, etc. M2+, M3+ ions alternately arrange in the main layers at a high atomic level to form the planar structure ( a , b axis direction), and the alternation of the positively charged layers and the negatively charged anionic layers ( c axis direction) constitute the three-dimensional structure of LDHs. There are many unique structural characteristic of LDHs, such as the high dispersion of the metal elements in the layers, the controllable particle size and thickness, topological transformation and so on. The above properties have provide LDH as photocatalysts as the followings reason. Firstly, the metal elements of LDHs are arranged in an alternating order at the atomic level with flexible compositions (such as Fe, Co, Ni, Ti, etc.), and can be directly used as photocatalysts due to the tunable band gap. Secondly, the topological transformation property can turn LDH materials into heterogeneous mixed metal oxides or highly supported metal-containing catalysts, which are not easily agglomerated even under reaction condition. Thirdly, based on the tunable particle size and thickness of LDHs, it is possible to adjust the morphology of LDHs into nanoscale, which can fully expose the active sites and enhance the catalytic performance. Based on the abundant adjustable properties of LDHs, the following structures can be well optimized, such as their composition, particle sizes, defects, abundant interfaces, the high dispersion characteristics, and tunable energy band structures, etc. by using LDHs as catalysts for the potential enhanced catalytic efficiency. In this review, in order to activate H ˗ O, C = O, NN and C ˗ C bonds under mild condition, a series of LDH-based photocatalysts have been finely synthesized (like NiTi-LDH nanosheets, ZnAl-LDH, CoFe alloy derived from LDH, Co/Fe-hetrostructure derived from LDH, Cr-containing LDH, etc.), and widely applied in solar-driven water splitting, CO2 reduction, CO hydrogenation to high carbon hydrocarbons, ammonia synthesis, degradation and so on. Collectively, with the multiscale structural regulation of the microstructure, mesoscopic interfacial structure and highly dispersed metal-supported structure, the following properties such as the band gap, defect and the interface of LDH-based photocatalysts can be well modulated, and the solar-driven catalytic performance are demonstrated to be comprehensively facilitated. Furthermore, the relationship among the preparation, structure and catalysis has been well discussed, which will provide a strategy for the rational design of efficient photocatalysts.

Structural and Magnetic Properties of Sn4+ Doped Strontium Hexaferrites Prepared via Sol–Gel Auto-Combustion Method

Sn–Zn–Co-substituted strontium M-type hexaferrite SrZn x Co x Sn2 x Fe12–4xO19 ( $x =0.0$ , 0.3, 0.5, and 0.7) was synthesized via modified sol–gel auto-combustion method. A microwave device was used to obtain the finest particles and to complete the combustion process. By substitution of tetravalent and divalent cations instead of iron, magnetic and structural properties of M-type hexaferrite were changed. So, the effects of Sn4+, Zn2+, and Co2+ doping on the structure and magnetic characterization of M-type hexaferrite were investigated. The Fourier transform infrared spectroscopy revealed bands at 430 and 590 cm−1, related to the stretching vibrating bonds of Fe–O. The X-ray diffraction analysis showed that all samples prepared were of P63/mmc symmetry and average crystal size of 68 nm. Field emission scanning electron microscopy analysis revealed the hexagonal plateletlike shape of all samples. Vibrating sample magnetometer results showed that by increasing the dopants content, coercivity ( $H_{c}$ ), and saturation magnetization ( $M_{s}$ ) changed drastically. Saturation magnetizations decreased during dopants displacement and then reach to the highest value (65.46 emu/g) at $x = 0.5$ then increasing of dopants to $x = 0.7$ , cause the reduction of $M_{s}$ (56.13 emu/g). Coercivity diminished by dopant substitution and the semi-hard samples were received as an alternative to the hard hexaferrite.

P-bearing Olivines from the “Luna-20” Soil Samples, Their Sources and Possible Phosphorus Substitution Mechanisms in Lunar Olivine

Rocks with P-bearing olivine were found in soil samples delivered by the “Luna-20” automated station. They are ascribed to the highland anorthosite–norite (more rarely, gabbro-norite)–troctolite rock series enriched in phosphorus and other incompatible elements, but are not related to typical KREEP rocks enriched in incompatible elements. Their source is presumably of hybrid origin and related to primary high- Mg suite (HMS) rocks. The occurrence of high- and low-Cr populations of P-bearing olivine in different structural rock types can be attributed to the annealing-related more rapid chromium diffusion (relative to that of phosphorus) in olivine from metamorphosed rocks. This assumption is supported by stoichiometric formula calculations of these olivines. An alternative explanation for these olivine populations is their derivation from at least two different sources. Disequilibrium crystallization of the P-bearing olivines, which is confirmed by an intricate phosphorus zoning, excludes the existence of P-rich melts, which is consistent with previous observations. At the same time, olivine fractionation can be responsible for the phosphorus content in lunar melts. The incorporation of phosphorus in olivine of the “Luna-20” anorthosite troctolites is presumably controlled by a coupled substitution mechanism of divalent cations and silicon for phosphorus and chromium in the tetrahedral and octahedral sites (Milman-Barris et al., 2008). Another possible mechanism is the substitution of divalent cations in octahedral sites by phosphorus and chromium, which provides the possible presence of P3+.

Tailoring magnetic properties of cobalt ferrite nanoparticles by different divalent cation substitution

Different divalent cation substituted Co-ferrite (MXCo1−XFe2O4, where M = Mg2+, Ni2+, Cu2+, Zn2+, with x = 0.20 and 0.75) nanoparticles were synthesized by sol–gel method and were annealed at 900 °C in air. After annealing, grain growth was observed for all the samples. With the substitution of Mg2+, Ni2+ and Cu2+ with x = 0.20, the magnetization of the as-prepared and the annealed samples was decreased from that of the Co-ferrite whereas Zn2+ substitution enhanced the magnetization. The highest magnetization values of 79.9 and 92.9 emu/g at 300 and 60 K respectively were observed for the Zn2+ substituted annealed sample with x = 0.20. For higher concentration of x = 0.75, the magnetization value was further decreased in all the samples and the lowest magnetization value of 5.1 emu/g was observed in the Zn2+ substituted annealed sample with x = 0.75 at 300 K. The coercivity was reduced in the samples except for the Cu2+ substituted sample. In the Cu2+ substituted sample with x = 0.75, the highest coercivity of 1.43 kOe at 300 K was observed after annealing. The changed cation distribution in the spinel structure, ionic magnetic moment and anisotropy compared to the Co2+ in these nanomaterials can explain the observed magnetic properties.

Structural influence of mixed transition metal ions on lithium bismuth borate glasses

Lithium bismuth borate glasses containing mixed transition metals having composition 7CoO·23Li2O·20Bi2O3·50B2O3 (CLBB), 7V2O5·23Li2O·20Bi2O3·50B2O3 (VLBB) and x(2CoO·V2O5)·(30 - x)Li2O·20Bi2O3·50B2O3 (x = 0.0 (LBB) and x = 2.0, 5.0, 7.0, 10.0 mol% (CVLBB1-4)) are synthesized via melt quench route. The synthesized compositions are investigated for their physical properties using density (D) and molar volume (Vm), thermal properties by analyzing DSC/TG thermo-graphs, structural properties using IR absorption spectra in the mid-IR range and optical properties using UV–Vis–NIR spectroscopy. The Electron Paramagnetic Resonance (EPR) spectra of vanadyl and cobalt ion have been analyzed to study compositional effects on spin-Hamiltonian parameters. The non linear variations in physical properties depict a strong structural influence of Co/V- oxides on the glassy matrix. The compositional variations in characteristic temperatures (glass transition temperature Tg, glass crystallization temperature Tp and glass melting temperature Tm) reveals that Tg for glass samples CLBB is relatively less than that of pure lithium bismuth borate (LBB) glass sample wherein Tg for sample VLBB is higher than that of LBB. The increase in Tg (as compared with LBB) with an enhanced substitution of mixed transition metal oxides (2CoO·V2O5) shows a progressive structure modification of bismuth borate matrix. These predictions are very well corroborated by corresponding compositional trends of Tp and Tm. FTIR studies reveal that Co2+& VO2+ ions lead to structural rearrangements through the conversion of three-coordinated boron into four coordinated boron and thereby reducing number of non-bridging oxygen atoms. Bismuth is found to exist in [BiO6] octahedral units only, whereas boroxol rings are not present in the glass network. The theoretical values of optical basicity (Λth) and corresponding oxide ion polarizability (αo2−) have also been calculated to investigate oxygen covalency of glass matrix. Trends in both these parameters suggested an increase in ionic bonding on substitution of divalent transition metal cations causing a more bonding compaction in glass structure. The UV–Vis–NIR spectra suggest that cobalt ions exist as Co2+ states in octahedral coordination in glass network. Inter-electronic repulsion parameter and crystal field splitting energy were evaluated to understand the site symmetry around Co2+-ion in glass. X-band EPR spectra suggest that vanadium ions (V4+) exists as VO2+-ions in octahedral coordination with tetragonal compression. Spin Hamiltonian parameters g-values and A-values of VO2+ ions in glass were calculated. For sample CLBB two resonance lines in EPR spectrum attribute to octahedral symmetry around Co2+-ions were observed.

Cation Substitution Effect on a Molecular Analogue of Perovskite Manganites

A recently synthesized Mn-containing molecule Ce2IIICeIVMn8IIIO8(O2CPh)18(HO2CPh) (Ce3Mn8III) structurally resembles the repeating unit of a bulk perovskite manganite. This resemblance brings forth the intriguing possibility of studying physical properties and effects that appear in both the molecule and the far more complex bulk perovskites, for example, effects of cation substitution, which in bulk manganites may lead to phase transition from metallic-ferromagnetic to insulating-paramagnetic as well as the colossal magnetoresistance effect. We investigate divalent and trivalent cation substitution in Ce3Mn8III molecules and its effects on ground-state magnetic configuration using first-principles-based approaches. One MnIII ion changes its valence to MnIV after trivalent (including La, Gd) cation substitution, while four MnIII ions become MnIV upon divalent (including Ca, Sr, Ba, and Pb) cation substitutions, all accompanied by vanishing local Jahn–Teller distortion around MnIV. The valence state of MnIV induced by cation substitutions can hop among Mn sites in molecule, and the calculated energy barrier for such state hopping is 0.25 to 0.6 eV/molecule. In addition, the charging energies of the Ce3Mn8III molecule and its derivatives are found to be strongly dependent on the spin direction of added electron.

Modelling how incorporation of divalent cations affects calcite wettability-implications for biomineralisation and oil recovery.

Using density functional theory and geochemical speciation modelling, we predicted how solid-fluid interfacial energy is changed, when divalent cations substitute into a calcite surface. The effect on wettability can be dramatic. Trace metal uptake can impact organic compound adsorption, with effects for example, on the ability of organisms to control crystal growth and our ability to predict the wettability of pore surfaces. Wettability influences how easily an organic phase can be removed from a surface, either organic compounds from contaminated soil or crude oil from a reservoir. In our simulations, transition metals substituted exothermically into calcite and more favourably into sites at the surface than in the bulk, meaning that surface properties are more strongly affected than results from bulk experiments imply. As a result of divalent cation substitution, calcite-fluid interfacial energy is significantly altered, enough to change macroscopic contact angle by tens of degrees. Substitution of Sr, Ba and Pb makes surfaces more hydrophobic. With substitution of Mg and the transition metals, calcite becomes more hydrophilic, weakening organic compound adsorption. For biomineralisation, this provides a switch for turning on and off the activity of organic crystal growth inhibitors, thereby controlling the shape of the associated mineral phase.

Degradation and hemostatic properties of polyphosphate coacervates

Sodium polyphosphate is a linear polymer formed from phosphate units linked together by sharing oxygen atoms. Addition of calcium to a solution of sodium polyphosphate results in phase separation and formation of a polyphosphate coacervate best described as a polymeric rich viscoelastic material. Polyphosphate coacervate is an interesting candidate as a biomaterial based on its ability to bind with different cations and to be loaded with drugs. Here, in vitro degradation and hemostatic properties of polyphosphate coacervates are comprehensively evaluated. We show that polyphosphate coacervates degrade and dissolve at a fast rate, losing half of their original mass in a week and transforming to mainly pyrophosphate after 4weeks. This burst dissolution phase happens earlier for the coacervate prepared from very short chain polyphosphate but overall using longer polyphosphate chains does not increase the coacervate longevity significantly. Substitution of Ca with Sr or Ba does not affect the hydrolysis of coacervates but slows down their dissolution into the media. In a whole blood clotting assay, coacervates profoundly decrease the clotting time especially when very long chain polyphosphates are used. While coacervate chain length and divalent cation type were found to significantly affect prothrombin time and thromboplastin time compared to the control, no discernible trends were observed. Platelets adhere in large numbers to coacervates, especially those containing long chain polyphosphate, but the cell morphology observed suggests that they might not to be fully activated. Overall, the long chain polyphosphate coacervate holds a great potential as a resorbable hemostatic agent. Statement of SignificanceDivalent cation additions to a sodium polyphosphate solution result in polyphosphate coacervates, or highly viscous gel-like materials, having great potential in bio-applications such as drug delivery and hemostasis. As these coacervates degrade in aqueous environments, we undertook a comprehensive evaluation to better understand the impact of polyphosphate chain length and divalent cation substitution on this hydrolytic response in order to better predict degradation behavior in the body. Furthermore, there is great interest in the role of polyphosphates in hemostasis following recent publications showing that platelets secrete polyphosphates upon thrombin stimulation. In this paper, we evaluate the hemostatic potential of polyphosphate coacervates as bulk constructs, demonstrating that indeed these materials hold great potential as a degradable hemostatic agent.