Tetravalent Ions Research Articles

Liquid–Liquid Extraction and Supported Liquid Membrane Transport of Neptunium(IV) Across a Flat-Sheet Supported Liquid Membrane Containing a TREN-DGA Derivative

ABSTRACT Liquid–liquid extraction and liquid membrane transport behavior of tetravalent actinide ions viz. Th(IV), Np(IV), and Pu(IV) were investigated for the first time using a diglycolamide (DGA) based dendrimer with a tris(2-aminoethyl)amine (TREN) scaffold as the organic extractant. The generation of 1 dendrimer with six DGA pendent moieties (termed as TREN-G1-DenDGA) extracted Np(IV) more effectively than the other two ions, the trend being Np(IV) > Pu(IV) > Th(IV). The extraction studies of Np(IV) from 3 M HNO3 indicated a 1:1 (metal:ligand) species and the extraction efficiency increased with increasing nitric acid concentration (1–6 M). The transport efficiency of Np(IV) increased with the nitric acid concentration (1–6 M) as well as with the ligand concentration. A very low concentration of 5.75 × 10−4 M ligand, when used as the carrier, resulted in the transport of ca. 25% metal ion transport in 5 h, which increased to >85% with 4.4 × 10−3 M ligand. The transport efficiency of the metal ion across the SLM followed the trend Np(IV) > Th(IV) > Pu(IV). The membrane stability was not satisfactory as seen over a period of 5 days suggesting long-term use may require regular replenishment of the carrier solvent. The effective diffusion coefficient (D eff) of Np(IV)-TREN-G1-DenDGA were determined by the lag-time method and was found to be 5.1 × 10−8 cm2/s.

SA Review: Effect of Substitution on Morphological and Magnetic behavior of W-type Hexagonal Ferrites

Hexaferrites have various applications in data storage and magnetic recording materials and in components in electrical devices, especially those operating at microwave/GHz frequencies. These compounds give appealing magnetic characteristics at less cost. Doping of divalent, trivalent and tetravalent ions into the hexagonal ferrite structure enhances the electromagnetic effects. Doping changes the electric and magnetic properties and magnetocrystalline anisotropic fields. In this review, we will explore the modifications in W-type ferrite in terms of magnetic properties, morphology, crystal structure, microwave absorption properties and reflection loss with substitution of different suitable and appropriate magnetic or non- magnetic divalent or trivalent ions into the lattice.

Investigation of the Phase Splitting Behaviour of U(VI) and Th(IV) loaded Trialkyl Phosphate Solvents in the Absence of Aqueous Phase

AbstractTri‐n‐butyl phosphate (TBP), a universally recognized solvent, has got lesser organic phase splitting or third phase formation tendency during the extraction of U(VI) as compared to tetravalent metal ions. Thus, the lighter members of trialkyl phosphates (TalP) (i. e.) tri‐n‐propyl phosphate (TPP) and triethyl phosphate (TEP) having higher third phase formation tendency would provide an opportunity to comprehend the aggregation of U(VI) loaded TalP solvents. As the above lighter TalPs exhibit higher aqueous solubility, the conventional measurement of third phase limit or Limiting Organic Concentration (LOC) by mixing organic and aqueous phases cannot be employed for the investigation of U(VI) third phase in TalPs. This has led to the development of a novel method to examine U(VI) third phase in aqueous soluble TalP solvent systems without aqueous feed solution. After validation, the newly developed method has then been utilized to determine the LOC for 1.1 M TPP in n‐alkane. The variation of extractant structure, diluent chain length, nature of metal ion and temperature on the third phase of 1.1 M TalP systems has been evaluated along with their molecular level understanding using Dynamic Light Scattering.

Experimental and computational investigation of divalent, trivalent, and tetravalent metal ion complexes of polyvinyl alcohol as adsorbents for fluoride remediation

Divalent, trivalent and tetravalent metal ion complexed polyvinyl alcohol (PVA) films are synthesised via solvent casting and used for fluoride removal from groundwater. Scanning electron microscopy depicts a variation in the morphology on the incorporation of these metal ions, while energy dispersive spectroscopy confirms the presence of the metal ions in the films. XRD analysis shows a decreased degree of crystallinity while TGA affirms the thermal stability of the metal ion complexed PVA films. The possible metal ion-binding interactions to PVA chains are elucidated by Density Functional Theory calculations. The quantum reactivity descriptors and natural bond orbital analysis assert that the complexation of two PVA chains with Zr4+ [(PVA)2Zr2(OH)4] is highly stable. The fluoride uptake by (PVA)2Zr2(OH)4 is thermodynamically favourable and occurs mainly by ligand to metal charge transfer interactions. Experimental fluoride adsorption studies confirm that PVA-Zr films remove ∼90% fluoride from 5 mg L−1 fluoride solution at pH 3–7. Moreover, the PVA-Zr films lower the fluoride content from 2.84 mg L−1 to 0.9 mg L−1 in the groundwater sample, which is below the permissible limit. Thus, it is proven experimentally and computationally that PVA-Zr films have potential commercial applicability in fluoride remediation.

Manganese ions substituted ZnO nanoparticles: Synthesis, microstructural and optical properties

Nanocrystalline Mn ions doped ZnO powder samples with a generic formula Zn1-xMnxO (x = 0.00, 0.02, 0.04, and 0.06) were prepared using conventional co-precipitation method. Confirmation of pure single-phase formation of all the ZnO samples was obtained by x-ray diffraction profiles. An average crystallite size in between 25 nm and 30 nm was calculated using Scherrer's formula. Williamson-Hall plots verified the existence of microstrain within the nanocrystals. Presence of bivalent, trivalent and tetravalent Mn ions in ZnO matrix was confirmed by x-ray photoelectron spectra analysis. Room temperature UV–Vis spectra studies confirmed that all the samples showed strong absorption near violet-blue region of EM spectrum. Photoluminescence spectra analysis confirmed the presence of both zinc and oxygen vacancies in doped samples.

Reaction between tetravalent cerium ion and chloride ion and effect of thiourea using cyclic voltammetry

To monitor the reaction between Ce4+ ion and Cl– ion at the electron level, an electrochemical experiment was designed in this work. Herein, the intermediate and final products that may be produced during the redox reaction are directly tracked by using cyclic voltammetry, and the influences of Ce4+ ion concentration, temperature and F– ion on the reduction peak potential of Ce4+ ion were investigated. The results show that Ce4+ ion reacts with Cl– ion through an irreversible reaction without any intermediate products, and the rate-determining step of the reaction is diffusion during the electrode reaction. The effects of temperature (20–40 °C) and Ce4+ ion concentration (0.04–0.12 mol/L) on the reduction peak potential of Ce4+ ion can be ignored, but the higher the molar ratio of F– to Ce4+ (0–3 mol/mol), the more easily the reduction of Ce4+ ion to Ce3+ ion occurs. Additionally, the Ce4+ ions are preferentially reduced by thiourea when thiourea is added in the HCl solution, and thiourea inhibits the oxidation of Cl– ions to Cl2 by forming a complex with Cl– ions. This work provides a theoretical basis for the role of thiourea in inhibiting Cl2 production and offers a new way to find new reductants.

Rational Design of Nonbonded Point Charge Models for Highly Charged Metal Cations with Lennard-Jones 12-6 Potential.

Here, we developed nonbonded point charge models using a simple Lennard-Jones (LJ) 12-6 potential for highly charged metal cations (18 trivalent and 6 tetravalent ions) for use with 11 water models of TIP3P, OPC3, SPC/E, SPC/Eb, TIP3P-FB, a99SB-disp, TIP4P-Ew, OPC, TIP4P/2005, TIP4P-D, and TIP4P-FB. The designed models simultaneously reproduce the hydration free energy (HFE) and ion-oxygen distance (IOD) in the first hydration shell with an error within 1 kcal/mol and 0.01 Å on average, respectively, and yield reasonable coordination numbers for most cations. Such performance is equivalent to the previously reported point charge models using a more complex 12-6-4 LJ-type potential, while the LJ R parameters of our models are much close to Shannon's revised effective ion radii than that of the 12-6-4 models. Our designed models overestimate the diffusion constants of several trivalent ions by 5-68%. The performance in predicting osmotic coefficients of trivalent chlorides in aqueous solution depends on the salt type. A calibration of cation-anion interacting LJ parameters reproduces the experimental osmotic coefficients of an AlCl3 solution at 0.2-3.0 mol/L. The effectiveness of our new models is further demonstrated by simulating a metalloprotein system with four force field/water combinations. This work facilitates accurate modeling of metal-containing systems by a variety of force fields and water models in aqueous solution.

Highly efficient uptake of tetravalent actinide ions from nitric acid feeds using an extraction chromatography material containing tetra-n-butyl diglycolamide and a room temperature ionic liquid

An extraction chromatography (XC) material containing N,N,N’,N’-tetra-n-butyl diglycolamide (TBDGA) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide (C4mim∙NTf2), a room temperature ionic liquid, was used for the uptake of the tetravalent actinide ions Th(IV), Np(IV), and Pu(IV) from nitric acid feed solutions. The uptake of the metal ions followed the trend: Th(IV) < Np(IV) < Pu(IV), which is the same as that of their ionic potential values. While a decrease in the Np(IV) and Pu(IV) uptake was seen with increasing HNO3 concentration at lower acidities, an opposite trend was observed at higher acidities. Th(IV) uptake was not affected with the acid concentration. In view of the very high uptake and its importance in the nuclear fuel cycle, the major part of the studies was carried out with Pu(IV) ion. The loaded Pu(IV) was back extracted from the XC material using a mixture of 0.5 M oxalic acid and 0.5 M nitric acid. The Pu(IV) uptake by the XC material was fitted into different kinetic and isotherm models. The results conformed to the pseudo-second order kinetic model and the Langmuir monolayer sorption model. Column studies were carried out using a feed having 1.6 mg/L Pu solution in 3 M HNO3. While the breakthrough was obtained after passing ca. nine bed volumes, a sharp elution peak was obtained with >99% recovery in about seven bed volumes.

Gas-phase structure, bonding, and fragmentation chemistry of the An (IV)-TMPDCAM complexes studied using mass spectrometry and theoretical calculation (An = Th and U).

Pyridine-2,6-dicarboxamides (PDCAMs) exhibit a certain extraction ability for tetravalent actinide ions, but quite limited information regarding the structures and reactivities of the corresponding An4+ -PDCAMs complexes is available. Neutral diamides can form multiply charged complexes with lanthanide and actinide cations, which are well suited for gas-phase investigations using electrospray ionization (ESI) mass spectrometry in conjunction with theoretical calculation. Binary Th (TMPDCAM)3 4+ /U (TMPDCAM)3 4+ (TMPDCAM =N,N,N',N'-tetramethylpyridine-2,6-dicarboxamide) complexes were generated in the gas phase via ES) of Th (ClO4 )4 /U (ClO4 )4 and TMPDCAM mixtures in acetonitrile; collision-induced dissociation (CID) was employed to reveal their fragmentation behaviors; the structure and bonding were investigated by density functional theory (DFT) calculation. An (TMPDCAM)3 4+ (An = Th and U) tetracations dominated the ESI mass spectra of An (ClO4 )4 and TMPDCAM mixtures in acetonitrile. DFT calculations indicate that the two An (TMPDCAM)3 4+ complexes have C3 geometry, and the bonding analyses demonstrate that the thorium or uranium center interacts with both Ocarbonyl and Npyridine , but the latter is weaker. CID of Th (TMPDCAM)3 4+ generated a series of multiply charged thorium-containing products via bond cleavages of the TMPDCAM ligand, whereas U (TMPDCAM)3 4+ yielded only oxygen extraction product UO (TMPDCAM)2+ and hydrolysis product UO (OH)+ . An4+ (An = Th and U) can form stable tetrapositive complexes in the gas phase on coordination of three neutral TMPDCAM ligands. The structure and bonding analyses indicate that the two An (TMPDCAM)3 4+ complexes possess twisted tricapped trigonal prismatic geometry and the An4+ centers are coordinated by six Ocarbonyl and three Npyridine atoms while the interactions between An4+ and Ocarbonyl are stronger. The fragmentation chemistry of Th (TMPDCAM)3 4+ and U (TMPDCAM)3 4+ is quite different from each other, which reveals that the gas-phase chemistry of quadruply charged actinide-diamide complexes is affected by the metal centers with distinct properties.

Elucidating the extraction behaviour of tri-n-alkyl phosphates and tris(2-methylbutyl) phosphate with nitrates of uranyl and tetravalent metal ions from infrared spectroscopy and dynamic light scattering studies: A distinct correlation from conformational changes and variation in size of aggregates

Extraction of tetravalent Zr(IV), Ce(IV), Th(IV) and Pu(IV) and hexavalent U(VI) nitrates, from their aqueous solutions by tri-n-butyl phosphate (TBP), tri-n-amyl phosphate (TAP) and tris-2-methyl-butyl phosphate (T2MBP) diluted to 30% with n-dodecane has been studied using infrared (IR) spectroscopy and dynamic light scattering (DLS) measurements. A comprehensive interpretation of observations, from the molecular perspectives offered by IR spectroscopy and DLS techniques, allows understanding the behaviour exhibited by different extractant-metal nitrate systems. Formation of metal nitrate-ligand complex involving phosphoryl oxygen as a neutral electron donor stands affirmed by the significant red-shifting of vibrational wavenumber associated with the characteristic P=O stretching mode. Conformational interconversion (repopulation) with the enrichment of ‘trans’ cluster of conformations within the organic phase as a consequence of loading of metal nitrates has been proposed as a probable cause for, the counter-intuitive, blue-shifting of the vibrational wavenumber associated with phosphoryl stretching. This conformational interconversion could be instrumental in the onset of formation of a third phase. Conclusive evidence, for preferential stabilization of ‘trans’ cluster of conformations in a polar environment, has been obtained from the combined use of Density Functional Theory (DFT) and IR spectroscopy. Coupling the scatter profile of aggregates with the molecular information reveals, a compromise of the polar volume of an aggregate and its non-polar surface area, which in turn determine the sizes to which aggregates could grow for a given extractant-metal nitrate system.

Charge Localization and Magnetic Correlations in the Refined Structure of U3O7.

Atomic arrangements in the mixed-valence oxide U3O7 are refined from high-resolution neutron scattering data. The crystallographic model describes a long-range structural order in a U60O140 primitive cell (space group P42/n) containing distorted cuboctahedral oxygen clusters. By combining experimental data and electronic structure calculations accounting for spin-orbit interactions, we provide robust evidence of an interplay between charge localization and the magnetic moments carried by the uranium atoms. The calculations predict U3O7 to be a semiconducting solid with a band gap of close to 0.32 eV, and a more pronounced charge-transfer insulator behavior as compared to the well-known Mott insulator UO2. Most uranium ions (56 out of 60) occur in 9-fold and 10-fold coordinated environments, surrounding the oxygen clusters, and have a tetravalent (24 out of 60) or pentavalent (32 out of 60) state. The remaining uranium ions (4 out of 60) are not contiguous to the oxygen cuboctahedra and have a very compact, 8-fold coordinated environment with two short (2 × 1.93(3) Å) "oxo-type" bonds. The higher Hirshfeld charge and the diamagnetic character point to a hexavalent state for these four uranium ions. Hence, the valence state distribution corresponds to 24/60 × U(IV) + 32/60 U(V) + 4/60 U(VI). The tetravalent and pentavalent uranium ions are predicted to carry noncollinear magnetic moments (with amplitudes of 1.6 and 0.8 μB, respectively), resulting in canted ferromagnetic order in characteristic layers within the overall fluorite-related structure.

Third phase formation behaviour of tris(2-methylbutyl) phosphate and tri-n-alkyl phosphates in the extraction of mineral acids and tetravalent metal ions

Abstract The formation of third phase is a detrimental phenomenon witnessed in the nuclear separation processes during the extraction of certain metal salts by an organic solution, which comprises of a neutral extractant, tri-n-butyl phosphate dispersed in a non-polar diluent, n-dodecane (n-C12H26). In the present work, a comparative analysis on the third phase formation behaviour of three trialkyl phosphates, TBP, its linear and branched higher homologues tri-n-amyl phosphate and tris(2-methylbutyl) phosphate (T2MBP), respectively, have been provided which will be useful for the identification of an extractant with minimum third phase formation tendency. The organic phase splitting behaviour during the extraction of three mineral acids (HClO4, HCl and HNO3) and two tetravalent metal nitrates (Th(IV) and Zr(IV)) by trialkyl phosphates has been investigated to understand the influence of anionic and cationic components, respectively, in third phase formation of trialkyl phosphates. The effect of structure of the alkyl groups of trialkyl phosphate and chain length of diluents on third phase formation during Zr(IV) extraction from HNO3 media have also been studied. Overall, the third phase formation behaviour of T2MBP was found to be lower both for the extraction of mineral acid and Zr(IV), thereby indicating its potentiality for applications in various solvent extraction processes.

Light-Activated Chemoresistive and Plasmonic-Resonant Optical Sensors for NO2 and H2 Sensing Based on ZnO Doped Nanoparticles

Light-Activated Chemoresistive and Plasmonic-Resonant Optical Sensors for NO2 and H2 Sensing Based on ZnO Doped Nanoparticles

Arsenic(III)-Capped 12-Tungsto-2-Arsenates(III) [M2(AsIIIW6O25)2(AsIIIOH)x]n- (M = CrIII, FeIII, ScIII, InIII, TiIV, MnII) and Their Magnetic Properties.

Six arsenic(III)-capped 12-tungsto-2-arsenates(III) of the type [M2(AsIIIW6O25)2(AsIIIOH)x]n- (M = CrIII, 1; FeIII, 2; ScIII, 3; InIII, 4; TiIV, 5; MnII, 6) have been synthesized in aqueous medium by direct reaction of the elements using a one-pot strategy and structurally characterized by FT-IR spectroscopy, single-crystal XRD, and elemental analysis. Polyanions 1-6 are comprised of two octahedrally coordinated guest metal ions M sandwiched between two {AsW6} units, resulting in a structure with C2h point-group symmetry. Polyanions 1-5 contain tri- and tetravalent metal ion guests M (M = CrIII, FeIII, ScIII, InIII, and TiIV, respectively), and they have one {AsIIIOH} group grafted on each {AsW6} unit, whereas the divalent MnII-containing derivative 6 has two such {AsIIIOH} groups grafted on each {AsW6} unit. Magnetic studies on polyanions 3-5 over the temperature range 1.8-295 K and magnetic fields of 0-7 T confirmed that they are diamagnetic. On the other hand, polyanions 1, 2, and 6 are strongly magnetic and follow the Curie-Weiss law above 30 K. The susceptibility plots of 1 and 6 exhibit broad peaks suggesting short-range antiferromagnetic ordering, while the very weak antiferromagnetic ordering of 2 is overshadowed by traces of a paramagnetic impurity. The magnetization data of 1, 2, and 6 at 1.8 K over 0-7 T were analyzed by using the Heisenberg exchange procedure. Small (negative) values of the obtained J values help in understanding the absence of long-range antiferromagnetic ordering.

ZnO thin films containing aliovalent ions for NO2 gas sensor activated by visible light

In this paper we report on the combined visible-light (red λ = 630 nm; green λ = 570 nm; purple-blue λ = 430 nm) and mild thermal-activation modes (25 °C–100 °C) towards ppb-level NO2 detection of ZnO nanocrystalline film containing trivalent (Al-Ga) and tetravalent (Si-Ge) ions. Both trivalent and tetravalent doping trigger visible light fast response/recovery behavior as respect to dark conditions. Remarkably Purple-blue light (λ = 430 nm) combined with thermal activation at 75 °C OT results in best performances in terms of variation of sensor resistance as compared to that in dry air, topping maximum gas relative response RR= RGas/RAir ≈ 20 for the 5% Si doped ZnO at 400 ppb NO2. Aliovalent doping of ZnO is obtained using a colloidal heat-up synthesis yielding highly transparent in the visible range degenerately doped n-type ZnO semiconductors films which were characterized by SEM, XRD, XPS techniques to assess morphology, crystal phases and concentration of surface oxygen vacancies, respectively. Optical characterization of the doped films showed a distinctive localized surface plasmon resonance (LSPR) peak in the near infrared region, deriving from the free charge carrier. Aluminum doping is the most effective to narrow the band gap of the doped ZnO films down to 3.22 eV. The influence of the relative humidity (RH) on the gas sensing performances is investigated and for 40% RH a slight decrease of the NO2 relative response was observed. A consistent model explaining the gas sensing mechanism under dark and light conditions and the influence of RH is presented.

New O3-Type Layer-Structured Na0.80[Fe0.40Co0.40Ti0.20]O2 Cathode Material for Rechargeable Sodium-Ion Batteries.

Herein, we formulated a new O3-type layered Na0.80[Fe0.40Co0.40Ti0.20]O2 (NFCTO) cathode material for sodium-ion batteries (SIBs) using a double-substitution concept of Co in the parent NaFe0.5Co0.5O2, having the general formula Na1-x[Fe0.5–x/2Co0.5–x/2M4+x]O2 (M4+ = tetravalent ions). The NFCTO electrode delivers a first discharge capacity of 108 mAhg−1 with 80% discharge capacity retention after 50 cycles. Notably, the first charge–discharge profile shows asymmetric yet reversible redox reactions. Such asymmetric redox reactions and electrochemical properties of the NFCTO electrode were correlated with the phase transition behavior and charge compensation reaction using synchrotron-based in situ XRD and ex situ X-ray absorption spectroscopy. This study provides an exciting opportunity to explore the interplay between the rich chemistry of Na1–x[Fe0.5–x/2Co0.5–x/2M4+x]O2 and sodium storage properties, which may lead to the development of new cathode materials for SIBs.

Extraction behavior of Pu(IV), Th(IV), and fission product elements with hexapropyl and hexabutyl phosphoramides

Abstract Hexapropyl phosphoramide (HPPA) and hexabutyl phosphoramide (HBPA) were examined for the macrolevel extraction and stripping of tetravalent metal ions such as Pu(IV) and Th(IV). The solvation number of Pu(IV) with both the phosphoramides were measured. The number of stages was evaluated for the quantitative extraction and stripping of Pu(IV) and Th(IV) in cross-current mode with 1.1 M phosphoramides in xylene from the nitric acid medium. The distribution ratios for the extraction of Th(IV) were measured with 1.1 M phosphoramides in xylene as a function of equilibrium aqueous phase Th(IV) and nitric acid concentration. In addition, distribution ratios for the extraction of fission product elements such as Zr, Tc, Ru, lanthanides (La, Pr, Nd and Gd) and activation product Am were also measured with 1.1 M HPPA and HBPA in n-Dodecane (n-DD) system as a function of aqueous phase nitric acid concentration. The extraction data generated with phosphoramides were compared with a 1.1 M TBP/n-DD system.

Speciation and removal of selenium (IV, VI) from water and wastewaters based on dried activated sludge before determination by flame atomic absorption spectrometry

In recent decades, large amount of pollutants enter to the environment due to development of technology. Therefore it is necessary to use ecofriendly sorbent to eliminate pollutants. In this research, an dried activated sludge (DAS) was used to decrease Se(IV) pollutant and the effect of operating parameters such as solution pH, the amount of biosorbent, contact time, temperature and initial concentration of selenium were studied. Kinetic data was adjusted to the Langmuir and Freundlich kinetic equations. It was resulted that the Freundlich equation with a correlation coefficient of 0.9956 has the Best match to tetravalent selenium biosorption on DAS. The FT-IR results showed that the biosorption mechanism of selenium tetravalent metal ion on DAS is because of the existence of functional groups on the DAS surface can interact with Se(IV) ions. This study aims to investigate the biosorption capacity of the DAS for tetravalent selenium ions in aqueous solutions.&#x0D; &#x0D;

Charge and spin degrees of freedom in A -site ordered YCu3Co4O12 and CaCu3Co4O12

Using soft x-ray absorption spectroscopy we were able to determine unambiguously the charge and spin states of the transition metal ions in stoichiometric $\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ and $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$. The trivalent and low-spin nature of both the Cu and Co ions in $\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ makes this correlated system to be effectively a nonmagnetic band semiconductor. The substitution of Y by Ca produces formally tetravalent Co ions but the doped holes are primarily on the oxygen ligands. Concerning the spin degrees of freedom, the trivalent Co ions in $\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ remain low spin upon the Y-Ca substitution, very much unlike the ${\mathrm{La}}_{1\text{\ensuremath{-}}x}{\mathrm{Sr}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$ system. The tetravalent Co ions in $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ are interestingly also in the low-spin state, which then explains the good electrical conductivity of $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{12}$ since charge exchange between neighboring ${\mathrm{Co}}^{3+}$ and ${\mathrm{Co}}^{4+}$ ions will not be hampered by the spin-blockade mechanism that otherwise would be in effect if the ${\mathrm{Co}}^{4+}$ and ${\mathrm{Co}}^{3+}$ spin quantum numbers were to differ by more than one-half. We infer that the stability of the Co low-spin state is related to the very short Co-O bond lengths.

Enhanced photocatalytic hydrogen production on tin disulfide self-assembled from ultrathin sheets with sulfur vacancies generated by doping indium ions

In consideration of comparable ionic radius between indium ions and tin ions, indium-doped SnS2 (In/SnS2) sample was designed and synthesized by one-pot solvothermal method. Its multi-level structure composed of 10-nm-thick ultrathin sheets can enhance utilization efficiency of solar light. The substitution of trivalent indium ions for tetravalent tin ions causes indium to form a negative charge center and simultaneously produces sulfur vacancies positively charged. As expected, the production of hydrogen on doped sample is up to 470 µmol g−1, which is about twice as high as that on SnS2. This is attributed to hierarchical structure composed of ultrathin sheets and effective attraction of hydrogen ions by negative charge on trivalent indium ions. The results suggest that doping the ions whose ionic radius is close to the radius of the anions or cations in the material into the lattice sites may provide a new tactic for the design of semiconductor photocatalytic materials.