Tetravalent Metal Research Articles

Thermal conductivity of rare-earth titanate pyrochlores

Pyrochlore oxides with the chemical formula ${R}_{2}{B}_{2}{\mathrm{O}}_{7}$ ($R=$ rare earth and $B=$ tetravalent metal) exhibit very low thermal conductivities (\ensuremath{\kappa}) and are considered as promising materials for thermal barrier coatings. To achieve better understanding of their intrinsic thermal properties, this study reports \ensuremath{\kappa} for single crystalline ${\mathrm{Gd}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Dy}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, and for a series of polycrystalline ${R}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, in the temperature range from 300 to 773 K. For the single crystals, \ensuremath{\kappa} values are evaluated in comparison to spinel ${\mathrm{MgAl}}_{2}{\mathrm{O}}_{4}$ and garnet ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ using the Slack equation. It is more difficult to obtain satisfactory analysis for the pyrochlores, and this is attributed to the strong involvement of low-lying optic phonons and very low energies of zone-boundary acoustic phonons. For polycrystalline ${R}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, \ensuremath{\kappa} values similar to single crystals are obtained. Comparison with published data shows a systematic trend of $\ensuremath{\kappa}({R}_{2}{\mathrm{Sn}}_{2}{\mathrm{O}}_{7})>\ensuremath{\kappa}({R}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7})>\ensuremath{\kappa}({R}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7})$ at 300 K, which reflects the increasing ionicity from ${\mathrm{Sn}}^{4+}$ to ${\mathrm{Ti}}^{4+}$ to ${\mathrm{Zr}}^{4+}$. For the three ${R}_{2}{B}_{2}{\mathrm{O}}_{7}$ systems, \ensuremath{\kappa} appears to decrease with either decreasing ionic radius or increasing cation mass of $R$.

Influence of Particle Size and Zeta Potential in Treating Highly Coloured Old Landfill Leachate by Tin Tetrachloride and Rubber Seed.

Old leachate normally has a low organic compound content, poor biodegradability and is hard to biologically treat. The efficacy of tetravalent metal salts as a coagulant and the application of a natural coagulant as a flocculant in landfill leachate treatment is still inconclusive. Hence, this study aimed to evaluate the potential application of tin tetrachloride (SnCl4) as the main coagulant and the rubber seed (Hevea brasiliensis) (RS) as the natural coagulant aid as the sole treatment in eradicating highly coloured and turbid stabilised landfill leachate present at one of the old local landfills in Malaysia. The standard jar test conducted revealed that SnCl4 was able to eliminate 99% and 97.3% of suspended solids (SS) and colour, respectively, at pH8, with 10,000 mg/L dosages, an average particle size of 2419 d·nm, and a zeta potential (ZP) of −0.4 mV. However, RS was found to be ineffective as the main coagulant and could only remove 46.7% of SS and 76.5% of colour at pH3 with 6000 mg/L dosages, and also exhibited smaller particles (933 d·nm) with ZP values of −6.3 mV. When used as a coagulant aid, the polymer bridging mechanism in RS helped in reducing the SnCl4 concentration from 10,000 mg/L to 8000 mg/L by maintaining the same performances. The presence of 1000 mg/L RS as a coagulant aid was able to remove 100% of SS and 97.6% of colour. The study concluded that RS has the potential to be used together with SnCl4 in treating concentrated leachate with SS and colour.

Investigation into Lewis and Brønsted acid interactions between metal chloride and aqueous choline chloride-oxalic acid for enhanced furfural production from lignocellulosic biomass

Furfural has been identified as a valuable biobased platform chemical that can be further converted into bioenergy and biochemicals. Furfural is derived from lignocellulosic biomass and can also be regarded as a sustainable alternative to petrochemical products. Herein, the performance of trivalent metal chlorides (FeCl3, AlCl3) and tetravalent metal chlorides (SnCl4, TeCl4) as Lewis acidic cocatalysts was investigated in an aqueous choline chloride-oxalic acid (16.4 wt% H2O) deep eutectic solvent (DES) system for producing furfural from oil palm fronds (OPFs). The metal chlorides with greater electrical field gradients were stronger Lewis acids that enhanced both furfural production and degradation reactions. The main degradation product in this reaction system was humin, and this result was confirmed by FTIR analysis. By subjecting OPFs to an aqueous DES reaction (120 °C, 45 min) with SnCl4 (2.50 wt%), a furfural yield of 59.4% was obtained; without incorporated metal chlorides, the furfural yield was 46.1%. Characterization studies showed synergistic Lewis and Brønsted acid interactions between metal chlorides and DES components. Overall, the residual OPFs showed high glucan content, which led to the production of glucose (71.4%) as a byproduct via enzymatic hydrolysis. Additionally, the aqueous DES system was recycled and reused for several additional runs. The proposed aqueous DES system presents a promising biorefinery approach for the conversion of OPFs to biochemicals.

Highly efficient potentiometric sensing device for gadolinium based on Tetraazacyclododecane-1, 4, 7, 10 -tetraaceticacid crown ether and multiwalled carbon nanotube composite

A hydrophilic cavity presents in tetraazacyclododecane-1, 4, 7, 10-tetraaceticacid crown ether (DOTA) provides the opportunity for Gadolinium (Gd3+) transfer from an aqueous medium to a lipophilic phase and mimic the ionophoric properties due to strong coordinating link. Therefore, we have developed Gd3+ ion selective electrode (ISE) incorporating synthesized nanocomposite of DOTA as an ionophore and multiwalled carbon nanotube (MWCNT) as signal enhancer in poly vinyl chloride (PVC) membrane sensor employing potentiometry. The composite DOTA-MWCNT was characterized by scanning electron microscopy (SEM). The Nernstian slope of 20.05 ± 0.18 mV per decade with linear range 1 × 10-2 to 1 × 10-8 M and the detection limit was found to be 7.2 ± 0.16 × 10-9 M. This electrode has an excellent selectivity over mono, bi, tri and tetravalent interferent metal species. The proposed sensor was favourably applied as an indicator electrode in the titration of Gd3+ ions with EDTA and recovery of gadolinium (III) from diverse synthetic samples. The presence of four ionizable carboxylic acids groups imparts advantages to DOTA-MWCNT composite in the formation of strong complexes and enhanced solubility of Gd3+ which became the basis for in-vivo analysis of Gd3+ in pharmaceutical and soil samples. DOTA-MWCNT as host forms 1:1 chelate complex with guest Gd3+ employing square wave voltammetry. The stability constant (Log K = 25.41) and Gibbs free energy (DG) of DOTA-MWCNT - Gd3+ complex was calculated which established exothermic and spontaneous inclusion mechanism. The higher stability constant obtained for DOTA-MWCNT chelate complex can provide the opportunity to researchers of biomedical science to minimize/control the amount of free Gd3+ release in the human body through the process of drug delivery.

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.

Rational Design of Nonbonded Point Charge Models for Monovalent Ions with Lennard-Jones 12-6 Potential.

Ions are of central importance in nature, and a variety of potential models was proposed to model ions in different phases for an in-depth exploration of ion-related systems. Here, we developed point charge models of 14 monovalent ions with the traditional 12-6 Lennard-Jones (LJ) potential for use in conjunction 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 reproduced the real hydration free energy (HFE) of ions and the ion-oxygen distance (IOD) in the first hydration shell accurately and simultaneously, a performance similar to the previously reported 12-6-4 LJ-type ion models (12-6 LJ plus an attractive C4 term for cations or a repulsive one for anions). This work, along with our previous work on di-, tri-, and tetravalent metal cations (J. Chem. Inf. Model. 2021, 61, 4031-4044; J. Chem. Inf. Model. 2021, 61, 4613-4629), demonstrates the feasibility of the simple 12-6 LJ potential in ion modeling. In order for the 12-6 LJ potential to reproduce both the HFE and IOD, the LJ R parameters need to be close to Shannon's ionic radii for the highly charged cations and to the Stokes's van der Waals (vdW) radii for the monovalent ions. With an additional C4 term, the R parameters of 12-6-4 LJ ion models agree well with the Stokes's vdW radii and have a more physical meaning. It appears that the C4 term can be merged into the 12-6 LJ potential by a rational tuning of R and the LJ well depth. Simulations of the osmotic coefficients of alkali chloride solutions and the properties of gaseous and solid alkali halides indicate the necessity of further optimizing ion-ion interactions via, for instance, targeting more properties or using a more physical (polarizable) model.

Metal–Support Interactions in Rhodium Catalysts Supported on Tetravalent Metal Pyrophosphates (MP2O7; M = Si, Ti, and Zr)

A series of tetravalent metal pyrophosphates (MP2O7; M = Si, Ti, and Zr) were studied as support materials for rhodium (Rh) catalysts to elucidate the effect of the M–O–P bond covalency on the inte...

Nano Sized Tin Zirconium Phosphate Ion Exchanger as Copper Scavenger

A new four component nano sized tin zirconium molybdophosphate, an inorganic ion exchanger of the class of tetravalent metal acid (TMA) salts has been synthesized by co-precipitation method and its ion exchange behaviour was studied. Characterization of the exchanger was done by ICP-AES method and structural studies were carried out using TGA, XRD and FTIR. From the XRD pattern studies, the synthesized ion exchanger was found to be size of 70- 75 nm. The sodium exchange capacity of material was found to be 3.92meq/g. The chemical resistivity of the material has been assessed in various acids, bases and organic solvents like 1M HNO3, IM H2SO4, acetic acid etc. The effects of temperature on capacity, effect of electrolyte concentration and analytical applications also were studied. The protons of hydroxyl groups were found to be the active site. The distribution coefficients of different metal ions like Pb2+, Cu2+, Co2+, Cd2+, Mn2+, Zn2+, Mg2+, Bi3+, Hg2+, Ni2+, Th4+, Ca2+ were studied. On the basis of distribution studies, it was found that the exchanger has high affinity towards Pb2+ and Cu2+ compared with other metal ions. Due to its high affinity towards copper metal ion, it can be used as copper scavenger for waste water treatment and its binary separation of Cu2+ from Mn2+, Mg2+, Cd2+ and Ni2+ was carried out. The UV- Visible Spectrophotometer model JASCO V660 with diffuse reflectance accessories is used to study the absorption of the copper ion on the ion exchange.

Fluorite-like hydrolyzed hexanuclear coordination clusters of Zr(IV) and Hf(IV) with syn-syn bridging N,N,N-trimethylglycine in soft crystal structures exhibiting cold-crystallization

Tetravalent metal ions are hydrolyzed under presence of N,N,N-trimethylglycine hydrochloride (betaine hydrochloride, [Hbet]Cl) in aqueous solutions to afford [M6(μ3-O)4(μ3-OH)4(μ-bet)8(κ-bet)4(H2O)4]12+ (M4+ = Zr4+ (1), Hf4+ (2)) as hydrated perchlorate salts. These compounds were characterized by single crystal X-ray diffraction, elemental analysis and IR spectroscopy. As a result, we have found that fluorite-like [M6O8] coordination clusters are formed through octahedral arrangement of six M4+ linked by μ3-O atoms. Additionally, each pair of neighboring M4+ are connected by the μ-bet ligand through a syn-syn bridging coordination of its carboxylate moiety. This interaction seems to prevent further growth of the fluorite structure leading to formation of MO2. It was difficult to directly distinguish each μ3-O atom to be μ3-OH− or μ3-O2− due to its strongly anisotropic thermal displacement in the obtained structures. Bond valence sum analysis suggested that four μ3-OH− and four μ3-O2− are alternately arranged in the [M6O8] core motifs. Indeed, such a symmetric structure of [M6(μ3-O)4(μ3-OH)4] was confirmed in another phase of 1 at 296 K, where 1 transforms to a monoclinic structure (1′). The number of ClO4− counteranions found in the structure determination is not enough to compensate + 12 charge of [M6(μ3-O)4(μ3-OH)4(μ-bet)8(κ-bet)4(H2O)4]12+ in any unit cells of 1, 1′ and 2. Instead, large solvent/ion accessible voids have been actually observed in their crystal structures, indicating that the missing ClO4− are located therein and are significantly disordered to make them invisible in the crystallography. DSC analysis revealed that ClO4− and H2O/H3O+ in the crystal lattice of 1 undergo unique structure relaxation and rearrangements pronounced by cold-crystallization to induce the phase transition from 1 to 1′ with elevating temperature.

Removal of lanthanum, cerium and thorium metal ions from aqueous solution using ZrT hybrid ion exchanger

In this paper, a hybrid exchanger, zirconium triethylenetetramine (ZrT), of the class of tetravalent metal acid (TMA) salts, has been synthesized by the sol–gel method. In the present work, an attempt has been to investigate the sorption behavior of lanthanum, cerium, and thorium metal ions towards ZrT exchanger in various electrolytes media with different concentrations. In order to understand the uptake behavior of ZrT, parametric studies, kinetic and thermodynamic studies have been investigated. Distribution studies data revealed the feasibility of binary lanthanide separations using ZrT and show possibility of its promising use as an efficient ion exchanger in the treatment of water containing radioactive metal waste. In general, the decay storage or ion exchange treatment is used for the treatment of aqueous waste generated from the low nuclear power reactor. As per the report (IAEA-TECDOC-654, 1992), such nuclear aqueous waste generated is found acidic in view of used acidic chemicals during the process. The use of ZrT will be effective or in other words, ZrT can be a potential candidate to be used as an ion-exchange material for the treatment of such nuclear aqueous waste, after optimizing the process parameters, in particular maintaining the pH in the range of 4–5.

Room temperature synthesis of high-quality Ce(IV)-based MOFs in water

There is a growing interest in the sustainable synthesis of Metal-Organic Framework materials (MOFs). This work addresses the exceptional ability of Ce(IV) for the preparation of high-quality MOFs based on carboxylates at room temperature, in water as solvent, and without any energy input. Thus, crystalline terephthalate-based UiO-66(Ce), fumarate-based UiO-66(Ce) and Ce-MOF-808 were successfully synthesized at room temperature by various new approaches. All these methodologies are novel, rapid, simple, reproducible, inexpensive, energetically efficient and relatively environmentally benign compared with the usual conventional methodologies and, unlike other room-temperature synthesis, leads to highly-crystalline samples. In particular, (i) both terephthalate- and fumarate-based UiO-66(Ce) were synthesized using water as a sole solvent and in the absence of any modulator or any other additive; (ii) terephthalate-based UiO-66(Ce) was prepared under systematically-designed different water/DMF molar ratio, selecting these solvents in order to start from clear solutions of both metal and linker sources, respectively; and (iii) terephthalate-based UiO-66(Ce) and Ce-MOF-808 were prepared in the presence of either acetic acid or formic acid as modulators, respectively. Therefore, this work provides novel strategies for the preparation of tetravalent metal based MOFs, which are in general scarce with respect to the whole number of known MOFs, particularly at room temperature.

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.

The influence of cation exchange and tetravalent metal substitutions in Lewis acidic BEA zeolites for phenol adsorption and Tautomerization: A computational study

The effect of cation exchange and tetravalent metal substitution in Lewis acidic BEA zeolites for phenol adsorption and tautomerization was investigated by deriving the relevant reaction profiles with density functional theory calculations. The strongest adsorption interaction is when phenol chemisorbed to Li-Sn-BEA, due to the highest charge transfers from phenol to zeolites. Based on overall activation energies, the catalytic activity for phenol tautomerization on Sn-BEA can be improved with the exchange of cations. The catalytic activity of tetravalent metal centers substituted into BEA is compared and found in the order of Zr ~ Hf > Sn > Ti.

Influence of Jatropha curcas seeds as a natural flocculant on reducing Tin (IV) tetrachloride in the treatment of concentrated stabilised landfill leachate

Stabilised leachate usually contains lower concentration of organic compounds than younger leachate; it has low biodegradability and generally unsuitable for biological treatment. The effectiveness of tetravalent metal salts in a coagulation-flocculation (C–F) process is still inclusive. Application of natural coagulants as an alternative to the chemical could reduce chemical usage, is less costly, and environmentally friendly. Hence, the objective of the current research is to examine the possibility of reducing the amount of Tin (IV) chloride (SnCl4) as a primary coagulant by adding Jatropha curcas (JC) as a flocculant as a sole treatment through the C–F process in treating concentrated suspended solids (SS) (547 mg/L), colour (19,705 Pt–Co) and chemical oxygen demand (COD) (4202 mg/L) in stabilised landfill leachate. The work also aims to evaluate the sludge properties after treatment. Functional groups, such as carboxylic acids, hydroxyl and amine/amino compounds (protein contents), were detected in the JC seed to facilitate the C–F process by neutralising the charge pollutant in water and cause the possibility of hydrogen bonding interaction between molecules. The combination of JC seed (0.9 g/L) as a flocculant reduced the dosage of SnCl4 as a coagulant from 11.1 g/L to 8.5 g/L with removals of 99.78%, 98.53% and 74.29% for SS, colour and COD, respectively. The presence of JC improved the sludge property with good morphology; the particles were in a rectangular shape, had clumps and strong agglomeration. These properties of sludge proved that JC seed could enhance the adsorption and bridging mechanism in the C–F procedure.

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.

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.

Novel two-step sintering and in situ bonding method for fabrication of ZrP2O7 ceramics

Sintering performance at high temperatures is a serious issue for tetravalent metal pyrophosphate MP2O7 ceramics (M = Ti, Zr, Hf, Ge, Sn, etc.). Herein, we investigated the influence of high synthesis temperatures and amounts of ZrP2O7 precursors on the properties of ZrP2O7 ceramics. A ZrP2O7 powder was first synthesised via a solid-state reaction; this powder was used in the fabrication of the ZrP2O7 ceramic using a combination of two-step sintering and in situ bonding using MgO as the sintering aid. The phase composition and microstructure of the ZrP2O7 powder as well as the ZrP2O7 ceramic were studied by X-ray diffraction and scanning electron microscopy. The physical properties and room-temperature thermal conductivity of the ZrP2O7 ceramic were investigated. The ceramic exhibited high thermal stability at 1350 °C. This study indicates that the mechanical properties of the ZrP2O7 ceramic can be enhanced while maintaining their low thermal conductivity by sintering it at 1300 °C with the addition of an appropriate amount of the ZrP2O7 precursors to the ZrP2O7 powder.

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.