Ratio In Solid Solution Research Articles

Controllable growth of (Hf, Zr)B2 solid solution coating via CVD for ultra-high temperature ablation of C/C composites

In this paper, we have successfully addressed the challenges of cracking and spalling in HfB2 coatings during ablation through the novel synthesis of (Hf, Zr)B2 solid solution coatings using the chemical vapor deposition (CVD) method. The ablation resistance of the coating exhibited an initially improving trend followed by a subsequently deterioration as the Zr content increased. When the Hf/Zr molar ratio in the (Hf, Zr)B2 solid solution coating was 1:1, a thicker Hf-Zr-O amorphous oxide layer was formed during ablation, which acted as a barrier, preventing the inward diffusion of oxygen. As a result, the (Hf0.5Zr0.5)B2 solid solution coating exhibited superior ablation resistance with a mass ablation rate of only −0.216 mg/s and a linear rate of −0.089 µm/s. These findings underscore the enormous potential of boride solid solution UHTC as exceptional candidates for ultra-high temperature ablation resistant applications.

Controllable synthesis and structure analysis of VCxO1-x solid solution by experiment and first-principles calculation

Vanadium oxycarbide (i.e. VCxO1-x) solid solution was expected to be a novel and promising ceramic materials in energy storage, catalysis and the preparation of metallic vanadium. The controllable synthesis and structure analysis of VCxO1-x solid solution are still rare. Here, VCxO1-x solid solution with different C/O molar ratio are successfully synthesized through a convenient carbothermal reduction of V2O3. The influences of reaction temperature, time, and C/V2O3 molar ratio in raw material are studied. It is found that carbothermal reduction must be carried out at higher temperature than 1500 °C in order to prepare single-phase VCxO1-x solid solution. C/O molar ratio in VCxO1-x solid solution can be well controlled by C/V2O3 molar ratio in raw material. Based on structure examination, it is confirmed that VCxO1-x is a continuous solid solution. Compared to VC, VCxO1-x solid solution exhibits better thermal stability and oxidation resistance. The lattice constant of VCxO1-x solid solution will increase with the increase of C content due to larger radius of C atom. Electronic properties of VCxO1-x solid solution were evaluated by first-principles calculations and experiments. The results demonstrated that VCxO1-x solid solution possesses high conductivity. The work is beneficial to controllable synthesis of VCxO1-x solid solution and promising applications in energy storage, catalysis and the preparation of metallic vanadium.

Estimation of phosphate extractability in flooded soils: Effect of solid-solution ratio and bicarbonate concentration

The Olsen method is widely used to determine bioavailable phosphate (P) in upland soils. It is also used in flooded soils, although different estimates of extractable-P are obtained under anoxic and oxic conditions. In this study, variations in extractable-P in three soils under different redox conditions were evaluated as a function of solid to solution ratio (SSR) (1:5–1:200) and bicarbonate concentration (0.1–1 M). The parameterized CD-MUSIC model was used to describe the data, with optimization of reactive surface area (RSA) and reversibly adsorbed-P (R–PO4). The RSA may vary due to the reductive dissolution of iron minerals and/or the formation of new reactive surfaces upon the establishment of reducing conditions. Changes in SSR and bicarbonate concentration significantly affected extractable-P under both oxic and anoxic conditions; more P was extracted under anoxic than under oxic conditions. The difference was 1.5–2 times greater for the highest SSR considered. In the soil samples with higher organic carbon content, the effect of bicarbonate concentration on extractable-P was remarkable. The large differences in extractable-P under oxic and anoxic conditions were probably due to differences in iron (hydr)oxide content. The CD-MUSIC model successfully predicted the effect of SSR on extractable-P under both conditions. R–PO4 data were fitted for oxic conditions and assumed unchanged for anoxic samples, while RSA data were fitted for both conditions. The RSA values were lower in anoxic than in oxic samples. Overall, our data and model calculations indicate that using wet soil samples obtained in-situ for evaluation of Olsen-P in submerged soils lead to a higher estimation of extractable-P than estimated in oxic soils. If soil testing in the presence of target plants confirms the reliability of in-situ sampling for Olsen-P estimation, the P fertilizer dose applied to submerged soils could be reduced, which is very important from environmental and economic perspectives.

First-principles design and experimental validation of β-Ti alloys with high solid-solution strengthening and low elasticities

β-Ti alloys with high strengths and low elasticities are suitable for application in biomaterials. However, to date, a clear and quantitative alloy design strategy to achieve alloys with these properties has not been developed. Herein, we designed β-Ti alloys with the required properties by first-principles calculations with experimental validations. Based on the design, N, O, Si, and Zr were selected as solute elements to realize β-Ti alloys with high solid-solution (SS) strengthenings and low Young's moduli. Compared to β-Ti alloys with other solute elements, β-type Ti–35 at% Ta alloys containing the abovementioned solute elements and fabricated by powder metallurgy demonstrated higher ratio of SS strengthening to modification in Young's modulus, validating the prediction by first-principles calculations. Among the β-Ti alloys with these solute atoms, the β-Ti alloy with N exhibited significant SS strengthening with the highest ratio of strength to Young's modulus. We believe that computational screening similar to the one in this study is effective in developing high-performance materials.

Optimization of Carboniferous Egyptian Kaolin Treatment for Pharmaceutical Applications

This paper quantitatively determines the occurrences of potentially toxic elements in Carboniferous kaolin in southwestern Sinai, Egypt. This research describes, in detail, the experimental treatment optimization to be used in pharmaceutical applications. The concentrations of As, Co, Ni, Pb, and V in these kaolin deposits exceed the Permitted Concentrations of Elemental Impurities for oral use in pharmaceutical applications. Herein, six desorbing agents (acetic acid, citric acid, DTPA, EDDS, EDTA, and NTA) were utilized as extracting solutions in batch-wise extractions to select the proper reagents. Parameters such as the pH, the mixing speed and time, and the solid–solution ratio were varied to optimize the extraction conditions. The findings indicate that citric acid and EDTA were effective in the removal of the aforementioned elements. The results reveal that the optimum removal of potentially toxic elements from kaolin can be achieved using citric acid and EDTA concentrations of 0.2 M and 0.1 M, respectively, for the treatment of 5 g of kaolin, under a pH of 4 for citric acid, and a pH of 10 for EDTA. The ideal mixing speed and time are 500 rpm and 6 h, respectively. Using 1:10 S/L of citric acid and EDTA showed removal rates of 100% for all the investigated PTEs. We recommend this treatment for different kinds of kaolin showing various degrees of contamination.

Electronic, mechanical and thermodynamic properties of ZrC, HfC and their solid solutions studied by first-principles calculation

The electronic properties, dynamic stabilities and mechanical properties of ZrC, HfC, and their solid solutions were determined using first-principles calculations. The crystal structures and elastic moduli of ZrxHf1−xC compounds were investigated under different transition metal atom solutions, and linear changes were observed in cell volumes, bond lengths and elastic properties with increasing hafnium atom content. The obtained phonon spectra and elastic constants show that all the compounds are dynamically and mechanically stable because they satisfy the corresponding stability criteria. The solid solutions of ZrC and HfC did not affect their electronic and mechanical properties. They are still metals, and their mechanical properties are comparable to those of ZrC and HfC. Moreover, the corresponding properties can be adjusted to some extent by changing the solid-solution ratio of the transition metal atoms. This provides a considerable advantage and convenience for the practical application of such materials.

Effects of Washing Solution, Washing Time, and Solid-Solution Rate on the Maximum Heavy Metals Removal Efficiency

In Korea, for heavy metal-contaminated soil, there are insufficient basic data as well as field application cases for soil washing. This study was conducted to suggest the significant factors and optimal operation conditions for the maximum heavy metal removal efficiency. Five types of washing solution [acid solution (HCl), citric acid, oxalic acid, EDTA, and CaCl2], washing time (10–360 min), and solid-solution ratio (1:2–1:100) were selected as significant operational factors. Non-observed effect concentration (NOEC) and central composite rotatable design (CCRD) were applied to derive the optimal conditions. The soil pH was slightly alkali, and it was highly contaminated by Cd (17.34 mg kg−1), Cu (307.76 mg kg−1), Pb (714.78 mg kg−1), and Zn (1755.47 mg kg−1), complexly. For all heavy metals, CaCl2, a neutral salt, was difficult to achieve the remediation goal. On the other hand, Cd, Cu, and Pb were removed successfully from the soil by acid solution, citric acid, oxalic acid, and EDTA. For Zn, only acid solution and oxalic acid could meet the remediation goal (300 mg kg−1). As the washing time increased, the heavy metal removal efficiency showed a tendency to increase overall. Especially, oxalic acid and acid solution were able to reach the highest efficiency point within 30 min, whereas citric acid and EDTA took 2 to 4 h at the longest. In the case of 1 M citric acid, through the CCRD experiment, optimal operation conditions (solid-solution ratio and washing time) could be deduced for each heavy metal. Furthermore, this series of processes can be utilized as a useful tool to find the optimal operating conditions and, at the same time, achieve the remediation goal.

Preliminary examination for revealing the provenance dependency of the lattice spacing of biotite for the provenance estimation of Atamadai-type pottery (2500–1500 BC) by XRD

A total of 77 pottery shards originating from the Middle Jomon period (2500–1500 BC) were excavated from the Hinoki site in Tochigi, Japan. Fifty-nine of the shards were Atamadai-type pottery in which fragments containing biotite were mixed during the manufacturing process. For the provenance estimation of the biotite temper in the Atamadai-type pottery pieces, the reliance of the biotite's lattice spacing on the samples’ origin was verified using X-ray diffraction (XRD) measurements of seven biotite-containing rocks possessing the different provenances. Three samples showed significant differences in the lattice spacing of biotite 001. The remaining samples indicated no significant differences. In addition to lattice spacing, the clarification of the provenance dependency also requires the measurement of the solid-solution ratio (Mg/Fe).

Evaluating the adsorption of Shanghai silty clay to Cd(II), Pb(II), As(V), and Cr(VI): kinetic, equilibrium, and thermodynamic studies.

The adsorption properties of Shanghai silty clay (SSC) towards heavy metal ions Cd(II), Pb(II), As(V), and Cr(VI) were investigated by batch experiments. The effects of solid-solution ratio, pH, temperature, reaction time, and metal concentration on sorption were analyzed. In order to better understand the adsorption mechanisms, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray fluorescence (XRF) were used to analyze the soil specimen before and after sorption. Three adsorption kinetic models and three adsorption isotherm models were used to analyze the adsorption characteristics. Thermodynamic parameters including changes in the Gibbs free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0) were also calculated. Sorption capacity of SSC was compared with other clay minerals reported in the literatures. The results show that the selectivity sequence is Pb(II) > Cd(II) > As(V) > Cr(VI), with equilibrium sorption capacities of 26.46, 8.90, 2.80, and 1.85mgg-1, respectively. Adsorption is largely effective on the clay surface rather than on the crystals. The clay surface turns to be flat and slippery after adsorption. The Langmuir model shows the best fit for Cd(II) and Pb(II) data, while Freundlich model is more suitable for As(V) and Cr(VI). The optimum solid-solution ratios for sorption of Cd(II), Pb(II), As(V), and Cr(VI) are 15, 6, 40, and 40g L-1, respectively. The optimum pHs for Cd(II), Pb(II), As(V), and Cr(VI) adsorption are 9.0, 6.0, 7.0, and 2.0, respectively. The pseudo-second-order kinetic is found to be the dominant sorption mechanism of these four ions on SSC. For Cd(II) and Pb(II), both particle diffusion and film diffusion are rate-limiting factors, whereas for As(V) and Cr(VI), intraparticle diffusion is the rate-controlling factor. The thermodynamic analysis reveals that the adsorption of Cd(II) and Pb(II) is spontaneous and endothermic and the system disorder increases, while adsorption of As(V) and Cr(VI) is exothermic and the system disorder decreases. Compared with most clay minerals, natural SSC exhibits comparable adsorption capacity and thus can potentially be used as a landfill liner material to retard the migration of heavy metals.

Investigation of Solid Solution Ratio and Study for Crystal and Electronic Structure and Battery Properties of Spinel-Type αMgCo1.5Mn0.5O4-(1-α)Mg(Mg0.33V1.57Ni0.1)O4 for Mg Rechargeable Battery Cathode Materials

1. Introduction The Mg secondary battery of which a high volume energy densities is expected as the next generation secondary battery. However the Mg diffusion is difficult, and it don’t achieve to practical use. The previous study reported the cathode material MgCo2-xMnxO4 with spinel type structure (x= 0.5)1) and Mg (Mg0.33V1.67-yNiy)O4 (y= 0.1) 2) so far at our laboratory. The former cathode can exhibit a high initial discharge capacity. However, the capacity retention ratio is low. On the other hand, the latter cathode can exhibit high capacity retention ratio. This research was performed to determine synthetic method of solid solution cathode αMgCo1.5Mn0.5O4-(1-α) Mg(Mg0.33V1.57Ni0.1)O4 (α = 0.1, 0.3, 0.5, 0.7, 0.9) which is new cathode material and to measure battery characteristics for the purpose of utilizing an advantage of these materials.The electrode was characterized by the Rietveld analysis to reveal charge-discharge mechanism. 2. Experimental Three synthetic routes were examined to obtain the solid solution materials: (1) solid phase method (2) mechanochemical method and (3) reverse coprecipitation method. The synthesis method (1), mixed each endmembers by an agate mortar, and calcined.The synthesis method (2), mixed each endmembers and obtained a target materials by only the mechanical milling. The synthesis method (3), mixed each metal-nitrate aqueous solutions as it was α = 0.1, 0.3, 0.5, 0.7, 0.9, calcined to get a target materials.The obtained materials were identified by XRD,ICP-AES, and performed the charge-discharge cycle tests using three electrode cell. Synchrotron X-ray diffraction measurement (BL19B2, SPring-8) was performed and the average structure was analyzed by a Rietveld analysis (RIETAN - FP). Furthermore, XAFS (BL14B2, SPring-8) revealed pristine and charging/discharging electrode redox mechanism. 3. Result and discussion The sample synthesized by method (1) wasn’t assigned to spinel structure, while the samples synthesized by method (2) and (3) were assigned to spinel structure with the space group of Fd-3m from the powder X-ray diffraction. The sample of synthesis method (1) and (2), approximately controlled on a metal composition by ICP - AES. However, V composition of synthesis method (3) controlled smaller than preparation composition. Good fitting was obtained about a powder sample of a synthesis method (2) and (3) as a result of the Rietveld analysis, however, it revealed Mg occupied 8a/16d site for each sample.A charge-discharge cycle test was carried out at 90 ° C using a three-electrode cell.the sample of a synthesis method (2) performed 15 cycles by the discharge capacity of about 80 mAh/g, and the sample of method (3) (α =0.5) performed 24 cycles by the discharge capacity of about 100 mAh/g while the sample of method (3) (α =0,3) achieved 60 cycles at the discharge capacity of about 160 mAh/g and it had high capacity ratio (Fig.1). Acknowledgement This work was supported by JST ALCA-SPRING Grant Number JPMJAC1301, References 1) M. Ichiyama, N. Ishida, N. Kitamura, Y. Idemoto, the 86th Electrochemical Society of Japan Meet summary and 3O20 (2019).2) N. Kawakami, N. Ishida, N. Kitamura, Y. Idemoto, the 59th Battery forum summary P.375(2018). Figure 1

Effect of Basicity on the Structure, Viscosity and Crystallization of CaO-SiO2-B2O3 Based Mold Fluxes

In this study, the structure, viscosity characteristics, and crystallization behavior of CaO-SiO2-B2O3 based melts were studied combining molecular dynamics (MD) simulation, Fourier transform infrared (FTIR) spectroscopy, rotating viscometer test, and FactSage thermodynamic calculation. The results showed that, in the ternary CaO-SiO2-B2O3 glass system, stable structural units of [SiO4]4− tetrahedral, [BO3]3− trihedral and [BO4]5− tetrahedral were formed, and the Si-O and B-O structure depolymerize with the basicity increase from 1.15 to 1.25, then the B-O structure become complex with the basicity further increase to 1.35. In fluorine-free mold fluxes, with the basicity increases, the viscosity at 1300 °C increases, the liquidus temperature decreases and then increases, the network structure polymerizes, it indicates that the structural complexity rather than the melting property change plays a predominant role in increasing the viscosity at 1300 °C. Moreover, due to the changes in crystallization phase and solid solution ratio, the viscosity-temperature curve of fluorine-free slag shows the characteristics of alkaline slag and the break temperature increase with the basicity increase. The MD simulation, FTIR experiment, viscosity test, and FactSage calculation results are verified and complemented each other.

Activation of grapefruit derived biochar by its peel extracts and its performance for tetracycline removal

A novel adsorbent derived from grapefruit peel (GP) based biochar (GPBC) was synthesized by combined carbonization of GP and subsequent activation by GP extracts. Compared to biochar without extracts activation, the technique granted GPBC-20 (with 1:20 of solid-solution ratio) more abundant surface functional groups, which exerts the adsorbent superior performance for tetracycline (TC) adsorption (37.92 mg/g v.s. 16.64 mg/g). The adsorption kinetics, isotherms and thermodynamics models were further used to evaluate the adsorption behavior of GPBC. The enhanced adsorption was analyzed by characterization of fresh and used GPBC, revealing that the adsorption mechanism was comprised of pore filling, charge interaction and chemical bonding. The comprehensive investigation of using agricultural waste extracts as activator to prepare its raw materials-based adsorbents may be of great significance for enhanced resource utilization.

Hydrometallurgical Regeneration of LiMn2O4 Cathode Scrap Material and Its Electrochemical Properties

AbstractThe main researches focus on the recovery of metal elements in lithium manganate and not consider regenerating the cathode scrap materials. In this study, first, the polyvinylidene fluoride (PVDF) binder is removed by a combination of solvent dissolution and heat treatment. PVDF is easily separated by dissolving in an N‐methyl‐2‐pyrrolidone solution at a heating temperature of 60 °C, stirring time of 50 min, and solid solution ratio of 80 g⋅L−1. The dissolution rate of the scrap material achieves 86.70 % under optimal conditions. Further, using inductively coupled plasma spectroscopy to define the Li and Mn metal contents, and the LiMn2O4 cathode material is regenerated by a hydrometallurgical method. At the optimum calcination conditions of 500 °C for 12 h, electrochemical performance show that there are obvious charge and discharge platforms in the charge/discharge curves, and high first‐cycle discharge capacity is 123.7 mAh g−1 (3.0–4.3 V and 0.1 C), after 50 cycles, it decrease to 83.2 mAh g−1.

Magmatic sulfides in high-potassium calc-alkaline to shoshonitic and alkaline rocks

Abstract. We investigate the occurrence and chemistry of magmatic sulfides and their chalcophile metal cargo behaviour during the evolution of compositionally different magmas from diverse geodynamic settings both in mineralised and barren systems. The investigated areas are the following: (a) the Miocene Konya magmatic province (hosting the Doğanbey Cu–Mo porphyry and Inlice Au epithermal deposits, representing post-subduction) and (b) the Miocene Usak basin (Elmadag, Itecektepe, and Beydagi volcanoes, the latter associated with the Kişladağ Au porphyry in western Turkey, representing post-subduction). For comparison we also investigate (c) the barren intraplate Plio-Quaternary Kula volcanic field west of Usak. Finally, we discuss and compare all the above areas with the already studied (d) Quaternary Ecuadorian volcanic arc (host to the Miocene Llurimagua Cu–Mo and Cascabel Cu–Au porphyry deposits, representing subduction). The volcanism of the newly studied areas ranges from basalts to andesites–dacites and from high-K calc-alkaline to shoshonitic series. Multiphase magmatic sulfides occur in different amounts in rocks of all investigated areas, and, based on textural and compositional differences, they can be classified into different types according to their crystallisation at different stages of magma evolution (early versus late saturation). Our results suggest that independently of the magma composition, geodynamic setting, and association with an ore deposit, sulfide saturation occurred in all investigated magmatic systems. Those systems present similar initial metal contents of the magmas. However, not all studied areas present all sulfide types, and the sulfide composition depends on the nature of the host mineral. A decrease in the sulfide Ni∕Cu (a proxy for the monosulfide solid solution (mss) to intermediate solid solution (iss) ratio) is noted with magmatic evolution. At an early stage, Ni-richer, Cu-poorer sulfides are hosted by early crystallising minerals, e.g. olivine–pyroxene, whereas, at a later stage, Cu-rich sulfides are hosted by magnetite. The most common sulfide type in the early saturation stage is composed of a Cu-poor, Ni-rich (pyrrhotite mss) phase and one to two Cu-rich (cubanite, chalcopyrite iss) phases, making up ∼84 and ∼16 area % of the sulfide, respectively. Sulfides resulting from the late stage, consisting of Cu-rich phases (chalcopyrite, bornite, digenite iss), are hosted exclusively by magnetite and are found only in evolved rocks (andesites and dacites) of magmatic provinces associated with porphyry Cu (Konya and Ecuador) and porphyry Au (Beydagi) deposits.

Simultaneously enhanced strength and ductility of 6xxx Al alloys via manipulating meso-scale and nano-scale structures guided with phase equilibrium

Excellent comprehensive mechanical properties including good formability, high strength and high ductility are prior demands for Al-Mg-Si-Cu alloys. This study utilizes calculation of phase diagram (CALPHAD) to simplify the alloy design and meet these demands. Specifically, CALPHAD was used to finely tune the Mg/Si atomic ratio in solid solution and accurately control the type and content of second phases, especially to avoid the formation of the harmful constituent phase β-AlFeSi. Constituents and dispersoids of only α-AlFeMnSi phase were found in the alloy prepared. An optimized microstructure with fine grains, micro scale constituents, densely distributed submicron scale dispersoids and extremely dense nano precipitates provides effective impediment to dislocation gliding and induces transgranular fracture. Therefore, the designed alloy has better comprehensive mechanical properties than other 6xxx series aluminum alloys, including excellent formability, strength and ductility. The low T4P strength of 149 MPa as well as the high elongation of 26.1% implies the alloy's applicability to automobile body panel forming. The yield strength was rapidly improved from 149 MPa to 277 MPa during the paint bake ageing, because the number density of precipitates is twice as high as that of some other 6xxx alloys. Meanwhile, the elongation was kept at a high level of 20.0%.

Kinetics and mechanisms of debromination of tetrabromobisphenol A by Cu coated nano zerovalent iron

Brominated flame retardants are of concern to our environment because of its endocrine disruptive, immune toxicant characteristics, and toxic brominated byproducts. As a potential remediation technology, debromination of tetrabromobisphenol A (TBBPA) from both aqua and soil by Cu coated nano zero-valent iron particles (Cu-nZVI) was investigated. Because of its catalytic reductive properties, Cu-nZVI has a potential for removing TBBPA. Batch experiments show that Cu-nZVI effectively debrominated TBBPA into tri-, di-, mono-bromobisphenol A, and bisphenol A (BPA) with a low suspension density (0.5 g L−1). As indicated by the low apparent activation energy (69.66 kJ mol−1), the optimal reaction condition was the Cu loading of 0.5 wt%, 27 °C and pH 5.0. Tetrabromobisphenol A (10 mg L−1) was transformed into several reaction products within 120 min, and BPA was detected as a major reaction product after 240 min. The reaction rate constant (kobs) was proportionally correlated to solid-solution ratio and temperature. The concentration of metals during the debromination was too low (less than 0.13 mg L−1) to induce an adverse effect on the ecosystem. During the redox reaction, a new mineral, magnetite formed on particles’ surface accompanied by the oxidation of Fe0 and the elevation of pH. This study suggests that Cu-nZVI has the potential to be explored for the rapid and complete debromination of brominated flame retardants in both aquatic and edaphic environments.

Uncertainty and variability in laboratory derived sorption parameters of sediments from a uranium in situ recovery site

This research assesses the ability of a GC SCM to simulate uranium transport under variable geochemical conditions typically encountered at uranium in-situ recovery (ISR) sites. Sediment was taken from a monitoring well at the SRH site at depths 192 and 193 m below ground and characterized by XRD, XRF, TOC, and BET. Duplicate column studies on the different sediment depths, were flushed with synthesized restoration waters at two different alkalinities (160 mg/l CaCO3 and 360 mg/l CaCO3) to study the effect of alkalinity on uranium mobility. Uranium breakthrough occurred 25% - 30% earlier in columns with 360 mg/l CaCO3 over columns fed with 160 mg/l CaCO3 influent water. A parameter estimation program (PEST) was coupled to PHREEQC to derive site densities from experimental data. Significant parameter fittings were produced for all models, demonstrating that the GC SCM approach can model the impact of carbonate on uranium in flow systems. Derived site densities for the two sediment depths were between 141 and 178 μmol-sites/kg-soil, demonstrating similar sorption capacities despite heterogeneity in sediment mineralogy. Model sensitivity to alkalinity and pH was shown to be moderate compared to fitted site densities, when calcite saturation was allowed to equilibrate. Calcite kinetics emerged as a potential source of error when fitting parameters in flow conditions. Fitted results were compared to data from previous batch and column studies completed on sediments from the Smith-Ranch Highland (SRH) site, to assess variability in derived parameters. Parameters from batch experiments were lower by a factor of 1.1 to 3.4 compared to column studies completed on the same sediments. The difference was attributed to errors in solid-solution ratios and the impact of calcite dissolution in batch experiments. Column studies conducted at two different laboratories showed almost an order of magnitude difference in fitted site densities suggesting that experimental methodology may play a bigger role in column sorption behavior than actual sediment heterogeneity. Our results demonstrate the necessity for ISR sites to remove residual pCO2 and equilibrate restoration water with background geochemistry to reduce uranium mobility. In addition, the observed variability between fitted parameters on the same sediments highlights the need to provide standardized guidelines and methodology for regulators and industry when the GC SCM approach is used for ISR risk assessments.

Enhanced visible light photocatalytic activity of the mechanochemically prepared nanosized ZnxCd1-xS/Zn-Al layered double hydroxide precursor heterojunctions

ZnxCd1-xS/Zn–Al layered double hydroxide (LDH) precursor heterostructured composites were synthesized by a one-step mechanochemical method. X-ray diffraction, Fourier transform-infrared spectroscopy, SEM-EDS and thermogravimetric analysis confirmed the formation of the ZnxCd1-xS/Zn–Al LDH precursor composites. X-ray photoelectron spectroscopy indicated the formation of a heterojunction structure. The photocatalytic degradation activity for methyl orange of the heterostructured composites was observed even under visible light irradiation and exhibited a large enhancement with the increase in the molar ratio of sulfide solid solution to LDH as well as the increase in the ratio of Cd to Zn. A detailed investigation on the mechanism for the enhanced photocatalytic activity was performed, particularly regarding to the efficient separation of photogenerated electrons and holes with the heterostructure. This work provides a very simple and environment-friendly way to fabricate a series of heterostructured photocatalysts based on LDH precursor with transition metal sulfide well dispersed inside.

Measuring and modeling metal ions adsorption on αAl2O3, SiO2 and TiO2 nanoparticles in the presence of organic ligands

Nanoparticles (NPs) can be used to remove metal ions from aqueous solutions. However, removal efficiency of metal ions using NPs is influenced by organic ligands. The aims of this study were to investigate cadmium (Cd), nickel (Ni) and zinc (Zn) removal using αAl2O3, SiO2 and TiO2 NPs, to study the effect of organic ligands on metal adsorption and to simulate metal removal in mixed metal–organic systems using PHREEQC program. The experiments were performed in the pH range 2.0–8.0, solid–solution ratio 0.5–10 g L−1, contact time 10 min to 24 h and the citric and malic concentration from 0.2 to 2 mM. Adsorption of metal ions increased with increasing initial pH, adsorbent dosage and contact time. In the presence of citric acid adsorption of Cd on SiO2 NPs decreased noticeably with increasing concentration of citric acid from 0 to 2 mM while an increase in adsorption was observed when 0.2 mM malic acid added to SiO2 NPs. The adsorption of Ni in the presence of citric acid was inhibited, and low malic acid concentration (0.2 mM) promoted Ni adsorption on SiO2 and αAl2O3 NPs. These findings reveal that metal adsorption in the presence of organic ligands was not constant. A double-layer model and the NICA-DONNAN model were used to simulate the adsorption behavior. The results showed that monodentate complexes provide the best fit to the data and that the model could be used as a tool to assess adsorption of metal ions on NPs in the presence of organic ligands.

Control of Molecular Rotor Rotational Frequencies in Porous Coordination Polymers Using a Solid-Solution Approach

Rational design to control the dynamics of molecular rotors in crystalline solids is of interest because it offers advanced materials with precisely tuned functionality. Herein, we describe the control of the rotational frequency of rotors in flexible porous coordination polymers (PCPs) using a solid-solution approach. Solid-solutions of the flexible PCPs [{Zn(5-nitroisophthalate)x(5-methoxyisophthalate)1-x(deuterated 4,4'-bipyridyl)}(DMF·MeOH)]n allow continuous modulation of cell volume by changing the solid-solution ratio x. Variation of the isostructures provides continuous changes in the local environment around the molecular rotors (pyridyl rings of the 4,4'-bipyridyl group), leading to the control of the rotational frequency without the need to vary the temperature.