Cation Molar Research Articles

Effect of Fe (III)/Fe (II) cation molar ratio variation on magnetite Fe3O4 nanoparticles synthesized from natural iron sand by co-precipitation method

Effect of Fe (III)/Fe (II) cation molar ratio variation on magnetite Fe3O4 nanoparticles synthesized from natural iron sand by co-precipitation method

The Electrocatalytic Activity of Au Electrodes Changes Significantly in Various Na+/K+ Supporting Electrolyte Mixtures

The potential of maximum entropy (PME) is an indicator of extreme disorder at the electrode/electrolyte interface and can predict changes in catalytic activity within electrolytes of varying compositions. The laser‐induced current transient technique is employed to evaluate the PME for Au polycrystalline (Aupc) electrodes immersed in Ar‐saturated cation electrolyte mixtures containing potassium and sodium ions at pH = 8. Five cation ratios (0.5 M K2SO4:0.5 M Na2SO4 = 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1:0) are explored, considering earlier studies that unveil cation‐dependent shifts at near‐neutral pH. Moreover, for all electrolyte compositions, electrochemical impedance spectroscopy is utilized to determine the double‐layer capacitance (CDL), the minimum of which should be close to the potential of zero charge (PZC). By correlating cation molar ratios with the PMEs and PZCs, the impact on the model oxygen reduction reaction (ORR) activity, assessed via the rotating disk electrode method, is analyzed. The results demonstrate a linear relationship between electrolyte cation mixtures and PME, while ORR activity exhibits an exponential trend. This observation validates the PME–activity link hypothesis, underscoring electrolyte components’ pivotal role in tailoring interfacial properties for electrocatalytic systems. These findings introduce a new degree of freedom for designing optimal electrocatalytic systems by adjusting various electrolyte components.

Highly efficient recovery of Zn2+/Cu2+ from water by using hydrotalcite as crystal seeds

The efficient and waste-free recovery of heavy metals is critical for heavy metal wastewater treatment. In this work, we explored how heavy metals can be recovered as valuable chemicals in the presence of crystal seeds. Hydrotalcite (one kind of layered double hydroxides (LDHs)) was used as crystal seeds to recover Zn2+ in the presence of Al3+ from water (i.e., seed-Zn2+-Al3+ system), which was compared with the monometallic heterogeneous system (seed-Zn2+) and direct coprecipitation (Zn2+-Al3+) system. Our results demonstrated that the seed-Zn2+-Al3+ system possessed a recovery rate of 2.6–2.8 times and a recovery kinetic rate of 2.7–5.9 times higher than those of the other two systems. Differing from the latter two systems, hydrotalcite seeds could induce Zn2+ and Al3+ to form ZnAl-LDH in seed-Zn2+-Al3+. Interestingly, the ZnAl-LDH presents a compositional divalent/trivalent cation molar ratio of ca. 3, which is comparable with the value in the hydrotalcite. It was demonstrated that the hydrotalcite seeds could act as a template to significantly induce the formation of ZnAl-LDH complying with the seed's structure and compositional ratio. Similar induction effect of seeds as the Zn2+ system was further verified in Cu2+ systems. This work provides a novel strategy for efficient recovery of heavy metals with product selectivity.

Structural Properties of HEHN- and HAN-Based Ionic Liquid Mixtures: A Polarizable Molecular Dynamics Study.

Molecular dynamics simulations of binary mixtures comprising 2-hydroxyethylhydrazinium nitrate (HEHN) and hydroxylammonium nitrate (HAN) were conducted using the polarizable APPLE&P force field to investigate fundamental properties of multimode propulsion (MMP) propellants. Calculated densities as a function of temperature were in good agreement with experiments and similar simulations. The structural properties of neat HEHN and HAN-HEHN provided insights into their inherent, protic nature. Radial distribution functions (RDFs) identified key hydrogen bonding sites located at N-H···O and O-H···O within a first solvation shell of approximately 2 Å. Angular distribution functions further affirmed the relatively strong nature of the hydrogen bonds with nearly linear directionality. The increased hydroxylammonium cation (HA+) mole fraction shows the influence of competitively strong hydrogen bonds on the overall hydrogen bond network. Dominant spatial motifs via three-dimensional distribution functions along with nearly nanosecond-long hydrogen bond lifetimes highlight the local bonding environment that may precede proton transfer reactions.

A thermodynamic model for sulfur content at sulfide saturation (SCSS) in hydrous silicate melts: With implications for arc magma genesis and sulfur recycling

Modeling the effect of H2O on the “sulfur content at sulfide saturation” (SCSS) in silicate melt is essential for the estimation of SCSS in both arc magmas and slab melts. Here we present a thermodynamic approach, in which, SCSS in hydrous silicate melt has been modeled as a combination of S dissolving as S2− and HS−/H2S, based on the sulfide capacity (CS2−) and the hydro-sulfide capacity (CHS), respectively. By adopting the thermodynamic framework of O’Neill and Mavrogenes (2002), S dissolution as HS−/H2S can be modeled in an analogous fashion to that for modeling S2− in anhydrous melt with the relation: lnHSSCSS=-ΔG°Fes-FeO/RT+lnCHS-lnaFeOmelt+lnaFeSsulfide. To obtain an expression for CHS, we compiled published experimental data on SCSS in hydrous silicate melts covering a PT range of 0.15–3 GPa and 785–1600 °C, and melt H2O contents of ∼1–13 wt%. While the contribution of S dissolving as S2− in basaltic and andesitic melts can be calculated based on the updated SCSS model for anhydrous basic melt from O’Neill (2021), S2− is considered negligible in rhyolitic and dacitic melts, i.e., when melt FeO content <∼5 wt%. We propose an expression for CHS as a function of temperature, mole fractions of cations for the normalized anhydrous melt composition, ln(XOH + XH2O), and a Na + K-Al term for alkaline-enriched rhyolitic melts. The coefficients for cation mole fractions are adopted from the expression for CS2− from O’Neill (2021); the coefficients for the 1/T and Na + K-Al terms are obtained from regression. The reproducibility of compiled SCSS values is ±50% for hydrous rhyolitic and dacitic melts, and ±10–30% for hydrous basaltic and andesitic melts, representing a significant improvement in comparison to previous models.Our model produces SCSS values for the primitive arc magmas compiled by Ruscitto et al. (2012), that are in most cases higher than the measured S contents, implying sulfide under-saturated conditions during mantle wedge melting. The contribution of H2S dissolution to the calculated SCSS values varies in a range of 70–1234 ppm, which increases with the increase of H2O content (0.3–6.2 wt%). H2S dissolution therefore contributes to the higher S content in arc basalt compared to MORB, an observation which is further corroborated by the positive correlation between H2O and S contents in primitive arc magmas. Applying our current model to experimentally produced sediment melts spanning a PT range of 690–1050 °C and 2.5–4.5 GPa, demonstrates that sediment melts, especially those of intermediate supercritical character with >25 wt% H2O and peralkaline in composition, can have high SCSS values as a result of H2S dissolution, and act as the transfer medium for S recycling between the slab and mantle wedge under reduced conditions.

Phase-field mobility for crystal growth rates in undercooled silicates, SiO2 and GeO2 liquids

A simple phase-field model (PFM) was used to calculate phase-field mobility, L, and crystal growth rates in crystallization of 11 oxides or mixed oxides in undercooled silicates, SiO2 and GeO2 liquids, and material dependence of the L was discussed to predict the temperature dependence of crystal growth-rates for unmeasured liquids. By comparing the experimental crystal growth rates and the PFM simulation, we determined the parameters, A, and B, of the L=AkBTΔT6π2λ3ηTmB: A=6.7×10-6 to 2.6 m4J−1s−1 and B=0.65 to 1.3, which were unique for the materials. Furthermore, our PFM simulation with the determined L reproduced the experimental crystal growth rates quantitively. In a log–log graph, the A depends on the diffusion coefficient of a cation and have a proportional relationship with the diffusion coefficient of the cation molar mass average per unit an oxygen molar mass at the melting point, Tm. The B in a compound is determined by the sum of the cation molar mass divided by the oxygen molar mass, ∑iMi/MO. The B in ∑iMi/MO≤25 decreases as the cation molar mass increases. Because the cation molar mass is proportional to the cation transfer’s inertial resistance, the B decreases with the inverse of the cation molar mass. The B saturates at approximately 0.67 during crystallization of heavy cation silicates in ∑iMi/MO≥25, resulting in the peak temperature of the crystal growth rate, Tp≈0.9Tm.

Hierarchical, template-free self-assembly morphologies in CeO2 synthesized via urea-hydrothermal method

Nano-crystalline CeO2 was synthesized via the urea-hydrothermal method without templates or structure-directing agents. The synthesis parameters Ce3+ to Ce4+ and urea to cation molar ratios, reaction temperature and reaction time were varied to analyze their effect on morphology, texture and reducibility. The analysis of the obtained morphologies provides strong evidence of a hierarchical and sequential template-free self-assembly process that evolves from shuttles to dumbbells to spheres. In all cases, the morphology of samples remains unchanged even after calcination at 500 °C. The presence of Ce4+ in the initial solution clearly provides the full self-assembly sequence and is decisive for obtaining non-hollow spheres of CeO2 with high specific surface area and high pore volume. Besides, if only Ce3+ is present, typical CeOHCO3 shuttle-like particles with orthorhombic structure are obtained. The use of Ce3+ in combination with Ce4+ produces partial sequences of the self-assembly process that provide a strong indication of the hierarchical sequence.The urea to cation molar ratio controls the nucleation process and proves to be crucial to obtain the self-assembly sequence. On the other hand, temperature and reaction time show a moderate effect on morphology.

Structural, optical and electrical properties of ZnO/ZnAl2O4 nanocomposites prepared via thermal reduction approach

ZnO/ZnAl2O4 nanocomposites (Z r A-MMO) with homogeneously distributed ZnAl2O4 nanoparticles in the interpenetrating network of ZnO were successfully prepared via two-step solution process, namely co-precipitation of Zn/Al–NO3 layered double hydroxide (Z r A-LDH) precursor and thermal treatment methods. The effect of cation molar ratio (r) between Zn2+ and Al3+ on the morphological, structural, thermal, optical as well as electrical properties of ZnO-based MMOs was investigated in detail. A mechanism study related to the surface modification, optical band edge alteration as well as improvement of electrical conductivity after phase transformation from LDH to MMO was also elucidated. The optimum Z5A-MMO sample presents the highest electrical conductivity of 8.23 × 10−3 S/cm as compared to 7.26 × 10−7 S/cm for the standard ZnO nanocrystal. It is believed that the bathochromic shift in optical band gap of Z5A-MMO plays a pivotal role in facilitating the photoemission process and leads to the increase in number of carrier concentration in the sample. This method could provide alternative pathways for fabricating a high electrical conductivity MMO-based material and benefit in future optoelectronic devices.

Silver Cation Coordination Study to AsW9 Ligand – A Trilacunar Arsenotungstate Compound

AbstractObjective: The main objective of this research is to find the coordination ratio between AsW9and Ag+, as a preliminary study for synthesizing a new silver-arsenotungstate complex. Material and method: The ligand:cation molar ratio in complexes was determined by conductometric and potentiometric titrations of AsW9with silver salts: CH3COOAg, AgNO3. Results: The ratio was obtained from the inflexion points of the curves when molar ratio was plotted versus conductivity, or from the equivalence point when silver added volume was plotted versus pH value. Each graphic shows one point of inflexion corresponding to 1:1.54 ratio of AsW9:Ag+. In the same manner, the equivalent volumes determined by graphical method gave the ratio 1:1.53. The spectral results confirmed that a AsW9:Ag+complex was formed since the ligand absorption maxima values have been changed from 190 nm to 197 nm in the case of using AgNO3and 196 nm for CH3COOAg corresponding to the W=Odbond, and from 246.5 nm to 274 nm (AgNO3) and 270 nm (CH3COO-Ag+) for the W-Ob,c-W bond. Conclusions: Silver cation exhibit a preference for AsW9in a ratio of 3 to 2. This ratio can be associated to a sandwich type arrangement, with two trilacunary Keggin building blocks incorporating 3 metal cations in a tetrahedral geometry.

Cu and Fe diffusion in rhyolitic melts during chalcocite “dissolution”: Implications for porphyry ore deposits and tektites

Copper diffusion plays an important role in natural processes, such as metal transport during the formation of magmatic-hydrothermal porphyry-type ore deposits and Cu isotope fractionation during tektite formation. Copper diffusion data in natural silicate melts, however, are limited. In this study, chalcocite (Cu 2 S) “dissolution” experiments were carried out using chalcocite-rhyolite diffusion “couples” to study Cu (and S) diffusion in rhyolitic melts. Instead of chalcocite dissolution as initially expected, our experiments show that Cu is transferred from the chalcocite crystal to the rhyolitic melt, and Fe is transferred from the rhyolitic melt to chalcocite, whereas the S concentration profile in the rhyolitic melt is essentially flat. From the Cu and Fe exchange profiles in the rhyolitic melts, Cu diffusivities and Fe diffusivities are obtained and reported. Copper diffusivity in rhyolitic melts containing 0.10 to 5.95 wt% H 2 O at temperatures of 750 to 1391 °C and pressures of 0.5 to 1.0 GPa can be described as: D Cu Rhy = exp [ - ( 14.75 ± 0.35 ) - ( 0.23 ± 0.10 ) w - ( 11647 ± 491 ) - ( 698 ± 117 ) w T ] , which allows the estimation of an activation energy for diffusion in dry rhyolitic melts to be 96.8 ± 4.1 kJ/mol. In the above equation, diffusivity ( D ) is in m 2 /s, T is the temperature in K, w is the H 2 O concentration in the rhyolitic melts in wt% and all errors reported are at 1σ level. Combining Cu diffusion data from this study and previous data in basaltic melt gives a general equation for Cu diffusivity in natural silicate melts: D cu = exp [ - ( 17.3 ± 0.9 ) + ( 3.8 ± 1.5 ) ( Si + Al-H ) - ( 4403 ± 1094 ) + ( 9700 ± 1921 ) ( Si + Al-H ) T ] , where Si+Al-H is the cation mole fraction of Si plus Al minus H in the silicate melt on a wet basis. Iron diffusivities obtained in this study, in anhydrous to 6 wt% H 2 O rhyolite, are combined with previous data to get a general equation for Fe diffusion in rhyolitic melts: D Fe Rhy = exp [ - ( 16.1 ± 1.7 ) - ( 19859 ± 2541 ) - ( 1218 ± 135 ) w T ] . Our data demonstrate that Cu diffusion is faster than H 2 O or Cl in rhyolitic melts containing 6 wt% water, which indicates that the scavenging and transport of Cu by a magmatic volatile phase during formation of porphyry-type ore deposits is not limited by diffusion of Cu. Based on our experimental data, Cu diffusivity is almost four orders of magnitude higher than Zn in anhydrous rhyolitic melts, which supports the explanation of more diffusive loss of Cu leading to more fractionated Cu isotopes than Zn isotopes in tektites.

A pseudo-quantitative ternary surfactant ion mixing plane phase diagram for a cationic hydroxyethyl cellulose with dodecyl sulfate counterion complex salt

The surfactant ion mixing plane phase diagram was constructed for cationic hydroxyethyl cellulose dodecyl sulfate (cat-HECDS), sodium dodecyl sulfate (NaDS) and water. The number of phases and structures present in the prepared ternary composition were assessed visually and guided the placement of phase boundaries. Two multi-phase regions surround a large, central one-phase isotropic region. In the dilute portion of the diagram, an isotropic-isotropic two-phase region exists along the water-complex salt axis. A concentrated multi-phase region adjacent to the water-NaDS axis includes a three-phase region defined as isotropic-hexagonal-monoclinic surrounded by three two-phase regions of isotropic-monoclinic, isotropic-hexagonal, and hexagonal-monoclinic.This phase diagram is similar to one previously published in this journal [Svensson et al., Colloids Surf. A, 228 (2003) 91–106]. Here the degree of cationic substitution on the polymer was reduced by half. This resulted in a shift in the locations of the phase boundaries, but not the phases and structures, present in this plane. Evaluating the phase boundaries as a function of anion:cation molar ratio highlighted the impact of the hydrophobic binding of excess surfactant monomers to the polycation-surfactant anion network on the phase transitions in the surfactant ion mixing plane phase diagrams for cat-HECDS.

Effect of hydrothermal treatment conditions on formation of nickel hydrogermanate with platy morphology

Study of the phase composition and morphology of products formed in a hydrothermal treatment of the Ni(OH)2–GeO2–H2O system with Ni/Ge cation molar ratios of 1, 1.5, and 2 in water and in aqueous solutions of HCl and NaOH demonstrated that the hydrothermal treatment products are composed of particles with plate-like morphology and average plate thickness of 40 nm and width of 500 nm. In this case, the phase composition of the products depends both on the molar ratio between the Ni and Ge cations and on the composition of the hydrothermal medium. Single-phase samples with structure similar to that of lizardite were obtained by treatment of a mixture with Ni/Ge = 1 in an alkaline medium or in a mixture with Ni/Ge = 1.5, irrespective of the composition of the medium. With the excess of GeO2, a talc-like phase is formed, whereas with the excess of Ni(OH)2, the samples contain crystalline nickel hydroxide in addition to the lizardite-like phase. Possessing magnetic and semiconductor properties, the single-phase nanopowders obtained in the study are promising as functional nanodispersed fillers of composite materials.

Composite modification mechanism of cationic modifier to amphoteric modified kaolin and its effects on surface characteristics

In this study, the changes of S DC curves (sum amount of dodecyl trimethyl ammonium cation and Ca2+/2 adsorbed on dodecyl dimethyl betaine-modified kaolin under different dodecyl trimethyl ammonium cation molar fractions) were analyzed to reveal the modification mechanism of cationic modifier (dodecyl trimethyl ammonium bromide) on amphoteric modified kaolin (kaolin modified by dodecyl dimethyl betaine). In addition, total organic carbon content and surface characteristics of different modified kaolins were analyzed using X-ray diffraction, specific surface area calculation, Fourier transform infrared spectroscopy, thermogravimetry, and scanning electron microscope. Results showed that: (1) “S DC” curves of compositely modified kaolin with dodecyl dimethyl betaine-modified ratios of 15, 30 and 60 % started to rise (appeared hydrophobic binding) at dodecyl trimethyl ammonium bromide-modified ratios of 16.80, 7.63, and 0.68 % (the critical point for different modification mechanisms), respectively. (2) Total organic carbon content of modified kaolins under different modification mechanisms showed hydrophobic modification mode > ion exchange and hydrophobic binding coexisting mode > ion exchange mode. Interlayer spacing showed no significant change under different modification modes. Specific surface area decreased slowly with enhanced hydrophobic modification mode. Fourier transform infrared spectroscopy and thermogravimetry results showed the modification effects of both dodecyl dimethyl betaine and dodecyl trimethyl ammonium bromide modification on kaolin surfaces. Scanning electron microscope results presented that the number of lamellar structures increased on clay surfaces with enhanced hydrophobic modification mode.

Crystal structure, phase transition and conductivity study of two new organic – inorganic hybrids: [(CH2)7(NH3)2]X2, X = Cl/Br

Two hybrids 1,7-heptanediammonium di-halide, [(C7H20N2]X2,X = Cl/Br crystallize in monoclinic P21/c, Z = 4. [(C7H20N2]Cl2: a = 4.7838 (2) Å, b = 16.9879 (8) Å, c = 13.9476 (8) Å, β = 97.773 (2)°, V = 1203.58(10) Å3, D = 1.137 g/cm3, λ = 0.71073 Å, R = 0.052 for 1055 reflections with I > 2σ(I), T = 298(2) K. [(C7H20N2]Br2: a = 4.7952 (10) Å, b = 16.9740 (5) Å, c = 13.9281 (5) Å, β = 97.793 (2)°, V = 1203.83(6) Å3, D = 1.612 g/cm3, λ = 0.71073 Å, R = 0.03 for 1959 reflections with I > 2σ(I) T = 298(2) K. Asymmetric unit cell of [(C7H20N2]X2,X = Cl/Br, each consist of one heptane-1,7-diammonium cation and two halide anions. The organic hydrocarbon layers pack in a stacked herring-bone manner, hydrogen bonded to the halide ions. Lattice potential energy is 1568.59 kJ/mol and 1560.78 kJ/mol, and cation molar volumes are 0.295 nm3 and 0.300 nm3 for chloride and bromide respectively. DTA confirmed chain melting transitions for both hybrids below T ∼ 340 K. Dielectric and ac conductivity measurements (290 < T K < 410; 0.080 < f kHz<100) indicated higher conductivity and activation energy of bromide for T > 340 K. Cross over from Jonscher's universal dielectric response at low temperatures T < 340 K to super-linear power law for T > 340 K is observed. At high temperatures halide ion hopping in accordance with the jump relaxation model prevails.

Effect of Ba/Y Molar Ratio on Superconducting Properties of BaTiO3-Doped YBa2Cu3 O 7−δ Films

YBa2Cu3 O 7−δ (YBCO) films with BaTiO3 (BTO) nanostructures were prepared by using the precursor solutions with different cationic molar ratios of Y:Ba:Cu = 1.0:1.6–2.0:3.0 in the TFA-MOD process. These YBCO films were deposited on (00 l)-oriented LaAlO3 single-crystal substrates using a spin coater. The high superconducting critical current density (J C) (77 K, self-filed) of more than 10 MA/cm2 for the final BTO-doped YBCO film was obtained. Moreover, the effect of different Ba/Y molar ratios in the precursor solution on superconducting properties of BTO-doped YBCO films was investigated. Compared with the BTO-doped YBCO film deposited by using the precursor solutions with Ba/Y molar ratio of 2.0, an enhancement of J C in a magnetic field for the film from the solution with Ba/Y molar ratio of 1.9 was achieved. For Ba/Y molar ratios of 1.6 and 1.7, a reduction of J C in a magnetic field occurred. The J C enhancement may be mainly ascribed to the enhanced flux pinning by the Y2Cu2 O 5 nanostructures with the optimal number dispersing in YBCO matrix.

Phenomenological study of viscosity and density of alkali metal hydroxide solutions

Alkaline solutions are widely used in many industries. For dilute solutions, physicochemical properties, such as solubility of gases, hydration numbers and mobility of ions are well known. A relatively new trend is using concentrated alkaline solutions to obtain ferrates. In these processes, the solution concentration of more than 8 M is used. Studying the processes of transport of matter and charge in concentrated alkaline solutions requires updating the data on the hydration numbers and radii of ions, the effect of concentration, viscosity and nature of electrolytes on them. A method for determining the hydration numbers of alkali metal cations in hydroxide solutions, based on calculating the number of water moles per mole of cations at concentrations close to the limit was proposed. In addition, the influence of ions, strengthening and breaking the solution structure on the density and viscosity of alkali metal solutions was examined. It was shown that primary hydration of ions has the predominant impact on the solution viscosity in dilute solutions, and secondary - in concentrated. It was found that a sharp increase in the solution viscosity with increasing concentration occurs with decreasing distance between ions up to 3,7×10 -7 m. At high concentrations, the solution density is higher in hydrated cations with smaller dimensions. High density of lithium hydroxide solutions in concentrations of from 2 to 4 M can be explained by the fact that the positively hydrated cation is embedded in the structure of water without a significant increase in its volume.

Transparent, high refractive index oxides: Control of the nanostructure of titanium hafnium oxide alloys by variation of the ion energy during reactive magnetron sputtering deposition

ABSTRACTA range of optical and optoelectronic applications would benefit from high refractive index (n), dense and transparent films that guide, concentrate and couple light. However, materials with high n usually have a high optical extinction coefficient (κ) which keeps these materials from being suitable for optical components that require long optical paths. We studied titanium hafnium oxide alloy films to obtain high refractive index (n&gt;2) with minimum optical extinction coefficients (κ &lt; 10−5) over the visible and near IR spectrum (380-930 nm). Titanium hafnium oxide alloys were deposited using pulsed DC reactive magnetron sputtering with and without RF substrate bias on silicon dioxide. For a given deposition condition intended for a specific titanium/hafnium molar fraction ratio, the ion energy of deposition species was explicitly controlled by varying the RF substrate bias. Spectroscopic ellipsometry, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS) and atomic force microscopy (AFM) were used to characterize the films. It appears that applying RF substrate bias reduces the nanocrystalline size, changes the surface morphology and increases the refractive index while maintaining comparable titanium/hafnium cation molar fraction. Precise control of the nanostructure of ternary metal oxides can alter their macroscopic properties, resulting in improved optical films.

Development of nonstoichiometric CuInS₂ as a light-harvesting photoanode and catalytic photocathode in a sensitized solar cell.

A simple one-pot approach was developed to obtain nonstoichiometric CuInS2 nanocrystals. Using this approach, both In-rich and Cu-rich CuInS2 nanocrystals could be reliably synthesized by tuning stoichiometric combinations of [Cu]/[In] precursor constituents. By designing Cu-rich CuInS2 heteronanostructures to serve as counter electrodes, quantum-dot-sensitized solar cells (QDSSCs) equipped with In-rich CuInS2 and CdS cosensitizers delivered a power conversion efficiency of 2.37%, which is significantly more efficient than conventional Pt counter electrodes. To the best of our knowledge, this study represents the first report utilizing nonstoichiometric CuInS2 nanocrystals as a photon-harvesting sensitizer comprised of a photoanode and photocathode in QDSSCs; also unique to this report, these nonstoichiometric CuInS2 nanocrystals were formed by simply changing the cationic molar ratios without complicated precursor preparation. Impedance spectroscopy and Tafel polarization indicated that these Cu-rich CuInS2 heteronanostructures had electrocatalytic activities (used for reducing S(2-)/Sn(2-)) that were superior to a Pt catalyst. Moreover, we demonstrated that Cu-rich CuInS2 heteronanostructures were also useful counter electrodes in dye-sensitized solar cells, and this finding revealed a promising conversion efficiency of 6.11%, which was ∼96% of the efficiency in a cell with a Pt-based counter electrode (6.32%).

In-situ Gas Dosed Powder Diffraction Under Industrially Relevant Conditions

The adsorption of small molecules onto functionalized, high surface area microporous materials is important for the advancement of industrial and environmental processes ranging from catalysis and chemical separations, to CO2 sequestration and energy storage. Over the past several years we have focused our research efforts on understanding the molecular interactions of these small molecules with a variety of microporous materials using in-situ powder diffraction methods to correlate structure with chemical properties. Background will be given on the design of gas dosing apparatus for in-situ diffraction studies at synchrotron X-ray and neutron powder beamlines. The result is that accurate doses can be made per quantity of interest (moles of cations, per unit cell, per pore, etc.), or under high pressures (100 bar), and/or chemical reactions can be followed versus temperature/pressure. Several of our recent investigations of CO2/N2/CH4 sorption in cation-exchange zeolites including Zeolite A (5A) and CHA are presented. While many industrial processes use zeolites to carry out these functions, more emphasis has been placed on metal-organic frameworks (MOFs) on late since their properties can be tuned by varying the synthetic components. A number of studies on an isostructural series, M-MOF-74, have been considered investigating why certain functionalization leads to increased specificity for applications such as CO2, O2, CO, and hydrocarbon separations. The ultimate goal is to use the knowledge gained to improve the design of new MOF materials.

Ferromagnetic excited-state Mn2+dimers in Zn1−xMnxSe quantum dots observed by time-resolved magnetophotoluminescence

Colloidal Mn${}^{2+}$-doped semiconductor nanocrystals are solution processable analogs of classic phosphor and diluted magnetic semiconductor materials with promising applications ranging from fluorescence microscopy to spintronic information processing. At doping levels of only a few cation mole percent, Mn${}^{2+}$ dimers form in appreciable concentration and cause shortened photoluminescence decay times and reduced luminescence circular polarization under applied magnetic fields. Here, we show that these differences allow the use of time-resolved magnetophotoluminescence measurements to investigate the magnetic properties of the luminescent dimer excited state in Zn${}_{1\ensuremath{-}x}$Mn${}_{x}$Se nanocrystals. These measurements reveal that Mn${}^{2+}$-Mn${}^{2+}$ dimers are coupled ferromagnetically in their luminescent excited state, in contrast with the antiferromagnetic coupling of their ground state. We find that Mn${}^{2+}$-Mn${}^{2+}$ dimers also luminesce with much purer circular polarization than Mn${}^{2+}$ monomers under applied magnetic fields. These results are explained well by perturbation theory and density functional theory analyses of the microscopic orbital exchange interactions within the photoexcited Mn${}^{2+}$-Mn${}^{2+}$ dimers. This discovery of photoswitchable dimer magnetism (from $S$ = 0 to $S$ = 4) with strong associated circularly polarized luminescence raises intriguing possibilities for optical spin manipulation in doped semiconductors.