Trivalent Al3 Research Articles

Promoting Strong Metal Support Interaction: Doping ZnO for Enhanced Activity of Cu/ZnO:M (M = Al, Ga, Mg) Catalysts

The promoting effect of Al, Ga, and Mg on the support in Cu/ZnO catalysts for methanol synthesis has been investigated. Different unpromoted and promoted ZnO supports were synthesized and impregnated with Cu metal in a subsequent step. All materials, supports, and calcined and activated catalysts were characterized by various methods, including contactless (microwave) conductivity measurements under different gas atmospheres. Small amounts of promoters were found to exhibit a significant influence on the properties of the oxide support, concerning textural as well as electronic properties. We found correlations between the conductivity of the ZnO support and the activity of the catalyst in the reverse water-gas shift reaction (rWGS) as well as in methanol synthesis. In rWGS the activation energy and reaction order in H2 are decreased upon promotion of the ZnO support with the trivalent promoters Al3+ and Ga3+, indicating an electronic promotion. In methanol synthesis, results point to a structural promotion by Al3+ and Ga3+. A detrimental effect of Mg2+ doping was observed in both reactions. This effect is discussed in the context of the reducibility of ZnO under reaction conditions, which can be tuned by the promoter in different ways. The reducibility is seen as a critical property for the dynamic metal support interaction of the Cu/ZnO system.

Preparation and properties of Li1.3Al0.3Ti1.7(PO4)3 by spray-drying and post-calcining method

Solid state electrolyte Li1.3Al0.3Ti1.7(PO4)3 is synthesized by spray-drying and post-calcining method. X-ray diffraction is employed to characterize the powders calcined in the range of 700–900°C for 2h, which indicates powders are well crystallized. FTIR shows trivalent cation Al3+ is substituted by Ti4+. The composite material appears as 2–5μm spherical particle. TG–DTA results confirm that the thermal decomposition of precursors obtained by spray-drying method occurred at lower temperature compares with solid phase synthesis method and sol–gel method. The ionic conductivity of the pellets reaches a maximum of 0.622mScm−1 at calcining temperature of 800°C.

Characteristics of TEMPO-oxidized cellulose fibril-based hydrogels induced by cationic ions and their properties

Cellulose microfibrils (CMFs) and cellulose nanofibrils (CNFs) were isolated from hardwood pulp by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation, which produced negatively-charged carboxylate groups on their surface. First, these CMFs and CNFs were used to prepare microgels and nanogels, respectively, at different concentrations of cellulose and trivalent Al3+ cation by inducing ionic interactions between the negatively charged carboxylates and the metal cation. Then, two other cations (i.e., divalent Ca2+ and monovalent H+ were employed to understand the structure–property relationship these hydrogels. We characterized their morphology, chemical groups, mechanical properties, surface area, and pore size, and evaluated their drug-release behaviors using theophylline. Compared to the hydrogels prepared from divalent or monovalent cations, both microgel and nanogel prepared from trivalent Al3+ showed the highest stiffness and compressive strength, which indicated that they possessed the strongest ionic cross-linking via intra- and inter-fibrillar interactions. With a decrease in the valency of the cation used, the surface area of both hydrogels decreased, while their pore radius and calculated fibril diameter increased, indicating that a higher valency cation produced a hydrogel with higher porosity and a tighter network structure. The nanogel prepared from Al3+ also showed the highest swelling ratio and the lowest release of theophylline, while that of microgel was, in contrast, consistent. The low total drug-release behavior in nanogels was attributed to their compact and highly porous structure. The Higuchi model was the best-fit model of drug release kinetics. These results indicate that the characteristics and internal structure of hydrogel has a great impact on its properties and drug-release profile, and that it may be possible to finely tune hydrogel properties and drug release profile by altering the internal structure of hydrogels during its preparation.

Effects of penta- and trivalent dopants on structure and conductivity of Li7La3Zr2O12

Due to their high ionic conductivity and stability versus metallic lithium, garnet-related Li7La3Zr2O12 (LLZ) are of interest as Li+ solid electrolytes. The correlation between structure and ion mobility in undoped, Ta5+, Nb5+, Ga3+ or Al3+ doped LLZ is studied combining molecular dynamics (MD) simulations and experimental characterisation. Neutron and in situ XRD powder diffraction are employed to analyse the Li and dopant distribution and temperature dependence of the structure. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and reducing local Li ordering. Trivalent doping Al3+ or Ga3+ on the Li site is slightly less effective in enhancing conductivity. Ga3+ doping on the La3+ site only helps to retain the cubic phase, but does not affect the mobile charge carrier concentration. The cooling rate after sintering is found to strongly affect both the ionic conductivity and its hysteresis on subsequent thermal cycling in the low temperature range, which can be attributed to local Li ordering as manifested by non-linear variations of the lattice parameters.

A Chalcone-Based Highly Selective and Sensitive Chromofluorogenic Probe for Trivalent Metal Cations.

A new chalcone-based probe for the chromofluorogenic sensing of trivalent (Al3+ , Fe3+ , Cr3+ , Ga3+ , In3+ and As3+ ) over mono- and divalent cations and anions is reported. In the presence of trivalent metal cations, the probe was able to display a remarkable color change from yellow to colorless that was clearly visible to the naked eye. Also, the initial strong yellow emission was gradually quenched and substituted by a weakly shifted band.

Nature of flocculation and tactoid formation in montmorillonite: the role of pH

The dissolution and swelling properties of montmorillonite at different pH have been studied, using small angle X-ray scattering (SAXS), imaging and osmotic stress methods combined with Monte Carlo simulations. The acidity of montmorillonite dispersions has been varied as well as the counterions to the net negatively charged platelets. At low pH, Na montmorillonite dissolves and among other species Al(3+) is released, hydrated, polymerized and then it replaces the counterions in the clay. This dramatically changes the microstructure of Na montmorillonite, which instead of having fully exfoliated platelets, turns into a structure of aggregated platelets, so-called tactoids. Montmorillonite dispersion still has a significant extra-lamellar swelling among the tactoids due to the presence of very small nanoplatelets.

Effects of Metal Ions on Crystal Morphology and Size of Calcium Sulfate Whiskers in Aqueous HCl Solutions

The effects of metal ions such as Na+, K+, Mg2+, Cu2+, Al3+, and Fe3+ on the crystal morphology and size of calcium sulfate whiskers in aqueous HCl solutions were investigated. The average diameter, aspect ratio, length, crystal water content, phase composition, and elemental composition of the products were determined and compared. When the concentration of monovalent Na+ or K+ ions was low, with the increase in the ion concentration, the average diameter increased and the aspect ratio decreased. However, with further increase in the ion concentration, the average diameter decreased. The presence of divalent Mg2+ or Cu2+ ions increased the crystal diameter and length. All the products were calcium sulfate hemihydrate in the presence of Na+, K+, Mg2+, or Cu2+ ions within the studied concentration range. The presence of trivalent Al3+ or Fe3+ ions at low concentrations resulted in bigger and shorter crystals; furthermore, at higher ion concentrations, partial phase transformation from calcium sulfate hemih...

Adsorption of a Switchable Cationic Surfactant on Natural Carbonate Minerals

Summary A switchable cationic surfactant (e.g., tertiary amine surfactant Ethomeen C12) was previously described as a surfactant that one can inject in high-pressure carbon dioxide (CO2) for foam-mobility control. C12 can dissolve in high-pressure CO2 as a nonionic surfactant and equilibrate with brine as a cationic surfactant. Here, we describe the adsorption characteristics of this surfactant in carbonate-formation materials. The adsorption of this surfactant is sensitive to the equilibrium pH, the electrolyte composition of the brine, and the minerals in carbonate-formation materials. Pure C12 is a nonionic surfactant. When it is mixed with brine, the solution has a high pH and limited solubility. However, when the surfactant solution in brine is equilibrated with high-pressure CO2, the pH is approximately 4; the surfactant switches to a cationic surfactant and becomes soluble. Thus, the adsorption is also a function of pH. The adsorption of C12 on calcite at low pH is low (e.g., 0.5 mg/m2). However, if the carbonate formation contains silica or clays, the adsorption is high, as is typical for cationic surfactants. The adsorption of C12 on silica decreases with an increase in divalent (Ca2+ and Mg2+) and trivalent (Al3+) cations. This is because of the competition for the negatively charged silica sites between the multivalent cations and the monovalent cationic surfactant. An additional effect of the presence of divalent cations in the brine is that it reduces the dissolution of calcite or dolomite in the presence of high-pressure CO2. The dissolution of calcite and dolomite is harmful because of formation damage and increased alkalinity. The latter raises the pH and thus increases the adsorption of C12 or even causes surfactant precipitation.

Influence of anionic vacancies on the conductivity of La9.33Si6−xAlxO26−x/2 oxide conductors with an oxyapatite structure

Al-doped oxyapatite-type lanthanum silicates La9.33Si6−xAlxO26−x/2□x/2 (x = 0, 0.4, 0.8 and 1) powders have been prepared by the solid state reaction at high temperature in order to determine the influence of anionic vacancies on the electrical properties of the material. The crystal structure and properties of La9.33Si6−xAlxO26−x/2□x/2 powders have been studied by X-ray diffraction (XRD) patterns, magic-angle spinning nuclear magnetic resonance (MAS-NMR) technique and complex impedance analysis. All the compounds of La9.33Si6−xAlxO26−x/2□x/2 oxyapatites doped with Al3+ consist of a hexagonal structure with a P63/m space group. Lanthanum silicates doped with trivalent Al3+ have a higher conductivity than those without trivalent Al3+ at the Si4+ site. The extra oxygen O(4) atoms in site 2a (0, 0, 0.25) occupy channels running through the structure that are responsible for the high oxygen ion conduction. However, Al substitution seems to produce oxygen vacancies and create another pathway for oxide ions. The expansion of the channels (La(1)–O(4) distance) leads to an increase in the conductivity. For the best sample (x = 1), the conductivity observed was 5 × 10−3 S cm−1 at 750 °C.

Structural and magnetic evaluation of substituted NiZnFe2O4 particles synthesized by conventional sol–gel method

The aim of this study is to evaluate the structural and magnetic properties of Ni–Zn doped ferrite with trivalent Al3+ and Cr3+ cations substitution in Ni0.6Zn0.4Fe2−xCrx/2Alx/2O4 (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) synthesized by employing conventional sol–gel method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), Mössbauer spectroscopy (MS) and vibrating sample magnetometer (VSM) analysis were carried out in order to characterize the structural and magnetic properties of particles. The XRD results confirmed the formation of single phase of spinel ferrite particles for a whole series of samples. The results of FTIR analysis indicated that the functional groups of Ni–Zn spinel ferrite were formed during the sol–gel process. Furthermore, FE-SEM micrographs revealed that the distribution of particles size is narrow. According to Mössbauer spectra,the doped cations are replaced in iron site occupancy of octahedral sites. It was found that with an increase in substitution contents magnetization decreased due to occupation of Al and Cr cations at low level substitutions in octahedral sites.

C–H Activation in Pyridoxal-5′-phosphate and Pyridoxamine-5′-phosphate Schiff Bases: Effect of Metal Chelation. A Computational Study

This study reports the carbon acidities of Cα and C4′ atoms in the Schiff bases of pyridoxal-5′-phosphate (PLP) and pyridoxamine-5′-phosphate (PMP) complexed with several biologically available metal ions (Mg2+, Ni2+, Zn2+, Cu2+, Al3+, and Fe3+). Density functional theory calculations were carried out to determine the free energies of proton exchange reactions of a set of 18 carbon acids and a Schiff base used as a reference species. The experimental pK(a) values of such carbon acids were used to calibrate the computed free energies in a range of 30 pK(a) units. Eventually, the pK(a)s of the chelates were obtained by calculating the corresponding free energies against the same reference species and by considering the previous calibration. The carbon acidity of Cα in the chelates of Mg2+, Ni2+, Zn2+, and Cu2+ varies between pK(a) 22 and pK(a) 13 whereas the pK(a) values of C4′ range between 18 and 7. Chelation of trivalent metals Al3+ and Fe3+ causes further decrease of the pK(a) values of Cα and C4′ down to 10 and 5, respectively. The results highlight the efficiency of the combined action of Schiff base formation and metal chelation to activate the Cα carbon of amino acids (pK(a) 29 for zwitterionic alanine). Our results explain that the experimental increase of transamination rates by Zn2+ chelation is due to stabilization of the reactive Schiff base species with respect to the free ligand under physiological pH conditions. However, the increase in reactivity for transamination due to Cu2+ and Al3+ chelation is mostly due to C–H ligand activation. Each metal ion activates the Cα and C4′ carbon atoms to a different extent, which can be exploited to favor specific reactions on the amino acids in aqueous solution. Metal chelation hinders both intramolecular and intermolecular proton-transfer reactions of the imino, phenol, and carboxylate groups. This is the only apparent inconvenience of metal complexes in enzymatic reactions, which, in turn, proposes their consideration for enzyme inhibition.

EPR study of chromium-doped forsterite crystals: Cr3+(M1) with associated trivalent ions Al3+ and Sc3+

Electron paramagnetic resonance (EPR) study of single crystals of forsterite co-doped with chromium and scandium has revealed, apart from the known paramagnetic centers Cr3+(M1) and Cr3+(M1)–\( V_{{{\text{Mg}}^{2 + } }} \)(M2) (Ryabov in Phys Chem Miner 38:177–184, 2011), a new center Cr3+(M1)–\( V_{{{\text{Mg}}^{2 + } }} \)(M2)–Sc3+ formed by a Cr3+ ion substituting for Mg2+ at the M1 structural position with a nearest-neighbor Mg2+ vacancy at the M2 position and a Sc3+ ion presumably at the nearest-neighbor M1 position. For this center, the conventional zero-field splitting parameters D and E and the principal g values have been determined as follows: D = 33,172(29) MHz, E = 8,482(13) MHz, g = [1.9808(2), 1.9778(2), 1.9739(2)]. The center has been compared with the known ion pair Cr3+(M1)–Al3+ (Bershov et al. in Phys Chem Miner 9:95–101, 1983), for which the refined EPR data have been obtained. Based on these data, the known sharp M1″ line at 13,967 cm−1 (with the splitting of 1.8 cm−1), observed in low-temperature luminescence spectra of chromium-doped forsterite crystals (Glynn et al. in J Lumin 48, 49:541–544, 1991), has been ascribed to the Cr3+(M1)–Al3+ center. It has been found that the concentration of the new center increases from 0 up to 4.4 × 1015 mg−1, whereas that of the Cr3+(M1) and Cr3+(M1)–\( V_{{{\text{Mg}}^{2 + } }} \)(M2) centers quickly decreases from 7.4 × 1015 mg−1 down to 3 × 1015 mg−1 and from 2.7 × 1015 mg−1 down to 0.5 × 1015 mg−1, i.e., by a factor of 2.5 and 5.4, respectively, with an increase of the Sc content from 0 up to 0.22 wt % (at the same Cr content 0.25 wt %) in the melt. When the Sc content exceeds that of Cr, the concentration of the new center decreases most likely due to the formation of the Sc3+(M1)–\( V_{{{\text{Mg}}^{2 + } }} \)(M2)–Sc3+ complex instead of the Cr3+(M1)–\( V_{{{\text{Mg}}^{2 + } }} \)(M2)–Sc3+ center. The formation of such ordered neutral complex is in agreement with the experimental results, concerning the incorporation of Sc into olivine, recently obtained by Grant and Wood (Geochim Cosmochim Acta 74:2412–2428, 2010).

Purification and Characterization of a Novel Anti-Proliferative Lectin from Morus alba L. Leaves

A novel anti-proliferative lectin was purified from Morus alba L. (Mulberry) leaves by a two step chromatographic procedure namely, immobilized metal ion affinity chromatography (IMAC) and convective interaction media (CIM) based anion exchange chromatography. The purified mulberry leaf lectin (MLL) was specific to galactose, galactosamine and N-acetyl galactosamine (GalNAc). MLL was homogenous with a molecular weight of ~56kDa in silver stained SDS-PAGE. The lectin showed RBC agglutination activity up to 40°C and was independent of pH above pH 6. Haemagglutination activity of purified MLL was not dependent on any metal ions. However, with high concentration of trivalent metal ions, Fe3+ and Al3+ and the divalent metal ion Fe2+, a three fold increase in agglutination activity was observed. The purified MLL showed an anti-proliferative activity towards human breast cancer cells (MCF-7) and colon cancer cells (HCT-15) with a higher potency towards MCF-7 cells. This is the first report on the anti-proliferative activity of a GalNAc specific lectin from M. alba.

Development of Ammonia Gas Sensors Based on Trivalent Al3+ Cation Conducting Solid Electrolyte

Abstract Solid electrolyte type ammonia (NH3) gas sensors were fabricated using Al3+ ion conducting (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte with an aluminum thin film as a reference electrode. A rare-earth ammonium sulfate double salt of R2(SO4)3·(NH4)2SO4 (R = rare earth) or a lanthanum oxysulfate La2O2SO4-based solid solution was selected as the auxiliary sensing electrode on the basis of thermal stability or water durability. Both sensors with R2(SO4)3·(NH4)2SO4 or La2O2SO4–NH4H2PO4 auxiliary sensing electrodes exhibited a quantitative and theoretical NH3 sensing performance at 230–300 or 170–190 °C, respectively; therefore, sensors based on the (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte are expected to be promising candidates as NH3 detectors that can operate in a wide temperature range of 170–300 °C by changing the auxiliary sensing electrode component.

Effect of post-precipitation conditions on surface properties of colloidal metal sulphide precipitates

Metal sulphide precipitation is important in several hydrometallurgical processes. However, challenges exist in solid–liquid separation and recovery of the colloidal precipitates produced in some systems. This study presents the effect of downstream processing options on the surface properties of colloidal particles produced during copper and zinc sulphide precipitation. XRD and EDAX characterisation indicated the copper precipitate was a mixture of covellite (63%) and copper hydroxysulphate (37%), while the zinc sulphide was more pure, but less crystalline. The effect on surface charge and aggregation tendency of different concentrations of background electrolyte (1–100mM KCl), suspension pH, aqueous sulphide, a divalent (Ca2+) and trivalent (Al3+) cation were studied. The magnitude of the negative surface charge increased with increasing suspension pH (pH 6 to pH 11) for both copper and zinc precipitates. The addition of aqueous sulphide (0.84mM) to the zinc precipitate resulted in a significant decrease in the zeta potential and suppressed aggregation, due to adsorption of the negatively charged sulphide ions. This effect was reduced at high ionic strength. A higher sulphide concentration was required to replicate the phenomenon with the copper precipitate due to sulphidisation of the copper hydroxysulphate initially. Addition of a divalent cation (Ca2+) to the suspension had little effect on the surface charge of the particles and did not promote aggregation. However, addition of a small amount (0.5mM) of Al3+ ions resulted in a significant change in surface charge (−30 to −10mV for copper and −23mV to −5mV for zinc) and subsequent aggregation. The results of this study show that downstream processing of colloidal metal sulphide precipitates, produced where supersaturation cannot be managed, can lead to effective solid–liquid separation, by changing the surface properties of the precipitate.

Determination of divalent trace metals in a soil sample using electrospray ionization mass spectrometry

A novel pre-separation technique for the determination of divalent trace heavy metals in a soil sample was developed, in which deferoxamine was used as a masking agent for trivalent metal ions, Al3+ and Fe3+, and a chelate column was applied to collect target heavy metal ions and to eliminate alkali metal and alkaline earth metal ions. Deferoxamine had such a strong and selective masking effect on Al3+ and Fe3+ that divalent trace heavy metals in the soil sample were well separated from considerably greater amounts of Al3+ and Fe3+. Consequently, the determination of four trace metals (Ni, Cu, Zn, and Pb) in a certified soil reference material (JSAC-0401) was successfully performed using electrospray ionization mass spectrometry (ESIMS).

Enhanced selectivity and capacity of adsorption of CO2 and CH4 in zeolite-like metal-organic frameworks with different extra-framework cations: a molecular simulation study

In this study, grand canonical Monte Carlo simulation was carried out to systematically study the effects of extra-framework cations on the capacity of storage and separation of carbon dioxide (CO2) and methane (CH4) in cation-exchanged rho-zeolite-like metal-organic framework (rho-ZMOF). Monovalent (Na+, NH4 + and Li+), divalent (Mg2+ and Sr2+) and trivalent (Al3+) cations with different ion radii were adopted as the representative extra-framework cations. The simulations of the single-component adsorption of CO2 molecules indicate that the varieties in extra-framework cations do not bring evident differences in the dispersion interaction contributions to the isosteric adsorption heats of CO2 but rather the electrostatic interaction contributions. Higher the valence a cation has, stronger the electrostatic interaction with CO2 is and, therefore, a higher storage capacity, though the corresponding accommodation number of the extra-framework cations is smaller. For the cations having the same valence, the storage capacity decreases with the increase in the accessible surface area and total free volume of the host structure. The single-component adsorption isotherms of CO2 and CH4 can be described by a dual-site Langmuir–Freundlich equation. Under typical operating conditions (298 K and 1 atm) in a pressure swing adsorption (PSA) process, the simulation results of the adsorption of CO2 and CH4 mixture demonstrate that the Al-exchanged rho-ZMOF exhibits an unprecedented high selectivity of CO2 over CH4 up to 112, compared with other metal-organic frameworks and nanoporous materials reported to date. Our results suggest that the variation of extra-framework cations is an efficient way to improve the adsorption capacity of the rho-ZMOF for the storage and separation of CO2 and CH4 mixtures using the PSA process at ambient temperature and pressure.

Charge Compensation and Ce3+Formation in Trivalent Doping of the CeO2(110) Surface: The Key Role of Dopant Ionic Radius

In this paper, we use density functional theory corrected for on-site Coulomb interactions (DFT + U) and hybrid DFT (HSE06 functional) to study the defects formed when the ceria (110) surface is doped with a series of trivalent dopants, namely, Al3+, Sc3+, Y3+, and In3+. Using the hybrid DFT HSE06 exchange-correlation functional as a benchmark, we show that doping the (110) surface with a single trivalent ion leads to formation of a localized MCe/ + OO• (M = the 3+ dopant), O− hole state, confirming the description found with DFT + U. We use DFT + U to investigate the energetics of dopant compensation through formation of the 2MCe′ +VO·· defect, that is, compensation of two dopants with an oxygen vacancy. In conjunction with earlier work on La-doped CeO2, we find that the stability of the compensating anion vacancy depends on the dopant ionic radius. For Al3+, which has the smallest ionic radius, and Sc3+ and In3+, with intermediate ionic radii, formation of a compensating oxygen vacancy is stable. On the...

Highly efficient, tunable and bright photoluminescence from hydrophobic silica gel nanoparticles

For the first time, we report a highly efficient, tunable and bright photoluminescence with external quantum yield up to ∼34% under 350 nm excitation from hydrophobic SiO2 gel nanoparticles. This is achieved by suitably modifying the relative surface states of the gel network with trivalent (Al3+/Ga3+) ions and emission from rare-earth (Eu3+) dopant. This attractive property arises from the intrinsic separation of absorption and the emission energies due to a large Stokes shift and offers opportunities for the design of novel nanophosphor based white light-emitting devices.

Thermal stability of metal-pitch deposits from a spruce thermomechanical pulp by use of a differential scanning calorimeter

Pitch-related deposition has been a significant issue in paper mills that produce wood-containing paper grades. A component analysis showed that a mill deposit sample was a mixture of wood resin, fiber, metal cations, and other inorganics. Based on the differential scanning calorimeter (DSC) method, some critical parameters, including pH, metal cations, and their interactions, on the thermal stability of pitch-related deposits were studied. The valency of metal cations determined the ability of capturing pitch the formation of deposits. Trivalent Al3+ or Fe3+ ions had much stronger effects than divalent Ca2+, Mg2+, or Mn2+. It was also found that a higher pH and trivalent Al3+ or Fe3+ increased the thermal stability of deposits formed in colloidal pitch solutions.