Chemistry

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Assessing the oxidation states and structural stability of the Ce analogue of brannerite
(Wiley, 2017) Aluri, Esther Rani; Bachiu, Lisa; Grosvenor, Andrew; Forbes, Scott; Greedan, John
The Ce‐containing analogue of brannerite (ie, UTi2O6) was previously considered to be stoichio- metric (ie, CeTi2O6); however, it has recently been determined that the material is O deficient. This oxygen‐deficient material has been suggested to be charged balanced by the presence of a minor concentration of Ce3+ or by the A‐site being cation deficient with the Ce oxidation state being 4+. A variety of Ti‐containing oxides (including brannerite) have been investigated as potential nuclear wasteforms, and it is necessary to understand the electronic structure of a proposed nuclear wasteform material as well as how the structure responds to radiation from incorporated waste elements. The radiation resistance of a material can be simulated by ion implantation. The objective of this study was to confirm the Ce oxidation state in the cation‐ and oxygen‐deficient material (ie, Ce0.94Ti2O6 − δ) and to determine how radiation damage affects this material. X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near‐edge spectros- copy were used to study Ce0.94Ti2O6 − δ before and after being implanted with 2 MeV Au− ions. Analysis of the Ce 3d XPS spectra from the as‐synthesized samples by using a previously developed fitting method has unequivocally shown that Ce adopts both 4+ (major) and 3+ (minor) oxidation states, which was confirmed by examination of magnetic susceptibility data. Analysis of XPS and X‐ray absorption near‐edge spectroscopy spectra from ion‐implanted materials showed that both Ce and Ti were reduced because of radiation damage and that the local coordination environments of the cations are greatly affected by radiation damage.
Coal-Based Activated Carbon via Microwave-Assisted ZnCl2 Activation for Methyl Violet 2B Dye Removal: Optimization, Desirability Function, and Adsorption Mechanism
(MDPI, 2023) Musa, Salis A.; Abdulhameed, Ahmed Saud; Baharin, Siti Nor Atika ; ALOthman, Zeid; Wilson, Lee; Jawad, Ali H.
In this work, activated carbon (referred to as MCAC) was produced by microwave radiation assisted ZnCl2 activation using Malaysian coal (MC) as a precursor. The Brunauer–Emmett–Teller findings indicate that the MCAC has a relatively large surface area (798.18 m2/g) and a mesoporous structure (average pore diameter of 3.67 nm). The removal of Methylene Violet (MV 2B) a cationic dye model, was employed to investigate the adsorption properties of MCAC. A numerical desirability function in the Box–Behnken design (BBD) was employed to optimize the independent crucial adsorption variables as follows: A: MCAC dose (0.02–0.1 g); B: pH (4–10); and C: time (5–25 min). The results of equilibrium and dynamic adsorption showed that the adsorption of MV 2B followed Freundlich and pseudo-second order models, respectively. The maximum amount of MV 2B dye that the MCAC could adsorb (qmax) was 134.1 mg/g. Electrostatic interactions, π-π stacking, H-bonding, and pore diffusion contribute to the adsorption of MV 2B dye onto the MCAC surface. This study demonstrates the potential to utilize MC as a low-cost precursor for the efficient synthesis of MAC and its utility for the removal of pollutants.
Connecting Molecular Conformation to Aggregation in P3HT Using Near Edge X-ray Absorption Fine Structure Spectroscopy
(American Chemical Society, 10/11/2017) Martinson, Mercedes; Urquhart, Stephen; Eger, Shaylin; Murcia, Victor; Ade, Harald; Collins, Brian
Carbon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) and UV-vis spectroscopy are used to examine differences between highly aggregated and poorly aggregated forms of the polymer poly(3-hexylthiophene) (P3HT), based on as-cast and annealed regio-random and regio-regular P3HT samples. UV-vis spectra show characteristic signatures of unaggregated P3HT in regio-random P3HT, and of H-aggregation in regio-regular P3HT samples. Distinct spectroscopic differences, including energy shifts, are observed in the NEXAFS spectra of aggregated P3HT relative to the unaggregated forms. These differences are reproduced with Transition – Potential Density Functional Theory (TP-DFT) calculations which explore aggregation and molecular confirmation. Differences in the NEXAFS spectra of P3HT are assigned to thiophene backbone twisting in the unaggregated forms of P3HT, and to various degrees of chain planarization in aggregated forms of P3HT that also correlate to the exciton bandwidth. These results open up the prospect of charactering conformation and related difficult to assess structural details through NEXAFS spectroscopy and correlative theory and electronic structure analysis.
Design, synthesis, catalytic application, and strategic redispersion of plasmonic silver nanoparticles in ionic liquid media
(Elsevier, 2014) Banerjee, Abhinandan; Theron, Robin; Scott, Robert WJ
Silver nanoparticles synthesized in tetraalkylphosphonium ionic liquids are found to be excellent catalysts for borohydride-induced reductive degeneration of Eosin-Y, a dye that has been classified as a Class 3 carcinogen by the International Agency for Research on Cancer. TEM images indicated that the size of the Ag nanoparticles was significantly influenced by heat-induced sintering. A strategy was devised to redisperse smaller Ag nanoparticles from their aggregated/sintered counterparts via a two-step protocol that involved oxidative etching of Ag nanoparticles, followed by a re-reduction step. This protocol led to a reduction in the sintered Ag nanoparticle size from 15.7 ± 6.1 nm to 3.7 ± 0.8 nm, which was consistent with the size of the as-synthesized nanoparticles. The as-synthesized and the redispersed Ag nanoparticles were found to catalyze the bleaching of Eosin-Y with comparable efficiencies; first order rate constants for Eosin Y reduction were ∼8 times higher for smaller Ag nanoparticles compared to their sintered counterparts. An examination of the kinetics of Ag nanoparticle etching was performed via temperature-controlled UV–vis spectroscopy. Changes in the oxidation state of Ag during this sequence of events were also followed by in situ X-ray absorption spectroscopy of Ag nanoparticles in the ionic liquid.
Effect of a Fluorinated Surfactant on Langmuir Monolayer Properties of Minimal-Linker Gemini Surfactants
(Elsevier B.V., 2024-07-08) Singh, Srikant K.; Paige, Matthew F.
A new class of carboxylic acid-terminated gemini surfactants which contain the smallest possible headgroup linker (a single bond) has recently been reported in the literature. In this current work, we have explored how Langmuir monolayers of two different alkyl tail chain length variants (n = 12, n = 16) of these surfactants, dubbed Cn-0-Cn, are impacted by mixing with a benchmark perfluorinated surfactant, perfluorotetradecanoic acid (PF). Pure PF and C16-0-C16 monolayers share similar general characteristics, yielding compact, incompressible, solid-like films at the air-water interface. In contrast, the shorter tail chain variant, C12-0-C12 forms expanded, compressible liquid-like films. While both tail chain variants formed mixed films with PF that were generally expanded in comparison with their pure components, and were also phase-separated, the extent of interactions between film components and the resulting micron-scale morphology of the mixed films were different for the two alkyl chain lengths. Overall, PF induces different packing behavior in both the systems and the observations are attributed to the difference in the dispersion forces originating from the tail chain length differences.
Electrocatalytic Oxidation of Nitrophenols via Ag Nanoparticles Supported on Citric-Acid-Modified Polyaniline
(MDPI, 2023) Khani, Milad; Sammynaiken, Ramaswami; Wilson, Lee
Citric-acid-modified polyaniline (P-CA) and P-CA modified with Ag nanoparticles (Ag@PCA) were prepared via an in situ reduction method. The physicochemical properties of P-CA and Ag@P-CA were compared to unmodified polyaniline (PANI) and PANI-modified Ag nanoparticles (Ag@PANI). Ag@P-CA had a lower content of aniline oligomers compared to Ag@PANI. P-CA and Ag@P-CA had a greater monolayer adsorption capacity for 2-nitrophenol and lower binding affinity as compared to PANI and Ag@PANI materials. X-ray photoelectron spectroscopy and cyclic voltammetry characterization provided reason and evidence for the higher conductivity of citric-acid-modified materials (P-CA and Ag@P-CA versus PANI and Ag@PANI). These results showed the potential utility for the optimization of adsorption/desorption and electron transfer steps during the electrochemical oxidation of nitrophenols. The oxidation process employs Ag@P-CA as the electrocatalyst by modifying polyaniline with Ag nanoparticles and citric acid, which was successfully employed to oxidize 2-nitrophenol and 4-nitrophenol with comparable selectivity and sensitivity to their relative concentrations. This work is envisaged to contribute significantly to the selective conversion of nitrophenols and electrocatalytic remediation of such waterborne contaminants.
Enantioselective Stetter Reactions Catalyzed by Bis(amino)cyclopropenylidenes: Important Role for Water as an Additive
(ACS Publications, 12/15/2020) Rezazadeh Khalkhali, Mehran; Wilde, Myron M. D.; Gravel, Michel
The first highly enantioselective intermolecular Stetter reaction using simple enones is reported. A series of novel chiral BAC structures were designed and prepared. They were tested in the Stetter reaction with simple aldehydes and enones. The products were generated in excellent yields and enantioselectivities (up to 92% ee). Surprisingly, a substoichiometric amount of water was crucial to obtain high enantioselectivities. Chiral BACs were also shown to catalyze 1,6-conjugate addition reactions with paraquinone methides enantioselectively.
A Fixed-Bed Column with an Agro-Waste Biomass Composite for Controlled Separation of Sulfate from Aqueous Media
(MDPI, 2023) Solgi, Mostafa; Steiger, Bernd; Wilson, Lee
An agro-waste composite with a pelletized form was prepared and characterized via IR and 13C solids NMR spectroscopy. Thermal gravimetry analysis (TGA) was used to study the weight loss profiles, while SEM images provided insight on the biocomposite morphology, along with characterization of the sulfate adsorption properties under equilibrium and dynamic conditions. The sulfate monolayer adsorption capacity (qe = 23 mg/g) of the prepared agro-waste pellets was estimated from the adsorption isotherm results by employing the Langmuir model, and comparable fitting results were obtained by the Freundlich model. The dynamic adsorption properties were investigated via adsorption studies with a fixed bed column at pH 5.2. The effects of various parameters, including flow rate, bed height and initial concentrations of sulfate, were evaluated to estimate the optimal conditions for the separation of sulfate. The experimental data of the breakthrough curves were analyzed using the Thomas and Yoon–Nelson models, which provided satisfactory best-fits for the fixed bed kinetic adsorption results. The predicted adsorption capacities for all samples according to the Thomas model concur with the experimental values. The optimum conditions reported herein afford the highest dynamic adsorption capacity (30 mg/g) as follows: 1100 mg/L initial sulfate concentration, 30 cm bed height and 5 mL/min flow rate. The breakthrough time was measured to be 550 min. This study contributes to a strategy for controlled separation of sulfate using a sustainable biocomposite material that is suitable for fixed-bed column point-of-use water treatment systems.
Following the Reactivity of Au25(SC8H9)18 - Clusters With Pd2+ and Ag+ Ions Using in Situ X-ray Absorption Spectroscopy: A Tale of Two Metals
(American Chemical Society, 2015) Shivhare, Atal; Lee, Kee Eun; Hu, Yongfeng; Scott, Robert WJ
This work examines the reaction between Au25(SC8H9)18– clusters with palladium acetate (Pd2+) and silver nitrate (Ag+) using UV–vis, transmission electron microscopy (TEM), extended X-ray absorption spectroscopy (EXAFS), and in situ liquid cell X-ray absorption spectroscopy (XAS). UV–vis results show that upon the addition of Pd2+ and Ag+ salts to Au25(SC8H9)18– clusters significant changes are seen in the optical properties of the clusters. In the case of Pd, there is little to no change in the size of the clusters evidenced by TEM, while for Ag systems, significant particle growth is seen. In situ XAS results show that Pd2+ reacts with the staple motifs of Au25(SC8H9)18– clusters and forms Pd(II) thiolate species, as shown by the Pd L3- and Au L3-edge data as well as Pd K-edge EXAFS results. However, Ag L3-edge data suggest that Ag+ reduces to Ag on the cluster core and does not form Ag(I) thiolate species. This work highlights the power of using in situ XANES to follow Au cluster transformations in liquid environments.
Following the Thermal Activation of Au25(SR)18 Clusters for Catalysis by X-Ray Absorption Spectroscopy
(American Chemical Society, 2013) Shivhare, Atal; Chevrier, Daniel; Purves, Randy W; Scott, Robert WJ
We show the thermal activation of phenylethanethiolate (L = SC8H9) and hexanethiolate (L = SC6H13) Au25L18 monolayer protected clusters (MPCs) on carbon black supports, followed by characterization with extended X-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy (TEM). EXAFS analysis shows that the thiolate stabilizers can be partially removed from the surface under mild heating conditions without significant changes in the cluster size. The resulting clusters are shown to be catalytically active for the reduction catalysis of 4-nitrophenol. EXAFS and TEM data show that thermal treatment under air at 200 °C leads to nearly complete removal of all of the thiolate stabilizers with little to no growth in cluster size, while cluster sintering was seen at higher calcination temperatures. The maximum catalytic activity for Au25(SC8H9)18 MPCs was seen at 250 °C activation conditions. These results are consistent with results reported earlier for Au25(SR)18 clusters on ceria by Jin et al., who suggested that cluster integrity was maintained during mild activation conditions. Here, EXAFS data unambiguously show that while the cluster size does not grow significantly, such mild heating conditions do lead to nearly complete removal of the thiolate stabilizers.
Following the Thermal and Chemical Activation of Supported Au Clusters using X-ray Absorption Spectroscopy
(Royal Society of Chemistry, 2016) Shivhare, Atal; Scott, Robert WJ
Al2O3-supported Au25(SC8H9)18 clusters with various Au loadings were thermally and chemically treated in order to determine the most efficient method towards the removal of thiolate stabilizers while avoiding unwanted increases in cluster size due to agglomeration and sintering. X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) were used to investigate samples before and after thermal and chemical treatments. Results show that while 250 °C thermal treatment leads to nearly complete removal of thiolate stabilizers, it comes with a concomitant increase in cluster size as sintering becomes problematic. In contrast, chemical reduction treatments using borohydride reducing agents does not lead to significant growth in cluster size, but only allows for partial thiolate removal. These results are important as many researchers look to determine optimal activation conditions for ultra-monodisperse Au and bimetallic clusters for use as model catalysts without destroying their original structures.
Identifying calcium-containing mineral species in the JEB Tailings Management Facility at McClean Lake, Saskatchewan
(Elsevier, 2016) Blanchard, Peter; Grosvenor, Andrew; Rowson, John; Hughes, Kebbi; Brown, Caitlin
The JEB Tailings Management Facility (TMF) is central to reducing the environmental impact of the McClean Lake uranium mill facility that is operated by AREVA Resources Canada. This facility has been designed around the idea that elements of concern (e.g., U, As, Ni, Se, Mo) will be controlled through equilibrium with precipitants. Confirming the presence of calcium-containing carbonates in the JEB TMF is the first step in determining if gypsum (CaSO4$2H2O) controls the concentration of HCO 3 (aq), limiting the formation of soluble uranyl bicarbonate complexes. A combination of X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), and microprobe X-ray fluorescence (XRF) mapping was used to analyze a series of tailings samples from the JEB TMF. Calcium carbonate in the form of calcite (CaCO3), aragonite (CaCO3), and dolomite (CaMg(CO3)2) were identified by analysing Ca K-edge m-XANES spectra coupled with microprobe XRF mapping. This is the first observation of these phases in the JEB TMF. The combination of m-XANES and XRF mapping provided a greater sensitivity to low concentration calcium species compared to the other techniques used, which were only sensitive to the major species present (e.g., gypsum).
Improving the Rates of Pd-Catalyzed Reactions by Exciting the Surface Plasmons of AuPd Bimetallic Nanotriangles
(Royal Society of Chemistry, 2017) Gangishetty, Mahesh K; Fontes, Adriana, M.; Malta, Marcos; Kelly, Timothy L; Scott, Robert WJ
Gold nanoparticles exhibit unique optical properties due to surface plasmon oscillations when they interact with light. By utilizing their optical properties, the rates of many chemical reactions have been improved in the presence of visible light. The properties of plasmonic nanoparticles are highly tunable based on the size and shape of the nanoparticle. Here, we have used anisotropic AuPd bimetallic nanotriangles to improve the rates of Pd-catalyzed reactions in the presence of visible light. We synthesized AuPd core–shell bimetallic nanotriangles and performed Suzuki cross-coupling and hydrogenation reactions in light and dark conditions. Upon illuminating AuPd nanotriangles with an array of green LEDs (power ∼ 500 mW), enhanced catalytic activity of palladium was observed. In order to understand the relative contributions of individual plasmonic effects, such as plasmonic hot electron transfer and plasmonic heating effects, the reaction temperatures were monitored, and careful control experiments were run at different temperatures. Our results indicated that the enhancement in the rate of these Pd-catalyzed reactions is primarily due to the plasmonic heating effect.
in situ X-ray Absorption Spectroscopic Analysis of Gold-Palladium Bimetallic Nanoparticle Catalysts
(American Chemical Society, 2013) MacLennan, Aimee; Banerjee, Abhinandan; Hu, Yongfeng; Miller, Jeffrey T; Scott, Robert WJ
Gold–palladium core–shell nanoparticles have been previously shown to be extremely effective catalysts for a number of oxidation reactions including the aerobic oxidation of alcohols. However, the novel activity and durability of such catalysts are still poorly understood, and there are several putative mechanisms by which oxidation reactions can proceed. Previously we showed that Pd(II) salts in the presence of Au nanoparticles were also effective catalysts for the room temperature oxidation of crotyl alcohol. Herein we show an in situ X-ray absorption spectroscopy (XAS) study at both the Pd–K and Pd-LIII edges of Au nanoparticle/Pd(II) salt solutions in the presence of crotyl alcohol. Liquid cells with X-ray permeable windows were used to obtain quick-scan XAS data during the oxidation of crotyl alcohol, allowing for time-resolved Pd speciation information and information about the reaction mechanism and kinetics. XAS measurements definitively show that the first step of this reaction involves Pd reduction onto the Au nanoparticles; in addition, further studies of the stability of the resulting Au–Pd core–shell nanoparticles toward oxygen gas suggests that the role of Au in such catalysts is to prevent the reoxidation of the catalytically active surface Pd atoms. Catalytic crotyl alcohol oxidation measurements were done which validated that the in situ reduction of Pd(II) in the presence of Au nanoparticles did indeed result in catalytically active AuPd bimetallic catalysts.
In situ X-ray absorption spectroscopic studies of magnetic Fe@FexOy/Pd nanoparticle catalysts for hydrogenation reactions
(Elsevier, 2017) Yao, Yali; Rubino, Stefano; Gates, Byron D; Scott, Robert WJ; Hu, Yongfeng
Core@shell Fe@FexOy nanoparticles (NPs) have attracted a great deal of interest as potential magnetic supports for catalytic metals via galvanic exchange reactions. In this study Fe@FexOy/Pd bimetallic NPs were synthesized through galvanic exchange reactions using 50:1, 20:1 and 5:1 molar ratios of Fe@FexOy NPs to Pd(NO3)2. The resulting Fe@FexOy/Pd NPs have Pd NPs on the Fe oxide surfaces, and still retain their response to external magnetic fields. The materials could be recovered after the reaction by an external magnetic field, and agitation of the solution via a magnetic field led to improvements of mass transfer of the substrates to the catalyst surface for hydrogenation reactions. The Fe@FexOy/Pd NPs derived from the 5:1 molar ratio of their respective salts (Fe:Pd) exhibited a higher catalytic activity than particles synthesized from 20:1 and 50:1 molar ratios for the hydrogenation of 2-methyl-3-buten-2-ol. The highest turnover frequency reached 3600 h−1 using ethanol as a solvent. In situ XANES spectra show that the Fe@FexOy NPs in the Fe@FexOy/Pd system are easily oxidized when dispersed in water, while they are very stable if ethanol is used as a solvent. This oxidative stability has important implications for the sustainable use of such particles in real world applications.
In situ X-ray Absorption Spectroscopic Study of Fe@FexOy/Pd and Fe@FexOy/Cu Nanoparticle Catalysts Prepared by Galvanic Exchange Reactions
(American Chemical Society, 2015) Yao, Yali; Patzig, Christian; Hu, Yongfeng; Scott, Robert WJ
Fe@FexOy core–shell nanoparticles have been previously shown to be a versatile support for catalytic metals such as Pd and Cu. However, the resulting structure, metal speciation, and performance of such catalysts in catalytic reactions are still poorly understood. Herein, we synthesize Fe@FexOy-supported Pd and Cu nanoparticles by controlling the molar ratios of Fe@FexOy nanoparticles to Pd2+ or Cu2+ species. Scanning transmission electron microscopy analyses show that Pd or Cu NPs are deposited on the exterior shell of the Fe@FexOy nanoparticles. In situ X-ray absorption near-edge structure (XANES) spectra were used to follow the formation processes of Fe@FexOy/Pd and Fe@FexOy/Cu nanoparticles and the performance of Fe@FexOy/Pd nanoparticles for Suzuki–Miyaura cross-coupling reactions. The results show that different molar ratios of Fe@FexOy nanoparticles to Pd2+ or Cu2+ lead to different morphologies of the resulting supported-NP structures. In situ XANES results show that Fe@FexOy nanoparticles can effectively fully reduce Pd or Cu salts over the course of ∼20 min to give small Pd or larger Cu nanoparticles on the surface and can also rereduce oxidized Pd in Suzuki–Miyaura cross-coupling reactions.
Internal molecular conformation of organic glasses: A NEXAFS study
(American Institute of Physics, 7/16/2021) Zuhaib, Amara; Urquhart, Stephen
The origin of the exceptional stability of molecular glasses grown by physical vapor deposition (PVD) is not well understood. Differences in glass density have been correlated with thermodynamic stability for thin films of N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) grown by PVD at specific substrate temperatures below the glass transition temperature. However, the relationship between the internal conformation of glass molecules and the thermodynamic properties of molecular glasses is not well studied. We use carbon 1s near edge x-ray absorption fine structure (NEXAFS) spectroscopy to examine different TPD sample preparations in which differences in the thermodynamic stability of the glass are known. Density functional theory simulations of the NEXAFS spectra of TPD allow us to attribute spectroscopic differences to changes in the internal conformation of the TPD molecule and relate this conformation to the stability of the TPD glass. This provides a direct experimental measurement of the internal conformation of molecules forming an organic glass.
Investigating the Geochemical Model for Molybdenum Mineralization in the JEB Tailings Management Facility at McClean Lake, Saskatchewan: An X‐ray Absorption Spectroscopy Study
(American Chemical Society, 2015) Blanchard, Peter; Hayes, John; Grosvenor, Andrew; Rowson, John; Hughes, Kebbi; Brown, Caitlin
The geochemical model for Mo mineralization in the JEB Tailings Management Facility (JEB TMF), operated by AREVA Resources Canada at McClean Lake, Saskatchewan, was investigated using X-ray Absorption Near-Edge Spectroscopy (XANES), an elemental-specific technique that is sensitive to low elemental concentrations. Twenty five samples collected during the 2013 sampling campaign from various locations and depths in the TMF were analyzed by XANES. Mo K-edge XANES analysis indicated that the tailings consisted primarily of Mo6+ species: powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3·8H2O), and molybdate adsorbed on ferrihydrite (Fe(OH)3 − MoO4). A minor concentration of a Mo4+ species in the form of molybdenite (MoS2) was also present. Changes in the Mo mineralization over time were inferred by comparing the relative amounts of the Mo species in the tailings to the independently measured aqueous Mo pore water concentration. It was found that ferrimolybdite and molybdate adsorbed on ferrihydrite initially dissolves in the TMF and precipitates as powellite.
Investigating the local structure of B-site cations in (1-x) BaTiO3exBiScO3 and (1-x)PbTiO3exBiScO3 using X-ray absorption spectroscopy
(Elsevier, 2018) Blanchard, Peter; Grosvenor, Andrew
The structural properties of (1-x)BaTiO3exBiScO3 and (1-x)PbTiO3exBiScO3 were investigated using powder X-ray diffraction and X-ray absorption spectroscopy. Diffraction measurements confirmed that substituting small amounts of BiScO3 into BaTiO3 initially stabilizes a cubic phase at x 1⁄4 0.2 before im- purity phases begin to form at x 1⁄4 0.5. BiScO3 substitution also resulted in noticeable changes in the local coordination environment of Ti4þ. X-ray absorption near-edge spectroscopy (XANES) analysis showed that replacing Ti4þ with Sc3þ results in an increase in the off-centre displacement of Ti4þ cations. Sur- prisingly, BiScO3 substitution has no effect on the displacement of the Ti4þ cation in the (1-x)PbTiO3 exBiScO3 solid solution.
Investigation of CeTi2O6- and CaZrTi2O7-containing glass–ceramic composite materials
(NRC Research Press, 2017) Paknahad, Elham; Grosvenor, Andrew
Glass–ceramic composite materials are being investigated for numerous applications (i.e., textile, energy storage, nuclear waste immobilization applications, etc.) due to the chemical durability and flexibility of these materials. Borosilicate and Fe–Al–borosilicate glass–ceramic composites containing brannerite (CeTi2O6) or zirconolite (CaZrTi2O7) crystallites were synthe- sized at different annealing temperatures. The objective of this study was to understand the interaction of brannerite or zirconolite-type crystallites within the glass matrix and to investigate how the local structure of these composite materials changed with changing synthesis conditions. Powder X-ray diffraction (XRD) and Backscattered electron (BSE) microprobe images have been used to study how the ceramic crystallites dispersed in the glass matrix. X-ray absorption near edge spectros- copy (XANES) spectra were also collected from all glass–ceramic composite materials. Examination of Ti K-, Ce L3-, Zr K-, Si L2,3-, Fe K-, and Al L2,3-edge XANES spectra from the glass–ceramic composites have shown that the annealing temperature, glass composition, and the loading of the ceramic crystallites in the glass matrix can affect the local environment of the glass–ceramic composite materials. A comparison of the glass–ceramic composites containing brannerite or zirconolite crystallites has shown that similar changes in the long range and local structure of these composite materials occur when the synthesis conditions to form these materials or the composition are changed.

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