Octahedral Al3 Research Articles

Illuminating tetracycline: The role of metal coordination in fluorescence emission and its optical detection potential

Rapid on-site detection of antibiotics such as tetracycline (TC) is crucial for understanding their elusive environmental fate. Fluorescence-based strategies are promising owing to their sensitivity and ease of use. This study demonstrates that Al3+–TC coordination significantly enhances the intrinsic fluorescence of TC at excitation/emission wavelengths of 395/490 and 270/490 nm. The fluorescence emission intensity is proportional to the TC concentration between 0.005 and 7.5 μmol/L TC, which increases the detection sensitivity by 40 times compared with the commonly used absorption signals. Density functional theory calculations, when combined with the independent gradient model, indicate that the six-membered chelate ring in the octahedral Al3+–TC complex restricts molecular motion, along with two intramolecular hydrogen bonds formed between TC and water ligands. These factors lead to a narrowing of the energy gap between the highest occupied and lowest unoccupied molecular orbitals upon complexation with Al3+. Consequently, the enhanced molecular rigidity and facilitated electron transfer result in a significant increase in the fluorescence quantum yield. This captivating fluorescence response significantly enhances the proficiency of optical signals in detecting TC, thereby enriching future environmental monitoring systems with greater diversity and adaptability.

Broadband near-infrared luminescence in a cubic pyrophosphate Al0.5Ta0.5P2O7:Cr3+ phosphor for multi-functional applications.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are considered as next-generation of NIR light sources for spectroscopy. However, it is still a challenge to develop an inexpensive broadband NIR phosphor with relatively long-wavelength (λem > 800 nm) emission. In this work, an octahedral Al3+-containing pyrophosphate Al0.5Ta0.5P2O7 with a cubic structure was chosen as a host for Cr3+. Synthesizing this material indicates that this phosphor exhibits a broadband NIR emission peaking at 850 nm with a full width at half maximum (FWHM) of 155 nm under 465 nm excitation. The crystal structure, morphology, local structure, and photoluminescence properties of this material were investigated in detail. The results revealed a full understanding of this new material. A NIR pc-LED device fabricated by using this material combined with a 450 nm LED chip generates a NIR output power of 10.7 mW and a NIR photoelectric conversion efficiency of 3.4% under a 100 mA driving current, which shows the possibility of this material to be utilized in NIR pc-LED applications. Moreover, this material exhibits a linear relationship between emission intensity, decay time and temperature in a wide temperature range, implying that excellent multi-model temperature sensing applications can be expected.

Systematic Study on the Synthesis and Magnetism Properties of Manganese Ferrite MnFe2O4 by an Oxidation Roasting Process

A low-cost and high-efficiency solid reaction method has been reported as an effective technology to synthesize manganese ferrite MnFe2O4 with a spinel crystal structure. This work clarified the underlying reason for the influence mechanism of SiO2 and Al2O3 on the synthesis of MnFe2O4. Synthetic MnFe2O4 polyhedral microparticles with a saturated magnetization of 71.19 emu/g, a ratio of saturation magnetization to residual magnetization (Ms/Mr) of 0.062 and a coercivity (Hc) of 6.50 Oe were successfully obtained at an oxidization roasting temperature of 1100 °C for 60 min. The experimental results indicate that the tetrahedral Mn2+ ions and octahedral Mn3+ ions in the crystal structure of manganese ferrite MnFe2O4 were replaced by tetrahedral Si2+ ions and octahedral Al3+ ions from (Mn2+)x(Fe2+)y(Si2+)1−x−y[Fe3+]2O4 and (Mn2+)[Fe3+]2−x[Al3+]xO4, respectively. In addition, hercynite FexMn1−xAl2O4 with a spinel crystal structure and olivine MnxFe2−xSiO4 with an orthorhombic crystal structure were partially formed in the synthesis of manganese ferrite MnFe2O4, in which some Fe2+ ions were easily replaced by Mn2+ ions to form stable hercynite MnAl2O4 and olivine Mn2SiO4 in these crystal structures. The current research work provides comprehensive insights for synthesizing manganese ferrite MnFe2O4 and continuously advances its technical progress.

Understanding the coordination behavior of antibiotics: Take tetracycline as an example

Gaining insight into the occurrence states of residual antibiotics is crucial to demystify their environmental behavior. However, the complexation of heteroatoms functioned on antibiotic molecules to metal ions in the water environment is not fully understood. This study reports that a fluorescence response was unexpectedly triggered by tetracycline (TC) and Al3+, serving as solid evidence to visualize the Al3+-TC coordination reaction. Differential electron absorption spectroscopy shows a quantifiable signal of the redshifted n–π* transition with a coordination reaction, which is also proportional to the fluorescence. The occurrence of Al3+-complexed TC also caused a split in retention time in liquid chromatogram. The TC ligands were re-released in the presence of stronger ligands competing for central Al3+. The complex ratio of Al3+-TC is confirmed to be 1:1 using Job’s plot with a stability constant of 1.01 × 106. Quantum chemical computations coupled with Gibbs free energy analysis simulated the formation of octahedral Al3+-TC configuration through a spontaneous bidentate chelation. This study helps convey a broad consensus and opens a new door in the mechanistic study of metal-involved antibiotic transformation process, leading to a better understanding that can ultimately be essential to reach the final goal of alleviating the antibiotic crisis.

Electro-Freezing of Supercooled Water Is Induced by Hydrated Al3+ and Mg2+ Ions: Experimental and Theoretical Studies.

This work reports that the octahedral hydrated Al3+ and Mg2+ ions operate within electrolytic cells as kosmotropic (long-range order-making) "ice makers" of supercooled water (SCW). 10-5 M solutions of hydrated Al3+ and Mg2+ ions each trigger, near the cathode (-20 ± 5 V), electro-freezing of SCW at -4 °C. The hydrated Al3+ ions do so with 100% efficiency, whereas the Mg2+ ions induce icing with 40% efficiency. In contrast, hydrated Na+ ions, under the same experimental conditions, do not induce icing differently than pure water. As such, our study shows that the role played by Al3+ and Mg2+ ions in water electro-freezing is impacted by two synchronous effects: (1) a geometric effect due to the octahedral packing of the coordinated water molecules around the metallic ions, and (2) the degree of polarization which these two ions induce and thereby acidify the coordinated water molecules, which in turn imparts them with an ice-like structure. Long-duration molecular dynamics (MD) simulations of the Al3+ and Mg2+ indeed reveal the formation of "ice-like" hexagons in the vicinity of these ions. Furthermore, the MD shows that these hexagons and the electric fields of the coordinate water molecules give rise to ultimate icing. As such, the MD simulations provide a rational explanation for the order-making properties of these ions during electro-freezing.

Achieving an ultra-high absorption efficiency in a monoclinic LiAlP2O7:Cr3+ near-infrared phosphor

Near-infrared phosphor-converted light-emitting diode (NIR pc-LED) is becoming a smart light source for portable multifunctional devices, utilizing in fields like bio-imaging, night-vision, and food-quality analysis. However, developing broadband, inexpensive, and efficient NIR phosphors are still in great challenges. Herein, we report a phosphate LiAlP2O7:Cr3+ phosphor by choosing highly distorted and inexpensive octahedral Al3+-containing compound as host. This material generates a broadband NIR emission with peak located at 844 nm and a full width at half maximum (FWHM) of 163 nm under 450 nm excitation. Amazingly, the absorption efficiency (AE) was measured to be as high as 64%, being higher than most of Cr3+-activated polycrystalline materials. Unfortunately, the internal quantum efficiency (IQE) was only 26.7%, and the emission intensity at 373 K kept only 56% of that at room temperature. The detailed reasons for these undesired properties are systematically investigated. Moreover, a prototype NIR pc-LED fabricated by using this material combining with 450 nm LED chip demonstrates a NIR output power of 9.7 mW and NIR photoelectronic conversion efficiency of 3.3% under 100 mA driving current, indicating the feasibility of this material to be applied in NIR pc-LEDs.

Surface Al and Co coordination for peroxymonosulfate activation: Identification and mechanism

Deciphering the metal-support interaction-oriented catalysis on millimeter-scaled catalysts is highly desirable yet remains scarce in Fenton-like catalysis. Herein, we fine-tune the support-surface reconstruction of Co2AlO4 on γ-Al2O3 millispheres and reveal the origins of its activity in peroxymonosulfate activation by nuclear magnetic resonance and X-ray photoelectron/adsorption spectroscopy. Calcination of γ-Al2O3 supports rearranged their surface octahedral, tetrahedral and pentacoordinate Al3+. The reconstructed tetrahedral and pentacoordinate Al3+ as binding sites regulated the formation of Co2AlO4 with coordinated Co3+/Co2+ redox centers via strong metal-support interactions. The activities of tailored Co2AlO4 @Al2O3 millispheres in activating peroxymonosulfate follow different binomial models, highly relying on their Co3+/Co2+ ratio, contents of lattice O and pentacoordinate Al3+. The Co-O-Al bonds endow the millimeter-scaled Co2AlO4 @Al2O3 with robust catalytic activity, stability and reusability. The exposed Co2AlO4 (200) surface is responsible for the decomposition of PMS into produce SO4• and 1O2 as the dominant oxidants for water detoxification.

Zwitter Ion-Promoted Hybrid 2D Materials for Energy Applications

Layer-by-layer assembly of thin films have received growing interest in a variety of applications worldwide. Methods for depositing films, patterning, unconventional assemblies, and approaches are gaining immense scientific advancements. The porous structures, tunable surface areas, remarkable thermal and mechanical stabilities, abundant reserves, and cost-effectiveness makes clays one of the most sought-after materials for plethora of applications. Interestingly, several naturally occurring silicates, viz. clay minerals have layered structure with possibility of interchangeable intercalated ions and tunable chemical properties. Among these clay minerals, Bentonite is very promising owing to its abundance, low cost, high surface area, porosity, and unique layered structure. Clay is composed of alternating tetrahedral silica (T) and octahedral alumina (O) sheets arranged in 1:1 ratio (T-O). The tetrahedral sheets are formed from Si4+ ions coordinated with oxygen, however in the octahedral sheet Al3+ metal ion is the central atom. Notably, naturally occurring Bentonite have some of the octahedral sites occupied by the Mg2+ and Fe2+ ions. The presence of these ions shows the tunable property of the octahedral layer that can concomitantly widen its applicability in the energy fields. Herein, we have put a focused effort in developing a sustainable, cost-effective, environmental benign, and biocompatible clay films having unique physical and chemical properties. We present a unique approach to develop clay galleries infused with intercalating quaternary ammonium salts. The insertion of such zwitter ions enhances the interlayer spacing, while simultaneously allowing to form durable clay films. The hybrid clay films have been characterized using the powder X-ray diffraction, X-ray photoelectron spectra, ATR-FTIR spectra, DSC-TGA, dynamic mechanical analyses, and imaging techniques. Effect of varying the carbon chain length in these zwitter ions have been verified to have a significant impact in controlling the interlayer spacing in the clay films. Further, the intercalation using zwitter ions led to the alternations in the electron environment of the dielectric silicate layers that has been confirmed using electrochemical and impedance spectroscopy studies. Owing to the high electronic resistance and high ionic conductivity present in the films, a series of impedance spectroscopy experiments were conducted in variety of electrolytes. The ionic conductivity of the hybrid clay films is remarkable, and a correlation have been established with the ionic size of the conducting ions. In metal ion batteries, where dendritic growth causes thermal degradation of the batteries, the hybrid clay films possess high thermal and mechanical stability that makes them versatile for energy materials. can provide The abundance and sustainability of clay minerals and a cost-effective approach to engineer these hybrid films may provide efficient avenues to develop new generation of battery separators and capacitors for future.

Mn ions‐activated Gd3(Al,Ga)5O12 garnet solid‐solution ceramics: Cation substitution for dual wavelength red‐emission

AbstractRed‐emitting color‐convertors have attracted considerable attention for promising applications in solid‐state lighting (SSL) to improve color rendition. However, the current nitride and fluoride phosphor powders have encountered several challenges, such as high cost, narrow emission bands, and insufficient stability during operation, which limit the development of high‐power full‐spectrum SSL. In this study, thermally robust Gd3(Al,Ga)5O12:Mn (GAGG:Mn) solid‐solution ceramics (SSCs) with dual wavelength red‐emission bands were prepared via an oxygen solid‐state sintering reaction. The doped Mn ions occupied octahedral Al3+ and Ga3+ sites to generate Mn4+ luminescent centers with pronounced deep‐red emissions peaking at 698 nm (2E → 4A2), and Mn2+ luminescent centers with broad red emissions at 628 nm (4T1 → 6A1). Because the cationic radius matching effect induced the regulation of valence state of Mn, the photoluminescence of the GAGG:Mn SSCs can be tailored by the substitution of Al3+ with Ga3+. Moreover, the Mn3+ also existed in the GAGG lattice host, and their concentration decreased with increasing Ga3+ contents owing to the mismatch of ionic radius between Mn3+ and Ga3+ ions. With the optimization of Al/Ga ratio and concentration of Mn ions, a broad emission band ranging from 550 to 800 nm (bandwidth = 250 nm) was achieved from Gd3Al3Ga2O12:0.3%Mn SSCs upon 465‐nm excitation. Moreover, the GAGG:Mn SSC has over 17‐fold enhanced thermal conductivity compared with the corresponding phosphor powder. This paper opens a door of regulating the valence state of luminescence centers with cation substitution and the application of oxide red‐emitting color‐convertors.

Enhancing propane direct dehydrogenation performances through temperature induced VOx dispersion and alumina support phase transformation

Vanadium oxide-based catalysts are promising candidates for propane direct dehydrogenation. A strategy was developed in the present study to enhance the intrinsic activity and coking-resistance of supported VOx catalysts at the same time. The annealing temperature and VOx surface density were identified as regulation parameters to tailor the dispersion of VOx and micro-environment of V-O-Al active sites. The surface acidic VOx was found capable of inducing local structure rearrangement of transition alumina and the transformation of amorphous δ- to more crystalline θ-alumina at relatively lower temperatures, contributing to lowering VOx-support interactions and enhancing VOx reducibility. The DFT calculations verify that the chemical states of V-O active sites could be tuned by the ligand Al3+ coordination micro-environment, and the octahedral Al3+ serving as ligands contributes to enhancing the reducibility and C–H bond rupture capability of V-O site. The annealing temperature was also found capable of dispersing VOx species over alumina surface with the optimal temperature dependent of specific VOx loadings. As a consequence, the intrinsic activity of 3.1 V/Al2O3-900 and the deactivation rate of 3.1 V/Al2O3-700 with dominantly isolated VOx is 1.4 times and 0.65 times that of 3.1 V/Al2O3-550, respectively.

First-principles modeling of the infrared spectrum of Fe- and Al-bearing lizardite

Abstract. The theoretical vibrational properties of a series of Fe- and Al-bearing lizardite models have been determined at the density functional theory level. Each periodic model displays a single cationic impurity substituted at an octahedral or tetrahedral site of a supercell of lizardite (Mg3Si2O5(OH)4) containing 162 atoms. The isovalent Fe2+ for Mg2+ substitution has been considered, as well as the heterovalent substitution of Fe3+ or Al3+ for Mg2+ or Si4+. Comparison of the theoretical absorption spectra with previously reported experimental spectra of natural and laboratory-grown lizardite samples allows us to propose an interpretation for most of the observed bands. Although the identification of specific bands related to octahedral Fe2+ in FTIR spectra is challenging, broad bands at 3584 and 3566 cm−1 reflect the occurrence of octahedral Al3+ and Fe3+, respectively, in the natural samples. These broad bands likely overlap with potential contribution related to tetrahedral Al3+. It is suggested that the modification of the H-bonding pattern related to the incorporation of trivalent ions at tetrahedral sites has an overall broadening effect on the interlayer-OH stretching bands of lizardite.

New Mg2+/Ge4+-Stabilized Gd3MgxGexAl5-2xO12:Ce Garnet Phosphor with Orange-Yellow Emission for Warm-White LEDs (x = 2.0-2.5).

By stabilization of the Gd3Al5O12 garnet by replacing 80% or more of Al3+ with Mg2+/Ge4+ pairs, a series of new orange-yellow-emitting Gd3MgxGexAl5-2xO12:Ce (x = 2.0-2.5) phosphors were successfully developed for potential application in warm-white-light-emitting diodes (WLEDs). Rietveld structure refinement proved that Mg2+ first substitutes the octahedral Al3+ ion, followed by the replacement of the tetrahedral Al3+ together with Ge4+. The band structure of the x = 2.0 typical garnet was analyzed via density functional theory (DFT) calculations. The incorporation of an increasing content of Mg2+/Ge4+ was experimentally shown to narrow the band gap and expand the unit cell of the garnet host and blue shift the emission/excitation wavelength and shorten the fluorescence lifetime of Ce3+. The photoluminescence behaviors were rationalized by considering the influence of Mg2+/Ge4+ on the crystal structure, band structure, and local coordination. An LED lamp fabricated by combining the (Gd2.97Ce0.03)Mg2Ge2AlO12 optimal phosphor with a 450 nm-emitting InGaN blue LED chip exhibited a color-rendering index of 71.6, luminous efficacy of 16.1 lm/W, and a low correlated color temperature of 2201 K under a driving current of 20 mA, indicating that phosphor may have potential application in warm WLEDs.

Mn3+ and the pink color of gem-quality euclase from northeast Brazil

Abstract Pink euclase of gem quality and centimeter size, presenting an unusual pink-orange coloration and a pink to orange pleochroism, was discovered near Livramento de Nossa Senhora, in Bahia State, Brazil. The origin of the pink coloration has been investigated using several spectroscopic techniques: UV-Vis-NIR spectroscopy, electron paramagnetic resonance (EPR), luminescence, and X-ray absorption near edge structure (XANES). The coloration is mainly due to the presence of Mn3+ substituted to octahedral Al3+ that causes an intense split band at about 18 500 and 21 000 cm−1. The crystal field splitting Dq, crystal field stabilization energy (CFSE), and Racah parameter B for Mn3+ are 2055.5 cm−1, 147 kJ/mol, and 886 cm−1, respectively. The Mn3+ molar extinction coefficient varies as a function of polarization, between 23 and 55 L.mol−1·cm−1. An additional absorption band, near 24 000 cm−1, together with the rising background toward the UV, tentatively assigned to the O → Fe3+ OMCT, contributes to the pink-orange hue. The in-situ UV-Vis-NIR spectra on heating up to 500 °C show a color change toward an intense, stable pink color. CIE colorimetric parameters demonstrate that the color of the investigated euclase remains in the pink domain before and after heat treatment. In the absence of Mn2+, shown by EPR and luminescence, the presence of Mn3+ evidences oxidative formation conditions due to contamination of the hydrothermal fluids by the surrounding host rock.

Studies of the EPR parameters and tetragonal distortion for the Cu2+ center in aluminium oxide

The electronic paramagnetic resonance (EPR) parameters (g factor gi , and hyperfine structure constants Ai , with i = || and ⊥) and tetragonal distortion of the Cu2+ center in Al2O3 are unified interpreted from the perturbation formulas for a 3d9 ion in tetragonally elongated octahedral. In the calculations, the impurity Cu2+ is found to occupy the host trigonally-distorted octahedral Al3+ site with the tetragonal elongation distortion due to the Jahn–Teller effect, despite the original trigonal distortion of the host cation site. The contributions to EPR parameters from both the spin–orbit coupling of the central ion and that of the ligands are taken into account. The defect structure of the Cu2+ center (characterized by the relative tetragonal elongation ratio η ≈ 4.3% along the C 4 axis) was determined from the calculation. Furthermore, the calculated results agree well with the experimental data and need fewer adjustable parameters than the previous studies.

Solid-State Recrystallization Pathways of Sodium Aluminate Hydroxy Hydrates.

Crystallization of Al3+-bearing solid phases from highly alkaline Na2O:Al2O3:H2O solutions commonly necessitates an Al3+ coordination change from tetrahedral to octahedral, but intermediate coordination states are often difficult to isolate. Here, a similar Al3+ coordination change process is examined during the solid-state recrystallization of monosodium aluminate hydrate (MSA) to nonasodium bis(hexahydroxyaluminate) trihydroxide hexahydrate (NSA) at ambient temperature. While the MSA structure contains solely oxolated tetrahedral Al3+, the NSA structure is a molecular aluminate salt solely based upon monomeric octahedral Al3+. Spontaneous recrystallization of MSA and excess sodium hydroxide hydrate into NSA over 3 days of reaction time was clearly evident in X-ray diffractograms and in Raman spectra. In situ single-pulse 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and 27Al multiple quantum (MQ) MAS NMR spectroscopy showed no evidence of intermediate aluminates, suggesting that transitional states, such as pentacoordinate Al3+, are short-lived and require spectroscopy with greater time resolution to detect. Such research is advancing upon a detailed mechanistic understanding of Al3+ coordination change mechanisms in these highly alkaline systems, with relevance to aluminum refining, corrosion sciences, and nuclear waste processing.

Green emitting Ba1.5Lu1.5Al3.5Si1.5O12: Ce3+ phosphor with high thermal emission stability for warm WLEDs and FEDs

By hetero-valence substituting Ba2+-Si4+ for Lu3+-Al3+ pair in Lu3Al5O12: Ce3+, a new green phosphor Ba1.5Lu1.5Al3.5Si1.5O12: Ce3+ (BLAS: Ce3+) has been obtained. It crystallizes in garnet structure with space group Ia-3d (230). In the structure, Ba2+ ions are incorporated into both dodecahedral Lu3+ and octahedral Al3+ sites while Si4+ ions only occupy tetrahedral Al3+ sites. Under the blue light irradiation of 450 nm, an intense green light peaking at 520 nm was observed and the PL spectrum can be fitted in two Gaussian components, due to the crystal field splitting of Ce3+ 5d states under D2 symmetry constrains. The optical doping concentration of BLAS: Ce3+ is 6% mol, of which the IQE and EQE are 89.1% and 51.8%, respectively. Furthermore, this sample exhibits an extremely good thermal stability, i.e. the integrated emission intensity is still more than 90% of the initial intensity at 480 K. Then, a w-LED device was fabricated from this new green phosphor BLAS: Ce3+ and commercial red phosphor (Ca,Sr)AlSiN3: Eu2+, which shows a quite high color rendering (Ra = 88.2) and a relatively low color temperature 4772 K. Besides, the phosphor exhibits a stable chromaticity under different acceleration voltages. The phosphor may be promising material for the development of solid-state lighting and display systems.

Unraveling Gibbsite Transformation Pathways into LiAl-LDH in Concentrated Lithium Hydroxide.

Gibbsite (α-Al(OH)3) transformation into layered double hydroxides, such as lithium aluminum hydroxide dihydrate (LiAl-LDH), is generally thought to occur by solid-state intercalation of Li+, in part because of the intrinsic structural similarities in the quasi-2D octahedral Al3+ frameworks of these two materials. However, in caustic environments where gibbsite solubility is high relative to LiAl-LDH, a dissolution-reprecipitation pathway is conceptually enabled, proceeding via precipitation of tetrahedral (Td) aluminate anions (Al(OH)4-) at concentrations held below 150 mM by rapid LiAl-LDH nucleation and growth. In this case, the relative importance of solid-state versus solution pathways is unknown because it requires in situ techniques that can distinguish Al3+ in solution and in the solid phase (gibbsite and LiAl-LDH), simultaneously. Here, we examine this transformation in partially deuterated LiOH solutions, using multinuclear, magic angle spinning, and high field nuclear magnetic resonance spectroscopy (27Al and 6Li MAS NMR), with supporting X-ray diffraction and scanning electron microscopy. In situ 27Al MAS NMR captured the emergence and decline of metastable aluminate ions, consistent with dissolution of gibbsite and formation of LiAl-LDH by precipitation. High field, ex situ 6Li NMR of the the progressively reacted solids resolved an Oh Li+ resonance that narrowed during the transformation. This is likely due to increasing local order in LiAl-LDH, correlating well with observations in high field, ex situ 27Al MAS NMR spectra, where a comparatively narrow LiAl-LDH Oh 27Al resonance emerges upfield of gibbsite resonances. No intermediate pentahedral Al3+ is resolvable. Quantification of aluminate ion concentrations suggests a prominent role for the solution pathway in this system, a finding that could help improve strategies for manipulating Al3+ concentrations in complex caustic waste streams, such as those being proposed to treat the high-level nuclear waste stored at the U.S. Department of Energy's Hanford Nuclear Reservation in Washington State, USA.

Substitutional site of Mn4+ ion and local compressibility of this Mn4+ center in Mn4+-doped Sr4Al14 O25 crystal

ABSTRACTThe local compressibility of (MnO6)8− octahedral cluster for Mn4+ ion in the octahedral Al3+ site of Sr4Al14O25:Mn4+ crystal is investigated by analyzing the dominant pressure dependence of R-line position (i.e. 2E→4A2 transition). The obtained local compressibility is much greater than that in Al2O3: Mn4+ crystal, suggesting that the average Al3+–O2− distance of the replaced (AlO6)9− octahedron in Sr4Al14O25 is much greater than that in Al2O3. By comparing the average Al3+–O2− distances in the three octahedral Al3+ sites, Al4, Al5 and Al6, in Sr4Al14O25 crystal, we propose that the dominant substitutional site of Mn4+ ion is Al4 site which has the largest average Al3+–O2− distance. The results are discussed.

Mineralogical and gemological characterization of emerald crystals from Paraná deposit, NE Brazil: a study of mineral chemistry, absorption and reflectance spectroscopy and thermal analysis

Abstract The Parana deposit, located at Southwestern Rio Grande do Norte state, in Brazil, is one of the few emerald deposits found at Borborema Province. The mineralization occurs in phlogopite schists and actinolite-phlogopite schists associated with pegmatites and albitites within the Portalegre Shear Zone. Unlike other well-known Brazilian emerald deposits, the mineralogy of Parana emeralds has remained poorly investigated for the last 40 years. In this study, we conducted mineralogical characterization of theses emeralds through gemological testing, mineral chemistry, absorption and reflectance spectroscopy, and thermal analysis. The Parana emeralds are bluish-green colored, characterized by high refractive index, several two-phase fluid inclusions and mica is the main mineral inclusion. Electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry analyses detected the presence of Fe2+ (0.43-1.94 wt.% FeO) and Cr3+ (0.04-0.14 wt.% Cr2O3) as the main chromophores replacing octahedral Al3+ in the crystal structure. In addition, substantial amounts of MgO (0.40-2.72 wt.%), Na2O (0.50-1.81 wt.%), and Cs2O (0.07-0.44 wt.%) were also identified. The main causes for its coloration were attributed to Cr3+ absorption features in visible spectral range, which were corroborated by absorption and reflectance spectra. The presence of types I and II H2O at channel-sites was recorded in Fourier-transform infrared spectra and demonstrated by dehydration processes observed in different thermal and thermogravimetric analyses.

Study on the Catalytic Effect of Nitric Acid Activated Myanmar Natural Clay for the Degradation of Plastic Wastes

In this study, the performance of different acid treated Myanmar Natural Clay (Mabisian) was conducted the pyrolysis of mixed plastic wastes, 40% high density polyethylene, 30% polypropylene, 25% low density polyethylene and 5% polystyrene. Mabisian clay was refluxed with different concentration of nitric acid (2M, 4M, 6M, 8M, 10M, 12M and 14M) at 100ºC for 3hrs followed by calcination at 500ºC for 1hr. The physico-chemical characteristics of resulted leached clay were studied by X-Ray Fluoresence spectroscopy (XRF), X-Ray Diffraction (XRD) and Fourier Transformed Infrared Spectroscopy (FTIR). The pyrolytic oil was characterized by Gas Chromatography – mass spectopy (GC-MS). XRF and FTIR studies indicated that acid treatment under reflux condition lead to the removal of octahedral Al3+ cations along with other impurities. The chemical treatment increased the Si/Al ratio. The maximum liquid yield (75%) was obtained at 12 M nitric acid, 3hr reaction time and 100 º C reaction temperatures. In addition, the percent peak area of gasoline range hydrocarbon was obtained 55.6% at optimum condition. Thus, the treated clay can be used as promising as catalyst support.