Nanocrystalline Zinc Aluminate Research Articles

Designed Y3+ Surface Segregation Increases Stability of Nanocrystalline Zinc Aluminate.

The thermal stability of zinc aluminate nanoparticles is critical for their use as catalyst supports. In this study, we experimentally show that doping with 0.5 mol % Y2O3 improves the stability of zinc aluminate nanoparticles. The dopant spontaneously segregates to the nanoparticle surfaces in a phenomenon correlated with excess energy reduction and the hindering of coarsening. Y3+ was selected based on atomistic simulations on a 4 nm zinc aluminate nanoparticle singularly doped with elements of different ionic radii: Sc3+, In3+, Y3+, and Nd3+. The segregation energies were generally proportional to ionic radii, with Y3+ showing the highest potential for surface segregation. Direct measurements of surface thermodynamics confirmed the decreasing trend in surface energy from 0.99 for undoped to 0.85 J/m2 for Y-doped nanoparticles. Diffusion coefficients calculated from coarsening curves for undoped and doped compositions at 850 °C were 4.8 × 10-12 cm2/s and 2.5 × 10-12 cm2/s, respectively, indicating the coarsening inhibition induced by Y3+ results from a combination of a reduced driving force (surface energy) and decreased atomic mobility.

An efficient removal of Indigo Carmine dye (IC) from aqueous medium using environmental friendly synthesized ZnAl2O4

In recent years, materials have not only shown significant application in human life but also have a very important role in various industries. Over the last few decades, metal oxide and mixed metal oxide (MMO) have been acknowledged as efficient and environment-friendly alternatives to present-day available materials for different chemical, food, dye, and pharmaceutical industries along with environmental treatments. In view of the significant use of MMO in different fields, in the current work, nanocrystalline zinc aluminate (ZnAl2O4) has been successfully synthesized by the eco-friendly, cost-effective solid-state Mechanochemical (MCh) method, and it is used for the photocatalytic degradation of Indigo Carmine (IC) pollutant present in the wastewater of different industries. Numerous appropriate techniques, like Fourier-transform infrared spectroscopy (FT-IR), Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV-DRS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM), were used for its characterization. It is revealed that ZnAl2O4 exhibits a pronounced photocatalytic activity under the influence of UV–visible light exposure. The present study also reveals a possible pathway for photocatalytic degradation of IC using liquid chromatography-mass spectrometry (LC-MS).

Al excess extends Hall‐Petch relation in nanocrystalline zinc aluminate

AbstractThe increase in hardness with decreasing grain size is a well‐established size effect known as the Hall‐Petch relationship. In ceramics, there has been controversy surrounding the existence of a low size limit below which size‐induced hardening no longer occurs and softening is observed instead. Here, this so‐called inverse Hall‐Petch relationship was observed in quasi‐stoichiometric dense nanocrystalline zinc aluminate while an extension of the normal Hall‐Petch behavior was demonstrated by Al‐rich zinc aluminate nanoceramics. Vickers hardness increased with grain refinement for quasi‐stoichiometric samples prepared by High Pressure Spark Plasma Sintering, exhibiting a maximum of 18.6 GPa at a grain size of 21.4 nm. Conversely, Al‐rich zinc aluminate produced by the same technique strengthened up to 19.2 GPa at 12.6 nm grain sizes. Cross‐sections of Vickers indentation imprints showed that while quasi‐stoichiometric zinc aluminate showed a change in sub‐surface cracking pattern from larger to smaller grain sizes (before and after the inverse Hall‐Petch), the Al‐rich samples had sub‐surface cracking similar to those found in large grain sizes in quasi‐stoichiometric samples. These results suggest that softening at small grain sizes is driven by the activation of shear and fracture at weak grain boundaries which can be mitigated by Al enrichment.

Low cost synthesis route of spinel ZnAl2O4

In this work, zinc aluminate nanopowder was synthesized by chemical combustion route within a small span of time using the commercially purchased zinc chloride and aluminum nitrate powder. The as synthesized nano powders obtained from chemical method was calcined at 800 °C. The single phase formation with a cubic spinel structure was confirmed from X-ray diffraction pattern. The average crystallite size calculated from intense X-ray diffraction peak using Scherer’s equation and Williamson-Hall equation are in the order of nanometer scale. The energy band gap was determined from UV–Visible spectroscopy to have the knowledge of variation of optical properties of nanocrystalline zinc aluminate than that of bulk zinc aluminate.

Grain boundary strengthening in nanocrystalline zinc aluminate

AbstractFully dense transparent zinc aluminate ceramics with nanoscaled grain sizes were fabricated by Deformable Punch Spark Plasma Sintering (DP‐SPS). Optical transmission spectra showed high transparency, with up to 70% transmitted light in the visible spectrum. Vickers hardness was measured and grain boundary strengthening observed, showing hardness increase from 18.2 GPa up to 22.5 GPa as the grain sizes decreased from 60.3 to 10.1 nm. The trend followed the Hall‐Petch relationship, with hardness linearly proportional to the inverse of square root of grain size. A low grain size limit reported in previous literature below which hardness decreases, known as inverse Hall‐Petch relationship, was not observed within the studied grain size range. Cross‐sections of the hardness tests' indentations were prepared by focused ion beam and observed by electron microscopy and showed radically different crack patterns underneath the indentation imprint when contrasting samples with dissimilar grain sizes, shedding light on the mechanisms behind the observed grain boundary hardening mechanisms.

Luminescent ceramic nano-pigments based on terbium-doped zinc aluminate: Synthesis, properties and performance

Nanocrystalline zinc aluminate (ZnAl2O4) doped with terbium (III) was synthesized using a chemical co-precipitation reaction followed by calcination. The system has an average crystallite size of 6.5 ± 2.0 nm, calculated by the X-ray diffraction data, which is in close agreement with the particle size determined via high resolution transmission electronic microscopy. Rietveld refinement of the X-ray powder diffraction profile of the samples confirms that the aluminum ions are substituted by terbium ions in the host lattice.The effects of the terbium concentration and particle size of the samples on their luminescence properties were studied. The photoluminescence spectra exhibited a green emission band, with an excitation wavelength of 230 nm. Technological tests in several ceramic applications confirmed that these pigments and their luminescence properties are very stable at high temperatures, and these results suggest that these pigments have the potential to be applied as satisfactory ceramic luminescent pigments.

Synthesis and characterization of nanocrystalline zinc aluminate spinel powder by sol–gel method

Single-phase nanocrystalline zinc aluminate (ZnAl2O4) spinel powder has been synthesized by the sol–gel method. Zinc aluminate nanoparticles were formed at 600°C, which is at much lower temperature than by solid state reactions. Formation of ZnAl2O4 and their particle size depend on the calcination temperature. Calcination temperature also affects the specific surface area and pore volume. The nanocrystalline zinc aluminate was characterized by powder X-ray diffraction, FT-IR spectroscopy, thermal gravimetric analysis, diffuse reflectance spectroscopy, surface area measurements, field emission scanning electron microscopy coupled with energy dispersive X-ray analysis and transmission electron microscopy. Catalytic reactivity of nanocrystalline zinc aluminate was tested for the reduction of 4-nitrophenol to 4-aminophenol using NaBH4.

A new approach: Synthesis, characterization and optical studies of nano-zinc aluminate

The present study reports a green chemistry approach for the biosynthesis of nano-zinc aluminate by a microwave method using high purity metal nitrates and aloe vera plant extract. Aloe vera extract simplifies the process and provides an alternative process for a simple and economical synthesis of nanocrystalline zinc aluminate. It is prepared by conventional and microwave method by with and without using the plant extract for comparison purpose. The obtained nanomaterials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX), high resolution transmission electron microscopy (HR-TEM) diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy. The XRD confirmed the formation of cubic structure of zinc aluminate. The formation of zinc aluminate phase is also confirmed by FT-IR. The change in morphology from nanorods to nanosheets from the conventional method to microwave method is clearly shown by HR-SEM. The optical properties were determined by DRS and PL spectra.

Optical properties of ZnAl2O4 nanomaterials obtained by the hydrothermal method

Nanocrystalline zinc aluminate, ZnAl2O4, was obtained by the hydrothermal method. After hydrothermal treatment the samples were heated at different temperatures. The precursors used in the hydrothermal synthesis of ZnAl2O4 were zinc nitrate hexahydrate and aluminum nitrate nonahydrate. Sodium hydroxide was used as a basic source. The obtained samples were analyzed by x-ray diffraction. The optical properties of nanocrystalline zinc aluminate were also determined by photoluminescence and photoluminescence excitation measurements taken with a conventional lamp as the excitation source and by UV/vis/NIR spectroscopy.

Soft chemical synthesis of nanosized zinc aluminate spinel from the thermolysis of different organic precursors

A new method of preparation of nanocrystalline zinc aluminate (ZnAl2O4) powder is described in this paper. Different organic acids are used as template material and nitric acid as an oxidant. Single phase ZnAl2O4 spinel can be formed at a much lower temperature through this route which gives nanocrystalline powder with uniform particle size and morphology. The powders are characterized by thermo gravimetric analysis (TGA), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), BET surface area analysis and field emission scanning electron microscopy (FE-SEM). The average crystallite size of the single phase material was of 20 to 30 nm and the surface area was found to be 21 to 27 m2g−1.

Synthesis and characterization of nanocrystalline zinc aluminate spinel by sol–gel technique using modified alkoxide precursor

Nanosized zinc aluminate spinel (gahnite, ZnAl2O4) powders were prepared by sol−gel technique at low sintering temperatures. Aluminium-sec-butoxide [Al(OsBu)3] and zinc nitrate hexahydrate Zn(NO3)2 . 6H2O were used as starting materials. Gels with and without chelating agent were prepared. Ethyl-acetoacetate (C6H10O3) was used as a chelating agent in order to control the rate of hydrolysis of Al(OsBu)3. The dried gels and thermally treated samples were characterized by means of Differential Thermal Analysis and Thermo-Gravimetric Analysis (DTA, TGA), X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). The surface area was measured by Brunauer-Emmet-Teller (BET) adsorption–desorption isotherms. It has been established that chelation enables to obtain a transparent gel. The thermal evolution of gels was characterized by two crystallization processes in the range 200–400 °C and 600–700 °C. Both processes yielded pure ZnAl2O4 as evidenced by XRD, i.e. zinc aluminate spinel powders were produced by gel heat-treatment at temperatures as low as 300 °C. The average gahnite crystallite size for the samples sintered in the temperature range of 400–1000 °C has been calculated from the broadening of XRD lines revealing that nanocrystalline powders were prepared. The surface areas measured for the samples fired at 700 °C for 2 h were 43.1 and 62.6 m2 g−1, for sample without and with the chelating agent, respectively. TEM micrographs confirmed the nano-scale size of particles.

Synthesis and physical characteristics of ZnAl 2O 4 nanocrystalline and ZnAl 2O 4/Eu core-shell structure via hydrothermal route

Nanocrystalline zinc aluminate (ZnAl 2O 4) particles with a spinel structure were prepared by hydrolyzing a mixture of aluminum chloride hexahydrate and zinc chloride in deionized water. It was found that pH value and reaction temperature play critical roles in the formation of nano-sized ZnAl 2O 4. Depending on pH values in the precursor solution, ZnAl layered double hydroxide (ZnAl-LDH), ZnO, boehmite or gibbsite could be formed. At pH 7 and T>120 °C, the nanocrystalline ZnAl 2O 4 particles with average particle size of ∼5 nm are easily synthesized through ZnAl layered double hydroxide (ZnAl-LDH). After surface treatment with R–OH by using the cationic surfactant CTAB, the ZnAl 2O 4/Eu core-shell structure can be developed. The ZnAl 2O 4/Eu core-shell structure can show both emissions from 5D 0 to 7F 2 sensitivity energy level and 5D 2 to 7F 0 depth energy level.

Hydrothermal synthesis of nanoporous zinc aluminate with high surface area

Hydrothermal treatment at low temperatures is proposed for obtaining a nanocrystalline zinc aluminate spinel of interesting properties from catalytic point of view, including high specific surface area (up to 340 m 2/g), nanoporosity, and narrow pore size distribution. The precursors for hydrothermal synthesis were basic aluminium nitrate having the empirical formula Al 2(OH) 6−x(NO 3) x wherein x was equal or closed to 1, and hydrated zinc acetate. The proposed synthesis, in contrast to other methods, does not require a high temperature calcination to obtain the spinel phase. The properties of hydrothermally obtained zinc aluminate spinel make them an advanced material suitable for use in catalytic or high-tech ceramic applications.