Effect of triethanolamine chelating agent on crystallinities,phase purities,and optical properties of zinc aluminate spinel synthesized by thermal decomposition

Zinc aluminates form a niche class of ceramics, which are useful in various applications, including photoelectronic devices, catalysts, and high efficacy optical materials. Selecting appropriate starting precursors is the key impertive to control synthetic parameters in ceramics syntheses for the improvement of phase purity and corresponding physicochemical properties. The current study reports the successful preparation of high crystallinity and purity of ZnAl₂O₄ via thermal decomposition of the metal complex precursor using triethanolamine (TEA) as the additive and chelating agent. The effects of calcination temperatures and the existence of TEA on the formation of the desired ZnAl₂O₄ and the suppression of ZnO impurity are thoroughly investigated. Herein, the correlation between the in-depth analysis of the thermal decomposition profile of the mixed metal-TEA precursor and the characteristic features of the obtained ZnAl₂O₄ product are highlighted. The variation of optical bandgap energy of the derived materials by controlling the structural defects via a variation of synthetic parameters is explored. The obtained results show strong evidence that the ZnAl₂O₄ powders derived from the thermal decomposition of the mixed metal-TEA precursor are superior in terms of crystallinity, phase purity, and optical properties to those without using the TEA chelating agent.     

Photocatalytic performance of Fe-substituted ZnAl2O4 powders under sunlight irradiation on degradation of industrial dyes

Using the sol–gel auto combustion method with diethanolamine (DEA) as fuel, a sequence of iron-substituted zinc aluminates, ZnFe_xAl_2-xO₄ powders, including variable Fe³⁺ ion concentrations (0 ≤ x ≤ 2) were effectively prepared. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer–Emmett–Teller (BET) method, UV–visible diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM) were employed to examine the structures, chemical bonds, morphologies, composition, surface area, and optical properties as well as the magnetic behavior of the obtained samples. A single-phase spinel structure was obtained for the calcined aluminate powders with different interplanar spacing and crystallite sizes, as revealed by the classification results. The bandgap energy (E_g) of adapted aluminates was in the range of 2.04-3.14 eV, identified as being much lower compared to the pure sample (5.60 eV). Thus, Fe³⁺-substituted ZnAl₂O₄ samples could be successfully photoexcited using both ultraviolet and visible light, as suggested by the results. Examination of how the four main pollutant types decay when irradiated by sunlight was carried out to assess the samples and establish photocatalytic activity. These contaminants included rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). The performance of photocatalytic degradation reached 98% after 150 min for all optimal samples of organic dyes. Besides, each of the altered photocatalysts could be recycled and displayed high stability. The S-shaped curve of ferrimagnetism can result in those samples as found by the magnetic measurements, though pure ZnAl₂O₄ displays diamagnetic characteristics. The adapted samples show intense improvement in the remanent magnetization (M_r) when compared to pure ZnAl₂O₄, signifying that magnetic photocatalyst recovery by applying an external magnetic field is easy. Thus, these results offer a convincing sign that ZnAl₂O₄ powders replaced by Fe³⁺ could provide the ability to aid in the ecologically friendly collection of solar energy.     

Syntheses and characterization of highly transparent ZnAl2O4 ceramic films using poly(acrylamide-co-acrylic acid) assisted microwave approach

Zinc aluminate nanopowders were synthesized via poly(acrylamide-co-acrylic acid) assisted microwave approach. The as-synthesized ZnAl₂O₄ nanopowders were characterized using X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM) and selected area of electron diffraction (SAED). The prepared ZnAl₂O₄ nanopowders exhibited a spinel cubic polycrystalline structure. The increase of poly(acrylamide-co-acrylic acid) amounts decreased the particle size of the ZnAl₂O₄ nanopowders. The poly(acrylamide-co-acrylic acid) enhanced the densification rate of ZnAl₂O₄. The increasing of poly(acrylamide-co-acrylic acid) amount decreased the sintering temperature from 1300 °C to 950 °C. The hot-compressed ZnAl₂O₄ nanopowders in the existence of 2 wt% of poly(acrylamide-co-acrylic acid) exhibited full density at 950?C in just 20 min. The ZnAl₂O₄ ceramic films revealed a high transparency of 83 ± 1% at a wavelength range from 450?1200 nm.     

Microwave Synthesis and Characterization of Spinel-type Zinc Aluminate Nanoparticles

In the present work, ZnAl₂O₄ nanoparticles have been synthesized with the aid of Zn(OAc)₂·2H₂O and Al(NO₃)₃·9H₂O as starting reagents in the presence of microwave irradiation. Besides, the effect of preparation parameters such as microwave power and irradiation time on the morphology and particle size of products was studied by SEM images. The as-prepared ZnAl₂O₄ nanoparticles were characterized extensively by techniques like XRD, TEM, SEM, FT-IR, PL, and EDS. Photoluminescence studies of the ZnAl₂O₄ nanoparticles displayed quantum confinement behavior with band gap of 3.2 eV. The XRD studies showed that pure orthorhombic ZnAl₂O₄ nanoparticles have been produced after calcination.     

Effects of the fuel type and fuel content on the specific surface area and magnetic properties of solution combusted CoFe2O4 nanoparticles

In this work, the different fuels (citric acid, glycine and urea) at the various fuel to oxidant ratios (ϕ=0.5, 0.75, 1 and 1.25) were used for solution combustion synthesis of CoFe₂O₄ nanoparticles. The phase evolution, microstructure, specific surface area and magnetic properties of the solution combusted CoFe₂O₄ nanoparticles were investigated by X-ray diffraction, thermal analysis, electron microscopy, adsorption-desorption isotherms and vibrating sample magnetometry techniques. The specific surface area of the combusted products decreased with the increase of fuel to oxidant ratio (ϕ), irrespective of the fuel type. However, the specific surface area for the glycine fuel was higher than the others, due to the higher combustion rate for releasing gaseous products. Furthermore, the solution combusted CoFe₂O₄ powders by the glycine fuel exhibited the higher saturation magnetization (63.6 emu/g) on account of their higher crystallinity and particle size.     

Sol-gel synthesis and characterization of ZnAl2O4 powders for transparent ceramics

The sol-gel synthesis of ZnAl₂O₄ ceramic powders from alkoxide and acetate sources of metals, as well as the microstucture and the hardness of the hot-pressed ZnAl₂O₄ specimens were considered. ZnAl₂O₄ powders were prepared by the hydrolysis of an alcohol solution of aluminium isopropoxide using an aqueous solution of zinc acetate followed by heat treatment. The thermal evolution of the ZnAl₂O₄ precursor was investigated. The effect of calcination temperature on the morphology and the specific surface area of ZnAl₂O₄ powders were also studied. The sintering of the resultant powders to the high transparent ceramic using a hot pressing with 1?wt% ZnF₂, as a sintering additive was successfully demonstrated. The in-line transmittance of ZnAl₂O₄ ceramics (1?mm thickness) achieved 80% in the visible region and 85% at 5?µm; Vickers hardness was 11.6?GPa.     

A study of salt-assisted solution combustion synthesis of magnesium aluminate and sintering behaviour

We synthesized nano MgAl₂O₄ with a ~80?nm particle size by salt-assisted solution combustion synthesis using LiCl as salt. Nano MgAl₂O₄ produced by conventional solution combustion synthesis commonly exhibits poor uniformity in terms of size with partially sintered particles and a high degree of agglomeration, leading to poor sinterability. It was found in this study that the use of the salt-assisted solution combustion method has successfully lowers the degree of agglomeration with uniform particle size and morphology, demonstrating superior sinterability. Conventional sintering in air atmosphere at 1550?℃ of MgAl₂O₄ obtained by salt-assisted solution combustion followed by calcination at 700–1100?℃ yielded up to 94% of relative density, while the conventional solution combustion method could not match this. In addition, using the spark plasma sintering technique, fully dense (over 99%) submicrometer (~340?nm) transparent polycrystalline MgAl₂O₄ with elevated mechanical properties (~16.6?GPa) was achieved. The salt-assisted solution combustion method could be effectively used for fully dense material, but can be further developed for various nano oxide materials where high dispersion with a low degree of agglomeration is preferred.     

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.     

Direct bandgap materials based on the thin films of SexTe100 ? x nanoparticles

In this study, we fabricated thin films of Se_xTe_{100 − x} (x = 0, 3, 6, 9, 12, and 24) nanoparticles using thermal evaporation technique. The results obtained by X-ray diffraction show that the as-synthesized nanoparticles have polycrystalline structure, but their crystallinity decreases by increasing the concentration of Se. They were found to have direct bandgap (E_g), whose value increases by increasing the Se content. These results are completely different than those obtained in the films of Se_xTe_{100 − x} microstructure counterparts. Photoluminescence and Raman spectra for these films were also demonstrated. The remarkable results obtained in these nanoparticles specially their controlled direct bandgap might be useful for the development of optical disks and other semiconductor devices.     

Sintering behavior of magnesium aluminate spinel MgAl2O4 synthesized by different methods

This paper is focusing basically on the ceramic technology, of which several methods for the synthesis of MgAl₂O₄ have been investigated. The synthesis conditions regarding the powders cleanliness, microstructure, and sintering parameters of MgAl₂O₄ were studied. MgAl₂O₄ powder was synthesized via conventional solid-state route using different milling process: vertical attrition milling, WAB as a high-energy horizontal attrition milling, and Pulverisette as a planetary ball miller, and via solution combustion route using Urea, Glycine, and a mixture of Urea/Glycine. Urea and Glycine was used as fuel. The white powders were obtained for all solid-state routes and for Urea-combustion technique. The black and gray powders were obtained in the case of combustion technique, respectively, using a fuel of Glycine and Glycine/Urea mixture. The obtained powders and pellets were characterized by XRD, SEM, and Dilatometry. The results show that, among all the solid-state route processes, wet attrition milling gives the better and clean spinel phase. The WAB milling and Pulverisette miller introduce a contamination by some yttria-stabilized zirconia balls in the corresponding powder. Furthermore, the flash combustion technique permit to have nanoparticles with a dense spinel phase of MgAl₂O₄ and with lower sintering temperature in less time and with no calcination step.     

Development of magnetic recyclable spinel photocatalysts with enhanced sunlight-driven degradation of industrial dyes

Nanocrystalline nickel and copper-substituted zinc aluminate spinel powders (Ni_xZn_1−xAl₂O₄ and Cu_xZn_1−xAl₂O₄) with different additional ion concentrations (0 ≤ x ≤ 1) were successfully synthesized by the sol-gel auto combustion method using diethanolamine (DEA) as a fuel. The structures, chemical bonds, morphologies, composition, surface area, and optical properties including the magnetic behavior of the obtained samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer-Emmett-Teller (BET) method, UV-visible diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM). All characterization results confirmed that a single-phase spinel structure was obtained for all calcined aluminate powders with various crystallite sizes and lattice constants. The band gap energy (E_g) of all modified aluminates is in the range of 2.99-3.15 eV, which was found to be much lower than that of the pure sample (5.60 eV). These results indicate that the Ni²⁺ and Cu²⁺-substituted ZnAl₂O₄ samples could be effectively photoexcited by both the ultraviolet and visible light. Evaluation of the samples to determine the photocatalytic activity was carried out through investigation of the way the four main pollutant types decompose when irradiated by sunlight. These pollutants were rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). For all optimum samples of organic dyes, the efficiency of photocatalytic degradation achieved 96% by the end of 150 min. Furthermore, each of the modified photocatalysts could be reused and showed a high degree of stability. According to magnetic measurements, the S-shaped curve of ferrimagnetism can arise in those samples with the optimum concentration, although pure ZnAl₂O₄ exhibits diamagnetic properties. In comparison to pure ZnAl₂O₄, the modified samples exhibit high enhancement in the remanent magnetization (M_r), which indicates that it is easy to recover those magnetic photocatalyst through the use of an external magnetic field application. These findings therefore serve as a strong indication that ZnAl₂O₄ powders substituted by both Ni²⁺ and Cu²⁺ may offer the capability to serve in environmentally beneficial harvesting of solar energy.     

Enhanced visible-light photocatalytic properties of g-C3N4 by coupling with ZnAl2O4

A series of g-C₃N₄/ZnAl₂O₄ composites were prepared using a conventional calcination method and the heterostructures were systematically characterized. It was found that the combination of g-C₃N₄ with ZnAl₂O₄ significantly improve their photocatalytic activities. The optimum photocatalyst of composite is at 5% (wt%) of ZnAl₂O₄, whose degradation efficiency for methyl orange (MO) was 96% within 120 min under visible-light irradiation. The formation of heterojunction between g-C₃N₄ and ZnAl₂O₄ can facilitate efficient charge separation of photogenerated electron-hole pairs, which were confirmed by electrochemical impedance spectroscopy (EIS). As a result, the photocatalytic properties of composites were enhanced.     

Characterization of ZnAl2O4 Obtained by Different Methods and Used as Catalytic Support of Pt

In this work the synthesis of a ZnAl₂O₄ spinel to be used as a support of metals and its characterization were studied. The methods used for the ZnAl₂O₄ preparation were: ceramic method (CM), mechanochemical synthesis in humid medium (HMS) and coprecipitation (COPR). ZnAl₂O₄ CM and ZnAl₂O₄ HMS showed negligible acidity, but the ZnAl₂O₄ COPR displayed a low acidity. The spinels obtained by COPR and HMS showed higher specific surface area and pore volumes than that prepared by the ceramic method. In addition the catalytic performance of Pt supported on the prepared spinel was evaluated in the n-butane dehydrogenation reaction. The Pt catalysts prepared with ZnAl₂O₄ COPR presented better activity and selectivity to olefins than the ones prepared with ZnAl₂O₄ HMS and ZnAl₂O₄ CM, which could be correlated with a higher metallic dispersion and lower particle sizes, detected by TEM. The acidity of ZnAl₂O₄ COPR, observed by isopropanol dehydration and TPD of pyridine, and the sequence of specific surface areas of the different spinels (ZnAl₂O₄ COPR > ZnAl₂O₄ HMS > ZnAl₂O₄ CM) are other important factors to define the final dispersion of the catalysts.     

Electrical and optical properties of Al-doped ZnO and ZnAl2O4 films prepared by atomic layer deposition

ZnO/Al₂O₃ multilayers were prepared by alternating atomic layer deposition (ALD) at 150°C using diethylzinc, trimethylaluminum, and water. The growth process, crystallinity, and electrical and optical properties of the multilayers were studied with a variety of the cycle ratios of ZnO and Al₂O₃ sublayers. Transparent conductive Al-doped ZnO films were prepared with the minimum resistivity of 2.4 × 10⁻³ Ω·cm at a low Al doping concentration of 2.26%. Photoluminescence spectroscopy in conjunction with X-ray diffraction analysis revealed that the thickness of ZnO sublayers plays an important role on the priority for selective crystallization of ZnAl₂O₄ and ZnO phases during high-temperature annealing ZnO/Al₂O₃ multilayers. It was found that pure ZnAl₂O₄ film was synthesized by annealing the specific composite film containing alternative monocycle of ZnO and Al₂O₃ sublayers, which could only be deposited precisely by utilizing ALD technology.     

Oxygen uncoupling behaviour for ilmenite ore oxygen carrier generated from a calcination treatment mixed with natural manganese ore

Chemical looping with O₂ uncoupling aims at using an oxygen carrier (OC) with O₂ uncoupling behaviour to promote fuel conversion. Natural ilmenite ores have been considered highly promising OCs for chemical looping technology; however, they do not possess any O₂ uncoupling behaviour. Mn-modified ilmenite ores as OCs are capable of O₂ uncoupling, while most of them are synthesized via complicated procedures by using costly chemicals. In this study, a strategy of calcination treatment on ilmenite ores mixed with manganese ores has been established to introduce Mn into the ilmenite OCs, endowing them with O₂ uncoupling behaviour in a simple and low-cost manner. The O₂ uncoupling behaviour from Mn-modified ilmenite ores is mainly due to the newly formed (Fe_1−xMn_x)₂O₃/(Fe_1−xMn_x)₃O₄ crystal phases generated during the calcination treatment, which also alleviate the thermodynamic limit of the Mn₂O₃-Mn₃O₄ redox pair. As a result, the Mn-modified ilmenite ore OCs can release O₂ at high temperatures when decreasing the oxygen partial pressure. But more importantly, the reduced OCs can be restored in the air isothermally. This established simple calcination treatment method can be used as a low-cost strategy for producing ilmenite-based OCs with O₂ uncoupling behaviour. The O₂ uncoupling behaviour is expected to be beneficial to chemical looping combustion of fuels, promote fuel conversion, minimize OC loading, and reduce energy consumption.     

Synthesis of (Fe,Cr)2O3 solid solution pigment powders for ink application

Iron chromite pigment was synthesized via solution combustion using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, and glycine, urea, citric acid, and ethylene glycol as fuels. The effect of postheating temperature on the structure, microstructure, and chromatic properties of the synthesized powders was also studied. X-ray diffraction patterns showed that the as-synthesized powders were amorphous to crystalline FeCr₂O₄ phases, depending on fuel type. Moreover, regardless of the fuel type, postheating led to the d-space shift and oxidation and formation of (Fe,Cr)₂O₃ solid solution. Phase transformation of FeCr₂O₄ to (Fe,Cr)₂O₃ solid solution was observed at 500/750°C depending on the dominant phase present in the as-synthesized particles. Fourier transform infrared analysis illustrated a shift in the band position of octahedral M–O and tetrahedral M–O bonds due to the movement of Fe cations and the lattice shrinkage by increasing the postheating temperature. Moreover, scanning electron micrographs showed that Fe_0.7Cr_1.3O₃ semispherical fine particles consisted mainly of porous and spongy FeCr₂O₄ particles due to the oxidation and phase transformation during postheating. According to chromatic measurements, the ink prepared by using the powders synthesized in the presence of glycine and post-heated at 500°C showed reddish-brown color which could be considered a promising candidate for tile decoration application. Furthermore, rheology studies revealed that the prepared ink showed non-Newtonian shear thinning behavior.     

Fuel effects on Li2CuP2O7 synthesized by solution combustion method for lithium-ion batteries

Lithium copper pyrophosphate has been synthesized by the solution combustion method for the first time. Urea and hexamethylenetetramine were used as fuel. The samples were successfully prepared in low reaction temperature and short reaction time. The products were structurally characterized by FT-IR and p-XRD. Thermal behavior of samples was also investigated through TG/DT analyses. Magnetic measurements showed that the urea- and hexamethylenetetramine-assisted Li₂CuP₂O₇ were paramagnetic at room temperature. Surface analyses indicated that the fuel types changed the surface properties of samples because of exothermic redox reaction during combustion, and electrochemical performances showed clear differences. The charge capacity of urea- and hexamethylenetetramine-assisted synthesized Li₂CuP₂O₇ was calculated as 180?mAhg^?1 and 146?mAhg^?1. Synthesis method enlarged the charge capacity and prepared lithium copper pyrophosphate to have a potential for use in lithium-ion batteries.     

Synthesis of high-surface-area micro/mesoporous ZnAl2O4 catalyst support and application in selective hydrogenation of o-chloronitrobenzene

High-surface-area ZnAl₂O₄ with micro/mesoporous frameworks was synthesized via a facile one-pot solvothermal approach without using any surfactants or post-treatment. The results revealed that the textural properties of micro/mesoporous ZnAl₂O₄ were tuned by changing alcohol/water mixture solvents used in solvothermal synthesis and Ag nanoparticles were dispersed uniformly on the surface of ZnAl₂O₄ supports. Especially, the supported Ag catalyst on the microporous ZnAl₂O₄ synthesized in methanol/water solvent exhibited good catalytic performance for liquid phase selective hydrogenation of o-chloronitrobenzene to o-chloroaniline, owing to the high dispersion of Ag nanoparticles and the strong metal-support interaction.     

Glycine-assisted solution combustion synthesis of NiCo2O4 electromagnetic wave absorber with wide absorption bandwidth

Design of high-performance electromagnetic (EM) wave absorbing materials has been regarded as an effective solution to excessive EM wave interference problem. As a promising candidate, NiCo₂O₄ absorbers have attracted enormous research attentions. However, currently reported morphology-manipulation synthetic methods of NiCo₂O₄ absorbers are time-consuming and require high energy consumption, which inhibit their practical applications. Herein, a more facile and cost-effective solution combustion synthesis was utilized to fabricate NiCo₂O₄ materials. The absorber prepared by using glycine as fuel displayed the best EM wave absorption performance. Impressively, ultra wide absorption bandwidth of 7.44 GHz from 10.56 GHz to 18 GHz could be achieved with relatively thin thickness of 2.1 mm NiCo₂O₄ sample fabricated in this work displayed the widest effective absorption bandwidth (EAB) among reported NiCo₂O₄-based EM wave absorbing materials so far. In view of its simple and low-cost synthetic process and excellent EM wave dissipation capacity, NiCo₂O₄ samples in this work showed great feasibility as practical absorber. In addition, our findings may also provide new sight for facile preparation of other high-performance EM wave absorbers by solution combustion synthesis instead of complex morphology-manipulation routes.     

Fabrication and photocatalytic properties of novel ZnO/ZnAl2O4 nanocomposite with ZnAl2O4 dispersed inside ZnO network

Novel ZnO/ZnAl₂O₄ nanocomposites with ZnAl₂O₄ nanoparticles homogeneously dispersed inside a network of ZnO are fabricated by thermal treatment of a single‐source precursor of ZnAl‐layered double hydroxides (ZnAl‐LDHs) at 800°C. The effects of the Zn/Al molar ratio of the LDH precursors on the structure, composition, morphology, textural as well as UV‐absorbing properties and photocatalytic activities of the nanocomposites are investigated in detail. The results show that the ZnO/ZnAl₂O₄ nanocomposites derived from the ZnAl‐LDHs precursors have superior photocatalytic performances to either single phase ZnO or similar ZnO/ZnAl₂O₄ samples fabricated by chemical coprecipitation or physical mixing method. The heterojunction nanostructure and the strong coupling between the ZnO and ZnAl₂O₄ phase derived from ZnAl‐LDHs precursors are proposed to contribute the efficient spatial separation between the photo‐generated electrons and holes, which can concomitantly improve the photocatalytic activities. © 2011 American Institute of Chemical Engineers AIChE J, 2012