Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe₃O₄) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe₃O₄ powders as characterized by X-ray diffractometry, infrared spectroscopy, N₂ adsorption–desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe₃O₄ powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe₂O₃ and FeO together with Fe₃O₄ phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m²/g was transformed to disintegrated structure (76.5 m²/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.     

Effects of annealing on the structural and magnetic properties of flame spray pyrolyzed MnFe2O4 nanoparticles

In this study, manganese ferrite (MnFe₂O₄) nanoparticles were produced through flame spray pyrolysis (FSP). To investigate the effects of heat treatment, the nanoparticles were annealed between 400 and 650°C for 4 h in air in a comparative manner. The structural, chemical, morphological, and magnetic properties of the nanoparticles were evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), dynamic light scattering (DLS), and vibrating sample magnetometry (VSM), respectively. The XRD results showed that the nanoparticles synthesized by the FSP method exhibited the MnFe₂O₄ spinel ferrite structure. The annealing process led to the decomposition of MnFe₂O₄ into various phases. According to the morphological analysis, the as-synthesized particles were hemispherical–cubic in shape and had an average particle size of less than 100 nm. In addition, the chemical bond structures of the nanoparticles were confirmed in detail by XPS elemental analysis. The highest saturation magnetization was recorded as 33.50 emu/g for the as-produced nanoparticles. The saturation magnetization of the nanoparticles decreased with increasing annealing temperature, while coercivity increased.     

盐助溶液燃烧法制备MnFe2O4催化过一硫酸盐降解双酚A

采用盐助溶液燃烧法制备磁性铁酸锰（MnFe₂O₄）,催化过一硫酸氢盐（PMS）氧化降解水溶液中的双酚A。通过XRD、BET等手段对制备的铁酸锰催化剂进行了表征。探究了MnFe₂O₄投加量、PMS投加量、溶液初始pH、淬灭剂、共存离子等因素对双酚A降解效果的影响,评估了MnFe₂O₄催化剂的循环利用性能。结果表明,MnFe₂O₄和PMS的最合理投加量分别为 0.3 g/L、0.3 mmol/L,初始pH为11.0时双酚A降解效果最好,60 min内的降解率可达99.3%。淬灭实验表明,催化体系中同时存在多种活性物质,¹O₂是主要活性物种。溶液中Cl^-、HCO₃^-和HPO₄^2-等共存离子的存在影响双酚A的降解。双酚A在60 min内的TOC去除率为34.9%,苯环断裂和开环反应是其主要降解路径。MnFe₂O₄催化剂循环使用三次后,双酚A的降解率仍保持在90.0%左右。     

Degradation of bisphenol A by peroxymonosulfate activated by MnFe2O4 prepared by salt-assisted solution combustion synthesis

Magnetic manganese ferrite (MnFe₂O₄) prepared by the salt-assisted solution combustion synthesis was used to activate peroxymonosulfate(PMS) to oxidize bisphenol A in aqueous solution. The prepared MnFe₂O₄ catalyst was characterized by XRD and BET. The effects of MnFe₂O₄ dosage, PMS dosage, initial pH of the solution, quencher, and co-existing ions on the degradation of bisphenol A were investigated. The reusability of the MnFe₂O₄ catalyst was evaluated through cycling experiments. The results showed that the best dosages of MnFe₂O₄ and PMS were 0.3 g/L and 0.3 mmol/L, respectively. When the initial pH was 11.0, the degradation rate of bisphenol A was 99.3% in 60 min. When putting some quenchers into the MnFe₂O₄/PMS catalytic system, all of them showed depression effects on degradation of bisphenol A, and the ¹O₂ was the main active species. The co-existing ions such as Cl^-, HCO₃^-, and HPO₄^2- in solution affected the degradation of bisphenol A. The TOC removal rate of bisphenol A within 60 min was 34.9%, the rupture and opening of benzene ring are the main reaction pathways. After the MnFe₂O₄ catalyst was recycled three times, the degradation rate of bisphenol A remained at about 90.0%.     

Combustion synthesis of InSe,In2Se3, and GaSe

InSe, In₂Se₃, and GaSe are important III‐VI semiconductors and are attractive for electronic, optical, and optoelectronic applications. This paper reports a fast and cheap way called combustion synthesis to prepare InSe, In₂Se₃, and GaSe. Bulk samples with relative densities up to 98% are directly produced in a few seconds. The samples show a high phase purity, correct stoichiometry, and lamellar crystals larger than 100 μm. By optical absorption, the bandgaps of InSe, In₂Se₃, and GaSe are determined to be 1.08, 1.24 and 1.75 eV, respectively.     

Magnetic properties and self-heat behaviors of core@shell structured MnFe2O4@Fe3O4 magnetic nanoparticles

In this work, a facile solvothermal synthesis of MnFe₂O₄ nanoparticles is followed by an easy and reproducible process to envelop the synthesized MnFe₂O₄ nanoparticles with iron oxide nanoparticles using ethanol and ethylene glycol as solvents. All prepared MnFe₂O₄ nanoparticles show a homogenous distribution of spherical particles with an average particle size between 12 and 16 nm. The encapsulation process of MnFe₂O₄ nanoparticles does not affect their homogenous distribution with a very thin layer of Fe₃O₄ on the shell structure. The magnetic properties showed a superparamagnetic character with enhanced magnetic properties of MnFe₂O₄@Fe₃O₄ compared to pure MnFe₂O₄, which has been verified by magnetization and electron spin resonance. The heating efficiency of the prepared samples was evaluated in terms of the specific loss power using the calorimetric method. The synthesized MnFe₂O₄ nanoparticles show a significantly high value of about 72 W/g, which got doubled in the core@shell structure and reached 140 W/g at 189 kHz and 10kA/m of the magnetic field.     

Solution combustion synthesis of FeCr2O4:Zn,Al pigment powders

FeCr₂O₄:Zn,Al pigment powders were prepared via a solution combustion synthesis method. Effects of Zn and Al dopants and less/extra Fe content on the structure, molecular bonds, and optical properties of powders were studied. Results showed that addition of dopants as well as extra/less content of Fe led to weaker combustion and consequently lower X-ray diffraction peak intensities, lattice parameters, and differential thermal analysis peak intensities. Moreover, Fourier transform infrared analysis illustrated that the band position of Cr–O and Fe–O bonds were shifted to higher frequencies with moving away from stoichiometry. In addition, scanning electron micrographs showed that in all samples, porous spongy microstructures were formed with highly flake-like agglomerated particles. Furthermore, there was a significant difference between the powder samples and the tiles colored with in glaze powders due to the partial dissolution of pigments in contact with the molten glaze of tiles. In comparison to the tile colored with the stoichiometric FeCr₂O₄ pigments without dopants, the color difference (ΔE) in the tiles colored by the iron chromite pigments doped with Zn and Al dopants and less/extra Fe content reached the high values as large as ΔE = 36.19. The solar reflectance values (R_s) in near-infrared region were above 50% in all samples. Near 80% R_s in the tile colored by the iron chromite pigment doped with 3 mol% Zn and the yellowish brown appearance (L* = 43.44, a* = 6.77, b* = 18.38, c* = 19.59, h = 69.79) showed that the sample was a good candidate for cool building materials such as roof tiles.     

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.     

Solution combustion synthesis of MnFeCoNiCu and (MnFeCoNiCu)3O4 high entropy materials and sintering thereof

Single-phase, fine-grained high entropy MnFeCoNiCu alloy and (MnFeCoNiCu)₃O₄ oxide powders have been pioneered by an in-situ solution combustion synthesis without post-treatment, utilizing alanine and glycine as organic reducers and ammonium nitrate as an auxiliary oxidizing agent. In order to regulate the porosity, homogeneity, phase composition and morphology of the obtained powders, multivariate studies on the influence of the following parameters were performed: type and quantity of reducers, pH of solution, ignition temperature, presence of oxidizing agent, etc.. It has been shown that the amount of the reducer holds the key for governing combustion temperature and speculation of lower and upper combustion limits in the systems under study. In turn, according to the temperature-time profiles of combustion, product microstructure, as well as phase composition of the product, the combustion area turned out to be divided into two sub-domains: volume combustion (with vigorous flaming) and self-propagation combustion. After thorough characterization, high entropy MnFeCoNiCu alloy and high entropy (MnFeCoNiCu)₃O₄ oxide powders were subjected to consolidation by spark plasma sintering and mechanical properties were evaluated. The influence of sintering temperature on the phase transformation of the products was revealed.     

Solution combustion synthesis of crystalline V2O3 and amorphous V2O3/C as anode for lithium-ion battery

In this paper, crystalline V₂O₃ and amorphous V₂O₃/C products are synthesized via one-pot solution combustion synthesis (SCS) method (completed within 2 minutes). The characteristics of combustion products could be tuned by changing the amounts of glucose. The as-synthesized crystalline V₂O₃ nanopowder consists of nanoparticles with average size of ~100 nm. Amorphous V₂O₃/C composite exhibits large porous microsheet structure in which oxygen vacancy-enabled amorphous V₂O₃ particles are embedded into N-doped carbon microsheets. The existence of oxygen vacancies can promote energetics for the transport of electrons and ions and maintain the integrity of sample surface morphology. Moreover, N-doping can enhance electrical conductivity and promote the diffusion of electrons and lithium ions. Amorphous V₂O₃/C composite possesses high reversible capacity and superior cycling stability (833 mAh g⁻¹ at 1 A g⁻¹ after 250 cycles, 867 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles), indicating its potential as excellent anode material for lithium-ion battery. The proposed one-step, time- and energy-efficient SCS method has the potential to prepare other oxygen vacancy-enabled transition metal oxides for energy storage.     

Solution combustion synthesis of new metal borophosphates (Fe1-xCrx)2B(PO4)3: Structural,thermal, surface,and magnetic properties

The new borophosphates were successfully synthesized by solution combustion synthesis assisted with glycine. The obtained materials were systematically characterized by Fourier-transform infrared spectroscopy, X-ray powder diffraction, UV–visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, Brauner-Emmett-Teller surface area, and magnetometry. The Rietveld refinements indicated that Fe₂B(PO₄)₃ is a hexagonal, space group P63/m with a = b = 8.029 and c = 7.408. As Cr substitutes the Fe atoms, there is a significant decrease in the lattice parameters. When all Fe atoms are replaced by Cr, Cr₂B(PO₄)₃ is formed and the structure turns out to be a trigonal, space group P3 with a = b = 7.950 and c = 7.360. The materials are thermally stable and demonstrate paramagnetic behavior at room temperature. The magnetization increases as the iron content increases because of the high magnetic moment of the iron ion. Temperature-dependent magnetic measurements reveal that Fe₂B(PO₄)₃ has a Néel transition at 30 K and the Néel temperature decreases with Cr substitution.     

Solution combustion synthesis of FeCr2O4 powders for pigment applications: Effect of fuel type

Solution combustion synthesis of iron chromite was reported using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, as well as glycine, urea, citric acid, and ethylene glycol as fuels. The influence of fuel type on the structure, molecular, microstructure as well as chromatic properties of samples was investigated. The X-ray diffraction (XRD) patterns showed that unlike themodynamical prediction, glycine fuel led to strongest combustion and consequent highest XRD peak intensities and lower lattice parameters. Moreover, the change of fuel type and mixing of fuels affected XRD data. Fourier transform infrared analysis showed that the band position of Cr–O and Fe–O bonds were shifted to higher frequencies by using of fuels with weaker combustion reactions. In addition, scanning electron micrographs showed that different morphologies of FeCr₂O₄ particles were obtained depending on the fuel type and ratios. Energy-dispersive X-ray spectroscopy analysis of the samples showed that oxygen concentration of samples was less than that of stoichiometric ratio of FeCr₂O₄ due to local reducing atmosphere. Furthermore, chromatic properties of the powders showed that the pigment synthesized with glycine fuel has a better and lighter grayish brown color than the other ones and can be used as a suitable industrial candidate to create a brown color in the ceramic glaze.     

Molten-salt-assisted combustion synthesis of B4C powders: Synthesis mechanism and dielectric and electromagnetic wave absorbing properties

A novel electromagnetic wave (EMW) absorber was prepared by combustion synthesis. Boron carbide (B₄C) powders with different grain sizes using a molten-salt-assisted combustion technique with B₂O₃, CB (carbon black), and Mg powders as starting materials, and NaCl as an additives. The effects of the NaCl content on the phase compositions and the microstructure of the products were characterized. A combustion front quenching method was used to elucidate the mechanism for the B₄C powders synthesis. The dielectric, and EMW absorbing properties in the X-band were also investigated. The results showed that the addition of NaCl significantly reduced the grain size of B₄C powders. Nanoscale B₄C powders with cubic polyhedral structures were synthesized using 6 wt% NaCl (labeled as N-6). According to the quenching test results can be obtained that the first step in the combustion synthesis was melting B₂O₃ into a glassy substance. At the same time, Mg melted and formed a liquid pool into which the NaCl dissolved, followed reduction of the B₂O₃ to B. The formed B eventually reacted with CB to form B₄C, and the B₄C particles precipitated from the matrices. The N-6 sample exhibits optimal dielectric and EMW absorbing properties, because of a high specific surface area that enhances interfacial and space charge polarization.     

燃烧法合成CaAl2O4:Eu2+,Nd3+长余辉材料

利用硝酸盐和尿素的氧化还原反应,通过燃烧合成法在较低的温度下合成了蓝紫色长余辉发光材料CaAl2O4：Eu^2 ,Nd^3 研究了炉温和可燃物等对发光材料性能的影响。结果表明：反应物置于温度为500℃的高温炉中发生点火燃烧得到的产物性能最好,其发射光谱的最强峰波长在450nm左右,与高温固相反应法比,激发光谱和发射光谱没有明显变化,燃烧法生成物的产物分散性好,制备过程具有合成温度低、反应时间短等优点。     

Enhanced sunlight driven photocatalytic activity and electrochemical sensing properties of Ce-doped MnFe2O4 nano magnetic ferrites

This research deals with the facile combustion synthesis of manganese ferrite (MFO) nanoparticle with different cerium concentration and their potential application as an efficient photocatalyst and chemical sensor. The concentration of introduced cerium affects the size, structure, compositional, morphological, optical, photoluminescence and magnetic properties of the ferrite nanoparticle. The X-ray diffraction pattern affirmed the arrangement of cubic spinel structure with the formation of secondary phase CeO₂ as the cerium concentration exceed 3 mol%. SEM micrographs revealed irregular morphology with more number of pores and voids. HRTEM along with SAED pattern revealed the crystalline cubic nature. The optical band gap deduced from UV–Vis-DRS spectra was observed to be in the range 2.3–2.8 eV. PL studies indicated a significant minimization in combination of electrons & holes in MnFe₂O₄ on addition of Ce dopant. VSM investigation demonstrated the soft magnetic nature of the prepared sample with moderate magnetization value. An excellent photocatalytic performance of Cerium doped MFO (3 mol%) towards MB and AR dye degradation was found to be 1.5 and 1.67 times more compared to host matrix under Sunlight irradiation that correlated to reduced band gap, Ce dopant and efficient separation of charge carriers. Cerium doped MFO (3 mol%) have high specific capacitance value of 471.7 and 1546.8 Fg^-1 for NaNO₃ and HCl electrolytes respectively, indicating the pseudo capacitance nature due to which it can be used as a supercapacitor. The synthesized nanoparticles can sense d-Glucose and Paracetamol even at a lower concentration varying from 1 to 10 mM. The synthesized Ce-doped MnFe₂O₄ nanomaterials have great potential to be used in the future production of promising active photocatalysts and sensitive chemical sensors for the identification and degradation of toxic industrial dyes for improved safety in the fields of environment and health care.     

Comparative study of Al2O3, HfO2, and HfAlOx for improved self‐compliance bipolar resistive switching

The comparison of resistive switching (RS) storage in the same device architecture is explored for atomic layer deposition (ALD) Al₂O₃, HfO₂ and HfAlO_x‐based resistive random access memory (ReRAM) devices. Among them, the deeper high‐ and low‐ resistance states, more uniform V_SET‐V_RES, persistent R_OFF/R_ON (>10²) ratio and endurance up to 10⁵ cycles during both DC and AC measurements were observed for HfAlO_x‐based device. This improved behavior is attributed to the intermixing of amorphous Al₂O₃/HfO₂ oxide layers to form amorphous thermally stable HfAlO_x thin films by consecutive‐cycled ALD. In addition, the higher oxygen content at Ti/HfAlO_x thin films interface was found within the energy dispersive spectroscopy analysis (EDS). We believe this higher oxygen content at the interface could lead to its sufficient storage and supply, leading to the stable filament reduction‐oxidation operation. Further given insight to the RS mechanism, SET/RESET power necessities and scavenging effect shed a light to the enhancement of HfAlO_x‐based ReRAM device as well.     

Combustion synthesis and characterization of Sr3Al2O6

In this paper, the synthesis by solution combustion (SCS) of tri-strontium aluminates (Sr₃Al₂O₆), using different fuel amounts, has been studied. The main objective was to understand the effect of the amount of fuel on phase formation, yield and purity of the product using urea as fuel. The combustion temperatures of each reaction were followed by digital pyrometry. Phase compositions were determined by X-ray diffraction (XRD). The microstructural characteristics during the SCS process were studied by field emission scanning electron microscopy (FESEM). The specific surface area was calculated with the BET model from adsorption data. The results showed that the Sr₃Al₂O₆ was the main phase obtained in all syntheses. This aluminate with high content of Sr is considered attractive for use in applications requiring radiopacity as biomaterials for dental and bone repair. The maximum measured temperature during synthesis, with excess fuel, was approximately 987°C. It was higher than that obtained in the case of using stoichiometric amounts of fuel which was 762°C. The product obtained in this second case had a submicrometer structure, with highly crystalline particles and a specific surface of 0.21 m²/g. It was higher than that obtained with excess of fuel (0.07 m²/g).     

Facile solid-state synthesis of tetragonal CuFe2O4 spinels with improved infrared radiation performance

Spinel materials are gradually becoming promising materials for high infrared emissivity owing to their unique crystal structure. However, the facile low-temperature solid-state synthesis of infrared radiation materials with superior emissivity remains a tremendous challenge. Herein, a general and simple approach for scalable synthesis of CuFe₂O₄ samples with spinel structure at low temperatures is smartly developed. The optimal experimental conditions for the infrared emissivity of CuFe₂O₄ are obtained by the detailed investigation into experimental parameters including calcination temperatures, heating rates, and the mass of polyvinyl pyrrolidone. Under the optimal experimental conditions, the infrared emission values of CuFe₂O₄ in the wavelength range of 3–5 μm can be as high as 0.986. More significantly, the work here will provide significant guidance for the efficient preparation of spinel materials with excellent infrared emissivity, especially at low temperatures.     

燃烧法快速合成铝酸锶基质长余辉发光材料

以燃烧法快速合成了Eu^2 ,Dy^3 掺杂的铝酸锶发光粉,发光粉经自然光激发可观察到明亮的黄绿光,余辉可达12h以上。用X射线粉末衍射、扫描电镜、透射电镜等分析了合成物的物相组成、显微结构与粒度等。结果表明;合成的发光粉主晶相是SrAl2O4,扫描电镜下呈卷曲片状,透射电镜下的一次粒子呈不规则粒状,粒子直径大多分布在60～100nm以内。通过对荧光分光光度计所测定的合成样品的激发光谱、发射光谱和衰减曲线等光谱分析发现;合成物的发光是Eu^2 的4f^65d^1→4f^7的电子跃迁,而发光体的长余辉特性是由于发光体中Dy^3 的空位陷阱作用。