A novel approach for solution combustion synthesis of tungsten oxide nanoparticles for photocatalytic and electrochromic applications

Tungsten oxide (WO₃) and tungsten oxide hydrate (WO₃.H₂O) nanoparticles were synthesized via a novel solution combustion synthesis (SCS) method. Various organic fuels (i.e. oxalic acid, glycine, and citric acid) and heat sources were used to obtain different morphologies of nanoparticles. Combustion thermodynamic relations were explained based on propellant chemistry. Adiabatic temperature (T_ad) and specific impulse (I_sp) were also obtained. The synthesized nanoparticles were investigated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and UV–Visible spectrophotometer. XRD patterns indicated that the structures were transformed from orthorhombic and amorphous structures to monoclinic and tetragonal ones, respectively, upon combustion on the hot plate. Fourier-transform infrared (FTIR) spectra provided evidence of WO₆ octahedral. SEM images showed different microstructures from sponge or rock-like to fine spherical particles with up to 100 nm size. The obtained band gap of all samples was higher than 2.6 eV which is the band gap of bulk tungsten oxide. The synthesized WO₃ nanoparticles showed over 50% photocatalytic efficiency for the degradation of azo dye. The results exhibited that the nanoparticles can be used to make the electroactive layer for electrochromic applications.     

Solution combustion synthesis of ZnO powders using CTAB as fuel

Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using cetyltrimethylammonium bromide (CTAB) as fuel. The effects of fuel to oxidant ratios (? = 0.5, 0.75, 1 and 1.5) on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy, and diffuse reflectance spectrometry techniques. The slow decomposition rate of CTAB guaranteed the direct formation of single phase and well-crystalline ZnO powders regardless of fuel content. The specific surface area of the as-combusted ZnO powders with platelet particles increased from 21 ± 1 to 35 ± 2?m²/g with fuel content. The band gap energy also increased from 2.99 to 3.13?eV due to the decrease of particle size. The as-combusted ZnO powders at ? = 1.5 exhibited the highest photodegradation (~69%) of methylene blue under ultraviolet light irradiation, due to their good crystallinity and smaller particle size.     

Synthesis of novel ZnO/carbon xerogel composites: Effect of carbon content and calcination temperature on their structural and photocatalytic properties

This paper reports the development of new ZnO/carbon xerogel composites (XZn w) for photocatalytic applications. The use of black wattle tannin as a precursor to the carbon xerogel aimed at reducing costs and environmental impacts. The composites were characterized by diffuse reflectance spectroscopy (DRS), BET surface area, scanning electron microscopy (FEG-SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), and X-ray diffraction (XRD). The photocatalytic performance of the materials was evaluated in the decomposition process of methylene blue, a known toxic pollutant. The impacts of the catalyst dosage and calcination temperature on the photocatalytic process were also examined systematically. The X-ray profiles of the XZn w evidenced the existence of the hexagonal structure of the zinc oxide (wurtzite) in the composites. The XPS and XRD analyses confirmed the incorporation of carbon in the zinc oxide crystalline structure. The higher carbon content resulted in a larger surface area. All composites presented the ability to absorb radiation in less energetic wavelengths, contrary to pure zinc oxide that only absorbs radiation of wavelengths below 420?nm. The optimal dosage and calcination temperature were found to be 0.2?g?L^?1 and 300?°C. All the developed composites displayed significant photocatalytic activities in the decomposition of methylene blue under both visible and solar light. The composites had superior photocatalytic efficiency under visible light when compared to pure zinc oxide. The XZn 0.5 presented the best degradation efficiency under visible radiation. All materials presented similar photocatalytic responses under solar light, evidencing the synergy between the carbon xerogel and the zinc oxide. The photocatalytic mechanism was evaluated by trapping experiments to be mainly controlled by the electron vacancies that are generated during the photoexcitation of the composites.     

An investigation of fuel precursors and calcination temperature to obtain mayenite (Ca12Al14O33) powders by solution combustion synthesis

The influence of the fuel (glycine, urea, citric acid and sucrose) and calcination temperature used to obtain calcium aluminate in the mayenite phase assisted by solution combustion synthesis (SCS) is the central point of this work. Thermal gravimetric analysis helps to establish the calcination temperatures used (1100, 1200 and 1300 °C). Using the X-ray diffraction technique (XRD) and complementary analyses, such as Raman spectroscopy, the specific surface area and laser granulometry, it was possible to elucidate the behavior and relationship of the fuel and heat treatment on the phase formation, crystallite size and powder crystallinity. Glycine showed better performance than other fuels, with the lowest calcination temperature, obtaining pure mayenite with nanometric crystallite size in all calcination ranges. Thus, it was observed that the type of fuel has an influence on obtaining pure mayenite, as well as the calcination temperature, and glycine reveals the best performance.     

Controlled synthesis of (CuO-Cu2O)Cu/ZnO multi oxide nanocomposites by facile combustion route: A potential photocatalytic,antimicrobial and anticancer activity

Photocatalytic activity of (CuO-Cu₂O)Cu/ZnO hetero-junction nanocomposites along with their luminescent, biological applications in the progress of anticancer and antibacterial agents is investigated. The Cu and Zn bi-components modified (CuO-Cu₂O)Cu/ZnO nanocomposites were synthesized via facile combustion route in the presence of controlled fuel to oxidizer ratio and were characterized by X-Ray Diffraction (XRD) patterns, Transmission electron microscopy (TEM), High resolution Transmission electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray photoelectron Spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and energy dispersive X-ray (EDX) analysis. The PL and UV–Visible diffused reflectance spectral (UV–Vis-DRS) techniques were used to measure the optical sensitivity and tuning of band gap in the samples. The excellent photocatalytic degradation of Methylene Blue and industrial waste water under Sunlight irradiation depends on the mass ratios of Cu/Zn. The findings show that the addition of a certain proportion of CuO, Cu₂O, ZnO, and Cu can promote efficiency in Sunlight harvesting and separation of charge carriers. Process parameters namely catalyst quantity, dye concentration and a proposal for the mechanism of degradation pathway, experiments for trapping and enhancer are investigated. The study of photoluminescence, CIE and CCT calculations suggests that the present nanocomposite may find applications as phosphor material in warm white LEDs. The second segment of this study deals with the investigation of antibacterial performance of composites upon Gram-negative and Gram-positive bacteria. The results indicate that nanocomposites can be used in antibacterial control systems and as an important growth inhibitor in various microorganisms. The cytotoxic effect of the (CuO-Cu₂O)Cu/ZnO (CCCZ11) nanocomposite was determined by colorimetric and flow cytometric cell cycle analysis. Our experimental results show that the nanocomposite can induce apoptosis and suppress the proliferation of HeLa cells. The applications of nanocomposites based on Cu, an abundant and inexpensive metal has created much interest in various multifunctional applications.     

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.     

Effect of fuel type on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Porous magnetite (Fe₃O₄) powders were synthesized by solution combustion method using the glycine and urea at different fuel to oxidant ratios (ϕ). The combustion behavior depended on the fuel type as characterized by thermal analysis. The structure and phase evolution investigated by X-ray diffraction method showed nearly single phase Fe₃O₄ powders which were achieved only by using the glycine fuel at ϕ=1. The specific surface area and porous structures of the as-combusted Fe₃O₄ powders were characterized by N₂ adsorption-desorption isotherms and scanning electron microscopy, respectively. The surface area using the glycine fuel (62.6 m²/g) was higher than that of urea fuel (42.5 m²/g), due to different combustion reactions. Magnetic properties of the as-combusted powders were studied by vibration sample magnetometry which exhibited the highest saturation magnetization of 74 emu/g using the glycine fuel at ϕ=1 on account of its high purity and large crystallite size.     

Garcinia xanthochymus mediated green synthesis of ZnO nanoparticles: Photoluminescence,photocatalytic and antioxidant activity studies

Green synthesis of multifunctional zinc oxide nanoparticles (ZnO Nps) was achieved employing water extract of Garcinia xanthochymus by solution combustion synthesis. The structure and morphology were determined by XRD, UV–visible and scanning electron microscopy studies. The ZnO Nps were evaluated for photoluminescence (PL), photocatalytic and antioxidant properties. The water extract was found to comprise significantly high amounts of polyphenols and flavonoids. Powder XRD studies indicate the formation of pure wurtzite structure with absorption maximum of 370 nm corresponding to band gap energy of 3.33 eV. SEM studies reveal the formation of spongy cave like structures. The PL spectra exhibited 4 emission edges at 397, 436, 556 and 651 nm upon excitation at 325 nm because of oxygen deficiencies and zinc interstitials. Nps exhibit remarkable photodegradation of methylene blue (MB) in presence of UV and sun light. They exhibit antioxidant activity by inhibiting the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals. Therefore, the study reveals an efficient, ecofriendly and simple method for the green synthesis of multifunctional ZnO Nps.     

Preparation of BaTiO3 nanopowders by the solution combustion method

Barium titanate was synthesized by the method of exothermal combustion in solutions using barium nitrate, titanium dioxide (TiO₂) and titanyl nitrate (TiO(NO₃)₂) as sources of titanium and barium and reducing agents such as glycine (C₂H₅NO₂), carbamide (СН₄N₂O) and glycerol (C₃H₅(OH)₃). In an effort to form a barium titanate phase, the materials synthesized using titanium dioxide were subjected to additional calcination at 800 °С. With titanyl nitrate the use of glycine and carbamide enabled carrying out a single-step synthesis of barium titanate. The obtained materials have pseudo-cubic lattice and are characterized by high stability of properties in a wide range of temperatures and frequencies of the electromagnetic field.     

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.     

In silico study and experimental evaluation of the solution combustion synthesized manganese oxide (MnO2) nanoparticles

An innovative system was proposed to overcome the major problem of particles' agglomeration during the solution combustion synthesis (SCS) process by using external oxygen sources, named OSCS. The effect of self-sustained exothermic SCS and OSCS process parameters on the structural properties and antioxidant activity of β-MnO₂ nanoparticles were investigated theoretically and experimentally. According to ab-initio molecular dynamic (AIMD), molecular dynamic (MD) simulations and experimental results, the crystallographic parameters, kinetic of phase transformation, thermal stability, microstructure, and the super-lattice defects of SCS and OSCS synthesized β-MnO₂ nanoparticles relied on the high established vacuum during the process. Interestingly, the specific surface area (S_BET) of the OSCS products was increased ～ 4 times, and particle size and band-gap (E_g) were significantly decreased. The results showed the synthesized β-MnO₂ nanoparticles were non-toxic with a high potential against free radicals; the calculated adsorption energy of O₂ on the (110) surface of the standard and SCS synthesized β-MnO₂ was about 0.19 and 6.85 eV, respectively.     

Cobalt oxide nanopowder synthesis using cellulose assisted combustion technique

Cobalt oxides nanopowders were prepared using novel cellulose assisted combustion synthesis and solution combustion synthesis techniques. The synthesis conditions were optimized to produce high surface area cobalt oxide nanopowders. Effect of precursors ratio on product properties (such as crystalline structure, nanoparticle size, surface area etc.) were studied and compared for the two methods. Thermodynamic calculations along with TGA/DTA studies were used to understand the synthesis mechanism leading to cobalt oxide formation. The synthesized nanopowders were characterized using various materials characterization techniques such as XRD, SEM and TEM.     

Crystallization behavior and density functional theory study of solution combustion synthesized silicon doped calcium phosphates

The influence of heat-treatment temperatures (700 °C, 900°C, 1200 °C) on the phase, physical properties, crystallization rate, and in vitro properties of the solution combustion synthesized silicon-doped calcium phosphates (CaPs) were investigated. The thermodynamic aspects (enthalpy, entropy, and free energy) of the synthesis process and the crystallographic properties of the final samples were first predicted and then confirmed using density functional theory (DFT). Results demonstrated that the crystallization rate was controlled by the fuel(s) type (glycine, citric acid, and urea) and the amounts of Si⁴⁺ ions (0, 0.1, 0.4 mol). The highest calculated crystallization rate values of the un-doped, 0.1, and 0.4 mol Si-doped samples were 64%, 22%, 38%, respectively. The obtained results from the DFT simulation revealed that crystal growth in the direction of c-axis of hydroxyapatite (HAp) structure could change the stability of (001) surface of (HAp). Also, the computational data confirmed the adsorption of Si–OH groups on the (001) surface of HAp during the SCS process with an adsorption energy of 1.53 eV. AFM results in line with DFT simulation showed that the observed change in the surface roughness of Si-doped CaPs from 2 to 8 nm could be related to the doping of Si⁴⁺ ions onto the surface of CaPs. Besides, the theoretical and experimental investigation showed that crystal growth and doping of Si⁴⁺ ions could decrease the activation energy of oxygen reduction reaction (ORR). Furthermore, the results showed that the crystallized HAp structure could have great potential to efficiently reduce oxidative stress in human body.     

Synthesis and photocatalytic activity of Na+ co-doped CaTiO3:Eu3+ photocatalysts for methylene blue degradation

The Na⁺ co-doped CaTiO₃:Eu³⁺ powders were produced through the solution combustion method. The phase structure and optical properties of the synthesized samples were adequately characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, ultraviolet–visible (UV–vis) diffuse reflection spectroscopy and scanning electron microscopy (SEM). The XRD patterns revealed that a low level of Eu³⁺ doping could not cause lattice distortion of CaTiO₃. Photoluminescence (PL) displayed the CaTiO₃:0.5% Eu³⁺ sample synthesized at 900 °C has the weakest PL emission and the low electrons and holes recombination rate. The morphology of the sample was small nanoscale spherical particles. The UV–vis diffuse reflection spectra proved that doping Na⁺ and Eu³⁺ enlarged the absorption region and reduced band energy of pure CaTiO₃. The photocatalytic properties of Na⁺ co-doped CaTiO₃:Eu³⁺ samples were investigated via degrading methylene blue (MB) under ultraviolet light irradiation. The CaTiO₃:0.5% Eu³⁺, 0.5% Na⁺ sample, by contrast, exhibited the greatest photocatalytic property and the degradation rate was as high as 96.62%, which makes it a promising multi-functional material (photocatalytic material and red phosphor) for decreasing organic pollution in water.     

Dual role of activated carbon as fuel and template for solution combustion synthesis of porous zinc oxide powders

In this work, nanosized zinc oxide (ZnO) powders were fabricated by urea–nitrate solution combustion synthesis using activated carbon as a structure-directing template and secondary fuel at different fuel–oxidant ratios. The as-synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption measurements, UV–Vis diffuse reflectance spectroscopy, and photoluminescence. The effect of fuel amount on photocatalytic activity of ZnO powders was evaluated by the degradation of an azo dye Orange G. It was observed that combustion synthesis with activated carbon as a secondary fuel had a profound effect on reducing crystallite size and enhancement of specific surface area. The crystallite size of the as-synthesized powders varied from 46 to 26 nm. The ZnO powder prepared at a fuel–oxidant ratio of 1.8 possessed the small crystallite size and high specific surface area of 69 m²/g. It correspondingly resulted in the highest dye removal percentage of 99% with a rate constant of 0.027 min⁻¹. The improvement in dye degradation can be due to the synergistic interaction and interplay of enhanced surface area and catalytic ability of the photocatalyst. This study provides a simple single-step synthesis methodology to produce metal oxide nanopowders with tunable surface properties for high potential applications in catalysis, optoelectronics, and gas sensors.     

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.     

Nano-sized plate-like alumina synthesis via solution combustion

Nano-sized plate-like alumina is an important inorganic material in catalytic, ceramic and electronic applications due to its unique two-dimensional structure and properties, while its facile synthesis is still under investigation. In this work, nano-sized alumina plate was synthesized by solution combustion method with glycine and polyvinyl alcohol as composite fuels for the first time. The calcination temperature during solution combustion process was optimized as confirmed by XRD, FT-IR, TG-DSC, Raman, ²⁷Al MAS NMR, SEM, TEM, and N₂ physisorbtion. Obtained alumina displayed special nano-sized plate morphology and porous structure. It was further adopted as support for cobalt acetate and used as catalyst for selective oxidation of cyclohexane. This work develops a facile approach to synthesize two-dimensional plate-like alumina for catalytic application.     

Solution combustion synthesis of ZnO powders using mixture of fuels in closed system

Single phase ZnO powders with wurtzite structure were synthesized by solution combustion method using various amounts of mixed glycine-citric acid fuel in the presence (open system) and absence (closed system) of air oxygen. Phase evolution, microstructure and optical properties were investigated by thermal analysis, X-ray diffractometry, electron microscopy and Raman, photoluminescence (PL) and diffuse reflectance spectrometry techniques. Rapid combustion reaction in closed system led to weak crystallinity, as confirmed by deep-level emissions in PL spectra. Larger spherical particles (~200?nm) were synthesized in open system at ? =?1. The as-combusted ZnO powders in closed system exhibited higher photocatalytic activity under ultraviolet irradiation, due to their higher adsorption capacity of methylene blue on ZnO surface. Photodegradation rate increased with the increase of fuel content in as-combusted ZnO powders produced by open route as a result of the reduction of particle size and band gap energy.     

Accelerated crystallization of CuAlO2 delafossite phase by controlling thermal regime during solution combustion synthesis

In the present study, for the first time, CuAlO₂ delafossite phase was successfully obtained through a one-step solution combustion synthesis (SCS) process. Moreover, in order to accelerate CuAlO₂ crystallization, two-step process, i.e. SCS followed by heat-treatment (different thermal regimes: continuous and discontinuous) without controlling the atmospheric oxygen, was applied. In the two-step process, heating time duration needed for the crystallization of CuAlO₂ was lowered to 30 min at 1100 °C by exerting SCS on the mixture of starting materials. It was found that different thermal regimes can highly affect the formation of CuAlO₂ phase. Furthermore, according to the SEM and TEM studies, it was revealed that the resultant powders have a flaky-shape morphology with lamellar structure.