Flame Synthesis Method Research Articles

Effect of NH3 addition on the preparation of nitrogen-doped carbon nanomaterials by flame synthesis method

Effect of NH3 addition on the preparation of nitrogen-doped carbon nanomaterials by flame synthesis method

A review of flame aerosol synthesis technology for the synthesis of nanoparticles and functional energy materials

The outstanding performance of nanomaterials in chemical, magnetic, electrical, catalytic, and mechanical properties has paved the way for the huge market in material fabrication, energy storage, electronics, and many other industries. Traditional synthesis methods are relatively stunted in industrial applicability and scalability due to complex manufacturing processes and long preparation times, hampering the development and commercialisation of nanomaterials. On the other hand, the flame synthesis method emerges as an inexpensive, efficient, and easily scalable method for the commercial production of nanoparticles. The present review aims to highlight the research status and applications of the nanomaterials synthesised by the flame aerosol method. The advancement of flame aerosol synthesis technologies is reviewed, with emphasis on the state-of-the-art flame reactor configuration and design. Critical flame parameters that govern the formation of nanoparticles in the flame are reviewed to provide an understanding of the formation criteria and growth of nanomaterials in the flame environment. The properties and characteristics of carbon-based, platinum group metal, metal oxide, bimetallic nanoparticles, perovskite and high entropy oxide nanomaterials produced by flame synthesis are extensively reviewed. In addition, commercial manufacturing of flame-synthesised materials along with applications of the nanomaterials in the field of thermal or photocatalytic energy storage, fuel cells, and gas sensing are presented.

Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic

The Hume-Rothery rules governing solid-state miscibility limit the compositional space for new inorganic material discovery. Here, we report a non-equilibrium, one-step, and scalable flame synthesis method to overcome thermodynamic limits and incorporate immiscible elements into single phase ceramic nanoshells. Starting from prototype examples including (NiMg)O, (NiAl)Ox, and (NiZr)Ox, we then extend this method to a broad range of Ni-containing ceramic solid solutions, and finally to general binary combinations of elements. Furthermore, we report an “encapsulated exsolution” phenomenon observed upon reducing the metastable porous (Ni0.07Al0.93)Ox to create ultra-stable Ni nanoparticles embedded within the walls of porous Al2O3 nanoshells. This nanoconfined structure demonstrated high sintering resistance during 640 h of catalysis of CO2 reforming of methane, maintaining constant 96% CH4 and CO2 conversion at 800 °C and dramatically outperforming conventional catalysts. Our findings could greatly expand opportunities to develop novel inorganic energy, structural, and functional materials.

Enhanced photocatalytic activity of zinc oxide and tin doped zinc oxide nanoparticles synthesized by direct injection flame synthesis

Pristine zinc oxide and tin doped zinc oxide (ZnO) nanoparticles were prepared using single step rapid direct injection flame synthesis (DIFS) method and compared. The results revealed prominent changes in morphological and optical properties due to the incorporation of Sn ions into ZnO matrix and its origin was discussed. Upon doping the ZnO nanoparticles experiences change in length along the c- axis which increases the volume of the unit cell and bond length of zinc and oxygen ions. Other than that, tin doping in ZnO introduces new intrinsic defect level which decreases the electron hole recombination rate at the interface and enhances the formation of hydroxyl radicals and superoxide which further improves the photocatalytic degradation of Methylene Blue (93%) compared to pure ZnO (81%).

Candle soot-metal-organic framework-based hierarchical electrode as high-performance anode for Li-ion batteries

Recently, cobalt oxide-based materials have been considered high-performance anode materials. However, cobalt oxide materials display drawbacks such as capacity fade, poor cycle life, and substantial structural strain. In this work, we report a facile synthesis of carbon-cobalt oxide composite to improve the electrode's storage capabilities and cycle life. First, metal–organic framework-based cobalt oxide nano leaves are synthesized by simple coprecipitation followed by calcination. After that, candle soot-derived carbon nanoparticles are uniformly deposited on the cobalt oxide nano leaves by a simple flame synthesis method to form a composite electrode. The fractal-like interconnected carbon nanoparticles improve the electron conducting pathways. In contrast, metal–organic framework-derived porous cobalt oxide nano leaves enhance energy storage abilities through reversible conversion reactions. The superior performance of the composite electrode is established from the galvanostatic charge–discharge experiments. Also, the composite electrode has delivered outstanding specific capacities of 811 and 503 mAh g−1 at 50 and 1000 mA g−1 current densities, respectively. Furthermore, the composite electrode exhibited good cyclic stability at 1000 mA g−1 current density by delivering an excellent specific charge capacity of 490 mAh g−1 even after 400 cycles. Therefore, these superior electrochemical properties confirm the potential applicability in high-performance and stable Li-ion batteries.

In Situ Flame-Synthesized Carbon Nanotubes on Carbon Paper as a Microporous Layer for Proton Exchange Membrane Fuel Cells

Microporous layer (MPL) is an important component of the gas diffusion layer (GDL), which can improve the mass transfer rate to enhance the performance of the proton exchange membrane fuel cell (PEMFC). Although the carbon nanotube (CNT) is a promising material for MPL, the preparation and usage of CNT in MPL have many problems, such as macropore blocking, complex and time-consuming preparation, and expensive equipment. In this paper, a simple and cost-effective flame synthesis method to prepare CNT as MPL for PEMFC is proposed. It only takes 30 s to form a three-dimensional porous structure by growing CNT on carbon paper, which changes the pore size distribution of the gas diffusion layer (GDL) and is beneficial for enhancing the mass transfer rate. The density of CNT grown inside the carbon paper is hierarchical. The catalyst of the CNT and the burning time significantly influenced the density of CNT and the properties of the GDL. The maximum power density reached 1184 mW cm–2 for the GDL prepared by this flame method, which indicates an increase by 24.2% compared to the commercial GDL. Furthermore, the analysis by electrochemical impedance spectroscopy (EIS) indicated that the mass transfer resistance of the GDL prepared by the flame method was smaller than that of the commercial GDL. These findings provide a promising approach for the preparation of MPL with CNT.

Enhanced photocatalytic activity of methylene blue dye by DIFS synthesized pure and Mn doped MgO nanostructures

A simple Direct Injection Flame Synthesis (DIFS) method is employed to prepare magnesium oxide (MgO) and manganese doped magnesium oxide (Mn:MgO) nanoparticles, and their photocatalytic ability against methylene blue (MB) dye was investigated. The prepared samples are characterized through XRD, Raman spectroscopy, UV-Visible spectroscopy, FESEM, photoluminescence (PL), and EDX analysis. XRD studies reveal that MgO and Mn:MgO nanoparticles contain pure cubical phases and their average crystallite size reduces when Mn is doped with MgO. The characteristics vibrations mode of the synthesized nanoparticles are analyzed from the Raman spectroscopic studies. As per the EDX data, the prepared samples are free from impurities. Pure MgO nanoparticles have irregular, nanocubical and nanoclustered formations, whereas Mn:MgO nanoparticles have crystalline, nanocubical, and nanoflakes structures, according to FESEM analysis. Doping Mn slightly increases the bandgap of the Mn:MgO nanoparticles. UV–visible spectroscopy analysis confirmed a red shift in the wavelength dependent absorbance curve. PL analysis confirms the vacancy and oxygen related defects that are generated due to the doping of Mn with MgO, which enhances the degradation of MB dye. The efficiency of MB degradation by MgO is determined to be 86% and Mn:MgO is about 99%. The analysis of the photocatalytic degradation process revealed that OH- and holes (h+) were crucial for the increased photocatalytic activity of Mn:MgO nanoparticles for MB degradation. The effect of catalyst's initial concentration and the catalysts reusability test were evaluated for five times without significantly losing activity each time. As a result, Mn:MgO is a useful and active catalyst that can be activated effectively using UVA-LEDs to break down and mineralize the wastewater's organics.

Light-trapping carbon nanotube forests in glass fibre-reinforced thermoplastic prepregs for efficient laser-assisted automated fibre placement

Laser-assisted automated fibre placement (LATP) is an emerging technology for manufacturing thermoplastic composite components. However, major challenges are still encountered for the LAFP process for glass fibre (GF) reinforced composites due to the high near-infrared (NIR) laser reflectance and transmission as well as resulting poor absorption of prepreg constituents. Inspired by the efficient light-trapping and photothermal characteristics of carbon nanotube (CNT) forest, we fabricate CNT forest onto the GF surface by rapid and low‐cost flame synthesis method, to enhance the photothermal conversion efficiency of poly-ether-ether-ketone (PEEK)/GF prepregs during LAFP process. CNT forests with different lengths, alignments and densities were produced by changing flame synthesis parameters. The spectroscopy results show that CNT forest suppresses transmission and reflection from GF and crystals in GF/PEEK prepreg within the NIR wavelength range at near normal incidence, decreasing transmission and reflectance to 0.3% and 7.9%, respectively, and increasing absorption to 91.8% at 1080 nm wavelength. Furthermore, CNTs forest improves the heating rate of GF/PEEK prepreg by more than 700% for a wide range of incident angles. Consequently, CNT forest enables a 400% increase in placement speed and a 79% reduction in energy consumption during LAFP process, while making negligible voids in the interlayer.

Optical hydrogen sensing by MoO3 films deposited by a facile flame synthesis method

Nanostructured MoO3 films were deposited on glass by an atmospheric solid-fed flame vapor deposition (SF-FVD) technique at different substrate temperatures (25 (SRT), 300 (S300) and 400 °C (S400)). FESEM showed web-like morphology for SRT and S300 and plate-like for S400. TEM revealed existing spherical at lower and 2D structures at higher temperatures. Monoclinic and orthorhombic phases were observed for SRT and S300/S400, respectively. With a sputter-deposited Pd film, MoO3 films turn dark blue after hydrogen exposure, for which localized surface plasmon resonance (LSPR) absorption bands have appeared in the NIR region. The LSPR showed a linear blue shift up to 35 nm with < 4% hydrogen concentration. Using a 640 nm LED light source, the capability at very low concentrations of hydrogen and different working temperatures (up to 200 °C) was investigated. Significant sensitivity was observed with a sigmoidal behavior toward hydrogen concentration (0.05–10%). Also, the repeatability and selectivity among interfering gases were desirable. Sample S300 at a working temperature of 150 °C showed the best sensing performance in coloration, reversibility and response time. Raman, XRD and FESEM were used that reveal structural and morphological degradation, where the partial formation of molybdenum oxide bronze (H0.93MoO3) was observed.

Investigation of structural, morphological, optical, elemental, and anticancer property of pure ZnO and PbO: ZnO nanocomposites prepared by flame synthesis method

In this work, Pure ZnO nanoparticles and a nanocomposite of PbO: ZnO were prepared by the flame synthesis method, and was analyzed for structural, morphological, optical, elemental, and biocompatibility studies. The structural analysis revealed a hexagonal structure for ZnO and an Orthorhombic structure for PbO: ZnO nanocomposite. Scanning electron microscopy (SEM) image showed a Nano-Sponge-like surface morphology for PbO: ZnO nanocomposite and energy dispersive spectra (EDS) confirmed the absence of undesired impurities. Transmission electron microscopy (TEM) image showed a particle size of ∼50 nm for ZnO and ∼20 nm for PbO: ZnO. Using Tauc plot the optical band gap was found to be 3.2 eV for ZnO and 2.9 eV for PbO: ZnO. Anticancer studies confirm the excellent cytotoxicity activity of both compounds. PbO: ZnO nanocomposite has demonstrated the highest cytotoxicity against the tumorigenic HEK 293 cell line with the lowest IC50 value of 13.04 μM. Our study shows that the prepared PbO: ZnO nanocomposite has a huge potential in cancer therapy.

Preparation and Characterization of Alumina Nanoparticles by Direct Injection Flame Synthesis

The article reports the synthesis of nano alumina particles by instant and continuous one step Direct Injection Flame Synthesis (DIFS) method. The synthesized nanoparticles were highly crystalline with orthorhombic crystal structure belonging to the space group of P222. The nano alumina particles have a crystallite size of 36 nm and the particle radius is calculated to be 24 nm. The synthesized nano alumina particle exhibits a spherical morphology with different radius. The particles were subjected to controlled aging process and the formation of encapsulation layer is reported. The thickness of the encapsulation layer is found to be ~ 4.5 nm.

Defects-driven photoconduction in one step direct injection flame synthesized inverse spinel Zn2SnO4 nanoparticles for photodetector applications

Pristine inverse spinel zinc stannate nanoparticles by a rapid and ceaseless one step Direct Injection Flame Synthesis (DIFS) method by utilizing the zinc and tin microparticles as the feedstock is reported. The correlation of mixed morphologies with variation in resident and oxidation time of the reactants in the flame during the synthesis is done by basic Fluid Dynamics equations. The surface level cation (tin and zinc) disordering, lowered conduction band minimum and oxygen vacancies derived shallow level defect states are observed. A simple photodetector is fabricated by coating the zinc stannate nanoparticles over the p-type silicon substrate. The presence of mixed morphologies enhances the light scattering and antireflection. The mechanism of p-silicon/n-zinc stannate photodetector based on chemisorption of atmospheric oxygen species (below band conduction process) with defect assisted recombination charge transport is discussed. High Dark/Photocurrent ratio of 90% and Detectivity of 1.05 × 1010 Jones in visible light photodetection is observed and explained.

Facile Construction and Fabrication of a Superhydrophobic and Super Oleophilic Stainless Steel Mesh for Separation of Water and Oil.

The fluoride-free fabrication of superhydrophobic materials for the separation of oil/water mixtures has received widespread attention because of frequent offshore oil exploration and chemical leakage. In recent years, oil/water separation materials, based on metal meshes, have drawn much attention, with significant advantages in terms of their high mechanical strength, easy availability, and long durability. However, it is still challenging to prepare superhydrophobic metal meshes with high-separation capacity, low costs, and high recyclability for dealing with oil–water separation. In this work, a superhydrophobic and super oleophilic stainless steel mesh (SSM) was successfully prepared by anchoring Fe2O3 nanoclusters (Fe2O3-NCs) on SSM via the in-situ flame synthesis method and followed by further modification with octadecyltrimethoxysilane (OTS). The as-prepared SSM with Fe2O3-NCs and OTS (OTS@Fe2O3-NCs@SSM) was confirmed by a field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectrometer (XPS), and X-ray diffractometer (XRD). The oil–water separation capacity of the sample was also measured. The results show that the interlaced and dense Fe2O3-NCs, composed of Fe2O3 nanoparticles, were uniformly coated on the surface of the SSM after the immerging-burning process. Additionally, a compact self-assembled OTS layer with low surface energy is coated on the surface of Fe2O3-NCs@SSM, leading to the formation of OTS@Fe2O3-NCs@SSM. The prepared OTS@Fe2O3-NCs@SSM shows excellent superhydrophobicity, with a water static contact angle of 151.3°. The separation efficiencies of OTS@Fe2O3-NCs@SSM for the mixtures of oil/water are all above 98.5%, except for corn oil/water (97.5%) because of its high viscosity. Moreover, the modified SSM exhibits excellent stability and recyclability. This work provides a facile approach for the preparation of superhydrophobic and super oleophilic metal meshes, which will lead to advancements in their large-scale applications on separating oil/water mixtures.

Structural and electrochemical investigations on impregnated carbon soot derived by flame synthesis method

Structural and electrochemical investigations on impregnated carbon soot derived by flame synthesis method

Conductivity enhancement of Al- and Ta-substituted Li7La3Zr2O7 solid electrolytes by nanoparticles

A nanopowder consisting of La2Zr2O7 particles with lithium containing species on their surface was prepared by spray flame synthesis and subsequently added to Li7La3Zr2O12 powder obtained by a conventional solid-state reaction. The spray flame synthesis method utilized in this work yields nanoparticles with a small size of approximately 5 nm, which is unprecedented within the scope of oxide-based ionic conductors for solid-state batteries. Remarkably, the addition of nanoparticles for sintering at a relatively low temperature of 1000 °C significantly improved the ionic conductivity by 50 %. In contrast, there was no influence of incorporating nanoparticles on the conductivity at sintering temperatures at or above 1100 °C, which is the typical temperature range applied for conventional sintering of Li7La3Zr2O12. Compared to prior published work with analogous materials, a more than twofold improvement in conductivity was demonstrated while the sintering temperature was decreased by 100 °C.

High Performance Asymmetric Supercapacitor Based on Hierarchical Carbon Cloth In Situ Deposited with h-WO3 Nanobelts as Negative Electrode and Carbon Nanotubes as Positive Electrode.

Urchin-like tungsten oxide (WO3) microspheres self-assembled with nanobelts are deposited on the surface of the hydrophilic carbon cloth (CC) current collector via hydrothermal reaction. The WO3 nanobelts in the urchin-like microspheres are in the hexagonal crystalline phase, and their widths are around 30–50 nm. The resulted hierarchical WO3/CC electrode exhibits a capacitance of 3400 mF/cm2 in H2SO4 electrolyte in the voltage window of −0.5~0.2 V, which makes it an excellent negative electrode for asymmetric supercapacitors. To improve the capacitive performance of the positive electrode and make it comparable with that of the WO3/CC electrode, both the electrode material and the electrolyte have been carefully designed and prepared. Therefore, the hydrophilic CC is further coated with carbon nanotubes (CNTs) to create a hierarchical CNT/CC electrode via a convenient flame synthesis method, and a redox-active electrolyte containing an Fe2+/Fe 3+ couple is introduced into the half-cell system as well. As a result, the high performance of the asymmetric supercapacitor assembled with both the asymmetric electrodes and electrolytes has been realized. It exhibits remarkable energy density as large as 403 μW h/cm2 at 15 mW/cm2 and excellent cyclic stability after 10,000 cycles.

Facile One-Step Flame Synthesis of La1−xSrxMnO3 Nanoparticles for CO Catalytic Oxidation

A large amount of CO as hazardous emission in the iron ore sintering process has caused severe harm to the environment and human health. To control the emission of CO more effectively, the preparation of highly efficient catalysts has attracted much attention. In this study, the La1-xSrxMnO3 (0 ≤ x &lt; 1) perovskite catalysts with different Sr2+ contents were prepared by the one-step flame synthesis method to treat CO pollutants in the iron and steel industry. The influence of Sr2+ doping on the structure and activity of catalytic were characterized and analyzed. La1-xSrxMnO3 perovskite catalysts exhibit good perovskite phases and loose spherical structures. The specific surface areas are between 4.1 and 12.0 m2 g−1. Combined with the results of H2-TPR and O2-TPD, the improvement of catalytic activity of La1-xSrxMnO3 perovskite can be attributed to the high concentration of active centers and oxygen vacancies. Significantly, the La0.4Sr0.6MnO3 catalyst presented the best reducibility and high content of absorbed active oxygen species, leading to a superior CO oxidation catalytic activity and reaches 50% CO conversion at 134.9°C and 90% at 163.2°C, respectively. The effects of water vapor and CO2 on the oxidation activity of La1-xSrxMnO3 perovskite was investigated. The flame-produced catalysts exhibit favorable catalytic stability and antisintering ability, achieving 100% CO conversion after fifth consecutive oxidation cycles.

A Brief Review on Recent Development of Carbon Nanotubes by Chemical Vapor Deposition

Development of carbon nanotubes was done by several methods like arc discharge, laser ablation, silane solution, flame synthesis method but the standard or famous technique using chemical vapor deposition (CVD). CVD is one of the approaches to develop CNT, due to easy control of the reaction course and high purity of the obtained materials. Various type of CVD present like thermal CVD, plasma enhanced CVD, or microwave plasma CVD. These kinds of types give the different advantage and drawbacks to the production of CNT and its preparations.

Multifunctional oil-produced reduced graphene oxide – Silver oxide composites with photocatalytic, antioxidant, and antibacterial activities

Graphene-based nanomaterials that combine significant photocatalytic, antioxidant and antibacterial activity are very attractive candidates for biomedical and environmental applications. Conventional chemical synthesis routes may contaminate the resultant materials with toxic molecules, compromising their properties and limiting their use in biomedical applications. Ideally, to avoid any contamination, the nanomaterials should be synthesized from non-toxic precursors and reagents, e.g. foodstuff via a simple technology that does not rely on the use of hazardous chemicals yet produces materials of high quality. Here, we report an environmentally friendly, low cost reduced graphene oxide-silver-silver oxide nanocomposite with strong photocatalytic, antioxidant and antibacterial activity for environmental remediation. The reduced graphene oxide (FRGO) is synthesized from edible sunflower oil via a simple flame synthesis method. Next, silver nanoparticles (Ag/AgO/Ag2O) are produced by phytochemical reduction of AgNO3 using a reducing agent based on flavonoids from Coleus aromaticus (Mexican mint), also used in food industry. Thus-obtained FRGO-Ag/AgO/Ag2O composite is characterized using X-ray diffraction spectroscopy, scanning electron microscopy, fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The degradation of anionic textile dye Methylene blue (MB) is used as a measure of photocatalytic activity of FRGO and FRGO/Ag/AgO/Ag2O, with solution pH, initial dye concentration, and quantity of the catalyst considered as influencing factors. FRGO-Ag/AgO/Ag2O composites show strong antioxidant activity, with improved radical inhibition as well as dye degradation properties when compared to pristine FRGO.

Modification of TiO2 and NiO charge selective mesoporous layers using excessive Y and Li additions for carbon based perovskite solar cells

Carbon based perovskite solar cells are rapidly emerging as promising photovoltaic devices, combining low cost production and prolonged device operation, due to the exclusion of polymeric conductors and integration of highly durable metal oxide charge selective layers. Modification of metal oxide mesoporous layers via element additions and enhancement of electrical conductivity is a major strategy for reduced internal resistances inside the cell. This work investigates the effect of excessive Y and Li additions on the charge selective mesoporous layers. A novel flame synthesis method can be successfully employed for production of yttrium added TiO2 (Y:TiO2) and conductive lithium added NiO (Li:NiO) nanoparticles. This novel methanol combustion method is an effective strategy for incorporation of additives into host lattices, resulting in modified mesoporous layers. Ultraviolet photoelectron spectroscopy studies reveal a profound effect of Li and Y additions on the electronic band structure of the particles. Electrochemical impedance studies confirms that modification of TiO2 with excessive yttrium atoms results in suppressed charge injection, where excessive lithium addition enhances the charge transport properties of the NiO layer. Power conversion efficiency of the pristine NiO based cells are enhanced from 8.38% to 9.63% upon lithium addition, in a TiO2/MgO/Li:NiO/carbon configuration.