No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
One-Step Solution Combustion Synthesis of Cobalt Nanopowder in Air Atmosphere: The Fuel Effect
Figures
Figures - uploaded by Alexander Khort
Author content
All figure content in this area was uploaded by Alexander Khort
Content may be subject to copyright.
Supplementary resource (1)
... Due to this feature, combustion of SCS precursors occurs even in inert atmospheres and in vacuum and result in high-quality NMs with homogeneous crystal phases. The method has previously been used to produce NMs of different functional classes, including pure and multicomponent metal NMs [33][34][35][36] , as well as simple and complex oxides [37][38][39] . Since SCS is one of few techniques that could easily be scaled-up for industrial production of a broad class of NMs, it is important to study particle properties as well as corrosion and dissolution characteristics of SCS NPs in e.g. ...
... φ represents the fuel-to-oxidiser molar ratio. The φ value was for all NMs equal to 1.75, a value shown to be within an optimal range for SCS of pure metals like Co and Ni 33,35 . ...
... After the precursor combustion, the powder was kept in the furnace for another 5 min for residual carbon burning out. The synthesis temperature was chosen based on previous studies by some of the authors 33,35 , showing the decomposition of initial compounds of the precursor during SCS to be complete at 500 °C. In this case, a temperature of 600 °C was high enough for complete decomposition of the metal nitrates and the fuel, and low enough to prevent metals from intensive oxidation or melting during the SCS reactions. ...
Pure metallic Co, Ni, and their bimetallic compositions of Co3Ni, CoNi, and CoNi3 nanomaterials were prepared by solution combustion synthesis. Microstructure, phase composition, and crystalline structure of these nanoparticles (NPs) were characterized along with studies of their corrosion and dissolution properties in synthetic freshwater with and without natural organic matter (NOM). The nanomaterials consisted of aggregates of fine NPs (3–30 nm) of almost pure metallic and bimetallic crystal phases with a thin surface oxide covered by a thin carbon shell. The nanomaterials were characterized by BET surface areas ranging from ~ 1 to 8 m2/g for the Ni and Co NPs, to 22.93 m2/g, 14.86 m2/g, and 10.53 m2/g for the Co3Ni, CoNi, CoNi3 NPs, respectively. More Co and Ni were released from the bimetallic NPs compared with the pure metals although their corrosion current densities were lower. In contrast to findings for the pure metal NPs, the presence of NOM increased the release of Co and Ni from the bimetallic NPs in freshwater compared to freshwater only even though its presence reduced the corrosion rate (current density). It was shown that the properties of the bimetallic nanomaterials were influenced by multiple factors such as their composition, including carbon shell, type of surface oxides, and the entropy of mixing.
... Due to this feature, combustion of SCS precursors occurs even in inert atmospheres and in vacuum and result in high-quality NMs with homogeneous crystal phases. The method has previously been used to produce NMs of different functional classes, including pure and multicomponent metal NMs [34][35][36][37] , as well as simple and complex oxides [38][39][40] . Since SCS is one of few techniques that could easily be scaled-up for industrial production of a broad class of NMs, it is important to study particle properties as well as corrosion and dissolution characteristics of SCS NPs in e.g. ...
... φ represents the fuel-to-oxidiser molar ratio. The φ value was for all NMs equal to 1.75, a value shown to be within an optimal range for SCS of pure metals like Co and Ni 34,36 . ...
... After the precursor combustion, the powder was kept in the furnace for another 5 min for residual carbon burning out. The synthesis temperature was chosen based on previous studies by some of the authors 34,36 , showing the decomposition of initial compounds of the precursor during SCS to be complete at 500 °C. In this study, a temperature of 600 °C was high enough for complete decomposition of the metal nitrates and the fuel, and low enough to prevent metals from intensive oxidation or melting during the SCS reactions. ...
Pure metallic Co, Ni, and their bimetallic compositions of Co 3 Ni, CoNi, and CoNi 3 nanomaterials were prepared by solution combustion synthesis. Microstructure, phase composition, and crystalline structure of these nanoparticles (NPs) were characterized along with studies of their corrosion and dissolution properties in synthetic freshwater with and without natural organic matter (NOM). The nanomaterials consisted of aggregates of fine NPs (3–30 nm) of almost pure metallic and bimetallic crystal phases with thin surface oxide covered by a thin carbon shell. The nanomaterials were characterized by BET surface areas ranging from ~ 1 to 8 m ² /g for the Ni and Co NPs, to 22.93 m ² /g, 14.86 m ² /g, and 10.53 m ² /g for the Co 3 Ni, CoNi, CoNi 3 NPs, respectively. More Co and Ni were released from the bimetallic NPs compared with the pure metals although their corrosion current densities were lower. In contrast to findings for the pure metal NPs, the presence of NOM increased the release of Co and Ni from the bimetallic NPs in freshwater compared to freshwater only even though its presence reduced the corrosion rate (current density). It was shown that the properties of the bimetallic nanomaterials were influenced by multiple factors such as their composition, including carbon shell, type of surface oxides, and the entropy of mixing.
... In Stage I, the initial mass loss was observed until 111 C, mainly because of the removal of moisture and the decomposition of the unreacted nitrate salts in the as-prepared powder [39]. On the other hand, the highest reduction in weight was determined in Stage II (~6.55%), which is attributed to the joint decomposition of glycine and Co(NO 3 ) 2 [40,41]. Glycine decomposition starts at around 215 C [41], when the amino group detaches, and a polymerization reaction occurs, which also results in the production of combustible gases such as NH 3 , N 2 O, CO 2 , and CO [40,42]. ...
... On the other hand, the highest reduction in weight was determined in Stage II (~6.55%), which is attributed to the joint decomposition of glycine and Co(NO 3 ) 2 [40,41]. Glycine decomposition starts at around 215 C [41], when the amino group detaches, and a polymerization reaction occurs, which also results in the production of combustible gases such as NH 3 , N 2 O, CO 2 , and CO [40,42]. This mixture of combustible gases intensifies heat exchange and mass transport in the system, and likely strengthens the reducing nature of the combustion system by hindering the inward diffusion of oxygen [40]. ...
... Glycine decomposition starts at around 215 C [41], when the amino group detaches, and a polymerization reaction occurs, which also results in the production of combustible gases such as NH 3 , N 2 O, CO 2 , and CO [40,42]. This mixture of combustible gases intensifies heat exchange and mass transport in the system, and likely strengthens the reducing nature of the combustion system by hindering the inward diffusion of oxygen [40]. At stage III, the remaining fuel continues to decompose, causing another 1.39% weight loss, which is likely due to the decomposition of the carboxyl groups found in glycine [43]. ...
In this work, porous spinel Co3O4 nanoparticles were synthesized through solution combustion. Initially, the effect of calcination on the morphology, phase composition, and electrocatalytic behavior towards oxygen evolution reaction (OER) of the synthesized oxides was investigated. As the as-synthesized powder prepared at stoichiometric conditions (fuel-to-oxidizer ratio, φ = 1) and pH = 3 was calcined at 300 and 500 °C, the products became more compact and dense. XRD results showed that a subsequent heat treatment is required to produce a single phase-oxide, as the as-synthesized sample was a mixture of spinel Co3O4 and monoclinic CoO. The mixed phase oxide exhibited excellent electrocatalytic performance in 1 M KOH with onset overpotential and Tafel slope values as low as 361 mV and 87.54 mV dec⁻¹, respectively. Its enhanced properties compared to the calcined samples could be ascribed to its high specific surface area, lower crystallinity, and excellent porosity. Following such findings, uncalcined samples were produced with different φ, and pH values. At φ = 1 and pH = 1, the sample registered an overpotential at 10 mA cm⁻² and Tafel slope of 434 mV and 74.93 mV dec⁻¹, respectively. The sample produced at φ = 0.5 and pH = 3, exhibited the best OER catalytic activity with an onset overpotential and Tafel slope as low as 334 mV and 61. 77 mV dec⁻¹. Catalytic activity enhancement is possibly due to better control of phase composition and morphology achieved by employing fuel-lean (φ < 1) and acidic conditions.
... 30−33 Another feature of the method is the formation of residual carbon as a product of incomplete combustion of an organic fuel in the case of an excess of fuel and/or of synthesis conducted in a protective (inert or reducing) atmosphere. 34,35 In most cases, residual carbon is a byproduct and as usually removed or ignored. Earlier, copper-29 and cobalt-based 36 nanocomposite materials with multilayered small-area G were obtained by the thermal decomposition of metal−organic precursors. ...
... The φ value was chosen based on our previous research 35,37,38 and additional preliminary study (not described here). It has been shown that an increase of the φ value leads to a substantial increase in the free carbon value. ...
... According to the methodology, as suggested in ref 35, the SCS process can be divided into four stages. At the first stage, residual water evaporates and the reacting system reaches the ignition temperature. ...
Graphene (G) and metal-decorated G nanocomposites are among the most promising materials for a wide variety of practical applications, and, therefore, the development of fast and reliable methods for nanocomposite synthesis is an important task. Herein we report the new fast approach for solution combustion synthesis (SCS) of large-area G–metallic nanocomposites in an air atmosphere. The G-based nanocomposites were obtained by a SCS using copper and nickel nitrates, as well as their stoichiometric mixture as the metal source and citric acid as a fuel and carbon source. The G structures started on the catalytic surface of freshly synthesized metallic nanograins during the combustion process and formed large-area free-standing films due to the high-energy and fast synthesis process. We proposed a mechanism of formation of the G-based nanocomposites. The phase compositions, structural features, and magnetization behavior of G@Cu, G@Ni, and G@CuNi nanocomposites are carefully studied and described. G@metal nanocomposites were studied as a material for the creation of a highly effective sensing element of semiconductor gas sensors.
... It includes two amino and one carbonyl groups and melts at 132°C [26]. The decomposition of urea proceeds in three stages [27]. At the first stage of SCS urea is partially evaporated (140-152°C). ...
... Then in the 152-160°C interval decomposition begins along with evaporation. The evolved gases contain NH 3 , a small amount of HNCO, and biuret [27] which is formed by reactions (4) and (5). ...
... The melt turns into an adhesive solid matrix at 225°C. According to the DTA results [27], the second stage is completed at 250°C. At the third stage of decomposition, from 250 to 360°C, only cyanuric acid, ammelide, and ammeline are present in any considerable quantities. ...
The composition of gels and xerogels, as well as their transformation during heating and dehydration, determine the thermochemistry of solution combustion synthesis reactions. An improved descriptive thermodynamic model of combustion processes was formulated on the basis of the investigated formation of complex compounds of metal ions with organic fuel (glycine, citric acid, urea, and PVA) in nitrate solutions. The intensity of SCS reactions was found to depend on the strength of Ni²⁺–ligand complexes. The effect of heat loss during combustion on the ΔTmax value was analyzed for the model system Ni(NO3)2·nH2O–Fuel–H2O. It was found the heat loss occurs due to the presence of various amounts of structurally-bound water in gels and xerogels before the combustion.
The temperature profiles of combustion during the synthesis of NiO with different types of fuel at φ = 1.0.
... One of the methods that recently showed potential applicability for industry scale synthesis of metallic NMs is solution combustion synthesis (SCS) [7]. Several single and multicomponent single-phase metallic NMs have been already synthesized by the SCS [8,9], and hexamethylenetetramine (HMTA) was considered as one of the best fuel/reducers for SCS of metallic NMs [10][11][12][13]. However, using HMTA in combination with several metal ions leads to HMTA hydrolysis and components sedimentation. ...
... The composition was chosen based on the results of a preliminary study (not shown here), as the combination with the lowest CA content, which gives stable metal nitrates-fuel solutions. The ϕ value was chosen based on previous researches, where both HMTA and CA fuels were used for SCS of various metal nanomaterials [10][11][12]. Such a high fuel content increases the degree of metal species reduction during the SCS process and helps protect the newly-formed metal nanoparticles from oxidation. ...
Solution combustion synthesis approach with hexamethylenetetramine/citric acid as mixed fuel was used for the synthesis of bimetallic single-phase nanomaterials in CoCu, CoNi, CoFe, and FeNi systems in the air. All obtained nanomaterials are characterized by fine crystallinity with crystallites sizes from 15 nm to 41 nm. The study shows the using mixed fuel in the synthesis approach allows obtaining CoNi and CoFe bimetallic phase, as synthesis in CoCu and FeNi systems results in obtaining split phases. Due to its higher stability in solutions the mixed fuel could be used for industrial scale-up of the solution combustion production of the polymetallic nanomaterials.
... Heating method in all the above approaches also have significant impact on the properties of the resulting materials. For example, microwave heating fundamentally differs from conventional thermal heating processes [80,81]. In this case, the heat is directly generated in the materials volume by the interaction of the electromagnetic field with electric and magnetic dipoles in the heated media. ...
... However, recent breakthroughs in understanding the reaction mechanism suggest otherwise [12]. Those studies revealed that, under certain conditions (typically with excess fuel), the intermediate gaseous combustion products form a reductive gas environment (typically hydrogen-based) that allows reduction of the metal oxide to form metals (Ni, Cu, Co, etc.) or alloys (NiCo, NiCu, etc.) during SCS [13,81,[89][90][91]123]. These promising results suggest that by understanding the fundamentals of combustion in reactive solutions researchers will able to synthesize a range of compounds including intermetallics, carbides, nitrides and others, which represents a significant broadening of the scope for potential SCS materials. ...
Specific applications of self-sustained reactions to fabricate advanced ceramics, along with details such as synthesis conditions, mechanism of microstructure formation, and material properties, are overviewed. The latest achievements in the field include analysis of three such synthetic routes: reactive spark plasma sintering, combustion synthesis with mechanical stimulation, and solution combustion synthesis. Examples of fabrication of high-temperature nanostructured ceramics and composites, as well as non-equilibrium ceramic phases are also discussed.
... In fact, cobalt NPs are the known active species for the reduction of 4-NP, which can be formed in solution combustion reactions when the N/G ratio is low. 32 For instance, mixing Co(NO 3 ) 2 and glycine at a N/G ratio of 0.75 in the solution combustion process, Khort et al. obtained a mixture of Co (6%), CoO (56%), and Co 3 O 4 (38%). 32 On the other hand, 4-NP reduction ability of α-Co(OH) 2 has been demonstrated by Khan et al. for a sample containing α-Co(OH) 2 , although the signal/noise ratio of the X-ray diffraction peaks of this phase was extremely low. ...
... 32 For instance, mixing Co(NO 3 ) 2 and glycine at a N/G ratio of 0.75 in the solution combustion process, Khort et al. obtained a mixture of Co (6%), CoO (56%), and Co 3 O 4 (38%). 32 On the other hand, 4-NP reduction ability of α-Co(OH) 2 has been demonstrated by Khan et al. for a sample containing α-Co(OH) 2 , although the signal/noise ratio of the X-ray diffraction peaks of this phase was extremely low. 33 Finally, the possible contributions of amorphous CoFe 2 O 3.66 and amorphous Fe 40 Co 60 O x phases in 4-NP reduction cannot be discarded as both of them have been utilized successfully in the catalytic oxidation of water and oxygen reduction reactions revealing superior performances than their respective crystalline counterparts. ...
Surface activation of catalysts is known to be an efficient process to enhance their activity in catalytic processes. The activation process includes the generation of oxygen vacancies, changing the nature of the catalyst surface from acidic to basic and vice versa, and the reduction of catalyst surface by H 2. On the other hand, magnetically separable catalysts are highly beneficial for their utilization in water or biological fluid-based catalytic processes, as they can be easily guided to the target site and recovered. Here, we present the fabrication of CoFe 2 O 4 and composites of Co 3 O 4 / CoFe 2 O 4 /α-Fe 2 O 3 and Co/CoFe 2 O 4 /α-Fe 2 O 3 through solution combustion process to utilize them as catalysts for 4-nitrophenol (4-NP) reduction. Although none of the as-prepared CoFe 2 O 4 and Co 3 O 4 /CoFe 2 O 4 was seen to be active in 4-NP reduction reaction, the surface of the composite gets activated by borohydride (NaBH 4) treatment to act as a highly active catalyst for 4-NP reduction. X-ray photoelectron spectroscopy of the composite revealed the formation of metal-hydroxide (M−O−H) species of both Co and Fe at its surface due to borohydride treatment. The mechanism of the surface activation and the dynamics of 4-NP reduction of the surface-activated composite have been studied, proposing a possible pathway for the reduction of 4-NP.
... Figures 1(f)-1(n) depict the micrographs and elemental distributions of the representative La(5B 0.2 )O 3 sample. Notably seen in the low-magnification landscape image ( Fig. 1(f)), the as-synthesized sample consists of granule-like agglomerates with porous microstructures due to the volatilized gas formed during the synthetic process, which is also confirmed by the highermagnification SEM image ( Fig. 1(g)) [28,37,38]. In addition, the energy dispersive spectroscopy (EDS) mappings (Figs. ...
High-entropy oxides (HEOs) have gained great attention as an emerging kind of high-performance anode materials for lithium-ion batteries (LIBs) due to the entropy stabilization and multi-principal synergistic effect. Herein, the porous perovskite-type RE(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 (RE (= La, Sm, and Gd) is the abbreviation of rare earth) HEOs were successfully synthesized by a solution combustion synthesis (SCS) method. Owing to the synergistic effect of lattice distortion and oxygen vacancies (OV), the Gd(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 electrode exhibits superior high-rate lithium-ion storage performance and excellent cycling stability. A reversible capacity of 403 mAh·g–1 at a current rate of 0.2 A·g–1 after 500 cycles and a superior high-rate capacity of 394 mAh·g⁻¹ even at 1.0 A·g–1 after 500 cycles are achieved. Meanwhile, the Gd(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 electrode also exhibits a pronounced pseudo-capacitive behavior, contributing to an additional capacity. By adjusting and balancing the lattice distortion and oxygen vacancies of the electrode materials, the lithium-ion storage performance can be further regulated.
... In [33], a combination of hexamethylenetetramine and citric acid (so-called "mixed fuel") was used for the synthesis of CoCu, CoNi, CoFe, and FeNi nanomaterials. The microwave-assisted method was used for the production of Co nanoparticles using various fuels (citric acid, glycine, urea, and hexamethylenetetramine) [34]. However, despite the amount of research devoted to the solution combustion synthesis of nanoparticles, the results of their application in the creation of catalysts for methane decomposition are poorly presented, especially when considering methane conversion, hydrogen yield, and carbon nanomaterials formed over these catalysts. ...
The synthesis of a 90% Ni/Al2O3 catalyst via solution combustion synthesis with various fuels was studied in this work. Catalysts with a high content of the active component (i.e., nickel) were obtained as a result of the combustion of Ni(NO3)2·6H2O and Al(NO3)3·9H2O mixtures with fuel. The fuels, such as hexamethylenetetramine, glycine, urea, starch, citric acid, and oxalic acid, were investigated. The synthesis was carried out in a furnace, with the temperature being raised from room temperature to 450 °C at a rate of 1 °C per min. The paper evaluates the efficiency of fuels and their effect on the structure and properties of catalysts, as well as their catalytic activity. The catalyst was used for the synthesis of hydrogen and carbon nanofibers by methane decomposition at 1 bar and 550 °C. The catalysts were tested in a vertical flow reactor without preliminary reduction. The obtained samples of catalysts and carbon nanomaterials were studied by transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction. The highest activity of the catalyst was obtained when citric acid was used as a fuel. The specific yields of hydrogen and carbon nanofibers were 17.1 mol/gcat and 171.3 g/gcat, respectively. Catalytic decomposition of methane led to the formation of cup-stacked carbon nanofibers.
... The modified one-step SCS approach for synthesizing Co and Ni NPs (in the following denoted Co SCS NPs and Ni SCS NPs), using hexamethylenetetramine (C 6 H 12 N 4 , HMT) as an organic fuel/reducer and cobalt or nickel nitrate hexahydrate as metal source/oxidizer is described elsewhere (Khort et al., 2017(Khort et al., , 2018. In short, 4.95 g of metal nitrite was dissolved in a minimum volume of hot distilled water and mixed with 1.39 g of HMT under constant stirring. ...
Expanding applications and production of engineered nanoparticles lead to an increased risk for their environmental dispersion. Systematic knowledge of surface transformation and dissolution of nanoparticles is essential for risk assessment and regulation establishment. Such aspects of Co- and Ni-based nanoparticles including metals, oxides, and solution combustion synthesized metal nanoparticles (metal cores with carbon shells) were investigated upon environmental interaction with organic matter, simulated by natural organic matter (NOM) and degradation products from zooplankton and algae (eco-corona biomolecules, EC) in freshwater (FW). The presence of NOM and EC in FW results in negative surface charges of the nanoparticles reduces the extent of nanoparticles agglomeration, and increases concentration, mainly due to the surface adsorption of carboxylate groups of the organic matter. The dissolution of the Co-based nanoparticles was for all conditions (FW, FW with NOM or EC) higher than the Ni-based, except for Co3O4 being nearly non-soluble. The surface transformation and dissolution of nanoparticles are highly exposure and time-dependent, and surface- and environment specific. Therefore, no general correlation was observed between dissolution and, particle types, surface conditions, or EC/NOM adsorption. This underlines the importance of thorough investigations of nanoparticles adsorption/desorption, degradation, and exposure scenarios for developing regulatory relevant protocols and guidelines.
... This method is based on a redox reaction starting from the reaction solution and self-sustaining due to the thermal effect of the combustion reaction [48][49][50]. The combination of high temperatures in the reaction zone and abundantly evolved gaseous products leads to the formation of nanocrystalline products aggregated into foam-like structures [51,52]. Solution combustion method allows not only to synthesize almost the entire series of stable rhombic REO (except ScFeO 3 and PmFeO 3 ), but also to obtain their metastable hexagonal forms [44,53,54]. ...
In this paper, nanopowders based on iron-deficient Sc2-xFexO3 (x = 0.17–0.47) nanocrystals with bixbyite structure and crystallite size of 3.7–38.9 nm were successfully synthesized via solution combustion. Variable glycine-to-nitrate (G/N) ratio was the main controlling factor. A wide range of experimental and computational methods were used to analyze the impact of spatial constraints on the resulting solid-state products. It was found that solution combustion mode greatly influenced on the temperature and gaseous products in the reaction zone. Volume (G/N = 0.4–0.8, Tmax = 1179–1511 °C), self-propagating (G/N = 1.0–1.4, Tmax = 614–957 °C) or smoldering (G/N = 0.2, Tmax = 443 °C) combustion modes were acquired during the synthesis depending on G/N ratio. It was shown that the formation of impurity phases of am-Fe2O3 (Tmax < 850 °C), c-Fe3O4 (900 °C < Tmax < 1500 °C) or c-FeO (Tmax > 1500 °C) was possible, depending on the combustion temperature. Besides, the combustion mode affected the porous and surfacial structure of resulting mesoporous nanopowders – specific surface area and total pore volume varied in ranges of 1.7–82.8 m²/g and 0.0088–0.1538 cm³/g, consequently. Chemical composition and unit cell parameters of Sc2-xFexO3 showed the positive deviation from Vegard's law. The average sizes of the interpore thickness (h) depending on G/N ratio were found from values of specific surface area and pycnometric density of nanopowders, which made it possible to establish the presence of spatial constraints for the crystals' growth of Sc2-xFexO3 at h values below 10 nm. Analysis of aspect (h/D) ratio allowed to determine synthetic parameters which led to mono- or polycrystalline structure of interpore space in resulting Sc2-xFexO3-based nanopowders. The results and patterns established in this paper allowed to synthesize a new type of foam-like functional materials based on rare-earth ferrites.
... The former NPs include Sb-based NPs (for example, used in sensors and semiconductors (Chin et al., 2010)), Sn-based NPs (e.g. in batteries (Zhang et al., 2008)), Co-and Ni-based NPs (e.g. magnetic applications (Khort et al., 2018;Johnston-Peck et al., 2009)), Mn NPs (e.g. water treatment), and Y 2 O 3 NPs (e.g. ...
Increased use and production of engineered nanoparticles (NPs) lead to an elevated risk of their diffuse dispersion into the aquatic environment and increased concern on unknown effects induced by their release into the aquatic ecosystem. An improved understanding of the environmental transformation processes of NPs of various surface characteristics is hence imperative for risk assessment and management. This study presents results on effects of natural organic matter (NOM) on the environmental transformation and dissolution of metal and metal oxide NPs of different surface and solubility properties in synthetic freshwater (FW) with and without NOM. Adsorption of NOM was evident on most of the studied NPs, except Sb and Sb2O3, which resulted in the formation of negatively charged colloids of higher stability and smaller size distribution compared with the same NPs in FW only. The dissolution rate of the NPs in the presence of NOM correlated with the strength of interactions between the carboxylate group of NOM and the particle surface, and resulted in either no (Mn, Sb, ZnO NPs), increased (Co, Sn NPs) and decreased (Ni, NiO, Sb2O3, Y2O3 NPs) levels of dissolution. One type of metal NP from each group (Mn, Ni, Sn) were investigated to assess whether observed differences in adsorption of NOM and dissolution would influence their ecotoxic potency. The results showed Mn, Ni, and Sn NPs to generate intracellular reactive oxygen species (ROS) in a time and dose-dependent manner. The extent of ROS generation in FW was similar for both Mn and Ni NPs but higher for Sn NPs. These findings are possibly related to interactions and infiltration of the NPs with the cells, which lead to redox imbalances which could induce oxidative stress and cell damage. At the same time, the presence of NOM generally reduced the intracellular ROS generation by 20–40% for the investigated NPs and also reduced cytotoxicity of Sn NPs, which can be attributed to the stronger interaction of carboxylate groups of NOM with the surface of the NPs.
... Until recently, only oxide materials were thus prepared. However, latest studies show the possibility of synthesizing nanopowders of metals Ni, Co, Cu, Pt [16] and Ni-Fe alloys [17,18]. ...
... Derivative modifications of the SCS approach have been developed over time: solgel combustion synthesis (SGCS) [40,[44][45][46] and spray solution combustion synthesis (SSCS) [47,48], allowing the synthesis of non-oxide compounds never obtained before by the SCS method. These include pure metals [47,49,50], binary metal alloys [51][52][53], nitride [45,54,55] and carbide [56] ceramics. Both methods have advantages over traditional SCS regarding process controllability by the precise control of the main synthesis parameters, such as fuel-to-oxidizer molar ratio (ϕ), furnace temperature (T furn ) and carrier gas flow rate [40]. ...
Multicomponent transition metal-based nanomaterials (MTMAs) are of interest to the materials science community because of their structure-tunable properties. However, it is challenging to support the phase stabilization and homogeneous distribution of the constituent elements within a single phase. Herein, we report the successful one-step combustion syntheses of a novel quaternary antiperovskite nitride, (Co 0.33 Cu 0.33 Ni 0.33) 4 N, and a ternary CoCuNi alloy as examples of MTMAs. The synthesized nanomaterials have hollow spherical and sponge-like morphologies. We also share the results of a study of the parameters that influence the alloy and nitride phase formation and discuss possible mechanisms for the combustion synthesis of the MTMAs. It was established that the synthesis approach as well as adjusting the environment conditions created through the main synthesis parameters, including molar ϕ ratio, furnace temperature (T furn) and carrier gas flow rate, are the key characteristics responsible for the formation and stabilization of specific phase composition and morphology of the final product. The optimal parameters for the ternary CoCuNi alloy synthesis by sol-gel combustion were ϕ in the range of 1.25-1.5. The stoichiometric (Co 0.33 Cu 0.33 Ni 0.33) 4 N phase stabilizes during a spray combustion synthesis with ϕ = 3, T furn = 900 • C and a flow rate of 4 L/min. The produced alloy possesses a high saturation magnetization of 74 emu/g, while the nitride retains only 11 emu/g. The study of the nitride phase's hydrogenation reaction showed ∼96 % efficiency of NH 3 evolution (3.797 mmol/g).
... The choice of the appropriate fuel should be a basic parameter since it is answerable for changing the mechanism and kinetics of the combustion and hence it allows the likelihood to control the product characteristics. The each fuel should act in various ways and as an outcome; its impact on the final product properties should be investigated [82]. There are no precise investigation about the attainability of choosing the correct fuel to grow new materials or improved with higher shading power [83][84][85][86][87]. Table 1 represents list of some fuels that are used in combustion synthesis process (see Table 1). ...
The combustion method is a material preparation method that is gaining popularity in the academic and industrial fields due to its simple and economical procedure for the preparation of advanced ceramics, catalysts and nanomaterials. Combustion method offers a flexible approach of obtaining nanomaterials. Energy necessities for the combustion method are constrained to the start step only, since the ideal products are obtained by utilizing the heat generated by exothermic reactions happening between the reactants. An assortment of advanced materials can be incorporated utilizing combustion synthesis, following two unique methods of the combination, one is self-propagating mode and the other is thermal explosion mode. In this review paper, special attention has been paid to some epic advances in nanomaterials and various applications of combustion synthesized nanomaterials.
... Morphology, microstructure, and elemental distribution of the prepared Al J Mater Sci reaction process [30][31][32]. Obviously, the TEM images under lower and higher magnifications in Fig. 2b, c confirm the prepared Al 3? -doped nanocrystalline powder is mainly composed of agglomerates constructed by many spherical ultrafine primary particles. The average crystallite size obtained from Rietveld refinement is 14 nm. ...
Owing to their entropy stabilization and multi-principal effect, transition-metal-based high-entropy oxides are attracting extensive attention as an effective family of anode materials for lithium ion batteries (LIBs). Herein, spinel-type (Al0.2CoCrFeMnNi)0.58O4-δ HEO nanocrystalline powder with high concentration of oxygen vacancies is successfully prepared by the method of solution combustion synthesis (SCS), and explored as a novel anode active material for LIBs. As compared to (CoCrFeMnNi)0.6O4-δ, the inactive Al³⁺-doped (Al0.2CoCrFeMnNi)0.58O4-δ anode provides more than twice the reversible specific capacity of 554 mAh g⁻¹ after 500 cycles at a specific current of 200 mA g⁻¹, accompanied with good rate capability (634 mAh g⁻¹ even at 3 A g⁻¹) and cycling performance. The enhanced electrochemical properties can be attributed to that inactive Al³⁺-doping resulted into the more space for Li⁺ intercalation and deintercalation, enhanced structural stability, and the improved electronic conductivity and Li⁺ diffusivity.
Graphical abstract
... The fast drying allows obtaining precursor in the form of a porous easy combustible foam. The temperature of the furnace for SCS reaction initiation was chosen based on an analysis of the result of our previous study 14,36,37 . It was shown, the decomposition of the precursor as a result of the combustion reaction mostly finishes up to ∼ 500 °C. ...
Abstract Graphene and its analogs in combination with metal nanopowders are among the most promising catalysts for various industry valuable processes. The newly obtained solution combustion synthesized graphene–Cu and graphene–CuNi nanocomposites were examined in heterogeneous catalysis of thermal activated CO oxidation and photoactivated degradation of acid telon blue and direct blue dyes. The nanocomposites are characterized by a closely connected solution combustion synthesized graphene-metal structure with a number of graphene layers from 1 to 3 and fine metal grains sizes of 31 nm (Cu) and 14 nm (CuNi). The experimental data showed the obtained graphene-metal nanocomposites are among the most effective catalysts for CO oxidation with a temperature of 100% conversion of 150 °C and 200 °C for Cu and CuNi containing catalysts, respectively. At the same time, both nanopowders were found inactive for dyes degradation.
... According to methodology, suggested in [48], the SCS process could be divided into 4 separate stages with an ignition temperature of 134°C and maximal combustion temperature of 538°C and represented as a complex of exothermic decomposition reactions of organic fuel and metals nitrate with the formation of metals oxide and a mixture of gases, like nitrogen, carbon dioxide, H 2 O and others. In this case, an excess of reducing agent, which, due to thermal decomposition, forms an inert or even reduction atmosphere in reaction volume over freshly synthesized metal oxide nanoparticles. ...
The fine bimetallic Cu-Ni integrated nanoparticles were obtained by the modified solution combustion synthesis in the air using glycine as a fuel. The synthesized nanoparticles were studied by XRD analysis using single-and two-phase approaches for Rietveld refinement simulation, by scanning TEM-EDX spectroscopy and HR TEM technics. The data analysis for nanoparticles' characteristics showed close integration of Cu and Ni crystalline structures, which tend to form a bimetallic alloy. The process of bimetallic nanoparticles' formation was computer simulated using the Monte Carlo method in the temperature range from 300 to 600 K. The simulation established the patterns of neck formation for two cases of the initial arrangement of copper and nickel nano-particles: direct contact and relative displacement of 0.2 nm. It was established, that in the case of relative displacement in comparison with the case of the direct contact the coalescence process is «delayed» by 60-80 K upon heating. A description of the energy spectra of two particles during the neck forming has been provided.
... Ref. [33] Ref. [34] Ref. [35] Ref. [ Table 2). The high M s values contribute to increasing permeability in GHz frequency range, which could effectively improve impedance matching, according to the Snoek's limit expressed as follows [30]: ...
Broadband and lightweight microwave absorbers have gained considerable research interest in overcoming electromagnetic interference pollution. Here, mixture of two phase (fcc and hcp) metallic cobalt powders with broadband absorption was synthesized through solvothermal method using ethylene glycol as the reducing agent. The effect of NaOH content on the structure and morphology of the prepared Co powders is investigated by X-ray diffraction and field-emission scanning electron microscopy. Ring samples of 7.00/3.04 mm of out/inner diameter were prepared with paraffin for microwave absorption testing by vector network analyzer. It was observed that the increase of NaOH content caused a relative higher generation of hcp-Co phase and formation of irregular microspheres. The reflection loss (RL) peak and effective absorbing bandwidth (EABW, RL ≤ − 10 dB) shifted towards lower frequency when the sample thickness increased from 1.00 to 3.00 mm with EABW covering almost all the C, X and Ku bands (4–18 GHz). The bi-phase Co prepared in a low base solution exhibited enhanced microwave absorption properties. The width of largest EABW has reached 6.33 GHz covering partial Ku band and almost all the X band with optimal RL of − 56.95 dB at a sample thickness of only 1.85 mm, which is superior to EABW of Co crystals reported earlier. We proposed that such a wide EABW is due to the fact of Z values closed to 1.0 (0.8 ≤ |Z| ≤ 1.2) at almost the whole frequency range. This indicates that the prepared bi-phase Co powders are excellent microwave absorbers with large bandwidth, have good prospects.
... All the samples were synthesized by the microwaveassisted SCS method, applied earlier for metallic nanopowder synthesis [39][40][41]. In general, bismuth(III)-nitrate pentahydrate with 2% excess and CA were dissolved in a minimum volume of acidic aqueous solution in order to prevent bismuth subnitrate precipitation. ...
In this study, nanocrystalline (18–28 nm) perovskite-like bismuth ferrite rare earth-doped powders (Bi 0.9 RE 0.1 FeO 3 , where RE = La (BLaFO), Eu (BEuFO), and Er (BErFO)) were obtained by microwave-assisted modification of solution combustion synthesis (SCS). The influence of high load La ³⁺ , Eu ³⁺ , and Er ³⁺ doping on structural, optical, and electrical properties of BiFeO 3 was investigated. It was found that rare earth doping along with fast phase formation and quenching significantly distorts the crystal cells of the obtained materials, which results in the formation of mixed rhombohedral- (R3c-) orthorhombic (Pbnm) crystal structures with decreased lengths of Bi-O and Fe-O bonds along with a decreasing radius size of doping ions. This promotes reduction of the optical band gap energy and suppression of ionic polarization at high frequencies and results in enhanced dielectric permittivity of the materials at 1 MHz.
... At the present time solution combustion synthesis is used for the preparation of oxide-based catalysts with a surface area higher than those obtained by coprecipitation methods. Recently, several metals (Ni, Cu, Fe, Co) have been synthesized by this method [6][7]. The aim of this work is to investigate the possibility of bimetallic catalysts synthesis by SCS in normal air atmosphere without additional post reduction and study of catalytic activity in CO oxidation. ...
Solution combustion synthesis (SCS) is typically used to produce nanostructured oxides and bulk metallic materials for a variety of application including catalysis. Here, we report SCS of thin films catalysts supported on mullite-cordierite ceramics. The catalysts were characterized by XRD, SEM/EDX, and their catalytic activity has been determined in CO oxidation. Also, the effect of different types of fuels (urea, citric acid and hexamethylenetetramine) on the combustion process and characteristics of resultant solid products were investigated.
Materials with multiple principal elements (middle- and high-entropy materials), are used in emerging applications in various fields due to their unique properties, driven by configuration entropy. Improved understanding and experimental...
The novelty of the present paper was the construction of a new reactor to synthesize the cobalt nanoparticles (NPs) by solution combustion synthesis (SCS) method for reducing the processing temperature of cobalt production. To perform the SCS process, a reactor was designed and constructed and the synthesis process was performed using cobalt (II) nitrate-6-water as oxidizer along with glycine and urea as fuels. The effect of the molar ratio of glycine fuel to oxidizer and fuel type parameters on the purity of the products were examined. The XRD and FESEM analysis were used to characterize the obtained products. Based on FESEM analysis and the Scherrer equation, the mean size of all samples was under 100 nm and the reactor loaded with the glycine fuel provided the lowest particle sizes by around 14 nm and produced particles with better surface adhesion. It was found that the glycine fuel was determined the best fuel compared to urea because of producing temperatures near 400°C. Compared to traditional gas-solid reactions, the operating temperature of this process was under 400°C which was considerably lower than the operating temperature of gas-solid reactions occurred at temperatures higher than 800°C.
With the increasing awareness of environmental protection and health, the preparation of metal oxide nanomaterials by environmentally friendly methods is favored by more and more researchers both at home and abroad. The preparation of metal oxide nanomaterials by a microwave-induced solution combustion synthesis method can significantly reduce the reaction time, energy consumption, and the use of toxic chemicals, which is an energy-saving, environmentally friendly method for nanomaterials synthesis. In addition, the microwave-induced solution combustion synthesis (MISCS) method has many advantages such as fast reaction speed, high selectivity, small product size, and homogeneous composition. This paper briefly describes the mechanism of the MISCS and its advantages in the synthesis of metal oxide nanomaterials, the related studies on microwave-induced solution combustion synthesis of metal oxide nanomaterials, and the effects of process parameters on the microstructure and properties of metal oxide nanomaterials synthesized by MISCS. Furthermore, some technical difficulties facing the synthesis of metal oxide nanomaterials by MISCS are summarized, and the future direction has also been prospected.
CeO2, Cu0.05Ce0.95O2-δ, Ni0.04Ce0.96O2-δ, Cu0.05Ni0.05Ce0.90O2-δ, catalysts were synthesised via solution combustion technique using urea as a fuel. The as pre-preared catalysts were characterised via X-ray powder diffraction, Brunauer-Emmett-Teller surface area analysis, transmission and scanning electron microscopy analysis. The characterisation techniques strongly suggested that all the catalysts were prepared successfully, and that copper and nickel were successfully incorporated into the lattice structure of ceria. The effect of the reaction conditions on the catalytic properties of the synthesised material were studied in detail using Cu0.05Ni0.05Ce0.90O2-δ as the model catalyst. The effect of temperature, solvents and co-oxidants was investigated in optimisation studies. A combination of acetonitrile, tert-butyl hydroperoxide and a temperature of 60 °C were found to be optimal after 24 hours and used for all catalysts. All catalysts were found to be active in styrene oxidation under these conditions, with styrene conversion as high as 69% over Ni0.04Ce0.96O2-δ, and selectivity to benzaldehyde and styrene oxide 38 and 26% respectively.
High-entropy oxides (HEOs) offer unique features through a combination of incompatible metal cations to a single crystalline lattice. Owing to their special characteristics such as abundant cation compositions, high entropy stabilization, chemical and thermal stability, and lattice distortion effect, they have drawn ever-increasing attention for various applications. However, very few studies have been reported for catalytic application, and developing HEOs with large surface areas for efficient catalytic application is still in infancy. Herein, we design nanostructured HEO of (FeNiCoCrCu)3O4 using metal-organic frameworks (MOFs) as sacrificial templates to achieve a large surface area, high density of exposed active sites, and more oxygen vacancies. Single-crystalline phase HEOs with surface area as large as 206 m2 g-1 are produced and further applied as bifunctional electrocatalysts for the urea oxidation reaction (UOR) and oxygen evolution reaction (OER). Benefiting from enhanced oxygen vacancies and a large surface area with abundant exposed active sites, the optimized HEO exhibited excellent electrocatalytic activity toward UOR with a very low potential of 1.35 V at the current density of 10 mA cm-2 and showed long-term stability for 36 h operation, making a significant catalytic performance over previously reported HEOs. Moreover, the HEO demonstrated an efficient catalytic performance toward OER with a low overpotential of 270 mV at 10 mA cm-2 and low Tafel slope of 49 mV dec-1. The excellent catalytic activity is ascribed to the starting MOF precursor and favorable high-entropy effect.
Mine gas explosion seriously threatens the safety of coal mine production. Existing gas explosion control materials and technologies cannot effectively control the occurrence of gas disasters. Aiming at the current limitations of powder explosion suppressants in suppressing gas explosions in mines, this paper analyzes the special flame retardant and explosion suppression effects of nano powders from the suppression effect of free radicals in the explosion process based on the theory of surface effects of nano powders. The anti-explosion mechanism of nano-powder on mine gas, and the performance characterization parameters of nano-anti-explosion powder were proposed. In this paper, the self-improved 20 L near-spherical gas explosion suppression experiment system is used to perform the explosion suppression experiment of nanometer powder. The results of this study show that compared with micron-level powders, nano-powders have a better anti-explosion effect. The maximum explosion pressure and average rate of pressure rise of methane have decreased by 70.5% and 90%, respectively, and the peak time of explosion pressure has been extended by 3 times. Therefore, thenano-explosion suppressing powder material can suppress the gas explosion in the mine and can effectively control the occurrence of gas disasters.
Superparamagnetic nanoparticles, exposed to an external variable magnetic field, undergo rapid excitation/relaxation. So-called soft magnets, typically iron-based, rapidly and completely relax when the magnetic field returns to zero. Instead, cobalt-based (CoB) hard magnets retain residual magnetization, a characteristic related with the procedure for nanoparticles (NPs) production. Many researchers are still attracted by the potential of CoB NPs for theranostics as multifaced signal probes for imaging, microrobots, enhanced thermo/radiation therapy, and drug release. Since iron oxide NPs are the only magnetic NPs approved for human use, they are of reference for analyzing the potential of the disregarded CoB NPs. In vitro observed toxicity of CoB NPs, largely attributable to cobalt ions and other chemical species released by dissolution, excluded them from further investigations in humans. Nevertheless, experimental evidences documenting the in vivo toxicity of engineered CoB NPs remain very few. The surface functionalization adds newer properties and could improve the biocompatibility of NPs, critical for the clinical exploitation. In our opinion, it would be worth to further exploit the potential of finely tunable properties of CoB NPs in in vivo systems in order to establish a systematic database of properties and effects suitable for human application.
An equimolar spinel (Al1/6Co1/6Cr1/6Fe1/6Mn1/6Ni1/6)3O4 high-entropy oxide (HEO) was developed as a novel oxide magnetic material. The as-synthesized nanocrystalline powder of high purity and homogeneity was obtained by a facile solution combustion synthesis method with an average crystalline size of about 12 nm. To prove utility, the magnetic property was measured and the as-synthesized nanocrystalline powder showed ferrimagnetism below the Curie temperature 248 K. The long-range ferrimagnetic behavior can be understood by the quite larger super-exchange interactions due to the extreme chemical disorder in the HEO.
A new class of high-entropy spinel oxides, (Cr0.2Fe0.2Mn0.2Ni0.2Zn0.2)3O4 and (Cr0.2Fe0.2Mn0.2Co0.2Zn0.2)3O4 nanocrystalline powders, has been synthesized by solution combustion synthesis. Their microstructures and magnetic properties were compared with those of (Cr0.2Fe0.2Mn0.2Co0.2Ni0.2)3O4. All the oxides were identified to have the spinel crystal structure (Fd-3m) with average crystallite size of about 24 nm, and their lattice parameters found to decrease with reduction in the electronegativity of Ni²⁺, Co²⁺ and Zn²⁺. Furthermore, nonmagnetic Zn²⁺ substitution for either magnetic Co²⁺ or Ni²⁺ weakened the ferromagnetic ordering and magnetic moments, showing the controllable magnetic property of this new class of high-entropy oxides.
The application of metabolites from the modern clinic (patient care environments including hospitals and medical facilities) has become an important part of energy research as these materials are readily available at low-cost and are non-toxic to handle in large quantities for catalyst development in the chemical industry. A modified Solution Combustion Synthesis (SCS) route was utilized in the preparation of nickel oxide, NiO nanomaterials using Dextran/Trisodium Citrate Dihydrate and Dextran/Sodium Carboxymethyl Cellulose (Na-CMC). The catalysts were then applied towards the electrocatalytic decomposition of urea, a metabolite from human and animal urine for Direct Urea Fuel Cell (DUFC) technology. Results from the catalysis demonstrated that the sample prepared via Dextran/Trisodium Citrate Dihydrate had the greatest Electroactive Surface Area (ESA) of 146 cm2mg, potentially a result of the well-defined clusters produced using the citrate coordinating species to produce individual particles.
A single-step method for the preparation of metastable ϵ-Fe 3 N nanoparticles by combustion of reactive gels containing iron nitrate (Fe(NO 3 ) 3 ) and hexamethylenetetramine (C 6 H 12 N 4 ) in an inert atmosphere is reported. The results of Fourier transform infrared spectroscopy (FTIR) and thermal analysis coupled with dynamic mass spectrometry revealed that the exothermic decomposition of a coordination complex formed between Fe(NO 3 ) 3 and HMTA is responsible for the formation of ϵ-Fe 3 N nanoscale particles with sizes of 5-15 nm. The magnetic properties between 5 and 350 K are characterized using a superconducting quantum interference device (SQUID) magnetometer, revealing a ferromagnetic behavior with a low-temperature magnetic moment of 1.09 μ B /Fe, high room temperature saturation magnetization (∼80 emu/g), and low remanent magnetization (∼15 emu/g). The obtained value for the Curie temperature of ∼522 K is close to that (∼575 K) for bulk Fe 3 N reported in the literature.
The available technologies used for the prepration of elemental silicon (Si), including the traditional carbothermal technology of producing bulk Si, pyrolysis-based methods of producing Si nanoparticles and the metallothermic fabrication of state of the art nanostructured Si powders are all considered energy and time-intensive processes, with ssociated environmental issues. Herein, for the first time, a combustion synthesis methogology, indicated by the occurance of an inginition event followed by the immediate completion of the process, is used for the prepration of nanostructured Si for energy applications. In this process, Si powders are directly extracted from sea sand by a novel ultra-fast shock-wave combustion synthesis (SWCS), in which KClO4 is employed as the combustion agent to promote the imediate reduction of SiO2. The reaction is completed at an ignition temperature of about 550 °C, requiring virtually no dwell time. The process is scalable, green and carbon-free with a low energy consumption of about 100 kWh ton-1, less than one percent of that of the current technologies. The Si product possesses a nanostructured mesoporous integrated sheet-like (NMIS) morphology, with an excellent and stable Li storage performance. The machanism involved in the proposed method is also discussed. The feasibility of SWCS approach for the preparation of Si is demonstrated in this article, based on which a variety of nanostructured materials is expected to be producible by this method.
A facile and efficient combustion synthesis method is proposed to synthesize single-crystal silver nanoparticles (AgNPs) by using high chemical activity nano-Aluminum powder as a reducing agent and silver oxide as an oxidant. The synthesized samples were characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and ultraviolet-visible spectroscopy analysis. The results indicate that the as-prepared spherical AgNPs are of a single-crystal structure with an average size of about 40 nm. Moreover, the formation mechanism of AgNPs was also investigated by closed bomb test and high-speed video recording. It is observed that a large amount of energy which is released instantaneously makes the reaction occur at a rapid speed, so that the nucleation rate of AgNPs is greater than the growth rate. This study opens up a promising route for high-yield and highquality AgNPs, as well as various other metal nanoparticles.
Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol-gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual properties are outlined. To demonstrate the versatility of the approach, several application categories of SCS produced materials, such as for energy conversion and storage, optical devices, catalysts, and various important nanoceramics (e.g., bio-, electro-, magnetic), are discussed.
To address the trade-off between strength and electrical conductivity, we propose a strategy: introducing precipitated particles into a structure composed of deformation twins. A Cu-0.3%Zr alloy
was designed to verify our strategy. Zirconium was dissolved into a copper matrix by solution treatment prior to cryorolling and precipitated in the form of Cu5Zr from copper matrix via a subsequent aging treatment. The microstructure evolutions of the processed samples were investigated by transmission electron microscopy and X-ray diffraction analysis, and the mechanical and physical behaviours were evaluated through tensile and electrical conductivity tests. The results demonstrated that superior tensile strength (602.04 MPa) and electrical conductivity (81.4% IACS) was achieved. This strategy provides a new route for balancing the strength and electrical conductivity of copper alloys, which can be developed for large-scale industrial application.
Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.
The effect of tetra ethyl ammonium bromide (TEAB) as an additive on the structural, morphological characteristics of the cobalt metal produced from aqueous sulphate solutions was investigated. The concentration of TEAB was varied in a range of 1-50 mg/L to evaluate its effect on current efficiency, energy consumption and quality of electrodeposited cobalt metal. Smooth and bright deposits of cobalt were obtained at low concentration of TEAB (10 mg/L) maintaining a current efficiency of 99.6%, with a low energy consumption of 2.38 kW·h/kg. X-ray diffraction studies reveal that (100) plane is the most preferred plane of crystal growth during cobalt electrodeposition. Scanning electron micrographs indicate that smooth and uniform deposit of cobalt is obtained at 10 mg/L beyond which the deposit quality deteriorates. Cyclic voltammetric studies indicate that the presence of TEAB in the electrolytic bath polarizes the cathode and decreases the cathodic current considerably. XPS results confirm the electrodeposition of high pure cobalt with no sign of chemical bonding with TEAB as evident from the FTIR spectra.
Refractory high-entropy alloys (HEAs) are a class of emerging multi-component alloys, showing superior mechanical properties at elevated temperatures and being technologically interesting. However, they are generally brittle at room temperature, fail by cracking at low compressive strains and suffer from limited formability. Here we report a strategy for the fabrication of refractory HEA thin films and small-sized pillars that consist of strongly textured, columnar and nanometre-sized grains. Such HEA pillars exhibit extraordinarily high yield strengths of ∼10 GPa-among the highest reported strengths in micro-/nano-pillar compression and one order of magnitude higher than that of its bulk form-and their ductility is considerably improved (compressive plastic strains over 30%). Additionally, we demonstrate that such HEA films show substantially enhanced stability for high-temperature, long-duration conditions (at 1,100 °C for 3 days). Small-scale HEAs combining these properties represent a new class of materials in small-dimension devices potentially for high-stress and high-temperature applications.
Colloidal assemblies are used to synthesize FCC cobalt nanoparticles. The particles are coated, extracted from micelles, and characterized by transmission electron microscopy, small angle X-ray scattering, and electron and X-ray diffraction spectroscopy. These cobalt metal particles are stable in air, have a narrow size distribution, and on deposition on a graphite support, spontaneously form a 2D hexagonal network. The magnetic properties are compared when they are dispersed in a solvent and organized in 2D superlattices. Changes in the hysteresis loop and in the blocking temperature are observed and attributed to collective flip of the magnetization of adjacent particles.
Recent multi-principal element, high entropy alloy (HEA) development strategies vastly expand the number of candidate alloy systems, but also pose a new challenge-how to rapidly screen thousands of candidate alloy systems for targeted properties. Here we develop a new approach to rapidly assess structural metals by combining calculated phase diagrams with simple rules based on the phases present, their transformation temperatures and useful microstructures. We evaluate over 130,000 alloy systems, identifying promising compositions for more time-intensive experimental studies. We find the surprising result that solid solution alloys become less likely as the number of alloy elements increases. This contradicts the major premise of HEAs-that increased configurational entropy increases the stability of disordered solid solution phases. As the number of elements increases, the configurational entropy rises slowly while the probability of at least one pair of elements favouring formation of intermetallic compounds increases more rapidly, explaining this apparent contradiction.
Ferromagnetic nanoparticles are covalently modified in order to enhance the dispersion stability as well as the antifouling properties. Insertion of an azide moiety allows “click”-reaction of a relevant tag molecule. This and the high saturation magnetization of the presented nanocomposite offer a promising platform for magnetic biosensors.
Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.
High-entropy alloys (HEAs) can have either high strength or high ductility, and a simultaneous achievement of both still constitutes a tough challenge. The inferior castability and compositional segregation of HEAs are also obstacles for their technological applications. To tackle these problems, here we proposed a novel strategy to design HEAs using the eutectic alloy concept, i.e. to achieve a microstructure composed of alternating soft fcc and hard bcc phases. As a manifestation of this concept, an AlCoCrFeNi2.1 (atomic portion) eutectic high-entropy alloy (EHEA) was designed. The as-cast EHEA possessed a fine lamellar fcc/B2 microstructure, and showed an unprecedented combination of high tensile ductility and high fracture strength at room temperature. The excellent mechanical properties could be kept up to 700°C. This new alloy design strategy can be readily adapted to large-scale industrial production of HEAs with simultaneous high fracture strength and high ductility.
The combustion synthesis technique using glycine and urea as fuels and cobalt nitrate as an oxidizer is capable of producing well-crystallized Co3O4, CoO, as well as metallic Co powders. An interpretation based on the thermodynamic viewpoint and the measurement of the combustion temperatures during the reactions occurring for various fuel-to-oxidant ratios was proposed for a study of the nature of combustion and its correlation with the characteristics of as-synthesized powders. The largest measured specific surface area of the powders was 36 m2/g at a 0.14 glycine-to-nitrate ratio. The crystallites were nano-sized ranging from approximately 23 to 90 nm.
We have synthesized polycrystalline samples of the noncentrosymmetric superconductor Mo3Al2C by arc and RF melting, measured its transport, magnetic and thermodynamic properties, and computed its band structure. Experimental results indicate a bulk superconducting transition at Tc∼9.2 K while the density of states at the Fermi surface is found to be dominated by Mo d orbitals. Using the measured values for the lower critical field Hc1, upper critical field Hc2, and the specific heat C, we estimated the thermodynamic critical field Hc(0), coherence length ξ(0), penetration depth λ(0), and the Ginzburg-Landau parameter κ(0). The specific-heat jump at Tc, ΔC/γTc=2.14, suggests that Mo3Al2C is moderately to strongly coupled, consistent with the fast opening of the gap, as evidenced by the rapid release of entropy below Tc from our electronic specific-heat measurements. Above 2 K the electronic specific heat exhibits the power-law behavior, suggesting that synthesis of single crystals and measurements at lower temperature are needed to establish whether the gap is anisotropic. The estimated value of the upper critical field Hc2(0) is close to the calculated Pauli limit, therefore further studies are needed to determine whether the absence of an inversion center results in a significant admixture of the triplet component of the order parameter.
Ni- and Co-substituted ZnO nanoparticles were synthesized using forced hydrolysis of acetate metallic salts in a polyol medium. The X-ray diffraction patterns show a hexagonal wurtzite structure (space group P63mc). The characteristic absorption bands of UV–vis-IR spectra are correlated with the d–d transitions of tetrahedrally coordinated Co2+ and Ni2+ ions in octahedral and tetrahedral sites. The photoluminescence spectra exhibited a typical ZnO UV-exitonic emission band around 380 nm and a broad band between 400 and 500 nm that might be ascribed to the intrinsic defects in the ZnO material. The transmission electron microscopy displays spherical particles with a diameter between 20 and 30 nm. The magnetic measurements reveal that Zn1–xNixO and Zn1–xCoxO nanoparticles show, respectively, ferromagnetic and paramagnetic behavior at 5 K. Homogeneous distributions of Co and Ni ions in the particles observed by filter imaging analysis indicates that there is no evidence of Co or Ni metal throughout the powders.
Co nanoparticles with three different crystal structures were synthesized in a microfluidic reactor through manipulation of reaction times, flow rates, and quenching procedures. Cobalt nanoparticles of face-centered cubic (β) phase were obtained from a high flow rate of the reactants followed by in situ quenching of the reaction. hcp and ε-cobalt nanoparticles were obtained at a low flow rate of the reactants followed by in situ quenching and delayed quenching, respectively. The crystal structures were characterized using Co K-edge X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction (XRD), and selected area electron diffraction (SAED). In situ XANES measurements on Co nanoparticles coming out of the outlet of the microfluidic reactor at different flow rates seem to indicate that the difference in flow rate influences the nucleation process in a critical way and that particle growth occurs mainly outside the reactor. The magnetic properties of the cobalt nanoparticles, measured using a SQUID magnetometer system, showed significant differences among the samples and are consistent with the three different crystal structures.
Exposes a Powerful Material-Making Tool Dedicated to the physical, chemical, and structural transformations that take place during combustion synthesis (CS) of advanced materials, Combustion for Material Synthesis analyzes the nature of solid flame phenomenon and provides readers with undisputed proof that 'fire' is a powerful tool used in making materials. Of interest to specialists in the field of materials engineering, this book explores the physical and chemical principles of synthesis of materials in the self-sustained combustion mode. It describes mechanisms for a variety of solid-solid and gas-solid reactions and examines structure and properties of different materials produced by CS. The authors discuss a wide range of topics, including phenomenology, theory, experimental methods and observations, as well as properties of the product synthesized and approaches for large-scale materials production using the combustion synthesis technique. They examine conventional concepts and present recent breakthroughs in the field of materials synthesis by rapid self-sustained reactions that include fabrication of different nanomaterials. They compare CS with other methods, factoring in different types of combustion processes, including processes that can occur in a vacuum, inert gas, or oxygen-free atmosphere. Covering research on topics that have been around for a while, but not widely circulated, this work: •Outlines in detail both fundamental aspects of CS, including modern theoretical approaches and advanced in situ experimental method •Examines the advantages and disadvantages, achievements, and challenges remained in heterogeneous combustion used for material synthesis •Explores the emergence of a new fundamental direction in material science, i.e., structural macrokinetics •Details new technologies that are based on fundamental scientific discoveries and innovative scientific ideas •Analyzes structure and properties of variety of CS materials, including nanomaterials Authored by world-recognized specialists in the field of combustion synthesis for advanced materials, Combustion for Material Synthesis presents the state of the art in R&D in the field of CS, focusing on the fabrication of novel materials. It is intended for researchers, engineers, and graduate students from different disciplines and is also suggested as recommended reading for materials science courses.
to Thermal Analysis Techniques and Applications Edited by Michael E. Brown Chemistry Department, Rhodes University, Grahamstown, South Africa KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW eBook ISBN: 0-306-48404-8 Print ISBN: 1-4020-0472-9 ©2004 Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow Print ©2001 Kluwer Academic Publishers Dordrecht All rights reserved No part of this eBook may be reproduced or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: http://kluweronline. com and Kluwer's eBookstore at: http://ebooks. kluweronline. com CONTENTS Preface to the First Edition, Chapman & Hall, London, 1988 ix About the First Edition of this Book x Preface to the Second Edition xi 1. INTRODUCTION 1. 1 Definition and History 1 1. 2 Thermal Analysis Instruments 4 References 11 2. THERMAL EVENTS 2. 1 Introduction 13 2. 2 The Solid State 13 2. 3 Reactions of Solids 14 2. 4 Decomposition of Solids 15 2. 5 Reaction with the Surrounding Atmosphere 16 2. 6 Solid-Solid Interactions 16 References 17 3. THERMOGRAVIMETRY (TG) Introduction 3. 1 19 3. 2 The Balance 19 3. 3 Heating the Sample 21 3. 4 The Atmosphere 24 3. 5 The Sample 26 3. 6 Temperature Measurement 26 3. 7 Temperature Control 28 Sample Controlled Thermal Analysis (SCTA) 29 3. 8 3. 9 Calibration 36 3. 10 Presentation of TG Data 37 3.
AbstractPure copper nanoparticles have previously been successfully produced by different combustion methods, but most of them require the usage of an inert atmosphere (N2, Ar) during synthesis process or the usage of addition post reducing of metal oxides. In this paper, novel modification of solution combustion synthesis technique for one-step metallic Cu nanoparticles preparation was developed. The main unique feature of our approach is the use of microwave assisted foam preparation. Also, the effect of different types of fuels (urea, citric acid, glycine and hexamethylenetetramine) on the combustion process and characteristics of resultant solid products were investigated. It was shown that the combination of microwave assistant foam preparation and using of hexamethylenetetramine as a fuel allows producing pure metallic Cu nanoparticles (~67 nm) by one-step solution combustion synthesis under normal air atmosphere without any post reduction.
This updated second edition puts nanotechnology into perspective by explaning issues in health, environmental and military application domains, and discusses the technology in the context of current media and ethical debates. © 2006 Dunod, Paris and 2009 The Institution of Engineering and Technology.
We report a template-free approach to prepare three-dimensional cobalt microspheres composed of nanosheets by a facile hydrothermal method. The synthesized 3D cobalt microspheres with diameter of approximately 1-2 μm have a nanosheet of ca. 18 nm. The samples were characterized by X-ray diffraction, SEM, TEM, and VSM techniques. It was found that the initial concentration of Co(NO3)2·4H2O and surfactant played an important role in the formation of 3D cobalt microspheres. The Ms value of 3D cobalt microspheres which obtained under the cationic surfactant is about 122.55 emu/g. Due to the specific structure and magnetic properties, these 3D cobalt microspheres are expected to have potential applications as candidates for catalysis, sensor and energy storage.
Hexagonal close packed dumbbell-shaped cobalt nanoparticles (Co0-hcp) have been fabricated by the polyol method. The thermal stability of these Co0-hcp nanoparticles has been studied under Fischer-Tropsch Synthesis (FTS) relevant environments such as H2 and H2/CO by using SiO2/SiNx TEM grids which allowed the structural changes of individual particles to be followed after each off line treatment. The TEM analyses demonstrated that the Co0-hcp nanodumbbells are very stable when thermally treated in H2 at 250 °C for 9 h followed by H2/CO at 230 °C, 16 bar for 5 h. These studies indicate that the hcp phase of Co is retained after FTS. Furthermore, subjecting the cobalt nanodumbbells to regeneration conditions such as reduction followed by oxidation led to hollow nanodumbbells with a polycrystalline cobalt oxide (Co3O4) shell (so-called Kirkendall effect) which disintegrated to smaller face centered cubic metallic cobalt (Co0-fcc) particles after further reduction.
Elucidating the connection between shape and properties is a challenging but essential task for a rational design of nano-particles at the atomic level. As a paradigmatic example we investigate how geometry can influence the magnetic properties of nano-particles, focusing in particular on platinum clusters of 1-2 nm in size. Through first-principle calculations, we have found that the total magnetisation depends strongly on the local atomic arrangements. This is due to a contraction of the nearest neighbor distance together with an elongation of the 2nd nearest neighbor distance, resulting in an inter-atomic partial charge transfer from the atoms lying on the sub-surface layer (donors) towards the vertexes (acceptors).
A spray solution combustion synthesis method has been developed to produce hollow spherical metal nanostructured particles. In this approach, combustion reactions in the liquid solution contribute 100% of the overall energy released during the synthesis process without the involvement of an external gaseous flame. It has been shown that this method is effective for the synthesis of spherical hollow particles of metals (Ni, Cu) with an average diameter of about 3 microns and wall thicknesses of about 20 nm.
Highly open metallic nanoframes represent an emerging class of new nanostructures for advanced catalytic applications due to their fancy outline and largely increased accessible surface area. However, to date, the creation of bimetallic nanoframes with tunable structure remains a challenge. Herein, we develop a simple yet efficient chemical method that allows the preparation of highly composition segregated Pt-Ni nanocrystals with controllable shape and high yield. The selective use of dodecyltrimethylammonium chloride (DTAC) and control of oleylamine (OM)/oleic acid (OA) ratio is critical to the controllable creation of highly composition segregated Pt-Ni nanocrystals. While DTAC mediates the compositional anisotropic growth, the OM/OA ratio controls the shapes of the obtained highly composition segregated Pt-Ni nanocrystals. To the best of our knowledge, this is the first report on composition segregated tetrahexahedral Pt-Ni NCs. Importantly, by simply treating the highly composition segregated Pt-Ni nanocrystals with acetic acid overnight, those solid Pt-Ni nanocrystals can be readily transformed into highly open Pt-Ni nanoframes, with hardly changed shape and size. The resulting highly open Pt-Ni nanoframes are high-performance electrocatalysts for both oxygen reduction reaction (ORR) and alcohol oxidations, which are far better than those of commercial Pt/C catalyst. Our results reported herein suggest that enhanced catalysts can be developed by engineering the structure/composition of the nanocrystals.
We report here the fabrication of cobalt nanoparticles using sodium borohydride reduction of cobalt chloride in an inversed micelle solution. Cobalt chloride hexahydrate is dissolved in the inversed micelle system, which is prepared by dissolving didodecyldimethylammonium bromide (DDAB) in toluene. Addition of sodium borohydride results in a stable black colloid. TEM shows average particle sizes range from about 20Åto 75Ådepending on the reaction temperature. The interaction between cobalt and the surrounding surfactant atoms quenches the saturation magnetization of cobalt atoms by almost 70% . Adding octyl sulfide into the cobalt colloid further quenches the magnetization, and it also increase the ordering of cobalt particles on the dried TEM grid.
The reaction of Ni(COD)(2) with Hz (3 bar) in CH2-Cl-2 in the presence of poly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of approximate to 30 nm, composed of individual 3-4 nm fee Ni particles and displaying a ferromagnetic behavior whereas the same reaction in the presence of PVP K 90 leads to 4 nm, well-dispersed fee Ni particles displaying a superparamagnetic behavior. In both cases the magnetic moment per atom is similar to the value found for bulk nickel, hence demonstrating the absence of oxidation of the surface of the particles.
New classes of reactive systems that are characterized by nano-scale heterogeneity and possess extremely high reactivity, as compared to that for similar reactive systems with micro-scale heterogeneity, have attracted a vast attention of many researchers. The recent developments and trends in combustion science toward such “nano” reactive media are presented. These systems include mechanically induced composite particles, sol–gels, super thermites and multilayer nano-foils. Various combustion-based applications of such nanostructured reactive systems are also discussed.
Over the last three decades, transition-metal-catalyzed organic transformations have been shown to be extremely important in organic synthesis. However, most of the successful reactions are associated with noble metals, which are generally toxic, expensive, and less abundant. Therefore, we have focused on catalysis using the abundant first-row transition metals, specifically cobalt. In this Account, we demonstrate the potential of cobalt catalysis in organic synthesis as revealed by our research.
To meet the demands of high-efficient microwave absorption materials, cobalt superstructure was synthesized and characterized. As SEM confirmed, the cobalt superstructure was assembled by flakes. The size of cobalt superstructure was about 10 μm, and the thickness of the flake was about 500 nm. The permittivity and permeability were investigated as a function of frequency in the microwave range of 1–18 GHz. Based on the LLG equation and exchange resonance mode, three magnetic resonances, including one natural resonance and two exchange resonances were discussed. The calculated reflection loss (RL) indicated the cobalt superstructure indicated the cobalt superstructure has potential application as a promising candidate for microwave absorption. The maximum RL reached as high as −77.29 dB with a matching thickness of 1.5 mm, and the effective bandwidth with a reflection loss less than −10 dB was 3.6 GHz from 9.85 to 13.45 GHz. For cobalt superstructure, magnetic loss mainly contributed even more than dielectric loss to the microwave absorption.
Cobalt hollow microspheres were prepared by a surfactant-assisted solvothermal method in water and ethanol mixed solution. The outer diameter ranged from 1.5 to 2 mu m, and the shell with average thickness of about 250 nm was constructed by smaller cobalt nanoparticles. The surfactant polyvinylpyrrolidone (PVP) was found to play an important role in the formation of such novel morphology. Room temperature magnetic measurement of the hollow microspheres demonstrated its enhanced ferromagnetic property with a coercivity of 202 Oe. The possible formation mechanism was also discussed. The result showed a potential application in ferrofluids and other related magnetic devices.
Cobalt catalysts supported on activated carbon and on carbon nanotubes (CNTs) with different porosities were prepared by an incipient wetness impregnation method and characterized by a series of methods. The samples were reduced and then evaluated in a fixed-bed reactor for Fischer–Tropsch (FT) synthesis. The porosity of the carbon support greatly influenced the microstructure, the reducibility, the dispersion, and the FT performance of the cobalt catalysts. The carbon structure and the cobalt dispersion determined CO conversion. CNTs with larger pore sizes were more stable at high temperature in a H2 atmosphere. The cobalt particle size impacted the CO turnover frequency (TOF) and the C5+ selectivity. Larger cobalt particles (up to 7 nm) resulted in higher TOF and C5+ selectivity; for cobalt particles larger than 7 nm, no such increase in these parameters was seen. The carbon support influenced the C5+ selectivity and the C5+ hydrocarbon distribution. Interestingly, the olefin/paraffin ratio of C2 was lower than that of C3 or C4 and a positive relationship existed between the C2–C4 olefin/paraffin ratio and the C5+ selectivity.
Three kinds of cobalt particles, S1, S2, and S3, with different morphologies and crystal structures were synthesized by reduction method in liquid phase as shown in (a), (b), and (c), respectively.
As shown in (d), the minimal reflection loss of S1 is − 7.25 dB at 18 GHz corresponding to 5.5 mm, and reflection loss values exceeding − 10 dB are not obtained.
The minimal reflection loss of − 12.57 dB for S2 is observed at 14.94 GHz corresponding to the thickness of 5 mm, and the reflection loss values exceeding − 10 dB are obtained in the range from 13.99 to 15.84 GHz (e).
An optimal reflection loss value of S3 is − 19.06 dB at 17.42 GHz. For the thickness of 5 mm the reflection loss values exceeding − 10 dB are observed in the range from 16.15 to 18 GHz (f).
We report the solution phase synthesis, the structural analysis and the magnetic properties of hybrid nano-structures combining two magnetic metals. These nano-objects are characterized by a remarkable shape, combining Fe nanocubes on Co nanorods. The topological composition, the orientation relationship and the growth steps have been studied by advanced electron microscopy techniques, such as HRTEM, electron tomography and state-of-the-art 3-dimensional elemental mapping by EDX tomography. The soft iron nanocubes behave as easy nucleation centers that induce the magnetization reversal of the entire nano-hybrid, leading to a drastic modification of the overall effective magnetic anisotropy.
Palladium nanoparticles are deposited on the surface of highly magnetic carbon-coated cobalt nanoparticles. In contrast to the established synthesis of Pd nanoparticles via reduction of Pd(II) precursors, the microwave decomposition of a Pd(0) source leads to a more efficient Pd deposition, resulting in a material with considerably higher activity in the hydrogenation of alkenes. Systematic variation of the Pd loading on the carbon-coated cobalt nanoparticle surface reveals a distinct trend to higher activities with decreased loading of Pd. The activity of the catalyst is further improved by the addition of 10 vol.% diethyl-ether to iso-propanol that is found to be the solvent of choice. With respect to activity (turnover frequencies up to 11095/h), handling, recyclability through magnetic decantation, and leaching of Pd (≤6 ppm/cycle), this novel magnetic hybrid material compares favorably to conventional Pd/C or Pd@CNT catalysts.
The electrochemical behavior of Co(II) in urea-choline chloride-CoCl2 melt was investigated by cyclic voltammetry at 373 K. The results show that the reaction of Co(II) to Co is irreversible and it proceeds via a one-step two electrons transfer process. The diffusion coefficient of Co(II) was estimated to be 1.7 × 10−6 cm2 s−1 at 373 K. Electrodeposition of cobalt was studied at different cathodic potentials (-0.80 to -0.95 V) and at different temperatures (353 to 383 K) in eutectic mixture of choline chloride and urea (1:2 molar ratio). The deposits were characterized using scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). SEM images show that uniform, dense, and compact deposits were obtained at -0.80 V within a temperature range of 353 K to 373 K. EDS and XRD analysis confirm that high-purity metallic Co deposits were obtained.
The mechanism of structural transformation during combustion of nickel nitrate (oxidizer)−glycine (fuel) system is investigated by using different in situ techniques, including time-resolved X-ray diffraction (TRXRD), thermogra-vimetric analysis (TGA), differential scanning calorimetry (DSC) with dynamic mass spectrometry (MS), and high-speed infrared thermal imaging. It is shown that for initial compositions with a relatively large fuel-to-oxidizer ratio (φ), pure Ni phase forms directly in the combustion front. For fuel-lean conditions, only NiO phase can be detected. Analysis of the obtained data, including transmission and scanning electron microscopy (TEM−SEM) studies of the quenched reaction fronts, allows us to suggest the intrinsic mechanism of pure metal formation in the investigated system. It is shown that the combustion front propagates because of the reaction between N 2 O and NH 3 , which are the products of decomposition of the oxidizer and fuel. The excess of NH 3 gas produced in fuel-rich conditions rapidly (<0.2 s) reduces nickel oxide to pure metal in the reaction front.
Nickel nanoparticles (<10 nm) were successfully synthesized using a reductive method of nickel chloride with sodium borohydride in the ethanol/polyvinylpyrrolidone (PVP) system. The effects of three factors, such as the concentration of the nickel ions, the time of reaction, and the amount of PVP (surfactant), were discussed. The possible growth process of the particles and optimum reactive conditions was also investigated. The result of transmission electron microscopy (TEM) reveals that these nickel nanoparticles are spherical. The average diameter could be controlled as 2–5 nm under selected conditions. High-resolution TEM and energy-dispersive spectroscopy results indicates that the nickel nanoparticles are pure. The UV–visible light absorption spectrum shows that the peaks of nickel nanoparticles moves toward the short wavelength along with the decrease of sizes.
We review the phenomenology of exchange bias and related effects, with emphasis on layered antiferromagnetic (AFM)–ferromagnetic (FM) structures. A compilation of materials exhibiting exchange bias and some of the techniques used to study them is given. Some of the applications of exchange bias are discussed. The leading theoretical models are summarized. Finally some of the factors controlling exchange bias as well as some of the unsolved issues associated with exchange bias are discussed.
Hydrogen production by methane decomposition has been studied using a cobalt catalytic system prepared by urea precipitation. Upon calcination, the as-synthesized material converts to cobalt oxide catalyst precursor, and further thermal treatment with different reducing gas yields the actual metallic cobalt catalyst for the reaction. The reduction environment of the cobalt precursor has a substantial effect on the catalytic activity as well as on the type of carbon deposited over the catalyst. Moreover, after being reduced, the atmosphere used for catalyst pre-treatment has also a great influence in the H-2 production, the best catalytic activity being obtained when heating under a nitrogen atmosphere. These conditions lead towards a smaller size of the bulk Co nanoparticles and, therefore, to a higher surface area compared to the other two employed pre-treatment atmospheres. This results in the production of a high amount of H-2 (ca. 33 mol/mol of Co after 72 h of reaction at 600 degrees C) over the N-2 pre-treated catalyst. Accordingly, the size of the final Co nanoparticles is an essential factor determining their activity in methane decomposition, hence the reduction and/or pre-treatment conditions must be conveniently selected to avoid as much as possible the sintering and aggregative growth of the Co-based nanoparticles. Apart from hydrogen production, it is demonstrated the possibility of graphene formation by methane decomposition over Co catalysts when methane is used as reduction agent.
The optical, structural, and magnetic properties of Co, Ni, and CoxNi100-x (0 < x < 100) alloy nanoclusters in silica host obtained by the sol−gel route are presented. Throughout the entire range of composition investigated, from pure Ni to pure Co, the nanoclusters exhibit an fcc structure, with lattice parameters increasing with the Co fraction in the system. This indicates Co−Ni alloy formation. It has also been observed that the average cluster diameter increases with increasing Co fraction in the system. An enhancement of the magnetic moment was exhibited in the pure Co and Ni samples, and good agreement between the measured values and those of the corresponding bulk alloys was found for the other samples. All composites are superparamagnetic at room temperature.
The thermal decomposition of Co(NO3)2·6H2O (1) as well as that one of NO[Co(NO3)3] (Co(NO3)2·N2O4) (2) was followed by thermogravimetric (TG) measurements, X-ray recording and Raman and IR spectra. The stepwise decomposition reactions of 1 and 2 leading to anhydrous cobalt(II)nitrate (3) were established. In N2 atmosphere, cobalt oxides are finally formed whereas in H2/N2 (10% H2) cobalt metal is produced. Rapid heating of cobalt(II)nitrate hexahydrate causes melting (formation of a hydrate melt) and therefore side reactions in the hydrate melt by incoupled reactions and evolution/evaporation of different species as, e.g., HNO3, NO2, etc. In case of larger amounts in dense packing in the sample container, the formation of oxo(hydoxo)nitrates is possible at higher temperature. For 2, its thermal decomposition to 3 was followed and its decomposition mechanism is proposed.
A new class of materials for catalysis have been intensively investigated, that is, ‘bimetallic nanoparticles’. Extensive studies of non-supported bimetallic nanoparticle dispersions, stabilized by polymers or ligands, started only about 10 years ago. Many preparative procedures have been proposed, and detailed characterizations have been carried out on bimetallic nanoparticles, thanks to the rapid improvement of analytical technology on surface and nanoscale materials. In this review, we focus on the preparation, characterization and application to catalysis of polymer- or ligand-stabilized bimetallic nanoparticles in dispersion, emphasizing our own work and introducing recent progress of this area.
We have fabricated cobalt nanoparticles using sodium borohydride reduction of cobalt chloride in a didodecyldimethylammonium bromide (DDAB)/toluene inverse micelle solution. The particle morphology changed from single particles to clusters as we increased the reaction temperature. Intracluster dipole−dipole interaction increased the blocking temperature and reduced the effective magnetic moment per cluster.
The reaction of Ni(COD)2 with H2 (3 bar) in CH2Cl2 in the presence of poly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of ≈30 nm, composed of individual 3−4 nm fcc Ni particles and displaying a ferromagnetic behavior whereas the same reaction in the presence of PVP K 90 leads to 4 nm, well-dispersed fcc Ni particles displaying a superparamagnetic behavior. In both cases the magnetic moment per atom is similar to the value found for bulk nickel, hence demonstrating the absence of oxidation of the surface of the particles.
Metallic nanoparticles are emerging as key materials use in catalysis, plasmonics, sensing, and spectroscopy. To approach these applications, the control of nanostructures provides increasing selectivity and functionality. This feature article highlights our recent research progress in this emerging field. This article discusses control of the shape of metallic nanostructures and their physical/chemical nature. The numer-ous approaches for synthesizing multishaped nanostructures include (i) the use of hard templates such as anodic aluminum oxide, (ii) the use of soft templates such as cetyltrimethylammonium bromide (CTAB), and (iii) the use of sacrificial templates. Finally, the use of such nanostructures in catalysis, sensing, and photothermal therapy are demonstrated. General strategies for these methods are discussed and related recent research directions will also be addressed in this feature article.