Effect Of Synthesis Variables Research Articles

Ni-Derived NiO Nanosphere Electrocatalyst for Hydrogen Evolution Reaction: The Effect of Synthesis Variables on Activity and Durability

Transition to a decarbonized society will rely on clean energy resources, in particular on "green” hydrogen—a renewable energy carrier that can be generated via water electrolysis [1]. Unlike proton exchange membrane water electrolyzers (PEMWE), anion exchange membrane water electrolyzers (AEMWEs) enable the use of earth-abundant transition metals in both the cathode and anode [2]. In addition, unlike liquid alkaline water electrolyzers, which use a highly concentrated alkaline media (6 M KOH), AEMWEs can operate with low-concentrated electrolyte, and even pure water [3]. Developing active and durable platinum group metal-free (PGM-free) electrocatalysts is crucial for the large-scale implementation of the AEMWE technology. Ni-based electrocatalysts have shown good activity towards the hydrogen evolution reaction (HER) in alkaline media [4]. Herein, carbon supported Ni-derived NiO nanosphere electrocatalysts are synthetized via a sol-gel method followed by thermal treatment under reducing atmosphere. We explored several synthesis parameters, i.e., Ni-to-carbon ratio, annealing temperature, and annealing time. We also investigated the impact of these synthesis variables on the HER activity in alkaline electrolyte. The catalysts were characterized by XRD, SEM, and EDS. The formation of Ni metal particles with a thin oxygen-rich layer on the surface was demonstrated by microscopy and crystallographic characterization. Following optimization, the HER overpotential of the best performing electrocatalyst at a current density of 10 mA cm−2 was reduced to ca. 130 mV. The catalyst durability was tested over 100 h in KOH solutions at different electrolyte concentrations using various testing protocols such as constant current hold and potential cycling. The catalyst showed higher HER activity (100 mV lower HER overpotential) and better durability behavior (0.15 mV/h lower degradation rate) compared to a commercial Ni supported Vulcan XC-72 electrocatalyst.

ZIF-8 with exceptional thermal stability: Role of organic cosolvents in phase control and structure stabilization

Thermal stability is one of the key factors in catalysis and high-temperature industrial applications. The thermal degradation of ZIF-8, particularly its nanocrystals, could result in a significant loss of surface area and crystallinity, limiting its large-scale applicability. In this study, ZIF-8 nanocrystals with improved thermal stability were synthesized at room temperature (RT) through a facile, one-pot method – an ultrasound-assisted, solvent-guided ZIF-8 growth. The effect of synthesis variables, including the type and concentration of solvent, ultrasonication, and synthesis time, in improving the material’s thermal stability was studied systematically. The as-prepared samples were analyzed by TGA/DSC, XRD, SEM/TEM, FTIR, and BET to monitor the weight loss with temperature, sample crystallinity, crystal morphology, chemical structure, and surface area. Notably, synthesis with 5 v/v% of n-hexane (ZIF-8new-ref) demonstrated the formation of highly-crystalline ZIF-8 nanocrystals with extraordinary thermal stability (with only ∼2.0–3.0 % weight loss up to 600 °C), large surface area (i.e., 975 m2 g−1), and an excellent particle size distribution in the range of 0.2–0.4 μm. More importantly, the short synthesis time (2 h) and sonication-assisted pretreatment of the precursor (for promoting solvent-ligand interaction) proved effective and played a crucial role in controlling ZIF-8’s thermal stability. The mechanism for the thermal stability enhancement was thus proposed. The highly thermally stable ZIF-8 nanocrystals were also synthesized with significantly reduced chemical usage, e.g., 1/11 of the normal ligand-to-metal ratio (70), achieving cost-effective and environmentally friendly synthesis.

Effects of Synthesis Variables on SAPO-34 Crystallization Templated Using Pyridinium Supramolecule and Its Catalytic Activity in Microwave Esterification Synthesis of Propyl Levulinate

A detailed investigation of the hydrothermal crystallization of SAPO-34 in the presence of the novel 1-propylpyridinium hydroxide ([PrPy]OH) organic structural directing agent is presented. The synthesis conditions are systematically tuned to investigate the effects of various parameters (viz. concentrations of each reactant, crystallization time, and temperature) on the nucleation and crystallization of SAPO-34. The results show that a careful variation in each of the synthesis parameters results in the formation of competing phases such as SAPO-5, SAPO-35, and SAPO-36. Pure and fully crystalline SAPO-34 can be crystallized using a precursor hydrogel of a molar ratio of 2.0 Al: 4.7 P: 0.9 Si: 6.7 [PrPy]OH: 148 H2O at 200 °C for only 19 h, which is a shorter time than that found in previous studies. The prepared SAPO-34 is also very active in the esterification of levulinic acid and 1-propanol. By using microwave heating, 91.5% conversion with 100% selectivity toward propyl levulinate is achieved within 20 min at 190 °C. Hence, the present study may open a new insight into the optimum synthesis study of other zeolites using novel pyridinium organic moieties and the opportunity of replacing conventional harmful and non-recyclable homogeneous catalysts in levulinate biofuel synthesis.

Development of highly active Cu-based CO2 hydrogenation catalysts by solution combustion synthesis (SCS): Effects of synthesis variables

This work investigates the effects of solution combustion synthesis (SCS) variables on the performance of copper-based catalysts for CO2 hydrogenation to methanol. The catalyst with a composition of 30wt%CuO50%ZnO/Al2O3 was prepared at various glycine to nitrates (G/O) ratios in the range between 0.1 and 1.23. A correlation of the effects of calcination and activation temperatures with catalytic activity was also studied. The catalyst synthesized at a G/O ratio of 0.206, calcined in air at 400 °C and activated in a stream of pure hydrogen at a temperature of 350 °C resulted in a significant improvement in the performance of the catalyst for CO2 hydrogenation. The exceptionally high catalytic performance of the catalyst was attributed to the synergic effects between small well-dispersed CuO nanoparticles and high number of induced copper phases. The highest activity of the catalyst was recorded at an operating temperature of 300 °C, a pressure of 85 bar and GHSV of 7000 h−1. The CO2 conversion, CO selectivity and methanol selectivity under these conditions were 30%, 38.60%, and 61.4%, respectively; whereas, methanol and CO yields were 0.52gMeOH/g-cat.h and 0.33gCO/g-cat.h, respectively.

Morphological Mapping of Hydrothermally Synthesised Nanoceria at High Ce Concentrations

AbstractSynthesis methods for different nanoparticulate morphologies are of increasing importance since the morphological features determine the redox performance in many applications. However, the effects of synthesis variables on the formation of these morphologies are not well understood and previous work has been limited to relatively low [Ce] and [NaOH]. The present work reports an investigation of the morphological development of nanoceria through the examination of the key processing variables for precipitation and hydrothermal synthesis at high [Ce] and [NaOH]. Characterisation included XRD, Raman, TEM, HRTEM, SAED, XPS, and BET. The resultant refined morphological map delineates the effects of [NaOH] and temperature on the morphological evolution of ceria nanoparticles synthesised from Ce(NO3)3 aqueous solutions in terms of morphology and grain size. The data show that temperature dominates the morphology but elevated [NaOH] and temperature both increase the nanoparticle size. Compared to synthesis at low concentrations, high [Ce] also promotes grain growth, although this is secondary to the effect of [NaOH]. Significantly, the increased grain sizes also enhance the concentrations of catalytically active sites (Ce3+ and charge‐compensating oxygen vacancies). The present work provides a platform of fundamental concepts for the control of experimental variables to synthesise predictable nanoparticulate characteristics.

Optimization of the Asymmetric Cellulose Acetate Membrane Synthesis Variables for Porosity and Pure Water Permeation Flux Using Response Surface Methodology: Microfiltration Application

Membranes play a vital role in membrane-based water treatment processes. Thus, improvement in the membrane fabrication stage can greatly affect the overall performance of these technologies. Accordingly, this study focuses on optimizing the fabrication process of a microfiltration cellulose acetate membrane prepared using a pore-templating method. The effects of synthesis variables and their interactions were investigated using face-centered composite design through response surface methodology (RSM). Calcium carbonate (CaCO3) and glycerin concentrations in the casting solution in addition to evaporation time and hydrochloric acid (HCl) bath time were selected as the independent variables, while the membrane porosity and pure water flux were considered as the response variables. Significant increase in both responses was observed by increasing CaCO3 and glycerin concentrations (P value < 0.05). However, the effect of evaporation time was found to be statistically insignificant on both responses. The effect of the HCl bath time was found to significantly affect the membrane porosity but not the pure water flux. RSM models for both responses were statistically evaluated in terms of the coefficient of determination (R2), and the estimated values (96.74% for the porosity model and 83.85% for the flux model) indicated good fit of the model to the experimental values. Multiple response optimization was employed, and the membrane produced at optimum conditions proved to have good agreement with the predicted values (16.2% error in flux and 3.66% error in porosity). The membrane was successfully applied for paint pigment rejection and oil emulsion rejection, and rejection efficiencies of 95.6% and 80% were achieved for color and oil, respectively, confirming the applicability of the membrane produced at the obtained optimum condition for wastewater treatment.

Design strategies for ceria nanomaterials: untangling key mechanistic concepts.

The morphologies of ceria nanocrystals play an essential role in determining their redox and catalytic performances in many applications, yet the effects of synthesis variables on the formation of ceria nanoparticles of different morphologies and their related growth mechanisms have not been systematised. The design of these morphologies is underpinned by a range of fundamental parameters, including crystallography, optical mineralogy, the stabilities of exposed crystallographic planes, CeO2-x stoichiometry, phase equilibria, thermodynamics, defect equilibria, and the crystal growth mechanisms. These features are formalised and the key analytical methods used for analysing defects, particularly the critical oxygen vacancies, are surveyed, with the aim of providing a source of design parameters for the synthesis of nanocrystals, specifically CeO2-x. However, the most important aspect in the design of CeO2-x nanocrystals is an understanding of the roles of the main variables used for synthesis. While there is a substantial body of data on CeO2-x morphologies fabricated using low cerium concentrations ([Ce]) under different experimental conditions, the present work fully maps the effects of the relevant variables on the resultant CeO2-x morphologies in terms of the commonly used raw materials [Ce] (and [NO3-] in Ce(NO3)3·6H2O) as feedstock, [NaOH] as precipitating agent, temperature, and time (as well as the complementary vapour pressure). Through the combination of consideration of the published literature and the generation of key experimental data to fill in the gaps, a complete mechanistic description of the development of the main CeO2-x morphologies is illustrated. Further, the mechanisms of the conversion of nanochains into the two variants of nanorods, square and hexagonal, have been elucidated through crystallographic reasoning. Other key conclusions for the crystal growth process are the critical roles of (1) the formation of Ce(OH)4 crystallite nanochains as the precursors of nanorods and (2) the disassembly of the nanorods into Ce(OH)4 crystallites and NO3--assisted reassembly into nanocubes (and nanospheres) as an unrecognised intermediate stage of crystal growth.

Effect of synthesis variables on the characteristics of magnesium hydroxide nanoparticles and evaluation of the fluorescence of functionalised Mg(OH)2 nanoparticles

Nanoparticles (NPs) of magnesium hydroxide appear to be an exceptional nanomaterial due to its biocompatibility and low toxicity. However, the mechanism by which the NPs act in the organism has been very difficult to study. In order to contribute to that challenge, in this work magnesium hydroxide was functionalised with organic fluorophores allowing the material to be traced during an in-vivo experiment. Magnesium hydroxide NPs were obtained by the co-precipitation method and analysed by TEM (Transmission electron microscopy), XRD (x-ray diffraction), Raman spectroscopy (RS) and FTIR (Fourier transform infrared spectroscopy). The effects of reaction time, agitation and stoichiometric ratios of the reagents (MgCl2:NaOH) on the NPs characteristics were studied. Mg(OH)2 NPs with average sizes below 65 ± 26 nm were obtained with hexagonal, circular or irregular platelet-shape. NPs with an average size of 41 ± 12 nm were functionalised with curcumin and rhodamine using (3-aminopropyl)-triethoxysilane (APTES) as a coupling agent. It was observed the positive effect of the addition of APTES keeping the Mg(OH)2 NPs dispersed. Moreover, it was found that incorporating APTES as a binding agent with curcumin quenched the fluorescence of curcumin on nanoparticles.

Synthesis of high purity hydroxy sodalite nanoparticles via pore-plugging hydrothermal method for inorganic membrane development: Effect of synthesis variables on crystallinity, crystal size and morphology

The effect of synthesis parameters on crystallinity, crystal size and morphology of hydroxy sodalite particles developed via the pore-plugging hydrothermal (PPH) synthesis method is reported in this study. The PPH method is promising in developing nanocomposite membrane materials with superior performance to those prepared from other methods. Towards developing high-quality nanocomposite sodalite/ceramic membrane for CO2 capture via the PPH method, obtaining high-purity sodalite (SOD) nanoparticles via PPH is essential. Thus effect of synthesis variables (e.g. ageing, interruption time, and synthesis temperature) on purity of as-prepared SOD crystals was investigated. A precursor solution with molar concentration of 5SiO2:0.5Al2O3:50Na2O:1005H2O was used in the synthesis. During the synthesis, 45 mL of the vigorously mixed precursor solution (with or without ageing) was poured into a Teflon-lined stainless-steel autoclave and subjected to PPH synthesis. Physico-chemical properties of the as-synthesized crystals were characterized with x-ray diffraction (XRD) for crystallinity and purity, scanning electron microscope (SEM) coupled with energy-dispersive x-ray spectrometer (EDS) for morphology and elemental composition, and Fourier transform infrared spectroscopy (FT-IR) for surface chemistry. In this study, the sizes of SOD crystals obtained was in the range of 227–493 nm and a percentage crystallinity of SOD crystals as high as 75% was obtained. When two interruptions of one hour each was introduced in the synthesis protocol (total synthesis time of 3.5 h), pure SOD crystals were obtained. The SEM images of this protocol revealed SOD crystals of typical thread ball aggregate similar to those reported in literature. Ageing the precursor prior to PPH was not instrumental to forming high-purity SOD crystals, and this could result in developing low-quality nanocomposite SOD/ceramic membranes via the PPH synthesis method. Furthermore, adjusting the synthesis temperature and interruption time of the PPH do have effect on the purity and crystallinity of the as-prepared SOD crystals.

Response Surface Methodology Optimized Sol–Gel Synthesis of Ag, Mg co-Doped ZnO Nanoparticles with High Photocatalytic Activity

In this paper, pure ZnO, Ag, and Mg mono-doped and co-doped ZnO nanoparticles were synthesized via sol-gel method. The synthesized nanoparticles were characterized using XRD, DRS, BET, TEM, SEM-EDX, and PL techniques. The photocatalytic activity of the prepared photocatalysts was evaluated in degradation Rhodamine B (RhB) dye. Response surface methodology (RSM) was used as a statistical technique for optimizing the effect of synthesis variables on the removal efficiency of RhB. The results predicted from RSM were found to be in good agreement with the experimental results as indicated by correlation coefficient (R2) of 0.9624. Furthermore, statistical tests such as ANOVA table and lack of fit indicated that the model was adequate for representing the experimental data. Ag and Mg co-doped ZnO nanoparticles demonstrated the highest photocatalytic activity in comparison with pure and mono-doped ZnO. Maximum photocatalytic activity of co-doped ZnO nanoparticles was observed for a sample with 3 wt % Ag, 4 wt % Mg calcined at 530°C.

LaFeO3 Perovskites Obtained from Different Methods for NO + CO Reaction, Modeling and Optimization of Synthesis Process by Response Surface Methodology

In this paper, LaFeO3 perovskite catalysts were synthesized by sol–gel combustion, pechini and co-precipitation methods and studied as catalysts for the catalytic reduction of NO with CO. The perovskite catalysts were characterized by XRD, BET, H2-TPR, SEM and DLS. The pechini synthesized perovskite showed the highest activity among the other catalysts in the catalytic reduction of NO with CO. The excellent catalytic activity of LaFeO3-pechini might be associated with its higher specific surface area, better low-temperature reducibility, more structural defects and more surface oxygen species. For pechini method as the best synthesize method, the effects of synthesis variables on activity of catalysts were studied by response surface methodology. RSM model could predict the experimental data for NO conversions at a good accuracy (R2 = 0.981). The model predicted that the relative importance of variables is as follows: calcination temperature > citrate/nitrate ratio > EG/citrate ratio. Under the optimum condition (citrate/nitrate ratio: 0.61, EG/citrate: 2.92 and calcination temperature: 600 °C), the predicted value of NO conversion (91.1%) was found to be in a good agreement with the corresponding actual value (89%).

Effect of synthesis variables of plasma synthesized polymers on growth of HepG2 cells

Effect of synthesis variables of plasma synthesized polymers on growth of HepG2 cells

Effect of synthesis variables on viscoelastic properties of elastomers filled with carbonyl iron powder

This work studies the influence of synthesis variables on the lineal viscoelastic properties of elastomers filled with soft magnetic particles. Three matrices [natural rubber (NR), high-temperature vulcanising silicone rubber (HTV-SR), and room-temperature vulcanising (RTV-SR)] and three volumetric particle contents (0%, 15%, and 30%) were studied. Anisotropic samples were synthesised with a softer matrix to obtain a larger magnetorheological (MR) effect, and the variation of their properties under an external magnetic field was examined. All samples were characterised within the lineal viscoelastic (LVE) region using a rheometer, because the MR effect is larger within this region. The influence of the matrix, particle content, and pre-structure on the viscoelastic properties of the synthesised samples was studied. The storage and loss modulus increased with the frequency owing to the viscoelastic behaviour of an elastomer in the rubbery phase. Both moduli also increased with the filler content. The influence of the filler is dependent on the matrix, and the maximum variation was seen in the NR-based samples. However, the maximum MR effect was seen in the samples with a softer matrix, and the effect was enhanced in the anisotropic samples. In this work, the MR effect on the loss modulus was studied, and the tendencies were found to be similar to those of the storage modulus. The main contribution of this work is that all dynamic behaviour results were comparable because all synthesis variables and characterisation conditions were identical. Therefore, how the particle content, frequency, and magnetic field affects each matrix can be studied.

Effect of synthesis variables of plasma synthesized polymers on growth of HepG2 cells

Low pressure plasma polymer films were synthesized using pyrrole and allylamine monomers and adding iodine was used (or not) for the reaction in both cases. They were polymerized on glass substrates under the same reaction conditions. Polymerization of allylamine was also studied at different operating powers. These thin polymer films were used as culture surfaces for HepG2 cells, a cell line derived from a human hepatoma. The proliferation, differentiation and two-dimensional propagation until obtaining monolayer of the cells was studied on the different synthetized films and correlations were established between the conditions of synthesis, the physicochemical characteristics obtained and the performance as substrates for the cellular growth.

UV-cured polysulfone-based membranes: Effect of co-solvent addition and evaporation process on membrane morphology and SRNF performance

Membranes consisting of a semi-interpenetrating network of polysulfone (PSU) and cross-linked polyacrylate were synthesized via non-solvent induced phase inversion followed by UV-treatment. Tetrahydrofuran (THF) or 1,4-dioxane (DIO) was added as co-solvent to the N,N-dimethylformamide (DMF)-based polymer solutions and cast films were subjected to evaporation prior to coagulation. Effects of synthesis variables on the membrane morphology and solvent resistant nanofiltration (SRNF) performance were investigated by using a Rose Bengal solution in isopropanol. By increasing the evaporation time from 0 to 100s for the membranes prepared with THF and DIO as co-solvent respectively, rejections increased from 65.3% to 94.2% and 60.1–89.1%, while permeances decreased from 0.29 to 0.01l/m2 h bar and 0.41–0.08l/m2 h bar. A similar effect was observed when the co-solvent/solvent ratio was increased from 0/100 to 100/0: rejections increased from 63.1% to 94.9% and 59.2–90.6%, while permeances decreased from 0.43 to 0.01l/m2 h bar for THF-based membranes and to 0.07l/m2 h bar for DIO-based membranes respectively. A post-treatment was performed to increase the flux by immersing UV-cured PSU-based films in DMF for 48h. The resultant membranes showed higher permeances and lower rejections, making them especially useful as potential candidates for stable supports to apply selective layers upon, such as e.g. in thin film composite (TFC) membranes. As observed in scanning electron microscopy, higher evaporation times and lower initial co-solvent concentrations resulted in less or even no macrovoids.

Enhanced photocatalytic degradation of an azo textile dye by using TiO2/NiO coupled nanoparticles: Optimization of synthesis and operational key factors

In this study, TiO2/NiO coupled nanoparticles were prepared by impregnation method. The effect of synthesis variables, such as NiO content and calcination temperature, were studied in the photocatalytic degradation of C.I. Basic Red 46 (BR46) as a model pollutant from textile industry. XRD, SEM, TEM, DRS, and EDX techniques were used for the characterization of the prepared nanoparticles. The coupling NiO as a p-type semiconductor with TiO2 as an n-type semiconductor could produce special electrons and hole transfers, which the n–p junction is able to facilitate the separation of the electron–hole pairs and thus improve photocatalytic activity of the TiO2 nanoparticles. TiO2/NiO coupled nanoparticles with NiO content of 30 wt% and calcination temperature of 650°C indicate the highest photocatalytic activity. The effect of operational variables were predicted and optimized using response surface methodology (RSM). The results showed that the predicted data from RSM was found to be in good agreement with the experimental results with a correlation coefficient (R2) of 0.9667. The maximum degradation efficiency (91.05%) was achieved at the optimum operational conditions: initial BR46 concentration of 10.21mgL−1, catalyst dosage of 0.46gL−1, irradiation time of 30min, and distance of the solution from UV lamp of 3cm.

TiO2/CeO2 Hybrid Photocatalyst with Enhanced Photocatalytic Activity: Optimization of Synthesis Variables

In this study, TiO2/CeO2 hybrid photocatalysts were prepared from a powder mixture of the corresponding component solid oxides. X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), and N2 physisorption techniques were used for the characterization of prepared photocatalysts. The synthesis variables were optimized in the photocatalytic removal of phenazopyridine (PhP) as a model drug contaminant using response surface methodology (RSM). The results showed that the predicted data from RSM was found to be in good agreement with the experimental results with a correlation coefficient (R2) of 0.9518. Optimization results showed that maximum removal efficiency was achieved at the optimum synthesis conditions: Ti/Ce weight ratio of 0.84:0.16, calcination temperature of 502 °C, and calcination time of 62 min. Results also showed that coupling TiO2 with CeO2 could produce special electrons and holes transfer from TiO2 to CeO2 which is able to facilitate the separation of the electron–hole pairs and thus improve photocatalytic activity of the hybrid photocatalyst. Effect of synthesis variables on the removal efficiency of PhP was estimated by the response surface and contour plots. The obtained results clearly demonstrated that experimental design approach was one of the reliable methods for modeling and optimization of the synthesis variables.

Pt Based Alloy Nanoparticles for Oxygen Reduction Prepared By a Solvothermal Method

In this study, platinum based alloy (PtNi, PtCo, PtNiCo) nanocatalysts with well controlled sizes and shapes have been synthesized using a one pot, facile and surfactant free solvothermal approach for application to the oxygen reduction reaction (ORR). Focus is on the fine-tuning of PtNi and PtNiCo nanostructure with the aim of achieving a defined particle geometry that can withstand treatment leading to a Pt-skin like structure and long electrochemical durability cycles. Effects of synthesis variables that include temperature, heating rate and the nature and ratio of metal precursor salts will be discussed. The samples were characterized using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), high-resolution scanning transmission electron microscopy (HR-STEM), energy-dispersive x-ray spectroscopy (EDS) and thermogravimetric analysis (TGA). EDS mapping and line scans coupled with HR-STEM imaging was utilized to study the elemental distribution within individual Pt alloy nanoparticles, for as prepared samples, electrochemically activated samples and samples after electrochemical durability cycling. The as-prepared samples were subjected to an electrochemical treatment (activation) in deaerated 0.1 M HClO4 to form a Pt-skin like structure. Activated samples exhibited ~ 3-10 fold greater enhancement in ORR activity than commercially available Pt-C in terms of both specific activity and mass activity. Furthermore, most Pt alloy particles retained their activity after the course of the electrochemical durability cycling.

Multivariate optimisation of TiO2/carbon nanocomposites for photocatalytic degradation of a reactive textile dye

In this study, the effect of synthesis variables on the photocatalytic activity of TiO2 nanoparticles and TiO2/C nanocomposites was evaluated by factorial design using a reactive dye as a model substrate. The most significant result demonstrated a significant effect of the pyrolysis temperature on the photocatalytic performance of both materials. For TiO2 nanoparticles, the lower temperatures of pyrolysis enhanced the photocatalytic activity because of the lower rutile content. Conversely, for nanocomposites, the optimum condition was represented by higher temperatures of pyrolysis, which resulted in greater concentrations of the rutile phase. In the latter case, the higher activity observed for the rutile phase was clear evidence of the favourable effect of the presence of carbon.

Cobalt nanoparticles prepared by three different methods

This work aimed to study cobalt nanoparticles (Co-NPs) preparation using three different methods in order to evaluate the effect of synthesis variables that can influence the nanoparticle size distribution and particle shape. The synthesised nanoparticles were characterised by Transmission Electron Microscopy. The first synthesis employed decomposition of Co2(CO)8, at high temperatures. This procedure resulted in spherical nanoparticles with low size distribution. The size of Co-NPs could be tuned by modification of precursor/surfactant, nevertheless the stirring and injection time influenced the size distribution. Using polyol process, at high temperatures, it was produced undefined-shape nanoparticles. This result suggests that the solution composition, i.e. the amount of trioctylphosphine and oleic acid was not suitable to control both size and shape of nanoparticles. Finally, the method based on reduction with NaBH4 resulted spherical nanoparticles with tiny sizes, indicating that in this case a variation on amount of reductant would be more efficient on the particle size control than a variation in concentration of oleic acid. These results indicated that, for each method, a different variable exists for the control of the distribution size and the shape of the formed particles.