Flame Spray Pyrolysis Synthesis Research Articles

Impact of Flame Conditions on the Pd‐O Structure and Methane Oxidation Activity over Ceria Support

AbstractIn this work, we employed flame spray pyrolysis (FSP), a high‐temperature synthesis method, to control the formation of Pd structures on the CeO2 support. Multiple types of Pd structures deposited on CeO2 are observed on FSP‐made samples. Our results show that the oxidizing environment during FSP synthesis facilitates the formation of incorporated Pd2+ structures, along with highly dispersed Pd2+, Pd0 nanoparticles, and Pd° clusters formed under the reducing synthesis condition. Notably, these Pd2+ species remained stable at temperatures up to 400 °C. The catalysts containing both highly dispersed Pd2+ nanoparticles and incorporated Pd2+ species demonstrated superior methane oxidation activity, with higher turnover frequencies than those containing only one type of Pd2+ structure. However, hydrothermal pretreatment in the presence of water vapor led to partial deactivation, likely due to structural alterations in the Pd species or the interaction with the CeO2 support, which reduced the stability and effectiveness of the active sites. This study underscores the importance of both highly dispersed and incorporated Pd2+ species in enhancing catalytic performance and highlights the challenges posed by water‐induced deactivation in practical applications.

Reaction-induced unsaturated Mo oxycarbides afford highly active CO2 conversion catalysts.

Sustainable CO2 conversion is crucial in curbing excess emissions. Molybdenum carbide catalysts have demonstrated excellent performances for catalytic CO2 conversion, but harsh carburization syntheses and poor stabilities make studies challenging. Here an unsaturated Mo oxide (Mo17O47) shows a high activity for the reverse water-gas shift reaction, without carburization pretreatments, and remains stable for 2,000 h at 600 °C. Flame spray pyrolysis synthesis and Ir promoter facilitate the formation of Mo17O47 and its in situ carburization during reaction. The reaction-induced cubic α-MoC with unsaturated Mo oxycarbide (MoOxCy) on the surface serves as the active sites that are crucial for catalysis. Mechanistic studies indicate that the C atom in CO2 inserts itself in the vacancy between two Mo atoms, and releases CO by taking another C atom from the oxycarbide to regenerate the vacancy, following a carbon cycle pathway. The design of Mo catalysts with unsaturated oxycarbide active sites affords new territory for high-temperature applications and provides alternative pathways for CO2 conversion.

Flame Spray Pyrolysis Synthesis of Ultra-Small High-Entropy Alloy-Supported Oxide Nanoparticles for CO2 Hydrogenation Catalysts.

The synthesis of high-entropy alloys (HEAs) with ultra-small particle sizes has long been a challenging task. The complex and time-consuming synthesis process hinders their practical application and widespread adoption. This study presents the novel synthesis of TiO2 nanoparticles loaded with a quinary high-entropy alloy through flame spray pyrolysis (FSP) for the first time. The extremely fast heating rate of flame combustion makes the precursor fast pyrolysis gasification, high temperature in the flame field promotes the metal vapor mixing uniformly, and the fast quenching process can reduce the particle aggregation sintering, the ultra-small particle size of HEA firmly attached to the TiO2 surface. The catalysts prepared via this gas-to-particle pathway exhibit excellent performance in CO2 hydrogenation, achieving a conversion rate of 62% at 450°C, and maintaining their activity for over 220h without significant particle agglomeration. This finding provides valuable insights for the future design of catalytically active materials with enhanced activity and long-term stability.

Utilizing the unique charge extraction properties of antimony tin oxide nanoparticles for efficient and stable organic photovoltaics

Simultaneously enhancing device performance and longevity, as well as balancing the requirements on cost, scalability, and simplification of processing, is the goal of interface engineering of organic solar cells (OSCs). In our work, we strategically introduce antimony (Sb 3+ ) cations into an efficient and generic n-type SnO 2 nanoparticles (NPs) host during the scalable flame spray pyrolysis synthesis. Accordingly, a significant switch of conduction property from an n-type character to a p-type character is observed, with a corresponding shift in the work function (WF) from 4.01 ± 0.02 eV for pristine SnO 2 NPs to 5.28 ± 0.02 eV for SnO 2 NPs with 20 mol. % Sb content (ATO). Both pristine SnO 2 and ATO NPs with fine-tuned optoelectronic properties exhibit remarkable charge carrier extraction properties, excellent UV resistance and photo-stability being compatible with various state-of-the-art OSCs systems. The reliable and scalable pristine SnO 2 and ATO NPs processed by doctor-blading in air demand no complex post-treatment. Our work offers a simple but unique approach to accelerate the development of advanced interfacial materials, which could circumvent the major existing interfacial problems in solution-processed OSCs. • Introducing antimony cations to effectively dope the n-type SnO 2 nanoparticles. • In-depth characterization of the cation doping effect and mechanisms. • Validation of the generic applicability of the p-type doped nanoparticles for organic photovoltaic applications. • Demonstrating efficient and stable organic solar cells based on state-of-the-art organic photovoltaic materials.

Surface effect of nano-sized cerium-zirconium oxides for the catalytic conversion of methanol and CO2 into dimethyl carbonate

The direct synthesis of Dimethyl carbonate (DMC) from methanol and CO2 is a green process which allows CO2 valorization. Among efficient catalysts, ceria, zirconia and cerium-zirconium mixed oxides are often reported as the most active catalysts. In a recent report, we discovered that cerium-zirconium mixed oxides prepared by Flame Spray Pyrolysis (FSP) show greater catalytic activities than those prepared by precipitation, although both exhibit very similar surface area and bulk features. The objective of this study was to find out the origins of the superior catalytic activities obtained by flame spray pyrolysis synthesis method by a deeper analysis of bulk and surface properties. We have opted to focus on mixed ceria-zirconia of equimolar composition (Ce0.5Zr0.5O2) as it exhibits maximum catalytic activity for both synthesis methods. Combining bulk and surface characterization as well as surface adsorption measurements using probe molecules, we propose that flame spray pyrolysis enables a surface enrichment in cerium oxide still in interaction with zirconium oxide that leads to a high concentration of adsorbed methanol at the surface, which might explain the greater activity of the catalysts prepared using this method. Beyond the application of DMC synthesis, we can anticipate that Flame Spray Pyrolysis synthesis should generate relative high surface area mixed oxides with different catalytic performances with respect to mixed oxides prepared at lower temperature owing their metastable nature.

Flame spray pyrolysis synthesis and H2S sensing properties of CuO-doped SnO2 nanoparticles

In this work, CuO-doped SnO2 (CuO/SnO2) nanoparticles with different CuO mass fractions (0–1.0 wt%) are synthesized by a flame spray pyrolysis (FSP) route and applied to fabricate thin-film gas sensors for H2S detecting. The nanoparticles are characterized by X-ray diffraction (XRD), N2-physisorption isotherms, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Within the 0–1.0 wt% CuO-doping concentrations, all of the nanoparticles predominantly exhibit a spherical structure with a diameter of 5–15 nm, and possess a quite large specific surface area (110–125 m2/g). These textural characterizations suggest that Cu atoms form substitution doping in polycrystalline SnO2 nanoparticles at low CuO levels (< 0.5 wt%), and they are segregated as CuO nanoclusters at high CuO concentrations (0.5–1.0 wt%). From gas-sensing measurements, the CuO doping significantly improves the H2S sensing performance of SnO2 nanoparticles, especially at the optimal CuO-doping mass fraction of 0.5 wt%. The optimal CuO-doped SnO2 gas sensor exhibits a highest response (Ra/Rg = 1056) under a condition of 10 ppm H2S atmosphere at 125 °C. This is probably because a large number of highly dispersed small CuO nanoclusters are supported on the surface of the nanoparticle for 0.5 wt% doping, forming abundant p-n junctions with SnO2. When the CuO/SnO2 composite is exposed to H2S, semiconducting CuO is converted to metallic-like CuS, thereby increasing electrical conductivity and resulting in a high response. In addition, the optimal sensor displays good cycle performance and high H2S selectivity against other toxic and flammable gases including NH3, H2 and CO. Therefore, the gas sensor of 0.5 wt% CuO-doped SnO2 made by the FSP shows a large potential for H2S detecting in practical industrial application.

Asymmetrical Double Flame Spray Pyrolysis-Designed SiO2/Ce0.7Zr0.3O2 for the Dry Reforming of Methane.

Silica has the potential to enhance the performance of ceria-zirconia as a support for the dry reforming of methane; however, controlling the integration of silica with the ceria-zirconia using flame spray pyrolysis (FSP) is a significant challenge. To address this challenge, an asymmetrically variable double-FSP (DFSP) system was established to control the SiO2 interaction with Ce0.7Zr0.3O2. The engineered materials were then utilized as supports for Ni for the dry reforming of methane. Initially, silica formation during FSP synthesis was examined where it was revealed that, at a low precursor concentration (<1.5 M tetraethyl orthosilicate in xylenes), the physical characteristics of the silica varied differently in relation to what is typically encountered during FSP synthesis. Explicitly, on using a 0.5 M tetraethyl orthosilicate precursor, increasing the FSP feed rate provided an increase in the specific surface area from 217 m2/g at 3 mL/min to 363 m2/g at 7 mL/min. Adopting this knowledge on silica formation under these conditions, the asymmetrical DFSP system was then exploited to regulate the integration of ceria-zirconia with the silica. To restrict the silica from coating the particles during DFSP, the intersection distance along the silica flame was tuned from 18.5 to 28.5 cm, whereas the distance along the ceria-zirconia flame was fixed at 5 cm. It was found that at short intersection distances the ceria-zirconia provided sites for silica nucleation and growth, resulting in high surface-area silica encapsulating the ceria-zirconia. At large intersection distances, encapsulation of the ceria-zirconia by silica was suppressed. An enhanced oxygen storage capacity and basicity along with the small Ni sizes facilitated by the longer intersection distances produced the most selective catalyst for the dry reforming of methane.

(Invited) Operando X-Ray Absorption Investigations into the Oxygen Evolution Activity, Stability, and pH Dependency of NixFe1-XOy Nanoparticles

Mixed Ni-Fe metal oxides currently represent some of the most attractive anode catalysts for the electrochemical splitting of water due to their low overpotentials for the oxygen evolution reaction (OER) in alkaline electrolytes. The concentrated potassium hydroxide solutions and anion exchange membranes that are typically employed in alkaline water electrolyzers, however, are prone to carbonation which can lead to significant shifts in the electrolyte pH from alkaline to quasi-neutral conditions (pH = 7-10). So far a fundamental understanding of how changes in the local pH environment induced via carbonation affect the catalyst electronic and surface structure, and ultimately the catalyst stability and electrochemical OER activity, is lacking. The importance of understanding this behavior is further highlighted by the potential application of Ni-Fe oxides as anode catalysts in co-electrolysis, where the electrochemical reduction of CO2 and the anodic evolution of oxygen occur in a carbonated, quasi-neutral pH environment. Here we demonstrate a practical and scalable flame-spray pyrolysis synthesis capable of producing highly crystalline Ni-Fe oxide (Ni1-xFexOy) nanoparticles with high surface areas (SABET ≈ 20 - 75 m2/g). The research presented herein focuses on expanding the current understanding of the influence of the local electronic and surface structures on the OER activity and electrochemical stability in both alkaline (pH = 13) and carbonated, quasi-neutral (pH = 9) electrolyte. The resulting operando XANES and EXAFS analyses of the Ni and Fe K-edges permit useful insight into the nature of the valence states and rearrangements in local structure that occur under operating conditions representative of alkaline water electrolysis and co-electrolysis. Combined with a broad range of ex situ physical characterization techniques, we then relate the structural, electronic, and morphological changes to the observed electrochemical OER activity and stability.

Morphology-Controlled One-Step Synthesis of Nanostructured LiNi1/3Mn1/3Co1/3O2 Electrodes for Li-Ion Batteries.

Nanostructured electrodes effectively enhance the kinetics of the charge/discharge process in lithium-ion (Li-ion) batteries. However, the fabrication of these electrodes often involves complex processing steps. This study demonstrates a one-step improved flame spray pyrolysis synthesis approach to directly deposit the most common Li-ion battery cathode material LiNi1/3Mn1/3Co1/3O2 onto current collectors, which is identified as reactive spray deposition technology (RSDT). Because of the economical and continuous nature of RSDT, the industrial scale of manufacturing nanostructured electrodes for Li-ion batteries can be potentially developed. Morphologies of the electrodes are well controlled so that their electrochemical properties can be tailored to accommodate intended applications. In detail, by adjusting the precursor concentration in the solution feed during the operation of RSDT, the specific surface area of synthesized material can be fine-tuned accordingly. Although the electrodes prepared with low precursor concentration exhibit the highest surface area and deliver the highest initial discharge capacity of 192.1 mAh g–1, the most stable cycling performance is demonstrated by the electrodes fabricated with high precursor concentration, retaining 93.6% of the initial capacity after 100 cycles in half-cell testing. This innovative direct deposition method considerably simplifies the manufacture process of high-performance nanostructured electrodes and enables effortless modification of their properties. Moreover, no hazardous waste is generated from this synthesis route.

Low temperature ethanol steam reforming for process intensification: New Ni/MxO–ZrO2 active and stable catalysts prepared by flame spray pyrolysis

Steam reforming of hydrocarbons is a mature technology and its implementation on other substrates such as bio-ethanol appears as a ready opportunity to produce H2 from renewable sources. The Low Temperature Ethanol Steam Reforming (LT-ESR, 300–500 °C) could be a really efficient technology from the energetic point of view. However, deactivation by coke deposition remains the biggest issue, due to inefficient carbon gasification by steam in such low temperature range. We demonstrated the feasibility of the process at low temperature taking into account both activity and deactivation issues. The attention was focused on the addition of basic promoters and on the development of an unconventional preparation procedure, in comparison with a traditional precipitation/impregnation route, to improve stability and activity.Therefore, in this work several catalysts were studied, differently promoted by alkali and alkali earth oxides (CaO, MgO, K2O) using a non conventional doping method. H2 yield and selectivity to CO demonstrated tightly related to the promoter adopted. Flame Spray Pyrolysis synthesis of nickel nanoparticles stabilized in a zirconia matrix (Ni/MxO-ZrO2) was performed, obtaining more stable catalysts toward deactivation by coking with respect to the analogous prepared by traditional precipitation/impregnation. The effect of the doping using a scalable one-pot technique was investigated by means of characterization of fresh catalysts and activity testing. Catalyst resistance toward deactivation was studied by SEM-EDX, TEM, Raman spectroscopy and temperature programmed analysis. Among the promoters, CaO and K2O showed the best performance, producing a reformate with low CO/CO2 ratio and, thus, leading to higher H2 yield with consequent lower impact on H2 purification in an integrated process. K2O deeply modified the chemical behaviour of the catalyst allowing to achieve a significant H2 production also at very low temperature (300 °C).

Flame spray pyrolysis synthesis of ceramic nanopigments CoCr2O4: The effect of key variables

Spinel structure CoCr2O4 was synthesized by the non-conventional method flame spray pyrolysis (FSP) and the traditional route solid state reaction, where the optical properties were evaluated. The influences of FSP conditions as pressure of dispersion air and ceramic load of the solution over optical properties were evaluated using a 22 full factorial design with one replica. The final products were applied in ceramic glazes to evaluate pigmenting power. Powders were characterized by X ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis-NIR spectroscopy and Colorimetry. Results show that ceramic pigments obtained by FSP have highest percent reflectance and brightness than solid state reaction powders; nevertheless, both pigments are adequate to ceramic application. Besides, experiments showed that ceramic load of the starting solution have a strong influence over particle properties.

Luminescent properties of scintillator nanophosphors produced by flame spray pyrolysis

In the present work flame spray pyrolysis synthesis and characterization of the nano-scale phosphors; M′-YTaO4 and M′-Y(Ta0.85Nb0.15)O4 have been studied for the first time. Phase and elemental analysis of the produced nanophosphors were carried out by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) measurements, respectively. The surface morphology and particle size of the nanophosphors were identified using scanning electron microscopy (SEM). The XRD results reveal that the nanophosphors have monoclinic M′-YTaO4 and M′-Y(Ta0.85Nb0.15)O4 phases belonging to the presence of M´-form of fergusonite structure. The particle sizes of the nanophosphors were found to be in the range of 50–100nm. The spectroscopic characterization was performed by both radioluminescence (RL) and thermally stimulated luminescence (TSL) measurements after exposure to X-ray irradiation. Also, photoluminescence and decay times were investigated under UV excitation. The nanophosphors can be concluded as appropriate emissive materials for imaging, display and scintillator applications due to the efficient photoluminescence, moderate radioluminescence (RL) and thermally stimulated luminescence characteristics.

Manipulating ceria-titania binary oxide features and their impact as nickel catalyst supports for low temperature steam reforming of methane

Mixed oxides of titanium with cerium were examined for the impact of their reducible oxide properties as a support for nickel-catalysed low temperature steam reforming of methane. Modifications to characteristics of the mixed oxide supports were obtained by varying the relative cerium/titanium composition and utilising different synthesis routes. Sol-gel and flame spray pyrolysis synthesis techniques were employed to achieve this purpose. The sol-gel-prepared supports exhibited improved methane conversion rates with an increased presence of cerium within the support while the catalysts with flame-made supports demonstrated poor stability upon incorporation of cerium at certain ratios. Despite the consistent high surface area and fine nickel dispersion across all flame-synthesised supports, the findings revealed that while these attributes are beneficial for steam reforming catalysis, they do not necessarily assure effective conversions. In addition to the above qualities, the sol-gel-synthesised materials demonstrated that crystalline features of the support also play a vital role in maintaining stable conversions at 500°C.

Liquid-feed flame spray pyrolysis as alternative synthesis for electrochemically active nano-sized Li2MnSiO4

A novel liquid-feed flame spray pyrolysis synthesis with reducing post-heat treatment yielding highly phase pure nano-sized and carbon-coated Li2MnSiO4 is reported. In contrast to most reported Li2MnSiO4 synthesis routes, aerosol combustion methods are highly scalable and not as time consuming as most wet chemical syntheses. Flame spray pyrolysis was performed using solutions with varying ratios of H2O, EtOH and p-Xylene. The importance of solution combustibility to form loosely agglomerated nanoparticles is highlighted. Particles from the p-Xylene-aided flame spray pyrolysis showed a mean particle size of 20 nm and Pmn2 1 structure after annealing and carbon coating. The electrochemical performance as a cathode material was assessed by galvanostatic cycling and in situ XRD in half cells. The highest discharge capacity observed was 190 mAh g−1 at room temperature and a rate of C/50.

Influence of the Synthesis Method on the Structure and CO2 Adsorption Properties of Ca/Zr Sorbents

The influence of the synthesis method has been investigated on the structure and CO2 adsorption properties of Ca/Zr sorbents. For this purpose, Ca/Zr sorbents are synthesized using co-precipitation, sol–gel, and deposition–precipitation methods and compared to our previously reported Ca/Zr sorbent prepared by the flame spray pyrolysis method. Among the various sorbents, the sorbent synthesized by the sol–gel method exhibits excellent adsorption capacity and remarkable multi-cycle stability compared to the sorbent synthesized by the flame spray pyrolysis synthesis method. This interesting and rather useful behavior was a result of surface properties of the sol–gel-synthesized sorbents. X-ray diffraction measurements indicate that the CaO phase was dominant with respect to the CaZrO3 phase in the case of the Ca/Zr sorbent prepared by the deposition–precipitation method. The opposite trend was observed for the sorbents synthesized by the remaining methods. Temperature-programmed desorption measurements show that the basic properties of the sorbents depend upon the synthesis method adopted. O 1s X-ray photoelectron spectroscopy (XPS) spectra confirms the formation of the CaZrO3 phase in the prepared sorbents. Transmission electron microscopy (TEM) measurements show that the Ca/Zr sorbent synthesized by the sol–gel method exhibits smaller crystallites similar to the flame-spray-pyrolysis-synthesized sorbent. TEM–energy-dispersive spectrometry and XPS atomic ratios show that the sol–gel-synthesized Ca/Zr sorbent has more CaO particles over the surface compared to the Ca/Zr sorbent prepared by flame spray pyrolysis and is responsible for the better CO2 capture performance observed.

Computational study of the effect of processing parameters on the formation and growth of ZrO2 nanoparticles in FSP process

Flame spray pyrolysis (FSP) offers a proven and inexpensive route for nanoparticle production. To date, the research on FSP made nanoparticles was focused mostly on the lab scale and medium scale production. Scale-up requirements for FSP process control need to be developed to define the operation window at industrial scale production rate. In this work, FSP synthesis of ZrO2 particles has been addressed from a process intensification perspective, since FSP characteristics perfectly fit into several fundamental process intensification aspects. The possible solutions for the precursor delivery system and the atomization quality at high precursor concentrations were investigated to intensify the production rate and reduce the cost of an additional solvent. The simulation results showed that the particle size could be controlled at near a constant (∼20nm) while the production rate was intensified by a factor of 5. Finally, the potential of gas to liquid flow ratio (GLFR) and replacing oxygen dispersion gas by air for further reducing the particle size and the production cost were investigated. The simulation results can be used as a framework of PI in FSP process design at industrial scale production.

Mixed Solvents Assisted Flame Spray Pyrolysis Synthesis of TiO2 Hierarchically Porous Hollow Spheres for Dye-Sensitized Solar Cells

A novel one-step and template-free preparation process had been developed to synthesize TiO2 hierarchically porous hollow spheres (HPHSs) by mixed solvents assisted flame spray pyrolysis (FSP). The as-obtained TiO2 HPHSs had hierarchically porous hollow structure such as central cavities, macropores on shells, and mesopores accumulated by TiO2 nanocrystallites. The unique hierarchically porous structure endowed the TiO2 spheres with high specific surface area and excellent light scattering property. A mechanism of the formation of TiO2 HPHSs depending on the competition between chemical reaction rate and diffusion rate of the components of the precursor was proposed, in which mixed solvents and short flame residence time were of importance. Furthermore, the dye-sensitized solar cells (DSSCs) performance of TiO2 HPHSs as light scattering layer was investigated. The photoelectric conversion efficiency (η) was improved by 38.2% (from 5.00% to 6.91%), comparing to that of single layer P25 films.

Two-Nozzle Flame Spray Pyrolysis (FSP) Synthesis of CoMo/Al2O3 Hydrotreating Catalysts

Two-nozzle frame spray analysis (FSP) synthesis of CoMo/Al2O3 where Co and Al are sprayed in separate flames was applied to minimize the formation of CoAl2O4 observed in one-nozzle flame spray pyrolysis (FSP) synthesis and the materials were characterized by N2-adsorption (BET), X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, Raman spectroscopy, transmission electron microscopy, and catalytic performances in hydrotreating. By varying the flame mixing distances (81–175 mm) the amount of CoAl2O4 could be minimized. As evidenced by UV–vis spectroscopy, CoAl2O4 was detected only at short flame mixing distances, where the flame conditions resemble one-nozzle FSP. Raman spectroscopy revealed that β-CoMoO4 was a component of all the catalysts (in the as-prepared oxidic form) together with alumina supported MoO x surface species. The only phase detected with XRD was γ-Al2O3. The FSP synthesized oxidic catalysts were activated by sulfidation without further heat treatments. The hydrodesulfurization activity of the best two-nozzle FSP catalysts, compared to the one-nozzle FSP catalysts, improved from 75 to 91 % activity relative to a commercial reference catalyst and the hydrodenitrogenation activity improved from 70 to 90 % relative activity. This suggests that better promotion of the active molybdenum sulfide phase was achieved when using two-nozzle FSP synthesis, probably due to less formation of the undesired phase CoAl2O4, which makes Co unavailable for promotion.

Exploring the relationship between surface structure and photocatalytic activity of flame-made TiO2-based catalysts

Bare titanium dioxides (TiO2) and doped with metal (Cu) or non-metal ion (F) were synthesized by a single-step flame spray pyrolysis (FSP) method. According to the BET, XRD, and TEM results, the Cu- and F-doped TiO2 nanoparticles synthesized by FSP possess comparable features in terms of surface area, crystallite size and phase composition, and morphology. However, the F-doped TiO2 exhibited the highest photocatalytic activity for the complete oxidation of acetaldehyde (ACE) even surpassing benchmarking Aeroxide TiO2 (P25). In contrast, Cu-doped TiO2 had a detrimental effect on the ACE photocatalytic oxidation. The proportion of native terminal hydroxyl groups, evaluated using high-field 1H MAS NMR, on the particle surface was varied by doping the TiO2 with either Cu or F ions during FSP synthesis. A relationship, whereby decreased terminal hydroxyl group content corresponded to elevated acetaldehyde photodegradation, was subsequently uncovered. The findings were reinforced by studying the XPS O 1s photopeaks in the region attributed to surface hydroxyl groups.

Flame spray pyrolysis synthesis and aerosol deposition of nanoparticle films

AbstractThe assembly of nanoparticle films by flame spray pyrolysis (FSP) synthesis and deposition on temperature‐controlled substrates (323–723 K) was investigated for several application‐relevant conditions. An exemplary SnO2 nanoparticle aerosol was generated by FSP and its properties (e.g., particle size distribution), and deposition dynamics were studied in details aiming to a simple correlation between process settings and film growth rate. At high precursor concentrations (0.05–0.5·mol/L), typically used for FSP synthesis, the nanoparticles agglomerated rapidly in the aerosol leading to large (&gt;100 nm) fractal‐like structures with low diffusivity. As a result, thermophoresis was confirmed as the dominant nanoparticle deposition mechanism down to small (≈40 K) temperature differences (ΔT) between the aerosol and the substrate surface. For moderate‐high ΔT (&gt;120 K), thermal equilibrium was rapidly obtained yielding a constant thermophoretic flux and film growth rate. A model was developed to predict the nanoparticle deposition rates by FSP synthesis at moderate‐high ΔT that does not require detailed analysis of the aerosol composition. Comparison with previous studies having similar nozzle geometries showed that the deposition rates of FSP‐made aerosols can be reasonably well predicted for various materials and flame conditions. © 2012 American Institute of Chemical Engineers AIChE J, 2012