An official website of the United States government
In dusty plasma environments, spontaneous growth of nanoparticles from reactive gases has been extensively studied for over three decades, primarily focusing on hydrocarbons and silicate particles. Here, we introduce the growth of titanium dioxide, a wide bandgap semiconductor, as dusty plasma nanoparticles. The resultant particles exhibited a spherical morphology and reached a maximum monodisperse radius of 235 ± 20 nm after growing for 70 s. The particle grew linearly, and the growth displayed a cyclic behavior; that is, upon reaching their maximum radius, the largest particles fell out of the plasma, and the next growth cycle immediately followed. The particles were collected after being grown for different amounts of time and imaged using scanning electron microscopy. Further characterization was carried out using energy dispersive x-ray spectroscopy, x-ray diffraction, and Raman spectroscopy to elucidate the chemical composition and crystalline properties of the maximally sized particles. Initially, the as-grown particles exhibited an amorphous structure after 70 s. However, annealing treatments at temperatures of 400 and 800 °C induced crystallization, yielding anatase and rutile phases, respectively. Annealing at 600 °C resulted in a mixed phase of anatase and rutile. These findings open avenues for a rapid and controlled growth of titanium dioxide via dusty plasma.
more »
« less
Spontaneous selective deposition of iron oxide nanoparticles on graphite as model catalysts
Iron oxide nanomaterials participate in redox processes that give them ideal properties for their use as earth-abundant catalysts. Fabricating nanocatalysts for such applications requires detailed knowledge of the deposition and growth. We report the spontaneous deposition of iron oxide nanoparticles on HOPG in defect areas and on step edges from a metal precursor solution. To study the nucleation and growth of iron oxide nanoparticles, tailored defects were created on the surface of HOPG using various ion sources that serve as the target sites for iron oxide nucleation. After solution deposition and annealing, the iron oxide nanoparticles were found to nucleate and coalesce at 400 °C. AFM revealed that the particles on the sp 3 carbon sites enabled the nanoparticles to aggregate into larger particles. The iron oxide nanoparticles were characterized as having an Fe 3+ oxidation state and two different oxygen species, Fe–O and Fe–OH/Fe–OOH, as determined by XPS. STEM imaging and EDS mapping confirmed that the majority of the nanoparticles grown were converted to hematite after annealing at 400 °C. A mechanism of spontaneous and selective deposition on the HOPG surface and transformation of the iron oxide nanoparticles is proposed. These results suggest a simple method for growing nanoparticles as a model catalyst.
more »
« less
- Award ID(s):
- 1725818
- PAR ID:
- 10197924
- Date Published:
- Journal Name:
- Nanoscale Advances
- Volume:
- 1
- Issue:
- 12
- ISSN:
- 2516-0230
- Page Range / eLocation ID:
- 4729 to 4744
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Heterogeneous ice nucleation is a common process in the atmosphere, but relatively little is known about the role of different surface characteristics on the promotion of ice nucleation. We have used a series of iron oxides as a model system to study the role of lattice mismatch and defects induced by milling on ice nucleation activity. The iron oxides include wüstite (FeO), hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), and goethite (FeOOH). The iron oxides were characterized by X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area measurements. The immersion freezing experiments were performed using an environmental chamber. Wüstite (FeO) had the highest ice nucleation activity, which we attribute to its low lattice mismatch with hexagonal ice and the exposure of Fe–OH after milling. A comparison study of MnO and wüstite (FeO) with milled and sieved samples for each suggests that physical defects alone result in only a slight increase in ice nucleation activity. Despite differences in the molecular formula and surface groups, hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), and goethite (FeOOH) had similar ice nucleation activities, which may be attributed to their high lattice mismatch to hexagonal ice. This study provides further insight into the characteristics of a good heterogeneous ice nucleus and, more generally, helps to elucidate the interactions between aerosol particles and ice particles in clouds.more » « less
-
The kinetics of model contaminant 4-chloronitrobenzene (4-ClNB) reduction by Fe( ii ) in aqueous suspensions containing either or both goethite (α-FeOOH) nanoparticles and kaolinite (Al 2 Si 2 O 5 (OH) 4 ) were quantified to elucidate the effects of nonreactive clay minerals on the attenuation of nitroaromatic groundwater contaminants by iron oxide nanoparticles. Increasing the amount of kaolinite in the presence of goethite decreased the reduction rate of 4-ClNB and competitive Fe( ii ) adsorption on kaolinite occurred. Cryogenic transmission and scanning electron microscopy (cryo-TEM and cryo-SEM) images did not reveal significant loss of accessible reactive surface area as a result of heteroaggregation. Sequential-spike batch reactors revealed that in the presence of kaolinite, 4-ClNB reduction rate decreased by more than a factor of three with extended reaction as a result of kaolinite dissolution and subsequent incorporation of Al and Si in goethite or on the goethite surface. The reactive sites residing on the {110} faces were comparatively more reactive in the presence of a large loading of kaolinite, resulting in shorter and wider goethite particles after reaction. These results elucidate the mechanisms by which nonreactive clays affect the reactions of Fe( ii )/iron oxides in groundwater systems and indicate that nonreactive clays are not passive components.more » « less
-
null (Ed.)Particle nucleation and growth of crystalline manganese oxide nanoparticles was examined in a complementary experimental and modelling study. Gas-to-particle conversion occurred in a flame-assisted chemical vapor deposition process whereby a premixed stagnation flame drove the high-temperature synthesis. The structure of the stagnation flame was computed using pseudo one-dimensional and axisymmetric two-dimensional methods to assess the accuracy of using a faster similarity-based calculation for flame-deposition design. The pseudo one-dimensional computation performs reasonably well for the narrow aspect ratio stagnation flow currently studied as evidenced by reasonable agreement between the measured flame position and both computational methods. Manganese oxide nanoparticles having II, II–III, III or IV oxidation states were observed depending on the flame conditions. These observations may be explained by size-dependent equilibria between nano-scale manganese oxide and surrounding gas-phase oxygen. Local equilibrium was assessed during the particle temperature–oxygen–time history to gain insight into oxide formation in the flame. Analysis of the saturation ratio for formation of condensed MnO in the flame indicates that nucleation may be limited by a thermodynamic barrier. This nucleation mechanism is supported by measured particle sizes smaller than what would be expected from a coagulation limited growth process. Nanocrystalline MnO, reported here for the first time by flame synthesis, was obtained in oxygen lean flames. MnO 2 is the phase predicted to be thermally stable as the particles approach the deposition surface, yet other metastable oxide phases were produced in many of the flames examined. In fact, MnO 2 was only observed in the smallest particle size conditions which may indicate that high cooling rates limit phase equilibrium to less massive particles.more » « less
-
The direct synthesis of highly water-soluble nanoparticles has attracted intensive interest, but systematic size control has not been reported. Here, we developed a general method for synthesizing monodisperse water-soluble iron oxide nanoparticles with nanometer-scale size increments from 4 nm to 13 nm in a single reaction. Precise size control was achieved by continuous growth in an amphiphilic solvent, diethylene glycol (DEG), where the growth step was separated from the nucleation step by sequential addition of a reactant. There was only one reactant in the synthesis and no need for additional capping agents and reducing agents. This study reveals the “living growth” character of iron oxide nanoparticles synthesised in an amphiphilic solvent. The synthetic method shows high reproducibility. The as-prepared iron oxide nanoparticles are extremely water soluble without any surface modification. Surprisingly, the synthesized 9 nm iron oxide nanoparticles exhibit extremely high transversal and longitudinal relaxivities of 425 mM −1 s −1 and 32 mM −1 s −1 respectively, which is among the highest transversal relaxivity in the literature for sub-10 nm spherical nanoparticles. This study will not only shed light on the continuous growth phenomenon of iron oxide nanoparticles in an amphiphilic solvent, but could also stimulate the synthesis and application of iron oxide nanoparticles. The continuous growth method could be further extended to other materials for the controlled synthesis of water-soluble nanoparticles.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9na00472f
