Single-step processing of copper-doped titania nanomaterials in a flame aerosol reactor (original) (raw)

Dopant-free, polymorphic design of TiO 2 nanocrystals by flame aerosol synthesis

A dopant-free aerosol synthesis of highly crystalline TiO 2 nanoparticles (20-35 nm) with tunable polymorphic content is demonstrated by rapid flame spray pyrolysis. By controlling precisely the total ambient oxygen partial pressure of the combustion in a quartz tube enclosure, anatase content as high as 96 wt% (4 wt% rutile) was obtained at high oxic flame conditions, while rutile content as high as 94 wt% (6 wt% anatase) was obtained under anoxic flames. The polymorphic variability lies within a narrow range of combustion equivalence ratios, that is, 1.0 o Fo1.5. Unlike any other flame aerosol syntheses, the anatase and rutile crystallite sizes were similar within each sample. Under highly oxic flame conditions (Fo 1.0), twinnings between anatase {0 1 1} planes could be observed, inferring oriented attachment taking place. Such mechanism could not, however, be seen under anoxic flame (F 4 1.0) possibly due to physical hindrance by surface carbonaceous content (typically o 2 wt%). The carbon content can be easily removed by short calcination without significantly affecting the surface areas and crystallite properties of the original TiO 2 nanocrystals, preserving hence its pristine state.

Synthesis of nanoparticles in a flame aerosol reactor with independent and strict control of their size, crystal phase and morphology

Nanotechnology, 2007

A flame aerosol reactor (FLAR) was developed to synthesize nanoparticles with desired properties (crystal phase and size) that could be independently controlled. The methodology was demonstrated for TiO 2 nanoparticles, and this is the first time that large sets of samples with the same size but different crystal phases (six different ratios of anatase to rutile in this work) were synthesized. The degree of TiO 2 nanoparticle agglomeration was determined by comparing the primary particle size distribution measured by scanning electron microscopy (SEM) to the mobility-based particle size distribution measured by online scanning mobility particle spectrometry (SMPS). By controlling the flame aerosol reactor conditions, both spherical unagglomerated particles and highly agglomerated particles were produced. To produce monodisperse nanoparticles, a high throughput multi-stage differential mobility analyser (MDMA) was used in series with the flame aerosol reactor. Nearly monodisperse nanoparticles (geometric standard deviation less than 1.05) could be collected in sufficient mass quantities (of the order of 10 mg) in reasonable time (1 h) that could be used in other studies such as determination of functionality or biological effects as a function of size.

Characteristics of Tio 2 Nanoparticles Synthesized Through Low Temperature Aerosol Process

As one of the important process alternatives for the synthesis of nano materials with lower costs, flexibility and versatility, vapor phase synthesis of titania nano particles continue to attract attention. A low temperature aerosol process for the synthesis of titania nano particles is demonstrated by elucidating the influence of temperature, molar ratio of H 2 O/TiCl 4 and concentration of precursors on particle size and phase composition. This paper highlights the advantages of employing amorphous phase titania powder as solid precursor for its transformation to the rutile phase at temperatures less than 973K through vapor phase hydrolysis of TiCl 4 . A mechanistic hypothesis is proposed to explain the catalytic role of water vapor in the enhancement of amorphous to anatase phase transformation at high (15 to 27) molar ratio of H 2 O/TiCl 4 .

Synthesis of non-aggregated titania nanoparticles in atmospheric pressure diffusion flames

Powder Technology, 2006

Flame aerosol synthesis has been employed to synthesize nanoscale titania (TiO 2 ) particles by oxidation of titanium tetraisopropoxide (TTIP) vapor. The influence of reactant mixing and flow rates on particle morphology, size and phase composition has been studied for two different diffusion flame configurations using transmission electron microscopy, X-ray diffraction and photon correlation spectroscopy. Spherical, loosely agglomerated powders with a minimum secondary particle size of 90 nm and a rutile content of up to 35 w % were obtained at low oxygen flow rates in the double diffusion flame, while large anatase-rich aggregates formed at high oxygen flow rates. It is shown that the degree of aggregation of the as-synthesized particles is represented better by the ratio of d PCS 3 /d TEM 3 , than by the ratio of d BET 3 /d XRD 3 commonly used in literature. The differences observed in particle morphology and phase composition can be explained by considering their time-temperature history as a function of flame configuration and gas flow rates.

Characteristics of Titania Nanoparticles Synthesized Through Low Temperature Aerosol Process

2005

As one of the important process alternatives for the synthesis of nano materials with lower costs, flexibility and versatility, vapor phase synthesis of titania nano particles continue to attract attention. A low temperature aerosol process for the synthesis of titania nano particles is demonstrated by elucidating the influence of temperature, molar ratio of H 2 O/TiCl 4 and concentration of precursors on particle size and phase composition. This paper highlights the advantages of employing amorphous phase titania powder as solid precursor for its transformation to the rutile phase at temperatures less than 973K through vapor phase hydrolysis of TiCl 4. A mechanistic hypothesis is proposed to explain the catalytic role of water vapor in the enhancement of amorphous to anatase phase transformation at high (15 to 27) molar ratio of H 2 O/TiCl 4 .

Characterization and sinterability of nanophase titania particles processed in flame reactors

Nanostructured Materials, 1996

Flame aerosol reactors are a routefor large scale processing of nanostructured materials. However, fundamentals about processing-structure-property relationships have not been extensively researched. This work utilized three dtflerent burners to obtain a wide range of flame processing conditions (different time-temperature histories) to study the formation of nanophase titaniaparticles. At low precursor reaction temperatures of about 400 "C, amorphous titania wasobtained. At intermediate temperaturesof900-1430"C,mixturesof anataseandrutile phase titania were obtained. At high temperatures of 1500-157O"C, spherical particles of 100% anatase titania were obtained. A qualitative explanation of the dtfferentphaseformation has been provided. Transmission Electron Microscopy was used to study particle morphology, size and agglomeration. Sizes of the titania particles produced by the designed burners variedfrom 10 to 100 nm, depending on processing conditions. In situ light scattering measurements were made to examine the evolution of the particle sizes. Post-sintering experiments were carried out to illustrate superior sinterability of the nanophase titania powders.

In Situ Charge Characterization of TiO2 and Cu–TiO2 Nanoparticles in a Flame Aerosol Reactor

Journal of Nanoparticle Research, 2012

Charge distribution characteristics were investigated for nanoparticles synthesized in a diffusion flame aerosol reactor. The nanoparticles considered were pristine TiO 2 and Cu-TiO 2 , with Cu dopant concentrations ranging from 1 to 5 wt% with particle size from 25 to 60 nm. In situ measurements were conducted by integrating a tandem differential mobility analyzer (TDMA) experimental setup with the flame aerosol reactor. A charging model was used to identify the important parameters that govern the two charging mechanisms (diffusion and thermo-ionization) in the flame and their relative importance at different operating parameters. The results indicate that TiO 2 and Cu-TiO 2 nanoparticles carry single as well as double unit charges. The charged fraction depends on particle size as well as on dopant concentration. The charged fraction increased with increasing particle size and decreased with copper dopant concentration. Measured charged fractions were similar for both the polarities at different mobility diameters. Based on the flame operating parameters, the calculations indicate that diffusion charging is dominant in the flame, which is consistent with the experimental results.

Flame-Nozzle Synthesis of Nanoparticles with Closely Controlled Size, Morphology and Crystallinity

Chemie Ingenieur Technik, 2002

A process for close control of primary particle size, morphology and crystallinity of flame-made nanoparticles is presented. According to this, freshly made titania aerosol nanoparticles are rapidly quenched in a critical flow nozzle, essentially freezing particle growth at desired levels. The nanoparticles are produced in a methane/oxygen diffusion flame reactor by oxidation of titanium-tetra-isopropoxide (TTIP). Precise control of the average primary particle size, reduced agglomeration and phase composition is achieved by positioning of the quenching nozzle above the burner and controlling gas and precursor flow rates. D