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Role of Surface Area, Primary Particle Size, and Crystal Phase on Titanium Dioxide Nanoparticle Dispersion Properties

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ABSTRACT

Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO2 nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO2 samples, and one commercial Degussa TiO2 sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl2) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO2 isoelectric point was found to be dependent on particle size. As anatase TiO2 primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO2 nanoparticle IEP was found to be insensitive to particle crystal structure.

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Different sized anatase TiO2 nanoparticles dispersed in DI water with the same mass concentration of 50 μg/ml: a pH and surface area concentration; b dispersion zeta potential and hydrodynamic diameter.
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Figure 6: Different sized anatase TiO2 nanoparticles dispersed in DI water with the same mass concentration of 50 μg/ml: a pH and surface area concentration; b dispersion zeta potential and hydrodynamic diameter.

Mentions: The effect of primary particle size on dispersion properties was examined by dispersing different sized anatase TiO2 in DI water. Since the same mass concentration (50 μg/ml) was used for all samples with differing particle sizes, the TiO2 particle surface area increased dramatically as particle size decreased (Figure 6a). Solution pH decreased with increasing particle surface area (as discussed earlier). Anatase TiO2 of 6 nm had the highest positive zeta potential due to its high IEP and low solution pH. A transition from positive to negative zeta potential happened between 16 and 26 nm. TiO2 of 104 nm has the highest negative zeta potential due to its low IEP and high solution pH. The average hydrodynamic diameter is not only a function of zeta potential and solution IS, but also a strong function of primary particle size. If no agglomeration occurs, i.e., the repulsive forces are completely dominant over the attractive forces, the hydrodynamic diameter should just reflect the primary particle size. The average hydrodynamic diameter increased from 67 to 490 nm as primary particle size increased from 6 to 104 nm (Figure 6b). The fact that the dispersion hydrodynamic diameter increment is not linearly proportional to primary particle size increment is due to particle–particle interaction that is affected by the dispersion zeta potential and IS. A detailed discussion of the reasons for the dispersion hydrodynamic diameter being larger than primary particle size can be found elsewhere [15].


Role of Surface Area, Primary Particle Size, and Crystal Phase on Titanium Dioxide Nanoparticle Dispersion Properties
Different sized anatase TiO2 nanoparticles dispersed in DI water with the same mass concentration of 50 μg/ml: a pH and surface area concentration; b dispersion zeta potential and hydrodynamic diameter.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211333&req=5

Figure 6: Different sized anatase TiO2 nanoparticles dispersed in DI water with the same mass concentration of 50 μg/ml: a pH and surface area concentration; b dispersion zeta potential and hydrodynamic diameter.
Mentions: The effect of primary particle size on dispersion properties was examined by dispersing different sized anatase TiO2 in DI water. Since the same mass concentration (50 μg/ml) was used for all samples with differing particle sizes, the TiO2 particle surface area increased dramatically as particle size decreased (Figure 6a). Solution pH decreased with increasing particle surface area (as discussed earlier). Anatase TiO2 of 6 nm had the highest positive zeta potential due to its high IEP and low solution pH. A transition from positive to negative zeta potential happened between 16 and 26 nm. TiO2 of 104 nm has the highest negative zeta potential due to its low IEP and high solution pH. The average hydrodynamic diameter is not only a function of zeta potential and solution IS, but also a strong function of primary particle size. If no agglomeration occurs, i.e., the repulsive forces are completely dominant over the attractive forces, the hydrodynamic diameter should just reflect the primary particle size. The average hydrodynamic diameter increased from 67 to 490 nm as primary particle size increased from 6 to 104 nm (Figure 6b). The fact that the dispersion hydrodynamic diameter increment is not linearly proportional to primary particle size increment is due to particle–particle interaction that is affected by the dispersion zeta potential and IS. A detailed discussion of the reasons for the dispersion hydrodynamic diameter being larger than primary particle size can be found elsewhere [15].

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO2 nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO2 samples, and one commercial Degussa TiO2 sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl2) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO2 isoelectric point was found to be dependent on particle size. As anatase TiO2 primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO2 nanoparticle IEP was found to be insensitive to particle crystal structure.

No MeSH data available.