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Shraddha Shekar, Markus Sander, Alastair Smith, Markus Kraft 17 September, 2010 A novel pathway for flame synthesis of silica nanoparticles

A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. [email protected]. Silica nanoparticles. Silica

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Page 1: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha Shekar, Markus Sander,Alastair Smith, Markus Kraft17 September, 2010

A novel pathway for flame synthesis of silica nanoparticles

Page 2: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Silica nanoparticlesSilica Nanoparticles: network of Si-O bonds such that Si:O = 1:2

Applications:

•Support material for functional/composite nanoparticles, catalysis

•Bio-medical applications, drug delivery

•Optics, optoelectronics, photoelectronics

•Fabrics, clothes

Page 3: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Physical systemPrecursor(TEOS) Flame reactor

P ≥ 1 atm

T ≈ 1100 - 1500 K

Silica nanoparticles

Macroscopic level questions:•Optimal process conditions?

•Final product properties?•Final particle size

distribution?Indu

stria

l Sc

ale

Mol

ecul

ar

Scal

e

Answers from molecular level studies:•How to determine the thermochemistry of the system?•What happens in the gas-phase?•How do gas-phase precursors form the particles?•How to describe the overall system from first-principles?

Page 4: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Methods: Ab initio modelling

Quantum Chemistrycalculations

Statistical Mechanics

H(T) S(T) Cp(T)

Thermochemistrycalculation

ChemicalKinetics

Equilibriumcalculation

Overall Model

Species generation

Population Balance Model

Ref: W. Phadungsukanan, S. Shekar, R. Shirley, M. Sander, R. H. West, and M. Kraft. First-principles thermochemistry for silicon species in the decomposition of tetraethoxysilane. J. Phys. Chem. A, 113, 9041–9049, 2009

Page 5: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Equilibrium Plot

Ref: W. Phadungsukanan, S. Shekar, R. Shirley, M. Sander, R. H. West, and M. Kraft. First-principles thermochemistry for silicon species in the decomposition of tetraethoxysilane. J. Phys. Chem. A, 113, 9041–9049, 2009

Page 6: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Reaction kinetics

• Equilibrium– Hints towards the

existence of stable intermediates & products.

– Intermediates Si(OH)x(OCH3)4-x Si(OH)y(OC2H5)4-y

– Main Product Si(OH)4

• Kinetics– Reaction set generated

to include all intermediates and products from equilbrium.

– Reactions obey Arrhenius law rate constant k = ATβe-Ea/RT

– Rate parameters (A, β, Ea) fitted to experimental vaues (a)

(a) J. Herzler, J. A. Manion, and W. Tsang. Single-Pulse Shock Tube Study of the decomposition of tetraethoxysilane and Related Compounds. J. Phys. Chem. A, 101,5500-5508, 1997

Page 7: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Reaction Mechanism• Heuristic reaction mechanism

C8H20O4SI = C6H16O4SI + C2H4 C6H16O4SI = C4H12O4SI + C2H4 C4H12O4SI = C2H8O4SI + C2H4 C2H8O4SI = H4O4SI + C2H4 C8H20O4SI = C7H17O4SI + CH3 C7H17O4SI = C2H4 + C5H13O4SI C5H13O4SI = C2H4 + C3H9O4SI C3H9O4SI = C2H4 + CH5O4SI CH5O4SI = H4O4SI + CH C7H17O4SI = C7H16O4SI + H C7H16O4SI = C6H13O4SI + CH3 C6H13O4SI = C6H12O4SI + H C6H12O4SI = C4H10O4SI + C2H2 C4H10O4SI = C2H8O4SI + C2H2 C8H20O4SI = C2H4 + C6H16O4SI2

C6H16O4SI2 = C2H4 + C4H12O4SI2C4H12O4SI2 = C2H4 + C2H8O4SI2 C2H8O4SI2 = C2H4 + H4O4SI C8H20O4SI = C2H5 + C6H15O4SI2 C6H15O4SI2 + H = C6H16O4SI2 C6H16O4SI2 = C2H5 + C4H11O4SI2 C4H11O4SI2 + H = C4H12O4SI2 C4H12O4SI2 = C2H5 + C2H7O4SI2 C2H7O4SI2 + H = C2H8O4SI2 C2H7O4SI2 = H3O4SI + C2H4 H3O4SI = H2O3SI + OH H2O3SI = SIO2 + H2O C6H15O4SI2 = C2H3 + C4H12O4SI2 C4H11O4SI2 = C2H3 + C2H8O4SI2 C2H8O4SI2 = H3O4SI + C2H3

Page 8: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Flux and Sensitivity Analyses

Main Reaction Pathway

Reaction number

Page 9: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Experimental validation

(a) J. Herzler, J. A. Manion, and W. Tsang. Single-Pulse Shock Tube Study of the decomposition of tetraethoxysilane and Related Compounds. J. Phys. Chem. A, 101,5500-5508, 1997

Page 10: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Optimisation Theory• Experimental data

• Model response with paramaters x

• and

xBAx For a simple linear model, K=1

cxBAcx 0,,

000 xBAcxEx ,, 220 cBcxc ,,Var

expexp0

exp

cxx 0

x Kxx ,...,1xwith

with uncertainty factor c andstandard normally distributed

A. Braumann, P. L. W. Man, and M. Kraft. Statistical approximation of the inverseproblem in multivariate population balance modelling. Ind. Eng. Chem. Res., 49:428–438, 2010. doi:10.1021/ie901230u

Page 11: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Model OptimisationThe rate parameters have been fitted to shock-tube experimental data provided by Herzler et al(a)

(a) J. Herzler, J. A. Manion, and W. Tsang. Single-Pulse Shock Tube Study of the decomposition of tetraethoxysilane and Related Compounds. J. Phys. Chem. A, 101,5500-5508, 1997

Step 2: Sensitivity AnalysisTo identify the 4 most sensitive parameters

Step 1: Low discrepancy seriesTo perform a pre-scan of parameters for 18 Si reactions.

Step 3: Response Surface MethodologyTo estimate model uncertainties

Uncertainties in model parameters for reactions R1 and R15

Page 12: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Gas-phase mechanism

Page 13: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Reactor Plot

Conclusion from kinetic model:

Si(OH)4 is the predominant gas-phase precursor

Page 14: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Main reaction pathway

Si

O

O

OO

H2C

CH2

CH2

H2C

-C2H4

H3C

H2C

CH3

H

Si

O

O

OO

H2C

CH2

CH3

H3CH3C

CH3

Si

O

O

OO

H3C

H3C

CH3

H3C

Si

OH

HO

HO

OH

H2CH

-C2H4

Si

O

O

OO

H3C

H3C

H

H

-C2H4

Si

O

O

OO

H2C

CH2

CH2

H2C

-C2H4

H3C

H2C

CH3

H

CH3-C2H4

Si

O

O

OO

H2C

CH2

CH2

HH3C

CH3

CH3-C2H4

Si

O

O

OO

H2C

CH2

H

HH3C

CH3

Si

O

O

OO

H

CH2

H

HH3C

-C2H4

-C2H4

Reaction Pathway 1

Reaction Pathway 2

Page 15: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Particle Model

Si

O

O

O

O

H

H

H

H

Si

O

O

O

O

H

H

H

H

-H2O Si

O

O

O

O

H

HH

Si

O

O

O

H

HH

INCEPTION

Si

O

O

O

OSi

O

O

Si

-nH2OSURFACEGROWTH

OSi

SiSi

Si SiO

n(-O-Si-O-Si-)

Si(OH)4 molecules in gas-phase undergo inception to form a dimer (-Si-O-Si). This dimer is considered to be the first particle.Particle growth then proceeds by subsequent removal of hydroxyl groups.

Page 16: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Particle Processes

[1]: M. Sander, R. H. West, M. S. Celnik, and M. Kraft. A Detailed Model for the Sintering of Polydispersed Nanoparticle Agglomerates, Aerosol Sci. Tech., 43, 978-989, 2009

New inception and surface growth steps have been incorporated in a previously developed stochastic particle model developed by Sander et al. [1].

Particle ineption

Surface growthCoagulation

Particle rounding due to surface growth

P = P(p1, p2, .....pn, C, I, S)

p = p(vi)

SinteringSurface reactionCondensationInception

Page 17: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Individual Processes and Rates1. Inception

2. Surface Reaction

Page 18: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Individual Processes3. Coagulation

Pi

Pj Pk

+

pi

pj

pi

pj pk

No Sintering Partial Sintering Complete Sintering

4. Sintering

Page 19: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Experimental Setup of Seto et al.

Ref: T. Seto, A. Hirota, T. Fujimoto, M. Shimada, and K. Okuyama. Sintering of Polydisperse Nanometer-Sized Agglomerates, Aerosol Sci. Tech., 27, 422-438, 1997

Reactor 1: T = 900oC

Particle formation zone

Reactor 2: T > 900oC

Particle heating zone

Page 20: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Model Optimisation

Ref (a): T. Seto, A. Hirota, T. Fujimoto, M. Shimada, and K. Okuyama. Sintering of Polydisperse Nanometer-Sized Agglomerates, Aerosol Sci. Tech., 27, 422-438, 1997

Material dependent sintering parameters are optimised

Optimisation method: LD series and RSM

Primary diameter (dp) and collision diameters (dc) fitted to experimental values at different temperatures.

Page 21: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Effect of temperature

•Sintering increases as temperature increases reducing the collision diameters.

•At a temperature of about 2000 C, the collision diameter and primary diameter become identical and particles become spherical.

Page 22: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Particle size distribution

Ref (a): T. Seto, A. Hirota, T. Fujimoto, M. Shimada, and K. Okuyama. Sintering of Polydisperse Nanometer-Sized Agglomerates, Aerosol Sci. Tech., 27, 422-438, 1997

Solid lines: ModelCircles: Experiments (a)

Page 23: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Model produced TEM-like images

Ref (a): T. Seto, A. Hirota, T. Fujimoto, M. Shimada, and K. Okuyama. Sintering of Polydisperse Nanometer-Sized Agglomerates, Aerosol Sci. Tech., 27, 422-438, 1997

Page 24: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Overall mechanism for particle formation

Si

O

O

O

O

H

H

H

H

Si

O

O

O

O

H

H

H

H

Si

O

O

O

O

H

HH

Si

O

O

O

H

HH

OHH

Si

O

O

O

O

H2C

CH2

CH2

H2CCH3

CH3

CH3

H3C

Si

O

O

O

O

H3C

H3C

CH3

H3C

Si

O

O

O

O

H

H

H

H

Si

O

O

O

O

H

H

H

Si

O

O

O

H

HH

Si

O

O

O

O

H

H

H

H

Si

O

O

O

O

H

HH

H

SiO

O

O

OH

H

H

H

Si

O

O

O

OH

H

H

H

Si

O

O

O

OSi

O

O

SiOSi

SiSi

Si SiO

Gas

-pha

sere

actio

nsPa

rticl

efo

rmat

i on

Parti

cle

g row

th

-2C2H4 -2C2H4

-2H2O

-nH2O

[monomer]

[primary particle]

(-O-Si-O-)n [Silica particle]

The gas-phase and particle model described above are coupled using an operator splitting technique to generate the overall model.

Page 25: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

Conclusion

1. New kinetic model proposed which postulates silicic acid Si(OH)4 as the main product of TEOS decomposition.

2. A novel pathway proposed for the formation of silica nanoparticles via the interaction of silicic acid monomers.

3. Feasibility of using first-principles to gather a deeper understanding of complex particle synthesis processes.

Page 26: A novel pathway for flame synthesis of silica nanoparticles...A novel pathway for flame synthesis of silica nanoparticles. Shraddha Shekar. ss663@cam.ac.uk. Silica nanoparticles. Silica

Shraddha [email protected]

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