μReactor Synthesis of Nano-Particles
Interest in Nano-Particles
In recent years, nano-particles have gained attention for their application in
a variety of fields. Nano-particles have a dimension between 1 and 100 nm,
a region where particles exhibit unique properties compared to their macro
scale counter parts. The chemical, electrical and optical properties of nanoparticles can be tuned based on particle size to meet the needs of specific
applications.
Eric Hostetler, Joe Ferron, Mohammad Al Falasi
Project Advisor: Dr. Greg Herman
Future µReactor System
Reaction Kinetics
Precursors are dissociated in water
Mass Production of Nano-Particles
To meet increasing demand for nano-particles tuned for specific
applications, better methods of mass production are needed.
Co-precipitation is a promising method of nano-particle synthesis which has
the advantage of cheap precursors and mild conditions relative to the solgel process, forced hydrolysis or decomposition reactions.
Continuous flow µreactors offer many advantages over batch reactors
including short mixing times, increased heat transfer and the ability to
make in-situ changes to the process.
Project Objective
Develop a continuous flow μreactor process for synthesis of nano-particles
in aqueous solution with in-situ monitoring of particle size and distribution.
• Build continuous flow µreactor system
• Study the synthesis of ZnO to determine parameters for in-situ tuning
of particle size.
• Evaluate particle measurement techniques for use as in-situ
monitoring devices.
Reactants are mixed, to increase the supersaturation
above a critical point (pH≈8.5) beginning nucleation of
Zn(OH)2.
Where supersaturation occurs when the product of a
reaction is insoluble. This can be expresses as a
supersaturation constant, which has a maximum value when
the reactant product is least soluble.
During the nucleation process particles below a certain size
(R*) are dissolved and particles above a critical size continue
to grow beyond the initial nucleation size.
• UV/Visible Spectrometry – Measure particle absorption and transmission
of light which changes due to nano-particle size.
• Fluorescence Spectrometry – Measure light emitted by particles when
excited by a coherent light source.
• Time-of-Flight Mass Spectrometry – Measure the mass to charge ratio of
particles being accelerated through a constant electrical potential.
Dynamic light scattering shows the most promise as an in-situ particle
analysis tool due to the range of particle sizes it can measure, the resolution
of measurements and the direct correlation to particle size.
Product Solution
Reaction
Vessel
80°C Water Bath
Peristaltic Pump
Reactants
Hot Plate with
Magnetic Stirrer
Thermocouples for
temperature Control
Increasing supersaturation will yield a greater number of
smaller nuclei.
Detection and Characterization
• Dynamic Light Scattering –Measure particle hydrodynamic radius based on
scattering of a coherent light source.
Circulated 80°C
Water Bath
T-mixer
When the solution containing Zn(OH)2 nuclei is heated, ZnO
is created.
In-situ detection of particle size and distribution is desired to allow on
stream tuning of nano-particles. A few detection techniques considered
during this project include:
μReactor versus Batch Reactor
μReactor:
Batch Reactor:
• T-mixer allows short mixing times
creating a homogenous solution
• Continuous flow allows in-situ
changes to the process
• Large surface area to volume ratio
of tubing allows short heating
times
• Reactants constantly mixed but
stagnant areas may cause
concentration gradients in solution
• Multiple runs must be made to
adjust the process
• Heating is less efficient and a few
minutes to reach reaction
temperature.
The rapid reaction at the particle surface is determined by
reactant diffusion rate.
The product is quenched with a large volume of DI water to
stop the reaction and increase the pH to below 8.5 causing
any remaining Zn(OH)2 to dissolve.
Acknowledgments
We would like to thank Dr. Phil Harding and Dr. Greg Herman for their guidance with this project,
Dr. Chih-Hung Chang , Dr. Brian Paul and Dr. Alex Yokochi for there insight into nano-particle
production using μreactors, Seung-Yeol Han use of his μreactor, Dylan Stankus for training and
guidance in particle measurement using DLS and Dr. Mohammad Azizian for training on the ICP tool.
References
• Chih-Hung Chang et. al, Synthesis and post-processing of nanomaterials using microwave technolgy, 02/01/2008.
•Brian L. Cushing, et al., Recent Advances in the Liquid-Phase Synthesis of Inorganic Nanoparticles, 08/20/2004.
•Chih Heng T. Tseng, et al., Continuous Precipitation of Ceria Nanoparticles from a Continuous, Draft ed. , 2010.
Current System
Additional pieces of the
planned μreactor system are
ordered and will be available
for future work on this project.
T-Mixer
Syringe
Pump
Stirred 85°C
Water Bath
Cold DI Water
and Surfactant
The current system has been
used to synthesize ZnO
particles based on the Coprecipitation reaction.
Future Work
•Integrate microwave system, in stream quenching and detection tools.
•Continue recipe development for desired nano-particle type.
•Test alternative solvents and surfactants for increased particle size control .