μ Reactor Synthesis of Nano-Particles

1. Eric Hostetler, Joe Ferron, Mohammad Al Falasi Project Advisor: Dr. Greg Herman Future µReactor System 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 nano-particles can be tuned based on particle size to meet the needs of specific applications. Reaction Kinetics Precursors are dissociated in water Mass Production of Nano-Particles Reactants are mixed, to increase the supersaturation above a critical point (pH≈8.5) beginning nucleation of Zn(OH)2. • 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 sol-gel 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. μReactor Synthesis of Nano-Particles 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. μReactor versus Batch Reactor Circulated 80°C Water Bath 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. Product Solution Reaction Vessel T-mixer Project Objective 80°C Water Bath Peristaltic Pump • 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 Hot Plate with Magnetic Stirrer Thermocouples for temperature Control Increasing supersaturation will yield a greater number of smaller nuclei. When the solution containing Zn(OH)2 nuclei is heated, ZnO is created. • μReactor: • 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 • Batch Reactor: • 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. Detection and Characterization 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. • 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: • Dynamic Light Scattering –Measure particle hydrodynamic radius based on scattering of a coherent light source. • 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. Current System Additional pieces of the planned μreactor system are ordered and will be available for future work on this project. The current system has been used to synthesize ZnO particles based on the Co-precipitation reaction. T-Mixer Stirred 85°C Water Bath Syringe Pump Cold DI Water and Surfactant 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. • 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 . 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. • ChihHeng T. Tseng, et al., Continuous Precipitation of Ceria Nanoparticles from a Continuous, Draft ed. , 2010.