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Investigations into Sulfobetaine-Stabilized Cu Nanoparticle Formation: Toward Development of a Microfluidic Synthesis

Yujun Song,^† E. E. Doomes,^† John Prindle,^‡ Roland Tittsworth,^† Josef Hormes,^† and Challa S. S. R Kumar*^†

Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, Louisiana 70806, and Chemical and Biomolecular Engineering Department, 300 Lindy Boggs, Tulane University, New Orleans, Louisiana 70118

J. Phys. Chem. B, 2005, 109 (19), pp 9330–9338

DOI: 10.1021/jp044777g

Publication Date (Web): April 22, 2005

†

Louisiana State University.

‡

Tulane University.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

The mechanistic aspects of the formation of sulfobetaine-stabilized copper nanoparticles were investigated by using in situ XANES (X-ray absorption near edge structure), UV−vis spectroscopy, and reaction calorimetry. The tetracoordinated sulfobetaine−Cu(II) complex was reduced to a stable sulfobetaine−Cu(I) complex prior to the formation of sulfobetaine-stabilized copper nanoparticles. The stability of the Cu(I) complex was found to be sensitive to the concentration of the sulfobetaine stabilizer and the addition rate of the reducing agent. It appears to exist primarily as a linear complex. A tetracoordinated Cu(I) complex as an intermediate has also been postulated. Based on the understanding from these investigations, a microfluidic process for copper nanoparticle synthesis was designed by using sulfobetaine−Cu(I) complex as the starting material. When compared with the copper nanoparticles synthesized by a conventional batch process, the microfluidic reactor process provided particles with a smaller size and narrower size distribution. The copper nanoparticles from the microreactor process could also be more easily purified and the particles were relatively stable in air. Both XRD and SAED indicated that the Cu nanoparticles synthesized have fcc structure.

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