Synthesis and Extraction of Monodisperse Sodium Carboxymethylcellulose-Stabilized Platinum Nanoparticles for the Self-assembly of Ordered Arrays

This paper presents a facile and effective nanoparticle synthesis approach based on aqueous sodium carboxymethylcellulose (CMC) solutions coupled with an organic phase extraction to yield dodecanethiol-capped Pt nanoparticle dispersions with narrow size distribution (using 0.15 wt % CMC in the system the average diameter = 3.9 nm, the standard deviation = 0.40 nm, and the relative standard deviation = 10.2%). CMC has been demonstrated by Fourier transform IR (FT-IR) spectra to anchor to the Pt particle surface via both −COO and −OH groups, thereby suppressing the growth and agglomeration of the particles. These CMC-stabilized Pt nanoparticles could be extracted from the aqueous solution to the hexane phase using dodecanethiol as an extractant with the assistance of concentrated HCl to adjust the pH of the solution. The concentrated monodisperse Pt nanoparticle dispersions within the hexane were subsequently self-assembled into closely packed and ordered arrays (or 2-D superlattices) by simply evaporating the hexane solvent. The molecular structure of the CMC enables this “green” and inexpensive polysugar to exert stronger interaction with particles compared with that of β- d -glucose (another “green” capping agent that exhibits the ability to passivate the particles surface via −OH groups). The additional interaction exerted by the −COO groups of CMC molecules plays an important role in passivating the Pt nanoparticle surface such that more narrow size distributions can be obtained. The narrower particle size distributions improve the ability to assemble these nanoparticle building blocks into ordered arrays. This has been systematically demonstrated through comparative experiments using CMC, β- d -glucose, or the absence of any capping agent before extraction. This study provides an opportunity for controlled synthesis and efficient construction of metallic nanoparticle ordered arrays using straightforward processing techniques.