Zhang et al. Nanoscale Research Letters 2012, 7:312 http://www.nanoscalereslett.com/content/7/1/312 N A N O E X P R E S S Open Access Synthesis of size-controlled monodisperse Pd nanoparticles via a non-aqueous seed-mediated growth Lei Zhang1,2, Lin Wang1,2, Zhiyuan Jiang1,2* and Zhaoxiong Xie1,2 Abstract We demonstrated that stepwise seed-mediated growth could be extended in non-aqueous solution (solvothermal synthesis) and improved as an effective method for controlling the uniform size of palladium nanoparticles (Pd NPs) in a wide range. The monodisperse Pd NPs with the size of about 5 nm were synthesized by simply reducing Pd (acac)2 with formaldehyde in different organic amine solvents. By an improved stepwise seed-mediated synthesis, the size of the monodisperse Pd NPs can be precisely controlled from approximately 5 to 10 nm. The as-prepared Pd NPs could self assemble to well-shaped superlattice crystal without size selection process. Keywords: Nanocrystalline materials, Crystal growth, Pd, Non-aqueous seed-mediated growth, Self-assembly Background As an important catalyst and a promising alternative of Pt-based catalysts, Pd has received continual interest in the past decades [1-4]. For example, Pd nanoparticles (Pd NPs) can be used as efficient catalysts for a large number of carbon-carbon coupling reactions [5,6] as well as hydrogenation/dehydrogenation reactions [7,8]. Pd NPs have also been demonstrated to exhibit efficient electrocatalytic activities in fuel cell reactions [9,10]. As one of the solid heterogeneous catalysts, the perform- ance of Pd strongly depends on the size and/or shape, especially in nanometer scale [11,12]. Therefore, synthe- sis of monodisperse Pd NPs with uniform shape has been an important subject of chemical research. Many methods, especially solution-based synthesis with various protecting agents, have been developed to prepare monodisperse Pd NPs [13-15]. However, most of the reported capping agents, which were used to stabilize Pd NPs and prevent their aggregation, have drawbacks under harsh catalytic reaction conditions because a ‘clean’ surface of the nanoparticles was difficult to get due to the pres- ence of bulky or strongly binding surfactants around these * Correspondence: zyjiang@xmu.edu.cn 1State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China 2Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China nanoparticles [16]. Recently, several groups have suc- ceeded in synthesizing monodisperse Pd NPs with a size smaller than 5 nm by applying oleylamine as the capping agent [17,18]. However, it remains a challenge to control the size of the Pd NPs in a wider range while keeping their uniformity. Seed-mediated growth was widely adopted in synthesis of nanoparticles with different size, but most of them were applied in aqueous solution [19-22]. There were few research reports concerning the seed-mediated growth in non-aqueous solution. In this communication, the stepwise seed-mediated growth was extended in non- aqueous solution (solvothermal synthesis) and improved as an effective method for controlling the uniform size of Pd NPs in a wide range. The seeds were prepared by sim- ply reducing palladium(II) acetylacetonate (Pd(acac)2) with formaldehyde in different organic amine solvents. The size of the monodisperse Pd NPs can be precisely controlled from about 5 to 10 nm. In addition, we con- cluded that amine groups played critical role in stabiliz- ing the Pd NPs. Methods Materials The synthesis was carried out using commercially avail- able reagents. Palladium(II) acetylacetonate, octadecyla- mine (98%) and n-octylamine (99%) were purchased © 2012 Zhang et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.