Colloids and Surfaces A: Physicochem. Eng. Aspects 466 (2015) 189–196 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journa l h om epage: www.elsevier.com/locate/colsurfa Preparation of stable sub 10 nm copper nanopowders redispersible in polar and non-polar solvents Partha Pratim Chowdhury, Aabid Hussain Shaik, Jayanta Chakraborty ∗ Department of Chemical Engineering, IIT Kharagpur, 721302, India h i g h l i g h t s • Sub 10 nm PVP–PEG protected cop- per nanoparticles have been pre- pared. • Centrifugation and ethanol precip- itation employed to prepare Cu nanopowder. • Cu nanopowder was redispersed in water, DMF, DMSO, chloroform. • Concentrated Cu colloid has been successfully phase transferred. • Toluene soluble Cu nanopowders have been successfully produced. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 14 June 2014 Received in revised form 25 September 2014 Accepted 16 October 2014 Available online 23 October 2014 Keywords: Nanopowder Copper nanoparticles Polymer stabilized copper nanoparticles Phase transfer Centrifugation a b s t r a c t In this work we prepare 10 nm copper nanopowders redispersible in various polar and non-polar solvents. First, concentrated colloid of copper nanoparticles protected by PVP–PEG is synthesized by a simple wet chemical method using hydrazine hydrate as reducing agent. Extremely stable copper nano-powder con- taining sub 10 nm particles can be readily prepared by drying this colloid. This powder readily disperses in water, DMF, DMSO and choloroform and produces a stable colloid. To increase the copper content of the powder, washing of the colloid using (i) high speed centrifugation and (ii) ethanol addition and centrifugation at lower speed have been successfully conducted. The high speed centrifugation increases the size of the colloid to 50 nm after re-suspension while the size remains sub-10 nm when washing is conducted using ethanol. Particles were also phase transferred successfully from the aqueous polymeric solution to toluene using a protocol previously used for gold nano-rods. Many other simpler phase trans- fer techniques have also been tried but such methods failed to transfer particles from such polymer loaded colloid efficiently. Stable organic dispersible nanopowders have been produced from the organosol. The particle size is preserved after phase transfer and redispersion in organic solvent. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Nanoparticles have become a popular product in the market for a variety of applications such as catalysis [1], biosensors [2], ∗ Corresponding author. Tel.: +91 3222283950. E-mail addresses: ppc.sodepore@gmail.com (P.P. Chowdhury), aabid.iitkgp@iitkgp.ac.in (A.H. Shaik), jayanta@che.iitkgp.ernet.in (J. Chakraborty). optoelectronics [3], absorbents [4] etc. Copper nanoparticles are of special interest because of its favourable properties and low cost. It has applications in various fields such as ink jet printing technology [5], catalysis [6], medicine [7], antimicrobial agents [8], etc. While a lot of other nanoparticles are available as nanopowder, copper nanoparticles are mostly obtained as colloidal solution. Literature on production of copper nanopowder is very sparse. The aim of this article is to demonstrate production of stable, re-dispersible sub-10 nm copper nano-powders. http://dx.doi.org/10.1016/j.colsurfa.2014.10.031 0927-7757/© 2014 Elsevier B.V. All rights reserved.