Synthesis of Copper Nanoparticles by Thermal Decomposition and Their Antimicrobial Properties

Copper nanoparticles were synthesized by thermal decomposition using copper chloride, sodium oleate, and phenyl ether as solvent agents. The formation of nanoparticles was evidenced by the X-ray diffraction and transmission electron microscopy. The peaks in the XRD pattern correspond to the standard values of the face centered cubic (fcc) structure of metallic copper and no peaks of other impurity crystalline phases were detected. TEM analysis showed spherical nanoparticles with sizes in the range of 4 to 18？nm. The antibacterial properties of copper nanoparticles were evaluated in vitro against strains of Staphylococcus aureus and Pseudomonas aeruginosa. The antibacterial activity of copper nanoparticles synthesized by thermal decomposition showed significant inhibitory effect against these highly multidrug-resistant bacterial strains. 1. Introduction Recently metallic nanoparticles (NPs) have attracted great interest because of their unique physical and chemical properties. Their properties can be controlled depending on the synthesis method. One of the main effects, which are enhanced by controlling particle size, is their antimicrobial action [1, 2]. The antimicrobial activity of NPs is known to be a function of surface area in contact with microorganisms. For this reason, high surface area NPs assure a wide range of reactions on the surface of microorganisms, inhibiting the normal function of cells or causing cell death [3]. Several methods have been used for the formation of copper nanoparticles. One of the first reported methods to obtain inorganic NPs is the chemical coprecipitation method, which involves nucleation and growth during the same process [4], but the main disadvantage of this process is the formation of agglomerated NPs with a wide size distribution. Nanometric particles with size control have been obtained through homogeneous precipitation reactions, which involve separation of nucleation and growth process. Under conditions of homogeneous precipitation, an abrupt nucleation occurs when reactive concentrations reach a supercritical saturation point [5], generating this way a homogeneous growth by solutes diffusion from solution to surface, achieving their final size. The key to obtain homogeneous particle size is the separation of nucleation and growth steps, avoiding nucleation during NPs growth step; if performed with direct heating of the mixture, a wide size distribution of NPs can be produced [5, 6]. Thermal decomposition of metallic precursors in presence of organic surfactants at high temperature is a method widely used due