NANO: Brief Reports and Reviews Vol. 7, No. 5 (2012) 1230005 (18 pages) © World Scienti¯c Publishing Company DOI: 10.1142/S1793292012300058 SELECTION OF A SUITABLE METHOD FOR THE SYNTHESIS OF COPPER NANOPARTICLES † ‡ ASIM UMER*, SHAHID NAVEED and NAVEED RAMZAN Department of Chemical Engineering University of Engineering and Technology, Lahore *[email protected] †[email protected] ‡[email protected] MUHAMMAD SHAHID RAFIQUE Department of Physics University of Engineering and Technology, Lahore shahidrafi[email protected] Received 12 June 2012 Accepted 4 September 2012 Published 22 November 2012 Various methods for the synthesis of copper nanoparticles employing chemical, physical and biological techniques considering bottom-up and top-down methods synthesis have been studied. The properties of copper nanoparticles depend largely on their synthesis procedures. The results from various investigations performed by di®erent scientists using these methods have been by 204.47.179.116 on 04/16/15. For personal use only. summarized. The applications, characterization techniques, advantages and disadvantages of NANO 2012.07. Downloaded from www.worldscientific.com each synthesis method are also the point of discussion. A detailed study of the results reveals that chemical reduction methods are most suitable for the synthesis of copper nanoparticles. Chemical reduction of copper salts using ascorbic acid (Vitamin C) is a new and green approach in which ascorbic acid is used both as the reduction and capping agent. This approach is the most e®ective and is also economical. Wide applications have been reported in various ¯elds, including heat transfer, catalyst production, electronics and medicine at a commercial scale. This process is nontoxic, environment-friendly and economical. The applications, characterization techniques, advantages and disadvantages of each synthesis method have been presented. Keywords: Nanotechnology; synthesis; copper nanoparticles; chemical reduction; microemulsion. 1. Introduction pharmaceutical, defense, transportations heat trans- Nanotechnology (science at 1À100 nanoscale1)isthe fer to sports and aesthetics. The applications of most promising technology that can be applied nanotechnology are totally dependent on the types of almost all spheres of life, ranging from electronics, the nanoparticles. Many types of nanoparticles are *Corresponding author. 1230005-1 A. Umer et al. being used for di®erent applications, such as metallic, In April 2010, researchers at the University of nonmetallic and magnetic; oxides; nanoparticles California, Los Angeles (UCLA) reported in the carbon and nanotubes. journal Cell that they have imaged a virus structure Metallic nanoparticles are of great interest due to at the atomic level. The electron-microscopic study their excellent physical and chemical properties, of nanoparticles was published in journal Nature such as high surface-to-volume ratio and high heat on 17 February 2011. For the ¯rst time in history, transfer (thermal conductivity). Amongst them, the measurement of atomic structure of nano- copper-based nanoparticles are of great interest due particle was possible. The ¯rst programmable to their low cost and easy availability and because nanowire circuit for nanoprocessors was developed they possess properties similar to that of other in 2011.7 metallic nanoparticles. Catalysts are mostly composed of metals whose selection signi¯cantly depends upon the surface area. High surface-to-volume ratios are the most 2. Historical Background crucial parameter for the selection of a catalyst, which is why this factor is investigated intensely.8 of Nanotechnology Nanoparticles of copper and its alloys have been Feynman (1959), in his famous lecture There's applied more often as catalysts due to their high Plenty of Room at the Bottom originated the idea of surface-to-volume ratio and less cost compared to molecular machines or nanotechnology.2 noble metals. They are used as waterÀgas shift The journey of nanotechnology began when catalysts and gas detoxi¯cation catalysts.9 The Tanigushi (1974) used the term \nanotechnology" most critical factor of a copper-based catalyst is the for the very ¯rst time in his paper on ion-sputter control of size, shape and surface properties of machining.3 The concept of Molecular Nano- the copper nanoparticles.10,11 technology was put forward by Drexler4 in 1979. In Copper nanoparticles have also been con- 1981, Binnig and Rohrer invented the scanning sidered10,11 as an alternative for noble metals in many tunneling microscope.5 The ¯rst technical paper on applications, such as heat transfer and microelec- molecular engineering with atomic precision was tronics.12 The microfabrication of conductive fea- published in 1981, while Bucky-ball was discovered tures like ink-jet printing technology is common. So in 1985. far, electronic devices have utilized noble metals like Fullerene is any molecule that is made up of gold and silver for printing highly conductive carbon, in the form of a hollow sphere, ellipsoid or elements. While the cost of noble metals is very high, by 204.47.179.116 on 04/16/15. For personal use only. tube. It was discovered by Kroto, Smalley and Curl copper is a low-cost and conductive material and is NANO 2012.07. Downloaded from www.worldscientific.com in 1985. In 1989, scientists at the IBM Research therefore, more promising for this technique.13 Center, San Jose, California, spelled out the company's logo using 35 xenon atoms. By doing so, 3. Synthesis Methods of Copper they further demonstrated how nanoparticles can be manipulated. The term Nano°uids6 was coined by Nanoparticles Choi in 1995. Nano°uid is a system in which The production of copper nanoparticles is much more nanoparticles are suspended in base °uids like challenging in comparison to noble metals because water, ethyl glycol, etc. The thermal properties of copper nanoparticles are quite sensitive to aqueous nano°uids are better than those of their parent solutions, and air is stable at these conditions. (base) °uids. Commercial applications of nano- When copper nanoparticles are placed in the technology were began in 2000. open air, aggregation appears immediately due to Until the beginning of the 20th century, the atomic surface oxidation. To avoid this problem, an inert theory was considered only as a mere hypothesis. It environment, such as argon or nitrogen14,15 is used. was ¯nally approved as a fact by the skillful exper- In some cases, inorganic solvents have been used. iments of the French Physicist Jean Baptiste Perrin.7 The presence of protective polymers18À21 or During 2009, the Environmental Protection Agency surfactants,22À25 are also employed for the synthesis (EPA) changed their strategy in order to receive of copper nanoparticles. However, copper is signi¯- more knowledge on how manufactured nanomater- cantly less expensive than silver and gold, therefore, ials may harm human health and the environment. it is economically attractive. 1230005-2 Selection of a Suitable Method for the Synthesis of Copper Nanoparticles Copper nanoparticles can be produced using Table 1. Standard reaction conditions for the production of many di®erent techniques, typically classi¯ed as Cu nanoparticles. bottom-up or chemical methods and top-down or Reducing 26 physical methods. agent Capping agent Conditions Rate Ref. In the bottom-up approach, the structure of Sodium PVP/PEG Ambient Fast 49 nanoparticles is constructed by atoms, molecules or borohydride clusters. In top-down approaches, a bulk piece of a Polyol PVP/PEG >120C Slow 49 required material is reduced to nanosized dimen- Isopropyl PVP/PEG 70À100C Slow 49 sions using cutting, grinding and etching tech- alcohol Sugar PVP/PEG 70À100C Slow 49 niques, i.e., nanomaterials are prepared from larger 27 Hydrazine PVP/PEG <70 C Moderate 49 entities without atomic-level control. 28 Ascorbic Ascorbic acid 80 C Moderate 58 Chemical reduction, microemulsion (colloidal) acid techniques,29 sonochemical reduction,30 electro- chemical,31 microwave-assisted,32 and hydrother- PVP ¼ polyvinylpyrrolidone, PEG ¼ polyethylene glycol. mal33 syntheses are the main techniques for the synthesis of nanoparticles through the chemical approach. Biological or biosynthesis34 techniques are simplest and the most commonly used synthetic also considered as bottom-up or chemical processes. method for copper nanoparticles. In fact, the pro- Physical methods for nanoparticles synthesis are duction of nanosized metal copper particles with laser (pulse) ablation,35 vacuum vapor deposition,36 good control of morphologies and sizes using 37 chemical reduction of copper salts can be pulsed wire discharge (PWD) and mechanical 30À32 milling.38 achieved. The standard reaction conditions are A wide range of nanoparticles can be produced mentioned in Table 1. using physical methods with little modi¯cation for In the chemical reduction techniques, a copper di®erent metals, but the main disadvantages of salt is reduced by a reducing agent such as sodium 28,40À43 Þ 32,44,45 these methods are the quality of the product, which borohydride, hydrazine (N2H4 , ascor- bate,46 polyol,47 isopropyl alcohol with cetyltrimethy- is less as compared to nanoparticles produced by 48 29 chemical methods. Usually these methods require lammonium bromide (CTAB), as well as glucose. costly vacuum systems or equipments to prepare Table 2 presents the published methods to synthesise nanoparticles (plasmas). copper NPs by chemical reduction in solution. During the chemical