Preparation of Copper Oxide (CuO) Nanoparticles and their

58 International Journal of Manufacturing, Materials, and Mechanical Engineering, 1(4), 58-64, October-December 2011

Preparation of Copper Oxide (CuO) Nanoparticles and their Bactericidal Activity F. M. Al-Marzouki, King Abdulaziz University, Saudi Arabia O. A. Al-Hartomy, King Abdulaziz University, Saudi Arabia M. A. Shah, King Abdulaziz University, Saudi Arabia

ABSTRACT Single crystalline nanoparticles of copper oxide (CuO) having almost uniform particle size of ~40±10nm have been synthesized by a facile and versatile route. The technique employed is free from toxic solvents, organics, and amines, and is based on a simple reaction of copper powder and de-ionized water (DI) at very low temperatures of 180oC. The morphology, chemical composition, and crystalline structure of the nanoparticles were carefully investigated by the various characterization techniques. Besides simplicity, the advantages of producing nanoparticles by this method are that it is easeful, flexible, fast, cost effective, and pollution free. The synthesized nanoparticles are under investigations for various applications including their antibacterial activity. Keywords:

Antibacterial Activity, Characterization, Nanoparticles, SEM, Synthesis

1. INTRODUCTION As a semiconductor with a narrow bandgap (Eg = 1.2eV), Copper oxide (CuO) is a unique monoxide compound (in monoclinic phase, different from normal rock salt type structure) for both fundamental investigations and practical applications. It has been used as heterogeneous catalysts in many important chemical processes, such as degradation of nitrous oxide with ammonia and oxidation of

DOI: 10.4018/ijmmme.2011100104

carbon monoxide, hydrocarbon and phenol in supercritical water. CuO can also be used as gas sensor, optical switch, magnetic storage media, lithium batteries and solar cells owing to its photoconductive and photochemical properties (Sambandan et al., 2005; Liu et al., 2006). It is well known that copper oxide have been used to disinfect liquids, solids and human tissue for centuries. Today it is used as water purifier, an algaecide, a fungicide and a nematocide as well as an antibacterial and antifouling agent (Ren et al., 2009). It is well known that copper oxides can be conveniently obtained by thermal decomposi-

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International Journal of Manufacturing, Materials, and Mechanical Engineering, 1(4), 58-64, October-December 2011 59

tion of copper salts (Han et al., 2008; Wang et al., 2002; Mang et al., 2008; Xu et al., 1999). However, it is too difficult to control the grain size of resulting copper oxide (CuO) particles through methods available, which is one of the essential requirements/conditions for the synthesis of nanomaterials. Moreover, the production in all cases required either elevated temperatures including prolonged reactions under special conditions or other tedious procedures in presence of harmful gases. In addition, most of the pathways suggested for the synthesis of CuO nanocrystals involve environmentally malignant chemicals and organic solvents which are toxic and not easily degraded in the environment. Environmental friendly chemical synthesis requires alternative solvents such as ionic liquids, liquid and water. Water is particularly attractive because it is inexpensive, safe, environmentally benign and bestowed with many virtues especially under supercritical conditions (Vostriko et al., 2009). Encouraged by the interesting and useful results (Shah et al., 2009), we decided to apply the approach to copper metal. Interestingly, uniform sized nanoparticles were obtained by a simple reaction of copper powder and de-ionized water at very low temperature of 180oC. The diameter of nanoparticles ranges from 30-50nm with an average diameter of 40nm. The bactericidal efficacy of the as prepared nano-CuO against Escherichia coli (Grame negative) and Staphylococcus aureus (Grame positive) bacteria was investigated. The reported method besides being organics free is economical, fast, environmentally benign and free of pollution, which will make it suitable for large scale production. The aim of the study is to provide the feasibility of the simple route for the preparation of copper oxide nanostructures without additives and to test their antibacterial efficiency. The prospects of the process are bright and promising.

2. EXPERIMENTAL 2.1. Materials Copper powder (Cu powder, Ranbaxy with diameter > 5μm) was used as a source of copper

and was cleaned by ultra-sonication in acetone and water for 10 minutes in each solvent. The de-ionized water was prepared in the laboratory. Teflon lined stainless steel was used for preparation purpose.

2.2. Preparation 2 mg of copper powder was added to 20 ml of de-ionized water in a glass vial. Few drops of ethylenediamine (en) were added to reaction mixture to avoid agglomeration. The reaction mixture was sonicated for about 30 minutes in a glass veil, transferred into a stainless steel Teflon lined metallic bomb of 100ml capacity and sealed under normal conditions. The closed chamber was then placed inside a preheated box furnace and the mixture was heated slowly (2oC/ min) to 180oC and maintained at this temperature for 12 hours. The furnace is allowed to cool after the desired time and the resulting suspension was centrifuged to retrieve the product, washed and then finally vacuum dried for few hours.

2.3. Characterization The as synthesized powder was directly transferred to FESEM chamber without coating. The morphology and the size of the products were carried out using high resolution FE-SEM (FEI NOVA NANOSEM-600) coupled with energy dispersive x-ray spectrometer (EDX). The features and shapes of the particles were also imaged by Transmission Electron Microscope (TEM) operated at 200kV. Structural information was given by powder X-ray diffraction (XRD) using a PAN analytical (X’ pert PW 3710,) diffractometer with 2θ ranging from 10-90o, using Cu Kα (λ =0.15141 nm) radiation operated at 40kV and 30mA.

2.4. Antimicrobial Test The antibacterial activity was tested against Grame positive Staphylococus aureus (S. aureus) bacteria and to Grame negative Escherichia coli (E.Coli) as well. The Staphylococus was resistant to gentamicine and to braymicine antibiotoxics. The second strain E.coil, Grame



Figure 1. Typical (a and b) low and (c and d) high-resolution FESEM images of CuO nanoparticles obtained by the reaction of copper metal powder with water at 180°C for 12h

negative bacteria was resistant to chloromphenicol and tetracycline.

3. RESULTS AND DISCUSSION 3.1. Morphology Figure 1 (a) and (b) show the low and high magnification FESEM images of the nanoparticles and confirms that the nanoparticles are grown with well defined morphology. The nanoparticles are almost spherical in shape and have diameters varying between 30 to 50nm, with an average diameter of 40nm. The particle size

was also examined using TEM. Figure 2 displays TEM micrographs of CuO revealing the average particle size is approximately 40nm. The influence of reaction conditions on physical properties of synthesized nanoparticles as well as mechanism is yet to be investigated.

3.2. Structural Characterization To identify the crystallinity and crystal phases of the as-grown structures, X-ray diffraction (XRD) analysis was performed and shown in Figure 3. All the peaks could be clearly indexed to monoclinic phase with lattice constants a = 0.4675, b = 0.3418 and c =



Figure 2. TEM micrograph of CuO nanoparticle

Figure 3. Corresponding XRD pattern of CuO nanoparticles. The inset shows the EDX pattern

0.5095 which were consistent with the literature (JCPDS-05-0661). The XRD diffraction peaks indicate small size of crystalline CuO particles. No diffraction peaks arising from any impurity can be detected in the pattern confirms that the grown products are pure. The result is quite different from the traditional process in which only amorphous phase can be obtained from the precipitates derived by solution process before calcinations and further

higher temperature heat treatment is normally required to induce crystallization (Yuan et al., 2007). Thus, this method, “the soft option of hydrothermal treatment” may be regarded as an alternative to calcinations for promoting the crystallization. The EDX pattern as shown in inset of Figure 3 confirms the composition of the sample shows no other peak for any other element has been found which again confirmed that nanoparticles are pure.



3.3. Bactericidal Tests The antibacterial activity of CuO nanoparticles were tested by treating staph aerues and E.coli with 2mgmL-1 of the nanoparticles. The minimal inhibitory concentration (MIC) of these particles on staph aureus and E. coli strains was found in both cases to be 0.625mg mL-1. The test was carried out in nutrient broth as traditional MIC test for bacteria. The tests were performed while the bacteria were grown in their broth medium. The results of the treatment before and after are shown in Figure 4. Overnight cultures of S. aureus and E. coli were grown on nutrient agar. These cultures were transferred into broth at pH 7, to final volume of 50ml, at an initial optical density of 0.1 and allowed to grow at 37oC and counted for viable bacteria by counting the colony forming units in each plate. Two controls were included in the experiment, one with the absence of bacteria and nanoparticles and second with bacteria but without the presence of bacteria.

3.4. Formation Mechanism The formation of copper oxide nanoparticles by the reaction of copper with water can be

explained by reaction mechanism. As initially, copper reacted with water and forms a protective hydroxide Cu(OH)2 layer with dissolved hydroxide ions onto the surfaces of the Cu foil according to the following reaction mechanism: Cu2+ + 2OH- → Cu(OH)2(s) As the concentration of the Cu2+ and OH‾ ions exceeds a critical value, the precipitation of CuO nuclei starts. The Cu(OH)2 can be transformed into the CuO crystals via the simple chemical reactions mentioned: Cu(OH)2(s) ∆ 2CuO (s) + 2H2O(l) →

The Cu metal on reaction with water slowly gives out hydrogen (g) and the liberated oxygen reacts with metal to give oxides as shown in the above reaction. The growth of nanoparticles could be occurring at the small oxide nuclei that may be present on the metal surfaces. Moreover, water at elevated temperatures plays an essential role in the precursor material transformation because the vapour pressure is much higher and the state

Figure 4. (c and d) Staphylococcus aureus (Grame positive) and Escherichia coli (Grame negative) bacteria before and after treatment of CuO nanoparticles respectively



of water at elevated temperatures is different from that at room temperature. The solubility and the reactivity of the reactants also change at high pressures and temperatures and high pressure is favorable for crystallizations (Wang et al., 2007). Due to the temperature and pressure in the autoclave under the hydrothermal condition, a completely different reaction mechanism and formation sequence may be rationalized. The steam is generated under high temperatures to produce a hydrostatic pressure which in turn imposes a profound effect on the ultimate microstructure of the oxides thus prepared. This autogeneous hydrostatic pressure can be as high as 9 bars under a hydrothermal temperature of 180◦C. Therefore, it can be said that in this aqueous system in the sealed autoclave, the temperature has much higher impact reaction rate, the morphology, as well as the reaction mechanism.

4. CONCLUSION Uniform sized ~ 40±10nm particles of copper oxide were synthesized by a very versatile, non toxic and environmental friendly approach at 180oC without using any organics. The process is a simple, efficient and one step synthesis. It may be extended to fabricate other metal oxide nanomaterials. The mechanism of nanoparticle formation has been discussed in relation to the sample preparation conditions in detail. The performance of the as synthesized particles was investigated and their excellent bacterial effected demonstrated. These can be recommended for the purification of medical and food equipments.

ACKNOWLEDGMENT The authors are thankful to the Deanship of research, KAU, Jeddah for financial support of this work. KACST, Riyadh is acknowledged for characterization of materials.

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F. M. Al_Marzouki has carried his studies including doctorate in UK and is working in King Abdul Aziz University, Jeddah, Saudi Arabia from the last three decades. He has been on various administrative posts from time to time and a reputed scientist. His interests include electrical measurements and application of materials in devices. To his credit are more than 50 peer reviewed papers, more than 100 in conference proceedings and is a member of many science academies. O. A. Al-Hartomy is a solid state physicist and has carried his entire studies in UK. A dedicated and a hard worker is a member of many societies besides occupying vital administrative post in Tabuk University in Saudi Arabia. M. A. Shah, is an author of “Principles of Nanoscience and Nanotechnology” and an explorer of a versatile technique “A Safe way to Nanotechnology” for the synthesis of nanomaterials. Dr. Shah graduated from the University of Kashmir, Srinagar and doctorate in Materials Science, from Jamia Millia Islamia, New Delhi in year 2000. In the same year 2000, he joined National Institute of Technology Srinagar as an Assistant professor and worked on various administrative posts. He has established World Bank funded Sophisticated Instrumentation Centre (SIC) which caters the needs of scientific fraternity of whole region and has received grants from other funding agencies. Recently, joined Faculty of Sciences, King Abdul Aziz University, Jeddah, Saudi Arabia, Dr. Shah is extending the novel approach to other oxides. He is a member of many science academies and societies. He is the corresponding author for this article.
