296 Int J Nanotechnology, Vol 10, Nos 3/4, 2013 Characteristics of colloidal copper particles prepared by using polyvinyl pyrrolidone and polyethylene glycol in chemical reduction method Chien Mau Dang, Chinh Dung Trinh and Dung My Thi Dang* Laboratory for Nanotechnology, Vietnam National University, Ho Chi Minh City, Community 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Vietnam Email: dmchien@vnuhcm.edu.vn Email: tdchinh@vnuhcm.edu.vn Email: dtmdung@vnuhcm.edu.vn *Corresponding author Eric Fribourg-Blanc CEA-LETI, MINATEC Campus, 17, rue des Martyrs, 38054 Grenoble Cedex 9, France Email: eric.fribourg-blanc@cea.fr Abstract: A simple chemical reduction method is used to prepare colloidal copper nanoparticles where polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) are used as stabiliser, size controller and capping agents The main purpose of this paper is to report about the large improvement in replacing PEG by PVP in the reduction synthesis of copper nanoparticles From the TEM results it was found that colloidal copper nanoparticles prepared by using PVP and PEG are well-dispersed From the UV-vis results, surface plasmon peak is very stable over time at 561 nm whereas when using (PEG) the peak shifts from 561 to 572 nm This comparison also shows that copper nanoparticles in the solution using (PVP) have a less dispersed size distribution while presenting an equivalent mean diameter Then it is observed that the oxidation time of copper nanoparticles at room temperature for solution using (PVP) is tenfold that of (PEG) capped nanoparticles Keywords: copper nanoparticle; reduction synthesis; polymer capping; PEG; PVP Reference to this paper should be made as follows: Dang, C.M., Trinh, C.D., Dang, D.M.T and Fribourg-Blanc, E (2013) ‘Characteristics of colloidal copper particles prepared by using polyvinyl pyrrolidone and polyethylene glycol in chemical reduction method’, Int J Nanotechnology, Vol 10, Nos 3/4, pp.296–303 Biographical notes: Chien Mau Dang received the MSc and PhD Degree in Materials Science from the National Polytechnic Institute in Grenoble (Grenoble INP), France in 1991 and 1994 In 1996 and 2007, he received the MSc Degree in Management from the University Pierre Mendes France and the Diploma of Copyright © 2013 Inderscience Enterprises Ltd Characteristics of colloidal copper particles 297 Habilitation for Research Direction in Materials and Process Engineering from the Grenoble INP From 1996 to 2004 he was Head of Department of Materials Science Fundamentals, Vice-Dean of Faculty of Material Technology, Ho Chi Minh City University of Technology From 2005 he is Associate Professor In 2006 he created the Laboratory for Nanotechnology, Vietnam National University, Ho Chi Minh City of which he is Director since then He is a member of several national level research bodies and councils He has authored or co-authored more than 40 publications and patents Chinh Dung Trinh currently is a Researcher at the Laboratory for NanoTechnology – HCM National University He graduated from the University of Science – HCM National University, majoring in Materials Science In 2010 he participated in the project: ‘Study and synthesis of copper nanoparticles for applications in inkjet printing technology’ Up to now he has been developing copper nanoparticles into complete conductive copper nanoparticle ink Dung My Thi Dang received the MS degree in Physics from the University of Science, Vietnam National University – Ho Chi Minh City in 2008 From then she is a Researcher at the Laboratory for Nanotechnology (LNT), Vietnam National University – Ho Chi Minh City She has studied the synthesis of copper and silver nanoparticle and inkjet ink formulation She has authored or co-authored more than ten publications in journals and conferences Eric Fribourg-Blanc received MS degree in Electrical Engineering from Ecole Centrale de Lille, France in (1997), MS and PhD in Electronics from University of Valenciennes, France (1997 and 2003) From 2003 he is a Researcher at CEA-LETI, Grenoble, France His research interests include: microtechnology and microfabrication on silicon and polymers He spent two years at the Laboratory for Nanotechnology in Vietnam (2009–2010) where he provided expertise and built up RFID and inkjet research activities He has (co-)authored more than 20 publications in peer reviewed journals and conferences and holds two patents He is a member of the Materials Research Society This paper is a revised and expanded version of a paper entitled ‘Characteristics of colloidal copper particles prepared by using Polyvinyl pyrrolidone (PVP) and Polyethylene glycols (PEG) in chemical reduction method’ presented at the ‘3rd International Workshop on Nanotechnology and Application (IWNA’2011)’, Vung Tau, Vietnam, 10–12 November 2011 Introduction In the recent decades, metallic and semi-conducting nanoparticles have been widely investigated In nanostructure form, these materials exhibit specific properties that are not presented in their bulk form Nanoparticles are studied for a long time and almost all monoatomic materials including gold [13], silver [12, 15–16] or copper are the subject of intense research due to their potential applications as optical sensors [11, 14], biological labels [18, 19] or conducting deposits [20] Nowadays according to the new trend of electronic industry, metallic nanoparticles are used to make conductive inks [10] that can be used to print electrical paths on different types of substrates There have been many 298 C.M Dang et al successful studies on inks based on silver as metallic nanoparticles Silver nanoparticles have many special characteristics that are of great advantage to make and preserve ink However, the limitation of silver nano ink is of having a high cost which makes it problematic to use in mass production Therefore, we have been studying the replacement of Ag nanoparticles by copper nanoparticles in order to reduce the manufacturing cost of ink There are many methods for copper nanoparticles synthesis including chemical reduction [2, 3], thermal decomposition [4, 5], polyol [1, 6], laser ablation [7], electron beam irradiation [8] and in situ chemical synthetic route [9] We have succeeded in making copper nanoparticles with an average diameter of less than 10 nm by chemical reduction method However, making copper nanoparticles for use in conductive ink presents many difficulties, which stem from peculiar properties of copper, such as easy agglomeration, fast oxidation in atmosphere and low stability of copper nanoparticles in solution Therefore, following our previous study we modified the capping agent (PEG) for PVP in the chemical reduction synthesis in order to study its effect on the properties of copper nanoparticles Materials and methods 2.1 Materials All chemicals were analytical grade as purchased and used without further purification Copper (II) sulphated pentahydrate salt, CuSO4•5H2O, with 98.0–102.0% in purity (Merck), was dissolved in deionised water Polyethylene glycol 6000 (PEG 6000 – Merck) and Polyvinyl pyrrolidone (PVP, average molecular weight of 40,000) were used as the capping agent Sodium borohydride (NaBH4 – Reagent Plus 99%, Sigma-Aldrich) was used as the main reducing agent while ascorbic acid (99.7%, Prolabo) was used as antioxidant of colloidal copper Sodium hydroxide NaOH (> 98%, China) was also used to adjust the pH and accelerate the reduction reaction in water 2.2 Synthesis of copper nanoparticles 2.2.1 PVP 40,000 as a capping layer Copper (II) sulphate pentahydrate salt, CuSO4•5H2O (0.01 M) is first dissolved in deionised water to obtain a blue coloured solution Then polyvinyl pyrrolidone (PVP) 40,000 (0.003 M) is dissolved in water and added to the aqueous solution containing the copper salt while vigorously stirring Ascorbic acid (0.02 M) and sodium hydroxide (0.1 M) are dissolved in water in a separate beaker and added to the synthesis solution Colour change occurs in the aqueous phase from white to yellow This solution is stirred for 90 Finally, a solution of NaBH4 (0.1 M) in deionised water is added to the solution under continuous rapid stirring An instant colour change occurs in the aqueous phase from yellow to violet The mixture is further stirred vigorously for around 10 at ambient atmosphere to allow the reaction to complete 2.2.2 PEG 6000 as a capping layer An ascorbic acid solution is prepared by dissolving 8.8 mg of ascorbic acid in ml of deionised water At the same time, a solution of copper (II) sulphate pentahydrate Characteristics of colloidal copper particles 299 CuSO4•5H2O (0.01 M) in deionised water is added to the ascorbic acid solution under strong magnetic stirring PEG 6000 (0.02 M aqueous solution) is then poured followed by the dropwise addition of a NaOH aqueous solution (0.1 M in deionised water) to adjust the pH up to 12 The mixture is stirred at room temperature for about 15 after which a solution of NaBH4 (0.1 M in deionised water) is added to the mixture under continuous strong stirring for about 10 in order to complete the reaction 2.3 Characterisation Synthesised samples were studied by UV-vis absorption spectroscopy from a doublebeam spectrophotometer (Varian Cary 100) in the wavelength range from 190 to 1100 nm Particle size was studied by using Transmission Electron Microscopy (TEM) Samples for TEM measurements were suspended in ethanol and ultrasonically dispersed Drops of the suspensions were placed on a copper grid coated with carbon Results and discussion 3.1 Stability UV-vis absorption spectra of copper nanoparticles are shown in Figures (PEG capping) and (PVP capping) The spectra were measured immediately after synthesis, then after 1–3 days from sample preparation For the PVP case, the spectra were measured immediately after synthesis, and after day, days, days and 20 days from sample preparation Figure The UV-vis spectra of colloidal copper nanoparticles synthesised in solution prepared with (PEG) at different times (see online version for colours) 2,5 Just after synthesis After days After day After days Absorbance (a.u.) 1,5 0,5 450 500 550 600 650 700 750 Wavelength (nm) The plasmon absorption band for copper nanoparticles has been reported to be in the range of 500–600 nm [9] The figures confirm that copper nanoparticles are formed Figure and Table show that colloidal copper nanoparticles in solution prepared with PEG absorbed around 570 nm On the third day, peaks of the spectra disappeared This 300 C.M Dang et al means that colloidal copper nanoparticles in solution prepared with PEG are only protected within a short time of days From the third day they are almost oxidised completely as seen by a black agglomerate accumulated at the bottom of the container Figure shows that the aborption of copper nanoparticles synthesised with PVP as capping agent display a broadband behaviour especially towards smaller wavelengths As shown in Table 1, the plasmon peak is stable one day after synthesis at 561 nm According to the insert in Figure 2, there still is an absorbing peak, identified at 572 nm, on the 20th day despite less pronounced and accompanied with a shoulder at smaller wavelength This proves that colloidal copper nanoparticles prepared using PVP as capping agent presents much better stability over time With PVP acting as a capping agent [17, 18], copper nanoparticles seem to be better protected against oxidisation over time Figure also shows that the intensity of the spectra peaks tends to decrease over time This means the number of absorption centres (colloidal copper nanoparticles) decreases over time It also means that colloidal copper nanoparticles prepared with PEG are only protected at the beginning but quickly start to modify in solution In Figure 2, the intensity of the spectra peaks increases over time in the first days after synthesis This might be related to a slow evolution of the nanoparticles which are not completely stabilised after synthesis This is then followed by a slight decrease of the intensity of the plasmon peak which we think is slowly weakened by oxidation of copper nanoparticles Figure The UV-vis spectra of colloidal copper nanoparticles synthesised in solution prepared with (PVP) at different times The insert is the UV-vis spectra of the colloidal copper nanoparticles after 20 days (see online version for colours) 0,9 0,8 Absorbance (a.u.) Absorbance (a.u.) 0,7 0,6 0,8 0,6 0,4 0,2 450 500 550 600 650 700 750 Wavelength (nm) 0,5 0,4 0,3 0,2 Just after synthesis After days 0,1 450 500 After days After days 550 600 650 700 750 Wavelength (nm) Table Plasmon resonance of colloidal copper nanoparticles synthesised in solution prepared with PEG and PVP at different times Immediately after synthesis After day After days After days With PEG 568 567 570 unidentified With PVP 570 561 562 561 Characteristics of colloidal copper particles 301 3.2 Uniformity and dispersity In Figure the copper nanoparticles particularly are rather defined But on the opposite, the particles in Figure cluster together to become hardly distinguishable The size distribution diagram was determined by manually defining the nanoparticles outline from the TEM picture based on contrast, then using ImageJ software for computing the average particle diameters From these two diagrams of particle size distribution the copper nanoparticles in solution using PEG and PVP have an average diameter of 43 nm and 45 nm, respectively, which can be considered almost identical at the actual precision But the distribution of the copper nanoparticles capped with PVP is visibly narrower than those capped with PEG The former is also resembling a normal-like distribution Those copper nanoparticles synthesised in aqueous solution keep having a rather large diameter but PVP capping improves the size distribution Transmission electron micrographs of Cu nanoparticles synthesised in solution using PEG Size distribution (%) Figure 18 16 14 12 10 0 10 20 30 40 50 60 70 80 90 100 Particle diameter (nm) Figure Transmission electron micrographs of Cu nanoparticles synthesised in solution using PVP Size distribution (%) 16 14 12 10 0 10 20 30 40 50 60 70 80 90 100 Particle diameter (nm) 3.3 Ink preparation and properties An ink using the copper nanoparticles capped with PVP was prepared by dispersing the copper nanoparticles in powder into 2-methoxyethanol, ethyleneglycol and methanol with proportions as presented in Table 302 C.M Dang et al Table Formulation of copper nanoparticle ink %wt Cu %wt Ethyleneglycol %wt 2-methoxyethanol %wt Methanol 0.1 70 19.9 10 In Figure 5, the newly prepared ink has a plasmon resonance peak at 596 nm which prove that the copper nanoparticles are stable in the solution The copper ink in this study had a measured viscosity of 13.5 cP and surface tension of 42.3 mN/m at metallic copper concentrations of 0.1% by weight This result is compatible with our inkjet equipment in later applications Figure UV-vis spectrum of the copper nanoparticle ink and image of the fresh copper nanoparticle ink (see online version for colours) Absorbance (a.u.) 1,5 0,5 450 500 550 600 650 700 750 Wavelength (nm) Conclusions In this paper, copper nanoparticles were successfully synthesised by chemical reduction method with two different capping molecules, namely PEG and PVP Using PVP as a capping agent showed an interesting improvement in the stability over time in solution at ambient atmosphere and dispersity Compared to PEG capped nanoparticles, the PVP copper nanoparticles show a tenfold improvement in time stability The copper ink in this study had a measured viscosity of 13.5 cP and surface tension of 42.3 mN/m at metallic copper concentrations of 0.1% by weight Although this concentration is low this result is a first step towards further research on copper nanoparticle ink Despite this cannot be considered enough for a real-world application in conductive ink synthesis, it lays the ground for future development towards a better control on copper nanoparticles synthesised by chemical reduction for conductive ink formulation Acknowledgements The authors appreciate the financial support of National Foundation for Science and Technology Development – Vietnam Characteristics of colloidal copper particles 303 References 10 11 12 13 14 15 16 17 18 19 20 Woo, K., Kim, D., Kim, J.S., Lim, S and Moon, J (2009) ‘Ink-jet printing of Cu#Ag-based highly conductive tracks on a transparent substrate’, Langmuir, Vol 25, No 1, pp.429–433 Wu, C., Mosher, B.P and Zeng, T (2006) ‘One-step green route to narrowly dispersed copper nanocrystals’, Journal of Nanoparticle Research, Vol 8, pp.965–969 Yu, W., Xie, H., Chen, L., Li, Y and Zhang, C (2009) ‘Synthesis and characterization of monodispersed copper colloids in polar solvents’, Nanoscale Research Letters, Vol 4, pp.465–470 Niasari, M.S and Davar, F (2009) ‘Synthesis of copper and copper(I) oxide nanoparticles by thermal decomposition of a new precursor’, Material Letters, Vol 63, pp.441–443 Niasari, M.S., Fereshteh, Z and Davar, F (2009) ‘Synthesis of oleylamine capped copper nanocrystals via thermal reduction of a new precursor’, Polyhedron, Vol 28, pp.126–130 Park, B.K., Kim, D., Jeong, S., Moon, J and Kim, J.S (2007) ‘Direct writing of copper conductive patterns by ink-jet printing’, Thin Solid Films, Vol 515, pp.7706–7711 Tilaki, R.M., Irajizad, A and Mahdavi, S.M (2007) ‘Size, composition and optical properties of copper nanoparticles prepared by laser ablation in liquids’, Applied Physics A, Vol 88, pp.415–419 Zhou, R., Wu, X., Hao, X., Zhou, F., Li, H and Rao, W (2008) ‘Influences of surfactants on the preparation of copper nanoparticles by electron beam irradiation’, Nuclear Instruments and Methods in Physics Research B, Vol 266, pp.599–603 Mallick, K., Witcomb, M.J and Scurrell, M.S (2006) ‘In situ synthesis of copper nanoparticles and poly(otoluidine): a metal–polymer composite material’, European Polymer Journal, Vol 42, pp.670–675 Lee, Y., Choi, J.R., Lee, K.J., Stott, N.E and Kim, D (2008) ‘Large-scale synthesis of copper nanoparticles by chemically controlled reduction for applications of inkjet-printed electronics’, Nanotechnology, Vol 19, No 41 Wu, C., Mosher, B.P and Zeng, T (2005) ‘Simple one-step synthesis of uniform disperse copper nanoparticles’, Materials Research Society Symposium Proceedings, Vol 879E, pp.Z6.3.1–6 Sarkar, S., Jana, A.D., Samanta, S.K and Mostafa, G (2007) ‘Synthesis of silver nano particles with highly efficient anti-microbial property’, Polyhedron, Vol 26, pp.4419–4426 Ding, J., Wang, H., Lin, T and Lee, B (2008) ‘Electroless synthesis of nano-structured gold particles using conducting polymer nanoparticles’, Synthetic Metals, Vol 158, pp.585–589 Song, C., Yang, M., Wang, D and Hu, Z (2010) ‘Synthesis and optical properties of ZnS hollow spheres from single source precursor’, Materials Research Bulletin, Vol 45, pp.10211025 Biỗer, M and iman, I (2010) ‘Controlled synthesis of copper nano using ascorbic acid in aqueous CTAB solution’, Powder Technology, Vol 198, pp.279–284 Li, X., Zhu, D and Wang, X (2007) ‘Evaluation on dispersion behavior of the aqueous copper nano-suspensions’, Journal of Colloid and Interface Science, Vol 310, pp.456–463 Feng, Z.V., Lyon, J.L., Croley, J.S., Crooks, R.M., Vanden Bout, D.A.V and Stevenson, K.J (2009) ‘Synthesis and catalytic evaluation of dendrimer encapsulated Cu nanoparticles’, Journal of Chemical Education, Vol 86, No 3, pp.386–372 Crisp, G.T and Gore, J (1997) ‘Preparation of biological labels with acetylenic linker arms’, Tetrahedron, Vol 53, No 4, pp.1505–1522 Menotta, M., Crinelli, R., Carloni, E., Bianchi, M., Giacomini, E., Valbusa, U and Magnani, M (2010) ‘Label-free quantification of activated NF-κB in biological samples by atomic force microscopy’, Biosensors and Bioelectronics, Vol 25, pp.2490–2496 Veluchamy, P., Tsuji, M., Nishio, T., Aramoto, T., Higuchi, H., Kumazawa, S., Shibutani, S., Nakajima, J., Arita, T., Ohyama, H., Hanafusa, A., Hibino, T and Omura, K (2001) ‘A pyrosol process to deposit large-area SnO2: F thin films and its use as a transparent conducting substrate for CdTe solar cells’, Solar Energy Materials and Solar Cells, Vol 67, pp.179–185  ... Characteristics of colloidal copper particles prepared by using Polyvinyl pyrrolidone (PVP) and Polyethylene glycols (PEG) in chemical reduction method presented at the ‘3rd International Workshop... majoring in Materials Science In 2010 he participated in the project: ‘Study and synthesis of copper nanoparticles for applications in inkjet printing technology’ Up to now he has been developing... irradiation [8] and in situ chemical synthetic route [9] We have succeeded in making copper nanoparticles with an average diameter of less than 10 nm by chemical reduction method However, making copper