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This article was downloaded by: [University of Toronto Libraries] On: 11 August 2014, At: 08:08 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Materials and Manufacturing Processes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lmmp20 Microwave-Assisted Synthesis of Silver Nanoparticles Using Chitosan: A Novel Approach a b a a c Ngoan Thi Nguyen , Binh Hai Nguyen , Duong Thi Ba , Dien Gia Pham , Tran Van Khai , b Loc Thai Nguyen & Lam Dai Tran a b Institute of Chemistry, Vietnam Academy of Science and Technology , Ha Noi , Viet Nam b Institute of Materials Science, Vietnam Academy of Science and Technology , Ha Noi , Viet Nam c Faculty of Materials Technology , Ho Chi Minh City University of Technology , Ho Chi Minh City , Viet Nam Accepted author version posted online: 20 Feb 2014.Published online: 01 Apr 2014 To cite this article: Ngoan Thi Nguyen , Binh Hai Nguyen , Duong Thi Ba , Dien Gia Pham , Tran Van Khai , Loc Thai Nguyen & Lam Dai Tran (2014) Microwave-Assisted Synthesis of Silver Nanoparticles Using Chitosan: A Novel Approach, Materials and Manufacturing Processes, 29:4, 418-421, DOI: 10.1080/10426914.2014.892982 To link to this article: http://dx.doi.org/10.1080/10426914.2014.892982 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content This article may be used for research, teaching, and private study purposes Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions Materials and Manufacturing Processes, 29: 418–421, 2014 Copyright # Taylor & Francis Group, LLC ISSN: 1042-6914 print=1532-2475 online DOI: 10.1080/10426914.2014.892982 Microwave-Assisted Synthesis of Silver Nanoparticles Using Chitosan: A Novel Approach Ngoan Thi Nguyen1, Binh Hai Nguyen2, Duong Thi Ba1, Dien Gia Pham1, Tran Van Khai3, Loc Thai Nguyen2, and Lam Dai Tran2 Institute of Chemistry, Vietnam Academy of Science and Technology, Ha Noi, Viet Nam Institute of Materials Science, Vietnam Academy of Science and Technology, Ha Noi, Viet Nam Faculty of Materials Technology, Ho Chi Minh City University of Technology, Ho Chi Minh City, Viet Nam Downloaded by [University of Toronto Libraries] at 08:08 11 August 2014 In this work, microwave-assisted (MwH) synthesis of silver nanoparticles (AgNPs) using chitosan was investigated The new method was compared against chemical reduction (CRed) by NaBH4 and conventional thermal method (CvH) The as-synthesized AgNPs were characterized by UV–Visible spectroscopy, transmission electron microscopy (TEM) and infrared spectroscopy The MwH method was found to effectively synthesize AgNPs of which properties were comparable CRed and CvH The average particle sizes of AgNPs produced by CRed, CvH and MwH were approximately 20, and nm, respectively The proposed approach can provide a viable green route for synthesizing AgNPs with high potential applicability Keywords Biodegradable; Chitosan; Green; Heating; Microwave; Nanoparticles; Reduction; Silver INTRODUCTION In recent years, metal nanoparticles (NPs) have attracted increasing attention due to their unique physical, chemical properties and numerous prospective applications [1, 2] In general, metal NPs can be synthesized by chemical or physical pathways The chemical method in which NPs are formed by reduction of metal ions in the solution is most widely used [2–6] due to its cost effectiveness, simple equipment and capability of large-scale production However, strong reducing agents such as NaBH4, citrate or ascorbate could be sources of environmental toxics or biological hazards [6] Therefore, alternative ‘‘green’’ agents derived from naturally occurring substances are desirable Natural polymers such as starch and chitosan (CS) are highly preferred due to their non-toxic properties and biocompatibility [7] Chitosan, N-deacethylated derivative of chitin, is a viable option since it is cheap, easily available [8], biocompatible, biodegradable and environmental-friendly [9] Various studies demonstrate that chitosan could be successfully used as a reducing and stabilizing agent in the synthesis of metal NPs [1, 2, 6] Despite the fact that chemical reducing reactions can generally take place at ambient conditions [10, 11], they require the input of additional thermal energy to achieve high reaction rate Traditional heating method in which the heat transfer is mainly driven by conduction and convection takes long time and can result in nonuniform temperature distribution Since morphology and properties of metal NPs strongly depend on experimental conditions [2], selection of an appropriate heating method would be essential to reproducibly synthesize metal NPs of desired properties Microwave-assisted (MwH) heating received considerable interests in organic synthesis [12, 13] and inorganic materials preparation [14, 15] due to its ability to generate the fast reaction times, high-throughput capabilities and beneficial crystallization effects [15] Rapid and uniform heating effects of microwave heating were reported to be conducive to synthesis of metal nanoclusters of small size and uniform dispersity [16] MwH heating was also shown to have marked effects on nucleation and growth mechanisms of NPs [17] In this study, a novel pathway to synthesize silver nanoparticles (AgNPs) using chitosan and MwH heating was investigated Properties of AgNPs produced were characterized by transmission electron microscopy (TEM), UV–vis and (infrared) IR spectroscopy and compared against those obtained by traditional chemical synthesis and conventional heating EXPERIMENTAL Chitosan was purchased from Tokyo Chemical Co Ltd Other reagents were of analytical grades In this research, MwH synthesis of AgNPs was studied and compared against chemical reduction (CRed) and conventional thermal (CvH) methods The schematic diagram of experimental procedures used is given in Fig Chitosan suspension in acetic acid solution was prepared by dissolving 0.5 g of chitosan in 100 mL of 2% acetic acid solution The mixture was vortexed until a Received December 12, 2013; Accepted January 9, 2014 Address correspondence to Lam Dai Tran, Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Ha Noi, Viet Nam; E-mail: lamtd@ims.vast.ac.vn Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lmmp 418 Downloaded by [University of Toronto Libraries] at 08:08 11 August 2014 MICROWAVE-ASSISTED SYNTHESIS OF SILVER NANOPARTICLES FIGURE 1.—Schematic diagram of experimental procedures for synthesizing silver nanoparticles (AgNPs) via different pathways homogeneous product was obtained Then, 20 mL of 0.1 M AgNO3 solution was added to 100 mL of chitosan suspension and the mixture was vigorously agitated by a magnetic stirrer for 30 Chemical reduction was conducted at room temperature by adding M NaBH4 solution (10 mL) to AgNO3=chitosan suspension with the initial molar ratio of NaBH4 to AgNO3 fixed at 1:1 The reaction was allowed to take place for 15 during which the suspension turned to dark brown color With respect to the production of AgNPs by conventional heating, 100 mL of AgNO3=chitosan suspension was heated on a hot-plate at 70 C and the sample was mixed by a magnetic stirrer In previous study [2], it was found that optimal reaction time for conventional heating method was about hr Therefore, the same holding time was used for this study Upon completion of the reaction, the suspension was observed to change from light-yellowish to light-brown color The MwH synthesis of AgNPs was conducted at 70 C for in a microwave oven (model MW-ER-01, Lab-kits) with output power fixed at 200 W The suspension obtained had a light-brown color The AgNPs were characterized using UV–visible spectroscopy, IR spectroscopy and TEM Prior to spectroscopy analysis, colloidal suspension of AgNPs was diluted by water to concentration of 200 ppm UV–visible spectra were recorded using a Beckman DU 520 UV–Vis spectrophotometer IR spectra were collected from 500 to 4000 cmÀ1 by Impact 410 (Nicolet) spectrophotometer (Carl Zeiss Jena) The morphology of the NPs was examined by Hitachi H7600 transmission electron microscope at 120 kV RESULTS AND DISCUSSION UV–Vis Absorption Spectra of Synthesized AgNPs In Fig 2, UV–Vis spectra of AgNPs obtained by CRed, CvH and MwH are comparatively presented The spectra exhibit surface plasmon resonance (SPR) 419 FIGURE 2.—The UV–visible spectra of silver nanoparticles produced by reducing with NaBH4 at room temperature (AgNPs1), conventional thermal method (AgNPs2) and microwave-assisted method (AgNPs3) peaks from 400 to 420 nm which clearly evidenced the formation of AgNPs The change in color of the suspensions (inset) further confirmed the UV–Vis data It was worth noting that AgNPs produced by CRed and MwH had significantly higher SPR band intensity than that of AgNPs obtained from CvH Since the intensity of SPR band depends on AgNPs concentration, it was obvious from UV–Vis spectra that the syntheses of AgNPs by MwH and CRed were more effective than CvH Similar trends were also noticed for the color intensity of the CRed, CvH and MwH suspensions The influence of MwH in the synthesis of noble metal NPs was previously investigated and compared to CvH [16, 17] Enhanced effectiveness was attributed to rapid and uniform heating of MwH [16] or alternately, marked effects of MwH on nucleation and growth mechanism of NPs [17] Analysis of TEM Images Figure shows the TEM images (Fig 3(a)–(c)) and particle size histograms (Fig 3(d)–(f)) of AgNPs obtained by CRed, CvH and MwH, respectively As illustrated in images, three methods produced AgNPs with approximate spherical shape Average diameters were estimated to be 20, and nm for AgNPs prepared by CRed, CvH and MwH, respectively Particle sizes varied from 5.0 to 27.0 nm for AgNPs1; 1.0–9.0 nm for AgNPs2 and 1.0–12.0 nm for AgNPs3 Analysis of IR Spectra Figure presents IR spectra of chitosan and AgNPs synthesized by CvH and MwH Broad peaks at 3440 cmÀ1 overlap –OH and –NH stretching vibrations Changes in intensity of peaks from 3300 to 3500 cmÀ1 were reportedly attributed to attachment of silver which affected N–H vibrations [18] Other authors suggested Downloaded by [University of Toronto Libraries] at 08:08 11 August 2014 420 N T NGUYEN ET AL FIGURE 3.—Transmission electron microscopy (TEM) images and particle size histograms of silver nanoparticles produced by chemical reduction (a, d), conventional heating (b, e) and microwave-assisted synthesis (c, f) Scale bar corresponds to 20 nm FIGURE 4.—Infrared spectra of chitosan (CS), silver nanoparticles synthesized by conventional heating (AgNPs2) and microwave-assisted method (AgNPs3) that variations of shape and intensity of peaks in this region resulted from contribution to reduction and stabilizing process [19] The bands from 1350 to 1390 cmÀ1 correspond to absorption of C–N vibrations and residual NO3 À1 [20]; hence change of peak intensity could indicate the presence of NO3 À1 after reaction of chitosan with AgNO3 The spectra of AgNPs produced by CvH and MwH exhibit blue shift of CS peak at 1646 cmÀ1 and 1560 cmÀ1 to 1634 cmÀ1 and 1544 cmÀ1, respectively Since these bands are associated with amines groups of chitosan, the shift of the peaks probably indicates attachment of AgNPs to amine groups which leads to change in molecular weight and subsequently, vibration intensity To verify if the reducing reaction was completed, AgNPs suspensions (AgNPs1, AgNPs3) were tested with solution of NaCl M (Fig 5) The results were negative which meant AgNPs suspensions were completely free from Agỵ1 Downloaded by [University of Toronto Libraries] at 08:08 11 August 2014 MICROWAVE-ASSISTED SYNTHESIS OF SILVER NANOPARTICLES FIGURE 5.Testing of residual Agỵ1 in AgNPs1 and AgNPs3 using M NaCl solution CONCLUSION In summary, the proposed MwH synthesis of AgNPs could successfully produce NPs with properties comparable to those obtained by traditional chemical reduction The formation of AgNPs was validated by TEM, UV–Vis and IR spectroscopic analysis The AgNPs synthesized by MwH had relatively uniform sizes with average diameter of approximately nm The findings revealed that the MwH method could serve as an alternative to traditional chemical reduction for green synthesis of AgNPs FUNDING This work was financially supported by the National Foundation for Science and Technology Development (NAFOSTED), project number 103.02-2011.57 Financial support was also provided in part by IFS grant (No F=5022-1) REFERENCES Huang, H.; 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Synthesis of Silver Nanoparticles Using Chitosan: A Novel Approach Ngoan Thi Nguyen1, Binh Hai Nguyen2, Duong Thi Ba1, Dien Gia Pham1, Tran Van Khai3, Loc Thai Nguyen2, and Lam Dai Tran2 Institute of