synthesis and surface chemistry of nano silver particles

Polyhedron 28 (2009) 2522–2530 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly Synthesis and surface chemistry of nano silver particles Revathi Janardhanan, Murugan Karuppaiah, Neha Hebalkar, Tata Narsinga Rao * International Advanced Research Center for Powder Metallurgy and New Materials, Balapur PO, Hyderabad 500005, India a r t i c l e i n f o Article history: Received 29 September 2008 Accepted May 2009 Available online 23 May 2009 Keywords: Nano silver Gluconic acid Diethyl amine Chemical synthesis a b s t r a c t In this report, we present a simple wet chemical route to synthesize nano-sized silver particles, and their surface properties are discussed in detail Silver nano particles of the size 40–80 nm are formed in the process of oxidation of glucose to gluconic acid by amine in the presence of silver nitrate, and the gluconic acid caps the nano silver particle The presence of gluconic acid on the surface of nano silver particles was confirmed by XPS and FTIR studies As the nano silver particle is encapsulated by gluconic acid, there was no surface oxidation, as confirmed by XPS studies The nano silver particles have also been studied for their formation, structure, morphology and size using UV–Visible spectroscopy, XRD and SEM Further, the antibacterial properties of these nano particles show promising results for E Coli The influence of the alkaline medium towards the particle size and yield was also studied by measuring the pH of the reaction for DEA, NaOH and Na2CO3 Ó 2009 Elsevier Ltd All rights reserved Introduction Metal nano particles have attracted a great deal of attention in recent years due to their optical, physical and chemical properties that differentiates them from bulk material properties Hence they find wide application in various fields like catalysis, photonics, optoelectronics, information storage, antibacterial applications, etc Silver powders, having ultra fine and uniformly distributed particle size, are of considerable use in the electronics industry as thick film conductors in integrated circuits due to their unique properties such as high electrical and thermal conductivity, high resistance to oxidation Recently a method was perfected for using nano silver particles in inkjet printing that could see circuits get even smaller and cheaper [1] Apart from electronic applications, it has been known for centuries that silver has bactericidal properties Silver is a safe and effective bactericidal metal because it is non-toxic to animal cells and highly toxic to bacteria such as Escherchia coli (E coli) and Staphylococcus aureas [2,3] Silver based compounds have been used in recent years to prevent bacterial growth in applications such as burn care [4] Silver doped polymer fabrics, catheters and polyurethane are well known for their antibacterial functionality [2,5] Colloidal silver [6,7], nano silver coated fabric [8], nano silver metal oxide granules [9] and nano silver coated ceramic materials [10] are used for antibacterial applications Nano silver in the form of powders as well as suspensions, due to the high surface to volume ratios, has been used in the above said applications as it enables the loading of small quantities of silver and thus makes the product cost effective Research* Corresponding author Fax: +91 40 24442699 E-mail address: tata@arci.res.in (T.N Rao) 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd All rights reserved doi:10.1016/j.poly.2009.05.038 ers around the world are trying to produce nanosized mono dispersed powders by different methods Pluym et al prepared nano silver powders by the technique of spray pyrolysis, with the production at a rate of 1–2 g/h [11], but the silver particles tend to be agglomerated, irregular shaped, and hollow due to solvent evaporation There are several aqueous based chemical methods [12–23] reported in the literature to produce nano silver While most of these reports deal with inorganic bases such as NaOH and Na2CO3 to control the pH to above 9, the contamination of silver with metals ions will cause limitations in specific applications such as electronics, and hence organic bases are required in the nano silver synthesis, as reported by Hsu and co-worker [23] The same group used organic bases such as triethyl amine and pyridine for contamination-free silver nanoparticles, useful for micro-interconnects, that cure at relatively lower temperatures Chaki et al used a non-aqueous single-phase preparation of Ag clusters from silver benzoate using triethylamine as the organic base [12] In both the organic base related studies, they have used external capping agents for stabilizing the powders or suspensions In all the cases, the stability and antibacterial activity are dependent on the surface chemistry of the silver produced For example, Kvítek et al [24] have reported a SDS stabilized nano silver suspension to have better dispersion and antibacterial action The best condition for high performance of nano silver, for either electronic or antibacterial applications, is that the particles should contain minimum or no capping agents so that the maximum surface is available for antibacterial action or sintering at low temperatures Apart from the contamination issues, we have also found that the yield of the nano silver in the reduction reaction depends on the strength of the base 2523 R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 In the present work, we have synthesised silver nanoparticles by an aqueous chemical method with an organic base and with no external capping agents, and carried out surface chemistry studies and compared the properties, such as stability and yield, with those obtained with inorganic bases, NaOH and Na2CO3 We made an attempt to synthesize nano silver colloids using a lower concentration of the reactants that could be stable for a few weeks without any surfactant Nano silver colloids prepared in the absence of surfactant using inorganic bases such as NaOH and Na2CO3 settle down immediately Hence we tried to explore the possibility of using an organic base, diethyl amine, that provides a good yield and low particle size in the absence of a protective agent It is interesting to explore the surface chemistry of the nano silver particles that confirms the capping by gluconic acid, which prevents the oxidation/sulfidisation of the nano silver particle as confirmed by XPS studies The suspensions made in this work using diethyl amine were found to be stable for nine months The merits of this method are that it is a room temperature process with glucose as a reducing agent, which also modifies the surface after undergoing oxidation to stabilize the suspension without the requirement of other Table Details of the reaction parameters used in the silver nanoparticles synthesis, corresponding size of the particles measured from the SEM micrographs and kmax observed for nano silver suspensions S No Concentration of AgNO3 (mM) Concentration of glucose (mM) Concentration of DEA (mM) kmax (nm) Powder/suspension Particle size from SEM (±10 nm) S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 3 100 100 100 50 100 300 5 5 50 50 50 40 40 40 115 115 77 23 58 87 115 58 58 58 432 426 436 464 suspension suspension suspension suspension powder powder powder powder powder powder 65 45 75 85 110 94 63 72 238 630 Fig SEM of silver nanoparticles (a) S2 (b) S3 (c) S4 (d) S7; inset shows the measured particle size distribution from the micrograph 2524 R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 external capping or stabilizing agent The resulting nano silver exhibit high antibacterial activity and is also useful for electronic interconnecting applications Experimental 2.1 Preparation of the nano silver suspension and powders Analytical grade of silver nitrate (Ultrafine Chemicals), glucose, diethyl amine, sodium carbonate and sodium hydroxide (Qualigens) were used as starting materials The different concentrations of aqueous solutions of silver nitrate and glucose solutions were mixed together and stirred to obtain a homogeneous solution An aqueous solution of diethyl amine (DEA) of a pre-decided molarity was added to it quickly and stirred vigorously Similar experiments were done with sodium carbonate and sodium hydroxide The color of the solution changed to black, brown and then finally a light green colored precipitate was obtained for higher concentrations S5–S10 After decanting and washing repeatedly to times with distilled water, the precipitate was collected and dried in air at 50– 60 °C The final pale green colored dried powder was subjected to further characterization and antibacterial tests The details of the reaction parameters for DEA are given in Table For the samples S1–S4 low concentrations of reactants were used and suspensions were obtained which were stable for a few weeks when prepared using DEA in contrast to NaOH and Na2CO3, which settled immediately Fig UV–Visible absorption spectra for silver nanoparticles for samples S1, S2, S3 and S4 Fig XRD of (a) silver nanoparticles and (b) silver oxide particles R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 To understand the exact role of glucose, the reactions were also performed without addition of glucose, keeping all the other reaction parameters the same In these reactions, a black colored powder was collected as the end product When the reactions were done without amine, the rate of reaction was found to be very slow and after 24 h the color of the solution changed to light brown Silver nano particles thus prepared were in the form of either stable suspensions or powders, depending on the reactant concentrations as mentioned in Table 2.2 Characterization of the nano silver powders The powders obtained under the various conditions were characterized using different techniques The particles were tested for their optical absorption property using a PELambda 650, Perkin–Elmer UV–Visible spectrometer, to ensure the formation of nano silver The suspensions were tested as prepared The powdered samples were prepared by dispersing them in water using stirring and sonication The powdered samples were subjected to X-ray diffraction (XRD) studies on a Bruker AXS D8 Advanced XRD to understand their structure The morphology, size and shape of the particles were obtained using an Hitachi Scanning Electron Microscope equipped with EDAX A drop of nano silver suspension or 2525 dispersed nano silver powders in water was placed on the carbon tape on an aluminum stub and dried Fourier Transform Infra Red (FTIR) spectroscopy was performed on a THERMO Nicolet Nexus 740 spectrometer The powdered samples were mixed with KBr and pelletized at 1000 psi pressure X-ray photoelectron spectroscopy (XPS) measurements were obtained on a KRATOS-AXIS 165 instrument equipped with dual aluminum–magnesium anodes using Mg Ka radiation The X-ray power supply was run at 15 kV and mA The pressure of the analysis chamber during the scan was 109 Torr The peak positions were based on calibration with respect to the C 1s peak at 284.6 eV The obtained XPS spectra were fitted using a non-linear square method with the convolution of Lorentzian and Gaussian functions after polynomial background subtraction from the raw data 2.3 Antibacterial test Nutrient agar was poured on two disposable sterilized Petri dishes and was allowed to solidify To understand the antibacterial activity of the nano silver powder, 0.1 gm of nano silver powder was mixed with ml of E coli bacterial water containing 170 CFU/ml One milliliter of the E coli bacterial water containing 170 CFU/ml was streaked on one agar plate and ml of the bacterial water mixed with nano silver powder was streaked on the other plate and it was spread uniformly Plates were incubated at 37 °C for 24 h Growth of the colonies of bacteria was observed A zone of inhibition test was done on the nano silver coated plastic The nano silver powder was ultrasonicated in acetone for and it was spin-coated on the plastic at 500 rpm Nutrient agar was poured on two Petri dishes The nano silver powder coated plastic and uncoated plastic were placed in the two Petri dishes and then the Nutrient agar was allowed to solidify ml of 170 cfu/ml concentrated E coli bacterial water was streaked on the two Petri dishes The plates were incubated at 37 °C for 24 h and then the zone of inhibition was observed Results and discussion The silver mirror test is commonly used to detect the presence of an aldehyde group in an organic compound Here excess ammo- Fig 4a FTIR spectra for (i) silver nitrate (ii) glucose (iii) gluconic acid (iv) silver nanoparticles (v) silver oxide particles Fig 4b Enlarged FTIR spectra for (i) gluconic acid and (ii) resolved spectrum of silver nanoparticles in the wavenumber range 1900–900 cmÀ1 2526 R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 nia and silver nitrate are reacted in the presence of the aldehyde which oxidizes to form carboxylic acid and release silver, which deposits on the glass container wall to give silver mirror The general reaction can be written as: RCHO ỵ 2AgNH3 ị2 OH ! RCOONH4 þ 2Ag þ 3NH3 þ H2 O ð1Þ Following this reaction, the process was modified to get silver nano particles Glucose was used as an aldehyde and an amine was used in the place of ammonia The proposed reaction mechanism for this reaction is very similar to that of the silver mirror test When the amine is dissolved in water, it withdraws hydrogen ions by leaving hydroxyl ions in solution The hydrated amine ion further reacts with silver nitrate to form a complex of silver The remaining hydroxyl ions oxidize the aldehyde group here in glucose to form gluconic acid and an electron is released in the process This electron reduces the silver complex to get metallic silver The DEA acts as a catalyst The reactions can be written as follows: NHC2 H5 ị2 ỵ H2 O ! ỵ NH2 C2 H5 ị2 ỵ OH 2ị R-CHO ỵ OH ! R-COOH ỵ H2 O ỵ 2e 3ị Agỵ þ eÀ ! Ag0 þ 2NHðC2 H5 Þ2 ð4Þ R ¼ ðCHOHÞ4 CH2 OH Some reactions were carried out in the absence of glucose to confirm its exact role in the silver formation It was observed that the absence of glucose in the reaction produces silver oxide (Ag2O) instead of metallic silver Here the silver complex formed with amine in presence of hydroxyl ions produces silver hydroxide which converts into silver oxide as: Fig 5a XPS core-lever spectra of C 1s for (i) silver and (ii) silver oxide particles 2AgOH ! Ag2 O ỵ H2 O 5ị Although glucose is a known reducing agent, its activity on silver nitrate was observed to be very weak in the absence of amine, and both reactants remain unreacted for many hours Yan et al., modified a fabric by using a similar process and deposited silver by heating the fabric [8] To investigate the effect of the concentration of the precursors towards the particle size of the nano silver, different studies were performed by varying the concentrations of glucose, silver nitrate and diethyl amine, as mentioned in Table The particle size was measured from SEM images and also from XRD data by calculating the average particle size using the Scherror formula, and both were found to be in agreement The AgNO3:glucose molar ratio was changed from 1:0.5 to 1:2 The concentration of glucose did not show much influence on the particle size, but was found to be very essential to form metallic silver nano particles, without which an oxide is formed as shown in reaction (4), indicating the role of glucose as a reducing agent The concentration of silver nitrate is one of the most important factors that decide the particle size As the concentration of silver nitrate is increased from to 300 mM, correspondingly the particle size increases from 40 to 630 nm and grows towards bulk silver The concentration of DEA was found to be another size controlling factor In the case of S2–S4 (suspensions) as DEA the concentration is decreased from 115 to 23 mM, the particle size increases from 40 to 100 nm, as mentioned in Table In the case of S5–S7 (powders) the increasing concentration of DEA shows a decrease in the average particle size from 110 to 63 nm The scanning electron micrograph and particle size distribution for the samples S2, S3 and S4 are shown in Fig 1a–c Nearly spherical particles are seen with a maximum number of particles in the size range of 40–50 nm, 50–70 nm and 80–100 nm for samples S2, S3 and S4, respectively The sharp boundaries of the particles clearly show non-agglomeration of particles even after drying, indicating that some factor is controlling and maintaining the nano Fig 5b XPS core-level spectra for Ag 3d in (i) silver and (ii) Ag2O particles 2527 R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 size of the silver particles Fig 1d shows a typical micrograph for a powder sample (S7) used for XPS and FTIR studies Here the particles in the size range of 60–70 nm are seen to be somewhat agglomerated as at some places necking between the particles is observed This is obvious for nano powders prepared using higher concentrations of precursors and dried in air at 50–60 °C The change in the particle size also reflected in the optical absorption studies The kmax values observed in the UV–Visible absorption studies for samples S1, S2, S3 and S4 are depicted in Fig The samples S1 and S2 show a blue shift in kmax, which is at 432 and 426 nm, respectively The decrease in the silver nitrate concentration has resulted in a smaller particle size The sample S3 and S4 were prepared with smaller concentrations of DEA as compared to S2 and show kmax at 433 and 464 nm, respectively, as shown in Fig It clearly shows a red shift in kmax from S2 to S4 with the decreasing concentration of DEA, and a decrease in the FWHM with an increase in concentration of DEA The powder samples did not show any clear absorption peaks in UV–Visible range This may be due to the agglomeration of the particles, observed in the SEM Typical XRD spectra are given in Fig 3a and b for silver and silver oxide, respectively The powdered silver nanoparticles show a cubic structure showing peaks at 2h: 38.1 (1 1), 44.2 (2 0), 64.4 (2 0) and 77.472(3 1), which match exactly with the standard data Fig 3b shows the spectra for particles prepared in the absence of glucose It shows the cubic phase of Ag2O, which is in good agreement with the literature [25] It was very interesting to understand the formation of nano particles with the change in reactant concentrations This was possible only when the particles were studied by FTIR, to understand the remains of the organic molecules, if any, after completion of the reaction The surface properties of the nano silver particles, studied using XPS, throw some light about their size controlling factors Fig 4ai–v shows the FTIR spectra recorded for silver nitrate, glucose, gluconic acid, silver nanoparticles and silver oxide nanoparticles, respectively The attempt made here is to only a qualitative study The IR spectrum for the silver nanoparticles (Fig 4aiv) shows various peaks The peaks at 3423 and 1605 cmÀ1 are very broad and strong, and can be assigned to the hydroxyl groups [25], either from glucose/gluconic acid, from adsorbed moisture or both A prominent and very sharp peak is observed at 1384 cmÀ1 which was concluded to be due to the nitrate ions when compared with the FTIR spectrum for silver nitrate, as shown in Fig 4ai Some other smaller peaks present at 1740, 1400, 1250, 1100 and 1039 cmÀ1 were also observed These peaks are absent in the silver oxide IR spectrum (v), which shows major peaks at 3380, 1651 and 1382 cmÀ1, and are due to the OH group [26], adsorbed moisture and nitrate impurities, respectively As explained in reaction (4), the gluconic acid is produced by oxidation of glucose and it may be present in the sample Hence these IR peaks were also compared with the glucose and gluconic acid peaks The smaller peaks in nano silver not match with those of glucose (Fig 4aii) but they match with many features in gluconic acid The FTIR spectrum of gluconic acid (i) and the resolved spectrum for nano silver powder (ii) was compared in the wave number region from 900 to 1900 cmÀ1, as depicted in Fig 4b The gluconic acid shows peaks at 1740, 1638, 1412, 1230, 1100, 1036 and 875 cmÀ1 Almost all these peaks match with those for the nano silver sample Thus a small amount of gluconic acid remains in the sample even after repetitive washings of the silver precipitate Fig 5ai shows the core-level spectrum for C 1s for the nano silver powder The broad peak can be fitted to four different components at binding energies 289.7, 288.1, 286.5 and 284.6 eV The peak at 284.6 eV is mostly due to the carbon present on the sample surface due to handling [27] This peak was observed in all samples While discussing the other two components, it is necessary to consider the gluconic acid molecule, the presence of which Table Comparison of sodium carbonate, diethyl amine and sodium hydroxide Sodium carbonate Diethyl amine Sodium hydroxide pKb Yield (%) Particle size (nm) 4.67 0.2 96 90 71 45 55 50 10 NaOH Amine Na 2CO3 pH 100 200 300 400 Time in seconds Fig 5c XPS core-level spectra for O 1s in (i) silver and (ii) silver particles Fig Photograph of antibacterial test (a) control (b) control with nano silver particles (c) control with uncoated plastic and (d) control with nano silver coated plastic 2528 R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 was observed in the FTIR studies In one gluconic acid molecule, depending on the functional groups attached, there are two types of carbons in the atomic ratio 1:5, as numbered below The carbon in carboxylic group shows a binding energy at 289 ± eV [28] The component at 288.1 eV is due to C-1, which is a carboxylic group Here the shift is observed towards a lower binding energy This is in good agreement with the literature, where carboxylic groups attached to a metal particle like Co, Cu show a binding energy shift to 288.1 eV [29] Also the standard data avail- able for silver acetate shows a XPS peak for carbon at 288.1 eV [30,31] It has been shown that the carboxylic acid group binds to silver surface in the case where citrate is used as the reducing agent In this case, it was shown that two carboxylic groups of the citrate bind to the Ag surface, having the third group normal to the surface, which make the Ag particle charged, and that is responsible for the electrostatic stability [32] However in the present case only one carboxylic acid is available on gluconic acid that is likely to bind with the Ag surface The capping of the silver particle controls the grain growth but does not provide charge to the particles The peak at 286.5 eV is due to C-2 (the carbon with OH groups) [33,34] The intensities of the corresponding XPS peaks are fairly in agreement with the atomic ratio of these carbons in the molecule A very small component at 289.7 eV may be due to some non-bonded gluconic acid The C 1s spectrum was also recorded for silver oxide powders where only two components were observed, at 284.5 and 286.5 eV, as shown in Fig 5aii The former peak is due to a carbon impurity The latter peak was unexpected and may be due to some unknown carbon contamination, as no C–O bond is possible in this sample Fig pH of the reaction for NaOH, DEA and Na2CO3 R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 The core-level spectrum for Ag 3d, shown in Fig 5bi, is fitted in two components, one is major and the second is very small in the% concentration ratio of (96:4) The peak at 368.2 eV is clearly due to metallic silver [25,35] A surprising small peak shifted to lower binding energy at 365.8 eV may be due to the surface silver atoms surrounded by the six carbon chain of gluconic acid molecules Unlike in the silver nanoparticles, silver oxide nanoparticles show only one peak at a binding energy of 367.4 eV, which is a characteristic for Ag2O, as shown in Fig 5bii Fig 5c–i shows the core-level spectra for O 1s in the case of silver nanoparticles It shows a broad peak which can be deconvoluted into three peaks at 535.0, 533.4 and 531.7 eV The first peak can be assigned to the adsorbed water [36] The component at 533.4 can be correlated to either C–O or C–OH present in the gluconic acid molecules [37–39] The peak at 531.7 eV was observed in all samples, and can be attributed to adsorbed oxygen on the surface as an impurity in the form of either atomic oxygen or in the hydroxyl form [40] Some of its contribution can also be due to organometallic oxygen Hoof et al studied Co and Cu bonded with organic molecules and found the binding energy of O 1s at 531.6 eV [29] Here if the silver atoms on the surface of the nanoparticles are bonded with carboxylic ions, the oxygen from the carboxylic group may show a binding energy at 531.7 eV The peculiar peak of silver oxide at 529.6 eV, as shown in Fig 5cii, is observed in the case of the silver oxide nanoparticles, but is absent in the silver nanoparticles Other than the oxide peak, the silver oxide nanoparticles show two components at 533.3 and 531.7 eV, which can be attributed to hydroxyl groups which may be present on the surface of the oxide particles and surface adsorbed oxygen, respectively This clearly tells us that the surface of the silver nanoparticles does not have any oxide layer as it is protected by gluconic acid molecules The reducing ability of aldehyde is dependant on the pH As already mentioned, if only glucose is added the reduction rate is very slow at room temperature because of the low pH We tried to explore the influence of different alkaline medium towards the particle size and yield of nano silver powder The pKb values, yield and particle size of nano silver powder for NaOH, Na2CO3 and DEA are listed in Table The changes in the pH of the solution for NaOH, Na2CO3 and DEA are shown in Fig The yield of the nano silver powder was found in increase with a decrease in the pKb value The lower the pKb value, the stronger is the basicity of the alkaline medium Under highly alkaline conditions, the aldehyde functional group in glucose gets converted to a ketone [41] As ketones are weak reducing agents when compared with aldehydes, the yield of the nano silver prepared by sodium hydroxide (pKb = 0.2) is less when compared with DEA and Na2CO3 [14,42] The reaction mechanism is the same in each case Gluconic acid formed as a by-product in the reaction acts as a capping agent This imparts a negative charge on the surface, which was confirmed by immediate adsorption of negatively charged silver particles on the anion exchange resin Amberlite IRA 400 [43] From all these results, the inference that can be drawn is like this As mentioned in Table 1, an increase in concentration of DEA reduces the size of nano silver particle As discussed earlier, the amine in aqueous solution forms a hydrated ion and hydroxy ions are left in the solution which in turn oxidizes glucose to form gluconic acid If the concentration of amine is greater then the number of hydroxy ions are present is greater and the amount of gluconic acid formed also increases These gluconic acid molecules present on the surface of the nano particles may act as a particle size controlling factor So in turn the amine concentration is determining the size of the particles for a particular set of concentrations of silver nitrate and glucose, as mentioned in Table (S2– S4) It is very easy to understand the increase in the size of particles with the concentration of AgNO3, due to the increase in the ratio of 2529 available gluconic acid to silver particles In the given set of conditions in Table 1, by increasing the concentration of glucose, the size remains unaffected as the glucose to gluconic acid conversion in the presence of amine is a size controlling factor and not just the glucose concentration Just by changing the molar ratio of reactants, we can get a stable nano silver suspension or powder The reactions for samples S5–S10 can be scaled up to a total volume of liters, which can yield 45–50 gm of nano silver powder which is quiet a substantial yield The powders of nano silver were tested for antibacterial properties on E coli The effect of the silver nano particles on E coli is shown in the photograph in Fig for sample S7 The number of E coli has been reduced by a considerable number because of the antibacterial action of the nano silver particles, whereas growth was observed in the control, as shown in Fig 7a and b, respectively The zone of inhibition observed for the nano silver powder coated plastic confirms the antibacterial action of the nano silver particles, whereas there was no zone of inhibition for the uncoated plastic, as shown in Fig 7c and d, respectively These observations clearly indicate the antibacterial properties of nano silver It is interesting to observe that, although the nanoparticles contain traces of gluconic acid on the surface, as is evident from the XPS analysis, the surface of the nano silver particle is still available for efficient antibacterial activity Conclusions The present work reveals a simple, cost effective wet chemical synthetic route to form nano silver powders Silver nano particles are formed in a simple oxidation–reduction reaction in diethyl amine, glucose and silver nitrate A blue shift in kmax observed for an increase in the diethyl amine concentration in samples S2–S4 was found to be the size controlling factor Detailed surface analysis studies using XPS and FTIR revealed the presence of gluconic acid that encapsulates the nano silver particle The negative charge on the surface due to the presence of gluconic acid was confirmed by anion exchange resin The antibacterial studies show very high activity against E coli This process of producing large scale silver nano powders with highly efficient antibacterial properties is certainly going to increase its commercial value and widen the application range Acknowledgement Authors would like to thank Dr B Sreedhar, IICT, Hyderabad for providing the XPS and FTIR facility References [1] Hsien-Hsueh Lee, Kan-Sen Chou, Nanotechnology 16 (2005) 2436 [2] U Klueh, V Wagner, S Kelly, A Johnson, J.D Bryers, J Biomed Mater Res 53 (2000) 621 [3] G Zhao, S.E Stevens, Biometals 11 (1998) 27 [4] H.J Klasen, Burns 26 (2000) 117 [5] J.W Cho, J.H So, Mater Lett 60 (2006) 2653 [6] J Yan, J Cheng, US 2003/0185889 A1, 2003 [7] R Prucek, L Kvitek, Chemica 43 (2004) 59 [8] J Yan, J Cheng, US Patent No 0190851 A1, 2003 [9] J Yan, J Cheng, US Patent No 6379712B1, 2002 [10] S Kawasumi, M Yamada M Honma, US Patent No 5824267, 1998 [11] T.C Pluym, Q.H Powell, A.S Gurav, T.L Ward, T.T Kodas, L.M Wang, H.D Glicksman, J Aerosol Sci 24 (1993) 383 [12] N.K Chaki, S.G Sudrik, H.R Sonawane, K Vijaymohanan, Chem Commun (2002) 76 [13] N.R Jana, L Gearheart, C.J Murphy, Chem Commun (2001) 617 [14] K.-S Chou, C.-Y Ren, Mater Chem Phys 64 (2000) 241 [15] H.S Zhou, T Wada, H Sasabe Komiyama, Appl Phys Lett 68 (1996) 1288 [16] P.Y Lim, R.S Liu, P.L She, C.F Hung, H.C Shih, Chem Phys Lett 420 (2006) 304 [17] H Katsuki, S Komarneni, J Mater Res 18 (2003) 747 [18] Y Sun, B Gates, B Mayers, Y Xia, Nano Lett (2002) 165 2530 [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] R Janardhanan et al / Polyhedron 28 (2009) 2522–2530 M.J Rosemary, T Pradeep, J Colloid Interface Sci 268 (2003) 81 S Mandal, S Arumugam, R Pasricha, M Sastry, Bull Mater Sci 28 (2005) 503 M Starowicz, B Stypula, J Banas´, Electrochem Commun (2006) 227 Y Dai, T Deng, S Jia, L Jin, F Lu, J Membr Sci 281 (2006) 685 S.L.-C Hsu, R.-T Wu, Mater Lett 61 (2007) 3719 L Kvítek, A Panáek, J Soukupová, M Kolárˇ, R Veerˇová, R Prucek, M Holecová, R Zborˇil, J Phys Chem C 112 15 (2008) 5825 X.-Y Gao, S.-Y Wang, J Li, Y.-X Zheng, R.-J Zhang, P Zhou, Y.-M Yang, L.-Y Chen, Thin Solid Films 455–456 (2004) 438 H.H Willard, L.L Merritt Jr., J.A Dean, F.A Settle, in: Instrumental Methods of Analysis, CBS Publishers and Distributors, Delhi, 1986, p 290 H Estrade-Szwarckopf, B Rousseau, J Phys Chem Solids 53 (1992) 419 U Gelius, P.F Heden, J Hedman, B.J Lindberg, R Manne, R Nordberg, C Nordling, K Siegbahn, Phys Scripta (1970) 70 D.L Hoof, D.G Tisley, R.A Walton, J Chem Soc., Dalton Trans (1973) 200 J.S Hammond, J.W Holubka, J.E Devries, R.A Duckie, Corros Sci 21 (1981) 239 P.V Kamat, M Flumiani, G.V Hartland, J Phys Chem B 102 (1998) 3123 L.J Gerenser, J Vac Sci Technol A (1990) 3682 [33] K Wagener, C Batich, B Kirsch, S Wanigatunga, J Polym Sci Part A 27 (1989) 2625 [34] A Hozumi, M Inagaki, N Shirahata, Appl Surf Sci 252 (2006) 6111 [35] John F Moulder, William F Stickle, Peter E Sobol, Kenneth D Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin–Elmer Corporation, Physical Electronics Division, 1992 [36] P.D Schulze, S.L Shaffer, R.L Hance, D.L Utley, J Vac Sci Technol A (1983) 97 [37] G Barth, R Linder, C Bryson, Surf Interf Anal 11 (1988) 307 [38] B.M DeKoven, P.L Hagans, Appl Surf Sci 27 (1986) 199 [39] T Ohta, M Yamada, H Kuroda, Bull Chem Soc Jpn 47 (1974) 1158 [40] C.M Worley, M.D Vannet, G.L Ball, W.E Moddeman, Surf Interf Anal 10 (1987) 273 [41] L Finar, Organic Chemistry Volume 1: The Fundamental Principles, Longman Singapore Publishers, Singapore, 1990 p 514 [42] L Kvítek, R Prucek, A Paná ek, R Novotny´, J Hrbá, R Zbo il, J Mater Chem 15 (2005) 1099 [43] S Panigrahi, S Kundu, S.K Ghosh, S ‘Nath, S Praharaj, S Basu, T Pal, Polyhedron 25 (2006) 1263  ... NaOH and Na2CO3, which settled immediately Fig UV–Visible absorption spectra for silver nanoparticles for samples S1, S2, S3 and S4 Fig XRD of (a) silver nanoparticles and (b) silver oxide particles. .. in (i) silver and (ii) silver particles Fig Photograph of antibacterial test (a) control (b) control with nano silver particles (c) control with uncoated plastic and (d) control with nano silver. .. properties of nano silver It is interesting to observe that, although the nanoparticles contain traces of gluconic acid on the surface, as is evident from the XPS analysis, the surface of the nano silver