Synthesis of silver nanoparticles by y-ray irradiation using pva as stabilizer

Journal of Chemistry, Vol. 45 (Special issue), P. 136 - 140, 2007<br /> <br /> <br /> SYNTHESIS OF SILVER NANOPARTICLES BY -RAY<br /> IRRADIATION USING PVA AS STABILIZER<br /> Received 15 October 2007<br /> Bui Duy Du1, Dang Van Phu2, Bui Duy Cam3, Nguyen Quoc Hien2<br /> 1<br /> Institute of Applied Materials Science, Vietnam National Institute for Science and Technology<br /> 2<br /> Research and Development Center for Radiation Technology, Vietnam Atomic Energy Commission<br /> 3<br /> Natural Science College, Hanoi National University<br /> <br /> SUMMARY<br /> Colloidal silver nanoparticles were synthesized by Co-60 ray irradiation of Ag+ in aqueous<br /> solution containing polyvinyl alcohol (PVA) as stabilizer and 0.5 M ethyl alcohol as free radical<br /> (OH•) scavenger. The effect of Ag+ concentration which varied from 1 to 50 mM on the saturated<br /> conversion dose (D) of Ag+ into Ag determined by UV-vis spectroscopy and the size of Ag<br /> nanoparticles characterized by transmission electron microscopy (TEM) were investigated. The<br /> dependence of D (kGy) and average size (d, nm) of Ag nanoparticles on Ag+ concentration was<br /> found out to be as: D (kGy) = 0.0041 [Ag+]2 + 0.8674 [Ag+] + 3.2262 (R2 = 0.9799) and d(nm)<br /> = 0.0016 [Ag+]2 + 0.136 [Ag+] + 7.068 (R2 = 0.9736) for Ag+ concentration from 1 to 50 mM<br /> stabilized by 2% PVA. Results indicated the Ag nanoparticles size to be in the range of 6 - 18 nm.<br /> The concentration of PVA (0.5 - 4.0%) in the irradiated solution also considerably affected the<br /> silver nanoparticles size which decreased with increasing the amount of PVA in the solution. Due<br /> to the unique features of the processing procedures, thus Co-60 ray irradiation has been<br /> considered as a suitable method for mass production of colloidal silver nanoparticles.<br /> <br /> I - INTRODUCTION is carried out under ambient pressure at room<br /> temperature 2) reducing agents are uniformly<br /> Silver nanoparticles have attractive distributed in the solution in neat portion as for<br /> considerable interest owing to their potential metal ions 3) reaction rate can be reliably<br /> applications in different areas such as in controlled by varying absorbed dose or<br /> medicine as biocides for burn and traumatic irradiation time 4) the product namely colloidal<br /> wound [1, 2] and radiotherapy [3], in catalysis silver nanoparticles can be obtained without<br /> [4], in electronics [5], as well as in agriculture contamination of excessive reductant.<br /> [6]. A number of methods have been developed The mechanism of the radiation method<br /> for the synthesis of silver nanoparticles based on the reduction of metal ions,<br /> stabilized by polymers such as chemical particularly Ag+ ions by hydrated electron (e-aq)<br /> reduction [7 - 10], electron and photochemical and hydrogen atom (H•) produced in solution<br /> reduction [11, 12], thermochemical treatment during irradiation [14, 16].<br /> [13] and ionizing radiation [14 - 19].<br /> H2O e-aq, H•, OH•, H2O2, H2, H3O+,..<br /> Compared with other methods of preparation<br /> (1)<br /> of silver nanoparticles, the radiation method 0 -<br /> provides several advantages such as: 1) process The solvated electrons with E (H2O/e aq) =<br /> <br /> 136<br />  2.87 VNHE and H• atoms with E0(H+/H•) = 2.3 Ag+ + H• Ag0 + H+ (3)<br /> VNHE are powerful reducing agents so that they 0<br /> Ag + Ag + +<br /> Ag + Ag +<br /> (4)<br /> 2 n+1<br /> easily reduce Ag+ ions to the zero-valent state •<br /> Ag0 with E0(Ag+/Ag0) = 1.8 VNHE as shown by OH radical formed during irradiation is<br /> (2), (3) and (4) [14, 16]. The reaction process strongly oxidative agent which must be<br /> can be written as follows: converted into reducing agent by reacting with<br /> alcohol (ethanol, isopropanol,..) resulting<br /> Ag+ + e-aq Ag0 (2) alcoholic radicals as follows [16, 17]:<br /> <br /> RCH2OH (R2CHOH) + OH• R•CHOH (R2•COH) + H2O (5)<br /> • • + 0 +<br /> R CHOH (R2 COH) + Ag n+1 Ag n +1 + RCHO (R2CO) + H (6)<br /> • • 0<br /> Alcohol is called as a free radical (OH ) scavenger. The R CHOH radical with E (RCH2OH/<br /> •<br /> R CHOH ) ~ 1.8 VNHE is not able to reduce free Ag+ ions in solution while they can reduce Ag+<br /> ions in cluster Ag+n+1 due to E0(Ag+/Ag0n) = 0.78 VNHE [3].<br /> The stabilizing effect of PVA can be described as in Fig. 1.<br /> <br /> R R<br /> O O ray<br /> H H H H o<br /> Ag n<br /> O O<br /> R R<br /> Figure 1: Schematic diagram of PVA stabilized silver nanoparticles ( : Ag+)<br /> <br /> II - EXPERIMENTAL which was diluted by water to 0.1 mM<br /> calculated as Ag+ concentration were taken on<br /> 1. Materials an UV-vis spectrophotometer model UV-<br /> 2401PC, Shimadzu, Japan. The size of the silver<br /> Silver nitrate and ethanol were analytical<br /> nanoparticles was measured using a<br /> grade from China, polyvinyl alcohol (PVA) with<br /> transmission electron microscope (TEM) model<br /> molecular weight Mw = 1.25×105 was from JEM 1010, JEOL, Japan operated at an<br /> Kuraray, Japan. Pure water for chromatography accelerating voltage of 80 kV.<br /> was from Merck, Germany.<br /> 2. Preparation of Ag+ solution and -ray III - RESULTS AND DISCUSSION<br /> irradiation<br /> Fig. 2 showed the relationship between<br /> The solutions containing PVA 0.5 M optical density of irradiated Ag+ solution with<br /> ethanol and Ag+ with different concentration different concentration and dose. It was<br /> from 1 to 50 mM in glass tubes that were observed from Fig. 2 that the optical density<br /> decreased by bubbling with nitrogen. The -ray increased with decreasing Ag+ concentration.<br /> irradiation was carried out on a Co-60 source<br /> with dose rate of 1.3 kGy/h at VINAGAMMA The saturated conversion dose (D-convert) is<br /> Center, Ho Chi Minh City. the absorbed dose for complete reduction of Ag+<br /> into metalic silver and it is one of the main<br /> 3. Characterization parameters for synthesizing colloidal silver<br /> Optical spectra of the irradiated Ag+ solution nanoparticles practically free from Ag+<br /> <br /> 137<br /> precursor. D-convert as a function of Ag+ brownish colloidal silver nanoparticle solutions.<br /> concentration was described in Fig. 3. The dose required for complete reduction of Ag+<br /> with the concentration above 10mM was<br /> 1.4 significantly lower than the value calculated<br /> 1mM<br /> 1.2 5mM theoretically about 16.67 kGy [17]. The reason<br /> 10mM for this phenomenon may be explained by occur<br /> 1 20mM<br /> 30mM other pathways for the reduction of Ag+ than the<br /> OD<br /> <br /> <br /> <br /> <br /> 0.8 50mM formation of silver by the radiolysis species in<br /> 0.6<br /> solution. For example, the direct interaction of<br /> radiation on PVA and ROH may raise<br /> 0.4 additional reduction species.<br /> 0.2 RH (PVA, ROH) R +H (8)<br /> 0<br /> Gautam et al. reported that PVA can act as a<br /> 0 8 16 24 32 40 48 chemical reducer through a reaction expressed<br /> Dose, kGy as following [13]:<br /> Figure 2: The relationship of optical density of R OH (PVA) + Ag+ R=O + Ag0 + H+ (9)<br /> irradiated Ag+ solutions and dose<br /> The reaction (9) may be another reason for<br /> 40 lowering the D-convert.<br /> Temgire and Joshi reported the preparation<br /> 32 of silver nanoparticle stabilized by PVA with<br /> different molecular weight by radiation method<br /> D, kGy<br /> <br /> <br /> <br /> <br /> 24 [16]. The maximum absorption wavelengths<br /> ( max.) for the colloidal silver nanoparticle<br /> solution obtained by Temgire and Joshi were<br /> 16<br /> almost in agreement with our results that varied<br /> from 400 to 420nm. However they used very<br /> 8 y = -0.0041x2 + 0.8674x + 3.2262<br /> low concentration of PVA as stabilizer then<br /> R2 = 0.9799<br /> their solutions of Ag nanoparticle were stable<br /> 0 only for a few days.<br /> 0 10 20 30 40 50 60 Figure 4 showed a typical TEM image and<br /> size distribution of Ag nanoparticles from the<br /> [Ag +], mM sample of 20 mM Ag+. It indicated in Fig. 4 that<br /> the Ag nanoparticles have spherical shape and<br /> Figure 3: The dependence of D-convert on Ag+ Gaussian size distribution.<br /> concentration The relationship of the average size of Ag<br /> The dependence of D-convert (kGy) on Ag+ nanoparticles and Ag+ concentration was<br /> concentration which varied from 1 to 50 mM described in Fig. 5. The average size of silver<br /> was found out to be as: particles was calculated to be as:<br /> <br /> D (kGy) = 0.0041 [Ag+]2 + 0.8674 [Ag+] + d(nm) = 0.0016 [Ag+]2 + 0.136 [Ag+] + 7.068<br /> 3.2262 (R2 = 0.9799) (7) (R2 = 0.9736) (10)<br /> The dose range in equation (7) was from Results obtained in equation (10) indicated<br /> about 4 to 36 kGy for the Ag+ concentration the Ag nanoparticles size to be in the range of 6<br /> from 1 to 50mM stabilized by 2%PVA. The - 18 nm for the Ag+ concentration from 1 to 50<br /> sample solutions after irradiation formed dark mM.<br /> <br /> 138<br />  40<br /> <br /> 32 b)<br /> a)<br /> <br /> <br /> <br /> <br /> Frequency, %<br /> 24<br /> <br /> 16<br /> <br /> 8<br /> <br /> 0<br /> 2.5 7.5 12.5 17.5 22.5<br /> Size, nm<br /> Figure 4: TEM image (a) and size distribution (b) of Ag nanoparticles stabilized by 2%PVA from<br /> sample of 20 mM Ag+<br /> 20 36<br /> <br /> 16 30<br /> d, nm<br /> <br /> <br /> <br /> <br /> 12 24<br /> dtb, nm<br /> <br /> <br /> <br /> <br /> 18<br /> 8<br /> 2<br /> y = 0.0016x + 0.136x + 7.068 12<br /> 4 2<br /> R = 0.9736<br /> 6<br /> 0<br /> 0<br /> 0 10 20 30 40 50 60<br /> +<br /> 0 1 2 3 4 5<br /> [Ag ], mM<br /> [PVA], g/100 ml<br /> <br /> Figure 5: The dependence of the average size of Figure 6: The dependence of silver particle size<br /> Ag nanoparticles on Ag+ concentration on PVA concentration (for 20 mM Ag+)<br /> <br /> Fig. 6 indicated that the average size of the lower than 20 nm with narrow size distribution<br /> silver nanoparticle decreased with the increase but the Ag+ concentration used was low (2 mM)<br /> in the amount of PVA in the solution. It was [18]. Bogle et al. used the 6 MeV electron<br /> also observed in Fig. 6 that PVA concentration irradiation to prepare Ag nanoparticles<br /> of about to 2.0 to 3.0% was a critical range for stabilized by PVA but the particle size they<br /> Ag+ concentration of 20 mM in order to obtain obtained was rather large varied from 60 to<br /> the smallest silver particles size of about 10 nm. 10nm [19]. Generally, the main parameters that<br /> Shin et al. prepared Ag nanoparticles by -ray affected the particles size are Ag+ concentration,<br /> irradiation method using PVP as stabilizer, they stabilizer and radiation ( -ray or electron).<br /> also obtained Ag nanoparticles in small size Based on the results obtained in this work, it<br /> 139<br /> that has been proposed that Co-60 ray 5. A. Kesow et al. J. Appl. Phys., 94, 6988<br /> irradiation could be applied as a suitable method (2003).<br /> for mass production of colloidal silver 6. H. J. Park et al. 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