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Colloids and Surfaces A: Physicochem. Eng. Aspects 320 (2008) 104–110

Synthesis of Ag/SiO2 nanocomposite material by adsorption phasenanoreactor technique

Xin Jiang ∗, Shi Chen, Congwen MaoCollege of Material and Chemical Engineering, Zhejiang University, Hangzhou 310027, China

Received 14 August 2007; received in revised form 11 January 2008; accepted 17 January 2008Available online 26 January 2008

bstract

Ag/SiO2 nanocomposite was synthesized in a nanoreactor formed by adsorption layer on silica surface. Ag nanoparticles were prepared by theeduction of Ag ion with ethanol at alkaline condition. By using TEM and XRD, the effects of NaOH concentration, water and temperature onhe appearance and grain size of Ag particles were analyzed, respectively. The adsorption curve of NaOH was measured by electrical conductivity

eter. The experiment result revealed that Ag grain size decreased while increasing NaOH concentration or while increasing water in our system.

g grain size increased with the increase of temperature. And Ag aggregated seriously when temperature is up to 60 ◦C. Finally, after exploring

he optimum conditions of reaction, we successfully obtained the well-distributed Ag nanoparticles on surface of silica, and average grain size ofg nanoparticles reached 5 nm.2008 Elsevier B.V. All rights reserved.

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eywords: Nanocomposite; Nanoparticles; Interface; Ag; SiO2

. Introduction

Nanoreactor is a new reaction technology [1] for prepara-ion of nanoparticles, which provides a relatively simple methodo adjust particles size distribution by means of restricting therowth of crystal nucleus in a narrow space. There are manyinds of nanoreactors. Shervani et al. [2] use microemulsions nanoreactor to prepare Ag and Cu nanocrystals. Nanoporoustructure of cellulose fiber is utilized as a nanoreactor to pre-are noble metals including Ag, Au, Pt and Pd by Kunitake3]. Rybak et al. [4] use air/water interface as a nanoreactoro synthesize silver nanoparticles, the size of which is withinnm. Dekany’s group [5] makes use of interlamellar space ofaolinite as a nanoreactor and obtains Ag nanoparticles with amall grain size. The interlamellar space limits particle growth;owever, larger silver particles may be formed on the exteriorurface of kaolinite. In recent years, Dekany’s group prepared

d [6,7], CdS [8], TiO2 [9], ZnO [10], and SnO [11] nanopar-

icles on the support surface by using the solid/liquid interfaces a nanophase reactor and based on thermodynamics of multi-

∗ Corresponding author. Fax: +86 571 87951227.E-mail address: jiangx@zju.edu.cn (X. Jiang).

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927-7757/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2008.01.027

omponent liquid mixture, they inferred that the adsorption ofifferent kinds of molecular was dissimilar and adsorption layeras mainly consisted of one component. Our research groupas already prepared TiO2 [12,13] and CuO [14] nanoparticlesn SiO2 surface and provided the direct experimental evidencebout the adsorption layer where the reaction just took place. Wend that it is unfavorable for the formation of adsorption layerith increasing temperature.Ag is an important inorganic material that has a wide appli-

ation perspective in superconducting [15], catalysis [16,17],hotosensitive components [18,19], etc. Nanoparticles of nobleetals have been the subject of much intensive research

ue to their potential applications in microelectronics and son [20,21]. Among the various methods to synthesize silveranoparticles, using silica as support has received a significantttention, owing to its amenable features, such as structural andhermal stability and weak interactions with silver particles [22].p to date, Ag/SiO2 nanocomposite has been synthesized by

everal chemical and physical routes, including sol–gel [23],F-sputtering [24,25], sonochemical deposition [26], thermal

ecomposition [27] and reverse micelle [28]. In this paper, wesed the adsorption layer on the surface of SiO2 as reactor torepare Ag/SiO2 nanocomposite material which had a smallverage grain size and was well-distributed. By using TEM and

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RD, the effects of NaOH concentration, water and tempera-ure on the appearance and composition of Ag particles werenalyzed, respectively.

. Experiment

.1. Preparation of Ag/SiO2 nanocomposite material

0.5 g SiO2 baked at 120 ◦C and 200 mL absolute ethyl alcoholere added and well mixed in triflask. After SiO2 was well-istributed, water with constant volume and NaOH with constantmount were added into the reaction system and then adsorbednder stirred and different temperature conditions. Because ofelective adsorption capacity of SiO2, NaOH/water-rich adsorp-ion layer that is just several nanometers thick and can be useds a nanophase reactor was formed gradually on the surface ofiO2. After the adsorption equilibrium was attained (24 h), Sil-er nitrate in ethyl alcohol (30 mL and 7.6 g L−1) was addedt a rate of 0.85 mL/min and reacts with NaOH and reducedy ethanol [29,30]. After reacting for a definite time, the prod-ct was gained by several centrifugation–redispersion–washingycles, and dried at room temperature.

.2. Reagent and apparatus

SiO2 (diameter was 12 nm, specific surface area was00 m2/g) was obtained from Deguass. Absolute ethyl alco-ol (analytical reagent) was distilled and stored over a 0.4 nmolecular sieve (SCR 4A, China). Silver nitrate (AgNO3,

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Fig. 1. TEM of Ag/SiO2 samples at different alkali concentration

ochem. Eng. Aspects 320 (2008) 104–110 105

nalytical reagent) was purchased from Shanghai Chemi-al Reagent Co. Ltd. Sodium hydroxide (NaOH, analyticaleagent) was purchased from Hangzhou Chemical Reagent Co.td.

Measurement of electrical conductivity was acquired withDS-11A electrical conductivity meter and DJS-1C platinumlack electrode. TEM was obtained by JEM-200CX transmis-ion elector microscope, XRD (the XRD peak within 35–40◦one in diffraction pattern was fitted by Cauchy equation andhen, according to Scherrer [31] equation, the average grain sizeas calculated) was obtained by D/max-rA X-ray diffraction

nstrument.

. Result and discussion

.1. Effect of the concentration of NaOH on synthesisg/SiO2 composite material

In the experiment we first studied the effect of NaOH concen-ration at 25 ◦C with 0.2 mL water addition. TEM measurementsere performed on Ag/SiO2 samples produced at different alkali

oncentration as shown in Fig. 1. Comparing the pictures inig. 1, we find that as the alkali concentration increases from.0170 to 0.135 g L−1, the amount of big black points on the pic-ures decrease by degrees, moreover, the amount of small black

oints increases gradually and the mount of total black pointstherwise increase, which manifests that with the increase oflkali concentration there are a larger amount of Ag nanoparti-les with smaller grain size.

(g L−1): (1) 0.0170, (2) 0.0337, (3) 0.0675, and (4) 0.135.

106 X. Jiang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 320 (2008) 104–110

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ig. 2. XRD patterns of samples from different NaOH concentration (g L−1):1) 0.0170, (2) 0.0337, (3) 0.0675, and (4) 0.135.

In order to further analyze the samples prepared, X-rayiffraction was used to estimate the crystal size of each sam-le we got. The result is shown in Fig. 2. It is clearly seen onhe XRD patterns that intensities of peaks are strengthened withncreasing NaOH concentration. In addition, all the character-stic peaks appear at their corresponding 2θ, and no novel peakomes out, which demonstrates that only Ag is produced. Onasis of the data of XRD, we fitted the curve in Fig. 3 represent-ng the relation between average grain size of Ag and NaOHoncentration. As Fig. 3 shown, the grain size of Ag nanoparti-les decreases from 8 to 5 nm as NaOH concentration increasesrom 0.0170 to 0.1350 g L−1. This is coincident with the resultrom TEM.

In the experiment, we measured the concentration of NaOHn bulk phase by introducing the electrical conductivity methodnd sequentially investigated the NaOH distribution betweenwo phases and its transfer process. The percentage of NaOHdsorbed on the surface of silica was exhibited in Fig. 4. It isound that at constant water concentration and temperature, theercentage of NaOH adsorbed on the surface of silica reaches anxtremum with the increase of alkali concentration. This may behe presumable cause to the result that the Ag grain size decreaseith the increase of NaOH concentration as mentioned above.

n other words, with the increase of NaOH concentration, the

oncentration of alkali in adsorption phase will become mucharger than that in alcohol phase, which leads to the reaction ofg production overwhelmingly occurs in the adsorption water

ayer on the surface of SiO2, and consequently, as a result of

Fig. 3. Change of grain size with NaOH concentration.

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ig. 4. Change of NaOH equilibrium adsorption rate with NaOH concentration.

ore crystal nucleus being formed, Ag grain sizes are generaluite small (about 5 nm).

.2. Analysis of the effect of water concentration onynthesis Ag/SiO2 composite material

In this experimental system in which a certain volume ofater (0, 0.1, 0.2, 0.5, 1.0, and 2.0 mL) and 0.054 g NaOH were

dded at 25 ◦C with other conditions unchanged, six series ofamples under different water concentration were obtained. Bysing electric conductivity method again, we observed that equi-ibrium percent of NaOH adsorbed on silica increased graduallyhile increasing the water concentration in system (Fig. 5).Fig. 6 shows analytical result of sample-appearance by

erforming TEM measurements on samples obtained under dif-erent water concentration. It is detected that Ag particles areistributed over the surface of silica in the form of massivegglomeration when the water concentration reaches practicallyero in system. Since part of NaOH (about 26%) is adsorbedn silica and the other is distributed in the bulk phase when

he water concentration is practically zero (Fig. 5), the reaction

ay take place either on the silica surface or in the bulk phase.owever, while water concentration increases gradually, on the

urface of silica the agglomerative substance is reducing, and

ig. 5. Change of equilibrium adsorption rate of NaOH vs. concentration ofater.

X. Jiang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 320 (2008) 104–110 107

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obe uncontrolled and agglomerated either on the surface of silicaitself or in the bulk phase into restricted growth in the adsorptionlayer. This results in the ultimate trend of change of Ag particlesdiameter and appearance.

Fig. 6. TEM of Ag/SiO2 samples under different concentration o

mall black points are increasing at all times. 0.50 vol% wateroncentration is obviously the breaking point, because the aggre-ation of Ag nanoparticles basically disappears. Finally whenhe water concentration arrives at 1.0 vol%, the agglomeration ofg is eliminated, and well-distributed small black points appearn most of the silica surface (about 5 nm). The experimentalesult reflects the trend: while increasing water, agglomerationf Ag particles is reduced; average grain size becomes smaller;istribution of Ag becomes better at the same time.

XRD of samples obtained at different water concentrations displayed in Fig. 7. It is found that grain diameter becomesmaller with increasing water, as shown in Fig. 8. As we canee from the TEM and XRD results at different concentration ofater, due to the increase of water, the appearance of Ag par-

icles changes from big agglomerated to small well-distributed.aking a comprehensive view on results from Figs. 5–8, it is

onceivable that the increase of water is just the process thatdsorption water layer on the surface of silica comes into being.n this way, with the formation of water layer, NaOH transformrom the bulk phase to the adsorbed water layer on the surface

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er (vol%): (a) 0, (b) 0.05, (c) 0.10, (d) 0.25, (e) 0.50, and (f) 1.0.

f silica, which changes the growth of Ag particles that used to

ig. 7. XRD patterns of samples from different concentration of water (vol%):a) 0, (b) 0.05, (c) 0.10, and (d) 0.25.

108 X. Jiang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 320 (2008) 104–110

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Fig. 8. Change of Ag grain size vs. concentration of water.

Moreover, from Fig. 7 it is found that, in the range of–0.25 vol% only Ag yield, but when the water concentrationrrives at 0.50 vol%, not only characteristic peaks of Ag iniffraction pattern exist but also new peaks appeared which isorresponded to Ag2O assured via comparison of XRD pictures.he peak turned up at 1.0 vol% water concentration is similar to

he peak turned up at 0.5 vol% water concentration, which meanshat both Ag particles and Ag2O exist in the products, and fur-hermore the intensity of Ag2O characteristic peak is enhanced

hile intensity of Ag characteristic peak abates comparatively.his may owe to the formation of adsorption layer that separatesg2O from ethyl alcohol and then causes the reduction of Ag2Oy ethyl alcohol to be partly ceased.

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Fig. 10. TEM at differ

Fig. 9. Change of grain diameter vs. temperature.

.3. Study on temperature effect on synthesis Ag/SiO2

omposite material

To get Ag/SiO2 samples, this series of experiments were car-ied out at different temperature (0, 25, 40, and 60 ◦C), and otheronditions set as before, 1.0 mL water together with 0.054 gaOH were added. By utilizing X-ray diffraction apparatus, we

an see that the increase of Ag grain diameter goes on pretty◦

ast in the range of 25–40 C and then inclines to be smooth

Fig. 9).Fig. 10 is the TEM picture at different temperature. As the

EM shown, when the temperature is 0 ◦C, small particles with

ent temperature.

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nm average diameter are generated at the surface of silica.hen the temperature is 25 ◦C, the diameter of particle we got

ncreases to about 5 nm. When the temperature reaches 40 ◦C,g diameters vary obviously with each other. Eventually when

he temperature arrives at 60 ◦C, Ag particles appear to be notnly big but also agglomerated seriously. The TEM result isn good agreement with the XRD result at different tempera-ure. Our former work [32] manifests that the adsorption layers divided into chemical adsorptive layer and physical adsorp-ive layer, and the latter becomes unstable at higher temperature.herefore we make a conclusion that the unstable water layerauses the place where Ag particles yield to be transformedrom the adsorption layer on the surface of silica at relativeow temperature (0–25 ◦C) to bulk phase or silica surface itselfdsorbing large amounts of NaOH at high temperature (60 ◦C).he change of reaction place leads to the change of Ag particleeneration mechanism, which changs the state of Ag particleeneration from adsorption-layer-restricted growth to uncon-rolled growth, and thus brings about the final change of Agarticle appearance.

. Conclusion

In summary, by adsorption phase nanoreactor technique,g/SiO2 nanocomposite material is synthesized. Average grain

ize of Ag nanoparticles reaches 5 nm. After exploring theptimum reaction condition, we successfully obtain the well-istributed Ag nanoparticles on surface of silica. Comparing theamples that we synthesized under different conditions, we madehose conclusions as follows: Ag grain size decreases from 8 tonm while increasing NaOH concentration or while increasingater in our system, and when the water concentration arrives at.50 vol%, the agglomeration of Ag is eliminated. Ag grain sizencreases with the increase of temperature. And Ag aggregateseriously when temperature is up to 60 ◦C.

cknowledgements

Financial support from the National Science Foundation ofhina Grants (Contract 20476088), Zhejiang Provincial Natu-

al Science Foundation of China (Y405125) and the Zhejiangcience & Technology Program (Contract 2004C31057) isratefully acknowledged.

eferences

[1] M.P. Pileni, Nanosized particles made in colloidal assemblies, Langmuir13 (1997) 3266–3276.

[2] Z. Shervani, Y. Ikushima, T. Yokoyama, M. Sato, Y. Hakuta, et al., Sizecontrolled synthesis of Ag and Cu nanocrystals in F-AOT/n-butanol/SCCO2 micromusions, Colloids Surf. A: Physicochem. Eng. Aspects 303(2007) 159–165.

[3] J. He, T. Kunitake, A. Nakao, Facile in situ synthesis of noblemetal nanoparticles in porous cellulose fibers, Chem. Mater. 15 (2003)

4401–4406.

[4] M.B. Rybak, M. Ornatska, K.N. Bergman, K.L. Genson, V.V. Tsukruk,Formation of silver nanoparticles at the air–water interface mediated bya monolayer of functionalized hyperbranched molecules, Langmuir 22(2006) 1027–1037.

[

[

ochem. Eng. Aspects 320 (2008) 104–110 109

[5] R. Patakfalvi, A. Oszko, I. Dekany, Synthesis and characterization of silvernanoparticle/kaolinite composites, Colloids Surf. A: Physicochem. Eng.Aspects 220 (2003) 45–54.

[6] Z. Kiraly, I. Dekany, A. Masralir, M. Bartok, In situ generation of palladiumnanoparticles in smectite clays, J. Catal. 161 (1996) 401–408.

[7] A. Szucs, F. Berger, I. Dekany, Preparation and structural properties ofPd nanoparticles in layered silicate, Colloids Surf. A: Physicochem. Eng.Aspects 174 (2000) 387–402.

[8] I. Dekany, L. Turi, G. Galbacs, J.H. Fendler, Cadmium ion adsorptioncontrols the growth of CdS nanoparticles on layered montmorillonite andcalumit surfaces, J. Colloid Interf. Sci. 213 (1999) 519–584.

[9] I. Ilisz, A. Dombi, K. Mogyorosi, I. Dekany, Photocatalystic water treat-ment with different TiO2 nanoparticles and hydrophilic/hydrophobic layersilicate adsorbents, Colloids Surf. A: Physicochem. Eng. Aspects 230(2004) 89–97.

10] G.R. Gattorno, P.S. Jacinto, L.R. Vazquez, J. Nemeth, I. Dekany, Novelsynthesis pathway of ZnO nanoparticles from the spontaneous hydrol-ysis of zinc carboxylate salts, J. Phys. Chem. B 107 (2003) 12597–12604.

11] L. Korosi, J. Nemeth, I. Dekany, Structural and photooxidation proper-ties of SnO2/layer silicate nanocomposites, Appl. Clay Sci. 27 (2004)29–40.

12] X. Jiang, T. Wang, W. Youwen, Preparation of TiO2 nanoparticles onsurface of SiO2 in binary liquids, Colloids Surf. 234 (2004) 9–15.

13] T. Wang, X. Jiang, X. Li, Preparation of TiO2 nanoparticles on surfaceof different supports by adsorption phase reaction technique, Acta Phys.Chim. Sin. 23 (2007) 1375–1380.

14] Y.P. Li, X. Jiang, T. Wang, Synthesis of CuO/SiO2 nanocomposite mate-rial using adsorption method, J. Zhejiang Univ. (Eng. Sci.) 39 (2005)1866–1870.

15] K. Tachikawa, A. Nagata, K. Togano, Advances in superconducting mate-rials, J. Jpn. Inst. Met. 66 (2002) 199–200.

16] P.J. Van Den Hoek, E.J. Baerends, Ethylene epoxidation on Ag (1 1 0): therole of subsurface oxygen, J. Phys. Chem. 93 (1989) 6469–6475.

17] P. Claus, H. Hofmeister, Electron microscopy and catalytic study of silvercatalysts: structure sensitivity of hydrogenation of crotonaldehyde, J. Phys.Chem. B 103 (1999) 2766–2775.

18] H. Tada, K. Teranishi, Y. Inubushi, Ag nanocluster loading effect on TiO2

photocatalytic reduction of bis(2-dipyridyl)disulfide to 2-mecaptopyridineby H2O, Langmuir 16 (2000) 3304–3309.

19] M.R. Hoffman, S.T. Martin, D.W. Bahnemann, Environmental applicationof semiconductor photo-catalysis, Chem. Rev. 95 (1995) 69–96.

20] Y. Zhou, H.Y. Shu, Y.W. Cui, G.L. Xiao, R.Z. Yu, Y.C. Zu, A novel ultravio-let irradiation photoreduction technique for the preparation of single-crystalAg nanorods and Ag dendrites, Adv. Mater. 11 (1999) 850–852.

21] M. Prudenziati, B. Morten, A.F. Gualtieri, M. Leoni, Dissolution kineticsand diffusivity of silver in glassy layers for hybrid microelectronics, J.Mater. Sci.: Mater. Electron. 15 (2004) 447–452.

22] L. Armelao, D. barreca, G. bottaro, A. Gasparotto, S. Gross, et al., Resenttrends on nanocomposites based on Cu, Ag and Au clusters: a closer look,Coord. Chem. Rev. 250 (2006) 1294–1314.

23] M. Epifani, C. Giannini, L. Tapfer, L. Vasanelli, Sol–gel synthesis andcharacterization of Ag and Au nanoparticles in SiO2, TiO2, and ZrO2 thinfilms, J. Am. Ceram. Soc. 83 (2000) 2385–2393.

24] P. Sangpour, O. Akhavan, A.Z. Moshfegh, RF reactive co-sputtered Au–Agalloy nanoparticles in SiO2 thin films, Appl. Surf. Sci. 253 (2007)7438–7442.

25] Y. Sarov, M. Nikolaeva, M. Sendova-Vassileva, D. Malinovska, J.C. Pivin,Optical properties of SiO2 thin layers with Ag nanoparticles, Vacuum 69(2003) 321–325.

26] V.G. Pol, D.N. Srivastava, O. Palchik, V. Palchik, M.A. Slifkiin, A.M.Weiss, A. Gedanken, Sonochemical deposition of silver nanoparticles onsilica spheres, Langmuir 18 (2002) 3352–3357.

27] W. Chen, J.Y. Zhang, Ag nanoparticles hosted in monolithic mesoporoussilica by thermal decomposition method, Scripta Mater. 49 (2003) 321–325.

28] J.L. Gong, J.H. Jiang, Y. Liang, G.L. Shen, R.Q. Yu, Synthesis andcharacterization of surface-enhanced raman scattering tags with Ag/SiO2

1 hysic

[

[

[31] R. Jenkins, R.L. Snyder, Introduction of X-ray Powder Diffractometry,

10 X. Jiang et al. / Colloids and Surfaces A: P

core–shell nanostructures using reverse micelle technology, J. Colloid

Interf. Sci. 298 (2006) 752–756.

29] M. Quinn, G. Mills, Surface-mediated formation of gold particles in basicmethanol, J. Phys. Chem. 98 (1994) 9840–9844.

30] Z.Y. Huang, G. Mills, B. Hajek, Spontaneous formation of silver particlesin basic 2-propanol, J. Phys. Chem. 97 (1993) 11542–11550.

[

ochem. Eng. Aspects 320 (2008) 104–110

Wiley, New York, 1996.32] X. Jiang, T. Wang, Study on adsorption and reaction mechanism of prepa-

ration of TiO2/SiO2 by adsorption phase technique, Appl. Surf. Sci. 252(2006) 8029–8035.