Preparation of inorganic silica nanofibers containing silver nanoparticles

Fibers and Polymers 2007, Vol.8, No.6, 591-600

591

Preparation of Inorganic Silica Nanofibers Containing Silver Nanoparticles

Kyung Dan Min, Ji Ho Youk1, Young-Je Kwark

2*, and Won Ho Park**

Department of Organic Materials and Textile System Engineering, Chungnam National University,

Daejeon 305-764, Korea1Department of Advanced Fiber Engineering, Intelligent Textile System Research Center,

Inha University, Incheon 402-751, Korea2Department of Organic Materials and Fiber Engineering, Soongsil University, Seoul 158-743, Korea

(Received August 17, 2007; Revised October 17, 2007; Accepted October 25, 2007)

Abstract: Silica nanofibers containing silver nanoparticles were successfully prepared using sol-gel chemistry and electro-spinning technique. Solution of tetraethly orthosilicate in ethanol containing silver nitrate was aged to have sufficient viscos-ity and electrospun to form nanofibers. Upon thermal treatment, the gelation reaction between silanols was completed in theprepared silica nanofibers, and at the same time, silver ions in the nanofiber changed to metallic silver or silver oxides. Thereduction of silver ions could be also achieved by UV irradiation, and the generated silver nanoparticles were present prefer-entially on the surface of the silica nanofibers. On testing release behavior of silver ions, it was found that most of silverremained in the silica nanofiber. The silica nanofibers containing silver nanoparticles exhibited excellent antibacterial anddeodorant properties.

Keywords: Silica nanofiber, Silver nanoparticle, Sol-gel chemistry, Electrospinning, Antibacterial activity

Introduction

Due to its low thermal conductivity, low thermal expansion

coefficient, good thermal stability, and good mechanical

properties, silica fiber has been widely used as a reinforcing

fiber in composites and heat insulating materials. The silica

fibers have been prepared from natural crystals. The molten

liquid of crystals at more than 2,000oC formed to glass rod,

and the end of the glass rod soften to draw fiber. This

conventional method has problems of requiring huge

amount of energy and insufficient purity of the prepared

fiber. To overcome these problems, sol-gel chemistry of

silicon alkoxides has been used [1]. Sol-gel chemistry of

silicon alkoxides could take place at low temperature to

form silicon oxides and, therefore, has been widely used to

prepare monoliths, powder, film coating, and fiber forms of

inorganic materials. The silica materials prepared in this

method have excellent thermal and mechanical properties

and have many potential applications.

Silver (Ag) ions and Ag compounds has been known to be

of antibacterial activity, non-toxic, thermal and chemical

stability [2-4]. Microorganisms with resistance to the anti-

microbial activity of Ag are exceedingly rare [5]. Because of

these properties, they have been widely used in various

biomedical fields, such as wound dressing materials, body

wall repairs, augmentation devices, tissue scaffolds, and

antimicrobial filters [6-13].

In this work, we prepared inorganic silica nanofiber webs

using electrospinning technique. Sol-gel chemistry of silicon

alkoxides was adapted to prepare spinning solution and

silver nitrate (AgNO3) was added to the spinning solution to

introduce Ag atoms into the silica nanofiber webs. Processing

conditions for electrospinning were optimized to prepare

nano-scale silica fibers, and the antibacterial properties and

air permeability of the prepared nanofibers were tested to

check the possibility of using these nanofiber webs in

filtration applications.

Experimental

Materials and Characterizations

Tetraethyl orthosilicate (TEOS, 95 %), nitric acid, ethanol,

and AgNO3 were purchased from commercial suppliers and

used as received without further purification.

Viscosity of silica solution during gelation process was

determined using Brookfield digital viscometer (Model

LVDV-E 230). Aliquot was extracted after pre-determined

time from the solution at 80 oC and cooled to room temperature

in a sealed vial before measuring viscosity. Fourier transformed

infrared spectroscopy (FT-IR) measurement was performed

using Nicolet Magma 560 with scanning number of 32 and

resolution of 9 cm−1. Sample films were prepared by pressing

powder of freeze dried nanofiber web with KBr. Wide angle

X-ray diffraction (XRD) was performed using wide angle X-

ray diffractormeter (Rigaku Co., D/MAX-2200) with Cu-Kα

radiation under conditions of 15 mA and 30 kV. Morphology

of the silica nanofiber was observed using scanning electron

microscopy (SEM, Hitachi S-2350). From the SEM images,

average diameter and its distribution of the nanofiber were

determined using SEM image analyzer (Scope Eye, VI

Technology). Thermogravimetric analysis (TGA) was performed

using Perkin-Elmer TGA-7 under nitrogen atmosphere in

the range of 30 ºC to 700 ºC with a heating rate of 10 ºC/**Corresponding author: [email protected]

**Corresponding author: [email protected]

592 Fibers and Polymers 2007, Vol.8, No.6 Kyung Dan Min et al.

min. Transmission electron microscopy (TEM) image of Ag

particles on silica nanofibers was obtained using JEM-2010

(JEOL Ltd.) in magnifications of 50,000 and 100,000. Sample

was prepared by mounting Ag containing silica nanofibers

on a copper grid coated with carbon. X-ray photoelectron

spectroscopy (XPS) analysis was performed using VG-

Scientific ESCALAB 250 with Al-Kα laser source. Elemental

analysis was performed using CE Instrument, EA 1110 to

determine the content of nitrogen atom of the Ag containing

silica nanofiber. Porosity of the nanofibers web was determined

using mercury porosimeter (Carlo Erba model 2000). UV-

visible (Perkin Elmer, Lambda 35) spectrophotometer was

used to follow the photoreduction of Ag+ ions to Ag

nanoparticles in silica nanofibers [14,15]. Inductively Coupled

Plasma (ICP, Perkin-Elmer Instruments, Optima 3300DV)

was used to check the releasing behavior of Ag+ ions. Air

permeability of nanofiber web was determined using TEXTEST

Instruments, FX 3300 following standard testing procedure

(ASTM D737-04).

Electrospinning of Silicates Using Sol-gel Chemistry

To a solution of TEOS in ethanol was added dropwise

nitric acid aqueous solution with continuous and vigorous

stirring (TEOS/water/ethanol/nitric acid=1/2/2/0.01) [16-18].

On adding nitric acid, hydrolysis and condensation reactions

take place while generating heat. When the mixture was

cooled to room temperature, AgNO3 (0.05~0.5 wt% to silicate)

was added. The homogeneous solution was aged for 70 min

at 80 oC with continuous stirring, and then cooled to room

temperature before spinning. The electrospinning setup used

in this study consisted of a syringe and needle (ID=0.84

mm), an aluminum collecting plate, and a high voltage

supply (Chungpa EMT). A syringe pump connected to the

syringe controlled the flow rate. The solutions were electrospun

at a positive voltage of 25 kV, a working distance of 10 cm

(the distance between the needle tip and the collecting plate),

and a solution flow rate of 3 ml/h. All electrospinning

procedures were carried out at room temperature.

Thermal Treatment and UV Irradiation of Silica/AgNO3

Nanofibers

The silica nanofibers were heated to pre-determined temper-

atures for 30 min and held at that temperature for another

30 min before cooling to room temperature. The treated

nanofiber was characterized with FT-IR, XRD, TGA, TEM,

and XPS. The silica/AgNO3 nanofibers on a glass slide were

irradiated with UV light at 254 nm using a 500 W high-

pressure Hg lamp system (StabiLight, NT-LS-HG50-SR).

The glass slide was washed with deionized water in an

ultrasonicator for 30 min and completely dried.

Antibacterial Properties Tests

The antibacterial activities of the silica nanofiber webs

with and without Ag nanoparticles were tested against

Staphylococcus aureus (ATCC 6538P) and Klebsiella

pneumonia (ATCC 4352) according to the (standard) testing

method for the antibacterial activity of textiles (KS K

0693:2001) [19]. The agar plates containing the test samples

and the control (blank) were incubated at 37 oC for 18 h. The

reductions of the bacteria were calculated according to the

following equation, Reduction (%)=(B−A)/B×100, where

A and B are the numbers of surviving cells (colony forming

units per milliliter) for the plates containing the test samples

and the control, respectively, after 1 h. Halo test was performed

following standard test procedure (AATCC 147-1998). Zone

of inhibition (W) was calculated as W=(T−D)/2, where T is

the total diameter of a sample and support and D is the

diameter of a sample. Deodorant test was performed following

Japan KAKEN test procedure. To a tetra bag containing 1 g

of sample was charged 3 l of ammonia gas. After 24 h, the

concentration of the gas was determined.

Results and Discussion

Electrospinning of Silica/AgNO3 Nanofibers

In electrospinning processes, the spinning solution should

have proper range of viscosity to form fibers in nano size.

Since the viscosity of the silicates solution increased as the

gelation between silicon alkoxides preceded, it was important

to precisely control the degree of the gelation reaction for the

successful nanofiber formation. Figure 1 shows the increase

of the viscosity over reaction time (gelation time). The

viscosity increased slightly for initial 55 min, and at which

point, it showed rapid increase indicating sufficient con-

densation between silanols. When the solutions were electrospun

Figure 1. Changes in viscosity of TEOS solution over gelation

time.

Silica Nanofibers Containing Silver Nanoparticles Fibers and Polymers 2007, Vol.8, No.6 593

Figure 2. SEM images of silica nanofibers electrospun after different gelation times; (a) 55 min, (b) 60 min, (c) 65 min, and (d) 70 min,

electrospinning conditions; voltage=25 kV, working distance=10 cm, mass flow rate=10 ml/hr.

Figure 3. Changes in average diameters of silica nanofibers electrospun under different processing conditions; (a) applied voltages, (b)

working distance, (c) mass flow rates, and (d) needle inner diameters.


under a standard condition of a positive voltage of 25 kV, a

working distance of 10 cm, and a solution flow rate of 3 ml/h,

the prepared silica nanofibers had morphologies of sprayed

particles when the gelation time was 55 min, beaded fibers

when it was 60 and 65 min, and finally homogeneous

nanofibers after 70 min of gelation time (Figure 2). Figure 3

shows the relationship between diameter of the prepared

silica fiber and the processing parameters, such as applied

voltage, working distance, mass flow rate, and diameter of

the spinning tip. Similar to the cases of other organic polymers,

diameter of the electrospun fiber decreased with increasing

applied voltage, decreasing working distance, and decreasing

mass flow rate, while the dependencies on the parameters

were slightly higher. On the other hand, tip size affected to

the diameter of the nanofibers greater than other parameters.

Therefore, gelation time and spinning tip size were the two

most important parameters in electrospinning of silicate

solution using sol-gel chemistry.

When salt is added to the spinning solution, increased

charge density of the solution enhances repulsion between

the materials to give homogeneous nanofibers with smaller

diameter. AgNO3 was expected to behave as a salt to do such

effects. Figure 4 shows the silica nanofibers containing varying

amounts of AgNO3. It shows a sharp decrease in diameter of

the nanofibers with only 0.05 % of AgNO3, with a continuous

decrease in diameter with increasing amount of AgNO3.

Effects of Thermal Treatment

The prepared silica nanofibers were heated up to 600oC to

complete the gelation reactions between silanols. Figure 5(a)

shows FT-IR spectra of the silica nanofibers. As the temperature

increased, intensity of the peaks at around 3390 and 950 cm−1

for silanols groups decreased. This result indicated that the

condensation reaction between silanols completed to become

Si-O-Si bonds with thermal treatment at 600oC. The same

result could be drawn from the wide angle X-ray diffraction

patterns of the silica nanofibers (Figure 5(b)). The peak at

2θ=9o induced from the ordered molecular alignment by the

hydrogen bonding between silanols decreased as the con-

densation proceeded and was finally disappeared completely

at 600oC. The porosity of the silica nanofibers determined

using mercury porosimeter was decreased from 95 % to

89 % after the thermal treatment at 600 oC, indicating more

compact structure was induced by the completed condensation

reactions.

TGA curves for the silica nanofibers are shown in Figure 6.

Three stages of weight reduction were observed. The first

one under 150 oC was for the vaporization of residual solvent.

The second one at 190-300 oC was from the condensation

reaction between unreacted ethoxy and hydroxyl groups,

which leaded removal of ethanol. The last stage of weight

loss at 300-500oC was thought to be from the condensation

between silanols. The weight reduction was higher for the

Figure 4. SEM images of silica nanofibers electrospun with different AgNO3 contents; (a) 0 wt%, (b) 0.05 wt%, (c) 0.1 wt%, and (d) 0.5 wt%.


silica nanofibers containing AgNO3, probably due to the

vaporization of nitro groups as NO or NO2 gases. Elemental

analysis for the nanofibers treated at various temperatures

revealed that nitrogen content decreased as increasing

temperature, and reached almost zero after 200oC (Figure

7). This result matched well with the TGA analysis results,

and implied that nitrate groups in AgNO3 could be easily

removed by thermal treatment to give reduced Ag metals.

TEM images of the silica nanofibers containing 0.5 wt%

of AgNO3 showed that the amount of the Ag nanoparticles

on the nanofibers surface seemed decreased as increasing

temperature (Figure 8(a)-(e)). It was not because the Ag

nanoparticles disappeared completely from the nanofibers

surface, but because Ag metals were oxidized to AgO or

AgO2 and presented homogeneously inside of the silica

nanofibers. This could be confirmed by XPS analysis. For

the silica/AgNO3 nanofibers, there were peaks at around 370 eV

for 3d3/2 and 3d5/2 orbitals of Ag atoms. As temperature

increased, intensities of these peaks decreased while new

peak at 710 eV appeared (Figure 9). The new peak was from

the oxidized Ag compound, and this result evidenced that

thermal treatment under air oxidized Ag atoms in the

Figure 5. (a) FT-IR spectra and (b) X-ray diffraction patterns of pure silica nanofibers and silica nanofibers containing 0.5 wt% AgNO3 and

silica nanofibers containing 0.5 wt% AgNO3 after thermal treatments at different temperature in air.

Figure 6. TGA curves of pure silica nanofibers and silica

nanofibers containing 0.5 wt% AgNO3.

Figure 7. Nitrogen content of 0.5 wt% AgNO3-containing silica

nanofibers after heat treatment at different temperature.


nanofibers. When the silica nanofibers were treated under

nitrogen atmosphere, on the other hand, Ag nanoparticles

were not oxidized and stayed onto the surface of the

nanofibers (Figure 8(f)). XPS data for the silica nanofibers

heated under nitrogen atmosphere showed peaks at around

370 eV for the non-oxidized Ag atoms, while no peaks at

710 eV for the oxidized compounds.

Effects of UV Irradiation

Ag+ ions in silica nanofibers could be reduced by UV

light to metallic Ag particles. UV light at 254 nm in UV-Vis

spectrophotometer (500 W) was used to follow the photoreduc-

tion process of Ag+ ions in silica nanofibers. As irradiation

time increased, maximum intensity of UV-vis spectrum

increased to reach a plateau after 4 h (insert in Figure 10).

Figure 8. TEM images of silica nanofibers containing 0.5 wt% AgNO3 after thermal treatment at different temperature (a) as spun,

(b) 150 oC, (c) 200 oC, (d) 400 oC, (e) 600 oC in air, and (f) 600 oC in N2. The scale bars correspond to 100 nm.

Figure 9. XPS spectra of silica nanofibers containing 0.5 wt% AgNO3; (a) regions for metallic Ag and (b) regions for oxidized Ag.


Also, the initial maximum peak at 420 nm shifted to 444 nm

after 4 h, without further change after then. This blue shift of

maximum peak indicated that size of the generated Ag

particle increased with the irradiation time. These results

indicated that the photoreduction of Ag+ ions was completed

with 4 h of UV irradiation under the tested conditions. The

generation of Ag nanoparticles could be observed using

TEM (Figure 11). After 1 h of UV irradiation, the Ag

particles were generated heterogeneously on the nanofibers

surface. The average size of the generated Ag particles was

50 nm after 1 h irradiation and increased to 73 nm after 4 h.

The selective formation of the Ag nanoparticles onto the

surface of the nanofibers after UV irradiation could be

explained by the followings: Firstly, the Ag+ ions presented

in the silica nanofibers migrated to the surface with the

evaporating solvent molecules during the electrospinning

process, and were reduce to Ag metals by UV irradiation.

Secondly, the Ag+ ions only on the nanofiber surface were

reduced by UV to form metallic Ag particles, and the ones

inside the nanofiber were not affected by the UV irradiation.

Release of Ag+ Ions and Antibacterial Activity of Silica/

AgNO3 Nanofibers

The release behavior of the Ag+ ions from the silica/

AgNO3 nanofibers in deionized water was examined at 37 oC.

The deionized water was shaken to simulate the local in vivo

release, and the concentration of Ag+ ions released onto

deionized water over time was checked using ICP (Figure

12). Without any treatment, the released Ag+ ion content in

water increased for 6 h, and after which point the remaining

Ag content in silica nanofibers was almost constant as 90 %.

The release of the Ag+ ions was suppressed with the UV

Figure 10. Changes in the wavelength of maximum absorption in

the UV absorption spectra of silica nanofibers containing 0.5 wt%

AgNO3 over UV-irradiation times (insert: intensity of maximum

absorption peak).

Figure 11. TEM images of silica nanofibers containing 0.5 wt% AgNO3 after UV-irradiation for different times; (a) as-spun, (b) 1 h, (c) 2 h,

(d) 3 h, and (e) 4 h.


irradiation, and it only proceeded for 1 h to reach a steady

value of 93 % of remaining Ag content in silica nanofibers.

This less release of the Ag+ ion was thought to be from the

reduction of the ionic Ag to metallic Ag. If the nanofiber

web was treated thermally at 600 oC, almost no Ag+ ions

were released from the web, probably due to the more compact

structure induced by the completed gelation reactions.

Antibacterial activities of the silica nanofibers containing

Ag nanoparticles were tested against Staphylococcus aureus

(ATCC 6538) and Klebsiella pneumoniae (ATCC 4352) by

checking the number of colonies after incubation. Compared

to the pure silica nanofibers that did not show any

antibacterial activity, the silica nanofibers containing 0.5 %

of AgNO3 showed enhanced antibacterial activities (bacteria

reduction>99. 9%). Thermal treatment at 600oC did not

harm the antibacterial activities of the silica nanofibers, and

similar bacterial cell reductions were observed with the

thermally treated sample (Figure 13, Table 1). On halo test,

though, the bacterial cells could grow on UV irradiated

silica/AgNO3 nanofiber web. As we discussed earlier, Ag

nanoparticles were generated by the UV irradiation, and they

might not release enough amounts of Ag+ ions to show

antibacterial behavior.

Deodorant activities of the silica/Ag nanofibers were

examined using NH3 as a test gas. Similar to the case for the

antibacterial activities, the silica/Ag nanofibers showed

Figure 12. Residual Ag contents in silica nanofibers after

extraction in water; (a) as spun, (b) after UV irradiation for 4 h, and

(c) after UV irradiation for 4 h followed by heat treatment at 600 oC

in air.

Figure 13. Clear zone of specimens against Staphylococcus aureus

(ATCC 6538P); (a) pure silica nanofibers, (b) silica nanofibers

containing 0.5 wt% AgNO3, (c) silica nanofibers containing 0.5

wt% AgNO3 after UV-irradiation for 4hr, and (d) silica nanofibers

containing 0.5 wt% AgNO3 after heat treatment at 600 oC in air.


excellent deodorant activities (Table 2).

Air Permeability of Silica Nanofiber Web

For filtering application, there should be sufficient amount

of void inside of the nanofiber webs. The air permeability of

silica nanofiber webs (thickness 170 µm) was compared

with the one of commercial HEPA filter (thickness 270 µm).

The silica nanofiber webs had lower number of air

permeability of 1.89 for the pure silica nanoweb, 1.47 for the

silica/AgNO3 nanoweb. Since size of the silica/AgNO3

nanoweb had smaller than that of the pure silica nanoweb,

air permeability of the silica/AgNO3 nanoweb was low.

However, the size of the nanofiber and pore size of the

nanoweb could be controlled by changing processing conditions

in electrospinning, it was expected to use the silica nanofiber

webs in filtering applications.

Conclusion

Silica nanofibers webs with antibacterial activity were

successfully prepared using sol-gel chemistry and electro-

spinning technique. The antibacterial activity was introduced

by adding silver nitrate into the spinning solution. The silver

ions could be reduced to metallic silver nanoparticles by

thermal treatment and/or UV irradiation, and the generated

silver nanoparticles were located preferentially on the surface of

nanofiber in an average diameter of 73 nm. Even though the

generated silver nanoparticles were on the surface, most of

silver remained in the silica nanofibers when the nanofibers

were immersed in water, which indicated that the antibacterial

effect of silver would continue for an extended time. The

silica nanofibers containing silver nanoparticles showed

excellent antibacterial and deodorant properties. The air

permeability of the nanofiber webs was lower than that of

commercial HEPA filter, and could be controlled by modifying

processing conditions of electrospinning. These results provided

a possibility of using the silica nanofibers containing silver

nanoparticles in filtering applications requiring antibacterial

properties as well as chemical and thermal stabilities.

Acknowledgement

This work was supported by the Program for the Training

of Graduate Students in Regional Innovation which was

conducted by the Ministry of Industry and Energy of the

Korean Government. It was also partially supported by the

Soongsil University Research Fund.

References

1. H.-J. Jeon, S.-C. Yi, and S. G. Oh, Biomaterials, 24, 4921

(2003).

2. M. Catauro, M. G. Raucci, F. de Gaetano, and A. Marotta,

J. Mater. Sci., 15, 831 (2004).

3. E. Verne, S. di Nunziio, M. Bosetti, P. Appendino, C. V.

Brovarone, G. Maina, and M. Cannas, Biomaterials, 26,

5111 (2005).

4. S. L. Percival, P. G. Bowler, and D. Russell, J. Hospital

Infection, 60, 1 (2005).

5. J. Y. Kim, S. E. Kim, J. E. Kim, J. C. Lee, and J. Y. Yoon,

J. Korean Soc. Environ. Eng., 27, 771 (2005).

6. B. Jansen, M. Rinck, P. Wolbring, A. Strohmeier, and T.

Jahnns, J. Biomater. Appl., 9, 55 (1994).

7. H. Y. Kang, M. J. Jung, and Y. K. Jeong, Korean J.

Biotechnol. Bioeng., 15, 521 (2000).

8. Q. L. Feng, J. Wu, G. Q. Chen, F. Z. Cui, T. N. Kim, and J.

O. Kim, J. Biomed. Mater. Res., 52, 662 (2000).

9. U. Klueh, V. Wagner, S. Kelly, A. Johnson, and J. D.

Bryers, J. Biomed. Mater. Res., 53, 621 (2000).

10. D. C. Clupper and L. L. Hench, J. Mater. Sci. Mater. Med.,

12, 917 (2001).

11. J. P. Guggenbichler, Mat.-wiss. u. Werkstofftech., 34, 1145

(2003).

12. I. Sondi and B. Salopek-Sondi, J. Colloid Interface Sci.,

Table 1. Antibacterial activities of pure silica nanofibers, silica nanofibers containing 0.5 wt% AgNO3, silica nanofibers containing 0.5 wt%

AgNO3 after UV-irradiation for 4hr, and silica nanofibers containing 0.5 wt% AgNO3 after thermal treatment at 600 oC in air

SampleStaphylococcus aureus (ATCC 6538P) Klebsiella pneumonia (ATCC 4352 )

Zone of inhibition (mm) Growth under the specimen Zone of inhibition (mm) Growth under the specimen

Ag 0 wt% 0 Growth 0 Growth

Ag 0.5 wt% 1.5 Non-growth 1.5 Non-growth

Ag 0.5 wt% after thermal

treatment at 600 oC1 Non-growth 1 Non-growth

Ag 0.5 wt% after UV irradiation 0 Growth 0 Growth

Table 2. Deodorant activity of pure silica nanofibers, silica

nanofibers containing 0.5 wt% AgNO3 and silica nanofibers

containing 0.5 wt% AgNO3 after thermal treatment at 600 oC in air

SampleAmmonia concentration (ppm)

Initial After 2 h After 24 h

Blank 40 37.1 31.1

Ag 0 wt% 40 23.3 18.3

Ag 0.5 wt% 40 <1.0 <1.0

Ag 0.5 wt% after thermal

treatment at 600 oC40 <1.0 <1.0


275, 177 (2004).

13. J. H. Yeum, H. D. Ghim, and Y. Deng, Fibers and

Polymers, 6, 277 (2005).

14. V. Hornebecq, M. Antonietti, T. Cardinal, and M. Treguer-

Delapierre, Chem. Master., 15, 1993 (2003).

15. X. Li, J. Zhang, W. Xu, H. Jia, X. Wang, B. Yang, B. Zhao,

B. Li, and Y. Ozaki, Langmuir, 19, 4285 (2003).

16. T. Peltola, M. Jokinen, S. Veittola, H. Fahiala, and A.

Yliurpo, Biomaterials, 22, 589 (2001).

17. Y. Xu, W. Zhou, L. Zhang, and L. Cheng, J. Mater. Pro.

Tech., 101, 44 (2000).

18. G. P. Fotou, S. E. Pratsinis, and N. G. Pinto, J. Non-Crystal.

Solids, 183, 135 (1995).

19. S. Zhang, R. Fu, D. Wu, W. Xu, Q. Ye, and Z. Chen,

Carbon, 42, 3209 (2004).

Preparation of inorganic silica nanofibers containing silver nanoparticles

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