The paper describes a gas phase process for the preparation of cotton fabrics coated with silver nanoparticles as antimicrobial agents. Silver nanoparticles are synthesized by means of atmospheric pressure electrical discharges (spark discharge and glow discharge) in pure inert gases, and the aerosols are passed through cotton fabric samples, where nanoparticles deposit. The particle size distribution of the aerosols is measured online during synthesis. Also, the cristallinity, size and morphology of the silver particles are analyzed. The mean size of the primary particles of silver varies from 4 nm to 18 nm, depending upon the type of discharge, the nature and flow rate of the gas. The bactericidal activity of the cotton samples doped with silver nanoparticles is assessed following the ISO 20743 method. All cotton samples show significant bactericidal property, although it degrades with increasing primary particle size and particle agglomeration. This purely physical aerosol route is a promising sustainable method for nanocoating of textiles

Blanes, M.

Feng, J.

Guo, X.

Hontanon, E.

Kruis, F. E.

Nirschl, H.

Santos, L.

Schmidt-Ott, A.

English

Hontañón, E.

Kruis, F.E.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 3 No 1, 01FNC03(5pp) (2014)   2304-1862/2014/3(1)01FNC03(5) 01FNC03-1  2014 Sumy State University Aerosol Route to Antibacterial Nanosilver Coating of Cotton Fabrics  E. Hontañón1,*, J. Feng2, M. Blanes3, X. Guo4, L. Santos5, A. Schmidt-Ott2, H. Nirschl4, F.E. Kruis1   1 Institute of Technology for Nanostructures and Center for Nanointegration Duisburg-Essen, CENIDE, University of Duisburg-Essen, Bismarckstr. 81, 47057 Duisburg, Germany 2 Department of Chemical Engineering, Delft University of Technology Julianalaan 136, 2628 BL Delft, The Netherlands 3 Department of Technical Finishing and Comfort, AITEX, Plaza Emilio Sala 1, 03801 Alcoy, Spain 4 Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, KIT, Straße am Forum 8, 76131 Karlsruhe, Germany 5 Foundation for the Promotion of the Textile Industry (FOMENTEX), Els Telers 20, 46870 Ontinyent, Spain   (Received 15 July 2014; published online 29 August 2014)  The paper describes a gas phase process for the preparation of cotton fabrics coated with silver nano-particles as antimicrobial agents. Silver nanoparticles are synthesized by means of atmospheric pressure electrical discharges (spark discharge and glow discharge) in pure inert gases, and the aerosols are passed through cotton fabric samples, where nanoparticles deposit. The particle size distribution of the aerosols is measured online during synthesis. Also, the cristallinity, size and morphology of the silver particles are analyzed. The mean size of the primary particles of silver varies from 4 nm to 18 nm, depending upon the type of discharge, the nature and flow rate of the gas. The bactericidal activity of the cotton samples doped with silver nanoparticles is assessed following the ISO 20743 method. All cotton samples show significant bactericidal property, although it degrades with increasing primary particle size and particle agglomera-tion. This purely physical aerosol route is a promising sustainable method for nanocoating of textiles.   Keywords: Silver nanoparticles, Primary particle size, Filtration, Cotton fabrics, Bactericidal property   PACS numbers: 81.20.Rg, 61.05.cf, 68.37.Lp                                                             * esther.hontanon@uni-due.de 1. INTRODUCTION  Silver nanoparticles with their unique chemical and physical properties are proving as an alternative for the development of antimicrobial agents for a variety of applications [1], among others, antibacterial textile fabrics [2]. In this regard, it has been reported that silver nanoparticle coated fabrics possess significant bactericidal property [3]. Nanosilver finishing of textile fabrics is commonly attempted by means of wet routes. Silver nanocolloids are prepared by reducing a silver salt in a solution by purely chemical process or assisted by irradiation with a light source (UV or laser) or by ultrasounds [4-5]. Also, surfactants and polymers are added to the solution for the stabilization of silver na-noparticles against agglomeration and for the control of nanoparticle size and shape [6-8]. Silver nanoparticles are then applied onto fabrics by using dip-pad-dry-cure methods. Nowadays, a growing need to develop eco-friendly processes is highlighted, which do not use toxic chemicals in the synthesis protocols and do not produce hazardous wastes [9]. This paper reports on a green aerosol process for nanosilver finishing of cotton fab-rics. Silver nanoparticles are synthesized by means of atmospheric pressure inert gas electrical discharge evaporating a silver electrode, leading to the formation of particles of a few nanometers in size. The aerosol then flows through the cotton fabric, where silver na-noparticles are partially retained. The size distribution of the primary particles mostly depends upon the type of discharge and nature of the carrier gas. The process is a purely physical one; there are no reactions, and byproducts and wastes are not produced. Stabilizers and modifiers are also not used. Furthermore, the gas is recirculated in a vacuum tight loop; thus, nanoparti-cles are not released during normal operation.  2. MATERIALS AND METHODS  2.1 Synthesis of Silver Nanoparticles  Silver nanoparticles are synthesized by electrical discharge between two electrodes in inert gas flow at atmospheric pressure. The aerosol generator consists of a cylindrical stainless steel chamber with several ports through which the electrodes are inserted and posi-tioned inside the chamber, the carrier gas enters and the aerosol exits the chamber. All ports are sealed by vacuum flanges and the chamber is evacuated (10-5 mbar) prior to nanoparticle synthesis. The electrodes are aligned facing each other a certain distance apart (gap). The discharge is driven by a capacitor charger formed from a high voltage power supply and a capaci-tor bank connected parallel each other and to the elec-trode gap. One electrode is connected to the positive high voltage output of the power supply and the other electrode is grounded. The current delivered by the power supply (  mA), charges the capacitor up to the point that the voltage across the gap exceeds the gas breakdown voltage (  kV) and, then, the capacitor dis-charges through the gap. This occurs as a pulse of du-ration of a few microseconds which repeats at a fre-quency that increases with current (spark discharge). By further increasing the current the voltage drops down to a few hundred of volts, capable to sustain a current of a few hundred of milliamps. Then, a continu-ous discharge regime is attained (glow discharge). Dur- E. HONTAÑÓN, J. FENG, M. BLANES, ET. AL. PROC. NAP 3, 01FNC03 (2014)   01FNC03-2 ing an electrical discharge, highly energetic positive ions are launched from the plasma towards the con-sumable electrode, where they interact with the surface atoms releasing electrons, heating and melting the electrode surface at the locations where the ions im-pinge. In glow discharge, Joule effect also contributes to heating the electrodes. As a result, material vaporiz-es from the electrode surface and enters the gap, where the vapor forms small nanoparticles (primary particles) that grow downwards of the plasma region. In this work, silver nanoparticles are produced in two setups optimized for spark discharge at the Delft University of Technology (Fig. 1a) and for glow discharge at the Uni-versity of Duisburg-Essen (Fig. 1b) [10, 11].     a    b  Fig. 1  Setup for the synthesis of silver nanoparticles by means of spark discharge (a) and glow discharge (b)  A major difference between the setups in Fig. 1 lies in the electrode and flow arrangement. The spark gener-ator uses two silver rods of the same diameter (7.0 mm) separated by a gap of 1 mm, across which the gas flows normally to the electrode axis (crossflow) in upward direction. During sparking both electrodes are about equally consumed. In the glow generator, the electrodes are a silver rod (10.0 mm) and a tungsten wire (1.6 mm) and the gap length is adjustable (1-15 mm). The gas flows parallel to the electrodes (coflow) in upward direc-tion. High purity electrodes ( 99.900%) and gases (99.999%) are used. The aerosol particle size distribution is monitored by using a differential mobility analyzer (DMA) together with an aerosol electrometer (AEM), and by a scanning mobility particle sizer (SMPS) followed by a condensation particle counter (CPC). Aerosol particles are collected onto TEM grids and PTFE filters. Particle crystallinity is analyzed by wide angle X-ray scattering (WAXS); primary particle size and particle morphology are determined by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM).   2.2 Application to Cotton Fabrics   Fig. 2a shows a SEM image of the woven cotton fab-ric used in this work (140-150 g/m2). Circular (7 and 9 cm) and rectangular (40×20 cm2) samples of cotton fab-rics are placed in gas tight holders and installed in the process line facing the aerosol flow. Then, the cotton samples are coated with silver nanoparticles by aerosol filtration. As the aerosol approaches a fiber, particles may deposit on the fiber by the simultaneous action of several mechanisms, as depicted in Fig. 2b [12]. Inertial impaction occurs when a particle, by its inertia, departs from the gas stream line and hits the fiber. Interception takes place because a particle has a finite size, which leads to deposition when the particle comes to a position within one particle radius of the fiber surface. For parti-cles smaller than a few tenths of micrometers, the Brownian motion can be sufficiently strong to move the particles from the flow streamline to the fiber. Electro-static forces arise when particles or fibers carry electri-cal charges. For nanoparticles, deposition on fibers takes place mainly by convective Brownian diffusion and interception. Impaction and electrostatic forces may also play important roles under certain conditions. The particle collection efficiency and flow pressure drop through the fabric (permeability) are the macroscopic parameters most relevant to aerosol filtration. They depend on the size distribution, morphology and charge state of the particles and on the gas filtration velocity.   2.3 Assessment of Bactericidal Property   The bactericidal activity of the cotton fabrics doped with silver nanoparticles is assessed against Staphylo-coccus aureus (SA), a Gram-positive bacterium, and Klebsiella pneumoniae (KP), a Gram-negative bacte-rium, according to the ISO 20743 test method, specific to antibacterial finished textile products. This quanti-tative method involves several basic steps: 1) sterilize (UV or autoclave) the sample to remove any ambient organisms or contaminants; 2) apply a known number of the target bacteria strain to the sample; 3) maintain the sample at room temperature to allow the bacteria to grow; 4) after a fixed time, extract and count the bacteria remaining on the sample; and 5) compare the remaining bacteria in the treated sample against an untreated sample of the same fabric to assess the anti-microbial performance resulting from the treatment. In ISO 20743, values of the antibacterial activity between 2 and 3 indicate “significant” antibacterial property and values above 3 correspond to “strong” bactericidal property.  qfabricsample exhaustcapacitor chargerV+CAg Agaerosol generatorArDMA AEMbypass flowMPSTEM gridICPCV+ CqqexhaustAgWDMAaerosol generatorcapacitor chargerRDCSMPSfabric samplePTFEfilterHEPAfilterroots  blowerN2 AEROSOL ROUTE TO ANTIBACTERIAL NANOSILVER COATING OF COTTON FABRICS PROC. NAP 3, 01FNC03 (2014)   01FNC03-3   a    b  Fig. 2  Cotton fabric (a) and mechanisms of particle capture on a fiber [12]  3. RESULTS AND DISCUSSION   Table 1 summarizes the main features of seven ex-periments in which silver nanoparticles were generated and deposited onto cotton fabrics via the aerosol route described in section 2. The size distribution of the pri-mary particles of silver was determined, and the values of the mode (most probable value) are given in Table 1.  Table 1 – Coating of cotton fabrics with silver nanoparticles: Filtration parameters, primary particle size and color of fabric sample after filtration    a Spark: 16 mJ, 60 Hz  - Ar, 10 lpm  - DMA+AEM, TEM b Glow: 400 mA, 300 V - N2, 500 lpm - SMPS c  Glow: 600 mA, 300 V - N2, 200 lpm - SAXS, TEM Fig. 3 shows TEM images of silver nanoparticles generated by spark discharge in Ar and deposited on a grid, and generated by glow discharge in N2 (600 mA, 200 lpm) and collected on a filter. A high population of nanoclusters of a few nanometers in size (<10 nm) are observed in Fig. 3a, whereas larger nanoparticles (10-20 nm) are seen in Fig. 3b. A diffractogram (SWAXS) of silver nanoparticles is depicted in Fig. 4; nanoparticles are polycrystalline and pure silver metal.    a     b  Fig. 3  Nanoclusters of silver obtained by spark discharge (a) and silver nanoparticles produced by glow discharge (b)    Fig. 4  Diffraction pattern of silver nanoparticles  40 50 60 70 80 90100101102103Ag(200) Background Ag NPsAg(111)Ag(311)Sacttering intensity (a.u.)Scattering angle 2Ag(222)Sam-ple Fabric surface area (cm2) Flow surface velocity (cm/s) Duration (h) Primary particle size (nm) Fabric  Color S1 63.6 2.6 7 4a yellow  S2 800 10.4 1 6b orange S3 4 dark orange S4 38.5 86.6 1.5 15-18c light gray S5 10 dark gray S6 3 dark gray S7 5 dark gray  E. HONTAÑÓN, J. FENG, M. BLANES, ET. AL. PROC. NAP 3, 01FNC03 (2014)   01FNC03-4 All samples changed color in the experiments. The color is determined by the primary particle size and the particle load on the fibers. The samples were analyzed by SEM. No particles were found on the fibers in sam-ples S1 and S2, and only scarcely in sample S3; alt-hough the color of the samples evidences they contain nanosilver (e.g. Fig. 5). The reason is that nanoparticles are below the SEM resolution limit (10 nm). The TEM images in Fig. 6a and Fig. 6b correspond to samples S4 and S6. The aerosol source is the same in both cases but the residence time and, hence, particle agglomera-tion is more significant for S6. Isolated small nanopar-ticles uniformly cover the cotton fiber in Fig. 6a, while larger agglomerates and much less small nanoparticles are observed in Fig. 6b.    Fig. 5  Sample S1 with yellow color imparted by nanosilver    a    b  Fig. 6  Cotton fibers coated with silver nanoparticles: Sam-ples S4 (a) and S6 (b) The results of the antimicrobial tests conducted with the cotton fabric samples are displayed in Fig. 7. The bactericidal activity of sample S1 for KP was not assessed. The antibacterial activity of all samples ex-ceeds 2 with the exception of sample S4 for SA. Sam-ples S1, S2 and S3 are coated with non-aggregated small nanoparticles (<10 nm), leading to “strong” bacte-ricidal activity, with values between 4 and 5 for both bacteria, almost regardless of the filtration time. Larg-er nanoparticles of different aggregation levels cover samples S4 to S7, resulting in “significant” bactericidal activity, with values above 2; except for S5, which anti-bacterial activity for SA reaches 4.82. Samples S6 and S7, containing larger fractions of particle agglomerates, show bactericidal activity for KP only slightly lower than that of samples S4 and S5, where nanoparticles are non-aggregated.     Fig. 7  Bactericidal activity of cotton fabrics coated with silver nanoparticles  4. CONCLUSIONS  A green aerosol process has been proved for antibac-terial nanosilver finishing of cotton fabrics. Fundamen-tal studies will be undertaken to gain insight into na-noparticle filtration behavior of cotton fabrics. Also, further effort will be made to optimize parameters most relevant to bactericidal property such as primary parti-cle size and nanoparticle load on cotton fibers. Finally, the wash durability of silver nanoparticle coatings on cotton fibers will be assessed.  ACKNOWLEDGEMENTS  This research work has been financially supported by the European Union´s Seventh Framework Program (EU FP7) under Grant Agreement No. 280765 (BUO-NAPART-E). The authors are grateful to Dr. David Ortiz de Zárate (Polytechnic University of Valencia, Spain) for enabling to perform SEM analyses of cotton fabrics samples.      0123456S1   SAS2   SAS2   KPS3   SAS3   KPS4   SAS4   KPS5   SAS5   KPS6   SAS6   KPS7   SAS7   KPSAKPBactericidalactivity AEROSOL ROUTE TO ANTIBACTERIAL NANOSILVER COATING OF COTTON FABRICS PROC. NAP 3, 01FNC03 (2014)   01FNC03-5 REFERENCES  1. M. Rai, A. Yadav, A. Gade, Biotechnol. Adv. 27, 76 (2009).  2. R. Dastjerdi, M. Montazer, Colloid Surface B 79, 5 (2010). 3. N. Gokarneshan, P.P. Gopalakrishnan, B. Jeyanthi, ISRN Nanomat. 193836 (2012). 4. S. Iravani, H. Korbekandi, S.V. Mirmohammadi, B. Zolfaghari, Res. Pharm. Sci. 9, 385 (2014). 5. H. Korkebandi, S. Iravani, Chapter 1: Silver Nanoparti-cles, Progress in Molecular and Environmental Bioengi-neering – From Analysis and Modeling to Technology Ap-plications (Ed. A. Carpi) (Intech: 2011).  6. Y. Tang, W. He, S. Wang, Z. Tao, L. Cheng, Crys-EngComm 16, 4431 (2014). 7. P.V. Dong, Ch.H. Ha, L.T. Binh, J. Kasbohm, Int. Nano Lett., 2, 9 (2012). 8. J.M. Rad, T.D. Isfahani, I. Hadi, S. Ghalamdaran, J. Sabbagzadeh, M. Sharif, Appl. Nanosci. 1, 27 (2011). 9. V.K. Sharma, R.A. Yngard, Y. Lin, Adv. Colloid Interface Sci. 145, 83 (2009). 10. T.V. Pfeiffer, J. Feng, A. Schmidt-Ott, Adv. Powder Res. 21, 56 (2014). 11. E. Hontañón, J.M. Palomares, M. Stein, X. Guo, R. Engeln, H. Nirschl, F.E. Kruis, J. Nanopart. Res. 15, 1957 (2013). 12. Ch. Wang, Y. Otani, Ind. Eng. Chem. Res. 52, 5 (2013).  

Aerosol Route to Antibacterial Nanosilver Coating of Cotton Fabrics

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 3 No 1, 01FNC03(5pp) (2014) 
 
 
2304-1862/2014/3(1)01FNC03(5) 01FNC03-1  2014 Sumy State University 
Aerosol Route to Antibacterial Nanosilver Coating of Cotton Fabrics 
 
E. Hontañón1,*, J. Feng2, M. Blanes3, X. Guo4, L. Santos5, A. Schmidt-Ott2, H. Nirschl4, F.E. Kruis1  
 
1 Institute of Technology for Nanostructures and Center for Nanointegration Duisburg-Essen, CENIDE, University 
of Duisburg-Essen, Bismarckstr. 81, 47057 Duisburg, Germany 
2 Department of Chemical Engineering, Delft University of Technology Julianalaan 136, 2628 BL Delft, The Netherlands 
3 Department of Technical Finishing and Comfort, AITEX, Plaza Emilio Sala 1, 03801 Alcoy, Spain 
4 Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, KIT, Straße am 
Forum 8, 76131 Karlsruhe, Germany 
5 Foundation for the Promotion of the Textile Industry (FOMENTEX), Els Telers 20, 46870 Ontinyent, Spain  
 
(Received 15 July 2014; published online 29 August 2014) 
 
The paper describes a gas phase process for the preparation of cotton fabrics coated with silver nano-
particles as antimicrobial agents. Silver nanoparticles are synthesized by means of atmospheric pressure 
electrical discharges (spark discharge and glow discharge) in pure inert gases, and the aerosols are passed 
through cotton fabric samples, where nanoparticles deposit. The particle size distribution of the aerosols is 
measured online during synthesis. Also, the cristallinity, size and morphology of the silver particles are 
analyzed. The mean size of the primary particles of silver varies from 4 nm to 18 nm, depending upon the 
type of discharge, the nature and flow rate of the gas. The bactericidal activity of the cotton samples doped 
with silver nanoparticles is assessed following the ISO 20743 method. All cotton samples show significant 
bactericidal property, although it degrades with increasing primary particle size and particle agglomera-
tion. This purely physical aerosol route is a promising sustainable method for nanocoating of textiles.  
 
Keywords: Silver nanoparticles, Primary particle size, Filtration, Cotton fabrics, Bactericidal property 
 
 PACS numbers: 81.20.Rg, 61.05.cf, 68.37.Lp 
 
 
                                                          
* esther.hontanon@uni-due.de 
1. INTRODUCTION 
 
Silver nanoparticles with their unique chemical and 
physical properties are proving as an alternative for 
the development of antimicrobial agents for a variety of 
applications [1], among others, antibacterial textile 
fabrics [2]. In this regard, it has been reported that 
silver nanoparticle coated fabrics possess significant 
bactericidal property [3]. Nanosilver finishing of textile 
fabrics is commonly attempted by means of wet routes. 
Silver nanocolloids are prepared by reducing a silver 
salt in a solution by purely chemical process or assisted 
by irradiation with a light source (UV or laser) or by 
ultrasounds [4-5]. Also, surfactants and polymers are 
added to the solution for the stabilization of silver na-
noparticles against agglomeration and for the control of 
nanoparticle size and shape [6-8]. Silver nanoparticles 
are then applied onto fabrics by using dip-pad-dry-cure 
methods. Nowadays, a growing need to develop eco-
friendly processes is highlighted, which do not use toxic 
chemicals in the synthesis protocols and do not produce 
hazardous wastes [9]. This paper reports on a green 
aerosol process for nanosilver finishing of cotton fab-
rics. Silver nanoparticles are synthesized by means of 
atmospheric pressure inert gas electrical discharge 
evaporating a silver electrode, leading to the formation 
of particles of a few nanometers in size. The aerosol 
then flows through the cotton fabric, where silver na-
noparticles are partially retained. The size distribution 
of the primary particles mostly depends upon the type 
of discharge and nature of the carrier gas. The process 
is a purely physical one; there are no reactions, and 
byproducts and wastes are not produced. Stabilizers 
and modifiers are also not used. Furthermore, the gas 
is recirculated in a vacuum tight loop; thus, nanoparti-
cles are not released during normal operation. 
 
2. MATERIALS AND METHODS 
 
2.1 Synthesis of Silver Nanoparticles 
 
Silver nanoparticles are synthesized by electrical 
discharge between two electrodes in inert gas flow at 
atmospheric pressure. The aerosol generator consists of 
a cylindrical stainless steel chamber with several ports 
through which the electrodes are inserted and posi-
tioned inside the chamber, the carrier gas enters and 
the aerosol exits the chamber. All ports are sealed by 
vacuum flanges and the chamber is evacuated (10-5 
mbar) prior to nanoparticle synthesis. The electrodes 
are aligned facing each other a certain distance apart 
(gap). The discharge is driven by a capacitor charger 
formed from a high voltage power supply and a capaci-
tor bank connected parallel each other and to the elec-
trode gap. One electrode is connected to the positive 
high voltage output of the power supply and the other 
electrode is grounded. The current delivered by the 
power supply (  mA), charges the capacitor up to the 
point that the voltage across the gap exceeds the gas 
breakdown voltage (  kV) and, then, the capacitor dis-
charges through the gap. This occurs as a pulse of du-
ration of a few microseconds which repeats at a fre-
quency that increases with current (spark discharge). 
By further increasing the current the voltage drops 
down to a few hundred of volts, capable to sustain a 
current of a few hundred of milliamps. Then, a continu-
ous discharge regime is attained (glow discharge). Dur-
 E. HONTAÑÓN, J. FENG, M. BLANES, ET. AL. PROC. NAP 3, 01FNC03 (2014) 
 
 
01FNC03-2 
ing an electrical discharge, highly energetic positive 
ions are launched from the plasma towards the con-
sumable electrode, where they interact with the surface 
atoms releasing electrons, heating and melting the 
electrode surface at the locations where the ions im-
pinge. In glow discharge, Joule effect also contributes 
to heating the electrodes. As a result, material vaporiz-
es from the electrode surface and enters the gap, where 
the vapor forms small nanoparticles (primary particles) 
that grow downwards of the plasma region. In this 
work, silver nanoparticles are produced in two setups 
optimized for spark discharge at the Delft University of 
Technology (Fig. 1a) and for glow discharge at the Uni-
versity of Duisburg-Essen (Fig. 1b) [10, 11].  
 
 
 
a 
 
 
 
b 
 
Fig. 1  Setup for the synthesis of silver nanoparticles by 
means of spark discharge (a) and glow discharge (b) 
 
A major difference between the setups in Fig. 1 lies 
in the electrode and flow arrangement. The spark gener-
ator uses two silver rods of the same diameter (7.0 mm) 
separated by a gap of 1 mm, across which the gas flows 
normally to the electrode axis (crossflow) in upward 
direction. During sparking both electrodes are about 
equally consumed. In the glow generator, the electrodes 
are a silver rod (10.0 mm) and a tungsten wire (1.6 mm) 
and the gap length is adjustable (1-15 mm). The gas 
flows parallel to the electrodes (coflow) in upward direc-
tion. High purity electrodes ( 99.900%) and gases 
(99.999%) are used. The aerosol particle size distribution 
is monitored by using a differential mobility analyzer 
(DMA) together with an aerosol electrometer (AEM), and 
by a scanning mobility particle sizer (SMPS) followed by 
a condensation particle counter (CPC). Aerosol particles 
are collected onto TEM grids and PTFE filters. Particle 
crystallinity is analyzed by wide angle X-ray scattering 
(WAXS); primary particle size and particle morphology 
are determined by small angle X-ray scattering (SAXS) 
and transmission electron microscopy (TEM).  
 
2.2 Application to Cotton Fabrics  
 
Fig. 2a shows a SEM image of the woven cotton fab-
ric used in this work (140-150 g/m2). Circular (7 and 9 
cm) and rectangular (40×20 cm2) samples of cotton fab-
rics are placed in gas tight holders and installed in the 
process line facing the aerosol flow. Then, the cotton 
samples are coated with silver nanoparticles by aerosol 
filtration. As the aerosol approaches a fiber, particles 
may deposit on the fiber by the simultaneous action of 
several mechanisms, as depicted in Fig. 2b [12]. Inertial 
impaction occurs when a particle, by its inertia, departs 
from the gas stream line and hits the fiber. Interception 
takes place because a particle has a finite size, which 
leads to deposition when the particle comes to a position 
within one particle radius of the fiber surface. For parti-
cles smaller than a few tenths of micrometers, the 
Brownian motion can be sufficiently strong to move the 
particles from the flow streamline to the fiber. Electro-
static forces arise when particles or fibers carry electri-
cal charges. For nanoparticles, deposition on fibers 
takes place mainly by convective Brownian diffusion 
and interception. Impaction and electrostatic forces may 
also play important roles under certain conditions. The 
particle collection efficiency and flow pressure drop 
through the fabric (permeability) are the macroscopic 
parameters most relevant to aerosol filtration. They 
depend on the size distribution, morphology and charge 
state of the particles and on the gas filtration velocity.  
 
2.3 Assessment of Bactericidal Property  
 
The bactericidal activity of the cotton fabrics doped 
with silver nanoparticles is assessed against Staphylo-
coccus aureus (SA), a Gram-positive bacterium, and 
Klebsiella pneumoniae (KP), a Gram-negative bacte-
rium, according to the ISO 20743 test method, specific 
to antibacterial finished textile products. This quanti-
tative method involves several basic steps: 1) sterilize 
(UV or autoclave) the sample to remove any ambient 
organisms or contaminants; 2) apply a known number 
of the target bacteria strain to the sample; 3) maintain 
the sample at room temperature to allow the bacteria 
to grow; 4) after a fixed time, extract and count the 
bacteria remaining on the sample; and 5) compare the 
remaining bacteria in the treated sample against an 
untreated sample of the same fabric to assess the anti-
microbial performance resulting from the treatment. In 
ISO 20743, values of the antibacterial activity between 
2 and 3 indicate “significant” antibacterial property 
and values above 3 correspond to “strong” bactericidal 
property.  
q
fabric
sample exhaust
capacitor 
charger
V+
C
Ag Ag
aerosol 
generator
Ar
DMA AEM
bypass flow
MPS
TEM 
grid
I
CPC
V+ C
q
q
exhaust
Ag
W
DMA
aerosol 
generator
capacitor 
charger
RDC
SMPS
fabric 
sample
PTFE
filter
HEPA
filter
roots  
blower
N2
 AEROSOL ROUTE TO ANTIBACTERIAL NANOSILVER COATING OF COTTON FABRICS PROC. NAP 3, 01FNC03 (2014) 
 
 
01FNC03-3 
 
 
a 
 
 
 
b 
 
Fig. 2  Cotton fabric (a) and mechanisms of particle capture 
on a fiber [12] 
 
3. RESULTS AND DISCUSSION  
 
Table 1 summarizes the main features of seven ex-
periments in which silver nanoparticles were generated 
and deposited onto cotton fabrics via the aerosol route 
described in section 2. The size distribution of the pri-
mary particles of silver was determined, and the values 
of the mode (most probable value) are given in Table 1. 
 
Table 1 – Coating of cotton fabrics with silver nanoparticles: 
Filtration parameters, primary particle size and color of fabric 
sample after filtration  
 
 
a Spark: 16 mJ, 60 Hz  - Ar, 10 lpm  - DMA+AEM, TEM 
b Glow: 400 mA, 300 V - N2, 500 lpm - SMPS 
c  Glow: 600 mA, 300 V - N2, 200 lpm - SAXS, TEM 
Fig. 3 shows TEM images of silver nanoparticles 
generated by spark discharge in Ar and deposited on a 
grid, and generated by glow discharge in N2 (600 mA, 
200 lpm) and collected on a filter. A high population of 
nanoclusters of a few nanometers in size (<10 nm) are 
observed in Fig. 3a, whereas larger nanoparticles (10-
20 nm) are seen in Fig. 3b. A diffractogram (SWAXS) of 
silver nanoparticles is depicted in Fig. 4; nanoparticles 
are polycrystalline and pure silver metal. 
 
 
 
a 
 
  
 
b 
 
Fig. 3  Nanoclusters of silver obtained by spark discharge (a) 
and silver nanoparticles produced by glow discharge (b) 
 
 
 
Fig. 4  Diffraction pattern of silver nanoparticles 
 
40 50 60 70 80 90
10
0
10
1
10
2
10
3
Ag(200)
 Background
 Ag NPs
Ag(111)
Ag(311)
S
ac
tt
er
in
g
 i
n
te
n
si
ty
 (
a.
u
.)
Scattering angle 2
Ag(222)
Sam-
ple 
Fabric 
surface 
area 
(cm2) 
Flow 
surface 
velocity 
(cm/s) 
Duration 
(h) 
Primary 
particle 
size 
(nm) 
Fabric  
Color 
S1 63.6 2.6 7 4a yellow  
S2 
800 10.4 
1 
6b 
orange 
S3 4 
dark 
orange 
S4 
38.5 86.6 
1.5 
15-18c 
light 
gray 
S5 10 
dark 
gray 
S6 3 
dark 
gray 
S7 5 
dark 
gray 
 E. HONTAÑÓN, J. FENG, M. BLANES, ET. AL. PROC. NAP 3, 01FNC03 (2014) 
 
 
01FNC03-4 
All samples changed color in the experiments. The 
color is determined by the primary particle size and the 
particle load on the fibers. The samples were analyzed 
by SEM. No particles were found on the fibers in sam-
ples S1 and S2, and only scarcely in sample S3; alt-
hough the color of the samples evidences they contain 
nanosilver (e.g. Fig. 5). The reason is that nanoparticles 
are below the SEM resolution limit (10 nm). The TEM 
images in Fig. 6a and Fig. 6b correspond to samples S4 
and S6. The aerosol source is the same in both cases 
but the residence time and, hence, particle agglomera-
tion is more significant for S6. Isolated small nanopar-
ticles uniformly cover the cotton fiber in Fig. 6a, while 
larger agglomerates and much less small nanoparticles 
are observed in Fig. 6b. 
 
 
 
Fig. 5  Sample S1 with yellow color imparted by nanosilver 
 
 
 
a 
 
 
 
b 
 
Fig. 6  Cotton fibers coated with silver nanoparticles: Sam-
ples S4 (a) and S6 (b) 
The results of the antimicrobial tests conducted 
with the cotton fabric samples are displayed in Fig. 7. 
The bactericidal activity of sample S1 for KP was not 
assessed. The antibacterial activity of all samples ex-
ceeds 2 with the exception of sample S4 for SA. Sam-
ples S1, S2 and S3 are coated with non-aggregated 
small nanoparticles (<10 nm), leading to “strong” bacte-
ricidal activity, with values between 4 and 5 for both 
bacteria, almost regardless of the filtration time. Larg-
er nanoparticles of different aggregation levels cover 
samples S4 to S7, resulting in “significant” bactericidal 
activity, with values above 2; except for S5, which anti-
bacterial activity for SA reaches 4.82. Samples S6 and 
S7, containing larger fractions of particle agglomerates, 
show bactericidal activity for KP only slightly lower 
than that of samples S4 and S5, where nanoparticles 
are non-aggregated.  
 
 
 
Fig. 7  Bactericidal activity of cotton fabrics coated with silver 
nanoparticles 
 
4. CONCLUSIONS 
 
A green aerosol process has been proved for antibac-
terial nanosilver finishing of cotton fabrics. Fundamen-
tal studies will be undertaken to gain insight into na-
noparticle filtration behavior of cotton fabrics. Also, 
further effort will be made to optimize parameters most 
relevant to bactericidal property such as primary parti-
cle size and nanoparticle load on cotton fibers. Finally, 
the wash durability of silver nanoparticle coatings on 
cotton fibers will be assessed. 
 
ACKNOWLEDGEMENTS 
 
This research work has been financially supported 
by the European Union´s Seventh Framework Program 
(EU FP7) under Grant Agreement No. 280765 (BUO-
NAPART-E). The authors are grateful to Dr. David 
Ortiz de Zárate (Polytechnic University of Valencia, 
Spain) for enabling to perform SEM analyses of cotton 
fabrics samples. 
 
 
 
 
 
0
1
2
3
4
5
6
S1   
SA
S2   
SA
S2   
KP
S3   
SA
S3   
KP
S4   
SA
S4   
KP
S5   
SA
S5   
KP
S6   
SA
S6   
KP
S7   
SA
S7   
KP
SA
KP
B
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 AEROSOL ROUTE TO ANTIBACTERIAL NANOSILVER COATING OF COTTON FABRICS PROC. NAP 3, 01FNC03 (2014) 
 
 
01FNC03-5 
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Aerosol Route to Antibacterial Nanosilver Coating of Cotton Fabrics

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