VIETNAM JOURNAL OF CHEMISTRY DOI: 10.15625/0866-7144.2014-0028
VOL. 52(5) 543-547 OCTOBER 2014
CHARACTERIZATION OF PARTICLES SIZE DISTRIBUTION FOR NANO SILVER SOLUTION PREPARED BY HIGH DC VOLTAGE
ELECTROCHEMICAL TECHNIQUE
Nguyen Minh Thuy', Nguyen Due Hung^*, Mai Van PhuocS Nguyen Nhi Tru^
Institute for Chemistry and Materials
^ Vietnam Institute for Tropical Technology & Environmental Protection Received: 25 March 2013; Accepted for Publication 15 October 2014
Abstract
Nano silver solution (nAgs) has been investigated and used intensively in different fields due to its antimicrobial effect. There are various methods to prepare nAgs: mechanical, chemical, or physical. However, nAgs obtained from the above methods usually leave undesired chemicals m solution, limiting its antimicrobial activity. Meanwhile, the electrochemical method, utilizuig anodic dissolution of metallic silver under high DC voltage to generate nAgs in double distilled water, giving highly pure product, is a new and promising technology. The method, using fiindamentally different principles, results m nAgs with substantially different properties, is being able to prepare nAgs of equal concentration to that produced via chemical methods.
Keywords: Nano silver solution; size distribution; nano particle; high DC voltage electrolysis.
1. INTRODUCTION
Nano silver particles can be prepared in various ways: physical methods such as PVD techniques, y irradiation or plasma-liquid electrochemistry [1-3];
mechanical method by grinding process [4];
chemical methods through the reduction of AgNOa by agents such as NaBHi [5], sucrose, glucose [6];
physico-chemical method via sol-gel reaction [7];
bio-reducfion of silver ions using several species of bacteria [8]. Methods combining electrochemical [9], ultrasonic and pulse effects [10] have also been applied to produce nAgs. Recently, nAgs has been prepared by dissolution of silver anode in double disfilled water under high DC voltage [11-13]. Such a solution would possess a high degree of purity meeting the requirement for medical and pharmaceutical applications. However, the particle size distribution of nAgs solution formed via this method is srill under question. For a better understanding process of nano silver formation, the characterization of particle size distribution has been investigated and discussed in this paper.
2. EXPERIMENTAL
The nAgs has been prepared with the system shown in figure I. The double wall reactor cell was
Figure I: Scheme of electrochemical system for preparing nAgs under high DC voltage made of transparent borosilicate glass with an outer compartment for water cooling circulation and inner compartment as an electrolyzer. The cylindrical 99.99% silver electrodes insulated by heat-cured epoxy were inserted into the electrolyzer at vertical positions. The DC voltage and current up to 25 kV and 250 mA respectively can be supplied steplessly to the electrodes by a rectifier. The recorded data of size distribution for nAgs prepared by high DC
543
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voltage electrolysis at different electrodes distances fi-om 350 to 1000 mm and by the chemical method were compared.
The particle morphology and shapes were determined by TEM imaging using JEM-1010 (JEOL, Japan). The size distribution was recorded by Partica LA-950 Laser Scattering Particle Size Distribution Analyzer (HORIBA, Japan) and by Nicomp 380 DLS, AccuSizer 780 AD (Agilent Technologies, Inc. USA).
3. RESULTS AND DISCUSSION
Fig. 2 shows TEM images depictmg the size of particles in nAgs prepared by high CXD voltage anodic dissolution process at electrode distances of 350, 600 and 1000 mm and the corresponding size distribution curves. The results indicate that particle size and size distribution curves are similar for all samples across different anode-cathode gaps (Fig. 2a).
Nguyen Due Hung, et al.
The TEM images indicate that the distribution of particle sizes ranges from 5.26 nm to 30.40 nm (Fig.
2b), beyond which particles agglomerate into large clusters, with the largest particles being over 100 nm. As a result, the particle distribution curves show two maximum peaks: the first peak at 200 nm, and the second peak around 3,000-10,000 nm (Fig. 2a).
Similarly, the Gaussian distribution shown at Fig. 3 are also obtained, using Nicomp 380 DLS.
It is clear from Fig. 3, the particle size disfribution graphs of nAgs prepared by high DC voltage anodic dissolution and by chemical method have similar shapes but different peak positions.
The maximum peaks of distribution curves recorded for 10 samples of nAgs prepared by chemical method (Ml, M2) compared to those from high DC voltage method with electrode distances ranging from 400 mm to 1000 mm (M3-M10) on Nicomp 380 DLS are presented in Tab. 1.
. J l J . « .
J
1 w^
1
Figm-el: TTie size distribution (a) and TEM images (b) in 20 nm and (c) in 100 mn scales for nAgs prepared by anodic dissolution under high DC voltage at 25 "C for 50 min with anode-cathode gaps of 350, 600 and 1000 mm Fig. 3, which illustrated the difference of size that the maximum peak locations of nAgs prepared distribution curver between two methods, indicates by chemical method fluctuate between 52.5 nm to
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135.5 nm (a, b) and the products formed by high DC voltage anodic dissolution at electrode distances of 500 mm and 700 mm are 599.5 and 40 (cd). For all samples, measured data were shown in table I.
Observation indicated that maximum peaks of nAgs prepared by high DC voltage method are located in a wider range of 40 nm to 772.7 nm with smallest value of 40 nm for the sample M7 (where electrode distance is 800 mm) and the largest value of 772.7
Characterization of particles size distribution...
nm for the sample M6 (where electrode distance is 700 mm). Therefore, distribution curves of chemical nAgs have different maximum peaks from those of electrochemical nAgs, which demonstrate that the particle sizes are quite different, even reaching micrometer scale.
Fig. 4 shows the parameters, derived from size distribution analysis for sample M7: Gaussian, multimodal, volumetric, and numerical distributions.
Figure 3: Gaussian size distribution of nAgs prepared by a,b - chemical method;
c,d - high DC voltage anodic dissolution at electrode distances 500 mm and 700 mm Table I: The peak maxima of Gaussian distribution for nAgs prepared by sol-gel and electrochemical at
different electrode's gaps and corresponding solution concentrations Method
Sample code Electrode gap, mm
CAE, mg/1 Peak maximum, nm
Chemical Ml 500 135.5
M2 1,000 52.5
High voltage electrochemical M3
400 355 145.7
M4 500 273 599.5
M5 650 194 178.9
M6 700 175 772.7
M7 800 164 40.0
M8 850 132 50.8
M9 900 109 96.0
MIO 1.000 103.5 94.8 Fig. 4a describes the Gaussian distribution
having a maximum peak at 40 nm, while multimodal intensity in Fig. 3b has three maximum peaks at 3.2 nm, 10 nm, and 67.8 nm. By using volumetric distribution in Fig.3c, the second and third peaks are reduced to small values; meanwhile in Fig. 4d, the numerical distribution shows 99.3% of maximum peak appearance only in the 2.5 nm region.
Therefore, it is concluded that the nAgs is a multi- dispersive system, and its size distribution is not a uniform smooth curve, but split into distinct regions.
In this case, intensity scattering determination is complex because particle size distribution is located in two regions: Mie (>150 nm), and Releigh (< 150 nm) [14-15].
The Gaussian, multimodal, volumefric and
numerical disfributions are similarly obtained for samples Ml and M2 prepared by chemical method, and samples M3 to MIO prepared by high DC voltage method. The results are presented in Tab. 2.
From these results, the correlation between particle size with TEM images is also noted, with nano particles having various sizes lying in different regions. This may be relevant to Uie nucleation and growth process of nanoparticles.
The results from Tab. 2 show that the distribution peaks of nAgs prepared by high DC voltage electrochemical method fluctuate in a wide range, from 2 nm to 150 nm, and are dependent on electrode distances. Particle size values arid percentages also fluctuate widely. This demonstrates that nanoparticles' nucleation and growth processes
VJC, Vol. 52(5), 2014 ^S^^" ^ " ^ ^ " " ^ ' ^' "'•
are influenced by various parameters and reaction conditions on electrodes and electrolytic reactions.
Figure 4: Size distribution analysis for sample M7 with elecfrode distance 800 mm - Gaussian distribution; b - multimodal distribution; c - volumetric distribution; d - numerical distribution
Table 2: Maximum values of particle size and percentage distribution determined by analysis with particle size distribution on Nicomp 380 DLS
Sample No Gaussian peak, nm
Multil modal Volumet-ric Nume- rical Region 1
Region 2
Region 3
Region 1
Region 2 nm
%
nm
%
nm
%
nm
%
nm
%
P size, nm
%
M l 135.5
3.0 1.6 14.3 9.2 86.2 89.1 2.9 95.5 12.5 4.1 2.8 99.4
M2 52.5 6.6 5.5 20.0 17.5 95.7 77.0 5.0 99.6 20.3 0.4
5 99.6
M3 145.7
24.1 7.9 147.2 92.1
- -
21.7 92.6 128.4
7.4 19.1 99.8
M4 599.5 152.5 66.3 774.7 33.7
- -
151.3 64.2 776.5 35.8 149.9 99.4
M5 178.9
19.4 2.6 95.5 37.3 370.9
60.1 19.2 87.3 94.4 10.0 19.0 99,2
M6 772.7 131.6 18.9 2165.7
81.1
- -
120.7 14.2 2235.5
85.8 108.2 99.2
M7 40.0 3.2 10.5 10.1 14.0 67.8 75.5 2.8 94.6
8.9 4.6 2.5 99.3
MS 50.8
2.1 4.9 6.3 17.1 42.8 78.1 2.0 86.9 5.3 12.5
2 86.9
M9 96.0 5.6 4.2 37.4 18.1 153.8
77.7 4.8 97.5 32.4 1.7 4.8 97.5
MIO 94.8 5.9 1.7 57.4 36.6 160.5 61.7
5.4 96.7 50.8 2.7 4.7 100 4. CONCLUSIONS
Method of anodic dissolution under high DC vol- tage to generate nAgs results in nanoparticle's scale from several nm to 50 nm as shown via TEM imag- ing, but these particles tend to agglomerate. The nAgs concentration depends on electrode distances
and reaches 355 ppm, which is comparable to that of other methods.
Nano size distribution curves of nAgs prepared by chemical method and high DC voltage have the same shape but different maximum peaks, which highly depend on reaction conditions and prepara- tion method. Because of incomparable particles size,
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the Gaussian distributions have broad peaks; howev- er, graphs obtained from the HORIBA device are separated into two regions, and those obtained from Nicomp 380 DLS have different distributions de- pending on analytical method.
Particle size distribution of nAgs prepared by anodic dissolution is multi-dispersive and discontinuous, resulting in regions of different particle dimensions and concentrations. This proves that the particles' nucleation and growth processes are influenced by various parameters of electrodes and electrolytic reactions.
Acknowledgement. Authors thank to NAFOSTED fund for contribution to implement Project 104.03-
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Corresponding author: Nguyen Due Hung Institute of Chemistry-Materials
17 Hoang Sam Stress, Cau Giay District, Hanoi, Vietnam E-mail: [email protected].