Download Preparation and Antibacterial Properties of Cu + CeO2/Cu Porous

Preparation and Antibacterial Properties of Cu + CeO2/Cu Porous Materials
YU Zhiming, NIU Yunsong, HAN Enhou
(State Key Lab for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, Wenhua Road 72, Shenyang
110016, Liaoning, China)
Abstract: The porous materials of Cu+CeO2/Cu were prepared by the electro-deposition on a precursor of conventional polyamide
foam. Their porosity and specific surface area were measured. Antibacterial properties of Cu+CeO2/Cu porous materials were
investigated. The results show that their porosity may reach above 95% and specific surface area is about 31.4 m2/cm3. The porous
materials of Cu + CeO2/Cu exhibited excellent antibacterial properties against E. coli, S. aureus and C. albicans.
Keywords: porous materials; Cu + CeO2/Cu; antibacterial properties
1
Introduction
Health and environment is the global topic of the 21st century. Except the natural factors such as the inheritance,
the environment plays an important role for the individuals’ life and health. It is necessary to sterilize and disinfect
in the air, on the surface of clothes and furniture, but the antimicrobial agents and disinfectors, which contain the
chemical compositions harmful to human health by the surface contact and gasification of the antimicrobial agents,
can only produce short-term effects in the daily life. Therefore, new antibacterial materials are generated —
inorganic antibacterial materials[1-5], which can have excellent persistent antibacterial effects and is harmless to
health.
Ag+, Cu2+ and Zn2+ are selected as antimicrobial ions in the inorganic antimicrobial materials. In the three ions,
the antibacterial effect of Ag+ is the best. However, the price of Ag is high, and Ag+ is allochromatic easily in the
light and heating. In addition, Ag+ is easily reacted with Cl-, HS- and S2- in the water to form the insoluble
precipitates, which make Ag+ lose the antibacterial activities[6-8]. Rare-earth elements which have unique
electronic structures and properties have been applied in metallurgical, petrochemical, medical, health industries
and so on. Rare-earth resources are very rich in China, which is extraordinary convenient to develop rare earth
products[9]. Foam of polyamide was used as precursor material in this study. Cu+CeO2/Cu porous antibacterial
material was prepared by electroplating, and was observed and evaluated on its morphology, physical properties
and antibacterial properties.
2
Experiment
2.1 Preparation of Antibacterial Materials
Conventional foam of polyamide was used as precursor material. After conducting treatment which makes the
foam of polyamide have enough conductivity, copper coatings with thickness of about 25μm were deposited on
the precursor by electroplating. Then, heat treatment was carried out at 700℃ for 2h in argon atmosphere, to
obtain Cu porous materials. Then, Cu+CeO2/Cu coatings with thickness of about 2μm were deposited on the Cu
porous material by electroplating with mechanical agitation, in the solution mixing the CeO2 micro powder (10g/l),
so that Cu+CeO2/Cu porous antibacterial materials were prepared.
2.2 Analysis and Characteristics
2.2.1 Physical property
The morphology images of the Cu+CeO2/Cu porous material were observed by scanning electron microscope
(SEM). The content of Ce in the coating was determined by Electron Spectroscopy (XL30). By comparing the
mass of porous material with that of solid material, the porosity of the Cu porous materials was calculated. The
porosity is given by the equation (1).
=
m  m0
×100%
m
（1）
In the equation (1),  is the porosity, m is the mass of Cu bulk material, and m0 is the mass of Cu+CeO2/Cu
porous antibacterial material.
Specific surface area of the porous materials was measured by the permeation method, which is given by the
equation (2).
S=14
 3 AP
1   2Q
(2)
In the equation (2), S is the specific surface area (m2/cm3), ε is the porosity of Cu+CeO2/Cu porous antibacterial
material, A is the area of the porous materials for the permeation measurement (m2). P is the press difference
between the two sides (MPa),  is the thickness of the porous materials (m),  is the conglutination coefficient
(Pa·S), and Q is the flux of gas, which passes the porous materials (m3/S).
2.2.2 Antibacterial test
For microbiological experimentation, Escherichia coli (ATCC 8099), Candida albicans (ATCC 10231) and
Staphylococcus aureus (ATCC 6538) were selected as indicators. The number of bacterial colonies was counted to
evaluate the antibacterial rate of Cu+CeO2/Cu porous antibacterial material. Each evaluation was carried out in
triplicate and values obtained of antibacterial rate(R) were calculated by the equation (3).
R=
C0  C
×100%
C0
(3)
In the equation (3), C0 is the colony forming unit of comparing material, C is the colony forming unit of
antibacterial material.
Moreover, Staphylococcus aureus (ATCC 6538) was selected as experimental culture with a starting colony
forming unit of 1.0×106cfu/mL. Contrast test was carried out on the antibacterial property between the Cu and
Cu+CeO2/Cu porous antibacterial materials. The antibacterial properties of Cu+CeO2/Cu porous antibacterial
materials against Escherichia coli (ATCC 8099) and Staphylococcus aureus (ATCC 6538) were estimated by the
experimentation of inhibition ring. Test bacteria inoculated on beveled the nutrient agar medium plates were
incubated for three generations to keep the activity of the test bacteria.
3 Results and Discussion
3.1 Microstructure and Chemical Composition
Figure 1 shows the SEM image of the Cu+CeO2/Cu porous antibacterial material. It can be seen that the
shape and size of pores is uniform in three directions, whose maximum diameter is about 0.6 mm.
Fig.1
SEM morphology of Cu + CeO2/Cu antibacterial material
Table 1 shows the result of electron spectroscopy of Cu+CeO2/Cu porous antibacterial material. From the Table
1, it follows that the content of Ce is about 2.5 % (mass percent) in the coating surface. The shape of CeO2 is
white spheric particle, whose diameter is about 1μm, from the orientation of the arrows in Figure 2.
3.2 Porosity and Specific Surface Area
The experimental results show that the porosity of Cu + CeO2/Cu porous antibacterial material is over 95%
which presents very high porosity. The specific surface area is about 31.4m2/cm3.
Table 1
Composition of Cu + CeO2/Cu antibacterial material
Element
Mass percentage /%
Atom percentage /%
O
1.52
5.85
Ce
2.50
1.10
Cu
95.96
93.05
CeO2 particles
Fig.2
Surface morphology of
Cu + CeO2/Cu antibacterial material
3.3 Antibacterial Performance
Antibacterial tests of Cu + CeO2/Cu porous antibacterial material against E. coli (3.75×106 cfu/mL), S. aureus
(1.0×106 cfu/mL) and C. albicans (3.75×106 cfu/mL) after 20min, 40min and 60min incubation respectively in
close contact were carried out. The specimens with the bacterial solution were incubated at (37±1) ℃ for 24 h.
Subsequently, their numbers of bacterial colonies were counted, listing in Table 2. From the Table 2, it can be
concluded that the Cu + CeO2/Cu porous material has very strong antibacterial activity against all the three test
bacteria. The antibacterial effect of the Cu + CeO2/Cu porous material against E. coli is the best of the three test
bacteria, whose percentage of dead cells of E. coli reached 98.2% after 20min incubation, 99.1% after 40min
incubation and 100% after 60min incubation. The colony forming unit against C. albicans after 60min was still
14cfu/ml, which presents that the antibacterial effect against C. albicans was a little worse than the other two.
Table 2
Antibacterial effect of Cu + CeO2/Cu porous material
colony forming unit /cfu/ml
culture
0
20min
40min
60min
E.coli
3.75×106
27.5
13
0
S.aureus
1.0×106
212
29
0
1580
385
14
C.albicans
3.75×10
6
The contrast test results of antibacterial property of Cu and Cu + CeO2/Cu antibacterial material are
summarized in the Table 3, whose experimental bacteria is S. aureus with starting colony forming unit of 1.0×106
cfu/ml. It can be seen from Table 3 that the antibacterial rates of those two materials were identical after 60min
incubation. The colony forming units of Cu + CeO2/Cu porous material after 20min and 40min are 27.5 and
13cfu/ml, which are 20.5 and 10cfu/ml higher than the Cu porous material. JING Hemin[10] has studied the
antibacterial property of stainless steel with cerium. It can be concluded from the test result, antibacterial property
of stainless steel containing 3% Ce is a bit inferior to the Cu porous material. Combining the data in our study, it
can be generalized that the antibacterial property of Cu porous material with a little CeO2 micro-powder is
changeable very little. Due to Ce of 2.5% (mass percentage) in the Cu + CeO2/Cu porous antibacterial material
replaces the copper, which makes copper expose less. Therefore, the releasing rate of Cu2+ is slightly slower,
which is useful in the occasion controlling the releasing rate of Cu2+.
Table 3
Comparison of antibacterial property of Cu and Cu + CeO2/Cu porous material
material
colony forming unit /cfu/ml
20min
40min
60min
Cu + CeO2/Cu
27.5
13
0
Cu
7
3
0
Figure 3 shows the results of inhibition ring. From Figure 3, in the test of sponge sample (white) against S.
aureus, no inhibition zone can be observed, while in the experiment of Cu + CeO2/Cu porous antibacterial
material, an inhibition ring of the inner diameter 20mm and outer diameter 36.2mm is generated. Figure 3 (b)
shows that in the test against E. coli, an inhibition ring of inner diameter 26.6 mm and outer diameter 39.7mm was
also produced.
(a)
S.aureus
Fig. 3
(b)
E.coli
Test results of inhibition ring
The main reason of the fast and high rate of antibacterial properties of Cu + CeO2/Cu porous antibacterial
material should be attributed to the high specific surface area and high surface activity in these porous materials. It
can release sufficient Cu2+ ions in the short period from the porous surface of those materials. It is well known that
Cu2+ is the main antibacterial ion in the Cu + CeO2/Cu porous antibacterial material. Yet the Antibacterial
mechanism of Cu2+ is as follows: when a small amount of Cu2+ ions reach the microbial cell wall, with the
teichoic acid bearing the negative charge in the cell wall of microbe and the adsorption of lipopolysaccharide to
the positive ions, Cu2+ ions absorb the teichoic acid and lipopolysaccharide very firm. As to the intrinsic
diffusing-promotion and the active transporting-action of cell membrane of bacteria, Cu2+ ions diffuse in and
break through the cell membrane into the cell. It can coagulate protein and destroy the activity of cell Synthase to
make the bacteria lose the ability of propagation, and the bacteria is finally killed [11, 12]. The antibacterial rate of
Cu + CeO2/Cu porous antibacterial material against C. albicans is lower than that of the other two. The cause may
be as follows: C. albicans is gram-positive bacteria, which has thicker cell wall than that of E. coli, and its volume
is five to six multiples than that of S. aureus. Taking the antibacterial mechanics into consideration together, it can
be considered that more time should be indispensable to kill the C. albicans.
4
Conclusions
(1)
Foam of polyamide was used as precursor material, and Cu+CeO2/Cu porous antibacterial material was
prepared by electroplating.
(2)
The porosity of Cu + CeO2/Cu porous antibacterial material is over 95%, whose specific surface area is
above 31.4m2/cm3.
(3)
The antibacterial properties of Cu+CeO2/Cu porous antibacterial material against the three kind of
familiar bacterias (E. coli, S. aureus and C. albicans) are excellent.
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This paper was originally issued in Chinese in Journal of Functional Materials (Gongneng Cailiao), 2009, 40(2): 265–267.
1) 论文所属一级二级学科：430.15
2) YU Zhiming(于志明，辽宁省沈阳市文化路 72 号，中国科学院金属研究所，024-23915877，[email protected])
3) Chongqing Instrument Materials Research Institute (重庆仪表材料研究所)