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Development of silane grafted ZnO core shell nanoparticles loaded diglycidyl epoxy nanocomposites film for antimicrobial applications
Materials Science and Engineering C 64 (2016) 286–292
Contents lists available at ScienceDirect
Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Development of silane grafted ZnO core shell nanoparticles loaded diglycidyl epoxy nanocomposites film for antimicrobial applications S. Suresh a,b,⁎, P. Saravanan c, K. Jayamoorthy c, S. Ananda Kumar d, S. Karthikeyan b,e a
Department of Physics, St. Joseph's College of Engineering, Chennai 600119, Tamil Nadu, India Department of Research and Development Centre, Bharathiar University, Coimbatore 641046, Tamil Nadu, India Department of Chemistry, St. Joseph's College of Engineering, Chennai 600119, Tamil Nadu, India d Department of Chemistry, Anna University, Chennai 600 025, Tamil Nadu, India e Department of Physics, Dr. Ambedkar Government Arts College, Chennai 600 039, Tamil Nadu, India b c
a r t i c l e
i n f o
Article history: Received 30 July 2015 Received in revised form 5 February 2016 Accepted 26 March 2016 Available online 30 March 2016 Keywords: APTES ZnO nanocomposites, XRD FT-IR Antimicrobial activity
a b s t r a c t In this article a series of epoxy nanocomposites film were developed using amine functionalized (ZnO-APTES) core shell nanoparticles as the dispersed phase and a commercially available epoxy resin as the matrix phase. The functional group of the samples was characterized using FT-IR spectra. The most prominent peaks of epoxy resin were found in bare epoxy and in all the functionalized ZnO dispersed epoxy nanocomposites (ZnO-APTES-DGEBA). The XRD analysis of all the samples exhibits considerable shift in 2θ, intensity and dspacing values but the best and optimum concentration is found to be 3% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposites supported by FT-IR results. From TGA measurements, 100 wt% residue is obtained in bare ZnO nanoparticles whereas in ZnO core shell nanoparticles grafted DGEBA residue percentages are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively, which is confirmed with ICP-OES analysis. From antimicrobial activity test, it was notable that antimicrobial activity of 7% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposite film has best inhibition zone effect against all pathogens under study. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Zinc oxide nanoparticles are being widely used in health care commercial products due to their unique properties such as UV light absorption and being catalytic, semi-conducting, magnetic and antimicrobial properties [1–3]. During last decade, nanomaterials are of considerable interest due to the functionalities unavailable to bulk materials. It is found that once the materials are prepared in the nanostructured forms, significant changes could occur to their physical, chemical and electrical properties [4]. Metal oxides such as TiO2, ZnO, MgO and CaO are generally regarded as safe materials to human beings and animals, which not only exhibit strong antibacterial activity in small amounts even in absence of light but also stable under harsh process conditions [5]. ZnO is an important basic material due to its low cost, large band gap (3.31 eV), large exciton binding energy (60 MeV), luminescent properties and as biocompatible antimicrobial material. ZnO nanoparticles are useful as antibacterial and antifungal agents when incorporated into materials, such as surface coatings (paints), textiles and plastics [6, 7]. The enhanced surface area of ZnO nanoparticles allows a much stronger interaction with bacteria [8–11]. This permits using a smaller amount of zinc oxide for the same or improved biostatic behaviour. ⁎ Corresponding author at: Department of Physics, St. Joseph's College of Engineering, Chennai 600119, Tamil Nadu, India. E-mail address: [email protected] (S. Suresh).
http://dx.doi.org/10.1016/j.msec.2016.03.096 0928-4931/© 2016 Elsevier B.V. All rights reserved.
Furthermore, nanoparticles have a large surface area to volume ratio that results in a significant increasing of the effectiveness in blocking the UV radiation when compared to bulk materials [12]. In this work, surface modification of nZnO was achieved with a 3aminopropyltriethoxysilane coupling agent and the surface modified nZnO in different concentrations was reinforced with epoxy resin to formulate nZnO reinforced epoxy nanocomposites film. The reinforcing effect of nZnO particles with epoxy resin towards microbial resistance was investigated by several techniques including Fourier transform infra-red (FTIR) spectra, XRD, SEM and antimicrobial studies. The results of these studies are discussed along with supporting evidence of the nanoparticle behaviour. Epoxy resin is a well known source material for manufacturing antifouling paints used in marine industries. So the main focus of this work to improve the antibacterial and antifungal properties of epoxy resin by silane grafted ZnO nanoparticles of various concentrations, which could be used in antifouling paints.
2. Experimental 2.1. Materials Zinc acetate, 3-aminopropyltriethoxysilane and all other reagents have been purchased from Sigma-Aldrich chemicals and used without further purification.
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2.2. Measurements
2.6. Preparation of ZnO nanoparticles
FT-IR enables samples to be examined directly in nanocomposite film without any further sample preparation. The infrared spectra were recorded using KBr pellet technique in BRUKER IFS 66 V model FT-IR spectrometer. The ZnO-APTES-DGEBA nanocomposites film have been characterized by X-ray diffraction (XRD) has been equipped with a Copper target (λ = 1.5405 Å) radiation using Guinier type camera used as focusing geometry and a solid state detector. Curved nickel crystal has been used as the monochromator to produce Cu Kα1 radiation in the range of 5°–90°. A JEOL JEM-3010 analytical transmission electron microscope, operating at 300 kV with a measured point-to-point resolution of 0.23 nm, has been used to characterize the spherical morphology of ZnO and ZnO-APTES core shell nanoparticles. The epoxy nanocomposites film samples have been then coated with a thin layer of gold by vaporization and morphology has been observed by scanning electron microscope (LEO 1455VP). The thermal properties of the designed samples were studied by thermogravimetric analysis (TGA) (TA instruments-2000 Perkin Elmer) at a heating rate of 10 °C/min in an inert N2 atmosphere. The acid digested samples were measured using Inductively Coupled Plasma Optical Emission Spectrometer (ISA JOBIN YVON 24 MODEL) to estimate the ZnO concentration in all the samples.
ZnO nanoparticles were made according to the method of Singh et al (2013) [13]. For the synthesis of ZnO, NaOH (0.4 M) and zinc acetate (0.2 M), solutions were mixed slowly with molar ratio of 2:1, respectively. The above solution was stirred for 10 min. After that, 1.2 ml of triethanolamine (TEA) was added and stirring continued for another 10 min. This solution was put for microwave irradiation at 700 W in two steps, that is, 40 °C for 20 min and 60 °C for 30 min. Resulting precipitate was washed with DI water 2–3 times before drying at 70 °C for 4 h, then crushed using mortar pestle and calcinated in air at 500 °C for 1 h.
2.3. 2.3. Test-pathogenic microorganisms Test pathogenic bacteria such as, Streptomyces, Staphylococcus aureus and Pseudomonas aeruginosa and fungi Aspergillus niger were used for in vitro antimicrobial activity. These selected pathogenic strains were obtained from Microbiological Division (Jayagen Biologics Analytical Laboratory, Jayagen Biologics and Chennai). 2.4. Antibacterial activity evaluation The epoxy nanocomposite films, containing between 1, 3, 5 and 7 wt% ZnO-APTES core shell nanoparticles were placed in the middle of sterile plates containing agar medium. The antibacterial activities of nanocomposite film samples were tested by an inhibition zone method. In this method the good mobility microbes were taken as the test pathogens. 100 ml Muller Hinton broth, 200 ml Muller Hinton agar, Petri dish and the samples were autoclaved at 121 °C, 15 psi for 15 min. A loop of the microbe's culture was inoculated from fresh colonies on agar plates into 100 ml Muller Hinton culture medium. The culture was allowed to grow until the optical density reached 0.2 at 600 nm (OD of 0.2 corresponding to a concentration of 108 CFU ml−1of medium). Then it was swabbed uniformly onto individual Mueller Hinton agar plates using sterile cotton swabs. The different wt% core shell nanoparticles loaded nanocomposite films were placed in the center of the culture swabbed petriplate in such a manner that the films are in contact with the culture. The petri dish plates were examined for possible clear zone formation after overnight incubation at 37 °C. The presence of clear zone around the nanocomposite films on the petri dish plates was recorded as an inhibition against the test microbial species. The entire experiments were conducted in a laminar hood to prevent any contamination.
2.7. Surface treatment of ZnO nanoparticles The introduction of reactive NH2 group onto the surface of ZnO nanoparticles was achieved through the reaction between 3aminopropyltriethoxysilane and the hydroxyl groups on the ZnO nanoparticle surface. Typically, 2.0 g ZnO nanoparticles and 2 ml 3aminopropyltriethoxysilane in 40 ml O-xylene were kept at 150 °C for 3 h under ultrasonic bath stirring and Argon protection. The reaction mixture was refluxed for 24 h. Rotary evaporator was used to remove the solvent form the APTES modified ZnO. After that, the ZnO nanoparticles were collected by filtration and rinsed three times with acetone. Afterwards, the APTES functionalized ZnO nanoparticles were dried under vacuum for 12 h [14]. 2.8. Preparation of ZnO-APTES-DGEBA nanocomposite films The epoxy nanocomposite films were prepared using a high speed disperser. The fabrication processes of ZnO-APTES-DGEBA nanocomposites were as follows. Different weight percentages of silane modified ZnO nanoparticles (0, 1, 3, 5 and 7 wt%) was directly added to vessel charged with epoxy resin (DGEBA) and solvent mixture (butanol/xylene) followed by addition of additives. The pigment was dispersed by stirring at 400 rotations per minute (RPM) for 30 min and then increasing the stirrer speed to 2000 RPM. The vessel was externally cooled using cold water to avoid rise in temperature during processing. The dispersion was continued for 45–60 min to give a uniform red nanocomposites. For curing, epoxy formulation and curing agent (HY951) were mixed in a weight ratio 100:58 of epoxy to amine. The mixture was degassed in the vacuum oven for another 20 min at 40 °C to remove any gas bubbles generated during the mixing process. Solvents mixture of xylene and butanol was used for dilution as per the convenience. By this method, different formulations were employed for preparation of nanocomposite films. The films were left for about 2 weeks at room temperature for complete curing. The reaction route of ZnO-APTESDGEBA nano-composite is depicted in Scheme 1. 3. Results and discussion ZnO-APTES core shell nanoparticles were analyzed by XRD, SEM, AFM measurements. Also, the functional group of these core shell nanoparticles was confirmed by FTIR spectroscopy. These results were reported earlier [15]. 3.1. TEM analysis unmodified ZnO and ZnO-APTES core shell nanoparticles
2.5. Anti-fungal evaluation The epoxy nanocomposite testing films were gently placed onto nutrient agar (potato dextrose agar, PDA) by which a fungal disk of A. niger at the center of Petri dish (90 mm diameter) was located between the test specimens. The distance from fungal disk to the edge of the specimens was fixed at 15 mm. The fungi were then incubated at 30 °C for 7 days. The fungal growth area was observed and reported in terms of fungal growth area.
The unmodified ZnO nanoparticles agglomerated severely as shown in Fig. 1a and the nanoparticles cannot be distinguished separately. Fig. 1b shows the TEM image of the modified ZnO-APTES nanoparticles. It can be clearly seen from the TEM image that most of the silane modified ZnO particles exhibit spherical morphology and no large agglomerations. TEM analysis is used to obtain the exact size distribution of all the metal oxides nanoparticles taken for studies. Most of the particles distributed are homogeneous and holds the size less than 16 nm. The
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Scheme 1. Reaction route of ZnO-APTES-DGEBA nanocomposite.
morphology with smooth and fused surfaces and weak accumulation of particles were clearly resolved from TEM images. 3.2. XRD analysis of ZnO-APTES-DGEBA nanocomposite film Fig. 2 shows the XRD patterns of 1%, 3%, 5% and 7% ZnO-APTESDGEBA nanocomposites, all the patterns are similar in structure and the peaks exhibit uniformly dispersed structure with no crystalline peaks corresponding to silane grafted ZnO core shell nanoparticles [16]. There is no peak obtained for 2θ between 10° to 20° for samples 1%, 3% and 5% ZnO-APTES-DGEBA nanocomposite films that are attributed to the decrease in intensities due to the incorporation of silane grafted ZnO core shell nanoparticles in epoxy resin. However higher concentration of 7% ZnO-APTES-DGEBA nanocomposite films shows some increase in intensities compared to other samples 1%, 3% and 5% ZnO-APTES-DGEBA. There is shift in the 2θ theta values of many intense peaks in all the samples 1%, 3%, 5% and 7% ZnO-APTES- DGEBA
nanocomposites compared to the DGEBA sample. The silane grafted ZnO core shell nanoparticles loaded DGEBA nanocomposites are effective for concentrations 1, 3 and 5%, whereas for 7% concentration it is not suitable to disperse ZnO-APTES in epoxy resin. This might be due to the agglomeration of nanoparticles within the epoxy resin at higher concentration. Even though all the samples show some response, the best and optimum concentration is 3% ZnO-APTES-DGEBA, supported by FT-IR results. 3.3. FT-IR analysis of ZnO-APTES-DGEBA nanocomposite film The structures of DGEBA resin and HY951 curing agent were confirmed by IR spectral analyses. The four different coating formulations exhibit different IR spectra. The IR spectrum of DGEBA resin reveals the presence of characteristic absorption bands for Ar\\C_C\\H stretching and bending\\CH2 and\\CH3 asymmetrical and symmetrical, \\C\\Ar\\O\\C stretching, and epoxy CH2–(O\\CH\\) ring
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Fig. 1. TEM photographs of (a) unmodified ZnO nanoparticles and (b) ZnO-APTES core shell nanoparticles.
stretching vibration. The presence of epoxy groups in IR spectra was proved from the presence of strong bands at 3056 cm− 1 (γ C\\H epoxy) and 915 cm−1 (γ C\\O epoxy). The 1, 4-substitution of aromatic ring was seen at 830 cm−1 for DGEBA resin. There was a broad band with very low intensity at 3429 cm−1 corresponding to the vibration mode of water OH group indicating the presence of small amount of water adsorbed on the nZnO crystal surface. The band at 1601 cm− 1 was due to the OH bending of water. A strong band at 530 cm−1 is attributed to the nZnO stretching band which is consistent with that reported before. The IR analysis carried out for HY951 curing agent reveals the presence of characteristic absorption bands for N\\H stretching and bending vibration. The broad doublet peak observed between 3340 and 3200 cm−1 may be due to the\\NH2 vibration absorption of amine compound. The aliphatic \\CH2 and \\CH3 vibrations were seen between 3000 and 2850 cm− 1 for the curing agent. The most obvious distinguishing features were that the curing agent spectra had an intense broad N\\H stretching absorption around 3300 cm−1. Fig. 3 shows the infrared spectra of all the coatings analyzed on KBr disk between the zone 400–4000 cm−1.
Fig. 2. XRD plot of ZnO-APTES-DGEBA nanocomposite films.
3.4. SEM analysis of ZnO-APTES-DGEBA nanocomposite film From the Fig. 4a and b, it was found that the ZnO-APTES core shell nanoparticles are spherical in shape. It shows that the ZnO-APTES core shell nanoparticles were homogeneously dispersed in epoxy matrix. The unmodified ZnO nanoparticles aggregated and a crack around the aggregation emerged in the coating after, because there was no grafted epoxy resin on the ZnO surface, the compatibility between ZnO and epoxy resin was poor and interface bonding between nanoparticles and epoxy resin was weak. With the increasing of the graft density, the compatibility and interface bonding between nanoparticles and epoxy resin were improved; the aggregation of ZnO-APTES and the cracks around the aggregation were decreased. When the ZnO-APTES with the maximum graft density on the surface were added into the coating, few ZnO-APTES agglomerations and no cracks between the interface of nanoparticles and epoxy matrix were observed. Therefore, the compatibility and interface bonding between nanoparticles and epoxy resin were improved with the increase of graft density on the surface
Fig. 3. FT-IR plot of ZnO-APTES-DGEBA nanocomposite films. (a) ‘1 wt%’, (b) ‘3 wt%’, (c) ‘5 wt%’, (d) ‘7 wt%’, (e) 0 wt% and (f) nano-ZnO.
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Fig. 4. (a) SEM image of ZnO-DGEBA nanocomposite film; (b) ZnO-APTES-DGEBA nanocomposite film.
of nanoparticles. As it can be observed, for sample containing unmodified ZnO nanoparticles, relatively large particle aggregates with a nonuniform distribution appeared on the surface of the samples. However, with ZnO-APTES core shell nanoparticles, the size of particle aggregates on the surface of the coating film less and more uniform distribution of nanoparticles was also achieved, as compared to its unmodified counterparts. However, in order to evaluate the homogeneity and distribution of the nanoparticles to the entire volume of the film, further studies are needed. 3.5. TGA and ICP-OES analysis of ZnO-APTES-DGEBA nanocomposite film Fig. 5 shows the TGA curve which exhibit two decomposition stages in all samples. In bare epoxy DGEBA sample the first decomposition stage starts at 325 °C and the second stage at 513 °C. The temperature of first decomposition stages for 1%-ZnOAPTES-DGEBA and 3%-ZnO-APTES-DGEBA increases compared to the DGEBA sample whereas it found decreased at higher concentrations of 5%-ZnO-APTES-DGEBA and 7%-ZnO-APTES-DGEBA. The temperature of second stage decomposition increases in all the samples compared to the DGEBA sample. The TGA measurements shows that bare ZnO nanoparticles doesn't decompose upto 600 °C, hence nearly 100 wt% residue is obtained in bare ZnO nanoparticles sample whereas in silane grafted ZnO loaded DGEBA samples residue percentages are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. These results exhibit the evidence for presence of ZnO-APTES core shell nanoparticles in epoxy coatings. Further the increase in residue weight percentage is due to the increase in ZnO- APTES concentrations. The
results has been confirmed with the ICP-OES results which shows 0.0, 0.264, 0.322, 0.431 and 0.583 mg/l of zinc ion concentration for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. 3.6. Antibacterial behaviour of ZnO-APTES-DGEBA nanocomposites Fig. 6a–c, shows the antibacterial effect of ZnO-APTES-DGEBA nanocomposites film against Streptomyces, S. aureus and P. aeruginosa. From the results obtained due to the antimicrobial activity of ZnO-APTESDGEBA nanocomposites film on Streptomyces was interesting to note that as the concentration of nanoparticles increases, the zone of inhibition also increases i.e. a minimum for control (almost none) to a maximum in 7 wt% (Table 1). The inhibitory effect of various concentrations of ZnO-APTES core shell nanoparticles (1, 3, 5 and 7 wt%) loaded epoxy nanocomposites film was examined through agar diffusion method. The growth inhibition of S. aureus and P. aeruginosa was increased at increased concentration of ZnO-APTES nanoparticles and the maximum inhibition of growth was obtained at 7 wt%. The minimum inhibitory effect of lower concentration of ZnO-APTES core shell nanoparticles loaded DGEBA was attributed to the inadequate concentration of nanoparticles in epoxy resin. Similarly, Li et al. [17] reported the antibacterial effect of ZnO powder coated PVC film against Grampositive and Gram-negative bacteria. The larger surface area and higher concentration are responsible for the antibacterial activity of ZnO nanoparticles [18,19]. The previously reports demonstrated that the generation of H2O2 from ZnO leads to the penetration of particles into the cell membrane of bacteria leads to the formation of injuries and finally the death of bacterium was occurred [20,21]. Conversely, the electrostatic interaction between bacterial cell surface and nanoparticles may be one of the reasons for the inhibition of growth [22,23]. Based upon the above possible phenomena, our present study reports the growth inhibition of Streptomyces, S. aureus and P. aeruginosa may be produced by the damage of the cell membrane. Enlarged antimicrobial image of ZnO-APTES-DGEBA nanocomposite film against Streptomyces shown in Fig. S1. 3.7. Antifungal behaviour of ZnO-APTES-DGEBA nanocomposites
Fig. 5. TGA curve of bare ZnO nanoparticles and ZnO-APTES-DGEBA nanocomposite film.
As per the literature survey there is limited studies carried out for antifungal activity of ZnO-APTES core shell nanoparticles. Fig. 6d, shows the inhibitory effect of ZnO-APTES core shell nanoparticles against the fungus A. niger. Herein, the maximum inhibition of fungal growth was achieved at 7 wt% and the Fig. 6d exhibits the increased concentration of ZnO-APTES core shell nanoparticles resulting in the decreased growth rate of A. niger. After 7 inoculation days, the fungal colonies were grown up only to extremity of the polymer fragment. Similar behaviour was observed at higher incubation times (14, 21, 28 and 60 days). In comparison, the samples containing 5%, 7 wt% ZnO-APTES core shell nanoparticles showed obvious inhibitory effects on fungal
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Fig. 6. Photographs of ZnO-APTES-DGEBA nanocomposite film against (a) Streptomyces; (b) Staphylococcus aureus; (c) Pseudomonas aeruginosa and (d) Aspergillus niger.
growth. Inhibition zone area of the fungus around the polymer nanocomposites increases with increasing concentration of ZnO-APTES core shell nanoparticles in polymer. The epoxy nanocomposites film having 7 wt% ZnO-APTES core shell nanoparticles display best inhibition zone, suggesting the mycotoxic effect of the zinc oxide. These aspects are in agreement with the previous observations [24].
3.8. Antimicrobial behaviour of bare ZnO nanoparticles The ability of bare ZnO inhibit the growth of tested strains is shown in Fig. 7. The microbial inhibitory activity was measured through zone of inhibition test. The result of this studies suggested that the inhibition zone of bare ZnO (3%) was enough to inhibit antibacterial and antifungal activity significantly towards test pathogens. The measured inhibitory zone values have been shown in Table 1. Bare ZnO nanoparticles shows better antimicrobial effect towards tested pathogens than ZnOAPTES-DGEBA nanocomposites. Enlarged antimicrobial image of bare ZnO nanoparticles against Streptomyces is shown in Fig. S2.
4. Conclusions A simple, rapid inexpensive method has been developed to prepare ZnO-APTES-DGEBA nanocomposites. The phase confirmation done using XRD analysis, there is considerable variation in 2θ, intensity and d-spacing for all the samples, which confirms the interaction of ZnOAPTES core shell nanoparticles with DGEBA bare epoxy resin. The results of FT-IR analysis suggest 3% ZnO-APTES-DGEBA nanocomposite is the best composition for grafting ZnO core shell nanoparticles compared to the other concentrations. The zone inhibition test results proved that the ZnO nanoparticles have potential to be used as an antimicrobial agent. The maximum inhibition growths for all microorganisms were achieved at 7 wt% of ZnO-APTES-DGEBA nanocomposite. From TGA measurements, 100 wt% residue is obtained in bare sample whereas ZnO grafted DGEBA residue percentage are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. These results have been confirmed with the ICP-OES results which shows 0.0, 0.264, 0.322, 0.431 and 0.583 mg/l of zinc ion concentration for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. In this study, the antifungal
Table 1 Antibacterial activity of ZnO-APTES-DGEBA nanocomposites and bare ZnO nanoparticles. Pathogen name
Pseudomonas aeruginosa Staphylococcus aureus Streptomyces Aspergillus niger
ZnO-APTES-DGEBA nanocomposites (mm)
Bare ZnO nanoparticles (mm)
1 wt%
3 wt%
5 wt%
7 wt%
1 wt%
3 wt%
5 wt%
7 wt%
– – – –
6 – 6 3
7 – 7 6
8 – 9 11
9 – – 12
10 – – 12
10 – 7 13
11 6 8 14
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Fig. 7. Photographs of bare ZnO nanoparticles against (a) Streptomyces; (b) Staphylococcus aureus; (c) Pseudomonas aeruginosa and (d) Aspergillus niger.
behaviour against A. niger for a set of ZnO-APTES core shell nanoparticles based nanocomposites was envisaged. The presence of fungi growth was observed for the 1 and 3 wt% ZnO-APTES-DGEBA nanocomposites but inhibition was observed at 5 and 7% ZnO-APTES-DGEBA nanocomposites. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.msec.2016.03.096. References [1] F. Porter, Zinc Handbook: Properties, Processing and Use in Design, CRC Press, Boca Raton, FL, 1991. [2] M. Li, S. Pokhrel, X. Jin, L. Madler, R. Damoiseaux, E.M. Hoek, Environ. Sci. Technol. 45 (2011) 755. [3] A.J. Huh, Y.J. Kwon, J. Control. Release 156 (2011) 128. [4] D.W. Bahnemann, C. Kormann, M.R. Hoffmann, J. Phys. Chem. 91 (1987) 3789. [5] P.K. Stoimenov, R.L. Klinger, G.L. Marchin, Langmuir 18 (2002) 6679. [6] D. Zvekic, V.V. Srdic, M.A. Karaman, M.N. Matavulj, Processing and Application of Ceramics, 52011 41. [7] C. Guo, Z. Zheng, Q. Zhu, X. Wang, Polym. Plast. Technol. 46 (2007) 1161. [8] R.H. Wang, J.H. Xin, X.M. Tao, W.A. Daoud, Chem. Phys. Lett. 398 (2004) 250. [9] R.H. Wang, J.H. Xin, X.M. Tao, Inorg. Chem. 44 (2005) 3926. [10] R.K. Dutta, P.K. Sharma, A.C. Pandey, Dig. J. Nanomater. Bios. 4 (2009) 83.
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Contents lists available at ScienceDirect
Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Development of silane grafted ZnO core shell nanoparticles loaded diglycidyl epoxy nanocomposites film for antimicrobial applications S. Suresh a,b,⁎, P. Saravanan c, K. Jayamoorthy c, S. Ananda Kumar d, S. Karthikeyan b,e a
Department of Physics, St. Joseph's College of Engineering, Chennai 600119, Tamil Nadu, India Department of Research and Development Centre, Bharathiar University, Coimbatore 641046, Tamil Nadu, India Department of Chemistry, St. Joseph's College of Engineering, Chennai 600119, Tamil Nadu, India d Department of Chemistry, Anna University, Chennai 600 025, Tamil Nadu, India e Department of Physics, Dr. Ambedkar Government Arts College, Chennai 600 039, Tamil Nadu, India b c
a r t i c l e
i n f o
Article history: Received 30 July 2015 Received in revised form 5 February 2016 Accepted 26 March 2016 Available online 30 March 2016 Keywords: APTES ZnO nanocomposites, XRD FT-IR Antimicrobial activity
a b s t r a c t In this article a series of epoxy nanocomposites film were developed using amine functionalized (ZnO-APTES) core shell nanoparticles as the dispersed phase and a commercially available epoxy resin as the matrix phase. The functional group of the samples was characterized using FT-IR spectra. The most prominent peaks of epoxy resin were found in bare epoxy and in all the functionalized ZnO dispersed epoxy nanocomposites (ZnO-APTES-DGEBA). The XRD analysis of all the samples exhibits considerable shift in 2θ, intensity and dspacing values but the best and optimum concentration is found to be 3% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposites supported by FT-IR results. From TGA measurements, 100 wt% residue is obtained in bare ZnO nanoparticles whereas in ZnO core shell nanoparticles grafted DGEBA residue percentages are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively, which is confirmed with ICP-OES analysis. From antimicrobial activity test, it was notable that antimicrobial activity of 7% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposite film has best inhibition zone effect against all pathogens under study. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Zinc oxide nanoparticles are being widely used in health care commercial products due to their unique properties such as UV light absorption and being catalytic, semi-conducting, magnetic and antimicrobial properties [1–3]. During last decade, nanomaterials are of considerable interest due to the functionalities unavailable to bulk materials. It is found that once the materials are prepared in the nanostructured forms, significant changes could occur to their physical, chemical and electrical properties [4]. Metal oxides such as TiO2, ZnO, MgO and CaO are generally regarded as safe materials to human beings and animals, which not only exhibit strong antibacterial activity in small amounts even in absence of light but also stable under harsh process conditions [5]. ZnO is an important basic material due to its low cost, large band gap (3.31 eV), large exciton binding energy (60 MeV), luminescent properties and as biocompatible antimicrobial material. ZnO nanoparticles are useful as antibacterial and antifungal agents when incorporated into materials, such as surface coatings (paints), textiles and plastics [6, 7]. The enhanced surface area of ZnO nanoparticles allows a much stronger interaction with bacteria [8–11]. This permits using a smaller amount of zinc oxide for the same or improved biostatic behaviour. ⁎ Corresponding author at: Department of Physics, St. Joseph's College of Engineering, Chennai 600119, Tamil Nadu, India. E-mail address: [email protected] (S. Suresh).
http://dx.doi.org/10.1016/j.msec.2016.03.096 0928-4931/© 2016 Elsevier B.V. All rights reserved.
Furthermore, nanoparticles have a large surface area to volume ratio that results in a significant increasing of the effectiveness in blocking the UV radiation when compared to bulk materials [12]. In this work, surface modification of nZnO was achieved with a 3aminopropyltriethoxysilane coupling agent and the surface modified nZnO in different concentrations was reinforced with epoxy resin to formulate nZnO reinforced epoxy nanocomposites film. The reinforcing effect of nZnO particles with epoxy resin towards microbial resistance was investigated by several techniques including Fourier transform infra-red (FTIR) spectra, XRD, SEM and antimicrobial studies. The results of these studies are discussed along with supporting evidence of the nanoparticle behaviour. Epoxy resin is a well known source material for manufacturing antifouling paints used in marine industries. So the main focus of this work to improve the antibacterial and antifungal properties of epoxy resin by silane grafted ZnO nanoparticles of various concentrations, which could be used in antifouling paints.
2. Experimental 2.1. Materials Zinc acetate, 3-aminopropyltriethoxysilane and all other reagents have been purchased from Sigma-Aldrich chemicals and used without further purification.
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2.2. Measurements
2.6. Preparation of ZnO nanoparticles
FT-IR enables samples to be examined directly in nanocomposite film without any further sample preparation. The infrared spectra were recorded using KBr pellet technique in BRUKER IFS 66 V model FT-IR spectrometer. The ZnO-APTES-DGEBA nanocomposites film have been characterized by X-ray diffraction (XRD) has been equipped with a Copper target (λ = 1.5405 Å) radiation using Guinier type camera used as focusing geometry and a solid state detector. Curved nickel crystal has been used as the monochromator to produce Cu Kα1 radiation in the range of 5°–90°. A JEOL JEM-3010 analytical transmission electron microscope, operating at 300 kV with a measured point-to-point resolution of 0.23 nm, has been used to characterize the spherical morphology of ZnO and ZnO-APTES core shell nanoparticles. The epoxy nanocomposites film samples have been then coated with a thin layer of gold by vaporization and morphology has been observed by scanning electron microscope (LEO 1455VP). The thermal properties of the designed samples were studied by thermogravimetric analysis (TGA) (TA instruments-2000 Perkin Elmer) at a heating rate of 10 °C/min in an inert N2 atmosphere. The acid digested samples were measured using Inductively Coupled Plasma Optical Emission Spectrometer (ISA JOBIN YVON 24 MODEL) to estimate the ZnO concentration in all the samples.
ZnO nanoparticles were made according to the method of Singh et al (2013) [13]. For the synthesis of ZnO, NaOH (0.4 M) and zinc acetate (0.2 M), solutions were mixed slowly with molar ratio of 2:1, respectively. The above solution was stirred for 10 min. After that, 1.2 ml of triethanolamine (TEA) was added and stirring continued for another 10 min. This solution was put for microwave irradiation at 700 W in two steps, that is, 40 °C for 20 min and 60 °C for 30 min. Resulting precipitate was washed with DI water 2–3 times before drying at 70 °C for 4 h, then crushed using mortar pestle and calcinated in air at 500 °C for 1 h.
2.3. 2.3. Test-pathogenic microorganisms Test pathogenic bacteria such as, Streptomyces, Staphylococcus aureus and Pseudomonas aeruginosa and fungi Aspergillus niger were used for in vitro antimicrobial activity. These selected pathogenic strains were obtained from Microbiological Division (Jayagen Biologics Analytical Laboratory, Jayagen Biologics and Chennai). 2.4. Antibacterial activity evaluation The epoxy nanocomposite films, containing between 1, 3, 5 and 7 wt% ZnO-APTES core shell nanoparticles were placed in the middle of sterile plates containing agar medium. The antibacterial activities of nanocomposite film samples were tested by an inhibition zone method. In this method the good mobility microbes were taken as the test pathogens. 100 ml Muller Hinton broth, 200 ml Muller Hinton agar, Petri dish and the samples were autoclaved at 121 °C, 15 psi for 15 min. A loop of the microbe's culture was inoculated from fresh colonies on agar plates into 100 ml Muller Hinton culture medium. The culture was allowed to grow until the optical density reached 0.2 at 600 nm (OD of 0.2 corresponding to a concentration of 108 CFU ml−1of medium). Then it was swabbed uniformly onto individual Mueller Hinton agar plates using sterile cotton swabs. The different wt% core shell nanoparticles loaded nanocomposite films were placed in the center of the culture swabbed petriplate in such a manner that the films are in contact with the culture. The petri dish plates were examined for possible clear zone formation after overnight incubation at 37 °C. The presence of clear zone around the nanocomposite films on the petri dish plates was recorded as an inhibition against the test microbial species. The entire experiments were conducted in a laminar hood to prevent any contamination.
2.7. Surface treatment of ZnO nanoparticles The introduction of reactive NH2 group onto the surface of ZnO nanoparticles was achieved through the reaction between 3aminopropyltriethoxysilane and the hydroxyl groups on the ZnO nanoparticle surface. Typically, 2.0 g ZnO nanoparticles and 2 ml 3aminopropyltriethoxysilane in 40 ml O-xylene were kept at 150 °C for 3 h under ultrasonic bath stirring and Argon protection. The reaction mixture was refluxed for 24 h. Rotary evaporator was used to remove the solvent form the APTES modified ZnO. After that, the ZnO nanoparticles were collected by filtration and rinsed three times with acetone. Afterwards, the APTES functionalized ZnO nanoparticles were dried under vacuum for 12 h [14]. 2.8. Preparation of ZnO-APTES-DGEBA nanocomposite films The epoxy nanocomposite films were prepared using a high speed disperser. The fabrication processes of ZnO-APTES-DGEBA nanocomposites were as follows. Different weight percentages of silane modified ZnO nanoparticles (0, 1, 3, 5 and 7 wt%) was directly added to vessel charged with epoxy resin (DGEBA) and solvent mixture (butanol/xylene) followed by addition of additives. The pigment was dispersed by stirring at 400 rotations per minute (RPM) for 30 min and then increasing the stirrer speed to 2000 RPM. The vessel was externally cooled using cold water to avoid rise in temperature during processing. The dispersion was continued for 45–60 min to give a uniform red nanocomposites. For curing, epoxy formulation and curing agent (HY951) were mixed in a weight ratio 100:58 of epoxy to amine. The mixture was degassed in the vacuum oven for another 20 min at 40 °C to remove any gas bubbles generated during the mixing process. Solvents mixture of xylene and butanol was used for dilution as per the convenience. By this method, different formulations were employed for preparation of nanocomposite films. The films were left for about 2 weeks at room temperature for complete curing. The reaction route of ZnO-APTESDGEBA nano-composite is depicted in Scheme 1. 3. Results and discussion ZnO-APTES core shell nanoparticles were analyzed by XRD, SEM, AFM measurements. Also, the functional group of these core shell nanoparticles was confirmed by FTIR spectroscopy. These results were reported earlier [15]. 3.1. TEM analysis unmodified ZnO and ZnO-APTES core shell nanoparticles
2.5. Anti-fungal evaluation The epoxy nanocomposite testing films were gently placed onto nutrient agar (potato dextrose agar, PDA) by which a fungal disk of A. niger at the center of Petri dish (90 mm diameter) was located between the test specimens. The distance from fungal disk to the edge of the specimens was fixed at 15 mm. The fungi were then incubated at 30 °C for 7 days. The fungal growth area was observed and reported in terms of fungal growth area.
The unmodified ZnO nanoparticles agglomerated severely as shown in Fig. 1a and the nanoparticles cannot be distinguished separately. Fig. 1b shows the TEM image of the modified ZnO-APTES nanoparticles. It can be clearly seen from the TEM image that most of the silane modified ZnO particles exhibit spherical morphology and no large agglomerations. TEM analysis is used to obtain the exact size distribution of all the metal oxides nanoparticles taken for studies. Most of the particles distributed are homogeneous and holds the size less than 16 nm. The
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Scheme 1. Reaction route of ZnO-APTES-DGEBA nanocomposite.
morphology with smooth and fused surfaces and weak accumulation of particles were clearly resolved from TEM images. 3.2. XRD analysis of ZnO-APTES-DGEBA nanocomposite film Fig. 2 shows the XRD patterns of 1%, 3%, 5% and 7% ZnO-APTESDGEBA nanocomposites, all the patterns are similar in structure and the peaks exhibit uniformly dispersed structure with no crystalline peaks corresponding to silane grafted ZnO core shell nanoparticles [16]. There is no peak obtained for 2θ between 10° to 20° for samples 1%, 3% and 5% ZnO-APTES-DGEBA nanocomposite films that are attributed to the decrease in intensities due to the incorporation of silane grafted ZnO core shell nanoparticles in epoxy resin. However higher concentration of 7% ZnO-APTES-DGEBA nanocomposite films shows some increase in intensities compared to other samples 1%, 3% and 5% ZnO-APTES-DGEBA. There is shift in the 2θ theta values of many intense peaks in all the samples 1%, 3%, 5% and 7% ZnO-APTES- DGEBA
nanocomposites compared to the DGEBA sample. The silane grafted ZnO core shell nanoparticles loaded DGEBA nanocomposites are effective for concentrations 1, 3 and 5%, whereas for 7% concentration it is not suitable to disperse ZnO-APTES in epoxy resin. This might be due to the agglomeration of nanoparticles within the epoxy resin at higher concentration. Even though all the samples show some response, the best and optimum concentration is 3% ZnO-APTES-DGEBA, supported by FT-IR results. 3.3. FT-IR analysis of ZnO-APTES-DGEBA nanocomposite film The structures of DGEBA resin and HY951 curing agent were confirmed by IR spectral analyses. The four different coating formulations exhibit different IR spectra. The IR spectrum of DGEBA resin reveals the presence of characteristic absorption bands for Ar\\C_C\\H stretching and bending\\CH2 and\\CH3 asymmetrical and symmetrical, \\C\\Ar\\O\\C stretching, and epoxy CH2–(O\\CH\\) ring
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Fig. 1. TEM photographs of (a) unmodified ZnO nanoparticles and (b) ZnO-APTES core shell nanoparticles.
stretching vibration. The presence of epoxy groups in IR spectra was proved from the presence of strong bands at 3056 cm− 1 (γ C\\H epoxy) and 915 cm−1 (γ C\\O epoxy). The 1, 4-substitution of aromatic ring was seen at 830 cm−1 for DGEBA resin. There was a broad band with very low intensity at 3429 cm−1 corresponding to the vibration mode of water OH group indicating the presence of small amount of water adsorbed on the nZnO crystal surface. The band at 1601 cm− 1 was due to the OH bending of water. A strong band at 530 cm−1 is attributed to the nZnO stretching band which is consistent with that reported before. The IR analysis carried out for HY951 curing agent reveals the presence of characteristic absorption bands for N\\H stretching and bending vibration. The broad doublet peak observed between 3340 and 3200 cm−1 may be due to the\\NH2 vibration absorption of amine compound. The aliphatic \\CH2 and \\CH3 vibrations were seen between 3000 and 2850 cm− 1 for the curing agent. The most obvious distinguishing features were that the curing agent spectra had an intense broad N\\H stretching absorption around 3300 cm−1. Fig. 3 shows the infrared spectra of all the coatings analyzed on KBr disk between the zone 400–4000 cm−1.
Fig. 2. XRD plot of ZnO-APTES-DGEBA nanocomposite films.
3.4. SEM analysis of ZnO-APTES-DGEBA nanocomposite film From the Fig. 4a and b, it was found that the ZnO-APTES core shell nanoparticles are spherical in shape. It shows that the ZnO-APTES core shell nanoparticles were homogeneously dispersed in epoxy matrix. The unmodified ZnO nanoparticles aggregated and a crack around the aggregation emerged in the coating after, because there was no grafted epoxy resin on the ZnO surface, the compatibility between ZnO and epoxy resin was poor and interface bonding between nanoparticles and epoxy resin was weak. With the increasing of the graft density, the compatibility and interface bonding between nanoparticles and epoxy resin were improved; the aggregation of ZnO-APTES and the cracks around the aggregation were decreased. When the ZnO-APTES with the maximum graft density on the surface were added into the coating, few ZnO-APTES agglomerations and no cracks between the interface of nanoparticles and epoxy matrix were observed. Therefore, the compatibility and interface bonding between nanoparticles and epoxy resin were improved with the increase of graft density on the surface
Fig. 3. FT-IR plot of ZnO-APTES-DGEBA nanocomposite films. (a) ‘1 wt%’, (b) ‘3 wt%’, (c) ‘5 wt%’, (d) ‘7 wt%’, (e) 0 wt% and (f) nano-ZnO.
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Fig. 4. (a) SEM image of ZnO-DGEBA nanocomposite film; (b) ZnO-APTES-DGEBA nanocomposite film.
of nanoparticles. As it can be observed, for sample containing unmodified ZnO nanoparticles, relatively large particle aggregates with a nonuniform distribution appeared on the surface of the samples. However, with ZnO-APTES core shell nanoparticles, the size of particle aggregates on the surface of the coating film less and more uniform distribution of nanoparticles was also achieved, as compared to its unmodified counterparts. However, in order to evaluate the homogeneity and distribution of the nanoparticles to the entire volume of the film, further studies are needed. 3.5. TGA and ICP-OES analysis of ZnO-APTES-DGEBA nanocomposite film Fig. 5 shows the TGA curve which exhibit two decomposition stages in all samples. In bare epoxy DGEBA sample the first decomposition stage starts at 325 °C and the second stage at 513 °C. The temperature of first decomposition stages for 1%-ZnOAPTES-DGEBA and 3%-ZnO-APTES-DGEBA increases compared to the DGEBA sample whereas it found decreased at higher concentrations of 5%-ZnO-APTES-DGEBA and 7%-ZnO-APTES-DGEBA. The temperature of second stage decomposition increases in all the samples compared to the DGEBA sample. The TGA measurements shows that bare ZnO nanoparticles doesn't decompose upto 600 °C, hence nearly 100 wt% residue is obtained in bare ZnO nanoparticles sample whereas in silane grafted ZnO loaded DGEBA samples residue percentages are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. These results exhibit the evidence for presence of ZnO-APTES core shell nanoparticles in epoxy coatings. Further the increase in residue weight percentage is due to the increase in ZnO- APTES concentrations. The
results has been confirmed with the ICP-OES results which shows 0.0, 0.264, 0.322, 0.431 and 0.583 mg/l of zinc ion concentration for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. 3.6. Antibacterial behaviour of ZnO-APTES-DGEBA nanocomposites Fig. 6a–c, shows the antibacterial effect of ZnO-APTES-DGEBA nanocomposites film against Streptomyces, S. aureus and P. aeruginosa. From the results obtained due to the antimicrobial activity of ZnO-APTESDGEBA nanocomposites film on Streptomyces was interesting to note that as the concentration of nanoparticles increases, the zone of inhibition also increases i.e. a minimum for control (almost none) to a maximum in 7 wt% (Table 1). The inhibitory effect of various concentrations of ZnO-APTES core shell nanoparticles (1, 3, 5 and 7 wt%) loaded epoxy nanocomposites film was examined through agar diffusion method. The growth inhibition of S. aureus and P. aeruginosa was increased at increased concentration of ZnO-APTES nanoparticles and the maximum inhibition of growth was obtained at 7 wt%. The minimum inhibitory effect of lower concentration of ZnO-APTES core shell nanoparticles loaded DGEBA was attributed to the inadequate concentration of nanoparticles in epoxy resin. Similarly, Li et al. [17] reported the antibacterial effect of ZnO powder coated PVC film against Grampositive and Gram-negative bacteria. The larger surface area and higher concentration are responsible for the antibacterial activity of ZnO nanoparticles [18,19]. The previously reports demonstrated that the generation of H2O2 from ZnO leads to the penetration of particles into the cell membrane of bacteria leads to the formation of injuries and finally the death of bacterium was occurred [20,21]. Conversely, the electrostatic interaction between bacterial cell surface and nanoparticles may be one of the reasons for the inhibition of growth [22,23]. Based upon the above possible phenomena, our present study reports the growth inhibition of Streptomyces, S. aureus and P. aeruginosa may be produced by the damage of the cell membrane. Enlarged antimicrobial image of ZnO-APTES-DGEBA nanocomposite film against Streptomyces shown in Fig. S1. 3.7. Antifungal behaviour of ZnO-APTES-DGEBA nanocomposites
Fig. 5. TGA curve of bare ZnO nanoparticles and ZnO-APTES-DGEBA nanocomposite film.
As per the literature survey there is limited studies carried out for antifungal activity of ZnO-APTES core shell nanoparticles. Fig. 6d, shows the inhibitory effect of ZnO-APTES core shell nanoparticles against the fungus A. niger. Herein, the maximum inhibition of fungal growth was achieved at 7 wt% and the Fig. 6d exhibits the increased concentration of ZnO-APTES core shell nanoparticles resulting in the decreased growth rate of A. niger. After 7 inoculation days, the fungal colonies were grown up only to extremity of the polymer fragment. Similar behaviour was observed at higher incubation times (14, 21, 28 and 60 days). In comparison, the samples containing 5%, 7 wt% ZnO-APTES core shell nanoparticles showed obvious inhibitory effects on fungal
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Fig. 6. Photographs of ZnO-APTES-DGEBA nanocomposite film against (a) Streptomyces; (b) Staphylococcus aureus; (c) Pseudomonas aeruginosa and (d) Aspergillus niger.
growth. Inhibition zone area of the fungus around the polymer nanocomposites increases with increasing concentration of ZnO-APTES core shell nanoparticles in polymer. The epoxy nanocomposites film having 7 wt% ZnO-APTES core shell nanoparticles display best inhibition zone, suggesting the mycotoxic effect of the zinc oxide. These aspects are in agreement with the previous observations [24].
3.8. Antimicrobial behaviour of bare ZnO nanoparticles The ability of bare ZnO inhibit the growth of tested strains is shown in Fig. 7. The microbial inhibitory activity was measured through zone of inhibition test. The result of this studies suggested that the inhibition zone of bare ZnO (3%) was enough to inhibit antibacterial and antifungal activity significantly towards test pathogens. The measured inhibitory zone values have been shown in Table 1. Bare ZnO nanoparticles shows better antimicrobial effect towards tested pathogens than ZnOAPTES-DGEBA nanocomposites. Enlarged antimicrobial image of bare ZnO nanoparticles against Streptomyces is shown in Fig. S2.
4. Conclusions A simple, rapid inexpensive method has been developed to prepare ZnO-APTES-DGEBA nanocomposites. The phase confirmation done using XRD analysis, there is considerable variation in 2θ, intensity and d-spacing for all the samples, which confirms the interaction of ZnOAPTES core shell nanoparticles with DGEBA bare epoxy resin. The results of FT-IR analysis suggest 3% ZnO-APTES-DGEBA nanocomposite is the best composition for grafting ZnO core shell nanoparticles compared to the other concentrations. The zone inhibition test results proved that the ZnO nanoparticles have potential to be used as an antimicrobial agent. The maximum inhibition growths for all microorganisms were achieved at 7 wt% of ZnO-APTES-DGEBA nanocomposite. From TGA measurements, 100 wt% residue is obtained in bare sample whereas ZnO grafted DGEBA residue percentage are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. These results have been confirmed with the ICP-OES results which shows 0.0, 0.264, 0.322, 0.431 and 0.583 mg/l of zinc ion concentration for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively. In this study, the antifungal
Table 1 Antibacterial activity of ZnO-APTES-DGEBA nanocomposites and bare ZnO nanoparticles. Pathogen name
Pseudomonas aeruginosa Staphylococcus aureus Streptomyces Aspergillus niger
ZnO-APTES-DGEBA nanocomposites (mm)
Bare ZnO nanoparticles (mm)
1 wt%
3 wt%
5 wt%
7 wt%
1 wt%
3 wt%
5 wt%
7 wt%
– – – –
6 – 6 3
7 – 7 6
8 – 9 11
9 – – 12
10 – – 12
10 – 7 13
11 6 8 14
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Fig. 7. Photographs of bare ZnO nanoparticles against (a) Streptomyces; (b) Staphylococcus aureus; (c) Pseudomonas aeruginosa and (d) Aspergillus niger.
behaviour against A. niger for a set of ZnO-APTES core shell nanoparticles based nanocomposites was envisaged. The presence of fungi growth was observed for the 1 and 3 wt% ZnO-APTES-DGEBA nanocomposites but inhibition was observed at 5 and 7% ZnO-APTES-DGEBA nanocomposites. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.msec.2016.03.096. References [1] F. Porter, Zinc Handbook: Properties, Processing and Use in Design, CRC Press, Boca Raton, FL, 1991. [2] M. Li, S. Pokhrel, X. Jin, L. Madler, R. Damoiseaux, E.M. Hoek, Environ. Sci. Technol. 45 (2011) 755. [3] A.J. Huh, Y.J. Kwon, J. Control. Release 156 (2011) 128. [4] D.W. Bahnemann, C. Kormann, M.R. Hoffmann, J. Phys. Chem. 91 (1987) 3789. [5] P.K. Stoimenov, R.L. Klinger, G.L. Marchin, Langmuir 18 (2002) 6679. [6] D. Zvekic, V.V. Srdic, M.A. Karaman, M.N. Matavulj, Processing and Application of Ceramics, 52011 41. [7] C. Guo, Z. Zheng, Q. Zhu, X. Wang, Polym. Plast. Technol. 46 (2007) 1161. [8] R.H. Wang, J.H. Xin, X.M. Tao, W.A. Daoud, Chem. Phys. Lett. 398 (2004) 250. [9] R.H. Wang, J.H. Xin, X.M. Tao, Inorg. Chem. 44 (2005) 3926. [10] R.K. Dutta, P.K. Sharma, A.C. Pandey, Dig. J. Nanomater. Bios. 4 (2009) 83.
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