Photochemical Deposition of Silver Nanoparticles on Clays and

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Photochemical Deposition of Silver Nanoparticles on Clays and Exploring Their Antibacterial Activity Patrícia C. Lombardo, Alessandra L. Poli, Lucas F. Castro, Janice R. Perussi, and Carla C. Schmitt* Instituto de Química de São Carlos, Universidade de São Paulo, Caixa Postal 780, 13560-970 São Carlos SP, Brazil

ABSTRACT: Photochemical method was used to synthesize silver nanoparticles (AgNPs) in the presence of citrate or clay (SWy-1, SYn-1, and Laponite B) as stabilizers and Lucirin TPO as photoinitiator. During the photochemical synthesis, an appearance of the plasmon absorption band was seen around 400 nm, indicating the formation of AgNPs. X-ray diffraction results suggested that AgNPs prepared in SWy-1 were adsorbed into interlamellar space, and moreover, showed some clay exfoliation. In the case of SYn-1, AgNPs was not intercalated. For the AgNP/Lap B sample, the formation of an exfoliated structure occurred. Transmission electron microscopy revealed the spherical shape of AgNPs for all samples. The particle sizes obtained for AgNP/ SWy-1, AgNP/SYn-1, and AgNP/Lap B were 2.6, 5.1, and 3.8 nm, respectively. AgNPs adsorbed on SYn-1 reveal nonuniform size and aggregation of some particles. However, AgNP/SWy-1 and AgNP/Lap B samples are more uniform and have diameters smaller than those prepared with SYn-1. This behavior is due to the ability to exfoliate these clays. The antibacterial activities of pure clays, AgNP/citrate, and AgNP/clays were investigated against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). AgNPs in the presence of clays (AgNPs/SYn-1 and AgNPs/SWy-1) showed a lower survival index percentage compared to those obtained for pure clays and AgNPs. The AgNP/SWy-1 sample showed good antibacterial activity against both tested species and the lowest survival index of 3.9 and 4.3 against E. coli and S. aureus, respectively. AgNPs are located in the interlayer region of the SWy-1, which has acid sites. These acidic sites may contribute to the release of Ag+ ions from the surface of AgNPs. On the other hand, Laponite B and AgNP/Lap B samples did not demonstrate any bactericidal activity. KEYWORDS: silver nanoparticles (AgNPs), clay, nanocomposites, UV irradiation, antibacterial activity obtain AgNPs.7 Like some examples, synthesis of AgNPs in the presence of kaolinite and montmorillonite can result in small AgNPs or Ag clusters in the interlayer region, as well as larger nanoparticles on the outer surface of clay.7,15−17 In the present paper, a fast photochemical synthesis of AgNPs by using citrate and/or clays such as SWy-1, SYn-1, and Laponite B was studied. The obtained samples were characterized by UV−vis, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Finally, the antibacterial activities of materials were investigated against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).

1. INTRODUCTION Silver nanoparticles (AgNPs) have been studied in recent years because of their strong surface plasmon absorption in the visible region. However, this property depends on the size and type of AgNPs, which influences their application such as antimicrobial materials,1 photocatalysis,2 and optoelectronics.3 Consequently, several methods have been reported for AgNPs preparation including reduction of silver nitrate with sodium borohydride, formaldehyde, UV irradiation,4−8 or photochemical synthesis.9,10 Moreover, to promote a homogeneity of colloidal dispersion and avoid the agglomeration between AgNPs polymers,11 surfactants and citrate12 are added. AgNPs can also be prepared by using clay dispersed in a solvent.8,13,14 This synthesis occurs within the clay because Ag+ ions penetrate the interlamellar regions of clay, which are also used for AgNPs’ growth inhibition during the reduction of silver. In this synthesis, clay layers behave as nanoreactors to © 2016 American Chemical Society

Received: May 3, 2016 Accepted: August 3, 2016 Published: August 3, 2016 21640

DOI: 10.1021/acsami.6b05292 ACS Appl. Mater. Interfaces 2016, 8, 21640−21647

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ACS Applied Materials & Interfaces

XRD was measured using a Bruker, D8 Advance diffractometer (Bruker, DEU) (Cu Kα radiation = 1.54 Å) in an angular range of 3°− 120° (2θ) with a 0.03° (2θ) step. The basal spacing of the samples was calculated using Bragg’s equation.20 FEI-TECNAI G2 -F20 microscope (FEI, Hillsboro, OR) equipped with an energy dispersive spectrometer (TECHNA, ITA) was used to obtain scanning transmission electron microscopy (STEM) images. Samples were drop-casted onto carbon-coated Cu minigrids (CF-200 Cu, Electron Microscopy Sciences, Hatfield, PA). The particle size distribution was estimated based on TEM micrographs using ImageJ software. 2.4. Effect on the Bacteria Survival. Antimicrobial activity of the samples (AgNPs, clays, and AgNP/clay) were determined against the methicilin-resistant Staphylococcus aureus (MRSA) (ATCC 33591) and Escherichia coli (ATCC 25922) using the 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay21 to count the number of live bacteria after the treatment. Bacteria density was standardized at 1.5 × 108 colony-forming units (CFU)/mL. Cultures (100 μL) were incubated with AgNPs (50 μL) and Muller Hinton broth (50 μL) for 24 h at 37 °C under orbital shaking. The control was performed incubating the bacteria with 50 μL of phosphate buffered saline (PBS). After incubation, the samples were centrifuged for 10 min at 1300 rpm and 50 μL of MTT (2 mg/ mL) was added to the precipitate. The samples were incubated at 37 °C for 30 min to allow reduction of MTT to purple formazan by live bacteria, and then the samples were centrifuged for 5 min at 6000 rpm. To solubilize the crystals, 50 μL of ethanol and 150 μL of a mixture containing PBS and isopropanol 1:1 were added. Survival index was determined colorimetrically by reading the absorbance at 560 nm measured on a plate reader (Benchmark, BIO-RAD, Hercules, CA). The experiments were performed in triplicate.

2. EXPERIMENTAL SECTION 2.1. Materials. Lucirin TPO (diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide) (Aldrich, St. Louis), silver nitrate (TEC-LAB, Brazil), and sodium citrate (J.T. Baker, Mexico) were used as received. The SWy-1 and SYn-1 montmorillonites were purchased from Source Clays Repository of the Clay Minerals Society, University of Missouri, Columbia, MO. The structural formulas of these samples are described by the Source Clays Repository as follows: M +0.61 [Al3.01Fe(III)0.41Mn0.01Mg0.54 Ti0.02][Si7.98Al0.02]O20(OH)4 for SWy-1 and (Mg 0.06 Ca0.04 Na0.12Ktr) [Al3.99Fe(III)trMntrTitr][Si6.50 Al1.50]O20(OH)4 with an unbalanced charge of 1.17 for SYn-1. Laponite B (Lap B) was obtained from Laporte Industries (Luton, U.K.), Na+0.7 [(Si8Mg5.5Li0.3)O20(OH)2.5F1.5]. The clays were purified as described elsewhere.18 2.2. Methods. AgNPs with citrate (AgNP/citrate) were prepared from the aqueous/methanol solution (90:10) of Lucirin TPO (0.2 mmol L−1), AgNO3 (0.2 mmol L−1), and citrate (1 mmol L−1). AgNPs with clay (AgNP/clay) were synthesized by using either SWy-1, SYn-1, or Lap B suspensions in Millipore water (1 g L−1), which were previously stirred for 24 h. A clay suspension with a concentration of 0.1 g L−1 was prepared by dilution of the former one. The final mixture was composed by Lucirin TPO (0.2 mmol L−1), AgNO3 (0.2 mmol L−1), and clay (0.1 g L−1). The silver nanoparticles were prepared by using a photochemical method. Before the synthesis all the samples were purged with nitrogen for 30 min. Then the solutions were placed in a UV light irradiation chamber containing eight UV germicidal lamps at 25 °C for 60 min. The lamps’ emission, at the sample position, was 254 nm and 584 mW m−2, and was measured with a SPR-01 Spectroradiometer (Luzchem, Ottawa, Ontario, Canada). The emission spectrum of the lamps and the absorption spectra of the Lucirin TPO are shown in Figure 1.

3. RESULTS AND DISCUSSION 3.1. Synthesis and Characterization of AgNP/Citrate. Figure 2a shows UV−vis spectra of Lucirin TPO (0.2 mmol L−1), AgNO3 (0.2 mmol L−1), and citrate (1 mmol L−1) solution as a function of irradiation time. During the irradiation, it is possible to observe the appearance of the plasmon absorption band around 400 nm, indicating the formation of nanoparticles. In the case of AgNPs smaller than 100 nm and with spherical morphology, the absorption band is usually located around 400−450 nm of the UV−vis spectrum.10,22 After irradiation, Lucirin TPO can undergo Norrish I cleavage to generate diphenylphosphine oxide radical and 2,4,6-trimethylbenzoyl radical.23 The radicals can promote the redox process, generating AgNPs and cationic form of radicals as shown in Scheme 1. Yagci et al. described the reduction of Cu(II) to Cu(I) by photochemical method using Lucirin TPO. The authors showed that the phosphonyl radical is responsible for the reduction process, and the benzoyl radicals, produced in the photo cleavage Lucirin TPO, do not suffer significant redox reactions.24 On the other hand, Zaarour et al. and Jradi et al. proposed that the reduction of silver can occur from benzoyl radical.25,26 Figure 2b shows the particle size distribution of AgNP/ citrate, obtained after 60 min of UV irradiation, in percentage of particle volume. AgNP/citrate present a bimodal particle size distribution with modal diameters centered at 12 and 72 nm. However, 93% of the population consists of particle size of 12 nm. Figure 2c−e show that spherical and stable AgNPs/citrate, 3 nm, were obtained. Stabilization of nanoparticles occurs due to the presence of citrate ions adsorbed on the surface of AgNPs

Figure 1. Emission spectra of the irradiating UV lamp and absorption spectra of the Lucirin TPO.

2.3. Characterization. The synthesis of AgNPs was followed by UV−vis analysis as a function of irradiation time. UV−vis measurements were recorded in a Shimadzu UV-2550 Spectrophotometer (Shimadzu, Kyoto, Japan) in the range of 300−600 nm. Dynamic light scattering (DLS) analyses were performed using a Zetasizer Nano ZS analyzer (Malvern Instruments, Malvern, Worcestershire, U.K.). DLS measures the autocorrelation of the temporal fluctuations of the intensity of scattered light due to Brownian motion of the particles and colloids. Correlation function denotes the measured scatter. This function is used to obtain translational diffusion coefficient by fitting method called cumulant analysis. Average hydrodynamic diameter (dH) can be obtained from translational diffusion coefficient by Stokes−Einstein equation. Further information about the technique can be found in another work.19 The DLS particle size estimations were made at fixed 173° backscattered He−Ne laser light with a wavelength λ = 633 nm. All measurements were made at 25 °C. The calculations were done using Malvern’s DTS software. All samples were analyzed in triplicate. 21641


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Figure 2. (a) Absorption spectra as a function of irradiation time, (b) particle size distribution in percentage of particle volume (DLS measurements), (c, d) dark field transmission electron micrographs of AgNP/citrate, and (e) particle size distribution estimated from TEM images.

Scheme 1. Synthesis of AgNPs by Photochemical Method

Figure 3. (a) Absorption spectra as a function of UV irradiation time for AgNP/SWy-1, (b) AgNP/SYn-1, and (c) AgNP/Lap B.

Lap B showed plasmon absorption band at 408, 402, and 400 nm, respectively, indicating that AgNPs stabilized by SYn-1 clay have a larger diameter than those stabilized by the SWy-1 and Lap B clays. These results corroborate with Slistan-Grijalva et al. theoretical calculations of AgNPs absorbance that showed the position of plasmon absorption band shifts to longer wavelengths with increasing particle radius.29

that create electrostatic repulsion between them and prevent their aggregation.27,28 3.2. Synthesis and Characterization of AgNP/Clay. The synthesis of AgNPs stabilized with different clays were followed by UV−vis spectra (Figure 3a−c), which show that in the presence of clay the plasmon absorption band occurs around 400−408 nm. The nanoparticles obtained in SYn-1, SWy-1, and 21642


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Figure 4. Particle size distribution in percentage of particle volume (DLS measurements) for (a) SWy-1 and AgNP/SWy-1, (b) SYn-1 and AgNP/ SYn-1, and (c) Lap B and AgNP/Lap B.

Figure 5. X-ray diffraction for (a, d) SWy-1 and AgNP/SWy-1; (b, e) SYn-1 and AgNP/SYn-1; (c, f) Laponite B and AgNP/Lap B.

changes in the interlayer spacing values of clay after silver photoreduction, indicating that AgNPs are not intercalated in the interlayer region of the clay (Figure 5b).30 For the AgNP/Lap sample, the clay peak at 2θ = 6.4° disappeared, suggesting formation of an exfoliated structure (Figure 5c).30 As shown in Figure 5d−f, all AgNP/clay samples present peaks at 2θ = 38.2°, 44.4°, 64.7°, and 77.6° attributed to the (111), (200), (220), and (311) crystallographic planes, respectively; therefore, silver crystals are face-centered cubic (fcc).32,33 The size of silver nanoparticles were calculated using Scherrer’s equation from (111) reflection peak in the XRD.34 The particle sizes obtained from XRD for AgNP/SWy-1, AgNP/SYn-1, and AgNP/Lap B samples were 3.3, 5.4, and 2.8 nm, respectively (Table 1).

DLS was used to determine the diameter of AgNP/clay particles and the results are shown in Figure 4a−c. As one can see in Figure 4a, SWy-1 clay shows a bimodal particle size distribution with 92% of particle size population centered at 668 nm and 8% at 129 nm. AgNPs/SWy-1, that is, AgNPs absorbed on the surface of SWy-1 clay, has 94% of population at 1082 nm and 6% at 122 nm. SYn-1 clay shows modal diameter centered at 413 nm (Figure 4b), and particle bimodal diameters of AgNP/SYn-1 samples are at 372 and 58 nm, which can be associated with AgNPs in SYn-1 suspension and AgNPs, respectively. Lap B clay shows a single population at 37 nm, and AgNP/ Lap B reveals the particle size distribution with two populations: at 20 and 96 nm (Figure 4c). The population of smaller diameter (20 nm) can be attributed to the formation of AgNPs, and the population at 96 nm can be attributed to AgNPs adsorbed onto the clay surface. The crystal structure and size of the AgNPs prepared on SWy-1, SYn-1, and Lap B clays were estimated using XRD analysis. Figure 5 shows the XRD of pristine clays and AgNP/ clay samples. As can be observed in Figure 5a, SWy-1 clay showed a signal at 2θ = 7.6°, which corresponds to an interlamellar spacing value of 11.6 Å. After nanoparticles formation, the clay peak (d001) intensity decreases and is shifted to smaller 2θ (2θ = 4.1°) value resulting in a new interlamellar spacing of 21.5 Å. This suggests the occurrence of intercalation along with some clay exfoliation.30 Ag+ ions can be adsorbed not only on the external surface and edges of clay but also in the interlamellar space. The nanoparticles formed may cause an increase in clay interlamellar spacing. Moreover, the intensity of the peaks of clay after AgNPs synthesis are significantly lower and wider than pure clays, indicating that the ordered structure of the clay is disturbed by nanoparticle formation.31 In the case of the AgNP/SYn-1 sample, the clay peak intensity at 2θ = 7.9° decreases; however, there were no

Table 1. Particle Diameter Obtained by XRD, DLS, and TEM particle diameter (nm) samples AgNP/citrate AgNP/SWy-1 AgNP/SYn-1 AgNP/Lap B

XRD 3.3 5.4 2.8

TEM 3.0 (±0.1) 2.6 (±0.1) 5.1 (±0.3) 3.80 (±0.02)

DLS 12.0 (±0.2) 58.0 (±1.6) 20.0 (±1.1)

It is worth noting that the diameters of AgNPs obtained by DLS are different from those estimated using the XRD and TEM techniques (Table 1). These differences are expected since the TEM and XRD measurements are performed with the sample in the solid state, while in the DLS the particle size measurements are made in the hydrated state. Thus, it is possible to assume that the size measured by TEM and XRD is the real size of AgNPs since DLS measures the hydrodynamic diameter, which exhibits overestimated value. 21643


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Figure 6. Dark field transmission electron micrographs and particle size distribution estimated from TEM images of (a−c) AgNP/SWy-1, (d−f) AgNP/SYn-1, and (g−i) AgNP/Lap B.

Figure 6 presents TEM images for AgNPs/clay samples, where one can observe small white spots attributed to the AgNPs. The images show that the nanoparticles are mainly located in clay (gray irregular shape), which is clearly visible for the samples of AgNP/SWy-1 (Figure 6a), AgNP/SYn-1 (Figure 6d), and AgNP/Lap B (Figure 6g). Moreover, it is observed that the AgNPs exhibited spherical morphology independent of the clay used for their synthesis. The particle sizes obtained from TEM for AgNP/SWy-1, AgNP/SYn-1, and AgNP/Lap B were 2.6, 5.1, and 3.8 nm, respectively (Table 1). AgNPs adsorbed on SYn-1 (Figure 6e) reveal nonuniform size and aggregation of some particles. However, AgNP/SWy-1 and AgNP/Lap B samples present uniform and smaller diameters (Figure 6b,h) than those prepared with SYn-1 (Figure 6f). The particle size distribution plot of these samples is narrower (Figure 6c,i. This behavior may occur due to exfoliation of SWy-1 and Lap B clays observed by XRD results. SWy-1 and Laponite has the ability to

exfoliate; small particles, consequently, showed good results as stabilizers of AgNPs. AgNPs were generated quickly, after 60 min of the UV irradiation, in the presence of photoinitiator. Some papers, which focus on the synthesis of AgNPs by UV irradiation in the presence of clays and without any photoinitiator are found. However, the nanoparticles are obtained after many hours of irradiation (approximately 3−96 h) and have broad distribution and larger sizes than those presented in this paper.8,35,36 3.3. Antibacterial Activity. The antibacterial activities of the pure clays, AgNP/citrate, and AgNP/clay samples were investigated against E. coli and S. aureus bacteria. The results of the survival index percentage against E. coli and S. aureus bacteria are given in Figure 7. Figure 7 shows that AgNP/citrate, SWy-1, and SYn-1 samples led to a decrease of the survival index for E. coli and S. aureus, which evidence slight antibacterial effect. This can be a result of AgNPs interaction with the aqueous phase, which promotes an oxidative release of Ag+ ions from 21644


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Figure 7. Survival index of E. coli and S. aureus bacteria incubated for 24 h at 37 °C under orbital shaking with AgNP/citrate, clays, and AgNP/clay samples.

AgNPs surface. Therefore, the antimicrobial mechanism of Ag+ ions action involves a linking of Ag+ ions to the functional groups of proteins and enzymes promoting the inactivation and inhibition of cell process.37 Under physiological conditions, the cell wall is negatively charged due to carboxyl, phosphate, and hydroxyl groups present on the surface of lipoproteins.37 On the other hand, pure clay dispersed in water exhibits negative charge. Consequently, bacteria would not be significantly attracted by clay, and that justifies the slight antibacterial activity of clay.38 Similar results were obtained by Hu and Xia, who studied the antibacterial activity of the montmorillonites on Escherichia coli K88. They observed that MMT showed some ability to reduce the bacterial counts.39 AgNPs/SYn-1 and AgNPs/SWy-1 showed an effect on CFU; however, a much lower survival index, especially for AgNPs/ SWy-1 compared to those obtained for pure clay and AgNP/ citrate (Table 2). Moreover, the AgNP/SWy-1 sample showed

Figure 8. Absorption spectra as a function of time for (a) AgNP/ citrate, (b) AgNP/SWy-1, (c) AgNP/SYn-1, and (d) AgNP/Lap B.

concentration adsorbed on AgNPs, and can be calculated according to the relation developed by Henglein (eq 1).40 1/2 ⎛ [Ag +] ⎞ λ = λ 0 ⎜1 + ⎟ [Ag] ⎠ ⎝

where λ0 and λ are wavelengths for zero concentration of Ag+ ions and for Ag+ ions concentration at t time, respectively. Silver concentration in the colloid, [Ag], is assumed as the precursor concentration used in the synthesis (0.2 mmol L−1) and [Ag+] is oxidized silver (Ag+ ions release from the AgNPs). Table 3 shows Ag+ ions concentration released into solution for different samples after 1 and 30 days.

Table 2. Survival Index for the Bacteria after Incubation with AgNPs, Clay, and AgNPs/Claya E. coli control AgNP/citrate Lap_B SYn-1 SWy-1 AgNP/Lap B AgNP/SYn-1 AgNP/SWy-1

100 83.0 122.3 75.9 68.1 119.8 65.3 3.9

± ± ± ± ± ± ± ±

0 4.6 35.5 0.6 1.8 9.7 4.5 0.1

Table 3. Ag+ Ions Concentration into Solution after 1 day and 30 days

S. aureus 100 71.5 147.2 67.8 91.4 109.2 66.6 4.3

± ± ± ± ± ± ± ±

(1)

0 6.5 30.9 1.9 12.1 23.1 7.8 0.1

[Ag+] (μmol L−1) samples

λo (nm)

λ (nm)

after 1 day

after 30 days

AgNP/citrate AgNP/SWy-1 AgNP/SYn-1 AgNP/Lap B

401 402 408 400

408 419 420 411

6.0 11.1 7.9 10.1

7.0 17.3 11.9 11.2

a

To obtain the experimental error, three independent experiments were carried out, and the mean value was used.

The highest Ag+ ions concentration released in the medium after 1 day and 30 days was obtained for AgNPs supported on SWy-1 clay (Table 3). These results of release may justify the strong antibacterial activity exhibited by the AgNP/SWy-1 sample. This good antibacterial activity of the AgNPs/SWy-1 material may be due to SWy-1 clay properties. In the case of SWy-1, AgNPs are located in the interlayer region of the clay (Figure 5a), which has acid sites.41 The presence of acidic sites on the clay interlayer region may contribute to the release of Ag+ ions from the surface of AgNP. Release studies showed that oxidation from Ag0 to Ag+ is dependent on oxygen and H+, so favored in acidic media.42 Moreover, the presence of interlamellar spaces on clay or the intercalation degree promotes a release mechanism of Ag+ by diffusion control.36 The structure in stacked parallel layers of

good antibacterial activity against both tested species and the lowest survival index of 3.9 and 4.3 against E. coli and S. aureus, respectively. The results of the antibacterial activity can be better understood by studying the release of Ag+ ions of the samples since antimicrobial action mechanism involves Ag+ ions. The release of Ag+ ions as a function of time can be estimated by UV−vis analysis. Figure 8 shows changes in the UV−vis spectra of the samples as a function of time. It was observed for all samples, a shift of the peak wavelength to longer wavelengths promoted by the oxidation of silver. The adsorption of Ag+ ions on AgNPs shifts the wavelength of the maximum absorption. The Ag+ ions concentration released is considered proportional to the Ag + ions 21645


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enhanced Raman Spectroscopy (SERS): Improvements in Surface Nanostructure Stability and Suppression of Irreversible Loss. J. Phys. Chem. B 2002, 106, 853−860. (4) Wojtysiak, S.; Kudelski, A. Influence of Oxygen on the Process of Formation of Silver Nanoparticles during Citrate/Borohydride Synthesis of Silver Sols. Colloids Surf., A 2012, 410, 45−51. (5) Chhatre, A.; Solasa, P.; Sakle, S.; Thaokar, R.; Mehra, A. Color and Surface Plasmon Effects in Nanoparticle Systems: Case of Silver Nanoparticles Prepared by Microemulsion Route. Colloids Surf., A 2012, 404, 83−92. (6) Praus, P.; Turicová, M.; Machovič, V.; Š tudentová, S.; Klementová, M. Characterization of Silver Nanoparticles Deposited on Montmorillonite. Appl. Clay Sci. 2010, 49, 341−345. (7) Patakfalvi, R.; Dékány, I. Synthesis and Intercalation of Silver Nanoparticles in Kaolinite/DMSO Complexes. Appl. Clay Sci. 2004, 25, 149−159. (8) Huang, H.; Yang, Y. Preparation of Silver Nanoparticle in Inorganic Clay Suspensions. Compos. Sci. Technol. 2008, 68, 2948− 2953. (9) Maretti, L.; Billone, P. S.; Liu, Y.; Scaiano, J. C. Facile Photochemical Synthesis and Characterization of Highly Fluorescent Silver Nanoparticle. J. Am. Chem. Soc. 2009, 131, 13972−13980. (10) Stamplecoskie, K. G.; Scaiano, J. C. Light Emitting Diode Irradiation Can Control the Morphology and Optical Properties of Silver Nanoparticles. J. Am. Chem. Soc. 2010, 132, 1825−1827. (11) Dong, R.-X.; Tsai, W.-C.; Lin, J.-J. Tandem Synthesis of Silver Nanoparticles and Nanorods in the Presence of Poly(Oxyethylene)Aminoacid Template. Eur. Polym. J. 2011, 47, 1383−1389. (12) Chadha, R.; Maiti, N.; Kapoor, S. Reduction and Aggregation of Silver Ions in Aqueous Citrate Solutions. Mater. Sci. Eng., C 2014, 38, 192−196. (13) Su, H.-L.; Lin, S.-H.; Wei, J.-C.; Pao, I.-C.; Chiao, S.-H.; Huang, C.-C.; Lin, S.-Z.; Lin, J.-J. Novel Nanohybrids of Silver Particles on Clay Platelets for Inhibiting Silver-Resistant Bacteria. PLoS One 2011, 6, e21125. (14) Miyoshi, H.; Ohno, H.; Sakai, K.; Okamura, N.; Kourai, H. Characterization and Photochemical and Antibacterial Properties of Highly Stable Silver Nanoparticles Prepared on Montmorillonite Clay in n-Hexanol. J. Colloid Interface Sci. 2010, 345, 433−441. (15) Belova, V.; Möhwald, H.; Shchukin, D. G. Sonochemical Intercalation of Preformed Gold Nanoparticles into Multilayered Clays. Langmuir 2008, 24, 9747−9753. (16) Ayyappan, S.; Subbanna, G. N.; Gopalan, R. S.; Rao, C. N. R. Nanoparticles of Nickel and Silver Produced by the Polyol Reduction of the Metal Salts Intercalated in Montmorillonite. Solid State Ionics 1996, 84, 271−281. (17) Hata, H.; Kobayashi, Y.; Salama, M.; Malek, R.; Mallouk, T. E. pH-Dependent Intercalation of Gold Nanoparticles into a Synthetic Fluoromica Modified with Poly(Allylamine). Chem. Mater. 2007, 19, 6588−6596. (18) Gessner, F.; Schmitt, C. C.; Neumann, M. G. Time-Dependent Spectrophotometric Study of the Interaction of Basic Dyes with Clays. I. Methylene Blue and Neutral Red on Montmorillonite and Hectorite. Langmuir 1994, 10, 3749−3753. (19) Santiago, P. S.; Moura, F.; Moreira, L. M.; Domingues, M. M.; Santos, N. C.; Tabak, M. Dynamic Light Scattering and Optical Absorption Spectroscopy Study of pH and Temperature Stabilities of the Extracellular Hemoglobin of Glossoscolex paulistus. Biophys. J. 2008, 94, 2228−2240. (20) Callister, W. D. Materials Science and Engineering: An Introduction; Wiley: New York, 2000. (21) Stevens, M. G.; Olsen, S. C. Comparative Analysis of Using MTT and XTT in Colorimetric Assays for Quantitating Bovine Neutrophil Bactericidal Activity. J. Immunol. Methods 1993, 157, 225− 231. (22) Dehnavi, A. S.; Aroujalian, A.; Raisi, A.; Fazel, S. Preparation and Characterization of Polyethylene/Silver Nanocomposite Films with Antibacterial Activity. J. Appl. Polym. Sci. 2013, 127, 1180−1190.

SWy-1 along with small size of AgNP favors antimicrobial activity of the material. On the other hand, Laponite B and AgNP/Lap B samples did not demonstrate any bactericidal activity. Consequently, the Laponite can be considered as inactive because the results suggest a slight increase in the number of bacteria (multiplication) in the presence of this clay.43,44 These results are similar to Ghadiri et al.,45 who studied the antimicrobial efficiency and cytotoxicity of Laponite clay. In their study, the Laponite did not show any antimicrobial property to the E. coli, Pseudomonas aeruginosa, and S. aureus bacteria, as well as no cytotoxic effect on fibroblast cells. Moreover, the authors noted an increase in the number of fibroblasts in the presence of Laponite.

4. CONCLUSION AgNPs were synthesized in SWy-1, SYn-1, Lap B, and citrate solutions by photochemical method using Lucirin TPO as photoinitiator. This methodology was a good tool to obtain AgNPs quickly. AgNP/citrate were observed by the appearance of the plasmon absorption band around 400 nm. Electron microscopy revealed AgNPs with spherical morphology. AgNPs adsorbed on SYn-1 reveal nonuniform size and aggregation of some particles. However, AgNP/SWy-1 and AgNP/Lap B samples are more uniform and have diameters smaller than those prepared with SYn-1. This behavior is due to the ability to exfoliate these clays. The AgNP/SWy-1 sample showed strong antibacterial activity against E. coli and S. aureus, for both Gram-negative and Gram-positive bacteria. It is well-known that it is more difficult to kill Gram-negative bacteria with any method so this is a very important result with clinical significance. The highest Ag+ ions concentration released in the medium was obtained for AgNPs supported on SWy 1-clay. These results of release justify the strong antibacterial activity exhibited by the AgNP/ SWy-1 sample. In summary, uniform and small size AgNPs can be prepared by fast (up to 60 min) photochemical synthesis by using clays. The structure in stacked parallel layers of SWy-1 along with a small size of AgNP favors antimicrobial activity of the material.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: 55-16-3373-8685. E-mail: [email protected] (C.C.S.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank FAPESP (2012/19656-0) and CNPq (490421/2013-0 and 308940/2013-0) for financial support and P. C. Lombardo also thank CAPES for a graduate fellowship. The authors are grateful to Prof. Ernesto R. Gonzales for assistance with DLS experiments.

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REFERENCES

(1) Dubas, S.; Kumlangdudsana, P.; Potiyaraj, P. Layer-by-Layer Deposition of Antimicrobial Silver Nanoparticles on Textile Fibers. Colloids Surf., A 2006, 289, 105−109. (2) Takai, A.; Kamat, P. V. Capture, Store, and Discharge. Shuttling Photogenerated Electrons across TiO2-Silver Interface. ACS Nano 2011, 5, 7369−7376. (3) Dick, L. A.; McFarland, A. D.; Haynes, C. L.; Van Duyne, R. P. Metal Film over Nanosphere (MFON) Electrodes for Surface21646


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ACS Applied Materials & Interfaces (23) Medsker, R. E.; Chumacero, M.; Santee, E. R.; Sebenik, A.; Harwood, H. J. 31P-NMR Characterization of Chain Ends in Polymers and Copolymers Prepared Using Lucirin TPO as a Photoinitiator. Acta Chim. Slov. 1998, 45, 371−388. (24) Yagci, Y.; Tasdelen, M. A.; Jockusch, S. Reduction of Cu(II) by Photochemically Generated Phosphonyl Radicals to Generate Cu(I) as Catalyst for Atom Transfer Radical Polymerization and Azide-Alkyne cycloaddition Click Reactions. Polymer 2014, 55, 3468−3474. (25) Zaarour, M.; El Roz, M.; Dong, B.; Retoux, R.; Aad, R.; Cardin, J.; Dufour, C.; Gourbilleau, F.; Gilson, J.-P.; Mintova, S. Photochemical Preparation of Silver Nanoparticles Supported on Zeolite Crystals. Langmuir 2014, 30, 6250−6256. (26) Jradi, S.; Balan, L.; Zeng, X. H.; Plain, J.; Lougnot, D. J.; Royer, P.; Bachelot, R.; Akil, S.; Soppera, O.; Vidal, L. Spatially Controlled Synthesis of Silver Nanoparticles and Nanowires by Photosensitized Reduction. Nanotechnology 2010, 21, 095605. (27) Yang, J.; Lee, J. Y.; Deivaraj, T. C.; Too, H.-P. A Highly Efficient Phase Transfer Method for Preparing Alkylamine-Stabilized Ru, Pt, and Au Nanoparticles. J. Colloid Interface Sci. 2004, 277, 95−99. (28) Tsuji, T.; Tsuji, M.; Hashimoto, S. Utilization of Laser Ablation in Aqueous Solution for Observation of Photoinduced Shape Conversion of Silver Nanoparticles in Citrate Solutions. J. Photochem. Photobiol., A 2011, 221, 224−231. (29) Slistan-Grijalva, A.; Herrera-Urbina, R.; Rivas-Silva, J. F.; Á valosBorja, M.; Castillón-Barraza, F. F.; Posada-Amarillas, A. Classical Theoretical Characterization of the Surface Plasmon Absorption Band for Silver Spherical Nanoparticles Suspended in Water and Ethylene Glycol. Phys. E 2005, 27, 104−112. (30) Xu, Y.; Ren, X.; Hanna, M. A. Chitosan/Clay Nanocomposite Film Preparation and Characterization. J. Appl. Polym. Sci. 2006, 99, 1684−1691. (31) Patakfalvi, R.; Oszkó, A.; Dékány, I. Synthesis and Characterization of Silver Nanoparticle/Kaolinite Composites. Colloids Surf., A 2003, 220, 45−54. (32) Coseri, S.; Spatareanu, A.; Sacarescu, L.; Rimbu, C.; Suteu, D.; Spirk, S.; Harabagiu, V. Green Synthesis of the Silver Nanoparticles Mediated by Pullulan and 6-Carboxypullulan. Carbohydr. Polym. 2015, 116, 9−15. (33) Movahedi, F.; Masrouri, H.; Kassaee, M. Z. Immobilized Silver on Surface-Modified ZnO Nanoparticles: As an Efficient Catalyst for Synthesis of Propargylamines in Water. J. Mol. Catal. A: Chem. 2014, 395, 52−57. (34) Ingham, B. X-Ray Scattering Characterisation of Nanoparticles. Crystallogr. Rev. 2015, 21, 229−303. (35) Darroudi, M.; Ahmad, M. B.; Shameli, K.; Abdullah, A. H.; Ibrahim, N. A. Synthesis and Characterization of UV-Irradiated Silver/ Montmorillonite Nanocomposites. Solid State Sci. 2009, 11, 1621− 1624. (36) Girase, B.; Depan, D.; Shah, J. S.; Xu, W.; Misra, R. D. K. SilverClay Nanohybrid Structure for Effective and Diffusion-Controlled Antimicrobial Activity. Mater. Sci. Eng., C 2011, 31, 1759−1766. (37) Sohrabnezhad, Sh.; Pourahmad, A.; Mehdipour Moghaddam, M. J.; Sadeghi, A. Study of Antibacterial Activity of Ag and Ag2CO3 Nanoparticles Stabilized Over Montmorillonite. Spectrochim. Acta, Part A 2015, 136, 1728−1733. (38) Herrera, P.; Burghardt, R. C.; Phillips, T. D. Adsorption of Salmonella Enteritidis by Cetylpyridinium-Exchanged Montmorillonite Clays. Vet. Microbiol. 2000, 74, 259−272. (39) Hu, C.-H.; Xia, M.-S. Adsorption and Antibacterial Effect of Copper-Exchanged Montmorillonite on Escherichia Coli K88. Appl. Clay Sci. 2006, 31, 180−184. (40) Henglein, A. Colloidal Silver Nanoparticles: Photochemical Preparation and Interaction With O2, CCl4, and Some Metal Ions. Chem. Mater. 1998, 10, 444−450. (41) Poli, A. L.; Batista, T.; Schmitt, C. C.; Gessner, F.; Neumann, M. G. Effect of Sonication on the Particle Size of Montmorillonite Clays. J. Colloid Interface Sci. 2008, 325, 386−390.

(42) Liu, J.; Hurt, R. H. Ion Release Kinetics and Particle Persistence in Aqueous Nano-Silver Colloids. Environ. Sci. Technol. 2010, 44, 2169−2175. (43) Hill, E. H.; Zhang, Y.; Whitten, D. G. Aggregation of Cationic pPhenylene Ethynylenes on Laponite Clay in Aqueous Dispersions and Solid Films. J. Colloid Interface Sci. 2015, 449, 347−356. (44) Maurin, V.; Croutxé-Barghorn, C.; Allonas, X.; Brendlé, J.; Bessières, J.; Merlin, A.; Masson, E. UV Powder Coatings Containing Synthetic Ag-Beidellite for Antibacterial Properties. Appl. Clay Sci. 2014, 96, 73−80. (45) Ghadiri, M.; Chrzanowski, W.; Rohanizadeh, R. Antibiotic Eluting Clay Mineral (Laponite®) for Wound Healing Application: An In Vitro Study. J. Mater. Sci.: Mater. Med. 2014, 25, 2513−2526.

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