CoreâShell AgCl@SiO2 Nanoparticles: Ag(I)-Based Antibacterial

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Core–Shell AgCl@SiO2 Nanoparticles: Ag(I)-Based Antibacterial Materials with Enhanced Stability Peng Tan, Yan-Hua Li, Xiao-Qin Liu, Yao Jiang, and Lin-Bing Sun ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00309 • Publication Date (Web): 03 May 2016 Downloaded from http://pubs.acs.org on May 7, 2016

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ACS Sustainable Chemistry & Engineering

Core–Shell AgCl@SiO2 Nanoparticles: Ag(I)-Based Antibacterial Materials with Enhanced Stability Peng Tan, Yan-Hua Li, Xiao-Qin Liu*, Yao Jiang, and Lin-Bing Sun* Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing Tech University, 5 Xinmofan Road, Nanjing 210009, China

*Corresponding author. E-mail: [email protected]; [email protected].

Keywords: silver chloride nanoparticles, antibacterial materials, light stability, one-pot synthesis, porous silica shell

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Abstract Silver (Ag)-based nanoparticles are one kind of highly effective antimicrobials widely used in medical devices, consumer products, and wound dressing. Although Ag(I) rather than Ag(0) are the active species in antibacterial processes, the use of Ag(I) as antibacterial materials is hindered by their instability towards light irradiation. In this paper, we report the fabrication of core–shell AgCl@SiO2 nanoparticles, which comprise a core of AgCl nanoparticles and a shell of porous silica, for antibacterial applications for the first time. The porous silica shells not only enhance the stability of AgCl by preventing the core from direct light irradiation, but also allow active Ag(I) to pass through continuously to inhibit the growth of bacteria. It is worth noting that the synthesis is achieved by a facile one-pot method in which the surfactant hexadecyltrimethylammonium chloride (CTAC) used for the formation of AgCl nanoparticles also acts as a structure-directing agent in subsequent creation of porous silica. Our results show that the obtained AgCl@SiO2 nanoparticles exhibit well-defined core–shell structure and are highly efficient in the growth inhibition of Escherichia coli (E. coli). More importantly, the stability of Ag(I) towards light irradiation is greatly enhanced by the protection of silica shell. The convenient fabrication, well-defined core–shell structure, and enhanced stability make AgCl@SiO2 nanoparticles highly promising for antibacterial applications.


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Introduction Life and health problems caused by bacterial surface contamination have troubled humans for many years.1-3 Adhered microbes on surfaces are difficult to kill since they can secrete exopolysaccharides and form a biofilm through continuous cell growth, which provides underlying microbes a preferable living environment.4-6 As a result, with the protection of biofilm matrix polymers, microbes cannot be directly attacked and destroyed by many natural and artificial chemical agents, which increases the risk of infection and has impacts on health medicine, food manufacturing, device failure, and so forth.7-10 Therefore, there is a significant interest in the development of antibacterial materials and surfaces which are efficient, low toxic, and long-acting. In the past decades, nanotechnology has a rapid development due to specific properties of nanoparticles such as large surface area and high responsiveness.11-15 Some functional nanoparticles have excellent biocompatibility and are highly potential for antibacterial applications.16,17 Among them, silver (Ag)-based nanoparticles are of extensive interest due to their good activity towards a broad range of bacteria as well as low toxic towards mammalian cells.18-21 It is believed that Ag(I) rather than Ag(0) are the main active species that inhibit the growth of bacteria, fungi, and viruses in antibacterial processes.22-24 Ag(0) on the surface of nanoparticles are firstly oxidized to Ag(I) by dissolved oxygen, and then disturb biochemical processes of cellular enzymes and DNA by coordinating to electron-donating groups since Ag(I) is a soft Lewis acid.25-28 By continuing to release Ag(I), these nanoparticles are active towards a broad range of bacteria. However, the indispensable oxidation process of these nanoparticles may cause a low releasing rate of Ag(I) in aqueous solution, resulting in their 3 ACS Paragon Plus Environment


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low antibacterial responsiveness and efficiency if used in an anaerobic environment.29-31 Therefore, if Ag(0) were substituted by sparingly soluble Ag(I) salts, the generation rate of Ag(I) would be greatly improved. Among various Ag(I) salts, AgCl is a preferable choice for antibacterial applications because it can provide a constant concentration of Ag(I) in aqueous solution [Ksp(AgCl) = 1.8×10−10, 25 oC]. However, the use of Ag(I) as antibacterial materials is significantly hindered by their instability towards light irradiation. It is therefore extremely desirable to develop AgCl antimicrobials with enhanced stability. Aiming to increase the stability, an interesting method has been employed by loading AgCl nanoparticles on silica and polymer supports.29,32,33 So far core−shell structured nanoparticles have never been employed for antibacterial applications, although the shell may play an important role in protecting the Ag(I) core. In this paper, we report the fabrication of core−shell AgCl@SiO2 antimicrobials by coating porous silica on AgCl nanoparticles for the first time (Figure 1). Highly biocompatible silica shell on one hand promotes the photo-stability of AgCl nanoparticles by preventing AgCl nanoparticles from direct light irradiation, and on the other hand provides channels for Ag(I) to pass through. The obtained materials are of excellent antibacterial performance on E. coli, and highly stable towards visible light. After recycling, these antimicrobials can be used repeatedly with a good antibacterial effect. Moreover, a facile one-pot method was employed for the synthesis of core−shell AgCl@SiO2 nanoparticles in which the surfactant hexadecyltrimethylammonium chloride (CTAC) acts as both the stabilizing agent in AgCl synthesis and the structure-directing agent for subsequent silica formation. Such a one-pot method not only reduces the operation procedures but decreases the production cost. The 4 ACS Paragon Plus Environment

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convenient synthesis, high antibacterial efficiency, and enhanced stability make AgCl@SiO2 nanoparticles highly promising for antibacterial applications.

Experimental Section Chemicals. Silver nitrate (AgNO3), sodium chloride (NaCl), hydrochloric acid (HCl), and ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd. Tetraethyl orthosilicate (TEOS) and CTAC were purchased from Aladdin Industrial Co., Ltd. E. coli was purchased from the Ministry of Health of the People’s Republic of China. All chemicals were used directly without further treatment. Deionized water was used for all of the experiments. Materials Synthesis. CTAC (0.0571 g, 0.18 mmol) was dissolved in water (97.0 mL) rapidly with vigorous stirring, followed by the addition of AgNO3 (1 mL, 0.5 mol L–1) and NaCl (1 mL, 0.5 mol L–1). After reaction for 3.5 h at 40 oC, AgCl nanoparticles were obtained. After the introduction of additional CTAC (0.0571 g, 0.18 mmol) as well as aqueous HCl (1 mL, 0.1 mol L–1), TEOS (6.2 mL) was added dropwise to the solution. After reaction for 12 h at 40 oC, the solid products AgCl@SiO2 were washed with ethanol three times. The surfactant CTAC was removed by extraction with ethanol. Materials Characterization. X–ray diffraction (XRD) patterns of the materials were recorded on a Bruker D8 Advance diffractometer with Cu Kα radiation in the 2θ range from 20o to 80o at 40 kV and 40 mA. Transmission electron microscopy (TEM) was performed on a JEM-200CX electron microscope operated at 200 kV. Scanning electronic microscopy (SEM) images were recorded on a Quanta200 electron microscope operating at 20 kV. The N 2 adsorption−desorption isotherms were measured using an ASAP2020 system at –196 oC. Prior



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to analysis, samples were evacuated at 100 oC for 2 h. The Brunauer–Emmett–Teller (BET) surface area was calculated at relative pressure ranging from 0.04 to 0.20. The total pore volume was derived from the amount adsorbed at a relative pressure of about 0.99. The pore size distributions were calculated from the adsorption isotherms by the density functional theory (DFT) method. Fourier transform infrared (IR) spectra were recorded on a Nicolet Nexus 470 spectrometer with KBr wafer. Diffuse reflectance UV-visible (UV-vis) spectra of the materials were recorded using a UV-2401PC spectrophotometer, and BaSO4 was used as an internal standard. The concentration of Ag(I) was measured on an inductive coupled plasma mass spectrometer (ICP-MS, Optima 5300DV). Stability tests were carried out by exposing antimicrobials to visible light for 2 h followed by the analysis using various techniques including XRD, UV-vis, and digital photographs. Antibacterial Tests. The antibacterial tests of AgCl nanoparticles and AgCl@SiO2 nanoparticles against E. coli (ATCC25922) were performed by the plate counting method according to the Technical Standard for disinfection. The bacterial suspensions employed for the tests contained ~107 colony forming units (CFU) per mL. Agar medium, fluid nutrient medium and phosphate buffer (PBS) were sterilized at 121 oC for 15 min in advance. AgCl@SiO2 nanoparticles (0.01 g) were mixed with PBS (1 mL) containing bacteria, followed by incubated at 37 oC for 6 h with gentle vibrating, and then gradient diluted with PBS solution. 0.1 mL of the above suspension was extracted and spread on an agar plate and cultured at 37 oC for 48 h. The number of discrete colonies was counted as the number of the remaining bacteria. Blank experiment was also conducted through the same process. The degree of bacteriostatic effect was presented as the reduction ratio of the bacteria. The 6 ACS Paragon Plus Environment

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equation for quantitative antibacterial evaluation is given by equation (1). (1)

Where R is the percentage reduction ratio; ‘‘A’’ represents the number of bacterial colonies from the untreated bacteria suspension and ‘‘B’’ is the number of bacterial colonies from the bacteria suspension treated by AgCl and AgCl@SiO2 nanoparticles. After antibacterial tests, AgCl and AgCl@SiO2 nanoparticles were recovered by centrifugation. After the removal of supernatant, the obtained solids were washed with ethanol three times and dried in a vacuum oven for 4 h. The solids were then irradiated under visible light for 8 h and reused for another round of antibacterial test. The above process was repeated three times. Because the light stability of AgCl and AgCl@SiO2 nanoparticles are different, we designed the experiment to examine their light stability and subquently demonstrates the protection of silica. When silica is coated on AgCl nanoparticles, the light stability of materials is greatly enhanced, which makes the materials highly promising in practical applications.

Results Structural and Surface Properties. SEM and TEM techniques were used to characterize the obtained nanoparticles. As shown in Figure 2a, AgCl nanoparticles have a well-defined spherical morphology and are highly dispersive. The size distribution is uniform and the average diameter is 110 nm in term of the further statistical result (Figure 2c). TEM images of AgCl nanoparticles are difficult to obtain because their spherical morphology is apt to destroy when exposed to high-power electron beams during measurements.34 7 ACS Paragon Plus Environment


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As clearly shown in Figure 2b, AgCl nanoparticles are successfully coated with silica shell after the hydrolysis and condensation of TEOS through a sol–gel process. No aggregation is observed, and the average diameter of AgCl@SiO2 nanoparticles is 124 nm, increasing by 14 nm in comparison with AgCl nanoparticles. A statistical result of specific diameters is also given in Figure 2d. It is worth noting that higher resolution TEM images (Figure 2f and inset) can be obtained, suggesting that AgCl@SiO2 nanoparticles are not as sensitive towards high-power electron beams as AgCl nanoparticles, indicative of improved stability. In addition, the core–shell structure can be clearly distinguished, providing a direct evidence of successful silica coating. IR spectra of AgCl and AgCl@SiO2 nanoparticles were recorded and shown in Figure 3. For AgCl nanoparticles, the sharp band around 2900 cm−1 can be assigned to the stretching vibration of the C–H bond arising from the alkyl chain of CTAC which is a surfactant capping on the surface of AgCl nanoparticles to lower their surface energy. In the case of AgCl@SiO2 nanoparticles, the band at 960 cm–1 is ascribed to the stretching vibrations of silanol groups (Si–OH),35-37 and the bands at 1090 and 805 cm–1 correspond to the asymmetric and symmetric stretching vibrations of Si–O–Si frameworks, respectively.38-40 These results give a clear component information of AgCl@SiO2 nanoparticles. There are no bands in the region of 2750–3000 cm–1 ascribed to the vibrations of –CH2– in CTAC, indicative of the complete removal of template in the final product, namely AgCl@SiO2 nanoparticles. The broad band around 3400 cm-1 can be ascribed to the O–H vibration of water.41 Figure 4 presents N2 adsorption–desorption isotherms and pore size distributions of different samples. No obvious increase is observed over the whole pressure range for the 8 ACS Paragon Plus Environment

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isotherm of AgCl nanoparticles, suggesting that only a tiny amount of N2 was adsorbed by AgCl nanoparticles, which is due to their smooth surface with negligible pores. After coating AgCl nanoparticles with silica, the adsorption amount of N2 increases obviously, and the isotherm presents type-IV shape. Pore size distributions (Figure 4b) show that the silica shell owns both mesopores (2.4-8.2 nm) and macropores (50 and 108 nm). Through these pore channels, Ag(I) can be released. Stability Examination. Figure 5 displays the XRD patterns of AgCl and AgCl@SiO2 nanoparticles. For AgCl nanoparticles, the diffraction peaks at 2θ of 27.9°, 32.3°, 46.3°, 54.9°, 57.6°, 67.6°, 74.5°, and 76.8°can be indexed to (111), (200), (220), (311), (222), (400), (331), and (420) reflections, respectively, which are characteristic of the AgCl phase.42-44 This suggests that the synthesized AgCl nanoparticles show a face-centered cubic (fcc) structure, and the positions of the peaks are in agreement with JCPDS data (No. 31-1238). Additionally, The sharp peaks indicate that AgCl nanoparticles are highly crystalline and no other characteristic peaks ascribed to impurities are observed. After coating silica shell, all of the diffraction peaks can be clearly identified and the peak intensity slightly decreases, suggesting that the cubic structure of AgCl nanoparticles is preserved. After light irradiation, the face-centered cubic structure of AgCl nanoparticles is preserved, but the intensity of all peaks decreases in comparison with the fresh samples, which can be explicated that parts of Ag(I) are reduced to Ag(0) on the surface. However, no peaks of Ag nanopartices were detected, probably due to their relative low amount and high dispersion. As for AgCl@SiO2 nanoparticles, no obvious change is observed in peak intensity after light irradiation. This suggests that the silica shell effectively enhances the stability of AgCl nanoparticles towards 9 ACS Paragon Plus Environment


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light irradiation. To further study the effect of light irradiation on samples, UV-vis spectra were also employed to monitor the change as depicted in Figure 6. There is a broad adsorption band in the region of 200−400 nm, which can be attributed to the adsorption for UV light of AgCl nanoparticles.45 An enhanced absorbance in visible light region (centered at about 550 nm) for AgCl nanoparticles is observed, suggesting that under the light irradiation, parts of Ag(I) are reduced on the surface of AgCl nanoparticles and form Ag nanograins.46 After coating with silica, the broad adsorption band has an obvious blue shift that is due to the dielectric property of silica.47 Although undergoing the same process, there is no remarkable change for AgCl@SiO2 nanoparticles. Silica shells act as a barrier for preventing from the direct light irradiation, which enhance the stability of AgCl nanoparticles. Besides UV-vis spectra, color changes of samples were also recorded by digital camera as shown in Figure 7. After light irradiation for 0.5 h, the color of AgCl nanoparticles becomes somewhat dark, and obviously dark after 2 h. However, the change of AgCl@SiO2 nanoparticles is not as obvious as AgCl nanoparticles. After light irradiation for 0.5 h, negligible change is observed, and the change after 2 h is less than that of AgCl nanoparticles after 0.5 h, which is in agreement with XRD and UV-vis results. Antibacterial Performance. Figure 8 displays the antibacterial activity of AgCl and AgCl@SiO2 nanoparticles on E. coli. with a 10–3 dilution multiple. Blank experiments were conducted two times for comparison. Figure 8g and h show that the number of remaining colonies is in the range of 600−700 in the absence of antibacterial materials. However, Figure 8a and b show that there is no remaining colonies on the agar plates of AgCl and AgCl@SiO2 10 ACS Paragon Plus Environment

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nanoparticles when they were used for the first time, suggesting that both of them possess remarkable growth inhibition towards E. coli. After recycling and light irradiation for 8 h, remaining colonies start to appear on agar plate containing AgCl nanoparticles, suggesting the decrease of antibacterial ability, while AgCl@SiO2 nanoparticles still have a good inhibiting effect (Figure 8c and d). As for the third cycle (Figure 8e and f), AgCl nanoparticles continue to lose antibacterial ability while AgCl@SiO2 nanoparticles exhibit much better stability. The remaining exact number of discrete colonies are listed in Table 1 in the dilution degree at 103 orders of magnitude. The antibacterial activities of AgCl nanoparticles used for three times are 100 %, 98.1 %, and 58.2 %, respectively, indicative of a remarkable activity loss. As for AgCl@SiO2 nanoparticles, antibacterial activities used for two times are both 100 %, no decrease is observed. When AgCl@SiO2 nanoparticles were used for the third time, the antibacterial activity can maintain the level at 89.8 %, which is much higher than that of AgCl nanoparticles (58.2 %). Obviously, AgCl@SiO2 nanoparticles present a much better long-acting inhibiting effect than AgCl nanoparticles. The results of ICP show that the content of Ag(I) is 75.3 and 63.9 wt% in AgCl and AgCl@SiO2 nanoparticles, respectively. When the samples were put into water, the amount of released Ag(I) is measured to be 0.88 and 0.69 mg L–1, respectively. The concentration of Ag(I) from AgCl nanoparticles is somewhat higher than that of AgCl@SiO2 nanoparticles due to the effect of silica, while both of them are sufficient to inhibit the growth of E. coli. To further examine the antibacterial behavior of present materials, two reference materials (i.e. SiO2 and Ag(I)-modified SiO2) were introduced. Figure 9 displays the antibacterial activity of these reference materials on E. coli. with a 10–4 dilution multiple. The blank 11 ACS Paragon Plus Environment


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experiment shows that the number of remaining colonies is 105. When SiO2 is used as the antibacterial material, the number of remaining colonies is 108, which is similar to that of the blank experiment and indicates the poor antibacterial activity of SiO2 due to its good biocompatibility. However, for Ag(I)-modified SiO2 containing 8 wt% AgNO3, the antibacterial activity reaches 100 %. These results demonstrate that Ag(I) rather than SiO2 acts as active sites that inhibits the growth of E. coli.

Discussion For the fabrication of core−shell AgCl@SiO2, AgCl nanoparticles are first prepared through a facile surfactant-assisted strategy. The surfactant, CTAC, is supposed to cap on the surface of AgCl nanoparticles because the metal surface usually bears negative charges which can absorb the electropositive end of CTAC by electrostatic force. In the synthesis of AgCl nanoparticles, CTAC is a surfactant that assists the nucleation and growth of nanoparticles, and plays a crucial role in improving their stability by steric effect where a bilayer structure of CTAC is formed in the solution.34 The inner layer is bound to the AgCl surface and the head groups of outer layer is in the aqueous solution as well as that the interaction of the two layers is by hydrophobic interaction.48 After the formation of AgCl nanoparticles, a porous silica shell is coated on the surface by the sol-gel method. Traditionally, as-prepared nanoparticles need to be washed several times and redispersed in the liquid phase for further coating. Even sometimes, it is necessary to modify their surface chemistry that is complex and time-consuming. In our synthetic system, the process is greatly simplified. The surfactant, CTAC, that serves as the stabilizing agent concentrates on the surface of AgCl nanoparticles


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in the first step can also serve as the template. In the synthesis of AgCl@SiO2 nanoparticles, the silica oligomers interact with the CTAC template via Coulomb forces, and both of them cooperatively assembly on the surface of the AgCl nanoparticles.49 As a result, silica source can be directly added into the mixture to construct core–shell nanoparticles without any additional treatment of AgCl nanoparticles. It not only simplifies synthetic procedures, but also reduces the production cost. Core–shell AgCl@SiO2 nanoparticles are thus synthesized by the facile one-pot method, and the pore channels of porous silica shell is beneficial to the release of Ag(I). Recently, the antibacterial mechanism study of Ag-based nanoparticles has been focused on the effect of Ag(I) as more and more works revealing its importance. Xiu et al.50 demonstrated that the released Ag(I) is the definitive factor that damages the bacterial cell for Ag nanoparticles by studying the antibacterial ability of Ag(I) and Ag(0) separately. lvask et al.51 revealed that the magnitude of toxicity of Ag nanoparticles correlates well with the amount of dissolved Ag(I). Many other researchers also reported the same results that dissolved Ag(I) of Ag-based nanoparticles plays a key role for antibacterial applications.22,25,52 In this work, our results show that compared with pure SiO2, Ag(I)-supporting SiO2 has a great increase in antibacterial activity, supporting the view that Ag(I) can effectively inhibit the growth of bacterial. Moreover, as antibacterial tests shown above, AgCl@SiO2 nanoparticles exhibit a better long-acting antibacterial performance than AgCl nanoparticles. The antibacterial process of AgCl@SiO2 nanoparticles can be described by two steps. First, the liquid diffuses into the pore channels of silica shell and contacts with the surface of AgCl nanoparticles to form an electrophoretic mobility. As a result, Ag(I) can be released into the 13 ACS Paragon Plus Environment


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liquid phase and pass through the pore channels by the driving force of concentration and potential gradient. Second, free Ag(I) attaches to the cell surface to produce an enhanced interfacial concentration and enters the cell, followed by disturbs the biochemical processes of cellular enzymes and DNA by coordinating to electron-donating groups. On the one hand, silica shell protects AgCl nanoparticles from direct light irradiation, avoiding the generation of small Ag nanograins on the surface. As a result, Ag(I) is able to release continuously at a fast rate. On the other hand, parts of free Ag(I) are apt to fix by the electrostatic attraction of silanols and concentrate on the surface of AgCl@SiO2 nanoparticles, which enhances the antibacterial performance of AgCl@SiO2 nanoparticles. Ag(I)-based nanoparticles are unstable when exposed to visible light, which is extremely adverse for antibacterial applications, and thus hinders the development of AgCl nanoparticles. Since Ag(I) plays a crucial role in antibacterial applications, it is extremely desirable to fabricate AgCl nanoparticles with enhanced stability. In the present study, we employ a one-pot method to fabricate AgCl@SiO2 nanoparticles with core−shell structure in which CTAC used for AgCl synthesis also acts as a structure-directing agent in subsequent silica coating, which not only promotes antibacterial activity, but also protects AgCl nanoparticles from direct light irradiation by the nonlinear light scattering of SiO2. In this case light intensity is greatly weakened due to the light–matter interaction resulting from inhomogeneity in the refractive index,53 thus AgCl@SiO2 nanoparticles exhibit a more stable light stability than that of AgCl nanoparticles despite the optical transparent characteristic of SiO2. In addition, the most part of AgCl nanoparticles surface is isolated from external environment to enhance their stability. The convenient synthesis, uniform core–shell structure, and excellent 14 ACS Paragon Plus Environment

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antibacterial performance make our antimicrobials highly promising for antibacterial applications.

Conclusions We demonstrate the successful fabrication of Ag(I)-based antimicrobials, AgCl@SiO2 nanoparticles, which comprise a core of AgCl nanoparticles and a shell of porous silica with enhanced stability. The antimicrobials are of well-defined core–shell nanostructure, excellent antibacterial activity, and good reusability. Our results show that the obtained antibacterial materials with highly open pores are beneficial to the release of Ag(I), exhibiting a remarkable inhibiting effect on the growth of E. coli. Besides, the fabrication method of AgCl@SiO2 nanoparticles simplifies the operation process and significantly reduces the cost. More importantly, due to the protection of silica shell, the nanoparticles are highly resistant to light irradiation and can be used repeatedly. The present study may open up an avenue for the fabrication of stable and efficient antibacterial materials through a facile way.

Acknowledgments. We acknowledge financial support of this work by the National Natural Science Foundation of China (21576137), the Distinguished Youth Foundation of Jiangsu Province (BK20130045), the Fok Ying-Tong Education Foundation (141069), the National Basic Research Program of China (973 Program, 2013CB733504), and the Project of Priority Academic Program Development of Jiangsu Higher Education Institutions.

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(38) Tan, P.; Qin, J.-X.; Liu, X.-Q.; Yin, X.-Q.; Sun, L.-B. Fabrication of Magnetically Responsive

Core-Shell

Adsorbents

for

Thiophene

Capture:

AgNO3-Functionalized

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Figure 1. Schematic diagram for the synthesis of AgCl and AgCl@SiO2 nanoparticles.


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Figure 2. SEM images of (a) AgCl and (b) AgCl@SiO2 nanoparticles, size distributions of (c) AgCl and (d) AgCl@SiO2 nanoparticles. (e, f) TEM images of AgCl@SiO2 nanoparticles.



AgCl

Transmittance (a.u.)

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AgCl@SiO2 CTAC

4000

3000

2000

1000 -1

Wavenumber (cm )

Figure 3. IR spectra of AgCl and AgCl@SiO2 nanoparticles as well as CTAC.


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a

3

40 30 20

AgCl@SiO2

10

AgCl

0 -10

b

-1

50

-3

60

Pore volume (10 cm g )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Volume adsorbed (cm3 g-1)

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0.2

0.4

0.6

0.8

1.5

1.0 AgCl@SiO2

0.5 AgCl

0.0 1

1.0

10

100

Pore size (nm)

Relative pressure (p/p0)

Figure 4. (a) N2 adsorption–desorption isotherms and (b) pore size distributions of AgCl and AgCl@SiO2 nanoparticles. Pore size distribution curves are plotted offset for clarity.


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Intensity (a.u.)


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AgCl AgCl after irradiation AgCl@SiO2 AgCl@SiO2 after irradiation

20

30

40

50

60

70

80

2(degrees)

Figure 5. XRD patterns of AgCl and AgCl@SiO2 nanoparticles before and after light irradiation for 2 h.


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AgCl AgCl after irradiation AgCl@SiO2 AgCl@SiO2 after irradiation

Absorbance (a.u.)

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200

300

400

500

600

700

800

Wavelength (nm)

Figure 6. UV-vis diffuse reflectance spectra of AgCl and AgCl@SiO2 nanoparticles before and after light irradiation.



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Figure 7. The images of AgCl nanoparticles (a) without irradiation, irradiated for (b) 0.5 h, and (c) 2 h as well as AgCl@SiO2 nanoparticles (d) without irradiation, irradiated for (e) 0.5 h, and (f) 2 h.


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Figure 8. Activity of AgCl and AgCl@SiO2 nanoparticles against E. coli by (a, b) first use, (c, d) second use, and (e, f) third use. (g, h) Blank antibacterial experiments in the absence of antibacterial materials.



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Figure 9. Activity of (a) SiO2 and (b) Ag(I)@SiO2 nanoparticles against E. coli. (c) Blank antibacterial experiments in the absence of antibacterial materials.


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Table 1. Antibacterial test results against E. coli. Number of remaining colonies

Reduction of E. coli

(×103 cell mL–1)

(%)

1

0

100

2

13

98.1

3

283

58.2

1

0

100

2

0

100

3

69

89.8

Blank

–

693

–

Blank

–

611

–

Sample

AgCl

AgCl@SiO2

Usage counter



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For Table of Contents Use only

Core–Shell AgCl@SiO2 Nanoparticles: Ag(I)-Based Antibacterial Materials with Enhanced Stability

Peng Tan, Yan-Hua Li, Xiao-Qin Liu*, Yao Jiang, and Lin-Bing Sun*

Core–shell AgCl@SiO2 antibacterial materials are successfully fabricated with enhanced light stability and exhibit high inhibiting activity in the growth of bacterial.


CoreâShell AgCl@SiO2 Nanoparticles: Ag(I)-Based Antibacterial

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CoreâShell AgCl@SiO2 Nanoparticles: Ag(I)-Based Antibacterial