- Email: [email protected]
Synthesis and characterization of Ag nanoparticles decorated mesoporous sintered activated carbon with antibacterial and adsorptive properties
Journal of Alloys and Compounds 647 (2015) 1007e1012
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Synthesis and characterization of Ag nanoparticles decorated mesoporous sintered activated carbon with antibacterial and adsorptive properties Wenxia Wang, Kaijun Xiao*, Tinglin He, Liang Zhu* School of Light Industry and Food Sciences, South China University of Technology, Guangzhou, Guangdong Province, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 January 2015 Received in revised form 24 March 2015 Accepted 28 May 2015 Available online 10 June 2015
In this study, the sliver nanoparticles (AgNPs) immobilized on the sintered activated carbon (Ag/SAC) were synthesized by the ultrasonic-assisted impregnation method and were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen adsorption. SEM showed that the AgNPs were well embedded in the SAC and immersion time had an important influence on final morphologies of AgNPs. Longer immersing duration caused significant aggregation of the AgNPs. The XRD data revealed that the successful synthesis of AgNPs on the SAC and immobilizing AgNPs on sintered active carbon did not change the crystalline degree of SAC. Texture characteristics were determined by analysis of the N2/77 K isotherms. The minimum inhibitory concentration (MIC) of Ag/SAC against Escherichia coli (DH5a) and Staphyloccocus aureus (ATCC 29213) was evaluated by a broth dilution method. MICs such as 5 mg/L (against E. coli) and 10 mg/L (against S. aureus) suggest that Ag/SAC have predominant antibacterial activity compared to active carbon. © 2015 Elsevier B.V. All rights reserved.
Keywords: Sintered activated carbon Silver nanoparticles Ultrasonic immersion method Antibacterial property
1. Introduction Carbon materials are finding an increasing number of applications in catalysis, either as supports or as catalysts on their own [1]. It is widely used due to its exceptionally high surface area (ranges from 500 to 1500 m2/g), well-developed internal microprosity, wide spectrum of surface functional groups [2], chemical stability and durability [3]. While application of activated carbon (AC) to wastewater treatment, through its efficient adsorbing capacity due to their extended surface area and high adsorption capacity [4], was often confronted with limitations because of the dispersion of PAC (powdered activated carbon) powder [5] and erosion and fracturing of GAC (granular activated carbon) [6] during regeneration process when ultrasound was employed. Nevertheless, problems still remain when the AC are used to purify drinking water because bacteria preferably adhere to solid supports made of carbon materials, indicating that AC have good biocompatibility. Bacteria may breed on the AC during the purification process, so that the AC itself becomes a pollutant [7].
* Corresponding authors. E-mail addresses: [email protected] (K. Xiao), [email protected] (L. Zhu). http://dx.doi.org/10.1016/j.jallcom.2015.05.180 0925-8388/© 2015 Elsevier B.V. All rights reserved.
To solve this issue from the root, it is inevitable and indispensable to use antibacterial agents. Silver has been extensively investigated and well known as a bacteriostatic agent since the ancient times and has been used in many forms in the treatment of infectious diseases. Similarly, metallic Ag nanoparticles, which exhibit more efficient antibacterial performance and catalytic properties in comparison with their bulk counterparts, were investigated intensively during the last decade [8e11]. Carbon materials have also been intensively exploited as one of the promising matrices for coating or supporting the magnetic nanoparticles owning to its chemical stability, biocompatibility, flexibility of surface modification and pore creation [12e14]. Therefore, many efforts have been paid for the preparation of silver-containing porous carbon materials, such as silver-containing activated carbon fibers (Ag/ACFs) [15e17], silver decorated carbon microspheres (Ag-CMSs) [18]. The sintered activated carbons (SAC) are novel porous carbon materials with many interesting properties, such as excellent adsorption capacity, excellent mechanical properties, easy for transport and recycling and environment friendly without causing dust pollution. Because of their unique properties, SAC are expected to be a promising silver-containing porous carbon materials. From these points of view, this study aims to prepare antibacterial SAC supporting silver and to evaluate the antibacterial effect
1008
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
of Ag/SAC against Staphylococcus aureus (ATCC 29213) and Escherichia coli (DH5a) using a broth dilution test. The influence of silver on the textural and surface properties of Ag/SAC is investigated by using nitrogen adsorption isotherms, X-ray diffraction (XRD), and scanning electron microscopy (SEM) measurements. Resistance of the Ag/SAC to water erosion is also discussed by using an attrition test. 2. Experimental 2.1. Materials Sintered activated carbon (SAC)was prepared in our laboratory by the same route introduced in our previous article [19]. Nitric acid Silver nitrate (AgNO3)was purchased from Chemical Reagent Co. (Shanghai, China). Soluble starch was supplied by Chemical Reagent Co. (Tianjin, China). All the reagents used in this research were of analytical grade and were used without any further purification. 2.2. Preparation of Ag/SAC hybrids Fig. 1. Schematic diagram of the bacterial culture and broth dilution tests.
AgNPs was prepared by ultrasonic-assisted chemical reduction. Glucose was used as reducing agent in the synthetic process. Then 0.1 mol/L silver nitrate, 0.4 mol/L glucose and 5 ml soluble starch were mixed uniformity in an ultrasonic bath and reacted at 60 Cfor 3 h. For Ag/SAC synthesis, the sample of SAC was first cut in small cubes with the side of 1e1.5 cm. Afterwards, the SAC was washed thoroughly with water and then dried at 60e65 Cfor 4 h. Then, the pretreated SAC were ultrasonicated in the AgNPs solution for 15, 30, 45 and 60 min, respectively. The Ag/SAC was allowed to take out of the solution, washed thoroughly with water and finally dried at 60 Cfor 4 h. For convenience, the sample of AgNPs immobilized on SAC were hereafter denoted as Ag/SAC-T, where T referred to the reaction time (15, 30, 45 and 60 min). 2.3. Characterization We processed the Ag/SAC hybrids with wet digesting method and concentration of Ag in the solution was determined in a Z-5000 atomic absorption spectrometer with an air/acetylene system. The average bulk structure of carbon materials can be readily revealed using X-ray diffraction [20]. The as-prepared Ag/SAC hybrids were characterized by powder XRD, which was carried out on a Bruker D8 Advance X-ray diffractometer using Cu Ka radiation with a l of 0.15418 nm at a scan rate of 4 min1. The surface morphology of Ag/ SAC was observed by SEM (Germany EVO LS10) with an accelerating voltage of 20 kV. The BrunauereEmmetteTeller (BET) specific surface areas of Ag/SAC were determined by a JW-BK222 automatic physical adsorber using highly purified nitrogen gas. The nitrogen adsorption was measured at 77 K and the pore size distribution was calculated by the density functional theory (DFT) method. Total pore volume (Vt) was estimated to be the liquid volume of nitrogen at a relative pressure of about 0.995. 2.4. Bacterial culture and test for antibacterial activity The present study investigated the qualitative and quantitative antibacterial activity of Ag/SAC hybrids against E. coli (DH5a) and S. aureus (ATCC 29213). As shown in Fig. 1, the bacterias E. coli and S. aureus was inoculated into lactose broth (LB) and cultured aerobically at 37 C for 24 h. Luria Bertani Broth (LB broth) was used as the diluent for the bacterial strains. Inoculates were prepared by suspending growth from overnight cultures in sterile LB media.
Approximately 8.5 105 CFU/mL bacteria were inoculated at 37 C for 4, 8, 24 and 30 h, respectively. Concentration of bacterial suspension was determined by spectrophotometry at 630 nm. 2.5. Resistance to water erosion of the Ag/SAC hybrids The resistance of the Ag/SAC hybrids to water erosion was determined by the attrition test. Ag/SAC samples of about 0.2 g were placed in 50 mL distilled water for 48 h at room temperature. Meanwhile, Ag/SAC samples of about 0.2 g were placed in 50 mL distilled water with shaking speed of 180r/min. The resistance of the SAC to water erosion was determined by the same route as a control group. The resistance to water erosion was measured by the residual silver content based on initial concentration after the attrition test. 3. Results and discussion 3.1. Morphology and structure of Ag/SAC hybrids The surface and cross-section morphologies of Ag/SAC hybrids with different reaction time are presented in Fig. 2 and Fig. 3. It is observed from Fig. 2a that the silver nanoparticles are deposited with good dispersity on the surface of SAC at 15 min. As shown in Fig. 2b,c and d, it is clear that the loading amounts of AgNPs increase with the increasing reaction time. The particles of silver becoming thicker and bigger aggregate into clusters and are fixed on the surface of SAC. The change tendency of AgNPs presented here is in agreement with that shown in Fig. 4. A possible explanation could be that once all of the bonding sites are filled, the AgNPs will aggregate into clusters and store up in the surface of the SAC. On the other hand, AgNPs tend to agglomerate to reduce the surface energy in reaction process when concentration of Agþ is too large, which will form particles with large size and poor disperse [21]. Whereas, it can be noticed that the Ag nanoparticles deposited on the cross-section of SAC are more homogeneous and smaller after 45 min compared with that on the surface of SAC. This is due to that some of the coated Ag particles have covered the surfaces of the fibers [16] and blocked the pores so that the large Ag particles can not get through the pores in the SAC.
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
Fig. 2. SEM images of the surface morphology of Ag/SAC (a) Ag/SAC-15; (b) Ag/SAC-30; (c)Ag/SAC-45; (d)Ag/SAC-60.
Fig. 3. SEM images of the cross-section morphology of Ag/SAC (a) Ag/SAC-15; (b) Ag/SAC-30; (c)Ag/SAC-45; (d)Ag/SAC-60.
1009
1010
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
Fig. 4. Ag quantification of the Ag/SAC measured by AAS.
The average bulk structure of carbon materials can bereadily revealed using X-ray diffraction. In Fig. 5, the X-ray diffraction patterns of the synthetic Ag/SAC hybrids and pristine SAC are compared. The broad diffraction peak at 2q ¼ 37.924 , 44.093 and 64.208 of the Ag/SAC hybrids is attributed to the indices (111), (200) and (220) and the values are in good agreement with JCPDS data of crystalline AgNPs (file nos. 04e0783 and 84e0713) [22]. As confirmed by XRD determinations, the crystalline pattern of SAC is still existed in the XRD patterns of Ag/SAC hybrids. The results illustrate that the micrographic structure and surface properties of pristine SAC have not been disrupted. To understand the influence of Ag nanoparticles on the development of pore structure in Ag/SAC hybrids prepared from SAC, the pristine SAC and Ag/SAC hybrids are characterized by N2 adsorption-desorption analyses. The nitrogen adsorptiondesorption isotherms of the pristine SAC and Ag/SAC hybrids are depicted in Fig. 6. On the one hand, it is obvious that the shape of isotherms is similar and both of them exhibit a convex upward
Fig. 6. Nitrogen adsorption-desorption isotherms at 77 K of the synthetic Ag/SAC hybrids and pristine SAC.
isotherm with steep slope at low P/Po. Besides, it can be noticed that the N2 uptakes of the synthetic Ag/SAC hybrids reduce compared with that of the pristine SAC. This is mainly because the AgNPs blocked the pores of the SAC and thus the adsorptive capacity decreases slightly. This phenomenon well agree with the SEM results. On the other hand, the isotherms of the SAC and Ag/SAC are incorporated by obvious hysteresis loop, which displays a type I isotherm according to the IUPAC classification [23]. In order to understand the pore structure quantitatively, characteristics of porosity of pristine SAC and the synthetic Ag/SAC hybrids are given in Table 1. Comparing with pristine SAC, the BET surface areas and total pore volume of Ag/SAC decreased 29.41% and 20.25%, respectively. This is mainly due to some pores located on SAC are covered by the AgNPs loaded on SAC, which is in agreement with the XRD analysis. 3.2. Antibacterial activity Microbicidal activity is an important indicator for antibacterial materials. As shown in Fig. 7, the bacilli in the test tubes with the synthetic Ag/SAC hybrids in the experimental groups were clear, while the bacilli without Ag/SAC or containing the pristine SAC were still turbid suspension. These results obviously indicate that the Ag/SAC possesses strong antibacterial activity against E. coli and S. aureus. We used the broth dilution method to measure the MIC in order to determine the antibacterial effect of Ag/SAC against the E. coli and S. aureus. Valodkar et al., 2011 [24] reported MIC values of 0.26 mg/L for 10 mM Ag nanoparticles and the MIC of 0.23 mg/L for 10 mM Ag/Cu alloy nanoparticles against lower bacterial
Table 1 Characteristics of porosity of pristine SAC and the synthetic Ag/SAC hybrids.
Fig. 5. XRD patterns of the synthetic Ag/SAC hybrids and pristine SAC.
Samples
BET surface area (m2/g)
Average pore diameter (nm)
Total pore volume (ml/g)
SAC Ag/SAC
582.039 410.887
2.261 2.334
0.079 0.063
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
1011
Fig. 7. Antibacterial activity of Ag/SAC against Escherichia coli (a) and Staphyloccocus aureus (b).
Fig. 8. Minimum inhibitory concentration (MIC) of Ag/SAC against Escherichia coli (a) and Staphyloccocus aureus (b).
concentrations (104 CFU/mL) of E. coli than were employed here (8.5 105 CFU/mL). Taner et al. (2011) [25] reported an MIC value only of >150 mg/L for Ag nanoparticles and identical values for MIC of Ag/Cu nanoparticles of 0.5 mg/L against high concentrations (108 CFU/mL) of E. coli. As shown in Fig. 8, the MICs value of Ag/SAC against E. coli and S. aureus reported here were 5 mg/L and 10 mg/L, respectively. However, the findings obtained here are not directly comparable with those of Valodkar et al. and Taner et al. This is mainly because that AgNPs were immobilined on the sintered activated carbon which served as stabilizing agent and made the MIC higher. Besides, Wen-Ru Li [26] reported that silver nanoparticles of 10 mg/ml have perfect antibacterial activity against E. coli cells of 107 cfu/ml. The results obtained suggested that the Ag/SAC have predominant antibacterial activity and thus be a potential carbon material to be used. The mechanism of inhibition of metals on E. coli and S. aureus has been reported by previous researchers. Y.E. Lin reported that AgNPs could affect some proteins and phosphate lipids and induce collapse of membrane, thereby leading to protein denaturation and cell death [27]. Simultaneously, silver nanoparticles also exhibited destabilization of the outer membrane and rupture of the plasma membrane, thereby causing depletion of intracellular ATP [28].
3.3. Resistance to water erosion of the Ag/SAC Atomic absorption spectrometry was used to determine the amount of AgNPs in water due to the high sensitivity, good accuracy and strong anti-interference ability. Table 2 showed the residual silver content of Ag/SAC in static water. It is evident that there is almost no sliver released when immersing in static water for more than 48 h, indicating that the Ag/SAC has stability in the application of water purification. From Fig. 9, the residual silver content of sample 4 in steam water is 0.035ug/L in the initial 5 min, while there is almost no sliver released in other samples. Besides, the content of silver released from the sample 1 is 87.67% lower than that of the sample 4 at the 720 min. It is revealed that the higher content of silver the samples contained, the more it tends to release in water. This is due to that in the samples of Ag/SAC with high content of silver, the
Table 2 The residual silver content of Ag/SAC hybrids in static water. The residual silver concentration in water (mg/L) Time (h) 48
Sample 1 Undetected
Sample 2 Undetected
Sample 3 Undetected
Sample 4 Undetected
1012
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
Fig. 9. The residual silver content of Ag/SAC in stream water.
sliver not only adsorb in the surface of SAC but also reunion on the surface of the silver particles. Thus the samples of Ag/SAC with high content of silver possess weaker adsorption ability and stability. As expected, some of the silver gradually strip due to the continuous impact of water, and the striped rate of sliver in the water increased at first, then decreased and trend to stable at last. These results suggest that the Ag/SAC has durable antibacterial properties. According to the ministry of health, the highest allowable concentration of sliver in drinking water is 50 u g/L. Therefore, the Ag/SAC has a certain degree of security, and can be used for the deep purification of drinking water. 4. Conclusion In conclusion, we develop a facile, green and cost effective approach for synthesis of the novel Ag/SAC hybrids without the use of any expensive instrument. SEM show that the AgNPs are well embedded in the SAC and immersion time has an important influence on final morphologies of AgNPs. Longer immersing duration causes significant aggregation of the AgNPs. The XRD data reveal that the successful synthesis of AgNPs on the SAC and the micrographic structure and surface properties of pristine SAC have not been disrupted. Antibacterial assays prove that the Ag/SAC hybrids exhibited excellent antibacterial properties, when the silver loading was 9.2 mg Ag per g carbon, the Ag/SAC hybrids had minimum inhibitory concentrations of 5 and 10 mg/L for E. coli and Staphyloccocus aureus, respectively. The Ag/SAC possessed outstanding stability due to the interaction between the Ag particles and activated carbon. In spite of the water corrosion, considerably low silver concentration (<50 mg/L) was detected in the solution after 3 h. Based on the data, it can be concluded that the newly developed Ag/SAC hybrids possess good adsorption properties, excellent antibacterial properties and outstanding stability, which are very promising for water purification and other largescale commerce application. Acknowledgments The authors are grateful for financially supported by the National Natural Science Foundation of China (No. 21176092). References [1] J.L. Figueiredo, M.F.R. Pereira, M.M.A. Freitas, J.J.M. Orfao, Characterization of active sites on carbon catalysts, Ind. Eng. Chem. Res. 46 (2007) 4110e4115.
[2] J. Rivera-Utrilla, M. Sanchez-Polo, V. Gomez-Serrano, P.M. Alvarez, M.C.M. Alvim-Ferraz, J.M. Dias, Activated carbon modifications to enhance its water treatment applications. An overview, J. Hazard Mater. 187 (2011) 1e23. [3] M.A.A. Zaini, Y. Amano, M. Machida, Adsorption of heavy metals onto activated carbons derived from polyacrylonitrile fiber, J. Hazard Mater. 180 (2010) 552e560. [4] K.Y. Yoon, J.H. Byeon, C.W. Park, J. Hwang, Antimicrobial effect of silver particles on bacterial contamination of activated carbon fibers, Environ. Sci. Technol. 42 (2008) 1251e1255. [5] Y.H. Lin, L.W. Huang, J.L. Hwang, Complete hydatidiform mole with a coexisting fetus resulting from in vitro fertilization, Int. J. Gynaecol. Obstet. 90 (2005) 74e75. [6] J.L. Lim, M. Okada, Regeneration of granular activated carbon using ultrasound, Ultrason. Sonochem 12 (2005) 277e282. [7] S.J. Park, Y.S. Jang, Preparation and characterization of activated carbon fibers supported with silver metal for antibacterial behavior, J. Colloid Interface Sci. 261 (2003) 238e243. [8] S. Li, X.L. Yan, Z. Yang, Y.Z. Yang, X.G. Liu, J. Zou, Preparation and antibacterial property of silver decorated carbon microspheres, Appl. Surf. Sci. 292 (2014) 480e487. [9] V.K. Sharma, R.A. Yngard, Y. Lin, Silver nanoparticles: green synthesis and their antimicrobial activities, Adv. Colloid Interfac. 145 (2009) 83e96. [10] A.M. Abdel-Mohsen, R. Hrdina, L. Burgert, R.M. Abdel-Rahman, M. Hasova, D. Smejkalova, M. Kolar, M. Pekar, A.S. Aly, Antibacterial activity and cell viability of hyaluronan fiber with silver nanoparticles, Carbohyd Polym. 92 (2013) 1177e1187. [11] L.Y. Guo, W.Y. Yuan, Z.S. Lu, C.M. Li, Polymer/nanosilver composite coatings for antibacterial applications, Colloid Surf. A 439 (2013) 69e83. [12] H.Z. Zardini, A. Amiri, M. Shanbedi, M. Maghrebi, M. Baniadam, Enhanced antibacterial activity of amino acids-functionalized multi walled carbon nanotubes by a simple method, Colloids Surf. B: Biointerfaces 92 (2012) pp.196e202. [13] L. Cheng, P. Guo, R. Wang, L. Ming, F. Leng, H. Li, X.S. Zhao, Electrocapacitiveproperties of supercapacitors based on hierarchical porous carbons from chest-nut shell, Colloids Surf. A: Physicochem. Eng. Asp. 446 (2014) pp.127e133. [14] S.M. Yuan, J.X. Li, L.T. Yang, L.W. Su, L. Liu, Z. Zhou, Preparation and lithiumstorage performances of mesoporous Fe3O4@C microcapsules, ACS Appl. Mater. Interacs 3 (2011) 705e709. [15] A. Oya, S. Yoshida, Y. Abe, T. Iizuka, N. Makiyama, Antibacterial activated carbon fiber derived from phenolic resin containing silver nitrate, Carbon 31 (1993) pp.71e3. [16] S.J. Park, Y.S. Jane, Preparation and characterization of activated carbon fiber supported with silver metal for antibacterial behavior, J. Colloid Interface Sci. 261 (2003) 238e243. [17] Y.L. Wang, Y.Z. Wan, X.H. Dong, G.X. Cheng, H.M. Tao, T.Y. Wen, Preparation and characterization of antibacterial viscose-based activated carbon fiber supporting silver, Carbon 36 (1998) 1567e1571. [18] S. Li, X.L. Yan, Z. Yang, Y.Z. Yang, X.G. Liu, J. Zou, Preparation and antibacterial property of silver decorated carbon microspheres, Appl. Surf. Sci. 292 (2014) 480e487. [19] K.J. Xiao, T.L. He, Y.R. Yin, W.W. Ma, Preparation and absorption characteristics of SAC, J. Food Sci. Tech. Mys 3 (2013) 1514e1517. [20] J. Rungby, S. Ellermann-Eriksen, G. Danscher, Effects of selenium on toxicity and ultrastructural localization of silver in cultured macrophages, Arch. Toxicol. 61 (1987) 40e45. [21] L. Xu, H.A. Li, J.X. Xia, L.G. Wang, H. Xu, H.Y. Ji, H.M. Li, K.Y. Sun, Graphitic carbon nitride nanosheet supported high loading silver nanoparticle catalysts for the oxygen reduction reaction, Mater. Lett. 128 (2014) 349e353. [22] A. Ahmad, P. Mukherjee, S. Senapati, D. Mandal, M.I. Khan, R. Kumar, M. Sastry, Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium oxysporum, Colloid Surf. B 28 (2003) 313e318. [23] R. Pierotti, J. Rouquerol, Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity, Pure Appl. Chem. 57 (1985) 603e619. [24] M. Valodkar, S. Modi, A. Pal, S. Thakore, Synthesis and anti-bacterial activity of Cu, Ag and CueAg alloy nanoparticles: a green approach, Mater. Res. Bull. 46 (2011) 384e389. [25] M. Taner, N. Sayar, I.G. Yulug, S. Suzer, Synthesis, characterization and antibacterial investigation of silverecopper nanoalloys, J. Mater. Chem. 21 (2011) 13150e13154. [26] W.-R. Li, X.-B. Xie, Q.-S. Shi, H.-Y. Zeng, Y.-S. Ou-Yang, Y.-B. Chen, Antibacterial activity and mechanism of silver nanoparticles on Escherichia coli, Appl. Microbiol. Biotechnol. 85 (2009) 1115e1122. [27] Y.E. Lin, R.D. Vidic, J.E. Stout, C.A. Mccartney, V.L. Yu, Inactivation of mycobacterium avium by copper and silver ions, Water Res. 32 (1998) 1997e2000. [28] C.N. Lok, C.M. Ho, R. Chen, Q.Y. He, W.Y. Yu, H. Sun, P.K.H. Tam, J.F. Chiu, C.M. Che, Proteomic analysis of the mode of antibacterial action of silver nanoparticles, J.Proteome Res. 5 (2006) 916e924.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Synthesis and characterization of Ag nanoparticles decorated mesoporous sintered activated carbon with antibacterial and adsorptive properties Wenxia Wang, Kaijun Xiao*, Tinglin He, Liang Zhu* School of Light Industry and Food Sciences, South China University of Technology, Guangzhou, Guangdong Province, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 January 2015 Received in revised form 24 March 2015 Accepted 28 May 2015 Available online 10 June 2015
In this study, the sliver nanoparticles (AgNPs) immobilized on the sintered activated carbon (Ag/SAC) were synthesized by the ultrasonic-assisted impregnation method and were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen adsorption. SEM showed that the AgNPs were well embedded in the SAC and immersion time had an important influence on final morphologies of AgNPs. Longer immersing duration caused significant aggregation of the AgNPs. The XRD data revealed that the successful synthesis of AgNPs on the SAC and immobilizing AgNPs on sintered active carbon did not change the crystalline degree of SAC. Texture characteristics were determined by analysis of the N2/77 K isotherms. The minimum inhibitory concentration (MIC) of Ag/SAC against Escherichia coli (DH5a) and Staphyloccocus aureus (ATCC 29213) was evaluated by a broth dilution method. MICs such as 5 mg/L (against E. coli) and 10 mg/L (against S. aureus) suggest that Ag/SAC have predominant antibacterial activity compared to active carbon. © 2015 Elsevier B.V. All rights reserved.
Keywords: Sintered activated carbon Silver nanoparticles Ultrasonic immersion method Antibacterial property
1. Introduction Carbon materials are finding an increasing number of applications in catalysis, either as supports or as catalysts on their own [1]. It is widely used due to its exceptionally high surface area (ranges from 500 to 1500 m2/g), well-developed internal microprosity, wide spectrum of surface functional groups [2], chemical stability and durability [3]. While application of activated carbon (AC) to wastewater treatment, through its efficient adsorbing capacity due to their extended surface area and high adsorption capacity [4], was often confronted with limitations because of the dispersion of PAC (powdered activated carbon) powder [5] and erosion and fracturing of GAC (granular activated carbon) [6] during regeneration process when ultrasound was employed. Nevertheless, problems still remain when the AC are used to purify drinking water because bacteria preferably adhere to solid supports made of carbon materials, indicating that AC have good biocompatibility. Bacteria may breed on the AC during the purification process, so that the AC itself becomes a pollutant [7].
* Corresponding authors. E-mail addresses: [email protected] (K. Xiao), [email protected] (L. Zhu). http://dx.doi.org/10.1016/j.jallcom.2015.05.180 0925-8388/© 2015 Elsevier B.V. All rights reserved.
To solve this issue from the root, it is inevitable and indispensable to use antibacterial agents. Silver has been extensively investigated and well known as a bacteriostatic agent since the ancient times and has been used in many forms in the treatment of infectious diseases. Similarly, metallic Ag nanoparticles, which exhibit more efficient antibacterial performance and catalytic properties in comparison with their bulk counterparts, were investigated intensively during the last decade [8e11]. Carbon materials have also been intensively exploited as one of the promising matrices for coating or supporting the magnetic nanoparticles owning to its chemical stability, biocompatibility, flexibility of surface modification and pore creation [12e14]. Therefore, many efforts have been paid for the preparation of silver-containing porous carbon materials, such as silver-containing activated carbon fibers (Ag/ACFs) [15e17], silver decorated carbon microspheres (Ag-CMSs) [18]. The sintered activated carbons (SAC) are novel porous carbon materials with many interesting properties, such as excellent adsorption capacity, excellent mechanical properties, easy for transport and recycling and environment friendly without causing dust pollution. Because of their unique properties, SAC are expected to be a promising silver-containing porous carbon materials. From these points of view, this study aims to prepare antibacterial SAC supporting silver and to evaluate the antibacterial effect
1008
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
of Ag/SAC against Staphylococcus aureus (ATCC 29213) and Escherichia coli (DH5a) using a broth dilution test. The influence of silver on the textural and surface properties of Ag/SAC is investigated by using nitrogen adsorption isotherms, X-ray diffraction (XRD), and scanning electron microscopy (SEM) measurements. Resistance of the Ag/SAC to water erosion is also discussed by using an attrition test. 2. Experimental 2.1. Materials Sintered activated carbon (SAC)was prepared in our laboratory by the same route introduced in our previous article [19]. Nitric acid Silver nitrate (AgNO3)was purchased from Chemical Reagent Co. (Shanghai, China). Soluble starch was supplied by Chemical Reagent Co. (Tianjin, China). All the reagents used in this research were of analytical grade and were used without any further purification. 2.2. Preparation of Ag/SAC hybrids Fig. 1. Schematic diagram of the bacterial culture and broth dilution tests.
AgNPs was prepared by ultrasonic-assisted chemical reduction. Glucose was used as reducing agent in the synthetic process. Then 0.1 mol/L silver nitrate, 0.4 mol/L glucose and 5 ml soluble starch were mixed uniformity in an ultrasonic bath and reacted at 60 Cfor 3 h. For Ag/SAC synthesis, the sample of SAC was first cut in small cubes with the side of 1e1.5 cm. Afterwards, the SAC was washed thoroughly with water and then dried at 60e65 Cfor 4 h. Then, the pretreated SAC were ultrasonicated in the AgNPs solution for 15, 30, 45 and 60 min, respectively. The Ag/SAC was allowed to take out of the solution, washed thoroughly with water and finally dried at 60 Cfor 4 h. For convenience, the sample of AgNPs immobilized on SAC were hereafter denoted as Ag/SAC-T, where T referred to the reaction time (15, 30, 45 and 60 min). 2.3. Characterization We processed the Ag/SAC hybrids with wet digesting method and concentration of Ag in the solution was determined in a Z-5000 atomic absorption spectrometer with an air/acetylene system. The average bulk structure of carbon materials can be readily revealed using X-ray diffraction [20]. The as-prepared Ag/SAC hybrids were characterized by powder XRD, which was carried out on a Bruker D8 Advance X-ray diffractometer using Cu Ka radiation with a l of 0.15418 nm at a scan rate of 4 min1. The surface morphology of Ag/ SAC was observed by SEM (Germany EVO LS10) with an accelerating voltage of 20 kV. The BrunauereEmmetteTeller (BET) specific surface areas of Ag/SAC were determined by a JW-BK222 automatic physical adsorber using highly purified nitrogen gas. The nitrogen adsorption was measured at 77 K and the pore size distribution was calculated by the density functional theory (DFT) method. Total pore volume (Vt) was estimated to be the liquid volume of nitrogen at a relative pressure of about 0.995. 2.4. Bacterial culture and test for antibacterial activity The present study investigated the qualitative and quantitative antibacterial activity of Ag/SAC hybrids against E. coli (DH5a) and S. aureus (ATCC 29213). As shown in Fig. 1, the bacterias E. coli and S. aureus was inoculated into lactose broth (LB) and cultured aerobically at 37 C for 24 h. Luria Bertani Broth (LB broth) was used as the diluent for the bacterial strains. Inoculates were prepared by suspending growth from overnight cultures in sterile LB media.
Approximately 8.5 105 CFU/mL bacteria were inoculated at 37 C for 4, 8, 24 and 30 h, respectively. Concentration of bacterial suspension was determined by spectrophotometry at 630 nm. 2.5. Resistance to water erosion of the Ag/SAC hybrids The resistance of the Ag/SAC hybrids to water erosion was determined by the attrition test. Ag/SAC samples of about 0.2 g were placed in 50 mL distilled water for 48 h at room temperature. Meanwhile, Ag/SAC samples of about 0.2 g were placed in 50 mL distilled water with shaking speed of 180r/min. The resistance of the SAC to water erosion was determined by the same route as a control group. The resistance to water erosion was measured by the residual silver content based on initial concentration after the attrition test. 3. Results and discussion 3.1. Morphology and structure of Ag/SAC hybrids The surface and cross-section morphologies of Ag/SAC hybrids with different reaction time are presented in Fig. 2 and Fig. 3. It is observed from Fig. 2a that the silver nanoparticles are deposited with good dispersity on the surface of SAC at 15 min. As shown in Fig. 2b,c and d, it is clear that the loading amounts of AgNPs increase with the increasing reaction time. The particles of silver becoming thicker and bigger aggregate into clusters and are fixed on the surface of SAC. The change tendency of AgNPs presented here is in agreement with that shown in Fig. 4. A possible explanation could be that once all of the bonding sites are filled, the AgNPs will aggregate into clusters and store up in the surface of the SAC. On the other hand, AgNPs tend to agglomerate to reduce the surface energy in reaction process when concentration of Agþ is too large, which will form particles with large size and poor disperse [21]. Whereas, it can be noticed that the Ag nanoparticles deposited on the cross-section of SAC are more homogeneous and smaller after 45 min compared with that on the surface of SAC. This is due to that some of the coated Ag particles have covered the surfaces of the fibers [16] and blocked the pores so that the large Ag particles can not get through the pores in the SAC.
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
Fig. 2. SEM images of the surface morphology of Ag/SAC (a) Ag/SAC-15; (b) Ag/SAC-30; (c)Ag/SAC-45; (d)Ag/SAC-60.
Fig. 3. SEM images of the cross-section morphology of Ag/SAC (a) Ag/SAC-15; (b) Ag/SAC-30; (c)Ag/SAC-45; (d)Ag/SAC-60.
1009
1010
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
Fig. 4. Ag quantification of the Ag/SAC measured by AAS.
The average bulk structure of carbon materials can bereadily revealed using X-ray diffraction. In Fig. 5, the X-ray diffraction patterns of the synthetic Ag/SAC hybrids and pristine SAC are compared. The broad diffraction peak at 2q ¼ 37.924 , 44.093 and 64.208 of the Ag/SAC hybrids is attributed to the indices (111), (200) and (220) and the values are in good agreement with JCPDS data of crystalline AgNPs (file nos. 04e0783 and 84e0713) [22]. As confirmed by XRD determinations, the crystalline pattern of SAC is still existed in the XRD patterns of Ag/SAC hybrids. The results illustrate that the micrographic structure and surface properties of pristine SAC have not been disrupted. To understand the influence of Ag nanoparticles on the development of pore structure in Ag/SAC hybrids prepared from SAC, the pristine SAC and Ag/SAC hybrids are characterized by N2 adsorption-desorption analyses. The nitrogen adsorptiondesorption isotherms of the pristine SAC and Ag/SAC hybrids are depicted in Fig. 6. On the one hand, it is obvious that the shape of isotherms is similar and both of them exhibit a convex upward
Fig. 6. Nitrogen adsorption-desorption isotherms at 77 K of the synthetic Ag/SAC hybrids and pristine SAC.
isotherm with steep slope at low P/Po. Besides, it can be noticed that the N2 uptakes of the synthetic Ag/SAC hybrids reduce compared with that of the pristine SAC. This is mainly because the AgNPs blocked the pores of the SAC and thus the adsorptive capacity decreases slightly. This phenomenon well agree with the SEM results. On the other hand, the isotherms of the SAC and Ag/SAC are incorporated by obvious hysteresis loop, which displays a type I isotherm according to the IUPAC classification [23]. In order to understand the pore structure quantitatively, characteristics of porosity of pristine SAC and the synthetic Ag/SAC hybrids are given in Table 1. Comparing with pristine SAC, the BET surface areas and total pore volume of Ag/SAC decreased 29.41% and 20.25%, respectively. This is mainly due to some pores located on SAC are covered by the AgNPs loaded on SAC, which is in agreement with the XRD analysis. 3.2. Antibacterial activity Microbicidal activity is an important indicator for antibacterial materials. As shown in Fig. 7, the bacilli in the test tubes with the synthetic Ag/SAC hybrids in the experimental groups were clear, while the bacilli without Ag/SAC or containing the pristine SAC were still turbid suspension. These results obviously indicate that the Ag/SAC possesses strong antibacterial activity against E. coli and S. aureus. We used the broth dilution method to measure the MIC in order to determine the antibacterial effect of Ag/SAC against the E. coli and S. aureus. Valodkar et al., 2011 [24] reported MIC values of 0.26 mg/L for 10 mM Ag nanoparticles and the MIC of 0.23 mg/L for 10 mM Ag/Cu alloy nanoparticles against lower bacterial
Table 1 Characteristics of porosity of pristine SAC and the synthetic Ag/SAC hybrids.
Fig. 5. XRD patterns of the synthetic Ag/SAC hybrids and pristine SAC.
Samples
BET surface area (m2/g)
Average pore diameter (nm)
Total pore volume (ml/g)
SAC Ag/SAC
582.039 410.887
2.261 2.334
0.079 0.063
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
1011
Fig. 7. Antibacterial activity of Ag/SAC against Escherichia coli (a) and Staphyloccocus aureus (b).
Fig. 8. Minimum inhibitory concentration (MIC) of Ag/SAC against Escherichia coli (a) and Staphyloccocus aureus (b).
concentrations (104 CFU/mL) of E. coli than were employed here (8.5 105 CFU/mL). Taner et al. (2011) [25] reported an MIC value only of >150 mg/L for Ag nanoparticles and identical values for MIC of Ag/Cu nanoparticles of 0.5 mg/L against high concentrations (108 CFU/mL) of E. coli. As shown in Fig. 8, the MICs value of Ag/SAC against E. coli and S. aureus reported here were 5 mg/L and 10 mg/L, respectively. However, the findings obtained here are not directly comparable with those of Valodkar et al. and Taner et al. This is mainly because that AgNPs were immobilined on the sintered activated carbon which served as stabilizing agent and made the MIC higher. Besides, Wen-Ru Li [26] reported that silver nanoparticles of 10 mg/ml have perfect antibacterial activity against E. coli cells of 107 cfu/ml. The results obtained suggested that the Ag/SAC have predominant antibacterial activity and thus be a potential carbon material to be used. The mechanism of inhibition of metals on E. coli and S. aureus has been reported by previous researchers. Y.E. Lin reported that AgNPs could affect some proteins and phosphate lipids and induce collapse of membrane, thereby leading to protein denaturation and cell death [27]. Simultaneously, silver nanoparticles also exhibited destabilization of the outer membrane and rupture of the plasma membrane, thereby causing depletion of intracellular ATP [28].
3.3. Resistance to water erosion of the Ag/SAC Atomic absorption spectrometry was used to determine the amount of AgNPs in water due to the high sensitivity, good accuracy and strong anti-interference ability. Table 2 showed the residual silver content of Ag/SAC in static water. It is evident that there is almost no sliver released when immersing in static water for more than 48 h, indicating that the Ag/SAC has stability in the application of water purification. From Fig. 9, the residual silver content of sample 4 in steam water is 0.035ug/L in the initial 5 min, while there is almost no sliver released in other samples. Besides, the content of silver released from the sample 1 is 87.67% lower than that of the sample 4 at the 720 min. It is revealed that the higher content of silver the samples contained, the more it tends to release in water. This is due to that in the samples of Ag/SAC with high content of silver, the
Table 2 The residual silver content of Ag/SAC hybrids in static water. The residual silver concentration in water (mg/L) Time (h) 48
Sample 1 Undetected
Sample 2 Undetected
Sample 3 Undetected
Sample 4 Undetected
1012
W. Wang et al. / Journal of Alloys and Compounds 647 (2015) 1007e1012
Fig. 9. The residual silver content of Ag/SAC in stream water.
sliver not only adsorb in the surface of SAC but also reunion on the surface of the silver particles. Thus the samples of Ag/SAC with high content of silver possess weaker adsorption ability and stability. As expected, some of the silver gradually strip due to the continuous impact of water, and the striped rate of sliver in the water increased at first, then decreased and trend to stable at last. These results suggest that the Ag/SAC has durable antibacterial properties. According to the ministry of health, the highest allowable concentration of sliver in drinking water is 50 u g/L. Therefore, the Ag/SAC has a certain degree of security, and can be used for the deep purification of drinking water. 4. Conclusion In conclusion, we develop a facile, green and cost effective approach for synthesis of the novel Ag/SAC hybrids without the use of any expensive instrument. SEM show that the AgNPs are well embedded in the SAC and immersion time has an important influence on final morphologies of AgNPs. Longer immersing duration causes significant aggregation of the AgNPs. The XRD data reveal that the successful synthesis of AgNPs on the SAC and the micrographic structure and surface properties of pristine SAC have not been disrupted. Antibacterial assays prove that the Ag/SAC hybrids exhibited excellent antibacterial properties, when the silver loading was 9.2 mg Ag per g carbon, the Ag/SAC hybrids had minimum inhibitory concentrations of 5 and 10 mg/L for E. coli and Staphyloccocus aureus, respectively. The Ag/SAC possessed outstanding stability due to the interaction between the Ag particles and activated carbon. In spite of the water corrosion, considerably low silver concentration (<50 mg/L) was detected in the solution after 3 h. Based on the data, it can be concluded that the newly developed Ag/SAC hybrids possess good adsorption properties, excellent antibacterial properties and outstanding stability, which are very promising for water purification and other largescale commerce application. Acknowledgments The authors are grateful for financially supported by the National Natural Science Foundation of China (No. 21176092). References [1] J.L. Figueiredo, M.F.R. Pereira, M.M.A. Freitas, J.J.M. Orfao, Characterization of active sites on carbon catalysts, Ind. Eng. Chem. Res. 46 (2007) 4110e4115.
[2] J. Rivera-Utrilla, M. Sanchez-Polo, V. Gomez-Serrano, P.M. Alvarez, M.C.M. Alvim-Ferraz, J.M. Dias, Activated carbon modifications to enhance its water treatment applications. An overview, J. Hazard Mater. 187 (2011) 1e23. [3] M.A.A. Zaini, Y. Amano, M. Machida, Adsorption of heavy metals onto activated carbons derived from polyacrylonitrile fiber, J. Hazard Mater. 180 (2010) 552e560. [4] K.Y. Yoon, J.H. Byeon, C.W. Park, J. Hwang, Antimicrobial effect of silver particles on bacterial contamination of activated carbon fibers, Environ. Sci. Technol. 42 (2008) 1251e1255. [5] Y.H. Lin, L.W. Huang, J.L. Hwang, Complete hydatidiform mole with a coexisting fetus resulting from in vitro fertilization, Int. J. Gynaecol. Obstet. 90 (2005) 74e75. [6] J.L. Lim, M. Okada, Regeneration of granular activated carbon using ultrasound, Ultrason. Sonochem 12 (2005) 277e282. [7] S.J. Park, Y.S. Jang, Preparation and characterization of activated carbon fibers supported with silver metal for antibacterial behavior, J. Colloid Interface Sci. 261 (2003) 238e243. [8] S. Li, X.L. Yan, Z. Yang, Y.Z. Yang, X.G. Liu, J. Zou, Preparation and antibacterial property of silver decorated carbon microspheres, Appl. Surf. Sci. 292 (2014) 480e487. [9] V.K. Sharma, R.A. Yngard, Y. Lin, Silver nanoparticles: green synthesis and their antimicrobial activities, Adv. Colloid Interfac. 145 (2009) 83e96. [10] A.M. Abdel-Mohsen, R. Hrdina, L. Burgert, R.M. Abdel-Rahman, M. Hasova, D. Smejkalova, M. Kolar, M. Pekar, A.S. Aly, Antibacterial activity and cell viability of hyaluronan fiber with silver nanoparticles, Carbohyd Polym. 92 (2013) 1177e1187. [11] L.Y. Guo, W.Y. Yuan, Z.S. Lu, C.M. Li, Polymer/nanosilver composite coatings for antibacterial applications, Colloid Surf. A 439 (2013) 69e83. [12] H.Z. Zardini, A. Amiri, M. Shanbedi, M. Maghrebi, M. Baniadam, Enhanced antibacterial activity of amino acids-functionalized multi walled carbon nanotubes by a simple method, Colloids Surf. B: Biointerfaces 92 (2012) pp.196e202. [13] L. Cheng, P. Guo, R. Wang, L. Ming, F. Leng, H. Li, X.S. Zhao, Electrocapacitiveproperties of supercapacitors based on hierarchical porous carbons from chest-nut shell, Colloids Surf. A: Physicochem. Eng. Asp. 446 (2014) pp.127e133. [14] S.M. Yuan, J.X. Li, L.T. Yang, L.W. Su, L. Liu, Z. Zhou, Preparation and lithiumstorage performances of mesoporous Fe3O4@C microcapsules, ACS Appl. Mater. Interacs 3 (2011) 705e709. [15] A. Oya, S. Yoshida, Y. Abe, T. Iizuka, N. Makiyama, Antibacterial activated carbon fiber derived from phenolic resin containing silver nitrate, Carbon 31 (1993) pp.71e3. [16] S.J. Park, Y.S. Jane, Preparation and characterization of activated carbon fiber supported with silver metal for antibacterial behavior, J. Colloid Interface Sci. 261 (2003) 238e243. [17] Y.L. Wang, Y.Z. Wan, X.H. Dong, G.X. Cheng, H.M. Tao, T.Y. Wen, Preparation and characterization of antibacterial viscose-based activated carbon fiber supporting silver, Carbon 36 (1998) 1567e1571. [18] S. Li, X.L. Yan, Z. Yang, Y.Z. Yang, X.G. Liu, J. Zou, Preparation and antibacterial property of silver decorated carbon microspheres, Appl. Surf. Sci. 292 (2014) 480e487. [19] K.J. Xiao, T.L. He, Y.R. Yin, W.W. Ma, Preparation and absorption characteristics of SAC, J. Food Sci. Tech. Mys 3 (2013) 1514e1517. [20] J. Rungby, S. Ellermann-Eriksen, G. Danscher, Effects of selenium on toxicity and ultrastructural localization of silver in cultured macrophages, Arch. Toxicol. 61 (1987) 40e45. [21] L. Xu, H.A. Li, J.X. Xia, L.G. Wang, H. Xu, H.Y. Ji, H.M. Li, K.Y. Sun, Graphitic carbon nitride nanosheet supported high loading silver nanoparticle catalysts for the oxygen reduction reaction, Mater. Lett. 128 (2014) 349e353. [22] A. Ahmad, P. Mukherjee, S. Senapati, D. Mandal, M.I. Khan, R. Kumar, M. Sastry, Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium oxysporum, Colloid Surf. B 28 (2003) 313e318. [23] R. Pierotti, J. Rouquerol, Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity, Pure Appl. Chem. 57 (1985) 603e619. [24] M. Valodkar, S. Modi, A. Pal, S. Thakore, Synthesis and anti-bacterial activity of Cu, Ag and CueAg alloy nanoparticles: a green approach, Mater. Res. Bull. 46 (2011) 384e389. [25] M. Taner, N. Sayar, I.G. Yulug, S. Suzer, Synthesis, characterization and antibacterial investigation of silverecopper nanoalloys, J. Mater. Chem. 21 (2011) 13150e13154. [26] W.-R. Li, X.-B. Xie, Q.-S. Shi, H.-Y. Zeng, Y.-S. Ou-Yang, Y.-B. Chen, Antibacterial activity and mechanism of silver nanoparticles on Escherichia coli, Appl. Microbiol. Biotechnol. 85 (2009) 1115e1122. [27] Y.E. Lin, R.D. Vidic, J.E. Stout, C.A. Mccartney, V.L. Yu, Inactivation of mycobacterium avium by copper and silver ions, Water Res. 32 (1998) 1997e2000. [28] C.N. Lok, C.M. Ho, R. Chen, Q.Y. He, W.Y. Yu, H. Sun, P.K.H. Tam, J.F. Chiu, C.M. Che, Proteomic analysis of the mode of antibacterial action of silver nanoparticles, J.Proteome Res. 5 (2006) 916e924.