Environ. Sci. Technol. 2010, 44, 7058–7062
Plasmon-Induced Inactivation of Enteric Pathogenic Microorganisms with Ag-AgI/Al2O3 under Visible-Light Irradiation XUEXIANG HU, CHUN HU,* TIANWEI PENG, XUEFENG ZHOU, AND JIUHUI QU State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China
Received December 2, 2009. Revised manuscript received August 9, 2010. Accepted August 12, 2010.
The plasmon-induced photocatalytic inactivation of enteric pathogenic microorganisms in water using Ag-AgI/Al2O3 under visible-light irradiation was investigated. The catalyst was found to be highly effective at killing Shigella dysenteriae (S. dysenteriae), Escherichia coli (E. coli), and human rotavirus type 2 Wa (HRV-Wa). Its bactericidal efficiency was significantly enhanced by HCO3- and SO42- ions, which are common in water, while phosphate had a slightly positive effect on the disinfection. Meanwhile, more inactivation of E. coli was observed at neutral and alkaline pH than at acid pH in Ag-AgI/Al2O3 suspension. Furthermore, the effects of inorganic anions and pH on the transfer of plasmon-induced charges were investigated using cyclic voltammetry analyses. Two electron-transfer processes occurred, from bacteria to Ag nanoparticles (NPs) and from inorganic anions to Ag NPs to form anionic radicals. These inorganic anions including OH- in water not only enhanced electron transfer from plasmon-excited Ag NPs to AgI and from E. coli to Ag NPs, but their anionic radicals also increased bactericidal efficiency due to their absorbability by cells. The plasmon-induced electron holes (h+) on Ag NPs, O2•-, and anionic radicals were involved in the reaction. The enhanced electron transfer is more crucial than the electrostatic force interaction of bacteria and catalyst for the plasmoninduced inactivation of bacteria using Ag-AgI/Al2O3.
Introduction Waterborne pathogens have a devastating effect on public health, causing countless cases of disease and contamination. Intestinal parasitic infections and diarrheal diseases caused by waterborne bacteria and enteric viruses have also become a leading cause of malnutrition because they lead to poor digestion (1-3). Part of the overarching goal of providing safe drinking water is to affordably and robustly disinfect water contaminated with traditional and emerging pathogens without creating additional problems due to the disinfection process itself. Traditional water disinfection processes rely heavily on chemical disinfectants and leave chemical disinfection byproduct in the finished drinking water (4). * Corresponding author phone: +86-10-62849628; fax: +86-1062923541; e-mail:
[email protected]. 7058
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 18, 2010
Therefore, the effective control of waterborne pathogens in drinking water calls for the development of new disinfection strategies. Numerous studies have suggested that photocatalytic disinfection is promising as a disinfection method due to its effectiveness against viral pathogens (3, 5, 6). Its application predominantly depends on the development of a new photocatalyst capable of inactivating viruses and other waterborne pathogens with much less energy use than UV and with sufficiently high throughput. Therefore, the development of visible-light photocatalysts has become one of the most important topics in the photocatalysis field for using solar energy. Noble metal nanoparticles (NPs) exhibit strong UV-vis absorption due to their plasmon resonance, which is produced by the collective oscillations of surface electrons (7, 8). Recently, studies have verified that the plasmon resonance results in the high photosensitivity of noble metal NPs, which is potentially applicable to the development of a new class of plasmonic photocatalysts and photovoltaic fuel cells (9-11). Several plasmonic photocatalysts have been developed for photocatalytic degradation in the visible or UV region of different organic pollutants. In particular, the plasmon-induced photocatalytic mechanism and the stability of NPs have been investigated in detail for Ag-AgI/Al2O3 in the photodegradation of organic contaminants (9). However, to our knowledge, these catalysts have not yet been applied widely to the disinfection of water. An in-depth understanding of the mechanism is essential to devise a strategy for applying the technology in a practical manner to efficiently kill a wide array of microorganisms. In the present study, the photocatalyst Ag-AgI/Al2O3 was used to investigate plasmon-induced photocatalytic inactivation of pathogenic microorganisms from mechanistic and kinetic viewpoints. Several ubiquitous waterborne enteric pathogenic microorganisms [i.e., Shigella dysenteriae, Escherichia coli, and human rotavirus type 2 Wa (HRV-Wa)] were selected to evaluate the activity and properties of the catalysts under visible-light irradiation. Ag-AgI/Al2O3 exhibited particularly good bactericidal performance compared to ordinary photocatalysts (12, 13). Its bactericidal efficiency was significantly enhanced by common inorganic anions in water including bicarbonate, phosphate, and sulfate. A plasmon-induced photocatalytic disinfection mechanism was verified by cyclic voltammetry (CV) analyses under a variety of experimental conditions.
Experimental Section Materials and Reagents. S. dysenteriae and E. coli purchased from the Institute of Microbiology, Chinese Academy of Sciences, were selected as representative pathogenic enteric bacterial microorganisms. HRV-Wa and host cell MA104 were obtained from the Wuhan Institute of Virology, Chinese Academy of Sciences. All other chemicals were of analytical grade, purchased from Beijing Chemical Company, and used without further purification. Deionized and doubly distilled water was used throughout the study. Preparation of Photocatalysts. According to our previous report (9), AgI/Al2O3 containing Ag 10 wt % was prepared using the deposition-precipitation method. Subsequently, Ag-AgI/Al2O3 was prepared via the photoreduction method. In Ag-AgI/Al2O3, the contents of Ag0 species were determined to be about 5.5 wt % using the semiquantitative method of UV-vis diffuse reflectance spectra (14-16). Characterization. The photocurrent from the various samples was measured in a basic electrochemical system (AMETEK; Princeton Applied Research, Oak Ridge, TN) with 10.1021/es1012577
2010 American Chemical Society
Published on Web 08/24/2010
a two-compartment, three-electrode electrochemical cell equipped with a photocatalyst photoanode (prepared by dipcoating and drying in air at 70 °C) and a platinum wire cathode in a 0.1 M Na2SO4 solution. The reference electrode was a saturated calomel electrode. The zeta potential of catalysts in KNO3 (10-3 M) solution was determined by three consistent readings with a Zetasizer 2000 (Malvern Co., Worcestershire, UK). Photocatalytic Disinfection. The stock suspensions of E. coli and S. dysenteriae were prepared following a procedure described elsewhere (12). E. coli and S. dysenteriae were incubated in Luria-Bertani nutrient solution at 37 °C for 18 h with shaking and then washed by centrifuging at 3000 rpm. The treated cells were then resuspended and diluted to about 2 × 108 colony forming units (CFU)/mL with 0.9% saline. HRV-Wa stocks were propagated, concentrated, and purified using previously described methods (17). The final HRV-Wa cell concentration was about 3.2 × 103 plaque forming units (PFU)/mL. Further details of the cell culture conditions are provided in the Supporting Information (SI). Photocatalytic disinfection was performed in a beaker with an aqueous suspension of each enteric pathogenic microorganism (30 mL) and 6 mg of catalyst powder. The light source was a 350-W Xe-arc lamp (Shanghai Photoelectron Device, Ltd., China). Light was directed through a water filter using different wavelength cutoff filters for λ > 420 and 450 nm and focused onto the beaker, wherein the intensities of the illumination were 2.36 and 2.15 mW/cm2, respectively. The temperature of the suspension was 25 °C. The corresponding light spectrum is shown in Figure S1 (SI). Prior to irradiation, the suspensions were magnetically stirred in the dark for about 30 min to establish adsorption/desorption equilibrium between the pathogenic microorganism and the surface of the catalyst under room air-equilibrated conditions. The initial solution pH was adjusted with a diluted aqueous solution of NaOH or HCl, and the solution pH varied by less than 1 pH unit throughout the reaction. A bacterial suspension without photocatalysts was irradiated as a control, and the reaction mixture in catalyst suspension with no visiblelight irradiation was used as a dark control. During the experiment, an aliquot of the reaction suspension was drawn at various reaction times and immediately diluted with 0.9% saline for bacteria and with Dulbecco’s modified Eagle’s medium for HRV-Wa. The bacterial concentrations of S. dysenteriae and E. coli were determined by the spread plate method on nutrient agar after growing for 48 h at 37 °C. Infectivity titers of HRV-Wa were enumerated by determining the 50% tissue culture infective dose (TCID50). All of these experiments were repeated three times. All materials used in the experiments were autoclaved at 121 °C for 25 min to ensure sterility.
Results and Discussion Pathogenic Microorganism Inactivation under Visible Light Irradiation. Detailed characterizations of Ag-AgI/Al2O3 and AgI/Al2O3 were provided in our previous report (9). Here, the bactericidal activities of the samples were evaluated by the inactivation of S. dysenteriae in water under visible-light irradiation. As shown in Figure 1, visible light alone had no bactericidal effects on S. dysenteriae. In contrast, an approximately 8.5 log removal of S. dysenteriae was attained within 10 and 15 min in Ag-AgI/Al2O3 suspension under λ > 420 nm and λ > 450 nm visible-light irradiation, respectively, while the same concentration of S. dysenteriae was completely removed after 25 min in AgI/Al2O3 suspension under λ > 420 nm visible-light irradiation. Furthermore, by inductively coupled plasma optical emission spectrometry analysis, the concentration of Ag+ released from the Ag-AgI/Al2O3 suspension ranged from 0.17 to 0.24 ppm during the photocatalytic reaction in deionized and doubly distilled water,
FIGURE 1. Temporal course of the S. dysenteriae inactivation (2 × 108 CFU/mL, pH ) 7.25) in aqueous dispersions containing 0.2 g/L catalyst: (a) Ag-AgI/Al2O3 in the dark, (b) no catalyst, (c) AgI/Al2O3 with λ > 420 nm, (d) Ag-AgI/Al2O3 with λ > 420 nm, (e) AgI/Al2O3 with λ > 450 nm, and (f) Ag-AgI/Al2O3 with λ > 450 nm. whereas in tap water the released Ag+ ranged from 0.01 to 0.1 ppm. An approximately 1.6 log removal of S. dysenteriae was attained after 40 min in the Ag-AgI/Al2O3 dark dispersion due to the released Ag+. Obviously, AgI/Al2O3 showed no photocatalytic activity at visible-light irradiation under λ > 450 nm because it absorbed hardly in the wavelengths range of λ > 450 nm (Figure S2). The results indicated that different photochemical processes occurred in the Ag-AgI/Al2O3 and AgI/Al2O3 suspensions with irradiation, which contributed to the different light absorption. As shown in Figure S2, the mesoporous Al2O3 was transparent at wavelengths between 200 and 800 nm. AgI/Al2O3 exhibited two absorption bands including 200-400 nm (UV) and 400-430 nm (visible) assigned to the light absorption of AgI. Besides these, Ag-AgI/ Al2O3 exhibited a band around 400-600 nm assigned to the surface plasmon absorption of Ag NPs. Therefore, the enhanced bactericidal activity of Ag-AgI/Al2O3 was due to the plasmon resonance of Ag NPs rather than the result of electron trapping by Ag NPs enhancing electron-hole separation. In particular, at wavelengths λ > 450 nm, Ag-AgI/ Al2O3 photocatalytic disinfection mainly resulted from the plasmon resonance of Ag NPs. In addition, the enteric pathogenic virus HRV-Wa, which is the most common cause of acute diarrhea in infants and young children, was also inactivated in visible light-illuminated Ag-AgI/Al2O3 suspension. A 3.2 log HRV-Wa was completely noninfectious within 40 min (Figure S3). Moreover, an 8.1 log E. coli was inactivated within 60 min. In addition, the inactivated pathogenic microorganisms were not reactivated after the photocatalytic oxidation. These results indicate that Ag-AgI/ Al2O3 is an effective plasmon-induced photocatalyst under visible light for inactivation of enteric pathogenic bacteria and viruses. Plasmon-Induced Photocatalytic Disinfection Kinetics. Effect of pH on Bactericidal Efficiency. Figure 2 shows the inactivation of E. coli in the irradiated Ag-AgI/Al2O3 suspension with varying initial pHs. Clearly, the bactericidal activity of Ag-AgI/Al2O3 increased significantly as the pH increased from 4.5 to 8.5. At pH 8.5, an 8 log inactivation of E. coli occurred at 50 min, whereas at pH 7.25 the same inactivation occurred at 60 min; at pH 4.5, the same inactivation needed even more time. In addition, no significant E. coli inactivation was observed in the Ag-AgI/Al2O3-free solution with the corresponding pH, indicating that E. coli could live in the tested pH range. The results did not correlate with the interaction of bacteria and Ag-AgI/Al2O3 as a semiconductor in photocatalytic disinfection (12, 18, 19). As shown in Figure S4, according to the charge properties of bacteria and the catalyst, electrostatic attraction existed between pH 4 and 6, VOL. 44, NO. 18, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
7059
FIGURE 2. Inactivation of E.coli (∼1 × 108 CFU/mL, 30 mL) at different starting pH in visible light-irradiated (λ > 420 nm) Ag-AgI/Al2O3 suspension (0.2 g/L): (a) pH ) 4.5 control, (b) pH ) 7.2 control, (c) pH ) 8.5 control, (d) pH ) 4.5, (e) pH ) 7.25, (f) pH ) 8.5.
FIGURE 3. Survival of E. coli (about 1 × 108 CFU/mL, 30 mL) with visible light-irradiated (λ > 420 nm) Ag-AgI/Al2O3 (0.2 g/L) dispersions starting at pH 7.25 under otherwise different conditions: (a) only Ag-AgI/Al2O3, (b) NaHCO3 with no catalyst, (c) Na2SO4 with no catalyst, (d) KH2PO4 with no catalyst, (e) NaHCO3, (f) Na2SO4, and (g) KH2PO4. Anion concentration: 0.1 M. leading to more E. coli adsorption onto the surface of the catalyst. For pH > 6, a repulsive electrostatic force occurred between them, leading to lower adsorption of E. coli. Based on the general photocatalytic disinfection mechanism, the former should result in higher bactericidal efficiency, while the latter should result in a lower one. In fact, the opposite results were obtained, indicating that different disinfection mechanisms existed in the reaction system. Effect of Inorganic Ions. The effects of several inorganic ions common in water on the bactericidal activity of Ag-AgI/ Al2O3 were investigated under visible-light irradiation. As shown in Figure 3, both HCO3- and SO42- ions significantly enhanced E. coli inactivation, while H2PO4- ions had a negative effect on the reaction at the initial stage, and a positive role to cause 8 log E. coli inactivation at the same time with that one in the Ag-AgI/Al2O3 suspension without any anion. The starting pH of the suspension was adjusted to 7.25 using HCl or NaOH solution, and subsequently, the pH did not change throughout the experiments. Under visible light, the individual ion species (HCO3-, SO42-, or H2PO4-) did not exhibit any bactericidal activity, indicating that these inorganic anions themselves were not toxic to E. coli. These results were in contrast to those found in the photodegradation of organics with visible-illuminated Ag-AgI/Al2O3 suspension, whereby the degradation of 2-chlorophenol (2CP) was markedly depressed by HCO3- (9). The same system exhibited a different performance for the disinfection and elimination of organics. Moreover, inorganic anions generally suppressed the bactericidal efficiency of the photocatalyst in photocatalytic disinfection. HCO3-, SO42-, and H2PO4- were found to have high adsorption on the surface of the catalyst. The adsorbed inorganic anions reacted with electron holes (h+) and adsorbed •OH on the catalyst to form HCO3•, SO4•-, 7060
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 18, 2010
FIGURE 4. Photocurrent changes at the Ag-AgI/Al2O3 photoanode under visible-light irradiation (λ > 420 nm) in air-saturated 0.1 M sodium sulfate aqueous solutions with different concentrations of E. coli. and H2PO4• (20), which were less reactive than h+ and •OH. For the general reaction system, HCO3-, SO42-, and H2PO4would play a negative role (18, 21, 22). In the Ag-AgI/Al2O3 suspension, the main reactive oxygen species (ROS) on Ag NPs were O2•- and excited h+, while the latter could be scavenged by these anions to form anion radicals, which were weaker oxidants for the degradation of organic compounds. However, since these anions could permeate the E. coli cell membrane and be absorbed by the cell (23), these anion radicals could lead to stronger bactericidal activity than excited h+ on Ag NPs, which were not absorbed into the cell. Overall, these results suggest that the process of plasmoninduced photocatalytic disinfection using Ag-AgI/Al2O3 involves more than one mechanism. Plasmon-Induced Photocatalytic Disinfection Mechanism. The increased activity of Ag-AgI/Al2O3 was the result of the photoexcited AgI semiconductor and plasmon-induced Ag NPs under visible-light irradiation (λ > 420 nm). However, the Ag NPs plasmon-induced photocatalysis predominated due to the stronger light absorption in the visible region. In a previous study (9), the mechanism of plasmon-induced photodegradation of organic pollutants by Ag NPs was verified by electron spin resonance and CV analyses. Two electron-transfer processes, from the excited Ag NPs to AgI and from 2-CP to the Ag NPs, occurred during the degradation of 2-CP in Ag-AgI/Al2O3 suspensions. Moreover, both O2•and excited h+ on Ag NPs were the main active species. However, different reaction processes occurred in the same system during the inactivation of pathogenic microorganisms. The effects of the pH and inorganic anions on the transfer of plasmon-induced charges were also investigated by CV analyses to illustrate the bactericidal mechanism of Ag-AgI/ Al2O3. Figure 4 shows the changes in the photocurrent at the Ag-AgI/Al2O3 photoanode under different conditions. In the absence of E. coli under visible irradiation, the photocurrent increased and then decreased to zero, resulting in a peak, which contributed to the oxidation of Ag NPs. With the addition of E. coli, the peak gradually decreased and became indiscernible at 8 × 107 CFU/mL. A similar phenomenon was observed with the addition of S. dysenteriae and HRVWa (Figure S5). The results revealed that the photocurrent was generated by the plasmon-induced Ag NPs under visiblelight irradiation; this led to the photooxidation of Ag NPs, which could then be reduced by pathogenic microorganisms to obtain photostable Ag NPs. However, the same phenomena were not observed under dark but otherwise identical conditions. In the dark, the oxidation peak of Ag NPs appeared due to the oxidation of O2 in the absence of E. coli, but did not disappear with the addition of E. coli. Thus, the plasmon induction of Ag NPs was essential for the electron transfer from E. coli to Ag NPs (Figure S5). Therefore, the plasmoninduced h+ on Ag NPs was still one of the primary active
FIGURE 6. Effect of pH on the photocurrent changes at the Ag-AgI/Al2O3 photoanode under visible irradiation in 0.1 M sodium sulfate aqueous solutions under various conditions.
FIGURE 5. Effects of NaHCO3 and KH2PO4 on the photocurrent changes at the Ag-AgI/Al2O3 photoanode under visible irradiation (λ > 420 nm) in 0.1 M sodium sulfate aqueous solutions under the specified conditions. species in the photocatalytic inactivation of pathogenic microorganisms besides O2•-. As shown in Figure 5A, the peaks of Ag NPs gradually decreased and became almost indiscernible at 0.1 M HCO3- with the addition of HCO3- in the absence of E. coli under visible-light irradiation. In contrast, the addition of NO3- did not have the same influence on the oxidation of Ag NPs under otherwise identical conditions (Figure S7). These results confirmed that HCO3could reduce the plasmon-induced Ag+ as electron donors to form HCO3•; thus, electron transfer occurred from HCO3to Ag NPs, but not between the plasmon-induced Ag+ and NO3-. In the presence of 0.1 M HCO3-, with the addition of E. coli, the oxidation peak also gradually decreased and completely disappeared at 4 × 107 CFU/mL E. coli (Figure 5B), while the peak completely disappeared at 8 × 107 CFU/ mL E. coli without HCO3-(Figure 4). These results indicated that HCO3- enhanced electron transfer and led to higher bactericidal activity. A similar phenomenon was observed at the Ag-AgI/Al2O3 photoanode in the presence of H2PO4-. With increasing H2PO4- concentration, the oxidation peak decreased and disappeared at 0.2 M H2PO4- (Figure 5C), which indicated that the reductive ability of H2PO4- was lower than that of HCO3-. At 0.1 M H2PO4-, with the addition of E. coli, the peak decreased as much as it did without H2PO4(Figure 5D), which was parallel with the inactivation of E. coli under the same conditions. Since the photocurrent was determined in an air-saturated 0.1 M sodium sulfate aqueous solution, the effect of SO42- on the electron transfer could not be observed. However, these observations verified that two electron transfers occurred from plasmon-induced h+ on Ag NPs during the inactivation of E. coli in the presence of these inorganic anions. One was from E. coli to Ag NPs, and the other was from inorganic anions to Ag NPs to form inorganic anion radicals. Thus, the plasmon-induced h+, inorganic radicals, and O2•- were involved in the inactivation of E. coli. These inorganic anions not only enhanced the reduction of plasmon-induced Ag+ by promoting two electron-transfer rates from the excited Ag NPs to AgI and from E. coli to the Ag NPs, but the anion radicals also exhibited higher bactericidal efficiency due to their absorbability by the pathogenic cells (23, 24). Similarly, pH had a similar effect on the electron transfer from Ag NPs to donors. As shown in Figure 6A, the oxidation peak of Ag NPs decreased as the pH of the initial solution increased in the absence of E. coli. The peak intensity at pH 4.5 was higher than that at pH 8.5, which paralleled the bactericidal activity at different pHs.
Moreover, the oxidation peak at pH 4.5 decreased slightly with increasing E. coli (as shown in Figure 6B), which was similar to the bactericidal efficiency under the same conditions. These results indicated that the plasmon-induced Ag+ was reduced by the adsorbed hydroxyl ions (OH-) on the catalyst. Thus, •OH was very possibly formed with the reaction of OH- and plasmon-induced h+ on Ag NPs. OH- ions also enhanced the electron transfer, leading to the higher bactericidal activity of Ag-AgI/Al2O3. Therefore, the Ag-AgI/ Al2O3 photocatalytic disinfection mainly depended on the transfer of plasmon-induced charges, which resulted in the formation of ROS. The presence of these ubiquitous anions in water benefited the electron transfer, and their anionic radicals resulted in higher bactericidal activity. Plasmonic photocatalysis is a very promising method of water disinfection.
Acknowledgments This work was supported by the NSFC (20807051, 50921064), 973 project (2010CB933600), and the National 863 Project of China (2008AA062501).
Supporting Information Available Preparation and analysis of HRV-Wa, spectral energy distribution of the spherical xenon lamp, diffuse reflectance UV-vis spectra and zeta potentials of samples, photocatalytic inactivation of E. coli and HRV-Wa in Ag-AgI/Al2O3 suspension, and effects of HRV-Wa, S. dysenteriae, and NO3-on photocurrent generation at the Ag-AgI/Al2O3 photoanodes. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) Lima, A. A.; Moore, S. R.; Barboza, M. S., Jr.; Soares, A. M.; Schleupner, M. A.; Newman, R. D.; Sears, C. L.; Nataro, J. P.; Fedorko, D. P.; Wuhib, T.; Schorling, J. B.; Guerrant, R. L. Persistent diarrhea signals a critical period of increased diarrhea burdens and nutritional shortfalls: A prospective cohort study among children in northeastern Brazil. J. Infect. Dis. 2000, 181, 1643–1651. (2) Montgomery, M. A.; Elimelech, M. Water and sanitation in developing countries: Including health in the equation. Environ. Sci. Technol. 2007, 41, 17–24. (3) Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgiadis, J. G.; Marinas, B. J.; Mayes, A. M. Science and technology for water purification in the coming decades. Nature 2008, 452, 301–310. (4) Muellner, M. G.; Wagner, E. D.; McCalla, K.; Richardson, S. D.; Woo, Y.-T.; Plewa, M. J. Haloacetonitriles vs. regulated haloacetic acids: Are nitrogen containing DBPs more toxic? Environ. Sci. Technol. 2007, 41, 645–651. (5) Li, Q.; Page, M. A.; Marinas, B. J.; Shang, J. K. Treatment of coliphage MS2 with palladium-modified nitrogen-doped titanium oxide photocatalyst illuminated by visible light. Environ. Sci. Technol. 2008, 42, 6148–6153. (6) Yu, H.; Quan, X.; Zhang, Y.; Ma, N.; Chen, S.; Zhao, H. Electrochemically assisted photocatalytic inactivation of Escherichia coli under visible light using a ZnIn2S4 film electrode. Langmuir 2008, 24, 7599–7604. (7) Jin, R.; Cao, Y. C.; Mirkin, C. A.; Kelly, K. L.; Schatzand, G. C.; Zheng, J. G. Photo-induced conversion of silver nanospheres to nanoprisms. Science 2001, 294, 1901–1903. VOL. 44, NO. 18, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
7061
(8) Link, S.; El-Sayed, M. A. Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in gold and silver nanodots and nanorods. J. Phys. Chem. B 1999, 103, 8410– 8426. (9) Hu, C.; Peng, T. W.; Hu, X. X.; Nie, Y. L.; Zhou, X. F.; Qu, J. H.; He, H. Plasmon-induced photodegradation of toxic pollutants with Ag-AgI/Al2O3 under visible-light irradiation. J. Am. Chem. Soc. 2010, 132, 857–862. (10) Awazu, K.; Fujimaki, M.; Rockstuhl, C.; Tominaga, J.; Murakami, H.; Ohki, Y.; Yoshida, N.; Watanabe, T. A plasmonic photocatalyst consisting of silver nanoparticles embedded in titanium dioxide. J. Am. Chem. Soc. 2008, 130, 1676–1680. (11) Wang, P.; Huang, B.; Qin, X.; Zhang, X.; Dai, Y.; Wei, J.; Whangbo, M. Ag@AgCl: A highly efficient and stable photocatalyst active under visible light. Angew. Chem., Int. Ed. 2008, 47, 7931–7933. (12) Hu, C.; Hu, X. X.; Guo, J.; Qu, J. H. Efficient destruction of pathogenic bacteria with NiO/SrBi2O4 under visible light irradiation. Environ. Sci. Technol. 2006, 40, 5508–5513. (13) Yu, J. C.; Ho, W. K.; Yu, J.; Yin, H.; Wong, P. K.; Zhao, J. Efficient visible-light-induced photocatalytic disinfection on sulfurdoped nanocrystalline titania. Environ. Sci. Technol. 2003, 39, 1175–1179. (14) Shimizu, K.; Tsuzuki, M.; Kato, K.; Yokota, S.; Okumura, K.; Satsuma, A. Reductive activation of O2 with H2-deduced silver clusters as a key step in the H2-promoted selective catalytic reduction of NO with C3H8 over Ag/Al2O3. J. Phys. Chem. C 2007, 111, 950–959. (15) Sato, K.; Yoshinari, T.; Kintaichi, Y.; Haneda, M.; Hamada, H. Remarkable promoting effect of rhodium on the catalytic performance of Ag/Al2O3 for the selective reduction of NO with decane. Appl. Catal., B 2003, 44, 67–78. (16) She, X.; Flytzani-Stephanopoulos, M. The role of Ag-O-Al species in silver-alumina catalysts for the selective catalytic reduction of NOX with methane. J. Catal. 2006, 237, 79–93.
7062
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 18, 2010
(17) Jean, J.; Blais, B.; Darveau, A.; Fliss, I. Simultaneous detection and identification of hepatitis A virus and rotavirus by multiplex nucleic acid sequence-based amplification (NASBA) and micro titer plate hybridization system. J. Virol. Methods 2002, 105, 123–132. (18) Rinco´n, A. G.; Pulgarin, C. Effect of pH, inorganic ions, organic matter and H2O2 on E. coli K12 photocatalytic inactivation by TiO2: Implications in solar water disinfection. Appl. Catal., B 2004, 51, 283–302. (19) Hamounda, T.; Baker, J. R., Jr. Antimicrobial mechanism of action of surfactant lipid preparations in enteric Gram-negative bacilli. Appl. Microbiol. 2000, 89, 397–403. (20) Ross, A. B.; Neta, P. Rate Constants for Reactions of Inorganic Radicals in Aqueous Solution; U.S. Department of Commerce, National Bureau of Standards: Washington, DC, 1979. (21) Maruga´n, J.; van Grieken, R.; Sordo, C.; Cruz, C. Kinetics of the photocatalytic disinfection of Escherichia coli suspensions. Appl. Catal., B 2008, 82, 27–36. (22) Alrousan, D. M. A.; Dunlop, P. S. M.; McMurray, T. A.; Byrne, J. A. Photocatalytic inactivation of E. coli in surface water using immobilized nanoparticle TiO2 films. Water Res. 2009, 43, 47– 54. (23) Criado, S.; Marioli, J. M.; Allegretti, P. E.; Furlong, J.; Rodrı´guez, N. F. J.; Ma´rtire, D. O.; Garcı´a, N. A. Oxidation of di- and tripeptides of tyrosine and valine mediated by singlet molecular oxygen, phosphate radicals and sulfate radicals. J. Photochem. Photobiol., B 2001, 65, 74–84. (24) Becker, D.; Razskazovskii, Y.; Callaghan, M. U.; Sevilla, M. D. Electron spin resonance of DNA irradiated with a heavy-ion beam (16O8+): Evidence for damage to deoxyribose phosphate backbone. Radiat. Res. 1996, 146, 361–368.
ES1012577
