DSpace at VNU: Bactericidal activity and silver release of porous ceramic candle filter prepared by sintering silica with silver nanoparticles zeolite for water disinfection

Home Search Collections Journals About Contact us My IOPscience Bactericidal activity and silver release of porous ceramic candle filter prepared by sintering silica with silver nanoparticles/zeolite for water disinfection This content has been downloaded from IOPscience Please scroll down to see the full text 2014 Adv Nat Sci: Nanosci Nanotechnol 035001 (http://iopscience.iop.org/2043-6262/5/3/035001) View the table of contents for this issue, or go to the journal homepage for more Download details: IP Address: 198.91.37.2 This content was downloaded on 21/02/2015 at 04:48 Please note that terms and conditions apply | Vietnam Academy of Science and Technology Advances in Natural Sciences: Nanoscience and Nanotechnology Adv Nat Sci.: Nanosci Nanotechnol (2014) 035001 (6pp) doi:10.1088/2043-6262/5/3/035001 Bactericidal activity and silver release of porous ceramic candle filter prepared by sintering silica with silver nanoparticles/ zeolite for water disinfection Thuy Ai Trinh Nguyen1,2, Van Phu Dang1, Ngoc Duy Nguyen1, Anh Quoc Le1, Duc Thanh Nguyen3 and Quoc Hien Nguyen1 Research and Development Center for Radiation Technology, Vietnam Atomic Energy Institute, 202 A Street 11, Linh xuan Ward, Thu duc District, Ho Chi Minh City, Vietnam Ho Chi Minh City University of Technology, Vietnam National University in Ho Chi Minh City, 268 Ly Thuong Kiet Street, Ho Chi Minh City, Vietnam Center for Nuclear Techniques, Vietnam Atomic Energy Institute, 217 Nguyen Trai Street, Ho Chi Minh City, Vietnam E-mail: hien7240238@yahoo.com Received 21 March 2014 Accepted for publication 19 May 2014 Published 12 June 2014 Abstract Porous ceramic candle filters (PCCF) were prepared by sintering silica from rice husk with silver nanoparticles (AgNPs)/zeolite A at about 1050 °C to create bactericidal PCCF/AgNPs for water disinfection The silver content in PCCF/AgNPs was of 300–350 mg kg−1 determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and the average pore size of PCCF/AgNPs was of 50–70 Å measured by Brunauer–Emmett–Teller (BET) method The bactericidal activity and silver release of PCCF/AgNPs have been investigated by flow test with water flow rate of L h−1 and initial inoculation of E coli in inlet water of 106 CFU/100 mL The volume of filtrated water was collected up to 500 L Results showed that the contamination of E coli in filtrated water was commercial silver-exchanged zeolite (granular) >commercial silver-exchanged zeolite (pellets) >AgNPs 100 nm Liu and Hurt [21] claimed that AgNPs can usually be oxidized in aqueous solution when exposed to air (equation (1)), which results in the release of silver ion under acidic conditions (equation (2)) as follows: Figure UV-Vis spectrum of 0.5% AgNPs/zeolite in 2% PVA Intensity solution 38.11° 44.29 ° [111] 64.45 ° [200] 2.3591 2.0436 [220] 1.4446 AgNPs/Zeolite 4A 77.41° [311] 1.2319 Zeolite 4A 10 20 30 40 50 60 70 80 Theta (degree) Figure XRD patterns of zeolite A and AgNPs/zeolite A incubated at 37 °C overnight (∼16 h) The counts of bacterial colonies were the surviving numbers of E coli [13] 2.3.2 Flow test The inlet water as described in figure was inoculated with E coli of ∼106 CFU/100 mL The bactericidal activity of PCCF/AgNPs was also investigated with the flow rate of ∼5 L h−1 The output water passed through PCCF/AgNPs was collected up to 500 L for assessment of the E coli contamination according to ISO 9308-1: 2000 [14] Results and discussion 3.1 Characteristics of AgNPs/zeolite Figure shows the maximum absorption wavelength (λmax) of AgNPs/zeolite at 427 nm Shameli et al also reported the characteristics of their AgNPs/zeolite products with the λmax values in the range of around 394–401 nm that correspond to AgNPs smaller than 10 nm [12] From the XRD pattern in figure 3, the average size of the metallic AgNPs deposited on zeolite was calculated using the peak at 2θ = 38.11° with full width at half maximum (FWHM) of about 0.277 and based on Debye–Scherrer’s formula: t = 0.9λ/Bcos θ as described by Jiang et al [15] 4Ag + O2 → 2Ag2 O, (1) 2Ag2 O + 4H + → 4Ag+ (2) According to Sotiriou and Pratsinis [22], the mechanism of AgNPs toxicity to bacteria depends strongly on Ag+ release, and Ag+ is the definitive molecular toxicant In recent years, several authors reviewed possible mechanisms of AgNPs [23, 24], but the exact mechanism is still not fully elucidated It was generally believed that silver ions interact Adv Nat Sci.: Nanosci Nanotechnol (2014) 035001 T A T Nguyen et al Figure EDX spectra of PCCF and PCCF/AgNPs 3.3 Content of silver release from PCCF/AgNPs into filtrated water Results in table proved that the contents of the silver released from PCCF/AgNPs in the filtrated water by flow test with the rate of ∼5 L h−1 were less than μg L−1 determined by neutron activation analysis (NAA) and ICP-MS methods The contents are far below the WHO guideline of 100 μg L−1 silver at maximum for drinking water [2] Results in table also indicate that both methods for determination of silver in water are in accordance with each other Oyanedel–Craver et al [9] and van Halem et al [10] also studied silver release from silver-impregnated porous ceramic pot filter for low cost household drinking water treatment However, they did not used a coupling agent like aminosilane to fix AgNPs to the ceramic wall, therefore silver was easily leaching from the pot and the bactericidal effect should be quickly decreased with the filtration time Thus, PCCF/AgNPs showed less silver release (∼1 μg L−1) compared to silver-impregnated porous ceramic even treated with coupling agent aminosilane (∼10 μg L−1) [8] Figure XRD patterns of PCCF and PCCF/AgNPs Table Some characteristics of PCCF/AgNPs Parameters Values Length (mm) Inner diameter (mm) Outer diameter (mm) PCCF/AgNPs weight (g) Mean pore size (μm) BET (m2 g−1) AgNPs content (mg kg−1) 200–202 30.4–30.6 50.6–50.8 300–350 0.005–0.007 1.5–2.5 300–350 3.4 Antimicrobial activity 3.4.1 In vitro test The surviving number of E coli in the tested medium was of 15 × 105; 5.8 × 105 and CFU ml−1 for control, PCCF and PCCF/AgNPs samples, respectively, as shown in figure The in vitro test results indicated that PCCF/AgNPs has highly bactericidal activity against E coli with bacterial cell wall, plasma membranes, bacterial DNA and protein, as well as ribosomes, resulting in bactericidal effects Therefore, silver ions released from AgNPs have been proven to be one possible mechanism; however, it is not the only mechanism for the antimicrobial activity of AgNPs Thus, it is expected that Ag+ is formed from AgNPs, Ag2O and/or Ag2O/AgNPs clusters when PCCF/AgNPs is in contact with water, and therefore Ag+ will be the main bactericidal agent during water filtration 3.4.2 Flow test The results in table indicated that the water filtrated though PCCF/AgNPs up to 500 L was not contaminated by E coli (