VIETNAM JOURNAL OF CHEMISTRY VOL. 51(5) 653-657 OCTOBER 2013
GAMMA-IRRADIATION SYNTHESIS OF SILVER NANOPARTICLES FIXING IN POROUS CERAMIC FOR APPLICATION IN
WATER TREATMENT
Dang Van Phu', Nguyen Thuy Ai Trinh\ Bui Duy Du^, Nguyen Quoc Hien' 'Research and Development Center for Radiation Technology, Vietnam Atomic Energy Institute
^Ho Chi Minh City University of Technology. Vietnam National University of Ho Chi Minh City
^Institute of Applied Material Science, Vietnam Academy of Science and Technology Received 10 September 2013
Abstract
The Ag nanoparticles in polyvinylpyrrolidone solution with concentration of 500 mg/L and their diameter of 10- 15 nm were synthesized on a large scale up to 100 L/batch by gamma irradiation route Porous ceramic candle samples were functionalized by treatment with a 3-amino-propyltriethoxysiIane coupling agent and then impregnated in Ag nanoparticles solution for fixing Ag nanoparticles. The load Ag nanoparticles content on porous ceramic was of about 200-250 mg/kg. The average pore size of porous ceramic/Ag nanoparticles was about 48.2 A. Owing to strong bonding of silver atoms to the wall of porous ceramic functionalized by 3-amino-propyltriethoxysilane, the contents of silver released from porous ceramic/Ag nanoparticles mto filtrated water by flow lest at a flow rate of about 5 L/h were less than 10 pg/L and was far below the requfred standard limit (< 100 pg/L) for drinking water. Thus, porous ceramic/Ag nanoparticles candles can be potentially applied for pomt-of-use drinking water treatment.
Keywords: Silver nanoparticles, porous ceramic, water treatment, gamma irradiation synthesis.
1. INTRODUCTION
Although many routes are available for the synthesis of nanoparticles to elate, there is an increasing demand to develop high yield, low cost, green chemistry and environmentally friendly procedures. According to many previous reports, for the synthesis of colloidal nanoparticles solution the gamma irradiation route provides several advantages and satisfy able to above demands [1-3]. Among of nanoparticles, excellent antibacterial activation and low cytotoxicity to human cells favor silver nanoparticles (AgNPs), making them applicable to water treatment [4, 5]. The presence of pathogenetic microbes in drinldng water is a potential health risk.
The removal of bacterial from water is an exfremely important process for drinking and sanitation systems especially against concerns on growing outbreaks of waterbome diseases [5]. According to WHO, the clean, potable water sources are not access able to at least one billion people in the world [6]. Recently, considerable interest has arisen in the use of AgNPs based on gigantic high antimicrobial
and biofouling improvement for water disinfection [7], In particular, the formation of by-products into water by conventional freatment techniques and the increasing of resistance of some pathogens to conventional disinfectants have encouraged researchers to explore the AgNPs [8]. The reliability and ease of operation of membrane-based water filfration systems such as polyurethane foam [9], paper sheet filter [6], porous ceramic filters [4, 10, 11] made them to be more and more widely used.
Traditional ceramics are often employed in water filfration because of the ease of creating a uniform stmcture of fine pores. Such ceramic stmctures can remove many water contaminants by size exclusion through the pores or by adhesion to the pore walls [12], However, porous ceramics (PC) can only block bacteria and do not have the capability to bil them [11]. Numerous investigations have been carried out on loading AgNPs with the functionalized PC filters as an effectively antimicrobial agent for water freatment [9, 10, 13]. Unfortunately, it is difficult to load the AgNPs were commonly inert on PC [11], so that silver releases into water filtrate with overdoses
653
VJCVol. 51(5), 2013
compared to the maximum standard limit of 0.1 mg/L, issued by the WHO and US-EPA [6, 13].
Several approaches were studied to improve on loading and holding abilities of AgNPs onto polymer and PC filters, mainly by usmg a coupler and/or modification by appropnate agents containing ftmctional groups which have affmity with AgNPs [4, 11]. However, it has still not been reported on production of fixing AgNPs in PC candles. In this study, we present a facile procedure for synthesis of large scale AgNPs/PVP solution. The domestic commercialized PC product was used for modifying and fixing with AgNPs through coordmation bonds by using aminosilane as coupling agent. The effect of aminosilane freatments in capacity of AgNPs immobilized in PC was investigated. The silver content released from PC/AgNPs mto filfrated water was also investigated by flowing test. The as- prepared PC/AgNPs candles grating containing antimicrobial AgNPs with on acceptable level of silver release, can be potentially further developed towards point-of-use drinking water freatment.
2. MATERL\LS AND METHODS 2.1. Materials and chemicals
AgN03 IS pure grade of China, Polyvinylpyrrolidone (PVP) is a pharmaceutical grade product from BASE, Germany. Absolute ethanol is product of Tmong Thmh Co., Vietnam.
Aminosilane (AS) namely 3- aminopropylfriethoxysilane is purchased from Merck, Germany. Commercial porous ceramic was supplied by a domestic Ceramic Co., Hai Duong, Viemam.
2.2. Methods
2.2.1. Synthesis of colloidal silver nanoparticles (AgNPs) solution
AgNPs/PVP solution was prepared through a modified our method as reported in previous work [1]. Briefly, PVP and ethanol (EtOH) were dissolved in water to prepare solution with the concenfration of 1% (w/v) and 5% (v/v), respectively. AgNOs was then dissolved in the above prepared solution to obtain final formulation: 5 mM AgVl% PVP/5%
EtOH/water to 100 L. The mixture was pomed into plastic cans with 25 L/can and tight sealing by a can cap. The irradiation of this solution for the synthesis of AgNPs was carried out on a Co-60 irradiator with dose rate about 1.2 kOy/h at VINAGAMMA Center, HCM City. Absorption spectra of irradiated AgNPs
Bui Duy Du, et al.
solution were taken on an UV-Vis specfrophotometer, Jasco V-630. The AgNPs sizes were measured using a transmission elecfron microscope (TEM), JEM 1010, JEOL, Japan.
2.2.2. Functionalization of PC by aminosilane (AS) PC samples of approximately 3.0x2.5x0.8 cm^
in size or PC candles with dimensions of 20x4x0.8 cm^ were cleanly freated in 10% H2SO4 at 60°C for 1 h, washed with water and dried at 110°C. Then it was impregnated in AS of 0.5-2% (v/v) in EtOH solution with different time durations. The PC impregnated with AS was dried at room temperature and then heated at 110°C m an oven 2 h for siloxan bonding between PC and AS (PC/AS).
2.2.3. Impregnation PC/AS in AgNPs solution The as-prepared PC/AS samples were further impregnated in AgNPs solution for 24 h. After that, it was washed in ulfrasonic water bath for 15 rmn.
with repetitively three times to remove all unbound AgNPs. AgNPs loaded PC samples (PC/AgNPs) was dried in a forced air oven at SO^C till brown-yellow PC/AgNPs were obtained. The content of AgNPs in PC/AgNPs was determined by ICP-AES method on a Perkin-Elmer, Optima 5300 DV. The presence of AgNPs in PC/AgNPs was assessed by energy- dispersive X-ray specfroscopy (EDS) on a JEOL 6610 LA and UV-Vis specfroscopy on a Jasco V- 630, The specific surface area, the pore size and pore volume were measured by BET method (Quantachrom Nova 1200) using N2 as the adsorbate.
2.2.4. Determination of Ag release
The PC/AgNPs candle was cormected to tap water with adjusted flow rate of ~5 L/h. The filh^ted water was collected for determination of the Ag content by neufron activation analysis at the Nuclear Research Institute, Dalat.
3. RESULTS AND DISCUSSION 3.L Synthesis of colloidal AgNPs solution
The method using radiation of gamma ray and elecfron beam provides several advantages compared to other methods, especially the pure AgNPs can be produced without contamination of excessive reductant and Ag* residue; and large scale production can be carried out at a comparatively
VJC, Vol. 51(5), 2013
reasonable cost [1-3], The mechanism of the vCo-60 irradiation method for synthesis of AgNPs/PVP solution was descnbed in the previous papers [1-3], Bnefly, the complex Ag*/PVP was reduced to AgNPs/PVP soluhon by hydrated electron (e'^q) and hydrogen atom (H*) which was generated by y-
Gamma-irradiation synthesis of silver.
radiolysis of aqueous solution [2]. In addition, tiie hydroxyl radical ('OH) reacts with alcohol (e.g.
ethanol, isopropanol,..) yielding hydroxyalkyl radical which is able to reduce Ag* ions absorbed on clusters to Ag°[l,2].
bl-S
Figure 1: (a) The view and UV-Vis spectmm of the AgNPs/PVP solution jude, (b) TEM rniage and (c) particles size histogramme of AgNPs
In Fig. 1, the irradiated Ag*/PVP solution showed red-brown and the maximum absorbed wavelength -400-410 nm, which are characterizatics for the colloidal AgNPs [1-3]. The TEM image showed the AgNPs were mainly sphere-shape. The average particles size of AgNPs/PVP as-prepared was of 13.7 nm, which is larger than that (-9.5 nm) as synthesized by Du et al. (2008) [1]. The reason can be explained by difference of adsorbing dose rate between small and large volume, the higher the
dose rate the smaller the particle size could be produced [2]. However, according to results reported by Pbu et al. [3] and Quang et al. [8] the AgNPs size -10-15 nm exhibited highly antimicrobial activity so as-prepared AgNPs/PVP on large scale can be used for fixing onto the wall of porous ceramic (PC) to create antimicrobial PC filters.
3.2. Optimization of concentration and treatment time of PC with AS
Table 1: Effect of freatment conditions of AS on silver content (mg/kg) in PC/AgNPs AS concentration (%), during 90 min.
0 7.5
0.5 94.5
1 192
2 228
3 234
5 255
AS h-eatnient time (min.), 2% AS 30
200 60 205
90 228
120 226
150 222
180 231 The results in table 1 indicated that the
appropriate concenfration of AS was of ~2% and the suitable immersion time was of 90-120 min. for maximum fixing AgNPs m PC/AgNPs of ca. 200- 250 mg/kg. As we known, this is fist time reported the optimization of freatment conditions of PC with AS. The mechanism of fix AgNPs in modified PC by AS was in detail explained by Lv et al. (2009) [11]. Briefly, the siloxan (-Si-O-Si-RNHz) bonds were formed during the PC immerged in AS solution and the PC/AS heated into an oven. After that, the coordination bonds (-R-NHj-Ag-AgNPs) of the - NH2 groups with the Ag atoms were formed during the shocking PC/AS in AgNPs solution. Lv et al.
(2009) also shidied to fix AgNPs in PC water treatinent, but they only prepared samples of IMx0.5cm'.
From EDS specfra in Fig. 2 showed that the composition of PC consists of three main elements
particularly Si, Al, O and small amount of Na and K, but without any frace of silver. After fixing AgNPs in PC, the peak at 3 keV and 3,2 keV appeared in EDS spectrum confirming the presence of silver in the composition of PC/AgNPs. The EDS spectmm was also used to confirm the presence of AgNPs m another AgNPs fixed materials [5, 6, 8, 12].
The observation from Fig. 2, that the PC/AgNPs was yellovrish colour after fixed with AgNPs that is also observed by previous studies [8, 11, 12]. The Xnm of AgNPs fixed onto PC was at ~405 nm with broad peak compared to the original AgNPs (data not shown). Thus, this peak indicated that AgNPs are present m the PC as reported by previous research works [9,11].
The BET is a good tool for charactenzation of porosity materials. Results in table 2 showed that the surface area, pore volume and pore size of
VJCVol. 51(5), 2013
PC/AgNPs simultaneously decreased in comparison to bare PC. This phenomenon can be attributed by
Bui Duy Du, et al.
the AS molecules and AgNPs coated on the surface and filled into the tiny pores of PC [8].
' PC/AgNPs
I J J
Figure 2: The porous ceramic candle samples and EDS specfra Table 2: Characteristics of blank PC and PC/AgNPs candle Parameters
Sliver content, mg/kg Specific surface area, mVg Average pore size, A Total pore volume, cmVg
PC Not detected
1.83 61.9 2.8x10'^
PC/AgNPs 200-250
1.51 48.2 1.8x10' 3i3. Content of silver release from PC/AgNPs candles into filtrated water by flowing test
Table 3: The silver content in the filfrated water released from PC/AgNPs candle Volume of filtrated water, L
Ag content, ixg/L
20 9.04
40 7.49
80 4,12
100 2.66
200 0.64
300 0.66
400 0.34
500 0.92 Results in Table 3 proved that the contents of the
silver releasing from PC/AgNPs candle in the filfrated water up to 500 L were less than 10 |J.g/L, which are far below the WHO guideline (<100 ^ig/L) for dnnking water. Previous smdies also studied of silver-impregnated porous ceramic pot filter for low- cost household dnnking water freatment [4, 6, 10, 12, 13].-However, they did not used coupling agent like AS to fix AgNPs, therefore silver was easily leaching from the pot with overdose and the antimicrobial effect should be decreased with the filfration time. Among the water freatment materials, ceramic filters (disk, candle and pot) proved to be one of the best freatment options for reducing bacteria contaminant in water [10, 12]. Therefore, the PC/AgNPs candle prepared in this study with stably fixing 200-250 mg AgNPs/kg is promising to apply for point-of-use drinking water freatment.
4. CONCLUSIONS
The colloidal AgNPs/PVP solution with the particles size of 10-15 nm and the AgNPs concenfration of 500 mg/L was synthesized by y- irradiation method. The fixing of AgNPs in PC through coordination bonds using AS as a coupling agent was performed. Results of flow test on silver
release indicated that the silver content in filfrated water were less than 10 ^tg/L, and it is far below the WHO guideline of 100 |j,g/L at maximum for drinking water. Thus, it is expected that the PC/AgNPs candles with the silver content of 200- 250 mg/kg have highly antimicrobial activity for point-of-use drinking water freatment.
REFERENCES
1. B. D. Du et al. Preparation of colloidal silver nanoparticles in poly(N-vinylpyrrolidone) by f- irradiation, J. Exp, Nanosci. 3, 207-213 (2008).
2. T. Ll, H. G. Park, S. H. Choi, y-lrradiation-induced preparation of Ag and Au nanoparticles and their characterizations. Mater. Chem. Phys. 105, 325-330 (2007).
3. D. V. Phu, et al. Synthesis and antimicrobial effects of colloidal silver nanoparticles in chitosan by y- i/TflJiarion, J. Exp. Nanosci 5, 169-179(2010).
4. W, Shen, et al. Ultrafine silver (II) oxide particles decorated porous ceramic composites for water tieatment, Chem. Eng. J., 175, 592-599 (20II).
5. Q. Bao, D. Zhang, P, Qi. Synthesis and characterization of silver nanoparticle and graphene oxide nanosheet composites as a bactericidal agent
VJC, V o l . 51(5), 2 0 1 3
for water disinfection, J. Colloid. Interf. Sci., 360, 463^70(2011).
u. T. A. Dankovich and D. G. Gray. Bactericidal paper impregnated with silver nanoparticles for point-of- use water treatment. Environ. Sci. Technol., 45, 1992-1998(2011).
7. K Zodrow, et al. Polysulfone ultrafiltiation membranes impregnated with silver nanoparticles show improved biofouling resistance and virus removal Water Res., 43, 715-723 (2009).
8 D. V. Quang, et al. Preparation of amino functionalized silica micro beads by dry method for supporting silver nanoparticles with antibacterial properties. Colloids and Surface A, Physicochem.
Eng. Aspects 389, 118-126(2011).
P. Jain, T. Pradeep. Potential of silver nanoparticle- coated polyurethane foam as an antibacterial water filter, Biotechnol. Bioeng., 90, 59-63 (2005).
Gamma-irradiation synthesis of silver...
. A. R. Bielefeldt, et al. Removal of virus lo protozoan sixed particles in point-of-use ceramic water filters.
Water Res., 44, 1482-1488 (2010).
. Lv Y. et al. Silver nanoparticle-decorated porous ceramic composite for water treatment". J. Membr Sci. 331, 50-56 (2009).
. C. Larimer, et al. The segregation of silver nanoparticles in low-cost ceramic water filters, Mater. Character., 61, 408-412 (2010).
. J. K. Mwabi, B B. Mamba, M. N B. Momba.
Removal of Escherichia coli and Faecal coliforms from surface water and groundwater by Household water treatment devices/systems A sustainable solution for improving water quality in rural community of the Southern African development community region, Int J. Envfron. Res. Public Health 9, 139-170 (2012).
Corresponding author: B u i D u y D u
Institute of Applied Material Science, V i e m a m A c a d e m y of Science and Technology E m a i l : v m a 9 8 0 2 @ g m a i l . c o m
P h o n e : 0 9 7 6 7 4 3 0 3 0 .
