Materials Science Forum Online: 2012-11-12 ISSN: 1662-9752, Vol. 729, pp 234-239 doi:10.4028/www.scientific.net/msf.729.234 2013 Trans Tech Publications, Switzerland Single, binary and ternary ion exchanged zeolite as an effective bioactive filler for biomedical polymer composites Péter Kaali 1, a, György Czél 2,b 1 College of Engineering, Swansea University, Singleton Park, Swansea, UK, SA1 6YH 2 Dep. of Polymer Engineering, Miskolc University, HU 3515 Miskolc-Egyetemvaros, Hungary a P.Kaali@swansea.ac.uk, b femczel@uni-miskolc.hu* Keywords: Ion-exchanged zeolite, bioactive filler, antimicrobial silver, copper zinc, AAS, EDX, ion distribution, antimicrobial test, minimum inhibitory concentration. Abstract. The preparation and modelling of single, binary and ternary ion exchanged zeolites that express antimicrobial efficiency is discussed. As experimental material A type zeolite was used and different variations of Ag, Cu and Zn ions were incorporated into the crystal structure. Antimicrobial efficiency is based on the ion concentration and ion release of the zeolite, therefore the maximum cation-exchange capacities (CEC) were determined for each of the single ions. After the determination of CEC the preparation of binary and ternary ion-exchanged zeolite samples were prepared by the mixture of silver, copper and zinc nitrate solutions and the composition of the samples was determined by atomic absorption spectroscopy (AAS). To verify the bioactive effect, the minimum inhibitory concentration (MIC) of single, binary and ternary ion-exchanged zeolite A was determined for bacteria strains. Introduction Zeolites are minerals that have a variety of natural and synthetic forms. Besides industrial use, zeolites have a high importance as food supplements and agents for medical treatments for both humans and animals [1, 2]. The biocide behaviour based on the ion exchange where the ions incorporated in the structure exchange with other ions (i.e. Na, K etc.) that can be found in the outer environment. For antimicrobial applications zeolites are usually filled with antimicrobial metallic ions (i.e. silver) that are slowly released during the whole service time. It has been reported by several studies that silver-zeolite has very good antimicrobial properties. However, there are other metallic ions (i.e. Cu, Zn) that show antimicrobial effect and can be used to treat zeolites, in order to make them applicable for antimicrobial purposes. If the ion release reaches a point, where the released concentration of the ions is below the minimum inhibitory concentration (MIC) of the present microorganism, the zeolite will lose its function. Therefore the determination of the ion release for certain antimicrobial applications is essential. In order to estimate the service time (antimicrobial effect) of the antimicrobial zeolite the understanding and investigation of ion exchange and re-exchange processes has a great importance. In the literature there are numerous publications that describe the single ion exchange mechanism of different zeolites with different ions. However, the number of papers that describes the binary or ternary ion-exchange properties and models of zeolites as complex multi-component systems is very limited [3, 4]. The current study aimed to prepare and characterize the ion release properties of single, binary and ternary ionexchanged zeolite systems for antimicrobial purposes, where the variation of silver, copper and zinc is incorporated into the zeolite structure. Materials and Sample preparation Synthetic A type zeolite, ZEOMIC AJ10D inorganic antimicrobial agent (Ag content 2.5%) was purchased from Sinanen Zeomic Co., Ltd. (Tokyo, Japan). Sodium-chloride (puriss. p.a., 99.5%), silver nitrate (purum p.a., crystallized, 99.0%), zinc nitrate hexahydrate (purum, 98%), copper nitrate trihydrate (puriss. p.a., 99-104%) were purchased from Sigma Aldrich (Stockholm, Sweden). All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-11/05/16,05:18:44)
Materials Science Forum Vol. 729 235 Methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, Pseudomonas aeruginosa ATCC 27853, Candida tropicalis ATCC 90874 were supplied by the Hungarian National Public Health and Medical Officer Service (Miskolc, Hungary). Determination routine of maximum ion-exchange capacity The maximum cation-exchange capacity (CEC) of the zeolite samples was determined for single ion systems by the Langmuir model [27]. Different dilutions of Ag, Cu and Zn nitrate solutions were prepared with a concentration of 1, 5, 7, 10, 20, 30, 50, 70 and 100 mmol/l. 10 ml of each solution was added to 0.25g of zeolite and was kept for 24h at room temperature under constant stirring. Then the ion-exchanged zeolites and solutions were separated by centrifugation and filtration and the remaining ion-concentration in the solutions was measured by atomic absorption spectrophotometer (AAS). The ion concentration that was transferred into the solid phase (zeolite) was calculated by the following equation: V qe = ( C Ce ), (1) 0 m where q e (mmol/g) refers to the concentration of ions in the solid phase, C 0 (mmol/l) is the initial concentration and C e (mmol/l) is the final concentration of the solution and V/m is the dilution ratio. The ion concentration of the solid phase was confirmed by Electron Dispersive X-ray Spectroscopy (EDX). Based on this the Langmuir adsorption isotherm can be drawn by the q e -C e function. The maximum ion capacity that can be transferred into the solid phase was calculated with the equation of the linearized Langmuir isotherms: 1 k L 1 1 = +, (2) q e Q C e Q where Q (mg/g) is the maximum amount of ions that can be transferred into the solid phase and k L 1 1 (mg/l) is a constant. By inserting a approximating strait line to the function, the gradient q e C e (m) and the intersection (b) was determined. Based on these values the unknown components of the equation ( Q, k L ) were calculated. Experimental Ion exchange and re-exchange reactions. It has been confirmed by recent studies that the sodium ions located in the structure of zeolites are the easiest to exchange to other metallic ions. Therefore, in the first phase of the ion-exchange reaction was the saturation of the zeolite with sodium ions. For this purpose 1g zeolite was added to 40 ml 1M diluted NaCl solution. The ion exchange took place at room temperature for 24 hours under constant stirring. The solution was replaced with fresh 1M NaCl every 8 hours. Then the zeolites were separated from the solution by filtration and washed 5 times with distilled water to remove the excess amount of chloride ions from the samples, and dried at 105 C. Preparation of single, binary and ternary ion-exchanged zeolite systems were performed in second phase. The zeolites were filled with Ag, Cu, Zn ions. In case of binary and ternary systems the combination of these ions were applied and the preparation of the following samples were obtained: Ag-Zn, Ag-Cu, Zn-Cu, Ag-Zn-Cu. In principle this ion-exchange procedure was identical to the first reaction. For single ion-exchanged systems 1g zeolite was added to 40 ml 0,1M Ag-, Cu-, or Zn-nitrate solutions and the reaction took place at room temperature for 24 hours under constant stirring. In case of binary and ternary systems the procedure was the same, where the ion-exchange reactions was performed with Ag-Zn, Ag-Cu, Zn-Cu and Ag-Zn-Cu nitrate solutions. The concentration of each component in the solution was 0,1M. After 24 hours the zeolites were separated from the solution by filtration, washed 5 times with distilled water and dried at 105 C. When ion-exchanged samples completely dried the re-exchange procedure was performed by adding 1 g zeolite to 40 ml NaCl solutions with the following concentrations: 1, 5, 7, 10, 20, 30, 50, 70, 100 and 1000 mmol/l. The reaction was carried out for 24 hours at room temperature with constant stirring. In this way the complex ion release of A type zeolite could be measured.
236 Materials Science, Testing and Informatics VI Figure 1. Silver, copper and zinc ion adsorption isotherms of zeolite A Figure 2. Linearized Langmuir isotherm of silver, copper and zinc exchanged zeolite A Fig.1. represents the ion adsorption of A zeolite. In order to confirm whether the zeolites became saturated at between 50 and 100 mmol/l initial solution concentration, the determination of the maximum ion exchange capacity is necessary. This parameter can be determined from the linearized Langmuir ion absorption isotherms or by equation (2). Fig. 2. presents the linearized Langmuir isotherm of the A zeolite. In sample A-Ag, A-Cu the measured ion concentration is approximately 8-10% lower than the theoretical saturation point, which is acceptable. In contrast, mostly all absorption isotherms showed a nearly saturated level of the samples. This significant difference between the theoretical and measured values may be due to the equilibrium between the sodium and exchanging ion, since the zeolite was previously saturated with sodium in order to maximize the ion absorption capacity. Based on the results it seems that the ion adsorption isotherms are more likely to show only the absorption capacity and do not take into account that the solid phase may contain additional ions that can be exchanged. After the theoretic determination of maximum ion adsorption capacities for the three metallic ions, the preparation of different multi ion containing systems was performed. The aim for single ion-exchanged system was to reach and confirm the theoretical saturation level of the zeolites, which was determined by the linearized Langmuir isotherms. The main objective of binary and ternary ion-exchanged systems was to determine the concentration distribution of the ions in the system if the initial concentration of Table 1. The EXD measured and the calculated maximum silver, copper and zinc ion concentrations Sample Ions (m/m%) Ag Cu Zn Ag 44,47 (43,48) Cu 9,25 (9,9) Zn 18,38 (18,68) Ag-Cu 34,71 4,87 Ag-Zn 40,8 3,37 Cu-Zn 8,43 7,39 Ag-Cu-Zn 35,7 4,85 1,58 *the values in brackets are the theoretically calculated maximum ion adsorption values each ion is equal in the ion-exchange solution. The results are presented in Table 1.As it can be obtained from both the adsorption isotherms and the EXD results, the silver cation was the most preferable by the zeolite. It is known that zeolite structures have selectivity against the different cations. In binary and ternary systems the amount of silver ions decreased compared to single ionexchanged systems but still zeolites absorbed them with the highest concentration. In the two component Ag-Cu and Ag-Zn systems the amount of Cu and Zn ions were similar, slightly more Cu was exchanged in the zeolite than zinc. However in the Zn-Cu and three component systems the amount of Zn was significantly lower than Cu. Ion release of single, binary and ternary ion-exchanged systems. The antimicrobial activity of zeolites is based on the amount of antimicrobial ions that are re-exchanged or released- from the structure during the use of the material. In the single ion systems the release of the ions depends on the exchanging cation, the ionic strength of the solution and the selectivity of the zeolite for the
Materials Science Forum Vol. 729 237 ingoing and out-coming ion. If the zeolite prefers the outgoing ion the ion release and exchange rate will be minimal. This is due to the ionic forces that keep the ions in the structure and results a decreased activity and mobility of the ion. If the system has better selectivity against the ions in the environment the ions in the zeolite can be easily exchanged. In multi-ionic systems this phenomenon is more complex. In binary or ternary ionic systems the ions in the structure have different selectivity and during a reexchange reaction these ions may compete with each other, which influences the release rate. Based on the location of the ions in the structure, ions that are more preferred by the zeolite can block the way of other ions that are less preferred. Due to this, both ions may stick in the system and no or minimal re-exchange could be observed. Figure 3 represents the released concentration of Ag, Cu and Zn ions from the different multi-ionic systems as a function of the initial concentration of sodium chloride solution. In all the samples Ag was the ion that was released with the least amount from the structure. The concentration of the out-coming silver ions increases as a function of the concentration of NaCl solution, however the release is not significant. The maximum released concentration of silver was found to be 0.35 mmol/l while the total silver concentration that may be released into the solution was 96.2 mmol/l. It was again confirmed at the sodium exchange to silver, that silver is highly preferred by zeolites. The high selectivity of silver may be one of the reasons for the low amount of silver release. Another reason could be the reduction of silver ions to silver-oxide, which may have occurred during the sample preparation at drying stage. It is known that silver ions in solutions are very sensitive to environmental impacts i.e. light, heat etc. therefore it is probable that ions are reduced to oxide during the drying of the samples. Figure 3. The release of silver ions as a function of initial sodium concentration Figure 4. The release of copper ions as a function of initial sodium concentration Copper and zinc ions are less sensitive and show relatively high stability in solutions or solid structures. For copper ion the lowest concentration was released from the zeolite in case of those binary and ternary systems (A-AgCu, A-AgZnCu) where silver was also present. The minimal copper release of these systems therefore can be influenced by the silver ion. In contrast, samples that not containing any silver ions released approximately 10 times more copper. As it is obvious from the ion-release graphs the zinc was released with the greatest amount from the structure. This ion does not seem to be influenced by the silver. The minimum amount of zinc was released from the ternary ion exchanged system and the highest amount was exchanged from the binary, zinc-copper zeolite. These results confirms, that copper and zinc ions due to their similar activity compete with each other during both the absorption and release. Antimicrobial activity. The minimum inhibitory concentration (MIC) of single, binary and ternary ion-exchanged zeolite A was determined for two bacteria strains (Methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, Pseudomonas aeruginosa ATCC 27853) and a mold (Candida tropicalis ATCC 90874) according to ISO 20776-1 standard test. The test was carried out at 37 C for 24h in test tubes by adding 10 ml
238 Materials Science, Testing and Informatics VI Figure 5. The release of zinc (c) ions as a function of initial sodium concentration mixture of the inoculums and the zeolite suspension. The concentration of the inoculum in the mixture was set to 5 10 5 CFU/mL, while 10 different dilutions of the zeolite were used (1028, 512, 256, 128, 64, 32, 16, 8, 4 and 2 ppm) to obtain the MIC. Table 2 represents the MIC of the zeolite samples against Candida tropicalis, Pseudomonas aeruginosa and methicillin-resistant Staphilococcus aureus (MRSA). In general the results indicated that ion-exchanged all zeolite samples showed good antimicrobial efficiency against all the three strains and the addition of further ions decreased this effect in most of the cases.the reference zeolite sample that didn t contain any ions didn t show any antimicrobial efficiency agains the three microorganisms. For Candida tropicalis the MIC of A-Ag, A-Cu and A- AgZn samples were superior compared to the other samples. In case of MRSA the MIC value of all zeolite samples increased. A-Cu and A-Zn samples didn t show any efficiency against this strain, however A-Ag, binary and ternary exchanged systems seemed to be equally effective. Compared to the other samples, A-Ag and A-AgCu exchanged samples were superior against Pseudomonas aeruginosa. Ag-AgZn and the ternary ion exchanged sample had the same MIC value against this strain (512 ppm) which is an acceptable antimicrobial performance. Table 2. Minimum inhibitory concentrations of ion exchanged A (ppm) Sample/Strain Candida tropicalis MRSA Pseudomonas aeruginosa REF >1024 >1024 >1024 Ag 2 512 128 Cu 2 >1024 1024 Zn 512 >1024 1024 AgCu 256 1024 256 AgZn 64 512 512 ZnCu 512 512 1024 AgZnCu 512 512 512 Summary The maximum ion exchange capacity of A type zeolite for silver, copper and zinc has been determined theoretically by linearized Langmuir isotherms. The theoretical data was in a good match with the data obtained from the experiments. Silver was the most preferable for zeolite A and was absorbed with the greatest amount in single, binary and ternary systems. Compared to samples that did not contain silver the release of copper and zinc was higher. The antimicrobial tests showed that the antimicrobial efficiency of the zeolite samples is ion and strain specific however in general silver in single ionic system was superior to the other samples. Besides copper, silver-zinc and the ternary ion exchanged samples showed good antimicrobial properties as well. Acknowledgements This work has been carried out as part of the TÁMOP-4.2.1.B-10/2/KONV-2010-0001 project in the framework of the New Hungarian Development Plan. The realization of this project is supported by the European Union, co-financed by the European Social Fund.
Materials Science Forum Vol. 729 239 References [1] Papaioannou, D., et al., The role of natural and synthetic zeolites as feed additives on the prevention and/or the treatment of certain farm animal diseases: A review. Microporous and Mesoporous Materials, 2005. 84(1-3): p. 161-170. [2] Flowers, J.L., S.A. Lonky, and E.J. Deitsch, Clinical evidence supporting the use of an activated clinoptilolite suspension as an agent to increase urinary excretion of toxic heavy metals. Nutrition and Dietary Supplements, 2009. 1: p. 11-18. [3] Barros, M.A.S.D., et al., Binary ion exchange of metal ions in Y and X zeolites. Brazilian Journal of Chemical Engineering, 2003. 20: p. 413-421. [4] Kim, J.S. and M.A. Keane, Ion Exchange of Divalent Cobalt and Iron with Na-Y Zeolite: Binary and Ternary Exchange Equilibria. Journal of Colloid and Interface Science, 2000. 232(1): p. 126-132.
Materials Science, Testing and Informatics VI 10.4028/www.scientific.net/MSF.729 Single, Binary and Ternary Ion Exchanged Zeolite as an Effective Bioactive Filler for Biomedical Polymer Composites 10.4028/www.scientific.net/MSF.729.234