Preparation of Nano Zinc Oxide and its Application in Leather as a Retanning and Antibacterial Agent

Transcription

1 Preparation of Nano Zinc Oxide and its Application in Leather as a Retanning and Antibacterial Agent H. R. Nawaz, B. A. Solangi, B. Zehra and U. Nadeem Abstract In this study, nano zinc oxide has been prepared by wet chemical method using zinc nitrate and sodium hydroxide precursors. Nano zinc oxide particles have been applied on goat skin during retanning, parallel to the control leather processing. Resulted leather has been subjected to determine the antibacterial activity by diffusion method using Bacillus subtilis, Escherichia coli & Clostridium perfringens species of bacteria. It has been observed that nano zinc oxide inhibits bacterial growth on leather without inserting bad effect on its quality. Key Words: Nano Zinc Oxide, Retanning Agent, Leather, Anti bacterial activity. I. INTRODUCTION Zinc Oxide has recently achieved special attention regarding potential electronic application due to its unique optical, electrical and chemical properties [1]. The availability of a wide range of nanostructures makes ZnO an ideal material for nanoscale optoelectronics [2] and piezoelectric nanogenerators [3] as well as an efficient material for biotechnology [4]. Furthermore, ZnO appears to be strongly resisted to microorganisms [5]. There are some reports [6] on the considerable antibacterial activity of CaO, MgO and ZnO, which is attributed to the generation of reactive oxygen species on the surface of these oxides. The advantage of using these inorganic oxides as antimicrobial agents is that they contain environmentally safe mineral elements essential to humans and exhibit strong activity even when administered in small amount. The activity is quantitatively evaluated by studying the growth medium caused by the bacterial metabolism [7]. Many researchers have attempted to correlate the biological activity of inorganic antibacterial agents with the size of the constituent particles [8]-[9]. The advantages of inorganic antibacterial materials over organic antibacterial materials are that the former show superior durability, less toxicity, greater selectivity and heat resistance. TiO 2 and ZnO nanostructures have been extensively studied as antimicrobial agents due to their photo catalytic activity under UV light [10], [11]. These antimicrobial substances based on inorganic chemicals have also been found to be effective for therapy. In addition to oxides, many researchers have also reported the antimicrobial activity of metal ions [12], [13]. Although many studies on the biological activity of ZnO have been carried out, most of these pertain to the antimicrobial effect of bulk ZnO with a large particle size. Yamamoto [14] studied the bacterial activity of ZnO with various particle sizes in the range of 0.1-1µm. Recently many antimicrobial chemicals for leather and textile have been banned in the whole world due to their carcinogenic effect and environmental toxicity. Now there is a much need to develop such anti microbial material for leather and textiles that would be useful for health and environment. Therefore, we emphasized on the synthesis and application of safe & potential nanomaterials for leather processing. In this study, we have prepared nano zinc oxide and then applied in leather retanning process. The resulted leather has been characterized for the antibacterial activity as well as for other physical characteristics. The results have shown that this leather has significant resistance against microbial growth without loosing other physical properties. Leather Research Centre, PCSIR D-102, S.I.T.E., South Avenue, Karachi, Pakistan. 164

2 II. EXPERIMENTAL PROCEDURE A. Materials Nutrient agar from Biom Laboratory, soluble starch from Sigma Aldrich Germany, zinc nitrate hexahydrate from Scharlau chemical,spain, Sodium Hydroxide from Merck, Germany, were used without further purification. Incubator from Nuve Laboratory Equipment Turkey and Autoclave from Electric Steroclave, USA were used in the experiments. Minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) were determined by the standard microbial test method. For tannery process all chemicals were commercial, purchased from the local market and used without further purification. Universal Testing Machine Tinius Olsen model H5KS was used for the physical testing of leather.uv spectra were taken on Thermo Electron Corporation Nicolet Evolution 100. B. Preparation of nano zinc oxide Zinc oxide nano-particles were prepared by wet chemical method using zinc nitrate and sodium hydroxide as precursors and soluble starch as a stabilizing agent as reported earlier [15]. Soluble starch solution 0.5% was prepared in 500ml of distilled water by slightly heating with stirring until clear solution was obtained gram zinc nitrate (0.1 mole) was added directly into the starch solution. Then the solution was kept under constant stirring to dissolve the zinc nitrate completely. After dissolution of zinc nitrate, 0.3 mol sodium hydroxide was added drop wise over a period of 2 hours. Addition was such a way that drops were added through touching the wall of beaker. After the completion of reaction, the solution was allowed to settle for overnight. Next day two phases were formed in the beaker, the supernatant solution was carefully discarded. The residue solution was centrifuged at 4500 rpm for 10 minutes. After centrifuged, supernatant solution was discarded carefully. Washing was carried out with distilled water until excess amount of bound starch as well as by products removed completely. After complete washing, the material was calcined at 80 o C for 24 hours in oven. During drying complete conversion of zinc hydroxide into zinc oxide takes place. C. Characterization of Nano Zno by Uv Bulk Zinc oxide, Zinc Nitrate and prepared nano Zinc oxide 1.0 g each were suspended in 100 ml of distilled water and then suspension was kept in ultrasonic T-14B Sonicator for 30 minutes. UV absorption spectra were recorded in the range nm. 165

3 Figure 1. UV Spectra of (a) Bulk Zinc Oxide. (b) Nano Zinc Oxide. (c) Zinc Nitrate. D. Application of nano ZnO in leather Processing: Three goat skins, wet blue processed at Leather Research Centre, by conventional chrome tanning process were selected for the retanning with prepared zinc oxide parallel to the control (without zinc oxide) as under; The resulted leathers were, horsed up overnight then set out and dry at room temperature. All chemicals were applied based on shaved weight of wet blue. Table I. Tannery Process Process Chemical Control Wash 300% Water 35 o C 1% NI Detergent 45 Minutes 0.5% Oxalic Acid Drain & Wash 200% Water 10 Minutes Re-Chroming 200% Water 10 Minutes 0.5% Formic Acid 4% Basic Chromium Sulphate 1% Sodium Bicarbonate Left overnight. Next Day run for 10 minutes drain & wash Neutralization 200% Water 1% Sodium Bicarbonate 1% Sodium Formate 166 ph Drain & Wash 300% Water 10 Minute Retanning 150% Water 50 o C 2% Tanigon OS (Syntan) 2% Tanigon R7 (Resin) 2% Tanigon RE (Acrylic) 30 Minutes 2% Lab. Prepared Zinc Oxide Fatliquoring 4% UPN (Fish Oil) 4% SR (Synthetic Fatliquor) 4% OIL 64 (Blended) 45 Minutes

4 Fixation 1.5% Formic Acid 30 Minutes ph 3.8 Table II Physical Characteristics of Resulted Leathers (Standard deviation was calculated from three observations given against each result) Sample Thickness Tear Strength %Elongation Tensile Strength Softness Fullness Grain Smoothness Color Zinc oxide treated leather (mm) (N/mm) (mm) (N/mm 2 ) (mm) Control E. Characterization of resulted crust for Antibacterial Activity: For antibacterial activity of nano zinc oxide treated leather as well as the control leather, Bacillus subtilis, Escherichia coli and Clostridium perfringens were isolated from the tannery waste water collected from Leather research Centre by Gram Staining. All glassware s were sterilized in the autoclave before starting the experiments. Nutrient Agar was used as a media for culturing of Bacillus subtilis, Escherichia coli, and Clostridium perfringens at 37 0 C in an incubator. The antibacterial activity of zinc oxide was measured by leather disks. The zone of inhabitation was observed after 24 hours incubation. A a d b e 167

5 c f c Figure 2. Photo images showing; a), inhibiting zone for Bacillus subtilis, b) Escherichia coli. c) Clostridium perfringens and (d,e & f) are control without zone respectively III. RESULTS AND DISCUSSION Nano zinc oxide powder was prepared by precipitation and calcination method as described in the experimental. Nano particles and their precursor were subjected to the UV spectra to confirm the conversion of zinc nitrate into zinc oxide. Zinc nitrate showed absorption at 300 nm, where as prepared ZnO at 370 nm. A very low peak of bulk ZnO was observed at 388nm.As the peak of bulk Zinc Oxide has been shifted to 370 nm which clearly evident the preparation of nano ZnO as shown in Figure 1. The sharpness of the peak confirms the nano dispersion of the material. This powder was used in leather processing at retanning stage to prepare bacterial growth resisting leather. Therefore, resulted crust leather was subjected to calculate the antibacterial activity. Bacterial resistance of leather was measured by diffusion method using Bacillus subtilis, Escherichia coli & Clostridium perfringens isolated from tannery area. The inhibition zones were clearly observed only around the sample disks as shown in Figure 2 (a,b,c). While control leather disks were completely surrounded by the bacterial colonies as in Figure 2 (d,e,f). This clearly showed the biocide action of ZnO on leather, that the nano ZnO killed bacteria and performed a protective action which was not observed in control leather. This is due to the generation of high rate of oxygen species from the surface of ZnO, which penetrate in the cell membrane and leads to the death of the bacteria. The generation of highly reactive species such as OH, H 2 O 2, and O 2-2 has already been explained else where [16]. The effect of nano ZnO on other physical properties such as tear strength, percentage elongation at break, tensile strength, thickness and softness of leather was evaluated using their ISO methods [17]-[21]. Leathers made in this study were also assessed for fullness, color and grain smoothness. The procedure for rating of leather was adopted to award the points for each functional property by leather experts. Results of physical testing are shown in table II. No significant deviation effect was observed on the physical characteristics of 168

6 resulted crusts. Minor variation in tear strength and grain smoothness of resulted crust is common due to the structural difference in leather. IV. CONCLUSION Currently, nano technology is being applied in all industries including leather. We have synthesized nano zinc oxide by precipitation method and applied in retanning of goat skin to prepare antibacterial leather. Resulted crust leather have shown very good inhibition zones around the sample disks. Other physical properties were found unaffected. It is concluded that nano ZnO may replace the toxic chemicals to be used for the preparation and safety of leather from microorganisms. ACKNOWLEDGEMENT We are very thankful to Mr. Muhammad Zeeshan (Senior Technician) and Mr. Raja Asad (Technician) for their assistance in leather processing for the application of products. REFERENCES [1] J. B. Baxter, and E.S.Aydil, Nanowire Based Dye Sensitized Solar Cells, Appl. Phys. Lett. 86, 53114, [2] M.H. Huang, S.Mao, H. Feick, H.Q. Yan, Y. Wu, H. Kind, E. Weber, R Russo, and P. Yang, ZnO Microrods Photodeposited with Au Ag Nanoparticles: Synthesis, Characterization and Application, In Sers. Science 292, 1897, [3] J. Song, J. Zhou, and Z.L. Wang, Piezoelectric and Semi conducting Coupled Power Generating Process of a Single ZnO Belt/Wire. A Technology for Harvesting Electricity from the Environment, Nano, Lett. 6, [4] Z.L. Wang, functional Oxides Nanobelts Materials, Properties and Potential Applications in Nanosystems and Biotechnology, Annu. Rev. Phys. Chem. 55, 159, [5] J.Sawai, H. Igarashi, A. Hashimoto, T. Kokugan,c, and M.Shimizu, Antibacterial Characteristics of Magnesium Oxide Powder. J. Chem. Eng. Japan 29, [6] J. Sawai, and T.Yoshikawa, Quantitative Evaluation of Antifungal Activity of Metallic Oxide Powders (MgO, CaO and ZnO) By an Indirect Conductimetric Assay, J. Appl. Microbiol. 96, [7] J. Sawai, R.Doi, Y. Maekawa, T. Yoshikawa, and H.Kojima, Short Communication Indirect Conductimetric Assay of Antibacterial Activities, J. Ind. Microbiol. Biotech. 29, [8] R.Brayner, R.Ferrari-lliou, N. Brivois, S. Djediat, MF.Benedetti, and F. Fievet, Toxicological Effect of Zno Nanoparticles Based on Bacteria, Nano Lett. 6, [9] P. K. Stoimenov, R.L. Klinger, G.L Marchin, and K.J Klabunde, Metal Oxide Nanoparticles as Bactericidal Agents, Langmuir 18, [10] A.Fortuny, C. Bengoa, J. Font, and A. Fabregat, Catalytic wet air oxidation of phenol using ceo 2 as the catalyst. Kinetic study and mechanism development, J. Hazard Mater 64, [11] S. Rana, J. Rawat, MM. Sorensson, and R.D.K Misra, Antimicrobial Function of Nd3+-Doped Anatase Titania-Coatednickel Ferrite Composite Nanoparticles: A biomaterial system, Biomater 2, [12] A.D. Russell, and W.B. Hugo, Antimicrobial Activity and Action of Silver. Prog. Med. Chem. 31, [13] S.Shanmugam, B.Viswanathan, and T.K. Varadarajan, A Novel Single Step Chemical Route For Noble Metal Nanoparticles Embedded Organic Inorganic Composite Films, Mater, Chem. Phys 95, [14] O.Yamamoto, Influence of particle size on the antibacterial activity of zinc oxide, Int. J. Inorg. Mater: 3, [15] A.Yadav, Virendra Prasad, A. A. Kathe, Sheela Raj, Deepti Yadav, C. Sundaramoorthy and N. Vignesharan. Functional Finishing In Cotton Fabrics Using Zinc Oxide Nanoparticles, Bull. Mater 169

7 Sci., Vol. 29, No. 6, [16] M. Fang, J. Chen, XL, H,Xu,P H. Yang and H F.Hildebrand. Inter. J. Antimicrobial Agents 27, [17] Standard Method for Conditioning of leather EN ISO [18] Determination of Tear Strength of Leather EN ISO [19] Determination of Tensile Strength and % Elongation of leather EN ISO [20] Determination of Softness of leather EN ISO [21] Determination of Thickness of leather EN ISO