Novel synthesis of Bis (N-oxopyridine-2-thionato) zinc (II) using solid precursors
Introduction
Bis (N-oxopyridine-2-thionato) zinc (II), commonly known as zinc pyrithione (ZPT), has been noted for an effective biocidal agent and widely employed as a preservative in cosmetics with their broad spectrum against gram negative and positive bacteria [1], [2].
Since Robinson researched the synthesis of ZPT using the aqueous solution of the sodium salt of 1-hydroxy-2-pyridine-thione and Zn(C5H4NSO)2 through transchelation method, ZPT has been typically prepared by water-soluble polyvalent metal acid salts such as ZnCl2, Zn(SO3)2, and Zn(CH3COO)2 and water-soluble pyrithione salts including dispergents or surfactants for producing monodispersed particles [3], [4]. In this liquid-phase transchelation route, however, nucleation and particle growth overlap, which is resulting in a broad size distribution of particles greater than 2 μm.
Here, we have attempted to develop the new method for the synthesis of sub-micron sized zinc pyrithione with a narrow particle size distribution at room temperature under ambient pressure. In order to prepare particles with narrow size distribution, it is necessary to shorten the germination period, which leads to provide simultaneous nucleation [5]. Insoluble or sparingly soluble solids of zinc precursors can serve as reservoir of nutrients for crystal growth due to high affinity between zinc and pyrithone. In the present study, the layered zinc hydroxide as a solid zinc precursor is introduced in synthesis of sub-micron leveled zinc pyrithione. Layered zinc hydroxides, so called zinc basic salts (ZBS), are anion exchangeable layer compounds whose structures are containing brucite-like layers where one fourth of octahedral sites are vacant. And tetrahedrally coordinated zinc cations are located in above and below the vacant octahedral site. The anions in the interlayer of ZBS have weakly interacted with tetrahedrally coordinated zinc atoms [6]. The solubility of ZBS in case of neutral pH region is known to be around 10−3 order at room temperature [7], [8].
In this study, we have synthesized ZPT with an average size of 0.7 μm using solid zinc precursors to control the reaction rate, and we have systematically investigated the structure of ZPT with powder X-ray diffraction (XRD) and electron scanning microscopy (SEM).
Section snippets
Experimentals
Pristine Zn5(OH)8(NO3)2·2H2O (hereafter abbreviated as ZBS-nitrate) was prepared by co-precipitaion reaction under N2 atmosphere to minimize the contamination of atmospheric CO2 as described previously [9]. Zn5(OH)8(CH3COO)2·nH2O and Zn5(OH)8(CH3(CH2)10CH2OSO3)2·nH2O (hereafter abbreviated as ZBS-acetate and ZBS-dodecylsulfate, respectively) were prepared by the anion exchange route in which ZBS-nitrate was dispersed in aqueous solution containing ammonium acetate and sodium dodecylsulfate. The
Results and discussion
Zinc basic salts show characteristic (00l) diffraction peaks indicating intrinsic layered structures, and the typical 2θ values indexed as (001) are 9.1° for Zn5(OH)8(NO3)2·2H2O, 6.7° for Zn5(OH)8(CH3COO)2·2H2O, and 2.8° for Zn5(OH)8(CH3(CH2)10CH2OSO3)2·2H2O [9]. Fig. 1A represents the XRD patterns for the reaction products prepared from ZBS-acetate as a function of reaction time. As seen in Fig. 1A, new diffraction peaks corresponding to zinc pyrithione are shown, and characteristic
Conclusion
The solid transchelation reaction has been established for the synthesis of zinc pyrithione nanoparticles to control the particle size and morphology. We have synthesized zinc pyrithione with a series of zinc basic salts as an insoluble zinc source. The products exhibit a narrow size distribution with the average size around 0.7 μm regardless of exchangeable anions existing in the layer. In the view of the kinetic of the reaction, however, natures of anion have an influence on the rate of solid
Acknowledgments
This work was supported by the SRC program of the Korea Science and Engineering Foundation (KOSEF) through the Center for Intelligent Nano-Bio Materials at Ewha Womans University (grant: R11-2005-008-01001-0). The authors are grateful for the financial support to participate in the international conference by the Science and Technology Amicable Research (STAR) Program of the Ministry of Science and Technology. Authors thank the Ministry of Education for the Brain Korea 21 fellowship.
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