We demonstrate here a novel oxidative process to control the metallic bismuth (Bi degrees) nanoparticles (NPs) formation in bismuth glass nanocomposites by using KClO(4) and KNO(3) as oxidant instead of usual reducing technique. The formation of Bi degrees NPs has been monitored by its distinctive surface plasmon resonance (SPR) band at 460 nm in the UV-vis absorption spectra. It is further confirmed by the TEM images of Bi degrees NPs using KNO(3) and KClO(4) which show the formation of spherical Bi degrees NPs of 2-15 nm sizes and the SAED pattern reveals their crystalline rhombohedral phase. Using this technique it is possible to control the SPR band of nanobismuth (Bi degrees) in bismuth glasses. (C) 2009 Elsevier B.V. All rights reserved

Karmakar, Basudeb

Singh, Shiv Prakash

IR@CGCRI - Central Glass and Ceramic Research Institute (CSIR)

 1 Oxidative control of surface plasmon resonance of bismuth nanometal in bismuth glass nanocomposites    Shiv Prakash Singh, Basudeb Karmakar*  Glass Technology Laboratory, Central Glass and Ceramic Research Institute (Council of Scientific and Industrial Research), 196, Raja S.C. Mullick Road, Kolkata 700032, India ______________________________________________________________________________________ ABSTRACT We demonstrate here a novel oxidative process to control the metallic bismuth (Bio) nanoparticles (NPs) formation in bismuth glass nanocomposites by using KClO4 and KNO3 as oxidant instead of usual reducing technique. The formation of Bio NPs has been monitored by its distinctive surface plasmon resonance (SPR) band at 460 nm in the UV-visible absorption spectra. It is further confirmed by the TEM images of Bio NPs using KNO3 and KClO4 which show the formation of spherical Bio NPs of 2-15 nm sizes and the SAED pattern reveals their crystalline rhombohedral phase. Using this technique it is possible to control the SPR band of nanobismuth (Bio) in bismuth glasses.  Keywords: Glasses, Bismuth nanoparticles, Transmission electron microscopy, Optical properties ______________________________________________________________________________________  * Corresponding author. Tel.: +91 33 2473 3496; fax: +91 33 2473 0957.  E-mail address: basudebk@cgcri.res.in (B. Karmakar)        2 1. Introduction  The successful progress of nanoscience and technology has been accelerated by discoveries of the various unique properties associated with the size and shape of the nanomaterials. Nanoparticles exhibit novel properties that notably different from those of corresponding bulk state due to the small size effect such as nanometals show a very intense color which is absent in the bulk material [1, 2]. During the past years, metal nanoparticles have mainly studied because of their unique physical and chemical properties and potential application in diverse areas, such as catalyst, electronic devices, optical applications, conductive materials, etc. A lot of interests have been given on the study of surface plasmon resonance [3-5] of metal NPs and their potential applications in plasmonics. When various applications in plasmonics are concerned, the greatest challenge is the development of the controlled synthetic methodologies. Numerous chemical approaches have been explored, and some have been proven to be successful in the control of size and morphology of the nanoproduct.   In recent times, glass researchers have been expressed their extensive interest in the bismuth glasses as it is one of the most important amongst the heavy metal oxide (HMO) glasses due to their several properties such as high refractive index, wide transmission window, broad band near infrared (NIR) luminescence, [6-10]  etc. Bismuth oxide glasses are usually obtained in dark-brown or black color, which deepens with increasing Bi2O3 content and when melted at higher temperature [7, 8]. Hence, it is very difficult to control the nanobismuth particle formation as well as its SPR in bismuth glasses. Therefore, synthesis of controlled Bio NPs [11] in bismuth glasses is very important both academically as well as technological point of views. Sanz et el. [7] and  3 Zhang et el. [8] have studied the transparency of bismuth glass by addition of color oxidizing additives as dopant such as As2O3, Sb2O3, CeO2 etc. However, they have not paid their attention to above issues. To the best of our knowledge there is no previous report on the control synthesis of Bio NPs and its plasmon in bismuth glasses by applying the oxidation technique using KNO3 and KClO4 as oxidant.   In view of above, in this communication we report the controlled formation of Bio NPs during melting process in the B2O3-ZnO-Bi2O3-SiO2- K2O glass system using KNO3 and KClO4 as oxidizing agent. The efficiency of oxidant on the formation of Bio NPs and its SPR in bismuth glasses is characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM), and selected area electron diffraction (SAED) analysis.   2. Experimental details  High purity chemicals of bismuth trioxide, Bi2O3 (99%, Loba Chemie), boric acid, H3BO3 (99.5%, Loba Chemie), zinc oxide, ZnO (99%, Loba Chemie), potassium carbonate, K2CO3 (99.9%, Loba Chemie), silicon dioxide, SiO2 (99.8%, Bremthaler/Quarzitwerk), potassium nitrate, KNO3 (99%, Loba Chemie) and potassium perchlorate, KClO4 (99%, Sigma, Aldrich) were used as raw materials. The composition (wt %) of glasses are: 19B2O3-23ZnO-45Bi2O3-9SiO2-(4-x)K2O-xK2O, where x is the equivalent amount of K2O (wt. %) has taken from KNO3 (x = 0, 0.2, 0.5, 0.9 and 1.4) and KClO4 (x = 0, 0.2, 0.3, 0.7 and 1) sources. 25 g glass was melted in a 50 ml high purity silica crucible at 1100oC in air for 30 min in a raising hearth electrical furnace with intermittent stirring for 0.5 min. The molten glass was cast into a carbon plate and annealed at 420oC for 2h to release the internal stresses. Samples of 2  0.01 mm thickness were prepared by cutting, grinding and polishing for optical measurements.  The UV-Vis absorption spectra in the range of 300-800 nm were recorded using a double beam UV-visible spectrophotometer (Lambda 20, Perkin-Elmer) at an error of +0.1 nm. The TEM and SAED images were taken using a FEI instrument (Tehnai-30, ST G2) operating at an accelerating voltage of 300 kV.   4 3. Results and discussion  The bismuth glasses are one of the most important among the heavy metal oxide glasses for its high refractive index. But the browning or blackening of bismuth glasses when melted at higher temperature are serious problem for controlling of Bio NPs and its SPR band. The intensity of browning or blackening increases with increase in melting temperature as well as Bi2O3 concentration due to auto-thermo reduction of Bi3+ ions to bismuth metal (Bio) during the melting process. The reduction of Bi2O3 occurs through the following thermal dissociation reaction [7, 8]                          2Bi2O3   ↔ 4Bio + 3O2                                                           (1)  The above equilibrium reaction shifted towards right side with the release of oxygen as melting temperature increases and the metallic Bio is formed. When the oxidizing agent, such as KNO3 or KClO4, is added in the glass composition, it increases the oxygen partial pressure as a result of its thermal dissociation during melting at high temperature as follow.                      2KClO4 = K2O + Cl2O     + 3O2  (2)                      2KNO3 = K2O + 2NO     +3/2O2                                 (3)             Consequently, the reaction of the Eq. (1) proceeds in the reverse direction due to reactions of the Eqs. (2) and (3). By comparing the standard reduction potentials [12] as listed in Table 1, it is clear that the standard potential of ClO4-/Cl- (1.34V) and NO3-/NO (0.96V) are higher than that of Bi+/Bio (0.50 V), Bi3+/Bio (0.31 V), Bi3+/Bi+ (0.20 V) and Bi3+/Bi2+ (<0.20 V) species, so it easily favors the backward reactions of the Eq. (1). It  5 suppresses the uncontrolled auto-reduction of Bi2O3. Hence, controlled formation of Bio NPs in the glasses gradually increases with increasing KClO4 or KNO3 content. The KClO4 is more effective than the KNO3 due to its higher reduction potential that is, it favors the oxidation reaction and reduces the uncontrolled formation of Bio nanometal more effectively than KNO3. This fact could be visualized clearly by the remarkable changes in the transparency as shown in the bottom photograph of Figs. 1 and 2.    The UV-Vis absorption spectra of bismuth glasses are shown in Figs. 1 and 2. The broad SPR absorption band at 460 nm is due to the Bio NPs. The spherical particle gives an SPR absorbance band centered at a wavelength, λ, which can be calculated by the relation [13]  λ2 = (2πc) 2 moNe2 (ε∞ + 2no2) / εo                                           (4) where c is the velocity of light, mo is the mass of particle, N is the concentration of the particle, e is the charge of the electron, ε∞ is the optical dielectric function of the metal, no is the refractive index (RI) of the host material and εo is the free-space permeability. From the Eq. 4, it is clear that the absorbance band position proportionate directly to the RI of the host material. The absorbance band of Bio NPs was observed in the host water (RI = 1.33) at around 400 nm [3] whereas our glass having higher RI (1.76) shows a red shift of the band to 460 nm. Khonthon et al. [8] has also reported the broad band due to SPR of Bio NPs at 460 nm, which is similar to our result. The absorption band of the base glass has shown in the inset of the Figs. 1 and 2. The base glass is black and shows a very weak SPR band. When 0.2 wt% of K2O from equivalent amount of oxidizing agent KNO3 or KClO4 has added to the base glass, the plasmon band has visualize very distinctly. The intensity of SPR band decreases with addition of further amount of KClO4 or KNO3 (up  6 to 1 or 1.4 equivalent wt % of K2O respectively). However, the SPR band position remains unchanged at 460 nm for all the cases of KNO3 and KClO4 containing glasses.  The significant effects of KNO3 and KClO4 are the controlled production of Bio NPs and removal of deep browning or blackening of bismuth glasses.      The TEM images of glass containing 0.2 wt % of K2O from KNO3 and KClO4 sources (Figs. 3 and 4) clearly reveals homogeneously dispersed and densely embedded Bio NPs of spherical shape with size range 2-5 nm and 10-15 nm respectively. The particle size of the Bio NPs in KClO4 treated glass shows smaller size (2-5 nm) than that of KNO3 containing glasses (10-15 nm) because it restricted the further formation of NPs more effectively due to its higher reduction potential (Eo = 1.34V) than that of KNO3 (Eo = 0.96V). Therefore, KClO4 treated glass have not shown any distinct SAED spots and lattice fringes in high resolution transmission electron microscopy (HRTEM) due to its very small particle size. The SAED image of KNO3 containing glass depicts the clear patterns of <024> and <119> hkl planes of rhombohedral Bi nanometallic particles. It also shows lattice fringes of <012> hkl planes in HRTEM image, which have been identified from the d-spacing as provided in the JCPDS File Card No.: 85-1329.        4. Conclusions  The formation of Bio NPs in bismuth glass nanocomposites have been controlled by a novel oxidation process using KClO4 and KNO3 as oxidant. The UV-visible absorption spectra show the characteristic invariable SPR band of Bio NPs at 460 nm. TEM images confirm the formation of spherical shaped rhombohedral Bio of 2-5 nm and 10-15 nm nanoparticles of KNO3 and KClO4 treated glasses respectively. The KNO3  7 treated glass shows the SAED pattern and HRTEM images of <119>, <024> and <012> planes of rhombohedral bismuth. The KClO4 is more efficient oxidant for the oxidation process of Bio/Bi+3 than that of KNO3.   Acknowledgements The authors gratefully acknowledge the financial support of the NMITLI Scheme of CSIR, New Delhi. They thank Dr. H. S. Maiti, Director of the institute for his keen interest and kind permission to publish this paper. They also acknowledge the Electron Microscope Division of this institute for recording the TEM and SAED images.   References [1] C. Gila, M.A. Villegasb, Mater. Chem. Phys. 88 (2004) 185.  [2] J. Bai, Q. Yang, M. Li, S. Wang, C. Zhang, Y. Li, Mater. Chem. Phys. 111 (2008) 205. [3] F. Gonella, P. Mazzoldi, Metal Nanocluster Composite Glasses, Handbook of Nanostructured Materials and Nanotechnology, Edited by H. S. Nalwa, Academic Press, London, 2000, p. 81. [4] P. Mulvaney, Langmuir, 12 (1999) 788.   [5] Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control, Edited by  B. Corain, G. Schmid, N. Toshima, Elsevier, Amsterdam, 2008. [6] H. Sun, L. Wen, S. Xu, S. Dai, L. Hu, Z. Jiang, Mater. Lett., 59 (2005) 959. [7] O. Sanz, E. Haro-Poniatowski, J. Gonzalo, J. M. Fernández Navarro, J. Non-Cryst. Solids, 352 (2006) 761.  8 [8] Y. Zhang, Y. Yang, J. Zheng, W. Hua, G. Chen, J. Am. Ceram. Soc., 91 (2008) 3410. [9] S. Khonthon, S. Morimoto, Y. Arai, Y. Ohishi, Opt. Meter., 2009, doi: 10.1016/j.optmat.2009.01.005 (In press). [10] S. Zhou, N. Jiang, B. Zhu, H. Yang, S. Ye, G. Laksminerayana, J. Hao, J. Qiu,  Adv. Funct. Mater., 18 (2008) 1407.  [11] W. Li, Mater. Chem. Phys. 99 (2006) 174. [12] P. Vanýsek, Electrochemical Series, CRC Hand Book of Chemistry and Physics, Edited by D. R. Lide, CRC Press, London,1994, p. 22. [13] P. D. Persans, K. L. Stokes, Embedded Nanocrystal Spectroscopy: Semiconductor and Metal Particles in Insulators., Handbook of Nanophase materials, Edited by A. N. Goldstein, Marcel Dekker, New York, 1997, p. 271.   Table 1 Reduction potentials of perchlorate, nitrate and bismuth ions.   Redox reaction  Reduction potential (Eo, V)   ClO4-/Cl-                                   NO3-/NO   1.34 0.96 Bi+ / Bio 0.50 Bi3+ / Bio 0.31 Bi3+ / Bi+ 0.20 Bi3+/ Bi2+ < 0.20a  a Exact value is not available       9 Figure caption  Fig. 1. (Color online) Absorbance spectra of glasses containing (a) 0 (inset), (b) 0.2, (c) 0.5, (d) 0.9, and (e) 1.4 wt. % of K2O from KNO3. Displayed photograph is of the polished glasses (thickness = 2 mm and identifiable by their bottom letters) laid on black lines to show their transparency to the naked eye.  Fig. 2. (Color online) Absorbance spectra of glasses containing (a) 0 (inset), (k) 0.2, (l) 0.3, (m) 0.7, and (n) 1.0 wt. % K2O from KClO4. Displayed photograph is of the polished glasses (thickness = 2 mm and identifiable by their bottom letters) laid on black lines to show their transparency to the naked eye.  Fig. 3. TEM, HRTEM images and SAED pattern of the glass containing 0.2 wt % of K2O (from KNO3).  Fig. 4. TEM images and SAED pattern of the glass containing 0.2 wt % of K2O (from KClO4).          10     300 400 500 600 700 800-0.20.00.20.40.6   Absorbance (a.u.)Wavelength (nm)b cd eSPR at 460 nm  Fig. 1. (Color online) Absorbance spectra of glasses containing (a) 0 (inset), (b) 0.2, (c) 0.5, (d) 0.9, and (e) 1.4 wt. % of K2O from KNO3. Displayed photograph is of the polished glasses (thickness = 2 mm and identifiable by their bottom letters) laid on black lines to show their transparency to the naked eye.         400 500 600 700 8000123  Absorbance (a.u.)Wavelength (nm)SPR at 460 nma 11     300 400 500 600 700 800-0.20.00.20.40.60.8  Absorbance (a.u.)Wavelength (nm)kl m nSPR at 460 nm  Fig. 2. (Color online) Absorbance spectra of glasses containing (a) 0 (inset), (k) 0.2, (l) 0.3, (m) 0.7, and (n) 1.0 wt. % K2O from KClO4. Displayed photograph is of the polished glasses (thickness = 2 mm and identifiable by their bottom letters) laid on black lines to show their transparency to the naked eye.        400 500 600 700 8000123  Absorbance (a.u.)Wavelength (nm)SPR at 460 nma 12        Fig. 3. TEM, HRTEM images and SAED pattern of the glass containing 0.2 wt % of K2O (from KNO3).            Fig. 4. TEM images and SAED pattern of the glass containing 0.2 wt % of K2O (from KClO4).  d012=3.2 Å 119  024  

Oxidative control of surface plasmon resonance of bismuth nanometal in bismuth glass nanocomposites

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Oxidative control of surface plasmon resonance of bismuth nanometal in bismuth glass nanocomposites

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