Biosynthesis of titanium dioxide nanoparticles using ...

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May 30, 2011 - A.Vishnu Kirthi, A. Abdul Rahuman ⁎, G. Rajakumar, S. Marimuthu, T. Santhoshkumar, ... G. Elango, A. Abduz Zahir, C. Kamaraj, A. Bagavan.
Materials Letters 65 (2011) 2745–2747

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Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t

Biosynthesis of titanium dioxide nanoparticles using bacterium Bacillus subtilis A.Vishnu Kirthi, A. Abdul Rahuman ⁎, G. Rajakumar, S. Marimuthu, T. Santhoshkumar, C. Jayaseelan, G. Elango, A. Abduz Zahir, C. Kamaraj, A. Bagavan Unit of Nanotechnology and Bioactive Natural Products, Post Graduate and Research Department of Zoology, C.Abdul Hakeem College, Melvisharam-632 509, Vellore District, Tamil Nadu, India

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Article history: Received 28 October 2010 Accepted 21 May 2011 Available online 30 May 2011 Keywords: Biosynthesis Bacillus subtilis Titanium dioxide Atomic force microscopy XRD FTIR

a b s t r a c t The present study reports a low-cost, new material, eco-friendly and reproducible microbes Bacillus subtilis mediated biosynthesis of TiO2 nanoparticles. Titanium dioxide nanoparticles synthesized from titanium as a precursor, using the bacterium, B. subtilis. The synthesized nanoparticles were characterized and confirmed as TiO2 nanoparticles by using the UV spectroscopy, XRD, FTIR, AFM and SEM analysis. The morphological characteristics were found to be spherical, oval in shape, individual nanoparticles as well as a few aggregates having the size of 66–77 nm. The XRD shows the crystallographic plane of anatase of TiO2 nanoparticles, indicating that nanoparticles structure dominantly correspond to anatase crystalline titanium dioxide. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Nanoparticles have demonstrated antimicrobial activities; the development of novel applications in this field makes them an attractive alternative to antibiotics. The recent discovery of the biosynthesis of metal nanoparticles points towards new biotechnological methods in materials science [1,2].Titanium dioxide (TiO2) nanoparticles form may be one of the most important materials for photocatalysts [3], cosmetics, and pharmaceuticals [4]. Bacillus subtilis is an aerobic, oxygen tolerant, spore forming bacteria which can survive even in the harsh unfavorable conditions, which makes it a suitable candidate for the biosynthesis of the metal nanoparticles like TiO2. Lengke et al. [5]demonstrated the synthesis of gold nanoparticles from B. subtilis and an airborne Bacillus sp. used to reduce Ag + ions to Ag 0 [6]. As such they are extremely energetic, adaptable and promising due to their potential metabolic fluxes. The capabilities of this benevolent microbe have not been taken into full use in terms of synthesizing metallic and/or oxide nanoparticles. In the present effort, B. subtilis has been taken in order to assess its potentiality as a putative candidate bacterium for the synthesis of TiO2 nanoparticles. It is an attempt to explore and establish a cost effective, eco-friendly and amenably reproducible approach for the purpose of scaling up and subsequent downstream processing. This effort has also been made to

⁎ Corresponding author. Tel.: + 91 94423 10155, + 91 04172 269009; fax: + 91 04172 269487. E-mail address: [email protected] (A.A. Rahuman). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.05.077

understand the mechanism of nano transformation of accomplishing biosynthesis at the extra-cellular level. 2. Materials and methods 2.1. Synthesis of TiO2 nanoparticles using B. subtilis B. subtilis cells were allowed to grow as suspension culture in sterile distilled water containing suitable carbon and nitrogen source for 36 h and this was treated as source culture. 25 ml of culture was taken and diluted four times by adding 75 ml of sterile distilled water containing nutrients. This diluted culture solution was again allowed to grow for another 24 h. 20 ml of 0.025 M TiO(OH)2 solution was added to the culture solution and it was heated on steam bath up to 60 °C for 10–20 min until white deposition starts to appear at the bottom of the flask, indicating the initiation of transformation. The culture solution was cooled and allowed to incubate at room temperature in the laboratory ambience. After 12–48 h, the culture solution was observed to have distinctly markable coalescent white clusters deposited at the bottom of the flask [7]. 2.2. Characterization of TiO2 particles The UV absorbance of the synthesized TiO2 nanoparticles was measured in Schimadzu 1601 spectrophotometer operated at a resolution of 1 nm. The synthesized nanoparticles were freeze dried, powdered and used for XRD analysis. The spectra were recorded in Bruker AXS D8 Advance X-ray diffractometer with Philips® PW 1830 X-ray generator. The diffracted intensities were recorded from 0° to

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Fig. 1. (A) UV absorption spectrum for the synthesized TiO2 nanoparticles showing peak at 366 nm, (B) indexed X-ray diffraction patterns of TiO2 at room temperature.

80° 2θ angles. The dried powder was diluted with potassium bromide in the ratio of 1:100 and recorded the spectrum in Thermo Nicolet, Avatar 370 Fourier Transform Infrared Spectrophotometer using the diffuse reflectance accessory. The spectrum was subjected to correction to get back the transmission spectrum. The surface morphology of the film samples was studied using atomic force microscopy (AFM). The AFM images were also used for the analysis of the fractal behavior as deposited and annealed films. Porosity, roughness and fractal dimension were evaluated by analyzing the AFM images using post image processing software (Nanoscope IIIa, Digital Instruments). Scanning electron microscopy (SEM) analysis was performed on a EOL Model JSM-6390LV. 3. Results and discussion The onset wavelength of the optical absorption for uncapped TiO2 appears at 366 nm in UV–vis spectroscopy (Fig. 1A), which is blueshifted compared to the bulk anatase TiO2, indicating the formation of nanoparticles solution. The surface modification of nanocrystalline anatase TiO2 particles with orthosubstituted hydroxylated enediols ligands which as well improves the optical response in the visible region [8]. The XRD pattern of the sample showed the presence of peaks (2θ = 27.811° (rutile form), 39.187° (anatase form), 41.236° (rutile form) and 54.323° (anatase form)), which is regarded as an attributive indicator of the biologically synthesized nanoparticles TiO2

crystallites. The main peak of θ = 27.811° (Fig. 1B) matches the (101) crystallographic plane of anatase of TiO2 nanoparticles, indicating that nanoparticles structure dominantly correspond to anatase crystalline. There is a slight increase in the peaks which may be the result of nanoparticles synthesized by microorganisms. The particles size estimation was performed by the Scherrer's formula. d=

0:9λ βcosθ

where d is the mean diameter of the nanoparticles, λ is wavelength of X-ray radiation source, β is the angular FWHM of the XRD peak at the diffraction angle θ. The FTIR spectra of TiO2 nanoparticles exhibited prominent peaks at 3430, 1578, 1451, 1123 cm − 1 (Fig. 2A). A broad peak at 3430 cm − 1 shows O\H stretching due to alcoholic group. Peak at 1578 cm − 1 indicates the presence of C_C ring stretching. The band observed at 1451 cm –1 is due to bending vibration of the CH2 in the lipids and proteins. The peak at 1123 cm –1 is due to the formation of the amide linkages between the bacterial proteins and the TiO2 formed during the reaction period. The AFM was performed in order to know the topological map of the surface of the synthesized nanoparticles. The surface area of the nanoparticles has increased dramatically showing with the increase in the peaks (Fig. 2B). The AFM clearly depicts the formation of the rutile and anatase forms in the TiO2 nanoparticles, and also the surface morphology of the

Fig. 2. (A) FTIR spectra of the B. subtilis synthesized of TiO2, (B) atomic force microscopic (AFM) image of the synthesized of TiO2 showing increased surface area.

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Fig. 3. (A and B) Scanning electron microscopic images of the TiO2 showing individual and aggregate forms of nanoparticles. (C) Particle size distribution showing size range of the synthesized TiO2 nanoparticles.

particles is uneven due to the presence of some of the aggregates and individual particles of TiO2. The SEM images of the B. subtilis synthesized TiO2 nanoparticles have shown spherical clusters of the nanoparticles (Fig. 3A and B). Nanoparticles were spherical, oval in shape, individual as well as a few aggregates having the size of 66–77 nm. The particle size distribution is shown in Fig. 3C. It reveals the morphological homogeneity with the grain size falling mostly in submicron range. The energy yielding material–glucose (which controls the value of oxidation–reduction potential (rH2)), the ionic status of the medium pH and overall rH2, which is partially controlled by the bicarbonate negotiate the synthesis of TiO2 nanoparticles in the presence of B. subtilis [7]. The synthesis of n-TiO2 might have resulted due to pH-sensitive membrane bound oxidoreductases and carbon source dependent rH2 in the culture solution. Composition of nutrient media, therefore, plays a pivotal role in biosynthesis of metallic and/or oxide nanoparticles which is done in the present investigation. 4. Conclusion To conclude, we have used a hitherto unreported, new material, inexpensive, non toxic, eco-friendly, abundantly available microorgan-

isms for the consistent and rapid synthesis of TiO2 nanoparticles. The synthesized TiO2 nanoparticles were characterized by using UV–vis, XRD, FTIR, AFM and SEM and the bacterial biosynthesis of the titanium dioxide provides a fast, purest form of producing nanoparticles. Acknowledgements The authors are grateful to C. Abdul Hakeem College Management, Dr. S. Mohammed Yousuff, Principal, Dr. K. Abdul Subhan, HOD of Zoology Department, for providing the facilities to carry out this work. Reference [1] [2] [3] [4] [5] [6] [7] [8]

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