Bio-mediated synthesis of TiO 2 nanoparticles and its photocatalytic effect on aquatic biofilm

Journal of Photochemistry and Photobiology B: Biology 110 (2012) 43–49

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Journal of Photochemistry and Photobiology B: Biology

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Bio-mediated synthesis of TiO2 nanoparticles and its photocatalytic effecton aquatic biofilm

Perumal Dhandapani, Sundram Maruthamuthu, Gopalakrishnan Rajagopal ⇑Biocorrosion Lab, Corrosion Protection Division, Council of Scientific & Industrial Research (CSIR) – Central Electrochemical Research Institute, Karaikudi 630 006, Tamilnadu, India

a r t i c l e i n f o

Article history:Received 9 January 2012Received in revised form 29 February 2012Accepted 5 March 2012Available online 17 March 2012

Keywords:Bacterial synthesisTiO2 nanoparticlesAquatic biofilmHydrogen peroxidePhotocatalytic effect

1011-1344/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.jphotobiol.2012.03.003

⇑ Corresponding author. Tel.: +91 4565 241399; faxE-mail address: [email protected] (G. Ra

a b s t r a c t

The nano-TiO2 was synthesized biologically employing Bacillus subtilis (FJ460362). These nanoparticleswere characterized by FTIR, TGA–DTA, UV–Visible spectroscopy, XRD and TEM. FTIR and TGA results con-firm that the organic impurities were completely removed while calcinating the resultant products. Bandgap value was estimated from the UV–Visible spectrum and anatase crystal phase was confirmed by XRD.TEM images reveal that these particles were agglomerated; mostly spherical in shape with an averageparticle size of 10–30 nm. The synthesized nano-TiO2 particles were coated on glass slides, biofilm weregrown and subjected to irradiation of polychromatic light to understand photocatalytic activity in con-trolling the aquatic biofilm. The bacterial killing process was established by Epi-fluorescence microscopy.The results reveal that biogenic TiO2 nanomaterial acts as good photocatalyst by the generation of H2O2 inthe vicinity of the TiO2-biofilm interfaces to suppress the growth of the aquatic biofilm.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

Utilization of microbes has emerged as a novel technology forsynthesis of various inorganic metal/metal oxides nanoparticles.The control of particle shape, size and monodispersity depend onthe process parameters. Synthesis of inorganic metal nanoparticlesusing biological entities has great interest due to their unusualoptical, chemical, photo electrochemical and electronic properties[1]. Especially Bacillus sp. easily undergo adaptation with heavymetals and it can produce unusual size and shape of inorganicnanoparticles through either intra or extra cellular mechanisms[2]. Microbial mediated synthesis of TiO2 nanoparticles was alsocarried out using Lactobacillus sp. and Bacillus sp. [3,4]. Bansal etal. [5] have also reported about the synthesis of silica and titaniananoparticles using fungus species. It was found that fungus se-creted extra cellular 21 and 24 kDa proteins, which are responsiblefor the hydrolytic conversion of hexafluorotitanate complexes intospherical shaped titania nanoparticles. Hence, it is possible thatmicrobial generated nanomaterials can be utilized for variousindustrial applications with an increase in their efficiency. In re-cent years, applications towards environmental cleanup have beenone of the most active topics in photocatalysis. The photocatalysistechnique is a simple, low cost and easily handling for large-scaleindustrial applications. Higher photocatalytic efficiency of nano-TiO2 can be used for decontamination, purification and decoloniza-tion of air and water from different environmental sources [6,7]

ll rights reserved.

: +91 4565 227779.jagopal).

and also employed for the removal of dye pollutants and bio-wasteorganic compounds [8,9]. Biofilm formation creates serious prob-lems of hygiene, odor and taste in cooling water as well as in drink-ing water systems [10]. The attachment of biofilm on the walls ofmetal surfaces encourages pitting corrosion on the transportingpipeline materials like mild steel, stainless steel, copper, finallymaterials failure. The corrosive bacterial biofilm enhances the cor-rosion products on the metal surface. It can lead to leaching orreleasing of toxic elements into drinking waters causing healthhazards [11]. Hence, the investigation of pipeline materials–bacte-rial interaction is one of the ongoing focuses in cooling waterindustry to prevent the material from corrosion by bacterial spe-cies [12]. A great deal of attention has been focused on the devel-opment of nano-crystalline semiconductor thin films of titaniumdioxide successfully achieved on the different substrates such asglass slide, stainless steel, and PVC materials [13–16]. The TiO2

films modification often brought exceptional advantage for thesubstrate, for improving corrosion resistance, elevating surfacehardness and preventing the bacterial attachment [15,16]. Differ-ent size and shape of TiO2 particles can be used for the photocata-lytic treatment of aquatic biofilm, pathogenic microorganisms andantibiotic resistant microbes has been recently reported [17,18].The photo catalyst (TiO2) will be located in center of substrateand bacteria attachment to them at time irradiation of light.The generation of free radical on the particle surface leads to thedestruction of the bacterial cell walls, results in decrease in thebacterial population within the biofilm [14]. There are numerousmethods are available for synthesis of TiO2 particle and theirincreasing efficiency for various applications such as waste water

44 P. Dhandapani et al. / Journal of Photochemistry and Photobiology B: Biology 110 (2012) 43–49

treatment, biosensors, solar cell panel, lithium-ion batteries, anti-bacterial activity, and anticancer therapy [19,20]. The applicationof biosynthesized nanoparticles for different applications is mini-mum. In the present study, bio-mediated synthesis of TiO2 nano-particles was carried out using Bacillus sp. collected from rareearth element soil environment. These TiO2 nanoparticles (ana-tase) were coated over glass slide to investigate biocidal/photocat-alytic activity on the aquatic biofilm.

2. Materials and method

2.1. Selection of bacterial species

In the present study, Bacillus subtilis (FJ460362) was isolatedfrom the Chavara (Kayankulam, Kerala, India) where rare earth ele-ment environment soil exists, which extends over 22 km. This spe-cies was used as template for the synthesis of TiO2 nanoparticles.

2.2. Preparation of biomass

The isolated B. subtilis (FJ460362) was inoculated in a 500 mlErlenmeyer flask containing 300 ml of 5% nitrate broth and incu-bated for 72 h in rotary shaker (200 rpm) at 27 �C. After incubation,the bacterium was harvested by centrifugation (6000 rpm for20 min). The pellet was washed with phosphate buffer saline (pH7.2) under sterile conditions and it was re-suspended with 20 mlof triple distilled water and was used for the synthesis of TiO2

nanoparticles.

2.3. Synthesis of TiO2 nanoparticles

About 500 ml of distilled water was taken in a 1-l conical flaskand 0.5 g of Potassium hexafluorotitanate was added to it. Thissolution was agitated by sonication to completely dissolve the sub-stance and 20 ml of biomass was added to it. The reaction betweenthe bacterial cell wall and Ti4+ ions was allowed to proceed for aperiod of 48 h. Insoluble white color precipitate was formed at bot-tom of the conical flask. It was centrifuged and the condensed pre-cipitate was washed with distilled water to obtain neutral pH andfinally washed with acetone and air-dried. The precipitate washeated for 3 h at 500 �C to remove the biomass organic contentsto get TiO2 crystalline particles.

Table 1Physico-chemical characteristics of pond water.

Parameters Value

Temperature 30.2 �CpH 7.6Dissolved oxygen 7.32Total solids 337 mg l�1

Total dissolved solids 288 mg l�1

Total suspended solids 49 mg l�1

Conductivity 525 ls cm�1

Chloride ions 80 mg l�1

Total hardness 130 mg l�1

2.4. Characterization of nanoparticles

Before and after calcination of biogenic TiO2 particles werecharacterized by FTIR. The sample was directly placed in the KBrcrystal and the spectrum was recorded in the transmittance modein the region of 400–4000 cm�1. The weight loss of TiO2 was mea-sured from room temperature up to 800 �C at a heating rate of10 �C/min in presence of air by Thermal gravimetric analysis(TGA) using TA Instruments SDT Q600. The UV–Visible spectrumof the TiO2 coated over glass slide over the range of 250–800 nmwas recorded using Spectra 50 ANALYTIKJENA spectrophotometer.The XRD pattern was recorded using computer controlled XRD-system, JEOL, JPX-8030 with Cu aK radiation (Ni filter = 13,418 Å)at the range of 40 kV, 20 A. The ‘peak search’ and ‘search match’program built in software (syn master 7935) was used to identifythe peaks. TiO2 particles were dispersed in water and cast onto acopper grid to study the sizes and morphology of the particles byTEM (Transmission Electron Microscopy) using Techai 20G2-FEI,Eindhoven, Netherland. From the TEM images the average of parti-cle size distribution was carried out using ImageJ software.

2.5. TiO2 particle coating preparation

Biologically synthesized TiO2 particle powder was mixed withsterile triple distilled water to prepare slurry. This slurry wascoated uniformly over the sterile glass slides. The TiO2 particlecoated glass slides were allowed to dry for 30 min at room temper-ature. The dried TiO2 particle coated slides were kept at 80 �C for2 h in a hot oven in order to get an adherent coating.

2.6. Biofilm formation

Pond water was rich in organic nutrients and also found to beenriched with microorganisms and was considered to be an idealmedium for growing and studying biofilm formation. Locally avail-able stagnant pond water was collected by sterile containers andused in the present investigation. The physico-chemical character-istics of the pond water are shown in Table 1. The pH of the watersample was 7.6, i.e., slightly alkaline. The total dissolved solid con-tent was 288 mg l�1, Chloride content was 80 mg l�1 while sulfatecontent was 16 mg l�1 and dissolved oxygen was 7.32 mg l�1 at30 �C. The total bacterial count was 4.5 � 105 CFU/ml [21]. TheTiO2 coated glass plates were kept in a tray, containing pond waterfor the growth of biofilm over them. The water was changed dailyfor the formation of biofilm up to 10 days.

2.7. Estimation of H2O2 production

The photocatalytic studies of TiO2 nanoparticles were carriedout using a Herber immersion type photoreactor HIPP-LP 618/116. The biofilm samples were exposed to UV-light (eight mercurylamps of 8 W each) for 20 min from distance of 15 cm. Differentamounts of nano-TiO2 powder of the study were weighed (2,4,6,8and 10 mg) added to a beaker containing 200 ml of pond waterseparately and aerated for uniform suspension. This water/TiO2

mixture was irradiated with polychromatic light source. Duringirradiation, peroxide strip (Merchoquant, Germany) was dippedinto the aqueous solution for estimation of hydrogen peroxideconcentration as adopted by Rajagopal et al. [14]. The peroxideconcentration within the TiO2 coated biofilm was also measuredby peroxide strip by placing it over the area of irradiation.

2.8. Bacterial destruction efficiency

TiO2 coated glass slides before and after illuminated light on thebiofilm samples was used for the study of photo killing efficiencyby employing Epi-fluorescence microscope. The biofilm sampleswere removed from medium and rinsed with 0.1 M phosphate buf-fer (pH 7.2) in order to remove any unattached aquatic bacterialspecies. The dual staining of fluorescein isothiocyanate (FITC) andPropidium iodide (PI) were used for the identifying living/deadcells on the biofilm samples [22]. About 0.5 ll of dual stain(FITC–PI; 1:1%) was added to biofilm samples and was incubated

P. Dhandapani et al. / Journal of Photochemistry and Photobiology B: Biology 110 (2012) 43–49 45

for 15 min. The excess stain was rinsed with sterile distilled waterand examined under the Epi-fluorescence microscope (E200 Cool-pix-Nikon, Tokyo, Japan).

2.9. Total viable bacterial counts

The biofilm were scrapped before and after illumination of lighton the TiO2 coated glass slides. The total viable bacteria of both thecases were enumerated by pour plate technique [23].

3. Results and discussion

3.1. Selection of bacterial species

The rare earth elements soil environment microbes are capableof heavy metals accumulation either by reduction or oxidation pro-cess [24,25]. The isolation and molecular identification of 27 rareearth environment bacterial species from Chavara rare earthelements environment soil and bioaccumulation of rare earthelements were studied by these bacterial species [25]. It is also ex-plained that the rare earth elements environmental bacteria ofPseudomonas and Bacillus sp. are capable of heavy metal accumula-tion [24]. These bacteria have excellent nucleation sites for mineralformation due to their high surface to volume ratio and electroneg-ative surface functional groups e.g. carboxyl, phosphoryl and hy-droxyl group [26]. Jha et al. [3] reported that 20 ml of 0.025 MTiO(OH)2 solution was added to the Lactobacillus sp. culture mediaand it was heated on steam bath at 60 �C for 10–20 min until whitedeposition starts to appear at the bottom of the flask and wereincubated for 12–48 h. Among the 27 bacterial species identifiedfrom Chavara soil, Bacillus sp. was identified as one of the mostpowerful bacteria, which is capable of delivering nanomaterialsin an efficient manner. Using 16S rRNA sequencing this bacteriumwas identified and the gene accession number (FJ1460362) was ob-tained from NCBI (National Center for Biotechnology Information).

3.2. TiO2 production efficiency

In present study, Bacillus sp. biomass is made to react withpotassium hexafluorotitanate to form a precipitate. The resultantprecipitate at different time intervals (6, 12, 24, 36 and 48 h) werecollected and transferred to an alumina crucible and heated at500 �C for 3 h, in order to remove the bioorganic contents to getTiO2 particles. The yield calculation of bio-mediated TiO2 particleswas carried out as below,

Weight of TiO2 ¼Weight of the precipitate with biomass

�Weight of the precipitate after heating ð1Þ

Fig. 1 shows the yield of TiO2 particles at different durations oftime. The TiO2 particles produced along with the biomass are

Fig. 1. Efficiency of TiO2 production at different durations of time.

removed, calcinated and weighted at 6, 12, 24, 36 and 48 h of theexperiment. It is clear from the figure, the TiO2 particles obtainedafter 6 h in about 0.1 mg and it has increased to 0.3 mg at the12 h. It is observed that the increase in weight of TiO2 produced in-creased with the reaction time up to 12 h and the rate of produc-tion becomes minimal afterwards. The remaining time periods of24, 36 and 48 h has shown a saturated level of TiO2 production.This clearly indicates that at the end of 12 h, maximum inorganicconstituents are converted into TiO2.

3.3. Characterization of TiO2 precipitate

3.3.1. FTIR analysisFig. 2 shows the FTIR spectrum of the TiO2 before and after heat-

ing process. From (Fig. 2a), it is observed that the bands at1452 cm�1, 1387 cm�1 and 1164 cm�1 were assigned to the bend-ing vibrations of primary and secondary amines and carboxylicgroups respectively. According to Hardy et al. [27] the carboxylicgroups were bound to TiAOATi. The band observed at 2928 cm�1

was assigned to the carboxylic groups. In addition, the peak at575 cm�1 corresponds to metal binding to carboxylic (M M C„O)groups. Mandal et al. [28] proposed that the proteins could bindwith nanoparticles either through free amine groups or crystallineresidues in the proteins. The carboxylic groups are known to coor-dinate with metal ions, which may act as a nucleation site fornanoparticle formation [29,30]. After the heating process (Fig. 2b)most of peaks corresponding to the organic functional groups weredisappeared and the intensity of TiAOATi (1064 cm�1) peak hasincreased. The peaks observed at 2926 cm�1, 1637 cm�1 and557 cm�1 might correspond to residue of bioorganic substances.It indicates that biotemplate or organic content for improving crys-talline nature of the particles was completely removed duringheating process.

3.3.2. TGA–DTA analysisFig. 3 represents the TGA/DTA spectra of biologically synthe-

sized TiO2 (12 h before heating precipitate). Three distinct slopesof weight loss processes were observed. The weight loss takes placeat 223 �C (4.1%), 334 �C (7.19%) and 659 �C (1.43%) respectively.This clearly indicates that about 85.91% residue was left over

Fig. 2. FTIR spectrum of the TiO2 (a) before and (b) after heating.

Fig. 3. TGA–DTA spectrum of biologically prepared TiO2.

46 P. Dhandapani et al. / Journal of Photochemistry and Photobiology B: Biology 110 (2012) 43–49

around 550 �C, while the bioorganic impurities were completely re-moved. Moreover the continuous heating of these precipitate im-proves their transformation of crystallinity. Many investigatorsalso reported that a temperature of 500–600 �C is required for theTiO2 precipitate to crystallize, which exhibits an improved photo-catalytic activity [31,32].

3.3.3. UV–Visible spectra analysisFig. 4 shows the UV–Visible spectra for the TiO2 nanoparticles

coated over glass slides. The UV–Visible spectrum exhibits awell-defined excitation absorption peak corresponding to anatasephase of nano-TiO2. The cut off wavelength of TiO2 nanoparticleswas observed at 379 nm. The band gap (Ebg) of TiO2 was calculatedusing,

Ebg ¼h� C

kð2Þ

where h = Plank constant (6.626 � 10�34 J), C = Speed of the light(3.0 � 108 m/s), k = cut off wavelength (379 � 10�9 m).

The band cap value of the TiO2 was found to be 3.273 eV. In thepresent study, the band gap value (3.273 eV) is closer to that ofanatase from of TiO2, which is used for understanding the photo-catalytic effect of TiO2 [33,34].

3.3.4. Crystal phase of TiO2 nanoparticlesFig. 5 shows the XRD pattern of the bio-mediated synthesis of

TiO2 nanoparticle after removing organic impurities by heating.

Fig. 4. UV–Visible spectrum of the TiO2 nanoparticles coated over glass slide.

The following peak signals at (101), (103), (004), (112), (200),(105), (211), (204), (220), (215) and (224) planes confirm thatthe formation of anatase crystal phase mostly, which coincideswith JCPD 89-4921 standard. Average particle size was calculatedusing Scherer’s equation:

d ¼ Kkb cos h

ð3Þ

where k is the X-ray wavelength, typically 1.54 Å, K is the shapefactor, (0.9), b is the line broadening at half the maximum inten-sity (FWHM) in radians, h is the Bragg angle, d is the particle size.The size of the bio-mediated TiO2 particle was found to be20.57 nm.

The previous investigation on fungus-mediated synthesis ofTiO2 was in the form of brookite crystal phase [5], which are lessphoto catalytically active compared to anatase. Many researchersclaimed that the anatase appears to be most photoactive and stablefor wide spread practical applications; where as rutile and brookiteare photo catalytically less active, although they show strong photoactivity [33,34].

3.3.5. Morphological analysis of TiO2 nanoparticlesFig. 6a shows the TEM image of TiO2 nanoparticles. It is eluci-

dated from the figure that the TiO2 particles were agglomerated;mostly spherical in shape and size of particles was in the rangeof 10–30 nm. Fig. 6b shows the particle size distribution of bio-mediated synthesis of TiO2 derived from image-J software. Itclearly indicates that the maximum distribution of the particle sizewere in the range of 15–20 nm. This result supports our XRD datain determining the particles size, which coincides with TEM image.Jha et al. [3] reported that Lactobacillus sp. mediated synthesis ofTiO2 nanoparticles were in spherical shape with an average sizeof 8–35 nm. The difference in size was explained, possibly due tothe fact that the nanoparticles are being formed at different timescales, which may limit their size due to constraints related tothe particles nucleation inside the organisms. This clearly indicatesthat the nanoparticles of TiO2 produced using Bacillus sp. were ofmore uniform in size when compared to Jha et al. [3]. Selected areaelectron diffraction (SAED) analysis of the TiO2 particles indicatedthat they were in crystalline in shape (Fig. 6 insert). The diffractionspots could be indexed based on the anatase structure of TiO2,which supports the present XRD result.

3.4. Photocatalytic activity studies

The biogenic TiO2 powder was suspended in 200 ml of pondwater and subjected to irradiation for 20 min from 15 cm distance.

Fig. 5. XRD pattern of TiO2 nanoparticles.

Fig. 6. TEM image of TiO2 nanoparticles (a) and (b) particle size distribution.

Fig. 7. Estimation of H2O2 produced (a) using TiO2 nanoparticles and (b) TiO2

coating under illumination of light.

1 For interpretation of color in Figs. 2–8, the reader is referred to the web version ofthis article.

P. Dhandapani et al. / Journal of Photochemistry and Photobiology B: Biology 110 (2012) 43–49 47

When biogenic anatase form of TiO2 is exposed to irradiation in anelectrolyte the following reactions are expected:

TiO2!hm

TiO2ðhþvb þ e�cbÞ ð4Þ

Hþvb þ OH� ! HO� ð5Þ

e�cb þ O2 ! O�2 ð6Þ

2HO� þ 2O�2 ! H2O2 þ O2 ð7Þ

H2O2 þ eþcb ! HO� þ OH� ð8Þ

The hydroxyl radical (OH�) which is generated at the surface ofTiO2 particle or at the TiO2/biofilm interface is mainly responsiblefor the formation of H2O2, is expected to destroy the microbeswithin the biofilm. The hydrogen peroxide produced during theabove reactions has a short life period, but sufficient enough toproduce significant results in bacterial destruction [14]. Fig. 7shows the estimation of H2O2 produced when TiO2 nanoparticleswere illuminated and also at the TiO2-coating on glass slides. Itclearly indicates that the observed concentration of H2O2 was3 ppm up to 2 mg of TiO2 powder suspension and while for10 mg of TiO2, a concentration of 12 ppm of hydrogen peroxidewas generated. Nanoparticles having larger surface area can offerhigh adsorption of reactants and large active catalytic sites aresuperior to dense films [35,36]. The production of H2O2 is compa-rably low in the case of TiO2 coating glass slide. It was due to thelesser-exposed active surface area of particles to irradiations [35].Rajagopal et al. [14] reported that 2 ppm of H2O2 was releasedwhile using TiO2 microparticles (50 lm) with illuminated light.Gumy et al. [35] also reported the biocidal activities of hydrother-mal synthesized TiO2 nanoparticles, where the concentration ofhydrogen peroxide was observed between 3 and 8 ppm. The resultsubstantiates the fact that when the particles sizes are uniform inthe range of 10–30 nm, the production rate of H2O2 has consider-ably increased.

3.5. Bacterial destruction efficiency studies

On the basis of hydrogen peroxide production in TiO2 coatedglass slide selected for the biocidal effect of photocatalytic activityto biofilm was studied by Epi-fluorescence microscope. The dualstaining of fluorescein isothiocyanate (FITC) and Propidium iodide(PI) were used in the present investigation. It is established that PIcan only stain the cells when the cell membrane is disrupted. FITCcan stain both the live and dead cells because it can penetrate intothe cell membrane [22]. Fig. 7 represents dual stained with bacte-rial biofilm on the (10 mg) TiO2 coated glass slide before and afterillumination of light. According to (Fig. 8a), the presence of green1

fluorescence indicated the presence of viable bacterial cells in nor-mal condition (without illumination of light). Fig. 8b shows thepopulation of the dead cells indicated by the presence of the redfluorescent spots after illuminating the biofilm.

This evidence supports the fact the generation of H2O2 at theTiO2–biofilm interfaces resulting in the destruction of the bacteriawithin biofilm. The amount of H2O2 generated on TiO2 particles hasalso been reported to achieve antibacterial activity against variousbacterial species [17,18,36]. When the TiO2 particles are irradiatedwith a polychromatic light leads to the generation of H2O2 at theparticles/medium interface which attacks the near by bacterialcells and create micropits on cell surface. It is due to the lipidper oxidation on bacterial cell wall membrane [17,18]. Before illu-minations of light on the TiO2 coated glass slide are shown thatbacterial cell surface was smooth (Fig. 8a), where as after illumina-tion of light on the glass slide are shown that micropits on the bac-terial cell membrane (Fig. 8b). This is further supported by totalviable bacterial count. The total bacterial count before illuminationof the biofilm was 4.6 � 106 CFU cm�2. While exposing the TiO2

coated glass slides to a polychromatic light for 20 min from15 cm distance, the total bacterial count was 4.1 � 102 CFU cm�2.This result indicates that H2O2 production in the interface de-stroyed the bacteria by 4-fold. Some bacterial species viz.Spirillum,Erwinia, Flavobacterium, Enterobacter and Klebsiella sp. werereported by Rajagopal et al. [14] as H2O2 tolerating species in thebiofilm. The present results clearly indicate that photocatalyticefficiency of TiO2 significantly improved with the size and shapeof the nanoparticle in agreement with previous investigators[17,18,36].

Bacterial cell wall damaged

(a)

(b)

Bacterial cell wall smooth surface

Fig. 8. Epi-fluorescence micrograph of (a) before illumination of the biofilm and (b) after illumination. Biofilm were stained with fluorescein isothiocyanate (FITC) andPropidium iodide (PI) dyes: Green fluorescence is characteristic of the live cells, whereas red fluorescence is due to dead cells.

48 P. Dhandapani et al. / Journal of Photochemistry and Photobiology B: Biology 110 (2012) 43–49

This technology can be utilized to replace the toxic substanceslike sodium thiocyanate, bromine-based compounds, ozone orchlorine in water treatment industries. It is an also as eco-friendlymethod to control the aquatic biofilm communities by photocata-lytic activity of TiO2.

4. Conclusions

The present study is truly a green cost-effective approach,capable of producing TiO2 nanoparticles. The microbial mediatedsynthesis of TiO2 exhibits greater advantage over other conven-tional techniques, as it produces a uniform spherical shaped TiO2

nanoparticle in 12 h. The synthesized TiO2 nanomaterial was con-firmed by XRD and TEM. Due to the photocatalytic effect at TiO2

surface of the nanoparticles hydroxyl radicals are generated whichare responsible for the formation of H2O2, at the interface todestroy the microbes within the biofilm. The H2O2 has a short lifeperiod, but sufficient enough to perform better in the destructionof the bacteria.

Acknowledgments

The authors are thankful to the Director, CSIR – Central Electro-chemical Research Institute, Karaikudi for giving permission tocommunicate the paper. The authors also wish to express thethanks to Mr. Rathish Kumar, Miss. S. Krithika and Mrs. Nalini ofInstrumentation Division of CECRI for their assistance in theutilization of Central Instrumentation facility.

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