Journal of Molecular Structure 1016 (2012) 30–38

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Journal of Molecular Structure

journal homepage: www.elsevier .com/locate /molstruc

Optical, dielectric and microscopic observation of different phasesTiO2 metal host nanowires

Kaushik Pal a, Tapas Pal Majumder a,⇑, Chirantan Neogy a, Subhas Chandra Debnath b

a Department of Physics, University of Kalyani, Kalyani 741 235, West Bengal, Indiab Department of Chemistry, University of Kalyani, Kalyani 741 235, West Bengal, India

a r t i c l e i n f o a b s t r a c t

Article history:Received 6 December 2011Received in revised form 10 February 2012Accepted 10 February 2012Available online 22 February 2012

Keywords:Bulk metal titaniumBulk anatase titanium (IV)1-d TiO2 nanowiresNanocabbagesDielectricAFM studies

0022-2860/$ - see front matter � 2012 Elsevier B.V. Adoi:10.1016/j.molstruc.2012.02.029

⇑ Corresponding author. Tel.: +91 33 2582 0184; faE-mail addresses: tpm@klyuniv.ac.in, tpmaju

Majumder).

We successfully obtained TiO2 nanowires (NWs)/nanocabbages (NCs) from different phases of bulk metaland anatase titanium powder, respectively. In this fabrication procedure, we prepared TiO2 nanowiresfrom anatase titanium those have very low diameters of the order of 1.5 nm with high yield. Thoseagglomerated nanowires turned to nanocabbages shaped structures with diameter of 42 nm afterannealed at high temperature having TiO2 anatase crystallinity. Again, synthesized nanowires from bulkmetal titanium have its large order diameters of the order of 11 nm and after annealed its length reducesto 120 nm with very short size nanowires of anatase with rutile crystalline impurity formed. Comparativestudy revealed that high crystalline hydrothermally synthesized TiO2 nanowires can only be obtainedusing bulk anatase (IV) titanium best reported than usual ordinary metal titanium. Interestingly the opti-cal, dielectric properties of such nanowires changed drastically due to changes of their structuralproperty owing to different phases of titanium powder introduced in this synthesis technique.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction preparation of TiO nanowires, nanorods, nanoparticles with very

Titanium oxide (TiO2) is currently used for extensive researchbecause of its wide range of potential applications. Titanium isthe ninth most abundant element in the Earth’s crust. TiO2, themost common compound of titanium, is often used in many appli-cations. It has received much attention because it may be appliedfor environmental photocatalytic [1] processes such as deodoriza-tion, prevention of strains, sterilization [2] and removal of pollu-tants from air and water [3–5]. Nanocrystalline titanate has beenthoroughly studied for applications in solar energy harvesting[6], biological coatings [7], sensors [8], optical devices [9,10], andphoto electrochemical conversion [11,12]. This material providesa significant scientific growth for ongoing research [13,3]. Nano-structured TiO2 materials with a typical dimension less than100 nm, have recently emerged on a large scale. Such materialsmax exhibit spheroidal nanocrystallite and nanoparticles forma-tion including most recently synthesized elongated nanotubes,nanosheets, and nanofibers. TiO2 may exist in three crystal phasessuch as anatase, rutile and brukite. The anatase and rutile phasesare well known and many studies on their synthesis, photocataly-sis and applications for catalyst supports have been reported. How-ever, a few works were reported till now in the literature about the

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x: +91 33 2582 8282.mder1966@gmail.com (T.P.

2

larger dimension of using bulk anatase titanium powder.Synthesis of single crystalline TiO2 nanowires has attracted

great interest because of their potential applications in novel pho-tovoltaic devices [14]. Many techniques have been developed toprepare TiO2 nanowires [15,17,18]. Feng et al. [16] prepared 1DTiO2 nanowire arrays (5 lm long) on TCO glass substrates by thehydrothermal method, and they also used the as-prepared nano-wires arrays in dye-sensitized solar cell (DSSC). Dong et al. [19]used P25 TiO2 nanoparticles as the precursor to prepare reticularTiO2 nanowires (diameter 10–30 nm) by the hydrothermal meth-od. But we want to focus specifically here on the synthesis ofTiO2 nanowires by using Ti powder through chemical route andannealing those are distributed uniformly with high yield havingvery low dimension. Whereas TiO2 nanowires those obtained frombulk metal titanium powder has less impact with their nanofabri-cation and we cannot obtain pure TiO2 nanostructures for suchcase because we cannot remove sodium titanate from desiredTiO2 nanowires. In addition, this titania has a high refractive indexof the order of 2.4–2.9 depending on the phase [20] which may beimportant for photonic band gap materials and other photonicapplications. In this paper we represent here, for the first time,the synthesis and characterization of stable suspensions and filmscomposed of fluorescent TiO2 nanowires. The size scale of thosenonreactors is in the range from 1 to 10 nm. This is a dynamic sys-tem at the micellar level. The micelles collide with each other andexchange their constituents rapidly, which is essential for carryingout chemical reactions [21].

K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38 31

Through past decade many researcher already synthesized TiO2

nanowires from bulk anatase titanium powder. In this paper, wehave really work hard and try to extend this synthesized procedureand obtained TiO2 nanowires with high yield having uniform scaleby using different phase of bulk titanium (metal and anatase)through chemical reduction process from sodium and potassiumhydrogen titanates with general chemical formula NayH2–y

TinO2n+1�xH2O. By acid washing of such materials, it results in ionexchange to produce the layered hydrogen titanates H2TinO2n+1�xH2O, which exhibits features similar to H2Ti3O7, H2Ti4O9�H2O,and other members of the hydrogen titanate family. After main-taining oxidation through annealed process for several times, thepreviously prepared sample changes into new crystalline pureTiO2 nanostructure formation. Newly, in this paper our main atten-tion is to focus about the interesting dielectric properties changedwith different diameters and lengths of excellent crystalline TiO2

nanowires/nanocabbages formed by agglomeration of nanowiresafter annealed at high temperature. The absorption and lumines-cence properties are suitably changing with various morphologicalgrowth of different size TiO2 nanostructures comparable to nano-wires growth from ordinary metal titanium powder.

2. Experimental

2.1. Synthesis of TiO2 nanowires (NWS) from bulk metal titaniumpowder

In this procedure, ordinary bulk metallic titanium powder(Atlanta Drugs and Chemicals, Merck) with 0.3 g was added into30 ml of 10 M NaOH and then stirred for transparent clear solution.This solution was put into a stainless steel coated Teflon-linedautoclave of 50 ml capacity and kept the system as a whole intoan oven at 119 �C for 19 h. After cooling the system naturally atroom temperature, the resulted bluish precipitation was collectedby filtration. The filtered materials was then washed with 0.1 MHCl (35% concentrated, Atlanta Drugs and Chemicals, Merck) anddistilled water in sequence for several times. The final productwas dried at 60 �C for 4 h. The obtained sky blue granule likesamples were annealed at 650 �C for 1 h in a heating chamber foroxidation and the desired samples kept for characterization.

Fig. 1. (a–c) FE-SEM image of sodium hydrogen titanate nanowires before annealedobtained from bulk metal titanium (Pal et al.).

2.2. Synthesis of TiO2 nanowires (NWs) from bulk anatase (IV)titanium powder

As similar to earlier, 40 ml mixture of 10 M NaOH and 5 MKOH was stirred vigorously in a magnetic stirrer (Remi) for15 mins till the clear transparent solution appeared. A 0.2 g ofanatase (IV) titanium powder (Anlanta Drugs and Chemicals,Sigma Aldrich) was mixed with 10 M of 30 ml NaOH and KOH(pellets) in a 100 ml beaker contained de-ionized distilled water.The resulted solution was then stirred for 25 mins. After stirringthe solution properly it was transferred into a stainless steelcoated Teflon-lined autoclave with capacity of 100 ml and the sys-tem as a whole was then put inside a heating chamber and waswaited for 19 h at 119 �C. Subsequently, the system was allowedto cool to room temperature naturally. The resultant samplewas filtered off from the resulted transparent solution with awhite precipitation inside the container. The filtered sample waswashed with 0.1 M HCl solution, 150 ml de-ionized distilled waterand 50 ml ethanol in sequence for several times until the impuri-ties removed from the desired samples. Then the sodium potas-sium titanate nanowires turned into hydrogen titanatenanowires and after annealed at high temperature turn into pureanatase TiO2 nanowires. The resulted sample was dried at 60 �Cfor 4 h in an oven. This final sample was annealed at 650 �C for

1 h in furnace and then it was collected for TiO2 nanomaterialsafter it cooled naturally at room temperature for characterization.Those above technique used for different TiO2 nanostructurespreparation from two different phase of bulk titanium. We useprogrammable Spin Coater (Apex Instruments Co., Model SCU-2008C) to deposit very thin film over ITO coated glass substratehaving conducting surface with different TiO2 nanostructuressample to study the behavior of dielectric properties.

3. Results and discussion

3.1. Morphology

From FE-SEM (Model: S4800 at 5.0 kV) micrograph of preparedsodium titanate nanowires from bulk Ti powder in 10 M NaOH sol-vent, we can predict its diameter of the order of 11 nm after an-nealed as shown in Fig. 1a–c with high resolution. After annealedit is clearly indicative that the prepared sample contains numerousTiO2 nanowires with average diameter ranged from 30.40 nm to34.85 nm having very short length of wires of the order from 109to 120 nm, illustrated in Fig. 2a and b. If we maintain annealed pro-

Fig. 2. (a and b) FE-SEM image of TiO2 nanowires after annealed obtained from bulkmetal titanium (Pal et al.).

Fig. 3. (a–c) FE-SEM image TiO2 nanowires before annealed obtained from bulkanatase titanium (Pal et al.).

32 K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38

cess for this sample at perfect temperature then it may be re-mained same with reduced diameter. But crystalline structure can-not confirm TiO2 NWs although it contains lots of impurities ofrutile phases which significantly high intense also shown in X-ray diffraction (Fig. 5a). Whereas, when we see further informationin addition of bulk anatase (IV) titanium powder into 10 M NaOHand 5 M KOH solution, FE-SEM observation reveals that we canfabricate uniform TiO2 nanowires with diameter of the order of1.5 nm and as well as length of the order of 653 nm with high yieldbefore annealed as shown in Fig. 3a–c corresponding to high mag-nification of FE-SEM micrograph. Fig. 4a and b clearly display thewell organized structure for both TiO2 nanowires reduced to TiO2

nanocabbages. Most interestingly we obtained well crystallinereducible nanowires that agglomerated and turned to nanocabbag-es with diameter of the order of 42 nm after annealed the nano-wires at 650 �C for 1 h duration of new nanostructure formationas depicted in inset of Fig. 4b and a, respectively.

The films of synthesized nanomaterials were characterized forstructural information by using X-ray diffraction. The XRD datawere recorded at a scan rate of 0.05� per sec by using a SeifertXRD 3000P diffractometer with Cu Ka radiation (0.01418 nm).Fig. 5a–c illustrates the XRD pattern of the synthesized nanowireswith all the diffraction peaks corresponding to the hexagonalwurzite phase of titanium. Obtained TiO2 nanowires from bulkmetal titanium powder are identified as (101), (103), (004),(112), (200), (105), (211), (118), (116), (220), (215) corre-sponds to anatase crystalline phase and the peaks are identifiedas (110), (101), (111), (204), (211) corresponds to rutile phaseas depicted in Fig. 5a [22,23]. We observed several sharp intensepeaks originated at (101), (004), (200), (105), (211) hkl planescorresponds to anatase crystalline of TiO2 nanowires obtainedfrom bulk anatase titanium with only one low intense impurity

peak at (110) due to rutile phase illustrated in Fig. 5b. ThoseTiO2 nanowires breaks and turns into new crystalline formationof nanocabbages shape after annealed it at 650 �C for 1 h durationand no such impurity peaks were detected very low intense (110)peak gradually diminishes. Therefore, we only found high intensediffraction peaks located at (101), (004) and (200) hkl planes cor-respond to anatase phase (Fig. 5c). It suggests that the obtainedTiO2 product is well crystallized fabrication with anatase phase(Fig. 5c). Those were very slightly shifted in angle as comparedwith two previous crystalline nanostructures as shown in Fig. 5aand b. The d-spacing of the sodium titanate and pure TiO2 NWshave been calculated by using the XRD analysis and the corre-sponding (hkl) planes were compared with standard JCPDS data.In case of solvothermal synthesis, concentration and annealedtemperature play an important role in the formation of new crys-tal structure with different shape and size of the nanostructureforms.

In contrast, silica gels appear to have a particular structure athigh water contents. The morphologies of deposited TiO2 NWs overdeposited SiO2 film were observed by AFM (Veeco, diInnova) asillustrated in Fig. 6a and b for before and after annealed TiO2

Fig. 5. XRD spectrum of: (a) TiO2 nanowires from bulk metal titanium afterannealed, (b) high intense peaks of TiO2 nanowires from bulk anatase titaniumbefore annealed and (c) well crystalline nanocabbages of pure TiO2 nanowires afterannealed (Pal et al.).

Fig. 4. (a and b) FE-SEM image of TiO2 nanowires accumulated into nanocabbagesafter annealed obtained from bulk anatase titanium (Pal et al.).

K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38 33

NW, respectively, obtained from bulk metal titanium whereasFig. 6c and d were displayed the surface of deposited TiO2 NWon deposited SiO2 film obtained from anatase titanium for beforeand after annealed (NC), respectively. The AFM top views of thefracture surfaces were prepared immediately prior to scan. Thefilm was constituted by a large number of particles with compactand sequential arrangement as shown in Fig. 6. The particles arerods like nature in their appearance and it exhibits a randomroughness on the surface having diameters of the order of 30–50 nm with their small grains. It is also found from the image thata few of interspaces exists among the particles. The mean rough-ness is the mean value of the surface relative to the center plane.The result showed that the roughness values of the nano-compos-ite materials were affected by the TEOS contents. AFM images of aglass substrate and spin coated films are 2.41 and 2.96 Å, respec-tively. The roughness is very similar to that of pure glass substrate,but the coated film has no defect on the surface. These results sug-gested that the domain size of the silica segment in the thin film isvery small, and the TiO2 nanowires growth was restricted in thethin film system due to the geometrical constraint. Thickness offilms can be measured from the AFM view and the value is1.15 lm (Fig. 6).

3.2. Dielectric properties of TiO2 nanostructures

Our main purpose in this paper is to investigate how the dielec-tric properties change with various morphological structures suchas size, diameters and length of TiO2 nanowires (NWs) after an-nealed. TiO2 nanowires agglomerated and formed into nanocab-bages (NCs) at different ambient conditions of time andtemperature. The frequency dispersion dielectric data were re-corded at room temperature with the frequency range from10 Hz to 13 MHz using a HP4192 Impedance Analyzer. The test

cells for dynamics measurement were prepared using 0.7 mm ITO-coated polished glass plates having 16 (4 mm � 4 mm) pixels im-printed on the ITO coating by photolithography. Homogeneous pla-

34 K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38

nar alignment was induced on the ITO coated glass plates thosewere spin-coated with TiO2 nanostructure samples. The thicknessof the cells was about 0.1 lm, thin enough to allow surfacestabilization of the specimen. Frequency dependent complexdielectric permittivity e⁄(x) is determined using the followingequation [24,25]

e�ðxÞ ¼ 1jxC0Z�ðxÞ ¼

CP

C0� j

1xC0RP

¼ e0 � ie00 ð1Þ

where e0

is the dielectric constant and e00 is the dielectric loss.This frequency dispersion di-electric data were recorded withinroom temperature of frequency range from 10 Hz to 13 MHz usinga HP4192 Impedance Analyzer on a 1 lm thick sample cell. Wherej denotes the square root of �1, x (=2Pf), is the angular frequency,Z stands for the complex impedance, C0 and Cp are the capacitances

Fig. 6. AFM topographic views of the fracture surfaces of TiO2 NWs of SiO2 coating glassand d) before and after annealed Ti-NWs and Ti-NC from bulk anatase titanium (Pal et

of the cell under the vacuum and that filled with a dielectric bulk,respectively, Rp is the effective parallel resistance of the dielectriccell (consisting of a planar LC bulk in this study), and e

0and e00 rep-

resent the real and imaginary parts of the complex dielectric con-stant, respectively. The value of dielectric constant is 4.56 at lowfrequency 10 kHz. It just decays at particular frequency 1957 kHzwith the increase of frequency and only shows normal dispersionin the system from 10 kHz to 10,000 kHz. It also shows a one stepbehavior corresponding to a single relaxation phenomenon asshown in Figs. 7a and 7b, resulted for Ti-NCs obtained from TiO2

NWs annealed obtained from bulk anatase titanium. The dielectricstrength is very low �0.047 and it decays in high frequency rangefor Ti-NWs after annealed, obtained from bulk metal titaniumpowder. Comparatively a clear and distinct relaxation peak at3353 kHz occurs due to Ti-NCs and no such peak found for Ti-NWs as shown in Fig. 7a and 7b.

substrate (a and b) before and after annealed TiO2 NWs from bulk metal titanium, (cal.).

Fig. 6 (continued)

K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38 35

3.3. Optical properties

For the measurement of ultraviolet-visible absorption spectra(Model: TCC-240A, UV-2401 PC, Shimadzu, Japan) and photolumi-nescence spectra (PL) (Model: LS55, Fluorescence spectrometer,PerkinElmer), the prepared TiO2 nanowires from metal and anatasetitanium powder were dissolved in ethanol solution homoge-neously and then spin coated (Apex Instruments Co. with modelSCU-2008C) on quartz substrates (2 cm � 2 cm) for obtaininguniform thin nanofilms of such. Ultraviolet spectra indicates thatthere is a clear and broad distinct peak with high intensity locatedat 565 nm in red shift region as shown in Fig. 8, due to pure TiO2

nanowires. In comparable with this there is no such absorption

band maxima observed for metal titanium oxide and its absorptionis totally decaying exponentially in red shift region with low inten-sity field. We obtained the typical evolution of (ahm)2 as a functionof the photon energy (hm) in our films as depicted in Fig. 9. Theoptical band gap energy (Eg) deduced from the equation as givenbelow:

I ¼ I0e�at with a = 1/t ln(I/I0)= 1/t ln(1/T) = 1/t ln(1/1 � A), whereT and A are the transmission and absorption coefficients, respec-tively. TiO2 powder has its high intrinsic band gap with 3.2 eVfor anatase and 3.0 eV for rutile phases [26]. We also checked theUV–visible absorption spectrum of the TNWs obtained from bulkof anatase and metal titanium powder. We have observed a prom-inent absorption band maxima, which is red shifted. The calculated

Fig. 7a. Variation of dielectric constant (e0) with frequency (f) for Ti-NWs (bulk

metal titanium) and Ti-NCs (bulk anatase titanium) after annealed at 650 �C (Palet al.).

Fig. 7b. Variation of dielectric loss (e00) with frequency (f) for Ti-NW (bulk metaltitanium) and Ti-NC (bulk anatase titanium) after annealed at 650 �C (Pal et al.).

36 K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38

energy band gap as shown in Fig. 9 is approximately 4.55 eV foranatase TNWs, a little bit higher than the bulk titanium powder(anatase) (3.2 eV). TNWs band gap is always higher than anatasephase of bulk titanium oxide due to quantum confinement effectbecause of nanostructure formation.

From Fig. 10 the PL emission spectra of the nanophase of differ-ent titanium specimens under an excitation wavelength 325–475 nm of adjusted excitation [27–29] and emission slit width 15and 12 nm respectively at room temperature. It can be seen thatthe nanophase TiO2 obtained from bulk metal titanium powderhas almost very low luminescence peak observed at 480 nm and508 nm wavelength region with a small shoulder peak at 461 nmobserved behind due to 325 nm excitation. Applying 475 nm exci-tation, two distinct clear and sharp broadening peaks appears at553 and 615 nm region. Those PL intensity peaks are shifted dueto higher range diameter of nanowires of the order of 11 nm. How-

ever, a broad visible emission band appears around 500 nm whenthe nanowires diameter reduces to 1.5 nm obtained from bulk ana-tase titanium illustrated in Fig. 11.Two distinct sharp peaks locatedat 506 and 558 nm region for 425 nm excitation. Also, the peakintensity of the visible emission band rapidly shifted at 553 and613 nm region with a hump at 613 nm resulted for 475 nm excita-tion. It is noted that both the excitation energy and the observedemission maximum energy lie within the band gap of TiO2, whichshows that, there must exist certain localized levels within the for-bidden gap because the direct electron transition between the va-lence band and the conduction band should be not allowed.However, a large number of surface broken or dangling bondsand defect centers intrinsically are existing in the nanosized mate-rials. Those can form various animated energy levels localizedwithin the forbidden gap. Therefore, it acts as the optical absorp-tion centers, which makes large modification for the optical prop-erties of such different phase of TiO2 nanomaterials.

Earlier researcher suggested that titanate nanowires were syn-thesized [30] based on the reaction at around 150 �C with a 10 MNaOH solution that yielded nanotubes. By increasing temperatureand/or concentration of NaOH, the prepared nanowires have givenhigh yield. Washing the tubes or wires with dilute HCl promotescomplete exchange of Na+ by H+ to form hydrogen titanates. Onheating the tubes, they convert to anatase but with the loss ofthe tubular morphology. In contrast the wires behave quite differ-ently. After washing with dilute acid and annealing it only for fixedtime and temperature duration, they convert to well crystallinepure TiO2 nanostructure formation, otherwise we cannot removehydrogen titanate from previously obtained sodium titanate nano-wires. Although we obtain TiO2 nanowires when bulk metal tita-nium powder dissolved into higher concentration of metalhydroxide solvent (NaOH or KOH). But after acid washing andannealing, we cannot obtain well crystalline TiO2 nanowires uni-formly distributed in large scale due to presence of high intense ru-tile impurities also shown in XRD pattern of Fig. 5a. Whereas a wellcrystalline pure TiO2 nanocabbages structure formation evolved inthis synthesis procedure that resulted after chemical reduction ofbulk anatase titanium dissolved into metal oxide. The desired sam-ples washed after filtration with dilute 0.1 M HCl and then an-nealed at standardized temperature 650 �C for 1 h. Hydrogentitanate nanowires have broken and TiO2 nanowires accumulatedto nanocabbages like shape with diameter of the order of 42 nmas observed in FE-SEM morphology (Fig. 4a and b). So we may sug-gest that many impurities appear which cannot remove after acidwashing and annealed as confirmed in Fig. 5a. So many disadvan-tages of TiO2 nanowires synthesis from ordinary metal titaniumpowder occur. There only possibility of well crystalline TiO2 nano-structure from anatase (IV) titanium is discussed in detail in aboveexperimental Section 2.2. Dehydration reaction mechanisms pro-ceed as follows and growth mechanism for variety of TiO2 nano-structures formation as shown in schematic Fig. 12.

(i) NaOH + TiO2 = Na4TiO3 + H2O(ii) Na4TiO3 (annealed at 650 �C 1 h) ? NaXH2–XTi3O7

(iii) H2Ti2O4(OH)2 ? H2O + H2Ti2O5 (Hydrogen titanatenanowires)

(iv) H2Ti2O5 (annealed at 650 �C 1 h) ? H2O + 2TiO2 (TiO2 nano-wires from bulkanatase titanium) (Table 1)

4. Conclusions

In summary, we reported a simple method for the fabrication ofbulk titanium powder on a large scale through hydrothermal tech-nique. The experimental results reveal that the diameters of nano-wires of different materials obtained from metal and anatasetitanium powder are changing drastically its structural properties

Fig. 9. Band gap energy in eV for TiO2 nanowires obtained from bulk metal andanatase titanium (Pal et al.).

Fig. 10. Photoluminescence spectra of metal TiO2 nanowires film of 325 and475 nm excitation (Pal et al.).

Fig. 8. Ultraviolet–visible absorption spectra of TiO2 nanowires obtained from bulk metal titanium and anatase titanium (Pal et al.).

Fig. 11. Photoluminescence spectra of anatase TiO2 nanowires film of 425 and475 nm excitation (Pal et al.).

K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38 37

as observed in X-ray diffraction. So, TiO2 nanowires obtained frombulk metal titanium have mixed crystalline structures containedlots of retiles impurities peaks as indicated in Fig. 5a, which cannotnot removed by acid washing and annealed for several times.Whereas less impurity well defined high intense crystalline peaksresulted due to high yield large scale uniform TiO2 nanowires ob-tained from bulk anatase titanium depicted in Fig. 5b and after an-nealed those TiO2 nanowires, a distinct and sharp well crystallinestructure formation illustrated in Fig. 5c. A low intense rutile impu-rity peak at (110) diminishes gradually comparable in Fig. 5a–c re-sulted to the benefit of synthesized TiO2 nanowires using bulkanatase titanium rather than ordinary metal titanium powder.Interestingly enough, the luminescence properties has been chan-ged due to its diameters and length. An interesting comparativeidea about the luminescence studies, i.e. no such symmetry ob-served in peak maxima for TiO2 nanowires from bulk metal tita-nium due to its non-uniformity and existence of another

Fig. 12. Growth schematic diagram of TiO2 nanostructures in different ambient condition of time and temperature (Pal et al.).

Table 1Growth mechanism and chemical reaction chart for different time and temperature ambient condition of titanium nanostructures synthesis (Pal et al.).

Nano morphology Bulk quality of TiO2 powder Hydroxide solvent Temp. (�C) Diameters of nanostructures

Nanowires (0.3 g) metal 10 M of 30 ml 119 11 nm (diameter) 232 nm (length)Nanowires – – Annealed at 650 30 nm (diameter) 120 nm (length)Nanowires (0.2 g) anatase 10 M of 30 ml NaOH and KOH 119 1.5 nm 653 nm (length)NanoCabbages – – Annealed at 650 42 nm

38 K. Pal et al. / Journal of Molecular Structure 1016 (2012) 30–38

impurities(rutile),which cannot be removed further. While, theluminescence peak intensity interestingly differ and remarkablesymmetry peak maxima observed resulted for TiO2 nanowires ob-tained from bulk anatase titanium because of its uniformity indiameters with size and shape. This present strategy of uniformnanowires fabrication by using bulk anatase titanium powder issimple, reproducible, high yield, easily operating chemical reduc-tion process and may be applied to scale up to industrial produc-tion of different nanostructures. Also a noticeable point is thatdielectric permittivity is too high for Ti-NC annealed after Ti-NW,which was obtained from bulk anatase Ti powder rather than an-nealed Ti-NW from bulk Ti metal powder. So, a bi stable dc switch-ing may be obtained using both the systems. That may be appliedfor electrical switch. The controllable growth of TiO2 nanostruc-tures described here may open up the possibility of exploring novelapplications in the areas of electronics and optoelectronic nanode-vices, in addition to high volume applications.

Acknowledgements

The work was supported by the funding agency DST,Government of India for providing the financial assistance withthe sanctioned Project number SR/S2/CMP-0020/2009. We arethankful to the Department of Biophysics, University of Kalyanifor performing AFM measurement. Mr. K. Pal is grateful to DSTfor providing his fellowship to success this total experimentalwork.

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