Transition Met Chem (2009) 34:915–923DOI 10.1007/s11243-009-9281-1 UV-sensitized nanomaterial semiconductor catalytic reduction of CoIII(N–N)33+/nm-TiO2 and Co:TiO2 formation: SEM-EDX and HRTEM analyses Krishnamoorthy Anbalagan Æ Lazor Devaraj Stephen Received: 17 July 2009 / Accepted: 8 September 2009 / Published online: 25 September 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Interfacial electron transfer induced by 254 nm light at nanomaterial (nm) titanium dioxide/CoIII(N–N)33? interface in binary mixed solvent media such as water/ methanol (or 1,4-dioxane) has been probed. The distinct photo reduction of cobalt(III) complexes, CoIII(N–N)33?; (N–N)=(NH3)2, en (1,2-diamino ethane), pn (1,2-diamino propane), tn (1,3-diamino propane), and bn (1,4-diamino butane), by excited nm-TiO2 particles: CoIII ? nm-TiO2 ? hm ? TiO2 (h?;e-) ? CoIII ? nm-TiO2 (h) ? CoII is solvent controlled. The electron transfer from the conduction band of TiO2 (e-, CB) onto the metal centre of the complex consists of (i) electron transport from CB into surface-adsorbed species A: CoIII(N–N)33? (ii) solution phase species B: CoIII(N–N)33?(sol.), accumulated at the surface of the nanoparticle. In addition, UV irradiation of CoIII(N–N)33? stimulates generation of CoIIaq ion, due to charge transfer transition, in solution phase. After UV irradiation, cobalt-implanted nm-TiO2 separated as gray ultrafine particles, which were isolated. Photo efficiency of the formation of CoII ion was estimated and the cobalt implanted nanomaterial crystals isolated from the photolyte solutions were subjected to SEM-EDX, X-ray mapping, and HRTEM-SAED analyses. Solvent medium was found to contribute in both the formation of CoII ion and interstitial insertion of cobalt into the lattice of nm-TiO2. Introduction Nanocrystalline semiconductor catalysts have become widely useful for many technological applications, mainly K. Anbalagan (&) L. D. Stephen Department of Chemistry, Pondicherry University, Pondicherry 605 014, India e-mail:
[email protected] due to their light transparency, charge separating properties, and electronic conductivity [1, 2]. Due to the high chemical stability and favorable energy band structure, titanium dioxide has drawn attention for its potential applications in photo catalysis in different fields. Semiconductors, especially TiO2, ZnO, and SnO2 are very promising components in the development of solar cells [3], electrochromic devices [4, 5], sensors [6, 7], photoelectrocatalytic and photochromic cells [8, 9]. Recent investigations have shown that Co(dbbip)22?/3? complexes are promising candidates [10] for use as redox mediators in dye-sensitized solar cells. Metal-doped semiconductors find extensive applications in conjunction with the lattice structures; for example, Chamber et al. [11, 12] reported that the local structural environment for Co species in anatase is similar to that of cobalt in CoTiO3 (highly distorted octahedral coordination with oxygen ligands). Nanosized metal-doped materials with novel morphologies can have somewhat better performance than bulk materials. From the point of view of kinetic investigations of electron transfer reactions of inorganic complexes in solution, mixed solvents have a number of distinct advantages. These include: (a) mixed solvents greatly influence the formation and stability of transition states [13]/ion-pairs [14]/excited states [15, 16], (b) they ensure definite rate of electron transfer reactions even in dilute solutions through potential matching, (c) the tuning of redox property is facile by the use of mixed solvents of varying compositions. However, despite these advantages, the potential of catalytic effect of TiO2 as electron transfer mediator with cobalt(III) complexes in binary-mixed solvents remains relatively unexplored. In this article, we have designed a novel solution chemical reaction route to study the interfacial ET processes and also report formation of surface-modified nm-TiO2 particles due to cobalt implantation. 123 SE image resolution: 3.0009.3-diamino propane). exhibiting two ligand to metal charge transfer (LMCT) bands.14 nm and a point-topoint resolution of 0. 80:20. Multiple photolysis experiments were performed under identical conditions to confirm the reproducibility. pn (1. and bn (1. working distance: 5–60 mm. one centered at 302. superhydrophilic films. The instrument has a Gatan digital camera. pressed powder samples were coated with a thin layer of evaporated carbon for conduction and examined at 25 kV accelerating voltage using a standardless procedure on a Hitachi S-3400N instrument equipped with a energy-dispersive X-ray microanalysis system. A significant difference of the surface morphology and structure of nm-TiO2 of the samples b and c could be seen. [21]. addition of nm-TiO2 provoked the complexes to degrade. Results and discussion Photoproduction of cobalt-implanted nm-TiO2 The photo reduction of CoIII(N–N)33? complexes has been investigated in water–methanol (or 1.2-diamino propane). In a typical experiment. and structural characteristics of ultrafine crystals of pure nano material powder TiO2 (abbreviated as a). nm-TiO2. However. Solution absorption measurements were made using a Shimadzu Model UV-2450 double beam UV–Vis spectrophotometer. Droplets of aqueous suspensions of the samples were placed on carbon-covered copper 123 Transition Met Chem (2009) 34:915–923 grids for 30 s. since nm-TiO2 illustrates an enhanced photo activity and porous selectivity due to the organized internal structure. 15. Three measurements were recorded for each sample over a sample area of 2 mm. Accln. Scanning electron microscopy and X-ray microanalyses (EDX) of the samples were performed on a Hitachi S3400N. etc. powder (labeled as sample: a).12 nm with standard probe and a variable temperature probe (100–500 K). SEM micrographs of CoIII(tn)33?/nm-TiO2 in water/methanol (90:10) at the initial (at 0 s) and after 120 s irradiation using k = 254 nm show the presence of disordered filaments leading to an almost ‘fluffy’ structure due to cobalt deposition. Complexes were photolysed by irradiation of 254 nm light source using 6 Watt Low Pressure Mercury Vapor Lamp (Germicidal G4T5. such as photoactive layers. significant aggregation of particles is observed. stirred.916 Experimental A series of CoIII(N–N)33?.4-dioxane) binary mixtures: (water:organic co-solvent = 95:5.60 9 10-3 M CoIII(N–N)33? (ionic strength: 0. The cobalt(III) complex is also a good UV light absorber. 85:15. Microscopy was carried out at different primary nominal magnifications in the range of M = 100 K up to 390 K. 3H) Model 3006. Photo irradiation was carried out at definite time intervals. and ultrasonicated. 90:10. magnification: 59 to 300. Pure semiconductor catalyst. and cobalt(II) was generated in either pure water or binary solvent media.3–349. bifunctional membranes sensors. Sigma-Aldrich) and pure crystals of CoIII(N–N)33?.1 M NaNO3) in neat water or water/(methanol or 1. that is. sample c). (Photochemical Reactors Ltd. UK). Therefore. 20]. samples isolated from the photolyte solution before irradiation (at 0 s.0 nm. abbreviated as sample b).4 nm (in water). Light intensities were measured by ferrioxalate actinometry [18] and quantum yield. Prior to analysis. High-resolution transition electron microscopy (HRTEM) scans of the samples were performed on a JEOL 3010 instrument with a UHR polepiece.1 nm and the second one at 466. 70:30). 75:25.88 9 10-3–5. maximum specimen size: 200 mm. Figure 1 exhibits the growth in photo efficiency (%).4-diamino butane) were prepared as in literature [17] and reagents used were generally of AnalaR grade (Sigma-Aldrich) samples. en (1. in which nm-TiO2 was introduced. which was excited with 254 nm light source. In a typical solution. The particle size in sample b is . (sample: c) were subjected to SEM and HRTEM analyses.2-diamino ethane). It was observed that the CoIII(N–N33? complexes are considerably stable in neat water on exposure to light over long periods of time [14. and after definite time of irradiation (at 120 s. This gave a lattice resolution of 0. Tables 1 and 2 illustrate the quantum yield of CoII formation.3 kV to 30 kV. and ultrafine crystals isolated from the photolyte solutions before irradiation at 0 s (labeled as sample: b) and after definite time interval at 120 s. which is altered by the increase in organic co-solvent content. thickness. nm-TiO2 suspension in neat water/binary solvent mixture was prepared by adding definite amounts of nanoparticulates (surface area = 200–220 m2/g.4-dioxane) solutions using nm-TiO2 as photo catalyst. UCo(II). the nano material crystalline powder from the photolyte solution was isolated and characterized. supernatant fluid was blotted off and the grids were left to air dry. Surface survey using SEM and EDX analyses Titanium dioxide semiconductor finds extensive use in a number of applications. was computed by estimating Co(II) by Kitson’s method [19]. Figure 2 shows the SEM images of surface morphology. (N–N)=(NH3)2. For the UV excitation studies. 80 mL cap.9–501. A lower coverage in the sample b and somewhat higher coverage in sample c are visible. which is strongly dependent on the mole fraction of the organic co-solvent present in the mixture. tn (1. voltage 0. in a small Quartz Immersion Well Model 3210. complex concentration was 3. 0109 293 1.5 10.4 13.351 ± 0.3 4.4 16.0 6.6 7.0471 293 8.3 293 15.5 300 12.7 5.3 3.002 0.8 14.7 13.9 15 0.8 293 6. [NaNO3] = 0.7 10.72 12.6 5.2 14.1 5.5 4.382 ± 0.9 1.4-dioxane mixtures (pH = 6.1 8.1602 293 20.2 14.6 1.003 Percentage increase in photoefficiency 5 10 0.8 3.376 ± 0.8 5.60 9 10-3 M.003 0.1 8. in which Ti:Co = 33.4 1.002 0.1 7.1 25 0.0728 300 293 7.4 5.008 300 0.5 293 21.3 13.9 8.361 ± 0.5 1.1 17.336 ± 0.0 20 0.4 3.003 Percentage increase in photoefficiency 5 0.1 6.6 1.1 13.9 4.1 1.1 300 8.4 12.7 8.2 7.001 0.336 ± 0.5 300 5.8 4.4 4.342 ± 0.376 ± 0.6 17.8 5.4 11.88 9 10-3 to 5.361 ± 0.4 9.317 ± 0.342 ± 0.004 0.8 1.82) 1.5 11.2 10.004 0.3 15.9 4.002 0.1 5.291 ± 0.1 2.0229 293 4.1 12.6 6.7 3.351 ± 0.2 4.5 9.0 300 14.9 17.1001 293 18.9 16.6 2.7 1.4 The estimated values of UCo(II) for complexes in neat water and the increase in values in percentage [Co(III) = 3.0229 293 4.002 0. This is very well confirmed by X-ray mapping.1 13.1 300 17.6 10 0.361 ± 0.4 300 14.9 1.1292 0.4-dioxane Temperature (K) % (v/v) x2 0 0 UCo(II) [CoIII(NH3)6]3? [CoIII(en)3]3? [CoIII(pn)3]3? [CoIII(tn)3]3? [CoIII(bn)3]3? 293 0.2 8.2 12.8 300 9.8 15.1 1.19:0.5 10.1 M 5–10 nm but the size becomes 25–60 nm in sample c.7 3.60 9 10-3 M.003 0.6 10.7 5.6 17.008 0.361 ± 0.4 12. Figures 3 and 4 present the EDX profiles and X-ray mapping of the samples.82) Methanol Temperature (K) % (v/v) x2 0 0 UCo(II) [CoIII(NH3)6]3? [CoIII(en)3]3? [CoIII(pn)3]3? [CoIII(tn)3]3? [CoIII(bn)3]3? 293 0.345 ± 0.9 7.007 0. [NaNO3] = 0.0831 The estimated values of UCo(II) for complexes in neat water and the increase in values in percentage [Co(III) = 3.0502 293 9.4 5.0659 30 0. It indicates the implantation and homogeneous distribution of cobalt on the lattice of titania.33:0 (before irradiation) and Ti:Co = 33.3 20 0.9 10.2 300 6.6 9.003 0.Transition Met Chem (2009) 34:915–923 917 Table 1 Photoreduction efficiency of cobalt(III)–alkyl amine complexes in air equilibrated water–methanol mixtures (pH = 6.1 M Table 2 Photoreduction efficiency of cobalt(III)–alkyl amine complexes in air equilibrated water-1.2 7.5 5.4 2.291 ± 0.5 3.7 7.2 300 2.0359 300 293 4.1 11.8 3.003 0.0 4.001 0.345 ± 0.5 18.2 300 10.317 ± 0.382 ± 0.2 9.2 25 30 0.7 6.4 7.88 9 10-3 to 5.8 15 0.7 7.4 7.3 1.3 2.7 0.7 3.008 0.007 0.008 300 0.8 4.1 9.2 13. in which a minimum percent of cobalt on the nm-surface is evident for all other 123 .21 (%) (after irradiation for 120 s).6 15. Therefore. at 120 s) size: 10 lm (inset: 5 lm) in water:methanol = 90:10 123 These reactions are taking place in competition with the undesirable back electron transfer.e-) ? hm ? Co(II) or (ii) charge transfer to metal transition (LMCT) leading to the generation of Co(II). open triangle CoIII(pn)33?. 1.1 0. b nm-TiO2/CoIII(tn)33? (before irradiation. which illustrate segregated but hexagonal patterns of the crystal lattice. 1 Dependence of quantum efficiency (in %) versus mole fraction of organic co-solvent (x2) in water–methanol. 1–3.918 Transition Met Chem (2009) 34:915–923 3þ Quantum Efficiency (%) 20 CoIII ðNNÞ3 3þ þS ! CoII ðNNÞ3 ðSþ Þ ! CoII ðLMCTÞ ð3Þ 16 12 8 4 0 0 0. a pure nmTiO2. The metal centre reduction could be due to (i) CoIII(N–N)33? ? nm-TiO2 (h?. filled square CoIII(bn)33? at 300 K complexes. Surface morphology and cobalt implantation According to HRTEM results. such as the mechanisms of adsorption. e Þ VB þ hm ! e ðCBÞ ð1Þ CoIII ðNNÞ3 3þ þ e ðCBÞ ! CoII ðNNÞ3 2þ ! CoII ð2Þ Fig. at 0 s). however.1 0. The weak fast Fourier transform (FFT) signals of Co for the samples (iii) and (iv) indicate the presence of some Co in the TiO2 matrix in the form of substituted particles. CB) and solvent-influenced LMCT transition of the complex as given in Eqs. 2 SEM images of pure and isolated samples. This suggests the possibility of a small quantity of Co occupying the substitutional sites of Ti of titania leading to solid solution of anatase nm-TiO2.2 x2 Fig. TiO2 ðhþ . 2). We would now like to address the question of photo reduction of CoIII by the nm-TiO2 surface (Eqs. the photo efficiency is gradually enhanced as given in Tables 1 and 2. The lattice fringes due to cobalt insertion are about 5 nm indicating the modified anatase product. the cobalt-implanted nm-TiO2 isolated from the photolyte solutions are mainly nanosized crystallites and contain relatively wide distributions. Figure 5 presents the HRTEM images of the samples a and b for a typical complex. desorption or the specific reactions of surface concentrated species. CoIII(tn)33?.05 0. CoIII(N–N)33? ? hm (LMCT) ? Co(II). Tables 1 and 2 illustrate that the photo efficiency of Co(II) production which is dependent on the organic co-solvent content of the medium. The differences observed in the quantum yields in the presence of nm-TiO2 suspensions of CoIII complexes in binary solvents could also be due to differences in the surface chemistries. size: 10 lm (inset: 5 lm) and (c) nm-TiO2/CoIII(tn)33? (after irradiation. The selected area electron diffraction (SAED) pattern further confirms the formation of cobalt . filled triangle CoIII(en)33?. reduction of cobalt(III) centre of the complex was competitively initiated by both nm-TiO2 (e-. Filled circle CoIII(NH3)63?. open square CoIII(tn)33?. 60 33. Weight % Atom % Formula 39. at 0 s. at 120 s. 123 .00 TiO2 CoO Tuning of photoreduction The photoredox processes of nm-TiO2:CoIII(N–N)33? can be tuned in water–methanol/1. X-ray mapping of (i) Ti and (ii) O (i) (ii) (iii) 5µm Element O Ti Co Total Net Counts 1615 38516 159 insertion on the surface of nm-TiO2 (Co:nm-TiO2).00 66. (after irradiation.33 100.19 0. which also ensures an efficient injection of electrons from the conduction band of titania to the metal centre of the complex ion leading to the formation of Co(II) species.4-dioxane solutions. obtained from the photolyte solution after high dose (at 120 s) of 254 nm light.59 0.94S 59.21 100. (before irradiation. sample c).00 66.95 100. X-ray mapping of (i) Ti and (ii) O (i) (ii) 5µm Element O Ti Total Net Counts 1259 41503 Weight % Atom % Formula 40. 4 EDX spectrum of Co:nm-TiO2 material isolated from the photolyte solution of nm-TiO2/CoIII(tn)33? complex in water:methanol = 90:10. there might not be amorphous products on the surface as the image shows regular lattice spacing.05S 59. 3 EDX spectrum of Co:nm-TiO2 material isolated from the photolyte solution of nm-TiO2/CoIII(tn)33? complex in water:methanol = 90:10.Transition Met Chem (2009) 34:915–923 919 Fig.47 100. sample b). simultaneously. Moreover. The cobalt phase is quite homogeneous with a diameter of about 5 nm with inter-cluster distance generally greater than 5 nm.00 TiO2 Fig.67 33. This suggests two features. the surface structure collapses readily leading to cobalt insertion with some agglomeration of nm-particles from size 5–10 to 25–60 nm. the target molecules [24] are adhered on photo catalyst particle surface. x2 = 0. Moreover. sample b) and b CoII:TiO2 (after irradiation. it is suggested that the density of CoIII(N–N)33? ion at the surface of semiconductor is enhanced by the hydrophobic nature of the CH3OH/C4H8O2 organic co-solvent molecules.4-dioxane. Thus.920 Transition Met Chem (2009) 34:915–923 Fig. addition of methanol (or 1. Evidently. A closer look at high-resolution images shows that the aggregates appear with the same crystallographic orientation. the shape and aggregation of particles might be different in binary solvent mixtures. 5. The condition provides prominent forward ET compared to back ET and the net effect is an enhanced-electron transfer rate. (i) the adsorbed molecules can efficiently reach light-activated sites and (ii) electron transfer is efficient due to mobility of the molecules near the surface at the interface. (ii) agglomeration of particle size. at 0 s. C4H8O2) in the medium increases the photo efficiency of reduction of metal ion of the complex mainly due to MLCT. As shown in Fig. The EDX spot probe analysis shows that Co loading is enhanced in all the samples after definite time (120 s) of irradiation. Therefore. excited nm-TiO2 transfers the 123 .4-dioxane. EDX analysis of cobalt-deposited TiO2 samples as illustrated in Figs. improved surface active sites of TiO2 would increase the mobility of electrons resulting in enhanced photo efficiency [23].4-dioxane controls water content in the pores during the loading of the metal complex due to surface adherence [22]. and (iii) insertion of the photo-generated Co(II) ion substitutionally into the lattice of titanium dioxide retaining the crystalline phase. which results in efficient accumulation of CoIII(N–N)33? near the active sites of nm-particles. simultaneously.4-dioxane) system.0831). d Lattice image taken from CoII:TiO2 away from segregated area (after irradiation) (inset selected area diffraction patterns (SADPs) taken from CoII:TiO2 and FFT for CoII:TiO2 surface modified semiconductor species was generated at the end of high dose of 254 nm irradiation. however.1602/ 1. Introduction of excess concentration of methanol/1. Moreover. the choice of the methanol or 1. 5 High-resolution TEM image of a CoII:TiO2 (before irradiation. which could affect (i) attachment of complex ion and (ii) detachment of the metal centre after reduction (EDX shows a small increase in Co on nm-surface). An interesting observation is the unique behavior of nm-photo catalysts in (i) enhanced activity. On the other hand. aggregates are visible both for TiO2 as well as CoII:nm-TiO2 in dried samples. c Lattice image taken from CoII:TiO2 away from segregated area (before irradiation) (inset selected area diffraction patterns (SADPs) taken from CoII:TiO2 and fast Fourier transform for CoII:TiO2 complex). complex cation-binding ability on nmTiO2 is established as the solvent environment is varied. Photo catalysis of nm-TiO2 in mixed solvents is more efficient. These observations strongly illustrate that adsorption/accumulation is a main factor responsible for the photo activity enhancement. at 120 s. Accordingly. when x2 = 0. sample c). This implies that a favourable interface exists in the electron transfer process in TiO2/CoIII(N–N)33?/water–methanol (1.4-dioxane ensures uniform distribution of the complex ion on the oxide surface and promotes electronic coupling of the donor–acceptor levels. 3 and 4 indicate that enhancement of Co(II) on the surface is more probable in solvent medium with higher organic co-solvent content (methanol. thereby CoIII centers could capture the photo-excited electrons. [26] reported the photo catalytic activity of TiO2 in hydrogen production from methanol/water solution. nm-TiO2 þ hm ! e ðCBÞ ð7Þ e ðCBÞ þ CoIII ðNNÞ3 3þ ðsol:SÞ ! CoII ðNNÞ3 2þ ðsol:SÞ ðmore efficientÞ ð8Þ less effecient Scheme 1 Reduction of target cobalt(III) complex ion as (i) surface adsorbed complex ion (Species A): Co(N–N)33?(sol. nm-TiO2 e- III Co Solution Species. Mechanism of solvent assisted [27] reduction of CoIII(N–N)33? on nm-TiO2 is as presented in the following Eqs. nm-TiO2 ð4Þ II ! Co ðNNÞ3 2þ . photo reaction was carried out in water–metanol/1.)).4dioxane solutions. heterogeneous solvation-induced interfacial electron transfer dynamics can be different between molecular donor and acceptors [28]. Solvent environment could modify the surface-solution species interaction due to hydrophobic/ hydrophilic contributions.e-) + III Co II Co more effecient Solution Species (B) TiO2(h+. ultimately. B Surface Species (A) TiO2(h+. filled circle organic co-solvent molecule) e ðCBÞ þ CoIII ðNNÞ3 3þ ðsol:Þ ! CoII ðNNÞ3 2þ ðsol:Þ ðless efficientÞ ð9Þ That is. species A: CoIII(N–N)33?(sol. it can be concluded that photoinduced reduction takes place (i) at the surface of semiconductor particle and (ii) at the solution phase of the surface. Kusumoto et al. it could be possible to apply some solvent designing for photo catalytic systems to enhance their activity. In this investigation.nm-TiO2 ! CoIII ðNNÞ3 3þ . That is.S) and (ii) solution phase complex ion (Species B): Co(N–N)33?(sol. the electron-hole recombination rate retards the product yield. for instance. and thus electron transfer is controlled by the electronic coupling strength between 123 . nm-TiO2 III 3þ Co ðNNÞ3 . however. nm-TiO2 ! Co ðNNÞ3 2þ þ nm-TiO2 ð6Þ Based on the observations.S) species ions is more in binary solvent mixture containing higher concentration of organic co-solvent than that of solvent mixture containing less or in neat water. efficiency of reduction of CoIII(N–N)33?(sol.S)) and at the solution phase where the complex species accumulation is more (solution phase complex ion. in which the efficiency of the photo catalyst and the medium to pass the photon energy to the reaction system is anticipated to be high. However.) and CoIII(N–N)33?(sol. where accumulation of the species is more predominant. 4–6. Scheme 1 represents the achieving of photoinduced electron transfer at the surface (surface complex ion. A Sensitization by nm-TiO2 Direct band-gap excitation of the semiconductor is achieved at k = 254 nm excitation (band gap & 3. It means the efficiency of electron transport is a function of densities of cationic complex and the influence of solvent [28]. along with the influence of the hydrophobic effect of –CH3 of CH3OH and –C4H8 skeleton of 1.) accumulated near the solution phase of nm-TiO2 surface (open circle water molecule. concerted geometrical and chemical environment of solvent cage of binary mixed solvents.e-) + III Co II Co ð5Þ II 2þ II Co ðNNÞ3 .4-dioxane shows an enhancement in photo efficiency as the organic co-solvent content in the medium increases. hm CoIII ðNNÞ3 3þ . species B: CoIII(N–N)33?(sol. All the Franck–Condon factors of the electron transfer reaction are available in parallel.2 ev) [25].Transition Met Chem (2009) 34:915–923 921 photo electron to surface as well as solution locations. Light absorption by the semiconductor particles leads to the generation of e-(CB). which is efficiently injected to the metal center as given in Eqs. eTiO 2 III Co hν Surface Species. 7–9. Meyer GJ (2005) Inorg Chem 44:6852–6864 4. Tachikawa T. Vidotti M. pp 92–93 30. Geethalakshmi T. The important observations are the unique behavior of nm-photo catalysts in enhanced activity. Diebold U (2001) Appl Phys Lett 79:3467–3469 13. Cinnsealach R. Majima T (2007) J Phys Chem C 111:5259–5275 . Thiele JU. Arico AS. Windisch CF Jr (2002) Thin Solid Films 418:197–210 12. Folks L. This implies that a favorable interface exists in the electron transfer process in TiO2/CoIII(N–N)33?/water– methanol (1. Anbalagan K. Kitson RE (1950) Anal Chem 22:664–667 20. agglomeration of particle size. Felber S. Boschloo G. Hotsenpiller PAM. and HRTEMSAED analyses. The interfacial electron-transfer processes are presumably associated with the spatial heterogeneities of the nanoscale local environments and the inhomogeneous vibronic coupling between the adsorbed molecules and the rough surfaces of the semiconductors [30]. Lydia IS (2008) Spectrochim Acta A 69:964–970 21. Ghosh HN (2001) J Phys Chem B 105:7000–7008 29. facilitated by solvation. Toma HI (2005) New J Chem 29:320–324 7. Fujitsuka M. Marks RF. Fitzmaurice D (1994) J Am Chem Soc 116:2629–2630 5. Lee MS. Marguerettaz X. Kubo W. Farrow RFC. More interestingly. Wada Y. Bolt JD. Kusumoto Y. Ngweniform P. It indicates that Co(II) ion is inserted into the lattice of the nm-particle leading to the formation of CoII:nm-TiO2 with high order of crystallinity. Kottayam. Anbalagan K. records his sincere gratitude to the Department of Science & Technology. Poonkodi SPR (2003) J Phys Chem A 107:1918–1927 15. Conclusion UV irradiation of nm-TiO2/CoIII(N–N)33? complexes in water–methanol/1. Scrosati B. Bchinger C. Principal Investigator. Nazeeruddin MK. Cordoba de Torresi SI. can modify the rate of reduction. Formiger ALB. Zakeeruddin SM. Peter LM. Pondicherry University for providing SEM instrumental facility. Wang CM. Thevuthasan S. Toma SH. Rao SN. Sprague J. O’Neil R. May V. can eliminate most of the undesired slowing down effect. Ahmmad B (2006) J Photochem Photobiol A 184:306–312 27. Droubay T. O’Reaban B. Binding in this way to the surface of TiO2 in a selected binary solvent medium. and insertion of the photo-generated Co(II) ion substitutionally into the lattice of titanium dioxide retaining the crystalline phase. Solvent medium was found to contribute in both the formation of CoII ion and interstitial insertion of cobalt in the lattice of nm-TiO2. which is due to accumulation of CoIII(N– N)33? at the pores due to solvation contributions. Lowekamp JB. 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