lable at ScienceDirect

Dyes and Pigments 109 (2014) 206e213

Contents lists avai

Dyes and Pigments

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

Photophysics and photochemistry of phenosafranine adsorbed on thesurface of ZnO loaded nanoporous materials

Senthil Kumar K a, b, 1, *, Chandramohan S c, Natarajan P a

a National Center for Ultrafast Processes, University of Madras, Chennai, Indiab Department of Chemistry, National University of Singapore, Singaporec Department of Chemistry, Anna University, BIT Campus, Tiruchirappalli, India

a r t i c l e i n f o

Article history:Received 4 February 2014Received in revised form7 May 2014Accepted 9 May 2014Available online 24 May 2014

Keywords:PhenosafranineZnOPhotosensitizationTransient absorptionNanoporous host materialsSinglet state charge injection

* Corresponding author. National Center for UltraMadras, Chennai, India.

E-mail address: senthilchem84@hotmail.com (S.K1 Present address: Department of Chemistry, Nati

Singapore.

http://dx.doi.org/10.1016/j.dyepig.2014.05.0080143-7208/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

The photosensitizing properties of phenosafranine adsorbed on surface of the zinc oxide (ZnO) loadednanoporous materials and colloidal zinc oxides have been investigated by the steady state, time resolvedfluorescence and transient absorption spectral studies. The ZnO loaded nanoporous materials wereprepared by ion-exchange method and the formation of ZnO nanoparticle inside the host materials werecharacterized by DRS, ICP-OES, XRD and BET-surface area technique. The steady state absorption andemission spectra of phenosafranine does not change when addition of ZnO colloids into the dye solution,the results suggested that excited singlet state of the dye does not participate in the charge injectionprocess. Whereas, singlet state charge injection occur when the dye adsorbed on the surface of ZnOloaded nanoporous materials. The time resolved fluorescence and picoseconds transient absorptionstudies of phenosafranine adsorbed on ZnO loaded host materials are investigated in detail, which woulduseful for making ZnO based dye sensitized solar cell.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Semiconductor nanoparticles TiO2, ZnO, etc., have been used aselectron relay in dye sensitized solar cells (DSSC). Electron mobilityon ZnO is much higher than TiO2, while the conduction band edgeof both nanoparticles is approximately the same. Therefore, ZnO is agood candidate for electron carrier in dye-sensitized solar cells.However, the conversion efficiencies of solar-to-electrical energy inZnO based dye sensitized solar cells are hitherto significantly lowerthan those reported for TiO2. The problems are mainly due to poorchemical stability of ZnO nanoparticle during adsorption of acidicnature of binding group of the dye. Encapsulation of ZnO nano-particles into nanoporous material will be preventing dissolution ofZnO by the acid binding group as the results enhancement in theenergy conversion efficiency.

Most of research on TiO2 deals with photocatalytic activities ofTiO2 nanoparticle with nanoporous host materials used as the solidsupport for the semiconductor [1e5]. The photosensitization of

fast Processes, University of

. K).onal University of Singapore,

TiO2 loaded into the nanoporous materials by organic dyes in theexcited state are well documented [6e10]. Recently, ZnO nano-particle loaded nanoporous materials are of interest in differentareas of research in chemistry and physics [11]. Since ZnO clustersare so small and unstable, various materials such as glass, polymersand porous silicate material are used as supports or stabilizers[12e16]. Nanoporous materials provide well-defined and well-ordered nanopores to confine ZnO clusters. Thus, the size andconfiguration of ZnO clusters can be modified using differentnanoporous host material. On the other hand, ZnO cluster encap-sulated in the zeolites shows catalytic activity for some organicreactions. Can Li et al. [11,17,18] reported the photoluminance ofZnO nanoparticles encapsulated into host materials such as zeolite-Y and ZSM-5 and their photoluminescence properties in hostmaterials.

To comparison to TiO2, few reports are available on preparationand characterization of ZnO loaded nanoporous materials. Best ofour knowledge, no report is available on photosensitization of ZnOencapsulated in nanoporous host materials by organic dyes. In thepresent work, we have investigated the singlet state charge injec-tion process of phenosafranine adsorbed on colloidal ZnO nano-particle and embedded into the nanoporous materials by usingsteady state, time resolved fluorescence and transient absorptionspectral studies in nano and picosecond time domain.

S.K. K et al. / Dyes and Pigments 109 (2014) 206e213 207

The phenazine family of dyes has been studied widely for theconversion of solar energy into the electrical energy because of itsstrong absorption in the visible region, photochemical stability andexcited state redox properties [19e22]. Phenosafranine(3,7ediaminoe5ephenylphenazinium chloride) absorbs stronglyin the visible region (500e550 nm) which is belongs to the phen-azine family of dyes. Phenosafranine has been extensively studiedas a photosensitizer in energy and electron transfer reactions inhomogenous and in heterogeneous media [19e24]. Photophysicaland photochemical behaviour of the dye in homogenous solutionand in covalently bound in polymer matrix are studied since fewdecades. These studies are important to understand the nature ofthe systems for the application in solar energy conversion [25e28].The dye has also been used to probe pH induced the dynamics ofpolymers in aqueous solution. Kamat et al. [29] studied thephotochemistry of phenosafranine surface adsorbed on the tita-nium dioxide and polymer thin film coated titanium dioxide byusing diffuse reflectance laser flash photolysis technique [30].Direct contact between the dye and TiO2 nanoparticles leads todecomposition of the dye molecules. Titanium dioxide semi-conductor coated with thin polymer film suppresses the chargeinjection process and improves the photostability of the dyemolecule. Similarly, nanoporous host materials provide the pho-tostability of the dye molecules and also enhance the charge in-jection process. The photosensitization of titanium dioxideencapsulated within nanoporous host materials by surface adsor-bed phenosafranine has been extensively studied [6,8].

2. Experimental section

2.1. Materials

Phenosafranine (PSþ) and nanoporous host materials; zeoliteeYand ZSMe5 were obtained from Aldrich and Sud Chemie Indiarespectively. All other chemicals were purchased from Qualigensand Merck fine chemicals.

2.2. Sample preparation

ZnO loaded nanoporous host materials (zeolite-Y and ZSM-5)were prepared by ion exchange method [17]. 1.0 g of host mate-rials was stirred with zinc nitrate solution (50 ml, 1 � 10�3 M) for24 h. The ion exchange of Naþ by Zn2þ occurred while stirringmixture of zinc nitrate and host material in aqueous solution for24 h. The zinc exchanged host material was washed with excessamount of distilled water. Formation of zinc oxide nanoparticlesinto the nanoporous materials of zeoliteeY and ZSM-5 host wereachieved by heating the sample at 250 �C for 6 h. The loading levelof zinc oxide within the host material was increased by repeatedion exchange procedure followed by heat treatment.

Incorporation of ZnO into the MCMe41 was achieved by sus-pending 1.0 g MCMe41 into 50 ml of 1 � 10�3 M zinc acetate dis-solved inwater solution for 6 h. Similar procedure was followed forthe preparation of increasing loading levels of ZnO into the nano-channels of MCMe41. The prepared ZnO loaded materials werecharacterized by XRD, BET surface area techniques and diffusereflectance spectroscopy. The actual amount of zinc present in thehost materials was determined by ICPeOES method.

The dye adsorbed on ZnO loaded the nanoporous host materialswas prepared by stirring mixture of 50 ml of the dye in aqueoussolution (5 � 10�5 M) and 1.0 g of host materials encapsulated ZnOnanoparticle for 4 h at room temperature. The resulting colouredsolid was filtered and washed with an excess amount of distilledwater. The concentration of the dye in the host material wasmaintained atz5 � 10�5 (mol of dye)/(g of host material). In order

to minimize the error due to weighing, bulk dye solution(1 � 10�3 M in 100 ml) was prepared and required volume of thesolution is used for the loading of the dye in ZSM-5, zeolite-Y andMCM-41. The prepared samples were characterized by XRD.

2.3. Characterization

BET surface measurements for nanoporous host materials;zeoliteeY, ZSMe5 and MCMe41 in presence and absence of ZnOnanoparticles were carried out using volumetric adsorptionequipment (ASAP 2010 micrometric USA) at 77 K. Powder Xeraydiffraction patterns of nanoporous materials and ZnO loadednanoporous materials were recorded using a diffractometer withCuKf radiation (l ¼ 1.5406 Å). The scanning rate was 0.02�/min inall cases.

Transmission electronmicroscopy (TEM)was carried out using aJEOL 3011 300 kV instrument with a UHR pale piece. The samplesprepared by dropping the dispersion of MCMe41 and ZnO loadedMCM-41 in ethanol on a copper grid and dried under ambientconditions.

Zinc as ZnO present in the ZSM-5, zeolite-Y and MCMe41 hostmaterials was determined by ICPeOES method using Perkin ElmerOptima 5300DV. The samples prepared for ICP-OES similar toprocedure reported earlier [7]. Diffuse reflectance spectra wererecorded using Agilant 8453 spectrophotometer equipped withlabsphere RSHeHPe8453 reflectance accessory. The scattered lightreflected by the solid surface corresponds to the intensity reflectedby bare host sample surface minus that absorbed by the chromo-phore. Diffuse reflectance plots matching the optical spectrum intransmission are obtained by subtracting reflectance (R) from barehost material, converting it into a function, F(R) by Kubulka Munkexpression.

Steady state fluorescence spectra of dyes adsorbed onto nano-porous host materials were carried out using Jobin YuonFluromaxe4 spectrophotometer in the front face configuration at45�.

Time resolved fluorescence decay was recorded by time corre-lated single photon counting techniques exciting the sample at430 nm laser. Data analysis was carried out by the software pro-vided by IBH (DAS-6), which is based on deconvolution techniquesusing nonlinear least-squares method and the quality of the fit aredetermined with the value of c2 < 1.2 and weighted residuals.

Picosecond transient absorption experiments were carried outusing Mode-Locked Nd:YAG laser system PY61C-10, (532 nm, 5 mj/pulse, FWHM 35 ps, 10 Hz repetition rate) detailed experimentalprocedure reported earlier [31].

3. Results and discussion

3.1. Characterization of ZnO loaded nanoporous materials

The powder X-ray diffraction patterns of nanoporous materialswith different ZnO loading are shown in Fig. S1. The Xeraydiffraction pattern of MCMe41 shows several peaks between 1.5and 10� suggests that the presence of well formed hexagonal in thenanoporous material pore arrays. The samples investigated exhibitstrong diffraction peaks demonstrating that nanoporous materials,zeoliteeY, ZSMe5 and MCMe41 have crystal structure identical tothose reported in the database. The XRD patterns of the host ma-terials are similar in the presence and absence of zinc oxide showsthat the crystallinity of the host material is unaffected even afterthe incorporation of zinc oxide nanoparticles. The results suggest-ing that the structural damage to the host lattice is insignificantduring the ioneexchange process with the ZnO particles residinginside the nanoporous of the materials. However, the crystallinity

Table 1The adsorption characteristics of nanoporous silicate materials in the presence andabsence of the ZnO nanoparticles.

Sample BET surfacearea (m2/g)

Microporevolume(cm3/g)

ZnO in %(w/w)

ZeoliteeY 845 0.382 0.00ZnOeY (1) 666 0.320 6.46ZnOeY (2) 659 0.317 6.87ZnOeY (3) 654 0.313 7.94ZnOeY (4) 650 0.311 8.30

ZSMe5 453 0.167 0.00ZnOeZSM(1) 358 0.191 0.72ZnOeZSM(2) 327 0.175 0.87ZnOeZSM(3) 374 0.197 5.03

MCMe41 1023 0.69 0.00ZnOeMCM(1) 804 0.52 3.78ZnOeMCM(2) 458 0.403 5.12ZnOeMCM(3) 413 0.394 6.90ZnOeMCM(4) 244 0.392 8.12

(1), (2), (3) … are sample number.

S.K. K et al. / Dyes and Pigments 109 (2014) 206e213208

of the nanoporous materials decreases marginally with increasingZnO loading beyond certain level as reported earlier [17]. Thepercentage of decrease in crystallinity of the host material can becalculated (Table S1) by measuring the intensity of the peak at 2q

Fig. 1. Diffuse reflectance spectra of ZnO nanoparticles in a) ZSMe5 zeolite (i): 0.72%, (ii): 0.(iii): 6.87%, (iv): 7.14% (v): 7.94% and (vi): 8.30% c) MCMe41 (i): 3.78%, (ii): 5.12%, (iii): 6.90

values of 2.6�, 6.19� and 8.03� for MCMe41, zeoliteeY a0nd ZSMe5respectively. ZeoliteeYa maximum of 4% decrease in crystallinity isobserved for the samples containing 8% of zinc oxide loading. A 10%decrease is observed in the case of ZSMe5 with the encapsulationof 0.8% zinc oxide loading in the nanochannels. In ZSM-5 encap-sulated ZnO, where ZnO loading is higher than 5%, the diffractionpattern of ZnO is observed at 2Ɵ ¼ 35�. Such types of diffractionpeak of ZnO particles are not observed in the case of zeoliteeY andMCMe41, even at higher ZnO loading. The absence of the ZnOdiffraction peaks indicates that ZnO has been highly dispersed intothe nanochannel and nanocavities of zeoliteeY and MCMe41.Similar observation was made in the case of ZnO loaded onto thezeoliteeY and ZSMe5 reported earlier [17,32e35].

Adsorption and desorption isotherms of nitrogen on the nano-porous host materials are shown in Figure S2. BET surface area andmicropore volume of nanoporous host materials with differentloading of level ZnO are given in Table 1. A decrease in the BETsurface area from 1023 to 312 cm3/g is observed in ZnO loadedMCM-41 with no considerable change in the XRD pattern indi-cating that ZnO nanoparticles are distributed uniformly within thenanochannels of MCMe41. Similar observation is observed inzeolite-Y and ZSM-5. In the case of ZSMe5, a decrease in the BETsurface area is observed when ZnO loading is up to 5%. When theZnO loading exceeds 5% the BET surface area of ZSMe5 do not

87%, (iii): 0.98%, (iv): 1.15%, (v): 1.32%, and (vi): 5.32% b) zeoliteeY (i): 5.46%, (ii): 6.46%,% and iv: 8.12%.

Fig. 2. (a) Diffuse reflectance absorption and (b) emission spectra of phenosafranine adsorbed on the i) eDeDe silica, ii) -;-;- MCMe41, iii) -✩-✩- ZSMe5 and iv) -⃠-⃠- zeoliteeY.

Table 2Photophysical characteristics of phenosafranine adsorbed on different nanoporoushost materials.

Host materials labs(nm)

lemi

(nm)Stokes shiftDv (cm�1)

t (ns)(% amplitude)

tav(ns)

Psaqa 520 590 2281 0.83 (100%) 0.83Silica 521 574 1772 0.67 (14%) 1.71

1.89 (86%)MCMe41 519 582 2085 0.34 (38%) 1.28

1.86 (62%)ZSMe5 523 577 1789 0.57 (32%) 1.03

1.26 (68%)ZeoliteeY 528 578 1638 0.39 (72%) 0.65

1.34 (28%)

a In aqueous solution.

S.K. K et al. / Dyes and Pigments 109 (2014) 206e213 209

change due to forming macrocrystalline ZnO on ZSMe5 surface.Based on the results of the XRD and BET surface area, we haveconcluded that the 5 weight% loading is critical threshold of ZnOdispersion on ZSMe5.

Transmission electron microscopic (TEM) image of MCMe41 isas displayed in Figure S3. indicates that MCMe41 has orderedmesoporous with uniform pore size while titanium dioxide loadedMCMe41 has less ordered mesoporous channels and also not ableto show zinc oxide within the nanochannels. These results suggestthat TEM image does not provide detailed information about ZnOnanoparticles residing inside the nanochannels.

Diffuse reflectance spectra of zinc oxide loaded nanoporousmaterials are shown in Fig. 1. Absorption band edge of ZnOencapsulated into the nanoporous host materials is blue shifted ascompared to the bulk ZnO powder. The observed decrease in theband edge is due to the size quantization of nanoparticles in theconfined geometries. The absorption band edge of ZnO nano-particles encapsulated into the nanoporous hostmaterials are givenin Table S1. The absorption band edge of the ZnO nanoparticles isblue shifted by 50e100 nm when compared to that of bulk ZnOpowder. The absorbance corresponding to ZnO increases with in-crease in concentration of zinc oxide without significant change inthe absorption band edge, which again indicates that the particlesize of the ZnO does not change at higher loading of zinc oxide inthe hostmaterial. The band edge of zinc oxide is shifted towards redregion of the spectrum above 5% of ZnO loading in ZSMe5. Both ofthe XRD, BET surface area and DRS results indicate that the 5weight% loading is critical threshold of ZnO dispersion on ZSMe5.

3.2. Steady state absorption and emission spectral properties of thedye adsorbed onto the nanoporous host materials

Phenosafranine shows maximum absorbance in the visibleregion at 520 nm in aqueous solution which is not significantlyaffected in different solvents [8]. The diffuse reflectance spectra ofphenosafranine adsorbed onto the nanoporous materials areshown in Fig. 2. The absorption peak maximum of the dye doesnot change significantly while adsorbed onto the nanoporous hostmaterials with different pore size and Si/Al ratio revealing that thedye is not sensitive to the structure and surface polarity of thehost materials. The fluorescence spectra of phenosafranine(Fig. 2(b)) are found to be influenced by the host materials. Thephotophysical properties of phenosafranine adsorbed on the sur-face of nanoporous host materials are given in Table 2. The

fluorescence emission maximum of the dye is blue shifted whenthe dye adsorbed on zeoliteeY, ZSMe5 and silica with respect tothat of the dye in aqueous solution. This observed shift in thefluorescence emission maximum is comparable to that of the dyein methanol:water mixture. Interestingly, the fluorescencemaximum of the dye adsorbed on the external surface of hostmaterials; zeoliteeY, ZSMe5 and silica remain unchanged eventhough surface polarities of the hosts are not the same. Thephotophysical properties of phenosafranine adsorbed onto theporous materials are well documented earlier [6,8,10]. Emissionspectral maximum of phenosafranine encapsulated into MCMe41is comparable to that observed in aqueous solution, which revealsthat the dye is present along with water molecules in the largerpores of MCM-41.

3.3. Photophysics of phenosafranine adsorbed on the surface of ZnOloaded nanoporous host materials

The fluorescence intensity of the dye in aqueous solution doesnot change with increasing concentration of colloidal ZnO nano-particle as shown in Fig. S4. The results suggest that singlet stateof dye do not involved in the charge injection processes in solu-tion. Interesting to note that the dye adsorbed onto the nano-porous materials shows a decrease in the fluorescence intensity(Fig. 3) with increasing various loading level of ZnO suggestingthat the singlet state charge injection occurs from the dye in theexcited singlet state to ZnO nanoparticles present inside the hostmaterials. Whereas, the dye involved in singlet state charge in-jection process with similar particle size of TiO2 nanoparticles

Fig. 3. Diffuse reflectance spectra (a, c and e) and fluorescence emission spectra (b, d and f) of phenosafranine adsorbed onto host material encapsulated with ZnO [(a and b)MCMe41 ((i): 0% ZnO, (ii): 3.78% ZnO, (iii): 5.12% ZnO, (iv): 6.90% ZnO and (v): 8.12% ZnO) (c and d) ZSMe5 ((i): 0% ZnO, (ii): 0.87% ZnO, (iii): 0.98% ZnO, (iv): 1.32% ZnO, and (v):5.03% ZnO); (e and f) zeoliteeY ((i): 0% ZnO, (ii): 5.46% ZnO, (iii): 6.87% ZnO, (iv): 7.14% ZnO and (v): 7.94% ZnO); ] (excitation at 520 nm).

S.K. K et al. / Dyes and Pigments 109 (2014) 206e213210

present in solution. The observed difference in the photophysics ofthe dye in colloidal solution is due to surface nature of semi-conductor nanoparticle in aqueous solution. Once semiconductornanoparticles are encapsulated into the host materials, the dyeshows similar photophysical behaviour even though surface na-ture of semiconductor particle is different. In general the chemicalstability of ZnO is lower than that of TiO2 which was found to beproblematic in the dye adsorption process. Several reports impliesthat dye adsorption is the main problem in ZnO based dye

sensitized solar cell [16e18]. i) Cells with higher dye loading isinefficient, whereas cells with lower dye loading show goodconversion efficiency and also ii) the acidic nature of the dyemolecule that leads to dissociation of ZnO. In this case, the hostmaterials could solve both problems i) it provide large volume ofspace for higher dye loading and ii) provide chemical stability ofZnO nanoparticles. The photosensitization of ZnO nanoparticlesencapsulated into the nanoporous silicate materials may improvethe conversion efficiency of the dye molecules.

S.K. K et al. / Dyes and Pigments 109 (2014) 206e213 211

The fluorescence decay profile observed for phenosafranine inZnO loaded nanoporous host material (Fig. S5) is fitted satisfactorilyto bi-exponential function with c2 < 1.5. In the case of ZnO loadedZSM-5 and zeolite-Y, the observed fluorescence lifetimes of the dyeare not affected notably with an increase in the loading of the ZnOinto the zeolite-Y cavity as indicated in Fig. 4. Recently, Corma andco-workers [36] reported the electron transfer from the excitedstate of Ru(bpy)32þ adsorbed on the external cups of ITQ-2 zeolite tomethyl viologen, MV2þ incorporated in the nanochannels. In thepresence of MV2þ, a considerable decrease in the emission intensity

Fig. 4. Plot of fluorescence lifetime (aec) and relative amplitude (def) of phenosafranine(excitation at 470 nm and emission decay monitored at 490 nm).

of the Ru(bpy)32þ was observed however emission lifetime essen-tially unaltered. The results are interpreted to be due to contactquenching between the excited state of Ru(bpy)32þ and MV2þ inclose proximity. Excited state of Ru(bpy)32þ ion shows normalemission properties when the MV2þis not in the vicinity of thecomplex. It has also been observed that TiO2 encapsulated withMCM-41 and porous silicates also show contact quenching by theexcited states of different dyes [37]. Based on these results it issuggested that the photosensitization of ZnO by surface adsorbedphenosafranine is occurs when the dye and ZnO (ZnO is present

versus ZnO loading; (a and d) zeoliteeY, (b and e) ZSMe5 and (c and f) MCMe41

S.K. K et al. / Dyes and Pigments 109 (2014) 206e213212

closer to the pore opening of host materials) are close proximity inthe host material. If the ZnO are present in interior of the hostmaterials, which are not involved in the quenching processes. In thecase of the dye encapsulated in the nanochannels of MCM-41, adecrease in the fluorescence lifetimewith increase in the loading ofZnO is observed whereas the fluorescence lifetimes are unalteredwhen the dye and titanium dioxide encapsulated into the nano-channels of MCMe41 [37]. The observed difference in the behav-iour of the dye in MCMe41 is due to the nature of thesemiconductor surface and the interaction with the nanoparticles.

3.4. Picosecond transient absorption spectral investigation ofphenosafranine adsorbed on ZnO loaded nanoporous host materials

Picosecond transient absorption spectra of phenosafranineadsorbed onto the external surface of the nanoporous ZSM-5 host,using 532 nm laser pulse, shows broad transient absorption from600 nm to 760 nm (Fig. 5, ZSM-5_Ps). The transients observed aresuggested to be due to the formation of the excited triplet state ofthe dye, trapped electron and oxidized phenosafranine radical[31,22]. In the case of ZnO loaded host materials, transient ab-sorption of phenosafranine dye shows two spectral maximum at~640 nm and 750 nm (Fig. 5, ZSM-5_ZnO_Ps andMCM-41_ZnO_Ps).It is suggested that in the presence of ZnO, the transient absorptionwith maximum at ~700 nm which is due to the trapped electronquenched as the results splitting of two bands observed at 640 nmand 750 nm is suggested to be due to the phenosafranine cationradical and triplet state of the dye. Similar observationwas reported[31] in the case of phenosafranine adsorbed on the Ni(bpy)32þ ionencapsulated in the supercages of the zeolite-Y host, in this casetransient absorption spectra slightly shifted red region due to sur-face nature of host materials are different. Based on the picosecondtransient absorption spectral studies, we conclude that the electrontransfer occurs from the excited state phenosafranine to entrappedZnO nanoparticles in nanoporous host materials. Phenosafranineadsorbed on ZnO loaded zeolite-Y does not observed such type oftransient spectrawhich indicates that electron transfermay be veryfast from the dye to ZnO in zeolite-Y host. The quenching of theexcited state of the dye is unknown to occur by diffusion process insolution. However, in the solid surface, the excited state formedundergo charge transfer processes when the quencher is present inthe vicinity of the excited state or mediated through lattice inpresence of adsorbed water molecules. Investigations reported inthe present systems are important to understand the excited state

Fig. 5. Transient absorption spectra of phenosafraine adsorbed onto the ZSM-5 andZnO loaded ZSM-5, MCM-41. (Excitation at 532 nm probe: white light delay: 133 ps).

processes in nanoporous solids for many applications in devicefabrication, sensors, and in other areas.

4. Conclusion

Encapsulation of zinc oxide nanoparticles into the nanoporoushost materials are prepared by ion exchange method and arecharacterized by XRD, BET, DRS and ICP-OES techniques. The resultsclearly showed that ZnO nanoparticles are present inside thenanoporous host materials and surface adsorbed ZnO nanoparticlesmay be negligible amount. The steady state absorption and emis-sion spectral investigation reveal that the excited state processes ofthe dye are not much influenced by structural variation of hostmaterials. The influence of the host materials on singlet statecharge injection of the dye is demonstrated by steady state fluo-rescence studies. The lifetime of the excited state of the dye in thehost does not change significantly in the presence of ZnO nano-particles indicating that the quenching mechanism is due toarrested movement of the dye and ZnO nanoparticles in host. Thepicoseconds transient absorption spectral studies clearly showsthat charge injection from pheneosafranine upon excitation to ZnOnanoparticle resides in the host materials. The nanoporous solidhost materials provide ultrafast charge separation and also stabilityof ZnO nanoparticles.

Acknowledgement

PN is the recipient of Indian National Science Academy SeniorScientist Fellowship. The authors acknowledge the financial sup-port received from the Department of Science and Technology,Government of India through the Raja Ramanna Fellowship (PN).NCUFP is supported by DST-IHRPA programme.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.dyepig.2014.05.008.

References

[1] O'Regan B, Gr€atzel M. Nature 1991;353:737.[2] Chen X, Mao SS. Chem Rev 2007;107:2891.[3] Panpa W, Sujardworakam P, Jinawath S. Appl Catal B Environ 2008;80:271.[4] Klimenkov M, Nepijko SA, Watz M. J Cryst Growth 2001;231:577.[5] Joswig JO, Roy S, Sarkar P, Springborg M. Chem Phys Lett 2002;365:75.[6] Easwaramoorthi S, Natarajan P. Micro Meso Mater 2005;86:185.[7] Senthilkumar K, Paul P, Selvaraju C, Natarajan P. J Phys Chem 2010;114:7085.[8] Easwaramoorthi S, Natarajan P. Micro Meso Mater 2009;117:541.[9] Senthil kumar K, Natarajan P. Mater Chem Phys 2009;117:365.

[10] Natarajan P, Duraimurugan K, Senthil kumar K. J Chem Sci 2011;123:531.[11] Chen J, Feng Z, Ying P, Li Can. J Phys Chem B 2004;108:12669.[12] Khouchaf L, Tuilier MH, Wark M, Soulard M, Kessler H. Micro Meso Mater

1998;20:27.[13] Readman JE, Gameson I, Hriljac JA, Edwards PP, Anderson PA. Chem Commun

2000;595.[14] Xia H, Tang F. J Phys Chem B 2003;107:9175.[15] Zhao X, Lu G, Millar GJ. J Porous Mater 1996;3:61.[16] Türk T, Sabin F, Vogler A. Mater Res Bull 1992;27:1003.[17] Shi J, Chen J, Feng Z, Wang X, Ying, Li Can. J Phys Chem B 2006;110:25612.[18] Fan F, Feng Z, Li Can. Acc Chem Res 2010;43:378.[19] Jockusch S, Timpe HJ, Schnabel W, Turro NJ. J Phys Chem A 1997;101:440.[20] John SA, Ramaraj R. J Electroanal Chem 1997;424:49.[21] Ziolkowski KRL, Vinodgopal K, Kamat PV. Langmuir 1997;13:3124.[22] Gopidas KR, Kamat PV. J Phys Chem 1990;94:4723.[23] Chaudhui R, Sengupta PK, Rohatgi mukhergee KK. J Photochem Photobio A

Chem 1997;108:261.[24] Rohatjee-Mukherjee KK, Bagchi M, Bhowmick BB. Electrochim Acta 1983;28:

293.[25] Ramaraj R, Natarajan P. J Chem Soc Faraday Trans 1989;85:813.[26] Natarajan P. J Macromol Sci Chem 1988;81:1285.[27] Viswananthan K, Natarajan P. Proc Indian Nat Sci Acad 1997;63:129.[28] Calzaferri G. Micro Meso Mater 2003;72:1.

S.K. K et al. / Dyes and Pigments 109 (2014) 206e213 213

[29] Sarkar N, Das K, Nath DN, Bhattacharyya K. Langmuir 1994;10:326.[30] Gopidas KR, Kamat PV. J Photochem Photobio A Chem 1989;48:291.[31] Kumar KS, Sudha T, Natarajan P. J Chem Sci; 2014. http://dx.doi.org/10.1007/

s12039-014-0643-7.[32] Zhang WH, Shi JL, Wang LZ, Yan DS. Chem Mater 2000;12:1408.[33] Hur SG, Kim TW, Hwang SJ, Hwang SH, Yang JH, Choy JH. J Phys Chem B

2006;110:1599.

[34] Wang F, Song H, Pan G, Fan L, Dai Q, Dong B, et al. Mater Res Built 2009;44:600.

[35] Cheng WX, Meng YQ, Chen YJ, Long YC. Micro Meso Mater 2012;153:198.[36] Corma A, Fornes V, Galletero MS, Garcia H, Scaiano JC. Chem Commun

2002;334.[37] Ananthanarayanan K, Natarajan P. Micro Meso Mater 2009;124:179.