Elsevier

Dyes and Pigments

Volume 109, October 2014, Pages 206-213
Dyes and Pigments

Photophysics and photochemistry of phenosafranine adsorbed on the surface of ZnO loaded nanoporous materials

https://doi.org/10.1016/j.dyepig.2014.05.008Get rights and content

Highlights

  • Photosensitization of phenosafranine adsorbed on ZnO loaded nanoporous materials.

  • Time resolved fluorescence spectroscopy of the dye in solid host materials.

  • No photoinduced charge transfer between phenosafranine to ZnO in solution.

  • Photoinduced electron transfer in solid host confirmed by transient absorption spectroscopy.

Abstract

The photosensitizing properties of phenosafranine adsorbed on surface of the zinc oxide (ZnO) loaded nanoporous materials and colloidal zinc oxides have been investigated by the steady state, time resolved fluorescence and transient absorption spectral studies. The ZnO loaded nanoporous materials were prepared by ion-exchange method and the formation of ZnO nanoparticle inside the host materials were characterized by DRS, ICP-OES, XRD and BET-surface area technique. The steady state absorption and emission 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 injection process. Whereas, singlet state charge injection occur when the dye adsorbed on the surface of ZnO loaded nanoporous materials. The time resolved fluorescence and picoseconds transient absorption studies of phenosafranine adsorbed on ZnO loaded host materials are investigated in detail, which would useful for making ZnO based dye sensitized solar cell.

Introduction

Semiconductor nanoparticles TiO2, ZnO, etc., have been used as electron relay in dye sensitized solar cells (DSSC). Electron mobility on ZnO is much higher than TiO2, while the conduction band edge of both nanoparticles is approximately the same. Therefore, ZnO is a good candidate for electron carrier in dye-sensitized solar cells. However, the conversion efficiencies of solar-to-electrical energy in ZnO based dye sensitized solar cells are hitherto significantly lower than those reported for TiO2. The problems are mainly due to poor chemical stability of ZnO nanoparticle during adsorption of acidic nature of binding group of the dye. Encapsulation of ZnO nanoparticles into nanoporous material will be preventing dissolution of ZnO by the acid binding group as the results enhancement in the energy conversion efficiency.

Most of research on TiO2 deals with photocatalytic activities of TiO2 nanoparticle with nanoporous host materials used as the solid support for the semiconductor [1], [2], [3], [4], [5]. The photosensitization of TiO2 loaded into the nanoporous materials by organic dyes in the excited state are well documented [6], [7], [8], [9], [10]. Recently, ZnO nanoparticle loaded nanoporous materials are of interest in different areas of research in chemistry and physics [11]. Since ZnO clusters are so small and unstable, various materials such as glass, polymers and porous silicate material are used as supports or stabilizers [12], [13], [14], [15], [16]. Nanoporous materials provide well-defined and well-ordered nanopores to confine ZnO clusters. Thus, the size and configuration of ZnO clusters can be modified using different nanoporous host material. On the other hand, ZnO cluster encapsulated in the zeolites shows catalytic activity for some organic reactions. Can Li et al. [11], [17], [18] reported the photoluminance of ZnO nanoparticles encapsulated into host materials such as zeolite-Y and ZSM-5 and their photoluminescence properties in host materials.

To comparison to TiO2, few reports are available on preparation and characterization of ZnO loaded nanoporous materials. Best of our knowledge, no report is available on photosensitization of ZnO encapsulated in nanoporous host materials by organic dyes. In the present work, we have investigated the singlet state charge injection process of phenosafranine adsorbed on colloidal ZnO nanoparticle and embedded into the nanoporous materials by using steady state, time resolved fluorescence and transient absorption spectral studies in nano and picosecond time domain.

The phenazine family of dyes has been studied widely for the conversion of solar energy into the electrical energy because of its strong absorption in the visible region, photochemical stability and excited state redox properties [19], [20], [21], [22]. Phenosafranine (3,7–diamino–5–phenylphenazinium chloride) absorbs strongly in the visible region (500–550 nm) which is belongs to the phenazine family of dyes. Phenosafranine has been extensively studied as a photosensitizer in energy and electron transfer reactions in homogenous and in heterogeneous media [19], [20], [21], [22], [23], [24]. Photophysical and photochemical behaviour of the dye in homogenous solution and in covalently bound in polymer matrix are studied since few decades. These studies are important to understand the nature of the systems for the application in solar energy conversion [25], [26], [27], [28]. The dye has also been used to probe pH induced the dynamics of polymers in aqueous solution. Kamat et al. [29] studied the photochemistry of phenosafranine surface adsorbed on the titanium dioxide and polymer thin film coated titanium dioxide by using diffuse reflectance laser flash photolysis technique [30]. Direct contact between the dye and TiO2 nanoparticles leads to decomposition of the dye molecules. Titanium dioxide semiconductor coated with thin polymer film suppresses the charge injection process and improves the photostability of the dye molecule. Similarly, nanoporous host materials provide the photostability of the dye molecules and also enhance the charge injection process. The photosensitization of titanium dioxide encapsulated within nanoporous host materials by surface adsorbed phenosafranine has been extensively studied [6], [8].

Section snippets

Materials

Phenosafranine (PS+) and nanoporous host materials; zeolite–Y and ZSM–5 were obtained from Aldrich and Sud Chemie India respectively. All other chemicals were purchased from Qualigens and Merck fine chemicals.

Sample preparation

ZnO loaded nanoporous host materials (zeolite-Y and ZSM-5) were prepared by ion exchange method [17]. 1.0 g of host materials was stirred with zinc nitrate solution (50 ml, 1 × 10−3 M) for 24 h. The ion exchange of Na+ by Zn2+ occurred while stirring mixture of zinc nitrate and host

Characterization of ZnO loaded nanoporous materials

The powder X-ray diffraction patterns of nanoporous materials with different ZnO loading are shown in Fig. S1. The X–ray diffraction pattern of MCM–41 shows several peaks between 1.5 and 10° suggests that the presence of well formed hexagonal in the nanoporous material pore arrays. The samples investigated exhibit strong diffraction peaks demonstrating that nanoporous materials, zeolite–Y, ZSM–5 and MCM–41 have crystal structure identical to those reported in the database. The XRD patterns of

Conclusion

Encapsulation of zinc oxide nanoparticles into the nanoporous host materials are prepared by ion exchange method and are characterized by XRD, BET, DRS and ICP-OES techniques. The results clearly showed that ZnO nanoparticles are present inside the nanoporous host materials and surface adsorbed ZnO nanoparticles may be negligible amount. The steady state absorption and emission spectral investigation reveal that the excited state processes of the dye are not much influenced by structural

Acknowledgement

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

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  • Cited by (4)

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    Present address: Department of Chemistry, National University of Singapore, Singapore.

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