Langmuir 1994,lO, 4446-4450
4446
Oil in Water Micellar Solution Used To Synthesize CdS Particles: Structural Study and Photoelectron Transfer Reaction C. Petit,?,$T. K. Jain,? F. Billoudet,?and M. P. Pileni*Vt?$ Laboratoire SRSI, URA CNRS 1662, Universite P et M Curie (Paris VI), B.P. 52, 4 Place Jussieu, 75231 Paris Cedex 05,France, and C.E.A.X.E. Saclay, DRECAM.-S.C.M, 91191 Gif sur Yvette Cedex, France Received April 20, 1994. In Final Form: September 7,1994@ Functionalized micelles have been used to make large nanosize particles (10 nm diameter). The micellar structure has been investigated by small angle X-ray scattering and quasi-elasticlight scattering. Cadmium sulfite particles have been characterized by transmission electron microscopy. The study of photoelectron transfer reaction from CdS to methylviologen shows that the back electron transfer reaction can be totally prevented by using a methylviologen dodecyl sulfate as an electron acceptor.
Introduction In the last few years, several groups made nanosize particles using organized assemblies.' In making chemical energy conversion and storage, several investigations of photoelectron transfer have been studied.2 Usually most of the particle sizes obtained with CdS as a semiconductor are on the order to 1 to 5 nm diameter; however the concentration of particles is very In the present paper, a functionalized surfactant is used to make 10-nm CdS particles. Cadmium and methylviologen dodecyl sulfate have been synthesized and t h e critical micellar concentrations of these surfactants have been determined. By small angle X-ray scattering(SAXS1 and quasi-elastic light scattering (QELS) the average size and shape of micelle has been deduced. Photoelectron transfer from CdS to methylviologen has been studied in micellar solution and the back electron transfer reaction has been totally prevented.
Experimental Section Sodium lauryl sulfate (SDS) was bought from BDH while were procured sodium sulfide (Na2S)and methylviologen (W+) from Janssen. The absorption spectra were obtained on a Hewlett-Packard HP8452A spectrophotometer.
* All correspondence to this author.
t Laboratoire SRSI.
C.E.A.-C.E.Saclay. Abstract published in Advance ACS Abstracts, November 1, 1994. (1)Photoinduced electron transfer; Chanon, M., Fox, M. A., Eds.; Elsevier Science Publishers: Amsterdam, 1988. (2)Kamat, P. V.; Dimitrijevic, N. M. Solar Energy 1990,44, 83. Kamat, P. V. In Kinetics and Catalysis in Microheterogeneous Systems: Gratzel, M., Kalyanasundaram, R,Eds.; Marcel Dekker: New York, 1991; pp 375-436. Henglein, A. Top. Curr. Chem. 1988,143, 113. Henglein,A. Chem.Reu. 1989,89,1861. Fox, M. A. Res. Chem.2ntermed. 1991, 15, 153. Gratzel, M. Heterogeneous Photochemical Electron Transfer; CRC Press: Boca Raton, FL, 1989;Vol. 89,p 1861. Fendler, J. H. Chem. Rev. 1987,87,877. (3)Mann, S.;Hannington, S.P.;Williams, R. J. P. Nature 1986,324, 565. Petit, C.; Pileni, M. P. J . Phys. Chem. 1988,92,2282. Zhao, X. K.;Baral, S.; Rolandi, R.; Fendler, J. H. J.Am. Chem. SOC.1988,110, 1012. Krishnan, M.; White, J. R.; Fox, M. A.; Bard,A. J. J . A m . Chem. SOC.1983,105,7002. Hilinski, E. F.;Lucas, P. A.; Wang, Y. J . Chem. Phys. 1988,89,3435. Liu, X.;Thomas, J. K Langmuir 1989,5 , 58. Herron, N.;Wang, Z.; Eddy, M. M.; Stuky,G . D.; Cox, D. E.; Moller, K.; Blin, T. J . Am. Chem. SOC.1989,111,530. Atkinson, P. J.; Grimson, M. J.; Heenan, R. K.; Howe, A. M.; Robinson, B. H.; J . Chem. SOC., Chem. Commun. 1989,1807.Petit, C.; Lixon, P.; Pileni, M. P. J . Phys. Chem. 1990,94,1598. Towey, T.H.; Khan-Lodl, A.; Robinson, B. H. J . Chem. Soc., Faraday Trans. 1990,86,3757. Motte, L.; Petit, C.; Lixon, P.; Pileni, M. P. Langmuir 1992,8,1049.
A Philips electron microscope (Model CM 20, 200 kV) was used to obtain electron micrographs of CdS particles. Flash photolysis experiments were carried out on an Applied Phytophysics apparatus. Yield of reduction was measured as reported by Bensasson et al., with triplet-triplet absorption of anthracene in cyclohexane solution by adopting 6 = 64 700 M-' cm-I at 422.5 nm with h = 0.71.4 Hydrodynamic radius of the entities was determined by quasielastic light scattering using a Brookhaven BI 2030 AT correlator. The surface tension measurements of cadmium lauryl sulfate (Cd(DS)Z) and methylviologen lauryl sulfate (MV(DS)z) were performed on a Kruss equipment. SAXS experiments were carried out with an equipment built in SCM-CEA, F r a n ~ e .The ~ X-ray source produces monochromatic Cu Ka X-rays beam at 1.54 A. The sample-to-detector distance is 210 cm. The experimental patterns are monitored by using a two-dimensional gas detector. Regrouping the isotropic signals allows reaching a high signal to noise ratio. Normalization at the absolute scale (cm-l) is obtained by procedure described in reference with a polymer standard.s Treatmentof the SAXSExperiments. The scattered X-ray intensity, Z(q),depends of the internal structure and the structural arrangement of the reverse micelles. The intensity is expressed as
where P(q) and S(q) are the form and structure factor, respectively. I ( q ) is measured as a function of the scattering wave vector, q , defined by
4~r
e
1
2
q = - sin -
@
(2)
where 0 and iare the scattering angle and the wavelength of the X-ray beam. The wave vector range under the present investigation is
3x
A-l
