الفهرس 
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Abstract
a facile and versatile solution-based approach was developed to prepare cadmium sulfide (cds)/polyaniline (pani) core/shell nanocomposites. well-defined cds nanoparticles with different particle sizes were prepared using chemical precipitation method. the cd:s molar ratio is considered as a determining factor in controlling the particle size in such a way that as the cd:s molar ratio increases the particle size decreases. the cds nanoparticles of different sizes were combined with pani via in situ polymerization in aqueous solution to obtain a new type of inorganic–organic nanocomposite. samples were characterized by using transmission electron microscope (tem), x-ray diffraction (xrd), fourier transform infrared (ftir), ultraviolet– visible spectrophotometer, fluorescence spectrofluorometer and electrical conductivity. the tem images show that the cds samples with cd:s molar ratio of 16:1, 8:1, 4:1 and 1:1 have a novel core/shell structure after reaction with aniline while those with cd:s molar ratio of 1:4, 1:8 and 1:16 do not show such a structure. the powder x-ray diffraction (xrd) patterns of the different cds nanoparticles indicate that the precipitated cds have the cubic crystal structure. the x-ray diffraction patterns of the cds/pani core/shell show that all the diffraction peaks from the nanocomposite samples can be attributed to the cubic phase of cds. no remarkable changes were noticed in the values of 2θ or the corresponding intensities due to the interaction between cds and aniline monomer. for samples of cd:s molar ratios of 16:1, 8:1, 4:1 and 1:1 the mid ftir absorption spectra of different cds/pani core/shell nanocomposites confirm the polymerization of aniline monomer at the surface of cds nanoparticles. the mid ftir absorption spectra show that no remarkable change in the vibrational spectra due to the interaction between aniline and cds nanoparticles with cd:s molar ratio of 1:4, 1:8 and 1:16 which strongly supports the tem results. the calculated bandgaps are higher than that of bulk value of cds indicating the strong quantum confinement. the bandgap energies gradually increases from 2.51 ev (cd:s 1:16) to 2.9 ev (cd:s 16:1). these changes have been attributed to the crystallite size-dependent properties of the energy band gap. the green emission of the prepared samples has been attributed to direct electron-hole recombination and sulfur vacancies, (vs 2+). the operation of vs as a fluorescence centre is explained on the basis of the lambe-klick mechanism. the steady state conduction of cds nanoparticles and cds/pani core/shell nanocomposites has been studied in order to throw some light on the nature of the conduction mechanisms operating in the used materials. it is found that the prepared samples exhibited space charge limited conduction. the dc conductivity has been measured in the temperature range from 25-300oc. it was found that the dc conductivity was increased as the particle sizes decreased. in addition, the dc conductivity of cds/pani core/shell nanostructure is higher than that of the corresponding naked cds nanoparticle. the observed dc conductivity data have been analyzed in the light of existing theoretical models.