Synthèse et caractérisation des nanoparticules de zinc sulfure dopées au cobalt et au nickel : application photo

Abstract

Zn (II), Co (II) and Ni (II) complexes were synthesized using aniline dithiocarbamate (sodium phenylcarbomodithioate) as ligand. Co (II) and Ni (II) complexes were synthesized in methanol while the Zn (II) complex was synthesized in methanol/water mixture in a ratio 1 :2 (M-L), with yields ranging from 25.4-74.0. These complexes were characterized by known physicochemical and spectroscopic methods. Melting point measurements showed that the ligand melted at a temperature of 181°C different from those of the synthesized complexes (Zn (II) (160ºC), Co (II) (220ºC) and Ni (II) (>300ºC (temperature limit of apparatus)), indicating that new compounds have been formed. The results of the solubility test showed that the Co (II) complex was soluble in acetone, THF and methanol, while the Zn (II) and Ni (II) complexes were sparingly soluble in these solvents. IR analysis confirmed the formation of aniline dithiocarbamate and the existence of coordination bond between the central metal and the donor S atoms of the ligand. Molar conductance measurements indicate that the complexes synthesized are all molecular in nature. On the basis of these analyses, combined with UV-Visible spectroscopy and the literature, tetrahedral structures were proposed.These different complexes were used as precursors for the preparation of undoped and thermolysed-doped ZnS NPs by varying reaction parameters such as : the nature of the stabilizing agent (olive oil and castor oil), the type of dopant (Co (II), Ni (II)) and the percentage of doping (5%, 10% and 20%). UV-Visible analysis of undoped and doped ZnS NPs showed a red-shift in their absorption bands. Powder XRD analysis revealed a cubic phase for undoped and doped ZnS NPs prepared in olive oil or castor oil. NP size calculated from the Debye Scherrer equation gave values between 12.00-56.60 nm for undoped and Co (II) or Ni (II)-doped ZnS NPs. Photoluminescence analysis revealed the presence of defects and recombination phenomena within the NPs. Varying reaction parameters affected the energy bandgap, crystallinity and size of doped and undoped NPs.The photocatalytic properties of undoped and dope ZnS NPs were evaluated by the degradation of a synthetic effluent of methylene blue. The results obtained showed that, all undoped and doped ZnS NPs synthesized with the different capping agents are photocatalytic active with degradation percentages ranging from 22.22% - 78.33% after 90 min of UV irradiation. The variation in the reaction parameters of synthesis of the doped and undoped ZnS NPs had an influence on the photocatalytic properties of the nanoparticles.