Synthèse et Caractérisation des Nanoparticules de Métaux Sulfures MS (M= Cu(II), Pb(II), Cd(II), Zn(II) et des Nanocomposites à base de CuxSy : Applications Photocatalytiques pour la dégradation du bleu de méthylène

Abstract

In this study, complexes of [Cu(L H) ]Cl , [Cu(L H) ]Cl .H O, [Cu(L H)Cl ], [Pb(L H) ]Cl , 122 2222 3 2 122 [Pb(L H) ]Cl .H O, [Zn(L H)Cl ] and [Cd(L H) Cl ] were synthesised from the ligands : 2- 2222 32 322 (thiophen-2-ylmethylene)hydrazine-1-carbothioamide (L1H), 2-(1-(thiophen-2- yl)ethylidene)hydrazine-1-carbothioamide (L2H) and 2-(4- dimethylamino)benzylidene)hydrazine-1-carbothioamide (L3H) and characterised using a variety of spectroscopic and elemental analysis techniques. The crystal structure of the [Cd(L3H) Cl ] complex was also elucidated by single-crystal X-ray diffraction. The Cd(II) 22 complex crystallises in a monoclinic crystal system with the space group P21/c. The as-prepared complexes were used as single-source precursors for the preparation of copper sulphide (Cu9S5) nanoparticles (NPs), lead sulphide (PbS) and CuS-CdS and CuS-ZnS nanocomposites by thermolysis at 190°C, 230°C, 250°C and 270°C using oleylamine (OLA), hexadecylamine (HDA), dodecylamine (DDA) and olive oil as capping agent. The structural, morphological and optical properties of the nanomaterials were studied using X-ray powder diffraction (p-XRD), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV-Visible spectroscopy. P- XRD revealed the Cu9S5 rhombohedral crystalline digenite phase with the R-3m space group for the Cu9S5 NPs and face-centred cubic for the PbS NPs. In contrast, XRD of the CuS-CdS and CuS-ZnS nanocomposites revealed a mixture of hexagonal CuS and CdS phases in the CuS-CdS nanocomposites and a mixture of hexagonal CuS and cubic ZnS phases in the CuS- ZnS nanocomposites. EDX analysis confirmed the presence of sulphur and metals in the nanomaterials obtained. The morphology and size of Cu9S5 and PbS nanoparticles determined using TEM showed nanoparticles with variable shapes ranging from cubic, rod-shaped or almost spherical for PbS nanoparticles and cubic, rectangular, semi-spherical and truncated for Cu9S5 nanoparticles. The TEM and SEM images of the CuS-CdS and CuS-ZnS nanocomposites revealed agglomerated flower-shaped particles with open porosities. Optical studies showed a general blue shift of the absorption band edge with energy band gaps ranging from 2.52 to 3.00 eV for Cu S NPs and 2.15 to 3.11 eV for PbS NPs. Whereas, xy bandgap energies of 2.84 eV and 3.12 eV for CuS-CdS and CuS-ZnS were obtained respectively, showing that the combination of CuS with CdS and ZnS has an effect on their optical properties, which probably explains the improved photocatalytic responses. The photocatalytic performance of the as-prepared materials was evaluated using the photodegradation of methylene blue (MB) dye under UV light irradiation. Best degradation Page xvi rates of around 54 %, 68 %, 65 % and 80 % were obtained with the CuS-CdS, PbS, CuS-ZnS and Cu9S5 nanomaterials respectively. The variation of the reaction temperature, the length of the carbon chain of the stabilising agent and the type of precursor showed an effect on the photocatalytic properties of the nanoparticles obtained. The photocatalytic performance of the nanocomposites observed could be attributed to the effect of CuS coupling on CdS and ZnS nanoparticles. CuxS-ZnO thin films were also deposited on the glass substrate at 300°C using the SPD method and then annealed at 400°C. p-XRD data of the Cu S-ZnO thin films deposited at x 300°C and after annealing at 400°C confirmed the formation of the CuxS-ZnO thin films. The EDX results showed that the surface of the thin films mainly contains the elements Cu, S, Zn and O, thus confirming the formation of Cu S-ZnO thin films. SEM analysis showed that after x x deposition of ZnO on glass/Cu S, the Cu S-ZnO composites have a granular surface with x surface cracks, whereas after annealing at 400°C, the thin films have a less compact appearance with fewer surface cracks. Atomic force microscopy (AFM) results showed that the average roughness increased with annealing, as did the degree of crystallinity. The study of the optical properties revealed that the bandgap energy (Eg) of the bare ZnO thin films decreased from 3.15 eV to 2.80 eV after the deposition of the ZnO thin film on the CuxS layer at 300°C and then from 2.8 to 2.08 eV after annealing at 400°C. The photocatalytic properties of the CuxS-ZnO thin films were evaluated under UV-Visible irradiation using a 10 ppm methylene blue solution. The CuxS-ZnO thin films annealed at 400°C showed improved photocatalytic properties compared with the CuxS-ZnO thin films deposited at 300°C, which could be due to the increased crystallinity that prevented electron-hole recombination. The photocatalytic activity of nanomaterials has potential for wastewater treatment.