Synthesis and crystal structure of bis(thiomorpholinyldithiocarbamato) Zn(II): structural, optical, and photocatalytic studies of ZnS nanoparticles from the complex

Bis(thiomorpholinyldithiocarbamato) Zn(II) complex was synthesized and characterized by single crystal X-ray crystallography and spectroscopic techniques. The molecular structure of the compound revealed a dimeric Zn(II) complex in which each Zn(II) ion is bound to one chelating and two bridging thiomorpholine ligands. The compound was thermolyzed at 130 degrees C in octadecylamine (ODA), hexadecylamine (HDA), and oleylamine (OLA) to prepare ZnS nanoparticles. Powder X-ray diffraction (PXRD) of the ZnS nanoparticles indicates mixtures of hexagonal and cubic crystalline phases depending on thermolysis temperature. HRTEM micrographs showed well-defined nanoparticles with particle size of 3.3-4.8 nm for ODA-ZnS, 2.5-4.2 nm for OLA-ZnS, while HDA-ZnS shows slightly bigger nanoparticles with particle size of 3.3-5.4 nm. Estimated optical band gaps are 3.58 eV for ODA-ZnS, 3.69 eV for HDA-ZnS and 3.72 eV for OLA-ZnS which indicate blue shift of the absorption band edges with respect to bulk ZnS (3.56 eV). The as-prepared ZnS nanoparticles were used as photocatalysts for the degradation of methylene blue dye. The degradation efficiency of the as-prepared ZnS nanoparticles are 58% for ODA-ZnS, 53% for OLA-ZnS, and 43% for HDA-ZnS. ODA-ZnS nanoparticles were used for the recycling test and showed good photostability and recyclability with 57% recovery percentage.