A new pyrazolyl dithioate function in the precursor for the shape controlled growth of CdS nanocrystals: optical and photocatalytic activities

Abstract

The dithiocarbazate functionalized 3,5-dimethyl pyrazole ligands and their cadmium(II) complexes e.g., [Cd(mdpa)₂Cl₂] (where mdpa is the methyl ester of 3,5-dimethyl pyrazole-1-dithioic acid) and [Cd(bdpa)₂Cl₂] (where bdpa is the benzyl ester of 3,5-dimethyl pyrazole-1-dithioic acid) have been synthesized. The complexes are used as single-source precursors (SPs) for the synthesis of spherical and rod-like CdS nanocrystals in a solvothermal process without using any external surfactants. In situ generated thiols (CH₃SH in the case of the mdpa complex and PhCH₂SH in the case of the bdpa complex) in thermolysis of the SP govern the growth of nanocrystals. The spherical and rod shaped CdS nanocrystals are produced in the presence of CH₃SH and PhCH₂SH, respectively. A possible growth mechanism of nanocrystals based on the preferential thiol bonding to the nucleus is discussed. The nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The UV-Vis spectroscopic studies of CdS nanocrystals show the quantum confinement effect with a band gap of 2.2 eV to 2.6 eV, and the narrow intense PL emissions of the samples are red-shifted (λ_max = 570 nm) due to trap-related electron–hole recombination. The CdS nanocrystals are successfully applied in the photodegradation of rose bengal (RB) and methylene blue (MB) dyes under visible light.