Mineralizer-Assisted Shape-Controlled Synthesis, Characterization, and Photocatalytic Evaluation of CdS Microcrystals

Abstract

High-quality, well-crystallized, single-crystal, wurtzite CdS hexagonal microtowers (with and without tubular structure) and CdS with octahedral geometry were successfully synthesized by tuning the solvent ratio of water and ethanol for the first time on a large scale without using any catalysts or templates. The products were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry, transmission electron microscopy, and field emission scanning electron microscopy. CdS with microtowers, octahedral geometry, and hexagonal plates was formed by thermal decomposition of cadmium thiocyanate at 400 °C under open atmospheric conditions. The influence of solvent, initial precursor concentration, decomposition temperature, and time on the morphology of CdS was investigated, and the results were discussed. The XRD results showed that the cadmium thiocyanate complex is completely decomposed into CdS at 300 °C for 2 h and the wurtzite phase was formed under all experimental conditions, which opens a door for well-crystallized, single-phase CdS synthesis on a large scale. The diffuse reflectance spectra showed that CdS microtowers have strong visible light absorption compared with the octahedral geometry, revealing the existence of a profound shape−property relationship of CdS. The CdS microtowers with a Pt cocatalyst showed a high rate of photocatalytic hydrogen production from water containing 0.1 M Na2S and 0.1 M Na2SO3 as sacrificial reagents under visible light irradiation (λ ≥400 nm). The possible growing mechanism of various types of the CdS morphology was also discussed.