Facile synthesis of cadmium sulfide and the effect of thermal annealing in N2-rich atmosphere on its structural, morphological, chemical, and optical properties

Abstract

This works aims to evaluate the effect of the annealing process under a nitrogen-rich atmosphere on the properties of cadmium sulfide (CdS). The CdS studied in this work was produced by a simple one-pot reaction between cadmium chloride and sodium sulfide in an aqueous solution. After the synthesis pathway, the powdered material was annealed in a furnace at different temperatures under an N2-rich atmosphere and the resulting samples were characterized to evaluate the transformations obtained. The X-ray diffraction results show that the annealing temperature has a major impact on the structural composition of the CdS, as new phases (CdO and CdSO4) are obtained at higher temperatures due to the oxidation of the samples. The scanning electron micrographs show that a higher annealing temperature leads to the coalescence of the CdS particles, as the spherical particles obtained without thermal treatment are transformed into a smooth surface at temperatures higher than 600 °C. The optical properties of the composite, such as bandgap energy and visible light absorption, can be modified using different annealing temperatures. The differential scanning calorimetry and thermogravimetry confirm the phase transformations observed, showing that the CdS is oxidized to CdO at temperatures above 700 °C.