Introduction

Cadmium sulfide (CdS) is a yellow or orange mineral that rarely exists. It was first prepared by Gay-Lussac in 1818 and used as a golden yellow pigment in the mid-18th century. Later on, the photocatalytic property of CdS was discovered. The first case of CdS used as a photocatalyst was reported by Frank et al. in 1977. In this work, CdS was applied for photocatalytic oxidations of cyanide and sulfite, and high photoactivity was obtained[1].

Uses

CdS, as an II-VI semiconductor with a direct bandgap of 2.4 eV, has received significant attention for various applications, such as nonlinear optical devices, flat-panel displays, light-emitting diodes, lasers, logic gates, transistors, photoresistors, solar cells, infrared waveguides, and splitters. It also shows versatility in nanostructures because of its relatively low work function, high refractive index, excellent transport properties, good chemical capability, thermal stability, high electronic mobility, and piezoelectric properties.

Structure

CdS has two types of crystal structures, as shown above: (a) cubic zinc blende and (b) hexagonal wurtzite structures[2]. The stacking sequence of zinc blende's close-packed (111) planes follows an ABCABCABC repeating pattern, whereas that of wurtzite follows an ABABAB pattern. Wurtzite CdS can be described as several alternating planes composed of tetrahedrally coordinated S2? and Cd2+ ions stacked along the c-axis. The oppositely charged ions produce positively charged Cd-(0001) and S-(0001) basal plane polar surfaces, inducing a normal dipole moment, spontaneous polarization along the c-axis, and divergence in the surface energy.

References

[1] Chang Cheng, Linxi Wang, Jiaguo Yu. “Chapter 5 - CdS-based S-scheme photocatalyst.”Interface Science and Technology 35 (2023): 175-199.

[2] Byung-Gi An. “Photosensors-based on cadmium sulfide (CdS) nanostructures: a review.” Journal of The Korean Ceramic Society 81 1 (2021): 631–644.