Growth of Hydrothermally Derived CdS-Based Nanostructures with Various Crystal Features and Photoactivated Properties

Abstract

CdS crystallites with rod- and flower-like architectures were synthesized using a facile hydrothermal growth method. The hexagonal crystal structure of CdS dominated the growth mechanisms of the rod- and flower-like crystallites under specific growth conditions, as indicated by structural analyses. The flower-like CdS crystallites had a higher crystal defect density and lower optical band gap value compared with the rod-like CdS crystallites. The substantial differences in microstructures and optical properties between the rod- and flower-like CdS crystallites revealed that the flower-like CdS crystallites exhibited superior photoactivity, and this performance could be further enhanced through appropriate thermal annealing in ambient air. A postannealing procedure conducted in ambient air oxidized the surfaces of the flower-like CdS crystallites and formed a CdO phase. The formation of heterointerfaces between the CdS and CdO phases mainly contributed to the improved photoactivity of the synthesized flower-like CdS crystallites.

Photoexcited Properties of Tin Sulfide Nanosheet-Decorated ZnO Nanorod Heterostructures

“…The optical absorption edges of the pure ZnO and ZnO–Sn 2 S 3 rods were evaluated by measuring the diffuse reflectance spectra of the samples and by converting these spectra into absorption coefficient spectra with the Kubelka–Munk function [21, 22]. Figure 4a displays the Kubelka–Munk conversion spectra of the pure ZnO and ZnO–Sn 2 S 3 nanorods.…”

“…A predictable photoexcited charge transfer between ZnO and Sn 2 S 3 can be noted. A previous study demonstrated that efficient spatial charge separation prolongs the lifetime of photoexcited charges in a semiconductor composite system [22]. In that study, a higher-than-usual number of photoexcited electrons near the surfaces of ZnO rods were captured by O 2 molecules to yield superoxide radical anions (O 2 ·− ) and hydrogen peroxide (H 2 O 2 ); subsequently, the reaction of O 2 ·− with H 2 O 2 generated ·OH.…”

“…In that study, a higher-than-usual number of photoexcited electrons near the surfaces of ZnO rods were captured by O 2 molecules to yield superoxide radical anions (O 2 ·− ) and hydrogen peroxide (H 2 O 2 ); subsequently, the reaction of O 2 ·− with H 2 O 2 generated ·OH. Moreover, a higher-than-usual number of photoexcited holes near the shell surfaces of the rod heterostructures oxidized H 2 O molecules to produce hydroxyl radicals (·OH), which were strong oxidizing agents that effectively decomposed MB [22]. The band configuration of the ZnO–Sn 2 S 3 heterostructure reduces the electron–hole recombination probability; this is similar to the ZnO–In 2 S 3 rod heterostructure system, which also exhibits higher photocatalytic properties than those of its ZnO counterpart [30].…”

Surface Morphology-Dependent Functionality of Titanium Dioxide–Nickel Oxide Nanocomposite Semiconductors

“…This can be understood from the possible band alignment between the TiO2 and NiO reported previously [26,27]. The subsequently formed hydroxyl radicals in the solution were strong oxidizing agents that effectively decomposed MB dyes [28,29]. The schematic figure of the photodegradation reaction of TiO2-NiO towards MB solution is illustrated in Figure 6c.…”

Fabrication of Nanosized Island-Like CdO Crystallites-Decorated TiO2 Rod Nanocomposites via a Combinational Methodology and Their Low-Concentration NO2 Gas-Sensing Behavior

“…The bandgap of the CdO film, calculated by extrapolating the linear portion of the curve until it intercepted the horizontal axis (photon energy), was approximately 2.36 eV. Furthermore, the diffuse reflectance spectra of the TiO 2 and TiO 2 –CdO rods were recorded and converted into absorption coefficient spectra by applying the Kubelka–Munk function [ 23 ] ( Figure 4 b). The optical absorbance edge of the TiO 2 rods was located in the UV region at a wavelength of approximately 400 nm.…”