Engineering of Solar Energy Harvesting Tb³⁺-Ion-Doped CdS Quantum Dot Glasses for Photodissociation of Hydrogen Sulfide

Abstract

The photocatalytic properties of CdS quantum dots (Q-dots) and Tb 3+ -doped CdS Q-dots dispersed in a borosilicate glass matrix were investigated for the photodissociation of hydrogen sulfide (H 2 S) into hydrogen (H 2 ) gas and elemental sulfur (S). The Q-dot-containing glass samples were fabricated using the conventional melt-quench method and isothermal annealing between 550 and 600 °C for 6 h for controlling the growth of CdS and Tb 3+ -ion-doped CdS Q-dots. The structure, electronic band gap, and spectroscopic properties of the Q-dots formed in the glass matrix after annealing were analyzed using Raman and UV–visible spectroscopies, X-ray powder diffraction, and transmission electron microscopy. With increasing annealing temperature, the average size range of the Q-dots increased, corresponding to the decrease of electronic band gap from 3.32 to 2.24 eV. For developing the model for photocatalytic energy exchange, the excited state lifetime and photoluminescence emission were investigated by exciting the CdS and Tb 3+ -doped CdS quantum states with a 450 nm source. The results from the photoluminescence and lifetime demonstrated that the Tb 3+ -CdS photodissociation energy exchange is more efficient from the excited Q-dot states compared to the CdS Q-dot glasses. Under natural sunlight, the hydrogen production experiment was conducted, and an increase of 26.2% in hydrogen evolution rate was observed from 0.02 wt % Tb 3+ -doped CdS (3867 μmol/h/0.5 g) heat-treated at 550 °C when compared to CdS Q-dot glass with a similar heat treatment temperature (3064 μmol/h/0.5 g). Furthermore, the photodegradation stability of 0.02 wt % Tb 3+ -CdS was analyzed by reusing the catalyst glass powders four times with little evidence of degradation.

A cubic Sm@CdS Q-dot glass as a photocatalyst for solar H2 generation

“…Initially, smaller quantum dots (1–2 nm) are formed, which further grow with temperature and form bigger quantum dots (up to 5 nm) as per the Ostwald ripening phenomenon. 26–28 Hence, it can be clearly seen that the average quantum dot size is 4–5 nm. The upper inset of Fig.…”

“…This result gives evidence that Sm 3+ ions occupy the lattice sites. 26,28 The SAED pattern of these nano crystallites in the glass matrix is shown in the lower inset of Fig. SI-II (ESI†).…”

“…30,31 The Raman spectra of bulk Sm-doped CdS QDs show a shift in the 1LO peak position of CdS nanoparticles towards the lower wavelength side. 28 It has been reported that phonon confinement, strain, defects, and broadening associated with the size distribution were important factors that affected the Raman spectra. The optical transmission spectra of CdS and Sm-doped CdS are shown in Fig.…”