A research team led by Prof CHEN Wei from both the Departments of Chemistry and Physics, National University of Singapore has developed a method for controllable introduction of two different types of defects, the disulfide anions (S22-) and the sulfide ion (S2-) vacancies into ZrS3 nanobelts (Figure (a) to (f)). The ZrS3 nanobelts are long one-dimensional nanostructures that look like ribbons. The researchers found that the S22- and S2- vacancies can be introduced into the nanobelt material through two different methods (Figure (g) and (h)). For S22- vacancies, this involves annealing the ZrS3 nanobelt at 700℃ under vacuum conditions. For S2- vacancies, a lithium-based hydrothermal method is used. By varying the annealing time (10, 15, and 20 mins) and amount of lithium present, defect engineered ZrS3 material with varying amount of S22- vacancies and S2- vacancies can be obtained.
The researchers found that this defect engineered ZrS3 material can enhance the photocatalytic production of H2O2 coupled with the selective oxidation of benzylamine to benzonitrile in water. They systematically investigated the effects of S22- and S2- vacancies on the charge carrier dynamics and photocatalytic performance. Their research findings show that the S22- vacancies can significantly facilitate the separation of photogenerated charge carriers. Separately, the S2- vacancies not only promote the electron conduction and hole extraction in the photocatalytic process but they also improve the kinetics of the benzylamine oxidation. These two different types of vacancies in the ZrS3 material work together to improve the performance of the photocatalytic reaction. Under illumination by a simulated sunlight, the ZrS3 material produces H2O2 and benzonitrile at a rate of 78.1 ± 1.5 and 32.0 ± 1.2 μmol h-1 respectively.
Prof Chen said, “Our research findings open up a new route for defect engineering and promise a potential strategy for the study of structure-activity relationships for the design and development of more efficient photocatalysts.”
Figure (a-f) shows the schematic process of the transformation of monoclinic zirconium trisulfide, ZrS3 (ICCD PDF no. 30-1498) into hexagonal zirconium sulfide, ZrS2 (ICCD PDF no. 11-0679) from the [010] (a-c) and [001] (d-f) views. Under heat treatment in vaccum conditions, ZrS3 (a, d) releases sulphur ions to form a distorted crystal structure of ZrS2 (b, e). The distorted crystal structure with the sulphur vacancies then undergoes structural relaxation by adjusting the length and angle of its bonds (c, f). Figure (g and h) shows the different type of sulphur vacancies. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of (g) ZrS3 with S22- vacancies and (h) ZrS3 with both S22- and S2- vacancies measured from a spherical aberration-corrected transmission electron microscope (TEM). Inset: the crystal lattice of ZrS3 along the [001] orientation. The red and yellow circles represent S22-and S2- vacancies, respectively. [Credit: Nature Communications]. Read the full story here.
